Determination of effective thermal conductivity of asphalt concrete with random aggregate microstructure

This paper intends to develop and validate an innovative method to determine the effective thermal conductivity of asphalt concrete considering thermal properties of individual components and volumetric compositions. Three-phase microstructure models (asphalt binder, aggregate, and air void) of asphalt concrete were randomly generated based on aggregate sizes and gradations. A finite-element (FE) model was developed to calculate the effective thermal conductivity of asphalt concrete by applying a steady heat transfer process. A multiscale simulation approach was used to consider the effect of different-sized aggregates at various length scales using a hierarchical framework that reduces computational cost. The prediction results were validated with experiment data and showed better accuracy than the results predicted from other analytical models. The influences of air void content and distribution, coarse aggregate content, aspect ratio of aggregate, asphalt binder with conductive and insulation additives, and lightweight aggregate on the effective thermal conductivity of asphalt concrete were analyzed. In general, the effective thermal conductivity decreases with the increase of air voids or the decrease of coarse aggregate content. However, when the distribution of air voids is nonuniform in asphalt concrete, the effective thermal conductivity may deviate from the normal range. On the other hand, the effective thermal properties of asphalt concrete could be equally affected by thermal modification of asphalt binder or replacement of lightweight aggregate.