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Sulapha Peethamparan - One of the best experts on this subject based on the ideXlab platform.
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Stepwise regression modeling for compressive strength of alkali-activated concrete
Construction and Building Materials, 2017Co-Authors: Robert J Thomas, Sulapha PeethamparanAbstract:Abstract This paper presents the results from a parametric experimental investigation of the compressive strength of alkali-activated concrete. The effects of Curing Condition (moist-cured versus heat-cured), sodium oxide dosage, silica dosage, silica modulus (relative dosage of silica to sodium), solution/binder ratio, and free water/binder ratio on the compressive strength of sodium silicate-activated fly ash and slag cement concrete are evaluated. More than 5000 specimens with 676 unique combinations of mixture proportion and Curing Condition were tested. The marginalized effects of each parameter indicate effects similar to those identified by previous studies. Predictive models for the compressive strength of fly ash and slag cement-based concretes are developed by stepwise regression analysis. Although the specific models presented in this paper are applicable only for the materials and activators identified herein, the modeling procedures are generalized results are of doubtless utility for the design of alkali-activated concrete mixtures.
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effect of specimen size and Curing Condition on the compressive strength of alkali activated concrete
Transportation Research Record, 2017Co-Authors: Robert J Thomas, Sulapha PeethamparanAbstract:Alkali-activated concrete is a rapidly emerging sustainable alternative to portland cement concrete. The compressive strength behavior of alkali-activated concrete has been reported by various studies to a limited extent, but these discussions have been based on minimal evidence. Furthermore, although it is known that specimen size has a distinct effect on the apparent compressive strength of concrete, this effect has yet to be modeled for alkali-activated concrete. This paper presents the results of a comprehensive study of the effects of Curing Condition (i.e., moist-cured at ambient temperature for 28 days or heat-cured at 50cC for 48 h) and specimen size on the compressive strength of sodium silicate–activated fly ash and slag cement concrete. The heat-cured strength of alkali-activated slag cement concrete was linearly related to the moist-cured strength; the former was about 5% greater than the latter. Heat Curing also improved the strength of alkali-activated fly ash concrete, although the effect w...
Guangcheng Long - One of the best experts on this subject based on the ideXlab platform.
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effect of subsequent Curing on surface permeability and compressive strength of steam cured concrete
Construction and Building Materials, 2018Co-Authors: Guangcheng LongAbstract:Abstract Steam Curing is commonly used to produce the prefabricated elements to meet the requirement of the high early strength. However, this Curing regime was proved to lead to the thermal damage on the microstructure and properties of concrete. And the subsequent Curing after initial steam Curing is critical to the development of performances of steam-cured concrete. In this study, four typical subsequent Curing Conditions simulating the extreme service environments were employed on the Curing of steam-cured concrete. And the surface permeability indexes involving water and air permeations and compressive strength were measured to analyze the effects of subsequent Curing Condition on performance of steam-cured concrete. The results indicate that the surface permeability and strength development of steam-cured concrete are remarkably influenced by the subsequent Curing Condition. The subsequent Curing such as long-term water-soaking Curing at 20 °C or oven-dry Curing at 60 °C deteriorates the performances of steam-cured concrete. Their surface permeability indexes are 75.1% and 88.0% higher than that of standard-cured concrete at 90 days, respectively. The continuous dissolution of calcium hydroxide is considered the main reason for deterioration of impermeability and strength of steam-cured concrete.
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effects of metakaolin on a novel aerated magnesium phosphate cement with high early strength
Construction and Building Materials, 2018Co-Authors: Gao Yi, Guangcheng Long, Bin Zhao, Youjun XieAbstract:Abstract Magnesium phosphate cement (MPC) was proved to be a cementitious material for preparing porous materials with high early-stage strength under standard Curing Condition. However, the poor water resistance of MPC-based porous materials limits the further application. This study employs metakaolin to improve the performance of aerated MPC. Testing results indicate that the presence of metakaolin produces more finer pores which makes the pore structure more homogeneous. For this reason, metakaolin improves both the compressive strength and water resistance with little negative impact on the thermal insulation property of aerated MPC. The metakaolin modified aerated MPC with a density of about 650 kg/m3 has 3-h strength of about 3 MPa and thermal conductivity of about 0.08 W/mK.
