In the prevailing structural design of asphalt pavements, fatiguecracking at the bottom of asphalt mixture layer is consideredto be a major failure mode of the pavement structure. In Japan,however, such failure has rarely been observed in the asphaltpavements with thick asphalt mixture layer including asphalt stabilizedbase course which has been in service for more than 20 years.Failure modes of the asphalt pavements are rutting and surfacecracking. The asphalt stabilized base courses in such pavementshave been alive without major repairing. Therefore, the conceptof the structural design should be reconsidered in terms of thefatigue cracking.

We conducted fatigue analysis for various asphalt pavementswith thick asphalt mixture layer in Japan. Radial strains at thebottom of asphalt mixture layer and vertical strains at the topof subgrade were calculated. Then, fatigue damages were estimatedby applying the calculated strains to fatigue curves presentedin the manual. In the analysis, wheel load distributions weretaken into account by employing the Miner's law. The results ofthe fatigue analysis showed that the fatigue crack at the bottomwould occur in the asphalt pavements with thick asphalt mixturelayer in less than 10 years. The results do not agree with ourfield experiences mentioned above.

We made an assumption that, at the strain level of less than200 micro, asphalt mixture would not fatigue because of the healingeffect. Being based on the assumption, we conducted the fatigueanalysis again. The results of the analysis seemed to be quitereasonable and agree with our experiences in Japan.