Structural Characterization of Micromechanical Properties in Asphalt Using Atomic Force Microscopy

Abstract

This paper semiquantitatively evaluates the microrheological properties of asphalt binder using atomic force microscopy. It also presents differences between these properties amongst the various microstructures within an asphalt binder, in addition to the influence of oxidative aging on these properties. Nano-indentation experiments performed within a microgrid of asphalt phases determined micromechanical properties such as stiffness, adhesion, and elastic/plastic behavior. The evaluated materials include asphalts AAB, AAD, and ABD from the Materials Reference Library of the Strategic Highway Research Program, chosen because of variations in crude source, chemical composition, and elemental analysis. Analysis of nano-indentation creep measurements corresponding to phase-separated regions revealed heterogeneous domains in asphalt with different mechanical properties, and oxidative aging induced substantial microstructural change within these domains, including variations in phase structure, properties, and distribution. The form and extent of these changes, however, were different for each asphalt. Interpretation of data collected from the atomic force microcopy experiments in this study advances understanding of the microstructural composition of asphalt binders and the response of the microstructural phases of the asphalt binder under load, in addition to how the mechanical responses in the phases change with aging.