Effects of Aggregate Surface and Water on Rheology of Asphalt Films

Abstract

Most tests used to evaluate moisture damage require compacted asphalt mixtures. The tests generally simulate field material and conditions and provide a performance-related parameter of moisture effects. In mixtures, however, variable asphalt-aggregate-air void structure contributes to the difficulty of isolating the fundamental rheological properties of an asphalt-aggregate bond. To avoid the complications and obtain the properties of the asphalt-aggregate interface, a new experimental design was developed in this study. This test features a dynamic shear rheometer (DSR) as an improved tool for evaluating interface properties. One key feature of the experimental design is the use of rock disks to simulate an asphalt-aggregate interface. The simulated interface is easily wet-conditioned in a water cup installed on the DSR. From various testing protocols, a stress sweep test that defines a linear viscoelastic (LVE) region is adopted to evaluate the interaction and moisture effects of selected specimens. A viscoelastic characteristic produced from stress sweep tests is recommended as the fundamental property of the interaction and can be used to evaluate moisture effects onto the rheological behavior. One of the critical findings is that the LVE complex modulus, G*, measured at relatively small strains or stresses cannot evaluate the moisture effects on the bond of the asphalt-aggregate interface. The LVE G* measured at high shear stresses are instead much more effective at evaluating such moisture effects. Therefore, the results indicate that the role of moisture damage in pavement problems such as rutting or fatigue needs to be evaluated at design stresses covering a nonlinear viscoelastic range. This study focuses on understanding more the basic characteristics of asphalt-aggregate interface than the bulk properties of mixtures.