The Experts below are selected from a list of 22188 Experts worldwide ranked by ideXlab platform
Sohei Nishio - One of the best experts on this subject based on the ideXlab platform.
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Early evaluation of Cover Concrete quality utilizing water intentional spray tests
Construction and Building Materials, 2020Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Yuya Kai, Sohei NishioAbstract:Abstract This study validated the effectiveness of a new, rapid, and cost-effective method to nondestructively evaluate the quality of early-age Cover Concrete using the water intentional spraying test (WIST). The WIST-measured water absorptivity at various ages, including promptly after demolding, was correlated with measured coefficient of air permeability, kT, (using a Torrent tester) at the age of three months as a robust durability indicator on 13 specimens produced using different cement types, curing periods, and water-to-binder ratios. The results indicated that WIST was highly sensitive in detecting poor- and normal-quality Concrete on the 1st and 7th day, respectively, following demolding.
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Durability index for quality classification of Cover Concrete based on water intentional spraying tests
Cement and Concrete Composites, 2019Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Sohei NishioAbstract:Abstract This study proposes a new durability indicator for classifying Cover Concrete quality through the total amount of sprayed water index (rW) using the water intentional spraying test (WIST). The usability of four WIST apparatuses was first verified through strong positive correlations between the previously proposed “repetition number of water spraying” index (rN) and the coefficient of air permeability, kT, (using a Torrent tester) that were individually measured on specimens produced with different cement types, water-to-binder ratios, and curing periods. Subsequently, a new equation was established showing the correlation between WIST apparatuses using rN and the amount of water for each spraying, W, in order to establish a generalized approach. A suggested range of rW indexes for quality classification of Cover Concrete was thereafter formulated and verified on the basis of good correlation between rW and kT. In addition, an innovative technique for expanding the usability of WIST was presented.
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Validation of simple nondestructive method for evaluation of Cover Concrete quality
Construction and Building Materials, 2019Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Yasutaka Kubori, Sohei NishioAbstract:Abstract The Water Intentional Spraying Test (WIST) was originally proposed as a simple nondestructive method for evaluating the Cover Concrete quality based on the “repetition number of water spraying,” rN. The validity of the test was verified in the present study by comparing rN with the coefficient of air permeability, kT, determined by the Torrent test. Both tests were conducted on three-month-old Concrete specimens produced with different cement types, water-to-cement ratios, and curing periods, using different measurement heights. A good relationship was observed between kT and rN, with the WIST also found to be sensitive for the detection of poor-quality Concrete.
Pilate Moyo - One of the best experts on this subject based on the ideXlab platform.
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Model for Cover cracking of RC beams due to partial surface steel corrosion
Construction and Building Materials, 2011Co-Authors: Goitseone Malumbela, Mark Alexander, Pilate MoyoAbstract:Abstract Cracking of the Cover Concrete due to steel corrosion is considered by many researchers to indicate the end-of-service life of corrosion-affected reinforced Concrete (RC) structures. Numerous models have been developed to predict the time from corrosion initiation to cracking of the Cover Concrete. In the previous models, Concrete with corroding steel bars was assumed to behave like a thick-walled cylinder under uniform internal pressure. Recent research publications have however, shown that steel corrosion is often concentrated on the surface of the steel that faces the direction of ingress of corrosion agents. This paper presents a model that relates the level of partial surface steel corrosion with the transverse and vertical strains measured on the exterior faces of corrosion-affected RC beams. The model assumes that the remaining section of the steel after corrosion is elliptical shaped. Finally, the model is calibrated with experimental data in the literature and it is shown that assuming uniform steel corrosion underestimates the internal pressure applied by the expansive corrosion products.
