Partial Healing — A New Approach for the Damage Process during Fatigue Testing of Asphalt Specimen

Abstract

Earlier findings in fatigue tests using a repeated sequence of a fixed number of cycles with a high deflection and a fixed number of cycles with a small deflection confirms the supposition that healing of the stiffness already occurs during the fatigue test and does not depend on a rest period of no loading at all. It was shown by theory and in practice that the decrease in temperature due to the decrease in dissipated energy per cycle when smaller strains were applied could not explain the amount of increase in the stiffness modulus. Further investigation of these findings and results has lead to a new material response model that describes both the evolution of the modulus and the phase lag of the complex stiffness model during fatigue testing. It should be marked that healing in this paper is only related to the complex stiffness modulus. This partial healing (PH) model is a material model for which the response in a point depends on the stress/strain state in that point (the rate of dissipated energy). Therefore the application of the PH model for the determination of the response (evolution of stiffness) of a finite specimen in a test will depend on the geometry and loading configuration of the specimen and the load mode. The PH model is applied on four point bending beam tests (4PB) in controlled deflection mode. The obtained parameters for the PH material model were used for the prediction of the stiffness evolution in uni-axial push-pull fatigue tests (UPP) on the same asphalt mix. A fair comparison was observed between the measured and predicted evolution of both the modulus and phase lag of the complex stiffness modulus in the UPP tests.