Effect of calcium sulfate type and dosage on the properties of high-belite sulfoaluminate cement

High-belite sulfoaluminate cement (HBSC), with low carbon dioxide emissions, can be used to repair old concrete. Calcium sulfate plays a significant role in hydration of ye'elimite, but a comprehensive study of the effects of the four different types and dosages of calcium sulfate on the hydration of HBSC is lacking. This study investigates the influence of different types (dihydrate, anhydrite, α-hemihydrate, and β-hemihydrate) and doses (2%, 4%, 6%, and 8%) of calcium sulfate on the hydration process and mechanical properties of HBSC. The findings indicate that the addition of calcium sulfate, specifically β-hemihydrate, had a significant impact on the reduction of setting times. The compressive strength of HBSC, particularly early strength, can be significantly increased by varying calcium sulfate dose and type, enhancing the performance of repair materials. The microstructure of ettringite is altered by different types of calcium sulfate, leading to varying pore structures and volume expansions.