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lateral deformation of rc beams under simultaneous load and steel corrosion
Construction and Building Materials, 2010Co-Authors: Goitseone Malumbela, M G Alexander, Pilate MoyoAbstract:Abstract Cracking of Cover Concrete due to steel corrosion is one of the clear physical indicators of loss of service life of corroding RC structures. Its prediction is therefore very important for service life modelling of these structures. Models developed to predict the time to Cover cracking assume that stresses due to steel corrosion follow the principles of a thick-walled cylinder under internal pressure. Considering the errors in the models, this paper contests the applicability of the thick-walled cylinder approach to model the time to Cover cracking as well as the rate of lateral expansion of Concrete after Cover cracking using experimental results from 12 RC beams (153 × 254 × 3000 mm) corroded under a sustained load. It is shown in the paper that, contrary to the assumptions of uniform expansion made in the thick-walled cylinder approach, before cracking of the Cover Concrete, tensile strains are applied on the face of beams where corrosion agents are drawn whilst other faces are in compression. Corroded steel coupons are used to verify that this variation of strains is caused by the corrosion process not being uniformly distributed around the steel bar. It is also shown in the paper how cracking and location of cracks affects the rate of lateral deformation of Concrete due to steel corrosion.
May Huu Nguyen - One of the best experts on this subject based on the ideXlab platform.
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Air permeability of Cover Concrete quality of precast box culverts affected by casting direction
CIGOS 2019 Innovation for Sustainable Infrastructure, 2020Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Saeko KajitaAbstract:Casting direction is an external factor that can influence the properties, including air permeability of Concrete structures. In the current study, the effect of this factor on the air permeability of precast box culverts was investigated. The Torrent air permeability test was used to measure coefficient of air permeability kT for two box culvert specimens produced using ordinary Portland cement, water-to-binder ratio of 0.485, different casting directions (vertical and horizontal) at the age of 3 months. The obtained results show the different Cover Concrete qualities between the surfaces of the horizontal casting specimen, whereas the shortcomings during casting process were detected of the vertical casting specimen.
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Early evaluation of Cover Concrete quality utilizing water intentional spray tests
Construction and Building Materials, 2020Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Yuya Kai, Sohei NishioAbstract:Abstract This study validated the effectiveness of a new, rapid, and cost-effective method to nondestructively evaluate the quality of early-age Cover Concrete using the water intentional spraying test (WIST). The WIST-measured water absorptivity at various ages, including promptly after demolding, was correlated with measured coefficient of air permeability, kT, (using a Torrent tester) at the age of three months as a robust durability indicator on 13 specimens produced using different cement types, curing periods, and water-to-binder ratios. The results indicated that WIST was highly sensitive in detecting poor- and normal-quality Concrete on the 1st and 7th day, respectively, following demolding.
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Durability index for quality classification of Cover Concrete based on water intentional spraying tests
Cement and Concrete Composites, 2019Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Sohei NishioAbstract:Abstract This study proposes a new durability indicator for classifying Cover Concrete quality through the total amount of sprayed water index (rW) using the water intentional spraying test (WIST). The usability of four WIST apparatuses was first verified through strong positive correlations between the previously proposed “repetition number of water spraying” index (rN) and the coefficient of air permeability, kT, (using a Torrent tester) that were individually measured on specimens produced with different cement types, water-to-binder ratios, and curing periods. Subsequently, a new equation was established showing the correlation between WIST apparatuses using rN and the amount of water for each spraying, W, in order to establish a generalized approach. A suggested range of rW indexes for quality classification of Cover Concrete was thereafter formulated and verified on the basis of good correlation between rW and kT. In addition, an innovative technique for expanding the usability of WIST was presented.
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Validation of simple nondestructive method for evaluation of Cover Concrete quality
Construction and Building Materials, 2019Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Yasutaka Kubori, Sohei NishioAbstract:Abstract The Water Intentional Spraying Test (WIST) was originally proposed as a simple nondestructive method for evaluating the Cover Concrete quality based on the “repetition number of water spraying,” rN. The validity of the test was verified in the present study by comparing rN with the coefficient of air permeability, kT, determined by the Torrent test. Both tests were conducted on three-month-old Concrete specimens produced with different cement types, water-to-cement ratios, and curing periods, using different measurement heights. A good relationship was observed between kT and rN, with the WIST also found to be sensitive for the detection of poor-quality Concrete.
