Long-term aging of recycled binders.
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Long-term aging of recycled binders.

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      Asphalt pavement is America’s most recycled material. Eighty million tons of asphalt, nearly 80% of all milled asphalt pavement, is recycled every year [1]. To effectively maintain its 40,000 miles of paved roads, the Florida Department of Transportation continues to refine its maintenance and rehabilitation methods. Hot in-place recycling is a rehabilitation method with recognized financial and environmental benefits when used properly. The primary concern with this method is the longevity of the recycled pavement. Aging of the recycled binder has a strong impact on the durability of the pavement. Asphalt binders harden with age and become prone to cracking. Rejuvenators are added to hard asphalt to enhance its rheological properties. Traditional methods that evaluate the effectiveness of binder rejuvenation only examine the early performance. However, the recycled asphalt should have acceptable long-term performance. The pavement might crack prematurely if the asphalt binder ages quickly. This research looks beyond early performance and evaluates long-term aging of recycled asphalt binders and compares it with that of virgin asphalt. Aging rates of recycled asphalt binders, rejuvenated by five different commercially available products, were studied and compared with the aging rate of the virgin binder. These rejuvenators were selected through a screening process based on their softening power and other considerations. The Pressure Aging Vessel (PAV) was used to simulate aging, and the high temperature Performance Grade (PG) was implemented to characterize the level of aging. The cracking resistance of recycled asphalt mixes was evaluated using the Texas Overlay Test. The change in the mix crack resistance over time was evaluated using the Accelerated Pavement Weathering System. The results showed a significant difference in the long-term aging of samples recycled with different recycling agents. While some samples aged significantly slower than the virgin binder, others aged faster. Analysis of the aging rates of binders revealed that selecting a proper recycling agent can extend the service life up to nine years. In contrast with original binders, the aging rate of recycled binders did not decrease significantly after the first 20 hours of PAV exposure. Therefore, even when recycled binders pass PG requirements, they might be less durable than virgin asphalt. Mix tests showed that rejuvenated mixes generally have a better initial fatigue and reflective cracking resistance than new mixes. However, their cracking resistance might drop faster over the pavement life. The knowledge obtained from this study identified approaches to evaluate long-term aging of recycled binders. Performing a durability test, limiting the aging rate, and increasing PAV exposure time are the three proposed alternative procedures. These procedures can be used to modify the specifications so that the longevity of the recycled asphalt is considered.
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