Effects of polycarboxylate superplasticiser on the early hydration properties of magnesium oxychloride cement

Magnesium oxychloride cement (MOC) exhibits better mechanical properties with a faster hydration rate than ordinary Portland cement (OPC). However, the rapid setting property of MOC limits its application in engineering applications. In this work, polycarboxylate superplasticiser (PCE) was used to improve the workability of MOC and its effect on the early hydration properties of MOC paste was investigated. The hydration process for MOC with five different PCE dosages of 0%, 0.4%, 0.6%, 0.8%, and 1% by weight of MgO was analysed using electrodeless resistivity. Optical microscopy was used to obtain the flocculation of fresh MOC paste and its rheological properties were tested to investigate its workability. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to analyse the effects of PCE on the phases and microstructures of the MOC paste. The results reveal that PCE significantly improves the rheological properties of MOC. The setting time of the MOC paste was retarded due to the PCE adsorbed on the cement particle surface, which prevented MgO particles from reacting with water. Meanwhile, MOC in the presence of certain PCE contents showed excellent mechanical properties due to a mass of formed gel-like 5MgO-MgCl2-8H2O crystals.