Fatigue life analysis of RAP-predominant asphalt mixtures using classical and VECD approaches

This study focused on the fatigue life of asphalt mixtures with very high RAP contents (>50%). The classical and viscoelastic continuum damage (VECD) approaches were deployed for the analysis of mixtures containing 57, 65, 73 and 100% RAP. The 2S2P1D model was used to calibrate the generalised-Maxwell (GM) for VECD analysis. Wöhler curve based on five classical criteria including (a) 50% reduction in stiffness, (b) inflection point of dissipated energy ratio (DER), (c) maximum phase angle of black curve, (d) axial strain difference (Δεiax) > 25% and (e) phase angle difference (Δφi) > 5° criteria were built and then compared with the Wöhler curves predicted by VECD analysis. It was found that 2S2P1D can be successfully used for calibrating GM. Additionally, the rate of change in the average released pseudo strain energy throughout the loading history (GR) vs. the fatigue life (Nf) was deployed to evaluate the fatigue performance. Both classical and VECD approaches establish a strong power law relationship between the fatigue life and strain levels. While, in the classical approach, fatigue life ranking of the mixtures depends on the strain level, VECD shows a ranking based upon %RAP. GR vs. Nf curves show the intrinsic fatigue properties change with RAP content variation.