Effect of Curing Conditions on the Properties of Magnesium Phosphate Cement and its Bonding Properties with Cement Mortar

Abstract

Magnesium phosphate cement (MPC) can be used as a rapid repair material due to its excellent mechanical properties and high bonding strength. However, the properties of MPC are significantly influenced by the environment but have been poorly studied in previous research. This paper researched the effects of four curing conditions on the properties and microstructures of hardened MPC, and the bonding mechanism between the MPC and OPC mortar was also investigated. The experimental results showed that water conditions decreased the mechanical strength and bonding strength compared to standard conditions, increasing the volume of large pores due to the dissolution of hydration products. Meanwhile, the phosphate hydrates were highly soluble in the alkaline solutions, leading to a significant increase in total porosity, but the compressive strength and bonding strength were not decreased due to the physical filling effect and chemical reaction of Ca(OH)₂. Additionally, the high temperature inhibited the hydration process of MPC, enhancing the decomposition of the main hydration product, and the bonding strength sharply decreased. Finally, the bonding mechanism between MPC and OPC included mechanical interlocking and chemical reactions. The former lost its effect in the heat due to the cracks and broken interfaces, and the latter was diminished in the wet environment for the phosphate was more likely to dissolve in the water instead of penetrating into the OPC phase. Therefore, the MPC is not suitable for wet environments and high-geothermal environments.