Understanding bitumen ageing by investigation of its polarity fractions
Johannes Mirwald, Stefan Werkovits, Ingrid Camargo, Daniel Maschauer, Bernhard Hofko, Hinrich Grothe
Abstract
Bitumen is a material of significant importance for the roadwork industry and hence for development of infrastructure, economy and society. Therefore, understanding its ageing behavior is one of the most crucial factors in the service life of a road. Standard chemo-mechanical analysis involving dynamic shear rheometer (DSR) and Fourier-Transformation Infrared (FTIR) spectroscopy is a good way to do so, but is only capable of capturing the material performance as a composite. By looking at bitumen’s polarity based molecular constituents and how they change during ageing, we go one step towards the molecular level and simultaneously correlate it directly to the initial binder state. In this study, various long-term aged (LTA) binders from the same base bitumen were investigated with FTIR spectroscopy, DSR, separated into their four polarity based (SARA) fractions and measured with FTIR spectroscopy subsequently. The results show a consistent trend in the three LTA binders across all analysis methods. The fractions showed that the most notable changes upon ageing occur in the aromatics, resins and asphaltenes. The formation of carbonyls can be tracked in the aromatics, resins and asphaltenes, while the formation of sulfoxides is found in the resins and asphaltenes. By the outcome of this study, we intend to contribute to a better understanding on how bitumen ages and how we can translate that knowledge to realistically simulate field ageing in the laboratory.