Time and Storage Dependent Effects of Bitumen—Comparison of Surface and Bulk

Abstract

Bitumen is a product obtained from crude oil refinement. Its complex nature demands for a sophisticated approach to thoroughly assess it and link chemical composition, mechanical behavior and microstructure. Besides conventional mechanical testing, performance based test methods like dynamic shear rheometer (DSR) or bending beam rheometer (BBR) are gaining importance since they describe the actual viscoelastic behavior versus time and temperature. Furthermore, Fourier-Transformation-Infrared (FTIR) spectroscopy has recently become one of the most used analytical methods in bitumen research. The method give information regarding chemical composition in terms of functional groups and can distinguish between different ageing states and different kinds of modification. The presented study shows time and storage dependent effects on the surface and in the bulk of bitumen. It focuses on three main questions: (a) Is the surface and bulk affected by exposition to visible light within a timespan of up to 20 days? (b) Do the changes on the surface correlate with changes in bulk properties? (c) Does the surface of bitumen passivate, preventing further atmospheric oxidation? To answer these questions, two different unmodified binders were prepared and measured with FTIR and DSR. Half of the samples were exposed to visible light, while the others were stored in the dark at a controlled laboratory atmosphere. The results of FTIR spectroscopy show that the surface, when stored in visible light, passivates significantly with increasing storage time. When stored in the dark, no relevant changes are measured. The results from bulk (DSR) show the same trends but to a much lesser extent, compared to the surface. An overall sample storage in the dark is recommended. FTIR measurements should be conducted within an hour after preparation, while DSR measurements can be done up to one day after preparation.