Hydration characteristics of calcium sulfoaluminate (CSA) cement/portland cement blended pastes

Abstract

The hydration characteristics of calcium sulfoaluminate cement (CSA) and ordinary Portland cement (OPC) blended pastes incorporating calcium sulfate (CS‾) are investigated. The experimental characterization techniques were employed and complemented with thermodynamic calculations to provide in-depth understanding of the hydration of CSA/OPC blended system. The results showed that the hydration of C3S in the CSA/OPC blended pastes was significantly delayed in comparison with the sole OPC paste. The delayed hydration of C3S negatively affected the strength development of the CSA/OPC pastes. As the amount of CS‾ increases, the induction period occurring between the initial peak and the intermediate peak was extended, thus increasing the initial setting time. The addition of CS‾ to the CSA/OPC blends led to the two phenomena in the hydration of C4A3S‾, (1) retardation of C4A3S‾ hydration, and (2) formation of more ettringite after a few hours of hydration. The thermodynamic calculations indicated that the setting of the CSA/OPC blended system is mainly facilitated by hydration of C4A3S‾ and by the formation of ettringite, while the major strength-giving phase is C–S–H that originates from the hydration of C3S.