The Experts below are selected from a list of 2613 Experts worldwide ranked by ideXlab platform
Georges Nahas - One of the best experts on this subject based on the ideXlab platform.
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a thermal active Restrained Shrinkage ring test to study the early age concrete behaviour of massive structures
Cement and Concrete Research, 2011Co-Authors: Matthieu Briffaut, Farid Benboudjema, Jeanmichel Torrenti, Georges NahasAbstract:Abstract 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 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.
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Numerical analysis of the thermal active Restrained Shrinkage ring test to study the early age behavior of massive concrete structures
Engineering Structures, 2011Co-Authors: Matthieu Briffaut, Farid Benboudjema, Jeanmichel Torrenti, Georges NahasAbstract:Abstract Several tests, devoted to the study of cracking due to autogenous and drying Shrinkage, exist in the literature. They are generally not relevant for the study of massive structures for which thermal strains plays a key role. Therefore, an active ring test has been developed to study cracking due to Restrained thermal Shrinkage. This test is an evolution of the Restrained Shrinkage ring test which allows us to take into account both autogenous and thermal Shrinkage. With this test, the early age cracking due to thermal Restrained Shrinkage (effect of the temperature rate), the influence of reinforcement and construction joints have been studied (Briffaut et al. (2011) [1] ). Nevertheless, in this test, several phenomena occur simultaneously (hydration, Shrinkage, creep…) and their effect cannot be easily decoupled. So, complementary tests have been performed to study each phenomenon separately and the ring test has been numerically simulated in order to identify coupling between creep and damage and to quantify the strength decrease due to construction joints. A good agreement between experimental and numerical results has been obtained for ring with reinforcement and construction joints. With the proposed model and the identified materials parameters validated on the active Restrained ring test, numerical simulations of the construction of a real massive structure have been performed, and a parametric study has been achieved to highlight the creep effect.
Young Soo Yoon - One of the best experts on this subject based on the ideXlab platform.
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Geometrical and boundary condition effects on Restrained Shrinkage behavior of UHPFRC slabs
KSCE Journal of Civil Engineering, 2017Co-Authors: Doo-yeol Yoo, Nemkumar Banthia, Young Soo YoonAbstract:Six large Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) slabs were fabricated and tested to investigate the Restrained Shrinkage and cracking behaviors. The use of expanded polystyrene and Teflon sheets with two different slab thicknesses was considered to improve the Shrinkage crack resistance. Free Shrinkage was simultaneously measured to evaluate the degree of restraint according to the above test parameters. The test results showed that free Shrinkage strains of -689 μe to -723 μe were obtained after 9 days, and prismatic specimens with a higher exposed surface area-to-volume ratio (S/V) had slightly higher free Shrinkage strains than those with a lower S/V. Increasing the concrete slab thickness and using expanded polystyrene and Teflon sheets were effective at reducing the degree of restraint and improving the Shrinkage crack resistance of the UHPFRC slabs. Among the various specimens, the slabs with the expanded polystyrene exhibited the lowest degree of restraint by 0.45 after 9 days.
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Influence of ring size on the Restrained Shrinkage behavior of ultra high performance fiber reinforced concrete
Materials and Structures, 2014Co-Authors: Doo-yeol Yoo, Jung Jun Park, Sung-wook Kim, Young Soo YoonAbstract:In order to evaluate the Restrained Shrinkage behavior of ultra high performance fiber reinforced concrete (UHPFRC), ring-tests with three different wall thicknesses and two different diameters of inner steel ring were performed. Partially exposed free Shrinkage and tensile tests were carried out simultaneously to assess the theoretical elastic stress, stress relaxation, degree of restraint and potential for cracking in the concrete. Test results indicated that the UHPFRC ring specimen with a thicker steel ring demonstrated a faster theoretical cracking time, higher stress relaxation and degree of restraint than that of a thinner steel ring, whereas those factors were rarely affected by the diameter of the inner steel ring. About 39–65 % of the theoretical elastic stress was relaxed by the sustained interface pressure. Since the actual residual tensile stress of all specimens was less than the tensile strength, the computed cracking potential varied from 0.43 to 0.7, and thus no Shrinkage crack was observed. Finally, the degree of restraint provided a linear relationship with the ratio of steel and concrete wall thickness.
