Influence of mixing time and coarse aggregate content on the flowability, setting time, and mechanical properties of cemented backfill

Ensuring the even mixing of filling slurry is crucial for the performance of cemented backfill, and mixing time is a key factor in this process. This study comprehensively investigates the effects of mixing time and coarse aggregate content on the fluidity, setting time, and mechanical properties of coarse aggregate backfill through extensive experiments. The results indicate no significant regularity in the vibration diffusion of the filling slurry at different regions of the mixing shaft, and positional variations do not impact the slurry's fluidity. Vibration diffusion initially increases and then decreases with prolonged mixing time, suggesting an optimal mixing time of within 9 minutes. The setting time of the filling slurry shows no significant variation across different regions of the mixing shaft. However, the setting time decreases with longer mixing times and increases with higher coarse aggregate content. The uniaxial compressive strength (UCS) of the backfill improves with extended mixing time, particularly benefiting early UCS. Incorporating an optimal amount of coarse aggregate, around 60 %, also enhances the UCS. Both extending the mixing time and adding an appropriate amount of coarse aggregate help suppress the expansion of destructive cracks and reduce internal void structures, thereby improving the overall mechanical properties of the backfill.