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influence of subsequent Curing on water sorptivity and pore structure of steam cured concrete
Journal of Central South University, 2012Co-Authors: Zhimin He, Guangcheng LongAbstract:Steam-cured Condition is found to cause larger porosity and worse properties of concrete compared with normal Curing Condition. For the sake of seeking effective measurements to eliminate this bad effect of steam-cured Condition on concrete, the water sorptivity and pore structure of steam-cured concretes exposed to different subsequent Curing Conditions were investigated after steam-Curing treatment. The capillary absorption coefficient and porosity of the corresponding concretes were analyzed, and their mechanisms were also discussed. The results indicate that water sorptivity and pore structure of steam-cured concrete are greatly influenced by the Curing Condition used in subsequent ages. Exposure steam-cured concrete to air Condition has an obviously bad effect on its properties and microstructures. Adopting subsequent Curing of immersing steam-cured concrete into about 20 °C water after steam Curing period can significantly decrease its capillary absorption coefficient and porosity. Steam-cured concrete with 7 d water Curing has minimum capillary absorption coefficient and total porosity. Its water sorptivity is decreased by 23% compared with standard Curing concrete and the porosity is 9.6% lower. Moreover, the corresponding gradient of water sorptivity and porosity of steam-cured concrete both decrease, thus microstructure of concrete becomes more homogeneous.
Qiang Wang - One of the best experts on this subject based on the ideXlab platform.
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influence of high volume electric furnace nickel slag and phosphorous slag on the properties of massive concrete
Journal of Thermal Analysis and Calorimetry, 2018Co-Authors: Qiang Wang, Zongxian Huang, Dengquan WangAbstract:This study applied high-volume electric furnace nickel slag (FS), phosphorous slag (PS) and a mixture of the two (FP) to massive concrete, and using fly ash (FA) as the control admixture, investigated the effects of FS and PS on the hydration and hardening process of the cementitious materials, the mechanical properties and the durability of the concrete. Two Curing Conditions were set, namely the standard Curing Condition and temperature-matched Curing Condition (or constant 25 and 50 °C). The hydration heat, hydration products, pore size distribution, mechanical properties and ability of the concrete to resist chloride ion penetration were tested. The results show that the activity of PS and FP is higher than that of FA, while that of FS is lower than that of FA; the improvement of FP on the pore structure of the hardened paste is close to that of FA at late ages under the standard Curing Condition but better than that of FA at all ages under the temperature-matched Curing Condition; high-volume FP concrete shows similar or even superior mechanical properties and permeability to chloride ions of concrete to high-volume FA concrete at late ages under both Curing Conditions.
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Hydration mechanisms of composite binders containing phosphorus slag at different temperatures
Construction and Building Materials, 2017Co-Authors: Zengqi Zhang, Qiang Wang, Jun YangAbstract:Abstract The hydration mechanisms of binders containing phosphorous slag at different temperatures were investigated by determining the hydration heat, reaction degree, non-evaporable water content, Ca(OH) 2 content and pore structure of the paste. In addition to plain cement, composite binders containing quartz having a particle size distribution similar to that of phosphorous slag were selected as the control sample. The results show that the retardation effect of the phosphorous slag is greater than its acceleration effect (nucleation effect and dilution effect) on the early hydration of cement. However, increasing the Curing temperature tends to reduce the retardation effect of phosphorous slag on the early hydration of cement. The addition of phosphorous slag increases the hydration degree of cement at later ages, particularly at high replacement ratio, but this acceleration effect on the late hydration of cement is weakened at high Curing temperature. Under high-temperature Curing Condition, the reaction degree of phosphorous slag is greater than that under normal-temperature Curing Condition at all ages, and thus, the contribution of phosphorous slag to the increment of the hydration product and the reduction in Ca(OH) 2 is greater. In the case of standard Curing, the pore structure of the paste containing phosphorous slag is coarser than that of the paste containing quartz at early ages, whereas the opposite trend is observed under high-temperature Curing Condition. At late ages, the pore structure of the paste containing phosphorous slag is finer than those of the plain cement paste and the paste containing quartz for both standard Curing and steam Curing. Increasing the Curing temperature tends to reduce the difference between the compressive strength of the plain cement mortar and that of the mortar containing phosphorous slag at early ages. At the same time, the late-age compressive strength of the mortar containing phosphorous slag surpasses that of the plain cement mortar much more at higher Curing temperature.
