Effect of moisture and porosity on the thermal properties of a conventional refractory concrete

An investigation was carried out to study the effect of moisture and porosity on the thermal conductivity, thermal diffusivity and specific heat of a conventional aluminous refractory concrete. The experimental technique employed was the hot wire parallel technique, and measurements were carried out from room temperature up to 1000 °C. The thermal conductivity and the specific heat were simultaneously determined from the same experimental thermal transient, and the thermal diffusivity was derived from these two properties. A 60 wt.% alumina grog and a 60 wt.% alumina calcium aluminate cement were the raw materials employed in this work. Five different porosity levels were obtained by proportioning three different aggregate grain sizes. Experimental results show a drastic influence of the moisture content on the thermal conductivity of the refractory concrete, doubling its value when compared with the same fired composition, depending on the temperature range considered in the measurements. It was also observed for the fired material, a smooth variation of the thermal conductivity with the temperature for each composition in the temperature range studied, and a modified form of the Loeb equation was employed to evaluate the thermal conductivity of the fully dense solid.