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Sample records for autogenous shrinkage cracking

  1. Mitigation strategies for autogenous shrinkage cracking

    DEFF Research Database (Denmark)

    Bentz, Dale P.; Jensen, Ole Mejlhede

    2004-01-01

    , the fundamental parameters contributing to the autogenous shrinkage and resultant early-age cracking of concrete are presented. Basic characteristics of the cement paste that contribute to or control the autogenous shrinkage response include the surface tension of the pore solution, the geometry of...... problem of early-age cracking due to autogenous shrinkage. Mitigation strategies discussed in this paper include: the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the cement particle size distribution, modification of the mineralogical composition of...... the field, it should be possible to minimize cracking due to autogenous shrinkage via some combination of the presented approaches....

  2. Mitigation strategies for autogenous shrinkage cracking

    DEFF Research Database (Denmark)

    Bentz, Dale P.; Jensen, Ole Mejlhede

    2004-01-01

    , the fundamental parameters contributing to the autogenous shrinkage and resultant early-age cracking of concrete are presented. Basic characteristics of the cement paste that contribute to or control the autogenous shrinkage response include the surface tension of the pore solution, the geometry of......As the use of high-performance concrete has increased, problems with early-age cracking have become prominent. The reduction in water-to-cement ratio, the incorporation of silica fume, and the increase in binder content of high-performance concretes all contribute to this problem. In this paper...... problem of early-age cracking due to autogenous shrinkage. Mitigation strategies discussed in this paper include: the addition of shrinkage-reducing admixtures more commonly used to control drying shrinkage, control of the cement particle size distribution, modification of the mineralogical composition of...

  3. Cracking in cement paste induced by autogenous shrinkage

    DEFF Research Database (Denmark)

    Lura, Pietro; Jensen, Ole Mejlhede; Weiss, Jason

    2009-01-01

    Detection and quantification of microcracks caused by restrained autogenous shrinkage in high-performance concrete is a difficult task. Available techniques either lack the required resolution or may produce additional cracks that are indistinguishable from the original ones. A recently developed...... shrinkage of the paste and may cause crack formation. The crack pattern is identified by impregnation with gallium and analyzed by optical and scanning electron microscopy. In this study, a non-linear numerical analysis of the samples was performed. Autogenous strain, elastic modulus, fracture energy, and...

  4. Identification of microcracks caused by autogenous shrinkage

    DEFF Research Database (Denmark)

    Lura, Pietro; Jensen, Ole Mejlhede; Guang, Ye;

    2005-01-01

    Detection and quantification of microcracks caused by restrained autogenous shrinkage in high-performance concrete is difficult. Available techniques either lack the required resolution or may cause further cracks indistinguishable from the original ones. The new technique presented in this paper...... the autogenous shrinkage and cause crack formation during hardening. Subsequently, liquid gallium is intruded into the cracks under pressure. After solidification of the gallium, the crack pattern is frozen and can be analyzed after plane polishing of the samples. The microcracks are identified by...

  5. Reduction of the Early Autogenous Shrinkage of High Strength Concrete

    OpenAIRE

    Drago Saje

    2015-01-01

    The results of a laboratory investigation on the early autogenous shrinkage of high strength concrete, and the possibilities of its reduction, are presented. Such concrete demonstrates significant autogenous shrinkage, which should, however, be limited in the early stages of its development in order to prevent the occurrence of cracks and/or drop in the load-carrying capacity of concrete structures. The following possibilities for reducing autogenous shrinkage were investigated: the use of lo...

  6. Reduction of the early autogenous shrinkage of high strength concrete

    OpenAIRE

    Saje, Drago

    2016-01-01

    he results of a laboratory investigation on the early autogenous shrinkage of high strength concrete, and the possibilities of its reduction, are presented. Such concrete demonstrates signiicant autogenous shrinkage, which should, however, be limited in the early stages of its development in order to prevent the occurrence of cracks and/or drop in the load-carrying capacity of concrete structures.he following possibilities for reducing autogenous shrinkagewere investigated: the use of low-hea...

  7. Reduction of the Early Autogenous Shrinkage of High Strength Concrete

    Directory of Open Access Journals (Sweden)

    Drago Saje

    2015-01-01

    Full Text Available The results of a laboratory investigation on the early autogenous shrinkage of high strength concrete, and the possibilities of its reduction, are presented. Such concrete demonstrates significant autogenous shrinkage, which should, however, be limited in the early stages of its development in order to prevent the occurrence of cracks and/or drop in the load-carrying capacity of concrete structures. The following possibilities for reducing autogenous shrinkage were investigated: the use of low-heat cement, a shrinkage-reducing admixture, steel fibres, premoistened polypropylene fibres, and presoaked lightweight aggregate. In the case of the use of presoaked natural lightweight aggregate, with a fraction from 2 to 4 mm, the early autogenous shrinkage of one-day-old high strength concrete decreased by about 90%, with no change to the concrete's compressive strength in comparison with that of the reference concrete.

  8. Effect of fly ash on autogenous shrinkage

    Energy Technology Data Exchange (ETDEWEB)

    Pipat Termkhajornkit; Toyoharu Nawa; Masashi Nakai; Toshiki Saito [Hokkaido University, Hokkaido (Japan). Division of Structural and Geotechnical Engineering, Graduate School of Engineering

    2005-03-01

    The correlation between autogenous shrinkage and degree of hydration of fly ash was determined with the selective dissolution method. Then, the relationship between the degree of hydration of fly ash and autogenous shrinkage was examined. The results showed that the degree of hydration of fly ash increased as its Blaine surface area increased. The degree of hydration of fly ash increased with time, and autogenous shrinkage increased corresponding to the increase in the degree of hydration of fly ash. Moreover, it was found that the total quantity of Al{sub 2}O{sub 3} in cement-fly ash samples affected autogenous shrinkage at early ages, but the long-term influence was very small.

  9. Autogenous shrinkage, speciality of high performance concretes

    OpenAIRE

    Vogrič, Nina

    2014-01-01

    Autogenous shrinkage is a consequence of self dessication in pores of hardened cement paste and is, at high performance concrete significantly greater than that of the ordinary concretes, mainly due to low water to cement ratio. In the graduation thesis we examined the main mechanisms that cause autogenous shrinkage. It can be reduced by internal curinginternal water reservoirs. As internal water reservoirs we used pre-soaked expanded clay Liapor. On specimens, in which we replaced 12 % of ag...

  10. Autogenous shrinkage of a self-compacting VHPC in isothermal and realistic temperature conditions

    OpenAIRE

    STAQUET, S; Boulay, C.; D'ALOIA, L; F. TOUTLEMONDE

    2006-01-01

    The autogenous shrinkage development at early age of a Very High Performance Concrete (VHPC) was analyzed in both situations : under standard isothermal (20°C) conditions and under realistic temperature conditions (same as the precambered steel-VHPC beam investigated in LCPC). Actually, a risk of cracking at very early age due to the transversally restrained shrinkage is probable in this kind of steel-VHPC composite structure (the concrete is cast around the steel girder) and the influence of...

  11. Temperature dependence of autogenous shrinkage of silica fume cement pastes with a very low water–binder ratio

    Energy Technology Data Exchange (ETDEWEB)

    Maruyama, I., E-mail: ippei@dali.nuac.nagoya-u.ac.jp [Graduate School of Environmental Studies, Nagoya University, ES Building, No. 539, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan); Teramoto, A. [Graduate School of Environmental Studies, Nagoya University, Faculty of Engineering, ES Building, No. 546, Furo-cho, Chikusa-ku, Nagoya 464-8603 (Japan)

    2013-08-15

    Ultra-high-strength concrete with a large unit cement content undergoes considerable temperature increase inside members due to hydration heat, leading to a higher risk of internal cracking. Hence, the temperature dependence of autogenous shrinkage of cement pastes made with silica fume premixed cement with a water–binder ratio of 0.15 was studied extensively. Development of autogenous shrinkage showed different behaviors before and after the inflection point, and dependence on the temperature after mixing and subsequent temperature histories. The difference in autogenous shrinkage behavior poses problems for winter construction because autogenous shrinkage may increase with decrease in temperature after mixing before the inflection point and with increase in temperature inside concrete members with large cross sections.

  12. Temperature dependence of autogenous shrinkage of silica fume cement pastes with a very low water–binder ratio

    International Nuclear Information System (INIS)

    Ultra-high-strength concrete with a large unit cement content undergoes considerable temperature increase inside members due to hydration heat, leading to a higher risk of internal cracking. Hence, the temperature dependence of autogenous shrinkage of cement pastes made with silica fume premixed cement with a water–binder ratio of 0.15 was studied extensively. Development of autogenous shrinkage showed different behaviors before and after the inflection point, and dependence on the temperature after mixing and subsequent temperature histories. The difference in autogenous shrinkage behavior poses problems for winter construction because autogenous shrinkage may increase with decrease in temperature after mixing before the inflection point and with increase in temperature inside concrete members with large cross sections

  13. Autogenous Shrinkage of High Strength Lightweight Aggregate Concrete

    Institute of Scientific and Technical Information of China (English)

    DING Qingjun; TIAN Yaogang; WANG Fazhou; ZHANG Feng; HU Shuguang

    2005-01-01

    The characteristic of autogenous shrinkage ( AS ) and its effect on high strength lightweight aggregate concrete (HSLAC) were studied. The experimental results show that the main shrinkage of high strength concrete is AS and the amount of cement can affect the AS of HSLAC remarkably. At the early stage the AS of HSLAC is lower than that of high strength normal concrete, but it has a large growth at the later stage. The AS of high strength normal concrete becomes stable at 90d age, but HSLAC still has a high AS growth. It is found that adjusting the volume rate of lightweight aggregate, mixing with a proper dosage of fly ash and raising the water saturation degree of lightweight aggregate can markedly reduce the AS rate of HSLAC.

  14. Autogenous shrinkage in high-performance cement paste: An evaluation of basic mechanisms

    DEFF Research Database (Denmark)

    Lura, Pietro; Jensen, Ole Mejlhede; van Breugel, Klaas

    2003-01-01

    In this paper, various mechanisms Suggested to cause autogenous shrinkage are presented. The mechanisms are evaluated from the point of view of their soundness and applicability to quantitative modeling of autogenous shrinkage. The capillary tension approach is advantageous, because it has a sound...

  15. The influence of granulation on lightweight aggregate on early autogenous shrinkage of high strength concrete

    OpenAIRE

    Maleš, Dijana

    2013-01-01

    Early autogenous shrinkage of high strength concretes is relatively large. It can be reduced by using internal water reservoirs. Lightweight aggregate was used for internal water reservoir. 12% of aggregate was replaced with pre-soaked lightweight aggregate in the concrete mixture. On the basis of experiments in the graduation thesis we studied the influence of granulation of lightweight aggregate on early autogenous shrinkage. The shrinkage was measured electronically during the first day. I...

  16. The influence of superabsorbent polymers on the autogenous shrinkage properties of cement pastes with supplementary cementitious materials

    DEFF Research Database (Denmark)

    Snoeck, D.; Jensen, Ole Mejlhede; De Belie, N.

    2015-01-01

    Fly ash and blast-furnace slag containing binders are frequently used in the construction industry and it is important to know the extent of autogenous shrinkage and its (ideal) mitigation by superabsorbent polymers in these systems as a function of their age. In this paper, the autogenous...... shrinkage was determined by manual and automated shrinkage measurements. Autogenous shrinkage was reduced in cement pastes with the supplementary cementitious materials versus Portland cement pastes. At later ages, the rate of autogenous shrinkage is higher due to the pozzolanic activity. Internal curing by...... means of superabsorbent polymers is successful, independent of this long term higher rate of shrinkage in mixtures with supplementary cementitious materials....

  17. Effect of mineral filler type on autogenous shrinkage of self-compacting concrete

    OpenAIRE

    Craeye, Bart; De Schutter, Geert; Desmet, Bram; Vantomme, John; Heirman, Gert; Vandewalle, Lucie; Cizer, Özlem; AGGOUN, S.; E. H. Kadri

    2010-01-01

    Based on an experimental programme, including autogenous shrinkage tests on concrete, ultrasonic monitoring of fresh concrete, and mercury intrusion porosimetry, the influence of the filler type on the autogenous shrinkage of self-compacting concrete has been investigated. The onset of percolating structure formation (time zero) is influenced by the filler type due to a possible accelerating effect of the filler on the cement hydration. Limestone filler accelerates the hydration process, and ...

  18. Mesocosmic study on autogenous shrinkage of concrete with consideration of effects of temperature and humidity

    Directory of Open Access Journals (Sweden)

    Yan HAI

    2009-12-01

    Full Text Available A study on the autogenous shrinkage (AS of concrete from a mesocosmic perspective was carried out using numerical simulation technology. The temperature history and the autogenous relative humidity (ARH, two factors that have been shown to have occasional influence on this process in previous studies, were introduced into this study. According to these concepts, a program for simulation of the temperature field, humidity field, and stress field based on the equivalent age method and a fully automatic aggregate modeling tool were used. With the help of these programs, the study of a small concrete specimen provided some useful conclusions: the aggregate and the matrix show distinct distribution properties in the temperature field, humidity field, and stress field; the aggregate-matrix interface has a high possibility of becoming the location of the initial cracking caused by AS of concrete; the distribution of random aggregates is extremely important for mesoscopical analysis; and the temperature history is the main factor affecting the AS of concrete. On the whole, inherent mechanisms and cracking mechanisms of AS of concrete can be explained more reasonably and realistically only by considering the different characteristics of material phases and the effects of temperature and humidity.

  19. Experimental Research on the Autogenous Shrinkage of MK High Performance Concrete

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Calcine and mill kaolin were used under agreeable technological conditions to generate matakaolin (MK). The autogenous shrinkage performance of high performance concrete added with MK was researched. It is shown that MK has an effective inhibitory action to early autogenous shrinkage of cement concrete, and the inhibitory action increases with the increase of MK. The autogenous shrinkage values from 24 hours after placement to 56 days are all higher than those of the contrasted concrete, among which, the value of the concrete with 5% MK is the highest. But the total shrinkage values in 56 days are all less than those of the contrasted test pieces. The total contraction after 24 h of placement decreases as the increase of MK, moreover,it is greatly less than that of the contrasted ones.

  20. Mesocosmic study on autogenous shrinkage of concrete with consideration of effects of temperature and humidity

    OpenAIRE

    Hai, Yan; Yue-ming ZHU

    2009-01-01

    A study on the autogenous shrinkage (AS) of concrete from a mesocosmic perspective was carried out using numerical simulation technology. The temperature history and the autogenous relative humidity (ARH), two factors that have been shown to have occasional influence on this process in previous studies, were introduced into this study. According to these concepts, a program for simulation of the temperature field, humidity field, and stress field based on the equivalent age method and a fully...

  1. Autogenous shrinkage of Ducorit S5R ASTM C 1698-09 test method

    DEFF Research Database (Denmark)

    Damkilde, Lars

    The report deals with experimental measurement of autogenous shrinkage of Ducorit S5R according to the test method ASTM C 1698-09. This test method measures the bulk strain of a sealed cementitious specimen, at constant temperature and not subjected to external forces, from the time of final...

  2. Measurement with corrugated tubes of early-age autogenous shrinkage of cement-based material

    DEFF Research Database (Denmark)

    Tian, Qian; Jensen, Ole Mejlhede

    2009-01-01

    The use of a special corrugated mould enables transformation of volume strain into horizontal, linear strain measurement in the fluid stage. This allows continuous measurement of the autogenous shrinkage of cement-based materials since casting, and also effectively eliminates unwanted influence on...

  3. Ultra high performance concrete made with rice husk ash for reduced autogenous shrinkage

    NARCIS (Netherlands)

    Van Breugel, K.; Van Tuan, N.

    2014-01-01

    Ultra High Strength Concrete (UHPC) is generally made with low w/c mixtures and by adding silica fume. Low w/c mixtures, however, exhibit high autogenous shrinkage, while a high amount of silica fume increases the price of these mixtures. For designing ultra high strength mixtures with low autogenou

  4. Study on effects of solar radiation and rain on shrinkage, shrinkage cracking and creep of concrete

    International Nuclear Information System (INIS)

    In this paper, the effects of actual environmental actions on shrinkage, creep and shrinkage cracking of concrete are studied comprehensively. Prismatic specimens of plain concrete were exposed to three sets of artificial outdoor conditions with or without solar radiation and rain to examine the shrinkage. For the purpose of studying shrinkage cracking behavior, prismatic concrete specimens with reinforcing steel were also subjected to the above conditions at the same time. The shrinkage behavior is described focusing on the effects of solar radiation and rain based on the moisture loss. The significant environment actions to induce shrinkage cracks are investigated from viewpoints of the amount of the shrinkage and the tensile strength. Finally, specific compressive creep behavior according to solar radiation and rainfall is discussed. It is found that rain can greatly inhibit the progresses of concrete shrinkage and creep while solar radiation is likely to promote shrinkage cracking and creep.

  5. Shrinkage of Concrete using Porous Aggregates

    OpenAIRE

    Valgeir Ó. Flosason 1987

    2014-01-01

    During its service life, concrete undergoes volume changes which can affect quality and durability of the concrete. There are several types of volume changes, but shrinkage is the type of volume change which is often responsible for cracking of the concrete. Shrinkage can be categorized due to several different mechanisms which cause shrinkage. The main types of shrinkage are plastic shrinkage, chemical shrinkage, autogenous shrinkage, drying shrinkage and carbonation shrinkage. In this ma...

  6. Test rig for early age measurements of the autogenous shrinkage of a concrete

    OpenAIRE

    Boulay, Claude

    2012-01-01

    A test rig designed for autogenous shrinkage measurements of concrete at early age is presented. It allows the recording of the deformations of a specimen protected against the desiccation at a constant temperature. Only one external displacement sensor is used. The specimens are cast in a flexible mould to avoid any friction. The test rig is immersed in a thermo controlled bath. Measurements can start just after the casting of the concrete. A series of four successive tests on the same concr...

  7. PLASTIC SHRINKAGE CRACKING OF FIBER REINFORCED CONCRETE

    OpenAIRE

    EREN, Özgür; Abdalkader, Ashraf

    2006-01-01

    The main objective of this study was to investigate the effect of fiber volume (i.e control, 0.5%, 1.0%, and 1.5%) and aspect ratios of 55, 65, and 80 of hooked-end steel fibers on the behaviour of plastic shrinkage cracking during the first few hours after mixing. Properties such as compressive strength, splitting tensile strength, VeBe time and wet density were investigated. During this research two different strength levels (56 and 73 MPa at 28 days) were studied. The follo...

  8. Measurement with corrugated tubes of early-age autogenous shrinkage of cement-based material

    DEFF Research Database (Denmark)

    Tian, Qian; Jensen, Ole Mejlhede

    2009-01-01

    The use of a special corrugated mould enables transformation of volume strain into horizontal, linear strain measurement in the fluid stage. This allows continuous measurement of the autogenous shrinkage of cement-based materials since casting, and also effectively eliminates unwanted influence on...... the measuring results from gravity, temperature variation and mould restraint. In this paper the principle of the corrugated tube measurement is described. A systematic study was carried out on the influence on the measuring results of the material properties, size effects and encapsulated air in the...

  9. Influence of Shrinkage-Reducing Admixtures on the Development of Plastic Shrinkage Cracks

    DEFF Research Database (Denmark)

    Lura, Pietro; Pease, Bradley Justin; Mazzotta, Guy;

    2007-01-01

    The term plastic shrinkage cracking is generally used to describe cracks that form between the time when concrete is placed and the time when concrete sets. This paper discusses how the evaporation of water causes concave menisci to form on the surface of fresh concrete. These menisci cause both...... settlement of the concrete and tensile stress development in the surface of the concrete, which increase the potential for development of plastic shrinkage cracks. Specifically, this paper studies the development of plastic shrinkage cracks in mortars containing a commercially available shrinkage......-reducing admixture (SRA). Mortars containing SRA show fewer and narrower plastic shrinkage cracks than plain mortars when exposed to the same environmental conditions. It is proposed that the lower surface tension of the pore fluid in the mortars containing SRA results in less evaporation, reduced settlement...

  10. Prevention of shrinkage cracking in tight concrete structures

    International Nuclear Information System (INIS)

    It is shown that crack formation and propagation in concrete members subjected to restrained shrinkage can be realistically predicted by means of a comprehensive approach including a diffusion analysis and fracture mechanics considerations. The conditions for stable crack propagation regarding dimensions of the concrete member, degree of restraint to the imposed deformation and material properties are discussed. Guidelines on the prevention of shrinkage cracking of concrete structures are given. (author). 10 refs., 5 figs

  11. Self-healing of drying shrinkage cracks in cement-based materials incorporating reactive MgO

    Science.gov (United States)

    Qureshi, T. S.; Al-Tabbaa, A.

    2016-08-01

    Excessive drying shrinkage is one of the major issues of concern for longevity and reduced strength performance of concrete structures. It can cause the formation of cracks in the concrete. This research aims to improve the autogenous self-healing capacity of traditional Portland cement (PC) systems, adding expansive minerals such as reactive magnesium oxide (MgO) in terms of drying shrinkage crack healing. Two different reactive grades (high ‘N50’and moderately high ‘92–200’) of MgO were added with PC. Cracks were induced in the samples with restraining end prisms through natural drying shrinkage over 28 days after casting. Samples were then cured under water for 28 and 56 days, and self-healing capacity was investigated in terms of mechanical strength recovery, crack sealing efficiency and improvement in durability. Finally, microstructures of the healing materials were investigated using FT-IR, XRD, and SEM-EDX. Overall N50 mixes show higher expansion and drying shrinkage compared to 92–200 mixes. Autogenous self-healing performance of the MgO containing samples were much higher compared to control (only PC) mixes. Cracks up to 500 μm were sealed in most MgO containing samples after 28 days. In the microstructural investigations, highly expansive Mg-rich hydro-carbonate bridges were found along with traditional calcium-based, self-healing compounds (calcite, portlandite, calcium silicate hydrates and ettringite).

  12. Autogenous Deformation and Change of the Relative Humidity in Silica Fume-Modified Cement Paste

    DEFF Research Database (Denmark)

    Jensen, Ole mejlhede; Hansen, Per Freiesleben

    1996-01-01

    Even during sealed curing and at a constant temperature a hardening cement paste will deform and the relative humidity within its pores will lower. This autogenous deformation and autogenous relative humidity change may be so significant that the cement paste cracks if the deformation is restrained....... This article focuses on the influence of silica fume addition on autogenous deformation and autogenous relative humidity change. Continuous measurement of autogenous deformation and autogenous relative humidity change for more than 1 year and 1« years, respectively, was performed. The investigations...... show thatsilica fume addition markedly increases the autogenous shrinkage as well as the autogenous relative humidity change....

  13. Development of Concrete Shrinkage Performance Specifications

    OpenAIRE

    Mokarem, David Wayne

    2002-01-01

    During its service life, concrete experiences volume changes. One of the types of deformation experienced by concrete is shrinkage. The four main types of shrinkage associated with concrete are plastic, autogeneous, carbonation and drying shrinkage. The volume changes in concrete due to shrinkage can lead to the cracking of the concrete. In the case of reinforced concrete, the cracking may produce a direct path for chloride ions to reach the reinforcing steel. Once chloride ions reach th...

  14. Development of concrete shrinkage performance specifications

    OpenAIRE

    Mokarem, David W.; Meyerson, Richard M.; Weyers, Richard E.

    2003-01-01

    During its service life, concrete undergoes volume changes. One of the types of deformation is shrinkage. The four main types of shrinkage associated with concrete are plastic, autogenous, carbonation, and drying shrinkage. The volume changes in concrete due to shrinkage can lead to the cracking of the concrete. In the case of reinforced concrete, the cracking may produce a direct path for chloride ions to reach the reinforcing steel. Once chloride ions reach the steel surface, the steel will...

  15. The Influence of Lightweight Aggregate on Internal Curing and Its Impact on Autogenous Shrinkage of High-Performance Concrete

    OpenAIRE

    Hartman, Neil J; Barrett, Timothy J.; Weiss, Jason

    2014-01-01

    In bridge deck construction high performance concrete is often desirable, however in practice it is generally susceptible to early-age shrinkage cracking resulting in an overall reduction in service life. This research seeks to assess the potential for reducing early-age shrinkage in new bridge deck construction through the use of internal curing, a process in which internal reservoirs supply water to the hydrating cement paste during the early stages of cement hydration. In North America, in...

  16. Evaluation of shrinkage and cracking in concrete of ring test by acoustic emission method

    Science.gov (United States)

    Watanabe, Takeshi; Hashimoto, Chikanori

    2015-03-01

    Drying shrinkage of concrete is one of the typical problems related to reduce durability and defilation of concrete structures. Lime stone, expansive additive and low-heat Portland cement are used to reduce drying shrinkage in Japan. Drying shrinkage is commonly evaluated by methods of measurement for length change of mortar and concrete. In these methods, there is detected strain due to drying shrinkage of free body, although visible cracking does not occur. In this study, the ring test was employed to detect strain and age cracking of concrete. The acoustic emission (AE) method was adopted to detect micro cracking due to shrinkage. It was recognized that in concrete using lime stone, expansive additive and low-heat Portland cement are effective to decrease drying shrinkage and visible cracking. Micro cracking due to shrinkage of this concrete was detected and evaluated by the AE method.

  17. Autogenous shrinkage in high-performance cement paste: An evaluation of basic mechanisms

    DEFF Research Database (Denmark)

    Lura, Pietro; Jensen, Ole Mejlhede; van Breugel, Klaas

    2003-01-01

    mechanical and thermodynamical basis. Furthermore, this mechanism is easily applicable in a numerical model when dealing with a continuously changing microstructure. In order to test the numerical model, autogenous deformation and internal relative humidity (RH) of a Portland cement paste were measured...

  18. Effect of steel fibers on plastic shrinkage cracking of normal and high strength concretes

    OpenAIRE

    Özgür Eren; Khaled Marar

    2010-01-01

    Naturally concrete shrinks when it is subjected to a drying environment. If this shrinkage is restrained, tensile stresses develop and concrete may crack. Plastic shrinkage cracks are especially harmful on slabs. One of the methods to reduce the adverse effects of shrinkage cracking of concrete is by reinforcing concrete with short randomly distributed fibers. The main objective of this study was to investigate the effect of fiber volume and aspect ratio of hooked steel fibers on plastic shri...

  19. Study of Drying Shrinkage Cracking by Lattice Gas Automaton and Environmental Scanning Electron Microscope

    OpenAIRE

    Jankovic, D.

    2005-01-01

    Numerical modeling of moisture flow, drying shrinkage and crack phenomena in cement microstructure, by coupling a Lattice Gas Automaton and a Lattice Fracture Model, highlighted the importance of a shrinkage coefficient (sh) as the most significant parameter for achieving realistic numerical results. Therefore, experiments on drying of cement paste samples were conducted in an Environmental Scanning Electron Microscope to find shrinkage coefficient relating shrinkage deformations and moistur...

  20. Prediction of shrinkage cracking age of concrete with and without expansive additive

    OpenAIRE

    Dung Tien Nguyen; Raktipong Sahamitmongkol; Lam Nguyen Trong; Sontaya Tongaroonsri; Somnuk Tangtermsirikul

    2010-01-01

    The aim of this research is to propose a model for predicting cracking age of concrete due to restrained shrinkage. Thisstudy focuses on analyzing shrinkage and expansion mechanisms in the expansive concrete to formulate a model that can beemployed to predict whether shrinkage cracking occurs or not. In case of conventional (non-expansive) concrete, this modelcan be applied by neglecting the early expansion due to expansive additive. Parameters considered in this model are restrainedexpansion...

  1. Shrinkage and cracking behavior of high performance concretes containing chemical admixtures

    Institute of Scientific and Technical Information of China (English)

    亓萌; 李宗津; 马保国

    2002-01-01

    Modern concretes often incorporate several chemical admixtures to alter the properties of fresh or hardened concrete. In this work, the influences of three types of chemical admixtures, calcium nitrite inhibitor (CNI), retarder (D-17) and superplasticizer (W-19) on free shrinkage and restrained shrinkage cracking of high performance concrete were experimentally investigated. The test results showed that, with the same water to binder ratio (0.4), mixtures containing D-17 of 0.25 percent or higher ratio of W-19 (2.76 percent) all exhibited a reduction in free shrinkage and shrinkage cracking width. However, the incorporations of various ratios of CNI into mixtures led to an increase in free shrinkage and shrinkage cracking width as compared to control mixture. In order to study the influence of CNI, the microstructure of concrete mixture containing CNI were investigated by Mercury Intrusion Porosimetry as well as Scanning Electronic Microscopy(SEM) technique.

  2. Effect of Pre-wetted Light-weight Aggregate on Internal Relative Humidity and Autogenous Shrinkage of Concrete

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    This research indicates that the gradient of internal relative humidity (IRH) decreases rapidly within 7-day curing age in HPC.The amount of water imported by pre-wetted light-weight aggregate can regulate IRH of concrete.By importing a proper amount of water, the process of the decline of IRH can be delayed and the antogenous shrinkage can be reduced.The relationship among the amount of water imported by pre- wetted lightweight aggregate, IRH and AS was established.The result provides a new method of reducing early AS and enhancing early cracking resistance of HPC.

  3. Can superabsorent polymers mitigate autogenous shrinkage of internally cured concrete without compromising the strength?

    DEFF Research Database (Denmark)

    Hasholt, Marianne Tange; Jensen, Ole Mejlhede; Kovler, Konstantin;

    2012-01-01

    The paper “Super absorbing polymers as an internal curing agent for mitigation of early-age cracking of high-performance concrete bridge decks” deals with different aspects of using superabsorbent polymers (SAP) in concrete to mitigate self-desiccation. The paper concludes that “Addition of SAP l...

  4. Study of Drying Shrinkage Cracking by Lattice Gas Automaton and Environmental Scanning Electron Microscope

    NARCIS (Netherlands)

    Jankovic, D.

    2005-01-01

    Numerical modeling of moisture flow, drying shrinkage and crack phenomena in cement microstructure, by coupling a Lattice Gas Automaton and a Lattice Fracture Model, highlighted the importance of a shrinkage coefficient (sh) as the most significant parameter for achieving realistic numerical result

  5. Restrained Shrinkage-Induced Cracking of Light Weight High Performance Fiber Reinforced Cementitious Composites

    Directory of Open Access Journals (Sweden)

    Shaikh F.U Ahmed

    2009-01-01

    Full Text Available Problem statement: Shrinkage induced cracking cause damage to reinforced concrete structures. An experimental study was conducted on restrained shrinkage test of cement mortar and light weight High Performance Fiber Reinforced Cementitious Composites (HPFRCC. Approach: Two types of light weight HPFRCC and a premix mortar containing small amount of fiber were included in the experiment. Results: Results showed the multiple cracks, as many as 49, in light weight HPFRCC specimens compared to few cracks (about six cracks in the premix mortar specimen. At the end of shrinkage test, the width of the cracks in the mortar specimen was more than 250 μm with the largest crack width of about 400 μm. However, the scenario was quite different in light weight HPFRCC specimens, where the width of almost all cracks was less than 100 μm. Conclusion: The higher number of multiple cracks with small cracks width in light weight HPFRCC specimens due to drying shrinkage was due to their strain hardening and ductile behavior compared to quasi brittle behavior of premix mortar where less number of wide cracks was observed.

  6. Crack development through plastic shrinkage in fresh concretes and mortars

    Directory of Open Access Journals (Sweden)

    Aguanell García, M.

    1989-09-01

    Full Text Available The rate of water evaporation in the exposed surfaces plays an important part in the development of cracks in fresh concretes and mortars before hardening is completed. This rate of evaporation depends on the drying power of the wind sweeping such surfaces as a function of the relative humidity, temperature and speed of the air. After many studies and research work on the subject of plastic cracking, the following axiom has been established: "Plastic shrinkage and cracking of concrete surfaces take place when water evaporates from the surface quicker than it can be replaced through exudation". Once the value of weather parameters are known, the extent of the risk of crack development can be known and preventive steps taken to overcome such risk. Obviously, such steps are all oriented to reducing or stopping evaporation and go from covering surfaces with wet sackcloth or plastic foil, through sprinkling water mists or lowering the concrete temperature, to using film-forming curing products. Another additional measure can be the addition of polypropelene fibers to the concrete while in the mixer, at the rate of 0.9 kg fiber to 1 m3 of concrete.

    En la formación de grietas en morteros y hormigones frescos, antes de finalizar el fraguado, tiene una primordial importancia la velocidad de evaporación del agua de las superficies expuestas al exterior, velocidad que depende del poder desecante de los vientos que barren estas superficies y que está en función de la humedad relativa del aire, de su temperatura y de su velocidad. Después de los múltiples estudios e investigaciones sobre este tema de la formación de las grietas plásticas, se ha llegado a establecer el siguiente axioma: "La retracción plástica y las grietas se producen, en las superficies del hormigón, cuando el agua se evapora de ellas más rápidamente que la que puede ser reemplazada por exudación." Conociendo el valor de los parámetros meteorol

  7. Prediction of shrinkage cracking age of concrete with and without expansive additive

    Directory of Open Access Journals (Sweden)

    Dung Tien Nguyen

    2010-10-01

    Full Text Available The aim of this research is to propose a model for predicting cracking age of concrete due to restrained shrinkage. Thisstudy focuses on analyzing shrinkage and expansion mechanisms in the expansive concrete to formulate a model that can beemployed to predict whether shrinkage cracking occurs or not. In case of conventional (non-expansive concrete, this modelcan be applied by neglecting the early expansion due to expansive additive. Parameters considered in this model are restrainedexpansion, free shrinkage, cracking strain that can be experimentally measured by experiment and tensile creep which isderived by back calculation. The model was verified by test results of expansive concrete mixtures as well as normal concretemixtures both with and without fly ash.

  8. Thermodynamics of Autogenous Self-healing in Cementitious Materials

    NARCIS (Netherlands)

    Huang, H.

    2014-01-01

    Concrete is a brittle composite cementitious material that easily fractures under tensile loading. Microcracks can appear throughout the concrete prior to application of any load because of temperature-induced strain and autogenous and drying shrinkage. There is no doubt that these cracks provide pr

  9. An integrated approach to soil structure, shrinkage, and cracking in samples and layers

    CERN Document Server

    Chertkov, V Y

    2014-01-01

    A recent model showed how a clay shrinkage curve is step-by-step transformed into the shrinkage curve of an aggregated soil at any clay content if it is measured on samples so small that cracks do not occur at shrinkage. Such a shrinkage curve was called a reference curve. The present work generalizes this model to any soil sample size or layer thickness, i.e., to any crack contribution to the shrinkage curve. The approach is based on: (i) recently suggested features of an intra-aggregate structure; (ii) detailed accounting for the contributions to the soil volume and water content during shrinkage; and (iii) new concepts of lacunar factor, crack factor, and critical sample size. The following input parameters are needed for the prediction: (i) all parameters determining the basic dependence of the reference shrinkage curve; (ii) parameters determining the critical sample size (structural porosity and minimum and maximum aggregate size at maximum swelling); and (iii) initial sample size or layer thickness. A ...

  10. Shrinkage cracking of lightweight concrete made with cold-bonded fly ash aggregates

    Energy Technology Data Exchange (ETDEWEB)

    Mehmet Gesoglu; Turan Ozturan; Erhan Guneyisi [Bogazici University, Istanbul (Turkey). Department of Civil Engineering

    2004-07-01

    Shrinkage cracking performance of lightweight concrete (LWC) has been investigated experimentally on ring-type specimens. LWCs with and without silica fume were produced at water-cementitious material ratios (w/cm) of 0.32 to 0.55 with cold-bonded fly ash coarse aggregates and natural sand. Coarse aggregate volume ratios were 30%, 45%, and 60% of the total aggregate volume in the mixtures. A total of 12 lightweight aggregate concrete mixtures was cast and tested for compressive strength, static elastic modulus, split-tensile strength, free shrinkage, weight loss, creep, and restrained shrinkage. It was found that the crack opening on ring specimens was wider than 2 mm for all concretes. Free shrinkage, weight loss, and maximum crack width increased, while compressive and split-tensile strengths, static elastic modulus, and specific creep decreased with increasing coarse aggregate content. The use of silica fume improved the mechanical properties but negatively affected the shrinkage performance of LWCs. Shrinkage cracking performance of LWCs was significantly poorer than normal weight concrete (NWC).

  11. Influence of Superplasticizers on Strength and Shrinkage Cracking of Cement Mortar under Drying Conditions

    Institute of Scientific and Technical Information of China (English)

    MA Baoguo; WANG Xin'gang; LI Xiangguo; YANG Lei

    2007-01-01

    The effects of polynaphthalene series superplasticizers(PNS) with a low content of sodium sulfate (H-UNF),with a high content of sodium sulfate(C-UNF) and polycarboxylate type superplasticizer (PC) on strength and shrinkage cracking of cement mortar under drying conditions were investigated by means of multi-channel ellipse ring shrinkage cracking test, free shrinkage and strength test. The general effect of PNS and PC is to increase the initial cracking time of mortars, and decrease the cracking sensitivity of mortars. As for decreasing the cracking sensitivity of mortars, PC>H-UNF>C-UNF. To incorporate superplasticizers is apparently to increase the free shrinkage of mortars when keeping the constant w/b ratio and the content of cement pastes. As for the effect of controlling the volume stability of mortars, PC>C-UNF>H-UNF. Maximum crack width of mortars containing PC is lower, but the development rate of maximum crack width of mortars containing H-UNF is faster in comparison with control mortars. The flexural and compressive strengths of mortars at 28-day increase with increasing superplasticizer dosages under drying conditions. PC was superior to PNS in the aspect of increasing strength.

  12. Effect of steel fibers on plastic shrinkage cracking of normal and high strength concretes

    Directory of Open Access Journals (Sweden)

    Özgür Eren

    2010-06-01

    Full Text Available Naturally concrete shrinks when it is subjected to a drying environment. If this shrinkage is restrained, tensile stresses develop and concrete may crack. Plastic shrinkage cracks are especially harmful on slabs. One of the methods to reduce the adverse effects of shrinkage cracking of concrete is by reinforcing concrete with short randomly distributed fibers. The main objective of this study was to investigate the effect of fiber volume and aspect ratio of hooked steel fibers on plastic shrinkage cracking behavior together with some other properties of concrete. In this research two different compressive strength levels namely 56 and 73 MPa were studied. Concretes were produced by adding steel fibers of 3 different volumes of 3 different aspect ratios. From this research study, it is observed that steel fibers can significantly reduce plastic shrinkage cracking behavior of concretes. On the other hand, it was observed that these steel fibers can adversely affect some other properties of concrete during fresh and hardened states.

  13. Surface Modification of Fly Ashes with Carbide Slag and Its Effect on Compressive Strength and Autogenous Shrinkage of Blended Cement Pastes

    Institute of Scientific and Technical Information of China (English)

    HAO Chengwei; DENG Min; MO Liwu; LIU Kaiwei

    2012-01-01

    Surfaces of grade Ⅲ fly ashes were modified through mixing with carbide slag and calcining at 850 ℃ for 1 h.Mineralogical compositions and surface morphology of fly ashes before and after modification were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM),respectively.Effect of surface-modified fly ashes on compressive strength and autogenous shrinkage of blended cement pastes was investigated.Microstructures of cement pastes were examined by backscattered electron (BSE) imaging and mercury intrusion porosimetry (MIP).The experimental results showed that β-C2S was formed on the surfaces of fly ashes after modification.Hydration of β-C2S on the surface-modified fly ashes densified interface zone and enhanced bond strength between particles of fly ashes and hydrated clinkers.In addition,surface modification of fly ashes tended to decrease total porosity and 10-50 nm pores of cement pastes.Surface modification of fly ashes increased compressive strength and reduced autogenous shrinkage of cement pastes.

  14. Numerical simulation of early-age shrinkage effects on RC member deflections and cracking development

    Directory of Open Access Journals (Sweden)

    P. Bernardi

    2016-07-01

    Full Text Available Shrinkage effects on short-term behavior of reinforced concrete elements are often neglected both in design code provisions and in numerical simulations. However, it is known that their influence on serviceability performance can be significant, especially in case of lightly-reinforced beams. As a matter of fact, the restraint provided by the reinforcement on concrete determines a reduction of the cracking load of the structural element, as well as an increase of its deflection. This paper deals with the modeling of early-age shrinkage effects in the field of smeared crack approaches. To this aim, an existing non-linear constitutive relation for cracked reinforced concrete elements is extended herein to include early-age concrete shrinkage. Careful verifications of the model are carried out by comparing numerical results with significant experimental data reported in technical literature, providing a good agreement both in terms of global and local behavior.

  15. Influence of specimen thickness on cracking behavior in restrained shrinkage ring test

    OpenAIRE

    Dong, W.; Zhou, X.; Wu, Z.

    2013-01-01

    The standard test method using circular ring is adopted to assess the potential cracking of restrained shrinkage concrete by ASTM and AASHTO, respectively. The difference of them is the ring specimen thickness, which are 37.5 mm and 75 mm. To investigate the mechanism of ring tests with two concrete thicknesses, a numerical approach is proposed to simulate stress development and crack initiation in restrained concrete ring subject to circumferential drying.Afictitious temperature field is app...

  16. Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

    Energy Technology Data Exchange (ETDEWEB)

    Beushausen, Hans, E-mail: hans.beushausen@uct.ac.za; Chilwesa, Masuzyo

    2013-11-15

    Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing was found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus. -- Highlights: •Parameter study on material characteristics influencing overlay cracking. •Analytical model gives good quantitative indication of overlay cracking. •Ring test presents good qualitative indication of overlay cracking. •Curing duration has little effect on overlay cracking.

  17. Assessment and prediction of drying shrinkage cracking in bonded mortar overlays

    International Nuclear Information System (INIS)

    Restrained drying shrinkage cracking was investigated on composite beams consisting of substrate concrete and bonded mortar overlays, and compared to the performance of the same mortars when subjected to the ring test. Stress development and cracking in the composite specimens were analytically modeled and predicted based on the measurement of relevant time-dependent material properties such as drying shrinkage, elastic modulus, tensile relaxation and tensile strength. Overlay cracking in the composite beams could be very well predicted with the analytical model. The ring test provided a useful qualitative comparison of the cracking performance of the mortars. The duration of curing was found to only have a minor influence on crack development. This was ascribed to the fact that prolonged curing has a beneficial effect on tensile strength at the onset of stress development, but is in the same time not beneficial to the values of tensile relaxation and elastic modulus. -- Highlights: •Parameter study on material characteristics influencing overlay cracking. •Analytical model gives good quantitative indication of overlay cracking. •Ring test presents good qualitative indication of overlay cracking. •Curing duration has little effect on overlay cracking

  18. A thermal active restrained shrinkage ring test to study the early age concrete behaviour of massive structures

    International Nuclear Information System (INIS)

    In massive concrete structures, cracking may occur during hardening, especially if autogenous and thermal strains are restrained. The concrete permeability due to this cracking may rise significantly and thus increase leakage (in tank, nuclear containment...) and reduce the durability. The restrained shrinkage ring test is used to study the early age concrete behaviour (delayed strains evolution and cracking). This test shows, at 20 oC and without drying, for a concrete mix which is representative of a French nuclear power plant containment vessel (w/c ratio equal to 0.57), that the amplitude of autogenous shrinkage (about 40 μm/m for the studied concrete mix) is not high enough to cause cracking. Indeed, in this configuration, thermal shrinkage is not significant, whereas this is a major concern for massive structures. Therefore, an active test has been developed to study cracking due to restrained thermal shrinkage. This test is an evolution of the classical restrained shrinkage ring test. It allows to take into account both autogenous and thermal shrinkages. Its principle is to create the thermal strain effects by increasing the temperature of the brass ring (by a fluid circulation) in order to expand it. With this test, the early age cracking due to restrained shrinkage, the influence of reinforcement and construction joints have been experimentally studied. It shows that, as expected, reinforcement leads to an increase of the number of cracks but a decrease of crack widths. Moreover, cracking occurs preferentially at the construction joint.

  19. The Evaluation of Polypropylene Fiber (FORTA FERRO) on the Strength and Control of the Cracks due to Concrete Shrinkage

    OpenAIRE

    KAMALIZADEH, Hassan; ADELI, Mehdi Mahdavi

    2015-01-01

    Abstract. Prevention of cracking is one of the most important and undeniable issues in reinforced concrete structures. In addition to making oxygen penetration into concrete possible and increasing the possibility of rebar corrosion, crack decreases the lifelong of the structure. If the concrete shrinkage is prevented, the tensile stress will lead to cracking in the section. In standard concrete with water to cement ratio above 45%, the shrinkage of concrete due to drying has been described a...

  20. Quantitative measurements of shrinkage and cracking during freeze-drying of amorphous cakes

    OpenAIRE

    Ullrich, Sabine

    2014-01-01

    In this thesis the influence of the formulation or the process on shrinkage and cracking was studied. Methods were developed to quantify the amount of both at the end of the lyophilization process (“endpoint evaluation method”) as well as in situ during drying (”kinetic method”). The endpoint evaluation method was used to investigate an apparent correlation between the content of non-frozen water in the maximum freeze-concentrated state, w ′ , of an amorphous cake and shrinkage. Model disacch...

  1. Modeling for prediction of restrained shrinkage effect in concrete repair

    International Nuclear Information System (INIS)

    A general model of autogenous shrinkage caused by chemical reaction (chemical shrinkage) is developed by means of Arrhenius' law and a degree of chemical reaction. Models of tensile creep and relaxation modulus are built based on a viscoelastic, three-element model. Tests of free shrinkage and tensile creep were carried out to determine some coefficients in the models. Two-dimensional FEM analysis based on the models and other constitutions can predict the development of tensile strength and cracking. Three groups of patch-repaired beams were designed for analysis and testing. The prediction from the analysis shows agreement with the test results. The cracking mechanism after repair is discussed

  2. SHRINKAGE REDUCTION AND CRACK PREVENTION OF ALKALI-ACTIVATED PHOSPHOROUS SLAG CEMENT

    Directory of Open Access Journals (Sweden)

    Yanan Wang

    2016-05-01

    Full Text Available The effects of fly ash, calcium oxide and polypropylene fiber on the physical and mechanical properties, shrinkage and cracking behaviors of alkali-activated phosphorous slag cement (AA-PS-C were studied. The results show that replacing 10-15% phosphorous slag by fly ash and adding calcium oxide as an expansive agent reduce the shrinkage of AA-PS-C. Fly ash will increase the flexural strength, although the compressive strength will be slightly decreased, while the calcium oxide expansive agent coated with aluminum stearate will slightly shorten the setting time and reduce the strength. Adding polypropylene fiber can greatly increase the crack-resistance of AA-PS-C.

  3. Shrinkage and Cracking Sensitivity of Cement Mortar Containing Fly Ash, Granulated Blast-furnace Slag and Silica Fume

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A laboratory study was undertaken to investigate drying shrinkage and cracking sensitivity subjected to restrained shrinkage of mortar containing fly ash (FA), granulated blast-furnace slag (GBFS) and silica fume (SF). Six mortar mixtures including control Portland cement (PC) and FA,GBFS and SF mortar mixtures were prepared. FA replaced the cement on mass basis at the replacement ratios of 20% and 35%, GBFS replaced the cement at the replacement ratios of 40%, SF replaced the cement at the replacement ratios of 8% and the blended mixtures with 20% FA, 20% GBFS and 8% SF. Water-cementitious materials ratio and sand-cementitious materials ratio were 0.4 and 2.0 for all mixtures, respectively. The mixtures were cured at 65% relative humidity and 20℃. The drying shrinkage value, initial cracking time and cracking width of the mortar samples were measured. The results show that all the mortar mixture containing FA exhibited the decrease of drying shrinkage.Moreover, initial cracking time was markedly delayed, and the crack width of the initial crack was reduced. However, the incorporations of various ratios of GBFS and SF led to an increase of drying shrinkage, initial cracking time and cracking width as compared to control mixture.

  4. A fracture mechanics-based method for prediction of cracking of circular and elliptical concrete rings under restrained shrinkage

    OpenAIRE

    Dong, W.; Zhou, X.; Wu, Z.

    2014-01-01

    A new experimental method, utilizing elliptical ring specimens, is developed for assessing the likelihood of cracking and cracking age of concrete subject to restrained shrinkage. To investigate the mechanism of this new ring test, a fracture mechanics-based numerical approach is proposed to predict crack initiation in restrained concrete rings by using the R-curve method. It has been found that numerical results accord well with experimental results in terms of cracking ages for both circula...

  5. Development and construction of low-cracking high-performance concrete (LC-HPC) bridge decks: Free shrinkage tests, restrained ring tests, construction experience, and crack survey results

    Science.gov (United States)

    Yuan, Jiqiu

    2011-12-01

    The development, construction, and evaluation of low-cracking high-performance concrete (LC-HPC) bridge decks are described based on laboratory test results and experiences gained during the construction of 13 LC-HPC bridge decks in Kansas, along with another deck bid under the LC-HPC specifications but for which the owner did not enforce the specification. This study is divided into four parts covering (1) an evaluation of the free shrinkage properties of LC-HPC candidate mixtures, (2) an investigation of the relationship between the evaporable water content in the cement paste and the free shrinkage of concrete, (3) a study of the restrained shrinkage performance of concrete using restrained ring tests, and (4) a description of the construction and preliminary evaluation of LC-HPC and control bridge decks constructed in Kansas. The first portion of the study involves evaluating the effects of the duration of curing, fly ash, and a shrinkage reducing admixture (SRA) on the free-shrinkage characteristics of concrete mixtures. The results indicate that an increase of curing period reduces free shrinkage. With 7 days of curing, concretes containing fly ash as a partial replacement for cement exhibit higher free shrinkage than concretes with 100% portland cement. When the curing period is increased to 14, 28, and 56 days, the adverse effect of adding fly ash on free shrinkage is minimized and finally reversed. The addition of an SRA significantly reduces free shrinkage for both the 100% portland cement mixture and the mixture containing fly ash. The second portion of the study investigates the relationship between the evaporable water content in the cement paste and the free shrinkage of concrete. A linear relationship between free shrinkage and evaporable water content in the cement paste is observed. For a given mixture, specimens cured for a longer period contain less evaporable water and exhibit lower free shrinkage and less weight loss in the free shrinkage

  6. Thermodynamics of Autogenous Self-healing in Cementitious Materials

    OpenAIRE

    Huang, H

    2014-01-01

    Concrete is a brittle composite cementitious material that easily fractures under tensile loading. Microcracks can appear throughout the concrete prior to application of any load because of temperature-induced strain and autogenous and drying shrinkage. There is no doubt that these cracks provide preferential access for aggressive agents to penetrate into the concrete, probably causing corrosion of reinforcement steel and degradation of concrete. As a result, the service life of reinforced co...

  7. New insights into autogenous self-healing with NMR tests

    OpenAIRE

    Huang, H; Ye, Guang; Pel, L.

    2015-01-01

    Concrete is a brittle composite cementitious material that easily fractures under tensile loading. Microcracks can appear throughout the concrete prior to application of any load because of temperature-induced strain and autogenous and drying shrinkage. There is no doubt that these cracks provide preferential access for aggressive agents to penetrate into the concrete, probably causing corrosion of reinforcement steel and degradation of concrete. As a result, the service life of reinforced co...

  8. Determination of Shrinkage Crack Risks in Industrial Concrete Floors through Analyzing Material tests

    OpenAIRE

    Hamad, Maitham

    2012-01-01

    The industrial concrete floor is a very important part of an industrial building, distribution center, storage or shopping mall, and it must have high quality surfaces for operation. To achieve the high quality we must know the problems and how to treat them. The most important problems on the concrete floors are: (i) cracks which are caused by shrinkage and creep, (ii) curling resulting in a loss of contact between concrete slab and sub-base, and (iii) unevenness In this thesis, it is aimed ...

  9. 粉煤灰水泥浆体的电阻率与化学收缩及自收缩的相互关系%Relations among electrical resistivity,chemical shrinkage and autogenous shrinkage of fly ash cement pastes

    Institute of Scientific and Technical Information of China (English)

    左义兵; 魏小胜

    2015-01-01

    为研究粉煤灰的硅酸盐水泥浆体的电阻率、化学收缩及自收缩的变化规律,定量描述水泥基材水化过程中自收缩和未充水毛细孔体积在化学收缩中所占的比例变化,测定了不同水胶比和粉煤灰掺量的早龄期水泥基浆体的电阻率、化学收缩和自收缩。结果表明:水泥基浆体在硬化减速期的电阻率随时间对数的曲线斜率 K 和浆体3 d 抗压强度成线性关系,并进一步论证了 K 值对水泥浆体结构密实速度的物理意义及其推测强度的应用价值;浆体的化学收缩和自收缩分别随水胶比升高或粉煤灰掺量增大而降低。浆体在24 h 后的单位体积化学收缩和30 h 后的自收缩随电阻率的发展均表现出线性关系。定量地提出了终凝后自收缩变化量与终凝后线性化学收缩变化量的比例参数γ的概念,较小的γ值表明:与未充水毛细孔相比,自收缩的比例很小;同一样品的比例参数γ表现出随水化时间逐渐减小。%The relationship among the electrical resistivity,chemical shrinkage and autogenous shrinkage is investigated.To quantitatively understand the volume proportions of autogenous shrinkage and volume of empty cavities to chemical shrinkage during the hydration of cementitious materials, the electrical resistivity,chemical shrinkage and autogenous shrinkage are measured for cement pastes with different water to binder ratios and fly ash replacements of cement by weight.A linear equation is established between electrical resistivity and time in logarithmic scale during decelerating period,in which the slope K has a linear relationship with compressive strength at 3 d.The chemical shrinkage and autogenous shrinkage of the pastes decrease with the increasing water-binder ratio or fly ash replacement.The proposed proportionγ,defined as the ratio of the autogenous shrinkage change to the linear chemical shrinkage change after final set

  10. Influence of inert fillers on shrinkage cracking of meta-kaolin geo-polymers

    International Nuclear Information System (INIS)

    Geo-polymers contain a network of tetrahedral coordinated aluminate and silicate, and are potential materials to immobilize/encapsulate nuclear wastes. They can exhibit shrinkage cracking when water is removed by drying, and in order to use geo-polymers for waste encapsulation this effect needs to be investigated and controlled. In this study, six different fillers were mixed with meta-kaolin and sodium silicate solution at high pH to form geo-polymers, and the influence of filler addition on mechanical properties has been determined. The fillers used were Fe2O3, Al2O3, CaCO3, sand, glass and rubber and these do not react during geo-polymerisation reactions. Geo-polymers were prepared containing 30 weight percent of filler. The mechanical properties of the geo-polymers were influenced by the type of filler, with low density fillers increasing mortar viscosity. Geo-polymer samples containing fine filler particles exhibited shrinkage cracking on drying. This was not observed when coarser particles were added and these samples also had significantly improved mechanical properties. (authors)

  11. Effect of Pulverized Fuel Ashes on Autogenous Shrinkage and Compressive Strength of Cement Pastes%粉煤灰对水泥浆体自收缩和抗压强度的影响

    Institute of Scientific and Technical Information of China (English)

    郝成伟; 邓敏; 莫立武; 刘开伟

    2011-01-01

    Autogenous shrinkage of cement pastes with different contents of pulverized fuel ashes(PFA) and different water-to-binder ratio were measured by a shrinkage test device. Compressive strength of sealed cement paste were also measured. The influence of PFA on the pore structures and micrograph of hydration products were investigated through mercury intrusion porosimetry(MIP) and scanning electron microscopy(SEM) , on which the influence mechanism was analyzed. Experimental results demonstrated that autogenous shrinkage of cement pastes decreased with the increased contents of PFA at early age (before 7 d) , this may be ascribed to inhibition of PFA on the shrinkage. After 7 d, however, both autogenous shrinkage, and compressive strength of cement pastes increased. This may be attributed to decrease of pore radius and densification of cement hydration products due to the pozzolanic reaction of fly ash.%设计组装了水泥浆体自收缩测量装置,进行了不同粉煤灰掺量和水胶比的水泥浆体自收缩和抗压强度测试,采用压汞测孔仪(MIP)、扫描电镜(SEM)等测试技术研究了粉煤灰对水泥浆体孔结构、产物形貌等微观结构的影响,并对其影响机理进行了分析.结果表明:粉煤灰能够有效抑制水泥浆体的早期自收缩,在7d前,其自收缩随着粉煤灰掺量的增加而减小;与纯硅酸盐水泥浆体相比,粉煤灰水泥浆体7d后的抗压强度增幅较大,但自收缩增长速率也趋于增大;火山灰反应引起的孔径细化、水化产物结构致密是粉煤灰影响水泥浆体自收缩和抗压强度的根本原因.

  12. A thermal active restrained shrinkage ring test to study the early age concrete behaviour of massive structures

    OpenAIRE

    BRIFFAUT, M; BENDOUJEMA, F; Torrenti, Jean Michel; NAHAS, G

    2011-01-01

    In massive concrete structures, cracking may occur during hardening, especially if autogenous and thermal strains are restrained. The concrete permeability due to this cracking may rise significantly and thus increase leakage (in tank, nuclear containment ) and reduce the durability. The restrained shrinkage ring test is used to study the early age concrete behaviour (delayed strains evolution and cracking). This test shows, at 20 °C and without drying, for a concrete mix which is representat...

  13. Shrinkage Cracking: A mechanism for self-sustaining carbon mineralization reactions in olivine rocks

    Science.gov (United States)

    Zhu, W.; Fusseis, F.; Lisabeth, H. P.; Xing, T.; Xiao, X.; De Andrade, V. J. D.; Karato, S. I.

