Up cycling of steel slags in cement production

Abstract

Steel slag, a by-product of the steelmaking process, poses significant environmental challenges due to its large volume and potential for environmental harm if improperly managed. This research explored the feasibility of integrating steel slag as a raw material in cement production, with a focus on its chemical composition, physical properties, and performance in cementitious applications. Randomly sampled steel slag was mixed with pozzolana, gypsum, and clinker in varying proportions, replacing clinker at percentages ranging from 5% to 20%. The formulated mixtures were then milled into a fine powder using a ball mill to produce steel slag cement. The chemical composition and fineness of the resulting cement were determined using X-ray fluorescence (XRF) analysis and the Blaine test, respectively. Cement paste and prisms were subsequently prepared to evaluate the physical properties of the cement. The standard consistency, setting time, and soundness of the cement paste were assessed using the Vicat apparatus which determines the water content, and Le Chatelier’s test which determines the expansion extent. Additionally, the compressive and flexural strengths of the cement prisms were measured using a universal testing machine. The chemical composition of slag and other raw materials showed high concentrations of CaO, SiO2, and Al2O3, with variations across samples. Fineness of cement increased with steel slag, enhancing early hydration but not necessarily strength. Consistency decreased with increase in steel slag, reducing water demand. The initial and final setting times for cement samples increased with increase in steel slag, giving a peak time at 20% slag with 301.5 and 405 minutes, correlating with the SiO2/Al2O3 ratio and cement particle size. Compressive and flexural strengths generally decreased with decrease in steel slag, though some improvements were noted at 28 days. Results showed that the chemical properties of steel slag were found to be similar to standard cement raw materials as outlined in US EAS 148-2, 2017 standard and physical tests confirmed that steel slagbased cements meet established standards for setting time, soundness and compressive strength as per US EAS 18-1, 2017 standard. Steel slag can be effectively used in cement production up to 15% by mass. Further studies are recommended for alternative soundness testing methods to accurately assess MgO-induced expansion, as well as performing a cost-benefit analysis to evaluate the financial viability of replacing clinker with steel slag in cement production.