Nonlinearity of bituminous materials for small amplitude cyclic loadings

This paper focuses on the influence of the cyclic loading amplitudes on the behaviour of bitumen and bituminous mixtures. The present work considers only rather small strain amplitude (lower than 100 mu m/m for mixtures and 10% for bitumen). Complex modulus tests on mixtures were conducted at four levels of strain amplitude for a large range of temperatures and frequencies. Tension-compression tests at the temperatures lower than 20 degrees C and shear tests at temperatures higher than 20 degrees C were performed to measure the complex modulus of bitumen which is used to produce the mixtures. Moreover, individual strain tests, strain sweep tests and fatigue tests at 10, 30 and 50 degrees C were carried out to study the influence of the strain amplitude and cyclic effects on the complex modulus of bitumen. The obtained results indicated that the nonlinearity (effect of strain amplitude) on both bitumen and bituminous mixtures respects the Time Temperature Superposition Principle (TTSP). However, the temperature-frequency has inverse effects on the nonlinear behaviour of bitumen and bituminous mixtures. The cyclic effect was shown to be not negligible when analysing the nonlinearity phenomenon.