Fatigue and healing characterization of asphalt mixtures
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This paper investigates the effect of the processes on fatigue fracture and fracture healing during controlled-strain, dynamic mechanical analysis (DMA) testing. Sand asphalt samples were fabricated with two SHRP-classified binders: AAD-I and AAM-I. DMA testing was performed at 25C and at 10 Hz. The mechanical response during DMA testing was monitored using three different damage indicators: (1) change in dynamic modulus; (2) change in pseudo stiffness; and (3) change in dissipated strain energy. When either of these parameters are plotted versus the number of load cycles, two inflection points are apparent that define a significant change in sample behavior due to damage. The second inflection point is a reasonable definition of failure, as it is strongly correlated with the peak of the plot of phase angle versus load repetitions. Furthermore, the phase angle drops precipitously at the second inflection point. By performing controlled-strain torsional fatigue tests at three different strain levels, each great enough to induce damage, a reproducible fatigue relationship (number of load cycles as a function of stress level) is developed. The introduction of several rest periods during testing lengthened fatigue life. Successful development of this testing method is suggested as a potential specification-type test method because of its efficiency, reproducibility, and reliability.