Reversible phenomena and fatigue damage during cyclic loading and rest periods on bitumen

This paper investigates the effects of reversible phenomena (nonlinearity, self-heating and thixotropy) and damage on bitumen. Four specimens were subjected to different cyclic loading tests: complex shear modulus (), strain amplitude sweeps (SAS) and Loading and Rest Periods (LRP). LRP test consists of applying series of cyclic loading at high strain amplitude (gamma(0)), such as in classical fatigue tests, followed by rest periods (five repetitions). During rest, G* was regularly measured. Specimen temperature was carefully measured during all tests. 2S2P1D rheological model was used along with tests to characterise linear viscoelastic behaviour, and to calculate the self-heating effect on the measured during LRP test SAS results were used to evaluate nonlinearity effect LRP results showed that temperature may significantly increase during loading. About 5 degrees C increase was observed after 10,000 cycles with gamma(0) = 2%. Such increase results in 70% to 80% modulus decrease, depending on the analysed gamma(0). Damage was found to cumulate linearly with the total number of applied cycles at fixed gamma(0), with negligible phase angle variation. After correcting temperature and damage effects, thixotropy evolution could be observed on Black diagrams, where a shared direction with nonlinearity was observed. This suggests a shared intrinsic mechanism, possibly on the microstructural level. Finally, it is clear that reversible phenomena play an important role on the measured , especially at higher gamma(0). Such effects could not be neglected for the analysed LRP tests (whose loading part is similar to classical fatigue tests). Tests producing less reversible effects should be preferred.