The Experts below are selected from a list of 291 Experts worldwide ranked by ideXlab platform
Kamal H Khayat - One of the best experts on this subject based on the ideXlab platform.
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Methodology to evaluate variations in concrete color caused by white Cement substitutions and forming materials
Materials and Structures, 2020Co-Authors: Wael A. Megid, Kamal H KhayatAbstract:An experimental program was conducted to develop a methodology to quantify the gradation of the concrete color. The proposed methodology was used to evaluate the effect of the supplementary Cementitious materials and the limestone filler used as partial substitution of white Cement in architectural precast concrete. The effect of the formwork materials on concrete color was also investigated. Conventional concrete mixtures were prepared using different binder types, including gray-high early Strength Cement, white Cement, limestone filler, blast-furnace slag, and metakaolin, to evaluate the compressive Strength development that are suitable for the precast architectural applications. The corresponded paste mixtures were prepared to evaluate the variations in concrete color with the time under the air-curing conditions. The proposed methodology was found to provide precise classification for color gradation of concrete. The ternary powder blend of 50% high early Strength Cement, 25% white Cement, and 25% high Blaine limestone filler, by mass, was found to be optimal to achieve reasonable white tint in compensation with the need to retain high early Strength. A superworkable concrete and two self-consolidating concrete mixtures were cast in a special Z -shaped mold built up using PVC, steel, plywood, and polyester filter liner. The color of concrete surfaces cast in the plywood and polyester filter lined formwork materials were found darker than that of the concrete cast in the PVC and steel formworks.
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influence of silica fume content on microstructure development and bond to steel fiber in ultra high Strength Cement based materials uhsc
Cement & Concrete Composites, 2016Co-Authors: Caijun Shi, Kamal H KhayatAbstract:Abstract The use of silica fume can significantly enhance mechanical properties of concrete given its beneficial filling and pozzolanic effects. In this study, a simple and effective double-side pullout testing method was adopted to characterize the interfacial bond properties, which include pullout load-slip relationship, bond Strength, and pullout energy, of steel fiber-matrix in ultra-high Strength Cement-based material (UHSC) with 0–25% silica fume by the mass of binder. The effects of silica fume content on flowability, heat of hydration, compressive and flexural Strengths, hydration products, and pore structure of matrix at different curing time were evaluated as well. Backscatter scanning electron microscopy (BSEM) and micro-hardness measurement were used to examine the quality of interfacial transition zone (ITZ) around the fiber. In terms of the results, the optimal silica fume content could be in the range of 15%–25%. UHSC mixtures with these dosages of silica fume showed significant improvement in pullout behavior. Its bond Strength and pullout energy at 28 d could increase by 170% and 250% compared to the reference samples without any silica fume. The microstructural observation verified the findings on the macro-properties development. Formation of more and higher Strength of hydration products and refinement of ITZ around the fiber ensured higher micro-hardness, and thus improved the bond to fiber.
Cheolwoo Park - One of the best experts on this subject based on the ideXlab platform.
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optimization of steam curing regime for recycled aggregate concrete incorporating high early Strength Cement a parametric study
Materials, 2018Co-Authors: Asad Hanif, Muhammad Usman, Cheolwoo ParkAbstract:This paper investigates the properties of steam cured recycled aggregate concrete (RAC), in an attempt to determine the optimum conditions of the steam-curing cycle for RAC, and incorporating high early Strength Cement (HESC). Varying conditions of steam curing were employed. The steam-curing cycle was set based on the peak temperature, and the duration for which the peak temperature was maintained. Three peak temperatures were used for steam curing, 50 °C, 60 °C, and 70 °C, maintained for up to two hours. The compressive Strength results indicated that the steam-curing cycle employing the peak temperature of 50 °C maintained for one hour with a total duration of four hours was the optimum for Strength development, both at the early and late stages of hydration. Determining the optimum steam-curing temperature and duration will help reduce the associated curing cost, thus further economizing the production cost of recycled aggregate concrete.
Ye Jia-yuan - One of the best experts on this subject based on the ideXlab platform.
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Research Progress in High Strength Cement-based Materials
Bulletin of the Chinese ceramic society, 2009Co-Authors: Ye Jia-yuanAbstract:High Strength Cement-based materials is an important branch in the development of Cement-based materials.High Strength concrete/High performance concrete(HSC/HPC),Densitified system containing homogeneously arranged ultrafine particles(DSP),Macro defect free Cement(MDF),Reactive powder concrete(RPC)and other high Strength Cement-based materials are reviewed in this paper,and several measurements for improving Strength of Cement-based materials are proposed.At last,the development direction of high-Strength Cement-based materials is explored and existing problems in high-Strength Cement-based materials are pointed out.
