Single-factor analysis and interaction terms on the mechanical and microscopic properties of cemented aeolian sand backfill

The use of aeolian sand (AS) as an aggregate to prepare coal mine cemented filling materials can resolve the problems of gangue shortage and excessive AS deposits. Owing to the lack of research on the mechanism of cemented AS backfill (CASB), the response surface method (RSM) was adopted in this study to analyze the influence of ordinary Portland cement (PO) content (x₁), fly ash (FA)–AS (FA–AS) ratio (x₂), and concentration (x₃) on the mechanical and microscopic properties of the CASB. The hydration characteristics and internal pore structure of the backfill were assessed through thermogravimetric/derivative thermogravimetric analysis, mercury intrusion porosimetry, and scanning electron microscopy. The RSM results show that the influence of each factor and interaction term on the response values is extremely significant (except x₁x₃, which had no obvious effect on the 28 d strength). The uniaxial compressive strength (UCS) increased with the PO content, FA–AS ratio, and concentration. The interaction effects of x₁x₂, x₁x₃, and x₂x₃ on the UCS at 3, 7, and 28 d were analyzed. In terms of the influence of interaction items, an improvement in one factor promoted the strengthening effect of another factor. The enhancement mechanism of the curing time, PO content, and FA–AS ratio on the backfill was reflected in the increase in hydration products and pore structure optimization. By contrast, the enhancement mechanism of the concentration was mainly the pore structure optimization. The UCS was positively correlated with weight loss and micropore content but negatively correlated with the total porosity. The R² value of the fitting function of the strength and weight loss, micropore content, and total porosity exceeded 0.9, which improved the characterization of the enhancement mechanism of the UCS based on the thermogravimetric analysis and pore structure. This work obtained that the influence rules and mechanisms of the PO, FA–AS, concentration, and interaction terms on the mechanical properties of the CASB provided a certain theoretical and engineering guidance for CASB filling.