The effect of cupola furnace iron slag on the physical and mechanical properties of alkali-activated fly ash-based mortars

Abstract This study investigates the physical and mechanical properties of alkali-activated mortars, in which thermal power plant fly ash (FA) was partially replaced by cupola furnace iron slag (IS). An optimal mix design determined through preliminary tests consisted of an aggregate-to-binder ratio of 1.5 (by weight), NaOH solution concentration of 10 M, Na₂SiO₃ (liquid) to NaOH (solid) ratio of 2, and a water-to-binder ratio of 0.3, all maintained consistently across mixtures. Chemical compositions and phase structures of raw materials were characterized using X-ray fluorescence (XRF) and X-ray diffraction (XRD), respectively. Particle size distribution was determined by laser diffraction analysis, and microstructural morphology was examined using scanning electron microscopy (SEM). Bulk density and apparent porosity were measured using Archimedes’ method with water as the immersion medium. Mechanical properties were evaluated through compressive strength and three-point bending tests after 28 days of curing. Results showed that mortars incorporating 75 wt% cupola furnace iron slag as a fly ash replacement exhibited superior performance, achieving a bulk density of 2118 kg/m³, apparent porosity of 12.2%, compressive strength of 44 MPa, and flexural strength of 10.2 MPa. These findings highlight the potential of iron slag as an effective supplementary material in alkali-activated mortars, enhancing mechanical properties and contributing to microstructural densification.