The role of admixed CaO in a sulphoaluminate cement system under winter environments

Sulfoaluminate cement (CSA) is a low-carbon binder and can be regarded as an ideal cementitious material for winter construction and repair projects. However, the admixed CaO on the performance of CSA and its mechanism is still unclear, as well as the investigations and applications of CSA in negative temperature environments are very limited. Therefore, the impact of CaO on the setting time, compressive strength, cooling curve, and microscopic properties of CSA composite are systematically investigated. The experimental results reveal that the admixed CaO can significantly improve the compressive strength of CSA composite at negative temperatures (e.g., −5 °C, −10 °C, and −20 °C), and the admixed 2% CaO is the most effective in enhancing the compressive strength of CSA paste. At the beginning of hydration, CaO-modified CSA paste shows a significant exothermic peak, thus the freezing process of the liquid phase is retarded and the CSA can sustain hydration at −20 °C. Remarkably, the admixed 2% CaO can reduce the freezing point of the liquid phase of CSA paste to −7.2 °C, accordingly, decreasing the amount of freezable water and the risk of frost damage.