University of California Pavement Research Center

Including some reclaimed asphalt in new asphalt concrete mixes used on pavements has attracted considerable interest from departments of transportation and other agencies mainly because of the cost savings and environmental benefits associated with substituting reclaimed binder for some virgin binder. However, the laboratory testing in this study, which was all undertaken on unaged asphalt specimens, has clearly shown that although adding reclaimed asphalt to new mixes is likely to increase mix stiffness, which in most instances is likely to improve its rutting resistance, the cracking resistance properties could be diminished. Preliminary findings from this study indicate that: The asphalt binder in reclaimed asphalt shingles (RAS) may not effectively mobilize and blend with virgin asphalt. If used as a binder replacement, this recycled asphalt could reduce the actual effective binder content in the mix, which could in turn lead to early cracking and raveling. The results of tests on the properties of blended virgin and reclaimed asphalt binders can be influenced by the chemistry of the solvent used to extract and recover the binders. Fine aggregate matrix (FAM) mix testing was found to be a potentially appropriate alternative procedure for evaluating the properties of blended asphalt binder in mixes containing relatively high quantities of reclaimed asphalt. Although considerable laboratory testing has been undertaken to evaluate the performance of mixes in which reclaimed/recycled asphalt binders are a partial replacement of virgin binders, only limited longer-term, full-scale field testing has been undertaken. Consequently, any potential effects of accelerated aging of these mixes caused by the presence of the aged reclaimed binder and its effects on long-term performance are not fully understood. Reclaimed/recycled binder cannot be considered as a generic material with consistent properties, and some form of mix performance testing (FAM or full-grading) needs to be undertaken to assess the influence of the reclaimed/ recycled binder replacement on longer-term performance. The known benefits of adding polymer to asphalt binders may be compromised if some of the virgin binder is replaced with binder from RAP or RAS. The use of a softer virgin binder to compensate for the stiffening effect of high RAP/RAS binder replacement rates (i.e., above 25 percent) appears to be justified. It is recommended that the benefits and risks of using reclaimed asphalt binders in pavement mixes be further quantified in additional laboratory testing on appropriately aged specimens, and in controlled full-scale field studies with associated laboratory testing. Accelerated loading tests are recommended as part of this research.