Towards a better understanding of bitumen chemistry, microstructure, and rheology

Bitumen is the residua of fractional distillation of crude oil. It generally consists of complex and a diverse variety of organic molecules and other heteroatoms. The nature and interactions between these molecules dictate the engineering properties of the bitumen. One of the attributes used to classify and examine these diverse constituent molecules is based on their relative polarities. Typically a bitumen is classified into four polarity based fractions, namely saturates, aromatics, resins and asphaltenes (SARA) using physical separation by precipitation and chromatography. Such separations require specialized equipment and expertise. In this study, two new fast and repeatable techniques of chromatography using disposable and inexpensive parts were developed. One of these methods 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 rheological, mechanical, and microstructural properties. Results show that parameters based on bitumen stiffness and tensile strength correlate well with these fractions. Similar relationship with more time dependent parameters was not conclusive. 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