Research progress on the water resistance of magnesium phosphate cement-based composites

Abstract

Magnesium phosphate cement (MPC), a novel cementitious material characterized by rapid setting and high early strength, shows great promise in the field of rapid infrastructure repair. However, its poor water resistance limits further development and broader application. This paper focuses on the water resistance of MPC by systematically analyzing its hydration mechanism and products and reviews research conducted over the past decade on influencing factors and improvement measures. Studies have shown that in terms of mix proportions, an optimal magnesium oxide to phosphate (M/P) molar ratio of 4:1 to 5:1 and a water-to-cement ratio of approximately 0.16 result in better water resistance. Regarding mineral admixtures, materials such as fly ash, metakaolin, slag, steel slag, sintered sludge ash, and red mud can enhance water resistance by filling pores and participating in hydration reactions. As for chemical admixtures, waterproofing agents, retarders, and inorganic salts can improve water resistance by forming hydrophobic layers, promoting the formation of crystalline products, or filling capillary pores, respectively. In terms of curing conditions, it is crucial to avoid humid environments during the curing stage, and extending the curing period under natural conditions before immersion in water also contributes to improved water resistance. These findings provide innovative insights for enhancing the water resistance of MPC and expanding its potential engineering applications.