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influence of alkali activators on the early hydration of cement based binders under steam Curing Condition
Journal of Thermal Analysis and Calorimetry, 2017Co-Authors: Dengquan Wang, Qiang Wang, Zhenggang FangAbstract:The effects of water glass, NaOH, Na2SO4, and Na2CO3 on the early hydration of plain cement and two composite binders incorporating 40 mass% ground granulated blast furnace slag (GGBS) and 40 mass% fly ash under the steam Curing temperature of 60 °C were investigated. Meanwhile, a 20 °C Curing Condition was set as a reference. The results showed that water glass, NaOH, and Na2CO3 can improve the exothermic rates of the binders at the acceleration period and promote the reaction of GGBS and fly ash. However, the alkali activators inhibited the hydration of Portland cement at the deceleration period, which was more significant at 60 °C. Thus, the alkali activators cannot efficiently increase the cumulative hydration heat within 16 h under steam Curing or even appear to decrease. Na2SO4 shows a better performance than the other three alkalis in the early hydration of the composite binders due to its promotion on the formation of AFt, but it cannot efficiently increase the cumulative hydration heat too. The results also showed that all of the alkali activators significantly decreased the form-removal strength of cement–GGBS composite binder. For cement–fly ash composite binder, the form-removal strengths of the samples activated by a low concentration of water glass and high concentration of Na2SO4 were close to that reacted with water, while the form-removal strengths of the samples activated by other alkaline solutions were lower. Overall, the four alkali activators cannot improve the form-removal strength of steam-cured mortar containing a large volume of mineral admixtures.
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influence of pre Curing time on the hydration of binder and the properties of concrete under steam Curing Condition
Journal of Thermal Analysis and Calorimetry, 2014Co-Authors: Qiang Wang, Mengyuan Li, Bo ZhangAbstract:There is a pre-Curing period before the freshly made concrete elements were exposed to steam Curing in the steam Curing process. In this paper, the influence of pre-Curing time on the hydration of binder and the properties of concrete under steam Curing Condition was investigated. Three binders were used: the pure cement, the binder containing high content of GGBS, and the binder containing high content of fly ash. Three pre-Curing times (1, 3, and 6 h) and one steam Curing period at 60 °C (over 8 h) were adopted. Results show that pre-Curing time has limited influence on the hydration degree of binder, and compressive strength and pore structure of paste. The influence of pre-Curing time has limited influence on the compressive strength and chloride permeability of the pure cement concrete and the concrete containing high content of GGBS at whether early or late ages, indicating that the proper pre-Curing time can be as short as 1 h for these two concretes. Increasing pre-Curing time enhances the late-age compressive strength of the concrete containing high content of fly ash significantly, but it has limited influence on the late-age permeability.
Paul Ziehl - One of the best experts on this subject based on the ideXlab platform.
