Recycling electric arc furnace slag through tailoring of ambient-cured alkali-activated mortar mix using hybrid AHP-GRA and TOPSIS

Utilizing Electric arc furnace slag (EAFS) as a precursor for alkali-activated mortar production reduces waste and supports alternative cement binders. Since the mix design includes multiple factors, the Taguchi DoE was employed by varying the modifier (fly ash) to precursor (EAFS) ratio (0–75% by mass), activator to precursor ratio (A/P) (0.52–0.66), sodium hydroxide (SH) concentration (8–14 M), and sodium silicate to sodium hydroxide ratio (SS/SH) (1.5–3.0). Analytic hierarchy process (AHP) weighted Grey relational analysis (GRA), and technique for order preference by similarity to ideal solution (TOPSIS), were utilized to achieve a high performing mix. Performance characteristics encompass flowability (flow%), final setting time (FST), compressive strength (f'_cu), and flexural strength (f'_cr). The optimized mix possessed 75% flowability, 575 min FST, 38 MPa f'_cu, 16 MPa f'_cr, and 3.75% water absorption. Precursor-to-modifier ratio dominates the mix design. The three mixes—optimized (M17), top-ranked (M8), and least-ranked (M1) were micro-structurally examined using powdered X-ray diffraction, X-ray fluorescence, scanning electron microscopy, energy dispersive X-ray spectroscopy, and Fourier transform infrared spectroscopy.