Discrete Element Analysis of the Influences of Aggregate Properties and Internal Structure on Fracture in Asphalt Mixtures

Abstract

Increased loads on hot-mix asphalt (HMA) pavements have necessitated the development of new-generation asphalt mixture designs that rely on stone-on-stone contact among coarse aggregates in resisting and distributing applied loads. These stone-on-stone contacts, however, promote localized internal stresses that could cause aggregate fracture. Therefore, it is imperative that methods are developed to analyze the contribution of the coarse aggregate structure and properties to HMA performance during mixture design. This paper introduces an approach that combines the discrete element method (DEM) and image processing techniques to analyze the combined effects of aggregate gradation, shape, stiffness, and strength on HMA resistance to fracture. The DEM input parameters were determined based on measuring aggregate and HMA properties. Consequently, the model was used to quantify the internal forces in asphalt mixtures and determine their relationship to aggregate fracture which cannot be accomplished by conventional experimental methods. The model was successful to large extent in representing the influence of variability in aggregate properties and blending two sources of aggregates on mixture strength. The results showed that the required aggregate strength and optimum blending limits to achieve certain mixture strength are dependent on mixture design.