Viscoelastic continuum damage finite element modeling of asphalt pavements for fatigue cracking evaluation

This paper documents the findings from the study of fatigue cracking mechanisms in asphalt pavements using the finite element program (VECD-FEP++) that employs the viscoelastic continuum damage model for the asphalt layer and a nonlinear elastic model for unbound layers. Both bottom-up and top-down cracks are investigated by taking several important variables into account, such as asphalt layer thickness, layer stiffness, pressure distribution under loading, and load level applied on the pavement surface. The cracking mechanisms in various pavement structures under different loading conditions are studied by monitoring a damage contour. Preferred conditions for top-down cracking were identified using the results from this parametric study. The conjoined damage contours in thicker pavements suggest that the through-the-thickness crack may develop as the bottom-up and top-down cracks propagate simultaneously and coalesce together, supporting observations from field cores and raising the question of the validity of traditional fatigue performance models that account for the growth of the bottom-up cracking only.