The potential usage of waste ferrochrome slag in alkali-activated mixes

Ferrochrome slag (FCS) is a by-product of the stainless-steel industry which is mostly discarded in landfills without being efficiently utilized. The production of industrial solid wastes like FCS has been increasing for several decades and escalating the environmental risks associated with them. To address this issue, this study concentrated on the usage of FCS as a partial substitution for blast furnace slag (BS) in manufacturing alkali-activated paste and mortar. BS was replaced with FCS in varying proportions up to 30% (wt.%) and activated with varying Na2O dosages. The fresh, physical, mechanical, and microstructural properties were investigated. The test outcomes indicated that FCS incorporation was beneficial in improving the flowability by consistently reducing both yield stress and plastic viscosity more than 54% and 70%, respectively, when FCS replacement was 30%. Furthermore, the inclusion of FCS alleviated the rapid setting issue of BS-based alkali-activated systems by delaying the setting times. The increase in Na2O concentration remarkably decreased the water absorption, open porosity and capillary sorptivity of the mortars, while no adverse effect was observed on the physical properties of the mortars with the FCS addition. The compressive strength of mortars increased between 152% and 254% when Na2O dosage was increased from 4% to 8%, while strength was mostly preserved with the addition of FCS. The higher Si/Al atomic ratio and the higher pH values was found favorable for the higher compressive strength of the mixes. The primary reaction product was found as C-A-S-H gels, whereas FCS addition increased the crystalline phases and favored the formation of M-A-S-H gels.