    2015-12-01

    The hydration and carbonation of olivine results in an up to ~44% increase in solid molar volume, which may choke off of fluid supply and passivate reactive surfaces, thus preventing further carbonation reactions. The carbonation of olivine has ben studied extensively in the laboratory. To date, observations from these experimental studies indicate that carbonation reaction rates generally decrease with time and the extent of carbonation is limited in olivine rocks. Field studies, however, show that 100% hydration and carbonation occur naturally in ultramafic rocks. The disagreement between the laboratory results under controlled conditions and the field observations underlines the lack of understanding of the mechanisms responsible for the self-sustaining carbonation interaction in nature. We developed a state-of-the-art pressurized hydrothermal cell that is transparent to X-rays to characterize the real-time evolution of pore geometry during fluid-rock interaction using in-situ synchrotron-based X-ray microtomography. Through a time series of high-resolution 3-dimensional images, we document the microstructural evolution of a porous olivine aggregate reacting with a sodium bicarbonate solution at elevated pressure and temperature conditions. We observed porosity increases, near constant rate of crystal growth, and pervasive reaction-induced fractures. Based on the nanometer scale tomography data, we propose that shrinkage cracking is the mechanism responsible for producing new reactive surface and keep the carbonation reaction self-sustaining in our experiment. Shrinkage cracks are commonly observed in drying mud ponds, cooling lava flows and ice wedge fields. Stretching of a contracting surface bonded to a substrate of nearly constant dimensions leads to a stress buildup in the surface layer. When the stress exceeds the tensile strength, polygonal cracks develop in the surface layer. In our experiments, the stretching mismatch between the surface and interior of

  14. Mitigation of Autogenous Shrinkage of Ultra-High Performance Concrete by Rice Husk Ash%稻壳灰抑制超高性能混凝土的自收缩机理分析

    Institute of Scientific and Technical Information of China (English)

    叶光; VT.NGUYEN

    2012-01-01

    在过去的十几年中,超高性能混凝土(UHPC)由于其优异的性能(如:超高强度,低渗透性和优良的耐久性)已经成为一种非常有前景的建筑材料。然而,UHPC也像普通高性能混凝土一样,由于水泥和硅灰的掺量比较高,使其具有很大的自收缩性能。寻求一种有效减少自收缩的方法是近年来水泥及混凝土研究领域的一个非常重要的任务。本研究中采用稻壳灰(RHA)降低UHPC自收缩。结果表明:由于RHA具有很高的活性Si02含量和特殊的多孔结构,添加20%平均粒径为5.6帅的RHA可以抵消水化15d后的UHPC的自收缩;RHA用于UHPC中不仅降低了成本,提高混凝土早期性能,同时也有益于减少环境污染。%Ultra-high performance concrete (UHPC) becomes one of promising concretes in the last decade due to its excellent per- formance such as ultra high strength, low permeability and very good durability. However, like high performance concrete, the UHPC is also subjected to high autogenous shrinkage due to a great amount of cement and silica fume used. The reduction of the autogenous shrinkage is an important task in the field of cement and concrete research. In this work, the rice husk ash (RHA) as an agriculture waste was used to mitigate the autogenous shrinkage of UHPC. The results show that RHA with a high content of amorphous SiO2 and the special porous structure. When 20% RHA with particle size of 5.6 μn was used, the shrinkage of UHPC was eliminated after curing for 15 d. RHA used in UHPC can reduce the cost, improve the early age properties of the UHPC and increase the environ- mental benefits because RHA has high content of atmorphous SiO2 and special structure.

  15. The influence of shrinkage-cracking on the drying behaviour of White Portland cement using Single-Point Imaging (SPI).

    Science.gov (United States)

    Beyea, S D; Balcom, B J; Bremner, T W; Prado, P J; Cross, A R; Armstrong, R L; Grattan-Bellew, P E

    1998-11-01

    The removal of water from pores in hardened cement paste smaller than 50 nm results in cracking of the cement matrix due to the tensile stresses induced by drying shrinkage. Cracks in the matrix fundamentally alter the permeability of the material, and therefore directly affect the drying behaviour. Using Single-Point Imaging (SPI), we obtain one-dimensional moisture profiles of hydrated White Portland cement cylinders as a function of drying time. The drying behaviour of White Portland cement, is distinctly different from the drying behaviour of related concrete materials containing aggregates. PMID:9875607

  16. Influence of MB-value of Manufactured Sand on the Shrinkage and Cracking of High Strength Concrete

    Institute of Scientific and Technical Information of China (English)

    WANG Jiliang; YANG Zhifeng; NIU Kaimin; KE Guoju; ZHOU Mingkai

    2009-01-01

    The relation between methylene blue (MB) value of MS and its limestone dust content and clay content was investigated. The effects of MB value ranging from 0.35 to 2.5 on the workability of fresh concrete and crack propagation characteristics at the age of 24 hours, and effects on the mechanical properties, dry shrinkage of the harden concrete were tested. The experimental results show that the MB value is not related with the limestone dust content of MS, but in direct proportion to clay content. With the increase of MB value, the concrete workability decreases, and the flexural strength and 7 d compressive strength reduce markedly, whearas the 28 d compressive strength is not affected. When the MB-value is less than or equal to 1.35, the change of the MB-valuehas a little influence on early plastic cracking and dry shrinkage property of concrete, but when the MB-value is more than 1.35, the tendency of plastic cracking and dry shrinkage is remarkable.

  17. Investigation of Concrete Mixtures to Reduce Differential Shrinkage Cracking in Composite Bridges

    OpenAIRE

    Nelson, Douglas A.

    2013-01-01

    The objective of the research presented in this thesis was to develop a concrete bridge deck topping mixture that resists the effects of differential shrinkage by decreasing shrinkage and increasing creep. . In addition, the amount of tensile creep that concrete experiences under long-term tensile stresses were quantified and compared to compressive creep values in order to gain a better understanding of how concrete behaves under tension. Test results show that the amount of tensile creep ex...

  18. Investigation of shrinkage and cracking of ophthalmic lens coating by a cycle test of UV radiation and high humidity

    Energy Technology Data Exchange (ETDEWEB)

    Tadokoro, N., E-mail: nobuyuki.tadokoro@hoyavc.com [Technical Research and Development Institute, VC company, HOYA Corporation, 37 Satukigaoka, Minakuchi-cho, Kouka-shi, Shiga 528-0062 (Japan); Jaisupap, K.; Sukbumperng, A.; Pannakarn, S.; Khraikratoke, S.; Jamnongpian, P.; Iwata, N. [PL Technical Department, HOYA Lens Thailand, 202 Moo1, Banwah (Hi-Tech) Industrial Estate (Epz), Banlane, Bang Pa-in, Ayutthaya 13160 (Thailand)

    2012-04-02

    This paper presents some ophthalmic lens coating failures such as shrinkage, cracking, and cracking with delamination caused by UV radiation, elevated temperature, and moisture. These phenomena are caused by: 1) interactions at the interface between the plastic substrate and the hard coating (HC), and 2) plastic deformation with stress and relaxation of the HC/substrate interface. This phenomenon leads to an understanding of the mechanical properties of ophthalmic lenses through a QUV test which is found to be a useful method in developing better ophthalmic lens systems. The coating failures were investigated by means of different analysis techniques including optical microscope, scanning electron microscope, atomic force microscope, thermo mechanical analysis, and dynamic secondary ion mass spectrometry.

  19. Investigation of shrinkage and cracking of ophthalmic lens coating by a cycle test of UV radiation and high humidity

    International Nuclear Information System (INIS)

    This paper presents some ophthalmic lens coating failures such as shrinkage, cracking, and cracking with delamination caused by UV radiation, elevated temperature, and moisture. These phenomena are caused by: 1) interactions at the interface between the plastic substrate and the hard coating (HC), and 2) plastic deformation with stress and relaxation of the HC/substrate interface. This phenomenon leads to an understanding of the mechanical properties of ophthalmic lenses through a QUV test which is found to be a useful method in developing better ophthalmic lens systems. The coating failures were investigated by means of different analysis techniques including optical microscope, scanning electron microscope, atomic force microscope, thermo mechanical analysis, and dynamic secondary ion mass spectrometry.

  20. Shrinkage Reducing Admixture for Concrete

    OpenAIRE

    ECT Team, Purdue

    2007-01-01

    Concrete shrinkage cracking is a common problem in all types of concrete structures, especially for structures and environments where the cracks are prevalent and the repercussions are most severe. A liquid shrinkage reducing admixture for concrete, developed by GRACE Construction Products and ARCO Chemical Company, that reduces significantly the shrinkage during concrete drying and potentially reduces overall cracking over time.

  1. 粉煤灰表面改性及其对水泥浆体强度和自收缩的影响%Surface Modification of Fly Ashes and Its Effect on Strength and Autogenous Shrinkage of Cement Pastes

    Institute of Scientific and Technical Information of China (English)

    郝成伟; 邓敏; 莫立武; 刘开伟

    2011-01-01

    研究了白云石对Ⅲ级粉煤灰表面改性,并测定了掺改性粉煤灰水泥浆体的自收缩和抗压强度.利用X射线衍射、扫描电镜和能谱分析等测试方法对经950℃煅烧1 h后改性粉煤灰的物相结构和化学组成进行了表征,通过背散射扫描电镜观察和压汞试验研究了掺改性粉煤灰水泥浆体的微观结构.结果表明:改性粉煤灰颗粒表面生成了具有水化活性的β-C2S,其水化产生C-S-H凝胶,明显改善水泥浆体中粉煤灰颗粒与水泥基体的界面,降低水泥浆体孔隙率,提高改性粉煤灰水泥浆体的早期强度.白云石分解的MgO水化产生膨胀,补偿水泥浆体自收缩.%The surface of Grade Ⅲ fly ash particles was modified via addition of dolomite and calcination at 950 ℃ for 1 h. The microstructure, mineral phase and chemical compositions of the modified fly ash were analyzed by X-ray diffraction (XRD), scanning electron microscope and energy dispersive spectrometer. In addition, the effect of modified fly ash on the autogenous shrinkage and compressive strength of cement pastes was invesfgated, and the microstructure of cement pastes was determined by mercury intrusion porosimetry and back scattered electron microscope. The results show that the β-C2S phases were formed on the surface of fly ash particles after the surface modification. Due to the hydration of β-C2S, the porosity of cement pastes with the modified fly ashes was decreased, and the early strength of fly ash cement pastes was increased. The hydration of MgO due to the decomposition of dolomite can generate the expansion, leading to the compensation of the autogenous shrinkage of cement paste.

  2. Slow strain rate stress corrosion cracking behaviour of as-welded and plasma electrolytic oxidation treated AZ31HP magnesium alloy autogenous laser beam weldment

    International Nuclear Information System (INIS)

    The joining of a thin section AZ31HP magnesium alloy was accomplished by laser beam welding in the autogenous mode using a Nd-YAG laser system. Micro hardness evaluation and slow strain rate tensile (SSRT) tests in air revealed that the weld metal had near-matching mechanical properties corresponding to that of the parent alloy. However, in terms of stress corrosion cracking (SCC) resistance as assessed by SSRT tests in ASTM D1384 solution, the weldment was found to have higher susceptibility compared to the parent alloy. The fracture in the weld metal/fusion boundary/HAZ interface suggested that the failure was due to the grain coarsening at the very narrow heat affected zone. The resistance to SCC of the parent alloy and the weldment specimens was found to improve slightly by the application of plasma electrolytic oxidation (PEO) coating from a silicate based electrolyte.

  3. Micro-crack detection in high-performance cementitious materials

    DEFF Research Database (Denmark)

    Lura, Pietro; Guang, Ye; Tanaka, Kyoji; Jensen, Ole Mejlhede

    Detection and quantification of microcracks due to autogenous shrinkage in high-performance concrete represents a problematic issue. Techniques based on crack impregnation typically require drying of the samples, which may introduce further cracks. Other non-destructive techniques, such as x......-ray tomography, do not allow sufficient resolution of microcracks. A new technique presented in this paper allows detection of microcracks in cement paste while avoiding artefacts induced by unwanted restraint, drying or temperature variations. The technique consists in casting small circular cylindrical samples...... of high-performance cement pastes in silicone moulds that exert minimal external restraint. Cast-in steel rods with varying diameter internally restrain the autogenous shrinkage and lead to crack formation. Dimensions of the steel rods are chosen so that the size of this restraining inclusion...

  4. A Preliminary Numerical Investigation on the Influence of Material Variability in the Early-Age Cracking Behavior of Restrained Concrete

    DEFF Research Database (Denmark)

    Radlinska, Aleksandra; Pease, Bradley Justin; Weiss, Jason

    2007-01-01

    The restraint of drying, autogenous, or thermal shrinkage can result in the development of tensile residual stresses. If the residual stresses that develop are large enough, they may cause cracking in the concrete. Substantial research has focused on the development of test methods to assess stress...

  5. Autogenous Deformation of Concrete

    DEFF Research Database (Denmark)

    Autogenous deformation of concrete can be defined as the free deformation of sealed concrete at a constant temperature. A number of observed problems with early age cracking of high-performance concretes can be attributed to this phenomenon. During the last 10 years , this has led to an increased...... focus on autogenous deformation both within concrete practice and concrete research. Since 1996 the interest has been significant enough to hold international, yearly conferences entirely devoted to this subject. The papers in this publication were presented at two consecutive half-day sessions at the...... American Concrete Institute’s Fall Convention in Phoenix, Arizona, October 29, 2002. All papers have been reviewed according to ACI rules. This publication, as well as the sessions, was sponsored by ACI committee 236, Material Science of Concrete. The 12 presentations from 8 different countries indicate...

  6. Influence of ultra-fine fly ash on hydration shrinkage of cement paste

    Institute of Scientific and Technical Information of China (English)

    GAO Ying-li; ZHOU Shi-qiong

    2005-01-01

    Hydration shrinkage generated by cement hydration is the cause of autogenous shrinkage of high strength concrete. It may result in the volume change and even cracking of mortar and concrete. According to the data analysis in a series of experimental studies, the influence of ultra-fine fly ash on the hydration shrinkage of composite cementitious materials was investigated. It is found that ultra-fine fly ash can reduce the hydration shrinkage of cement paste effectively, and the more the ultra-fine fly ash, the less the hydration shrinkage. Compared with cement paste without the ultra-fine fly ash, the shrinkage ratio of cement paste reduces from 23.4% to 39.7% when the ultra-fine fly ash replaces cement from 20% to 50%. Moreover, the microscopic mechanism of the ultra-fine fly ash restraining the hydration shrinkage was also studied by scanning electron microscopy, X-ray diffraction and hydrated equations. The results show that the hydration shrinkage can be restrained to a certain degree because the ultra-fine fly ash does not participate in the hydration at the early stage and the secondary hydration products are different at the later stage.

  7. HETEK - Control of Early Age Cracking in Concrete

    DEFF Research Database (Denmark)

    Jensen, Ole Mejlhede; Christensen, Søren Lolk; Dela, Birgitte Friis;

    1997-01-01

    This report deals with autogenous shrinkage of two concretes and the corresponding mortars. The theory of self-desiccation and autogenous deformation is presented. Autogenous shrinkage of mortar is measuredin a paste dilatometer at constant and varying temperatures. Similarly the autogenous shrin...... shrinkage of the concrete is measured in a concrete dilatometer developed in this project. The results are discussed in relation to thermal expansion, activation energy and maturity transformation....

  8. Modelling of reinforcement corrosion - Investigations on the influence of shrinkage and creep on the development of concrete cracking in the early propagation stage of reinforcement corrosion

    Energy Technology Data Exchange (ETDEWEB)

    Bohner, E.; Mueller, H.S. [University of Karlsruhe (Germany). Institute of Concrete Structures and Building Materials

    2006-12-15

    Since the initiation stage of the damage process due to reinforcement corrosion had been successfully investigated in the recent past, the damage progress in the propagation stage is currently in the focus of research. This work deals with the mechanisms of cracking and spalling due to corrosion of reinforcement and aims for the development of an analytic prediction model of the damage process. On this occasion the influence of shrinkage and creep on the stress condition within the concrete cover is of major importance to the subsequent analysis of the crack formation due to reinforcement corrosion in the early propagation stage. (Abstract Copyright [2006], Wiley Periodicals, Inc.)

  9. Plastic Shrinkage Cracking Behavior of Pavement Cement Concrete at Early Age%路面水泥混凝土的早期塑性开裂性能

    Institute of Scientific and Technical Information of China (English)

    王稷良; 田波; 张擎

    2012-01-01

    针对目前路面水泥混凝土易于出现塑性开裂的情况,为更合理优化路面混凝土原材料与配合比设计参数,采用笠井芳夫教授提出的大板法,对比研究了水泥细度、矿物掺和料种类及掺量、混凝土配合比设计参数对路面混凝土早期塑性开裂性能的影响.试验结果表明,水泥的比表面积越大,矿物掺和料掺量越高,水灰比越小,混凝土浆集比越大时,越不利于路面水泥混凝土的塑性开裂控制.且相对于粉煤灰与矿粉,硅灰作为矿物掺和料时,硅灰将更显著降低混凝土抗塑性开裂等级.为提高路面水泥混凝土的抗裂性,宜选择比表面积小于360 kg/m3的水泥,水灰比大于0.4、浆集比小于275:725的配合比设计参数.当混凝土中掺加活性矿物掺和料时,应加强混凝土的早期养护,以抑制塑性裂缝的出现.%To cope with the situation that present pavement cement concrete is easy to appear plastic shrinkage cracking, in order to optimize the raw materials and the mix design parameters of pavement concrete more reasonably, the influence of fineness of cement, species and mixing amount of mineral admixture and concrete mix design parameters on early plastic shrinkage cracking performance of pavement cement concrete was comparatively studied by using the plate method proposed by Professor Kasai. The test results show that (1) it would be more detrimental to the control of plastic shrinkage cracking of pavement cement concrete when the cement specific surface area was larger, the content of mineral admixture became higher, the water-cement ratio turned smaller, and the cement paste-aggregate ratio trended to be greater; (2) relative to fly ash and mineral powder, silica fume will reduce the level of plastic shrinkage cracking resistance of concrete more significantly when used as mineral admixture; (3 ) in order to improve the crack resistance of pavement cement concrete, the mix design parameters should be

  10. Measuring autogenous strain of concrete with corrugated moulds

    DEFF Research Database (Denmark)

    Tian, Qian; Jensen, Ole Mejlhede

    A reliable technique to quantify autogenous strain is a prerequisite to numerical modeling in stress calculations for high performance concrete. The introducing of a special kind of corrugated tube mould helps to transforming volume strain measurement into liner strain measurement in horizontal...... direction for fluid concrete, which not only realizes the continuous monitoring of the autogenous shrinkage since casting, but also effectively eliminates the disturbance resulting from gravity, temperature variation and mould restraint on measuring results. Based on this measuring technique, this paper...

  11. Shrinkage Reducing Admixtures in Construction

    OpenAIRE

    Seguí Femenias, Yurena

    2011-01-01

    Cracking caused by drying or autegenous shrinkage is a real risk for cementitious material and compromise its durability as crack may serve as intgression paths for gases and salts or might permit leaching. Due to special requirements as application thickness, spray application, etc. on the one hand and durability as well as strength on the other hand repair mortars show an increased shrinkage and crack probability, which is highly undesired. In this study it will be investigated wich are the...

  12. Influence of temperature on autogenous deformation and relative humidity change in hardening cement paste

    DEFF Research Database (Denmark)

    Jensen, Ole Mejlhede; Hansen, Per Freiesleben

    1999-01-01

    This paper deals with autogenous deformation and autogenous relative humidity change (RH change) in hardening cement paste. Theoretical considerations and experimental data are presented, which elucidate the influence of temperature on these properties. This is an important subject in the control...... of early age cracking of concrete. It is demonstrated that the traditional maturity concept generally is not applicable to autogenous deformation and autogenous RH change. (C) 1999 Elsevier Science Ltd. All rights reserved....

  13. Shrinkage of Hong Kong granite aggregate concrete

    OpenAIRE

    Kwan, AKH; Au, FTK; Wong, HHC; Ng, PL

    2010-01-01

    In the design of many concrete structures, it is important to assess the amount of shrinkage that could occur because shrinkage could lead to extensive cracking or substantial prestress loss. A number of shrinkage models have been developed all over the world but they differ widely from each other, indicating that the shrinkage of concrete is dependent on the characteristics of the materials used and the local conditions. Early experimental studies in Hong Kong suggested that the shrinkage of...

  14. Impact of internal water reservoirs and steel fibres content on shrinkage of high strength concrete

    OpenAIRE

    Udir, Rok

    2014-01-01

    Due to its low water/cement ratio, high-strength concrete has a more pronounced early-age autogenous shrinkage. This thesis studies how to mitigate that by means of pre-soaked lightweight aggregate, various fractions and steel fibers. In the experimental part of the study, we measured the autogenous and total shrinkage of high-strength concrete, and used the results to calculate the contribution of drying shrinkage. We also measured the compressive strength of hardened concrete mixtures, and ...

  15. Shrinkage Behaviour of Fibre Reinforced Concrete with Recycled Tyre Polymer Fibres

    Directory of Open Access Journals (Sweden)

    Marijana Serdar

    2015-01-01

    Full Text Available Different types of fibres are often used in concrete to prevent microcracking due to shrinkage, and polypropylene fibres are among the most often used ones. If not prevented, microcracks can lead to the development of larger cracks as drying shrinkage occurs, enabling penetration of aggressive substances from the environment and reducing durability of concrete structures. The hypothesis of the present research is that polypropylene fibres, used in concrete for controlling formation of microcracks due to shrinkage, can be replaced with recycled polymer fibres obtained from end-of-life tyres. To test the hypothesis, concrete mixtures containing polypropylene fibres and recycled tyre polymer fibres were prepared and tested. Experimental programme focused on autogenous, free, and restrained shrinkage. It was shown that PP fibres can be substituted with higher amount of recycled tyre polymer fibres obtaining concrete with similar shrinkage behaviour. The results indicate promising possibilities of using recycled tyre polymer fibres in concrete products. At the same time, such applications would contribute to solving the problem of waste tyre disposal.

  16. Shrinkage behavior of a self-compacting concrete: Vedenje samozgoščevalnega betona pri krčenju:

    OpenAIRE

    Belas, Nadia; Bendani, Karim; Bouhamou, Nasr-Eddine; Mebrouki, Abdelkader

    2013-01-01

    This paper presents the influence of the mixing constituents on the behavior of self-compacting concretes (SCCs), especially, the effect of the paste volume in their fresh and hardened state. It explains the roles of the pore network and the microstructure of the hydrates in drying and autogenous shrinkage of SCCs. Several tests such as slump flow, L-box, sieve stability, bleeding, mechanical strength, free shrinkage (drying and autogenous shrinkage) and microstructural tests (mineralogical c...

  17. Measuring autogenous strain of concrete with corrugated moulds

    DEFF Research Database (Denmark)

    Tian, Qian; Jensen, Ole Mejlhede

    direction for fluid concrete, which not only realizes the continuous monitoring of the autogenous shrinkage since casting, but also effectively eliminates the disturbance resulting from gravity, temperature variation and mould restraint on measuring results. Based on this measuring technique, this paper......A reliable technique to quantify autogenous strain is a prerequisite to numerical modeling in stress calculations for high performance concrete. The introducing of a special kind of corrugated tube mould helps to transforming volume strain measurement into liner strain measurement in horizontal...

  18. Inlfuence of Additives on Shrinkage and Early-age Crack Resistance of Slag Cement Concrete%外加剂对矿渣水泥混凝土收缩与早期抗裂的影响

    Institute of Scientific and Technical Information of China (English)

    韩静云; 宋旭艳; 郜志海

    2016-01-01

    选用木钠减水剂、UEA-H膨胀剂、早强剂、柠檬酸缓凝剂以常用掺量外掺入矿粉水泥中,检测其化学收缩和干缩性能,同时将各掺量的外加剂分别引入到矿渣水泥混凝土中,检测其抗压强度以及早期抗裂性能,结果表明:木钠减水剂增加矿渣水泥的早期化学收缩,也增大矿渣水泥胶砂的干缩值;UEA-H膨胀剂增加矿渣水泥的化学收缩,并能降低矿渣水泥胶砂的干缩;早强剂则在早期就大幅度增加矿渣水泥的化学收缩,对胶砂体系干缩性能影响与基准矿渣水泥体系相当;柠檬酸缓凝剂能降低矿渣水泥的化学收缩值,但会提高胶砂体系的干缩值。木钠减水剂、UEA-H膨胀剂和早强剂都能提高矿渣水泥混凝土的早期抗裂性能,其中早强剂在所选用的几种外加剂中效果最好,而缓凝剂对矿渣水泥混凝土早期抗裂性能具有不利影响。%Sodium ligninsulfonate water reducer, UEA-H expansive agent, early strength agent and citric acid retarder could be introduced into slag cement, and then chemical shrinkage and dry shrinkage of system may be tested. After slag concrete with various additives respectively can be prepared, its compressive strength and early crack resistance may be determined. The results can show that: sodium ligninsulfonate water reducer can increase early chemical shrinkage and dry shrinkage of slag cement. UEA-H expansive agent can increase chemical shrinkage and reduce dry shrinkage of slag cement. Early strength agent can substantially increase early chemical shrinkage of slag cement. Inlfuence of early strength agent on dry shrinkage of slag cement may be similar to fundamental slag cement. Citric acid retarder can reduce chemical shrinkage of slag cement, but may improve dry shrinkage of cement system. Sodium ligninsulfonate water reducer, UEA-H expansive agent, early strength agent could improve early cracking resistance of slag concrete

  19. Properties of low drying-shrinkage concrete with shrinkage-reducing admixture

    International Nuclear Information System (INIS)

    Effects on drying shrinkage of concrete were tested by using cement, the limestone coarse aggregate and the shrinkage-reducing admixture. As the results, the drying shrinkage of concrete was realized below 400x10-6. By using this low drying-shrinkage concrete, to prevent cracking on concrete structure during the long service life and to secure the measuring accuracy of concrete structure related the accelerator are expected. (author)

  20. Analysis, prediction, and case studies of early-age cracking in bridge decks

    Science.gov (United States)

    ElSafty, Adel; Graeff, Matthew K.; El-Gharib, Georges; Abdel-Mohti, Ahmed; Mike Jackson, N.

    2016-06-01

    Early-age cracking can adversely affect strength, serviceability, and durability of concrete bridge decks. Early age is defined as the period after final setting, during which concrete properties change rapidly. Many factors can cause early-age bridge deck cracking including temperature change, hydration, plastic shrinkage, autogenous shrinkage, and drying shrinkage. The cracking may also increase the effect of freeze and thaw cycles and may lead to corrosion of reinforcement. This research paper presents an analysis of causes and factors affecting early-age cracking. It also provides a tool developed to predict the likelihood and initiation of early-age cracking of concrete bridge decks. Understanding the concrete properties is essential so that the developed tool can accurately model the mechanisms contributing to the cracking of concrete bridge decks. The user interface of the implemented computer Excel program enables the user to input the properties of the concrete being monitored. The research study and the developed spreadsheet were used to comprehensively investigate the issue of concrete deck cracking. The spreadsheet is designed to be a user-friendly calculation tool for concrete mixture proportioning, temperature prediction, thermal analysis, and tensile cracking prediction. The study also provides review and makes recommendations on the deck cracking based mainly on the Florida Department of Transportation specifications and Structures Design Guidelines, and Bridge Design Manuals of other states. The results were also compared with that of other commercially available software programs that predict early-age cracking in concrete slabs, concrete pavement, and reinforced concrete bridge decks. The outcome of this study can identify a set of recommendations to limit the deck cracking problem and maintain a longer service life of bridges.

  1. Analysis, prediction, and case studies of early-age cracking in bridge decks

    Science.gov (United States)

    ElSafty, Adel; Graeff, Matthew K.; El-Gharib, Georges; Abdel-Mohti, Ahmed; Mike Jackson, N.

    2016-05-01

    Early-age cracking can adversely affect strength, serviceability, and durability of concrete bridge decks. Early age is defined as the period after final setting, during which concrete properties change rapidly. Many factors can cause early-age bridge deck cracking including temperature change, hydration, plastic shrinkage, autogenous shrinkage, and drying shrinkage. The cracking may also increase the effect of freeze and thaw cycles and may lead to corrosion of reinforcement. This research paper presents an analysis of causes and factors affecting early-age cracking. It also provides a tool developed to predict the likelihood and initiation of early-age cracking of concrete bridge decks. Understanding the concrete properties is essential so that the developed tool can accurately model the mechanisms contributing to the cracking of concrete bridge decks. The user interface of the implemented computer Excel program enables the user to input the properties of the concrete being monitored. The research study and the developed spreadsheet were used to comprehensively investigate the issue of concrete deck cracking. The spreadsheet is designed to be a user-friendly calculation tool for concrete mixture proportioning, temperature prediction, thermal analysis, and tensile cracking prediction. The study also provides review and makes recommendations on the deck cracking based mainly on the Florida Department of Transportation specifications and Structures Design Guidelines, and Bridge Design Manuals of other states. The results were also compared with that of other commercially available software programs that predict early-age cracking in concrete slabs, concrete pavement, and reinforced concrete bridge decks. The outcome of this study can identify a set of recommendations to limit the deck cracking problem and maintain a longer service life of bridges.

  2. Soil shrinkage characteristics in swelling soils

    International Nuclear Information System (INIS)

    The objectives of this presentation are to understand soil swelling and shrinkage mechanisms, and the development of desiccation cracks, to distinguish between soils having different magnitude of swelling, as well as the consequences on soil structural behaviour, to know methods to characterize soil swell/shrink potential and to construct soil shrinkage curves, and derive shrinkage indices, as well to apply them to assess soil management effects

  3. Influence of fly ash fineness on water requirement and shrinkage of blended cement mortars

    Directory of Open Access Journals (Sweden)

    Vanissorn Vimonsatit

    2015-12-01

    Full Text Available In this paper, the influence of fly ash fineness on water requirement and shrinkage of blended cement mortar was studied. The results indicate that the water requirement and shrinkage characteristic of the blended cement mortar are dependent on fly ash fineness and replacement level. The use of coarse fly ash slightly reduces the water requirement but greatly reduced the drying and the autogenous shrinkage of the blended cement mortars and the reduction is more with an increase in the fly ash replacement level. The finer fly ashes further reduce the water requirement, but increase the drying and the autogenous shrinkages as compared with coarser fly ash. The incorporation of superplasticizer drastically reduces the water requirement, but the effect on the drying and autogenous shrinkages of the normal Portland cement mortar is small. However, for the fly ash mortar, the use of superplasticizer results in a decrease in drying shrinkage and in a substantial increase in the autogenous shrinkage particularly for the fine fly ash at a high replacement level.

  4. The soil reference shrinkage curve

    CERN Document Server

    Chertkov, V Y

    2014-01-01

    A recently proposed model showed how a clay shrinkage curve is transformed to the soil shrinkage curve at the soil clay content higher than a critical one. The objective of the present work was to generalize this model to the soil clay content lower a critical one. I investigated (i) the reference shrinkage curve, that is, one without cracks; (ii) the superficial layer of aggregates, with changed pore structure compared with the intraaggregate matrix; and (iii) soils with sufficiently low clay content where there are large pores inside the intraaggregate clay (so-called lacunar pores). The methodology is based on detail accounting for different contributions to the soil volume and water content during shrinkage. The key point is the calculation of the lacunar pore volume variance at shrinkage. The reference shrinkage curve is determined by eight physical soil parameters: (1) oven-dried specific volume; (2) maximum swelling water content; (3) mean solid density; (4) soil clay content; (5) oven-dried structural...

  5. Shrinkage Reducing Measures for Engineering Cementitious Composites

    Institute of Scientific and Technical Information of China (English)

    YANG Yingzi; YAO Yan; GAO Xiaojian; DENG Hongwei; YU Pengzhan

    2008-01-01

    Inhibition measurement of shrinkage of engineering cementitious composites(ECC) was investigated due to typical ECC with higher free drying shrinkage.The effects of expanded admixture (EA),shrinkage reducing admixture (SRA),coarse sand+stone powder (CS+SP)and superabsorbent polymer (SAP) on drying shrinkage and mechanical properties were studied.The experimental results show that ECC incorporating EA,SRA and coarse sand can retain around 60% of the typical ECC's free drying shrinkage.Superabsorbent polymerl(SAP) can delay the development of free drying shrinkage of ECC at different ages,and the effect of SAP is not distinct like the actions of EA,superabsorbent polymer(SRA) and coarse sand.Significantly,SAP may act as artificial flaw to form a more homogeneous defect system that increases the potential of saturated multiple cracking,hence the ductility of ECC will be improved greatly.

  6. Computation of shrinkage stresses in prestressed concrete containments

    International Nuclear Information System (INIS)

    According to a survey, surface cracking on PCRVs and PCCs under the investigations is confined to drying shrinkage and thermal strain effects and no instances of structurally significant cracking was been found. In this paper, the authors use FEM to compute humidity distribution in drying concrete and shrinkage stresses by internal restraint. Since PCC is built segment by segment in several years, a computational model taking into account construction sequence is presented and shrinkage stresses by external restraints are calculated with the model

  7. Effect of Cement Type on Autogenous Deformation of Cement-Based Materials

    DEFF Research Database (Denmark)

    Pietro, Lura; Ye, Guang; van Breugel, Klaas

    2004-01-01

    In this paper, measurements of non-evaporable water content, chemical shrinkage, autogenous deformation, internal relative humidity (RH), pore solution composition, and early-age elastic modulus are presented and discussed. All experiments were performed on Portland cement and blast-furnace slag ......, taking into account the influence of the dissolved salts in the pore solution, 2) the BFS cement paste studied shows pronounced self-desiccation and self-desiccation shrinkage, mainly caused by its very fine pore structure.......In this paper, measurements of non-evaporable water content, chemical shrinkage, autogenous deformation, internal relative humidity (RH), pore solution composition, and early-age elastic modulus are presented and discussed. All experiments were performed on Portland cement and blast-furnace slag...

  8. Assessment of measures to mitigate concrete shrinkage

    OpenAIRE

    Nunes, Júlio; Camões, Aires

    2013-01-01

    Concrete can have high tendency to shrink over time and this can cause its cracking and thus jeopardize its durability and increase significantly maintenance, repair or rehabilitation costs. In this context, this study intends to evaluate measures to mitigate concrete shrinkage through the incorporation of different percentages of fly ash (FA), shrinkage reducing admixtures (SRA) or superabsorbent polymers (SAP). For this, one has developed an experimental campaign on mortar specimens that co...

  9. Creep and shrinkage modelling of HPC : Based on the evolution of the degree of hydration and the internal relative humidity

    OpenAIRE

    STAQUET, S; TAILHAN, JL; ESPION, B

    2005-01-01

    The purpose of this paper is to present a creep and shrinkage modelling of high performance concrete (HPC) based on chemo-physical phenomena. For each component of the delayed effects (autogeneous shrinkage, desiccation shrinkage, basic creep, desiccation creep), a modelling based on the evolution of the temperature, the degree of hydration and the internal relative humidity of concrete computed with the CESAR-LCPC fem code is proposed.

  10. Shrinkage Properties of Cement Stabilized Gravel

    DEFF Research Database (Denmark)

    Lund, Mia Schou Møller; Hansen, Kurt Kielsgaard

    2014-01-01

    shrinkage properties of cement stabilized gravel have been documented under various temperature and relative humidity conditions. Two cement contents corresponding to a 28-days compressive strength of 6.2 MPa and 12.3 MPa have been tested and compared. It is found that the coefficient of linear expansion...... for the two cement contents is 9.9 × 10-6 ⁰C-1 and 11.3 × 10-6 ⁰C-1, respectively. Furthermore, it is found that reflecting cracking can mainly be explained by temperature dependent shrinkage rather than moisture dependent shrinkage....

  11. Reducing drying shrinkage of concrete by treatment of aggregate

    OpenAIRE

    Kwan, AKH; Fung, WWS; Wong, HHC

    2010-01-01

    Drying shrinkage of concrete has been found to cause cracking, water leakage and other serviceability problems and is thus an important research topic. In early studies, it has been found that the shrinkage of concrete varies with the rock aggregate used. This is partly because the aggregate also shrinks and the shrinkage of aggregate is dependent on the type of rock from which the aggregate is derived. However, there have been few studies on the shrinkage of rock and how the shrinkage of agg...

  12. Investigation on the Free and Restrained Shrinkage of Self-compacting Concrete

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    A novel ellipsis-ring cracking apparatus with an automatic monitoring system was used to measure the restrained shrinkage and initial cracking time of self-compacting concrete (SCC). The free shrinkage, restrained shrinkage and strength were integrated to evaluate the effect of the mineral admixtures and content of cementitious materials on shrinkage of SCC. The experimental results show that the initial cracking time of SCC incorporating fly ash was delayed, the shrinkage value and rate was reduced.The hydration achievement of silica fume increased free shrinkage and reduced initial cracking time of FA-SCC comparing to control sample, but silica fume improved the mechanical properties of FA-SCC in early age. As same strength, with the reducing the content of cementitious materials, the initial cracking time of SCC delayed and cracking sensitivity decreased markedly, especially when the content of cementitious materials achieve 450 kg/m3.

  13. Shrinkage anisotropy characteristics from soil structure and initial sample/layer size

    CERN Document Server

    Chertkov, V Y

    2014-01-01

    The objective of this work is a physical prediction of such soil shrinkage anisotropy characteristics as variation with drying of (i) different sample/layer sizes and (ii) the shrinkage geometry factor. With that, a new presentation of the shrinkage anisotropy concept is suggested through the sample/layer size ratios. The work objective is reached in two steps. First, the relations are derived between the indicated soil shrinkage anisotropy characteristics and three different shrinkage curves of a soil relating to: small samples (without cracking at shrinkage), sufficiently large samples (with internal cracking), and layers of similar thickness. Then, the results of a recent work with respect to the physical prediction of the three shrinkage curves are used. These results connect the shrinkage curves with the initial sample size/layer thickness as well as characteristics of soil texture and structure (both inter- and intra-aggregate) as physical parameters. The parameters determining the reference shrinkage c...

  14. PLASTIC SHRINKAGE CONTROLLING EFFECT BY POLYPROPYLENE SHORT FIBER WITH HYDROPHILY

    Science.gov (United States)

    Hosoda, Akira; Sadatsuki, Yoshitomo; Oshima, Akihiro; Ishii, Akina; Tsubaki, Tatsuya

    The aim of this research is to clarify the mechanism of controlling plastic shrinkage crack by adding small amout of synthetic short fiber, and to propose optimum polypropylene short fiber to control plastic shrinkage crack. In this research, the effect of the hydrophily of polypropylene fiber was investigated in the amount of plastic shrinkage of mortar, total area of plastic shrinkage crack, and bond properties between fiber and mortar. The plastic shrinkage test of morar was conducted under high temperature, low relative humidity, and constant wind velocity. When polypropylene fiber had hydrophily, the amount of plastic shrinkage of mortar was restrained, which was because cement paste in morar was captured by hydrophilic fiber and then bleeding of mortar was restrained. With hydrophily, plastic shrinkage of mortar was restrained and bridging effect was improved due to better bond, which led to remarkable reduction of plastic shrinkage crack. Based on experimental results, the way of developing optimum polypropylene short fiber for actual construction was proposed. The fiber should have large hydrophily and small diameter, and should be used in as small amount as possible in order not to disturb workability of concrete.

  15. The influence of shrinkage reducing admixtures on plastic shrinkage

    Directory of Open Access Journals (Sweden)

    Mora, J.

    2003-12-01

    Full Text Available Shrinkage reducing admixtures (SRAs are viable alternatives for reducing plastic shrinkage cracking in concrete. The objective of the present paper is to study early age plastic shrinkage in restrained concrete elements, where three different SRAs have been used. The influence of the admixture is analyzed through the following measurements: capillary pressure, evaporation, temperature evolution, crack evolution and settlement. The tests for studying the cracking and deformation were made on two different configurations (i.e., restrained prisms with reduced cross-section and restrained panel, in a wind tunnel, with controlled wind temperature and velocity. The conclusions obtained indicate the viability of the use of this type of admixture and the usefulness of the test methods.

    Los aditivos reductores de retracción (SRAs se plantean, hoy en día, como una alternativa viable para reducir la fisuración por retracción plástica. El objetivo del presente artículo es conocer mejor y predecir el comportamiento a primeras edades de la retracción plástica en elementos estructurales coaccionados, a los que se les ha añadido diversos aditivos reductores de retracción (tres tipos diferentes. Esta influencia se analiza a través de las siguientes propiedades: presión capilar, evaporación, evolución de temperaturas, evolución de fisuración, y deformaciones verticales de asentamiento. Los ensayos para estudiar la fisuración y las deformaciones se han realizado sobre diferentes configuraciones (prisma restringido con estrangulamiento y panel restringido, en un túnel de viento, con temperaturas y velocidades de viento controladas. Las conclusiones obtenidas señalan la viabilidad del empleo de este tipo de aditivos y la bondad de los métodos experimentales utilizados.

  16. Evaluation Analysis on Anti-cracking Performance of Semi-rigid Base Courses Based on Grey Relational Grade

    OpenAIRE

    Jinpeng Zhang

    2009-01-01

    The theory of grey relational grade was applied to calculate the relational grades between the maximum dry shrinkage strain and some evaluation indices of cracking resistance to dry shrinkage, and the relational grades between the maximum thermal shrinkage strain and some evaluation indices of cracking resistance to thermal shrinkage. The study results indicate that the relation between dry shrinkage energy anti-cracking coefficient and the maximum dry shrinkage strain and the relation betwee...

  17. Cure shrinkage in epoxy grouts for grouted repairs

    Science.gov (United States)

    Shamsuddoha, Md.; Islam, Md. Mainul; Aravinthan, Thiru; Manalo, Allan; Lau, Kin-tak

    2013-08-01

    Structures can go through harsh environmental adversity and can experience material loss and cracks during their service lives. Infill material is used to ensure a supporting bed for a grouted repair. Epoxy grouts are used for repairing and rehabilitating structures, such as foundations, bridges, piers, transportation pipelines, etc., because they are resistant to typical chemicals and possess superior mechanical properties than other grouts. The resin based infill used inside the void or cracked space of the repair is vulnerable to shrinkage. When these filled grouts have high resin content, cracks can develop from residual stresses, which can affect the load transfer performance. It follows that interlayer separation and cracking of infill layer can occur in a grouted repair. In this study, volumetric shrinkage of two epoxy grouts was measured over 28 days using a Pycnometer. The highest volumetric shrinkage measured after 7 days was found to be 2.72%. The results suggest that the volumetric shrinkage can be reduced to 1.1% after 7 days, through the introduction of a coarse aggregate filler; a 2.5 times reduction in shrinkage. About 98% and 92% of the total shrinkage over the 28 day period, of the unfilled and filled grouts respectively, was found to occur within 7 days of mixing. The gel-time shrinkages were also calculated, to determine the "postgel" part of the curing contraction which subsequently produces residual stresses in the hardened grout systems.

  18. Development of shrinkage resistant microfibre-reinforced cement-based composites

    Science.gov (United States)

    Hamedanimojarrad, P.; Adam, G.; Ray, A.; Thomas, P.; Vessalas, K.

    2012-06-01

    Different shrinkage types may cause serious durability dilemma on restrained concrete parts due to crack formation and propagation. Several classes of fibres are used by concrete industry in order to reduce crack size and crack number. In previous studies, most of these fibre types were found to be effective in reducing the number and sizes of the cracks, but not in shrinkage strain reduction. This study deals with the influence of a newly introduced type of polyethylene fibre on drying shrinkage reduction. The novel fibre is a polyethylene microfibre in a new geometry, which is proved to reduce the amount of total shrinkage in mortars. This special hydrophobic polyethylene microfibre also reduces moisture loss of mortar samples. The experimental results on short and long-term drying shrinkage as well as on several other properties are reported. The hydrophobic polyethylene microfibre showed promising improvement in shrinkage reduction even at very low concentrations (0.1% of cement weight).

  19. The influence of steel fibres content and pre-soaked lightweight aggregate on shrinkage of high strength concrete

    OpenAIRE

    Žnidaršič, Špela

    2012-01-01

    This thesis studies high strength concrete reinforced with steel fibers and pre-soaked lightweight aggregate. Steel fibers added to the steel mixture represented 0.5% of the total volume. 12% of the aggregate was replaced with pre-soaked lightweight aggregate. The focus of the analysis was on the autogenous shrinkage, which is very distinct at high strength concrete. The shrinkage was measured electronically during the first day. Later we measured it with a mobile displacement transducer.Besi...

  20. Multipass autogenous electron beam welding

    International Nuclear Information System (INIS)

    A multipass, autogenous welding procedure was developed for 7.6 mm (0.3 in.) wall thickness Type 304L stainless steel cylinders. The joint geometry has a 1.5 mm (0.06 in.) root-face width and a rectangular stepped groove that is 0.762 mm (0.03 in.) wide at the top of the root face and extends 1.5 mm in height, terminating into a groove width of 1.27 mm which extends to the outside of the 1.27 mm high weld-boss. One weld pass is made on the root, three passes on the 0.762 mm wide groove and three passes to complete the weld. Multipass, autogenous, electron beam welds maintain the characteristic high depth-to-width ratios and low heat input of single-pass, electron beam welds. The increased part distortion (which is still much less than from arc processes) in multipass weldments is corrected by a preweld machined compensation. Mechanical properties of multipass welds compare well with single-pass welds. The yield strength of welds in aluminum alloy 5083 is approximately the same for single-pass or multipass electron beam and gas, metal-arc welds. The incidence and size of porosity is less in multipass electron beam welding of aluminum as compared to gas, metal-arc welds. The multipass, autogenous, electron beam welding method has proven to be a reliable way to make some difficult welds in multilayer parts or in an instance where inside part temperature or weld underbead must be controlled and weld discontinuities must be minimized

  1. The physical effects of an intra-aggregate structure on soil shrinkage

    CERN Document Server

    Chertkov, V Y

    2014-01-01

    Clay and soil containing it have shrinkage curves that are qualitatively different in shape. The objective of this work is to qualitatively show with maximum simplicity, how a clay shrinkage curve turns into a soil shrinkage curve. Because of the crack volume the measured shrinkage curve is not the single-valued feature of a soil. We use a concept of the reference shrinkage curve that is only stipulated by soil shrinkage without cracking, single-valued, and qualitatively similar to an observed shrinkage curve. We also use new concepts of an intra-aggregate soil structure: (i) a rigid superficial layer of aggregates that loses water during shrinkage; and (ii) lacunar pores (micro-cracks) inside an intra-aggregate clay that change in volume during shrinkage. Then, through a series of consecutive steps, illustrating each step by a separate graphic presentation, we move from a clay shrinkage curve to a soil shrinkage curve with predicted qualitative features that coincide with those experimentally observed in num...

  2. Shrinkage of polypropylene fibre reinforced high strength concrete

    OpenAIRE

    Zajec, Matija

    2012-01-01

    In this diploma paper we deal with the analysis of high strength concrete, micro-reinforced with polypropylene fibers. We used four different lengths of polypropylene fibers: 6mm, 12 mm, 18 mm and 30 mm. The share of fibers in each concrete mixture is 0.5 % of the total volume. With high strength concretes autogenous shrinkage is very intensive, so the first day we measured it electronically with dial gauges. Later we measured the shrinking with a mobile displacement transducer. We measured a...

  3. Experimental Investigation of Shrinkage of Nano Hair Reinforced Concrete

    OpenAIRE

    Yadollah Batebi; Alireza Mirzagoltabar; Seyed Mostafa Shabanian; Sara Fateri

    2013-01-01

    Basically most of cement based mixtures are likely shrinking. Use of fibers is not a new idea in this case. Previously, there were some evidences that horse hair, straw and cotton fibers were used in mud and mortars in ancient times. Then, utilizing these fibers in concrete mixture may increase concrete workability and decrease shrinkage cracks. Due to nano cross-section of hair and its proper tensile strength this project investigates its application to reduce the shrinkage of concrete mixtu...

  4. WITH SHRINKAGE COMPENSATED

    Directory of Open Access Journals (Sweden)

    Nguyen The Vinh The Vinh

    2012-09-01

    Full Text Available The results of the development of organic-mineral modifiers to the increasing component for high-strength concrete. The effect of modifiers designed for mobility, strength and shrinkage of cement paste.

  5. Significance of Shrinkage Induced Clamping Pressure in Fiber-Matrix Bonding in Cementitious Composite Materials

    DEFF Research Database (Denmark)

    Stang, Henrik

    1996-01-01

    The present paper accesses the significance of shrinkage inducedclamping pressure in fiber/matrix bonding mechanisms incementitious composite materials. The paper contains a description of an experimental setup whichallows mbox{measurement} of the clamping pressure which develops on anelastic...... inhomogeneity embedded in a matrix consisting of acementitious material undergoing shrinkage during hydration(autogenous shrinkage). Furthermore, the paperpresents the analysis necessary to perform an interpretation of the experimental results and which allows for thedetermination of the clamping pressure...... used in high performance cementitious composite materials.Assuming a Coulomb type of friction on the fiber/matrix interface andusing typical values for the frictional coefficient it is shownthat the shrinkage induced clamping pressure could be one of the mostimportant factors determining the frictional...

  6. A relation between relative density, alloy composition and sample shrinkage for nanoporous metal foams

    International Nuclear Information System (INIS)

    Nanoporous metal foams synthesized by dealloying inherently undergo dimensional changes (shrinkage). If these changes are unaccounted for in the measurement of relative density, this can be underestimated, causing up to an order of magnitude error in weight-normalized properties. In constrained samples the shrinkage leads to build-up of tensile stress that modifies the porosity and may lead to crack formation. A relationship between shrinkage, relative density and atomic fraction is proposed and experimentally verified.

  7. 30 CFR 35.20 - Autogenous-ignition temperature test.

    Science.gov (United States)

    2010-07-01

    ... 30 Mineral Resources 1 2010-07-01 2010-07-01 false Autogenous-ignition temperature test. 35.20... Autogenous-ignition temperature test. (a) Purpose. The purpose of this test, referred to hereinafter as the ignition-temperature test, is to determine the lowest autogenous-ignition temperature of a hydraulic...

  8. Shrinkage reduction of dental composites by addition of expandable zirconia filler

    DEFF Research Database (Denmark)

    Skovgaard, M.; Almdal, Kristoffer; Sørensen, Bent F.;

    2011-01-01

    A problem with dental resin composites is the polymerization shrinkage, which makes the filling loosen from the tooth or induces crack formation. We have developed an expandable metastable tetragonal zirconia filler, which upon reaction with water, is able to counter the polymer shrinkage....... The shrinkage of the composite was calculated from density measurements using Archimedes method. The rate of the phase transformation in resin was measured by determining the volume fraction of monoclinic zirconia (vm). The composite had a vm of 0.5 after 8 h of water storage. The overall shrinkage...

  9. 9 CFR 113.113 - Autogenous biologics.

    Science.gov (United States)

    2010-01-01

    ... applicable standard requirement potency tests provided in 9 CFR part 113. If the culture of microorganisms... 9 Animals and Animal Products 1 2010-01-01 2010-01-01 false Autogenous biologics. 113.113 Section... information. (If any of the data are unavailable, the applicant for authorization should indicate that...

  10. Plastic shrinkage of mortars with shrinkage reducing admixture and lightweight aggregates studied by neutron tomography

    Energy Technology Data Exchange (ETDEWEB)

    Wyrzykowski, Mateusz, E-mail: mateusz.wyrzykowski@empa.ch [Empa, Swiss Federal Laboratories for Materials Science and Technology, Concrete and Construction Chemistry Laboratory, Dübendorf (Switzerland); Lodz University of Technology, Department of Building Physics and Building Materials, Lodz (Poland); Trtik, Pavel [Paul Scherrer Institute, Laboratory for Neutron Scattering and Imaging, Villigen (Switzerland); Empa, Swiss Federal Laboratories for Materials Science and Technology, Concrete and Construction Chemistry Laboratory, Dübendorf (Switzerland); Münch, Beat [Empa, Swiss Federal Laboratories for Materials Science and Technology, Concrete and Construction Chemistry Laboratory, Dübendorf (Switzerland); Weiss, Jason [Purdue University, School of Civil Engineering, West Lafayette (United States); Vontobel, Peter [Paul Scherrer Institute, Laboratory for Neutron Scattering and Imaging, Villigen (Switzerland); Lura, Pietro [Empa, Swiss Federal Laboratories for Materials Science and Technology, Concrete and Construction Chemistry Laboratory, Dübendorf (Switzerland); ETH Zurich, Institute for Building Materials (IfB), Zurich (Switzerland)

    2015-07-15

    Water transport in fresh, highly permeable concrete and rapid water evaporation from the concrete surface during the first few hours after placement are the key parameters influencing plastic shrinkage cracking. In this work, neutron tomography was used to determine both the water loss from the concrete surface due to evaporation and the redistribution of fluid that occurs in fresh mortars exposed to external drying. In addition to the reference mortar with a water to cement ratio (w/c) of 0.30, a mortar with the addition of pre-wetted lightweight aggregates (LWA) and a mortar with a shrinkage reducing admixture (SRA) were tested. The addition of SRA reduced the evaporation rate from the mortar at the initial stages of drying and reduced the total water loss. The pre-wetted LWA released a large part of the absorbed water as a consequence of capillary pressure developing in the fresh mortar due to evaporation.

  11. Plastic shrinkage of mortars with shrinkage reducing admixture and lightweight aggregates studied by neutron tomography

    International Nuclear Information System (INIS)

    Water transport in fresh, highly permeable concrete and rapid water evaporation from the concrete surface during the first few hours after placement are the key parameters influencing plastic shrinkage cracking. In this work, neutron tomography was used to determine both the water loss from the concrete surface due to evaporation and the redistribution of fluid that occurs in fresh mortars exposed to external drying. In addition to the reference mortar with a water to cement ratio (w/c) of 0.30, a mortar with the addition of pre-wetted lightweight aggregates (LWA) and a mortar with a shrinkage reducing admixture (SRA) were tested. The addition of SRA reduced the evaporation rate from the mortar at the initial stages of drying and reduced the total water loss. The pre-wetted LWA released a large part of the absorbed water as a consequence of capillary pressure developing in the fresh mortar due to evaporation

  12. Influence of shrinkage-reducing admixture on drying shrinkage and mechanical properties of high-performance concrete

    Institute of Scientific and Technical Information of China (English)

    Nguyen Quangphu; Jiang Linhua; Liu Jiaping; Tian Qian; Do Tienquan

    2008-01-01

    High-performance concrete (HPC) has specific performance advantages over conventional concrete in strength and durability. HPC mixtures are usually produced with water/binder mass ratios (mw/mB) in the range of 0.2-0.4, so volume changes of concrete as a result of drying, chemical reactions, and temperature change cannot be avoided. For these reasons, shrinkage and cracking are frequent phenomena. It is necessary to add some types of admixture for reduction of shrinkage and cracking of HPC. This study used a shrinkage-reducing admixture (SRA) for that purpose. Concrete was prepared with two different mw/mB(0.22 and 0.40) and four different mass fractions of SRA to binder (w(SRA) = 0%, 1%, 2%, and 4%). The mineral admixtures used for concrete mixes were: 25% fly ash (FA) and 25% slag by mass of binder for the mixture with mw/mB=0.40, and 15% silica fume (SF) and 25% FA for the mixture with mw/ma=0.22. Tests were conducted on 24 prismatic specimens, and shrinkage strains were measured through 120 days of drying. Compressive strength, splitting strength, and static modulus of elasticity were also determined. The results show that the SRA effectively reduces some mechanical properties of HPC. The reductions in compressive strength, splitting tensile strength, and elastic modulus of the concrete were 7%-24%, 9%-19%, and 5%-12%, respectively, after 90 days, compared to concrete mixtures without SRA. SRA can also help reduce drying shrinkage of concrete. The shrinkage strains of HPC with SRA were only as high as 41% of the average free shrinkage of concrete without SRA after 120 days of drying.

  13. Influence of shrinkage-reducing admixture on drying shrinkage and mechanical properties of high-performance concrete

    Directory of Open Access Journals (Sweden)

    Nguyen Quangphu

    2008-12-01

    Full Text Available Abstract: High-performance concrete (HPC has specific performance advantages over conventional concrete in strength and durability. HPC mixtures are usually produced with water/binder mass ratios (mW/mB in the range of 0.2-0.4, so volume changes of concrete as a result of drying, chemical reactions, and temperature change cannot be avoided. For these reasons, shrinkage and cracking are frequent phenomena. It is necessary to add some types of admixture for reduction of shrinkage and cracking of HPC. This study used a shrinkage-reducing admixture (SRA for that purpose. Concrete was prepared with two different mW/mB (0.22 and 0.40 and four different mass fractions of SRA to binder (w(SRA = 0%, 1%, 2%, and 4%. The mineral admixtures used for concrete mixes were: 25% fly ash (FA and 25% slag by mass of binder for the mixture with mW/mB = 0.40, and 15% silica fume (SF and 25% FA for the mixture with mW/mB = 0.22. Tests were conducted on 24 prismatic specimens, and shrinkage strains were measured through 120 days of drying. Compressive strength, splitting strength, and static modulus of elasticity were also determined. The results show that the SRA effectively reduces some mechanical properties of HPC. The reductions in compressive strength, splitting tensile strength, and elastic modulus of the concrete were 7%-24%, 9%-19%, and 5%-12%, respectively, after 90 days, compared to concrete mixtures without SRA. SRA can also help reduce drying shrinkage of concrete. The shrinkage strains of HPC with SRA were only as high as 41% of the average free shrinkage of concrete without SRA after 120 days of drying.

  14. Influence of shrinkage-reducing admixture on drying shrinkage and mechanical properties of high-performance concrete

    OpenAIRE

    Nguyen Quangphu; Jiang Linhua; Liu Jiaping; Tian Qian; Do Tienquan

    2008-01-01

    Abstract: High-performance concrete (HPC) has specific performance advantages over conventional concrete in strength and durability. HPC mixtures are usually produced with water/binder mass ratios (mW/mB) in the range of 0.2-0.4, so volume changes of concrete as a result of drying, chemical reactions, and temperature change cannot be avoided. For these reasons, shrinkage and cracking are frequent phenomena. It is necessary to add some types of admixture for reduction of shrinkage and crac...

  15. Physical modeling of the soil swelling curve vs. the shrinkage curve

    CERN Document Server

    Chertkov, V Y

    2014-01-01

    Physical understanding of the links between soil swelling, texture, structure, cracking, and sample size is of great interest for the physical understanding of many processes in the soil-air-water system and for applications in civil, agricultural, and environmental engineering. The background of this work is an available chain of interconnected physical shrinkage curve models for clay, intra-aggregate matrix, aggregated soil without cracks, and soil with cracks. The objective of the work is to generalize these models to the case of swelling, and to construct the physical-swelling-model chain with a step-by-step transition from clay to aggregated soil with cracks. The generalization is based on thorough accounting for the analogies and differences between shrinkage and swelling and the corresponding use, modification, or replacement of the soil shrinkage features. Two specific soil swelling features to be used are: (i) air entrapping in pores of the contributing clay; and (ii) aggregate destruction with the f...

