Laboratory Assessment on the Thermal Conductivity Behavior of Biopolymer Hydrogel, Graphite, and Fly Ash Mixture

This study aims to assess feasibility of microbial biopolymer application to enhance thermal dissipation efficiency of backfill soils surrounding underground electricity cable tunnels. In detail, microbial biopolymer, graphite, and fly ash were suggested as additional additives, and different combinations of additives were assessed through a laboratory thermal conductivity measurement system. The effects of additive content on soil-additive admixture and water content were evaluated. The soil-biopolymer mixture has 15.2% higher thermal conductivity at 20% water content than untreated soil, but is 11.3% lower at 10% water content, so the biopolymer itself does not significantly contribute to the improvement of soil thermal conductivity. However, in the case of the soil-biopolymer-graphite mixture, the thermal conductivity increased by up to 46.4% compared to the untreated soil at a water content of 20%, which was 16.9% higher than that of the soil-graphite mixture. This is due to the pore-clogging behavior of the microbial biopolymer.