Laboratory Validation of an Endurance Limit for Asphalt Pavements (2013) / Chapter Skim
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5 Beam Fatigue Testing Beams were prepared using vibratory loading applied by a servohydraulic loading machine. A mold was used with inside dimensions larger than the required dimensions of the beam to allow for sawing to achieve standardized specimen dimensions.
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6rest periods with a frequency of 10 Hz according to AASHTO T321, while others used a 0.1s sinusoidal loading followed by a rest period. Figure 7 shows the waveform used in the study, which required a software modification in the operating system of the loading machine.
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7 St re ss o r St ra in St re ss o r St ra in 0 0 St re ss o r St ra in Time Lag Stress Strain or Deflection Time Time Time 0 Stress Strain Deflection First Few Cycles During Test (a) Sinusoidal (AASHTO T321)
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8was decided to use two replicates in the rest of the study. In the beam fatigue study, the results from a total of 468 tests were analyzed to develop the SR model as discussed in the subsequent section.
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9 Beam Fatigue Test X Uniaxial Fatigue Test 4.5 9.5 4.5 9.5 4.5 9.5 4.5 9.5 4.5 9.5 4.5 9.5 Strain Level Rest Period (seconds) 0 x x x 1 5 x x x x 10 0 x x x 1 x 5 x x x 10 x 0 x 1 x 5 x 10 0 x x x 1 5 x x x 10 x 0 x x x 1 x 5 x x x x 10 0 1 x 5 10 0 x x x 1 x x 5 x x 10 0 x x x 1 5 x x x 10 x 0 x 1 5 x 10 PG 58-28 4.2 5.2 4.2 5.2 4.2 5.2 Temperature (F)
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10 y = 0.8942x + 0.078 R2 = 0.891 Se/Sy=0.32 N=934 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Pr e di ct ed SR Measured SR Figure 10. Predicted versus measured SR for the beam fatigue SR model.
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11 0 50 100 150 200 250 1 2 5 10 20 En du ra n ce Li m it, µε Rest Period, seconds Eo=3000 ksi Eo=1000 ksi Eo=200 ksi Eo=50 ksi Figure 12. Summary of endurance limit values versus several rest periods and stiffness values using the beam fatigue test model.
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12 (rest period and AC moduli [Eo]
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