A strain-controlled hot-mix asphalt fatigue model considering low and high cycles

The fatigue life of hot-mix asphalt (HMA) is widely accepted as the number of loading cycles required to reach 50% of its initial flexural stiffness (Nf-50%). However, it is difficult to recognise the threshold between the elastic, where no damage occurs, and plastic ranges, where cracks begin to initiate. Phenomenological fatigue behaviours under cyclic loading are classified into three stages: primary (high dissipated strain-energy change without cracking), secondary (constant dissipated strain-energy change between two consecutive hysteresis loading loops) and tertiary (rapid change in dissipated strain energy after crack initiation). However, the threshold between the secondary and tertiary stages cannot be considered fatigue failure using the Nf-50% criterion. This study clarifies the dissipated energy changes during loading and proposes four parameters to define fatigue behaviour of 13-mm dense-graded HMA using bending beam at various strain amplitudes. In addition, a fatigue life threshold, at the transition from stable behaviour to the fatigue failure, is also proposed.