Evaluation of Recycling Agent and Extender Dosage Selection Procedures to Restore the High-Temperature Climatic Performance Grade

Abstract

Dosage selection is important for effective use of recycling agents and extenders in asphalt pavements. A standardized protocol for extender and recycling agent dosage selection does not presently exist. NCHRP Project 09-58 established a recycling agent dosage selection procedure that aims to restore the desired high-temperature grade of a blend of recycled binder, virgin binder, and additive. Their simplified procedure relies on the existence of class-specific relationships between the blended system high-temperature grade and additive content. Further, the dosage selection procedure assumes complete recycled binder availability. There is general consensus that complete recycled binder availability is not achieved in practice, which may yield asphalt mixtures with poor rutting performance. This study seeks to evaluate the universality of the slopes proposed in NCHRP Project 09-58 to both extenders and recycling agents and evaluate the rutting resistance of asphalt mixtures prepared using additive dosages selected to restore the high-temperature grade of the blended binder system. This study encompasses one reclaimed asphalt pavement (RAP) and one recycled asphalt shingles (RAS) mixture. Two extender and two recycling agent products were evaluated. The results indicate that different additive types yield different slopes of the blended system high-temperature grade versus additive content. The results also show that uncertainty should be accounted for when establishing a dosage selection procedure to ensure that the blended binder grade does not fall below the desired value. The rutting resistance of mixtures prepared using additive dosages intended to restore the high-temperature grade all passed recommended Hamburg wheel-track criteria.