Degree of rap binder activation and its impact on recycled asphalt mixture design

Abstract

The reclaimed asphalt pavement (RAP) heterogeneity is cited in the literature as a critical issue to increase the percentage of RAP in asphalt mixtures. The presence of RAP clusters (RAP particles that are together as a single aggregate) and lack of detailed information about the RAP history are key aspects. The current practice to design recycled mixtures typically assume 100% of RAP binder activation and RAP aggregates with clusters fully dissociated. However, during hot mixture asphalt production, part of the RAP binder is activated, and part of the clusters are dissociated. It is unclear the impact of partial RAP binder activation on the design of recycled mixtures. This dissertation is divided in three main parts. First, stages of binder extraction were performed in six RAP materials to partially activate the RAP binder and create different levels of cluster dissociation. The Micro-Deval was also used to induce cluster dissociation by combining temperature and abrasion. Then, the changes in gradation and aggregates’ shape properties were measured. Second, the binder recovered after each stage of extraction was evaluated in terms of its rheological properties, the polarity-based fractions, and the Fourier transform infrared spectroscopy. Based on the results obtained in the first and second parts, an asphalt mixture design was simulated using different RAP percentages considering two scenarios: (i) RAP binder properties after complete binder extraction (full activation, and all cluster dissociated), and (ii) RAP binder partially activated, and clusters partially dissociated. The results indicate that there was a significant impact of the partial cluster dissociation on the recycled mixture aggregate properties (gradation and shape), mainly when the level of RAP binder activated is between 40% and 70%. Blending charts should be ideally based on the active RAP binder properties instead of the properties after complete extraction. This would facilitate the choice of the correct recycling agent when the partial RAP binder activation scenario is considered.