Study on phase stability of magnesium oxychloride cement

Enhancing the stability of magnesium oxychloride cement (MOC) will allow greater production and application of magnesium oxychloride cement.The formation,solution and phase change of hydration products in an MgO-MgCl2-H2O system were analyzed by the thermodynamics method.Experiments were done testing resistance of the concrete to immersion in water and examining the phase change rules for the curing of magnesium oxychloride cement at various MgO/MgCl2 molar ratios.The results showed that pH values of solutions in which MOC concrete is immersed clearly influenced phase stability of hydration products.A higher pH value led to lower solubility and better phase stability of hydration products.When the solution's pH value was higher than 10.37,the precipitation of a significant volume of Mg(OH)2 crystals decreased phase stability of hydration products.With increased MgO/MgCl2 molar ratio (lower than 6),increased MgO in the hydration products enhanced the alkalinity of the solution and phase stability was improved.However,when the MgO/MgCl2 molar ratio was higher than 6 excessive MgO existed in the hydration products.Such concrete may be damaged by the excessive crystallization stress of a great deal of Mg(OH)2 formation.