Permeable Porosity and Thermal Conductivity of Construction Materials

Water permeable porosities and thermal conductivity of ceramic construction materials have been experimentally determined in this work. The samples were selected so as to obtain a wide variation in their apparent porosity. To study the influence of porosity on thermal conductivity, thermal conductivities of all the samples were measured in oven dried and water saturated conditions. A model relating porosity with thermal conductivity of these materials is proposed. In the model, two types of pores are hypothesized, namely; enclosed pores and enclosing pores. The three-dimensional steady-state heat transfer through unit cells containing each of the two types of pores, is solved to evaluate their effective thermal conductivity. By using the law of mixture for the random distribution of the type of pores, an equation combining the conductivities of the two cells is framed to get overall effective thermal conductivity of the material, in both dry and saturated states. The experimentally determined values of thermal conductivities reported in literature for some bricks are then compared with those predicted through this model.