Oxidative ageing or ageing of bituminous blends has largely been of interest to investigators, due to its direct consequence to asphalt deterioration. Many distress types, such as cracking and ravelling, are affected by the ageing process. Although changes of rheological and mechanical properties have been well documented, most theories remain rooted in upper scales and a thorough understanding of the mechanisms is still to be investigated. As articulated by Petersen, two main possible paths have been proposed for the oxidation chemistry, namely a fast-spurt and slow-long term one. Challenges arise when attempting to support experimentally the aforementioned mechanisms. Besides that, it remains to be shown whether the underlying mechanisms are reasonable in the context of the complex composition of bitumen affected by the coupled reaction-diffusion phenomenon.
Proposed ageing mechanisms
Petersen, J. C. and Glaser, R. (2011). Asphalt oxidation mechanisms and the role of oxidation products on age-hardening revisited. Road Materials and Pavement Design, 12(4):795–819.
The fast reaction forms mainly sulfoxides and free organic radicals, whereas the slow one produces both sulfoxides and carbonyls.
Bitumen modeling classification
Bitumen ageing is a multiscale / multiphysics problem.
Methodology and objectives
During this project, a fundamental investigation for the formation of chemical components after artificial controlled and simulated ageing will be conducted for three binders of different origins and types. Initiating by the proposed routes, a comprehensive chemical analysis will be developed to support or modify the main considerations, hitherto, for the ageing mechanisms. For that reason the utilization of spectrometry, microscopy and novel devices is favourable. In the framework of this research, it is considered also important to distinguish between the governing fractions of bitumen in order to elucidate the role of the different fractions, such as maltenes and asphaltenes throughout oxidation.
What is missing for gaining a deeper understanding in terms of fundamental properties of bitumen ageing is the oxidation kinetics for the coupled reaction-diffusion phenomenon. Making use of pure nitrogen and dry air in an appropriate device will overcome this obstacle and account for the pure diffusion and reaction-diffusion respectively. This part can be easily combined with rheological properties, such as complex modulus and viscosity before and after ageing and a regression analysis for the correlation of the meaningful chemical and rheological properties will be performed. The optimum goal is to bridge the gap between the ageing mechanisms, expressed with the formation of indicative components as well as radicals, and the phenomenological performance of binders by developing eventually an efficient predictive ageing model boosted by the molecular scale.
Novel techniques and ageing simulations will be used for this purpose.
- Fast-SARA analysis
- Gel Permeation Chromatography (GPC)
- Dynamic Vapor Sorption (DVS)
- Fourier-Transform Infrared spectroscopy (FT-IR)
- Hydrogen and Carbonyl Nuclear Magnetic Resonance (H & C-NMR)
- Electron Paramagnetic Resonance (EPR)
- Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)
- Thin-film oven test (TFOT)
- Rolling thin-film oven test (RTFOT)
- Pressure ageing vessel (PAV)
- Dynamic Shear Rheometer (DSR)