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Field Control and Performance of Asphalt Mixtures Containing Greater than 25 Percent Reclaimed Asphalt Pavement : Draft Final Report
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    The Alabama Department of Transportation (ALDOT) and other highway agencies are interested in utilization of higher percentages of reclaimed asphalt pavement (RAP) in asphalt mixtures. There are a number of research studies at both state and national levels examining mix design and production issues related to high RAP content mixes. One of the mix design issues deals with the grade of virgin binder that should be used with RAP mixtures. The traditional approach has been to use a softer grade of virgin asphalt to rejuvenate the aged binder in the RAP, specifically for RAP contents above 15 to 20 percent. A number of recent studies have indicated that softer binders may not be necessary, whereas other pavement engineers have suggested combining warm mix asphalt (WMA) technologies with higher RAP content mixes as a means of achieving more durable asphalt binder films. Most highway agencies have decades of experience with hot mix asphalt (HMA) containing low percentages of RAP (i.e., below 25% by weight of aggregate). Although there have been studies to directly compare the performance of virgin mixtures with mixtures containing RAP, there is a general perception that RAP mixtures may be more susceptible to various modes of cracking (i.e. fatigue, thermal, reflection). This is due to the fact that the RAP binder is aged, stiffer, and less strain tolerant than a virgin binder. As the RAP proportion increases, there is the potential for an increase in mixture stiffness and a decrease in resistance to cracking. Therefore, numerous recent research efforts have strived to increase the RAP percentage without sacrificing performance. The principal concern of highway agencies is that a high percentage of RAP may significantly reduce the performance of the pavements, resulting in increased pavement rehabilitation costs. Therefore, before specifying high RAP percentages, agencies want assurance that high RAP mixes will provide satisfactory field performance.
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