FATIGUE ANALYSIS OF ASPHALT PAVEMENTS WITH THICK ASPHALT MIXTURE LAYER

In the prevailing structural design of asphalt pavements, fatigue cracking at the bottom of the asphalt mixture layer is considered to be a major failure mode of the pavement structure. In Japan, however, such failure has rarely been observed in the asphalt pavements with a thick asphalt mixture layer, including asphalt stabilized base course which has been in service for more than 20 years. Failure modes of the asphalt pavements are rutting and surface cracking. The asphalt stabilized base courses in such pavements have been alive without major repairing. Therefore, the concept of the structural design should be reconsidered in terms of the fatigue cracking. We conducted fatigue analysis for various asphalt pavements with thick asphalt mixture layer in Japan. Radial strains at the bottom of the asphalt mixture layer and vertical strains at the top of the subgrade were calculated. Then, fatigue damages were estimated by applying the calculated strains to fatigue curves presented in the manual. In the analysis, wheel load distributions were taken into account by employing Miner's law. The results of the fatigue analysis showed that the fatigue crack at the bottom would occur in the asphalt pavements with thick asphalt mixture layer in less than 10 years. The results do not agree with our field experiences mentioned above. We made an assumption that, at the strain level of less than 200 micro, the asphalt mixture would not experience fatigue because of the healing effect. Based on this assumption, we conducted the fatigue analysis again. The results of the analysis seemed to be quite reasonable and agree with our experiences in Japan.