Effect of Partial Blending on High Content Reclaimed Asphalt Pavement (RAP) Mix Design and Mixture Properties

Reclaimed Asphalt Pavement (RAP) material, especially high RAP content mixture, is nowadays receiving more interest in asphalt pavement construction. When determining the optimum asphalt content (OAC) in RAP mixture design, RAP partial blending is sometimes neglected and total blending is assumed. Such an assumption influences the virgin binder content determination and can contribute to the poor fatigue and cracking performance of high RAP pavement in the field. This paper studied the impact of RAP partial blending on the OAC of mixtures with varied RAP content up to 40%. A Laboratory Hamburg Wheel Tracking Test, an IDT fracture test, and an SCB test were performed on mixtures designed by different methods to evaluate rutting and cracking performance. In particular, a partial blending design method was proposed to improve the mixture performance by adjusting the virgin binder content through the RAP blending ratio. It was found that the optimum virgin binder content decreased as the RAP content increased; the Superpave volumetric method required the lowest OAC while the partial blending method required the highest OAC. The rutting performance of the RAP mixtures considering partial blending was slightly lower than other mixtures. However, all RAP mixtures showed better rutting resistance than virgin mixtures. The cracking performance of the high RAP mixtures was significantly improved if the partial blending effect was considered in the design.