Enhancing concrete performance with steel slag aggregate: an experimental investigation

The utilisation of steel slag (SS) waste, a by-product of steel manufacturing, as a partial replacement for natural aggregate (NA) in concrete was investigated, aiming to reduce environmental issues such as land occupation and water pollution, while minimising the ecological footprint of NA production. Twelve concrete mixes were prepared with steel slag coarse aggregate (SSCA) replacing 10–60% of NA and steel slag fine aggregate (SSFA) replacing 10–50% of NA in 10% increments. The mechanical, durability and microstructural properties of the concretes were evaluated. The results indicate that the optimal replacement levels were 40% SSCA and 30% SSFA. At 90 days, compared with conventional concrete, the compressive strength increased by 22.8% with 30% SSFA and by 8.6% with 40% SSCA. Split tensile and flexural strengths were also improved, showing gains up to 12.7% and 11%, respectively. The modulus of elasticity increased by 6.10% and 5.44% for the mix with 30% SSFA and the mix with 40% SSCA. Durability assessments revealed reduced chloride ion permeability (20–30%), lower strength loss under acid attack (23–26%) and decreased deterioration from sulfate exposure (16–20%). Scanning electron microscopy and X-ray diffraction analyses confirmed enhanced interfacial transition zones and the formation of cementitious phases (C₃S and C₂S). Overall, the results indicate that incorporating SS as aggregate enhances performance and promotes sustainable concrete production.