Utilisation of Ferrochrome Slag for Partial Cement Replacement Technical Evaluation and Life Cycle Assessment of Water-Based and Alkali-Activated Systems

Abstract

The high greenhouse gas emissions associated with cement production, together with increasing industrial residue generation, create a need for alternative binder materials. Ferrochrome slag (FCS) is generated in large quantities during high carbon ferrochrome production but currently exhibits limited utilisation potential due to low reactivity and chromium-related concerns. This study therefore evaluated processed ferrochrome slag (PFCS) as a partial cement replacement in water-based and alkali-activated cementitious systems. To improve the utilisation potential of FCS, PFCS was produced through slag treatment, water granulation, drying, and grinding to increase the amorphous phase content and reduce chromium-containing phases. Binder systems containing 10– 30% PFCS were initially screened using Vicat setting time measurements. Based on the screening results, systems containing 20% PFCS were further evaluated using isothermal calorimetry, BET, SEM, compressive strength, and Cr(VI) leaching. To evaluate the environmental performance of the selected mortars, a life cycle assessment (LCA) was performed. The experimental results showed that the 20% PFCS + Water systems exhibited hydration development similar to the cement reference despite prolonged setting behaviour, indicating participation of PFCS in the hydration reactions. Alkali activation further increased PFCS participation and resulted in higher cumulative heat release, although delayed hydration development was observed. Results from the environmental assessment further showed that PFCS incorporation reduced global warming potential compared with the cement reference. The water-based PFCS system showed the most favourable balance between hydration behaviour, chromium stability, and environmental performance. However, PFCS processing increased freshwater ecotoxicity impacts as a result of FeSi consumption during slag treatment. Alkali activation additionally increased chromium release together with surplus ore potential and freshwater ecotoxicity impacts associated with alkali activator and PFCS production. Overall, the results indicate that PFCS shows potential for partial cement replacement, although optimisation of processing and activation conditions is required to balance technical performance, chromium stability, and environmental impacts.