Validating the Fatigue Endurance Limit for Hot Mix Asphalt (2010) / Chapter Skim
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Appendix A - Proposed Standard Practice for Predicting the Endurance Limit of Hot Mix Asphalt (HMA) for Long-Life Pavement Design
Appendix A - Proposed Standard Practice for Predicting the Endurance Limit of Hot Mix Asphalt (HMA) for Long-Life Pavement Design
Pages 96-104
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From page 96... ...
3.2 Long-Life Pavement Design – a pavement designed to last a minimum of forty years without bottom-up fatigue failure, or need for structural strengthening. 3.3 Normal strain levels – strain levels where failure (50 percent of initial stiffness)
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From page 97... ...
It involves collecting beam fatigue test data at specified strain rates, predicting the endurance limit based on a log-log extrapolation, and then running tests at the predicted strain level to confirm endurance limit behavior. Since the tests conducted at the predicted strain level should not fail, the failure point is extrapolated from the test data by use of one of several different techniques to confirm the endurance limit of the asphalt mixture.
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From page 98... ...
The coefficient of variation of the log (base 10) of the fatigue life of a properly conducted beam fatigue tests at normal strain levels is 5.4 and 6.8 percent, respectively, for within- and betweenlab variability.
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From page 99... ...
10. Data Analysis to Extrapolate Long-life Fatigue Tests Beam fatigue tests conducted at low strain levels are unlikely to fail in a reasonable number of cycles.
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From page 100... ...
The stiffness ratio is the stiffness measured at cycle n, divided by the initial stiffness, determined at the 50th cycle. Tsai reports that at a given cycle n, the beam being tested has a probability of survival past cycle n equal to the stiffness ratio times 100 percent.
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From page 101... ...
In most cases, low strain fatigue tests can be most accurately extrapolated using the singlestage Weibull function. However, in some cases, there are three distinct slopes to the transformed data, in which case the three-stage Weibull function may be used to provide a better estimate of the fatigue life.
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From page 102... ...
PG 76-22 Optimum Plus Sample 9 at 200 ms Stage 1 Stage 2 Stage 3 Stage 1 Initial Heating Stage 2 Stage 3 LN (n1)
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From page 103... ...
11.1.4 Normal Strain Tests 11.1.4.1 Micro-strain level 11.1.4.2 Number of cycles (measured) to 50 percent of initial stiffness 11.1.5 Low Strain Tests 11.1.5.1 Method of Extrapolation 11.1.5.2 Equation used for extrapolation and R2 value for equation 11.1.5.3 Extrapolated fatigue life Nf for 50 percent of initial stiffness 11.1.6 Endurance Limit 11.1.6.1 Log-Log plot of data with cycles to failure on x-axis and micro-strain on y-axis.
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From page 104... ...
"Using the Three-Stage Weibull Equation and Tree-Based Model to Characterize the Mix Fatigue Damage Process." In Transportation Research Record No. 1929, Transportation Research Board, Washington, DC, 2005, Pp 227-237.
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