Improved Procedure for Laboratory Aging of Asphalt Binders in Pavements

Use of the Superpave asphalt binder specification (AASHTO M320) requires short- and long-term aging procedures that accurately and reliably predict or rank the asphalt binder aging that occurs in hot mix asphalt (HMA) during field mixing and compaction and in service. The resources available to the Strategic Highway Research Program (SHRP) asphalt research program did not allow a conclusive investigation of either short- or long-term binder aging, specifically for modified systems. The procedures used in the Superpave mix design method -- the rolling thin film oven test (RTFOT, AASHTO T240) and the pressure-aging vessel (PAV, AASHTO PP1) -- were selected because of previous experience with their use and the promise they showed during development and in very limited validation with unmodified asphalt binders recovered from in-service pavements. Recent research and experience show that the RTFOT, while satisfactory for unmodified binders, is not an appropriate aging procedure for modified binders. During the test, modified asphalt binder films often do not flow within the rotating bottle, violating the basic premise of the test method, i.e., that the binder is exposed to heated air in a continuously moving thin film. This problem was evaluated in National Cooperative Highway Research Program (NCHRP) Project 9-10, "Superpave Protocols for Modified Asphalt Binders"; that research reached the same conclusion, that the present RTFOT does not adequately simulate the aging of modified asphalt binders that occurs in the field. Work is underway in NCHRP Project 9-23, "Environmental Effects in Pavement Mix and Structural Design Systems," to (1) verify the estimated period or rate of aging simulated by the current Superpave long-term binder aging and HMA conditioning procedures -- AASHTO PP1 and PP2 -- with data from Long Term Pavement Performance Seasonal Monitoring Program (LTPP SMP) and other relevant field experiments and (2) recommend any revisions to the procedures necessary to better match the laboratory aging to the original estimates. Due to the lack of SMP sections constructed with modified asphalt binders, this effort will necessarily concentrate on the behavior of unmodified materials. There has been considerable activity in recent years, both in the United States and in other countries, to find a more effective laboratory-aging procedure for asphalt binders. Most of this activity has focused on mimicking the physical property changes that occur during field aging; however, researchers have also considered chemical changes that occur during aging, particularly with respect to the kinetics of long-term field aging. Therefore, the development of new binder aging procedures should preferably consider both short- and long-term aging as well as the physicochemical characterization of the asphalt. Clearly, a new procedure to properly mimic short-term and long-term aging must be developed that is suitable for routine specification use, is user friendly, and has a short completion cycle. A single procedure, as long as it properly represents both short- and long-term field-aging mechanisms, should ideally replace both the RTFOT and PAV procedures. However, the approach selected in this project is to develop a procedure that is suitable for short-term aging and extendible to long-term aging. The first step, undertaken here, is the identification of potential procedures for calibration and validation with the laboratory aging of HMA mixes. Field calibration and validation will be pursued in future projects. The objective of this study is to develop and validate a recommended procedure for the short-term laboratory aging of asphalt binders usable in a purchase specification such as AASHTO M320 that (1) is equally applicable to neat and modified materials, (2) mimics the physical changes that occur in HMA mixes conditioned in accordance with AASHTO PP2, (3) quantifies binder volatility, and (4) is extendible to long-term binder aging.

Language

  • English

Project

  • Status: Completed
  • Funding: $519481.00
  • Contract Numbers:

    Project 9-36

  • Sponsor Organizations:

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590

    American Association of State Highway & Transportation Officials (AASHTO)

    444 North Capitol Street, NW, Suite 225
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001
  • Project Managers:

    Harrigan, Edward

  • Performing Organizations:

    Advanced Asphalt Technologies, LLC

    108 Powers Court, Suite 100
    Sterling, VA  United States  20166-9321
  • Principal Investigators:

    Anderson, David

  • Start Date: 20030217
  • Expected Completion Date: 0
  • Actual Completion Date: 20110930
  • Source Data: RiP Project 8550

Subject/Index Terms

Filing Info

  • Accession Number: 01549323
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 9-36
  • Files: RiP
  • Created Date: Dec 31 2014 1:01AM