Endurance Limit of Hot Mix Asphalt Mixtures to Prevent Fatigue Cracking in Flexible 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 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 objectives of this study are to (1) test the hypothesis that there is an endurance limit in the fatigue behavior of HMA mixtures and measure its value for a representative range of HMA mixtures and (2) recommend a procedure to incorporate the effects of the endurance limit into mechanistic pavement design methods.

Language

  • English

Project

  • Status: Completed
  • Funding: $750000.00
  • Contract Numbers:

    Project 9-38

  • Sponsor Organizations:

    Federal Highway Administration

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

    American Association of State Highway and Transportation Officials (AASHTO)

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

    National Cooperative Highway Research Program

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

    Brown, E

  • Performing Organizations:

    Auburn University

    National Center for Asphalt Technology
    310 Sanford Hall
    Auburn, Alabama  United States  36849-5131
  • Principal Investigators:

    Brown, E

  • Start Date: 20040123
  • Expected Completion Date: 0
  • Actual Completion Date: 20090731
  • Source Data: RiP Project 8992

Subject/Index Terms

Filing Info

  • Accession Number: 01463122
  • Record Type: Research project
  • Source Agency: National Cooperative Highway Research Program
  • Contract Numbers: Project 9-38
  • Files: RiP, USDOT
  • Created Date: Jan 3 2013 2:17PM