Influence of selected reactive oxygen species on the long-term aging of bitumen

The aging of bitumen is a major contributor to the failure of asphalt pavements. Realistic and accurate laboratory aging methods can predict bitumen durability and guarantee the use of high-quality components in asphalt pavement. However, current standardized aging methods do not incorporate atmospheric parameters, besides elevated temperatures and molecular oxygen. Crucial chemical components like reactive oxygen species (ROS), e.g. nitrogen oxides (NO_x) or ozone (O₃), are completely neglected. This study focusses particularly on the reactivity of individual ROS, such as nitrogen monoxide (NO), nitrogen dioxide (NO₂) and O₃, in regards to the long-term aging (LTA) of three unmodified bitumen. For LTA an adapted version of the Viennese Binder Aging method was used and the aged bitumen samples were analyzed with the dynamic shear rheometer and Fourier-Transform-Infrared spectroscopy, respectively. The results show that NO as a single component does not induce significant aging, whereas NO₂ leads to severe bitumen deterioration, which is even more accelerated when a second oxygen source is present. In comparison, the reactivity of O₃ is rather mild and it did not cause additional aging for two of the investigated binders. This study provides evidence, that ROS play a crucial role in bitumen aging and should thus not be neglected when addressing realistic aging conditions in the laboratory.

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