Effects of limestone powder on the hydration and microstructure development of calcium sulphoaluminate cement under long-term curing

In order to explore the effects of limestone powder on the long-term performance of calcium sulphoaluminate (CSA) cement, the hydration process and microstructure development of CSA cement incorporated with limestone powder are investigated at the ages from 1 day to 1 year. Three limestone powder dosages, such as 5%, 15% and 25% are considered. Three techniques, such as isothermal calorimetry, X-ray diffraction (XRD) and thermogravimetry (TG) were used to study the hydration process of cement pastes. Mercury intrusion porosimetry (MIP) was used to determine the pore structure of cement pastes. The results show that like in Portland cement, the addition of limestone powder in CSA cement can participate the reactions and form hemicarboaluminate phase. The difference is that monocarbonate phase is not found in the CSA-limestone powder binary system at the curing age from 1 day to 1 year. The addition of limestone powder can reduce the total porosity and critical pore size at 1 day. At long-term curing period, the critical pore size of CSA cement replaced by 5% limestone powder is almost equally to that of CSA cement.