Evaluation of Fatigue Cracking Resistance of Asphalt Mixtures Using Apparent Damage Capacity

The prediction of fatigue cracking is one of the critical items to assess the service life of flexible pavements. Accordingly, researchers have developed several test methods and index parameters to predict pavement performance based on fatigue damage. Recently, researchers at North Carolina State University developed a new index parameter, referred to as apparent damage capacity ($S_{\mathrm{app}}$), which is based on the simplified viscoelastic continuum damage (S-VECD) model. This index parameter is obtained by performing cyclic tension tests and using the simplified viscoelastic continuum damage model with a dissipated pseudoenergy concept (the so-called $D^R$ failure criterion). This paper presents $D^R$ and $S_{\mathrm{app}}$ values for 10 different asphalt mixtures commonly used in Georgia. The relationships among $D^R$, $S_{\mathrm{app}}$, and mix design factors such as nominal maximum aggregate size (NMAS), asphalt binder type, and binder content were investigated to determine ways that these factors affect $D^R$ and $S_{\mathrm{app}}$. The $S_{\mathrm{app}}$ parameter was found to have a strong relationship with the polymer modification and NMAS of the asphalt mixtures. Based on the experimental data and the Georgia Department of Transportation’s practical guidelines for specific mixtures, this study developed $S_{\mathrm{app}}$ threshold values for different traffic levels. Finally, the experimental data were used to run pavement performance analyses using AASHTOWare Pavement ME Design software and FlexPAVE; the latter uses the S-VECD model for cracking evaluation. Top-down and bottom-up cracking performance was determined from a 10.2 cm (4 in.) thick single-layer pavement and a 15.2 cm (6 in.) thick 2-layer pavement. The results are used to discuss the different ways the two programs evaluate cracking.