Comparison of Fatigue Analysis Approaches for Hot-Mix Asphalt to Ensure

Fatigue cracking is a primary form of distress in hot-mix asphalt. The long-term nature of fatigue due to repeated loading and aging and its required tie to pavement structure present challenges in terms of evaluating mixture resistance. This project focused on comparing stiffness and fatigue life output from two recently developed approaches that use repeated direct tension tests: the Modified Calibrated Mechanistic with Surface Energy (CMSE*) approach and the Push-Pull Viscoelastic Continuum Damage (PP-VECD) approach. The CMSE* and the PP-VECD approaches were applied to both laboratory and field specimens for two mixtures, one from SH 24 in the Paris (PAR) District and one from US 277 in the Laredo (LRD) District of the Texas Department of Transportation, and the results were compared. Both approaches can be used to characterize mixture fatigue resistance with relatively low variability. Based on stiffness, both approaches predict better resistance (lower stiffness) for the PAR mixture based on laboratory results but that the mixtures would have equivalent resistance based on field results for the CMSE* approach. There was also good agreement between laboratory and field specimens for the LRD mixture. The two approaches define fatigue failure in different ways, and thus the rankings of mixture resistance may be different. For the CMSE* approach, the stiffer LRD mixture based on laboratory specimens results in a longer fatigue life, while for the PP-VECD approach, this mixture results in a shorter fatigue life. In addition, the PP-VECD approach outputs significantly lower fatigue lives than the CMSE* approach does due to differences in the analysis including critical strain values and accumulation of damage. The CMSE* approach only requires a single test sequence, and thus fewer resources in terms of specimens and time are needed. However, the PP-VECD approach is more user friendly in terms of the analysis, and some of the required inputs (E*) can be used to evaluate mixture resistance to other distresses. Field specimens can be tested and analyzed using both approaches. Ultimately, the laboratory approach used should tie to field performance.