Effect of mineral admixtures on flow properties of fresh cemented paste backfill: Assessment of time dependency and thixotropy

Abstract

Cemented paste backfill (CPB), an engineered mix consisting typically of tailings, cement and water, has become a regularly used structural material in most mines worldwide. The performance of the CPB structure is dependent both on the quality of each constituent and the rheological behavior of fresh CPB during placement into mined-out voids. A connection between the backfill's rheological behavior and the structural changes governing thixotropy and structural breakdown can provide a better understanding of the different yield stress-viscosity results. In this study, the mineral admixture effect on rheological properties of fresh CPB slurry is studied by considering a combined assessment of time dependency and thixotropy. A total of three mineral admixtures such as fly ash (FA), granulated blast furnace slag (Slag) and silica fume (SF) were used for the preparation of CPB material. The rheological parameters, mainly yield stress and plastic viscosity, were examined by the Bingham model. Results indicate that the thixotropy of fresh CPB decreases with FA dosage, while the addition of Slag and SF gives lower thixotropy values at early ages, and a higher rate of thixotropy acquisition at a later age. A partial replacement of cement with FA leads to an increase in the static deformability and significant improvement in fluidity of CPB, and a plot of thixotropy versus plastic viscosity results in a linear correlation between them. Moreover, the addition of slag particles reduces the yield stress and plastic viscosity of CPB, while SF-containing CPB exhibits improved yield stress and lower plastic viscosity. Plotting thixotropy versus plastic viscosity generates a poor linear relation for SF- and Slag-containing CPB slurries. The findings of this study will be useful in the lucrative design, efficient operation and safe production of early-age CPB material.