Impact of High RAP Contents on Structural and Performance Properties of Asphalt Mixtures

Abstract

Currently, highway agencies in Illinois are exploring the feasibility of using of higher amounts of reclaimed asphalt pavement (RAP) in asphalt mixtures. Concerns about variability in aggregate gradation and higher stiffness of aged RAP binder have limited this use, however. This research project was designed to characterize the performance of hot-mix asphalt (HMA) with high amounts of RAP and to identify any special considerations that must be met to utilize these higher RAP contents. Two material sources from two districts were used to prepare eight 3/4-in nominal maximum aggregate size (NMAS) N90 binder mix designs. The mix designs included a control mix with 0% RAP and three HMAs with 30%, 40%, and 50% RAP for each district. A base asphalt binder (PG 64-22) was used in the mix design process; a single-bumped binder (PG 58-22) and a double-bumped binder (PG 58-28) were also used to prepare specimens for performance testing. The tests conducted on the HMAs were moisture susceptibility, flow number, complex modulus, beam fatigue, semi-circular bending, and wheel tracking. All tested HMAs with RAP performed equal to or better than the mixtures prepared with virgin aggregate. The study found that HMAs with high RAP content (up to 50%) can be designed with desired volumetrics. RAP fractionation proved to be very effective. Asphalt binder-grade bumping is vital for HMAs with 30% RAP content and above.