  16. Experimental Investigation of Shrinkage of Nano Hair Reinforced Concrete

    Directory of Open Access Journals (Sweden)

    Yadollah Batebi

    2013-01-01

    Full Text Available Basically most of cement based mixtures are likely shrinking. Use of fibers is not a new idea in this case. Previously, there were some evidences that horse hair, straw and cotton fibers were used in mud and mortars in ancient times. Then, utilizing these fibers in concrete mixture may increase concrete workability and decrease shrinkage cracks. Due to nano cross-section of hair and its proper tensile strength this project investigates its application to reduce the shrinkage of concrete mixtures. For this purpose, human hair fibers were used in 0.4 and 0.8 and 1.2 weight percent and the length of the fibers in each case varied between 15 and 60 millimeter and the samples were made of dimensions of 40×40×160 millimeters. Results are shown as considerable amount of hair may reduce in the shrinkage in the hair reinforced concrete.

  17. Generalized double Pareto shrinkage

    CERN Document Server

    Armagan, Artin; Lee, Jaeyong

    2011-01-01

    We propose a generalized double Pareto prior for Bayesian shrinkage estimation and inferences in linear models. The prior can be obtained via a scale mixture of Laplace or normal distributions, forming a bridge between the Laplace and Normal-Jeffreys' priors. While it has a spike at zero like the Laplace density, it also has a Student's t-like tail behavior. Bayesian computation is straightforward via a simple Gibbs sampling algorithm. We investigate the properties of the maximum a posteriori estimator, as sparse estimation plays an important role in many problems, reveal connections with some well-established regularization procedures and show some asymptotic results. The performance of the prior is tested through simulations and application to real data.

  18. Comparative Study on Clˉ Penetration in Cracked High Ductility and Low Shrinkage Material and Steel Fiber Concrete%开裂后延性材料与钢纤维混凝土抗氯离子侵蚀对比

    Institute of Scientific and Technical Information of China (English)

    张君; 钟海涛; 居贤春; 王贯明

    2012-01-01

    The effect of cracks in steel fiber concrete(SFRC) and high ductility and low shrinkage material (LSECC) on Cl- penetration was investigated by pre-induced flexural cracks in concrete beams. The cracked beams with different crack width or tensile strains were then continuously soaked with 3% (by mass) NaCl solution or undergone drying and wetting cycles. The content(by mass) of Cl~ in concrete at the locations of cracks was determined by drilling powder sample with electric hammer. The experimental results show that the influence of cracks on the Cl- penetration is very significant. The content of Cl~ at the location of cracks in SFRC is 3 - 4 times compared to the place without cracks. The Cl~ content in SFRC is increased with increase of the crack width for the specimens soaked for 30 d. At 60 d after soaked, the content of Cl~ becomes almost constant irrespective of the penetration depth. Under drying and wetting conditions, the content of Cl- in SFRC greatly increases compared to those of continuously soaked. By contrast, LSECC can apparently reduce the content of Cl- , especially under drying and wetting conditions. The resistance to Cl- penetration for LSECC is obviously significant.%通过施加弯曲荷载预先在混凝土梁中产生宽度不等的裂缝或不同的拉应变损伤,然后以3%(质量分数)NaCl溶液连续浸泡或干湿循环方法对混凝土梁进行氯离子侵蚀.测定混凝土裂缝处氯离子含量,研究比较钢纤维混凝土和高延性低收缩材料(LSECC)中裂缝对氯离子侵蚀性能的影响.结果表明:混凝土中裂缝对氯离子渗透影响显著,裂缝大大加快了氯离子的侵蚀.钢纤维混凝土裂缝处氯离子含量(质量分数)最高可达相同浸泡龄期无裂缝处的3~4倍.连续浸泡30 d时,钢纤维混凝土裂缝处氯离子含量随裂缝宽度的增大而增加,连续浸泡60 d时氯离子含量基本达到饱和.干湿循环条件下,钢纤维混凝土所受的

  19. Shrinkage stress in concrete under dry-wet cycles: an example with concrete column

    Science.gov (United States)

    Gao, Yuan; Zhang, Jun; Luosun, Yiming

    2014-02-01

    This paper focuses on the simulation of shrinkage stress in concrete structures under dry-wet environments. In the modeling, an integrative model for autogenous and drying shrinkage predictions of concrete under dry-wet cycles is introduced first. Second, a model taking both cement hydration and moisture diffusion into account synchronously is used to calculate the distribution of interior humidity in concrete. Using the above two models, the distributions of shrinkage strain and stress in concrete columns made by normal and high strength concrete respectively under dry-wet cycles are calculated. The model results show that shrinkage gradient along the radial direction of the column from the center to outer surface increases with age as the outer circumference suffers to dry. The maximum and minimum shrinkage occur at the outer surface and the center of the column, respectively, under drying condition. As wetting starts, the shrinkage strain decreases with increase of interior humidity. The closer to the wetting face, the higher the humidity and the lower the shrinkage strain, as well as the lower the shrinkage stress. As results of the dry-wet cycles acting on the outer circumference of the column, cyclic stress status is developed within the area close to the outer surface of the column. The depth of the influencing zone of dry-wet cyclic action is influenced by concrete strength and dry-wet regime. For low strength concrete, relatively deeper influencing zone is expected compared with that of high strength concrete. The models are verified by concrete-steel composite ring tests and a good agreement between model and test results is found.

  20. Cracks in base-restrained plain and reinforced concrete walls

    OpenAIRE

    OUZAA, Kheira; BENMANSOUR, Mohammed Benali

    2010-01-01

    This study deals with the problem of shrinkage cracks in reinforced concrete walls restrained at the base. A finite element model to study cracking of the wall was proposed. Nonlinear behavior of concrete was considered by means of a smeared crack approach. The equations proposed by ACI Committee 209 were used to model the mechanical properties of concrete, as well as the average concrete shrinkage within the thickness of the wall. It was found that the suggested model closely pred...

  1. Shrinkage and Expansive Strain of Concrete with Fly Ash and Expansive Agent

    Institute of Scientific and Technical Information of China (English)

    GAO Peiwei; LU Xiaolin; TANG Mingshu

    2009-01-01

    The effects of fly ash and MgO-type expansive agent on the shrinkage and expan-sive strain of concrete with high magnesia cement were investigated. The results show that high volumes of fly ash may reduce the shrinkage strain of concrete and inhibit the expansive strain of concrete with MgO-type expansive agent, but can not eliminate the shrinkage of concrete. MgO-type expansive agent may produce expansive strain and compensate the shrinkage strain of concrete, re-lieve the cracking risk, but the hydration product of magnesia tends to get together in paste and pro-duce expansive cracking of concrete with high magnesia content according to SEM observation.

  2. Shrinkage Behaviour of Fibre Reinforced Concrete with Recycled Tyre Polymer Fibres

    OpenAIRE

    Marijana Serdar; Ana Baričević; Marija Jelčić Rukavina; Martina Pezer; Dubravka Bjegović; Nina Štirmer

    2015-01-01

    Different types of fibres are often used in concrete to prevent microcracking due to shrinkage, and polypropylene fibres are among the most often used ones. If not prevented, microcracks can lead to the development of larger cracks as drying shrinkage occurs, enabling penetration of aggressive substances from the environment and reducing durability of concrete structures. The hypothesis of the present research is that polypropylene fibres, used in concrete for controlling formation of microcr...

  3. Effect of the Key Mixture Parameters on Shrinkage of Reactive Powder Concrete

    OpenAIRE

    Shamsad Ahmad; Ahmed Zubair; Mohammed Maslehuddin

    2014-01-01

    Reactive powder concrete (RPC) mixtures are reported to have excellent mechanical and durability characteristics. However, such concrete mixtures having high amount of cementitious materials may have high early shrinkage causing cracking of concrete. In the present work, an attempt has been made to study the simultaneous effects of three key mixture parameters on shrinkage of the RPC mixtures. Considering three different levels of the three key mixture factors, a total of 27 mixtures of RPC w...

  4. Autogenic training as a therapy for adjustment disorder in adolescents

    Directory of Open Access Journals (Sweden)

    Jojić Boris R.

    2005-01-01

    Full Text Available INTRODUCTION Autogenic training is a widespread technique used in psychotherapy. The British school of autogenic training cites a large list of diseases, health states, and life changes, in which autogenic training can be of help. We wanted to explore the application of autogenic training as a therapy for adjustment disorder in adolescents. The sample consisted of a homogeneous group of 31 individuals, with an average age of 17.3±0.2 years, who were diagnosed with adjustment disorder, F 43.2, in accordance with ICD 10 search criteria. OBJECTIVE The aim of our work was to figure out the influence of autogenic training on adjustment disorder, through biophysical and biochemical indicators, and to research the efficacy of autogenic training as a therapy for adjustment disorder in adolescents. METHOD We observed adjustment disorder indicators and their changes in three phases, using initial, final, and control values, which we measured immediately before the beginning, immediately after the completion, and six months after the completion, of the practical course in autogenic training. We measured systolic and diastolic arterial blood pressure, brachial pulse rates, cortisol levels in plasma, cholesterol levels in blood, as well as glucose concentrations. During that period, autogenic training was employed as the sole therapy. RESULTS The study confirmed our preliminary assumptions. The measurements we performed showed that arterial blood pressure, pulse rates, cholesterol and cortisol concentrations, after the application of autogenic training among adolescents suffering from adjustment disorder, were lower than the initial values. They remained lower even six months after the completion of the practical course in autogenic training. CONCLUSION We concluded that autogenic training significantly decreases the values of physiological indicators of adjustment disorder, diminishes the effects of stress in an individual, and eases the adaptation of

  5. Preparation of High Shrinkage Polypropylene

    Institute of Scientific and Technical Information of China (English)

    吕文军; 王华平; 李建梅; 张玉梅

    2001-01-01

    The common PP chips have been used to prepare high shrinkage PP fibers with shrinkage in boiling water higher than 50%. Meanwhile, the process conditions on fiber structure and properties have been discussed in detail. With the increase of drawing temperature, the shrinkage in boiling water of the fiber increases at first,and then decreases in the temperature range from 70℃ to 100℃. The better drawing temperature is from 75℃ to 85℃ according to the melt index of the PP material. The shrinkage in boiling water of PP fiber increases with the increase of pump delivery. The orientation factor and crystallinity increase with the increase of drawing temperature. With an increase in drawing temperature,unit-cell numbers and monomer unit numbers in every crystal nucleus tend to increase, but unit volume crystal nucleus tend to reduce.

  6. The origin of early age expansions induced in cementitious materials containing shrinkage reducing admixtures

    International Nuclear Information System (INIS)

    Studies on the early-age shrinkage behavior of cement pastes, mortars, and concretes containing shrinkage reducing admixtures (SRAs) have indicated these mixtures frequently exhibit an expansion shortly after setting. While the magnitude of the expansion has been noted to be a function of the chemistry of the cement and the admixture dosage; the cause of the expansion is not clearly understood. This investigation uses measurements of autogenous deformation, X-ray diffraction, pore solution analysis, thermogravimetry, and scanning electron microscopy to study the early-age properties and describe the mechanism of the expansion in OPC pastes made with and without SRA. The composition of the pore solution indicates that the presence of the SRA increases the portlandite oversaturation level in solution which can result in higher crystallization stresses which could lead to an expansion. This observation is supported by deformation calculations for the systems examined.

  7. Modelling autogenous expansion for magnesia concrete in arch dams

    Institute of Scientific and Technical Information of China (English)

    Feng JIN; Guoxin ZHANG; Xiaoqing LUO; Chuhan ZHANG

    2008-01-01

    Magnesia Concrete is a kind of expansive con-crete used in Chinese hydraulic engineering more and more widely. To evaluate the effects of autogenous expan-sion on the stresses of arch dams, a simple model of auto-genous expansion for Magnesia Concrete in dam engineering is presented. This model is based on three assumptions: 1) the total amount of autogenous expan-sion of Magnesia Concrete is related only to the properties of materials and mixing of concrete; 2) the autogenous expansion of Magnesia Concrete is irreversible due to the irreversibility of hydration reaction of Magnesia in the concrete; 3) the autogenous expansion strain rates of Magnesia Concrete bear a relation between temperature and residual Magnesia per unit volume of concrete. The model is verified by some experimental data of autogen-ous expansion of Magnesia Concrete and field-measured data of an arch dam in China. Embedded into finite ele-ment arch dam simulation software, this model is employed to simulate the effects of autogenous expansion of Magnesia Concrete in hydraulic engineering.

  8. 自密实混凝土的收缩性能研究%Shrinkage of self-compacting concrete

    Institute of Scientific and Technical Information of China (English)

    杜艳静; 叶燕华; 朱国平; 刘霞

    2009-01-01

    Self-compacting concrete features good construction and filling performance.The good mechanical properties and durability are ob-vious when concrete was hardened.ha recent years,it is obtained more and more attention on projects.However,with the reduction of water to cement ratio and the incorporation of mineral admixture, the volume stability of self-compacting concrete can not be ignored.Especially the au-togenous shrinkage, it has already become one of the main reasons for cracking and influenced the durability of self-compacting concrete seri-ously.In view of the research and current application situations of self-compacting concrete, different factors impacting on the volume stability of self-compacting concrete and the corresponding experimental study methods were introduced.It attached importance to the research of shrink-age.It also pointed out that the concrete is a very complicated system in construction, and a comprehensive analysis should be done for shrink-age of self-compacting concrete.%近年来,自密实混凝土由于具有良好的施工性能和填充性能,并在硬化后具有良好的力学性能和耐久性,从而在工程应用中得到越来越多的关注.但随着水胶比的降低和矿物掺合料的掺入,使得自密实混凝土的体积稳定性变得不容忽视,尤其是自收缩,它已经成为产生裂缝的主要原因之一,严重影响到自密实混凝土的耐久性.基于自密实混凝土的研究和应用现状,对自密实混凝土收缩的影响因素、试验方法以及研究的重要性进行了探讨.从工程实际出发,考虑自密实混凝土的复杂特性,对自密实混凝土的收缩性能进行综合分析.

  9. Drying Shrinkage Characteristics of Concrete Reinforced With Oil Palm Trunk Fiber

    Directory of Open Access Journals (Sweden)

    Zakiah Ahmad

    2010-05-01

    Full Text Available Concrete is subject to some form of restraint, such as steel reinforcement, forms or adjacent members. As concrete begins to lose volume, the restraint inhibits movement, which then induces tensile stress in the concrete. Once the tensile capacity of the concrete has been exceeded, it will crack. Therefore this paper reports on a study of shrinkage of plain and concrete reinforced with bio-waste fiber namely oil palm trunk fiber (OPTF. Metallic rings are the most widely used devices to test the restrain shrinkage of concrete. When the concrete deforms due to shrinkage, the ring restrains the material and tensile stresses are induced. However in this investigation, square column with PVC ring was used to determine the time for concrete specimens to crack under restrained shrinkage. Forty five test specimens of square columns sized 400 mm x 400mm with height of 150 mm were manufactured using Grade 30 concrete with 25 mm length OPTF at different volume percentage of OPTF; 0%, 1%, 2%, 3% and 4% of the total concrete volume. Thick PVC pipe with different diameters; 150mm, 250 mm and 350 mm were cast at the centre of the specimens to act as stiff cores which provide the internal restraint. It is shown with the ring setup that the cracking potential of concrete under restrained shrinkage can be classified on the basis of how long it takes the material to crack or the rate of stressdevelopment in the material at various percentages of fibers. The contributions of fibers were evaluated by using crack width and length. It was found that by increasing the fiber content has resulted in reduction in drying shrinkage as well as controlling the cracking.

  10. Study on strength and shrinkage of high performance concrete with compound mineral admixtures%双掺矿物掺合料高性能混凝土的强度与收缩试验研究

    Institute of Scientific and Technical Information of China (English)

    赵素梅; 贡金鑫

    2016-01-01

    对双掺粉煤灰和矿渣的高性能混凝土进行了强度和收缩试验,分析了粉煤灰和矿渣双掺比例(1∶2、2∶3、1∶1)及双掺总量(30%、40%、50%)的影响。研究表明,在双掺比例相同的条件下,随着双掺总量的增加,高性能混凝土强度降低,总收缩和干缩降低,自收缩增加;在双掺总量相同的条件下,随着双掺比例的增加,高性能混凝土早期强度降低,后期强度增加、总收缩降低、自收缩减少和干缩增加。在双掺情况下,单独增加粉煤灰或矿渣的掺量,粉煤灰降低早期强度和总收缩的效果更明显,但矿渣引起自收缩增大的幅度大于粉煤灰引起自收缩减小的幅度;相比于粉煤灰,矿渣降低干缩的效果更明显;矿渣增大自收缩的幅度远小于其降低干缩的幅度。通过回归分析得到了双掺高性能混凝土的收缩计算式。%Experiments were made on the strength and shrinkage properties of high performance concrete with fly ash( FA)and ground granulated blast furnace slag(GGBFS),including the effect of the ratio of FA to GGBFS(1∶2,2∶3,1∶1)and the amount of FA and GG-BFS(30%,40%,50%).The results show that in the case of identical ratio of FA to GGBFS,the strength of the concrete decreases with the increase of the amount of the compound mineral admixtures,while the total shrinkage strain and the drying shrinkage strain reduces and the autogenous shrinkage strain increases. In the case of identical amount of the compound mineral admixtures,the strength of con-crete decreases at early age and increases later with the increase of ratio of FA to GGBFS,while total shrinkage strain and autogenous shrinkage strain decreases and drying shrinkage strain increases. For the compound mineral admixtures,the strength and total shrinkage strain of concrete decrease at early age with the increase of amount of FA or GGBFS. Contrast to GGBFS,the influence of FA is greater

  11. Autogenous Phenomena in Cement-Based Materials

    DEFF Research Database (Denmark)

    Jensen, Ole Mejlhede

    , som styrer deformationsforløbet. I forbindelse med denne afhandling er disse to fænomener blevet studeret gennem flere år. Den gennemgående tilgang har været at variere en lang række systemparametre – bl.a. temperatur, mikrosilicatilsætning, cementtype og vand/cement-forhold – og via en efterfølgende...... meningsfuld, eksperimentel definition af afbinding samt en operationel, teoretisk beskrivelse af sammenhængen mellem autogen deformation og RF-ændring. Specifikt vedrørende den foreslåede løsningsstrategi for autogent svind åbner denne afhandling op for en række nye muligheder. Som et eksempel på dette kan...

  12. Preliminary test-shrinkage estimators

    Directory of Open Access Journals (Sweden)

    H. H. Lemmer

    1983-03-01

    Full Text Available The advantages of using the very simple shrinkage estimator TL proposed by Lemmer rather than that proposed by Mehta and Srivivasan in the case of preliminary test estimators for parameters of the normal, binomial and Poisson distributions are examined.

  13. Sealing of cracks in cement using microencapsulated sodium silicate

    OpenAIRE

    Giannaros, Petros; Kanellopoulos, Antonios; Al-Tabbaa, Abir

    2016-01-01

    Cement-based materials possess inherent autogenous self-healing capability allowing them to seal, and potentially heal, microcracks. This can be improved through the addition of microencapsulated healing agents for autonomic self-healing. The fundamental principle of this self-healing mechanism is that when cracks propagate in the cementitious matrix, they rupture the dispersed capsules and their content (cargo material) is released into the crack volume. Various healing agents have been expl...

  14. Shrinkage estimators for covariance matrices.

    Science.gov (United States)

    Daniels, M J; Kass, R E

    2001-12-01

    Estimation of covariance matrices in small samples has been studied by many authors. Standard estimators, like the unstructured maximum likelihood estimator (ML) or restricted maximum likelihood (REML) estimator, can be very unstable with the smallest estimated eigenvalues being too small and the largest too big. A standard approach to more stably estimating the matrix in small samples is to compute the ML or REML estimator under some simple structure that involves estimation of fewer parameters, such as compound symmetry or independence. However, these estimators will not be consistent unless the hypothesized structure is correct. If interest focuses on estimation of regression coefficients with correlated (or longitudinal) data, a sandwich estimator of the covariance matrix may be used to provide standard errors for the estimated coefficients that are robust in the sense that they remain consistent under misspecification of the covariance structure. With large matrices, however, the inefficiency of the sandwich estimator becomes worrisome. We consider here two general shrinkage approaches to estimating the covariance matrix and regression coefficients. The first involves shrinking the eigenvalues of the unstructured ML or REML estimator. The second involves shrinking an unstructured estimator toward a structured estimator. For both cases, the data determine the amount of shrinkage. These estimators are consistent and give consistent and asymptotically efficient estimates for regression coefficients. Simulations show the improved operating characteristics of the shrinkage estimators of the covariance matrix and the regression coefficients in finite samples. The final estimator chosen includes a combination of both shrinkage approaches, i.e., shrinking the eigenvalues and then shrinking toward structure. We illustrate our approach on a sleep EEG study that requires estimation of a 24 x 24 covariance matrix and for which inferences on mean parameters critically

  15. Functional Horseshoe Priors for Subspace Shrinkage

    OpenAIRE

    Shin, Minsuk; Bhattacharya, Anirban; Johnson, Valen E.

    2016-01-01

    We introduce a new shrinkage prior called the functional horseshoe prior that encourages shrinkage towards parametric classes of functions. Unlike existing shrinkage priors for parametric models, the shrinkage acts on the shape of the function rather than sparsity of model parameters. We compare its performance with classical nonparametric estimators and a number of penalized likelihood approaches, and we show that the proposed procedure outperforms the competitors in the considered simulatio...

  16. Influence of shrinkage porosity on fatigue performance of iron castings and life estimation method

    Directory of Open Access Journals (Sweden)

    Wei Liu

    2016-01-01

    Full Text Available Shrinkage porosity exists more or less in heavy castings, and it plays an important role in the fatigue behavior of cast materials. In this study, fatigue tests were carried out on the QT400-18 cast iron specimens containing random degrees of shrinkage porosity defect. Experimental results showed that the order of magnitude of life scattered from 103 to 106 cycles when the shrinkage percentage ranged from 0.67% to 5.91%. SEM analyses were carried out on the shrinkage porosity region. The inter-granular discontinuous, micro cracks and inclusions interfered with the fatigue sliding or hindering process. The slip in shrinkage porosity region was not as orderly as the ordinary continuous medium. The shrinkage porosity area on fracture surface (SPAFS and alternating stress intensity factor (ASIF were applied to evaluate the tendency of residual life distribution; their relationship was fitted by negative exponent functions. Based on the intermediate variable of ASIF, a fatigue life prediction model of nodular cast iron containing shrinkage porosity defects was established. The modeling prediction was in agreement with the experimental results.

  17. Effect of the Key Mixture Parameters on Shrinkage of Reactive Powder Concrete

    Directory of Open Access Journals (Sweden)

    Shamsad Ahmad

    2014-01-01

    Full Text Available Reactive powder concrete (RPC mixtures are reported to have excellent mechanical and durability characteristics. However, such concrete mixtures having high amount of cementitious materials may have high early shrinkage causing cracking of concrete. In the present work, an attempt has been made to study the simultaneous effects of three key mixture parameters on shrinkage of the RPC mixtures. Considering three different levels of the three key mixture factors, a total of 27 mixtures of RPC were prepared according to 33 factorial experiment design. The specimens belonging to all 27 mixtures were monitored for shrinkage at different ages over a total period of 90 days. The test results were plotted to observe the variation of shrinkage with time and to see the effects of the key mixture factors. The experimental data pertaining to 90-day shrinkage were used to conduct analysis of variance to identify significance of each factor and to obtain an empirical equation correlating the shrinkage of RPC with the three key mixture factors. The rate of development of shrinkage at early ages was higher. The water to binder ratio was found to be the most prominent factor followed by cement content with the least effect of silica fume content.

  18. Effect of the key mixture parameters on shrinkage of reactive powder concrete.

    Science.gov (United States)

    Ahmad, Shamsad; Zubair, Ahmed; Maslehuddin, Mohammed

    2014-01-01

    Reactive powder concrete (RPC) mixtures are reported to have excellent mechanical and durability characteristics. However, such concrete mixtures having high amount of cementitious materials may have high early shrinkage causing cracking of concrete. In the present work, an attempt has been made to study the simultaneous effects of three key mixture parameters on shrinkage of the RPC mixtures. Considering three different levels of the three key mixture factors, a total of 27 mixtures of RPC were prepared according to 3(3) factorial experiment design. The specimens belonging to all 27 mixtures were monitored for shrinkage at different ages over a total period of 90 days. The test results were plotted to observe the variation of shrinkage with time and to see the effects of the key mixture factors. The experimental data pertaining to 90-day shrinkage were used to conduct analysis of variance to identify significance of each factor and to obtain an empirical equation correlating the shrinkage of RPC with the three key mixture factors. The rate of development of shrinkage at early ages was higher. The water to binder ratio was found to be the most prominent factor followed by cement content with the least effect of silica fume content. PMID:25050395

  19. Minimum Reinforcement in Concrete Structures under Restrained Shrinkage and Thermal Actions

    DEFF Research Database (Denmark)

    Christiansen, Morten Bo; Nielsen, Mogens Peter

    1999-01-01

    The present paper deals with minimum reinforcement to ensure limitation of crack widths in concrete structures subjected to small imposed strains, such as those from restrained shrinkage or thermal actions. A theory is presented, which models the behaviour of a tensile member from zero load to...

  20. Computed tomography evaluation of autogenous graft in sinus lift surgery

    International Nuclear Information System (INIS)

    The objective was to quantify bone formation within autogenous bone grafts and autogenous bone grafts in combination with platelet-rich plasma obtained either from apheresis or centrifugation using computed tomography. This prospective, double-blind study was conducted in 34 male and female adult patients (mean age of 28 years and 8 months), with either unilateral or bilateral pneumatization of the maxillary sinuses, requiring bone graft for dental implant. All patients were submitted to computed tomography examinations prior and six months after sinus lift surgery. Fifty-three maxillary sinuses were operated and divided into three distinct groups: autogenous bone graft, autogenous bone graft in combination with platelet-rich plasma obtained by centrifugation, and autogenous bone graft in combination with platelet-rich plasma obtained by apheresis. The results showed that computed tomography demonstrated bone growth in height and width between the initial and the follow-up computed tomography scans in all three groups. However, no statistical difference was found either for bone height or width. It was concluded that clinical evidence demonstrates the effectiveness of autogenous bone grafts, particularly when used in combination with bone growth factors such as platelet-rich plasma, which allow prosthetic and functional restoration of maxillofacial structures through fixation of dental implants. (author)

  1. Cracking Tendency of Restrained Concrete at Early Ages

    Institute of Scientific and Technical Information of China (English)

    BA Hengjing; SU Anshuang; GAO Xiaojian; TAO Qi

    2008-01-01

    A modified testing system characterized by full automation, steady operation and high accuracy of strain and stress measurements was developed to determine the cracking tendency of high strength concrete (HSC) in restrained condition at early ages. The shrinkage stress and the tensile creep behavior of HSC at early ages were investigated. The influence of W/C ratio and curing conditions on the early-age shrinkage stress and tensile creep was evaluated. It was found that the lower W/C ratio and drying curing condition resulted in higher shrinkage stress, stress induced tensile creep and greater cracking tendency.

  2. Assessment of autogenous Type 410S stainless steel welds in replacement steam generator tube support structures

    International Nuclear Information System (INIS)

    To eliminate fretting wear caused by flow-induced vibration in recirculating steam generators, tubes are separated from each other by tube support lattice bars. In the U-bend portion of the tube bundle, rows of tubes are separated by fan bars that radiate from collector bars located in the straight-leg portion of the steam generator. The replacement steam generators constructed by Babcock ampersand Wilcox International use Type 410S stainless steel with a specified maximum hardness of Rb 95 for tube support lattice bars, collector bars, and fan bars. An autogenous weld is used to join the fan bar to the collector bar. Corrosion tests were conducted to assess the stress corrosion cracking (SCC) susceptibility of welded type 410S stainless steel. These tests included constant-extension-rate (CERT) tests and long-term immersion tests on 410S in various welded and heat-treated conditions. The results of this test program demonstrate that, when highly stressed, the as-welded 410S weld joints are susceptible to SCC in steam generator environments. However, highly stressed 410S autogenous welds given a post-weld heat treatment were not susceptible to SCC even under faulted steam generator operating conditions

  3. Accounting for PDMS shrinkage when replicating structures

    DEFF Research Database (Denmark)

    Madsen, Morten Hannibal; Feidenhans'l, Nikolaj Agentoft; Hansen, Poul-Erik;

    2014-01-01

    Polydimethylsiloxane (PDMS) is a widely used material for fabrication of microfluidic devices and for replication of micro- and nanotextured surfaces. Shrinkage of PDMS in the fabrication process can lead to leaking devices and poor alignment of layers. However, corrections to the mold master are...... seldom applied to counteract the shrinkage of PDMS. Also, to perform metrological measurements using replica techniques one has to take the shrinkage into account. Thus we report a study of the shrinkage of PDMS with several different mixing ratios and curing temperatures. The shrinkage factor, with its...

  4. Shrinkage limit of soil mixtures

    International Nuclear Information System (INIS)

    Shrinkage limit, one of the Atterberg limits, is widely linked with many plasticity-based soil behaviors. However, in a great majority of these cases, such correlations have been found to exhibit poor performance. Recently, it has been brought out that the shrinkage limit of a natural soil does not depend upon plasticity characteristics, and it is primarily governed by the relative grain size distribution of the soil. The present study confirms this mechanism with the results obtained using clay-clay, clay-non-cohesive soil, and non-cohesive soil mix systems. The present study gains importance from the point of view of criteria with respect to the design of back fill materials to be used in various applications, such as nuclear waste disposal projects

  5. Effect of Expansive Admixtures on the Shrinkage and Mechanical Properties of High-Performance Fiber-Reinforced Cement Composites

    OpenAIRE

    Won-Chang Choi; Hyun-Do Yun

    2013-01-01

    High-performance fiber-reinforced cement composites (HPFRCCs) are characterized by strain-hardening and multiple cracking during the inelastic deformation process, but they also develop high shrinkage strain. This study investigates the effects of replacing Portland cement with calcium sulfoaluminate-based expansive admixtures (CSA EXAs) to compensate for the shrinkage and associated mechanical behavior of HPFRCCs. Two types of CSA EXA (CSA-K and CSA-J), each with a different chemical composi...

  6. An investigation into cracking in nickel-base superalloy repair welds

    OpenAIRE

    Rush, M. T.; Colegrove, Paul A.; Zhang, Z; Courtot, B.

    2010-01-01

    The nickel-base superalloy Rene 80 is considered very susceptible to liquation and strain-age cracking. Material in the solutionised condition is welded using the Cold Metal Transfer, or CMT process (with ductile filler alloy) and autogenously using a laser. Grain size is shown to have a significant effect on cracking. Using the CMT, welding power is shown to have high significance on the level of cracking, whereas welding speed has little effect. When welding using the lase...

  7. Spontaneous shrinkage of vestibular schwannoma

    Science.gov (United States)

    Romani, Rossana; Pollock, Jonathan

    2016-01-01

    Background: “Watch, wait, and rescan” (WWR) has an established place as a successful management option for a significant proportion of vestibular schwannomas (VS) as an alternative to microsurgical removal or stereotactic radiotherapy. VS may grow slowly and continuously, followed by stagnation or even shrinkage. We present two case reports of spontaneous shrinkage of VS along with a review of the literature. Case Description: A 29-year-old female presented with a progressive history of visual blurring and intermittent diplopia over 2 months. A 29 mm of maximum intracranial diameter (ICD) VS with secondary obstructive hydrocephalus was diagnosed. The patient underwent a ventriculo-peritoneal shunt with resolution of her symptoms and opted for initial WWR management. Interval scanning between 2007 and 2014 showed progressive reduction in the maximum ICD together with reduction in the degree of central tumor enhancement. Maximum ICD at most recent follow up was 22 mm. A 28-year-old female was referred with right sensorineural deafness. A right VS of maximum ICD of 27 mm was diagnosed. Initial WWR management was planned after discussion. Serial imaging showed an initial increase in the size of the tumor followed by progressive reduction in size. The most recent follow up showed a maximum ICD of 20 mm. Conclusion: Early WWR management can be associated with spontaneous shrinkage of VS over time. Prospective clinical study of larger numbers of such cases using the UK VS database may help to identify predictive factors for the spontaneous regression of VS. PMID:27280055

  8. Smooth Adaptation by Sigmoid Shrinkage

    Directory of Open Access Journals (Sweden)

    Atto AbdourrahmaneM

    2009-01-01

    Full Text Available This paper addresses the properties of a subclass of sigmoid-based shrinkage functions: the non zeroforcing smooth sigmoid-based shrinkage functions or SigShrink functions. It provides a SURE optimization for the parameters of the SigShrink functions. The optimization is performed on an unbiased estimation risk obtained by using the functions of this subclass. The SURE SigShrink performance measurements are compared to those of the SURELET (SURE linear expansion of thresholds parameterization. It is shown that the SURE SigShrink performs well in comparison to the SURELET parameterization. The relevance of SigShrink is the physical meaning and the flexibility of its parameters. The SigShrink functions performweak attenuation of data with large amplitudes and stronger attenuation of data with small amplitudes, the shrinkage process introducing little variability among data with close amplitudes. In the wavelet domain, SigShrink is particularly suitable for reducing noise without impacting significantly the signal to recover. A remarkable property for this class of sigmoid-based functions is the invertibility of its elements. This propertymakes it possible to smoothly tune contrast (enhancement, reduction.

  9. Numerical and experimental studies of drying and shrinkage induced microcracking in concrete

    Science.gov (United States)

    Jankovic, D.

    2007-12-01

    The aim of this research is to investigate moisture flow in cement paste and Interface Transition Zone, around aggregate, as well as associated shrinkage induced strains, and subsequent microcracking. Two coupled methods are used: numerical simulations and experiments. The moisture flow is numerically simulated by Lattice Gas Automata, while drying experiments are performed in Environmental Scanning Electron Microscope (ESEM) in order to determine drying deformations and shrinkage coefficient. The moisture movement simulation by Lattice Gas Automata, a type of cellular automata, involves different drying collision rules, which results in different density (moisture content) at each node. Special attention is given to the effect of the presence of aggregate particles on the moisture flow in concrete, which are considered rigid obstacles. The shrinkage deformation is considered a linear function of the moisture content if the relative humidity, RH does not exceed 40%. The calculated moisture gradient from the numerical analysis and an assumed shrinkage coefficient are used to calculate drying shrinkage induced strains and stresses using the basic equations. To determine the drying shrinkage coefficient for the RH range 100% to 20%, new experimental techniques of drying in ESEM are used. Small paste samples are cast in a specially developed mould with 2 mm thickness and afterwards carefully grounded and polished to a thickness of required 1 mm. The used variables in the tests are: various cement types, w/c ratio, sample age and curing conditions. Drying shrinkage displacements and strains are determined in order to calculate the drying shrinkage coefficient. These experimentally obtained values of the coefficient are compared with the literature data and used in numerical simulations of shrinkage induced strains, stresses and cracking in drying concrete.

  10. Chloride Ingress in Concrete Cracks under Cyclic Loading

    DEFF Research Database (Denmark)

    Küter, André; Geiker, Mette Rica; Olesen, John Forbes;

    2005-01-01

    increasing focus on the need for modeling the ingress of chloride into cracked concrete. Present models quantify chloride ingress in static cracks only, although several structural applications display dynamic loading conditions in an environment containing chlorides, e.g. marine structures and car parks....... Preliminary investigations have been undertaken to quantify the effect of dynamic load application on the chloride ingress into concrete cracks. Specimens were designed allowing ingress of a chloride solution into a single crack of a saturated unreinforced mortar beam. One set of specimens was subjected to a...... load frequency of ten applications per minute and a second set to one application per hour simulating static cracks, however limiting the ingress hampering effects of autogenous healing and a possible dense precipitation on the crack faces. The averaged chloride exposure interval of the crack faces was...

  11. A numerical analysis method on thermal and shrinkage stress of concrete

    International Nuclear Information System (INIS)

    Thermal stress often causes cracks in large scale concrete such as that for dam construction. The drying shrinkage of concrete causes cracks in concrete structures. These thermal stress and drying shrinkage stress may be the main reasons cracks occur in concrete, however there is few research which dealt with both stresses together. The problems on the thermal stress and the drying shrinkage are not independent, and should be dealt with together, because both temperature and water content of concrete affect hydration reaction, and the degree of hydration determines all the characteristics of concrete at early age. In this study, the degree of hydration is formulated experimentally, and a numerical stress analysis method taking the hydration reaction in consideration is presented. The formulation of the rate of hydration reaction, the method of analyzing thermal and drying shrinkage stresses, the analytical results for a concrete column and the influence that continuous load exerted to the tensile strength of concrete are reported. The relatively high stress nearly equal to the tensile strength of concrete arises near the surface. (K.I.)

  12. Crack Formation During Hardening in Fibre Reinforced Concrete

    DEFF Research Database (Denmark)

    Olesen, John Forbes; Stang, Henrik

    1996-01-01

    The objective of this project is to establish models for the development of cracks in the early age of fibre reinforced concrete due to restrained shrinkage and temperature variations. These models will be based on measurements of age dependant material properties including the post crack respons...

  13. Towards a better understanding of the cracking behavior in soils

    Science.gov (United States)

    Understanding and modeling shrinkage-induced cracks helps bridge the gap between flow problem in the laboratory and at the field. Modeling flow at the field scale with Darcian fluxes developed at the laboratory scales is challenged with preferential flows attributed to the cracking behavior of soils...

  14. Shrinkage behavior of self-compacting concrete

    Institute of Scientific and Technical Information of China (English)

    Farhad ASLANI; Shami NEJADI

    2012-01-01

    In the structures where long-term behavior should be monitored and controlled,creep and shrinkage effects have to be included precisely in the analysis and design procedures.Shrinkage varies with the constituent and mixture proportions,and depends on the curing conditions and the work environment as well.Self-compacting concrete (SCC) contains combinations of various components,such as aggregate,cement,superplasticizer,water-reducing agent and other ingredients which affect the properties of the SCC including shrinkage.Hence,the realistic prediction shrinkage strains of SCC are an important requirement of the design process for this type of concrete structures.This study reviews the accuracy of the conventional concrete (CC) shrinkage prediction models proposed by the international codes of practice,including CEB-FIP (1990),ACI 209R (1997),Eurocode 2 (2001),JSCE (2002),AASHTO (2004; 2007) and AS 3600 (2009).Also,SCC shrinkage prediction models proposed by Poppe and De Schutter (2005),Larson (2007),Cordoba (2007) and Khayat and Long (2010) are reviewed.Further,a new shrinkage prediction model based on the comprehensive analysis on both of the available models,i.e.,the CC and the SCC is proposed.The predicted shrinkage strains are compared with the actual measured shrinkage strains in 165 mixtures of SCC and 21 mixtures of CC.

  15. Knuckle Cracking

    Science.gov (United States)

    ... Our Faculty Our Staff Rheumatology Specialty Centers Knuckle Cracking Q & A September 10, 2007 By Arthritis Center ... immediately. Question: Are there any side effects to cracking knuckles? There is no evidence that cracking knuckles ...

  16. Autogenous healing properties of cement-based grouts

    International Nuclear Information System (INIS)

    This report presents the results of a study conducted to provide information on the ability of cement-based grouts to self-seal. Autogenous sealing was investigated both on bulk grouts and in thin films of grouts. In both cases, the self-sealing capabilities of the cement-based grouts were investigated with water flowing through the grout. Autogenous sealing was studied through changes in pore structure (decrease in pore radius and volume of pores) and changes in the rate of water flow through the cement-based grouts. (author)

  17. Cause analysis of cracks in circulating water culvert of Daya Bay Nuclear Power Station

    International Nuclear Information System (INIS)

    In view of the widespread cracks discovered in the reinforced-concrete circulating water culvert of Daya Bay Nuclear Power Station, cause analysis for the cracks is made in terms of construction and design. It is concluded that the cracks mainly resulted from shrinkage and temperature. Corresponding countermeasures are put forward thereafter for reference of similar projects

  18. Influence of Nano-SiO2 on the Consistency, Setting Time, Early-Age Strength, and Shrinkage of Composite Cement Pastes

    Directory of Open Access Journals (Sweden)

    Yu Chen

    2016-01-01

    Full Text Available The study outlined the raw materials and mix proportions to prepare composite cement pastes with the addition of silica-based micro- and nanoparticles. The effects of amorphous nano-SiO2 on the early-age properties, including the consistency, setting time, early-age strength, and chemical and autogenous shrinkages, were investigated. Under the condition of the same dosage of superplasticizer used, the consistency of cement paste with nano-SiO2 is higher than that with silica fume. Significant reductions of the initial and final setting times are observed especially for nano-SiO2 addition groups, and the time difference between the initial and final setting times goes up with the increasing proportions of nano-SiO2. The addition of nano-SiO2 is more helpful to the improvement of early-age strengths of the paste with or without fly ash admixed than silica fume additive for the same mass proportion. Both the chemical and autogenous shrinkages of cement paste develop with the increasing amount of micro- or nanolevel silica particles; however, nano-SiO2 plays a more active role than silica fume in inspiring early-age shrinkage. The physical and chemical mechanisms of nano-SiO2 in cement paste are also discussed.

  19. Accounting for PDMS shrinkage when replicating structures

    International Nuclear Information System (INIS)

    Polydimethylsiloxane (PDMS) is a widely used material for fabrication of microfluidic devices and for replication of micro- and nanotextured surfaces. Shrinkage of PDMS in the fabrication process can lead to leaking devices and poor alignment of layers. However, corrections to the mold master are seldom applied to counteract the shrinkage of PDMS. Also, to perform metrological measurements using replica techniques one has to take the shrinkage into account. Thus we report a study of the shrinkage of PDMS with several different mixing ratios and curing temperatures. The shrinkage factor, with its associated uncertainty, for PDMS in the range 40 to 120 °C is provided. By applying this correction factor, it is possible to replicate structures with a standard uncertainty of less than 0.2% in lateral dimensions using typical curing temperatures and PDMS mixing ratios in the range 1:6 to 1:20 (agent:base). (technical note)

  20. Autogenous Metallic Pipe Leak Repair in Potable Water Systems.

    Science.gov (United States)

    Tang, Min; Triantafyllidou, Simoni; Edwards, Marc A

    2015-07-21

    Copper and iron pipes have a remarkable capability for autogenous repair (self-repair) of leaks in potable water systems. Field studies revealed exemplars that metallic pipe leaks caused by nails, rocks, and erosion corrosion autogenously repaired, as confirmed in the laboratory experiments. This work demonstrated that 100% (N = 26) of 150 μm leaks contacting representative bulk potable water in copper pipes sealed autogenously via formation of corrosion precipitates at 20-40 psi, pH 3.0-11.0, and with upward and downward leak orientations. Similar leaks in carbon steel pipes at 20 psi self-repaired at pH 5.5 and 8.5, but two leaks did not self-repair permanently at pH 11.0 suggesting that water chemistry may control the durability of materials that seal the leaks and therefore the permanence of repair. Larger 400 μm holes in copper pipes had much lower (0-33%) success of self-repair at pH 3.0-11.0, whereas all 400 μm holes in carbon steel pipes at 20 psi self-repaired at pH 4.0-11.0. Pressure tests indicated that some of the repairs created at 20-40 psi ambient pressure could withstand more than 100 psi without failure. Autogenous repair has implications for understanding patterns of pipe failures, extending the lifetime of decaying infrastructure, and developing new plumbing materials. PMID:26057741

  1. Modeling of drying shrinkage of concrete specimens at the meso-level

    OpenAIRE

    Idiart Castellano, Andrés Enrique; López Garello, Carlos María; Carol, Ignacio

    2010-01-01

    In this paper, an existing mesomechanical model for cementitious materials is extended to the domain of diffusion-driven phenomena. The model is based on the Finite Element Method, and uses zerothickness interface elements equipped with a fracturebased constitutive formulation to represent cracks. The new developments presented in this paper consist of the application of the model to the hygro-mechanical coupled analysis of drying shrinkage in concrete specimens, explicitly taking in...

  2. Drying Shrinkage Characteristics of Concrete Reinforced With Oil Palm Trunk Fiber

    OpenAIRE

    Zakiah Ahmad; Azmi Ibrahim,; Paridah MD Tahir

    2010-01-01

    Concrete is subject to some form of restraint, such as steel reinforcement, forms or adjacent members. As concrete begins to lose volume, the restraint inhibits movement, which then induces tensile stress in the concrete. Once the tensile capacity of the concrete has been exceeded, it will crack. Therefore this paper reports on a study of shrinkage of plain and concrete reinforced with bio-waste fiber namely oil palm trunk fiber (OPTF). Metallic rings are the most widely used devices to test ...

  3. Breast specimen shrinkage following formalin fixation

    Directory of Open Access Journals (Sweden)

    Horn CL

    2014-02-01

    Full Text Available Christopher L Horn, Christopher Naugler Department of Pathology and Laboratory Medicine, University of Calgary, and Calgary Laboratory Services, Calgary, AB, Canada Abstract: Accurate measurement of primary breast tumors and subsequent surgical margin assessment is critical for pathology reporting and resulting patient therapy. Anecdotal observations from pathology laboratory staff indicate possible shrinkage of breast cancer specimens due to the formalin fixation process. As a result, we conducted a prospective study to investigate the possible shrinkage effects of formalin fixation on breast cancer specimens. The results revealed no significant changes in tumor size, but there were significant changes in the distance to all surgical resection margins from the unfixed to fixed state. This shrinkage effect could interfere with the accuracy of determining distance to margin assessment and tumor-free margin assessment. Thus, changes in these measurements due to the formalin fixation process have the potential to alter treatment options for the patient. Keywords: breast margins, formalin, shrinkage, cancer

  4. Volumetric polymerization shrinkage of contemporary composite resins

    Directory of Open Access Journals (Sweden)

    Halim Nagem Filho

    2007-10-01

    Full Text Available The polymerization shrinkage of composite resins may affect negatively the clinical outcome of the restoration. Extensive research has been carried out to develop new formulations of composite resins in order to provide good handling characteristics and some dimensional stability during polymerization. The purpose of this study was to analyze, in vitro, the magnitude of the volumetric polymerization shrinkage of 7 contemporary composite resins (Definite, Suprafill, SureFil, Filtek Z250, Fill Magic, Alert, and Solitaire to determine whether there are differences among these materials. The tests were conducted with precision of 0.1 mg. The volumetric shrinkage was measured by hydrostatic weighing before and after polymerization and calculated by known mathematical equations. One-way ANOVA (a or = 0.05 was used to determine statistically significant differences in volumetric shrinkage among the tested composite resins. Suprafill (1.87±0.01 and Definite (1.89±0.01 shrank significantly less than the other composite resins. SureFil (2.01±0.06, Filtek Z250 (1.99±0.03, and Fill Magic (2.02±0.02 presented intermediate levels of polymerization shrinkage. Alert and Solitaire presented the highest degree of polymerization shrinkage. Knowing the polymerization shrinkage rates of the commercially available composite resins, the dentist would be able to choose between using composite resins with lower polymerization shrinkage rates or adopting technical or operational procedures to minimize the adverse effects deriving from resin contraction during light-activation.

  5. A Shrinkage Estimator for Combination of Bioassays

    Institute of Scientific and Technical Information of China (English)

    Jian Xiong; D.G. Chen; Zhen-hai Yang

    2007-01-01

    A shrinkage estimator and a maximum likelihood estimator are proposed in this paper for combination of bioassays. The shrinkage estimator is obtained in closed form which incorporates prior information just on the common log relative potency after the homogeneity test for combination of bioassays is accepted. It is a practical improvement over other estimators which require iterative procedure to obtain the estimator for the relative potency. A real data is also used to show the superiorities for the newly-proposed procedures.

  6. Measuring techniques for autogenous strain of cement paste

    DEFF Research Database (Denmark)

    Lura, Pietro; Jensen, Ole Mejlhede

    2006-01-01

    the volumetric method. Water absorption is driven by a lowering of the water activity in the cement paste due to dissolved salts in the pore fluid and to self-desiccation. From the moment of casting, significant water uptake was registered in all experiments. This water uptake influenced the......Volumetric measurement of autogenous strain is frequently performed by placing the fresh cement paste in a rubber membrane submerged in water. The volume change of the cement paste is measured by the amount of water displaced by the submerged sample. Volumetric and linear measurements of autogenous...... strain should in principle give identical results. However, the measuring results from the volumetric method are typically 3-5 times higher than the results from the linear technique. In this paper, water uptake from the buoyancy bath through the rubber membrane is identified as the principal artefact of...

  7. Measuring techniques for autogenous strain of cement paste

    DEFF Research Database (Denmark)

    Lura, Pietro; Jensen, Ole Mejlhede

    2007-01-01

    the volumetric method. Water absorption is driven by a lowering of the water activity in the cement paste due to dissolved salts in the pore fluid and to self-desiccation. From the moment of casting, significant water uptake was registered in all experiments. This water uptake influenced the......Volumetric measurement of autogenous strain is frequently performed by placing the fresh cement paste in a rubber membrane submerged in water. The volume change of the cement paste is measured by the amount of water displaced by the submerged sample. Volumetric and linear measurements of autogenous...... strain should in principle give identical results. However, the measuring results from the volumetric method are typically 3-5 times higher than the results from the linear technique. In this paper, water uptake from the buoyancy bath through the rubber membrane is identified as the principal artefact of...

  8. Photogrammetric Assessment of Flexure Induced Cracking of Reinforced Concrete Beams under Service Loads

    OpenAIRE

    Pease, Bradley Justin; Geiker, Mette Rica; Stang, Henrik; Weiss, Jason

    2006-01-01

    Reinforced concrete structures are known to crack due to restrained shrinkage, temperature gradients, application of load, and expansive reactions. Cracks provide paths for rapid ingress of moisture, chlorides, and other aggressive substances, which may affect the long-term durability of the structure. For example, concrete cracks located at the reinforcing steel may contribute to a rapid corrosion initiation and propagation. Previous research has shown that cracked reinforced concrete under ...

  9. Solidification shrinkage of Ni-Cr alloys

    Energy Technology Data Exchange (ETDEWEB)

    Xiao Feng [Materials Interfacial Physical-Chemistry Research Institute, Chongqing Institute of Technology, No. 4 Xingsheng Road, Yangjiaping, Chongqing 400050 (China); Yang Renhui [Materials Interfacial Physical-Chemistry Research Institute, Chongqing Institute of Technology, No. 4 Xingsheng Road, Yangjiaping, Chongqing 400050 (China)]. E-mail: yangrh2004@21cn.com; Fang Liang [Department of Applied Physics, Chongqing University, No. 174 Shazhong Road, Shapingba, Chongqing 400044 (China); Zhang Chi [Materials Interfacial Physical-Chemistry Research Institute, Chongqing Institute of Technology, No. 4 Xingsheng Road, Yangjiaping, Chongqing 400050 (China)

    2006-07-25

    Ni-Cr superalloy is widely used in casting of critical components in gas-turbine engines. Because of the significant change in density of alloy in mushy state, porosity is likely to arise in the alloy parts due to the solidification shrinkage. On the other hand, because Ni-Cr alloy is very hard and difficult to be machined, the net-shape casting of the alloy is a cheap process. Therefore, it is essential to measure the solidification shrinkage of mushy alloy for obtaining low-cost net-shape casting ingot without inner porosity. However, there have been a few reports on the solidification shrinkage of the liquid Ni-Cr alloy. In this work, the solidification shrinkage of Ni-Cr alloy was calculated by measuring its density using modified sessile drop method. It has been found that, for Ni-(0-24.53)% Cr alloys, the solidification shrinkage value fluctuates in the range of 0.91-2.02% and it tends to increase with increasing Cr concentration in 0-10% Cr. However, for Cr concentration more than 10%, the solidification shrinkage holds on a certain value of 2.00%.

  10. Microfibres and hydrogels to promote autogenous healing in cementitious materials

    OpenAIRE

    Snoeck, Didier; Dubruel, Peter; De Belie, Nele

    2013-01-01

    Cementitious materials are sensitive to crack formation and it would be beneficial if the material could stop the crack propagation, repair the damage and reach again the original liquid-tightness and/or strength. Therefore, a cementitious material with synthetic microfibres and superabsorbent polymers (SAPs) is proposed. Upon crack formation, the microfibres will become active and due to the bridging action, they will stop the opening of a crack, forcing the cementitious material to crack so...

  11. Reducing the morbidity involved in harvesting autogenous rib cartilage.

    Science.gov (United States)

    Siegert, Ralf; Magritz, Ralph

    2009-08-01

    Although the use of autogenous cartilage is the gold standard in auricular reconstruction, its main disadvantage is the morbidity due to harvesting the cartilage. This includes postoperative pain, visible scar, and possibly asymmetry and reduced stability of the thorax. To reduce all of these drawbacks, we describe some modifications that reduce pain to a low tolerable level, hide the scar invisibly in the submammary fold in females, and induce regeneration as well reestablish stability of the rib defect. PMID:19809948

  12. Reorganization of the brain and heart rhythm during autogenic meditation

    OpenAIRE

    Dae-Keun Kim; Jyoo-Hi Rhee; Seung Wan Kang

    2014-01-01

    The underlying changes in heart coherence that are associated with reported EEG changes in response to meditation have been explored. We measured EEG and heart rate variability (HRV) before and during autogenic meditation. Fourteen subjects participated in the study. Heart coherence scores were significantly increased during meditation compared to the baseline. We found near significant decrease in high beta absolute power, increase in alpha relative power and significant increases in lower(a...

  13. Durability and Shrinkage Characteristics of Self-Compacting Concretes Containing Recycled Coarse and/or Fine Aggregates

    Directory of Open Access Journals (Sweden)

    Mehmet Gesoglu

    2015-01-01

    Full Text Available This paper addresses durability and shrinkage performance of the self-compacting concretes (SCCs in which natural coarse aggregate (NCA and/or natural fine aggregate (NFA were replaced by recycled coarse aggregate (RCA and/or recycled fine aggregate (RFA, respectively. A total of 16 SCCs were produced and classified into four series, each of which included four mixes designed with two water to binder (w/b ratios of 0.3 and 0.43 and two silica fume replacement levels of 0 and 10%. Durability properties of SCCs were tested for rapid chloride penetration, water sorptivity, gas permeability, and water permeability at 56 days. Also, drying shrinkage accompanied by the water loss and restrained shrinkage of SCCs were monitored over 56 days of drying period. Test results revealed that incorporating recycled coarse and/or fine aggregates aggravated the durability properties of SCCs tested in this study. The drying shrinkage and restrained shrinkage cracking of recycled aggregate (RA concretes had significantly poorer performance than natural aggregate (NA concretes. The time of cracking greatly prolonged as the RAs were used along with the increase in water/binder ratio.

  14. Subband-Adaptive Shrinkage for Denoising of ECG Signals

    Directory of Open Access Journals (Sweden)

    Kumaravel N

    2006-01-01

    Full Text Available This paper describes subband dependent adaptive shrinkage function that generalizes hard and soft shrinkages proposed by Donoho and Johnstone (1994. The proposed new class of shrinkage function has continuous derivative, which has been simulated and tested with normal and abnormal ECG signals with added standard Gaussian noise using MATLAB. The recovered signal is visually pleasant compared with other existing shrinkage functions. The implication of the proposed shrinkage function in denoising and data compression is discussed.

  15. The treatment of recalcitrant post-traumatic nightmares with autogenic training and autogenic abreaction: a case study.

    Science.gov (United States)

    Sadigh, M R

    1999-09-01

    Recurrent and frightening dreams are commonly experienced by patients who suffer from post-traumatic stress disorder after a motor vehicle accident. Such nocturnal episodes, if left untreated, can result in the experience of severe distress with physical, emotional, and psychophysiological concomitant. The present single-case study investigated the effects of the standard autogenic exercises and autogenic abreaction in reducing the frequency and severity of post-traumatic nightmares in a survivor of a car crash. The patient was also instructed in two additional organ-specific formulas in order to improve her sleep. The results of the study showed that the interventions were successful in effectively treating the patient's distressing nightmares. Follow-up data suggested that the treatment effects persisted after the termination of therapy. Suggestions for future investigations are discussed. PMID:10652639

  16. Heat shrinkage of electron beam modified EVA

    Energy Technology Data Exchange (ETDEWEB)

    Datta, S.K.; Chaki, T.K.; Bhowmick, A.K. [Indian Institute of Technology, Kharagpur (India). Rubber Technology Center; Tikku, V.K.; Pradhan, N.K. [NICCO Corporation Ltd., (Cable Div.), Calcutta (India)

    1997-10-01

    Heat shrinkage of electron beam modified ethylene vinyl acetate copolymer (EVA) has been investigated over a range of times, temperatures, stretching, irradiation doses and trimethylolpropane trimethacrylate (TMPTMA) levels. The irradiated (radiation dose 50 kGy and TMPTMA level 1%) and stretched (100% elongation) sample shrinks to a maximum level when kept at 453K temperature for 60 s. The heat shrinkage of samples irradiated with radiation doses of 20, 50, 100 and 150 kGy increases sharply with increasing stretching in the initial stage. Amnesia rating decreases with increasing radiation dose and TMPTMA level as well as gel content. The high radiation dose and TMPTMA level lower the heat shrinkage due to the chain scission. The effect of temperature at which extension is carried out on heat shrinkage is marginal. The irradiated (radiation dose 50 kGy and TMPTMA level 1%) EVA tubes of different dimensions expanded in a laboratory grade tube expander show similar behaviour at 453K and 60 s. The X-ray and DSC studies reveal that the crystallinity increases on stretching due to orientation of chains and it decreases to a considerable extent on heat shrinking. The theoretical and experimental values of heat shrinkage for tubes and rectangular strips are in good accord, when the radiation dose is 50 kGy and TMPTMA level 1%. (author).

