Low temperature rheological properties of asphalt mixtures containing different recycled asphalt materials

Reclaimed Asphalt Pavement (RAP) and Recycled Asphalt Shingles (RAS) are valuable materials commonly reused in asphalt mixtures due to their economic and environmental benefits. However, the aged binder contained in these materials may negatively affect the low temperature performance of asphalt mixtures. In this paper, the effect of RAP and RAS on low temperature properties of asphalt mixtures is investigated through Bending Beam Rheometer (BBR) tests and rheological modeling. First, a set of fourteen asphalt mixtures containing RAP and RAS is prepared and creep stiffness and m-value are experimentally measured. Then, thermal stress is calculated and graphically and statistically compared. The Huet model and the Shift-Homothety-Shift in time-Shift (SHStS) transformation, developed at the École Nationale des Travaux Publics de l'État (ENTPE), are used to back calculate the asphalt binder creep stiffness from mixture experimental data. Finally, the model predictions are compared to the creep stiffness of the asphalt binders extracted from each mixture, and the results are analyzed and discussed. It is found that an addition of RAP and RAS beyond 15% and 3%, respectively, significantly change the low temperature properties of asphalt mixture. Differences between back-calculated results and experimental data suggest that blending between new and old binder occurs only partially. Based on the recent finding on diffusion studies, this effect may be associated to mixing and blending processes, to the effective contact between virgin and recycled materials and to the variation of the total virgin-recycled thickness of the binder film which may significantly influence the diffusion process.