Morphological analysis of bitumen phases using atomic force microscopy

Abstract

The structure of asphalt is generally considered to be a colloidal system where high molecular weight components (asphaltenes) are dissolved into an oily lower molecular weight matrix (maltenes). To better understand the morphology of the asphalt binder, the different components associated with this material were analysed under topographic and phase detection atomic force microscopy, and optical microscopy, for a specific asphalt binder type. The analysed asphalt binder was identified as a multi-phase type asphalt binder that exhibits four distinct phases: the para-phase which serves as a dispersing medium to the catana-phase (‘bee’ structure), the per-phase (area surrounding the catana-phase), as well as the sal-phase (smaller dispersed phase). A component analysis of the asphalt binder yielded that a form of the per-phase and catana-phase can be associated with the aromatics. The sal-phase was observed on the asphaltenes and resins. Furthermore, an additional filament-type structure was also identified on the resins. The analysis was also complemented by combining individual Saturates-Aromatics-Resins-Asfaltenes (SARA) components of the asphalt binder to observe the evolution of the different structures and morphology present in the asphalt binder. Enriched asphalt binder with 50% of each of the SARA fraction at a time was also analysed. It was determined that the size and shape of the different structures are a function of the combination of the different asphalt components. The effect of polymer modification and ageing due to temperature was briefly analysed. The results were also correlated with detailed infrared spectroscopy (FTIR) analysis of the different asphalt components.