Expansion Properties of Cemented Foam Backfill Utilizing Coal Gangue and Fly Ash

The cemented backfill (CB) utilizing coal gangue (CG) and fly ash (FA) is widely applied in coal mines. However, the bleeding and shrinkage of CB leads to insufficient contact with surrounding rock, which is not beneficial for controlling roof subsidence and even stope stability. Herein, a cemented foam backfill (CFB) formulation is demonstrated, employing hydrogen dioxide (H2O2) as a chemical foaming agent. The cement and FA show noticeable inhibiting effects on volume expansion due to the network formed by their hydrates. Moderately lower cement, FA, and solid concentration are beneficial to improve volume increment and prolong expanding duration. A foaming coefficient (k) is proposed in theory to evaluate the foaming efficiency. The k em values, determined by volume evolution experiments of CFB slurries, provide a calculation basis for the needed dosage of H2O2 solution targeting specific volume increment. CFB specimens with expanding ratios of 21%similar to 103% and densities of 994 similar to 592 kg/cm(3) were prepared, with an actual foaming coefficient of 52.40 cm(3)/g and uniaxial compressive strength (UCS) of 0.32 similar to 0.55 MPa. The mass of H2O2 solution was 1.9%similar to 11.3% of cement and 0.29%similar to 1.67% of total solid materials by weight. The UCS decline compared to CB was attributed to rich pores observed by CT and carbonation indicated by X-ray diffraction (XRD).

Automated summary

The cemented foam backfill using hydrogen dioxide as a foaming agent is proposed to mitigate the issues of bleeding and shrinkage in coal mines. The formulation with lower cement, fly ash, and solid concentration shows improved volume increment and prolonged expanding duration.