Influence of internal and external factors on the fluidity of modified magnesium slag-based backfill materials

Adequate fluidity is essential for conveying mine-fill material. Modified Magnesium Slag-Based Backfill (MFPB), a novel waste-based material, requires a clear understanding of the factors influencing its slurry fluidity. This is crucial for optimizing proportions and promoting the effective application of MFPB. This study examines the impact of internal factors (solid phase composition and mass concentration) and external factors (standing time and temperature) on the fluidity of MFPB. The analysis incorporates rheological, slump, and microscopic investigations. The primary findings indicate that: (1) The rheological profiles of MFPB slurries align with the Hershel-Bulkley model. (2) Variations in external factors can directly influence the gradation structure and floc network formation within the system, consequently impacting the fluidity of the slurry. (3) Reducing MMS, increasing FA or AS, and decreasing mass concentration impede particle flocculation. This leads to the desta-bilization of the skeletal structure, greater access to free water, and increased fluidity of the slurry. (4) Within internal factors, the influence of standing time is more pronounced than that of temperature. Slurry left for a duration exhibits a "stress overshoot" phenomenon at shear rates of 0-5 s(-1), linked to particle settling, hydration and flocculation. Rheological parameters and slurry fluidity "weaken" as standing time and temperature increase. (5) Environmental scanning electron microscopy analysis indicates that prolonged standing time or elevated temperature results in a more developed flocculated structure of the MFPB slurry. This development reduces pores and hinders the free flow of water, contributing to increased yield stress and apparent slurry viscosity. In summary, MFPB demonstrates favorable fluidity under various influencing factors, showcasing potential applications in complex working conditions. This study serves as essential reference and theoretical guidance for the promotion, application, and performance optimization of MFPB.