The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Velu Saraswathy - One of the best experts on this subject based on the ideXlab platform.
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estimation of the permeability of silica fume Cement Concrete
Construction and Building Materials, 2010Co-Authors: Hawo Song, Sanghyeok Nam, Jongchul Jang, Seungwoo Pack, Velu SaraswathyAbstract:Abstract Deterioration and durability of Concrete structures mainly depend on permeability of Concrete. Silica fume (SF) as a mineral admixture for high performance Concrete produces more discontinues and impermeable pore structure in Concrete. The higher permeability reductions with silica fume are due to pore size refinement and matrix densification, reduction in content of Ca(OH)2 and Cement paste-aggregate interfacial refinement. During the hydration process the transition interfacial zone is gradually densified due to pozzolanic reaction between silica fume and calcium hydroxide. Based on a microstructure model, a procedure for predicting the permeability of high strength silica fume Cement Concrete is developed by considering water-to-binder ratio, silica fume replaCement ratio and degree of hydration as major influencing factors. Results of the permeability calculated using the procedure is verified with the available literature. Subsequently, effects of silica fume on the permeability of Concrete are evaluated. Finally, optimum silica fume replaCement ratios that reduce the permeability of Concrete reasonably are proposed for durable Concrete.
Mohammed K Ibrahim - One of the best experts on this subject based on the ideXlab platform.
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shrinkage of plain and silica fume Cement Concrete under hot weather
Cement & Concrete Composites, 2007Co-Authors: Omar Baghabra S Alamoudi, M Maslehuddin, M Shameem, Mohammed K IbrahimAbstract:Supplementary Cementing materials (SCMs) are widely used these days to improve the durability of Concrete. Silica fume has gained world wide acceptance due to its high pozzolanic reactivity compared to other SCMs. While silica fume Cement Concrete has several advantages over other blended Cement Concretes its main draw back is increased plastic and drying shrinkage, particularly under hot weather conditions. This paper reports results of a study conducted to assess these properties of plain and silica fume Cement Concrete specimens cast and cured in the field under hot weather conditions. The effect of specimen size and method of curing on plastic and drying shrinkage and some of the mechanical properties of silica fume and plain Cement Concrete specimens were evaluated. Results indicated that the type of Cement significantly affected both the plastic and drying shrinkage of Concrete in that these values in the silica fume Cement Concrete specimens were more than those in the plain Cement Concrete specimens. As expected, the shrinkage strains in both the plain and silica fume Cement Concrete specimens cured by continuous water-ponding were less than that in similar Concrete specimens cured by covering them with wet burlap. The results point to the importance of selecting a good quality silica fume and good curing for avoiding cracking of Concrete due to plastic and drying shrinkage, particularly under hot weather conditions.
Xingyi Zhu - One of the best experts on this subject based on the ideXlab platform.
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thermal expansion prediction of Cement Concrete based on a 3d micromechanical model considering interfacial transition zone
Construction and Building Materials, 2018Co-Authors: Xingyi Zhu, Ziwei Dai, Jianming Ling, Long ChenAbstract:Abstract Thermal expansion of Concrete is a main factor of Concrete failures especially in underground waterproof engineering, overlong structural engineering and mass Concrete construction. Thus, the coefficient of thermal expansion (CTE) of Concrete is an important parameter to be determined. A micromechanical model, namely the 3D Two-Layer Built-in Model is developed to obtain the overall CTE of Cement Concrete. The existence of interfacial transition zone (ITZ) between aggregate and Cement paste is considered in the model, and the ITZ model is simplified as a spring layer with a certain stiffness k. According to the existing testing data of three types of Cement Concrete whose aggregates are siliceous river gravel (RG), dolomitic limestone (DL) and granite (GR) respectively, the CTEs of prediction model are obtained and validated by the measured values. Moreover, the effects of interface, water Cement ratio, volume fraction ratio of fine aggregate to coarse aggregate, air voids, CTE of coarse aggregate and elastic modulus of Cement paste on the CTE are analyzed.
