Effect of Jatropha curcas extract and cement–slag binder on the rheology and backfilling performance of high concentration fly ash slurry

Fly ash generated from coal-fired power plants should be disposed and effectively utilized in the long run. The present work examines the influence of a natural extract isolated from the Jatrophacurcas plant in the range of concentrations 0.1–1.3 g/L on the surface activity and rheological properties of high concentration fly ash slurries with different amounts of cement and slag as binders. The surface activity of the extract was studied as a function of concentration to determine the effective concentration for the stabilization of the slurry. The total solid concentration of the slurry was kept at 70%, 73% and 75% with fly ash to binder ratio of 8:2. The binder was 20% of the solid fraction which was either 20% cement, 20% slag or a mixed 10% cement–10% slag composition and the remaining 80% was fly ash. Shear‑stress values were estimated from the rheological measurements within the shear-rate range of 10–200 s−1. The apparent viscosity increased with increasing the solid concentration and varied with extract concentration indicating the surface-active role of extract in modifying the particle interactions and slurry flow behavior. To establish the suitability of the treated slurry for backfilling operations, compressive strength was determined at natural extract concentrations of 0.3, 0.7, and 0.9 g/L for curing times of 7, 14, and 28 days.