Inorganic Acid Resistance Performances of Magnesium Phosphate Cement: A Two-Year Observation

Magnesium phosphate cement (MPC), a cementitious material that hardens through an acid-base reaction, is theoretically expected to exhibit strong acid resistance. However, studies on the durability of MPC in acidic environments remain limited. This study aims to systematically evaluate the acid resistance of MPC in common inorganic acid solutions across various pH levels. By measuring changes in compressive strength, mass loss, apparent changes, pH changes, and the microstructure evolution of MPC under acidic conditions, the mechanisms and influencing factors of its acid resistance are revealed. The results indicate that at pH levels of 1.0 and 2.0, MPC's resistance to H₂SO₄ and HCl erosion is markedly superior compared to its performance against H₃PO₄, as evidenced by compressive strength retention, mass loss, and visible erosion. At pH levels above 2.0, MPC demonstrates robust resistance to all tested corrosive media, with compressive strength retention ranging from 68.9% to 86.9%, irrespective of the acid source. Although new corrosion products form in these acidic environments, the adverse effects of NH₄/P loss from struvite, along with the redissolution of corrosion products due to their higher solubility, increase porosity and subsequently reduce the mechanical strength. Nevertheless, considering that strength retention is significantly higher than that of other cement-based materials reported in the literature, MPC still exhibits good acid resistance and is suitable for environments requiring enhanced resistance to acid corrosion.