Characterising the ductility and fatigue crack resistance potential of asphalt mixes based on the laboratory direct tensile strength test

As a means to investigate the applicability of the direct tensile strength (DT) test as a surrogate fatigue crack test, the ductility and fatigue crack resistance potential of various asphalt (HMA) mixes were evaluated in the laboratory using the DT test, at ambient temperature (20ºC) and a displacement loading rate of 1,27 mm/min. Various HMA mixes were included in the DT test program and the results were compared with those of the Overlay Tester, also conducted at ambient temperature. Up to 23 commonly used Texas HMA mixes with different mix design characteristics were evaluated and are discussed in this paper. The results indicated that the mix design volumetrics, such as the asphalt binder content and aggregate gradation, play a significant role in the ductility and fatigue crack resistance potential of HMA mixes. The dense-to fine-graded HMA mixes with high asphalt binder content exhibited better ductility potential and laboratory fatigue crack resistance than the coarse- and open-graded mixes. Overall, the DT test was found to be a promising surrogate fatigue crack test for mix design and HMA mix screening for fatigue crack resistance in the laboratory. Recommendations to improve the test protocol are included in the paper. However, sample fabrication and test set-up were the two critical issues found to be associated with the DT test