Effect of red mud and citric acid on the mechanical properties and water resistance of magnesium oxychloride cement

Methods The effect of varying RM/C ₆ H ₈ O ₇ contents on the setting time, compressive strength, water resistance, and microstructure of RM-MOC was analyzed. Results: The addition of RM/C6H8O7 prolonged the setting time and enhanced water resistance, though it reduced mechanical strength. Mechanistic analysis revealed that RM reduced Phase 5 formation in RM-MOC, whereas C ₆ H ₈ O ₇ facilitated the generation of M-S-H and Mg-Cl-Si-Al-H gels with homogeneous structure and high polymerization. These gel refine the pore structure and densify RM-MOC, thereby improving water resistance and compensating for the strength loss due to reduced Phase 5. Under the synergistic action of RM and C ₆ H ₈ O ₇ , RM-MOC achieves a compressive strength of 59 MPa and softening coefficients of 0.8 (7 d) and 0.78 (14 d) even at a high RM proportion of 60%, demonstrating effective waste valorization and simultaneous enhancement of material properties. Conclusions: This study provides a novel strategy for developing high-performance, low-cost, and environmentally friendly magnesium cement materials.