The combined effect of loading frequency, temperature, and stress level on the fatigue life of asphalt paving mixtures using the IDT test configuration

The main objective of this study was to investigate the combined effect of the loading frequency, temperature, and stress level on the fatigue life of asphalt paving mixtures. Asphalt mixtures were designed using the Superpave design procedure using a 60/70-penetration grade asphalt binder having a Superpave performance grade of PG 64-10 and crushed limestone aggregate. The indirect tension (IDT) fatigue test was used to determine the fatigue behavior of asphalt mixtures. The IDT fatigue test was conducted in the stress-controlled mode of loading using five stress levels: 288, 360, 432, 504, and 576 kPa (approximately in the range of 42-84 psi loading) representing truck or heavy traffic loadings in real-life conditions, two intermediate temperatures: 20 and 30 C, and four loading frequencies: 3, 5, 8, and 10 Hz representing truck speeds of about 12.5-45 km/h. Three replicates were used for each IDT fatigue test. A total of 120 IDT fatigue tests were conducted in this study. Findings of the study showed that the increase in loading frequency resulted in an increase in the fatigue life at the two test temperatures 20 and 30 C. In addition, the rate of increase in the fatigue life with the loading frequency was exponential, and the difference in the fatigue life (N_f) between the different loading frequencies was found to be higher at lower stress levels than that at higher strain levels at the two temperatures. It was also found that the difference in the fatigue lives between the different stress levels was much higher at higher loading frequencies than that at lower loading frequencies for both temperatures. For the stress-controlled mode of loading, which was used in this study, an increase in temperature provided shorter fatigue lives for asphalt mixtures.