Engineering assessment of sustainable building concretes with red mud and copper slag: mechanical performance, heavy metal leaching and radiological evaluation

The decarbonisation of the cement sector requires the adoption of supplementary cementitious materials, many of which remain underexplored despite accumulating in large volumes in landfills. From a sustainable engineering perspective, valorising these resources is key to advancing low-carbon building practices. This study investigates the use of industrial by-products – red mud and copper slag – in Portland cement–based and alkali-activated concretes to evaluate their suitability for building and civil engineering applications. Mechanical performance, heavy metal leachability under different aqueous environments, and radiological protection aspects were assessed. Concretes were produced with siliceous and granitic aggregates, the latter requiring careful engineering evaluation due to naturally occurring radioactive elements. This work contributes to addressing a knowledge gap, as it provides a combined engineering assessment of heavy metal leaching and radiological behaviour in red mud and copper slag concretes for building use. Leached heavy metal and radionuclide concentrations remained below regulatory limits for all formulations, confirming their safety as building materials. Portland cement, blended, and 100% slag alkali-activated concretes achieved compressive strengths of ∼30 MPa, suitable for structural building and civil engineering applications. Mixes containing red mud and slag reached 18–23 MPa, appropriate for non-structural building components. These results support the safe use of red mud and copper slag as sustainable engineering materials for low-carbon building construction.