Thermal conductivity and specific volume heat capacity of bentonite-fly ash-based fluidized thermal backfill

Thermal characteristics such as thermal conductivity and specific volume heat capacity are the significantly important parameters for the backfill materials for underground power cable. Herein, the thermal characteristics of fly ash (fluidizer), bentonite, and their mixes (fly ash content: 20%, 40%, 50%, and 70% by mass) were measured using a KD2 Pro thermal probe, and the effect of fly ash content and volumetric water content were studied. The experimental results indicate that the thermal conductivity and specific volume heat capacity increased with increase in the fly ash content and the volumetric water content. Further, a correlation between thermal conductivity versus volumetric air content and fly ash has been established based on experimental results. The established correlation was verified with the data obtained from the present study as well as from the data available in existing works of the literature. The proposed calculation model estimated the thermal conductivity with relative error of 8.53-16.40% of bentonite and bentonite-fly ash mixture. The predicted result showed that the established correlation will be useful to predict the thermal conductivity of bentonite-fly ash or similar soil and soil mixtures. The experimental outcomes can be widely applicable for thermal backfill applications for underground power cable systems.