Strength Characteristics and Micro-Mechanism of Silty Soil Modified by Red Mud Co-Cement

Red mud (RM) is a kind of solid waste produced during the bauxite refining process, which can cause significant environmental pollution when stored in large quantities. To address this issue and to improve the reuse rate of RM, this study investigates the feasibility of using RM as a roadbed filling material, specifically in combination with cement, using modified silty sand (P.O-RMS). Therefore, mechanical and microscopic tests are conducted with different RM contents ( W RM ), cement contents ( W P.O ), and curing ages to analyze the P.O-RMS′ strength, deformation characteristics, and microstructure formation mechanism. Additionally, the radioactivity and heavy metal concentrations of P.O-RMS are also detected. Mechanical test results showed that the unconfined compressive strength (UCS) of P.O-RMS does not increase monotonically with the increase of W RM , and the peak strength appears at W RM = 20%. Although adding RM has a negative impact on the toughness of P.O-RMS at the initial curing ages of 7 days and 28 days, they still meet the requirements of the Chinese standard for high-grade highway base strength. Scanning electron microscope testing shows that the gel products produced by cement hydration increase with the amount of RM, and reach their maximum at W RM = 20%. Therefore, W RM = 20% is recommended as the optimum admixture of P.O-RMS. The usage of RM as a filling material for roadbed construction in this study not only aligns with the principles of sustainable development, but also provides a crucial theoretical foundation for the effective utilization of RM resources.