Crack propagation modeling in flexible pavement structures

Current state of the practice pavement design methods use mechanistic-empirical approach, some of which relates maximum tensile strain in the asphalt layer of the uncracked pavement to fatigue life. This approach has been useful for pavement design, however the relationship is not mechanistically tied to material properties. Fracture mechanics uses material properties to estimate crack propagation based on stress intensity factors. Fatigue life is obtained from the integration of crack propagation over the pavement thickness.; This research demonstrates crack propagation in a pavement can be evaluated using a three-dimensional model, with a friction interface at both the boundaries between the surface and the base course, and the crack surfaces. Three different traffic load positions must be considered, i.e., approaching the crack, over the crack, and leaving the crack. These different load positions produce mode I crack opening or mode II in-plane shear, or combination of both. Mode I stress intensity factor increases with crack length, until it reaches a peak value. Beyond this point, the stress intensity factor starts declining. It finally becomes zero for {dollar}c/hsb1{dollar} less than 90%. Mode II stress intensity factor grows similar to mode I, however it never drops to zero. In the fatigue analysis both stress intensity factors are used to estimate pavement life.; The reasonableness of the analysis method was tested by comparing the results to the Shell method of pavement design. This comparison demonstrated that the pavement fatigue life predictions are reasonable using material constants obtained from the literature.