Olive Pomace Fly Ash as an Alternative Alkaline Activator for Electric Arc Furnace Slag for Sustainable Cementitious Materials

Abstract

This study analyzes the potential of olive pomace fly ash (OPFA) as an alternative alkaline activator for electric arc furnace slag (EAFS) in the manufacture of sustainable cementitious materials. Cements were prepared by replacing 30–50 wt% of EAFS with OPFA and compared with control cements activated with potassium hydroxide (KOH) at concentrations of 4 and 8 M. Cements were characterized by bulk density, water absorption, total porosity, compressive and flexural strength, as well as analytical techniques such as XRD, FTIR and SEM-EDS. The results reveal that the incorporation of 40 wt% OPFA provides optimum properties, reaching maximum compressive and flexural strengths of 20.0 MPa and 5.7 MPa, respectively, after 28 days of curing. These improvements are attributed to the increased formation of C,K-A-S-H gel, which incorporates Fe, the main reaction product that densifies the matrix and reduces porosity. However, 30 wt% OPFA provides insufficient alkali content, which limits the reaction, while excess alkali at 50 wt% OPFA reduces mechanical performance due to unreacted residues and increased interconnected porosity. Compared to KOH-activated cements, which achieve maximum flexural and compressive strengths of 4.4 and 9.5 MPa (EAFS/KOH-8M binders), the results confirm the potential of OPFA as an alternative activator, with significant sustainability advantages.