Detection of Recycled Asphalt Pavement (RAP) in Bituminous Mixtures
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2004-06-01
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Edition:Final report
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Abstract:The overall goal of this study was to assist the Illinois Department of Transportation (IDOT) in identifying and developing methods for quality assurance of hot-mix asphalt (HMA) containing recycled asphalt pavement (RAP). Although the use of RAP can lead to economical and environmental benefits, the assurance of proper RAP handling and usage in HMA is needed to ensure adequate pavement performance. The two main areas of investigation in this study were: 1) to evaluate current practices for RAP handling and monitoring in Illinois; and 2) to identify and/or develop laboratory tests to detect and quantify the amount of RAP in a given mixture. A detailed survey of Illinois contractors was used to characterize current practices of RAP stockpiling and handling, and to assess the capabilities of the current infrastructure of HMA plants in Illinois, particularly with respect to the ability to control and monitor the rate of RAP proportions in a given mixture. Since most plants have the capability of recording mix composition, it is recommended the IDOT require these records to be kept as part of routine HMA quality control. The results of the plant surveys also suggest that it may be feasible at this time for IDOT to phase in the requirement for all HMA plants to be capable of recording mixture proportions during production including RAP, since the cost of upgrading the relatively small number of plants without this capability is not cost prohibitive to the contractor. Laboratory investigations led to the successful development of prototype test methods for both rapid and rigorous determination of the presence and quantity of RAP in a mixture sample. The most promising rapid detection method developed involves a visual inspection of residue obtained after subjecting the sample to careful washing with solvents. For more rigorous determination of RAP amount, the binder from the mixture in question is recovered and tested in the dynamic shear rheometer, along with samples of the virgin binder and recovered binder to determine the in-situ RAP percentage. Two sets of blind samples were used to validate the most promising rapid and rigorous test methods. Although promising results were obtained, more testing is recommended in order to validate the forensic RAP detection and quantification methods developed in this study for a broader range of materials, including polymer-modified asphalts. /Abstract from report summary page/
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