Improved hydration and properties of magnesium oxysulfate (MOS) cement using sodium silicate as an additive

Magnesium oxysulfate (MOS) cement has many advantages, such as high early strength, low thermal conductivity, excellent fire and corrosion resistance. However, its strength is less stable and its water resistance is relatively poor, which limits its wide use in civil engineering. In this study, the MOS cement specimens with different amount of sodium silicate (SS) as an additive were manufactured before subjected to a series of laboratory tests, including dispersion tests, strength tests, SEM, XRD and Isothermal Calorimetry analysis to evaluate their modified properties. The experimental results show that an increase of the amount of SS consistently reduces the initial setting time, dispersion and fluidity performance of MOS cement paste because of the SS accelerated endothermic reaction during hydration process of MOS. An addition of the amount of SS up to 0.5% of the mass of MgO significantly increases the long-term strength and water resistance of MOS cement. This attributes to the fact that SS enhances microstructure and refines the coarse pores of hardened MOS paste, and thus forms much denser paste, although it does not change the category of hydration phase composition in hardened MOS cement.