Thermal enhancement of gangue-cemented paste backfill with graphite and silica sand: an experimental investigation

Thermal conductivity of mine backfill is vital for understanding the geothermal energy extraction potential in deep underground mines. Geothermal energy extraction efficiency could be improved with higher thermal conductivity of backfill. Thermal conductivities of gangue-cemented paste backfill enhanced with graphite and silica sand were investigated through laboratory tests in this article. The thermal conductivity measurement was conducted using the Hot Disk Thermal Constants Analyzer. Effects of graphite and silica sand on the thermal conductivity, slump, and compressive strength of gangue-cemented paste backfill were analyzed. The results highlighted the favorable influence of graphite on the thermal performance of backfilling materials, with adverse effect on the mechanical behavior and negative impact on the flowability. Thermal conductivity of gangue-cemented paste backfill markedly increased with graphite ratio, while more water is consumed for the workable slurry with the increased graphite ratio, which also leads to the degradation of compressive strength. The reasonable graphite content should be determined with the expected thermal enhancement and acceptable compressive strength. The addition of silica sand can effectively enhance the thermal conductivity of GCPB without degrading the compressive performance and flow performance. This study would provide a new insight into the design of backfill considering the thermal conductivity and lay a foundation for the efficient geothermal energy in deep mines.