Investigation of aged, non-aged bitumen and their bitumen fractions

Abstract

In road construction the main application of bitumen is as binder for asphalt. The viscoelastic, adhesive and mostly black material is mainly obtained as a residue from petroleum distillation. Other origins for bitumen exist, but this thesis discusses only bitumen originating from crude oil. Bitumen can be separated into four fractions. The separation takes place in two steps. The first step is the precipitation of asphaltenes, done by filtering bitumen dissolved in n-heptane. The remaining part, called maltenes, is then in the second step separated by liquid column chromatography into saturates, aromatics and resins. Polarity increases form saturates to resins and asphaltenes are in the polarity range of aromatics and resins. Asphaltenes form a black powder and decompose when heated above 350 °C. The asphaltene fraction consists of large molecules containing hetero atoms like oxygen, nitrogen, sulphur and metal atoms. Due to fused aromatic rings asphaltenes can exhibit fluorescence, but they do not show fluorescence in the solid state, only when dissolved they fluoresce. Asphatenes have a major contribution on all physical properties, as they increase alongside of resins. During ageing bitumen gets stiffer (less viscous), so their fluorescence signal decreases. Resins are a black solid at room temperature and liquefy at higher temperature. The exhibited fluorescence is contributed to its molecular structure containing aromatic rings. They increase during ageing. Aromatics are viscous and appear dark red. They contribute the most to the fluorescence of bitumen. Other fractions (most resins) seem to quench the fluorescence of the aromatics leading to the spectrum of maltenes. Asphaltenes decreases the intensity further, but no additional change in curve progression takes place. Aromatics act as solution for asphaltenes and resins and are decreasing during ageing, probably changing to resins and asphaltenes, due to oxidation. Saturates are a colourless liquid, which behaves purely viscous like aromatics. The saturate concentration is not altered during ageing, so their contribution to any property remains constant. A part fluoresces, but the main part shows fewer to no signals. During ageing the fractions asphaltenes and resins increase in content as aromatics decrease. Due to the change in these three fractions the fluorescence signal lessens. Infrared spectroscopy indicates that oxygen is taken up during ageing - oxidation process. Effects on the microstructure are that the catana and peri-phase increase in size shown by atomic force microscopy. The mechanism for laboratory liquid ageing is different from standard laboratory ageing methods or field ageing, indicated by fluorescence and infrared spectroscopy.