Hydration Mechanism of Sustainable Clinker-Free Steel Slag Binder and Its Application in Mine Backfill

More than 600 million tons of slag are generated globally every year, leading to multiple environmental issues. Thus, research on applications of slags is crucial. The use of steel slag in cement is limited by its low hydraulic activity and volumetric instability. In the current study, we present a clinker-free steel slag binder (SSB) and discuss the coupled alkali–sulfate activation mechanism. The f-CaO was consumed during hydration, thus minimizing the expansion risk. SSB hydration products demonstrated a higher quantity and quality compared with cement, indicating excellent performance. We tested the SSB in a practical mine backfill application, investigating the effects of binder content, concentration, and aggregate grain size on the mechanical and rheological properties of the backfilling mixtures. The results demonstrate the ability of SSB to completely replace Portland cement with half the binder content dose without affecting the strength or flowability of the backfilling mixtures.