Calibration of Alligator Fatigue Cracking Model for 2002 Design Guide

Abstract

In AASHTO's 2002 design guide, the classic 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 bottom-up alligator fatigue cracking was based on a mechanistic approach to calculate stress and strain. An empirical approach then related these strains to fatigue damage in pavement caused by traffic loads. To provide credibility to the new design procedure, the theoretically predicted distress models must be calibrated to “real-world” performance. In fact, calibration of these distress models is considered to be the most important activity to facilitate implementation, acceptance, and adoption of the design procedure and to establish confidence in the entire procedure. The procedure followed for the national calibration of the alligator fatigue–cracking model used in the AASHTO 2002 design guide is discussed. This calibration study used data from all over the United States, with 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 a linear layer elastic analysis procedure. The initial (base) reference model used in the calibration was the Asphalt Institute MS-1 model. This model was used to compute the damage caused by traffic loads and pavement structure. Predicted damage was then correlated to the measured fatigue cracking in the field, and a transfer function was obtained for the alligator fatigue–cracking distress.