Fatigue Crack Growth Analysis of Hot-Mix Asphalt Employing Semicircular Notched Bend Specimen

Abstract

The fatigue fracture behavior of three hot asphalt mixes (HMA) was studied using a newly proposed semi-circular notched bending specimen geometry. This simple specimen geometry has the advantage of being able to obtain four test specimens directly from one cylindrical gyratory compacted core, reducing the scatter in data associated with different cores of heterogeneous materials such as HMAs. These mixtures consisted of a control, a crumb rubber (CR) modified asphalt mixture and a chemically modified crumb rubber (CMCR) asphalt mixture. The mixtures were designed to meet as close as possible the same Superpave PG grade and the two rubber mixes contained the same weight percent of crumb rubber. Fatigue crack growth tests were conducted using a servo-hydraulic MTS under tension/tension load control at room temperature and a frequency of 0.5.Hz. The maximum and minimum fatigue loads were kept constant for the three asphalt mixtures. It was found that the chemical modification of the crumb rubber has considerably enhanced the fatigue behavior in comparison with the control and the crumb rubber mixes. This finding is in complete agreement with our earlier J-integral results obtained for the same mixtures using the same semi-circular specimen geometry. Scanning electron microscopy of the fatigue fracture surfaces (ahead of the initial crack tip) of the three mixtures was performed to identify the fatigue damage species associated with each HMA mix. The semi-circular bend specimen has been found to be a suitable geometry for not only static fracture, but fatigue crack growth analysis.