Performance Evolution and Degradation Mechanism of Chemically Bonded Phosphate Ceramic Cement Under Freeze–Thaw Cycles

This study investigates the performance variations in chemically bonded phosphate ceramic (CBPC) cement under different media (water and 3% NaCl solution) environments subjected to varying numbers of freeze-thaw cycles, including changes in compressive strength, mass loss rate, phase composition, microstructure, external pH, and ion concentration, with the aim of elucidating its long-term durability degradation mechanisms and microstructural evolution. The results show that both the mass and compressive strength of CBPC cement first increase and then decrease with increasing freeze-thaw cycles. After 400 cycles, the compressive strength decreases by 29.91% in water and 25.16% in salt solution. The pH value rises with cycling, along with increased concentrations of K⁺, Mg²⁺, and PO₄^3-, while Na⁺ and Cl^- concentrations decrease in salt solution. XRD/Rietveld analysis reveals that the content of MgKPO₄·6H₂O decreases from 28.1% to 19.5% (water) and 20.7% (salt), with a gradual reduction in crystallinity. TG/DTG and FTIR results confirm these findings, showing extensive microcracking in hydration products, which aligns with the observed macro-performance changes.