Analysis of the Role of Recycled Material Agglomerations on the Location of Fracture in Asphalt Mixtures

Abstract

Studies have demonstrated that recycled material agglomerations are a primary inhibitor of recycled binder availability in asphalt mixtures containing reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS). The literature also suggests that the dispersion of available recycled binder within the virgin binder matrix is variable. This study integrated precedent from portland cement concrete petrography by analyzing the distribution of recycled and virgin binder along the fracture surface of five asphalt mixtures to better understand the implications of recycled material agglomerations and heterogeneous blending on performance using tracer-based energy dispersive X-ray spectroscopy (EDS) analysis. Inspection of sawn asphalt mixture surfaces indicated the presence of recycled material agglomerations in all mixtures evaluated. Fatigue fracture surfaces were obtained using Asphalt Mixture Performance Tester (AMPT) cyclic fatigue testing and preserved via embedment in epoxy. EDS analysis of the fracture surface of asphalt mixture fatigue test specimens revealed that failure occurs within the virgin binder matrix and around recycled material agglomerations, suggesting that the agglomerations act as black rocks. Quantitative EDS analysis demonstrated recycled binder availabilities ranging from approximately 40% to 90% for the five mixtures evaluated in this study, suggesting that considerable variation can exist among recycled material sources. The degree of blending was comparable for all mixtures evaluated. EDS analysis of bulk specimens conducted in areas without agglomerations generally yielded availability and degree of blending results that were in close agreement with those obtained from fatigue fracture surfaces.