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investigation of early compressive strength of fly ash based geopolymer concrete
Construction and Building Materials, 2016Co-Authors: Lateef Assi, Edward Deaver, Mohamed K Elbatanouny, Paul ZiehlAbstract:Abstract Development of sustainable construction materials has been the focus of research efforts worldwide in recent years. Concrete is a major construction material; hence, finding alternatives to ordinary Portland cement is of extreme importance due to high levels of carbon dioxide emissions associated with its manufacturing process. This study investigates the effects of activating solution type, Curing procedure, and source of fly ash in relation to the resulting compressive strength of fly ash-based geopolymer concrete. The fly ash-based geopolymer paste microstructure was observed and density, absorption and voids were measured. Two activating solutions were used: a) a mixture of sodium hydroxide, silica fume, and water; and b) a mixture of sodium hydroxide solution, sodium silicate, and water. Test results indicate that the resulting concrete has the potential for high compressive strength and the compressive strength is directly affected by the source of fly ash. Results further indicate that compressive strength is not significantly affected by the Curing Condition when silica fume is used in the activating solution in comparison to the use of sodium silicate.
Jianming Yang - One of the best experts on this subject based on the ideXlab platform.
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influence of nickel slag powders on properties of magnesium potassium phosphate cement paste
Construction and Building Materials, 2019Co-Authors: Qi Wang, Changjuan Yu, Xuancheng Xu, Linlin Chong, Jianming Yang, Qisheng WuAbstract:Abstract This paper aims to study the effect of nickel slag powders on the properties of potassium magnesium phosphate cement (MKPC) paste. MKPC pastes containing different contents of nickel slag powders were prepared. We then tested their fluidity, setting time, compressive strength, the residual ratio of compressive strength under water Curing Condition, shrinkage deformation and hydration temperature. The micro morphology and the phase compositions of hardened MKPC pastes were also analyzed. The results indicate that adding some nickel slag powders in MKPC can improve the particle gradation of alkali components in MKPC and further improve the fluidity of fresh MKPC paste. The water stability of MKPC paste can be improved obviously by adding 30–40% nickel slag powders. The 60-day compressive strength of MKPC paste with 30–40% nickel slag powers exceeds 70 MPa and the residual ratio of compressive strength under water Curing Condition is higher than 100%. This should be attributed to the decrease in the proportion of harmful pores in hardened MKPC paste with some nickel slag powers. In addition, adding some nickel slag powders can obviously reduce the shrinkage deformation of MKPC paste. The 60-day drying shrinkage rate of hardened MKPC paste with 30% nickel slag powders is only 48.2% of that of the reference sample without nickel slag powders. This is attributed to the improvement of particle size distribution of alkali components, the micro-aggregate effect of nickel slag powders and less water use. These factors result in the decrease in the total porosity of the hardened MKPC paste with nickel slag powders and finally smaller shrinkage deformation.
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the effect of seawater Curing on properties of magnesium potassium phosphate cement
Construction and Building Materials, 2017Co-Authors: Jianming Yang, Qingqing Tang, Zhixiang SunAbstract:Abstract This paper investigated the effect of early seawater Curing on properties of magnesium potassium phosphate cement (MKPC) paste. First, the MKPC paste was prepared by mixing overburning MgO powders, KH 2 PO 4 , the composite retarder (CR) and water in a certain proportion. Then, we measured the compressive strength, drying shrinkage deformation, and mass change of it under different Curing Conditions. The results were as follows. For MKPC paste specimens under seawater Curing Condition, the hydration ages before they were soaked in seawater had a significant effect on their compressive strength, drying shrinkage and mass increase. For MKPC paste specimens cured in seawater after 3-day natural Curing, their 28-day and 60-day compressive strengths were 112.8% and 105.4% of those of MKPC paste specimens with same hydration ages under natural Curing Condition, respectively. In addition, the 60-day shrinkage strain of them (0.82 × 10 −4 ) was significantly less than that of MKPC paste specimens with the same hydration age under natural Curing Condition (5.14 × 10 −4 ). Moreover, they had higher mass increase ratio (1.23%). These were due to higher production, higher degree of crystallinity and less defects of MKP crystals, and more perfect pore size distribution in MKPC specimens soaked in seawater after 3-day natural Curing.
