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Validating the Fatigue Endurance Limit for Hot Mix Asphalt (2010) / Chapter Skim
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Pages 7-14

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From page 7...
... Arguments for the Existence of the Endurance Limit Pavements have been designed primarily to resist rutting of the subgrade and bottom-up fatigue cracking. In classical pavement design, as design load applications increase, pavement thickness must also increase.
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From page 8...
... (180 mm) thick, rutting tended to occur in the HMA layers.
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From page 9...
... . In this study, three unmodified asphalt binders with different temperature susceptibilities and two modified asphalt binders -- produced using one base asphalt and two levels of modification 9 Effect of Change in Factor Factor Change in Factor On Stiffness On Fatigue Life in Controlled Stress Mode of Test On Fatigue Life in Controlled Strain Mode of Test Asphalt Penetration decrease increase increase decrease Asphalt Content increase increasea increasea increaseb Aggregate Type increase in rough texture and angularity increase increase decrease Aggregate Gradation open to dense increase increase decreased Air Void Content decrease increase increase increased Temperature decrease increasec increase decrease Notes: aReaches optimum level above that required by stability considerations.
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From page 10...
... Tests were conducted at an initial strain level of 400 ms, and findings indicated that the fatigue lives of the two modified asphalt binders were an order of magnitude greater than the fatigue life of one of the unmodified asphalt binders (produced from the same source as the base asphalt used to create the modified asphalt binders)
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From page 11...
... ." In summary, there appears to be significant historical data indicating that the laboratory fatigue performance of modified asphalt mixtures is greater than mixtures made with unmodified asphalt binders. In some reported cases, modified asphalt mixtures have exhibited an order of magnitude greater fatigue life compared to unmodified asphalt mixtures.
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From page 12...
... mixtures to examine the effect of increasing asphalt binder content. Flexural beam fatigue tests conducted at 600 ms indicated a slight increase in fatigue life with the 0.5% higher asphalt content.
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From page 13...
... They concluded that low strain testing in the range of 70 ms resulted in "extraordinarily long fatigue life." Researchers at the University of Illinois, under the direction of Carpenter, have conducted a number of low strain beam fatigue tests that indicated a break in fatigue life behavior for samples with fatigue lives in excess of 11 million cycles (37)
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From page 14...
... . Overloads, or strain levels exceeding the endurance limit, are most likely to occur either in the warmest summer months (37)
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Key Terms

  • endurance limit
  • fatigue life
  • million cycles
  • dissipated energy
  • loading cycles

  • beam fatigue
  • unmodified asphalt
  • initial stiffness
  • shift factor
  • asphalt binders

  • modified asphalt
  • asphalt pavements
  • asphalt content
  • shift factors
  • versus load

  • optimum asphalt
  • bottom layer
  • plateau value
  • performance test
  • uniaxial tension

  • strain levels
  • strain level
  • highway research
  • asphalt binder
  • pavement design

  • base asphalt
  • versus loading
  • equivalent annual
  • loading cycle
  • rich bottom


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