Evaluation Of The Fatigue Properties Of Bituminous Binders

The fatigue damage of bituminous binder has been one of the most important factors which lead to the fatigue damage of asphalt mixtures, because of the persistent increase in road traffic. The application of perpetual pavement has made fatigue damage one of the most needed preventive damages, so the study on fatigue performance of bituminous binder is needed. However, the current fatigue evaluation methods for bituminous binders have received considerable criticism for their defects in reflecting the accumulation process of fatigue damage and in evaluation of the fatigue properties of modified fatigue bituminous binder. It is needed to find a new evaluation method to evaluation the fatigue properties of both bituminous binder and modified bituminous binder correctly.In this paper, the authors came up with a new way to evaluation the fatigue property of bituminous binder. A new type of specimen and a new test system were introduced to avoid the problem of adhesion failure between rotor and bituminous binder and to test the "true" fatigue response. Considering the fact that load- resisting property and crack propagation rate varied from binders to binders, the fatigue failure point was defined as the point where the complex modulus began a sharp failure propagation drop. The fatigue failure occurred where all of the properties changed very rapidly with additional load repetitions. Considering the fact that the torque measured via machine differed the actual torque in material, a calibration factor (CF), was introduced into the test.In the stress controlled mode, the author conducted the fatigue tests on AH-70 binders and special attention was given to stress, temperature and frequency that affected the fatigue properties of bituminous binders and responding fatigue equations were established. The results showed that their fatigue properties dropped with the increase of stress and temperature and had remarkable dependence on the frequency at the low level of stress, which witnessed a nadir at 10Hz and peaked at 20Hz. Such tests were also conducted on SBS modified binders. Temperature and frequency had complex importance on their fatigue properties. The effects of temperature and frequency were heavy subjected to the level of stress. In the high level of stress then fatigue properties increased with the drop of temperature. The effects of frequency showed little comparability.In strain controlled mode, the fatigue tests were conducted on aged bituminous binders. The results showed that their fatigue lives gradually decreased with the extension of aged effect and UV ageing had most remarkable effect. UV ageing had more importance on the fatigue properties than other specifications of modified bituminous binders. As for the fatigue property, the effect of UV was 1.5 times of that of NEA.The result showed that this new method can evaluate the fatigue property of bituminous binder correctly. This research lays a foundation for the work to seek after new ways to evaluate the fatigue properties of bituminous binders.