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Abstract
Asphalt binder fatigue resistance is important in determining overall pavement fatigue performance. One procedure commonly used to characterise asphalt binder fatigue resistance is the time sweep test, which consists of repeated cyclic loading in the dynamic shear rheometer (DSR). Generally, apparent changes in complex modulus and phase angle with respect to number of loading cycles are used to define fatigue performance. Although results from DSR testing have been shown to correlate well with asphalt mixture fatigue performance, the mechanisms responsible for changes in binder properties in the DSR were previously not well understood. Results in this study demonstrate that fracture can explain the changes in loading resistance during fatigue testing in the DSR. Under cyclic torsional loading of cylindrical specimens, fracture manifests as a circumferential crack that starts at the periphery of a sample and propagates inward, reducing the effective sample radius. Digital visualisation of binder specimens following testing allows for determination of the fractured and intact sample radius. Predictions of fracture propagation based on measurements of loading resistance and fracture mechanics concepts agreed favourably with direct measurements based on visualisation. Furthermore, it is shown in this study that fracture morphology and progression of crack growth of asphalt binders under time sweep testing match those observed for other materials under similar loading conditions. Based on these findings, fracture mechanics concepts are used to present an analysis framework that allows for predicting binder fatigue life at any loading amplitude using the results of a single time sweep test.