Validating the Fatigue Endurance Limit for Hot Mix Asphalt (2010) / Chapter Skim
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Although the endurance limit is defined as an essentially infinite fatigue life for metal alloys, testing for an infinite life is impractical. The endurance limit must be defined in practical, usable terms if it is to have meaning.
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. Considering this shift factor, laboratory testing to 50 million cycles would equate to approximately 500 million loading cycles in the field or approximately the maximum possible loading in a 40-year period.
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A 3.7% reduction in air voids was observed, resulting in a target air voids content of 3.3 ± 0.5% for the optimum plus asphalt content samples. Phase II Additional testing was completed at the end of Phase I to examine the variability of beam fatigue testing and calculation of the endurance limit and the affect of binder grade on the endurance limit.
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NCAT later added a second IPC Global beam fatigue device. The Asphalt Institute had some difficulties testing at low strain levels and testing to greater than 10 million cycles to failure with their Interlaken hydraulic load frame.
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Indirect Tensile Testing The literature indicates that parameters from the indirect tensile strength test, AASHTO T322, may be correlated with parameters related to the endurance limit. This test was considered as a possible surrogate test, which could be conducted more expediently, than the long-duration beam fatigue tests.
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