Adding Effects of CaF₂ and TiO₂ as Mineralizers on the Sintering Temperature and Hardening Properties of Calcium Sulfoaluminate Cement

Abstract

The influences of CaF₂ and TiO₂ as a mineraliser on the sintering temperature, phase formation, setting times, and the mechanical and hydration properties of calcium sulfoaluminate (C₄A₃S) were investigated. The results showed that the addition of CaF₂ and TiO₂ by 0.5 and 0.2 wt.% can reduce the sintering temperature of C₄A₃S from 1300 to 1100°C. The addition of appropriate amounts of CaF₂ and TiO₂ promoted hydration and significantly improved the compressive strength of C₄A₃S cement (CSC). The compressive strength and hydration speed of CSC containing 0.5 wt.% CaF₂ increased with an increase in the TiO₂ contents from 0 to 0.2 wt.% at all curing ages. However, when the TiO₂ content was increased to 0.25 wt.%, a significant reduction in the compressive strength of CSC was observed. The initial and final setting times of CSC containing 0.5 wt.% CaF₂ both decreased with increasing TiO₂ content. Compared with the control paste, the 15-h and 28-d compressive strength of CSC containing 0.5 wt.% CaF₂ and 0.2 wt.% TiO₂ increased from 30.4 and 79.2 MPa to 46.2 and 88.3 MPa, respectively. The hydration speed of CSC containing 0.5 wt.% CaF₂ and 0.2 wt.% TiO₂ was almost three times that of CSC without CaF₂ and TiO₂. Therefore, the optimum amounts of CaF₂ and TiO₂ that should be added to C₄A₃S as a mineraliser are 0.5 and 0.2 wt.%, respectively.