Experimental determination and fractal modeling of the effective thermal conductivity of autoclave aerated concrete (AAC) impregnated with paraffin for improved thermal storage performance

Abstract Autoclave aerated concrete (AAC) was incorporated with paraffin to form novel composite building materials with improved thermal storage capacity. The composite samples were prepared by impregnating RT28 paraffin into three types of AAC with different porosities. The effective thermal conductivity of the paraffin/AAC composites was measured at both 20 °C and 35 °C, while the paraffin was in solid and liquid phases, respectively. A fractal model was developed to predict the effective thermal conductivity of the composites. Both the experimental results and model predictions showed that the thermal conductivity increases with raising the paraffin content, leading to deterioration of the thermal insulation performance of pristine AAC. The volumetric heat capacity of the composites was also measured to derive the thermal effusivity, which serves as a measure for thermal storage performance of building materials. To reach a compromise among the various considerations, it was suggested that an intermediate paraffin content, about two thirds of the saturated level, is appropriate for all samples because it is unnecessary to fully impregnate the AAC samples with paraffin at the cost of reducing the insulation performance and increasing the risk of paraffin leakage upon melting.