Temperature and moisture dependence on the thermal conductivity of wood-cement-based composite: experimental and theoretical analysis

Results are presented of a study on the effect of moisture contents and temperature on the thermal conductivity of wood-aggregate-clay-cement composites, energy saving concretes. The thermal conductivity has been measured in the range of 2-60 degrees C, which covers the majority of thermal conditions in which the material is used. The unit cell of the parallel model, already validated for dry wood concretes, i.e. two-phase system, has been extended in order to calculate the thermal conductivity of wood concretes for various moisture contents. Experimental results show a significant dependence of thermal conductivity on moisture contents and temperature. The theoretical analysis of these phenomena has been conducted in two stages using the classical De Vries approach. The first stage consists of estimating the thermal conductivity at low temperatures for the three-phase system (i.e. unsaturated materials) using a modified unit-cell parallel model. The validity of the expression developed is then tested by comparing experimental results with computed values of effective thermal conductivity. The second part consists of determining the 'f' factor that characterizes the effects of temperature on thermal conductivity. The experimental results of thermal conductivity at various moisture contents and temperatures were compared with the results obtained from De Vries's approach and a very high level of agreement was observed.