Implementation of NCHRP 9-44A Fatigue Endurance Limit Prediction Model in Mechanistic-Empirical Asphalt Pavement Analysis Web Application

One of the essential components of various design methods for perpetual (or long-life) flexible pavements is elimination (or minimization) of bottom-up fatigue cracking. For this purpose, the concept of the fatigue endurance limit (FEL) is used. The FEL is defined as a strain threshold below which fatigue damage does not accumulate for any number of load repetitions. Different ranges of FEL values have been reported in the literature. Recent studies have showed that FEL is not a single value and depends on several factors. The NCHRP 9-44A project resulted in an FEL prediction model based on the micro-crack healing concept and stiffness, both of which can fluctuate throughout the service life of a pavement. In this study, NCHRP 9-44A FEL prediction model was implemented in the Mechanistic-Empirical Asphalt Pavement Analysis (MEAPA) web application to investigate the effect of fluctuating FEL on bottom-up fatigue cracking prediction in three typical road sections (low, medium, and high traffic) in Michigan. The critical bottom-up fatigue strains, predicted FEL, and predicted fatigue cracking for each road section have been compared. The results revealed that implementation of FEL is critical for accuracy in the prediction of fatigue cracking in relatively thick pavements that are subjected to high traffic loading. The effect of FEL, however, was minimal in thin pavements with low traffic levels. Therefore, given that the mechanistic-empirical pavement design methods are typically used while designing highly trafficked pavements (e.g., highways, arterials, etc.), proper implementation of the FEL concept in pavement design is very important.