Performance of magnesium oxysulfate cement modulated by magnesium salt anions: Hydration products, microstructure, and stability analysis

Magnesium oxysulfate (MOS) cement is a cementitious material formed through the hydration reaction of light-burnt magnesia and magnesium sulfate solutions as the primary raw materials. During the construction process, harmful anions are easily introduced into MOS cement, affecting the formation of the main hydration product 517 phase. Therefore, to improve the adaptability of MOS cement to harmful anions and complex environmental changes, this study investigated the effects of adding magnesium salts containing various anions (Mg(OH) 2 , Mg(HCO 3 ) 2 , MgCl 2 ·6 H 2 O, Mg(NO 3 ) 2 ·6 H 2 O and MgHPO 4 ·3 H 2 O) on the properties of a hardened paste of magnesium oxysulfate (MOS) cement. Research has shown that the introduction of low levels of exogenous anions does not significantly disrupt the structure of the main hydration product 517 phase in MOS cement but rather promotes the formation of amorphous phases within the system. In the specific doping-modified MOS system, the grain size of the 517 phase changes, the stability of the material is enhanced, ion leaching is reduced, and the material has excellent compressive strength. X - (Cl - , HCO 3 - , NO 3 - , HPO 4 2- , OH - ) can partially replace SO 4 2- in the original structure of the 517 phase to form a phase similar to ‘X-517.’ The microstructure is reconstructed. In summary, the type and dosage of magnesium salt containing different anions have been demonstrated to have a significant effect on the hydration behavior, phase structure evolution and macroproperties of MOS cement systems.