Challenges and opportunities in the high-quality rejuvenation of unmodified and SBS modified asphalt mixtures: State of the art

The reuse of reclaimed asphalt pavement (RAP) in its highest quantity and quality is currently a focus point of researchers in pavement engineering. The increased use of RAP can lead to several possible pavement distresses due to the presence of brittle aged binder in it. One of the prospective methods is to employ rejuvenators to restore the original properties of binders in RAP by balancing its chemical fractions. However, undesirable results were reported when using various RAP materials with rejuvenators. It is now believed that most commercially available rejuvenators are mainly only effective for the RAP mixes containing unmodified binders (RAP-UB) but not for the ones containing SBS modified binders (RAP-SBS). This review article highlights the critical differences between unmodified and SBS modified binders in terms of aging and rejuvenation chemistry. Further, specific rejuvenator types, and rejuvenation mechanisms, as well as material cost benefits are summarized. It is concluded that the high-quality rejuvenation of RAP-SBS presents significant differences to that of RAP-UB and requires not only the chemical fraction readjustment of aged binder but also the structural regeneration of SBS degradation products. Practitioners must take this variance into account when designing mixes that contain large quantities of SBS modified RAP.