ABSTRACT
Fatigue damage of viscoelastic materials like asphalt concrete can be due to creep of the material under the sustained loading, or it can be due to the repetitiveness and the dynamic nature of the loading. The conventional method to identify the right mechanism behind fatigue damage is to conduct fatigue tests at different frequencies. If the damage is due to creep processes then the time-to-failure at different frequencies would be the same. If instead the damage is due the repetitiveness of the load, then the number of cycles to failure would be the same. This approach of identifying mechanisms behind fatigue is, however, simplistic, as it involves the comparison of measurements made only at the point of failure. In this study, fatigue tests conducted at different frequencies were analyzed in a different manner. Instead of just comparing the time-to-failure or the number of cycles to failure, the entire process of decay of the apparent dynamic modulus over the duration of the fatigue test was compared. The variation of the apparent modulus and apparent phase angle with time was found to not vary from one frequency to another, indicating that the fatigue damage of asphalt concrete occurs through creep mechanisms.
