Effect of aluminum dihydrogen phosphate in enhancing mechanical properties and water resistance of magnesium phosphate cement

Abstract

Incorporating aluminum dihydrogen phosphate into magnesium phosphate cement (MPC), including magnesium ammonium phosphate cement (AMAPC) and magnesium potassium phosphate cement (AMKPC), significantly enhances both compressive strength and water resistance. The results show that AMAPC-3 exhibited a remarkable increase in compressive strength, maintaining a compressive strength retention ratio of 0.83 after 60 days. The addition of aluminum dihydrogen phosphate introduced extra phosphate ions that facilitated the hydration of unreacted MgO, resulting in an increased formation of hydration products such as struvite and k-struvite. Furthermore, it participated in independent hydration reactions, generating new phase Al(OH)₃ gel and Al(PO₄)·2H₂O gel, which contributed to a denser microstructure. Microstructural analysis confirmed a refined pore structure and reduced porosity in the modified cements. These findings position aluminum dihydrogen phosphate as an effective modifier for enhancing the water resistance and mechanical properties of MPCs.