A micromechanics-based approach for determining presence and amount of recycled asphalt pavement material in asphalt concrete

The economical use of pavement milling in recent years has resulted in the availability of significant amounts of recycled asphalt pavement (RAP). The use of RAP in new asphalt concrete mixtures can result in cost savings for both aggregate and asphalt binder. When properly utilized in mix design and production, lower costs can be realized without a sacrifice in the serviceability of the pavement. However, cost savings may not be realized by the owner and there may be a loss in serviceability of the pavement when unauthorized use occurs. This study was conducted to modify and/or develop a test to determine the presence and amount of RAP in post-production mixtures as a practical quality assurance tool. A testing and analysis procedure was developed to identify the presence and amount of RAP in asphalt mixtures. The development of the procedure was carried out by testing of laboratory as well as plant mixtures with known RAP amounts. To validate the most promising method two sets of blind samples were evaluated. An extensive testing of RAP materials from various sources was also carried out to determine the effect of RAP variability on newly developed procedures. From a literature review it was identified that asphalt binder properties change most dramatically with aging and therefore a procedure based on testing of asphalt binders was developed. An extensive procedure coupled with an analysis technique based on micromechanics was developed for determining amount of RAP in the asphalt concrete.