Sustainable synergies: Performance evaluation of cement mortar with red mud and industrial by- products

This study examines the potential of red mud, a by-product of the alumina industry, as a partial replacement for cement in mortar, aiming to advance sustainable construction in line with UN SDGs 9, 11, and 12. Red mud was incorporated at 10–90 % by weight, together with 4 % Ground Granulated Blast Furnace Slag (GGBS) or 4 % fly ash as supplementary cementitious materials. The mixes were tested for compressive strength, flexural strength, water absorption, apparent porosity, and bulk density at 3, 7, and 28 days. The optimum performance was achieved with 30–40 % red mud and GGBS, yielding a 28-day compressive strength of 19.29 MPa and flexural strength of 4.55 MPa, outperforming both control and fly-ash-based mixes. Higher red-mud levels increased water absorption (approximately 18 %) and porosity (approximately 15 %). Microstructural analyses (SEM-EDX, XRD, FTIR) confirmed the formation of Calcium Silicate Hydrate (C-S-H), Calcium Aluminate Hydrate (C-A-H), and ettringite phases. The research introduces a novel tri-component binder system (cement-red mud-GGBS/fly ash) that transforms industrial waste into a durable, low-carbon construction material, promoting resource circularity and carbon reduction.