Experimental and empirical assessment of concrete containing treated steel slag as coarse aggregate

The sustainable utilization of industrial by-products in concrete is gaining prominence due to the depletion of natural resources and environmental concerns. This study investigates the use of treated steel slag as a partial replacement of natural coarse aggregate in M25 grade concrete, focusing on mechanical properties, durability performance, microstructural characteristics, and empirical modeling. Concrete mixes with 0-50% steel slag replacement were evaluated for compressive, split tensile, and flexural strengths at 7, 14, and 28 days, while durability assessments included water absorption, rapid chloride penetration, and resistance to sulfate, acid, and alkaline exposure. Microstructural analyses using XRD, FTIR, SEM, and EDAX revealed that slag treatment stabilizes free CaO/MgO, enhances C-S-H gel formation, and improves aggregate-paste bonding. Results indicate that 30% steel slag replacement yields optimum performance, with maximum compressive (28.25 MPa), tensile (2.98 MPa), and flexural strength (3.73 MPa), coupled with enhanced durability due to matrix densification and reduced porosity. A quadratic regression model effectively predicted compressive strength, confirming the experimentally determined optimum. Overall, the study establishes that treated steel slag is a viable, sustainable coarse aggregate substitute, improving both the mechanical and durability performances of structural concrete while promoting circular economy principles in construction.