The measurement of the thermal conductivity of solid aggregates using the transient plane source technique

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.