Research on the Hydration Properties of CAS-CSH Cement System at Different Temperatures.

Sulphoaluminate cement has the advantage of low-temperature application performance, but its hydration mechanism at low temperatures is not yet clear. Anhydrous calcium sulfoaluminate (CAS) is the main mineral in the composition of sulfoaluminate cement clinkers. In this paper, CAS mixed with gypsum (CaSO∙2HO) to form a CAS-CSH cement system; X-ray diffraction (XRD), thermogravimetric analysis (TG-DTG), scanning electron microscopy (SEM) and mercury intrusion analysis (MIP) to clarify the effect of temperatures on the hydration properties of CAS-CSH cement system. The results showed that hydration of the CAS-CSH cement system could carry on at low temperatures, even at -15 °C. The main hydration product was ettringite. Low temperatures did not change the types of the hydration products, but the low temperature of 0 °C was more favorable for the formation of ettringite. The early hydration of the CAS-CSH cement system was inhibited by the decrease in temperature. However, hydration of the cement at 0 °C continued at a high rate after one day. Morphologies of the ettringite for the CAS-CSH cement system at -15 °C were needle-like structures, while they were of columnar structure at 0 °C. The compressive strength of samples at 0 °C reached 82 MPa, which is significantly higher than that at 20 °C.