Fatigue Characteristics of Asphalt Concrete from Asphalt Slab Tests

It is widely known that pavement fatigue life is often greater than that predicted based on laboratory bending beam or indirect tensile fatigue tests. Among many factors contributing to this difference, the effect of sample dimensions on fatigue life can be significant due to the multiphase nature of asphalt concrete. In this research, fatigue tests were conducted on asphalt slabs, which realistically simulate the fatigue cracks in pavements, to investigate crack initiation and propagation. The fatigue crack at the underside of asphalt slabs was identified as a semielliptical surface crack, which is the same type of fatigue crack found in pavements. A three-dimensional finite-element analysis was conducted to evaluate the stress intensity factor. Parisʹs law was used to characterize the crack propagation rate. The fatigue crack initiation life and propagation life determined from this research were compared with those calculated using the Strategic Highway Research Program existing parameters and equation. It was found that the two results are significantly different. The factors that may contribute to this difference were discussed.