Effect of thermal activation on the phase composition, microstructure and cementing performance of 5Mg(OH)2•MgSO4•7H2O

To reduce carbon dioxide emissions, environmental pressure caused by the magnesium oxysulfate (MOS) cement production process or the expiration of service life must be avoided. This experiment investigated the changes in the phase structure and microstructure of the 517 phase (5 Mg(OH)2 center dot MgSO4 center dot 7H2O) after medium-or high-temperature treatment and its performance after remixing with water. The results were characterized by X-ray diffraction (XRD), thermal gravity-differential thermal gravity (TG-DTG), and scanning electron microscopy (SEM). The results show that the 517 phase can be dehydrated to form a mesophase after medium-temperature treatment, and these mesophase structures decompose with increasing treatment time. These mesophase products have cementing properties, and the 517 phase can be reformed by mixing the mesophase with water and has a certain strength. The raw material of MOS cement obtained from 517 treated at 500 degrees C has high activity, so a retarder is needed to reform the 517 phase. The modified sample has higher mechanical properties, which can meet the application needs.