Rheological investigation of asphalt mixtures containing RAP and RAS

Reclaimed Asphalt Pavement (RAP) and Recycled Asphalt Shingles (RAS) are valuable materials commonly reused in asphalt mixtures due to economic and environmental benefits. However, the aged binder in these materials may negatively influence the low temperature properties of the final asphalt mixtures. In this paper, the effect of adding RAP and RAS on low temperature properties of asphalt mixtures is investigated through Bending Beam Rheometer (BBR) tests and rheological modelling. First, a set of fourteen asphalt mixtures containing different amounts of RAP and RAS are prepared and creep stiffness experimentally measured. Then, the Huet model and the Ecole Nationale des Travaux Publics de l’Etat (ENTPE) transformation 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 discussed. Experimental measurements indicate that the addition of RAP and RAS significantly affects low temperature performance of asphalt mixture. Differences between back-calculated results and experimental data suggest blending between new and old binder is only partial. 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.