Rheological and mechanical performance analysis and proportion optimization of cemented gangue backfill materials based on response surface methodology.

Cemented backfill mining is a green mining method that enhances the coal mining rate and the safety of mined-out regions. To transport the cemented gangue backfill material (CGBM) into the mined-out regions, it is essential to ensure high flowability and adequate compressive strength after hardening. Based on the response surface methodology (RSM), 29 experiments were conducted in this paper to test the yield stress and plastic viscosity of CGBM slurry. Cubic specimens with dimensions of 100 mm were prepared and underwent uniaxial compression tests to obtain the compressive strength at a curing age of 28 days. Quadratic polynomial regression models were established for yield stress, plastic viscosity, and compressive strength to explore the effects of fly ash content, water-cement ratio, mass concentration, and superplasticizer dosage on the properties of CGBM. Multi-objective optimization was conducted to determine the optimal material proportion of CGBM. The research results indicate that (1) the mass concentration most profoundly affected the yield stress and plastic viscosity of CGBM, and it increased with an increase in mass concentration. Fly ash content had an inverse relationship with compressive strength. Superplasticizer was found to improve the flowability and strength of CGBM. (2) The established response surface model could reflect the relationship between CGBM's material proportion and rheological and mechanical properties, and predict relevant parameters. (3) Multi-objective optimization determined the optimal proportion of CGBM to be 80% fly ash content, 54% water-cement ratio, 79% mass concentration, and 3% superplasticizer dosage. The research findings offer valuable guidance to mining backfill engineering.