Investigating the Mechanical Properties of Self-compacting Concrete with Partial Replacement of Red Mud and Iron Slag

The pursuit of eco-friendly construction materials has encouraged the incorporation of industrial by-products as substitutes for conventional cement and aggregates. This research examines the fresh and mechanical behaviour of M25 grade self-compacting concrete (SCC) by introducing red mud (RM) as a partial replacement for cement and iron slag (IS) as a substitute for fine aggregates. One control mix and five modified mixes were prepared, with RM content varying from 5–25% and IS from 10–50%. Workability characteristics were studied through slump flow, T₅₀, V funnel, and L-box tests, in accordance with EFNARC guidelines, while the hardened properties were assessed through compressive, split tensile, and flexural strength tests at curing periods of 7, 28, and 56 days. The findings revealed that the mix containing 5% RM and 10% IS (M1) showed the most favourable balance of workability and strength, slightly outperforming the control mix. The blend with 10% RM and 20% IS (M2) achieved comparable strength to the control, whereas higher substitution levels (M3–M5) caused gradual reductions in both fresh and hardened properties. Even so, all mixtures satisfied the minimum strength criteria for M25 grade concrete. It was concluded that the optimum replacement level is 5% RM with 10% IS, beyond which the performance deteriorates, making higher proportions unsuitable for structural applications. The incorporation of RM and IS thus not only improves the sustainability profile of SCC but also contributes to the effective management of industrial waste in construction.