Design and evaluation of magnesium phosphate cement mortar protective layer for concrete structure protection in salt lake environment

Abstract

Magnesium phosphate cement (MPC) is recognized as an ideal material for concrete protection in salt lakes due to its rapid hardening, high early strength, good bonding, and volume stability. In this study, the MPC mortar was modified with mineral admixtures and polymers and its performance under simulated salt lake conditions was tested. The modified MPC mortar showed better volume deformation compatibility: after 90‑day immersion and wet‑dry cycles, linear expansion rates were 0.6 × 10−4 and 1.4 × 10−4, respectively. It also demonstrates excellent bonding performance with Portland cement mortar substrates. After long immersion, flexural and shear bond strength retention exceeded 94% and 83%, and remained above 79% and 72% after wet–dry cycles, respectively. The MPC layer reduced mass change, water absorption, chloride migration (>65%), and sulfate content in the 0–5 mm surface layer (∼50%). The filling effect of admixtures and the film‑forming effect of polymers jointly enhanced compactness and protective performance.