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effect of interfacial transition zone on the young s modulus of carbon nanofiber reinforced Cement Concrete
Cement and Concrete Research, 2018Co-Authors: Xingyi Zhu, Yuan Gao, Ziwei Dai, David J Corr, Surendra P ShahAbstract:Abstract Identifying the properties of the region where the Cement paste meets the aggregate surface (interfacial transition zone, ITZ) is critical to understanding the strength and fracture behavior of carbon nanofiber (CNF) reinforced Cement Concrete. In this study, the finite element method is employed to investigate the effect of the ITZ on the Young's modulus of Cement Concrete made with CNF. The numerical models for Cement Concrete with and without CNF are constructed based on the digital image processing technique. To consider the interface effect, the concept of “effective aggregate” is put forward, namely, the Young's modulus and Poisson's ratio for each aggregate particle are replaced by an effective Young's modulus and effective Poisson's ratio, in which the effect of thickness and the Young's modulus of ITZ is taken into account in an averaged manner. Then, the quantitative nanomechanical mapping (based on atomic force microscopy) technique is adopted to measure the Young's modulus and thickness of ITZ with and without CNFs, which are further used as the input parameters in the numerical model. The numerical simulation results are verified by experimental testing, which indicates that the ITZ effect should be considered when implementing the numerical simulation. In addition, this analysis shows that compared with the plain Cement Concrete, CNFs can greatly enhance the mechanical properties of ITZ, which will in turn improve the Young's modulus of Cement Concrete significantly. Finally, the effect of thickness and Young's modulus of ITZ on the Young's modulus of CNF reinforced Cement Concrete is also discussed.
Mohamed Lachemi - One of the best experts on this subject based on the ideXlab platform.
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performance of volcanic ash and pumice based blended Cement Concrete in mixed sulfate environment
Cement and Concrete Research, 2006Co-Authors: Khandaker M A Hossain, Mohamed LachemiAbstract:The deterioration of Concrete structures due to the presence of mixed sulfate in soils, groundwater and marine environments is a well-known phenomenon. The use of blended Cements incorporating supplementary Cementing materials and Cements with low C{sub 3}A content is becoming common in such aggressive environments. This paper presents the results of an investigation on the performance of 12 volcanic ash (VA) and finely ground volcanic pumice (VP) based ASTM Type I and Type V (low C{sub 3}A) blended Cement Concrete mixtures with varying immersion period of up to 48 months in environments characterized by the presence of mixed magnesium-sodium sulfates. The Concrete mixtures comprise a combination of two Portland Cements (Type I and Type V) and four VA/VP based blended Cements with two water-to-binder ratio of 0.35 and 0.45. Background experiments (in addition to strength and fresh properties) including X-ray diffraction (XRD), Differential scanning calorimetry (DSC), mercury intrusion porosimetry (MIP) and rapid chloride permeability (RCP) were conducted on all Concrete mixtures to determine phase composition, pozzolanic activity, porosity and chloride ion resistance. Deterioration of Concrete due to mixed sulfate attack and corrosion of reinforcing steel were evaluated by assessing Concrete weight loss and measuring corrosion potentials and polarization resistance atmore » periodic intervals throughout the immersion period of 48 months. Plain (Type I/V) Cement Concretes, irrespective of their C{sub 3}A content performed better in terms of deterioration and corrosion resistance compared to Type I/V VA/VP based blended Cement Concrete mixtures in mixed sulfate environment.« less
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performance of volcanic ash and pumice based blended Cement Concrete in mixed sulfate environment
Cement and Concrete Research, 2006Co-Authors: Khandaker M A Hossain, Mohamed LachemiAbstract:Abstract The deterioration of Concrete structures due to the presence of mixed sulfate in soils, groundwater and marine environments is a well-known phenomenon. The use of blended Cements incorporating supplementary Cementing materials and Cements with low C3A content is becoming common in such aggressive environments. This paper presents the results of an investigation on the performance of 12 volcanic ash (VA) and finely ground volcanic pumice (VP) based ASTM Type I and Type V (low C3A) blended Cement Concrete mixtures with varying immersion period of up to 48 months in environments characterized by the presence of mixed magnesium–sodium sulfates. The Concrete mixtures comprise a combination of two Portland Cements (Type I and Type V) and four VA/VP based blended Cements with two water-to-binder ratio of 0.35 and 0.45. Background experiments (in addition to strength and fresh properties) including X-ray diffraction (XRD), Differential scanning calorimetry (DSC), mercury intrusion porosimetry (MIP) and rapid chloride permeability (RCP) were conducted on all Concrete mixtures to determine phase composition, pozzolanic activity, porosity and chloride ion resistance. Deterioration of Concrete due to mixed sulfate attack and corrosion of reinforcing steel were evaluated by assessing Concrete weight loss and measuring corrosion potentials and polarization resistance at periodic intervals throughout the immersion period of 48 months. Plain (Type I/V) Cement Concretes, irrespective of their C3A content performed better in terms of deterioration and corrosion resistance compared to Type I/V VA/VP based blended Cement Concrete mixtures in mixed sulfate environment.