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influence of reinforcing bar type on autogenous Shrinkage stress and bond behavior of ultra high performance fiber reinforced concrete
Cement & Concrete Composites, 2014Co-Authors: Doo-yeol Yoo, Jung Jun Park, Sung-wook Kim, Young Soo YoonAbstract:Abstract This study investigated the effects of reinforcing bar type and reinforcement ratio on the Restrained Shrinkage behaviors of ultra high performance fiber reinforced concrete (UHPFRC), including autogenous Shrinkage stress, degree of restraint, and cracking potential. In addition, the influence of the type and embedment length of reinforcing bars on the bond behavior of UHPFRC was evaluated by performing pullout test. Three different reinforcing bars (deformed steel bar, round steel bar, and GFRP bar) were investigated in the Restrained Shrinkage and pullout tests. The GFRP bar exhibited the best performance in relation to the autogenous Shrinkage stress, degree of restraint, and cracking potential because of its low stiffness. The highest bond strength was obtained for the deformed steel bar, and the bar yielding was observed when the bar embedment length of lb = 2db was used. The round steel bar exhibited the poorest behaviors for both of the Restrained Shrinkage and pullout.
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properties and prediction model for ultra high performance fiber reinforced concrete uhpfrc ii evaluation of Restrained Shrinkage characteristics and prediction of degree of restraint
Journal of the Korean Society of Civil Engineers A, 2012Co-Authors: Doo-yeol Yoo, Jung Jun Park, Sung-wook Kim, Young Soo YoonAbstract:In this study, to evaluate the Shrinkage behavior of ultra high performance fiber reinforced concrete (UHPFRC) under Restrained condition, Restrained Shrinkage test was performed according to ring-test mostly used at home and abroad. Ring-test was performed with the various thicknesses and radii of inner steel ring to give different degree of restraint. Free Shrinkage and tensile tests were carried out simultaneously to estimate the degree of restraint, stress relaxation, and Shrinkage cracking potential. Test results indicated that the average steel strain and residual tensile stress were reduced as the thicker inner steel ring was used, whereas degree of restraint was increased. The steel strain, residual tensile stress and degree of restraint were hardly affected by the size of radius of inner ring. In the case of all ring specimens, Shrinkage crack did not occur because the residual tensile stress was lower than the tensile strength. About 39~65% of the elastic Shrinkage stress was relaxed by the sustained interface pressure, and the maximum relaxed stress was increased as the thicker inner ring was applied. Finally, the degree of restraint with age was predicted by performing non-linear regression analysis, and it was in good agreement with the test results.
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An Evaluation on the Restrained Shrinkage of Ultra-High Performance Concrete
Key Engineering Materials, 2012Co-Authors: Jung Jun Park, Doo-yeol Yoo, Sung-wook Kim, Young Soo YoonAbstract:Since ultra-high performance concrete (UHPC) is subject to large occurrence of Shrinkage at early age due to its low water-to-cement ratio, the mixing of large quantities of powdered admixtures and the absence of coarse aggregates, UHPC presents large risks of Shrinkage cracking caused by the restraints provided by the form and reinforcing bars. Accordingly, this study intends to evaluate the Shrinkage behavior of UHPC under Restrained state by performing Restrained Shrinkage test using ring-test. The test results reveal that increasing thickness of the inner ring increases the tensile creep at early age leading to the reduction of the average strain and residual stress of the inner ring.
Matthieu Briffaut - One of the best experts on this subject based on the ideXlab platform.
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a thermal active Restrained Shrinkage ring test to study the early age concrete behaviour of massive structures
Cement and Concrete Research, 2011Co-Authors: Matthieu Briffaut, Farid Benboudjema, Jeanmichel Torrenti, Georges NahasAbstract:Abstract 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 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.
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Numerical analysis of the thermal active Restrained Shrinkage ring test to study the early age behavior of massive concrete structures
Engineering Structures, 2011Co-Authors: Matthieu Briffaut, Farid Benboudjema, Jeanmichel Torrenti, Georges NahasAbstract:Abstract Several tests, devoted to the study of cracking due to autogenous and drying Shrinkage, exist in the literature. They are generally not relevant for the study of massive structures for which thermal strains plays a key role. Therefore, an active ring test has been developed to study cracking due to Restrained thermal Shrinkage. This test is an evolution of the Restrained Shrinkage ring test which allows us to take into account both autogenous and thermal Shrinkage. With this test, the early age cracking due to thermal Restrained Shrinkage (effect of the temperature rate), the influence of reinforcement and construction joints have been studied (Briffaut et al. (2011) [1] ). Nevertheless, in this test, several phenomena occur simultaneously (hydration, Shrinkage, creep…) and their effect cannot be easily decoupled. So, complementary tests have been performed to study each phenomenon separately and the ring test has been numerically simulated in order to identify coupling between creep and damage and to quantify the strength decrease due to construction joints. A good agreement between experimental and numerical results has been obtained for ring with reinforcement and construction joints. With the proposed model and the identified materials parameters validated on the active Restrained ring test, numerical simulations of the construction of a real massive structure have been performed, and a parametric study has been achieved to highlight the creep effect.