Renbo Zhang - One of the best experts on this subject based on the ideXlab platform.
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cracking of Cover Concrete due to non uniform corrosion of corner rebar a 3d meso scale study
Construction and Building Materials, 2020Co-Authors: Renbo Zhang, Xiuli DuAbstract:Abstract Corrosion of steel in Concrete structures is one of the main causes of structural durability failure. In order to study the rust cracking behavior of the Concrete protective layer, a three-dimensional meso-scale model of Concrete was established. In the approach, the Concrete was regarded as a three-phase composite composed of coarse aggregates, mortar matrix and the interfacial transition zones (ITZs). The non-uniform radial displacement method was used to characterize the mechanical effect of steel rust on the surrounding Concretes. The cracking behavior of Concrete Cover caused by non-uniform corrosion of corner reinforcement was simulated based on the meso-scale method. The rust expansion pressures on the surrounding Concretes due to non-uniform corrosion of corner rebar were explored. Moreover, the influences of steel bar diameter, Cover thickness and corrosion distribution mode on the cracking of Cover Concrete were investigated. The simulation results indicate that the non-uniform rust pattern of the steel bar makes rust expansion pressure smaller than the uniform rust. The random distribution of aggregates has little effect on the cracking mode of the Concrete protective layer. With the increase of the ratio of the thickness of Concrete Cover to the diameter of steel bar, the maximum rust expansion pressure of Concrete increases. Bar diameter has a negligible influence on the cracking pattern of Concrete.
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investigation on the cracking behavior of Concrete Cover induced by corner located rebar corrosion
Engineering Failure Analysis, 2015Co-Authors: Liu Jin, Renbo ZhangAbstract:Abstract Non-uniform corrosion of reinforcement causes Concrete cracking in chloride contaminated RC structures. Due to the special boundary conditions, the Concrete Cover with corner located rebar is often subjected to the attack of chloride ions in a marine environment from two directions, and thus the corresponding non-uniform corrosion distribution should be different from the one for side-located rebar. The aim of the work is to explore the effect of corner located rebar corrosion on the cracking of Cover Concrete. For corner located rebar, an improved non-uniform corrosion distribution model was established based on the analysis results of two-dimensional chloride diffusion in Concrete. Considering the heterogeneities of Concrete, a meso-scale mechanical model and method for the study on the failure behavior of Concrete Cover was built. In the analysis model and method, the non-uniform radial displacement distribution was adopted to simulate the corrosion expansion behavior of the rebar. The cracking of Concrete Cover with corner located rebar was simulated and studied. The present approach was verified by the available experimental observations. The influences of Concrete heterogeneity, corrosion distribution types, rebar diameter and Concrete Cover thickness on the failure patterns of Concrete Cover and the expansive pressure were investigated. The simulation results indicate that the developed approach can well describe the cracking behavior of Cover Concrete and the corrosion-expansion behavior of steel rebar.
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modeling the cracking of Cover Concrete due to non uniform corrosion of reinforcement
Corrosion Science, 2014Co-Authors: Xiuli Du, Renbo ZhangAbstract:Abstract In situations when external chloride penetration is the cause of depassivation, the corrosion process may start from the outer region of a rebar, which might expand non-uniformly. Therefore, the main objective of the present work is to explore the effect of non-uniform corrosion on cracking behavior of Cover Concrete. The influences of Concrete heterogeneities and the porous layer generated at the rebar/Concrete interface on the failure patterns and the corrosion level of Cover Concrete are considered. The random aggregate structures of Concrete are built, and the Concrete is regarded as a composite composed of three phases, i.e. the aggregate, mortar matrix, and the interfacial transition zones (ITZs). The plasticity damaged model is employed to describe the mechanical properties of the mortar matrix and the ITZs, and it is assumed that the aggregate is elastic. Non-uniform radial displacement with a half ellipse shape is adopted to describe the expansion distribution of the corrosion products. The failure pattern and the corrosion pressure of Cover Concrete, and the critical corrosion level when the Cover Concrete cracks due to non-uniform corrosion expansion are studied based on the meso-scale numerical method. The comparison of the simulation results with the available test results on the failure pattern of Cover Concrete shows fairly good agreement. Moreover, the influence of meso-structural heterogeneities is explored, and the cracking behavior obtained under non-uniform and uniform expansion conditions are compared. Finally, the influences of Cover thickness, rebar diameter and the location of rebar (namely side-located rebar and corner-located rebar), on the failure pattern and the corrosion level are examined.
