Adam Ramm, UT-Austin

"Optical Characterization of Asphalt Binder Microstructure"

Abstract: This dissertation presents results of optical characterization of asphalt binder microstructure. We use noncontact optical microscopy methods to observe microstructure at the surface as well as in the bulk of asphalt binder samples. Normal incidence optical microscopy is used to image elongated, striped, surface microstructures (known as ’bees’ since they resemble bumble-bees) with comparable resolution to atomic force microscopy (AFM). Narrow band dark field optical microscopy is used to measure surface microstructure areal density and bulk microstructure volume density. Short wavelength illumination images surface microstructures, while longer wavelength near infrared (NIR) illumination penetrates into the bulk and images sub-surface microstructures. We subject the binder to temperature cycles and observe the resulting microstructure kinetics. We benchmark these optical measurements with rheometry measurements obtained from identical thermal cycles. We also use optical methods to observe surface ’bee’ microstructure variations due to interfacial tension modifications and compare these results to thin film mechanics theory.