Adherence Energy of Asphalt Thin Films Measured by Force-Displacement Atomic Force Microscopy

Viscoelastic materials exhibit rate- and temperature-dependant behavior in terms of stress-strain response and fracture. As a representative of this class of materials, rate-dependant fracture should be expected for the bituminous asphalt binders used in the construction of pavement. Preliminary results are reported regarding studies using atomic force microscopy (AFM) to determine rate- and temperature-dependent adhesive fracture in bitumen thin films. This AFM technique involves creating then fracturing a microadhesive contact joint between a bitumen thin film and a glass microbead tip affixed to a cantilever by application of a direct tensile force to the contact. The mechanical work required to fracture this contact is measured as a function of temperature and separation rate. Results of this study suggest that adherence fracture energy of bitumen films is rate and temperature dependant based on measures of energy dissipation at and below the temperature of 25 degrees C. These materials also exhibit a viscoelastic to viscous transition in adhesive behavior above 25 degrees C attributed to observed loss of energy dissipation.