The impact of aging heterogeneities within RAP binder on recycled asphalt mixture design

The degree of binder activation in reclaimed asphalt pavement (RAP) is a critical aspect that should be considered in the design of recycled asphalt mixtures. It is widely believed that binder from RAP is less than 100% activated, which implies that part of the RAP binder will be inactive in the mixing process. It is important to quantitatively assess whether there is any significant difference between the active and the inactive binder as typical recycled mixture design insinuates 100% binder activation and complete homogenization of the virgin and RAP binder. The objective of this study is to evaluate aging heterogeneities within RAP binder as an imperative step to improve the design of recycled asphalt mixtures. Stages of binder extraction were performed on six RAP materials to artificially activate different RAP binder layers. After each extraction, the binder recovered was evaluated in terms of its rheological properties, polarity-based fractions, and Fourier transform infrared spectroscopy. Based on the results, an asphalt mix design was simulated using different RAP percentages considering the impact of RAP binder aging heterogeneities. Overall, the analysis implied that it may not be a realistic assumption to consider full RAP binder homogeneity. Based on the simulation performed, blending charts used to design recycled asphalt mixtures should be ideally based on the active RAP binder properties instead of the properties of the RAP binder after complete binder extraction. This would facilitate in choosing the correct virgin binder when the partial RAP binder activation scenario is considered.