An experimental investigation and fractal modeling on the effective thermal conductivity of novel autoclaved aerated concrete (AAC)-based composites with silica aerogels (SA)

Improving the thermal insulating performance of porous building material is of great practical significance for energy-efficient buildings. In this work, silica aerogels (SA) having ultralow thermal conductivity were incorporated into autoclaved aerated concrete (AAC) via physical solution impregnation method to further improving its thermal insulating performance. As expected, the addition of SA lowers the thermal conductivity of the composites and the improvement in thermal insulating performance depends on porosity of the pristine AAC. At the SA loading of similar to 7 wt.%, the highest relative improvement was found to be nearly 30%. Two types of fractal models, i.e., parallel and serial, were established to predict the thermal conductivity of the SA-AAC composites. It was observed that the serial model could match well with the experiment data of the AAC-300 and AAC-400-based composites. A hybrid model of the two types was proposed so as to predict the data for the composites more satisfactorily. This modeling effort helped us better understand the role of the impregnated SA on the heat conduction mechanisms in the composites. As an extra bonus, the compressive strength and the capillary water absorption coefficient of the composites were found to increase and decrease slightly, respectively, with increasing the SA content. The lower water absorptivity indicates a better potential durability. The results shed light on the great potential of such composites in real-world applications if the cost issue can be addressed by future advances in materials fabrication technologies.