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Title
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Towards an enhanced understanding of the oxidative ageing mechanisms in bitumen
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Author
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Abstract
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| The ageing phenomenon in asphalt and its binding medium, the bitumen, is well documented in the scientific literature with regard to its rheomechanical effects. To understand the ‘whys’ behind these alterations one should seek additionally on the chemistry of bitumen. This dissertation supports experimentally the hypothesis of an oxidation scheme consisting of a fast and a slow rate-determining phase. This is achieved by utilising various unmodified bituminous binders of different origin of crude source, refinery process and performance both in oxidation kinetics and with standard lab ageing simulations. The findings of Electron Paramagnetic Resonance (EPR) and Fourier Transform Infrared (FTIR) Spectroscopy manage to distinguish the two phases, while Proton Nuclear Magnetic Resonance (H-NMR) Spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) unravel the main oxygenated products in bitumen. Chemical investigations of the SARA fractions show additionally the effect of ageing on the different fractions. Moreover, each contribution of the coupled reaction-diffusion is studied with FTIR and Dynamic Vapour Sorption (DVS). Next, the fundamental mechanisms for the development of a peculiar microstructure, the bee structures in bitumen, were explored and validated via Differential Scanning Calorimetry (DSC) and Wide Angle X-ray Diffraction (WAXD). In this dissertation, the hypothesis that the crystallisable compounds in bitumen are the main reason for such structures is adopted, and thus various waxy binders were studied for the effect of lab ageing with Atomic Force Microscopy (AFM) and Confocal Laser Scanning Microscopy (CLSM). Image processing methods allowed to conclude that the bee coverage is reduced upon ageing. Additionally, the oxygenated products as revealed by the ageing mechanisms in bitumen were linked via multivariate statistics to advanced rheological parameters extracted via the Dynamic shear Rheometer (DSR). Convergence of the fast rate-determining phase and the short-term lab ageing was found both for chemistry and rheology. The dissertation ends with the description of a thermodynamics of irreversible processes model for the fast rate-determining oxidation phase, with the model accounting for reasonable changes of the SARA fractions with oxidation. All in all, this dissertation provides a deeper scientific insight into the oxidative ageing mechanisms in bitumen and clarifies the relationship between chemical and rheological characteristics, which may contribute as a guideline to a more sustainable road infrastructure in the future. |
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Language
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English
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Publication
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Antwerp
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University of Antwerp, Faculty of Applied Engineering
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2022
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Volume/pages
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xii, 158 p.
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Note
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Van den bergh, Wim [Supervisor]
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Soenen, Hilde [Supervisor]
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Full text (open access)
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