Kenichiro Nakarai - One of the best experts on this subject based on the ideXlab platform.
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Air permeability of Cover Concrete quality of precast box culverts affected by casting direction
CIGOS 2019 Innovation for Sustainable Infrastructure, 2020Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Saeko KajitaAbstract:Casting direction is an external factor that can influence the properties, including air permeability of Concrete structures. In the current study, the effect of this factor on the air permeability of precast box culverts was investigated. The Torrent air permeability test was used to measure coefficient of air permeability kT for two box culvert specimens produced using ordinary Portland cement, water-to-binder ratio of 0.485, different casting directions (vertical and horizontal) at the age of 3 months. The obtained results show the different Cover Concrete qualities between the surfaces of the horizontal casting specimen, whereas the shortcomings during casting process were detected of the vertical casting specimen.
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Early evaluation of Cover Concrete quality utilizing water intentional spray tests
Construction and Building Materials, 2020Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Yuya Kai, Sohei NishioAbstract:Abstract This study validated the effectiveness of a new, rapid, and cost-effective method to nondestructively evaluate the quality of early-age Cover Concrete using the water intentional spraying test (WIST). The WIST-measured water absorptivity at various ages, including promptly after demolding, was correlated with measured coefficient of air permeability, kT, (using a Torrent tester) at the age of three months as a robust durability indicator on 13 specimens produced using different cement types, curing periods, and water-to-binder ratios. The results indicated that WIST was highly sensitive in detecting poor- and normal-quality Concrete on the 1st and 7th day, respectively, following demolding.
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Durability index for quality classification of Cover Concrete based on water intentional spraying tests
Cement and Concrete Composites, 2019Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Sohei NishioAbstract:Abstract This study proposes a new durability indicator for classifying Cover Concrete quality through the total amount of sprayed water index (rW) using the water intentional spraying test (WIST). The usability of four WIST apparatuses was first verified through strong positive correlations between the previously proposed “repetition number of water spraying” index (rN) and the coefficient of air permeability, kT, (using a Torrent tester) that were individually measured on specimens produced with different cement types, water-to-binder ratios, and curing periods. Subsequently, a new equation was established showing the correlation between WIST apparatuses using rN and the amount of water for each spraying, W, in order to establish a generalized approach. A suggested range of rW indexes for quality classification of Cover Concrete was thereafter formulated and verified on the basis of good correlation between rW and kT. In addition, an innovative technique for expanding the usability of WIST was presented.
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Validation of simple nondestructive method for evaluation of Cover Concrete quality
Construction and Building Materials, 2019Co-Authors: May Huu Nguyen, Kenichiro Nakarai, Yasutaka Kubori, Sohei NishioAbstract:Abstract The Water Intentional Spraying Test (WIST) was originally proposed as a simple nondestructive method for evaluating the Cover Concrete quality based on the “repetition number of water spraying,” rN. The validity of the test was verified in the present study by comparing rN with the coefficient of air permeability, kT, determined by the Torrent test. Both tests were conducted on three-month-old Concrete specimens produced with different cement types, water-to-cement ratios, and curing periods, using different measurement heights. A good relationship was observed between kT and rN, with the WIST also found to be sensitive for the detection of poor-quality Concrete.
