Uniaxial compressive strength of cemented coal gangue backfill based on response surface methodology.

Cemented Coal Gangue Backfill (CCGB) plays a pivotal role in sustainable mining practices, as its uniaxial compressive strength (UCS) directly dictates backfill stability, mining safety, and operational efficiency. However, existing research has yet to fully elucidate how key mix proportion parameters synergistically influence UCS across different curing stages, leaving a critical gap in optimizing CCGB performance. This study addresses this limitation by systematically investigating the factors governing CCGB's UCS under varied mix designs. First, single-factor tests identified optimal ranges for critical variables: mass concentration (80%-81%), fly ash content (3-4 kg), and fine gangue ratio (35%-45%). Using the response surface method (RSM), we then developed quadratic polynomial regression models for 1-day and 28-day UCS, which demonstrated excellent fit with R² values of 0.9672 and 0.9575, respectively. Our results reveal that the interaction between mass concentration and fly ash content exerts a more significant impact on UCS than the fine gangue ratio alone. Additionally, microscopic analysis indicates that during hydration, pozzolanic reactions and cement hydration reactions proceed in alternation rather than isolation-a mechanism previously underexplored in literature.