  17. Heat shrinkage of electron beam modified EVA

    International Nuclear Information System (INIS)

    Heat shrinkage of electron beam modified ethylene vinyl acetate copolymer (EVA) has been investigated over a range of times, temperatures, stretching, irradiation doses and trimethylolpropane trimethacrylate (TMPTMA) levels. The irradiated (radiation dose 50 kGy and TMPTMA level 1%) and stretched (100% elongation) sample shrinks to a maximum level when kept at 453K temperature for 60 s. The heat shrinkage of samples irradiated with radiation doses of 20, 50, 100 and 150 kGy increases sharply with increasing stretching in the initial stage. Amnesia rating decreases with increasing radiation dose and TMPTMA level as well as gel content. The high radiation dose and TMPTMA level lower the heat shrinkage due to the chain scission. The effect of temperature at which extension is carried out on heat shrinkage is marginal. The irradiated (radiation dose 50 kGy and TMPTMA level 1%) EVA tubes of different dimensions expanded in a laboratory grade tube expander show similar behaviour at 453K and 60 s. The X-ray and DSC studies reveal that the crystallinity increases on stretching due to orientation of chains and it decreases to a considerable extent on heat shrinking. The theoretical and experimental values of heat shrinkage for tubes and rectangular strips are in good accord, when the radiation dose is 50 kGy and TMPTMA level 1%. (author)

  18. Addressing concrete cracking in NPPs

    International Nuclear Information System (INIS)

    The phenomenon of concrete cracking is one of the most frequently encountered deterioration at NPPs as it has been shown by a wide Survey of NPPs performed by IAEA in 1994-95 It can be due to a multitude of causes such as the normal ageing process (shrinkage, creep, prestressing force loss) as well as exposure to the environment (temperature variation, moisture, freeze/thaw, etc) The above mentioned Survey has also shown that in 64% of cases, no action was taken or required. It became also obvious that there is a lack of guidance as when remedial actions are needed. The paper describes, with the help of a Flow Chart, the various stages to be considered, from the first step of identification of cracks, to the definition of causes, evaluation of extent of damage, evaluation of effect/implications (safety, reliability), to the final step of deciding if repair action is required. Finally, based upon a wide literature survey the paper proposes in a Chart format, Criteria for addressing concrete cracks in NPPs., when taking in considerations all these factors. This paper discusses the process which should lead to the selection of an effective repair method and proposes, based upon worldwide standards and literature, criteria which should lead to the decision whether to repair or not concrete cracks, after the cracks have been identified and evaluated, addressing the entire range of aspects involved. (author)

  19. Influences of Reinforcement on Differential Drying Shrinkage of Concrete

    Institute of Scientific and Technical Information of China (English)

    GAO Xiaojian; QU Guangbin; ZHANG Ailian

    2012-01-01

    Shrinkage strain of concrete specimen with different reinforcement configuration was measured at various depths from the exposed surface by using several pairs of displacement sensors.Only one surface of the concrete specimen was exposed to dry condition during the experiment.The results show that differential shrinkage strain occurs in both plain and steel reinforced concrete specimens according to depths from the exposed surface.A higher reinforcement ratio results in a greater restraint against shrinkage of concrete nearby reinforcement rebar and a worse differential shrinkage strain distribution in the concrete specimen.The restraint against shrinkage of concrete becomes lower with the increasing distance from reinforcement rebar.Under the same reinforcement arrangement,a higher free shrinkage of concrete leads to a stronger restraint against shrinkage and a higher shrinkage stress formation in local concrete.The relationship between shrinkage strain and reduction of relative humidity in reinforced concrete structure is far different from that in plain concrete.

  20. Moisture migration and shrinkage of hardened cement paste at elevated temperatures

    International Nuclear Information System (INIS)

    The drying shrinkage of concrete is caused by the loss of water in the concrete. The moisture diffusion behavior influences the mechanical properties of concrete. When concrete is exposed to high temperature, the rate of moisture migration becomes fast, and moisture gradient is formed. This gradient causes cracks on the concrete surface. Accordingly, it is important to study on the relation between the drying shrinkage and the water diffusion in concrete when its mechanical properties at elevated temperature are discussed. In this paper, the results of the experiment which was carried out by using thin-walled cylinder specimens kept at different temperature and stress are reported. The specimens, the drying shrinkage of concrete and acoustic emission (AE), the thermal expansion of hardened cement paste, the influence that temperature change exerted to the drying shrinkage, and the influence that compressive stress and temperature exerted to water migration are described. The thin-walled cylinder specimens were useful for these experimental studies. (K.I.)

  1. Soil cracking modelling using the mesh-free SPH method

    CERN Document Server

    Bui, H H; Kodikara, J; Sanchez, M

    2015-01-01

    The presence of desiccation cracks in soils can significantly alter their mechanical and hydrological properties. In many circumstances, desiccation cracking in soils can cause significant damage to earthen or soil supported structures. For example, desiccation cracks can act as the preference path way for water flow, which can facilitate seepage flow causing internal erosion inside earth structures. Desiccation cracks can also trigger slope failures and landslides. Therefore, developing a computational procedure to predict desiccation cracking behaviour in soils is vital for dealing with key issues relevant to a range of applications in geotechnical and geo-environment engineering. In this paper, the smoothed particle hydrodynamics (SPH) method will be extended for the first time to simulate shrinkage-induced soil cracking. The main objective of this work is to examine the performance of the proposed numerical approach in simulating the strong discontinuity in material behaviour and to learn about the crack ...

  2. Assesment risk of fracture in thin-walled fiber reinforced and regular High Performance Concretes sandwich elements

    DEFF Research Database (Denmark)

    Hodicky, Kamil; Hulin, Thomas; Schmidt, Jacob Wittrup;

    2013-01-01

    High Performance Concrete Sandwich Elements (HPCSE) are an interesting option for future low or plus energy building construction. Recent research and development work, however, indicate that such elements are prone to structural cracking due to the combined effect of shrinkage and high temperature...... load. Due to structural restraints, autogenous shrinkage may lead to high self-induced stresses. Therefore autogenous shrinkage plays important role in design of HPCSE. The present paper assesses risk of fracture due to autogenous shrinkage-induced stresses in three fiber reinforced and regular High...... Performance Concretes (HPC). The research work described in this paper contains a description of experimental setup that allows measurement of effective shrinkage in HPC, which develops on an elastic inhomogeneity embedded in HPC matrix undergoing shrinkage during hydration (autogenous shrinkage). The test...

  3. The development trends of shrinkage stope leaching

    International Nuclear Information System (INIS)

    The shrinkage stope leaching is a comprehensive method of mining and hydrometallurgy containing the mining technology (involve developing, cutting, drilling, blasting, caving ore and moving some ores to ground) and leaching ore (include distributing solution, percolation leaching, bottom collecting solution, recovering solution containing metal and processing). Due to integration process, the mining and hydrometallurgy processes are greatly shortened, and the economic profits are very remarkable. The development history of shrinkage stope leaching is presented, and the property of its subject is briefly described. Using several typical examples, its characteristics are summarized and several problems to be resolved are discussed. Finally its development prospect is made

  4. Autogenous Regulation of Splicing of the Transcript of a Yeast Ribosomal Protein Gene

    Science.gov (United States)

    Dabeva, Mariana D.; Post-Beittenmiller, Martha A.; Warner, Jonathan R.

    1986-08-01

    The gene for a yeast ribosomal protein, RPL32, contains a single intron. The product of this gene appears to participate in feedback control of the splicing of the intron from the transcript. This autogenous regulation of splicing provides a striking analogy to the autogenous regulation of translation of ribosomal proteins in Escherichia coli.

  5. Autogenous regulation of splicing of the transcript of a yeast ribosomal protein gene.

    OpenAIRE

    Dabeva, M. D.; Post-Beittenmiller, M A; Warner, J R

    1986-01-01

    The gene for a yeast ribosomal protein, RPL32, contains a single intron. The product of this gene appears to participate in feedback control of the splicing of the intron from the transcript. This autogenous regulation of splicing provides a striking analogy to the autogenous regulation of translation of ribosomal proteins in Escherichia coli.

  6. Adjuvant auricular electroacupuncture and autogenic training in rheumatoid arthritis: a randomized controlled trial. Auricular acupuncture and autogenic training in rheumatoid arthritis

    DEFF Research Database (Denmark)

    Bernateck, M; Becker, M; Schwake, C;

    2008-01-01

    BACKGROUND: In contrast to psychological interventions the usefulness of acupuncture as an adjuvant therapy in rheumatoid arthritis (RA) has not yet been demonstrated. OBJECTIVE: The efficacy of auricular electroacupuncture (EA) was directly compared with autogenic training (AT). METHODS: Patients...

  7. Creep and shrinkage effects on integral abutment bridges

    Science.gov (United States)

    Munuswamy, Sivakumar

    Integral abutment bridges provide bridge engineers an economical design alternative to traditional bridges with expansion joints owing to the benefits, arising from elimination of expensive joints installation and reduced maintenance cost. The superstructure for integral abutment bridges is cast integrally with abutments. Time-dependent effects of creep, shrinkage of concrete, relaxation of prestressing steel, temperature gradient, restraints provided by abutment foundation and backfill and statical indeterminacy of the structure introduce time-dependent variations in the redundant forces. An analytical model and numerical procedure to predict instantaneous linear behavior and non-linear time dependent long-term behavior of continuous composite superstructure are developed in which the redundant forces in the integral abutment bridges are derived considering the time-dependent effects. The redistributions of moments due to time-dependent effects have been considered in the analysis. The analysis includes nonlinearity due to cracking of the concrete, as well as the time-dependent deformations. American Concrete Institute (ACI) and American Association of State Highway and Transportation Officials (AASHTO) models for creep and shrinkage are considered in modeling the time dependent material behavior. The variations in the material property of the cross-section corresponding to the constituent materials are incorporated and age-adjusted effective modulus method with relaxation procedure is followed to include the creep behavior of concrete. The partial restraint provided by the abutment-pile-soil system is modeled using discrete spring stiffness as translational and rotational degrees of freedom. Numerical simulation of the behavior is carried out on continuous composite integral abutment bridges and the deformations and stresses due to time-dependent effects due to typical sustained loads are computed. The results from the analytical model are compared with the

  8. Autogenic-Feedback Training Exercise (AFTE) Method and System

    Science.gov (United States)

    Cowings, Patricia S. (Inventor)

    1997-01-01

    The Autogenic-Feedback Training Exercise (AFTE) method of the present invention is a combined application of physiologic and perceptual training techniques. such as autogenic therapy and biofeedback. This combined therapy approach produces a methodology that is appreciably more effective than either of the individual techniques used separately. The AFTE method enables sufficient magnitude of control necessary to significantly reduce the behavioral and physiologic reactions to severe environmental stressors. It produces learned effects that are persistent over time and are resistant to extinction and it can be administered in a short period of time. The AFTE method may be used efficiently in several applications, among which are the following: to improve pilot and crew performance during emergency flying conditions; to train people to prevent the occurrence of nausea and vomiting associated with motion and sea sickness, or morning sickness in early pregnancy; as a training method for preventing or counteracting air-sickness symptoms in high-performance military aircraft; for use as a method for cardiovascular training, as well as for multiple other autonomic responses, which may contribute to the alleviation of Space Motion Sickness (SMS) in astronauts and cosmonauts; training people suffering from migraine or tension headaches to control peripheral blood flow and reduce forehead and/or trapezius muscle tension; training elderly people suffering from fecal incontinence to control their sphincter muscles; training cancer patients to reduce the nauseagenic effects of chemotherapy; and training patients with Chronic Intestinal Pseudo-obstruction (CIP).

  9. Variation of Shrinkage Strain within the Depth of Concrete Beams

    OpenAIRE

    Jong-Hyun Jeong; Yeong-Seong Park; Yong-Hak Lee

    2015-01-01

    The variation of shrinkage strain within beam depth was examined through four series of time-dependent laboratory experiments on unreinforced concrete beam specimens. Two types of beam specimens, horizontally cast and vertically cast, were tested; shrinkage variation was observed in the horizontally cast specimens. This indicated that the shrinkage variation within the beam depth was due to water bleeding and tamping during the placement of the fresh concrete. Shrinkage strains were measured ...

  10. No advantage to rhBMP-2 in addition to autogenous graft for fracture nonunion.

    Science.gov (United States)

    Takemoto, Richelle; Forman, Jordanna; Taormina, David P; Egol, Kenneth A

    2014-06-01

    Bone morphogenetic proteins are a necessary component of the fracture healing cascade. Few studies have delineated the efficacy of iliac crest bone graft and recombinant human bone morphogenetic protein 2 (rhBMP-2), especially, in comparison with the gold standard treatment of nonunion, which is autogenous bone graft alone. This study compared the outcome of patients with fracture nonunion treated with autogenous bone graft plus rhBMP-2 adjuvant vs patients treated with autogenous bone graft alone. A total of 118 consecutive patients who were to undergo long bone nonunion surgery with autogenous bone graft (50) or autogenous bone graft plus rhBMP-2 (68) were identified. Surgical intervention included either harvested iliac autogenous bone graft or autogenous bone graft plus 1.5 mg/mL of rhBMP-2 placed in and around the site of nonunion. No differences were found in the distribution of nonunion sites included within each group. Twelve-month follow-up was obtained on 100 of 118 patients (84.7%). Analyses of demographic characteristics (including tobacco), medical comorbidities, previous surgeries, and nonunion type (atrophic vs hypertrophic) did not differ. Postoperative complication rates did not differ. The percentage of patients who progressed to union did not differ. Mean time to union in the autogenous bone graft plus rhBMP-2 group was 6.6 months (±3.9) vs 5.4 (±2.7) months in the autogenous bone graft-only group (P=.06). Rates of revision (16.2% for rhBMP-2 plus autogenous bone graft vs 8% for autogenous bone graft) did not differ statistically (P=.19), nor did 12-month scores of pain and functional assessment. Although rhBMP-2 is a safe adjuvant, there was no benefit seen when rhBMP-2 was added to autogenous bone graft in the treatment of long bone nonunion. Given its high cost, rhBMP-2 should be reconsidered as an aid to autogenous bone graft in the treatment of nonunion. PMID:24972432

  11. Effect of Expansive Admixtures on the Shrinkage and Mechanical Properties of High-Performance Fiber-Reinforced Cement Composites

    Directory of Open Access Journals (Sweden)

    Won-Chang Choi

    2013-01-01

    Full Text Available High-performance fiber-reinforced cement composites (HPFRCCs are characterized by strain-hardening and multiple cracking during the inelastic deformation process, but they also develop high shrinkage strain. This study investigates the effects of replacing Portland cement with calcium sulfoaluminate-based expansive admixtures (CSA EXAs to compensate for the shrinkage and associated mechanical behavior of HPFRCCs. Two types of CSA EXA (CSA-K and CSA-J, each with a different chemical composition, are used in this study. Various replacement ratios (0%, 8%, 10%, 12%, and 14% by weight of cement of CSA EXA are considered for the design of HPFRCC mixtures reinforced with 1.5% polyethylene (PE fibers by volume. Mechanical properties, such as shrinkage compensation, compressive strength, flexural strength, and direct tensile strength, of the HPFRCC mixtures are examined. Also, crack width and development are investigated to determine the effects of the EXAs on the performance of the HPFRCC mixtures, and a performance index is used to quantify the performance of mixture. The results indicate that replacements of 10% CSA-K (Type 1 and 8% CSA-J (Type 2 considerably enhance the mechanical properties and reduce shrinkage of HPFRCCs.

  12. Effect of expansive admixtures on the shrinkage and mechanical properties of high-performance fiber-reinforced cement composites.

    Science.gov (United States)

    Choi, Won-Chang; Yun, Hyun-Do

    2013-01-01

    High-performance fiber-reinforced cement composites (HPFRCCs) are characterized by strain-hardening and multiple cracking during the inelastic deformation process, but they also develop high shrinkage strain. This study investigates the effects of replacing Portland cement with calcium sulfoaluminate-based expansive admixtures (CSA EXAs) to compensate for the shrinkage and associated mechanical behavior of HPFRCCs. Two types of CSA EXA (CSA-K and CSA-J), each with a different chemical composition, are used in this study. Various replacement ratios (0%, 8%, 10%, 12%, and 14% by weight of cement) of CSA EXA are considered for the design of HPFRCC mixtures reinforced with 1.5% polyethylene (PE) fibers by volume. Mechanical properties, such as shrinkage compensation, compressive strength, flexural strength, and direct tensile strength, of the HPFRCC mixtures are examined. Also, crack width and development are investigated to determine the effects of the EXAs on the performance of the HPFRCC mixtures, and a performance index is used to quantify the performance of mixture. The results indicate that replacements of 10% CSA-K (Type 1) and 8% CSA-J (Type 2) considerably enhance the mechanical properties and reduce shrinkage of HPFRCCs. PMID:24376382

  13. Patterns of cracking in soils due to drying and wetting cycles

    OpenAIRE

    Ledesma Villalba, Alberto; Cordero Arias, Josbel Andreina; Cuadrado Cabello, Agustín; Prat Catalán, Pere

    2014-01-01

    There is a well reported evidence of cracking in clayey or silty soils when drying. Shrinkage in the soil mass and also boundary conditions generate a nonhomogeneous stress state locally producing tensile stresses and eventually cracking. This process has been analysed in detail by several authors. However, the evolution of such cracks due to further relative humidity changes (i.e. wetting and drying again) has been rarely considered in the reported experiments. This paper describes a particu...

  14. Application of digital image correlation to full-field measurement of shrinkage strain of dental composites

    Institute of Scientific and Technical Information of China (English)

    Jian-ying LI; Andrew LAU; Alex S.L.FOK

    2013-01-01

    Objectives:Polymerization shrinkage of dental composites remains a major concern in restorative dentistry because it can lead to micro-cracking of the tooth and debonding at the tooth-restoration interface.The aim of this study was to measure the full-field polymerization shrinkage of dental composites using the optical digital image correlation (DIC) method and to evaluate how the measurement is influenced by the factors in experiment setup and image analysis.Methods:Four commercial dental composites,Premise Dentine,Z100,Z250 and Tetric EvoCeram,were tested.Composite was first placed into a slot mould to form a bar specimen with rectangular-section of 4 mm×2 mm,followed by the surface painting to create irregular speckles.Curing was then applied at one end of the specimen while the other part were covered against curing light for simulating the clinical curing condition of composite in dental cavity.The painted surface was recorded by a charge-coupled device (CCD) camera before and after curing.Subsequently,the volumetric shrinkage of the specimen was calculated with specialist DIC software based on image cross correlation.In addition,a few factors that may influence the measuring accuracy,including the subset window size,speckle size,illumination light and specimen length,were also evaluated.Results:The volumetric shrinkage of the specimen generally decreases with increasing distance from the irradiated surface with a conspicuous exception being the composite Premise Dentine as its maximum shrinkage occurred at a subsurface distance of about 1 mm instead of the irradiated surface.Zl00 had the greatest maximum shrinkage strain,followed by Z250,Tetric EvoCeram and then Premise Dentine.Larger subset window size made the shrinkage strain contour smoother.But the cost was that some details in the heterogeneity of the material were lost.Very small subset window size resulted in a lot of noise in the data,making it difficult to discern the general pattern in the strain

  15. Cracking resistance performance of super vertical-distance pumped SFRC

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    The mix ratio of steel fiber reinforced concrete(SFRC)was optimized using the principles that workability must meet the pumping demand and anti-cracking performance should be optimal.The effect of SFRC on the initial cracking load,the ultimate load and the crack width of the reinforced concrete (RC) member were analyzed in this paper.It was found that the admixture had good preservation of moisture and adhesion and the fibers distributed homogeneously in one hour out of the machine.According to the pumping results,the SFRC could be pumped vertically up to 306 m.Based on the standard computation formula of cracks,the maximum crack width of an RC member with 0.8% steel fiber (by volume) is about 32% lower than that of standard RC member.Through an experimental research on full-scale model tests for the steel and concrete composite anchorage zone on a pylon,the SFRC not only remarkably increases the crack resistance and the ultimate load,but the initial load also improves 33% approximately.It is also indicated that plastic shrinkage cracking of SFRC in which volume fraction of steel fibers is 0.8% can be restrained obviously and the unrestrained drying shrinkage can be diminished by about 50% at early age.The results confirmed that the SFRC can lessen the shrinkage crack of concrete and enhance markedly the direct tensile strength.Therefore,the SFRC can solve the key question of crack resistance for the anchorage zone of a bridge tower.

  16. Shrinkage characteristics of briquette during pyrolysis using online images collection

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Z.; Guo, Z.; Yuan, Z.; Wang, Z. [Chinese Academy of Sciences, Beijing (China)

    2005-10-15

    A new method was applied to study the shrinkage characteristics of coal during pyrolysis by realtime online images collection and computer image processing. The swelling and shrinkage characteristics of the briquette with different density were monitored using a digital camera during pyrolysis. Transient swelling and shrinkage phenomena were observed, and quantitative swelling and shrinkage were measured by computer images processing. The results show that the briquette begins to shrink at 400{sup o}C, and has two shrinkage ranges at 400 to 550{sup o}C and 650 to 800{sup o}C. The lateral shrinkage and volume shrinkage decrease with the increase of briquette densities. The lateral shrinkage and the volume shrinkage were 12 to 18% and 32 to 44%, respectively at 1000{sup o}C for 4 briquette samples with different densities. The volume shrinkage releases to sample contents of both the volatile matter and the ash. Generally, the volume shrinkage at 1000{sup o}C increases linearly with the increases of the volatile matter or the decrease of the ash content of briquette samples. 10 refs., 7 figs., 2 tabs.

  17. Confidence intervals for the shrinkage estimator

    Energy Technology Data Exchange (ETDEWEB)

    Nilsen, Odd Bjarte; Asche, Frank; Tveteras, Ragnar

    2005-08-01

    Shrinkage estimators have recently become popular in estimation of heterogeneous models on panel data. In this paper we show that the estimated covariance matrix in the posterior distribution of the shrinkage estimator fails to include the variability of the hyper parameters. Hence, standard confidence intervals for the parameters based on the ''estimated posterior'' distribution, are too narrow and thus the t-statistic is upward biased. The bootstrap method, which incorporates some of the variability in the hyper parameters, is an alternative method to obtain confidence intervals for the parameters. Our empirical example show that one has to be aware of the method used, since it can lead to significantly different economic conclusions. (Author)

  18. Distinct spontaneous shrinkage of a sporadic vestibular schwannoma.

    Science.gov (United States)

    Huang, Xiaowen; Caye-Thomasen, Per; Stangerup, Sven-Eric

    2013-04-01

    We present a case with outspoken spontaneous vestibular schwannoma shrinkage and review the related literature. The patient was initially diagnosed with a left-sided, intrameatal vestibular schwannoma, which subsequently grew into the cerebello-pontine angle (CPA), followed by total shrinkage of the CPA component without any intervention over a 12-year observation period. The literature on spontaneous tumor shrinkage was retrieved by searching the subject terms "vestibular schwannoma, conservative management" in PubMed/MEDLINE database, without a time limit. Of the published data, the articles on "shrinkage" or "negative growth" or "regression" or "involution" of the tumor were selected, and the contents on the rate, extent and mechanism of spontaneous tumor shrinkage were extracted and reviewed. The reported rate of spontaneous shrinkage of vestibular schwannoma is 5-10% of patients managed conservatively. Extreme shrinkage of the tumor may occur spontaneously. PMID:22858145

  19. Shrinkage Approach for Gene Expression Data Analysis

    Czech Academy of Sciences Publication Activity Database

    Haman, Jiří; Valenta, Zdeněk

    2013-01-01

    Roč. 9, č. 3 (2013), s. 2-8. ISSN 1801-5603 Grant ostatní: UK(CZ) SVV-2013-266517 Institutional support: RVO:67985807 Keywords : microarray technology * high dimensional data * mean squared error * James-Stein shrinkage estimator * mutual information Subject RIV: IN - Informatics, Computer Science http://www.ejbi.org/img/ejbi/2013/3/Haman_en.pdf

  20. Momentum universe shrinkage effect in price momentum

    OpenAIRE

    Jaehyung Choi; Sungsoo Choi; Wonseok Kang

    2012-01-01

    We test the price momentum effect in the Korean stock markets under the momentum universe shrinkage to subuniverses of the KOSPI 200. Performance of the momentum strategy is not homogeneous with respect to change of the momentum universe. It is found that some submarkets generate the higher momentum returns than other universes do but large-size companies such as the KOSPI 50 components hinder the performance of the momentum strategy. The observation is also cross-checked with size portfolios...

  1. Autogenic reaction synthesis of photocatalysts for solar fuel generation

    Energy Technology Data Exchange (ETDEWEB)

    Ingram, Brian J.; Pol, Vilas G.; Cronauer, Donald C.; Ramanathan, Muruganathan

    2016-04-19

    In one preferred embodiment, a photocatalyst for conversion of carbon dioxide and water to a hydrocarbon and oxygen comprises at least one nanoparticulate metal or metal oxide material that is substantially free of a carbon coating, prepared by heating a metal-containing precursor compound in a sealed reactor under a pressure autogenically generated by dissociation of the precursor material in the sealed reactor at a temperature of at least about 600.degree. C. to form a nanoparticulate carbon-coated metal or metal oxide material, and subsequently substantially removing the carbon coating. The precursor material comprises a solid, solvent-free salt comprising a metal ion and at least one thermally decomposable carbon- and oxygen-containing counter-ion, and the metal of the salt is selected from the group consisting of Mn, Ti, Sn, V, Fe, Zn, Zr, Mo, Nb, W, Eu, La, Ce, In, and Si.

  2. Three-dimensional modeling of solidification shrinkage

    Energy Technology Data Exchange (ETDEWEB)

    Raessi, M.; Mostaghimi, J. [Univ. of Toronto, Dept. of Mechanical and Industrial Engineering, Centre for Advanced Coating Technologies, Toronto, Ontario (Canada)]. E-mail: mraessi@mie.utoronto.ca

    2003-07-01

    The three-dimensional model of droplet impact and solidification developed by M. Pasandideh-Fard et al. has been modified to include the solidification shrinkage and the associated fluid flow induced due to density difference of solid and liquid phases. A fixed-grid control volume discretization of the momentum and energy equations, combined with a volume-tracking algorithm to track the free surface has been used. The governing equations for conservation of mass, momentum and energy are derived by assuming different yet constant solid and liquid densities. The analytical solution of the Stefan problem has been used to validate the model. The model was also applied to a planar (one-dimensional) solidification of finite extent of pure tin in which the final height of completely solidified tin is known analytically. The numerical and analytical solutions were in good agreement in these two validating problems. Finally the model was used to simulate solidification shrinkage of molten tin in a cubical container. The effects of solidification shrinkage were predicted well in the free surface. (author)

  3. Shrinkage deformation of cement foam concrete

    Science.gov (United States)

    Kudyakov, A. I.; Steshenko, A. B.

    2015-01-01

    The article presents the results of research of dispersion-reinforced cement foam concrete with chrysotile asbestos fibers. The goal was to study the patterns of influence of chrysotile asbestos fibers on drying shrinkage deformation of cement foam concrete of natural hardening. The chrysotile asbestos fiber contains cylindrical fiber shaped particles with a diameter of 0.55 micron to 8 microns, which are composed of nanostructures of the same form with diameters up to 55 nm and length up to 22 microns. Taking into account the wall thickness, effective reinforcement can be achieved only by microtube foam materials, the so- called carbon nanotubes, the dimensions of which are of power less that the wall pore diameter. The presence of not reinforced foam concrete pores with perforated walls causes a decrease in its strength, decreases the mechanical properties of the investigated material and increases its shrinkage. The microstructure investigation results have shown that introduction of chrysotile asbestos fibers in an amount of 2 % by weight of cement provides the finely porous foam concrete structure with more uniform size closed pores, which are uniformly distributed over the volume. This reduces the shrinkage deformation of foam concrete by 50%.

  4. PECULIARITIES OF APPLICATION THE METHOD OF AUTOGENIC TRAINING IN THE CORRECTION OF EATING BEHAVIOR

    OpenAIRE

    Shebanova, Vitaliya

    2014-01-01

    The article presented peculiarities of applying the method of autogenic training in the correction of eating disorders. Described stages of correction work with desadaptive eating behavior. Author makes accent on the rules self-assembly formula intentions.

  5. Adjuvant auricular electroacupuncture and autogenic training in rheumatoid arthritis: a randomized controlled trial

    DEFF Research Database (Denmark)

    Bernateck, M.; Becker, M.; Schwacke, C.;

    2008-01-01

    BACKGROUND: In contrast to psychological interventions the usefulness of acupuncture as an adjuvant therapy in rheumatoid arthritis (RA) has not yet been demonstrated. OBJECTIVE: The efficacy of auricular electroacupuncture (EA) was directly compared with autogenic training (AT). METHODS: Patient...

  6. Shrinkage vs. anti-shrinkage of the diffraction cone in the exclusive vector mesons production

    CERN Document Server

    Ivanov, I P

    2003-01-01

    We investigate the energy behavior of the diffraction cone in the exclusive vector meson production in diffractive DIS within the k_t-factorization approach. In our calculations, we make full use of fits to the unintegrated gluon structure functions extracted recently from experimental data on F_2p. Confirming early predictions, we observe that shrinkage of the diffraction cone due to the slope of the Pomeron trajectory is significantly compensated by the anti-shrinkage behavior of the gamma -> V transition. In order to match recent ZEUS data on the energy behavior of the diffraction slope, alpha^prime_eff(J/psi, exp.) = 0.115 +/- 0.018 (stat.) +0.008-0.015(syst.) GeV^-2, we had to use an input value alpha^\\prime_Pomeron = 0.25 GeV^-2. We investigate the compensation effect in detail and give predictions for Q^2-dependence of the rate of cone shrinkage for different vector mesons.

  7. The use of autogenous fascia lata to correct lid and orbital deformities.

    OpenAIRE

    Flanagan, J C; Campbell, C. B.

    1981-01-01

    Autogenous and homologous fascia lata have been used to correct many problems in ophthalmic surgery. This paper has described the use of autogenous fascia late to correct lid retraction secondary to thyroid ophthalmopathy, cicatricial entropion and extruding orbital implants. The surgical procedures have been briefly discussed, as well as the presentation of one clinical example of each procedure the pathologic and immunologic aspects of fascia lata grafts will be reported at a later date.

  8. Bone regeneration in surgically created defects filled with autogenous bone: an epifluorescence microscopy analysis in rats

    OpenAIRE

    Marcos Heidy Guskuma; Eduardo Hochuli-Vieira; Flávia Priscila Pereira; Idelmo Rangel-Garcia Junior; Roberta Okamoto; Tetuo Okamoto; Osvaldo Magro Filho

    2010-01-01

    Although the search for the ideal bone substitute has been the focus of a large number of studies, autogenous bone is still the gold standard for the filling of defects caused by pathologies and traumas, and mainly, for alveolar ridge reconstruction, allowing the titanium implants installation. OBJECTIVES: The aim of this study was to evaluate the dynamics of autogenous bone graft incorporation process to surgically created defects in rat calvaria, using epifluorescence microscopy. MATERIAL A...

  9. Eyelid-associated complications after autogenous fat injection for cosmetic forehead augmentation

    OpenAIRE

    Paik, Ji-Sun; Cho, Won-Kyung; Park, Gyeong-Sin; Yang, Suk-Woo

    2013-01-01

    Background We report two cases of unilateral upper eyelid swelling with multiple small lumps as an unusual complication of autogenous fat injection for cosmetic forehead augmentation. Case presentation Two female patients were referred to our clinic for unusual unilateral eyelid swelling, with multiple small lumps. The duration of symptoms differed in each case, but both patients had a history of autogenous fat injection for cosmetic forehead augmentation at a local plastic surgery clinic. Th...

  10. Method of as-cast crack prediction within solidified layer

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Based on the numerical simulation of solidification of castings, a thermal stress formula and a thermal crack initiation criterion are proposed. Using these formulas, cast steel wheels with a diameter of 800 mm and aluminum alloy electromagnetic casting (EMC) slabs with a size of 1300 mm × 480 mm are employed to testify the positions of cracks through conventional thermal elastic-plastic analyses and low magnifying structure observations. The results show that the numerical prediction of cracks agrees with the measured results, and the cracks do not necessarily occur on the defects such as shrinkage holes (wheel) and porosity (EMC slab). It is also found that surface temperature control is an effective means to avoid the crack formation.

  11. Formation of cracks on photodegraded nylon 6 filaments

    International Nuclear Information System (INIS)

    Cracks were found on the surface of drawn nylon 6 filaments irradiated with ultraviolet (UV) light from a mercury lamp under various humidities at room temperature. The cracks were formed perpendicular to the fiber axis and were of varying sizes. No cracks were observed on undrawn filaments or drawn filaments exposed to UV light in a dry atmosphere. Considerable shrinkage was found in drawn samples by thermomechanical analysis indicating the presence of residual stress in the material. The cracking is explained in terms of the residual stress and plasticization by moisture. The presence of water appears to play an important role in the formation of cracks on nylon fibers which have been subjected either to UV light or to ν-ray irradiation

  12. Distinct spontaneous shrinkage of a sporadic vestibular schwannoma

    DEFF Research Database (Denmark)

    Huang, Xiaowen; Cayé-Thomasen, Per; Stangerup, Sven-Eric

    2013-01-01

    We present a case with outspoken spontaneous vestibular schwannoma shrinkage and review the related literature. The patient was initially diagnosed with a left-sided, intrameatal vestibular schwannoma, which subsequently grew into the cerebello-pontine angle (CPA), followed by total shrinkage...... of the CPA component without any intervention over a 12-year observation period. The literature on spontaneous tumor shrinkage was retrieved by searching the subject terms "vestibular schwannoma, conservative management" in PubMed/MEDLINE database, without a time limit. Of the published data, the articles...... on "shrinkage" or "negative growth" or "regression" or "involution" of the tumor were selected, and the contents on the rate, extent and mechanism of spontaneous tumor shrinkage were extracted and reviewed. The reported rate of spontaneous shrinkage of vestibular schwannoma is 5-10% of patients managed...

  13. Shrinkage estimation with a matrix loss function

    CERN Document Server

    Abu-Shanab, Reman; Strawderman, William E

    2011-01-01

    Consider estimating the n by p matrix of means of an n by p matrix of independent normally distributed observations with constant variance, where the performance of an estimator is judged using a p by p matrix quadratic error loss function. A matrix version of the James-Stein estimator is proposed, depending on a tuning constant. It is shown to dominate the usual maximum likelihood estimator for some choices of of the tuning constant when n is greater than or equal to 3. This result also extends to other shrinkage estimators and settings.

  14. Huadong sintering model about expansion and shrinkage

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    The whole sintering course from the beginning of heating to the end of heat preservation stage was studied by taking into account the influence of pressing. It was found that there exist expanding mechanism and shrinking mechanism in the sintering process, and the expanding mechanism is always acting before the shrinking mechanism. Whether the sintering body shrinks or expands depends on the interaction between the two mechanisms. And according to this, the Huadong sintering model in account of expansion and shrinkage mechanism was given.

  15. Mechanical Self-shrinkage of Artillery Barrels

    Directory of Open Access Journals (Sweden)

    Ioan Ciorba

    2012-09-01

    Full Text Available Objective of this paper is to define what self-shrink artillery barrel is. She is considered to be a compound barrel like as a thick-walled tube (k>2, in his wall being introduced a state of stress and strain using specific technological proceeds. This type of treatment is aimed to increase the artillery barrel load capacity and wear resistance in operation. The experimental part was realized using an industrial plant at Mechanical Factory of Resita. This part presents a comparative study between mechanical self-shrinkage on artillery head barrel, first using a mandrel and seconds a ball.

  16. Real Time Shrinkage Studies in Photopolymer Films Using Holographic Interferometry

    OpenAIRE

    Moothanchery, Mohesh; Naydenova, Izabela; Bavigadda, Viswanath; Martin, Suzanne; Toal, Vincent

    2012-01-01

    Polymerisation induced shrinkage is one of the main reasons why photopolymer materials are not more widely used for holographic applications. The aim of this study is to evaluate the shrinkage in an acrylamide photopolymer layer during holographic recording using holographic interferometry. Shrinkage in photopolymer layers can be measured by real time capture of holographic interferograms during holographic recording. Interferograms were captured using a CMOS camera at regular intervals. The ...

  17. Drying Shrinkage Microcracking in Cement-based Materials

    OpenAIRE

    Bisschop, J.; Van Mier, J.G.M.

    2002-01-01

    In this paper the nature of drying shrinkage microcracking in a variety of model cementbased materials, as well as in more practical types of concrete is described. The model mixtures were studied to elucidate the mechanisms of drying shrinkage microcracking and the factors that influence these mechanisms. This fundamental knowledge is important for the development of microstructural models that predict concrete behaviour. The degree and evolution of drying shrinkage microcracking in concrete...

  18. Untangling climatic and autogenic signals in peat records

    Science.gov (United States)

    Morris, Paul J.; Baird, Andrew J.; Young, Dylan M.; Swindles, Graeme T.

    2016-04-01

    Raised bogs contain potentially valuable information about Holocene climate change. However, autogenic processes may disconnect peatland hydrological behaviour from climate, and overwrite and degrade climatic signals in peat records. How can genuine climate signals be separated from autogenic changes? What level of detail of climatic information should we expect to be able to recover from peat-based reconstructions? We used an updated version of the DigiBog model to simulate peatland development and response to reconstructed Holocene rainfall and temperature reconstructions. The model represents key processes that are influential in peatland development and climate signal preservation, and includes a network of feedbacks between peat accumulation, decomposition, hydraulic structure and hydrological processes. It also incorporates the effects of temperature upon evapotranspiration, plant (litter) productivity and peat decomposition. Negative feedbacks in the model cause simulated water-table depths and peat humification records to exhibit homeostatic recovery from prescribed changes in rainfall, chiefly through changes in drainage. However, the simulated bogs show less resilience to changes in temperature, which cause lasting alterations to peatland structure and function and may therefore be more readily detectable in peat records. The network of feedbacks represented in DigiBog also provide both high- and low-pass filters for climatic information, meaning that the fidelity with which climate signals are preserved in simulated peatlands is determined by both the magnitude and the rate of climate change. Large-magnitude climatic events of an intermediate frequency (i.e., multi-decadal to centennial) are best preserved in the simulated bogs. We found that simulated humification records are further degraded by a phenomenon known as secondary decomposition. Decomposition signals are consistently offset from the climatic events that generate them, and decomposition

  19. Silorane- and high filled-based"low-shrinkage" resin composites: shrinkage, flexural strength and modulus

    Directory of Open Access Journals (Sweden)

    Cesar Augusto Galvão Arrais

    2013-04-01

    Full Text Available This study compared the volumetric shrinkage (VS, flexural strength (FS and flexural modulus (FM properties of the low-shrinkage resin composite Aelite LS (Bisco to those of Filtek LS (3M ESPE and two regular dimethacrylate-based resin composites, the microfilled Heliomolar (Ivoclar Vivadent and the microhybrid Aelite Universal (Bisco. The composites (n = 5 were placed on the Teflon pedestal of a video-imaging device, and VS was recorded every minute for 5 min after 40 s of light exposure. For the FS and FM tests, resin discs (0.6 mm in thickness and 6.0 mm in diameter were obtained (n = 12 and submitted to a piston-ring biaxial test in a universal testing machine. VS, FS, and FM data were submitted to two-way repeated measures and one-way ANOVA, respectively, followed by Tukey's post-hoc test (a = 5%. Filtek LS showed lower VS than did Aelite LS, which in turn showed lower shrinkage than did the other composites. Aelite Universal and Filtek LS exhibited higher FS than did Heliomolar and Aelite LS, both of which exhibited the highest FM. No significant difference in FM was noted between Filtek LS and Aelite Universal, while Heliomolar exhibited the lowest values. Aelite LS was not as effective as Filtek LS regarding shrinkage, although both low-shrinkage composites showed lower VS than did the other composites. Only Filtek LS exhibited FS and FM comparable to those of the regular microhybrid dimethacrylate-based resin composite.

  20. Autogenous training--an anxiolytic and a factor contributing to the improvement of the quality of life.

    Science.gov (United States)

    Gruden, V

    1999-06-01

    Autogenous training in its narrow sense of meaning belongs to the group of supportive psychotherapeutic techniques. In fact, it is an autosuggestive relaxation. Autogenous training has been for decades successfully used as prevention to anxious reactions. Since anxiety is an etiological factor of numerous psychic and psychosomatic disturbances, positive implications of autogenous training have been considerably broadened. Life without anxiety belongs to a more qualitative form of life. Autogenous training directs the trainee towards introspection and self-analysis. Self-respect (self-esteem) is the consequence of our own work on ourselves. PMID:10402736

  1. Towards a first classification of aerosol shrinkage events

    Directory of Open Access Journals (Sweden)

    E. Alonso-Blanco

    2015-09-01

    Full Text Available This work presents for the first time a classification of shrinkage events based on the aerosol processes that precede them. To this end, 3.5 years of continuous measurements (from 2009 to 2012 of aerosol size distributions, obtained with a Scanning Mobility Particle Sizer (SMPS at an urban background site in Southern Europe, have been interpreted. 48 shrinkage events were identified and analysed, all occurring during spring and summer when the atmospheric conditions are more favourable for their development. In this study the shrinkage events took place mostly towards the end of the day, and their occurrence could be associated to atmospheric dilution conditions and a reduction in photochemical activity. The shrinkage rate (SR varied between −1.0 and −11.1 nm h−1 (average value of −4.7 ± 2.6 nm h−1. Changes in particle concentrations corresponding to the nucleation and Aitken modes were detected, whereby an increase in the number of particles in the nucleation mode often coincided with a reduction in the Aitken mode. The accumulation mode did not undergo significant changes during these processes. In addition, in some cases, a dilution of the total particle number concentration in the ambient air was observed. Following the proposed methodology, three groups of events have been identified: Group I (NPF + shrinkage, Group II (aerosol growth process + shrinkage and Group III (pure shrinkage events. The largest number of shrinkage events has been observed in the absence of prior processes, i.e. pure shrinkage events, followed by Group I events and finally Group II events. Although this analysis has confirmed that the triggering of shrinkage events is clearly linked to the atmospheric situation and the characteristics of the measurement area, this classification may contribute to a better understanding of the processes involved and the features that characterize shrinkage events.

  2. Towards a first classification of aerosol shrinkage events

    Science.gov (United States)

    Alonso-Blanco, E.; Gómez-Moreno, F. J.; Núñez, L.; Pujadas, M.; Cusack, M.; Artíñano, B.

    2015-09-01

    This work presents for the first time a classification of shrinkage events based on the aerosol processes that precede them. To this end, 3.5 years of continuous measurements (from 2009 to 2012) of aerosol size distributions, obtained with a Scanning Mobility Particle Sizer (SMPS) at an urban background site in Southern Europe, have been interpreted. 48 shrinkage events were identified and analysed, all occurring during spring and summer when the atmospheric conditions are more favourable for their development. In this study the shrinkage events took place mostly towards the end of the day, and their occurrence could be associated to atmospheric dilution conditions and a reduction in photochemical activity. The shrinkage rate (SR) varied between -1.0 and -11.1 nm h-1 (average value of -4.7 ± 2.6 nm h-1). Changes in particle concentrations corresponding to the nucleation and Aitken modes were detected, whereby an increase in the number of particles in the nucleation mode often coincided with a reduction in the Aitken mode. The accumulation mode did not undergo significant changes during these processes. In addition, in some cases, a dilution of the total particle number concentration in the ambient air was observed. Following the proposed methodology, three groups of events have been identified: Group I (NPF + shrinkage), Group II (aerosol growth process + shrinkage) and Group III (pure shrinkage events). The largest number of shrinkage events has been observed in the absence of prior processes, i.e. pure shrinkage events, followed by Group I events and finally Group II events. Although this analysis has confirmed that the triggering of shrinkage events is clearly linked to the atmospheric situation and the characteristics of the measurement area, this classification may contribute to a better understanding of the processes involved and the features that characterize shrinkage events.

  3. Physical modeling of shrink-swell cycles and cracking in a clayey vadose zone

    CERN Document Server

    Chertkov, V Y

    2014-01-01

    Physical understanding of the crack origin and quantitative physical prediction of the crack volume variation far from the clay soil surface are necessary to protect the underlying aquifers from pollutants. The basis of this work is an available physical model for predicting the shrinkage and swelling curves in the maximum water content range (the primary curves) and crack volume variation. The objective of the work is to generalize this model to the conditions of the deep layer of a clayey vadose zone with the overburden pressure, multiple shrinkage-swelling, and variation of water content in a small range. We aim to show that the scanning shrinkage and swelling curves, and steady shrink-swell cycles existing in such conditions, inevitably lead to the occurrence of cracks and a hysteretic crack volume. The generalization is based on the transition to the increasingly complex soil medium from the contributive clay, through the intra-aggregate matrix and aggregated soil with no cracking, to the soil with crack...

  4. Development of Internally Cured Concrete for Increased Service Life

    OpenAIRE

    Schlitter, John; Henkensiefken, Ryan; de Castro, Javier; Raoufi, Kambiz; Weiss, Jason; Nantung, Tommy

    2010-01-01

    Higher strength, lower water to cement ratio (w/c) concrete has been advocated over the last two decades due to its increased strength and reduced permeability. The lower w/c of these concretes makes them susceptible to autogenous shrinkage. This autogenous shrinkage can be significant and can be a contributing factor to early age cracking. Internal curing was investigated as a potential method to improve the durability of concrete pavements and bridge decks. Prewetted lightweight aggregate w...

  5. Dynamics of tissue shrinkage during ablative temperature exposures

    International Nuclear Information System (INIS)

    There is a lack of studies that examine the dynamics of heat-induced shrinkage of organ tissues. Clinical procedures such as radiofrequency ablation, microwave ablation or high-intensity focused ultrasound, use heat to treat diseases such as cancer and cardiac arrhythmia. When heat is applied to tissues, shrinkage occurs due to protein denaturation, dehydration and contraction of collagen at temperatures greater 50 °C. This is particularly relevant for image-guided procedures such as tumor ablation, where pre- and post-treatment images are compared and any changes in dimensions must be considered to avoid misinterpretations of the treatment outcome. We present data from ex vivo, isothermal shrinkage tests in porcine liver tissue, where axial changes in tissue length were recorded during 15 min of heating to temperatures between 60 and 95 °C. A mathematical model was developed to accurately describe the time and temperature-dependent shrinkage behavior. The shrinkage dynamics had the same characteristics independent of temperature; the estimated relative shrinkage, adjusted for time since death, after 15 min heating to temperatures of 60, 65, 75, 85 and 95 °C, was 12.3, 13.8, 16.6, 19.2 and 21.7%, respectively. Our results demonstrate the shrinkage dynamics of organ tissues, and suggest the importance of considering tissue shrinkage for thermal ablative treatments. (paper)

  6. Coping with shrinkage in Europe's cities and towns

    NARCIS (Netherlands)

    Hospers, G-J.

    2013-01-01

    An increasing number of cities and towns in Europe are facing population decline. In this article we focus on the challenges of this urban shrinkage process from a policy perspective. After a short review of the main causes and consequences of urban shrinkage in Europe, two common public policy resp

  7. Brain structural alterations in obsessive-compulsive disorder patients with autogenous and reactive obsessions.

    Directory of Open Access Journals (Sweden)

    Marta Subirà

    Full Text Available Obsessive-compulsive disorder (OCD is a clinically heterogeneous condition. Although structural brain alterations have been consistently reported in OCD, their interaction with particular clinical subtypes deserves further examination. Among other approaches, a two-group classification in patients with autogenous and reactive obsessions has been proposed. The purpose of the present study was to assess, by means of a voxel-based morphometry analysis, the putative brain structural correlates of this classification scheme in OCD patients. Ninety-five OCD patients and 95 healthy controls were recruited. Patients were divided into autogenous (n = 30 and reactive (n = 65 sub-groups. A structural magnetic resonance image was acquired for each participant and pre-processed with SPM8 software to obtain a volume-modulated gray matter map. Whole-brain and voxel-wise comparisons between the study groups were then performed. In comparison to the autogenous group, reactive patients showed larger gray matter volumes in the right Rolandic operculum. When compared to healthy controls, reactive patients showed larger volumes in the putamen (bilaterally, while autogenous patients showed a smaller left anterior temporal lobe. Also in comparison to healthy controls, the right middle temporal gyrus was smaller in both patient subgroups. Our results suggest that autogenous and reactive obsessions depend on partially dissimilar neural substrates. Our findings provide some neurobiological support for this classification scheme and contribute to unraveling the neurobiological basis of clinical heterogeneity in OCD.

  8. Numerical model predictions of autogenic fluvial terraces and comparison to climate change expectations

    Science.gov (United States)

    Limaye, Ajay B. S.; Lamb, Michael P.

    2016-03-01

    Terraces eroded into sediment (alluvial) and bedrock (strath) preserve an important history of river activity. River terraces are thought to form when a river switches from a period of slow vertical incision and valley widening to fast vertical incision and terrace abandonment. Consequently, terraces are often interpreted to reflect changing external drivers including tectonics, sea level, and climate. In contrast, the intrinsic unsteadiness of lateral migration in rivers may generate terraces even under constant rates of vertical incision without external forcing. To explore this mechanism, we simulate landscape evolution by a vertically incising, meandering river and isolate the age and geometry of autogenic river terraces. Modeled autogenic terraces form for a wide range of lateral and vertical incision rates and are often paired and longitudinally extensive for intermediate ratios of vertical-to-lateral erosion rate. Autogenic terraces have a characteristic reoccurrence time that scales with the time for relief generation. There is a preservation bias against older terraces due to reworking of previously visited parts of the valley. Evolving, spatial differences in bank strength between bedrock and sediment reduce terrace formation frequency and length, favor pairing, and can explain sublinear terrace margins at valley boundaries. Age differences and geometries for modeled autogenic terraces are consistent, in cases, with natural terraces and overlap with metrics commonly attributed to terrace formation due to climate change. We suggest a new phase space of terrace properties that may allow differentiation of autogenic terraces from terraces formed by external drivers.

  9. Executive functions and memory in autogenous and reactive subtype of obsessive-compulsive disorder patients.

    Science.gov (United States)

    Aydın, Pinar Cetinay; Koybasi, Gulperi Putgul; Sert, Engin; Mete, Levent; Oyekcin, Demet Gulec

    2014-05-01

    There are concurrently with different results of studies about cognitive functions of Obsessive-Compulsive Disorder (OCD), impairment in non-verbal memory and executive functioning in OCD, has shown consistent results in several studies. In this study, 62 OCD patients and 40 healthy controls were participated. Firstly, cognitive functions of OCD group and healthy control group were compared in terms of scores in Stroop Test, Wisconsin Cart Sorting Test (WCST), Auditory Consonant Trigram Test (ACTT), Controlled Word Association Test (CWAT), Rey Auditory Verbal Learning Test (RAVLT), Digit Span Test (DST). And then, two patient groups of OCD patients (patients with autogenous obsessions and patients with reactive obsessions) were compared in terms of the scores of same tests, with a hypothesis that claims, cognitive functions of patients with autogenous obsessions, who shown schizotypal personality features and thought disorder in higher ratio, will show more impairment than cognitive functions of patients with reactive obsessions. Significant impairment was found in OCD patients in terms of Stroop test and WCST scores when compared to scores of healthy controls. There was no difference pointed out between cognitive functions of patients with autogenous obsessions and reactive obsessions. Due to limited number of patients with autogenous obsessions in current study, any future research with greater sample size will be helpful to explain the cognitive functions in OCD with autogenous and reactive obsessions. PMID:24582324

  10. Aspects of energy reduction by autogenous copper production in the copper smelting plant Bor

    International Nuclear Information System (INIS)

    This work presents a comparative analysis of the energy consumption during copper production by the “standard” procedure (roasting in a fluo–solid reactor and smelting in a reverberatory furnace) in the Smelting Plant in Bor with modern autogenous procedures. All forms of expended energy were reduced to primary energy or to the same energy form, i.e., to the energy equivalent of the process (EEP), the raw material and the process materials. In addition, the energy equivalent of the process and waste products (water vapour, thermal energy and similar) were balanced. To complete the consumption of all energy generating products in copper production, they were reduced to conditional fuel (coal equivalent = 29.3 MJ/kg). Additionally, this study suggests replacement of the existing technology by an appropriate autogenous procedure and considers the prospects for further development of mining and metallurgy in Bor. Estimates of development perspectives for copper production should be comprehensive, based on complete and relevant data, as well as on real considerations of future development in world production. -- Highlights: ► “Standard” autogenous copper production in the Smelting Plant, Bor, Serbia. ► Comparation of energy consumption in “standard” with other autogenous procedures. ► All forms of energy are reduced to energy equivalent and conditional fuel. ► Replacement of existing technology with the appropriate autogenous procedure. ► Perspectives of further development of mining and metallurgy in Bor.

  11. Reconstruction of mandibular defects with autogenous bone grafts: a review of 30 cases

    International Nuclear Information System (INIS)

    Multitudes of options are available for reconstruction of functional and cosmetic defects of the mandible, caused by various ailments. At the present time, autogenous bone grafting is the gold standard by which all other techniques of reconstruction of the mandible can be judged. The purpose of this study was to evaluate the outcome of different osseous reconstruction options using autogenous bone grafts for mandibular reconstruction. Methods: This Interventional study was conducted at Department of Oral and Maxillofacial Surgery, King Edward Medical University/Mayo Hospital Lahore, from January 2008 to July 2009 including one year follow-up. The study was carried out on thirty patients having bony mandibular defects. They were reconstructed with the autogenous bone grafts from different graft donor sites. On post-operative visits they were evaluated for outcome variables. Results: Success rate of autogenous bone grafts in this study was 90%. Only 10% of the cases showed poor results regarding infection, resorption and graft failure. Conclusion: Autogenous bone grafts, non-vascularized or vascularized, are a reliable treatment modality for the reconstruction of the bony mandibular defects with predictable functional and aesthetic outcome. (author)

  12. Effectiveness of shrinkage-reducing admixtures on Portland pozzolan cement concrete

    Directory of Open Access Journals (Sweden)

    Videla, C.

    2005-06-01

    Full Text Available Drying shrinkage causes tensile stress in restrained concrete members. Since all structural elements are subject to some degree of restraint, drying shrinkage is regarded to be one of the main causes of concrete cracking. The purpose of the present study was to evaluate the effectiveness of SRA in reducing drying shrinkage strain in Portland pozzolan cement concrete. The major variables examined included slump, admixture type and dose, and specimen size. The measured results indicate that any of the admixtures used in the study significantly reduced shrinkage. Concrete manufactured with shrinkage reducing admixtures shrank an average of 43% less than concrete without admixtures. As a rule, the higher the dose of admixture, the higher was its shrinkage reduction performance. The experimental results were compared to the shrinkage strain estimated with the ACI 209, CEB MC 90, B3, GL 2000, Sakata 1993 and Sakata 2001 models. Although none of these models was observed to accurately describe the behaviour of Portland pozzolan cement concrete with shrinkage reducing admixtures, the Sakata 2001 model, with a weighted coefficient of variation of under 30%, may be regarded to be roughly adequate.

    La retracción por secado es un fenómeno intrínseco del hormigón que produce tensiones de tracción en elementos restringidos de hormigón. Puesto que todos los elementos presentan algún grado de retracción, se considera a la retracción por secado como una de las principales causas de agrietamiento en proyectos de construcción en hormigón. Por lo tanto, el objetivo de esta investigación fue evaluar la efectividad de los aditivos reductores de retracción (SRA en hormigones fabricados con cemento Portland puzolánico. Las variables principales estudiadas incluyen el asentamiento de cono de Abrams, marca y dosis de aditivo reductor de retracción, y tamaño de espécimen de hormigón. Los resultados obtenidos permiten concluir que el uso de

  13. Photogrammetric Assessment of Flexure Induced Cracking of Reinforced Concrete Beams under Service Loads

    DEFF Research Database (Denmark)

    Pease, Bradley Justin; Geiker, Mette Rica; Stang, Henrik; Weiss, Jason

    2006-01-01

    Reinforced concrete structures are known to crack due to restrained shrinkage, temperature gradients, application of load, and expansive reactions. Cracks provide paths for rapid ingress of moisture, chlorides, and other aggressive substances, which may affect the long-term durability of the...... structure. For example, concrete cracks located at the reinforcing steel may contribute to a rapid corrosion initiation and propagation. Previous research has shown that cracked reinforced concrete under static flexural loading may have an increased ingress of chloride ions along the reinforcement/concrete...... interface. The aim of this paper is to provide a detailed description of the development of cracks in reinforced concrete under flexural load. Cracking at both realistic service load levels (1.0-1.8 times estimated cracking load) and unrealistically high service load levels (> 0.5 times beam capacity) has...

  14. Drying Shrinkage of Recycled Aggregate Reinforced Concrete Shear Wall%再生骨料钢筋混凝土剪力墙干燥收缩性能

    Institute of Scientific and Technical Information of China (English)

    崔正龙; 庄宇; 汪振双

    2011-01-01

    在约束条件下对再生骨科钢筋混凝土剪力墙和普通钢筋混凝土剪力墙进行了干燥收缩应变测试,同时观察墙体表面干燥收缩裂缝产生的情况.结果表明:2种剪力墙内部收缩应变均明显小于相应的外表面收缩应变;2种剪力墙内部收缩应变相差不大;再生骨料钢筋混凝土剪力墙外表面收缩应变明显比普通钢筋混凝土剪力墙小,而细微收缩裂缝则明显增多.%Drying shrinkage strains of recycled aggregate reinforced concrete shear wall and common reinforced concrete shear wall were measured under constraint conditions, and cracks situations on shear wall surface were observed. The results reveal that for recycled aggregate reinforced concrete shear wall and common reinforced concrete shear wall, the internal shrinkage strain are obviously less than surface shrinkage strain. There is a little difference of internal shrinkage strains between recycled aggregate reinforced concrete shear wall and common reinforced concrete shear wall. The surface shrinkage strain of recycled aggregate reinforced concrete shear wall is obviously lower than that of common reinforced concrete shear wall, while micro shrinkage cracks is obviously more than the latter.

  15. Influence of cracks on chloride penetration and corrosion initiation time

    OpenAIRE

    Audenaert, K.; De Schutter, G.; L. Marsavina

    2009-01-01

    Chloride initiated reinforcement corrosion is the main durability problem for concrete structures in a marine environment. If the chlorides reach the reinforcement steel, it will depassivate and start to corrode in presence of air and water. Since the corrosion products have a larger volume than the intial products, concrete stresses are induced, leading to spalling and degradation of the concrete structures. If cracks, caused by early drying, thermal effects, shrinkage or overstress, are pre...

  16. Influence of cracks on chloride penetration in concrete

    OpenAIRE

    Audenaert, K.; Schutter, G. de; MARSAVINA, L

    2009-01-01

    Chloride initiated reinforcement corrosion is the main durability problem for concrete structures in a marine environment. If the chlorides reach the reinforcement steel, it will depassivate and start to corrode in presence of air and water. Since the corrosion products have a larger volume than the initial products, concrete stresses are induced, leading to spalling and degradation of the concrete structures. If cracks, caused by early drying, thermal effects, shrinkage movements or overstre...