Omar Baghabra S Alamoudi - One of the best experts on this subject based on the ideXlab platform.
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estimation of minimum detectable concentration of chlorine in the blast furnace slag Cement Concrete
Nuclear Instruments & Methods in Physics Research Section B-beam Interactions With Materials and Atoms, 2011Co-Authors: A A Naqvi, M A Garwan, Mohammed Maslehuddin, M M Nagadi, Omar Baghabra S Alamoudi, M RaashidAbstract:Abstract The Prompt Gamma Neutron Activation Analysis technique was used to measure the concentration of chloride in the blast furnace slag (BFS) Cement Concrete to assess the possibility of reinforCement corrosion. The experimental setup was optimized using Monte Carlo calculations. The BFS Concrete specimens containing 0.8–3.5 wt.% chloride were prepared and the concentration of chlorine was evaluated by determining the yield of 6.11, 6.62, 7.41, 7.79 and 8.58 MeV gamma-rays. The Minimum Detectable Concentration (MDC) of chlorine in the BFS Cement Concrete was estimated. The best value of MDC limit of chlorine in the BFS Cement Concrete was found to be 0.034 ± 0.011 and 0.038 ± 0.012 wt.% for 6.11 and 6.62 MeV prompt gamma-rays. Within the statistical uncertainty the lower bound of the measured MDC of chlorine in the BFS Cement Concrete meets the maximum permissible limit of 0.03 wt.% of chloride set by the American Concrete Institute.
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prompt gamma analysis of fly ash silica fume and superpozz blended Cement Concrete specimen
Applied Radiation and Isotopes, 2009Co-Authors: A A Naqvi, M A Garwan, Mohammed Maslehuddin, M M Nagadi, Omar Baghabra S Alamoudi, M RaashidAbstract:Preventive measures against corrosion of reinforcing steel require making the Concrete dense by adding pozzolanic materials, such as fly ash, silica fume, Superpozz, blast furnace slag, etc. to Portland Cement. In order to obtain the desired strength and durability of Concrete, it is desirable to monitor the concentration of the pozzolan in the blended Cement Concrete. Addition of pozzolan to blended Cement changes the overall concentration of calcium and silicon in the blended Cement Concrete. The resulting variation in calcium and silicon gamma-ray yield ratio from blended Cement Concrete has found to have an inverse correlation with concentration of fly ash, silica fume, Superpozz, blast furnace slag in the blended Cement Concrete. For experimental verification of the correlation, intensities of calcium and silicon prompt gamma-ray due to capture of thermal neutrons in blended Cement Concrete samples containing 5-80% (by weight of Cement) silica fume, fly ash and Superpozz were measured. The gamma-ray intensity ratio was measured from 6.42 MeV gamma-rays from calcium and 4.94 MeV gamma-ray from silicon. The experimentally measured values of calcium to silicon gamma-ray yield ratio in the fly ash, silica fume and Superpozz Cement Concrete specimens agree very well with the results of the Monte Carlo simulations.
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shrinkage of plain and silica fume Cement Concrete under hot weather
Cement & Concrete Composites, 2007Co-Authors: Omar Baghabra S Alamoudi, M Maslehuddin, M Shameem, Mohammed K IbrahimAbstract:Supplementary Cementing materials (SCMs) are widely used these days to improve the durability of Concrete. Silica fume has gained world wide acceptance due to its high pozzolanic reactivity compared to other SCMs. While silica fume Cement Concrete has several advantages over other blended Cement Concretes its main draw back is increased plastic and drying shrinkage, particularly under hot weather conditions. This paper reports results of a study conducted to assess these properties of plain and silica fume Cement Concrete specimens cast and cured in the field under hot weather conditions. The effect of specimen size and method of curing on plastic and drying shrinkage and some of the mechanical properties of silica fume and plain Cement Concrete specimens were evaluated. Results indicated that the type of Cement significantly affected both the plastic and drying shrinkage of Concrete in that these values in the silica fume Cement Concrete specimens were more than those in the plain Cement Concrete specimens. As expected, the shrinkage strains in both the plain and silica fume Cement Concrete specimens cured by continuous water-ponding were less than that in similar Concrete specimens cured by covering them with wet burlap. The results point to the importance of selecting a good quality silica fume and good curing for avoiding cracking of Concrete due to plastic and drying shrinkage, particularly under hot weather conditions.