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Evaluation of the combined effects of reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAS), and different virgin binder sources on the performance of blended binders for mixes with higher percentages of RAP and RAS : a national center for su
  • Published Date:
    2015-11-01
  • Language:
    English
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Evaluation of the combined effects of reclaimed asphalt pavement (RAP), reclaimed asphalt shingles (RAS), and different virgin binder sources on the performance of blended binders for mixes with higher percentages of RAP and RAS : a national center for su
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    This report summarizes the main findings from a project funded by the National Center for Sustainable Transportation (NCST) to investigate the use of higher percentages of reclaimed asphalt pavement (RAP) and reclaimed asphalt shingles (RAS) as a replacement for a percentage of the virgin binder in new asphalt mixes in California. The research focused on testing procedures that do not first require chemical extraction and recovery of the age-hardened asphalt binders from the RAP and RAS. Five different asphalt binders covering two performance grades (PG 64-16 and PG 58-22) and sourced from three California refineries were evaluated in this study. The influence of two different percentages of RAP (25 and 40 percent by binder replacement) and one percentage of RAS (15 percent by binder replacement) were evaluated through partial factorial asphalt binder testing and full factorial fine aggregate matrix (FAM) mix testing. The effect of a petroleumbased rejuvenating agent added to selected mixes (with 40 percent RAP and 15 percent RAS) was also investigated. Testing was limited to the intermediate temperature properties of the mixes (i.e., 4°C to 40°C). Key observations and findings from this project include the following: - Asphalt binder extracted and recovered from RAS could not be tested due to its very high stiffness. The RAS binder was not sufficiently workable to mold samples for testing in a dynamic shear rheometer (DSR). - Testing procedures were developed as part of this preliminary testing phase to measure dynamic shear modulus at different temperatures and frequencies, and a method for preparing and testing FAM mix specimens was developed. Cylindrical specimens 0.5 in. (12.5 mm) in diameter cored from a Superpave gyratory-compacted FAM mix specimen were tested using a torsion bar fixture in a DSR. Preliminary testing of FAM mixes prepared with materials passing the #4, #8, or #16 (4.75 mm, 2.36 mm, or 1.18 mm) sieves indicated that this approach is repeatable and reproducible, and produces representative results for characterizing the performance related properties of composite binder at binder replacement rates up to 40 percent and possibly higher. Use of materials passing the #8 sieve (2.36 mm) is recommended. - The effect of RAP in increasing the stiffness of blended binders was dependent primarily on the asphalt binder grade and, to a lesser extent, by the source of asphalt binder. - Statistical analyses of the test results indicated that RAP and RAS content, asphalt binder grade and source, and rejuvenating agent all had a significant influence on FAM mix stiffness, as expected. - The FAM mixes containing RAS showed similar stiffnesses to the corresponding control mixes (i.e., containing no reclaimed materials), suggesting that the RAS binder did not effectively blend with the virgin binder at the temperatures and mixing durations used in this study. - The influence of rejuvenating agent on reducing the blended binder and FAM mix stiffnesses was evident. Additional testing (beyond the scope of this study) is required to evaluate the long-term behavior of mixes produced with rejuvenating agents to 2 determine whether the benefits are limited to production and early life, or whether they extend through the design life of the layer. - Reasonable correlations were observed between the stiffnesses of asphalt binder and the stiffnesses of FAM mixes at testing frequencies ranging from 0.1 Hz to 10 Hz. Discrepancies between the two measured stiffnesses may be an indication that complete blending of the virgin and reclaimed asphalt binders was not achieved in the FAM mix, but was forced during the chemical extraction and recovery. This warrants further investigation. Based on the findings from this study, FAM mix testing is considered to be a potentially appropriate procedure for evaluating the properties of blended asphalt binder in mixes containing relatively high quantities of RAP and RAS. Further testing on a wider range of asphalt binder grades, asphalt binder sources, and RAP and RAS sources is recommended to confirm this conclusion and to develop models for relating binder properties determined from FAM mix testing to those determined from conventional performance grade testing. Chemical analyses of blended binders may provide additional insights for interpreting test results and warrant further investigation.
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