In unsponsored dissertation research that was conducted after the completion of the RP 2018-13 project, interlayer shear fatigue (ISF) tests were conducted to evaluate the effects of tack coat type and application rate on test specimens' resistance to interlayer shear failure under fatigue loading. The ISF test results delineated the shear performance of different tack coat materials and application rates, whereas the interface shear strength test could not.
The laboratory shear fatigue test is performed under much larger stress levels than what is expected at the asphalt layer interface in the field. These large stress levels are necessary to accelerate the test so that it can be completed within a reasonable time (normally less than a day). The objective of this research is to determine whether the difference in shear fatigue performance observed from the previous studies does matter in the field condition.
To accomplish this objective, the NCSU research team used FlexPAVETM, a three-dimensional viscoelastic finite element program that is capable of simulating the moving loads, to simulate the stress states at the bottom of asphalt overlays with varying thicknesses under various loading and temperature conditions. The results from this study indicate that the observed effects of tack coat material type and application rates on shear fatigue performance from the ISF test can be significant in the stress states of pavements in field conditions. The findings from this study suggest that the ISF test should be used in future studies to evaluate the effect of tack coats and provide solutions for debonding distress in North Carolina.
