Despite recent advancements in the design of asphalt mixtures containing Reclaimed Asphalt Pavement (RAP), many states are still cautious in their regulations to avoid durability problems related to the recycling process. In many states, RAP is currently not allowed in highest-class asphalt mixtures and in polymer-modified asphalt products. In addition, high percentages of RAP exceeding 25% are not commonly used in practice. On the other hand, many state agencies are taking a more aggressive approach by considering increasing the allowable percentages of RAP in hot-mix asphalt (HMA) to take full advantage of this promising technology. For instance, up to 50% RAP has been used in some asphalt mixtures, which produced an acceptable level of performance. However, to ensure successful use of RAP, confidences in the mixture design procedure require addressing many concerns related to the interaction between virgin and recycled materials and durability of the produced mixture. Current AASHTO recommendations make it difficult to design asphalt mixtures with high-RAP contents. Modifications to the current specifications are needed to assure agencies that satisfactory performance will result from the use of high-RAP content HMA mixes. A review of the RiP and TRIS databases was conducted. There are many ongoing and recently concluded NCHRP research projects that are related to this research topic including NCHRP 9-12 (Incorporation of Reclaimed Asphalt Pavement in the SuperPave System), NCHRP Report 452 (Recommended Use of Reclaimed Asphalt Pavement in the SuperPave Mix Design Method: Technician's Manual), NCHRP 9-33 (A Mix Design Manual for Hot Mix Asphalt) and NCHRP 9-46 (Improved Mix Design, Evaluation, and Materials Management Practices for HMA with High RAP Content) To allow for incorporating RAP in the design of HMA, many States have relied on blending charts developed by the Asphalt Institute in the late 1980s. Most States have also established limits on the maximum percentage of RAP that can be used. A percentage of RAP ranging between 10 to 50% is typically used. However, high percentages of RAP are not commonly used in practice. With the introduction of the SuperPave mixture design procedure, many questions were raised about the proper method by which to incorporate RAP in the produced SuperPave HMA. Despite that the original SuperPave mixture design procedure did not incorporate the use of RAP; many states have continued its use. In 1997, The FHWA RAP expert task force developed guidelines for the design of SuperPave mixtures containing RAP. Under those guidelines, RAP can be used up to about 15% without changing the virgin binder grade from that selected for the project location and conditions. Between 15 and 25% RAP, the high and low temperature grades of the virgin binder are both reduced by one grade to account for the stiffening effect of the aged binder (e.g., a PG 58-28 would be used instead of a PG 64-22). If over 25% RAP is to be used in the mix, blending charts are developed to determine the percentage of RAP that can be used with a given virgin binder. These guidelines were confirmed by the research findings of NCHRP 9-12. A serious concern that directly affects the performance of HMA incorporating RAP relates to the level of blending that occurs between the residual and virgin asphalt binders. The level of blending affects both the performance of the produced HMA and the economic competitiveness of the recycling process. If the designer assumes that the materials totally blend when it is actually behaving as a black rock, the mixture will not be stiff enough. In contrast, if it is assumed that RAP does not blend with the virgin asphalt when it is actually blending, then the mixture will be stiffer than expected. The problem can be further complicated if one considers that the blending process may take some time to occur and is influenced by the rejuvenating agent. The level of blending b

Research should be undertaken to 1) establish mechanistic test criteria for asphalt mixtures (warm and hot) containing high-RAP content and/or reclaimed asphalt shingles (RAS); and 2) propose asphalt mixture specifications that incorporate the mechanistic test criteria based on the results of the study.

It is anticipated that two field projects from each participating state will be included. Each project will consist of a conventional mixture and a mixture containing high RAP content and/or RAS. Thus, a total of four mixtures will be evaluated. Each participating state is expected to provide the followings: • JMF (mixture design information); • Sufficient loose mixture (conventional mix, RAP mix, RAP and/or RAS sources) for physical and mechanical tests; • Field cores LTRC or NCAT laboratory will perform the following: Testing and Analysis (4 mixtures described above) Extractions and PG Grading, 4 mixes and 2 RAP stockpiles (w/ GPC) Recovered Aggregate Properties Semi-circular bend test, SCB Overlay tester test, OT Energy Ratio Test Beam Fatigue Test Pseduo visco-elastic continuum damage, SVECD Data Analysis and preparation of Final Report Total per state cost of project: $84,000k ($28,000 each year for 3 years)

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