Framework for Level-I Alligator Cracking Methodology for Use in the Mechanistic-Empirical (M-E) Pavement Design Guide

The recently published Mechanistic-Empirical Pavement Design Guide (MEPDG) includes a global flexure fatigue model that can be used for Level 3 material input. This paper develops a typical framework for highway agencies to follow to calibrate their laboratory results and determine Level 1 flexure fatigue input for use in the design guide. An extensive flexure fatigue testing program was carried out on six hot-mix asphalt (HMA) materials typically used by the Arizona Department of Transportation. General fatigue models are developed using both constant strain and constant stress modes of loading. The general fatigue lab models were then calibrated to the global fatigue model in the MEPDG to be used as an input to Level 1 design. Shift factors were developed for each mix used and for different thicknesses of asphalt layers. The shift factor decreased from 20 at a 1-in. layer to 9 at a 4-in. layer, after which it remained constant. The procedure used in this paper serves as a guide for other agencies to follow to obtain Level 1 fatigue data input for the M-E Pavement Design Guide.