  17. Comparative fine structure of eggs of autogenous and anautogenous Culex pipiens (Diptera: Culicidae).

    Science.gov (United States)

    Soliman, Belal A; Tewfick, Maha K; Wassim, Nahla M

    2014-12-01

    Culex (Cx.) pipiens is the potential vector human filariasis in Egypt. However, autogenous Cx. pipiens may be less efficient vector of Wuchereria (W.) bancrofti in endemic areas of Egypt compared to anautogenous counterparts. In this study, an attempt was made to differentiate eggs of autogenous and anautogenous Cx. pipiens using scanning electron micrographs. The results indicated that eggs of both species appear to be similar to great extent in surface morphology. Eggs of both forms are black and elongate-oval. Width is greatest at the anterior end. The posterior end is pointed. The micropylar disc is apparent with distinct edge. Exochorionic bridges are angular. Size of both eggs represented by length and width are comparable. In both eggs, length is greater than width. However, eggs of both forms can be distinguished from each other by the exochorionic bridges being longer and thinner in the autogenous eggs than in the anautogenous eggs. PMID:25643517

  18. Self-stresses and Crack Formation by Particle Swelling in Cohesive Granular Media

    OpenAIRE

    El Youssoufi, Moulay Saïd; Delenne, Jean-Yves; Radjai, Farhang

    2005-01-01

    We present a molecular dynamics study of force patterns, tensile strength and crack formation in a cohesive granular model where the particles are subjected to swelling or shrinkage gradients. Non-uniform particle size change generates self-equilibrated forces that lead to crack initiation as soon as strongest tensile contacts begin to fail. We find that the coarse-grained stresses are correctly predicted by an elastic model that incorporates particle size change as metric evolution. The tens...

  19. Effective Expansion: Balance between Shrinkage and Hygroscopic Expansion.

    Science.gov (United States)

    Suiter, E A; Watson, L E; Tantbirojn, D; Lou, J S B; Versluis, A

    2016-05-01

    The purpose of this study was to investigate the relationship between hygroscopic expansion and polymerization shrinkage for compensation of polymerization shrinkage stresses in a restored tooth. One resin-modified glass-ionomer (RMGI) (Ketac Nano, 3M ESPE), 2 compomers (Dyract, Dentsply; Compoglass, Ivoclar), and a universal resin-based composite (Esthet•X HD, Dentsply) were tested. Volumetric change after polymerization ("total shrinkage") and during 4 wk of water storage at 37°C was measured using an optical method (n= 10). Post-gel shrinkage was measured during polymerization using a strain gauge method (n= 10). Extracted human molars with large mesio-occluso-distal slot preparations were restored with the tested restorative materials. Tooth surfaces at baseline (preparation), after restoration, and during 4 wk of 37°C water storage were scanned with an optical scanner to determine cuspal flexure (n= 8). Occlusal interface integrity was measured using dye penetration. Data were analyzed using analysis of variance and post hoc tests (significance level 0.05). All tested materials shrunk after polymerization. RMGI had the highest total shrinkage (4.65%) but lowest post-gel shrinkage (0.35%). Shrinkage values dropped significantly during storage in water but had not completely compensated polymerization shrinkage after 4 wk. All restored teeth initially exhibited inward (negative) cuspal flexure due to polymerization shrinkage. Cuspal flexure with the RMGI restoration was significantly less (-6.4 µm) than with the other materials (-12.1 to -14.1 µm). After 1 d, cuspal flexure reversed to +5.0 µm cuspal expansion with the RMGI and increased to +9.3 µm at 4 wk. After 4 wk, hygroscopic expansion compensated cuspal flexure in a compomer (Compoglass) and reduced flexure with Dyract and resin-based composite. Marginal integrity (93.7% intact restoration wall) was best for the Compoglass restorations and lowest (73.1%) for the RMGI restorations. Hygroscopic

  20. Self-Shrinkage Behaviors of Waste Paper Fiber Reinforced Cement Paste considering Its Self-Curing Effect at Early-Ages

    Directory of Open Access Journals (Sweden)

    Zhengwu Jiang

    2016-01-01

    Full Text Available The aim of this paper was to study how the early-age self-shrinkage behavior of cement paste is affected by the addition of the waste paper fibers under sealed conditions. Although the primary focus was to determine whether the waste paper fibers are suitable to mitigate self-shrinkage as an internal curing agent under different adding ways, evaluating their strength, pore structure, and hydration properties provided further insight into the self-cured behavior of cement paste. Under the wet mixing condition, the waste paper fibers could mitigate the self-shrinkage of cement paste and, at additions of 0.2% by mass of cement, the waste paper fibers were found to show significant self-shrinkage cracking control while providing some internal curing. In addition, the self-curing efficiency results were analyzed based on the strength and the self-shrinkage behaviors of cement paste. Results indicated that, under a low water cement ratio, an optimal dosage and adding ways of the waste paper fibers could enhance the self-curing efficiency of cement paste.

  1. Comparative Analysis of Measured and Predicted Shrinkage Strain in Concrete

    Directory of Open Access Journals (Sweden)

    Kossakowski P. G.

    2014-06-01

    Full Text Available The article discusses the issues related to concrete shrinkage. The basic information on the phenomenon is presented as well as the factors that determine the contraction are pointed out and the stages of the process are described. The guidance for estimating the shrinkage strain is given according to Eurocode standard PN-EN 1992-1-1:2008. The results of studies of the samples shrinkage strain of concrete C25/30 are presented with a comparative analysis of the results estimated by the guidelines of the standard according to PN-EN 1992-1- 1:2008

  2. Hydration of Portoguese cements, measurement and modelling of chemical shrinkage

    DEFF Research Database (Denmark)

    Maia, Lino; Geiker, Mette Rica; Figueiras, Joaquim A.

    2008-01-01

    Development of cement hydration was studied by measuring the chemical shrinkage of pastes. Five types of Portuguese Portland cement were used in cement pastes with . Chemical shrinkage was measured by gravimetry and dilatometry. In gravimeters results were recorded automatically during at least...... seven days, dilatometers were manually recorded during at least 56 days. The dispersion model was applied to fit chemical shrinkage results and to estimate the maximum (or ultimate) value for calculation of degree of hydration. Except for a pure Portland cement best fits were obtained by the general...

  3. Shrinkage calibration method for μPIM manufactured parts

    DEFF Research Database (Denmark)

    Quagliotti, Danilo; Tosello, Guido; Salaga, J.;

    2016-01-01

    were compared with the sintered parts (final products) calculating the percentage of shrinkage after sintering. Successively, the expanded uncertainty of the measured dimensions were evaluated for each single part as well as for the overall parts. Finally, the estimated uncertainty for the shrinkage...... was evaluated propagating the expanded uncertainty previously stated and considering green and sintered parts correlated. Results showed that the proposed method can be effective instating tolerances if it is assumed that the variability on the dimensions induced by the shrinkage equals the propagated...

  4. Holographic grating formation in dry photopolymer film with shrinkage

    Institute of Scientific and Technical Information of China (English)

    Luo Shou-Jun; Liu Guo-Dong; He Qing-Sheng; Wu Min-Xian; Jin Guo-Fan; Shi Meng-Quan; Wang Tao; Wu Fei-Peng

    2004-01-01

    An important issue in developing applications for photopolymers in holography is the effect of shrinkage on recording properties. In this paper, we introduce a model to describe real-time formation of a single grating in photopolymers at any geometrical angle, under the assumption that the shrinkage is in proportion to the polymerization. This model combines polymerization kinetics with the coupled-wave theory, explaining the shrinkage effect on the diffraction efficiency. The model is validated by comparing its predictions with the experimental results for a film of 99μm thickness.

  5. STRENGTH SHRINKAGE AND CREEP OF CONCRETE IN TENSION AND COMPRESSION

    Directory of Open Access Journals (Sweden)

    S A Kristiawan

    2006-01-01

    Full Text Available Strength, shrinkage and creep of concrete in tension and compression have been determined and the relationship between those properties was studied. Direct tensile tests were applied to measure those properties in tension. The relationship of creep in tension and compression was determined based on the measurement of creep at similar stress and similar stress/strength ratio. It is found that concrete deforms more in tension than in compression. Except for concrete with a higher water/cement ratio, the use of pulverised fuel ash, ground granulated blast furnace slag, superplasticizer and shrinkage reducing admixture has no effect on strength. However, they affect creep and shrinkage of concrete.

  6. Comparative Analysis of Measured and Predicted Shrinkage Strain in Concrete

    OpenAIRE

    Kossakowski P. G.; Raczkiewicz W.

    2014-01-01

    The article discusses the issues related to concrete shrinkage. The basic information on the phenomenon is presented as well as the factors that determine the contraction are pointed out and the stages of the process are described. The guidance for estimating the shrinkage strain is given according to Eurocode standard PN-EN 1992-1-1:2008. The results of studies of the samples shrinkage strain of concrete C25/30 are presented with a comparative analysis of the results estimated by the guideli...

  7. Prediction of Concrete Creep and Shrinkage: Past, Present and Future

    International Nuclear Information System (INIS)

    The first part of the paper summarizes various aspects of the prediction of concrete creep and shrinkage to be discussed in the conference lecture. They include the theories of physical mechanism, prediction models, constitutive equations, computational approaches, probabilistic aspects, and research directions. The second part then presents two new prediction models. One of them deals with the approximate prediction formulae for pore relative humidity distributions, required for realistic creep and shrinkage analysis, and the other deals with the extrapolation of short time measurements of creep and shrinkage into long times

  8. Influence of nano-material on the expansive and shrinkage soil behavior

    Energy Technology Data Exchange (ETDEWEB)

    Taha, Mohd Raihan, E-mail: drmrt@eng.ukm.my; Taha, Omer Muhie Eldeen, E-mail: omar82@eng.ukm.my [Universiti Kebangsaan Malaysia, Department of Civil and Structural Engineering (Malaysia)

    2012-10-15

    This paper presents an experimental study performed on four types of soils mixed with three types of nano-material of different percentages. The expansion and shrinkage tests were conducted to investigate the effect of three type of nano-materials (nano-clay, nano-alumina, and nano-copper) additive on repressing strains in compacted residual soil mixed with different ratios of bentonite (S1 = 0 % bentonite, S2 = 5 % bentonite, S3 = 10 % bentonite, and S4 = 20 % bentonite). The soil specimens were compacted under the condition of maximum dry unit weight and optimum water content (w{sub opt}) using standard compaction test. The physical and mechanical results of the treated samples were determined. The untreated soil values were used as control points for comparison purposes. It was found that with the addition of optimum percentage of nano-material, both the swell strain and shrinkage strain reduced. The results show that nano-material decreases the development of desiccation cracks on the surface of compacted samples without decrease in the hydraulic conductivity.

  9. Studies on heat shrinkage PVC tubes

    International Nuclear Information System (INIS)

    Radiation crosslinking of PVC was investigated for the purpose of obtaining a suitable formulation for heat shrinkable tube. PVC was not only compounded with various crosslinking agents and plasticizers to evaluate their effects on the radiation sensitivity, heat shrinkable property and other mechanical properties, but also mixed with NBR, crosslinking agents and plasticizers to obtain efficient crosslinking yield and suitable mechanical properties for heat shrinkable tube. Gel yield of PVC increased with increasing unsaturation levels per molecular weight of crosslinking agents. Among crosslinking agents tested, TMPTMA with three unsaturated groups showed highest gel yield, while PVC containing NBR was more sensitive to crosslinking than PVC itself regardless the types of crosslinking agents and plasticizers. Tensile strength was increased with increasing radiation dose and gel percent, but elongation decreased. It was found that gel percent was increased with increasing radiation dose, heat transformation was decreased with increasing gel percent. When NBR was mixed with PVC, the radiation dosage required for enhancing yield of gel percent and heat transformation were found to be much smaller comparing with the case containing no NBR. Therefore, the addition of NBR to PVC was very effective to increase heat-resisting property of PVC. Heat shrinkage was not much varied with radiation dose, the types of crosslinking agents and plasticizers, but it was increased remarkably with decreasing stretching temperature and increasing annealing temperature. (Author)

  10. Hot-cracking mechanism in CO/sub 2/ laser beam welds of dissimilar metals involving PH martensitic stainless steels

    International Nuclear Information System (INIS)

    Autogenous CO/sub 2/ laser beam welds were made between Alloy HP 9-4-20 and both 15-5 PH and PH 13-8 Mo stainless steel. Small scale circular-patch test specimens revealed that the combination involving the Nb-bearing alloy, 15-5 PH, was far more crack susceptible than the combination involving the Nb-free alloy, PH 13-8 Mo. Analytical electron microscopy was used to identify an NbC/austenite eutectic-like constituent as being responsible for the cracking phenomenon

  11. Creep and Shrinkage of High Strength Concretes: an Experimental Analysis

    Directory of Open Access Journals (Sweden)

    Berenice Martins Toralles carbonari

    2002-01-01

    Full Text Available The creep and shrinkage behaviour of high strength silica fume concretes is significantly different from that of conventional concretes. In order to represent the proper time-dependent response of the material in structural analysis and design, these aspects should be adequately quantified. This paper discusses an experimental setup that is able to determine the creep and shrinkage of concrete from the time of placing. It also compares different gages that can be used for measuring the strains. The method is applied to five different concretes in the laboratory under controlled environmental conditions. The phenomena that are quantified can be classified as basic shrinkage, drying shrinkage, basic creep and drying creep. The relative importance of these mechanisms in high strength concrete will also be presented.

  12. Nanocavity Shrinkage and Preferential Amorphization during Irradiation in Silicon

    Institute of Scientific and Technical Information of China (English)

    ZHU Xian-Fang; WANG Zhan-Guo

    2005-01-01

    @@ We model the recent experimental results and demonstrate that the internal shrinkage of nanocavities in silicon is intrinsically associated with preferential amorphization as induced by self-ion irradiation.

  13. Applying strain into graphene by SU-8 resist shrinkage

    Science.gov (United States)

    Takamura, Makoto; Hibino, Hiroki; Yamamoto, Hideki

    2016-07-01

    We investigated the use of the shrinkage of SU-8 resist caused by thermal annealing to apply strain into graphene grown by the chemical-vapor-deposition (CVD) method. We demonstrate that the shrinkage of resist deposited on top of graphene on a substrate induces a local tensile strain within a distance of 1–2 μm from the edge of the resist. The thermal shrinkage of SU-8 will allow us to design the local strain in graphene on substrates. We also show that the shrinkage induces a large tensile strain in graphene suspended between two bars of SU-8. We expect that a much larger strain can be induced by suppressing defects in CVD-grown graphene.

  14. Assessment of early-age cracking of high-performance concrete in restrained ring specimens

    Directory of Open Access Journals (Sweden)

    Quang-phu NGUYEN NGUYEN

    2010-03-01

    Full Text Available High-performance concrete (HPC is stronger and more durable than conventional concrete. However, shrinkage and shrinkage cracking are common phenomena in HPC, especially early-age cracking. This study assessed early-age cracking of HPC for two mixtures using restrained ring tests. The two mixtures were produced with water/binder mass ratio (mW/mB of 0.22 and 0.40, respectively. The results show that, with greater steel thickness, the higher degree of restraint resulted in a higher interface pressure and earlier cracking. With steel thickness of 6 mm, 19 mm, and 30 mm, the age of cracking were, respectively, 12 days, 8 days, and 5.4 days with the mW/mB = 0.22 mixture; and 22.5 days, 12.6 days, and 7.1 days with the mW/mB = 0.40 mixture. Cases of the same steel thickness show that the ring specimens with a thicker concrete wall crack later. With the mW/mB = 0.22 mixture, concrete walls with thicknesses of 37.5 mm, 75 mm, and 112.5 mm cracked at 3.4 days, 8.0 days, and 9.8 days, respectively; with the mW/mB = 0.40 mixture, the ages of cracking were 7.1 days, 12.6 days, and 16.0 days, respectively.

  15. Autogenous temporalis fascia patch graft for porous polyethylene (Medpor) sphere orbital implant exposure

    OpenAIRE

    Sagoo, M S; Olver, J M

    2004-01-01

    Background: Temporalis fascia has been recommended for hydroxyapatite sphere exposure. The aim of this study was to identify potential risk factors for exposure of porous polyethylene (Medpor) sphere implants and evaluate the use of autogenous temporalis fascia as a patch graft for exposure.

  16. Silicate minerals for CO2 scavenging from biogas in Autogenerative High Pressure Digestion

    NARCIS (Netherlands)

    Lindeboom, R.E.F.; Ferrer, I.; Weijma, J.; Lier, van J.B.

    2013-01-01

    Autogenerative High Pressure Digestion (AHPD) is a novel concept that integrates gas upgrading with anaerobic digestion by selective dissolution of CO2 at elevated biogas pressure. However, accumulation of CO2 and fatty acids after anaerobic digestion of glucose resulted in pH 3–5, which is incompat

  17. The diffraction cone shrinkage speed up with the collision energy

    CERN Document Server

    Schegelsky, V A

    2011-01-01

    The multiperipheral ladder structure of the Pomeron leads to the quite natural conclusion that the elastic slope Bel is not simple linear function of the colliding particles energy logarithm. The existing experimental data on the diffraction cone shrinkage points to such "complicated" dependence indeed. The shrinkage diffraction cone speed up with the beam energy is directly connected with an extreme rise of total cross-section (Froissart limit).

  18. Creep and Shrinkage of a High Strength Concrete Mixture

    OpenAIRE

    Townsend, Bradley Donald

    2003-01-01

    In addition to immediate elastic deformations, concrete undergoes time-dependent deformations that must be considered in design. Creep is defined as the time-dependent deformation resulting from a sustained stress. Shrinkage deformation is the time-dependent strain that occurs in the absence of an applied load. The total strain of a concrete specimen is the sum of elastic, creep, and shrinkage strains. Several test beams for the Pinnerâ s Point Bridge have been produced by Bayshore Co...

  19. Reduction of polyester resin shrinkage by means of epoxy resin

    International Nuclear Information System (INIS)

    The possibility was investigated of reducing the shrinkage of unsaturated polyester resin taking place in radiation-induced curing, by the addition of epoxy resin. In order to combine chemically both resins, the epoxy component was modified by introducing unsaturated bonds via acrylamide and N-hydroxymethyloloacrylamide. A composition of 90% unsaturated polyester resin and 10% acrylamide-modified epoxy resin, filled with silica (1:1.5), showed a volume shrinkage below 2%. (author)

  20. Modeling of damage due to shrinkage in autoclaved aerated concrete

    OpenAIRE

    Koudelka, T.; Kruis, J.; Sysala, S.; M. Vokáč

    2015-01-01

    The paper deals with numerical modeling of damage evolution in autoclaved aerated concrete (AAC) due to shrinkage. It represents coupled thermo-hydro-mechanical problem where the temperature and moisture transports are fully coupled. The mechanical problem is partially coupled with transport part because the AAC shrinkage is influenced by moisture evolution. These models were implemented to the SIFEL software package and they were used for numerical simulation of drying wall made from AAC blo...

  1. Shrinkage and swelling properties of flocculated mature fine tailings

    OpenAIRE

    Yao, Y; Van Tol, A.F.; Van Paassen, L.A.; Vardon, P.J.

    2014-01-01

    In the atmospheric fines drying technique, mature fine tailings (MFT) are treated with polymers and deposited in thin layers on a sloped surface for sub-aerial drying. During the whole drying period, the tailings deposits can experience rewetting during periods of rainy weather or as result of the the placement of new layers. This paper addresses the shrinkage and swelling behavior of flocculated MFT (FMFT) under drying and rewetting cycles. The shrinkage and swelling paths of tailing samples...

  2. Permeability Enhancement in Fine-Grained Sediments by Chemically Induced Clay Fabric Shrinkage

    Energy Technology Data Exchange (ETDEWEB)

    Wijesinghe, A M; Kansa, E J; Viani, B E; Blake, R G; Roberts, J J; Huber, R D

    2004-02-26

    The National Research Council [1] identified the entrapment of contaminants in fine-grained clay-bearing soils as a major impediment to the timely and cost-effective remediation of groundwater to regulatory standards. Contaminants trapped in low-permeability, low-diffusivity, high-sorptivity clays are not accessible to advective flushing by treatment fluids from permeable zones, and slowly diffuse out to recontaminate previously cleaned permeable strata. We propose to overcome this barrier to effective remediation by exploiting the ability of certain nontoxic EPA-approved chemicals (e.g., ethanol) to shrink and alter the fabric of clays, and thereby create macro-porosity and crack networks in fine-grained sediments. This would significantly reduce the distance and time scales of diffusive mass transport to advectively flushed boundaries, to yield orders of magnitude reduction in the time required to complete remediation. Given that effective solutions to this central problem of subsurface remediation do not yet exist, the cost and time benefits of successful deployment of this novel concept, both as a stand-alone technology and as an enabling pre-treatment for other remedial technologies that rely on advective delivery, is likely to be very large. This project, funded as a 1-year feasibility study by LLNL's LDRD Program, is a multi-directorate, multi-disciplinary effort that leverages expertise from the Energy & Environment Directorate, the Environmental Restoration Division, and the Manufacturing & Materials Evaluation Division of Mechanical Engineering. In this feasibility study, a ''proof-of-principle'' experiment was performed to answer the central question: ''Can clay shrinkage induced by ethanol in clay-bearing sediments overcome realistic confining stresses, crack clay, and increase its effective permeability by orders of magnitude within a time that is much smaller than the time required for diffusive mass transport of

  3. Crack formation and fracture energy of normal and high strength concrete

    Indian Academy of Sciences (India)

    F H Wittmann

    2002-08-01

    The crack path through composite materials such as concrete depends on the mechanical interaction of inclusions with the cement-based matrix. Fracture energy depends on the deviations of a real crack from an idealized crack plane. Fracture energy and strain softening of normal, high strength, and self-compacting concrete have been determined by means of the wedge splitting test. In applying the numerical model called “numerical concrete” crack formation in normal and high strength concrete is simulated. Characteristic differences of the fracture process can be outlined. Finally results obtained are applied to predict shrinkage cracking under different boundary conditions. Crack formation of high strength concrete has to be seriously controlled in order to achieve the necessary durability of concrete structures.

  4. NSCLC tumor shrinkage prediction using quantitative image features.

    Science.gov (United States)

    Hunter, Luke A; Chen, Yi Pei; Zhang, Lifei; Matney, Jason E; Choi, Haesun; Kry, Stephen F; Martel, Mary K; Stingo, Francesco; Liao, Zhongxing; Gomez, Daniel; Yang, Jinzhong; Court, Laurence E

    2016-04-01

    The objective of this study was to develop a quantitative image feature model to predict non-small cell lung cancer (NSCLC) volume shrinkage from pre-treatment CT images. 64 stage II-IIIB NSCLC patients with similar treatments were all imaged using the same CT scanner and protocol. For each patient, the planning gross tumor volume (GTV) was deformed onto the week 6 treatment image, and tumor shrinkage was quantified as the deformed GTV volume divided by the planning GTV volume. Geometric, intensity histogram, absolute gradient image, co-occurrence matrix, and run-length matrix image features were extracted from each planning GTV. Prediction models were generated using principal component regression with simulated annealing subset selection. Performance was quantified using the mean squared error (MSE) between the predicted and observed tumor shrinkages. Permutation tests were used to validate the results. The optimal prediction model gave a strong correlation between the observed and predicted tumor shrinkages with r=0.81 and MSE=8.60×10(-3). Compared to predictions based on the mean population shrinkage this resulted in a 2.92 fold reduction in MSE. In conclusion, this study indicated that quantitative image features extracted from existing pre-treatment CT images can successfully predict tumor shrinkage and provide additional information for clinical decisions regarding patient risk stratification, treatment, and prognosis. PMID:26878137

  5. Variation of Shrinkage Strain within the Depth of Concrete Beams

    Directory of Open Access Journals (Sweden)

    Jong-Hyun Jeong

    2015-11-01

    Full Text Available The variation of shrinkage strain within beam depth was examined through four series of time-dependent laboratory experiments on unreinforced concrete beam specimens. Two types of beam specimens, horizontally cast and vertically cast, were tested; shrinkage variation was observed in the horizontally cast specimens. This indicated that the shrinkage variation within the beam depth was due to water bleeding and tamping during the placement of the fresh concrete. Shrinkage strains were measured within the beam depth by two types of strain gages, surface-attached and embedded. The shrinkage strain distribution within the beam depth showed a consistent tendency for the two types of gages. The test beams were cut into four sections after completion of the test, and the cutting planes were divided into four equal sub-areas to measure the aggregate concentration for each sub-area of the cutting plane. The aggregate concentration increased towards the bottom of the beam. The shrinkage strain distribution was estimated by Hobbs’ equation, which accounts for the change of aggregate volume concentration.

  6. VERIFICATION OF 3-PHASES COMPOSITE MODEL FOR DRYING SHRINKAGE OF CONCRETE WITH DEFFERENT AGGREGATE PROPERTIES

    Science.gov (United States)

    Tanaka, Kie; Shima, Hiroshi

    Properties of aggregate are not taken into account in current codes for drying shrinkage of concrete although the drying shrinkage is affected by the properties of aggregate. Aggregate restrains cement paste from shrinkage so that the drying shrinkage of concrete is controlled by drying shrinkage and Young's modulus of aggregate itself. The effect of the aggregate properties on drying shrinkage of concrete can be calculated by composite model in which concrete consists of cement paste and aggregate. Several different kind of coarse aggregate were used in order to verify a 3-phases composite model for drying shrinkage. Drying shrinkage and Young's modulus of cement paste, aggregate and concrete were measured. It was verified that drying shrinkage of concrete can be estimated accurately by the composite model associating with both drying shrinkage and Young's modulus of aggregate.

  7. Shrinkage behaviour and related corrosion performance of low-pH cementitious materials based on OPC or CAC

    Directory of Open Access Journals (Sweden)

    García-Calvo, J. L.

    2016-03-01

    Full Text Available Prior to using low-pH cementitious materials in underground repositories for high level waste, the characteristics determining their long-term durability must be analysed in depth. In this sense, different shrinkage tests have been made on mortar and concrete specimens using low-pH cement formulations based on ordinary portland cement (OPC or calcium aluminate cement (CAC, with high mineral admixtures contents. They showed similar autogenous shrinkage than samples without mineral admixtures but higher drying shrinkage when materials based on OPC with high silica fume contents were considered. Besides, as the use of reinforced concrete could be required in underground repositories, the susceptibility of reinforcement to corrosion when using low-pH cementitious materials based on OPC was analyzed, considering carbon steel and galvanized steel. In the formers corrosion was detected due to the low pore solution pH but any problem was detected when galvanized reinforcement were used.Previo al empleo de materiales con cementos de bajo pH en almacenamientos geológicos profundos (AGP de residuos radiactivos de alta actividad, características relacionadas con su durabilidad a largo plazo deben ser verificadas. Así, su estabilidad volumétrica se ha analizado en morteros y hormigones de bajo pH basados en OPC o CAC, con elevados contenidos de adiciones minerales. Estos presentaron retracciones autógenas similares a las medidas en materiales convencionales, pero retracciones por secado mayores en los basados en OPC y altos contenidos de humo de sílice. Dado que en zonas de los AGP podría emplearse hormigón armado, también se evaluó la susceptibilidad a la corrosión de aceros al carbono y aceros galvanizados en materiales de bajo pH basados en OPC. Se detectó un inicio temprano de corrosión en los primeros debido al bajo pH presente en el fluido de los poros de estos materiales, sin detectarse problemas al emplear aceros galvanizados.

  8. TESTING AND ANALYSIS OF CAP CONCRETE STRESS AND STRAIN DUE TO SHRINKAGE, CREEP, AND EXPANSION FINAL REPORT

    Energy Technology Data Exchange (ETDEWEB)

    Guerrero, H.; Restivo, M.

    2011-08-01

    In-situ decommissioning of Reactors P- and R- at the Savannah River Site will require filling the reactor vessels with a special concrete based on materials such as magnesium phosphate, calcium aluminate or silica fume. Then the reactor vessels will be overlain with an 8 ft. thick layer of Ordinary Portland Cement (OPC) steel reinforced concrete, called the 'Cap Concrete'. The integrity of this protective layer must be assured to last for a sufficiently long period of time to avoid ingress of water into the reactor vessel and possible movement of radioactive contamination into the environment. During drying of this Cap Concrete however, shrinkage strains are set up in the concrete as a result of diffusion and evaporation of water from the top surface. This shrinkage varies with depth in the poured slab due to a non-uniform moisture distribution. This differential shrinkage results in restraint of the upper layers with larger shrinkage by lower layers with lesser displacements. Tensile stresses can develop at the surface from the strain gradients in the bulk slab, which can lead to surface cracking. Further, a mechanism called creep occurs during the curing period or early age produces strains under the action of restraining forces. To investigate the potential for surface cracking, an experimental and analytical program was started under TTQAP SRNL-RP-2009-01184. Slab sections made of Cap Concrete mixture were instrumented with embedded strain gages and relative humidity sensors and tested under controlled environmental conditions of 23 C and relative humidities (RH) of 40% and 80% over a period of 50 days. Calculation methods were also developed for predictions of stress development in the full-scale concrete placement over the reactor vessels. These methods were evaluated by simulating conditions for the test specimens and the calculation results compared to the experimental data. A closely similar test with strain gages was performed by Kim and Lee for

  9. Self-stresses and Crack Formation by Particle Swelling in Cohesive Granular Media

    CERN Document Server

    Youssoufi, M S E; Radjai, F; Delenne, Jean-Yves; Radjai, Farhang; Youssoufi, Moulay Said El; ccsd-00003083, ccsd

    2004-01-01

    We present a molecular dynamics study of force patterns, tensile strength and crack formation in a cohesive granular model where the particles are subjected to swelling or shrinkage gradients. Non-uniform particle size change generates self-equilibrated forces that lead to crack initiation as soon as strongest tensile contacts begin to fail. We find that the coarse-grained stresses are correctly predicted by an elastic model that incorporates particle size change as metric evolution. The tensile strength is found to be well below the theoretical strength as a result of inhomogeneous force transmission in granular media. The cracks propagate either inward from the edge upon shrinkage and outward from the center upon swelling.

  10. Stress corrosion cracking and vibration corrosion cracking

    International Nuclear Information System (INIS)

    Under certain conditions of stress practically all metallic materials are subject to such cracking corrosion processes. They are much feared because as a rule they are not recognized until the damage - leakage of a container, fracture of a component part-occurs. They may belong to the category of either stress corrosion cracking or vibration corrosion cracking, depending on the different mechanisms of the damage process. As the denominations indicate, one constitutes the interaction between local corrosion attack and mainly static tensile stress (load stress and/or non-load stress) and the other a combination of varying mechanical stress over time and corrosion. Hydrogen-induced cracking is a special form of stress corrosion cracking characterized by trapping of atomic hydrogen in material and subsequent cracking owing to the interaction with mechanical stress. (orig./HP)

  11. Gear Crack Propagation Investigation

    Science.gov (United States)

    1995-01-01

    Reduced weight is a major design goal in aircraft power transmissions. Some gear designs incorporate thin rims to help meet this goal. Thin rims, however, may lead to bending fatigue cracks. These cracks may propagate through a gear tooth or into the gear rim. A crack that propagates through a tooth would probably not be catastrophic, and ample warning of a failure could be possible. On the other hand, a crack that propagates through the rim would be catastrophic. Such cracks could lead to disengagement of a rotor or propeller from an engine, loss of an aircraft, and fatalities. To help create and validate tools for the gear designer, the NASA Lewis Research Center performed in-house analytical and experimental studies to investigate the effect of rim thickness on gear-tooth crack propagation. Our goal was to determine whether cracks grew through gear teeth (benign failure mode) or through gear rims (catastrophic failure mode) for various rim thicknesses. In addition, we investigated the effect of rim thickness on crack propagation life. A finite-element-based computer program simulated gear-tooth crack propagation. The analysis used principles of linear elastic fracture mechanics, and quarter-point, triangular elements were used at the crack tip to represent the stress singularity. The program had an automated crack propagation option in which cracks were grown numerically via an automated remeshing scheme. Crack-tip stress-intensity factors were estimated to determine crack-propagation direction. Also, various fatigue crack growth models were used to estimate crack-propagation life. Experiments were performed in Lewis' Spur Gear Fatigue Rig to validate predicted crack propagation results. Gears with various backup ratios were tested to validate crack-path predictions. Also, test gears were installed with special crack-propagation gages in the tooth fillet region to measure bending-fatigue crack growth. From both predictions and tests, gears with backup ratios

  12. Method of Preventing Shrinkage of Aluminum Foam Using Carbonates

    Directory of Open Access Journals (Sweden)

    Takashi Nakamura

    2011-12-01

    Full Text Available Metallic foams are commonly produced using titanium hydride as a foaming agent. Carbonates produce aluminum foam with a fine and homogenous cell structure. However, foams produced using carbonates show marked shrinkage, which is clearly different from those produced using titanium hydride. It is essential for practical applications to clarify foam shrinkage and establish a method of preventing it. In this research, cell structures were observed to study the shrinkage of aluminum foam produced using carbonates. The cells of foam produced using dolomite as a foaming agent connected to each other with maximum expansion. It was estimated that foaming gas was released through connected cells to the outside. It was assumed that cell formation at different sites is effective in preventing shrinkage induced by cell connection. The multiple additions of dolomite and magnesium carbonate, which have different decomposition temperatures, were applied. The foam in the case with multiple additions maintained a density of 0.66 up to 973 K, at which the foam produced using dolomite shrank. It was verified that the multiple additions of carbonates are effective in preventing shrinkage.

  13. Gore-Tex small-vessel angioplasty: A suitable substitute for the use of autogenous saphenous vein grafts

    OpenAIRE

    Garcia-Rinaldi, Raul; Rea, John E.; Gallagher, Michael W.; Laevsky, Marlene J.; Ogburn, Michael; Porter, Robert H.

    1980-01-01

    Autogenous saphenous vein has been the material of choice for small-vessel angioplasty and for circulatory access graft reconstruction. In an effort to conserve autogenous saphenous vein, we used expanded polytetrafluoroethylene (PTFE) grafts in 45 patients over a 12-month period. We used Gore-Tex* to reconstruct 17 circulatory access grafts, 16 carotid arteries, two brachial arteries, seven femoral arteries, and three popliteal anterior or posterior tibial arteries. The indications for recon...

  14. STUDY ON THE EVALUATION FOR DRYING SHRINKAGE PROPERTIES OF COARSE AGGREGATE

    Science.gov (United States)

    Yamada, Hiroshi; Katahira, Hiroshi; Watanabe, Hiroshi

    Drying shrinkage of coarse aggregate is one of principal indexes to evaluate drying shrinkage of concrete. However, testing of drying shrinkage of a coarse aggregate particle has not been commonly conducted. We carried out measurement of drying shrinkage of a coarse aggregate particle using wire strain gauges and discussed the variation in the measurement. We found that variation among particles in drying shrinkage strain of coarse aggregate is intrinsic and much bigger than test result due to the simplified unidirectional strain measurement under the assumption of ignoring multi-axial strain field. Strong relationship between the mean value of drying shrinkage strain of coarse aggregate and drying shrinkage strain of concrete prism specimens was observed, which indicates that measured drying shrinkage strain of aggregate particles intrinsically contains large variation, however the mean value is an effective index to estimate drying shrinkage of concrete.

  15. Ventilation and radon reduction in shrinkage method uranium mine

    International Nuclear Information System (INIS)

    Through investigation about status of uranium mine ventilation system of shrinkage method, it showed that the mined-out areas is the main radon pollution source for multi-level shrinkage method excavating ventilation, not only enter-air pollution but also air leaking. As a result, the radon and radon daughter concentrations of underground air were higher than the national standard. Aimed at the existent problems, a study on the radon reduction ventilation technique of shrinkage method mine was carried out. A ventilation mode of downward forced ventilation in stope and discontinuous ventilation network in mine is put forward. Combined with the practical circumstance of one uranium mine, the ventilation system of the mine has been rectified, the better result was obtained, and the radon and radon daughter concentrations of underground air decreased by 50%-80%. (authors)

  16. Accurate characterisation of post moulding shrinkage of polymer parts

    DEFF Research Database (Denmark)

    Neves, L. C.; De Chiffre, L.; González-Madruga, D.;

    2015-01-01

    The work deals with experimental determination of the shrinkage of polymer parts after injection moulding. A fixture for length measurements on 8 parts at the same time was designed and manufactured in Invar, mounted with 8 electronic gauges, and provided with 3 temperature sensors. The fixture was...... used to record the length at a well-defined position on each part continuously, starting from approximately 10 minutes after moulding and covering a time period of 7 days. Two series of shrinkage curves were analysed and length values after stabilisation extracted and compared for all 16 parts. Values...... were compensated with respect to the effect from temperature variations during the measurements. Prediction of the length after stabilisation was carried out by fitting data at different stages of shrinkage. Uncertainty estimations were carried out and a procedure for the accurate characterisation of...

  17. Density gradients and the expansion-shrinkage transition during sintering

    Energy Technology Data Exchange (ETDEWEB)

    Lu, Peizhen K.; Li Wenxia; Lannutti, John J

    2004-04-19

    Links between density gradients, internal microstructure and in situ sintering shrinkage in compacts formed from spray-dried alumina powder are established using a laser dilatometer and X-ray computed tomography (CT). All samples initially have the same overall density but different internal structures. An expansion-shrinkage transition occurs between 1000 and 1100 deg. C. Forming conditions appear to play a role: the samples compacted at 25% RH (Relative Humidity) shrank more rapidly than those compacted at 98% RH below 1300 deg. C; above 1300 deg. C, however, the specimen formed at 98% RH shrank more rapidly. CT examination following sintering showed both preservation and exaggeration of the original density gradients. Microstructural connectivity apparently contributes to both the observed macroscopic expansion and the onset of shrinkage. Discrete element modeling clearly suggests that the effective 'transmission' of particle-level behavior to the macroscopic level is controlled both by internal agglomerate density and initial agglomerate bonding.

  18. Prediction of ALLOY SHRINKAGE FACTORS FOR THE INVESTMENT CASTING PROCESS

    Energy Technology Data Exchange (ETDEWEB)

    Sabau, Adrian S [ORNL

    2006-01-01

    This study deals with the experimental measurements and numerical predictions of alloy shrinkage factors (SFs) related to the investment casting process. The dimensions of the A356 aluminum alloy casting were determined from the numerical simulation results of solidification, heat transfer, fluid dynamics, and deformation phenomena. The investment casting process was carried out using wax patterns of unfilled wax and shell molds that were made of fused silica with a zircon prime coat. The dimensions of the die tooling, wax pattern, and casting were measured, in order to determine the actual tooling allowances. Several numerical simulations were carried out, to assess the level of accuracy for the casting shrinkage. The solid fraction threshold, at which the transition from the fluid dynamics to the solid dynamics occurs, was found to be important in predicting shrinkage factors (SFs). It was found that accurate predictions were obtained for all measued dimensions when the shell mold was considered a deformable material.

  19. Combined use of autogenic therapy and biofeedback in training effective control of heart rate by humans

    Science.gov (United States)

    Cowings, P. S.

    1977-01-01

    Experiments were performed on 24 men and women (aged 20-27 yr) in three equal groups who were taught to control their own heart rates by autogenic training and biofeedback under dark and sound-isolated conditions. Group I was parasympathetic dominant, group II was sympathetic dominant, and group III consisted of parasympathetic-dominant subjects and controls who received only biofeedback of their own heart rates. The results corroborate three hypotheses: (1) subjects with para-sympathetic-dominant autonomic profiles perform in a way that is both qualitatively and quantitatively different from subjects with sympathetic-dominant autonomic profiles; (2) tests of interindividual variability yield data relevant to individual performance in visceral learning tasks; and (3) the combined use of autogenic training, biofeedback, and verbal feedback is suitable for conditioning large stable autonomic responses in humans.

  20. Polymerization shrinkage stress of composites photoactivated by different light sources.

    Science.gov (United States)

    Pires-de-Souza, Fernanda de Carvalho Panzeri; Drubi Filho, Brahim; Casemiro, Luciana Assirati; Garcia, Lucas da Fonseca Roberti; Consani, Simonides

    2009-01-01

    The purpose of this study was to compare the polymerization shrinkage stress of composite resins (microfilled, microhybrid and hybrid) photoactivated by quartz-tungsten halogen light (QTH) and light-emitting diode (LED). Glass rods (5.0 mm x 5.0 cm) were fabricated and had one of the surfaces air-abraded with aluminum oxide and coated with a layer of an adhesive system, which was photoactivated with the QTH unit. The glass rods were vertically assembled, in pairs, to a universal testing machine and the composites were applied to the lower rod. The upper rod was placed closer, at 2 mm, and an extensometer was attached to the rods. The 20 composites were polymerized by either QTH (n=10) or LED (n=10) curing units. Polymerization was carried out using 2 devices positioned in opposite sides, which were simultaneously activated for 40 s. Shrinkage stress was analyzed twice: shortly after polymerization (t40s) and 10 min later (t10min). Data were analyzed statistically by 2-way ANOVA and Tukey's test (alpha=5%). The shrinkage stress for all composites was higher at t10min than at t40s, regardless of the activation source. Microfilled composite resins showed lower shrinkage stress values compared to the other composite resins. For the hybrid and microhybrid composite resins, the light source had no influence on the shrinkage stress, except for microfilled composite at t10min. It may be concluded that the composition of composite resins is the factor with the strongest influence on shrinkage stress. PMID:20069256

  1. Histomorphometric Evaluation of Anorganic Bovine Bone Coverage to Reduce Autogenous Grafts Resorption: Preliminary Results

    OpenAIRE

    C Maiorana; Beretta, M.; G B Grossi; Santoro, F.; A. Scott Herford; Nagursky, H; CICCIÙ, M.

    2011-01-01

    Physiologic resorption due to remodeling processes affects autogenous corticocancellous grafts in the treatment of atrophic jawbone alveolar ridges. Such a situation in the past made overgrafting of the recipient site mandatory to get enough bone support to dental implants in order to perform a prosthetic rehabilitation. Anorganic bovine bone, conventionally used to treat alveolar bone deficiencies in implant surgery, showed a high osteoconductive property thanks to its micro and macrostructu...

  2. Measuring Autogenic Recharge over a Karst Aquifer Utilizing Eddy Covariance Evapotranspiration

    OpenAIRE

    Nico M. Hauwert; John M. Sharp

    2014-01-01

    Autogenic, or direct aquifer recharge can best be measured as the remainder of a water balance utilizing precise measurement of precipitation, evapotranspiration (ET) and runoff. ET is the largest component of a precipitation water balance and can be measured within 5% using an eddy covariance system with Bowen-ratio energy balance corrections. Water balance components of precipitation, evapotranspiration, internal runoff, soil moisture were measured using a eddy covari...

  3. Autogenous transplantation of mandibular third molar to replace tooth with vertical root fracture

    OpenAIRE

    Asgary, Saeed

    2009-01-01

    Autogenous tooth transplantation (ATT) can be considered when there is a hopeless molar tooth and suitable donor present. This report presents an unconventional case of successful ATT of a third molar replacing the adjacent fractured second molar in a 33 year old woman. This wisdom tooth had completely developed roots. Root-end filling with Calcium Enriched Mixture (CEM) cement was performed in the third molar. The second molar was extracted non-traumatically without any bone removal; the wis...

  4. Anatomic study of the lacrimal fossa and lacrimal pathway for bypass surgery with autogenous tissue grafting

    OpenAIRE

    Hai Tao; Zhi-zhong Ma; Hai-Yang Wu; Peng Wang; Cui Han

    2014-01-01

    Purpose: To study the microsurgical anatomy of the lacrimal drainage system and to provide anatomical evidence for transnasal endoscopic lacrimal drainage system bypass surgery by autogenous tissue grafting. Materials and Methods: A total of 20 Chinese adult cadaveric heads in 10% formaldehyde, comprising 40 lacrimal ducts were used. The middle third section of the specimens were examined for the following features: the thickness of the lacrimal fossa at the anterior lacrimal crest, vertical ...

  5. Crack path and fracture surface modifications in cement composites

    Directory of Open Access Journals (Sweden)

    Sajjad Ahmad

    2015-10-01

    Full Text Available There is a tremendous increase in the use of high strength and high performance self-consolidating cementitious composites due to their superior workability and mechanical strengths. Cement composites are quasi-brittle in nature and possess extremely low tensile strength as compared to their compressive strength. Due to the low tensile strength capacity, cracks develop in cementitious composites due to the drying shrinkage, plastic settlements and/or stress concentrations (due to external restrains and/or applied stresses etc. These cracks developed at the nanoscale may grow rapidly due to the applied stresses and join together to form micro and macro cracks. The growth of cracks from nanoscale to micro and macro scale is very rapid and may lead to sudden failure of the cement composites. The present paper reports the modifications in the crack growth pattern of the high performance cement composites to achieve enhanced ductility and toughness. The objective was accomplished by the incorporation of the micro sized inert particulates in the cement composite matrix. The results indicate that the incorporation of micro sized inert particles acted as the obstacles in the growth of the cracks thus improving the ductility and the energy absorption capacity of the self-consolidating cementitious composites.

  6. Behavior of cracked materials

    CERN Document Server

    François, Marc Louis Maurice

    2009-01-01

    Due to their microstructure, quasi brittle materials present rough cracks. Under sliding of the crack lips, this roughness involves in one hand induced opening and in the other hand some apparent plasticity which is due to the interlocking of the crack lips combined with Coulomb's friction. The proposed model is written under the irreversible thermodynamics framework. Micromechanics uses the Del Piero and Owen's structured deformation theory. Opening of the crack depends upon the crack shape and the relative sliding of the crack lips. The thermodynamic force associated to the sliding has the mechanical meaning of the force acting in order to make the crack slide. Yield surface is defined as a limitation of this force with respect to the Coulomb's friction and the Barenblatt cohesion. The crack orientation is defined as the one for which the criterion is reached for the lowest stress level. A decreasing cohesion, respect to sliding is supposed. Tension and compression reference cases are envisaged.

  7. Shrinkage Prediction for the Investment Casting of Stainless Steels

    Energy Technology Data Exchange (ETDEWEB)

    Sabau, Adrian S [ORNL

    2007-01-01

    In this study, the alloy shrinkage factors were obtained for the investment casting of 17-4PH stainless steel parts. For the investment casting process, unfilled wax and fused silica with a zircon prime coat were used for patterns and shell molds, respectively. Dimensions of the die tooling, wax pattern, and casting were measured using a Coordinate Measurement Machine in order to obtain the actual tooling allowances. The alloy dimensions were obtained from numerical simulation results of solidification, heat transfer, and deformation phenomena. The numerical simulation results for the shrinkage factors were compared with experimental results.

  8. Shrinkage of magnetic domains in superconductor/ferro-magnet bilayer

    Energy Technology Data Exchange (ETDEWEB)

    Tamegai, T; Nakao, Y; Nakajima, Y, E-mail: tamegai@ap.t.u-tokyo.ac.j [Department of Applied Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2009-03-01

    Shrinkage of magnetic domains in a ferromagnetic garnet film in contact with a superconducting Pb film is experimentally investigated by magneto-optical imaging. Non-equilibrium effects due to pinning of magnetic domains are suppressed by demagnetizing the sample by AC magnetic field. Although qualitative behavior follows the theoretical prediction, much larger shrinkage of the width of magnetic domains is observed. Possible origins for this discrepancy are discussed. We also confirm the magnetic shielding of the stray field from the garnet film by Pb by observing magnetic domain structures from the Pb side.

  9. Crack mitigation in concrete bridge decks through experimental analysis and computer modeling

    Science.gov (United States)

    Richardson, Douglas M.

    Bridge deck cracking can cause deterioration of bridge decks, leading to a shorter life span and poor performance. Throughout the US, cracking has been identified as a problem, with transverse cracking along the deck at regular spacings being the most prominent type. This problem is usually caused by drying shrinkage within the concrete. The material properties, restraint, and distances without expansion joints all affect the crack pattern within the deck. This study will delve into the reasons that bridge decks crack, the strains that are associated with drying shrinkage, and possible methods for abating its effects. The research is divided into two parts, the first being laboratory experimentation, which was conducted through the use of two 7 ft. x 10 ft. experimental concrete bridge bays. Each bay was instrumented with strain and temperature gages throughout the deck and girders, which collected data for six months. The first deck was poured with a control concrete mix used currently in Illinois. The second deck was poured with a type K expansive concrete, which could battle the effects of shrinkage. For both decks, the results suggest a compressive strain throughout the rebar and along the top surface of the concrete, except for the locations where cracks are found (at these locations the strain slopes upward into tension). The strain in the type K deck, though, was notably less than that in the control deck and the onset of cracking was delayed by three weeks, giving the indication of an improvement over the current mix design. The second portion of the research was focused on using a finite element model to replicate the bridge bay and study the results. Equivalent temperature loading was used to apply the shrinkage loads recorded during the experimental portion of the research. The model was then expanded to encompass a full-scale bridge and in order to provide some insight into shrinkage strain in the real world. The end goal is to help alleviate cracking

  10. Weld cracking - some examples

    International Nuclear Information System (INIS)

    The possible causes of cold cracking can be relatively clearly defined according to today's state of knowledge. By knowing these causes, it is possible to control the risk of cold cracking to the greatest extent; with the knowledge of the position and dimensions of these cracks, as well as the time of their occurence together with an optimization of the testing technique, the detection control of the cracking freedom can be almost considered as solved. (orig.)

  11. Tubing weld cracking test

    International Nuclear Information System (INIS)

    A tubing weld cracking (TWC) test was developed for applications involving advanced austenitic alloys (such as modified 800H and 310HCbN). Compared to the Finger hot cracking test, the TWC test shows an enhanced ability to evaluate the crack sensitivity of tubing materials. The TWC test can evaluate the cracking tendency of base as well as filter materials. Thus, it is a useful tool for tubing suppliers, filler metal producers and fabricators

  12. Autogenous standard versus inside-out vein graft to repair facial nerve in rabbits

    Institute of Scientific and Technical Information of China (English)

    TANG Jie; WANG Xue-mei; HU Jing; LUO En; QI Meng-chun

    2008-01-01

    To evaluate autogenous vein grafts and inside-out vein grafts as conduits for the defects repair in the rabbit facial nerves.Methods:The 10 mm segments of buccal division of facial nerve were transected for 48 rabbits in this study.Then the gaps were immediately repaired by autogenous vein grafts or inside-out vein grafts in different groups. All the animals underwent the whisker movement test and electrophysiologic test during the following 16 weeks at different time points postoperatively. Subsequently,the histological examination was performed to observe the facial nerve regeneration morphologically.Results:At 8 weeks after operation,the facial nerve regeneration has significant difference between the experimental group and the control group in electrophysiologic test and histological observation. However,at the end of this study,16 weeks after operation,there was no significant difference between inside-out vein grafts and standard vein grafts in enhancing peripheral nerve regeneration.Conclusion:This study suggest that both kinds of vein grafts play positive roles in facial nerve regeneration after being repaired immediately,but the autogenous inside-out vein grafts might accelerate and facilitate axonal regeneration as compared with control.

  13. Alternative method to treat oroantral communication and fistula with autogenous bone graft and platelet rich firbin

    Science.gov (United States)

    Niedzielska, Iwona; Borgiel-Marek, Halina; Różanowski, Bartosz

    2016-01-01

    Background Removing a tooth from the jaw results in the occurrence of oroantral communication in beneficial anatomic conditions or in the case of a iatrogenic effect. Popularized treatments of the oroantral communication have numerous faults. Large bone defect eliminates the chance to introduce an implant. Purpose of this work was assessment of the usefulness of autogenous bone graft and PRF in normal bone regeneration in the site of oroantral communication. Material and Methods Bone regeneration in the site of oroantral communication was assessed in 20 patients. Bone defects were supplemented autogenous bone graft from mental protuberance in 14 cases and from oblique line in 6 cases. The graft was covered with a PRF membrane. Results In the study group in all cases closure of the oroantral communication was observed. The average width of the alveolar was 13 mm and the average height was 12.5 mm. In 3 patients an average increase of alveolar height of 1.5 mm was observed. Conclusions This method may be the best option to prepare alveolar for new implant and prosthetic solutions. Key words:Oroantral communication, oroantral fistula, autogenous bone graft, bone regeneration, platelet rich fibrin. PMID:27475687

  14. Technical innovations in ear reconstruction using a skin expander with autogenous cartilage grafts.

    Science.gov (United States)

    Dashan, Yu; Haiyue, Jiang; Qinghua, Yang; Bo, Pan; Lin, Lin; Tailing, Wang; Yanmei, Wang; Xiao, Qin; Hongxing, Zhuang

    2008-01-01

    Pioneers such as Tanzer and Brent have established the foundations of microtia reconstruction using an autogenous costal cartilage framework. The framework and its skin coverage are the two limiting factors in ear reconstruction. At the present time autogenous rib cartilage and mastoid skin are still first choice materials for most surgeons. They have the combined advantages of well-matched texture and colour. To reconstruct a symmetrical, accurate, prominent auricle and minimise as much as possible the chest wall deformity caused by rib cartilage harvesting, we set out to improve our techniques for cartilaginous framework definition and to use the remnant ear to enhance the projection of the reconstructed ear. Since 2000, 342 cases (366 ears) were treated using our current techniques. Data pertaining to complications were recorded. Final results were assessed a minimum of 1 year postoperatively. The follow-up period ranged from 1 to 6 years. Most of the patients with microtia were satisfied with the results of their ear reconstruction. In conclusion, our techniques help to reduce the quantity of rib cartilage needed to fabricate ear framework and minimise chest wall deformity. The frameworks are accurate, prominent and stable. Reconstructed ears are similar in colour and appearance to the normal side. Our innovations are practical and reliable for microtia reconstruction using skin expanders in combination with a sculpted autogenous rib cartilage framework. PMID:18849209

  15. Drying shrinkage of mortars with limestone filler and blast-furnace slag

    Directory of Open Access Journals (Sweden)

    Carrasco, M. F.

    2003-12-01

    Full Text Available During the 1990's the use of cements made with port land clinker and two mineral admixtures, called ternary or blended cements, has grown considerably. Nowadays, cements containing several combinations of fly ash and silica fume, blast-furnace slag and silica fume or blast-furnace slag and limestone filler are commonly used. There are numerous works on the influence of blended cements on the fresh state and mechanical properties of mortar and concrete, but the their deformations due to drying shrinkage are not so well described. Analysis of drying shrinkage is relevant because this property influences the possibility of cracking occurrence and, hence, the deterioration of mechanical and durable properties of concrete structures. This paper evaluates the influence on the drying shrinkage of mortars of variable contents of limestone filler and/or blast-furnace slag in Portland cement. Additionally, flexion strength and non evaporable water content were evaluated. Test results show that the inclusion of these mineral admixtures, Joint or separately, increments drying shrinkage of mortars at early ages. Despite this fact, mortars made with limestone filler cement are less susceptible to cracking than mortars made with cements incorporating blast-furnace slag or both admixtures.

    Durante los años 90 el uso de cementos fabricados con clínker Portland y dos adiciones suplementarias (cementos ternarios o compuestos se ha incrementado en forma considerable. En la práctica, es cada vez más común el empleo de estos cementos conteniendo combinaciones de ceniza volante y humo de sílice, escoria y humo de sílice o escoria y filler calcáreo. En la actualidad existen numerosos estudios sobre la influencia de los cementos compuestos en las características en estado fresco y las propiedades mecánicas de morteros y hormigones, pero las deformaciones que estos materiales sufren debido a la retracción por secado no son tan conocidas. El análisis de

  16. Research on thermal effect and temperature control measures for crack prevention of spillway tunnel concrete lining%泄洪洞混凝土衬砌温变效应及温控防裂措施研究

    Institute of Scientific and Technical Information of China (English)

    司政; 李守义; 陈尧隆; 杨杰

    2011-01-01

    [Objective]The research on thermal effect of spillway tunnel concrete lining was conducted to provide references to choose control measures for crack prevention.[Method]According to a spillway tunnel lining concrete cracks after pouring the high strength silica powder concrete, considering concrete mechanical parameters varying with time and impacts on thermal stress of concrete pouring process, the lining concrete temperature field and stress field were analyzed by a 3-D finite element program.[Result]Lining sidewall and footwall concrete surface early stage thermal stress exceeds tensile strength of corresponding age,so cracks would be found on the concrete surface.The cracks appeared on lining concrete is closely related to high temperature of hydration heat of concrete, fast growth of elastic modulus, concrete curing mode and large autogenous volume deformation and large shrinkage deformation.The author proposes that surface heat preservation can decrease concrete surface early stage thermal stress greatly, which can prevent surface crack; using low heat concrete and decreasing pouring temperature can improve later stage thermal stress of lining concrete.[Conclusion]Three temperature control measures can effectively improve the stress state of concrete lining,and prevent or reduce the appearance of cracks.%[目的]研究混凝土衬砌的温变效应,为混凝土防裂措施的选择提供参考.[方法]针对某工程泄洪洞衬砌高强硅粉混凝土浇筑后出现的裂缝,在考虑混凝土热力学参数随龄期变化及混凝土实际浇筑过程对温度应力的影响,采用三维有限元程序对衬砌混凝土浇筑全过程进行仿真分析.[结果]衬砌边墙、底板混凝土表面早期应力超过相应龄期的抗拉强度,混凝土表面将出现裂缝.泄洪洞混凝土衬砌裂缝的产生,与混凝土水化热温升高且速度快、弹性模量增长快、混凝土养护方式以及混凝土自生体积变形和干缩变形大等密

  17. Deconvolution using singular integral regularization and curvelet shrinkage

    Energy Technology Data Exchange (ETDEWEB)

    Ma Jianwei [Department of Engineering Mechanics, Tsinghua University, Beijing 100084 (China)], E-mail: jma@tsinghua.edu.cn

    2007-08-20

    A special inverse problem, image deconvolution/deblurring is considered in this Letter by combining a singular integral regularization with a constrained curvelet shrinkage. The proposed technique is quite efficient and stable for recovery of texture when the observed image is contaminated with noise. Numerical experiments illustrate the good performance in comparison to some existing methods.

  18. Local shrinkage rules, L\\'evy processes, and regularized regression

    CERN Document Server

    Polson, Nicholas G

    2010-01-01

    We use L\\'evy processes to generate joint prior distributions for a location parameter $\\bbeta = (\\beta_1,...,\\beta_p) $ as $p$ grows large. This leads to the class of local-global shrinkage rules. We extend this framework to large-scale regularized regression for $p>n$ problems, and provide thorough comparisons with current methodologies.

