Opening-Mode Cracking in Asphalt Pavements Crack Initiation and Saturation

Opening-mode cracking has been commonly found in asphalt pavements and other layered materials with nearly uniform crack spacing. Due to the deformation mismatches between surface overlay and base layer of pavements, longitudinal tensile stress is induced in the surface course. When it reaches a certain level, transverse cracks will initiate at the surface to release the energy stored in the asphalt materials. When crack spacing reduces to a certain value, crack density is saturated and no new crack forms. This paper investigates the crack initiation and saturation for opening-mode cracking. Using elastic governing equations and a weak form stress boundary condition, we derive an explicit solution of elastic fields in the surface course and obtain the energy release rate, so that opening-mode cracking initiation can be determined by fracture energy criterion. Interestingly, the longitudinal stress between such cracks along the surface undergoes a transition from tensile to compressive with increasing applied tensile loading, which implies crack saturation. This explicit formulation is applicable to pavement structure design and opening-mode cracking analysis of asphalt pavements. If a loading condition is fixed, there exists a critical thickness of the surface overlay, below which no crack forms. Parametric analyses of opening-mode cracking are conducted considering the material stiffness, fracture toughness, interface conditions, and loading conditions. The viscoelastic effect of asphalt materials on the crack development is also discussed.