Thermal Conductivity of Bentonite Grout Containing Graphite or Chopped Carbon Fibers

The effectiveness of chopped carbon fibers to enhance the thermal conductivity of bentonite-based grout was examined. Fibers of 3 mm and 150 μm in length were added to sodium bentonite and silica sand mixtures at different volumetric concentrations. The thermal conductivity of the resulting composite material was then measured using a non-steady-state needle probe technique. The conductivities of the fibrous materials were compared to bentonite and sand mixtures containing natural flake graphite and milled, compressed exfoliated graphite at corresponding volumetric concentrations. The resulting conductivities for all tested materials increased with the volumetric fraction of additive. However, the 3-mm carbon fibers were more effective as compared to either granular graphite; at a volume fraction of 0.68% the 3-mm fibers were approximately twice as effective as either form of graphite.