Synergistic Effects of EAF Slag Aggregate, Silica Fume, and Fibers on Mechanical and Microstructural Performance of Sustainable Concrete

This study evaluates concrete in which natural aggregates (NAs) are replaced by electric arc furnace (EAF) slag siderurgical aggregate (SA), with partial cement replacement by silica fume and reinforcement using steel and polypropylene fibers. Mechanical tests (compressive and flexural) at 7, 28, and 90 days and microstructural analyses (SEM/EDS) of the interfacial transition zone (ITZ) were conducted. Optimal mixes containing 8% silica fume and 0.6% fiber volume exhibited an average ITZ thickness reduction from 27.8 ± 3.2 μ m (control) to 15.4 ± 2.1 μ m ( n = 20 fields), and compressive strength gains of up to 21% at 28 days (and up to 30% at 90 days for SA-C-100 mixes). Statistical significance was assessed using one-way ANOVA. These results demonstrate the synergistic effect of SA, silica fume, and fibers on densifying the ITZ and improving flexural toughness, and provide practical recommendations for mass concrete applications.