Understanding the role of fillers in the hydration of citrate-activated BOF slag binder using PARC analysis

This study investigates the hydration of basic oxygen furnace (BOF) slag pastes activated with tri-potassium citrate and the role of fine limestone and quartz fillers. Quantitative XRD, SEM–EDX with PARC, and mass balance modelling were combined to follow phase reactivity and hydrate formation. Brownmillerite (C₂F) and C₂S were identified as the main reactive phases. At 7 days, both contributed equally to hydrogarnet and C-S-H formation, while by 56 days C₂S became dominant. Fillers modified this balance: limestone mainly increased the overall hydrate content without altering the assemblage, whereas quartz enhanced late C₂S reactivity, raising C-S-H and hibschite proportions and lowering katoite. Hydrogarnets remained the major hydration product throughout, with a shift from katoite to silica-rich compositions over time. Deviations between modelled and experimental volatile contents highlight the influence of carbonation and variable hydrate stoichiometry, which are not captured in the current model.