The National Academies Press

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Pages 44-58

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From page 44... ... The characteristic damage curve is used to predict the number of cycles to failure at different strain amplitudes to determine the fatigue endurance limit of the mixture. Fatigue tests with increasing strain amplitude are run in uniaxial tension to directly identify the fatigue endurance of the mixtures. Read the entire page →
From page 45... ... \| Test Monotonic Test Fatigue Test Comments (After Core and Cut) Constant Amplitude Increasing Amplitude 1 8.6 Broke during \|E* Read the entire page →
From page 46... ... Master Curve at 20°C Individual Specimens 0 10000 20000 30000 40000 50000 1.E-03 1.E-01 1.E+01 1.E+03 1.E+05 1.E+07 Reduced Frequency, Hz D yn am ic M od ul us , M Pa Figure 5.3. Dynamic modulus master curves for PG 67-22 optimum plus. Read the entire page →
From page 47... ... for all four mixtures together. The shift factors determined from the dynamic modulus master curves were then used to shift the individual phase angle curves at each temperature to obtain the phase angle master curve for each specimen. Read the entire page →
From page 48... ... Master Curve at 20°C Individual Specimens 0 20 40 60 1.E-03 1.E-01 1.E+01 1.E+03 1.E+05 1.E+07 Reduced Frequency, Hz Ph as e A ng le , D eg re e Figure 5.8. Phase angle master curves for PG 67-22 optimum plus. Read the entire page →
From page 49... ... and (b) show the characteristic curve fits for all mixtures obtained using the generalized power model and exponential model, respectively. Read the entire page →
From page 50... ... Individual Specimens Generalized power model Exponential model 0 0.25 0.5 0.75 1 0 0.5 1 1.5 S 2 2.5 3 C Figure 5.13. Characteristic curves using on-specimen LVDTs for PG 67-22 optimum plus. Read the entire page →
From page 51... ... Generalized power model (b) Exponential model 2 2.5 3 C Figure 5.15. Read the entire page →
From page 52... ... Due to machine compliance, the actual strains measured by the LVDTs were roughly one-quarter of the applied crosshead strain, so the strain amplitude was increased for subsequent tests. The fatigue tests are neither controlled strain nor controlled stress tests, rather a mixed mode of loading occurs because the crosshead rate is controlled, but the on-specimen strains are used for analysis. Read the entire page →
From page 53... ... . Evaluation of Endurance Limit Prediction from Characteristic Damage Curves Once dynamic modulus, initial stiffness, testing frequency, and damage curve coefficients are known, the strain level required to sustain any number of design load repetitions can be predicted. Read the entire page →
From page 54... ... Plot of strain level versus load repetitions for PG 67-22 optimum. Exponential model Generalized power model 1.0E-05 1.0E-04 1.0E-03 1.0E-02 1.0E+00 1.0E+081.0E+061.0E+041.0E+02 St ra in Number of repetitions Figure 5.20. Read the entire page →
From page 55... ... Generalized power models (b) Negative exponential models Figure 5.23. Read the entire page →
From page 56... ... Asphalt Mixture Grade Damage Characteristic Curve Form 67-22 Optimum 76-22 Optimum 67-22 Optimum+ 76-22 Optimum+ Exponential model 96 70 64 47 Generalized power model 261 197 194 164 0.0000 0.0001 0.0002 0.0003 67-22 @ Optimum 76-22 @ Optimum 67-22 @ Optimum+ 76-22 Optimum+ St ra in Asphalt concrete mix Exponential Model Generalized Power Model Figure 5.24. Comparison of critical strain to sustain 50 million cycles for all mixtures. Read the entire page →
From page 57... ... Stress versus pseudo strain plots for PG 67-22 optimum plus. Read the entire page →
From page 58... ... Another alternative is to run load-controlled tests and determine the appropriate load levels by using the measured dynamic modulus and target strain amplitude. A draft Proposed Standard Practice for Predicting the Endurance Limit of Hot Mix Asphalt (HMA) Read the entire page →

From page 44...

... The characteristic damage curve is used to predict the number of cycles to failure at different strain amplitudes to determine the fatigue endurance limit of the mixture. Fatigue tests with increasing strain amplitude are run in uniaxial tension to directly identify the fatigue endurance of the mixtures.