  19. Robust Gene Selection based on Minimal Shrinkage Redundancy

    Czech Academy of Sciences Publication Activity Database

    Kalina, Jan; Valenta, Zdeněk

    ISCB, 2012. s. 67. ISBN 978-82-8045-026-5. [Annual Conference of the International Society for Clinical Biostatistics /33./. 19.08.2012-23.08.2012, Bergen] Institutional support: RVO:67985807 Keywords : dimensionality reduction * shrinkage estimation * robustness Subject RIV: BB - Applied Statistics, Operational Research

  20. Shrinkage of Newly Formed Particles in an Urban Environment

    Czech Academy of Sciences Publication Activity Database

    Škrabalová, Lenka; Zíková, Naděžda; Ždímal, Vladimír

    2015-01-01

    Roč. 15, č. 4 (2015), s. 1313-1324. ISSN 1680-8584 R&D Projects: GA ČR GAP209/11/1342 Institutional support: RVO:67985858 Keywords : aerosol dynamics * ultrafine particles * particle shrinkage Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.094, year: 2014

  1. Hot cracking studies on CrMoV and NiCrMoV turbine rotor steels during welding

    International Nuclear Information System (INIS)

    Four different rotor materials, three CrMoV steels and a NiCrMoV steel, were investigated both with respect to solidification and HAZ liquation cracking. It involved the Varestraint testing using autogeneous gas tungsten arc welding at two different heat inputs, and metallographic examinations using optical, scanning and/or transmission electron microscopy. An increase in heat input/unit length (from 1.2 to 2.7 KJ/mm) or an increase in travel speed at the same low heat input (1.2 KJ/mm) tends to produce more solidification cracking. In the case of CrMoV steels, 1950s air melted rotors (Buck and the Gallatin rotors) showed worse solidification cracking susceptibility than the modern Bethlehem forging vacuum poured, 2A. The modern NiCrMoV forging, also vacuum-poured, 3A, however, showed worse solidification cracking susceptibility than the old air-melted Gallatin rotor. Therefore, the harmful effects of Ni on solidification cracking was confirmed. Its role is understood as having favored the austenite formation, thus resulting in more primary austenite solidification. This gives rise to heavy segregation of impurities such as S and P at the austenite grain boundaries. Detrimental effects of sulfur and phosphorus both on solidification and the HAZ hot cracking were confirmed. Addition of Ce or Ti to the Buck rotor with the greatest solidification cracking susceptibility helped improve cracking resistance

  2. Hot cracking studies on CrMoV and NiCrMoV turbine rotor steels during welding

    Energy Technology Data Exchange (ETDEWEB)

    Yoo, S.Y.

    1986-01-01

    Four different rotor materials, three CrMoV steels and a NiCrMoV steel, were investigated both with respect to solidification and HAZ liquation cracking. It involved the Varestraint testing using autogeneous gas tungsten arc welding at two different heat inputs, and metallographic examinations using optical, scanning and/or transmission electron microscopy. An increase in heat input/unit length (from 1.2 to 2.7 KJ/mm) or an increase in travel speed at the same low heat input (1.2 KJ/mm) tends to produce more solidification cracking. In the case of CrMoV steels, 1950s air melted rotors (Buck and the Gallatin rotors) showed worse solidification cracking susceptibility than the modern Bethlehem forging vacuum poured, 2A. The modern NiCrMoV forging, also vacuum-poured, 3A, however, showed worse solidification cracking susceptibility than the old air-melted Gallatin rotor. Therefore, the harmful effects of Ni on solidification cracking was confirmed. Its role is understood as having favored the austenite formation, thus resulting in more primary austenite solidification. This gives rise to heavy segregation of impurities such as S and P at the austenite grain boundaries. Detrimental effects of sulfur and phosphorus both on solidification and the HAZ hot cracking were confirmed. Addition of Ce or Ti to the Buck rotor with the greatest solidification cracking susceptibility helped improve cracking resistance.

  3. Shrinkage of Grand Fir Wood and its Variability within the Stem

    Directory of Open Access Journals (Sweden)

    Jiří Lukášek

    2012-06-01

    Full Text Available This study presents the results of the experiment focused on assessment of the shrinkage of Grand fir (Abies grandis /Douglas/ Lindl. wood and its variability in relation to the position in the stem. The examined sample trees came from the Černokostelecka Area in the Czech Republic. Tangential shrinkage was 7.1 %, radial 3.3 % and volumetric shrinkage 10.5 %. The results show evident influence of the horizontal position on the evaluated features. The lowest shrinkage values are attained close to the pith; shrinkage toward the bark shows a rising trend. In terms of vertical position, the distribution of shrinkage in the stem did not show any apparent trend. Although the dependence of shrinkage on density proved to be statistically significant, density explains only a small portion of the shrinkage variability.

  4. Study of ‘real’ shrinkage by ESEM observations and digital image analysis

    OpenAIRE

    Jankovic, D.

    2007-01-01

    Defining the 'real' shrinkage values of concrete is still a subject of much debate. In shrinkage experiments size effects are inherently present. Through an attempt to determine the real shrinkage of cement-based materials, these size effects have to be eliminated or at least reduced as much a possible. In this contribution drying shrinkage experiments on thin cement paste samples are discussed. Thin-cast Portland cement paste specimens (2 mm) are used, polished to 1 mm with specially designe...

  5. Modified Dugdale cracks and Fictitious cracks

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1998-01-01

    A number of theories are presented in the literature on crack mechanics by which the strength of damaged materials can be predicted. Among these are theories based on the well-known Dugdale model of a crack prevented from spreading by self-created constant cohesive flow stressed acting in local a......-critical loads. Such information, which cannot be obtained experimentally, are needed in viscoelastic lifetime analysis.Finally, the question is considered whether or not fracture properties experimentally determined are real (genuine) material properties.......A number of theories are presented in the literature on crack mechanics by which the strength of damaged materials can be predicted. Among these are theories based on the well-known Dugdale model of a crack prevented from spreading by self-created constant cohesive flow stressed acting in local...... (displacement) respectively of material considered. The practical applicability of the two models is limited such that predicted strength sigma_CR must be less than sigma_L/3, which corresponds to an assumption that fictitious cracks are much smaller than real crack lengths considered. The reason for this...

  6. Infiltration and Bypass Flow of Cracking Puddled Soils

    Directory of Open Access Journals (Sweden)

    M.J. Islam

    2004-01-01

    Full Text Available A study of infiltration and bypass flow was conducted in a wet soil bin with three different soils treatments (sandy loam, clay loam and clay soil to determine the swelling behaviour of cracking puddled soils by watering and its impact on bypass flow. Infiltration rate for the soils was recorded after puddling the soils. Then the puddled soils were allowed to dry for a period of up to 15 days. After that the plots were rewetted in order to observe the swelling and bypass behaviour of cracked soils. From this study it is observed that the infiltration rates of puddled soils were very low (0.03-0.05 mm h-1 mainly due to the puddling effect. The study indicates that cracks on puddled soils at 15th day�s of drying are effectively irreversible. The maximum bypass flow was recorded for the clay loam soil. During the first day, the flow rate was extremely high at 313 mm h-1. But this higher rate gradually reduced from the second day and onwards. The bypass flow rate for the clay loam and clay soil was almost same. The study reveals that it is not possible to swell up shrinkage cracks on puddled soils by watering alone. Re-working of the soil is necessary to seal the cracks.

  7. Elevated temperature crack growth

    Science.gov (United States)

    Kim, K. S.; Vanstone, R. H.

    1992-01-01

    The purpose of this program was to extend the work performed in the base program (CR 182247) into the regime of time-dependent crack growth under isothermal and thermal mechanical fatigue (TMF) loading, where creep deformation also influences the crack growth behavior. The investigation was performed in a two-year, six-task, combined experimental and analytical program. The path-independent integrals for application to time-dependent crack growth were critically reviewed. The crack growth was simulated using a finite element method. The path-independent integrals were computed from the results of finite-element analyses. The ability of these integrals to correlate experimental crack growth data were evaluated under various loading and temperature conditions. The results indicate that some of these integrals are viable parameters for crack growth prediction at elevated temperatures.

  8. Eliminating cracking during drying

    OpenAIRE

    Jin, Qiu; Tan, Peng; Schofield, Andrew B.; Xu, Lei

    2013-01-01

    When colloidal suspensions dry, stresses build up and cracks often occur - a phenomenon undesirable for important industries such as paint and ceramics. We demonstrate an effective method which can completely eliminate cracking during drying: by adding emulsion droplets into colloidal suspensions, we can systematically decrease the amount of cracking, and eliminate it completely above a critical droplet concentration. Since the emulsion droplets eventually also evaporate, our technique achiev...

  9. Experimental Verification of the Concrete Shrinkage Strains Course According to En 1992-2 Standard

    Directory of Open Access Journals (Sweden)

    Raczkiewicz W.

    2015-06-01

    Full Text Available The article provides basic information about the shrinkage of concrete and discusses the major impact on the size and course of the shrinkage. There are the guidelines to estimate the shrinkage strain of concrete bridge structures for the high tensile strength-SCI in accordance with PN-EN 1992-2. The article presents the results of experimental studies which aim was to analyze the course of shrinkage in two types of specimens made of different composition mixes. The studies have also made possible to verify the actual size of the shrinkage strain and designated ones on the basis of the PN-EN 1992-2.

  10. Research and Application of the Mathematic Model for the Washing Shrinkage of Woven Fabric

    Institute of Scientific and Technical Information of China (English)

    2007-01-01

    Having analyzed the relationships between washing shrinkage and weaving technique, parameters, material properties of woven fabrics and studied the shrinkage mechanism and its mathematical model of the plain fabric,researchers set up a shrinkage model of the twills and satins and proposed a method for calculating the washing shrinkage based on weaving technique and parameters of fabrics. Shrinkage experiments of silk habotai, silk twill and silk satin fabrics were performed. The results were compared with those of the theoretical computations, and it has been proven that the theoretical method is reliable.

  11. Influence of Cracking on the distribution of Suction profile of a clay soil:comparative Approach by modeling of thermo-fluid coupling

    International Nuclear Information System (INIS)

    Soil shrinks as it desiccates, and the magnitude of shrinkage can be large for clay soils, rich in fine particles. Soil drying leads to cracks formation, causing a phenomenon of high significance in environmental geotechnics. To illustrate the effect of cracking, a numerical model of soil atmosphere interaction has been developed taking into account the thermo fluid coupling of an unsaturated clay soil. The model is used to simulate the evolution if suction during the drying process. The study simulates firstly the model of an intact soil. Then, the study is extended to investigate the case of a cracked soil. The main results showed a significant influence of the presence of crack on the suction profile.In cracked soil, further loss of moisture occurs as direct evaporation from crack followed by an increase of the suction in the soil. High suction is initially concentrated on the head of the crack then extended to both vertical and horizontal sideway directions. (author)

  12. Autogenous bone graft and ePTFE membrane in the treatment of peri-implantitis. II. Stereologic and histologic observations in cynomolgus monkeys

    DEFF Research Database (Denmark)

    Schou, Søren; Holmstrup, Palle; Skovgaard, Lene Theil; Stoltze, K.; Hjørting-Hansen, Erik; Gundersen, Hans Jørgen G.

    autogenous bone graft; guided bone regeneration; histology; membrane; non-human primates; oral implants; osseointegration; pathalogy; peri-implantitis; stereology; treatment......autogenous bone graft; guided bone regeneration; histology; membrane; non-human primates; oral implants; osseointegration; pathalogy; peri-implantitis; stereology; treatment...

  13. Crack identification in elasticity

    International Nuclear Information System (INIS)

    Crack and defect, e.g. hole, identification in elasticity, is formulated as an output optimization problem, where predictions of a suitably parametrized mechanical model are compared with measured data. For the mechanical part the elastostatic analysis is done by the boundary element method, including hypersingular boundary elements for the cracks. In addition, unilateral contact effects along the crack boundaries, i.e., the possibility of partially closed cracks, are considered. Unilateral crack identification has been studied. The numerical solution of the (ill-posed) inverse problem usually requires the use of specialized algorithms and techniques. Among others, we consider neural networks, filter-driven optimization and genetic algorithms. It seems that classical optimization works only in connection with sensitivity analysis for the accurate calculation of the first derivatives for classical cracks and for unilateral cracks). A short review of recent contributions in this area together with the numerical results of our on-going investigation will be presented in the conference. The effect of unilateral contact on the crack identification will be examined. Multiple-crack and multipleload identification problems will be considered. The effectiveness of various solution algorithms will be discussed. Promising directions of further research in this area will be pointed out. Refs. 7 (author)

  14. Early-age volume changes of extrudable reactive powder concrete

    OpenAIRE

    De Noirfontaine M.N.; Mounanga P.; Khelidj A.; Dunstetter F.; Cherkaoui K.; Courtial M.

    2010-01-01

    This article presents a study on the early-age autogenous deformations of Extrudable Reactive Powder Concretes (ERPCs), especially designed for the making of concrete pipes by extrusion. Different ERPC mixtures, with variable amounts of polycarboxylate superplasticizer (SP), have been investigated. Results on 28-day mechanical properties, early-age hydration rate, autogenous shrinkage and premature cracking risk are analyzed and discussed in relation with the ERPC mix parameters.

  15. Early-age volume changes of extrudable reactive powder concrete

    Directory of Open Access Journals (Sweden)

    De Noirfontaine M.N.

    2010-06-01

    Full Text Available This article presents a study on the early-age autogenous deformations of Extrudable Reactive Powder Concretes (ERPCs, especially designed for the making of concrete pipes by extrusion. Different ERPC mixtures, with variable amounts of polycarboxylate superplasticizer (SP, have been investigated. Results on 28-day mechanical properties, early-age hydration rate, autogenous shrinkage and premature cracking risk are analyzed and discussed in relation with the ERPC mix parameters.

  16. Internal water curing with Liapor aggregates

    DEFF Research Database (Denmark)

    Lura, Pietro

    2005-01-01

    Internal water curing is a very efficient way to counteract self-desiccation and autogenous shrinkage in high performance concrete, thereby reducing the likelihood of early-age cracking. This paper deals with early-age volume changes and moisture transport in lightweight aggregate concrete realized...... with wet lightweight aggregates. Lightweight aggregate concrete mixtures with different degree of saturation and different particle size of the lightweight aggregates were studied and compared to normal weight concrete. Autogenous deformations, selfinduced stresses in fully restrained conditions...

  17. Early-age volume changes of extrudable reactive powder concrete

    Science.gov (United States)

    Cherkaoui, K.; Courtial, M.; Dunstetter, F.; Khelidj, A.; Mounanga, P.; de Noirfontaine, M. N.

    2010-06-01

    This article presents a study on the early-age autogenous deformations of Extrudable Reactive Powder Concretes (ERPCs), especially designed for the making of concrete pipes by extrusion. Different ERPC mixtures, with variable amounts of polycarboxylate superplasticizer (SP), have been investigated. Results on 28-day mechanical properties, early-age hydration rate, autogenous shrinkage and premature cracking risk are analyzed and discussed in relation with the ERPC mix parameters.

  18. Evaluation of ABM/P-15 versus autogenous bone in an ovine lumbar interbody fusion model

    OpenAIRE

    Sherman, Blake P.; Lindley, Emily M.; Turner, A. Simon; Seim III, Howard B.; Benedict, James; Burger, Evalina L; Patel, Vikas V.

    2010-01-01

    A prospective, randomized study was performed in an ovine model to compare the efficacy of an anorganic bovine-derived hydroxyapatite matrix combined with a synthetic 15 amino acid residue (ABM/P-15) in facilitating lumbar interbody fusion when compared with autogenous bone harvested from the iliac crest. P-15 is a biomimetic to the cell-binding site of Type-I collagen for bone-forming cells. When combined with ABM, it creates the necessary scaffold to initiate cell invasion, binding, and sub...

  19. Effect of Oxygen Concentration on Autogenous Ignition Temperature and Pneumatic Impact Ignitability of Nonmetallic Materials

    Science.gov (United States)

    Smith, Sarah

    2009-01-01

    Extensive test data exist on the ignitability of nonmetallic materials in pure oxygen, but these characteristics are not as well understood for lesser oxygen concentrations. In this study, autogenous ignition temperature testing and pneumatic impact testing were used to better understand the effects of oxygen concentration on ignition of nonmetallic materials. Tests were performed using oxygen concentrations of 21, 34, 45, and 100 %. The following materials were tested: PTFE Teflon(Registered Trademark), Buna-N, Silicone, Zytel(Registered Trademark) 42, Viton(registered Trademark) A, and Vespel(Registered Trademark) SP-21.

  20. Stepwise surgical approach to diabetic partial foot amputations with autogenous split thickness skin grafting

    Directory of Open Access Journals (Sweden)

    Crystal L. Ramanujam

    2016-06-01

    Full Text Available In the surgical treatment of severe diabetic foot infections, substantial soft tissue loss often accompanies partial foot amputations. These sizeable soft tissue defects require extensive care with the goal of expedited closure to inhibit further infection and to provide resilient surfaces capable of withstanding long-term ambulation. Definitive wound closure management in the diabetic population is dependent on multiple factors and can have a major impact on the risk of future diabetic foot complications. In this article, the authors provide an overview of autogenous skin grafting, including anatomical considerations, clinical conditions, surgical approach, and adjunctive treatments, for diabetic partial foot amputations.

  1. Internal curing with lightweight aggregate produced from biomass-derived waste

    International Nuclear Information System (INIS)

    Shrinkage of concrete may lead to cracking and ultimately to a reduction of the service life of concrete structures. Among known methods for shrinkage mitigation, internal curing with porous aggregates was successfully utilized in the last couple of decades for decreasing autogenous and drying shrinkage. In this paper, the internal curing performance of pre-saturated lightweight aggregates produced from biomass-derived waste (bio-LWA) was studied. In the first part of this paper, the microstructure of the bio-LWA is investigated, with special focus on their pore structure and on their water absorption and desorption behavior. The bio-LWA has large porosity and coarse pore structure, which allows them to release the entrained water at early age and counteract self-desiccation and autogenous shrinkage. In the second part, the efficiency of internal curing in mortars incorporating the bio-LWA is examined by neutron tomography, internal relative humidity and autogenous deformation measurements

  2. Internal curing with lightweight aggregate produced from biomass-derived waste

    Energy Technology Data Exchange (ETDEWEB)

    Lura, Pietro, E-mail: pietro.lura@empa.ch [Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf (Switzerland); Institute for Building Materials (IfB), ETH Zürich (Switzerland); Wyrzykowski, Mateusz [Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf (Switzerland); Department of Building Physics and Building Materials, Lodz University of Technology (Poland); Tang, Clarence [Siam Research and Innovation, SCG Cement–Building Materials, Saraburi (Thailand); Lehmann, Eberhard [Paul Scherrer Institut, 5232 Villigen PSI (Switzerland)

    2014-05-01

    Shrinkage of concrete may lead to cracking and ultimately to a reduction of the service life of concrete structures. Among known methods for shrinkage mitigation, internal curing with porous aggregates was successfully utilized in the last couple of decades for decreasing autogenous and drying shrinkage. In this paper, the internal curing performance of pre-saturated lightweight aggregates produced from biomass-derived waste (bio-LWA) was studied. In the first part of this paper, the microstructure of the bio-LWA is investigated, with special focus on their pore structure and on their water absorption and desorption behavior. The bio-LWA has large porosity and coarse pore structure, which allows them to release the entrained water at early age and counteract self-desiccation and autogenous shrinkage. In the second part, the efficiency of internal curing in mortars incorporating the bio-LWA is examined by neutron tomography, internal relative humidity and autogenous deformation measurements.

  3. Experimental study on shrinkage characteristics of semi-coke/coke under gradient temperature during coking process

    Energy Technology Data Exchange (ETDEWEB)

    Fu, Z.; Guo, Z.; Wang, S. [Chinese Academy of Sciences, Beijing (China)

    2006-04-15

    A furnace equipped with a removable measuring scale in the side was applied to study on the shrinkage characteristics of semi-coke/coke under gradient temperature during coking process. 1500 g coking coal was used in the test. The effects of coking time, central temperature, heating-up rate and gradient temperature on lateral shrinkage were studied under different heating rate. The results show that the coal begins to shrink at a central temperature range of 280 to 360{sup o}C and ends at about 900{sup o}C. The lateral shrinkage is in a range of 5 mm to 8.5 mm and lateral shrinkage ratio is 7 to 12%. Generally, the gradient temperature increases and lateral shrinkage decreases with increasing heating-up rate and density. The central temperature of beginning shrinkage, the second shrinkage peak, gradient temperature of different locations and shrinkage coefficient of coal decreases with the increase of heating rate. The central temperature of beginning shrinkage and gradient temperature of different locations increase with increasing density. But the increase of density has no influence on shrinkage coefficient and shrinkage peak. In addition, the temperature rise rates at different locations are different during different coking stages. 9 refs., 9 figs., 1 tab.

  4. Structural Considerations on Fatigue Cracks

    Directory of Open Access Journals (Sweden)

    Cornel Bit

    2015-07-01

    Full Text Available This paper has been focused on the modern theoretical and experimental investigations on fatigue of metals which are now largely concentrated on three important areas: fatigue crack nucleation, short crack growth and long crack propagation. The main differences concerning the short cracks and long cracks mechanical investigation analysis have been presented.

  5. Structural Considerations on Fatigue Cracks

    OpenAIRE

    Cornel Bit

    2015-01-01

    This paper has been focused on the modern theoretical and experimental investigations on fatigue of metals which are now largely concentrated on three important areas: fatigue crack nucleation, short crack growth and long crack propagation. The main differences concerning the short cracks and long cracks mechanical investigation analysis have been presented.

  6. Combinatorial Selection and Least Absolute Shrinkage via the CLASH Algorithm

    CERN Document Server

    Kyrillidis, Anastasios

    2012-01-01

    The least absolute shrinkage and selection operator (LASSO) for linear regression exploits the geometric interplay of the $\\ell_2$-data error objective and the $\\ell_1$-norm constraint to arbitrarily select sparse models. Guiding this uninformed selection process with sparsity models has been precisely the center of attention over the last decade in order to improve learning performance. To this end, we alter the selection process of LASSO to explicitly leverage combinatorial sparsity models (CSMs) via the combinatorial selection and least absolute shrinkage (CLASH) operator. We provide concrete guidelines how to leverage combinatorial constraints within CLASH, and characterize CLASH's guarantees as a function of the set restricted isometry constants of the sensing matrix. Finally, our experimental results show that CLASH can outperform both LASSO and model-based compressive sensing in sparse estimation.

  7. Shrinkage Estimation of the Power Spectrum Covariance Matrix

    CERN Document Server

    Pope, Adrian C

    2007-01-01

    We introduce a novel statistical technique, shrinkage estimation, to estimate the power spectrum covariance matrix from a limited number of simulations. We optimally combine an empirical estimate of the covariance with a model (the target) to minimize the total mean squared error compared to the true underlying covariance. We test our technique on N-body simulations and evaluate its performance by estimating cosmological parameters. Using a simple diagonal target, we show that the shrinkage estimator significantly outperforms both the empirical covariance and the target individually when using a small number of simulations. We find that reducing noise in the covariance estimate is essential for properly estimating the values of cosmological parameters as well as their confidence intervals. We extend our method to the jackknife covariance estimator and again find significant improvement, though simulations give better results. Even for thousands of simulations we still find evidence that our method improves es...

  8. Exploiting tumor shrinkage through temporal optimization of radiotherapy

    CERN Document Server

    Unkelbach, Jan; Hong, Theodore; Papp, David; Ramakrishnan, Jagdish; Salari, Ehsan; Wolfgang, John; Bortfeld, Thomas

    2013-01-01

    In multi-stage radiotherapy, a patient is treated in several stages separated by weeks or months. This regimen has been motivated mostly by radiobiological considerations, but also provides an approach to reduce normal tissue dose by exploiting tumor shrinkage. The paper considers the optimal design of multi-stage treatments, motivated by the clinical management of large liver tumors for which normal liver dose constraints prohibit the administration of an ablative radiation dose in a single treatment. We introduce a dynamic tumor model that incorporates three factors: radiation induced cell kill, tumor shrinkage, and tumor cell repopulation. The design of multi-stage radiotherapy is formulated as a mathematical optimization problem in which the total dose to the liver is minimized, subject to delivering the prescribed dose to the tumor. Based on the model, we gain insight into the optimal administration of radiation over time, i.e. the optimal treatment gaps and dose levels. We analyze treatments consisting ...

  9. Image Variational Denoising Using Gradient Fidelity on Curvelet Shrinkage

    Directory of Open Access Journals (Sweden)

    Roysam Badrinath

    2010-01-01

    Full Text Available A new variational image model is presented for image restoration using a combination of the curvelet shrinkage method and the total variation (TV functional. In order to suppress the staircasing effect and curvelet-like artifacts, we use the multiscale curvelet shrinkage to compute an initial estimated image, and then we propose a new gradient fidelity term, which is designed to force the gradients of desired image to be close to the curvelet approximation gradients. Then, we introduce the Euler-Lagrange equation and make an investigation on the mathematical properties. To improve the ability of preserving the details of edges and texture, the spatial-varying parameters are adaptively estimated in the iterative process of the gradient descent flow algorithm. Numerical experiments demonstrate that our proposed method has good performance in alleviating both the staircasing effect and curvelet-like artifacts, while preserving fine details.

  10. The sparse Laplacian shrinkage estimator for high-dimensional regression

    CERN Document Server

    Huang, Jian; Li, Hongzhe; Zhang, Cun-Hui; 10.1214/11-AOS897

    2011-01-01

    We propose a new penalized method for variable selection and estimation that explicitly incorporates the correlation patterns among predictors. This method is based on a combination of the minimax concave penalty and Laplacian quadratic associated with a graph as the penalty function. We call it the sparse Laplacian shrinkage (SLS) method. The SLS uses the minimax concave penalty for encouraging sparsity and Laplacian quadratic penalty for promoting smoothness among coefficients associated with the correlated predictors. The SLS has a generalized grouping property with respect to the graph represented by the Laplacian quadratic. We show that the SLS possesses an oracle property in the sense that it is selection consistent and equal to the oracle Laplacian shrinkage estimator with high probability. This result holds in sparse, high-dimensional settings with p >> n under reasonable conditions. We derive a coordinate descent algorithm for computing the SLS estimates. Simulation studies are conducted to evaluate ...

  11. Shrinkage rate in two-phase carbon materials under irradiation

    International Nuclear Information System (INIS)

    A method is suggested for calculating the radiation stability of carbon materials consisting of two phases which differ in the degree of perfection of the crystalline lattice. It was found that the rate of shrinkage of a double phase carbon material induced by the radiation is the sum of rates of shrinkage of its phases multiplied by a proportionality factor equal to the weight proportions of the phases. The calculated rates agree satisfactorily with data from experiments conducted on specimens of GMZ graphite impregnated with pyrocarbon or phiA resin and irradiated with a fluence of 8x1021 neutr/cm2 in the range of temperatures of 300-900 deg C

  12. Shrinkage and trajectory of the flat jet with inclination angle

    Institute of Scientific and Technical Information of China (English)

    Shufeng Ye; Yusheng Xie; Hongzhi Guo; Ye Huang; Shantong Jin

    2003-01-01

    The performance of the flat jet with an inclination angle was investigated by a water model. A mathematical model for theshrinkage and the trajectory of the flat jet with an inclination angle was derived theoretically and verified by experimental data of thewater model. The experimental results indicate that the inclination angle (α) has no influence on the shrinkage of the flat jet, theshrinkage of the flat jet along the width direction decreases with the increasing of the initial velocity at the exit (u0) and the initialthickness of the flat jet (t0). Enough bigger initial exit velocity (u0) and initial thickness can suppress the shrinkage of the flat jetalong the width direction and keep the flat jet stabilized. In addition, the trajectory of the flat jet with an inclination angle is parabolicand must be taking into consideration when to determine the striking distance.

  13. Numerical Analysis of Hot Cracking in Laser-Hybrid Welded Tubes

    Directory of Open Access Journals (Sweden)

    Moritz Oliver Gebhardt

    2013-01-01

    Full Text Available In welding experiments conducted on heavy wall pipes, the penetration mode (full or partial penetration occurred to be a significant factor influencing appearance of solidification cracks. To explain the observed phenomena and support further optimization of manufacturing processes, a computational model was developed, which used a sophisticated strategy to model the material. High stresses emerged in the models in regions which showed cracking during experiments. In partial penetration welding, they were caused by the prevention of weld shrinkage due to the cold and strong material below the joint. Another identified factor having an influence on high stress localization is bulging of the weld.

  14. Three Dimensional Numerical Simulation for the Driving Force of Weld Solidification Cracking

    Institute of Scientific and Technical Information of China (English)

    Zhibo DONG; Yanhong WEI; Renpei LIU; Zujue DONG

    2005-01-01

    The double ellipsoidal model of heat source is used to analyze the thermal distributions with a three dimensional finite element method (FEM). In the mechanical model, solidification effects are treated by a dynamic element rebirth scheme. The driving force is obtained in the cracking susceptible temperature range. Moreover, this paper presents the effect of solidification shrinkage, external restraint, weld start locations and material properties on the driving force. The comparison between the simulated driving force and the experimental measurements of the material resistance predicts the susceptibility of weld metal solidification cracking.

  15. Optimal Linear Shrinkage Estimator for Large Dimensional Precision Matrix

    OpenAIRE

    Taras Bodnar; Arjun K. Gupta; Nestor Parolya

    2013-01-01

    In this work we construct an optimal shrinkage estimator for the precision matrix in high dimensions. We consider the general asymptotics when the number of variables $p\\rightarrow\\infty$ and the sample size $n\\rightarrow\\infty$ so that $p/n\\rightarrow c\\in (0, +\\infty)$. The precision matrix is estimated directly, without inverting the corresponding estimator for the covariance matrix. The recent results from the random matrix theory allow us to find the asymptotic deterministic equivalents ...

  16. The Process of Shrinkage as a Challenge to Urban Governance

    Directory of Open Access Journals (Sweden)

    Stryjakiewicz Tadeusz

    2016-06-01

    Full Text Available For many decades most researchers, planners and local authorities have been focusing almost exclusively on urban growth and its socio-economic and spatial consequences. However, in the current debate concerning the future of cities and regions in Europe the process of their shrinkage starts to attract more attention. In the conditions of a declining population, urban governance is an important challenge for local authorities, being usually much more difficult than during the periods of population growth.

  17. Bayesian Shrinkage Estimation of Quantitative Trait Loci Parameters

    OpenAIRE

    Wang, Hui; Zhang, Yuan-Ming; Li, Xinmin; Masinde, Godfred L.; Mohan, Subburaman; Baylink, David J.; Xu, Shizhong

    2005-01-01

    Mapping multiple QTL is a typical problem of variable selection in an oversaturated model because the potential number of QTL can be substantially larger than the sample size. Currently, model selection is still the most effective approach to mapping multiple QTL, although further research is needed. An alternative approach to analyzing an oversaturated model is the shrinkage estimation in which all candidate variables are included in the model but their estimated effects are forced to shrink...

  18. Shrinkage, creep and frost resistance of self-compacting concrete

    OpenAIRE

    Heirman, Gert; Vandewalle, Lucie

    2005-01-01

    Although already many researches exist about self-compacting concrete (SCC), it is still remarkable to notice that very little fundamental data have been published concerning its durability. This knowledge is, however, of extreme importance for a good and durable construction practice. For that reason, this article outlines laboratory studies concerning durability aspects as shrinkage, creep, salt frost scaling and internal frost resistance of 7 self-compacting concrete mixtures (SCC) and 1 r...

  19. STRENGTH SHRINKAGE AND CREEP OF CONCRETE IN TENSION AND COMPRESSION

    OpenAIRE

    S A Kristiawan

    2006-01-01

    Strength, shrinkage and creep of concrete in tension and compression have been determined and the relationship between those properties was studied. Direct tensile tests were applied to measure those properties in tension. The relationship of creep in tension and compression was determined based on the measurement of creep at similar stress and similar stress/strength ratio. It is found that concrete deforms more in tension than in compression. Except for concrete with a higher water/cement r...

  20. Investigation on Cracking of Concrete Shear Wall under Exceeded Temperature Differences Rate

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    In situ, the changes of temperature, deformation, and stressing of steel bar of C40 reinforced concrete shear wall were measured, respectively. The results are obvious that the temperature change of climate is one of the most effective factors which could lead the concrete shear wall to cracking at earlier age. The temperature differences between inside and outside concrete shear wall are so large that the concrete will gain larger shrinkage. This larger shrinkage which is caused by the temperature reducing ratio will gain the strained action of head, end and reinforced steel bar of concrete shear wall. This action can lead to tensile stress on the surface and inside concrete shear wall. If the tensile stress would exceed the pull strength of concrete, the concrete shear wall would crack and cause deterioration. Thus, the enhancing curing of concrete shear wall in suit at earlier age, and controlling temperature reducing ratio and deform caused by shrinkage, will be available treatments which control occurring and developing of cracking on concrete shear wall.

  1. Shrinkage of vitreous body caused by hydroxyl radical

    Energy Technology Data Exchange (ETDEWEB)

    Park, Myoung Joo; Shimada, Takashi; Matuo, Yoichirou; Akiyama, Yoko; Izumi, Yoshinobu; Nishijima, Shigehiro [Osaka University, Osaka (Japan)

    2008-12-15

    In the study, we examined the effect of hydroxyl radical generated by {gamma}-ray and UV irradiation on shrinkage of vitreous body. Change in gel ratio of vitreous body and change in the properties of its components (collagen, sodium hyaluronate) were analyzed. By comparing these results, the amount of hydroxyl radical, which induces the considerable shrinkage of vitreous body, was evaluated from theoretical calculation based on experimental condition and some reported kinetic parameters. It was concluded that the integrated amount of hydroxyl radical required to liquefy half of the vitreous body (vitreous body gel ratio = 50%) was estimated as 140 {mu}molg{sup -1} from {gamma}-ray irradiation experiment. Also, from UV irradiation experiment result, it was confirmed that the effect of hydroxyl radical is larger than that of other reactive species. The causes of shrinkage of vitreous body are supposed as follows, 1) decrease in viscosity by cleavage of glycoside bond in sodium hyaluronate, 2) leaching of collagen from vitreous body and 3) leaching of crosslinked products and scission products of collagen.

  2. Sealing of cracks in cement using microencapsulated sodium silicate

    Science.gov (United States)

    Giannaros, P.; Kanellopoulos, A.; Al-Tabbaa, A.

    2016-08-01

    Cement-based materials possess an inherent autogenous self-healing capability allowing them to seal, and potentially heal, microcracks. This can be improved through the addition of microencapsulated healing agents for autonomic self-healing. The fundamental principle of this self-healing mechanism is that when cracks propagate in the cementitious matrix, they rupture the dispersed capsules and their content (cargo material) is released into the crack volume. Various healing agents have been explored in the literature for their efficacy to recover mechanical and durability properties in cementitious materials. In these materials, the healing agents are most commonly encapsulated in macrocontainers (e.g. glass tubes or capsules) and placed into the material. In this work, microencapsulated sodium silicate in both liquid and solid form was added to cement specimens. Sodium silicate reacts with the calcium hydroxide in hydrated cement paste to form calcium-silicate-hydrate gel that fills cracks. The effect of microcapsule addition on rheological and mechanical properties of cement is reported. It is observed that the microcapsule addition inhibits compressive strength development in cement and this is observed through a plateau in strength between 28 and 56 days. The improvement in crack-sealing for microcapsule-containing specimens is quantified through sorptivity measurements over a 28 day healing period. After just seven days, the addition of 4% microcapsules resulted in a reduction in sorptivity of up to 45% when compared to specimens without any microcapsule addition. A qualitative description of the reaction between the cargo material and the cementitious matrix is also provided using x-ray diffraction analysis.

  3. BWR internal cracking issues

    International Nuclear Information System (INIS)

    The regulatory issues associated with cracking of boiling water reactor (BWR) internals is being addressed by the Nuclear Regulatory Commission (NRC) staff and is the subject of a voluntary industry initiative. The lessons learned from this effort will be applied to pressurized water reactor (PWR) internals cracking issues

  4. Crack layer theory

    Science.gov (United States)

    Chudnovsky, A.

    1984-01-01

    A damage parameter is introduced in addition to conventional parameters of continuum mechanics and consider a crack surrounded by an array of microdefects within the continuum mechanics framework. A system consisting of the main crack and surrounding damage is called crack layer (CL). Crack layer propagation is an irreversible process. The general framework of the thermodynamics of irreversible processes are employed to identify the driving forces (causes) and to derive the constitutive equation of CL propagation, that is, the relationship between the rates of the crack growth and damage dissemination from one side and the conjugated thermodynamic forces from another. The proposed law of CL propagation is in good agreement with the experimental data on fatigue CL propagation in various materials. The theory also elaborates material toughness characterization.

  5. Treatment of an Immature Autogenous Arteriovenous Fistula with Percutaneous Transluminal Angioplasty

    International Nuclear Information System (INIS)

    The purpose of this study was to evaluate the efficacy of percutaneous transluminal angioplasty (PTA) in facilitating maturation of autogenous arteriovenous fistulae. There were 12 immature autogenous arteriovenous fistulae. We performed 15 PTAs transvenously. Post-intervention anatomic and clinical successes were estimated, and the 6-month and 1-year primary and secondary patency rates were calculated using Kaplan-Meier analysis. All immature fistulae had underlying stenosis (n=20): arteriovenous anastomosis (n=1) and venous outflow (n=19): 1) within 5 cm from the anastomosis (n=10); 2) more than 5 cm but less than 10 cm from the anastomosis (n=5); 3) more than 10 cm from the anastomosis, including central veins (n=4). Six fistulae had two or more stenoses. Repeat intervention was necessary in two patients. The anatomical success rate was 94.3%, and the clinical success rate was 86.7%. The 6-month and 1-year primary patency rates were 72.7% and 54.5%, and the secondary patency rates were 100% and 81.8%, respectively. All immature hemodialysis fistulae have underlying stenosis, most of which are located near the arteriovenous anastomosis. Early interventional procedures are helpful in the salvage and maintenance of immature arteriovenous fistulae, with a high degree of success

  6. Treatment of an Immature Autogenous Arteriovenous Fistula with Percutaneous Transluminal Angioplasty

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Hyoung Rae [Kangwon National University, Chuncheon (Korea, Republic of)

    2008-11-15

    The purpose of this study was to evaluate the efficacy of percutaneous transluminal angioplasty (PTA) in facilitating maturation of autogenous arteriovenous fistulae. There were 12 immature autogenous arteriovenous fistulae. We performed 15 PTAs transvenously. Post-intervention anatomic and clinical successes were estimated, and the 6-month and 1-year primary and secondary patency rates were calculated using Kaplan-Meier analysis. All immature fistulae had underlying stenosis (n=20): arteriovenous anastomosis (n=1) and venous outflow (n=19): 1) within 5 cm from the anastomosis (n=10); 2) more than 5 cm but less than 10 cm from the anastomosis (n=5); 3) more than 10 cm from the anastomosis, including central veins (n=4). Six fistulae had two or more stenoses. Repeat intervention was necessary in two patients. The anatomical success rate was 94.3%, and the clinical success rate was 86.7%. The 6-month and 1-year primary patency rates were 72.7% and 54.5%, and the secondary patency rates were 100% and 81.8%, respectively. All immature hemodialysis fistulae have underlying stenosis, most of which are located near the arteriovenous anastomosis. Early interventional procedures are helpful in the salvage and maintenance of immature arteriovenous fistulae, with a high degree of success

  7. Simultaneous implant placement with ridge augmentation using an autogenous bone ring transplant.

    Science.gov (United States)

    Omara, M; Abdelwahed, N; Ahmed, M; Hindy, M

    2016-04-01

    The severely defective socket, in which implant placement within the remaining bone will result in a significantly off-axis implant position, precludes immediate implant placement and requires bone grafting as an initial surgical intervention. The aims of this study were to evaluate autogenous chin bone ring consolidation after the augmentation of severely defective sockets and the clinical application of these rings in the premolar-molar region with simultaneous implant placement in a one-stage procedure. Ten patients with 12 defective sockets were included. Sockets were prepared with a trephine bur. Bone rings with a tapped implant osteotomy were harvested from the chin with a larger trephine bur. Bone rings were fitted in the prepared sockets. An implant drill was used to prepare the bone apical to the ring through its central osteotomy. Implants were screwed through the rings and the apical bone. Patients were examined clinically and radiographically immediately and at 6 months postoperative. Crestal bone changes were measured and evaluated statistically. All grafted sockets showed bone healing with no significant crestal bone resorption and no infection; only one ring showed dehiscence, which healed during the follow-up period. All implants showed radiographic evidence of osseointegration. The autogenous chin bone ring augmentation technique was found to be a reliable alternative method for the management of severely defective sockets. PMID:26644216

  8. Autogenous tibial strut grafts used in severe kyphoscoliosis:surgical policies and preliminary results

    Institute of Scientific and Technical Information of China (English)

    CHEN Hui; QIU Yong; WANG Bin; YU Yang; ZHU Ze-zhang ZHU Li-hua

    2005-01-01

    Background Surgery for severe kyphoscoliosis is frequently unsatisfying because of loss of correction, high rate of pseudarthrosis and neurological complications.Several authors reported that the anterior fusion with strut grafts might improve the surgical outcome.This article describes and assesses the surgical strategies and the application of autogenous tibial strut in the treatment of severe kyphoscoliosis.Results The mean preoperative and postoperative kyphosis was 82°and 52°respectively, and the mean scoliosis was 84°and 44°respectively.Complications included pseudarthrosis (2 cases, one with graft fracture and the other with hook displacement), posterior elements fractures (4), pleura penetrations (3, in the plastic surgery of the thoracic cage), dura tear (2), exudative pleuritis (2, in the anterior surgery), and tibia fracture of the harvesting site (1).The mean loss of correction in coronal and sagittal plane was 6° and 7° respectively.Except for 1 case, the patients with incomplete paraplegia showed improvements to varying extents.Conclusion Autogenous tibial strut can provide excellent support to the kyphoscoliotic spine: it reduces pseudarthrodic rate, loss of correction and complications of graft harvest, it also prevents the occurrence of neurological impairment.

  9. Causes of Early Age Cracking on Concrete Bridge Deck Expansion Joint Repair Sections

    Directory of Open Access Journals (Sweden)

    Jared R. Wright

    2014-01-01

    Full Text Available Cracking of newly placed binary Portland cement-slag concrete adjacent to bridge deck expansion dam replacements has been observed on several newly rehabilitated sections of bridge decks. This paper investigates the causes of cracking by assessing the concrete mixtures specified for bridge deck rehabilitation projects, as well as reviewing the structural design of decks and the construction and curing methods implemented by the contractors. The work consists of (1 a comprehensive literature review of the causes of cracking on bridge decks, (2 a review of previous bridge deck rehabilitation projects that experienced early-age cracking along with construction observations of active deck rehabilitation projects, and (3 an experimental evaluation of the two most commonly used bridge deck concrete mixtures. Based on the literature review, the causes of concrete bridge deck cracking can be classified into three categories: concrete material properties, construction practices, and structural design factors. The most likely causes of the observed early-age cracking were found to be inadequate curing and failure to properly eliminate the risk of plastic shrinkage cracking. These results underscore the significance of proper moist curing methods for concrete bridge decks, including repair sections. This document also provides a blueprint for future researchers to investigate early-age cracking of concrete structures.

  10. Small-crack test methods

    Science.gov (United States)

    Larsen, James M.; Allison, John E.

    This book contains chapters on fracture mechanics parameters for small fatigue cracks, monitoring small-crack growth by the replication method, measurement of small cracks by photomicroscopy (experiments and analysis), and experimental mechanics of microcracks. Other topics discussed are the real-time measurement of small-crack-opening behavior using an interferometric strain/displacement gage; direct current electrical potential measurement of the growth of small cracks; an ultrasonic method for the measurement of the size and opening behavior of small fatigue cracks; and the simulation of short crack and other low closure loading conditions, utilizing constant K(max) Delta-K-decreasing fatigue crack growth procedures.

  11. Shrinkage during holographic recording in photopolymer films determined by holographic interferometry.

    Science.gov (United States)

    Moothanchery, Mohesh; Bavigadda, Viswanath; Toal, Vincent; Naydenova, Izabela

    2013-12-10

    Shrinkage of photopolymer materials is an important factor for their use in holographic data storage and for fabrication of holographic optical elements. Dimensional change in the holographic element leads to a requirement for compensation in the reading angle and/or wavelength. Normally, shrinkage is studied at the end of the polymerization process and no information about the dynamics is obtained. The aim of this study was to use holographic interferometry to measure the shrinkage that occurs during holographic recording of transmission diffraction gratings in acrylamide photopolymer layers. Shrinkage in photopolymer layers can be measured over the whole recorded area by real-time capture of holographic interferograms at regular intervals during holographic recording using a complimentary metal-oxide-semiconductor camera. The optical path length change, and hence the shrinkage, are determined from the captured fringe patterns. Through analysis of the real-time shrinkage curves, it is possible to distinguish two processes that determine the value of shrinkage in the photopolymer layer. These processes are ascribed to monomer polymerization and crosslinking of polymer chains. The dependence of shrinkage of the layers on the conditions of recording such as recording intensity, single or double beam exposure, and the physical properties of the layers, such as thickness, were studied. Higher shrinkage was observed with recordings at lower intensities and in thinner layers. Increased shrinkage was also observed in the case of single beam polymerization in comparison to the case of double beam holographic exposure. PMID:24513896

  12. Shrinkage characteristics of Casuarina wood during devolatilization in a fluidized bed combustor

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, R.Renu; Kolar, Ajit Kumar [Heat Transfer and Thermal Power Lab, Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036, Tamil Nadu (India); Leckner, Bo [Department of Energy Conversion, Chalmers University of Technology, SE-412 96 Goeteborg (Sweden)

    2006-02-15

    The shrinkage characteristics of Casuarina wood in terms of the effect of fuel particle shape and size on the longitudinal, transverse, and volumetric shrinkage during devolatilization in a laboratory scale bubbling fluidized bed combustor are presented. Shrinkage of single fuel particles was measured in the longitudinal and transverse directions (with respect to the wood fibre) for various fuel particle shapes-like disc (l/d=0.2-0.67), cylinder (l/d{sup 1}) and rod (l/d=2-10). The fuel particle dimensions ranged from 5 to 100mm. The effect of the bed temperature on the shrinkage was studied by varying the bed temperature in the range of 650-850{sup o}C. Fuel particle shape and size were found to influence the shrinkage in the two mutually perpendicular directions. The variation in the fuel particle heating rates for various shapes and sizes was found to be the cause of the variation in the shrinkage values. For all the shapes and sizes considered, the longitudinal shrinkage was found to be in the range of 6.5-24%, the transverse shrinkage from 14% to 29%, and the volumetric shrinkage from 35% to 58%. The average volumetric shrinkage was estimated to be 47% with a standard deviation of +/-3.8%. Shrinkage increased negligibly with the increase in bed temperature. Increase in fuel particle density led to a decrease in volumetric shrinkage, however, this effect was not conclusive because of the effect of other factors-like chemical composition and wood type. Correlations for estimating the shrinkage coefficients in the two principal directions are presented. (author)

  13. The effect of solidification rate on the growth of small fatigue cracks in a cast 319-type aluminum alloy

    Energy Technology Data Exchange (ETDEWEB)

    Caton, M.J.; Jones, J.W.; Boileau, J.M.; Allison, J.E.

    1999-12-01

    A study was conducted to investigate the effect of solidification rate on the growth behavior of small fatigue cracks in a 319-type aluminum alloy, a common Al-Si-Cu alloy used in automotive castings. Fatigue specimens were taken from cast material that underwent a hot isostatic pressing (HIP) process in order to eliminate shrinkage pores and to facilitate the observation of surface-initiated cracks by replication. Naturally initiated surface cracks ranging in length from 17 {micro}m to 2 mm were measured using a replication technique. Growth rates of the small cracks were calculated as a function of the elastic stress-intensity-factor range ({Delta}K). Long-crack growth-rate data (10 mm {le} length {le} 25 mm) were obtained from compact-tension (CT) specimens, and comparison to the small-crack data indicates the existence of a significant small-crack effect in this alloy. The solidification rate is shown to have a significant influence on small-crack growth behavior, with faster solidification rates resulting in slower growth rates at equivalent {Delta}K levels. A stress-level effect is also observed for both solidification rates, with faster growth rates occurring at higher applied-stress amplitudes at a given {Delta}K. A crack-growth relation proposed by Nisitani and others is modified to give reasonable correlation of small-crack growth data to different solidification rates and stress levels.

  14. The effect of solidification rate on the growth of small fatigue cracks in a cast 319-type aluminum alloy

    Science.gov (United States)

    Caton, M. J.; Jones, J. Wayne; Boileau, J. M.; Allison, J. E.

    1999-12-01

    A study was conducted to investigate the effect of solidification rate on the growth behavior of small fatigue cracks in a 319-type aluminum alloy, a common Al-Si-Cu alloy used in automotive castings. Fatigue specimens were taken from cast material that underwent a hot isostatic pressing (HIP) process in order to eliminate shrinkage pores and to facilitate the observation of surface-initiated cracks by replication. Naturally initiated surface cracks ranging in length from 17 µm to 2 mm were measured using a replication technique. Growth rates of the small cracks were calculated as a function of the elastic stress-intensity-factor range (Δ K). Long-crack growth-rate data (10 mm≤length≤25 mm) were obtained from compact-tension (CT) specimens, and comparison to the small-crack data indicates the existence of a significant small-crack effect in this alloy. The solidification rate is shown to have a significant influence on small-crack growth behavior, with faster solidification rates resulting in slower growth rates at equivalent Δ K levels. A stress-level effect is also observed for both solidification rates, with faster growth rates occurring at higher applied-stress amplitudes at a given Δ K. A crack-growth relation proposed by Nisitani and others is modified to give reasonable correlation of small-crack growth data to different solidification rates and stress levels.

  15. Cracked fuel mechanics

    International Nuclear Information System (INIS)

    Fuel pellets undergo thermally induced cracking during normal reactor operation. Some fuel performance codes have included models that address the effects of fuel cracking on fuel rod thermal and mechanical behavior. However, models that rely too heavily on continuum mechanics formulations (annular gaps and solid cylindrical pellets) characteristically do not adequately predict cladding axial elongations. Calculations of bamboo ridging generally require many assumptions concerning fuel geometry, and some of the methods used are too complex and expensive to employ on a routine basis. Some of these difficulties originate from a lack of definition of suitable parameters which describe the cracked fuel medium. The methodology is being improved by models that describe cracked fuel behavior utilizing parameters with stronger physical foundations instead of classical continuum formulations. This paper presents a modelling concept and a set of measurable parameters that have been shown to improve the prediction of the mechanical behavior of cracked fuel/cladding systems without added computational expense. The transition from classical annular gap/cylindrical pellet models to modified bulk properties and further to local behavior for cracked fuel systems is discussed. The results of laboratory experiments to verify these modelling parameters are shown. Data are also presented from laboratory experiments on unirradiated and irradiated rods which show that fuel rod mechanical response depends on fuel fragment size. The impact of these data on cracked fuel behavior and failure modelling is also discussed. (author)

  16. Bone healing around nanocrystalline hydroxyapatite, deproteinized bovine bone mineral, biphasic calcium phosphate, and autogenous bone in mandibular bone defects

    DEFF Research Database (Denmark)

    Broggini, Nina; Bosshardt, Dieter D; Jensen, Simon S;

    2015-01-01

    with nanocrystalline hydroxyapatite (HA-SiO), deproteinized bovine bone mineral (DBBM), biphasic calcium phosphate (BCP) with a 60/40% HA/β-TCP (BCP 60/40) ratio, or particulate autogenous bone (A) for histological and histomorphometric analysis. At 2 weeks, percent filler amongst the test groups (DBBM (35.65%), HA...

  17. Effect of aluminum silicate fiber modification on crack-resistance of a ceramic mould

    Directory of Open Access Journals (Sweden)

    Jiang Yehua

    2012-11-01

    Full Text Available To improve the crack-resistance of the mould for silica sol bonded quartz based ceramic mould casting, aluminum silicate fibers with the diameter ranging from 5 µm to 25 µm and the length about 1 mm were dispersed in the ceramic mould. The effect of the aluminum silicate fibers on the tensile strength, shrinkage rate and the cracking trend of the ceramic mould were investigated. In the ceramic slurry, quartz sand was applied as ceramic aggregate, silica sol containing 30% silicon dioxide as bonder, and the weight ratio of quartz sand to silica sol was 2.69; the dispersed fibers changed from 0 to 0.24vol.%. The mould samples were formed after the slurry was poured and gelled at room temperature, and then sintered at different temperatures ranging from 100 to 800 ℃ to measure the tensile strength and shrinkage rate. The results show that, with the aluminum silicate fiber addition increasing from 0 to 0.24vol.%, the tensile strength increases linearly from 0.175 MPa to 0.236 MPa, and the shrinkage rate decreases linearly from 1.75% to 1.68% for the ceramic mould sintered at 400 ℃, from 1.37% to 1.31% for the ceramic mould at room temperature. As the sintering temperature was raised from 100 ℃ to 800 ℃, the tensile strength increases, and the shrinkage rate decreases at all temperatures, compared with those without fiber dispersion, but their variation patterns remain the same. Furthermore, the cracking trend of the mould and its decreasing proportion were defined and analyzed quantitatively considering both effects of the fiber dispersion on the strength and shrinkage. The cracking trend appears to decrease linearly with increasing fiber content and to reach the maximum reduction of 28.8% when 0.24vol.% fiber was dispersed. Therefore, the investigation proposes a new method to improve the crack-resistance of the ceramic mould, i.e., inorganic fiber dispersion into the ceramic mould.

  18. Exploiting tumor shrinkage through temporal optimization of radiotherapy

    International Nuclear Information System (INIS)

    In multi-stage radiotherapy, a patient is treated in several stages separated by weeks or months. This regimen has been motivated mostly by radiobiological considerations, but also provides an approach to reduce normal tissue dose by exploiting tumor shrinkage. The paper considers the optimal design of multi-stage treatments, motivated by the clinical management of large liver tumors for which normal liver dose constraints prohibit the administration of an ablative radiation dose in a single treatment. We introduce a dynamic tumor model that incorporates three factors: radiation induced cell kill, tumor shrinkage, and tumor cell repopulation. The design of multi-stage radiotherapy is formulated as a mathematical optimization problem in which the total dose to the normal tissue is minimized, subject to delivering the prescribed dose to the tumor. Based on the model, we gain insight into the optimal administration of radiation over time, i.e. the optimal treatment gaps and dose levels. We analyze treatments consisting of two stages in detail. The analysis confirms the intuition that the second stage should be delivered just before the tumor size reaches a minimum and repopulation overcompensates shrinking. Furthermore, it was found that, for a large range of model parameters, approximately one-third of the dose should be delivered in the first stage. The projected benefit of multi-stage treatments in terms of normal tissue sparing depends on model assumptions. However, the model predicts large dose reductions by more than a factor of 2 for plausible model parameters. The analysis of the tumor model suggests that substantial reduction in normal tissue dose can be achieved by exploiting tumor shrinkage via an optimal design of multi-stage treatments. This suggests taking a fresh look at multi-stage radiotherapy for selected disease sites where substantial tumor regression translates into reduced target volumes. (paper)

  19. Sparse electromagnetic imaging using nonlinear iterative shrinkage thresholding

    KAUST Repository

    Desmal, Abdulla

    2015-04-13

    A sparse nonlinear electromagnetic imaging scheme is proposed for reconstructing dielectric contrast of investigation domains from measured fields. The proposed approach constructs the optimization problem by introducing the sparsity constraint to the data misfit between the scattered fields expressed as a nonlinear function of the contrast and the measured fields and solves it using the nonlinear iterative shrinkage thresholding algorithm. The thresholding is applied to the result of every nonlinear Landweber iteration to enforce the sparsity constraint. Numerical results demonstrate the accuracy and efficiency of the proposed method in reconstructing sparse dielectric profiles.

  20. Reaction cross sections of hypernuclei and the shrinkage effect

    CERN Document Server

    Akaishi, T

    2013-01-01

    We calculate the reaction cross sections for $^6{\\rm Li}$ and $^7_{\\Lambda}{\\rm Li}$ on a $^{12}{\\rm C}$ target at $100\\,{\\rm MeV/nucleon}$ using the Glauber theory. To this end, we assume a two-body cluster structure for $^6$Li and $^7_{\\Lambda}{\\rm Li}$, and employ the few-body treatment of the Glauber theory, that is beyond the well known optical limit approximation. We show that the reaction cross section for $^7_{\\Lambda}{\\rm Li}$ is smaller than that for $^6$Li by about 4\\%, reflecting the shrinkage effect of the $\\Lambda$ particle.

  1. Noise Reduction in Magnetic Resonance Images using Wave Atom Shrinkage

    Directory of Open Access Journals (Sweden)

    J.Rajeesh, R.S.Moni, S.Palanikumar, T.Gopalakrishnan

    2010-06-01

    Full Text Available De-noising is always a challenging problem in magnetic resonance imaging andimportant for clinical diagnosis and computerized analysis, such as tissueclassification and segmentation. It is well known that the noise in magneticresonance imaging has a Rician distribution. Unlike additive Gaussian noise,Rician noise is signal dependent, and separating signal from noise is a difficulttask. An efficient method for enhancement of noisy magnetic resonance imageusing wave atom shrinkage is proposed. The reconstructed MRI data have highSignal to Noise Ratio (SNR compared to the curvelet and wavelet domain denoisingapproaches.

  2. Total Variation based Multivariate Shearlet Shrinkage for Image Reconstruction

    Directory of Open Access Journals (Sweden)

    Shengqian Wang

    2013-01-01

    Full Text Available Shearlet as a new multidirectional and multiscale transform is optimally efficient in representing images containing edges. In this paper, a total variation based multivariate shearlet adaptive shrinkage is proposed for discontinuity-preserving image denoising. The multivariate adaptive threshold is employed to reduce the noise. Projected total variation diffusion is used to suppress the pseudo-Gibbs and shearlet-like artifacts. Numerical experiments from piecewise-smooth to textured images demonstrate that the proposed method can effectively suppress noise and nonsmooth artifacts caused by shearlet transform. Furthermore, it outperforms several existing techniques in terms of structural similarity (SSIM index, peak signal-to-noise ratio (PSNR and visual quality.

