Preparation and properties of alite-modified calcium sulfoaluminate cement

Calcium sulfoaluminate cement (CSA) has the characteristics of rapid hardening, high early strength, high corrosion resistance and high impermeability, but its ability to continue to show strength increases at middle and late ages is poor. In this study, this drawback was improved by clinker mineral design. Alite (C₃S) in Portland cement clinker was used as a seed crystal to induce new C₃S in CSA clinker. The role of the introduction of C₃S and the effect of commonly used CSA admixtures on the setting time and hydration properties of alite-modified CSA (AMCSA) are described in this paper. Due to the hydration characteristics of C₃S, it was found that its introduction effectively improved the bond strength of the mortar and the strength growth persistence in middle and late stages. Commonly used CSA admixtures (e.g. lithium carbonate and boric acid) had the same effect on the setting time and hydration properties of the AMCSA mortar. The addition of lithium carbonate accelerated the cement hydration rate and shortened the setting time, which is beneficial for super early strength of mortar and enabled compressive strengths of up to 4·67, 9·10 and 22·49 MPa at 30 min, 1 h and 4 h, respectively. The addition of boric acid retarded the cement setting time due to a reduction in the hydration rate.