Synergistic effects of red mud, phosphogypsum and rice husk ash in cement

Red mud, a primary by-product of alumina production, poses significant environmental challenges due to its alkalinity and low hydraulic activity. This study investigates the synergistic modification of red mud with phosphogypsum and rice husk ash for use in cement mortar. Mechanical properties and microstructure were evaluated by strength tests and FTIR, XRD, and FE-SEM analyses at 3, 7, and 28 days of hydration. Results indicate that replacing 5% of cement with G2-modified red mud yields optimal performance. The 7-day compressive strength of G2-5 reached 38.15 MPa, a 20.7% increase over the reference mortar (CK, 31.6 MPa). Even at a 10% replacement level, the modified mortar meets relevant strength requirements. Early-strength enhancement is mainly attributed to the synergistic effects of phosphogypsum and rice husk ash, which promote calcium hydroxide consumption and improve matrix densification. Overall, this study demonstrates a feasible and sustainable approach for utilizing red mud in cement-based materials.