Determine the degree of blending between rap and virgin binder using the superpave volumetric mixture design

Adding reclaimed asphalt pavement (RAP) into asphalt mixes is a common practice and has many merits such as reducing costs and emissions. In the recent decade, many state highway agencies have embarked on investigating asphalt mixes with high RAP content. As the RAP content increases, understanding how well the RAP binder blends with virgin binder becomes more crucial. Lack of knowledge on how much of residual RAP binder actively blends with virgin binder during production is one of the reasons preventing full exploitation of RAP materials. Obviously, the amount of aged RAP binder blending into virgin binder affects properties of asphalt mixes. A study was undertaken to investigate the degree of blending, i.e., the amount of RAP binder blended with virgin binder, through the Superpave volumetric mix design. This research was unique and innovative in the sense that extracted RAP aggregate was blended with virgin aggregate at two different gradation levels to simulate zero blending and full blending. These two scenarios along with actual RAP blending were used in the Superpave volumetric mix design to determine optimum asphalt content and degree of blending. Through volumetric mix design paired with simulated cases, it was estimated that approximately 75% residual RAP binder interacted with the virgin binder in terms of blending and contribution to the final mix.