Calibration and Validation of the Shell Fatigue Model Using AC10 And AC14 Dense Graded Hot Mix Asphalt Fatigue Laboratory Data

Abstract

Mechanistic Empirical pavement design has been adopted by New Zealand and Australia for more than a decade ago and recently by many other countries around the world. The detailed procedures for the mechanistic empirical analysis are detailed in the Austroads and New Zealand supplement publications. Because the mechanistic empirical analysis relies on empirical performance models that are very dependent on material types and environmental conditions, the success of the design procedure depends on the use of well designed, calibrated and validated performance models. In the Austroads Mechanistic Empirical pavement design, fatigue and rutting are the two performance indicators used in the design. Austroads guidelines adopt Shell fatigue transfer function to predict the fatigue life of asphalt pavements. However, it was observed by many practitioners and confirmed by this study that Shell Transfer functions significantly overestimate the design thickness or in other words underestimate the fatigue life of the asphalt mixes. In this paper, calibration and validation of the Shell fatigue transfer function which is currently adopted in the Austroads design guidelines are demonstrated. The calibration factor based on the four points bending fatigue test results was found to be in the order of 5.7. Using the calibrated Shell model produced a 26% to 27% thinner asphalt thickness compared to the current Austroads design guidelines.