Disproving bottom-up fatigue cracking in well-constructed asphalt pavements

Traditionally, asphalt pavements are believed to fail structurally in one of two ways, either deformation resulting from subgrade failure or bottom-up fatigue cracking. However, after many years of diagnosing the cause of a wide range of pavement failures, the author has yet to see that a well-constructed asphalt pavement over 150 mm thick has failed through bottom-up fatigue cracking. This paper reports on research to consider whether bottom-up fatigue cracking actually occurs in practice. The research involved examining traditional failure modes, considering methods for calculating base strain in flexible pavements and comparing the values, examining the concept of fatigue endurance limit, contemplating the types of deformation and looking at how pressure dissipates in typical asphalt pavements. The conclusion drawn is that bottom-up fatigue cracking does not occur in well-constructed asphalt pavements of even moderate thickness.