Doo-yeol Yoo - One of the best experts on this subject based on the ideXlab platform.
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Geometrical and boundary condition effects on Restrained Shrinkage behavior of UHPFRC slabs
KSCE Journal of Civil Engineering, 2017Co-Authors: Doo-yeol Yoo, Nemkumar Banthia, Young Soo YoonAbstract:Six large Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) slabs were fabricated and tested to investigate the Restrained Shrinkage and cracking behaviors. The use of expanded polystyrene and Teflon sheets with two different slab thicknesses was considered to improve the Shrinkage crack resistance. Free Shrinkage was simultaneously measured to evaluate the degree of restraint according to the above test parameters. The test results showed that free Shrinkage strains of -689 μe to -723 μe were obtained after 9 days, and prismatic specimens with a higher exposed surface area-to-volume ratio (S/V) had slightly higher free Shrinkage strains than those with a lower S/V. Increasing the concrete slab thickness and using expanded polystyrene and Teflon sheets were effective at reducing the degree of restraint and improving the Shrinkage crack resistance of the UHPFRC slabs. Among the various specimens, the slabs with the expanded polystyrene exhibited the lowest degree of restraint by 0.45 after 9 days.
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Influence of ring size on the Restrained Shrinkage behavior of ultra high performance fiber reinforced concrete
Materials and Structures, 2014Co-Authors: Doo-yeol Yoo, Jung Jun Park, Sung-wook Kim, Young Soo YoonAbstract:In order to evaluate the Restrained Shrinkage behavior of ultra high performance fiber reinforced concrete (UHPFRC), ring-tests with three different wall thicknesses and two different diameters of inner steel ring were performed. Partially exposed free Shrinkage and tensile tests were carried out simultaneously to assess the theoretical elastic stress, stress relaxation, degree of restraint and potential for cracking in the concrete. Test results indicated that the UHPFRC ring specimen with a thicker steel ring demonstrated a faster theoretical cracking time, higher stress relaxation and degree of restraint than that of a thinner steel ring, whereas those factors were rarely affected by the diameter of the inner steel ring. About 39–65 % of the theoretical elastic stress was relaxed by the sustained interface pressure. Since the actual residual tensile stress of all specimens was less than the tensile strength, the computed cracking potential varied from 0.43 to 0.7, and thus no Shrinkage crack was observed. Finally, the degree of restraint provided a linear relationship with the ratio of steel and concrete wall thickness.
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influence of reinforcing bar type on autogenous Shrinkage stress and bond behavior of ultra high performance fiber reinforced concrete
Cement & Concrete Composites, 2014Co-Authors: Doo-yeol Yoo, Jung Jun Park, Sung-wook Kim, Young Soo YoonAbstract:Abstract This study investigated the effects of reinforcing bar type and reinforcement ratio on the Restrained Shrinkage behaviors of ultra high performance fiber reinforced concrete (UHPFRC), including autogenous Shrinkage stress, degree of restraint, and cracking potential. In addition, the influence of the type and embedment length of reinforcing bars on the bond behavior of UHPFRC was evaluated by performing pullout test. Three different reinforcing bars (deformed steel bar, round steel bar, and GFRP bar) were investigated in the Restrained Shrinkage and pullout tests. The GFRP bar exhibited the best performance in relation to the autogenous Shrinkage stress, degree of restraint, and cracking potential because of its low stiffness. The highest bond strength was obtained for the deformed steel bar, and the bar yielding was observed when the bar embedment length of lb = 2db was used. The round steel bar exhibited the poorest behaviors for both of the Restrained Shrinkage and pullout.
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properties and prediction model for ultra high performance fiber reinforced concrete uhpfrc ii evaluation of Restrained Shrinkage characteristics and prediction of degree of restraint
Journal of the Korean Society of Civil Engineers A, 2012Co-Authors: Doo-yeol Yoo, Jung Jun Park, Sung-wook Kim, Young Soo YoonAbstract:In this study, to evaluate the Shrinkage behavior of ultra high performance fiber reinforced concrete (UHPFRC) under Restrained condition, Restrained Shrinkage test was performed according to ring-test mostly used at home and abroad. Ring-test was performed with the various thicknesses and radii of inner steel ring to give different degree of restraint. Free Shrinkage and tensile tests were carried out simultaneously to estimate the degree of restraint, stress relaxation, and Shrinkage cracking potential. Test results indicated that the average steel strain and residual tensile stress were reduced as the thicker inner steel ring was used, whereas degree of restraint was increased. The steel strain, residual tensile stress and degree of restraint were hardly affected by the size of radius of inner ring. In the case of all ring specimens, Shrinkage crack did not occur because the residual tensile stress was lower than the tensile strength. About 39~65% of the elastic Shrinkage stress was relaxed by the sustained interface pressure, and the maximum relaxed stress was increased as the thicker inner ring was applied. Finally, the degree of restraint with age was predicted by performing non-linear regression analysis, and it was in good agreement with the test results.
