Effect of Metakaolin on Water Resistance of Magnesium Oxychloride Cement

In this paper, the effects of metakaolin (MK) on the properties of magnesium oxychloride cement (MOC) such as setting time, hydration process, mechanical properties, compactness, phase composition, and microstructure were investigated by using macroscopic or microscopic testing techniques. It was revealed that the addition of MK decreased the setting time, accelerated the hydration process, and improved the water resistance of MOC. Mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), and scanning electron microscopy (SEM) results showed that MK did not change the phase composition of MOC before and after water immersion but promoted the formation of 5Mg(OH)(2)center dot MgCl2 center dot 8H(2)O (phase 5) before water immersion and inhibited the decomposition of phase 5 after water immersion. Based on the strength retention and relative dynamic elastic modulus, a comprehensive model with which to evaluate water resistance of MOC was proposed. This model could normalize multiple parameters and reduce the test error. For MOC, the optimal amount of MK was 20%.