Flowability of modified magnesium slag-fly ash cemented coal gangue slurry in industrial loop-pipe tests

Industrial-grade loop tests were conducted on modified backfill slurry (a slurry prepared with a modified magnesium slag-fly ash binder and coal gangue aggregate) across mass concentrations (64-72%) and flow rates (1.0-2.7 m/s) to analyze pipeline transportation characteristics. Results demonstrate that pressure loss increases linearly with flow rate, confirming Bingham plastic behavior, while exhibiting a nonlinear relationship with mass concentration. Critically, elbow section pressure loss measured 4-8 times greater than straight pipe sections across all tested conditions, with significantly higher growth rates. Rheological coefficients derived via linear fitting (R² ≥ 0.91) for straight pipes revealed an exponential increase with rising concentration (R² ≥ 0.91). Leveraging this exponential relationship, a predictive model for straight-pipe pressure loss was developed. Validation showed high accuracy, with absolute errors between predicted and experimental results ranging from 0.02% to 18.04%. The model was extended to predict pressure loss under broader operational parameters (concentration, flow rate, pipe diameter). Key simulations demonstrated that at 80% concentration and 2.8 m/s flow rate, increasing pipe diameter from 100 to 175 mm reduced pressure loss by approximately 50% and markedly decelerated its growth rate. Furthermore, pressure loss disparities between different flow velocities at identical concentrations diminished with larger diameters. These findings confirm that up-sizing pipe diameter effectively mitigates pressure losses induced by elevated mass concentration and flow velocity. For engineering applications, selecting larger pipelines enables simultaneous achievement of high flow rates and high concentrations during transport. The study establishes a reliable predictive framework and provides significant reference basis for optimizing the safe, efficient, and economical pipeline transport of modified backfill slurry in industrial settings.