Identifying fatigue failure in asphalt binder time sweep tests

Identification of fatigue failure of asphalt binder in time sweep test results remains a question crucial to asphalt binder fatigue performance evaluation and prediction. This paper presents a comparison of different analysis approaches for defining the occurrence of fatigue failure during time sweep fatigue tests conducted in both control-displacement and control-stress loading modes. The candidate failure definitions evaluated include the traditional 50% reduction in stiffness parameter (S0.5), dissipated energy indicators including the dissipated energy ratio (DER) and the ratio of dissipated energy change (RDEC), as well as two phenomenological parameters corresponding to the peak in S × N and peak in phase angle. Both phenomenological parameters and dissipated energy based indicators were found to be effective in defining fatigue failure. Statistical analysis results further indicate that maximum S × N, maximum phase angle and RDEC approach provide equivalent fatigue life results, however, peak in S × N is strongly recommended for detecting fatigue failure of asphalt binder in time sweep tests because it is easy to calculate and well defined.