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Long-term aging of recycled binders.
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  • Abstract:
    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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