Asad Hanif - One of the best experts on this subject based on the ideXlab platform.
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Steam-cured recycled aggregate concrete incorporating moderately high early Strength Cement: effect of binder content and curing conditions
SN Applied Sciences, 2019Co-Authors: Yongjae Kim, Wonjun Park, Asad HanifAbstract:Steam curing employed for faster Strength gain due to higher hydration rate may lead to shrinkage issues, and hence the use of moderately high early Strength Cement (MESC) is proposed instead of typically used high early Strength Cement (HESC) which has a high C3S content. This paper evaluates the suitability of MESC for use in precast concrete. The objective was to (i) determine the feasibility of MESC in recycled aggregate concrete (RAC), (ii) determine the optimum steam curing conditions (curing duration, maximum temperature, and duration of holding maximum temperature), and (iii) evaluating the beneficial use of reduced binder content to compensate for steam curing. Four series of RAC were developed which were subjected to nine different steam curing condition, and the resulting Strength properties were determined. Though all the developed concrete specimens achieved the design Strength of 30 MPa, those cured at 50 °C with 1 h duration of exposure to maximum temperature exhibited the best performance. Further, it was found that even though reducing the binder content reduces the ultimate Strength at 28-day age, curing at 70 °C with 2 h exposure to maximum temperature duration (for 7% reduction in binder volume) leads to merely 11.8% Strength decline. It is concluded that MESC can be effectively used in steam cured RAC instead of OPC and HESC with meagre Strength loss when cured at maximum temperature of 50 °C maintained for 1 h while the total curing time being 4.5 h. Thus, utilizing MESC in RAC shall not only help combat the persistently declining natural resources but also reduced the associated carbon dioxide emissions, thereby promoting sustainable development.
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optimization of steam curing regime for recycled aggregate concrete incorporating high early Strength Cement a parametric study
Materials, 2018Co-Authors: Asad Hanif, Muhammad Usman, Cheolwoo ParkAbstract:This paper investigates the properties of steam cured recycled aggregate concrete (RAC), in an attempt to determine the optimum conditions of the steam-curing cycle for RAC, and incorporating high early Strength Cement (HESC). Varying conditions of steam curing were employed. The steam-curing cycle was set based on the peak temperature, and the duration for which the peak temperature was maintained. Three peak temperatures were used for steam curing, 50 °C, 60 °C, and 70 °C, maintained for up to two hours. The compressive Strength results indicated that the steam-curing cycle employing the peak temperature of 50 °C maintained for one hour with a total duration of four hours was the optimum for Strength development, both at the early and late stages of hydration. Determining the optimum steam-curing temperature and duration will help reduce the associated curing cost, thus further economizing the production cost of recycled aggregate concrete.
Konstantin Sobolev - One of the best experts on this subject based on the ideXlab platform.
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Ultra-high Strength Cement-based composites designed with aluminum oxide nano-fibers
Construction and Building Materials, 2019Co-Authors: Scott Muzenski, Ismael Flores-vivian, Konstantin SobolevAbstract:Abstract The use of nanomaterials has become a popular way to improve the performance of Cement-based composites. At the same time, ultra-high Strength concrete is becoming more widely used. These materials provide superior durability to infrastructure elements, reducing the need for maintenance or early replaCement. The performance boost is achieved by producing a denser microstructure and, in the case when nanofibers are used, may reduce the initiation of cracks. Aluminum oxide nanomaterials have the potential to provide a significant increase in compressive Strength of Cement-based materials. Here, the effect of incorporation of aluminum oxide nanofibers in oil well Cement based mortars and composites is reported. The design of ultra-high Strength concrete often requires a precisely tuned aggregate gradation, the use of specific Cement types and high quantities of silica fume and superplasticizers along with high temperature and curing under elevated pressure. It was demonstrated that the use of small quantities of aluminum oxide nanofibers in an oil well Cement based mortar could provide a compressive Strength approaching 200 MPa. These levels were achieved at a considerably lower dosage of silica fume. It is envisioned that the high Strength matrix is formed due to the reinforcing of calcium silicate hydrate layers which are formed around the nanofibers. This research demonstrated that due to a “shish kebab” effect the addition of well-dispersed aluminum oxide nanofibers at a very small dosage of 0.25% (by mass of Cement) could provide up to 30% increase in compressive Strength of Cementitious systems, helping to meet the benchmarks for ultra-high Strength Cement-based composites.
