Abbildung und Analyse der Bitumen Mikrostruktur : Beschreibung des Alterungsverhaltens auf Basis mikrostruktureller Information

Abstract

Understanding a materials microstructure is a vital and necessary premise to comprehend the ageing and corrosion of the very same. As the bitumen microstructure is much debated and unravelling its basic principles a keystone when looking at asphalt recycling, it became the first focal point of this study. By use of CLSM and AFM imaging, the microstructure was visualized in very high quality. The similar size of the phenomena indicates that identity or at least a strong linkage between the two can reasonably be assumed. Complementary use of fluorescence spectroscopy allowed the identification of the fluorescent centres visible in the CLSM images as the aromatics phase. These findings are incorporated into the modern micelle image, which is based on the agglomeration tendencies of asphaltenes proven beyond doubt, to create a new model of ageing. This new model is perfectly capable to explain the impact of short- and long-term ageing on the microstructure as well as "thermal healing" of asphalt by identifying the embrittlement of bitumen as a diffusion problem of polar oxidation products into the inner core of the micelle. Additionally, the laboratory ageing methods and field ageing were studied on carefully selected and unique samples. Those samples include seven to twenty-four year old roadwork not disturbed by maintenance or reconstruction, as well as a sample from a three year old highway already exhibiting strong signs of material failure. Partially, also the virgin binder was preserved in sealed metal cans, providing an original and un-oxidized sample for chemical and spectral investigation. Methods were investigated for their compliance with field ageing and it was found that they are generally in good accordance with the field samples, except for the influence of UV-radiation on SBS degradation in wear course.