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The ability of different types of sand to preserve the integrity of calcium sulfoaluminate cement cement mortar during exposure to elevated temperatures

Tchekwagep Jean Jacques Kouadjo, Zengyao Wang, Fengzhen Yang, Piqi Zhao, Huang Shifeng, Wang Shoude, Cheng Xin Cheng

Materials Science Poland

2022

Vol. 40, No. 4

64--77

Due to the depletion of natural sand resources, it is urgent to develop synthetic sand that will replace the natural one in the production of concrete. In this study, we carried out descriptive inspection of mortar working performance, mechanical properties and internal cracking under three different application schemes of fine aggregate, including natural, artificial, and basalt sand. Tests showed that the mortar with river sand had more internal cracking and lowest strength as the temperature rises. The artificial and basalt sand had better resistance and less internal cracking than river sand at high temperature. The compressive strength of basalt sand mortar (BSM) was slightly higher than that of artificial sand mortar (ASM), while the compressive strength value of river sand mortar (RSM) was the lowest at room temperature. However, when heated to 100°C, the RSM had 48% loss of strength, followed by the BSM at 45.4% and ASM at 11.6%. Above 100°C, none of the mortar samples meet the requirement of the calcium sulfoaluminate cement 42.5. The average atomic ratios (Ca/Si, Ca/Al, and Ca/Si) for the ASM and BSM increased with the rise in temperature. XRD showed that above 100°C, the diffraction peaks of Ettringite (AFt) disappeared, the number of CaSO4 diffraction peaks decreased significantly, the intensity decreased, and a diffraction peak of CaCO3 appeared.

Quantitative Rietveld analysis of the decomposition of hardened rapid sulphoaluminate cement after exposure to elevated temperatures

Tchekwagep Jean Jacques Kouadjo, Chen Dangui, Mukhopadhyay Anol K., Wang Shoude, Huang Shifeng, Cheng Xin

Archives of Civil and Mechanical Engineering

2021

Vol. 21, no. 3

576--594

Concrete made from rapid sulphoaluminate cement is widely used today, especially in China. It is likely to continue gaining popularity since its manufacture produces less CO2 than the process of manufacturing ordinary Portland cement. Elevated temperatures are among the most serious threats to the structural stability of this product. In the present study, laboratory tests were carried out, through Rietveld analysis and other systematic testing, on samples of hardened rapid sulphoaluminate cement paste exposed to six different temperatures. As the temperature increased, the content of minerals that contribute to rapid sulphoaluminate cement strength was reduced. There was also an increase in porosity. The results show that the chemical dehydration of rapid sulphoaluminate cement after exposure to elevated temperatures is great enough to increase the local pores’ absorption, a change that can be fatal to rapid sulphoaluminate cement concrete’s strength. This understanding could help us characterize strength reduction in a more effective manner, not just in laboratory samples but also in actual structures containing rapid sulphoaluminate cement that has been exposed to elevated temperatures.