Effects of AH(3) and AFt on the Hydration–Hardening Properties of the [Formula: see text]- [Formula: see text]-H(2)O System

This study aimed to reveal the effects of the hydration products AH(3) and AFt phases on the hydration and hardening properties of calcium sulfoaluminate (CSA) cement. In addition, the effects of anhydrite ([Formula: see text]) and gypsum ([Formula: see text]) on the properties of CSA cement were compared. Calcium sulfoaluminate ([Formula: see text] was synthesized with analytical reagents, and the [Formula: see text]- [Formula: see text]-H(2)O system with different molar ratios of [Formula: see text] and [Formula: see text] was established. The phase compositions and contents of AFt and AH(3) were determined by X-ray diffraction (XRD), Rietveld quantitative phase analysis, and thermogravimetric analysis (TG). The effects of pore structure and hydration product morphology on mechanical properties were analyzed by mercury intrusion porosity (MIP) and scanning electron microscopy (SEM). The results showed that the compressive strength exhibited a correlation with the AH(3) content. In the case of relatively sufficient anhydrite or gypsum, [Formula: see text] has a high degree of hydration, and the AH(3) content can be considered to contribute more to the strength of the hardened cement paste. When anhydrite was selected, the combined and interlocked AFt crystals were covered or wrapped by a large amount of AH(3). The mechanical properties of the hardened cement paste mixed with anhydrite were better than those of that mixed with gypsum.