Relationships Between the Fatigue Properties of Asphalt Binders and the Fatigue Performance of Asphalt Mixtures (2022) / Chapter Skim
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From page 19... ...
19 Research Approach Binders Sixteen binders were selected specifically for testing in NCHRP 09-59. These represented a wide range of binder types and grades: • Six polymer-modified binders, • One binder modified with ground-tire rubber, • Two modified with recycled engine oil bottoms (REOB)
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20 Relationships Between the Fatigue Properties of Asphalt Binders and the Fatigue Performance of Asphalt Mixtures aged ("residual") asphalt.
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Research Approach 21 NCHRP 09-59 Mixtures A 9.5-millimeter (mm) nominal maximum aggregate size (NMAS)
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22 Relationships Between the Fatigue Properties of Asphalt Binders and the Fatigue Performance of Asphalt Mixtures In the mix design study, one asphalt (AAG-1) with a granite aggregate (NMAS of 12.5 mm)
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Research Approach 23 the temperature at which the loss modulus G′ = 17.5 MPa at a frequency of 10 Hz. Only one test temperature was run using this protocol, as problems seemed to occur at temperatures much higher or lower than this value.
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24 Relationships Between the Fatigue Properties of Asphalt Binders and the Fatigue Performance of Asphalt Mixtures at the center of the beam were recorded and used to calculate the flexural stiffness. The stiffness at the 50th loading cycle was defined as the initial stiffness of each beam specimen.
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Research Approach 25 of the fingerprint dynamic modulus results to the corresponding dynamic modulus results determined in the dynamic modulus test was used as a quality control indicator, and test results were accepted when the DMR was between 0.9 and 1.1. The uniaxial cyclic fatigue test was conducted at three strain levels (by controlling the maximum displacement of the actuator)
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26 Relationships Between the Fatigue Properties of Asphalt Binders and the Fatigue Performance of Asphalt Mixtures characteristic curve and cracking resistance for each mixture on the basis of the S-VECD model. More detailed information about the dynamic modulus and uniaxial cyclic fatigue is included in Appendix C.
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Research Approach 27 = × ε ( )
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28 Relationships Between the Fatigue Properties of Asphalt Binders and the Fatigue Performance of Asphalt Mixtures As explained in Appendix D, testing during NCHRP 09-59 suggests that binder FSC and mix FSC are not identical but are close over the range of data analyzed during NCHRP 09-59. The difference may arise from the complex state of stress existing in the asphalt binder in a mixture as compared with the uniaxial stress typically used in binder testing.
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Research Approach 29 analysis of the relationship between fatigue exponent and phase angle difficult or impossible. Fortunately, as part of the SHRP fatigue test program, a temperature dependence experiment was done in which a mix made with a single binder (AAD-1)
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30 Relationships Between the Fatigue Properties of Asphalt Binders and the Fatigue Performance of Asphalt Mixtures Determining the FFPR values from fatigue data involved fitting the observed fatigue data to the GFTAB model, as explained in Appendix D. The research team used Microsoft Excel Solver, which employs non-linear least squares to determine model parameters.
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Research Approach 31 = −1 (7) 11 12C C SC where C = pseudo stiffness, S = damage parameter, and C11, C12 = material constants.
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32 Relationships Between the Fatigue Properties of Asphalt Binders and the Fatigue Performance of Asphalt Mixtures Ni = number of loading cycles in loading step i, γi = shear strain in binder (%) , k1 = constant determined through statistical analysis to be 2, and δ = binder phase angle (degrees)
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Research Approach 33 The GRP was calculated using an equation suggested by Rowe (2011)
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34 Relationships Between the Fatigue Properties of Asphalt Binders and the Fatigue Performance of Asphalt Mixtures a given temperature and loading frequency, rather than inherent overall strain tolerance. For this reason, GRP should be evaluated in comparison with FSC (FFPR × FSC*
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Research Approach 35 where CH = damage ratio after healing, C = damage ratio before considering healing, and RH = healing ratio (0 for no healing, 1 for complete healing)
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