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

Abstract 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 ( G ∗ ), strain amplitude sweeps (SAS) and Loading and Rest Periods (LRP). LRP test consists of applying series of cyclic loading at high strain amplitude ( γ 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 G ∗ tests to characterise linear viscoelastic behaviour, and to calculate the self-heating effect on the measured G ∗ during LRP test. SAS results were used to evaluate nonlinearity effect. LRP results showed that temperature may significantly increase during loading. About 5 °C increase was observed after 10,000 cycles with γ 0 = 2%. Such increase results in 70% to 80% modulus decrease, depending on the analysed γ 0 . Damage was found to cumulate linearly with the total number of applied cycles at fixed γ 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 G ∗ , especially at higher γ 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.