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In predicting the overall thermal conductivity of composite porous structures such as building materials or soils, the thermal conductivities of their solid components must be known in order to apply some theoretical models. Horai proposed a method to determine the thermal conductivity of solid particles. The material under study is first ground to a fine powder. This powder is then carefully saturated with a fluid and the thermal conductivity of this mixture is measured using the `needle probe' method. Finally, the conductivity of the solid phase is evaluated using a mixing-law model, namely the mean of the so-called `Hashin and Shtrikman bounds'. We have introduced a slightly different version of this method that uses the `transient plane source' (TPS) technique recently developed by Gustafsson for simultaneously measuring both the thermal conductivity and the thermal diffusivity of solids or fluids. An adapted experimental device has been designed and our approach has been validated through measuring, at room temperature, the thermal conductivities of the well-known minerals quartz, calcite and kaolinite. Afterwards, while considering that our method had become fully operational, we studied the thermal conductivity of the solid aggregates of a light-weight, energy-saving concrete whose solid phase is a mixture of natural clay, hardened cement paste and wood aggregates in various proportions.

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From the set of existing models available for predicting the thermal conductivity of porous materials such as soils, building materials, etc. two models based on two different approaches have been selected in order to estimate the thermal conductivity of moist wood concrete. The first model is based on the strictly mathematical solution to the heat conduction equation using a continuous medium approximation. The second employs the Ohm's law approach. Besides the characteristics of the various phases, such as each phase's thermal conductivity and its volume fraction, both the Pande and Gori and the Jackson and Black models take into account the geometrical arrangement of the particles by introducing a morphological parameter such as the coefficient of effective continuous medium, P and the stereological concept of contiguity, respectively. A new parameter named the liquid-liquid contiguity has been introduced to preserve the validity of the model as proposed by Jackson and Black for saturation greater than 0.9. Based on the same electrical analogy as Jackson and Black, an expression for calculating the effective thermal conductivity of unsaturated material has been proposed. A new coaxial thermal probe, developed at the LTHE (France), has been used for measuring thermal conductivity at various moisture contents. One original feature of the corresponding probe is its very low mass by unit length-less than 10 g m −1 . It allows for taking measurements even if the thermal contact is very poor. Calculated values of the effective thermal conductivity of these materials have been compared with experimental measurements. These models are found to yield predictions which agree quite closely with experimental data for wood concrete for different amounts of wood aggregates and saturation degrees.