  3. Dynamic Void Growth and Shrinkage in Mg under Electron Irradiation

    Energy Technology Data Exchange (ETDEWEB)

    Xu, W. Z. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering; Zhang, Y. F. [Idaho National Lab. (INL), Idaho Falls, ID (United States); Cheng, G. M. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering; Jian, W. W. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering; Millett, P. C. [Univ. of Arkansas, Fayetteville, AR (United States). Dept. of Mecanical Engineering; Koch, C. C. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering; Mathaudhu, S. N. [U.S. Army Research Office, Research Triangle Park, NC (United States). Materials Science Division; Zhu, Y. T. [North Carolina State Univ., Raleigh, NC (United States). Dept. of Materials Science and Engineering

    2014-04-30

    We report in-situ atomic-scale investigation of void evolution, including growth, coalescence and shrinkage, under electron irradiation. With increasing irradiation dose, the total volume of voids increased linearly, while nucleation rate of new voids decreased slightly, and the total number of voids decreased. Some voids continued to grow while others shrank to disappear, depending on the nature of their interactions with nearby self-interstitial loops. For the first time, surface diffusion of adatoms was observed largely responsible for the void coalescence and thickening. These findings provide fundamental understanding to help with the design and modeling of irradiation-resistant materials.

  4. Effects of low-level laser therapy on autogenous bone graft stabilized with a new heterologous fibrin sealant.

    Science.gov (United States)

    de Oliveira Gonçalves, Jéssica Barbosa; Buchaim, Daniela Vieira; de Souza Bueno, Cleuber Rodrigo; Pomini, Karina Torres; Barraviera, Benedito; Júnior, Rui Seabra Ferreira; Andreo, Jesus Carlos; de Castro Rodrigues, Antonio; Cestari, Tania Mary; Buchaim, Rogério Leone

    2016-09-01

    Autogenous bone grafts are used to repair bone defects, and the stabilization is needed for bone regeneration. Laser photobiomodulation is a modality of treatment in clinical practice for tissue regeneration, and it has therapeutic effects as an anti-inflammatory, analgesic and modulating cellular activity. The aim of the present study was to evaluate the effects of low-level laser therapy (LLLT) on an autogenous bone graft integration process stabilized with a new heterologous fibrin sealant. Forty rats were divided into two groups: Autogenous Fibrin Graft (AFG, n=20), in which a 5mm dome osteotomy was conducted in the right parietal bone and the graft was adhered to the left side using fibrin sealant; and Autogenous Fibrin Graft Laser (AFGL, n=20), which was subjected to the same procedures as AFG with the addition of LLLT. The treatment was performed immediately following surgery and then three times a week until euthanasia, using an 830nm laser (30mW, 6J/cm(2), 0.116cm(2), 258.6mW/cm(2), 2.9J). Five animals from each group were euthanized at 10, 20, 30 and 40days postoperative, and the samples were submitted to histomorphological and histomorphometric analysis. Partial bone regeneration occurred, with new bone tissue integrating the graft to the recipient bed and small areas of connective tissue. Comparative analysis of the groups at the same intervals revealed minor interfaces in group AFGL, with statistically significant differences (p<0.05) at all of the analyzed intervals (10days p=0.0087, 20days p=0.0012, 30days p<0.0001, 40days p=0.0142). In conclusion, low-level laser therapy stimulated bone regeneration and accelerated the process of integration of autogenous bone grafts. PMID:27497370

  5. Allogeneic and autogenous transplantations of MSCs in treatment of the physeal bone bridge in rabbits

    Directory of Open Access Journals (Sweden)

    Urbanova Lucie

    2008-09-01

    Full Text Available Abstract Background The aim of this experimental study on New Zealand's white rabbits was to find differences in the results of treating the distal physeal femoral defect by the transplantation of autologous or allogeneic mesenchymal stem cells (MSCs. After the excision of a created bone bridge in the distal physis of the right femur, modified composite scaffold with MSCs was transplanted into the defect. In animal Group A (n = 11 autogenous MSCs were implanted; in animal Group B (n = 15 allogeneic MSCs were implanted. An iatrogenic physeal defect of the left femur of each animal not treated by MSCs transplantation served as control. The rabbits were euthanized four months after the transplantation. The treatment results were evaluated morphometrically (femoral length and valgus deformity measurement and histologically (character and quality of the new cartilage. Results Four months after the transplantation, the right femurs of the animals in Group A were on average longer by 0.50 ± 0.04 cm (p = 0.018 than their left femurs, the right femurs of rabbits in Group B were on average longer by 0.43 ± 0.01 cm (p = 0.028 than their left femurs. 4 months after the therapeutic transplantation of MSCs valgus deformity of the distal part of the right femur of animals in Group A was significantly lower (by 4.45 ± 1.86° than that of their left femur (p = 0.028, in Group B as well (by 3.66 ± 0.95° than that of their left femur p = 0.001. However, no significant difference was found between rabbits with transplanted autogenous MSCs (Group A and rabbits with transplanted allogeneic MSCs (Group B either in the femur length (p = 0.495, or in its valgus deformity (p = 0.1597. After the MSCs transplantation the presence of a newly formed hyaline cartilage was demonstrated histologically in all the animals (both groups. The ability of transplanted MSCs to survive in the damaged physis was demonstrated in vivo by magnetic resonance, in vitro by Perls reaction

  6. On the Strong Convergence of the Optimal Linear Shrinkage Estimator for Large Dimensional Covariance Matrix

    OpenAIRE

    Taras Bodnar; Arjun K. Gupta; Nestor Parolya

    2013-01-01

    In this work we construct an optimal linear shrinkage estimator for the covariance matrix in high dimensions. The recent results from the random matrix theory allow us to find the asymptotic deterministic equivalents of the optimal shrinkage intensities and estimate them consistently. The developed distribution-free estimators obey almost surely the smallest Frobenius loss over all linear shrinkage estimators for the covariance matrix. The case we consider includes the number of variables $p\\...

  7. Moisture Diffusivity and Shrinkage of Fruit and Cladode of Opuntia ficus-indica during Infrared Drying

    OpenAIRE

    Amira Touil; Saber Chemkhi; Fethi Zagrouba

    2014-01-01

    Drying behaviour of prickly pear cladodes and fruits was studied with an Infrared dryer. The volume shrinkage for Opuntia ficus-indica products is calculated and a linear relation was established to describe the experimental variation of shrinkage of the product versus its moisture content. Effective diffusion coefficient of moisture transfer was determined using the Fick law at three drying temperatures (40, 50, and 60°C). Shrinkage was also included into the diffusion model for the determin...

  8. Impact of internal water reservoirs in high-strenght concretes on drying shrinkage

    OpenAIRE

    Lisec, Damjan

    2013-01-01

    This thesis discussed the impact of internal curing on shrinkage of high-strength concretes, especially due to drying shrinkage. The shrinkage is more pronounced in the concrete due to the lack of water during the process of hydration, which is the result of low water/cement ratio. Among the several methods of internal curing of concretes internal curing with presoaked lightweight aggregate was selected. The impact of internal curing with pre-soaked lightweight aggregate concrete was st...

  9. Experimental Study on Forecasting Mathematical Model of Drying Shrinkage of Recycled Aggregate Concrete

    OpenAIRE

    Guo, Yuanchen; Wang, Xue

    2012-01-01

    On the basis of basic law in AASHTO2007 model, the forecasting mathematical model of drying shrinkage of recycled aggregate concrete (RAC) is established by regression analysis and experimental study. The research results show that (1) with the replacement rate of RCA increases, the drying shrinkage value of RAC increases; this trend is even more obvious in the early drying time. (2) The addition of fly ash can inhibit the drying shrinkage of RAC, but the effect is not very obvious. Specifica...

  10. Shrinkage degree in $L_2$-re-scale boosting for regression

    OpenAIRE

    Xu, Lin; Lin, Shaobo; Wang, Yao; Xu, Zongben

    2015-01-01

    Re-scale boosting (RBoosting) is a variant of boosting which can essentially improve the generalization performance of boosting learning. The key feature of RBoosting lies in introducing a shrinkage degree to re-scale the ensemble estimate in each gradient-descent step. Thus, the shrinkage degree determines the performance of RBoosting. The aim of this paper is to develop a concrete analysis concerning how to determine the shrinkage degree in $L_2$-RBoosting. We propose two feasible ways to s...

  11. Investigations of linear contraction and shrinkage stresses development in hypereutectic al-si binary alloys

    OpenAIRE

    J. Mutwil; Kujawa, K.; G. Bajon; P. Hajn

    2009-01-01

    Shrinkage phenomena during solidification and cooling of hypereutectic aluminium-silicon alloys (AlSi18, AlSi21) have been examined. A vertical shrinkage rod casting with circular cross-section (constant or fixed: tapered) has been used as a test sample. Two type of experiments have been conducted: 1) on development of the test sample linear dimension changes (linear expansion/contraction), 2) on development of shrinkage stresses in the test sample. By the linear contraction experiments the l...

  12. Ethylene by Naphta Cracking

    Science.gov (United States)

    Wiseman, Peter

    1977-01-01

    Presents a discussion of the manufacture of ethylene by thermal cracking of hydrocarbon feedstocks that is useful for introducing the subject of industrial chemistry into a chemistry curriculum. (MLH)

  13. Collapse-type shrinkage characteristics in plantation-grown eucalypts: I . Correlations of basic density and some structural indices with shrinkage and collapse properties

    Institute of Scientific and Technical Information of China (English)

    WUYi-qiang; HAYASHIKazuo; LIUYuan; CAIYing-chun; SUGIMORIMasatoshi; LUOJian-ju

    2005-01-01

    Collapse-type shrinkage is one of highly refractory drying defects in low-medium density plantation-grown eucalypt wood used as solid wood products. Basic density (BD), microfibril angle (MFA), double fibre cell wall thickness (DWT), proportion of ray parenchyma (RP), unit cell wall shrinkage, total shrinkage and residual collapse, which are associated with collapse-type shrinkage characteristics, were investigated by using simple regression method for three species of collapse-susceptible Eucalyptus urophyll, E. grandis and E.urophyllaxE.grandis, planted at Dong-Men Forest Farm in Guangxi autonomous region, China. The results indicated that : unit cell wall shrinkage had a extremely strong positive correlation with BD, moderately strong positive correlation with DWT, and a weakly or moderately negative correlation with RP and MFA; total shrinkage was positively correlated with BD, DWT and RP and negatively related to MFA, but not able to be predicted ideally by any examined factors alone owing to lower R2 value (R2≤0.5712); residual collapse was negatively correlated with BD and DWT, linearly positively correlated with MFA, and had strongly positive linear correlation with RP. It is concluded that BD can be used as single factor (R2≥0.9412) to predicate unit cell wall shrinkage and RP is the relatively sound indicator for predicting residual collapse

  14. Modelling of Corrosion Cracks

    DEFF Research Database (Denmark)

    Thoft-Christensen, Palle

    Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed.......Modelling of corrosion cracking of reinforced concrete structures is complicated as a great number of uncertain factors are involved. To get a reliable modelling a physical and mechanical understanding of the process behind corrosion in needed....

  15. Design changes of device to investigation of alloys linear contraction and shrinkage stresses

    Directory of Open Access Journals (Sweden)

    J. Mutwil

    2009-07-01

    Full Text Available Some design changes in device elaborated by author to examination of linear contraction and shrinkage stresses progress of metals and alloys during– and after solidification have been described. The introduced changes have been focused on design of closing of shrinkage test rod mould. The introduced changes have been allowed to simplify a mounting procedure of thermocouples measuring a temperature of the shrinkage rod casting (in 6 points. Exemplary investigation results of linear contraction and shrinkage stresses development in Al-Si13.5% alloy have been presented.

  16. Non-invasive prediction of skin flap shrinkage: a new concept based on animal experimental evidence.

    Science.gov (United States)

    Lim, K H; Jeyapalina, S; Ho, H N; Chew, C M; Chen, P C Y; Teo, C L; Lim, B H

    2008-01-01

    A non-invasive, in vivo method has been developed to predict the skin flap shrinkage (retraction) following a harvest. It involves the use of a novel custom-designed extensometer to measure the force-displacement behaviour of skin and subsequent data analysis to estimate the shrinkage. In validation experiments performed on pigs, this method has been shown to produce results with an average absolute error of 6.0% between the actual and predicted shrinkages. This may be close to what an experienced surgeon would estimate subjectively, thus indicating the potential usefulness of this method to predict flap shrinkage of patient's donor sites. PMID:18485350

  17. Experimental Verification of the Concrete Shrinkage Strains Course According to En 1992-2 Standard

    OpenAIRE

    Raczkiewicz W.; Bacharz M.; Bacharz K.

    2015-01-01

    The article provides basic information about the shrinkage of concrete and discusses the major impact on the size and course of the shrinkage. There are the guidelines to estimate the shrinkage strain of concrete bridge structures for the high tensile strength-SCI in accordance with PN-EN 1992-2. The article presents the results of experimental studies which aim was to analyze the course of shrinkage in two types of specimens made of different composition mixes. The studies have also made pos...

  18. Retrograde tracing of fluorescent gold after autogenous nerve transplantation on spinal cord injured in rats

    DEFF Research Database (Denmark)

    Lin, X; Liu, W; Ding, Ming;

    2016-01-01

    Objective To investigate the changes of the fluorescent gold retrograde tracing autogenous nerve transplantation on spinal cord injured in rats. Methods The animals were divided into two groups, with modified Allen impact method to establish model of spinal cord injury. After 4 weeks, the...... transplantation group using autologous sural nerve graft to repair spinal cord injury period and non-transplantation group was only exposed incision without treatment. In the 4, 6 and 8 weeks after operation, the retrograde tracing of FG Fluoro-Gold was performed to discover the recovery of the axial plasma.......01). Conclusion After spinal cord injury, autologous nerve graft was repaired and survived well and promote the recovery of spinal cord injury segment shaft pulp transportation function....

  19. Effect of Autogenous Arc Welding Processes on Tensile and Impact Properties of Ferritic Stainless Steel Joints

    Institute of Scientific and Technical Information of China (English)

    A K Lakshminarayanan; K Shanmugam; V Balasubramanian

    2009-01-01

    The effect of autogeneous arc welding processes on tensile and impact properties of ferritic stainless steel conformed to AISI 409M grade is studied.Rolled plates of 4 mm thickness have been used as the base material for preparing single pass butt welded jointa.Tensile and impact properties,microhardness,microstructure,and fracture surface morphology of continuous current gas tungsten arc welding (CCGTAW),pulsed current gas tungsten arc welding (PCGTAW),and plasma arc welding (PAW) joints are evaluated and the results are compared.It is found that the PAW joints of ferritic stainless steel show superior tensile and impact properties when compared with CCGTAW and PCGTAW joints,and this is mainly due to lower heat input,finer fusion zone grain diameter,and higher fusion zone hardness.

  20. Autogenous vaccination for control of yersiniosis (Yersiniosis salmonis in the salmonid aquaculture in Republic of Macedonia

    Directory of Open Access Journals (Sweden)

    Cvetkovik Aleksandar

    2009-05-01

    Full Text Available The aim of this study was to produce an autogenous vaccine from Yersinia ruckeri isolate and to test it’s efficacy in field conditions. Colonies of Yersinia ruckeri biotype I isolated from rainbow trout with haemorrhagic septicemia were cultivated in TSB and inactivated with formalin. The vaccine was diluted and administered by immersion of rainbow trout fry (~ 4.5 g BW in the vacinal suspension. The experimental infection was done 28 days post vaccination by immersing the fry in infectious suspension of the same isolate. Mortality of the control and vaccinated fish was 87% and 11%, respectively. Vaccinated fish showed high level of gained specific resistance to the infection (RPS 87,4%.

  1. Histological evaluation of healing after transalveolar maxillary sinus augmentation with bioglass and autogenous bone

    DEFF Research Database (Denmark)

    Stavropoulos, Andreas; Sima, Catalin; Sima, Andrea; Nyengaard, Jens; Karring, Thorkild; Sculean, Anton

    2012-01-01

    OBJECTIVES: The aim was to evaluate histologically the outcome of a bioglass and autogenous bone (at 1 : 1 ratio) composite implantation for transalveolar sinus augmentation. METHODS: In 31 patients, during implant installation ca. 4 months after sinus augmentation, biopsies were harvested through...... inside the sinus and the transalveolar osteotomy, respectively, qualified for analysis. The tissue fractions occupied by newly formed bone (mineralized tissue+bone marrow), soft connective tissue, residual biomaterial+empty spaces, and debris inside the sinus cavity or the transalveolar osteotomy were...... estimated. RESULTS: Bone and connective tissue fraction in the newly formed tissues inside the sinus cavity averaged 23.4 ± 13.2% and 54.1 ± 23.5%, respectively. Residual biomaterial, empty spaces, and debris averaged 1.9 ± 3.5%, 10.5 ± 6.3%, and 8.4 ± 14.5%, respectively. In the transalveolar osteotomy...

  2. Costs and outcomes of endovascular treatment of thrombosed dialysis autogenous fistulae.

    Science.gov (United States)

    Coentrao, Luis

    2013-01-01

    Functional vascular access is a prerequisite for adequate haemodialysis treatment in patients with end-stage renal disease. Autogenous arteriovenous fistulae are considered superior to synthetic grafts and central venous catheters; however, fistulae are not without problems. Fistulae thrombosis has become a clinical challenge in nephrology practice, with relevant clinical implications for dialysis patients. Several studies have reported on the feasibility and relatively high-clinical success rate of the endovascular approach to thrombosed fistulae in recent years. However, as repeated interventions are usually required to achieve long-term access survival, maintenance of a previously thrombosed fistulae could be a highly expensive policy. The goals of this article are to provide the reader an insight into the multiple endovascular approaches for thrombosed arteriovenous fistulae, bearing in mind its clinical effectiveness and financial implications. PMID:23897178

  3. Modeling crack growth during Li insertion in storage particles using a fracture phase field approach

    Science.gov (United States)

    Klinsmann, Markus; Rosato, Daniele; Kamlah, Marc; McMeeking, Robert M.

    2016-07-01

    Fracture of storage particles is considered to be one of the major reasons for capacity fade and increasing power loss in many commercial lithium ion batteries. The appearance of fracture and cracks in the particles is commonly ascribed to mechanical stress, which evolves from inhomogeneous swelling and shrinkage of the material when lithium is inserted or extracted. Here, a coupled model of lithium diffusion, mechanical stress and crack growth using a phase field method is applied to investigate how the formation of cracks depends on the size of the particle and the presence or absence of an initial crack, as well as the applied flux at the boundary. The model shows great versatility in that it is free of constraints with respect to particle geometry, dimension or crack path and allows simultaneous observation of the evolution of lithium diffusion and crack growth. In this work, we focus on the insertion process. In particular, we demonstrate the presence of intricate fracture phenomena, such as, crack branching or complete breakage of storage particles within just a single half cycle of lithium insertion, a phenomenon that was only speculated about before.

  4. Response Predicting LTCC Firing Shrinkage: A Response Surface Analysis Study

    Energy Technology Data Exchange (ETDEWEB)

    Girardi, Michael; Barner, Gregg; Lopez, Cristie; Duncan, Brent; Zawicki, Larry

    2009-02-25

    The Low Temperature Cofired Ceramic (LTCC) technology is used in a variety of applications including military/space electronics, wireless communication, MEMS, medical and automotive electronics. The use of LTCC is growing due to the low cost of investment, short development time, good electrical and mechanical properties, high reliability, and flexibility in design integration (3 dimensional (3D) microstructures with cavities are possible)). The dimensional accuracy of the resulting x/y shrinkage of LTCC substrates is responsible for component assembly problems with the tolerance effect that increases in relation to the substrate size. Response Surface Analysis was used to predict product shrinkage based on specific process inputs (metal loading, layer count, lamination pressure, and tape thickness) with the ultimate goal to optimize manufacturing outputs (NC files, stencils, and screens) in achieving the final product design the first time. Three (3) regression models were developed for the DuPont 951 tape system with DuPont 5734 gold metallization based on green tape thickness.

  5. Physical Model of Drying Shrinkage of Recycled Aggregate Concrete

    Institute of Scientific and Technical Information of China (English)

    GUO Yuanchen; WANG Xue; QIAN Jueshi

    2015-01-01

    We prepared concretes (RC0, RC30, and RC100) with three different mixes. The pore-size distribution parameters of RAC were examined by high-precision mercury intrusion method (MIM) and nuclear magnetic resonance (NMR) imaging. A capillary-bundle physical model with random-distribution pores (improved model, IM) was established according to the parameters, and dry-shrinkage strain values were calculated and verified. Results show that in all pore types, capillary pores, and gel pores have the greatest impacts on concrete shrinkage, especially for pores 2.5-50 and 50-100 nm in size. The median radii are 34.2, 31, and 34 nm for RC0, RC30, and RC100, respectively. Moreover, the internal micropore size distribution of RC0 differs from that of RC30 and RC100, and the pore descriptions of MIM and NMR are consistent both in theory and in practice. Compared with the traditional capillary-bundle model, the calculated results of IM have higher accuracy as demonstrated by experimental veriifcation.

  6. Using inverted autogenous veins to substitute arteries in a canine model

    Directory of Open Access Journals (Sweden)

    Nikeghbalian Saman

    2010-01-01

    Full Text Available Aims : Rapid harvesting of autogenous graft over a wire is an optional way in trauma surgery and it places the inverted conduit so that its adventitial layer is within the lumen of the graft. Our aim of this study was to compare the patency of inverted autogenous graft vs noninverted graft in dogs. Settings and Design : Experimental animal models. Materials and Methods : In this experimental study, 12 dogs were anesthetized and 10 cm of the external jugular vein was excised. The vein was equally divided into two 5-cm sections. One section was inverted and the other was left intact. Afterward, 5 cm of both the femoral arteries were removed and the right (inverted and the left (not inverted arteries were grafted, respectively. The patency of the arteries was evaluated by Color Doppler ultrasonography immediately postoperation and up to 6 months thereafter. Statistical Analysis : Data were analyzed with Fisher′s exact test using SPSS version 15. P value below 0.05 was significant. Results: None of the 12 inverted vein grafts were patent at 3 rd to 14 th days follow-up with Doppler ultrasonography. All of them were completely obstructed by thrombosis. However, 11 (92% of the noninverted vein grafts were patent both at 3 and 6 months follow-up. One of the noninverted grafts was almost completely obstructed with thrombosis (90% and the other 2 were incompletely obstructed with intimal thickening. Conclusions : Despite many favorable results in the previous studies with regard to excellent patency of inverted vein graft, our results were disappointing and we recommend using the graft in the right direction and taking care to preserve the intima intact.

  7. Crack growth and rupture characteristics of stress corrosion cracks

    International Nuclear Information System (INIS)

    The contribution describes rupture-mechanical studies on stress-corrosion cracks which occurred at components during use. The tests are complemented by test specimens with stress-corrosion cracks which were induced in the laboratory. The tests show that the stress-corrosion cracks of the tested higher-tensile heat-treatable steels have an intercrystalline crack development, crack branchings and multiple cracks with differing linear and depth expansions. With the same external stress and fracture toughness, the load on stress-corrosion cracks must be at least 1.4 times higher in order to initiate the fracture. The critical crack sizes are at least two times bigger than the result of a fracture-mechanical evaluation based on clean and unbranched cracks. (orig./RHM)

  8. Shrinkage of renal tissue after impregnation via the cold Biodur plastination technique.

    Science.gov (United States)

    Pereira-Sampaio, Marco A; Marques-Sampaio, Beatriz P S; Sampaio, Francisco J B; Henry, Robert W

    2011-08-01

    Thorough dehydration is a key for good plastination and invariably it leads to shrinkage. Shrinkage during plastination has been studied to lesser extent. Shrinkage was studied in 10 pig kidneys including regional shrinkage (cortex, medulla, sinus) and at which stages of the process (dehydration, impregnation, curing) shrinkage occurred. Kidneys were fixation by perfusion of 10% neutral buffered formalin solution via the renal artery. The vessels and ureter were filled with colored silicone (Dow Corning, Silastic E RTV Silicone Rubber) and the kidneys were cut into one centimeter transverse slices. Two slices of each kidney were plastinated via the classic von Hagens' method. Slices were photographed at the same focal length after preparation and at the end of each stage of plastination. Slice surface area was determined by a point-counting planimetry method. Post dehydration shrinkage of the kidney was 10.21% while post impregnation 10.11%. After completion of plastination, total area of kidney slice shrinkage was 19.72%. Cortical area shrunk 12.81% after dehydration and 13.16% after impregnation. After plastination, cortical area had shrunk 24.28%. No significant shrinkage occurred in the medulla and sinus. Results demonstrate that kidney shrinkage during impregnation is as intense as during dehydration. Significant shrinkage occurred in the renal cortex but not in the medulla and sinus. This demonstrates that different tissue types, even in the same specimen, have different rates of shrinkage during dehydration and impregnation. Therefore, plastinated specimens should be used carefully in research where obtaining measures is important. PMID:21714112

  9. Stress/strain distributions for weld metal solidification crack in stainless steels

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    This paper has simulated the driving force of solidification crack of stainless steels, that is, stress/strain field in the trail of molten pool. Firstly, the effect of the deformation in the molten pool was eliminated after the element rebirth method was adopted. Secondly, the influence of solidification shrinkage was taken into account by increasing thermal expansion coefficients of the steels at elevated temperatures. Finally, the stress/strain distributions of different conditions have been computed and analyzed. Furthermore, the driving force curves of the solidification crack of the steels have been obtained by converting strain-time curves into strain-temperature curves, which founds a basis for predicting welding solidification crack.

  10. Interpretation of Coal-Seam Sequestration Data Using a New Swelling and Shrinkage Model

    Energy Technology Data Exchange (ETDEWEB)

    Siriwardane, H.J.; Smith, D.H.

    2006-10-01

    This paper deals with the influence of swelling and shrinkage of coal on the production of methane from, and sequestration of carbon dioxide in, a coalbed reservoir. A three-dimensional swelling and shrinkage model was developed. It is based on constitutive equations that account for coupled fluid pressure-deformation behavior of a porous medium that undergoes swelling and shrinkage. The swelling and shrinkage strains are computed on the basis of the amounts of different gases (e.g., CO2, CH4) sorbed or desorbed. The amounts of sorption and desorption are computed from measured isotherms with the aid of the Ideal Adsorbed Solution model for mixed gases. The permeability of the reservoir is modified according to the swelling-shrinkage model. The paper presents numerical results for the influence of swelling and shrinkage on reservoir performance during injection of carbon dioxide. The paper includes results from a number of examples, and analysis of a field injection into a coal seam at a site in the San Juan basin. Results show that with the incorporation of swelling and shrinkage into the analysis, it is possible to get a better history-match of production data. Results also show that coal swelling can reduce the injection volumes of carbon dioxide significantly. The interpretation of field data with the new swelling-shrinkage model shows that the coal swelling during carbon dioxide sequestration in coal-seams is an important factor that can influence field performance.

  11. Exercise in injection moulding: Predicting the non-uniform shrinkage from PVT data

    DEFF Research Database (Denmark)

    Rasmussen, Henrik Koblitz; Eriksson, Torbjörn Gerhard

    the mould and the cooled plastic bars (i.e. the shrinkage or expansion) is measured. Five types of polymer bars for different temperatures and pressures are manufactured for both PP and PC. The aim is to understand the relation between the process parameters (temperature and pressure - e.g. PVT data...... shrinkage/expansion and relate these results to the measurements....

  12. To develop a quantitative method for predicting shrinkage porosity in squeeze casting

    Institute of Scientific and Technical Information of China (English)

    Shaomin Li; Kenichiro Mine; Shinji Sanakanishi; Koichi Anzai

    2009-01-01

    In order to secure high strength and high elongation of suspension parts, it is critical to predict shrinkage porosity quantitatively. A new simulation method for quantitative predic'don of shrinkage porosity when replenishing molten metal has been proposed for squeeze casting process. To examine the accuracy of the calculation model, the proposed method was applied to a plate model.

  13. Cell Shrinkage is Essential in Lysophosphatidic Acid Signaling in Ehrlich Ascites

    DEFF Research Database (Denmark)

    Pedersen, Susanne; Hoffmann, Else Kay; Hougaard, Charlotte;

    2000-01-01

    ; (ii) a subsequent cell shrinkage and increased polymerization of F-actin, and (iii) activation of a Na(+)/H(+) exchange, resulting in a concentration-dependent intracellular alkalinization. The EC(50) value for the LPA-induced rate of alkalinization was estimated at 0. 37 nm LPA. When cell shrinkage...

  14. Effect of cure cycle on enthalpy relaxation and post shrinkage in neat epoxy and epoxy composites

    DEFF Research Database (Denmark)

    Jensen, Martin; Jakobsen, Johnny

    2016-01-01

    cycle. Enthalpy recovery is found to exert a minor impact on the sample dimension during reheating since a non-reversing shrinkage is observed during reheating. This shrinkage is ascribed to structural changes on molecular level in the specimen and it is inferred that samples with a high initial...

  15. Spontaneous tumour shrinkage in 1261 observed patients with sporadic vestibular schwannoma

    DEFF Research Database (Denmark)

    Huang, Xiaoshan; Caye-Thomasen, P; Stangerup, S-E

    2013-01-01

    To determine the rate of spontaneous tumour shrinkage in a group of patients with sporadic vestibular schwannoma managed with a 'wait and scan' approach.......To determine the rate of spontaneous tumour shrinkage in a group of patients with sporadic vestibular schwannoma managed with a 'wait and scan' approach....

  16. Modeling dental composite shrinkage by digital image correlation and finite element methods

    Science.gov (United States)

    Chen, Terry Yuan-Fang; Huang, Pin-Sheng; Chuang, Shu-Fen

    2014-10-01

    Dental composites are light-curable resin-based materials with an inherent defect of polymerization shrinkage which may cause tooth deflection and debonding of restorations. This study aimed to combine digital image correlation (DIC) and finite element analysis (FEA) to model the shrinkage behaviors under different light curing regimens. Extracted human molars were prepared with proximal cavities for composite restorations, and then divided into three groups to receive different light curing protocols: regular intensity, low intensity, and step-curing consisting of low and high intensities. For each tooth, the composite fillings were consecutively placed under both unbonded and bonded conditions. At first, the shrinkage of the unbonded restorations was analyzed by DIC and adopted as the setting of FEA. The simulated shrinkage behaviors obtained from FEA were further validated by the measurements in the bonded cases. The results showed that different light curing regimens affected the shrinkage in unbonded restorations, with regular intensity showing the greatest shrinkage strain on the top surface. The shrinkage centers in the bonded cases were located closer to the cavity floor than those in the unbonded cases, and were less affected by curing regimens. The FEA results showed that the stress was modulated by the accumulated light energy density, while step-curing may alleviate the tensile stress along the cavity walls. In this study, DIC provides a complete description of the polymerization shrinkage behaviors of dental composites, which may facilitate the stress analysis in the numerical investigation.

  17. Computed tomography evaluation of autogenous graft in sinus lift surgery; Analise por tomografia computadorizada do enxerto autogeno na cirurgia de 'sinus lift'

    Energy Technology Data Exchange (ETDEWEB)

    Ajzen, Sergio Aron; Moscatiello, Rafael Andrade; Lima, Aida Maria Custodio de; Moscatiello, Vitoria Aparecida Muglia; Helio Kiitiro Yamashita [Universidade Federal de Sao Paulo (UNIFESP/EPM), SP (Brazil). Dept. de Diagnostico por Imagem; Mosacatiello, Rafael Muglia; Nishiguchi, Celso Itiro [Universidade Federal de Sao Paulo (UNIFESP/EPM), SP (Brazil). Disciplina de Tecnica Operatoria e Cirurgia Experimental; Alves, Maria Teresa de Seixas [Universidade Federal de Sao Paulo (UNIFESP/EPM), SP (Brazil). Disciplina de Anatomia Patologica

    2001-02-01

    The objective was to quantify bone formation within autogenous bone grafts and autogenous bone grafts in combination with platelet-rich plasma obtained either from apheresis or centrifugation using computed tomography. This prospective, double-blind study was conducted in 34 male and female adult patients (mean age of 28 years and 8 months), with either unilateral or bilateral pneumatization of the maxillary sinuses, requiring bone graft for dental implant. All patients were submitted to computed tomography examinations prior and six months after sinus lift surgery. Fifty-three maxillary sinuses were operated and divided into three distinct groups: autogenous bone graft, autogenous bone graft in combination with platelet-rich plasma obtained by centrifugation, and autogenous bone graft in combination with platelet-rich plasma obtained by apheresis. The results showed that computed tomography demonstrated bone growth in height and width between the initial and the follow-up computed tomography scans in all three groups. However, no statistical difference was found either for bone height or width. It was concluded that clinical evidence demonstrates the effectiveness of autogenous bone grafts, particularly when used in combination with bone growth factors such as platelet-rich plasma, which allow prosthetic and functional restoration of maxillofacial structures through fixation of dental implants. (author)

  18. NUMERICAL ANALYSIS OF CRACK AND STRAIN BEHAVIOR OF RC SLAB IN STEEL-CONCRETE COMPOSITE GIRDER UNDER NEGATIVE BENDING

    Science.gov (United States)

    Sakaguchi, Junichi; Nakajima, Akinori; Suzuki, Yasuo

    The sophisticated numerical analysis method is required to simulate the strain behavior of the reinforcement and the crack width of the RC slab, although many researches are conducted on the cracking behavior of the RC slab in the composite girder under the negative bending. In this paper, the numerical analysis method is constructed to evaluate the strain behavior of the reinforcement and the crack width of the RC slab in the steel-concrete composite girder subjected to the negative bending. The analysis method using the rigid body spring model takes into account the imperfect composite action between the steel girder and the RC slab, the bond between the reinforcement and the concrete, and the shrinkage of the concrete. As a result, it is confirmed that the analysis method can simulate the crack and the strain behavior of RC slab quantitatively in the steel-concrete composite girder under the negative bending.

  19. Statistical crack mechanics

    International Nuclear Information System (INIS)

    Although it is possible to simulate the ground blast from a single explosive shot with a simple computer algorithm and appropriate constants, the most commonly used modelling methods do not account for major changes in geology or shot energy because mechanical features such as tectonic stresses, fault structure, microcracking, brittle-ductile transition, and water content are not represented in significant detail. An alternative approach for modelling called Statistical Crack Mechanics is presented in this paper. This method, developed in the seventies as a part of the oil shale program, accounts for crack opening, shear, growth, and coalescence. Numerous photographs and micrographs show that shocked materials tend to involve arrays of planar cracks. The approach described here provides a way to account for microstructure and give a representation of the physical behavior of a material at the microscopic level that can account for phenomena such as permeability, fragmentation, shear banding, and hot-spot formation in explosives

  20. Crack propagation in Hastelloy X

    International Nuclear Information System (INIS)

    The fatigue and creep crack growth rates of Hastelloy X were examined both in air and impure helium. Creep crack growth rate is higher in air and impure helium at 6500C. Initial creep crack growth from the original sharp fatigue crack is by an intergranular mode of fracture. As the cracking accelerates at higher stress intensities, growth is by a mixed mode of both intergranular and transgranular fracture. Fatigue crack growth rate increases with increasing temperature and decreasing frequency for the range of stress intensities reported in the literature and is lower in impure helium than in air

  1. Remote reactor repair: Avoidance of He-induced cracking with GMAW

    International Nuclear Information System (INIS)

    In 1986, the Savannah River Plant engaged in a project to repair stress corrosion cracks in the vessel of C-Reactor. The through-wall cracks were repaired by patching, but numerous small leaks were discovered around the peripheral fillet weld of the patches. When the weld cracking problem was discovered, the repairs were halted and a diagnostic program begun. It was discovered that the source of the leaks was an interconnected network of cracks in the heat-affected zone (HAZ) of the vessel wall. This program indicated that He-induced cracking might be avoided under suitable welding conditions. Experiments were directed towards producing weld metal overlays with minimal base metal penetration. These overlays were oscillated deposits of Type 308L stainless steel on Type 304L base metal. Welding procedures were developed to use deposit overlays in the flat position on Type 304 stainless steel plates ranging in thickness from 1/4 to 1/2 in. (6.4 to 12.7 mm). At least two levels of heat input were used on each coupon. Autogenous gas tungsten-arc weld passes at various heat inputs, including that used on C reactor, were also made for comparison purposes. As heat inputs and/or He concentration increased, toe cracking did occur, as evidenced by dye penetrant indications. Each sample was sectioned transversely to the weld and examined metallographically. For the gas metal arc welding overlays, there was little evidence of damage at low heat inputs and low He concentrations, but as these parameters increased damage began to be detectable. The results have been used to establish the dependence of damage threshold on He concentration and welding heat input. Future work on this continuing program will include extensive mechanical properties testing of the HAZ and the fusion line. This information will be used to delineate reactor repair welding procedures for a broad range of He concentrations

  2. Investigation of Hot Cracking Sensitivity of Al 6061-T6 Alloy during Pulsed GTA Welding

    International Nuclear Information System (INIS)

    The temperatures and steep thermal gradients associated with welding, produce high tresses and complex transient stress patterns. These factors often combine to produce racking in the weld and HAZ region. Cracking is a major concern in welding aluminum alloys. This is due to the relatively high thermal expansion of aluminum, he large change in volume upon solidification and the wide solidification temperature range. High heat inputs, resulting from high currents and slow welding speeds, increase the thermal stress, solidification shrinkage and partially melted region, thus contributing to both the weld solidification cracking and HAZ liquation cracking. Aluminum alloys continue to be studied by many investigators, since many of the higher strength aluminum alloys arc susceptible to cracking in one or both of the weld metal and the partially molten heat affected zone, forming liquation cracks in the latter case. A1 6061-T6 alloy, one of the most widely used industrial heat treatable aluminum alloys, is particularly prone to cracking during arc welding. High-energy beam processes, such as electron beam welding that result in minimal heat input educe crack sensitivity, but their high cost limits their applications. In this study, the conventional continuous current gas tungsten arc welding process was improved by using pulsed-arc welding. Pulsed GTAW reduces the heat input and improves the weld penetration. The Unrestraint test to compare the hot cracking sensitivities of different alloys during using both GTA and gas metal arc (GMA) welding was developed by Savage and Lundin in 1965. In the present paper, the effects of using pulsed GTAW process on the observed solidification cracking and HAZ liquation , racking arc examined, using the Unrestraint test and plates of a commercial heat of Al 6061-T6 alloy. Microstructural characteristics of the Unrestraint tested welds were evaluated by optical and scanning electron microscopy and by energy-dispersive spectroscopy for

  3. Crack-arrest technology

    International Nuclear Information System (INIS)

    Over the last several years, the Heavy Section Steel Technology (HSST) Program has conducted several fracture mechanics experiments on large specimens that produced crack-arrest fracture-toughness values above 220 MPa·√m, which is the limit imposed by the ASME Code and the limit included in the Issues on Pressurized Thermal Shock studies. It is therefore appropriate and timely to investigate the influence that these high crack-arrest data have on the integrity assessment of nuclear Reactor Pressure Vessels (RPVs). A review of the evolution of the Pressurized Thermal Shock (PTS) issue and current methods of analysis provides insight into the motivation for the HSST Program performing the large-specimen fracture mechanics experiments. During the early 1970s, it was recognized that RPVs could be subjected to severe thermal shock as the result of a large-break loss-of-coolant accident (LBLOCA). Analyses performed at that time indicated that thermal shock alone would not result in failure (through-wall cracking) of the vessel. However, a combination of pressure and a less severe thermal shock, the result of some postulated transients, could result in vessel failure. In March 1978, such a transient occurred at the Rancho Seco nuclear power plant. As a result of these events, parametric PTS studies were undertaken. Because of the apparent need for and the existence of high-temperature crack-arrest capability, the NRC HSST Program and others began to investigate the effect of higher crack-arrest values on the probability of failure and to determine if these values actually exist for prototypical RPV materials. This report describes the results of HSST Program large-specimen crack-arrest testing

  4. Creep and shrinkage analysis for concrete spent fuel dry storage module

    International Nuclear Information System (INIS)

    CANDU reactors are designed in Canada and are built and operated worldwide to produce electricity economically with no emission of green house gases. This paper presents creep and shrinkage analysis for a concrete spent fuel dry storage module of a CANDU nuclear power plant. Creep and shrinkage analysis was performed using a method outlined in American Concrete Institute (ACI) code, and then the creep and shrinkage strains were analyzed in a finite element model to obtain the structural behavior of the concrete module. This demonstrated that the creep and shrinkage analysis for concrete spent fuel dry storage is reasonable. AECL's spent fuel dry storage module is adequate to resist the time-dependent effects due to creep and shrinkage of concrete. (author)

  5. Modeling the combined impact of moisture and char shrinkage on the pyrolysis of a biomass particle

    Energy Technology Data Exchange (ETDEWEB)

    Kenneth M. Bryden; Mathew J. Hagge [Iowa State University, Ames, IA (USA). Department of Mechanical Engineering

    2003-09-01

    A detailed computational model of pyrolysis of a moist, shrinking biomass particle is presented. This model is used to examine the effect of varying the moisture content for a single shrinking biomass particle subjected to a constant external temperature. Particle half-thicknesses ranging from 5{mu} m to 2 cm, temperatures from 800 to 2000 K, moisture contents from 0 to 30% (dry basis), and shrinkage factors from 1.0 to 0.4 are examined. The impact of moisture content and shrinkage was found to be a function of pyrolysis regime. In general, coupling between moisture content and shrinkage was found to result in longer pyrolysis times than if they were considered separately. Additionally, coupling between moisture content and shrinkage increased tar yield and decreased light hydrocarbon yield compared to considering moisture and shrinkage separately. 29 refs., 10 figs., 4 tabs.

  6. Creep and shrinkage analysis for concrete spent fuel dry storage module

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, D. [Atomic Energy of Canada Limited, Chalk River, Ontario (Canada)], E-mail: zhangd@aecl.ca

    2009-07-01

    CANDU reactors are designed in Canada and are built and operated worldwide to produce electricity economically with no emission of green house gases. This paper presents creep and shrinkage analysis for a concrete spent fuel dry storage module of a CANDU nuclear power plant. Creep and shrinkage analysis was performed using a method outlined in American Concrete Institute (ACI) code, and then the creep and shrinkage strains were analyzed in a finite element model to obtain the structural behavior of the concrete module. This demonstrated that the creep and shrinkage analysis for concrete spent fuel dry storage is reasonable. AECL's spent fuel dry storage module is adequate to resist the time-dependent effects due to creep and shrinkage of concrete. (author)

  7. Marginal adaptation of a low-shrinkage silorane-based composite: A SEM-analysis

    DEFF Research Database (Denmark)

    Schmidt, Malene; Bindslev, Preben Hørsted; Poulsen, Sven;

    2012-01-01

    Introduction. Shrinkage during polymerization of resin-based composite materials may lead to gap formation and hamper the marginal adaptaion of the restorations. To reduce the problem of polymerization shrinkage, a new composite material (Filtek™ Silorane, 3M-ESPE, Germany), with a reduced...... shrinkage, has been marketed. Objective. To investigate whether reduced polymerization shrinkage improves the marginal adaptation of composite restorations. Material and methods. A total of 156 scanning electron microscopy (SEM) pictures (78 baseline, 78 follow-up) of the occlusal part of Class II...... restorations in molars were included in the study. The restorations originated from a randomized clinical trial, conducted in 2007-2009 which compared the clinical performance of a low-shrinkage composite material (Filtek™ Silorane) with that of a methacrylate-based composite material (Ceram•X™mono). Epon...

  8. Pyrolysis of large wood particles: a study of shrinkage importance in simulations

    Energy Technology Data Exchange (ETDEWEB)

    Michel Bellais; K.O. Davidsson; T. Liliedahl; K. Sjoestroem; J.B.C. Pettersson [Royal Institute of Technology, Stockholm (Sweden). Chemical Technology

    2003-08-01

    Shrinkage models have been developed and included in a model for the pyrolysis of large wood particles. Shrinkage is modelled in three different ways: uniform shrinkage, shrinking shell and shrinking cylinders. These models and a reference model without shrinkage are compared with experimental data for mass loss versus time during pyrolysis of birch cylinders at different temperatures. In the experiments a wood particle was introduced into a pyrolysis furnace held at constant temperature. The particle mass and volume were recorded using a balance and a video camera. Uniform shrinkage slows down the pyrolysis whereas shrinking shell and cylinder models enhance the pyrolysis rate. The effect was sufficiently small to be neglected given the uncertainty about some wood physical properties. 9 refs., 3 figs., 1 tab.

  9. Modeling of damage due to shrinkage in autoclaved aerated concrete

    Czech Academy of Sciences Publication Activity Database

    Koudelka, T.; Kruis, J.; Sysala, Stanislav; Vokáč, M.

    Vol. 1648. Melville, NY: AIP Publishing, 2015 - (Simos, T.; Tsitouras, C.), 090012-1-090012-4. (AIP Conference Proceedings. 1648). ISBN 978-0-7354-1287-3. ISSN 0094-243X. [International Conference on Numerical Analysis and Applied Mathematics 2014 (ICNAAM-2014). Rhodes (GR), 22.09.2014-28.09.2014] R&D Projects: GA ČR GA13-18652S Institutional support: RVO:68145535 Keywords : autoclaved aerated concrete * isotropic damage * shrinkage * coupled problems Subject RIV: JM - Building Engineering http://scitation.aip.org/docserver/fulltext/aip/proceeding/aipcp/1648/10.1063/1.4912400/1.4912400.pdf?expires=1427792299&id=id&accname=guest&checksum=6AE655B2B43B3EDCD5D3CA15B4C56CB7

  10. A consistent partly cracked XFEM element for cohesive crack growth

    DEFF Research Database (Denmark)

    Asferg, Jesper L.; Poulsen, Peter Noe; Nielsen, Leif Otto

    2007-01-01

    Present extended finite element method (XFEM) elements for cohesive crack growth may often not be able to model equal stresses on both sides of the discontinuity when acting as a crack-tip element. The authors have developed a new partly cracked XFEM element for cohesive crack growth with extra...... was used to solve the non-linear equations. The performance of the element is illustrated by modelling fracture mechanical benchmark tests. Investigations were carried out on the performance of the element for different crack lengths within one element. The results are compared with previously...... enrichments to the cracked elements. The extra enrichments are element side local and were developed by superposition of the standard nodal shape functions for the element and standard nodal shape functions for a sub-triangle of the cracked element. With the extra enrichments, the crack-tip element becomes...

  11. Diagnostics - Crack Detection '87

    International Nuclear Information System (INIS)

    The Proceedings of the International Symposium Diagnostics -Crack Detection '87 which was held from June 23 to 26 1987 in Sala (CSSR) contains 5 papers falling under the INIS Subject Scope. The said papers mainly deal with the problems of in-service diagnostics of pumps and steam turbines of nuclear power plants with WWER reactors, as well as crack detection of materials and welded joints of equipment and the control of the water regimen of the primary circuit of such power plants. (Z.M.)

  12. Maxillary sinus floor augmentation with Bio-Oss or Bio-Oss mixed with autogenous bone as graft in animals

    DEFF Research Database (Denmark)

    Jensen, T; Schou, S; Stavropoulos, Andreas;

    2012-01-01

    The objective of the present systematic review was to test the hypothesis of no differences between the use of Bio-Oss or Bio-Oss mixed with autogenous bone as graft for maxillary sinus floor augmentation (MSFA) applying the lateral window technique, as evaluated in animals. A MEDLINE (Pub...... graft improved significantly with increased proportion of Bio-Oss. Bone regeneration, bone-to-implant contact (BIC), biomechanical implant test values, and biodegradation of Bio-Oss after MSFA with Bio-Oss or Bio-Oss mixed with autogenous bone have never been compared within the same study in animals......Med), Embase, and Cochrane Library search in combination with a hand-search of relevant journals was conducted by including animal studies published in English from 1 January 1990 to 1 June 2010. The search provided 879 titles and 14 studies fulfilled the inclusion criteria. The volumetric stability of the...

  13. Repair of the inferior vena cava with autogenous peritoneo-fascial patch graft following abdominal trauma: a case report.

    Science.gov (United States)

    Emmiler, Mustafa; Kocogullari, Cevdet Ugur; Yilmaz, Sezgin; Cekirdekci, Ahmet

    2008-01-01

    Abdominal vascular injuries are among the most challenging and lethal injuries in traumatized patients. Inferior vena cava is the most frequently injured vein during the blunt or penetrating trauma. The primary repair, end to end anastomosis, endovascular stenting, or graft interposition with autogenous or synthetic materials should be considered in selected cases. However, in cases the synthetic graft was preferred, intestinal contaminations due to small or large bowel perforation accompanying the trauma have been cited as a limiting factor for the use of such grafts as in the current case. However, a previous history of lower leg variceal surgery prevents the use of great saphenous vein as a graft. So in the present case, the authors report a patient with inferior vena cava injury repaired with autogenous peritoneo-fascial graft. The authors have used APF graft in traumatic inferior vena cava injury for the first time. PMID:18667465

  14. REDUCTION OF MOBILITY OF PERIODONTALY AFFECTED TEETH AFTER GINGIVAL AUGMENTATION WITH AN AUTOGENOUS GINGIVAL GRAFT (Case Report.

    Directory of Open Access Journals (Sweden)

    Kamen Kotsilkov

    2015-02-01

    Full Text Available INTRODUCTION: The most severe complication of advanced periodontal lesions is the loss of teeth due to terminal attachment loss and high grade mobility. The goals of the treatment are the improving the plaque control stabilizing of the mobile teeth and arresting of the progression of gingival recession achieving gingival augmentation with adequate vestibulum depth. The autogenous graft is considered to be the most efficient approach where a significant increase of the attached gingiva is needed. OBJECTIVE: This presentation demonstrates the capacity of the autogenous gingival graft approach to reduce the high grade tooth mobility and to augment keratinized gingiva. METHODS: V.T. (46 with moderate generalized periodontitis. The examination reveals thin periodontal biotype, Class IV recessions on 31,41 with III grade mobility and terminal attachment loss, narrow vestibulum and lack of attached gingiva. An autogenous graft technique was selected to achieve simultaneous gingival augmentation and correction of vestibulum depth. RESULTS: A significant and stable increase of the attached gingiva is observed which led to better access for oral hygiene thus creating better conditions for successful long-term outcome. The root coverage was more that 40% and the tooth mobility was decreased to grade I. CONCLUSION: In the limitations of the presented case the free autogenous graft technique seems an appropriate approach in cases with deep Class IV recessions and high grade toot mobility in mandibular frontal area creating proper conditions for effective oral hygiene and decreasing tooth mobility by creating a sufficient amount of attached gingiva needed for the long term maintenance.

  15. Comparative studies on the biology and filarial susceptibility of selected blood-feeding and autogenous Aedes togoi sub-colonies

    Directory of Open Access Journals (Sweden)

    Anuluck Junkum

    2003-06-01

    Full Text Available Blood-feeding and autogenous sub-colonies were selected from a laboratory, stock colony of Aedes togoi, which was originally collected from Koh Nom Sao, Chanthaburi province, Southeast Thailand. Comparative biology and filarial susceptibility between the two sub-colonies (blood-feeding: F11, F13; autogeny: F38, F40 were investigated to evaluate their viability and vectorial capacity. The results of comparison on biology revealed intraspecific differences, i.e., the average egg deposition/gravid female (F11/F38; F13/F40, embryonation rate (F13/F40, hatchability rate (F11/F38; F13/F40, egg width (F11/F38, wing length of females (F13/F40, and wing length and width of males (F11/F38 in the blood-feeding sub-colony were significantly greater than that in the autogenous sub-colony; and egg length (F11/F38 and width (F13/F40, and mean longevity of adult females (F11/F38 and males (F13/F40 in the blood-feeding sub-colony were significantly less than that in the autogenous sub-colony. The results of comparison on filarial susceptibility demonstrated that both sub-colonies yielded similar susceptibilities to Brugia malayi [blood-feeding/autogeny = 56.7% (F11/53.3%(F38, 60%(F13/83.3%(F40] and Dirofilaria immitis [blood-feeding/autogeny = 85.7%(F11/75%(F38, 45%(F13/29.4%(F40], suggesting autogenous Ae. togoi sub-colony was an efficient laboratory vector in study of filariasis.

  16. Comparative studies on the biology and filarial susceptibility of selected blood-feeding and autogenous Aedes togoi sub-colonies

    OpenAIRE

    Anuluck Junkum; Wej Choochote; Atchariya Jitpakdi; Somjai Leemingsawat; Narumon Komalamisra; Narissara Jariyapan; Chavalit Boonyatakorn

    2003-01-01

    Blood-feeding and autogenous sub-colonies were selected from a laboratory, stock colony of Aedes togoi, which was originally collected from Koh Nom Sao, Chanthaburi province, Southeast Thailand. Comparative biology and filarial susceptibility between the two sub-colonies (blood-feeding: F11, F13; autogeny: F38, F40) were investigated to evaluate their viability and vectorial capacity. The results of comparison on biology revealed intraspecific differences, i.e., the average egg deposition/gra...

  17. Effect of Biofeedback-assisted Autogenic Training on Headache Activity and Mood States in Korean Female Migraine Patients

    OpenAIRE

    Kang, Eun-Ho; Park, Joo-Eon; Chung, Chin-Sang; Yu, Bum-Hee

    2009-01-01

    Biofeedback with or without combined autogenic training is known to be effective for the treatment of migraine. This study aimed to examine the effect of biofeedback treatment on headache activity, anxiety, and depression in Korean female patients with migraine headache. Patients were randomized into the treatment group (n=17) and monitoring group (n=15). Mood states including anxiety and depression, and psychophysiological variables such as mean skin temperature of the patients were compared...

  18. Autogene Regenerationserscheinungen in erzgebirgischen Moorwäldern und deren Bedeutung für Schutz und Entwicklung der Moore

    OpenAIRE

    Wendel, Dirk

    2011-01-01

    - Ziele der Arbeit - Ziel vorliegender Arbeit ist, zu analysieren und zu beurteilen, in welchem Umfang autogene Moorregeneration nach anthropogenen Störungen auftritt, welche Voraussetzungen sie erfordert und welche Prozesse von Bedeutung sind. Forstliche und naturschutzfachliche Relevanz der Erkenntnisse sind zu prüfen. - Versuchsanlage und Methoden - Die Versuchsanlage umfasst verschiedene räumliche Skalenebenen und Zeitabschnitte. Im Untersuchungsraum sächsisches Erzgebirge bef...

  19. Exchanging reamed nailing versus augmentative compression plating with autogenous bone grafting for aseptic femoral shaft nonunion: a retrospective cohort study

    OpenAIRE

    Jiang-ying, Ru; Yun-fei, Niu; Yu, Cong; Wen-bo, Kang; Hai-bin, Cang; Jian-ning, Zhao

    2015-01-01

    Objective: The purpose of this study was to compare the outcomes of exchanging reamed nailing (ERN) and augmentative compression plating (ACP) with autogenous bone grafting (BG) for the treatment of aseptic femoral shaft nonunion secondary to the treatment of intramedullary nailing (IMN).Methods: A multicenter retrospective study was performed for 178 patients (180 cases) of aseptic femoral shaft nonunion secondary to first treatment of IMN. All cases were fixed with either ERN (n=87) or ACP ...

  20. Microstructure Characterization and Stress Corrosion Evaluation of Autogenous and Hybrid Friction Stir Welded Al-Cu-Li 2195 Alloy

    Science.gov (United States)

    Li, Zhixian; Arbegast, William J.; Meletis, Efstathios I.

    1997-01-01

    Friction stir welding process is being evaluated for application on the Al-Cu-Li 2195 Super-Light Weight External Tank of the Space Transportation System. In the present investigation Al-Cu-Li 2195 plates were joined by autogenous friction stir welding (FSW) and hybrid FSW (friction stir welding over existing variable polarity plasma arc weld). Optical microscopy and transmission electron microscopy (TEM) were utilized to characterize microstructures of the weldments processed by both welding methods. TEM observations of autogenous FSW coupons in the center section of the dynamically-recrystallized zone showed an equiaxed recrystallized microstructure with an average grain size of approx. 3.8 microns. No T(sub 1), precipitates were present in the above-mentioned zone. Instead, T(sub B) and alpha precipitates were found in this zone with a lower population. Alternate immersion, anodic polarization, constant load, and slow strain tests were carried out to evaluate the general corrosion and stress-corrosion properties of autogenous and hybrid FSW prepared coupons. The experimental results will be discussed.

