Role of temperature on hydration and microstructure of calcium sulfoaluminate-based cement

Calcium sulfoaluminate belite (CSAB) cement is an alternative low carbon binder with ye’elimite, belite and calcium sulfate as the primary reactive phases. Ye’elimite hydrates rapidly to form ettringite, which contributes to a dense microstructure, rapid setting and high early-age strength. However, exposure to elevated temperatures can affect the stability of ettringite. This study focuses on the effect of elevated temperatures on the formation and stability of ettringite in CSAB binder systems with varying calcium sulfate-to-ye’elimite ratio. Samples at different ages of curing were exposed to temperatures up to 80°C. The results show that elevated temperatures did not significantly hinder the formation of ettringite, with stable ettringite forming up to 80°C. However, the elevated temperature directly affected the pore structure, increasing the critical pore size. Prolonged exposure to 80°C also resulted in an increased cumulative pore volume, which contributed to a compressive strength loss. After prolonged exposure to 80°C, the CSAB binder recorded a strength loss of 12%, while the binders with additional 5% and 15% calcium sulfate had strength reductions of 33% and 18%, respectively.