Effects of nano-silica and silica fume on properties of magnesium oxysulfate cement

Abstract

As a new type of material, magnesium oxysulfate (MOS) cement shows advantages of fire resistance, low alkalinity, light weight, and good decorative value. However, the low strength of MOS cement limits its largescale applications in civil engineering, strength can be increased by adding appropriate admixtures. By adding different dosages (1, 3, 5%) of nano-silica (NS) and silica fume (SF), this paper studied the effects of the dosages on the compressive strength and water resistance of MOS cement. The phase composition and microstructure of MOS cement hydration products were analyzed by X-ray diffraction and scanning electron microscopy. The hydration process and pore size distribution of MOS cement were measured by hydration heat release rate and mercury intrusion porosimetry. The results show that the use of NS and SF as admixtures can inhibit the direct hydration of MgO to form Mg(OH)2 and promote the formation of the 5Mg(OH)2·MgSO4·7H2O (5·1·7 phase), improve the strength and water resistance of MOS cement to a certain extent.