Hydration analysis of phosphogypsum cementitious materials: mechanisms of mechanical property changes under water resistance experiments

Phosphogypsum is restricted as a building material because of its poor water resistance. In this study, phosphorus building gypsum, cement, and lime were used as the main materials, and water reducer and retarder were used as additives to prepare phosphorus gypsum cementitious materials under low water–cement ratio. Concurrently, the mechanical properties and hydration mechanism of phosphogypsum cementitious materials were investigated during both hydration and soaking processes, alongside a discussion on optimization strategies for enhancing their water resistance. The findings indicate that under low water–cement ratio conditions, rapid hydration of a substantial amount of phosphorus building gypsum occurs, leading to the formation of a spatial skeleton and significant enhancement in compressive strength. Some segments of the phosphorus building gypsum hydration process experience delay or cessation, while certain constituents of cement are densely packed, forming a compact system. Submerging in clear water gradually provides an adequate water environment, allowing for complete hydration of both phosphorus building gypsum and cement components, effectively filling the pores. Water immersion results in a material loss in the phosphogypsum cementitious system, leaving the pores formed after dissolution incompletely filled. In low water–cement ratio phosphogypsum cementitious systems, the secondary hydration process avoids exposure to a flowing solution environment, thereby circumventing material loss and achieving a complete and dense phosphogypsum cementitious system.