Investigating Pozzolanic Reactivity of Ground Ferronickel Slag Through the R3 Test for Its Potential Use as Alternative Supplementary Cementitious Material

This study investigates the pozzolanic reactivity of ferronickel slag (FNS), the fourth most discharged smelting by-product in China. Cumulative heat of hydration (R3) tests were conducted on FNS with varying fineness levels (111.27 to 4.5 μm) to compare its performance with conventional supplementary cementitious materials (SCMs). The R3 results ranged from 34 to 132 J/g, increasing with finer particle size. Notably, the coarsest FNS showed reactivity similar to quartz filler (34 J/g), while the finest sample exhibited a 3.9-fold increase, though still only half that of fly ash (222 J/g). Similar trends were observed in bound water content and portlandite consumption. Calcium silicate hydrate (C–S–H) was the sole reaction product detected, indicating a pozzolanic reaction. Finer FNS particles enhanced the initial dissolution of Si and Mg, with dissolved silicon playing a key role in C–S–H formation. Despite magnesium being a major component of FNS, its dissolution remained limited (< 2.1 mg/L). A mortar strength test further validated the limited reactivity of FNS, showing a modest reduction in strength when 25% FNS was incorporated. These findings highlight that while grinding improves FNS reactivity, it remains less effective than conventional SCMs, suggesting the need for additional activation methods to enhance its performance.