Unveiling Impacts of Loading Waveforms on Fatigue Endurance Limits of Asphalt Mixture Using Phenomenological Fatigue-Life and Dissipated-Energy Approaches

Abstract The fatigue endurance limit (FEL) of asphalt mixtures stands as a critical parameter in perpetual pavement design. Traditionally, FEL is estimated via laboratory fatigue tests utilizing simplified haversine/sinusoidal loading waveforms. However, the strain waveforms within asphalt layers induced by traffic loads are significantly more complex than the haversine/sinusoidal patterns, impacting the reliability of FEL assessments. This study aims to investigate the FELs of asphalt mixtures under the conventional haversine waveform and the actual strain waves in the pavement generated by single-axle and tandem-axle loads. Both the phenomenological fatigue-life approach and dissipated-energy approach are used for FEL evaluation. Comparison results imply that FEL values of asphalt mixtures are affected by the strain waveform. Specifically, the single-axle waveform results in the highest FEL value, followed by the haversine waveform, while the tandem-axle waveform generates the lowest FEL value. This trend indicates that the FEL determined from a haversine waveform underestimates the FEL for single-axle waveforms but overestimates it for tandem-axle waveforms. Therefore, it is recommended to apply the actual strain waveforms occurring in field asphalt layers to identify the FEL of mixtures, rather than relying on simplified waveforms like the haversine one.