A Probabilistic Understanding of the Effect of Voids and Layer Thickness on Interconnectivity of Voids in Asphalt Mixes: An Agent-Based Modeling Approach

Abstract

Saturation of voids in pavement layers and accumulation of water at the interface with an underlying layer may lead to moisture damage in asphalt pavements. Interconnected voids facilitate the flow of water through hot mix asphalt (HMA) layers. Connectivity of the voids depends on their location within the asphalt mix layer—adjacent voids are more likely to be connected than nonadjacent voids. This paper reports the results of a study that was carried out with agent-based modeling (ABM) to evaluate the effect of the random location of the air voids on their adjacentness and hence connectivity. The pavement layer was modeled as a two-phase system consisting of air voids and mix, with a range of air void percentage and layer thickness, with a water source on the surface. Each model, with a specific layer thickness and void percentage, was simulated 1,000,000 times, in each of which the voids were placed at random locations. The results were analyzed in terms of saturated void percentage and percentage of saturated voids at the bottom of the layer. The conclusions are that the connectivity of voids is affected significantly by both percentage of voids and ratio of the layer thickness to void size (ratio). Beyond a threshold ratio of 3, the connectivity drops significantly. A ratio of >4 is needed to ensure a low probability of overall saturation and saturation at the bottom of the layer.