Characterization of microdamage and healing of asphalt concrete mixtures

The pseudo-strain concept based on Schapery's extended nonlinear elastic-viscoelastic correspondence principle is demonstrated by a considerable database to be able to characterize both microdamage and microdamage healing during the damage process. A change in pseudo stiffness can be used to quantify microdamage and healing during the fatigue test. Pseudo stiffness decreases consistently with increasing number of loading cycles, indicating that microdamage occurs during the fatigue test. The significant recovery of pseudo stiffness after rest periods demonstrates a healing effect due to rest periods. Dissipated pseudo-strain energy is a strong and consistent quantifier of damage and healing. High levels of cumulative dissipated pseudo-strain energy are consistent with high levels of fatigue damage, whereas low levels of cumulative pseudo-strain energy are associated with fatigue damage resistance. Pseudo stiffness is the chord slope of the stress-pseudo strain hysteresis loop. Since linear viscoelastic-based time effects are eliminated in this approach, pseudo stiffness and/or pseudo-strain energy are superior indicators of damage than either stiffness or total dissipated strain energy. The effects of rest periods on fatigue life extension due to healing of microcracks are significant. It has been demonstrated that longer rest periods result in more healing, and in turn in greater fatigue life.