FATIGUE EVALUATION OF ASPHALT MIXTURES USING DISSIPATED ENERGY AND VISCOELASTIC CONTINUUM DAMAGE APPROACHES (WITH DISCUSSION)

The fatigue performance of asphalt mixtures has historically been evaluated using phenomenological approaches. As the asphalt industry moves towards more mechanistic and performance-based design methods, researchers have developed more fundamental approaches to evaluate fatigue. This paper presents a comparison of the viscoelastic, continuum damage (VECD) and dissipated energy (DE) approaches using uniaxial direct tension fatigue tests performed on eight WesTrack mixtures. The two approaches are also compared to the traditional phenomenological approach relating the initial strain to the number of cycles to 50% reduction in initial stiffness. The number of cycles to failure calculated using the VECD and DE failure criterion are highly correlated and are very similar if a modified DE failure criterion is applied. The VECD approach successfully ranks the fatigue performance of mixtures with various air void and asphalt contents for a particular gradation, but the ranking between two gradations did not agree with the observed field performance. The DE approach shows promise for ranking the field performance of the mixtures; however limited data at different strain amplitudes made it difficult to state any conclusions with confidence.