The National Academies

NCHRP 09-44 [Completed]

Developing a Plan for Validating an Endurance Limit for HMA Pavements

  Project Data
Funds: $250,000
Research Agency: Advanced Asphalt Technologies, LLC
Principal Investigator: Dr. Ramon Bonaquist
Effective Date: 4/17/2007
Completion Date: 2/28/2009

Bottom-up fatigue cracking occurs when traffic loads result in tensile strains of a magnitude sufficient to initiate cracking that eventually propagates through the hot mix asphalt (HMA) layers. Identifying the design parameters that preclude the initiation and propagation of fatigue cracks will result in long-life pavement designs that are not overly conservative. The strain level in an asphalt layer below which fatigue damage does not occur, known as the endurance limit, has not been established for HMA pavements.

The current state of pavement design does not recognize endurance limits for HMA pavements. Both the 1993 AASHTO pavement design guide and the Mechanistic-Empirical Pavement Design Guide (developed in NCHRP project 1-37A) yield pavement designs in which the pavement thickness increases as design traffic increases.

Research to establish the existence of an endurance limit for HMA mixes was completed in NCHRP Project 9-38, Endurance Limit of Hot Mix Asphalt Mixtures to Prevent Fatigue Cracking in Flexible Pavements. The experimental plan developed here will be implemented in NCHRP Project 9-44A.

The objectives of this study were to prepare plans to (1) validate the existence of an endurance limit for HMA mixes in pavements through an analysis of laboratory and field data; (2) determine, insofar as possible, the shift factor between the endurance limits for HMA mixes measured in the laboratory and the field; and (3) identify and recommend methodologies for incorporating an endurance limit in HMA mechanistic-empirical pavement design. The plan makes use of materials and performance data from appropriate U.S. and worldwide field and accelerated pavement test programs.

Product Availability: The project final report is available online as NCHRP Web-Only Document 134,
An Experimental Plan for Validation of an Endurance Limit for HMA Pavements.

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