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The development process included a number of phases, which are described in the report. Included in this report are the following: 1) a state-of-knowledge review for fatigue response of asphalt aggregate mixes, 2) a description of a pilot test program and its results, 3) a description of an expanded test program using the equipment and methodology selected in the pilot test program, and 4) a description of a mix analysis and design system, which can be used to mitigate fatigue cracking.
This dissertation presents the viscoelastic characterization of asphalt concrete in indirect tensile testing and the development of a simple performance test for fatigue cracking. The analytical solutions to calculate creep compliance and center strain from displacements measured on the specimen surface were developed based upon the theory of viscoelasticity. These developments were verified by 3-D finite element viscoelastic analysis and tests. A simple performance test was developed based on these solutions and work potential theory. To evaluate its validity, the indirect tensile tests were performed on WesTrack asphalt mixtures varying aggregate gradations, asphalt contents, and air void contents. Fracture energy obtained from indirect tensile strength testing and creep testing was highly correlated with field performance of these mixtures at WesTrack. A combination of indirect tensile creep and strength testing was proposed as a simple performance test for fatigue cracking. Recommendations for expanding the applicability of the simple performance test developed are provided.
A variety of testing methods are employed by researchers to characterize the fatigue performance of asphalt concrete. These testing methods need to be evaluated based on their performance to characterize the fundamental properties and field performance of mixtures. In this study, the indirect tensile tests and the uniaxial tests were investigated. The indirect tensile creep tests and the uniaxial tensile creep tests were performed on a North Carolina mix to study the characterization of the fundamental properties and on WesTrack mixes to study the characterization of field performance. It was found that that the values of creep compliance from the indirect tensile creep and the unaxial tensile creep tests on North Carolina mix cannot be compared favorably. Fracture energies from the indirect tensile strength tests on WesTrack mixes highly correlate with the field performances, while those from uniaxial direct tension tests did not match field performances. It is believed that anisotropicity could be the cause of differences in performance of the two test methods. It is disconcerting when researchers attempt to establish a constitutive relationship between the property parameters of mixtures and laboratory fatigue life using different testing methods, without knowing if the laboratory fatigue life from these testing methods really reflects field performance. Further research is needed to obtain a better understanding of different testing methods.