Investigating the water resistance of magnesium oxychloride cement with different hydration products

Magnesium oxychloride cement (MOC) is favoured for its light weight, high early strength and good thermal conductivity. However, its poor water resistance limits its use in construction and civil engineering. The main hydration products of MOC (phase 5 (5Mg(OH)2.MgCl2.8H2O) and phase 3 (3Mg(OH)2.MgCl2.8H2O)) tend to hydrolyse in water, causing its poor water resistance. Notably, phase 3 decomposes faster. To compare their stabilities in water, experiments were conducted using X-ray diffraction and scanning electron microscopy to analyse microstructural changes. The results showed that phase 3 fully decomposed within 3 days of water immersion, while phase 5 decomposed more slowly, with complete decomposition taking 28 days.