Connections between asphaltene microstructures in aged asphalt binders and performance-related engineering properties

Numerous studies have been conducted to evaluate the property variations of asphalt binders from different sources and their property evolutions during the aging process. Most existing studies, however, are focused on asphalt binder properties at the macroscopic level. The fundamental mechanisms that drive the property variations and evolutions are seldom explored. In this study, attempts were made to identify the physicochemical origins of property variations in aged asphalt binders. Eight aged asphalt binders from different sources were used for investigation. The asphaltene contents of the binders were determined, and the zero-shear viscosities (ZSVs) of the binders and their maltene phases were tested at different temperatures. The size of asphaltenes in the asphalt binders was examined and approximately quantified with the assistance of scanning transmission electron microscopy (STEM) and image analysis. Solvent was not used in sample preparation; therefore, asphaltene microstructures in the STEM images represent the true states of observable asphaltenes in asphalt binders. It was found that asphaltene content and the ZSV of maltenes can well explain most of the commonly reported rheological properties of asphalt binders, including ZSV, dynamic viscosity, rutting parameter, fatigue parameter, phase angle, crossover frequency, Glover-Rowe (G-R) parameters, etc. However, asphaltene content cannot explain the fatigue performance of asphalt binders, for which the quantity of large-size asphaltene microstructures is the most important factor and maltene viscosity also likely plays a role. Besides revealing the connections between asphalt binder properties and its microscopic characteristics, the findings of the study may be used in material selection and the identification of proper engineering tests for asphalt binders.