Recycled Asphalt-Highway Systems

Developing Design Methodology To Incorporate Reclaimed Asphalt Pavement (RAP) in Flexible Pavement Systems

More than 90% of roads are constructed with Hot Mix Asphalt (HMA). As in every road system, over time the riding quality of pavement decreases and sometimes the entire HMA layer requires a reconstruction. Reconstruction involves HMA layer to be removed and the material produced from this process is referred as reclaimed asphalt pavement (RAP). Currently in Virginia, up to 30% of processed RAP is allowed to be re-used to create HMA mixtures for new roadways, however despite this practice there are approximately 4.7 million tons of accessed RAP stockpiled in Virginia that could also be potentially reused. Based on the recent surveys over the last five years and as documented by Virginia Center for Transportation Innovation and Research (VCTIR) on a recently completed study (VCTIR Report No. 15-R6, 2015), it is known that RAP is one of the most frequently considered recycled materials for subbase and base courses for paved roads among the Department of Transportation Agencies throughout the U.S.

Although recycling asphalt aggregate is a novel idea, it requires careful consideration. The purpose of this research is to develop design and implementation guidance to allow maximum percentage of RAP that can be used in unbound base aggregate (UAB). As a recycled material, the variation within the properties of the existing RAP stockpiles must be carefully evaluated. Previous studies indicate that RAP has reasonable elastic properties but also potentially adversely affect the plastic deformation of the base aggregates. Therefore in this study, RAP will be mixed virgin aggregate and specific design mixtures will be created to capture the differences between RAP properties among different locations within the State. Performance tests will be conducted in SGI laboratory to evaluate the admixtures and to create thresholds. Design guidelines developed based on the laboratory tests will be put to test by constructing actual size field test sections that will be open to traffic and monitored with different field instrumentation. During construction, a side study will also be conducted to evaluate the most appropriate methods to perform quality control in the field. It is expected that results of this research to have noticeable effect on the current understanding of how to create RAP/virgin aggregate admixtures without adversely affecting the overall performance of the base layer as well as identifying the proper methods to perform field quality control tests. 

For related publications see: Ullah et al. (2018)