Laboratory Evaluation of the Effectiveness of Rejuvenation in Multiple Hot Recycling of Asphalt Mixtures

Because of the widespread use of reclaimed asphalt (RA) in new asphalt mixtures, multiple RA recycling is expected to become a common practice. Thus, the long-term properties of multiaged RA as well as the effectiveness of multiple-cycle rejuvenation of RA need to be properly investigated. Given this background, the present study was aimed at evaluating at laboratory scale the feasibility of multiple hot recycling of RA at both short-term aging (STA) and long-term aging (LTA) conditions. The effectiveness of rejuvenation of multiple recycled mixtures was also assessed. In particular, the effect on mixture performance of the rejuvenator addition at different recycling stages was evaluated both after mix rejuvenation and at the end of laboratory-simulated LTA. To these aims, the evolution of linear viscoelastic properties and tensile strength of a plant-produced asphalt mixture has been investigated over a series of short-term and long-term simulative aging cycles carried out with or without the addition of a rejuvenator product. The experimental findings mainly showed that recycling effect (i.e., stiffening and embrittlement) seems to stabilize over cycles with an effective rejuvenating contribution because of the recycling agent. Nevertheless, a specific design of the rejuvenator content considering the actual RA properties instead of requiring a fixed dosage based on RA binder content is only necessary because the recycling history undergone by RA (i.e., number of recycling cycles and use of rejuvenator over the different cycles) clearly affects the final properties of the recycled mixes.