Identification of compositional heterogeneity and influence of chemical fractions on surface microstructures through bitumen optical microscopy

Bitumen is the residua of fractional distillation of crude oil. It generally consists of complex and a diverse variety of organic molecules and other hetero-atoms. The nature and interactions between these molecules dictate the engineering properties of the bitumen. One of the attributes that is used to classify and examine these diverse constituent molecules is based on their relative polarities. In parallel, significant research has been conducted on bitumen surface microstructure, commonly referred as ‘bee structure’. Typically a bitumen is classified into four polarity based chemical fractions, namely saturates, aromatics, resins and asphaltenes (SARA) using physical separation by precipitation and chromatography. Such separations generally require specialised equipment and expertise. In this study, a fast and repeatable technique of chromatography using disposable and inexpensive parts were developed, named ‘SiSara’. This method was then used to fractionate a large set of bitumens in order to compare the constitution of the bitumens based on these fractions to their microstructural properties. Microscopic observation of surface microstructures indicates similarity among bitumens from the same producer. There was also a good correlation between SARA parameters and surface microstructure for bitumens from the same producer. However, this relationship was unique for each producer and not global suggesting that other factors related to the crude source need to be considered as well.