A homogenization-based model for the effective thermal conductivity of bentonite–sand-based buffer material

A homogenization-based effective thermal conductivity model was proposed for unsaturated compacted bentonite–sand-based buffer materials. The microstructure of the mixture was approximated with pores and sand particles of spheroidal shape and random orientation embedded in the homogeneous bentonite matrix. By virtue of the analytical solution to the inhomogeneous inclusion problem in heat conduction, the model was developed using homogenization techniques such as the Mori–Tanaka (MT) and interaction direct derivative (IDD) schemes for different consideration of the interactions between pores, sand particles, and the bentonite matrix. The proposed estimates are dependent on the thermal conductivities of the bentonite matrix, the liquid and gas phases and sand, porosity, the degree of saturation, sand content, and the aspect ratios of pores and sand particles. The proposed model was validated against four sets of laboratory measurement data on the Kunigel-V1, MX-80, Kyungju, and GMZM bentonite–sand mixtures. It is demonstrated that although with simplified considerations of the microstructural features and mechanisms, the model predicts the effective thermal conductivity of the bentonite–sand mixtures with a fairly good agreement.