  1. Ultrasonography-guided Balloon Angioplasty in an Autogenous Arteriovenous Fistula: Preliminary Results

    International Nuclear Information System (INIS)

    Percutaneous trasnluminal angioplasty (PTA) of a malfunctioning arteriovenous fistula (AVF) in hemodialysis patients requires the use of contrast angiography and fluoroscopy guidance. We attempted to perform this procedure under duplex ultrasound guidance to reduce the amount of contrast agent administered and to reduce the radiation dose during the interventional procedures. From September 2006 to February 2007, 45 patients received interventional treatment due to malfunctioning hemodialysis access in our hospital. Among the patients, we selected 10 patients diagnosed with stenosis of an autogenous arteriovenous fistula based on a physical examination. There were six males and four females aged 51-78 years (mean age, 59 years). Seven of these patients had a Brescia-Cinimo type fistula and three patients had a basilic vein transposition. All procedures were performed in the angiography suite. All procedures that required angioplasty were performed under duplex ultrasound guidance and then contrast angiography was performed to confirm the final patency of the vessels. Conventional angioplasty was also performed under fluoroscopy guidance for any lesions that required an additional angioplasty. The volume flow before and after the PTA and procedure time were recorded. Clinical success was defined as the performance of one or more successful hemodialysis sessions after treatment. Eight of ten patients did not require an additional angioplasty by conventional angiography after the duplex- guided angioplasty. One case showed recoiling of stenosis after the duplex-guided PTA and another case was missed at duplex scanning due to the extremely short nature of the recoiling of stenosis. The mean volume flow before and after PTA was 167 ml/min (range, 80-259 ml/min) and 394.2 ml/min (range, 120-586 ml/min), respectively. No complications associated with the duplex-guide procedure occurred. In nine cases, PTA enabled hemodialysis to be conducted more than one time. In one

  2. Ultrasonography-guided Balloon Angioplasty in an Autogenous Arteriovenous Fistula: Preliminary Results

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ji Chang [Daejeon St Mary' s Hospital, Daejeon (Korea, Republic of); Cho, June Sik [Chungnam National University College of Medicine, Daejeon (Korea, Republic of)

    2007-09-15

    Percutaneous trasnluminal angioplasty (PTA) of a malfunctioning arteriovenous fistula (AVF) in hemodialysis patients requires the use of contrast angiography and fluoroscopy guidance. We attempted to perform this procedure under duplex ultrasound guidance to reduce the amount of contrast agent administered and to reduce the radiation dose during the interventional procedures. From September 2006 to February 2007, 45 patients received interventional treatment due to malfunctioning hemodialysis access in our hospital. Among the patients, we selected 10 patients diagnosed with stenosis of an autogenous arteriovenous fistula based on a physical examination. There were six males and four females aged 51-78 years (mean age, 59 years). Seven of these patients had a Brescia-Cinimo type fistula and three patients had a basilic vein transposition. All procedures were performed in the angiography suite. All procedures that required angioplasty were performed under duplex ultrasound guidance and then contrast angiography was performed to confirm the final patency of the vessels. Conventional angioplasty was also performed under fluoroscopy guidance for any lesions that required an additional angioplasty. The volume flow before and after the PTA and procedure time were recorded. Clinical success was defined as the performance of one or more successful hemodialysis sessions after treatment. Eight of ten patients did not require an additional angioplasty by conventional angiography after the duplex- guided angioplasty. One case showed recoiling of stenosis after the duplex-guided PTA and another case was missed at duplex scanning due to the extremely short nature of the recoiling of stenosis. The mean volume flow before and after PTA was 167 ml/min (range, 80-259 ml/min) and 394.2 ml/min (range, 120-586 ml/min), respectively. No complications associated with the duplex-guide procedure occurred. In nine cases, PTA enabled hemodialysis to be conducted more than one time. In one

  3. 混凝土施工裂缝产生原因及其治理%Discussion on concrete construction cracking causes and treatment

    Institute of Scientific and Technical Information of China (English)

    王晓丽

    2015-01-01

    介绍了混凝土裂缝的基本情况,对温度裂缝、塑性收缩裂缝、沉降裂缝的产生原因及表现形式进行了分析,提出了优化配合比设计、掺用石块、加强原材料控制等裂缝的防治措施,以提高工程的整体质量。%The paper introduces basic concrete cracking conditions,analyzes temperature cracking,plastic shrinkage cracking and subsidence cracking causes and forms,and puts forwards cracks preventing measures,such as optimizing mixing proportion design,mixing stone,and strengthening raw material control,with a view to improve integral engineering quality.

  4. Catalytic cracking process

    Science.gov (United States)

    Lokhandwala, Kaaeid A.; Baker, Richard W.

    2001-01-01

    Processes and apparatus for providing improved catalytic cracking, specifically improved recovery of olefins, LPG or hydrogen from catalytic crackers. The improvement is achieved by passing part of the wet gas stream across membranes selective in favor of light hydrocarbons over hydrogen.

  5. Crack detection '86

    International Nuclear Information System (INIS)

    The participants of the conference heard 36 papers of which 13 were incorporated in INIS. The incorporated papers deal with the quality control of the equipment of nuclear power plants, with technical specifications and possibilities of diverse crack detection devices, as well as with personnel training for nondestructive materials testing. (E.S.)

  6. Cracking the Credit Hour

    Science.gov (United States)

    Laitinen, Amy

    2012-01-01

    The basic currency of higher education--the credit hour--represents the root of many problems plaguing America's higher education system: the practice of measuring time rather than learning. "Cracking the Credit Hour" traces the history of this time-based unit, from the days of Andrew Carnegie to recent federal efforts to define a credit hour. If…

  7. Neural crack identification

    International Nuclear Information System (INIS)

    The inverse, crack identification problem in elasticity can be formulated as an output error minimization problem which, nevertheless, can not be solved without difficulties by classical numerical optimization. A review of all these previous results, where we used neural networks, filter-driven optimization and genetic algorithms is presented and in a companion lecture during this conference. The use of neural networks for the solution of the inverse problem makes possible the on-line solution of the problem. In fact, one usually approximates the inverse mapping (measurements versus crack quantities). Most of the effort is spent for the learning of this relation, while a sufficiently trained neural network provides predictions with, practically, zero computational cost. Potential applications include on-line, in-flight health monitoring systems with applications in civil and mechanical engineering and production control. In this paper we present new developments in the design of specialized neural networks for the solution of the crack identification problem. Emphasis is posed on the effective use of the learning data, which are produced by the boundary element method. Several technical data will be discussed. They include thoughts about the effective choice of the neural network architecture, the number of training examples and of the learning algorithms will be provided, together with the results of our recent numerical investigation. A detailed application for one or more elliptical cracks using static analysis results with the use of back-propagation trained neural networks will be provided. The general methodology follows our previously published results. By using more refined algorithms for the numerical solution of the neural network learning problem, which are based on the MERLIN optimization system developed in the department of the second author, we are able to solve complicated tasks. First results based on dynamic investigations (wave propagation driven

  8. Crack Cocaine and Infectious Tuberculosis

    OpenAIRE

    Story, A.; Bothamley, G.; Hayward, A.

    2008-01-01

    We hypothesize that crack cocaine is independently associated with smear-positive tuberculosis (TB). In a case-control study of TB in London, 19 (86%) of 22 crack cocaine users with pulmonary TB were smear positive compared with 302 (36%) of 833 non-drug users. Respiratory damage caused by crack cocaine may predispose drug users to infectivity.

  9. Crack patterns over uneven substrates.

    Science.gov (United States)

    Nandakishore, Pawan; Goehring, Lucas

    2016-02-28

    Cracks in thin layers are influenced by what lies beneath them. From buried craters to crocodile skin, crack patterns are found over an enormous range of length scales. Regardless of absolute size, their substrates can dramatically influence how cracks form, guiding them in some cases, or shielding regions from them in others. Here we investigate how a substrate's shape affects the appearance of cracks above it, by preparing mud cracks over sinusoidally varying surfaces. We find that as the thickness of the cracking layer increases, the observed crack patterns change from wavy to ladder-like to isotropic. Two order parameters are introduced to measure the relative alignment of these crack networks, and, along with Fourier methods, are used to characterise the transitions between crack pattern types. Finally, we explain these results with a model, based on the Griffith criteria of fracture, that identifies the conditions for which straight or wavy cracks will be seen, and predicts how well-ordered the cracks will be. Our metrics and results can be applied to any situation where connected networks of cracks are expected, or found. PMID:26762761

  10. Study of the early age cracking of concrete massive structures: effect of the temperature decrease rate, steel reinforcement and construction joints

    International Nuclear Information System (INIS)

    At early-age, massive concrete structures (ex. nuclear power plant) are submitted to strains due to the hydration reaction. If they are restrained, crossing cracks can occurs. This cracking may increase significantly the concrete wall permeability. The objectives of this work was to characterize the early age concrete behavior (thermal and endogenous shrinkage, basic and thermal transient creep, mechanical characteristic evolution) as well as develop a new device to study the early age cracking of a concrete structure submitted to restrained shrinkage. The experimental campaign achieved with this new device (called thermal active ring test) and the numerical analysis of the test thanks to finite element simulations allows us to evaluate the coupling between creep and damage, to identify the tensile strength decrease due to construction joints and to quantify the effect of reinforcement on the concrete behaviour. Moreover, with this device, permeability measurements have been performed on a cracked specimen. Finally, numerical simulations of massive structures highlight the influence of boundary conditions for restrained shrinkage and the influence of the coupling between creep and damage on the damage pattern. (author)

  11. Crack formation of steel reinforced concrete structure under stress in construction period

    Directory of Open Access Journals (Sweden)

    Hua Zhu

    2016-03-01

    Full Text Available To obtain deformation rules of steel reinforced concrete structure under stress, this study explored the crack formation in construction period. A novel structure system – steel reinforced concrete structure with shear wall and truss at the bottom was analyzed using on-the-spot test in combination with theoretical simulation analysis with SAP2000 software. It was found that, factors influencing crack formation of steel reinforced concrete structure in construction period included construction load, creep of concrete, shrinkage of concrete, displacement of bond of section steel and concrete as well as leveling. In the construction period, the simulated results and the measured results were highly fitted under the influence of time-variant characteristics such as compressive strength, elasticity modulus, creep and shrinkage. Through processing and analyzing the measured data, we obtained the development rules of crack formation of steel reinforced concrete structure with different strength grades as well as deformation rules of time-varying structure system in construction period, figured out the reason for the difference between the simulated results and the measured results, analyzed the deformation of structural components under stress in construction period and proposed some suggestions. This work is beneficial to ensure safe and high-efficient operation of construction

  12. Layer model for long-term deflection analysis of cracked reinforced concrete bending members

    Science.gov (United States)

    Bacinskas, Darius; Kaklauskas, Gintaris; Gribniak, Viktor; Sung, Wen-Pei; Shih, Ming-Hsiang

    2012-05-01

    A numerical technique has been proposed for the long-term deformation analysis of reinforced concrete members subjected to a bending moment. The technique based on the layer approach in a simple and rational way deals with such complex issues as concrete cracking and tension-stiffening as well as creep and shrinkage. The approach uses the material stress-strain relationships for compressive concrete, cracked tensile concrete and steel. Such effects as linear and nonlinear creep, cracking, tension-stiffening as well as the reduction in concrete tension strength due to sustained loading have been taken into account. The shrinkage effect has been modeled by means of adequate actions of axial force and bending moment. A statistical deflection calculation analysis has been carried out for 322 experimental reinforced concrete beams reported in the literature. The comparative analysis of the experimental and the modeling results has shown that the proposed technique has well captured the time-deflection behavior of reinforced concrete flexural members. The results of the predictions by ACI 318 and Eurocode 2 design codes have been also discussed.

  13. Modified Dugdale crack models - some easy crack relations

    DEFF Research Database (Denmark)

    Nielsen, Lauge Fuglsang

    1997-01-01

    The Dugdale crack model is widely used in materials science to predict strength of defective (cracked) materials. A stable Dugdale crack in an elasto-plastic material is prevented from spreading by uniformly distributed cohesive stresses acting in narrow areas at the crack tips. These stresses are......_Ldelta_CR where sigma_L is strength, and at the same time constant flow stress, of the uncracked material while delta_CR is flow limit (displacement).Obviously predictions by the Dugdale model are most reliable for materials with stress-strain relations where flow can actually be described (or well approximated......) by a constant flow stress (sigma_L). A number of materials, however, do not at all exhibit this kind of flow. Such materials are considered in this paper by Modified Dugdale crack models which apply for any cohesive stress distribution in crack front areas. Formally modified Dugdale crack models...

  14. Investigations of linear contraction and shrinkage stresses development in hypereutectic al-si binary alloys

    Directory of Open Access Journals (Sweden)

    J. Mutwil

    2009-07-01

    Full Text Available Shrinkage phenomena during solidification and cooling of hypereutectic aluminium-silicon alloys (AlSi18, AlSi21 have been examined. A vertical shrinkage rod casting with circular cross-section (constant or fixed: tapered has been used as a test sample. Two type of experiments have been conducted: 1 on development of the test sample linear dimension changes (linear expansion/contraction, 2 on development of shrinkage stresses in the test sample. By the linear contraction experiments the linear dimension changes of the test sample and the metal test mould as well a temperature in six points of the test sample have been registered. By shrinkage stresses examination a shrinkage tension force and linear dimension changes of the test sample as well a temperature in three points of the test sample have been registered. Registered time dependences of the test bar and the test mould linear dimension changes have shown, that so-called pre-shrinkage extension has been mainly by mould thermal extension caused. The investigation results have shown that both: the linear contraction as well as the shrinkage stresses development are evident dependent on metal temperature in a warmest region the sample (thermal centre.

  15. Polymerisation shrinkage versus layer thickness of a dentine bonding resin: Method development

    Directory of Open Access Journals (Sweden)

    Jafarzadeh T

    2002-07-01

    Full Text Available Dentine bonding systems are usually unfilled, and so their shrinkage may be significant. High"nshrinkage may cause internal stress at the interface between resin-composite restoration and the dentine"nsubstrate. Failure of the adhesive interface may be observed due to the interna! stress. The aims of this"nstudy were:"nA To obtain a suitable method for measuring the kinetics of polymerisation shrinkage in unfilled resm at different thicknesses, particularly for thin films."nB Consideraing the effect of thickness on shrinkage."nScotchbond Multipurpose (3M adhesive bond resin was used. To overcome the particular challenges presented by thin films, a filled-ring measurement procedure was used. Also, a non-contact laser analogue displacement sensor system was developed and applied to measure polymerisation shrinkage. Regression analysis was performed on a complete data set. Non-linear regression analysis established a logarithmic relationship between polymerisation shrinkage and layer thickness. The method applied in this study was found to be sensitive and accurate procedure for determining photo-polymerisation shrinkage of thin films. Polymerisation shrinkage increased with logarithmic of the adhesive thickness.

  16. A Novel Albumin-Based Tissue Scaffold for Autogenic Tissue Engineering Applications

    Science.gov (United States)

    Li, Pei-Shan; -Liang Lee, I.; Yu, Wei-Lin; Sun, Jui-Sheng; Jane, Wann-Neng; Shen, Hsin-Hsin

    2014-07-01

    Tissue scaffolds provide a framework for living tissue regeneration. However, traditional tissue scaffolds are exogenous, composed of metals, ceramics, polymers, and animal tissues, and have a defined biocompatibility and application. This study presents a new method for obtaining a tissue scaffold from blood albumin, the major protein in mammalian blood. Human, bovine, and porcine albumin was polymerised into albumin polymers by microbial transglutaminase and was then cast by freeze-drying-based moulding to form albumin tissue scaffolds. Scanning electron microscopy and material testing analyses revealed that the albumin tissue scaffold possesses an extremely porous structure, moderate mechanical strength, and resilience. Using a culture of human mesenchymal stem cells (MSCs) as a model, we showed that MSCs can be seeded and grown in the albumin tissue scaffold. Furthermore, the albumin tissue scaffold can support the long-term osteogenic differentiation of MSCs. These results show that the albumin tissue scaffold exhibits favourable material properties and good compatibility with cells. We propose that this novel tissue scaffold can satisfy essential needs in tissue engineering as a general-purpose substrate. The use of this scaffold could lead to the development of new methods of artificial fabrication of autogenic tissue substitutes.

  17. Results of autogenous trephine biopsy needle bone grafting in fractures of radius and ulna.

    Science.gov (United States)

    Lakhey, S; Shrestha, B P; Pradhan, R L; Pandey, B; Rijal, K P

    2005-01-01

    Cortico-Cancellous bone graft harvested from the anterior iliac crest by the conventional open method is associated with more morbidity and is more time consuming as compared to the percutaneous method using trephine biopsy needle. The aim of the study was to determine whether cancellous bone graft harvested from anterior iliac crest using trephine biopsy needle consistently achieved bone union in comminuted fractures and fractures of more than 3 weeks duration of radius and ulna and also to determine the morbidity at the donor site. Autogenous cancellous bone graft was harvested percutaneously from 28 iliac crests in 16 patients and applied at fracture sites of 30 forearm bones using a 4mm trephine biopsy needle after the fractures had been fixed with plate and screws. The patients were followed up regularly upto 6 to 9 months post - operatively in the OPD to determine the union status of the fractured bones and the morbidity at the donor site. 29 of the 30 fractures of the forearm bones united without any problems. The shaft of a trephine got bent during the harvesting procedure at the beginning of the study due to improper technique. Cancellous bone graft harvested from the anterior iliac crest results in predictable good union results in comminuted fractures of forearm bones and also fractures presenting after 3 weeks of injury. It is also an easier and quicker way of harvesting bone graft and is associated with lesser morbidity and earlier recovery as compared to conventional open method. PMID:16554860

  18. Cephalic Arch Stenosis in Autogenous Haemodialysis Fistulas: Treatment With the Viabahn Stent-Graft

    International Nuclear Information System (INIS)

    Cephalic arch stenosis (CAS) is an important and common cause of dysfunction in autogenous haemodialysis fistulas that requires multiple reinterventions and aggressive surveillance. We evaluated the safety and efficacy of the Viabahn stent-graft for the management of CAS. Between April 2005 and October 2011, 11 consecutive patients [four men and seven women (mean age 56.7 years)] with CAS and dysfunctional fistulas were treated with insertion of 11 Viabahn stent-grafts. Six stent-grafts were inserted due to residual stenosis after angioplasty and five for fistuloplasty-induced rupture. No patient was lost to follow-up. The technical and clinical success rate was 100 %. Primary access patency rates were 81.8 % [95 % confidence interval (CI) 0.482–0.977] at 6 months and 72.7 % (95 % CI 0.390–0.939) at 12 months. Secondary access patency rates were 90.9 % at 6 months (95 % CI 0.587–0.997). There were no procedure-related complications. Mean follow-up was 543.8 days (range 156–2,282). The use of the Viabahn stent-graft in the management of CAS is technically feasible and, in this small series, showed patency rates that compare favorably with historical data of angioplasty and bare stents.

  19. Autogenic Feedback Training Exercise and pilot performance: enhanced functioning under search-and-rescue flying conditions

    Science.gov (United States)

    Cowings, P. S.; Kellar, M. A.; Folen, R. A.; Toscano, W. B.; Burge, J. D.

    2001-01-01

    Studies have shown that autonomous mode behavior is one cause of aircraft fatalities due to pilot error. In such cases, the pilot is in a high state of psychological and physiological arousal and tends to focus on one problem, while ignoring more critical information. This study examined the effect of training in physiological self-recognition and regulation, as a means of improving crew cockpit performance. Seventeen pilots were assigned to the treatment and control groups matched for accumulated flight hours. The treatment group contained 4 pilots from HC-130 Hercules aircraft and 4 HH-65 Dolphin helicopter pilots; the control group contained 3 pilots of HC-130s and 6 helicopter pilots. During an initial flight, physiological data were recorded on each crewmember and an instructor pilot rated individual crew performance. Eight crewmembers were then taught to regulate their own physiological response levels using Autogenic-Feedback Training Exercise (AFTE). The remaining participants received no training. During a second flight, treatment participants showed significant improvement in performance (rated by the same instructor pilot as in pretests) while controls did not improve. The results indicate that AFTE management of high states of physiological arousal may improve pilot performance during emergency flying conditions.

  20. Biological and physical properties of autogenous vascularized fibular grafts in dogs

    International Nuclear Information System (INIS)

    The biological and biomechanical properties of normal fibulae, fibulae that had had a sham operation, and both vascularized and non-vascularized autogenous grafts were studied in dogs at three months after the operation. The study was designed to quantify and correlate changes in these properties in orthotopic, stably fixed, weight-bearing grafts and to provide a baseline for additional studies of allografts. The grafts were eight centimeters long and internally fixed. The mechanical properties of the grafts were studied by torsional testing. Metabolic turnover of the grafts was evaluated by preoperative labeling of the dogs with 3H-tetracycline for resorption of bone mineral and with 3H-proline for turnover of collagen. Cortical bone area and porosity were measured. Postoperative formation of bone was evaluated by sequential labeling with fluorochrome. The vascularized grafts resembled the fibulae that had had a sham operation and those that had not had an operation with regard to the total number of osteons and the remodeling process, as measured both morphometrically and metabolically. The vascularized grafts were stronger and stiffer than the non-vascularized grafts and were not different from the bones that had had a sham operation. In contrast, the non-vascularized grafts were smaller, weaker, less stiff, and more porotic, had fewer osteons, and demonstrated increased turnover and resorption compared with the vascularized grafts, the bones that had had a sham operation, and the bones that had not been operated on

  1. Histological evaluation of the influence of magnetic field application in autogenous bone grafts in rats

    Directory of Open Access Journals (Sweden)

    Ponzoni Deise

    2009-01-01

    Full Text Available Abstract Background Bone grafts are widely used in oral and maxillofacial reconstruction. The influence of electromagnetic fields and magnets on the endogenous stimulation of target tissues has been investigated. This work aimed to assess the quality of bone healing in surgical cavities filled with autogenous bone grafts, under the influence of a permanent magnetic field produced by in vivo buried devices. Methods Metal devices consisting of commercially pure martensitic stainless steel washers and titanium screws were employed. Thirty male Wistar rats were divided into 3 experimental and 3 control groups. A surgical bone cavity was produced on the right femur, and a bone graft was collected and placed in each hole. Two metallic washers, magnetized in the experimental group but not in the control group, were attached on the borders of the cavity. Results The animals were sacrificed on postoperative days 15, 45 and 60. The histological analysis of control and experimental samples showed adequate integration of the bone grafts, with intense bone neoformation. On days 45 and 60, a continued influence of the magnetic field on the surgical cavity and on the bone graft was observed in samples from the experimental group. Conclusion The results showed intense bone neoformation in the experimental group as compared to control animals. The intense extra-cortical bone neoformation observed suggests that the osteoconductor condition of the graft may be more susceptible to stimulation, when submitted to a magnetic field.

  2. Response of spinal myoclonus to a combination therapy of autogenic training and biofeedback

    Directory of Open Access Journals (Sweden)

    Kempuraj Duraisamy

    2007-10-01

    Full Text Available Abstract Introduction Clinical evidence indicates that certain types of movement disorders are due to psychosomatic factors. Patients with myoclonic movements are usually treated by a variety of therapeutic agents. Autogenic training (AT, a recognized form of psychosomatic therapies, is suitable for certain types of neurological diseases. We describe a patient with myoclonus who failed to respond to conventional medical therapy. His symptoms were exaggerated by psychogenic factors, especially anger. Case presentation A 42-year-old man was admitted to our hospital, Preventive Welfare Clinic, for severe paroxysmal axial myoclonus of the left shoulder and abdominal muscles. The initial diagnosis was "combination of spinal segmental myoclonus and propriospinal myoclonus". The myoclonic movements did not occur during sleep but were aggravated by bathing, alcohol drinking, and anger. Psychological examination indicated hostile attribution. Although considered not to be a case of psychogenic myoclonus, a "psychogenic factor" was definitely involved in the induction of the organic myoclonus. The final diagnosis was "combination of spinal segmental myoclonus and propriospinal myoclonus accompanied by features of psychosomatic disorders". The patient underwent psychosomatic therapy including AT and surface electromyography (EMG-biofeedback therapy and treatment with clonazepam and carbamazepine. Results AT and EMG-biofeedback resulted in shortening the duration and reducing the amplitude and frequency of the myoclonic discharges. Conclusion Psychosomatic therapy with AT and surface EMG-biofeedback produced excellent improvement of myoclonic movements and allowed the reduction of the dosage of conventional medications.

  3. Effect of ultraviolet-treated autogenous blood on some hematologic indexes in horses

    International Nuclear Information System (INIS)

    Comparative clinical and experimental investigations were carried out on 18 clinically normal horses. It was found that the single transfusion of in vitro UV-treated autogenous blood, following a previously described method, was tolerated well by horses and did not lead to any deviations from the normal indices. Under the effect of the treated blood there was an increase in the hemoglobin content, rise in the erythrocyte and leukocyte count with slightly expressed hyper-leukocytosis and weak neutrophilia (simple regeneration of the blood). The sedimentation of erythrocytes also showed higher rates as early as the first hour following the autohemotransfusion, remaining at the attained level up to the fourth day, while on the sixth day it again came back to the initial value. The contents of calcium and inorganic phosphorus rose, showing a slightly expressed shift to the physiologic level without reaching it. The changes in the phagocytic activity of the blood showed that the autohemotransfusion stimulates phagocytosis. Along with these effects the bacteriostatic titer of the blood, as recorded with the use of the anthrax bacillus as early as the first hour, was likewise favourably affected, the highest titers being observed at the 24th and 48th hour. (author)

  4. CHANNEL SHRINKAGE AND ITS INSTABILITY IN THE LOWER YELLOW RIVER1

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    From the mid 1980s through the late 1990s, the channel of the lower Yellow River experienced serious shrinkage, which has decreased the flood conveyance of the channel and the sediment carrying capacity of the flow, raised the water levels of floods, and, thus, severely threatened the safety of flood control along the river. The completion of Xiaolangdi Dam in 1999 could help mitigate the channel shrinkage problem, but the situation has not changed yet. This paper analyses the characteristics, mechanisms, and conditions resulting in channel shrinkage, points out channel instabilities, and puts forward approaches of channel rehabilitation.

  5. Development of a coal shrinkage-swelling model accounting for water content in the micropores

    Energy Technology Data Exchange (ETDEWEB)

    Prob Thararoop; Zuleima T. Karpyn; Turgay Ertekin [Pennsylvania State University, University Park, PA (United States). Petroleum and Natural Gas Engineering

    2009-07-01

    Changes in cleat permeability of coal seams are influenced by internal stress, and release or adsorption of gas in the coal matrix during production/injection processes. Coal shrinkage-swelling models have been proposed to quantify such changes; however none of the existing models incorporates the effect of the presence of water in the micropores on the gas sorption of coalbeds. This paper proposes a model of coal shrinkage and swelling, incorporating the effect of water in the micropores. The proposed model was validated using field permeability data from San Juan basin coalbeds and compared with coal shrinkage and swelling models existing in the literature.

  6. Hinge-free topology optimization with embedded translation-invariant differentiable wavelet shrinkage

    DEFF Research Database (Denmark)

    Yoon, G. H.; Kim, Y. Y.; Bendsøe, Martin P.;

    2004-01-01

    method to find hinge-free designs using multiscale wavelet-based topology optimization formulation. The specific method developed in this work does not require refinement of the analysis model and it consists of a translation-invariant wavelet shrinkage method where a hinge-free condition is imposed in...... the multiscale design space. To imbed the shrinkage method implicitly in the optimization formulation and thus facilitate sensitivity analysis, the shrinkage method is made differentiable by means of differentiable versions of logical operators. The validity of the present method is confirmed by...

  7. Experimental demonstration of shrinkage of magnetic domains in a superconductor/ferromagnet bilayer

    Energy Technology Data Exchange (ETDEWEB)

    Tamegai, Tsuyoshi; Nakao, Yoshio; Mohan, Shyam; Nakajima, Yasuyuki, E-mail: tamegai@ap.t.u-tokyo.ac.jp [Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)

    2011-02-15

    The shrinkage of magnetic domains in a superconductor/ferromagnet bilayer is studied experimentally using Pb as a superconductor and a garnet film with maze domains as a ferromagnet. The effects of trapped flux in a superconductor and the pinning of magnetic domain boundaries are carefully minimized by using a high-quality Pb single crystal and an AC demagnetization technique. A temperature independent shrinkage of magnetic domains by a factor {approx} 0.89 is obtained below the superconducting transition of Pb. The slightly suppressed shrinkage ratio as compared with the theoretical prediction can be explained by a finite gap between the Pb crystal and the garnet film.

  8. Thermomechanical simulation of the selective laser melting process for PA12 including volumetric shrinkage

    Science.gov (United States)

    Riedlbauer, D.; Steinmann, P.; Mergheim, J.

    2015-05-01

    The present contribution is concerned with the finite element simulation of the thermomechanical material behavior in the selective laser melting process for PA12. In the process shrinkage of the powder material is observed when becoming melt, as the porous character of the powder vanishes due to the phase transition. A nonlinear thermomechanical finite element model is developed, which captures the shrinkage of the material and includes temperature dependent material parameters. The model is used to simulate the shrinkage of the material in the process, where an adaptive mesh refinement is applied for increasing the accuracy of the simulation. The results are qualitatively compared with experimental data and show a good agreement.

  9. Effects of drying conditions, admixtures and specimen size on shrinkage strains

    International Nuclear Information System (INIS)

    The paper presents the results of an experimental investigation on the effects of drying conditions, specimen size and presence of plasticizing admixture on the development of shrinkage strains. The measurements are taken in a harsh (50 deg. C and 5% R.H.) and a moderate environment (28 deg. C and 50% R.H.). The results include strain development at various levels of cross sections of concrete prisms. The drying conditions are found to be the dominant parameter affecting the shrinkage strain development particularly in specimens of smaller sizes. The effect of plasticizing admixture on shrinkage strains is negligible

  10. Choked flow through cracks

    International Nuclear Information System (INIS)

    The leaks through steam-generator cracks are the subject of a research carried out in cooperation between EDF and UCL. A software called ECREVISSE to predict the mass flow rate has been developed and has been successfully validated. The purpose of the paper is to present the mathematical model used in ECREVISSE as well as some comparison between the results and the presently available data. The model takes into account the persistence of some metastable liquid in the crack and the special flow pattern which appears in such particular geometry. Although the model involves the use of several correlations (friction, heat transfer), no adjustment of parameters against the data has been needed, neither in the single-phase part of the flow, or in the two-phase part. (authors). 8 figs., 1 tab., 20 refs

  11. Delayed hydride cracking: alternative pre-cracking method

    International Nuclear Information System (INIS)

    The internal components of nuclear reactors built-in Zr alloys are prone to a failure mechanism known as Delayed Hydride Cracking (DHC). This situation has triggered numerous scientific studies in order to measure the crack propagation velocity and the threshold stress intensity factor associated to DHC. Tests are carried out on fatigued pre-crack samples to ensure similar test conditions and comparable results. Due to difficulties in implementing the fatigue pre-crack method it would be desirable to replace it with a pre-crack produced by the same process of DHC, for which is necessary to demonstrate equivalence of this two methods. In this work tests on samples extracted from two Zr-2.5 Nb tubes were conducted. Some of the samples were heat treated to obtain a range in their metallurgical properties as well as different DHC velocities. A comparison between velocities measured in test samples pre-cracked by fatigue and RDIH is done, demonstrating that the pre-cracking method does not affect the measured velocity value. In addition, the incubation (tinc), which is the time between the application of the load and the first signal of crack propagation, in samples pre-cracked by RDIH, was measured. It was found that these times are sufficiently short, even in the worst cases (lower speed) and similar to the ones of fatigued pre-cracked samples. (author)

  12. Subcritical crack growth in marble

    Science.gov (United States)

    Nara, Yoshitaka; Nishida, Yuki; Toshinori, Ii; Harui, Tomoki; Tanaka, Mayu; Kashiwaya, Koki

    2016-04-01

    It is essential to study time-dependent deformation and fracturing in various rock materials to prevent natural hazards related to the failure of a rock mass. In addition, information of time-dependent fracturing is essential to ensure the long-term stability of a rock mass surrounding various structures. Subcritical crack growth is one of the main causes of time-dependent fracturing in rock. It is known that subcritical crack growth is influenced by not only stress but also surrounding environment. Studies of subcritical crack growth have been widely conducted for silicate rocks such as igneous rocks and sandstones. By contrast, information of subcritical crack growth in carbonate rocks is not enough. Specifically, influence of surrounding environment on subcritical crack growth in carbonate rock should be clarified to ensure the long-term stability of a rock mass. In this study, subcritical crack growth in marble was investigated. Especially, the influence of the temperature, relative humidity and water on subcritical crack growth in marble is investigated. As rock samples, marbles obtained in Skopje-City in Macedonia and Carrara-City in Italy were used. To measure subcritical crack growth, we used the load relaxation method of the double-torsion (DT) test. All measurements by DT test were conducted under controlled temperature and relative humidity. For both marbles, it was shown that the crack velocity in marble in air increased with increasing relative humidity at a constant temperature. Additionally, the crack velocity in water was much higher than that in air. It was also found that the crack velocity increased with increasing temperature. It is considered that temperature and water have significant influences on subcritical crack growth in marble. For Carrara marble in air, it was recognized that the value of subcritical crack growth index became low when the crack velocity was higher than 10-4 m/s. This is similar to Region II of subcritical crack growth

  13. An improved adaptive wavelet shrinkage for ultrasound despeckling

    Indian Academy of Sciences (India)

    P Nirmala Devi; R Asokan

    2014-08-01

    Ultrasound imaging is the most widely used medical diagnostic technique for clinical decision making, due to its ability to make real time imaging for moving structures, low cost and safety. However, its usefulness is degraded by the presence of signal dependent speckle noise. Several wavelet-based denoising schemes have been reported in the literature for the removal of speckle noise. This study proposes a new and improved adaptive wavelet shrinkage in the translational invariant domain. It exploits the knowledge of the correlation of the wavelet coefficients within and across the resolution scales. A preliminary coefficient classification representing useful image information and noise is performed with a novel inter-scale dependency measure. The spatial context adaptation of the wavelet coefficients within a subband is achieved by a local spatial adaptivity indicator, determined by using a truncation threshold. A weighted signal variance is estimated based on this measure and used in the determination of a subband adaptive threshold. The proposed thresholding function aims to reduce the fixed bias of the soft thresholding approach. Experiments conducted with the proposed filter are compared with the existing filtering algorithms in terms of Peak-Signal to Noise Ratio (PSNR), Mean Square Error (MSE), Structural Similarity IndexMeasure (SSIM), Equivalent Number of Looks (ENL) and Edge Preservation Index (EPI). A comparison of the results shows that the proposed filter achieves an improvement in terms of quantitative measures and in terms of visual quality of the images.

  14. An Iterative Shrinkage Approach to Total-Variation Image Restoration

    CERN Document Server

    Michailovich, Oleg

    2009-01-01

    The problem of restoration of digital images from their degraded measurements plays a central role in a multitude of practically important applications. A particularly challenging instance of this problem occurs in the case when the degradation phenomenon is modeled by an ill-conditioned operator. In such a case, the presence of noise makes it impossible to recover a valuable approximation of the image of interest without using some a priori information about its properties. Such a priori information is essential for image restoration, rendering it stable and robust to noise. Particularly, if the original image is known to be a piecewise smooth function, one of the standard priors used in this case is defined by the Rudin-Osher-Fatemi model, which results in total variation (TV) based image restoration. The current arsenal of algorithms for TV-based image restoration is vast. In the present paper, a different approach to the solution of the problem is proposed based on the method of iterative shrinkage (aka i...

  15. Polymerization Shrinkage and Flexural Modulus of Flowable Dental Composites

    Directory of Open Access Journals (Sweden)

    Janaína Cavalcanti Xavier

    2010-09-01

    Full Text Available Linear polymerization shrinkage (LPS, flexural strength (FS and modulus of elasticity (ME of low-viscosity resin composites (Admira Flow™, Grandio Flow™/VOCO; Filtek Z350 Flow™/3M ESPE; Tetric Flow™/Ivoclar-Vivadent was evaluated using a well-established conventional micro-hybrid composite as a standard (Filtek Z250™/3M ESPE. For the measurement of LPS, composites were applied to a cylindrical metallic mould and polymerized (n = 8. The gap formed at the resin/mould interface was observed using SEM (1500×. For FS and ME, specimens were prepared according to the ISO 4049 specifications (n = 10. Statistical analysis of the data was performed with one-way ANOVA and the Tukey test. The conventional resin presented significantly lower LPS associated with high FS and ME, but only the ME values of the conventional resin differed significantly from the low-viscosity composites. The relationship between ME and LPS of low-viscosity resin composites when used as restorative material is a critical factor in contraction stress relief and marginal leakage.

  16. Flood control and shrinkage in the Haihe River Mouth

    Institute of Scientific and Technical Information of China (English)

    胡世雄; 王兆印; 李行伟

    2001-01-01

    Because of overusing water resources in the upper and middle reaches of the Haihe Basin, less and less water flows to the river mouth. The Haihe River flow is cut off in most time of the seasons, sediment deposited in the river mouth channel is rarely scoured away, and many of the river mouth channels have been shrinking quickly. The discharge capacity of the channel is consequently reduced greatly, which results in more and more serious flood hazard. Many tide gates have been built for storing fresh water and preventing the salty and turbid water. The channel downstream of the gate is silting up and people have to dredge the channel every year before the flood season. This paper studies the laws of the siltation and strategies controlling channel shrinkage. The strategies are digger dredging, trailer dredging, scouring with pumping water or storing tidal water, building double guiding dikes and building a new gate. Comparison of various strategies is performed, suggesting the most effective strategy con

  17. Shrinkage, abrasion, erosion and sorption of clay plasters

    Directory of Open Access Journals (Sweden)

    Minke, G.

    2011-09-01

    Full Text Available At the Buildung Research Institute (FEB, Faculty of Architecture, University of Kassel, Germany, in the last years several hundred tests were made to study the characteristics of different loam mortars in respect of their linear shrinkage, absorption of humidity and their resistance against abrasion and erosion. In order to get data about abrasion and erosion new test methods and special apparatusses were developed. The mortars tested, chosen from the market, showed extremely varying test results.

    En el Laboratorio de Construcciones Experimentales (FEB de la Facultad de Arquitectura, Universidad de Kassel, Alemania, fueron testeados cientos de diferentes pruebas de revoque de barro para estudiar su contracción durante el secado, su absorción de humedad y su resistencia contra abrasión, erosión y absorción. Para recibir datos sobre abrasión y erosión, nuevas aparatos y metodos fueron desarrollados. Los resultados de los revoques comprados en el mercado muestran gran diferencias en los valores.

  18. Creep and Shrinkage of Concrete: Physical Origins, Practical Measurements

    International Nuclear Information System (INIS)

    Subcommittee 4 of RHJEM TC 107-CSP has established recommendations for shrinkage and creep tests. These recommendations are based on physical and mechanical analysis of these tests, to ensure that they provide reproducible and objective results. But the complete specification of these tests must also make it possible to respond to diversified needs: in particular, industrial users (contractors, suppliers of materials, etc.) are increasingly led to request such tests, and the type of experimental data they expect can be quite different from what is expected by people who draft regulations or develop numerical models. This paper therefore presents, in a first part, reflexions concerning these needs, which are found to be highly varied and rapidly evolving. In a second part, the importance of the scale effect that makes it tricky to attempt any extrapolation of the available experimental results in two directions (to the long term and to large thicknesses), is reviewed. In the absence of a satisfactory explanation of this scale effect, a practical method is proposed that can be used to get round this difficulty experimentally and to deal with certain engineering problems

  19. Crack interaction with microstructure

    Directory of Open Access Journals (Sweden)

    Sharvan Kumar

    2007-09-01

    Full Text Available Designing microstructure for damage tolerance requires a detailed understanding of how an advancing crack interacts with the microstructure (and sometimes modifies it locally at multiple length scales. Advances in experimental techniques, such as the availability of well-controlled straining stages for optical and electron microscopes, the focused ion beam, electron backscattered diffraction, and nanoindentation, enable probing at these length scales in real time and through interrupted tests. Simultaneously, increasing computational power coupled with new computational methods, such as finite element analysis (FEA incorporating cohesive elements at the continuum level, discrete dislocation methodology at the mesoscopic level, and coupled atomistic/continuum methods that transitions atomic level information to the mesoscopic level, have made it possible to begin addressing these complex problems. By reviewing crack growth in a variety of multiphase alloys including steels, titanium aluminides, Mo alloys, and nanocrystalline metals, we demonstrate various aspects of crack interaction with microstructure, and how these problems are being addressed through experiments and computations.

  20. Effect of Included Angle in V-Groove Butt Joints on Shrinkages in Submerged Arc Welding Process

    Directory of Open Access Journals (Sweden)

    N. LAKSHMANA SWAMY

    2012-04-01

    Full Text Available The problems of distortion, residual stresses and reduced strength of structure in and around a welded joint are of major concern in the shipbuilding industry and in other similar manufacturing industries. The predictions of the degree of shrinkages in ship panels due to welding are of great importance from the point of view of dimensional control and it is important to analyze transverse and longitudinal shrinkage. This paper deals with the experimental analysis of transverse and longitudinal shrinkage in single and double V-groove butt joints in submerged arc welding by varying included angle and keeping process parameters constant. It is found that, the maximum shrinkage was at the centre of the plate and minimum at the ends. It is also found that, the transverse and longitudinal shrinkage increase with increase in the included angle. There is a significant increase in the transverse shrinkage and small variation in longitudinal shrinkage.

  1. Monitoring of pre-release cracks in prestressed concrete using fiber optic sensors

    Science.gov (United States)

    Abdel-Jaber, Hiba; Glisic, Branko

    2015-04-01

    Prestressed concrete experiences low to no tensile stresses, which results in limiting the occurrence of cracks in prestressed concrete structures. However, the nature of construction of these structures requires the concrete not to be subjected to the compressive force from the prestressing tendons until after it has gained sufficient compressive strength. Although the structure is not subjected to any dead or live load during this period, it is influenced by shrinkage and thermal variations. Thus, the concrete can experience tensile stresses before the required compressive strength has been attained, which can result in the occurrence of "pre-release" cracks. Such cracks are visually closed after the transfer of the prestressing force. However, structural capacity and behavior can be impacted if cracks are not sufficiently closed. This paper researches a method for the verification of the status of pre-release cracks after transfer of the prestressing force, and it is oriented towards achievement of Level IV Structural Health Monitoring (SHM). The method relies on measurements from parallel long-gauge fiber optic sensors embedded in the concrete prior to pouring. The same sensor network is used for the detection and characterization of cracks, as well as the monitoring of the prestressing force transfer and the determination of the extent of closure of pre-release cracks. This paper outlines the researched method and presents its application to a real-life structure, the southeast leg of Streicker Bridge on the Princeton University campus. The application structure is a curved continuous girder that was constructed in 2009. Its deck experienced four pre-release cracks that were closed beyond the critical limits based on the results of this study.

  2. An Analytical Approach of the Behavior of Fiber Reinforced High Shrinkage Materials

    Directory of Open Access Journals (Sweden)

    H. Katkhuda

    2010-01-01

    Full Text Available This study presents an analytical approach to predict the behavior of fiber-reinforced materials with high shrinkage properties. A simple model formed of a rigid fiber embedded in a cylindrical elastic matrix presenting high shrinkage properties was analyzed. Isotropy and homogeneity of the two constituents, the fiber and matrix, as well as the shrinkage of the matrix were assumed for simplification. The analytical analyses included the variations of the state of link at the fiber-matrix interface due to its effect on the global behavior of fiber-reinforced material. The study showed the effect of the bond strength on the bond length, the effect of the bond length on free shrinkage, the effect of the age of the composite material on the bond length and the effect of the fiber volumetric fraction on the equivalent mean length.

  3. Astrocytic mechanisms explaining neural-activity-induced shrinkage of extraneuronal space

    DEFF Research Database (Denmark)

    Østby, Ivar; Øyehaug, Leiv; Einevoll, Gaute T;

    2009-01-01

    Neuronal stimulation causes approximately 30% shrinkage of the extracellular space (ECS) between neurons and surrounding astrocytes in grey and white matter under experimental conditions. Despite its possible implications for a proper understanding of basic aspects of potassium clearance...

  4. Shrinkage Behavior of High Performance Concrete at Different Elevated Temperatures under Different Sealing Conditions

    Institute of Scientific and Technical Information of China (English)

    PAN Zhihua; NAKAMURA Hidemi; WEE Tionghuan

    2006-01-01

    The shrinkage behavior of high performance cement concrete made from Portland cement, ultra fine granulated blast furnace slag and pulverized fly ash with addition of superplasticizer at different temperatures from ambient temperature to 120 ℃ under different sealing conditions was investigated by means of length change measurement on cylindrical concrete specimens along with curing age. Results show that drying shrinkage deformations of titled concrete specimens increased rapidly as the curing temperature rose. The development of drying shrinkage deformation can be efficiently controlled with the aid of aluminum tape sealing as compared with the unsealed specimens, especially when the curing temperature is below 60℃, although it will increase dramatically when the curing temperature is elevated to above 90℃. Polymer coating on concrete specimens showed a similar effect on the control of drying shrinkage as the sealing operation with aluminum tape.

  5. Shrinkage insensitivity of NKCC1 in myosin II-depleted cytoplasts from Ehrlich ascites tumor cells

    DEFF Research Database (Denmark)

    Hoffmann, Else K; Pedersen, Stine F

    2007-01-01

    Protein phosphorylation/dephosphorylation and cytoskeletal reorganization regulate the Na(+)-K(+)-2Cl(-) cotransporter (NKCC1) during osmotic shrinkage; however, the mechanisms involved are unclear. We show that in cytoplasts, plasma membrane vesicles detached from Ehrlich ascites tumor cells (EATC......) by cytochalasin treatment, NKCC1 activity evaluated as bumetanide-sensitive (86)Rb influx was increased compared with the basal level in intact cells yet could not be further increased by osmotic shrinkage. Accordingly, cytoplasts exhibited no regulatory volume increase after shrinkage. In cytoplasts......, cortical F-actin organization was disrupted, and myosin II, which in shrunken EATC translocates to the cortical region, was absent. Moreover, NKCC1 activity was essentially insensitive to the myosin light chain kinase (MLCK) inhibitor ML-7, a potent blocker of shrinkage-induced NKCC1 activity in intact...

  6. Shrinkage estimators for out-of-sample prediction in high-dimensional linear models

    CERN Document Server

    Dicker, Lee

    2011-01-01

    We study the unconditional out-of-sample prediction error (predictive risk) associated with two classes of smooth shrinkage estimators for the linear model: James-Stein type shrinkage estimators and ridge regression estimators. Our study is motivated by problems in high-dimensional data analysis and our results are especially relevant to settings where both the number of predictors and observations are large. Two important aspects of our approach are (i) the data are assumed to be drawn from a multivariate normal distribution and (ii) we take advantage of an asymptotic framework that is appropriate for high-dimensional datasets and offers great simplifications over many existing approaches to studying shrinkage estimators for the linear model. Ultimately, our results comport with classical results and show that significant reductions in out-of-sample prediction error may be had by utilizing shrinkage estimators, as opposed to the ordinary least squares estimator. However, our results also provide a means for ...

  7. Numerical Simulation on Open Wellbore Shrinkage and Casing Equivalent Stress in Bedded Salt Rock Stratum

    Directory of Open Access Journals (Sweden)

    Jianjun Liu

    2013-01-01

    Full Text Available Most salt rock has interbed of mudstone in China. Owing to the enormous difference of mechanical properties between the mudstone interbed and salt rock, the stress-strain and creep behaviors of salt rock are significantly influenced by neighboring mudstone interbed. In order to identify the rules of wellbore shrinkage and casings equivalent stress in bedded salt rock stratum, three-dimensional finite difference models were established. The effects of thickness and elasticity modulus of mudstone interbed on the open wellbore shrinkage and equivalent stress of casing after cementing operation were studied, respectively. The results indicate that the shrinkage of open wellbore and equivalent stress of casings decreases with the increase of mudstone interbed thickness. The increasing of elasticity modulus will reduce the shrinkage of open wellbore and casing equivalent stress. Research results can provide the scientific basis for the design of mud density and casing strength.

  8. Stein-Rule Estimation and Generalized Shrinkage Methods for Forecasting Using Many Predictors

    DEFF Research Database (Denmark)

    Hillebrand, Eric Tobias; Lee, Tae-Hwy

    We examine the Stein-rule shrinkage estimator for possible improvements in estimation and forecasting when there are many predictors in a linear time series model. We consider the Stein-rule estimator of Hill and Judge (1987) that shrinks the unrestricted unbiased OLS estimator towards a restricted...... the Stein-rule shrinkage. We conduct Monte Carlo simulations to examine these parameter regions. The overall picture that emerges is that the Stein-rule shrinkage estimator can dominate both OLS and principal components estimators within an intermediate range of the signal-to-noise ratio. If the...... signal-to-noise ratio is low, the PC estimator is superior. If the signal-to-noise ratio is high, the OLS estimator is superior. In out-of-sample forecasting with AR(1) predictors, the Stein-rule shrinkage estimator can dominate both OLS and PC estimators when the predictors exhibit low persistence....

  9. The Shrinkage Behavior and Surface Topographical Investigation for Micro Metal Injection Molding

    DEFF Research Database (Denmark)

    Islam, Aminul; Giannekas, Nikolaos; Marhöfer, David Maximilian;

    2014-01-01

    especially when it is compared with micro molding of thermoplastics. The current paper presents a thorough investigation on the process of metal injection molding where it systematically characterizes the effects of important process conditions on the shrinkage and surface quality of molded parts with micro....... Among the different process parameters studied, the melt temperature was the most influential parameters for better replication and dimensional stability of the final part. The results presented in the paper clearly show that the shrinkage in metal part is not uniform in the micro scale. It depends on...... the feature dimensions and also on the process conditions. A thin section of the part exhibits higher relative shrinkage compared with a thicker section. Based on these findings, it can be concluded that a micro part molded by MIM process will have higher relative shrinkage compared to a macro part...

  10. Study of the Effect of Shrinkage Porosity on Strength Low Carbon Cast Steel

    Science.gov (United States)

    Ol'khovik, E.

    2015-09-01

    Today there are many computer systems for modeling of the casting technology processes. All of them allow calculating the availability and distribution of the shrinkage porosity in the test casting, but this information allows only making changes in existing casting technology. In this paper you obtain the information about changes in the local and structural mechanical properties of the casting in the presence of its volume shrinkage porosity. Article presents the results of direct experimental studies of technological defects (shrinkage and gas porosity) impact on the mechanical properties of low carbon steel castings. Methods of investigation are also disclosed, including the methods for producing of molded samples obtained at different process conditions and the crystallization apparatus which is described for the measuring of the density of the samples. There are the mathematical relationship for the elastic modulus, yield stress, elongation and fatigue characteristics fracture cast steel with low carbon content in the presence of the volumetric shrinkage porosity.

  11. Combined effect of expansive and shrinkage reducing admixtures to obtain stable and durable mortars

    International Nuclear Information System (INIS)

    In order to improve the dimensional stability of cement based mortars, the effects produced on cement hydration of a shrinkage reducer (propyleneglycol ether based-SRA) and an expansive admixture (calcium oxide based-EXP) were investigated. Mortar samples (prepared without admixtures or with SRA or EXP or SRA and EXP) were compared through compressive strength measurements, water evaporation, restrained shrinkage and restrained expansion measurements. Setting time and free expansion were also detected on cement paste specimens. A synergistic effect on the shrinkage reduction was observed when the shrinkage reducing admixture and the expansive agent were used together. In order to clarify this phenomenon, the hydration of cement pastes containing these kinds of admixtures was followed by ESEM-FEG (environmental scanning electron microscopy-field emission gun), TG (thermogravimetry), specific surface area measurements (by BET-Brunauer-Emmet-Teller-method) and XRDS (X-ray diffraction spectroscopy)

  12. Strength and Drying Shrinkage of Alkali-Activated Slag Paste and Mortar

    Directory of Open Access Journals (Sweden)

    Mao-chieh Chi

    2012-01-01

    Full Text Available The aim of this study is to investigate the strengths and drying shrinkage of alkali-activated slag paste and mortar. Compressive strength, tensile strength, and drying shrinkage of alkali-activated slag paste and mortar were measured with various liquid/slag ratios, sand/slag ratios, curing ages, and curing temperatures. Experimental results show that the higher compressive strength and tensile strength have been observed in the higher curing temperature. At the age of 56 days, AAS mortars show higher compressive strength than Portland cement mortars and AAS mortars with liquid/slag ratio of 0.54 have the highest tensile strength in all AAS mortars. In addition, AAS pastes of the drying shrinkage are higher than AAS mortars. Meanwhile, higher drying shrinkage was observed in AAS mortars than that observed comparable Portland cement mortars.

  13. Study of swelling-shrinkage regularity of montmorillonite crystal and its relation with matric suction

    Institute of Scientific and Technical Information of China (English)

    谭罗荣; 孔令伟

    2001-01-01

    The swell-shrinking mineral of saturated and unsaturated expansive soil has important effect on engineering mechanical behavior. Based on the swelling-shrinkage change regularity of montmorillonite crystal in this paper, the actions between various interlayers of montmorillonite crystal are generally summarized as two kinds of action potentials-shrinkage potential and swelling potential. Moreover, through the experimental research and analysis, the expression formula for variations of the swelling potential and shrinkage potential with interlayer distance is presented, and the regularity of matric suction variations with interlayer distance is also obtained for unsaturated expansive soil. It may provide a new theoretical basis and research path for further research on the swelling-shrinkage mechanism of expansive soil and matric suction potential of unsaturated soil.

  14. In Search of a New Approach for Urban Policies Under Shrinkage Tendencies in Poland

    Directory of Open Access Journals (Sweden)

    Emilia Jaroszewska

    2014-12-01

    Full Text Available The new demographic, social, economic and cultural conditions that appeared in Poland after 1990 have crucially influenced the transformation of its cities in both quantitative and qualitative terms. One of the manifestations of those changes is an increasingly visible process of shrinkage of many of them. The overcoming of its detrimental effects will be one of the most important challenges for planning and urban policy in Poland in the 21stcentury. This article seeks to identify new urban policy challenges that Polish cities have to meet in the face of advancing urban shrinkage. It starts with the presentation of theoretical issues concerning urban policy and urban shrinkage. Discussed next are the formation of urban policy in Poland and major aspects of the transformation and shrinkage of Polish cities after 1990. Special emphasis is put on the need to work out a new, integrated urban policy that would allow them to adapt to the negative demographic trends observed.

  15. DEVELOPMENT OF ORGANIC-MINERAL MODIFIERS TO OBTAIN HIGH-STRENGTH CONCRETE WITH SHRINKAGE COMPENSATED

    OpenAIRE

    Nguyen The Vinh The Vinh; Nguyen Dinh Trinh Dinh Trinh; Bazhenov Yuri Mihajlovich

    2012-01-01

    The results of the development of organic-mineral modifiers to the increasing component for high-strength concrete. The effect of modifiers designed for mobility, strength and shrinkage of cement paste.

  16. Spiral crack patterns observed for melt-grown spherulites of poly(L-lactic acid) upon quenching.

    Science.gov (United States)

    Matsuda, Futoshi; Sobajima, Takamasa; Irie, Satoshi; Sasaki, Takashi

    2016-04-01

    In this paper, we demonstrate the characteristic spiral cracking that appears on the surface of melt-grown poly(L-lactic acid) (PLLA) spherulites with relatively large sizes (greater than 0.4mm in diameter). The crack occurs via thermal shrinkage upon quenching after crystallization. Although concentric cracks on polymer spherulites have been found to occur in quite a few studies, spiral crack patterns have never been reported so far. The present spiral crack was observed for thick spherulites (> 10 μm), whereas the concentric crack pattern was frequently observed for thin spherulites (typically 5μm). The present PLLA spherulites exhibited a non-banded structure with no apparent structural periodicity at least on the scale of the spiral pitch, and thus no direct correlation between the crack pattern and the spherulitic structure was suggested. The spiral was revealed to be largely Archimedean of which the spiral pitch increases with an increase in the thickness of the spherulite. This may be interpreted in terms of a classical mechanical model for a thin layer with no delamination from the substrate. PMID:27085999

  17. Analysis of the status of pre-release cracks in prestressed concrete structures using long-gauge sensors

    Science.gov (United States)

    Abdel-Jaber, H.; Glisic, B.

    2015-02-01

    Prestressed structures experience limited tensile stresses in concrete, which limits or completely eliminates the occurrence of cracks. However, in some cases, large tensile stresses can develop during the early age of the concrete due to thermal gradients and shrinkage effects. Such stresses can cause early-age cracks, termed ‘pre-release cracks’, which occur prior to the transfer of the prestressing force. When the prestressing force is applied to the cross-section, it is assumed that partial or full closure of the cracks occurs by virtue of the force transfer through the cracked cross-section. Verification of the closure of the cracks after the application of the prestressing force is important as it can either confirm continued structural integrity or indicate and approximate reduced structural capacity. Structural health monitoring (SHM) can be used for this purpose. This paper researches an SHM method that can be applied to prestressed beam structures to assess the condition of pre-release cracks. The sensor network used in this method consists of parallel long-gauge fiber optic strain sensors embedded in the concrete cross-sections at various locations. The same network is used for damage detection, i.e. detection and characterization of the pre-release cracks, and for monitoring the prestress force transfer. The method is validated on a real structure, a curved continuous girder. Results from the analysis confirm the safety and integrity of the structure. The method and its application are presented in this paper.

  18. Analysis of the status of pre-release cracks in prestressed concrete structures using long-gauge sensors

    International Nuclear Information System (INIS)

    Prestressed structures experience limited tensile stresses in concrete, which limits or completely eliminates the occurrence of cracks. However, in some cases, large tensile stresses can develop during the early age of the concrete due to thermal gradients and shrinkage effects. Such stresses can cause early-age cracks, termed ‘pre-release cracks’, which occur prior to the transfer of the prestressing force. When the prestressing force is applied to the cross-section, it is assumed that partial or full closure of the cracks occurs by virtue of the force transfer through the cracked cross-section. Verification of the closure of the cracks after the application of the prestressing force is important as it can either confirm continued structural integrity or indicate and approximate reduced structural capacity. Structural health monitoring (SHM) can be used for this purpose. This paper researches an SHM method that can be applied to prestressed beam structures to assess the condition of pre-release cracks. The sensor network used in this method consists of parallel long-gauge fiber optic strain sensors embedded in the concrete cross-sections at various locations. The same network is used for damage detection, i.e. detection and characterization of the pre-release cracks, and for monitoring the prestress force transfer. The method is validated on a real structure, a curved continuous girder. Results from the analysis confirm the safety and integrity of the structure. The method and its application are presented in this paper. (paper)

  19. Crack bridging in stress corrosion cracking of duplex stainless steels

    International Nuclear Information System (INIS)

    Wedge open loaded (WOL) specimens of age hardened Zeron 100 duplex stainless steel were tested in 3.5 wt % NaCl solution with cathodic polarizes applied at-900m V/SCE to investigate stress corrosion cracking mechanism in duplex stainless steel. The interaction between microstructure and mechanism of stress corrosion cracking was studied. Fracture mechanism was studied by using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The material was found cracked by ferrite cleavage, austenite tearing and austenite dissolution by environment. The ferrite cleavage took place along [100] planes and [112] twin habit planes. The austenite grains appear to act as crack bridging and crack arrester and failed by tearing and stress corrosion cracking. (author)

  20. CRACKS IN ROADWAY COVERING: METHODS FOR IMPROVEMENMT OF CRACK RESISTANCE

    Directory of Open Access Journals (Sweden)

    I. I. Leonovich

    2014-11-01

    Full Text Available Crack formation is presently considered as an actual problem in the global practice. The paper provides various approaches pertaining to improvement of asphalt-concrete composition with the purpose to prevent formation of temperature and fatigue cracks and develop design and technology measures for avoidance of reflection cracking in asphalt-concrete strengthening layers. However there is no comprehensive solution of the problem that combines a material science and affirmative approaches. Existing technology for crack sealing in roadway covering is rather efficient at the stage of its operation and makes it possible to eliminate cracks  depending on their nature and opening width but there is no efficient diagnostic and control system for preventing cracks with opening width up to1 mmwith the purpose to exclude their further development.