Impact of RAP on the Volumetric, Stiffness, Strength, and Low-Temperature Properties of HMA

Abstract

The increasing cost of virgin asphalt and aggregate has increased the interest in using higher percentages of recycled asphalt pavement (RAP) in hot mix asphalt (HMA) mixtures. The purpose of this research project was to gain a better understanding of how the addition of RAP affects interaction among the aged and virgin binders and the overall properties of HMA. The effects of the addition of RAP were evaluated on a macroscopic scale by comparing the volumetric properties, dynamic modulus, and strength parameters of a series of specimens containing different percentages of RAP from two different sources. Also, the viscoelastic properties of the blended or rejuvenated binder in the recycled mix were back-calculated from the macroscopic properties of the mix using the Hirsch model. Studies have shown that this back-calculation method offers advantages like elimination of the need for extraction of blended binder, the ability to use indirect tension test specimens, and the use of a mechanistic based approach. The back-calculated viscoelastic properties were subsequently used to determine the low-temperature performance grade of the binder in the recycled mix. This research project showed that the percentage of RAP affects the properties of the mixture with respect to mixture volumetrics, dynamic modulus, and strength.