Research on Deterioration Behavior of Magnesium Oxychloride Cement Under High Humidity and High Temperature

To clarify the deterioration behavior of magnesium oxychloride cement (MOC) under conditions of high humidity and high temperature, we first placed MOC slurry samples in a simulated environment with a relative humidity of 97 ± 1% and a temperature of 38 ± 2 °C; then, we observed the changes in the macroscopic and microscopic morphology, water erosion depth, bulk density, phase composition, and mechanical properties of the samples. The results show that, over time, under the promotion of high temperature, water molecules infiltrate the MOC samples. This results in the appearance of cracks on the macroscopic surface of the MOC samples due to the volume expansion caused by the hydrolysis of P5 (5Mg(OH)₂·MgCl₂·8H₂O) and the hydration of unreacted active MgO in the samples. The microscopic morphology of the samples changes from needle/gel-like, to flake-like, and finally leaf-like. Simultaneously, the major phase composition turns into Mg(OH)₂. Since the structure of the samples becomes looser and the content of the main strength phase decreases, the overall compressive strength and flexural strength are both reduced. The compressive strength of the MOC slurry samples (0 day) is 93.2 Mpa, and the flexural strength is 16.4 MPa. However, after 18 days of treatment, water molecules reach the center of the MOC samples, and the MOC samples completely lose their integrity. As a result, their compressive and flexural strengths cannot be obtained.