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Successful Use of Reclaimed Asphalt Pavement in Asphalt Mixtures
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Over 99 percent of reclaimed asphalt pavement (RAP) is put back to use, with most of it in asphalt pavements. Using RAP in asphalt mixtures can provide initial cost savings by replacing a portion of the aggregate and virgin asphalt binder in the asphalt mixture. It is important to consider the engineering performance of mixture containing RAP, as well as sustainable benefits and recognize that long RAP transportation distances can offset the environmental benefits. This keeps the RAP from being discarded in landfills. Improvements in mixture design and materials processing and handling have increased the amount of RAP that can be used in asphalt mixtures. The performance history of RAP mixtures over the past 50 years, when properly engineered, produced, and constructed, can provide comparable levels of service as asphalt mixtures with no reclaimed materials, referred to as virgin asphalt mixtures. The participating State DOTs indicated that optimizing RAP for good pavement performance can be accomplished through: 1) regular review of DOT specifications and mixture design procedures; 2) monitoring pavement performance; 3) working with asphalt producers, and 4) performing research as a basis for changes. However, in some cases, the durability of asphalt mixtures containing RAP has been poor. Additionally, State DOT rationale for using RAP can be for very different reasons with different goals. Virtual field visits of State DOTs regularly using RAP in asphalt mixtures revealed that DOTs with detailed policy and specifications on RAP use had obtained good control and pavement performance. A wide range of techniques and criteria used by State DOTs specifying and designing mixtures and pavements incorporating RAP were identified and summarized. All of the participating State DOTs indicated the desire to use mixture performance tests. Some wanted to use them for mixture designs in a BMD approach, for test strips (startup evaluations) and production or acceptance. Common themes with this were the need to get adequate virgin asphalt binder in mixtures, the need for appropriately setting performance test criteria and recognition of the benefit of long-term aging cracking test specimens. Another common theme was recognition that the resources required to implement BMD or use of performance tests on a regular basis are significant and may not be available in the short-term.