Early hydration of CSA cement modified with styrene–butadiene copolymer dispersion

The effect of styrene–butadiene copolymer (SB) dispersion on the early hydration of calcium sulfoaluminate (CSA) cement was investigated. Pastes with five different ratios (0, 5, 10, 15 and 20%) of SB to CSA cement at a constant water to cement ratio of 0·4 were investigated by ultrasonic measurements, isothermal calorimetry, X-ray diffraction, thermogravimetry and scanning electron microscopy. It was found that SB retarded the initial hydration of the CSA cement paste within 3 h, during which time the formation of ettringite was strongly delayed. The hydration degree of the CSA cement paste was caught up by that of the SB-modified CSA cement paste at 3 h based on ultrasonic and calorimetry analysis. In addition, an increase in the addition of SB led to the generation of more ettringite and aluminium hydroxide. The most ettringite was formed and the size of ettringite crystals was increased in the pastes with 20% SB. Meanwhile, the addition of SB tended to reduce the amount of hemicarboaluminate in CSA cement pastes.