Effects of unreactive MgO and impurities in light burned MgO on the hydration process and performance of base magnesium sulfate cement

In this work, the effects of unreactive MgO and impurities in light burned MgO (LBM) on the hydration process and performance of the resulting base magnesium sulfate (BMS) cements have been systematically investigated. The BMS cements prepared by LBM and by MgO derived from precipitate of brine (PBM) were characterized by XRD, SEM, TG-DSC, MIP, etc. The setting time and electrical resistivity during the early hydration process of the cements were also measured. The results show that the compressive strength of LBM-BMS cement is almost equivalent to that of PBM-BMS cement since the unreactive MgO and impurities in LBM might play a role of microaggregates. However, the unreactive MgO and impurities show a negative impact on the early hydration process. The water resistance of LBM-BMS cement is found to be far inferior to that of PBM-BMS cement due to larger mean pore diameter and more capillary pores and macropores in LBM-BMS cement, together with the instability of unreactive MgO and MgCO3 in water environment. The results suggest that it might be inappropriate to use LBM as the feedstock for preparing BMS cement in a long-range consideration. Instead, PBM would be a promising candidate for preparing BMS cement with a better performance. (C) 2019 Elsevier Ltd. All rights reserved.