Mechanical and microstructural analysis of cemented tailings backfill by copper slag through alkaline activation emphasizing red mud

Copper slag (CS) exhibits pozzolanic activity in alkaline cementitious systems, making it a suitable supplementary cementing material for cemented tailings backfill (CTB) with reduced carbon emissions. However, its utilization is constrained by the unacceptable cost of alkaline materials, e.g., NaOH and CaO. In this paper, the CTB bound by CS activated using red mud (RM) has been investigated through mechanical and microstructural analysis. The results show that RM content and curing time significantly affect UCS development throughout the CTB life cycle. The CTB containing 1.5 % RM and 3 % RM exhibit lower strength values at 28 d compared to the control group without RM, measuring 3.07 MPa and 2.65 MPa, respectively. Despite this reduction, the cost calculation confirms that using RM as a partial substitute for NaOH reduces the CTB cost by approximately 50 %. Microstructural analysis reveals that the RM particles in CTB were bonded together by gels, and the amounts of gels on the surface of the aggregated particles and other crystals increased with the increasing RM contents. Further, its strong alkalinity facilitates the decomposition of Al monomers from RM and partially replaces Si in the C-S-H gel to form C-A-S-H gel. This study corroborates the feasibility of preparing CTB bound by CS activated using RM, providing new insights into the application of RM and CS.