Fatigue cracking failure criterion for flexible pavements under moving vehicles

An improved fatigue cracking criterion for flexible pavements is developed. It relates the allowable number of load repetitions with the maximum tensile strain at the bottom of the asphalt concrete layer that causes cracking there. The criterion is established by combining an empirical relationship providing the number of load repetitions as a function of the layer thicknesses and the axle loading as obtained by the AASHO Road Test with that maximum tensile strain developed at the bottom of the asphaltic layer. Because this maximum tensile strain is computed by a FEM that analyses pavements under moving vehicles and assumes the asphaltic layer to behave as a linear viscoelastic material, the resulting failure criterion takes into account speed and viscoelastic material behavior. Thus, this criterion is an improved version of the existing ones based on static or dynamic loading and linear elastic material behavior.