Laboratory Validation of an Endurance Limit for Asphalt Pavements

National Cooperative Highway Research Program (NCHRP) Project 9-44A extended the results and findings of NCHRP Project 9-38, "Endurance Limit of Hot Mix Asphalt Mixtures to Prevent Fatigue Cracking in Flexible Pavement." Project 9-44A paid particular attention to the influence of asphalt binder and mixture properties on the fatigue endurance limit and to the relationship of the endurance limit to the phenomenon of healing hypothesized to occur in asphalt mixtures during the rest period between load applications in the laboratory and in pavements. The research investigated the relationship of the fatigue endurance limit to factors such as asphalt binder rheology, air voids, asphalt content, temperature, strain level, number of load cycles, and rest period between load cycles. Both beam fatigue (AASHTO T321) and uniaxial compression-tension testing were conducted according to a factorial design that permitted statistical analysis of the main factor and up to three-factor interactions. Robust regression models were developed that described the effect of the main factors and factor interactions on the stiffness ratio (SR). Testing was conducted with rest periods of 0, 1, 5, and 10s between load cycles. The endurance limit can then be determined for any mixture initial stiffness as the strain at SR = 1, i.e., for the condition in which complete healing of the fatigue damage takes place after each load cycle. The research reaffirmed the existence of the HMA fatigue endurance limit and demonstrated that the endurance limit is the result of a balance between loading damage and the healing, i.e., damage recovery, that happens during rest periods and that the value of the limit varies with the mixture initial stiffness (acting as a surrogate for binder rheology, air voids, asphalt content, and temperature) and the duration of the rest period. It was also found that for a load cycle of 0.1s, a rest period greater than 5 to 10s (from beam fatigue testing) or greater than 3s (from uniaxial testing) will not produce additional healing of the fatigue damage in the laboratory. This report fully documents the research and discusses incorporation of the endurance limit derived from the SR regression model formalism as an algorithm in Pavement Mechanistic Empirical Design software and other design methods.


  • English

Media Info

  • Media Type: Digital/other
  • Features: Appendices; Figures; Photos; References; Tables;
  • Pagination: 36p
  • Serial:
    • NCHRP Report
    • Issue Number: 762
    • Publisher: Transportation Research Board
    • ISSN: 0077-5614

Subject/Index Terms

Filing Info

  • Accession Number: 01502764
  • Record Type: Publication
  • ISBN: 9780309283663
  • Report/Paper Numbers: Project 9-44A
  • Files: TRIS, TRB, ATRI
  • Created Date: Dec 31 2013 9:18AM