Study On Asphalt Mixture Fatigue Threshold Based On The Design Idea Of Long-Life Asphlat Pavement

This study relies on the Ministry of Transport Industry Joint scientific and technological project"The Application Research about Long-Life Asphalt Pavement Structure under Heave Traffic". Based on long-life asphalt pavement design idea, this study tentatively researches the fatigue threshold of asphalt mixture. According to the results of literature review, the fatigue threshold of asphalt mixtures, i.e. fatigue limited strain, exist theoretically and is the critical index for the design of long-life asphalt pavement. The current fatigue model of asphalt mixture can't describe the fatigue behavior exactly under the low strain condition. Therefore, it is premise for economical and reasonable long-life asphalt pavement to study the fatigue threshold testing method and choose the proper values for different asphalt mixtures.Three kinds of asphalt mixture AC-25, ATB-25 and AC-20 are designed to prepare specimens. The mixture of AC-20 adopts modified asphalt and the principle of mixture gradation design is closed to the engineering practice. The designing gap rate of specimens is 6%. Four points bending fatigue tests were performed with the separate control strains, under the condition of 15℃&10Hz and the half lost waveform load to obtain the corresponding fatigue numbers. The complement indexes including dynamic stability, low-temperature bending fracture strain and freeze-thaw splitting residual strength ratio were also tested to ensure the used mixtures in this study satisfy practice requirements.By analyzing the classical fatigue models home and abroad, the fatigue threshold parameters are introduced into the traditional fatigue equation and the power function model with three parameters is established to illustrate the fatigue threshold phenomenon precisely. The fatigue thresholds for the three kinds of mixtures above are presented separately using the fatigue threshold model. On the other hand, the low strain additional fatigue, establishing decline equation concern with strength modulus and fatigue life to forecast low strain fatigue life and get the low strain fatigue life under the test condition was complemented. By comparing the traditional model and three parameters models, it was concluded that the latter model is more reliable and representative in estimating low strain fatigue life. The classic pavement structures are redesigned adopting the fatigue thresholds by Finite Element Methods. The design results show that the semi-rigid base and flexible base structure have the potential to achieve long life.