Waste Valorisation: Copper Slag as a Sustainable Replacement of Natural Aggregates for Concrete

The copper industry generates approximately 24.6 million tons of copper slag (CS) annually, equivalent to about 2.2 tons of CS per ton of copper produced, creating a major waste management challenge. Meanwhile, concrete is one of the most widely used construction materials worldwide, with nearly 11 billion tons produced each year. This high demand requires large volumes of natural aggregates, leading to environmental impacts associated with their processing and transportation. This study evaluates mortar and concrete mixtures incorporating CS to assess the feasibility of valorising this industrial waste as an alternative aggregate in cementitious materials. The experimental programme included in this study tests to determine the workability and mechanical properties for different aggregate replacement ratios. The results show that replacing 40% of the fine aggregate with CS improves mortar performance, increasing compressive and flexural strength by at least 13.9% compared with reference mixtures. For concrete, up to 100% aggregate replacement was feasible, achieving compressive strength gains of up to 11.9%. Given that aggregates represent about 70–80% of the concrete volume, the incorporation of CS offers a promising strategy for large-scale waste valorisation and natural resource conservation.