Fatigue Behavior of Bitumen and Mastic Using Higher-Order Harmonics

The fatigue life of the bituminous pavement is influenced by the fatigue behavior of each of its constituents. This study focuses on the fatigue behavior of bituminous material at two scales: bitumen and mastic. Conventional methods to determine the fatigue life of bitumen using time sweep tests make use of post-processing techniques established for bituminous mixtures and these post-processing techniques make use of linear viscoelastic parameters for the same. In this study, a new approach based on higher-order harmonic information obtained from a response stress waveform when subjected to repeated strain-controlled oscillatory shear loading is used. This approach works on the assumption that the occurrence/evolution of higher-order harmonics in a material exhibiting linear/nonlinear response when subjected to repeated loading is attributed to damage. For this, time sweep data at different frequencies and strain amplitudes are obtained using the large-amplitude oscillatory shear mode for bitumen and mastic under unaged and long-term aged conditions for 20000 cycles. The fatigue life is determined using the new approach involving the use of higher-order harmonics along with two conventional approaches and compared. Also, a fatigue range is established using these approaches to ascertain the influence of strain amplitude, frequency and aging on the fatigue behavior of bitumen and mastic.