Rheological and Strength Properties of Steel-Slag Cemented Paste Backfill: Link to Gypsum Type and Dosage

This paper aims to study the effects of gypsum type and dosage on the rheological and strength properties of steel-slag cemented paste backfill (SSB-CPB) using fluorogypsum (FG), phosphogypsum (PG), and desulfurization gypsum (DG). Experimental results indicate that the yield stress and the viscosity of fresh SSB-CPB are the smallest when using FG, followed by PG, and the highest when using DG. The strength of hardened SSB-CPB is the lowest when using PG, regardless of curing time, and is the highest when using DG after 3 and 7 days of curing or FG after 14 and 28 days of curing. With the increase of DG dosage, yield stress and viscosity of fresh CPB increase, while the strength of hardened CPB first increases and then decreases. For the rheological properties, the zeta potential changes the yield stress of fresh SSB-CPB, while the internal particle size and pH affect its viscosity. For the strength property, regardless of the effect of gypsum type or dosage, the changes in the results of microscopic experiments for hardened paste and SSB-CPB are critical indicators that the strength of SSB-CPB varies. When steel slag dosage is 35%, the best gypsum dosage is 24% and gypsum type is DG in the SSB for backfill. The findings of this study contribute to an enhanced understanding of the backfill binder material, which has beneficials of lower greenhouse gas emission, avoidance of natural raw materials excavation, saving environmental taxes, and reducing backfill costs.