Fabrication of high-strength, water-resistant homogeneous magnesium oxysulfate cement via synergistic modification with citric acid and sodium alginate

Despite its status as a low-carbon and environmentally friendly cement, the limited mechanical stability and water resistance of magnesium oxysulfate (MOS) cement have constrained its broader application and development. This study comprehensively investigates the synergistic effects of citric acid (CA) and sodium alginate (SA) modifications on MOS cement. The results demonstrate that incorporating a combination of 1.2 % CA and 0.4 % SA into MOS cement significantly enhances its mechanical strength and water resistance. Specifically, the 28-day compressive strength increased from 34.66 MPa to 83.71 MPa, representing an improvement of 141.5 %, while the softening coefficient improved from 0.44 to 0.89, corresponding to an increase of 102.3 %. Furthermore, the sedimentation stability of modified MOS cement was significantly improved, with the standard deviation of longitudinal density decreasing from 44.25 kg/cm3 to 9.48 kg/cm3 . The modification mechanism involves the ionization of H+ from CA, which inhibits the formation of Mg(OH)2, while its hydroxyl and carboxyl groups chelate with Mg2+, promoting the substantial formation of 5Mg(OH)2 & sdot;MgSO4 & sdot;7 H2O and enhancing the mechanical properties of the MOS cement. Meanwhile, SA forms a three-dimensional gel network with Mg2+ in the system, filling large pores and improving both the water resistance and sedimentation stability of the MOS cement. This synergistic modification strategy successfully develops MOS cement with excellent comprehensive performance.