Ceramics-Silikáty 64, (1) 7 - 17 (2020)

Magnesium oxysulfate (MOS) cement is a newly-developed material，which shows the advantages of being protected from steel, being light weight, having low alkalinity, being fire-proof, and having a decorative value. Large-scale applications of MOS cement in civil engineering have been restricted by its low strength, which can be improved by adding the proper additives. Here, the effects of dihydrogen phosphate on the setting time, compressive strength, and water resistance of the MOS cement have been studied. The studies on the effects of dihydrogen phosphate on the hydration process of the MOS cement have been studied relative to the hydration-heat release rate. X-ray diffraction, scanning electron microscopy, and mercury intrusion porosimetry were used to examine the hydration products and the pore-size distribution of the MOS cement. The analytical results show that dihydrogen phosphate as an admixture can reduce the direct hydration of MgO into Mg(OH)₂, promote the formation of the 5·1·7 strength phase, and improve the strength and water resistance of the cement to some extent. However, dihydrogen phosphate will prolong the setting time of the cement to some extent.