Development of Phenomenological Top-Down Cracking Initiation Model for Mechanistic–Empirical Pavement Design

The phenomenon of top-down cracking in asphalt pavements has drawn increased attention in recent years, yet the asphalt pavement field still lacks an effective top-down crack initiation model. Many factors contribute to the initiation and propagation of top-down cracking. This study developed a phenomenological top-down crack initiation model for mechanistic–empirical pavement design. Pavements at FHWA's accelerated loading facility were used to develop a top-down crack initiation model based on the failure strain of asphalt mixtures, as obtained from indirect tensile testing. It was found that the current Mechanistic– Empirical Pavement Design Guide top-down cracking model failed to predict top-down cracking in the wheelpath in the field accurately, whereas the proposed failure strain–based top-down cracking model was effective in predicting top-down cracking in the field. In addition, the Level 2 prediction of failure strain is developed here; it is based on binder failure shear strain, air void content, asphalt content, and percentage of aggregate passing U.S. Number 4 and Number 200 sieves. Further studies are needed to validate this new top-down cracking model and to develop an effective crack propagation model.