Optimizing the Gradation of Fine Processed Reclaimed Asphalt Pavement and Aggregate Blends for Unbound Base Courses

Abstract

The purpose of this research was to investigate the effect of changes in grain size distribution to the permanent deformation of two different fine processed reclaimed asphalt pavement (RAP) blended with base course virgin aggregate (VA). Grain size distribution of the RAP-VA blends were created following two different approaches. The first approach was based on mixing RAP and VA to have one grain size distribution, regardless of how much RAP was added to VA (here referred to as the engineered mixture design). The second approach was based on mixing RAP and VA with as-is gradation from the plants to proportions determined by weight and not controlling the outcome of the specific grain size of the mixture. This approach resulted in various grain size distributions (here referred as the as-is mixture design). The engineered mixture design was useful to quantify the effect of adding RAP to the blends, but was not a realistic approach to create blends that may be achieved in the field. The as-is mixture design could not only be achieved in the field, as demonstrated in this study, but also resulted in better performance in terms of permanent deformation. This manuscript describes the comparison of these two approaches and a methodology to optimize the gradation and develop thresholds for RAP-VA blends that may result in similar or better performance than the 100% as-is VA that is used to construct base course in pavement systems.