Innovative enhancement of self-compacting concrete using varying percentages of steel slag: an experimental investigation into fresh, mechanical, durability, and microstructural properties

Self-Compacting Concrete (SCC) is a highly flowable concrete that can spread into place, fill formwork, and encapsulate reinforcement without mechanical consolidation. This study investigates the use of steel slag as a partial replacement for fine aggregate in SCC, with replacement levels ranging from 0 to 70%. Eight different mixes were prepared and tested for their fresh, mechanical, durability, and microstructural properties. Materials used include Ordinary Portland Cement (OPC) conforming to IS 269:2015, natural river sand, crushed granite, steel slag, potable water, and a polycarboxylate ether superplasticizer. The concrete mix design was based on IS 10262:2019 and EFNARC guidelines for SCC. Fresh properties were assessed using slump flow, T50 time, V-funnel, and L-box tests following EFNARC specifications. Mechanical properties were evaluated through compressive strength, splitting tensile strength, and flexural strength tests. Durability properties were assessed by water absorption, sulfate attack resistance, and freeze-thaw cycle tests. Microstructural properties were analyzed using Scanning Electron Microscopy (SEM), Thermogravimetric Analysis (TGA), and X-Ray Diffraction (XRD). The results indicate that a 50% replacement level of steel slag optimizes the properties of SCC, leading to enhanced flowability, higher compressive strength (up to 59.3 MPa at 28 days), and improved durability against sulfate attack and freeze-thaw cycles. The microstructural analysis confirmed a denser matrix with increased formation of calcium silicate hydrate (CSH) at this optimal replacement level. These findings suggest that incorporating steel slag into SCC not only enhances its performance but also contributes to sustainable construction by reducing the need for natural aggregates and utilizing industrial byproducts.