Multiscale evaluation of asphalt binder rejuvenation dosing and efficacy

Abstract

The final composition of asphalt binder in an asphalt mix can vary depending if it is a neat, virgin binder, or a blend of neat binder with reclaimed asphalt pavement (RAP), modifiers, and/or rejuvenators. As recycling of asphalt concrete becomes more commonplace worldwide, so too must be the use of chemical rejuvenators which can restore the original properties of the associated asphalt binder, contributing to the performance and therefore sustainability aspect of this material. In this context, this work aimed to evaluate the influence of rejuvenation in different proportions of aged and unaged binder, as well as the best way to dose rejuvenators, taking into consideration aspects that go beyond the Superpave Performance Grading characterization of binders. In the first phase of this study, when rejuvenator contents based on low PG recovery were proportionally added to different aged/unaged binder blends, it was observed that restoration of ductility and strength of the rejuvenated aged binder was limited. However, when an additional cycle of aging was applied to simulate the new service life of recycled material, the rejuvenated recycled material generally performed better than unrejuvenated recycled material. This long term effect can better differentiate the performance of different rejuvenators. Afterwards, the dosing procedure was investigated using an extensive range of dosages. An optimal dosage determination approach was developed and verified by means of the rejuvenation of aged asphalt mixtures from the rheological, mechanical, and chemical perspectives. Finally, the differences between laboratory-aged binder and laboratory-aged mixtures when rejuvenators are used was investigated, and it was determined that the mechanisms of rejuvenation at the two scales are not completely alike. Key findings also include the importance of re-aging asphalt binder blends before testing when a rejuvenator is used and the dominance of unaged binder within binder blends with limited replacement with recycled asphalt. Overall, this work opens the door to future studies of rejuvenation of asphalt using different approaches than those which have been conventionally used, including consideration of amount of replaced binder, using nonlinear viscoelastic characterization, fundamental chemical studies, and the method of addition based on mixture versus binder scale studies.