Development of a Balanced Mix Design Method in Oregon to Improve Long-Term Pavement Performance

Abstract

Most state Departments of Transportation (DOTs) and asphalt contractors do not think that commonly used asphalt mixture properties, such as voids in mineral aggregate (VMA), voids filled with asphalt (VFA), and dust-to-binder ratio, reflect the long-term performance of asphalt mixtures. In addition, there are several new additives, polymers, rubbers, and high-quality binder types incorporated into asphalt mixtures today. Volumetric mixture design methods are not capable of capturing the benefits of using all these new technologies on asphalt mixture performance. Furthermore, the interaction of virgin binders with reclaimed asphalt pavement (RAP) mixtures with high binder replacement contents and the level of RAP binder blending into the asphalt mixture are still not well understood. Because of all these complications related to the more complex structure of asphalt mixtures, simple volumetric evaluations to determine the optimum binder content may not result in reliable asphalt mixture designs. Two volumetrically identical mixtures may provide completely different rutting and cracking performance according to laboratory tests. For all these reasons, in this study performance tests for rutting and cracking are incorporated into current asphalt mixture design methods to make it possible to validate or revise the optimum binder content determined by the volumetric mix design method (the only method currently used for asphalt mix design).