Propagation Mechanisms for Surface-Initiated Longitudinal Wheelpath Cracks

Field observation of cores and trench sections extracted from asphalt concrete highway pavements exhibited propagation of surface-initiated longitudinal wheelpath cracks. The initiation for these cracks was explained by high-contact stresses induced under radial truck tires; however, the mechanisms for surface crack propagation have not been explained. A combination of finite element modeling and fracture mechanics was selected for physical representation and analysis of a pavement with a surface crack. An approach was developed to model a cracked pavement and predict pavement response in the vicinity of the crack and throughout the depth of the asphalt layer. Analysis of pavement response indicated that the mechanism for crack propagation was primarily tensile. Shear stresses were not significant to control crack growth, regardless of load position. Effects of pavement structure and load spectra (magnitude and position) were evaluated in a comprehensive parametric study of the cracked pavement. Load positioning had the most effect on crack propagation, along with asphalt and base layer stiffness. The direction of crack growth was computed and changed with increased crack length. Therefore, identification of a tensile failure mechanism for crack propagation was accomplished, along with demon stration of the importance of defining load spectra and inspection of the change in direction of crack growth. Most important, the defined mechanism offered an explanation for crack propagation and confirmed observations of crack growth in the field.