Influence of gypsum content on the hydration and performance of low-temperature belite sulfoaluminate clinkers

This study systematically investigated the effect of gypsum, added after clinker firing during cement preparation, on the hydration behaviour and performance of belite calcium sulfoaluminate (BCSA) clinkers synthesised at a low temperature of 1150°C, with clinkers prepared at 1250°C evaluated for comparison. A series of analytical techniques including X-ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and compressive strength tests were performed. The results showed that the addition of gypsum accelerated the early hydration of BCSA clinkers. Increasing gypsum content promoted the formation of ettringite while inhibiting the hydration of belite and the precipitation of monosulfate and strätlingite. Clinkers produced at 1150°C exhibited greater hydration reactivity of ye’elimite than those prepared at 1250°C. The increased consumption of aluminium hydroxide indicated greater belite dissolution in clinkers synthesised at lower temperature. BCSA clinkers gained strength rapidly at early ages from fast ye’elimite hydration, while later strength depended on belite hydration. Higher gypsum content increased early-age strength but reduced strength at later ages. Clinkers fired at 1150°C exhibited higher strength than those prepared at 1250°C. It is noteworthy that low-temperature firing offers significant benefits in performance and environmental sustainability for BCSA clinker production.