Mechanisms of the effects of external fields and polycarboxylic acids on the performance of gangue-based non-cementitious filling slurry

This study focuses on the non-cementitious filling technology for underground coal mines, where the filling slurry is prepared using coal gangue as the aggregate, supplemented by fly ash. Based on the slurry ratio determined in the preliminary tests, the rheological characteristics of the slurry are optimized and controlled through the introduction of external fields (microwave and magnetic fields) and synergistic additives (polycarboxylic acids). The mechanism of this regulation is investigated. The results showed that gangue activated by an 800 W microwave and magnetized water produced by a 1.35 T magnetic field and the addition of 0.04% polycarboxylic acid were the optimal conditions for one-factor exploration. Using the response surface method for optimization, when the microwave power was 778.40 W, the magnetic induction intensity was 1.31 T, and the polycarboxylic acid addition was 0.03%, the slurry slump extension increased by 11%, the plastic viscosity decreased by 38.41%, and the fluidity significantly improved. Microwaves altered the mineral composition, particle size distribution, and microscopic morphology of the gangue. This led to changes in the specific surface area and free water content of the slurry, which in turn affected the slurry fluidity and stability. Magnetized mixing water reduced the surface potential of gangue particles, enhancing the penetration and diffusion ability of water molecules and improving slurry fluidity. An appropriate amount of polycarboxylic acid formed a solventized water film on the surface of the gangue, reducing the surface potential, enhancing wettability, and improving slurry fluidity. The optimized control of the slurry using microwaves, magnetic fields, and polycarboxylic acids enhances fluidity while maintaining stability, providing crucial guidance for improving the safety and economic viability of underground coal gangue backfilling technology.