Evaluation of Non-Solvent Methods to Characterize Reclaimed Asphalt Pavement Binder
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Increases in material costs have led many agencies to consider allowing higher percentages of reclaimed asphalt pavement (RAP) in asphalt mixes. However, as RAP percentages increase, the stiffness of the overall mix is likely to increase as well. Therefore, it is necessary to determine the properties of the RAP binder. Current procedures include conducting a solvent extraction to remove the aged binder from the RAP, distilling the aged binder from the solvent, and testing the recovered binder in accordance with standard binder grading tests. For high RAP content mixes, blending charts are then used to determine either the grade of virgin binder to add to the mixture or the amount of RAP that can be used. However, blending charts assume complete blending of the RAP and virgin binder. This research study examines the use of mix tests and prediction models as an alternative approach to characterizing the RAP mixtures. Several materials were utilized in this investigation, including 100% virgin, 100% RAP, and plant produced mixtures containing up to 25% recycled materials. Each mix was subjected to dynamic modulus testing. The data from these tests, along with volumetric properties, were used with the Hirsch model and Christensen-Anderson model to backcalculate binder properties. These properties were then compared to measured values from standard binder grading tests. The results indicated that the backcalculation technique was feasible for characterizing RAP binders. A sensitivity analysis was also performed using laboratory produced mixtures which varied by asphalt type, RAP source, and RAP content (20%, 35%, and 50%). Dynamic modulus tests were conducted and backcalculated binder properties were compared among the contributing factors. The trends were not as expected, with both the dynamic modulus and backcalculated properties exhibiting insensitivity to both binder grade and RAP percentage. It is recommended that further analysis be performed to determine the cause of these insensitivities.