Blending and diffusion of reclaimed asphalt pavement and virgin asphalt binders

An experimental study to understand the properties of reclaimed asphalt pavement (RAP), virgin binder and their respective blends was conducted. It was found that the current AASHTO (American Association of State Highway and Transportation Officials) M 323 specification recommendation to use one-grade softer performance graded asphalt at > 15% RAP addition may not be justified. It is demonstrated that a binder grade change is not necessary up to 25% RAP in most blends. The ability of RAP and virgin binders to blend by diffusion at typical asphalt-mix production and placement temperatures and times was measured by a dynamic shear rheometer. A simulation showed that a complete binder blending in both hot-mix asphalt and warm-mix asphalt applications is reached within minutes after mixing. Nevertheless, binder layer thickness in the mix has a significant impact in these simulations and further understanding of binder film thickness in asphalt mix is necessary to accurately estimate degree of blending. Real mix data from Carpenter and Wolosick [(1980). Modifier influence in the characterization of hot-mix recycled material. Transportation Research Record, 777, 15-22] were successfully fitted with the diffusion model, demonstrating that the diffusion as measured for binders follows the same fundamental processes in the asphalt mix.