AbstractThe high alkalinity and storage of red mud (RM) make it a major environmental problem. In this paper, the mineral composition, hydration process, and microstructure of red mud-cement based grouting materials (RCGM) are studied by means of the differential thermal analyzer, X-ray diffraction (XRD) diffractometer, isothermal calorimeter, and scanning electron microscope. The action mechanism of RM after thermal activation (TRM) and mechanical activation (SRM) on the mechanical properties of RCGM is summarized, respectively. The results show that a small amount of RM, SRM, and TRM can improve the early strength of RCGM, and the effect of TRM is the best. The RM will reduce the late strength of sample. The SRM and TRM still promote the strength of sample, and the compressive strength of SRM-80 and TRM-80 meet the requirements of grouting engineering. The RM, SRM, and TRM don’t change the hydrate phase of RCGM, and hematite and nepheline mainly play a filling role in the material system. A small amount of RM, SRM, and TRM can promote the hydration process of ordinary portland cement (PC), whereas excessive RM, SRM, and TRM can delay the hydration process of PC. Before hydration heat release for 15 h, the RM, SRM, and TRM can accelerate the reaction rate in the early stage of hydration induction, which is independent of activation mode and dosage on RM. Among them, SRM-20 and TRM-20 have the best effect on promoting hydration. The microstructure analysis shows that RM, SRM, and TRM mainly improve the mechanical properties of RCGM through the microfilling. Mechanical activation and thermal activation can improve the activity of RM, and the effect of TRM is more obvious.