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

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.