Crack Evolution of Bitumen Under Torsional Shear Fatigue Loads

This study aims to model crack evolution in bitumen under a torsional shear fatigue load by dynamic shear rheometer (DSR). Fatigue crack length in the bitumen was predicted using a damage mechanics-based DSR cracking (DSR-C) model. The crack evolution is modelled using a pseudo J-integral based Paris’ law. Frequency weep tests and time sweep fatigue tests were conducted on an unmodified bitumen 40/60 and a polymer-modified bitumen X-70 at different temperatures, frequencies and loading amplitudes. Results demonstrate that the pseudo J-integral Paris’ law can accurately predict the crack evolution in the bitumen under the torsional shear fatigue load. A stiffer bitumen due to decreasing temperature has a smaller Paris’ law coefficient A and a greater exponent n, which proves that the fatigue crack grows faster at a lower temperature. The Paris’ law coefficients A and n are temperature-dependent fundamental material properties, which are independent of loading frequency or loading amplitude.