Application of Elastic-Viscoelastic Correspondence Principle to Determine Fatigue Endurance Limit of Hot-Mix Asphalt

The fatigue endurance limit is one of the properties of hot-mix asphalt (HMA) that govern fatigue behavior of flexible pavements. Some approaches for determining the endurance limit of HMA are empirical in nature, such as the phenomenological approach. This often requires a series of tests at different strain levels and subsequent determination of the relationship between strain and number of repetitions for failure. The mechanics-based dissipated energy approach is more fundamental. However, it fails to take viscoelastic effects into account. Both approaches require considerable amounts of time and resources. This paper presents an alternative approach for determining the fatigue endurance limit of asphalt concrete by means of the elastic-viscoelastic correspondence principle, by separating the effect of viscoelasticity from that of damage development. Three different asphalt concrete mixes, replicates of the National Center for Asphalt Technology (NCAT) test track mixes, were tested for validation of the proposed methodology. Initially the cut and cored samples were tested for dynamic modulus to construct the master curves. With the data, viscoelastic properties were determined by interconversion techniques. In the next stage, fatigue tests were conducted under different strain amplitudes, starting from low to high. Then the strain data were converted to pseudostrain via the elastic-viscoelastic correspondence principle. The endurance limit was determined by identifying the strain level at which a loop between stress and pseudostrain began to develop. Endurance limit values thus determined are comparable to those obtained by flexural tests performed at NCAT. The proposed methodology can contribute to considerable savings in time and resource requirements.