Practical Tools for Optimizing Recycled Materials Content and Recycling Agent Dosage for Improved Short- and Long-Term Performance and Rejuvenated Binder Blends and Mixtures
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2019 Association of Asphalt Paving Technologist. All Rights Reserved. The use of large quantities of reclaimed asphalt pavement (RAP) and recycled asphalt shingles (RAS) in asphalt mixtures is desirable due to environmental and economic benefits. However, recycled asphalt mixtures with high recycled materials contents are usually less workable; difficult to compact in the field; and more prone to cracking, raveling and other durability-related pavement distresses. Recycling agents can rejuvenate the aged binders in the recycled materials to different degrees depending on type and dosage, facilitating the inclusion of increased amounts of recycled materials. Recycling agents modify the ultimate performance of the corresponding rejuvenated asphalt mixtures, thus estimating an optimum recycling agent dosage is critical to maximize its benefit without compromising the short- and long-term performance of the rejuvenated asphalt mixture. This study provides tools for estimating recycling agent dosage based on a target climate with minimum laboratory efforts by considering the type, source, and amount of recycled materials, and the source and grade of the base (virgin) binder. A total of 15 different recycled binder blends (base and recycled binders) and 32 different rejuvenated binder blends (recycled binder blends with recycling agent) were considered, including materials from eight states across the United States. Blending charts for recycled binder blends were established and verified, and later used to develop relationships to estimate the optimum dosage of recycling agent. The recycling agent optimum dosages were determined to match the continuous high-temperature performance grade (PGH) of the recycled binder blend to that required by the target climate, as this dosage yielded the best performance for rejuvenated binders and mixtures. Long-term rejuvenating effectiveness of recycling agents was verified by extensive evaluation of rejuvenated binder blends and mixtures. Discussion on optimizing RAP/RAS and base binder proportions and controlling the maximum dosage of recycling agent for economic and pavement performance considerations was also provided. Finally, practice-ready guidelines for evaluation, materials selection/optimization, and design of rejuvenated asphalt mixtures with high recycled materials contents were proposed.
