Rheology of Thin Asphalt Films in Contact with Aggregate

ABSTRACT A specially designed shear viscometer fixture was built to investigate the physical properties of thin asphalt films between aggregate plates. Viscosities were measured using the specially designed fixture in an Instron instrument. The properties of thin asphalt films are not predictable from thick (1.0 mm) films on steel plates, which are used in the current Superpave® specification. Rheological properties of thin films (20 microns thick) of neat SHRP asphalt AAD-1, PAV-aged AAD-1 (20 hours at 100°C), and decanedicarboxylic acid-modified AAD-1 were determined at 25°C using the specially designed fixture. Atomic force microscopy (AFM) was applied to investigate the surface roughness profiles of different substrates including glass and aggregate plates. It was found that the roughness of the glass plate was only 20nm disparity in height, approximately one one-thousandth of the film thickness being studied. The AFM profiles of the polished aggregate plates used in the study showed that they had a surface roughness of approximately two microns, i.e., approximately ten percent of the film thickness. The results showed that thin film physical properties are dependent upon asphalt composition, aggregate type, oxidation, and asphalt modification. Separately, preliminary results from a water soaking experiment show that the specially designed fixture may be a useful tool for the characterization of moisture damage