Evaluation of Durability and Homogeneity of Rejuvenated Asphalt Binders

Despite the widespread recycling of Reclaimed Asphalt Pavement (RAP), a large portion of it is still wasted. One of the main reasons is the concern with the performance of high RAP mixtures. Asphalt binder aging and subsequent rejuvenation is one source of uncertainty. Rejuvenators are frequently added to high RAP mixes to enhance the properties of the binder. This enhancement is often perceived as simply lowering the viscosity. Two important parameters that are not adequately addressed by existing methods are durability and homogeneity of the recycled binder. This research investigated these two concerns and provided quantitative indicators to measure them. The durability of rejuvenated binders was investigated through studying their long-term aging. Superpave PG tests and aging procedures were used for this purpose. Results indicated that the type and dosage of the rejuvenator has a significant impact on the aging of a rejuvenated binder. While using a proper rejuvenator can prolong the life of the binder, choosing a wrong product causes the binder to age significantly faster. The asphalt film that coats aggregates is not necessarily homogeneous. Different layers of the film are affected differently by aging and rejuvenation processes. A staged extraction method was implemented to provide representative samples from the different layers of asphalt. The stiffness of each sample was measured by Dynamic Shear Rheometer testing. Results indicated that most of the rejuvenator is absorbed by outer layers immediately after blending. As the mixture ages, the rejuvenator continues diffusing into the inner layers. Outer layers are also affected more intensely by the aging. The coupled effects of aging and rejuvenation make the recycled binder more homogeneous than virgin asphalt. This property can facilitate the use of higher target PG values for recycled binders without compromising the long-term performance. This research introduces two quantitative measures, critical PAV time and Durability Index, for evaluating the durability of recycled binders and two other parameters, Stiffness Gradient Factor and Homogeneity Index for describing the binder film homogeneity. These indicators and the knowledge obtained from this research make it possible to design and evaluate the binder rejuvenation process in a more effective manner