Effect of aggregates and water contents on the properties of magnesium phospho-silicate cement

Properties of magnesium phospho-silicate cement (MPSC) mortars with different fine aggregates, and different water contents were investigated in the present work. Three types of fine aggregates, natural sand, dead burnt magnesia and alumina particles were used. Two types of hard burnt magnesia powder with MgO content 89.51 and 71.50 wt.% were used as binder. Compressive strength of MPSC mortar with different water/binder ratios were determined at ages of 1, 3, 7, and 24 h. The 3, 7, and 28 day compressive strength and modulus of elasticity were also tested. It was found that the compressive strength of MPSC mortar decreases with the increase of sand content, regardless of sand type. However, the strength reduction of MPSC mortars formed with magnesia and alumina sand was much smaller than that of mortars formed with natural sand. Moreover, in spite of the raw materials, compressive strength and elastic modulus of MPSC decreased with the increase of water/binder ratio at all ages. The hydrate products were analysed by XRD and TG-DTA, and the porosity of MPSC mortar was analysed by MIP. Results showed total porosity increased with the increase of water content. The content of hydrate product of MPSC, phosphate hexahydrate, also increased with the increase of water content. However, it seems that the change of mechanical properties of MPSC is mainly controlled by increase of total porosity which was determined by water content.