Setting, bleeding, and hardening strength properties of coarse aggregate backfill slurry

Abstract

This work systematically investigates the effects of coarse aggregate (CA) type, dosage, and slurry concentration on the backfill slurry's setting, bleeding, and hardening strength properties. Rod milling sand (RMS) and waste rock (WR) were selected as CA, the backfill slurry's concentration ranged from 76% to 79%, its replacement rate of tailings with RMS and WR was between 40% and 60%, and its cure period was 3, 14 and 28 days. Then, the fresh backfill slurry was subject to setting and bleeding experiments, and the hardened backfill slurry was submitted to UCS tests. Finally, a CPB curing time of 28 days was chosen for microstructure experiments to reveal the mechanism of the effect of slurry concentration and CA dosage on CPB hardened strength. The results showed that the initial and final setting times reduce as concentration increases and increase as tailings/CA (T/CA) decreases. The effect of concentration and CA dosage on the bleeding properties of backfill slurry is not apparent. Increasing the slurry concentration increases the amount of C-S-H gel inside the CPB, which improves its mechanical behavior. The CPB has optimal physical properties when the slurry concentration is 77%− 78%, and the amount of WR is 50%. The study results can provide a theoretical basis for the preferential selection of backfill materials in mines.