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Ageing of bitumen changes its stiffness related properties and is thought to have a considerable impact on its fatigue performance. Time sweep tests are a commonly used methodology to evaluate the fatigue performance of bitumen over the course of its lifetime. This study comparatively evaluated the fatigue performance of six aged bitumen samples using various commonly employed time sweep testing-based approaches, including conventional methods (50% reduction in complex modulus and peak in phase angle) and newer methods (peak in S × N and two dissipated-energy-based approaches). The statistical analysis of the results illustrated that although the trends of fatigue life versus ageing levels were similar, different methods had significantly varying results. It was generally seen that ageing increased stiffness and the calculated fatigue life of bituminous binders improved when commonly applied strain levels of 5% and 7.5% were used. This result demonstrates the need to develop more robust methods to fully capture the true fatigue related deterioration of aged binders in the future. Among all the methods, the peak in S × N approach was found to be the most efficient based on the criteria used in the study and was the recommended approach considering current limitations. It showed no apparent defects and had the best correlations with other methods when the applied strains were 5% and 7.5%.
Hu et al. (Sat,) studied this question.