A Circular Economy Approach to Cement Production: Integrating Untreated Moroccan EAF Steel Slag for Performance and Sustainability

Partial substitution of ordinary Portland cement (OPC) with supplementary cementitious materials is a key strategy for reducing the clinker factor and associated CO2 emissions from cement production. This study investigates the feasibility of incorporating untreated electric arc furnace steel slag (EAF-SS), collected from a steel plant in Kenitra, Morocco, as a partial replacement of OPC in Portland cement. The material was characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), and particle size distribution (PSD) analysis. Cement blends containing 2–15 wt.% EAF-SS as a replacement of OPC were prepared and tested in accordance with EN standards to evaluate consistency, setting time, density, porosity, and compressive and flexural strengths at 2, 7, and 28 days. Increasing EAF-SS content from 2% to 15% slightly delayed the initial setting time by 3–17 min and reduced early-age compressive strength from 36 MPa for OPC to 26 MPa for the 15% blend at 2 days. At 28 days, mixtures containing 2–5% EAF-SS achieved compressive strengths of 42–52 MPa, satisfying class 42.5R requirements, whereas higher replacement levels (10–15%) reduced strength to 36–39 MPa. Flexural strength decreased from 7.5 MPa for OPC to 5.7 MPa for the 15% blend at 2 days and to 7.3 MPa at 28 days, while density decreased by 2–4% and total porosity increased from 12% to 18% with increasing slag content. Drying shrinkage decreased slightly with increasing EAF-SS content, from 630 µm/m for OPC to 560 µm/m for BC15 at 28 days, suggesting a modest beneficial effect on dimensional stability. The investigated slag exhibited an Fe2O3 content of ~57 wt.%, substantially higher than values commonly reported for many European and Chinese EAF slags. Accordingly, the novelty of the present work lies not simply in the geographical origin of the material, but in the standardized experimental assessment of a compositionally atypical, untreated, Fe-rich EAF steel slag used directly as a partial replacement of OPC in Portland cement. The study is intended as a first performance-oriented evaluation of this Moroccan by-product under EN-based testing conditions, rather than as a complete mechanistic or environmental assessment. These findings support the feasibility of low-level EAF-SS incorporation in blended cement and indicate a potential contribution to clinker factor reduction and associated CO2 savings under the assumptions adopted in this study. However, the environmental benefit assessment remains preliminary and should be confirmed by full life-cycle and leaching analyses.