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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
Details:
  • Publication/ Report Number:
    UCPRC-RR-2015-06
  • Resource Type:
  • Geographical Coverage:
  • Format:
  • Abstract:
    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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