Calibration of Alligator Fatigue Cracking Model for 2002 Design Guide (05-2620)
Mohamed El-Basyouny, Parsons Corporation
Matthew W. Witczak, Arizona State University

In the 2002 Design Guide the classical fatigue cracking mechanism, which normally initiates at the bottom of the asphalt layer and propagates to the surface (bottom-up cracking), was studied. The prediction of the bottom-up “alligator” fatigue cracking was based on a mechanistic approach to calculate the stresses and strain. An empirical approach then related these strains to fatigue damage in the pavement due to traffic loads. To provide credibility to the new design procedure, the theoretically predicted distress models must be calibrated to the “real world” performance. In fact, the calibration of these distress models is considered to be the most important activity to facilitate the implementation, acceptance, and adoption of the design procedure and establish confidence in the entire procedure. This paper discusses the procedure followed for the national calibration of the alligator fatigue-cracking model used in the 2002 Design Guide. This calibration study used data from all over the United States, having different environments, material and traffic. A total of 82 pavement sections from 24 different states were used in the calibration. Tensile strain at the bottom of each asphalt layer was calculated using linear layer elastic analysis procedure. The initial (base) reference model used in the calibration was the Asphalt Institute MS-1 model. This was used to compute the damage caused by the traffic loads and pavement structure. Predicted damage was then correlated to the measured fatigue cracking in the field and a transfer function obtained for the alligator fatigue cracking distress.