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An Evaluation on the Restrained Shrinkage of Ultra-High Performance Concrete
Key Engineering Materials, 2012Co-Authors: Jung Jun Park, Doo-yeol Yoo, Sung-wook Kim, Young Soo YoonAbstract:Since ultra-high performance concrete (UHPC) is subject to large occurrence of Shrinkage at early age due to its low water-to-cement ratio, the mixing of large quantities of powdered admixtures and the absence of coarse aggregates, UHPC presents large risks of Shrinkage cracking caused by the restraints provided by the form and reinforcing bars. Accordingly, this study intends to evaluate the Shrinkage behavior of UHPC under Restrained state by performing Restrained Shrinkage test using ring-test. The test results reveal that increasing thickness of the inner ring increases the tensile creep at early age leading to the reduction of the average strain and residual stress of the inner ring.
Kypros Pilakoutas - One of the best experts on this subject based on the ideXlab platform.
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A numerical study on the effect of Restrained Shrinkage on rapid hardening plain and recycled clean steel fibre concrete overlays
Construction and Building Materials, 2020Co-Authors: Hajir Al-musawi, Maurizio Guadagnini, Haidong Huang, Kypros PilakoutasAbstract:Abstract This article presents FE numerical studies on Restrained Shrinkage of plain and fibre reinforced rapid hardening mortars. Moisture diffusivity analysis is coupled with structural analysis to calculate the evolution of hygral stresses, strains and cracking over time. The numerical results are validated against results from analytical models and compared to measured experimental values. Parametric studies are carried out to examine the effect of the interface stiffness, moisture content of the substrate layer and overlay depth on Restrained Shrinkage strain and stresses of overlays. Fibre inclusion is shown to reduce the risk of deterioration by slowing down the evolution of local slippage and controlling crack widths. It is also found that the uniform Shrinkage strain distribution that is assumed in analytical models underestimates the hygral tensile stresses of overlays compared to real non-linear strain distribution. A modification to account for this effect is proposed through Shrinkage amplification factor. This approach is expected to provide a better estimation of the risk of cracking in overlays.
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Free and Restrained Shrinkage of Hybrid Steel Fibres Reinforced Concrete
High Tech Concrete: Where Technology and Engineering Meet, 2017Co-Authors: Zahran Al-kamyani, Kypros Pilakoutas, Maurizio Guadagnini, Panos PapastergiouAbstract:Concrete elements are always subjected to a certain degree of restraint caused by internal reinforcement, connected elements, external boundaries, or a combination thereof. The degree of restraint provided may affect considerably how concrete Shrinkage cracks develop, thus affecting structural behaviour. The effect of restraint is complex to quantify and still poorly understood. This paper introduces a methodology to simulate and quantify more accurately real life restraining factors for structures. To achieve this, an experimental programme was undertaken to examine the free and Restrained Shrinkage of Steel Fibre Reinforced Concrete (SFRC). The performance of seven SFRC mixes using various dosages of Recycled Tyre Steel Fibres (RTSF) and Manufactured Undulated Steel Fibres (MUND) is examined. The drying Shrinkage was monitored over a period of ten months. The results show that Shrinkage strains were very similar in terms of free and Restrained Shrinkage, whilst the plain concrete exhibited the lowest strains. The variation in Shrinkage strain seems to be mostly related to the initial water content and volume of entrained air voids. Specimens subjected to Restrained Shrinkage showed about half the strain measured on free Shrinkage specimens. Free Shrinkage tests showed that the resulting strains were lower than the values predicted by fib MC 2010 and EC 2004, possibly due to the use of GGBS as cement replacement. This confirms that more environmentally friendly cementitious materials and fibres can help mitigate Shrinkage effects.
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Assessment of Post-Restrained Shrinkage Mechanical Properties of Concrete
ACI Materials Journal, 2016Co-Authors: Khaleel H. Younis, Kypros PilakoutasAbstract:Restrained Shrinkage-induced cracks can cause issues with serviceability, structural integrity, and durability in concrete, but are difficult to predict. This paper proposes a simple and economical test rig for Restrained Shrinkage and associated procedures to assess the post-Shrinkage mechanical properties (compressive and flexural strength) of concrete. The results show that the restraining factor of the proposed rig is dependent on the time and the stiffness of the concrete. Results of residual mechanical properties show that Restrained Shrinkage-induced cracks can affect the mechanical behavior (flexural and compressive strength and stiffness) of concrete by up to 21%. © 2016, American Concrete.