The correlation between asphalt viscosity increase on oxidative aging and the carbonyl compounds formed (almost exclusively ketones) has been well established; however, the effect of sulfoxide formation on physical properties during age hardening has received little attention. Evidence is presented in this paper that shows that the alcohols, which are formed concurrently with the sulfoxides from the same hydroperoxide precursors as the ketones, have a similar effect on asphalt viscosity increase as does the ketones. These alcohols are the main contributors to oxidative age hardening of high sulfur asphalts. Analysis of the kinetic data for ketone and sulfoxide formation during asphalt oxidation also provides additional evidence for the validity of the dual asphalt oxidation mechanism previously reported.

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European refining, French in particular, is currently going through a phase of rationalization and search for maximum flexibility in crude supplies. For users of bitumen, this creates concerns about the quality and consistency of products delivered, especially as the European standard EN 12591 appears to them as insufficient to ensure satisfactory performance of the finished products, particularly in the case of specialty products such as high modulus asphalt, polymer modified bitumen, and bitumen emulsions. In this context, the search for correlations between bitumen properties and the performance of the finished product is more relevant than ever. The study presented here is focused on asphalt made with pure bitumen. It was based on a standard design, but with two different types of aggregates. After a preliminary selection, 8 bitumen (20/30, 35/50 and 50/70 pen. grades) were selected. The characterization of asphalt mixes covers all the usual characteristics (stiffness modulus, resistance to rutting and fatigue, resistance to thermal cracking, water sensitivity). The characterization of binders, besides conventional testing, includes the rheological properties (DSR, MSCR, and BBR tests) and the compositional analysis, particularly infra-red spectroscopy and SARA analysis. These tests were performed on the original binders, after RTFO, after RFFO + PAV as well as on the binders recovered from asphalt. This project was conducted as a collaboration between Eurovia and the Western Research Institute (WRI) which performed the compositional analysis of binders, including the SAR-AD™ (WRI improved SARA separation technique) and the chemometrics analysis using their software ExpliFit™.

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A simple dual-mechanism model successfully fits the oxidation of 12 unmodified asphalt binders originating from a wide variety of sources. The kinetic formulation includes fast and slow reaction paths in parallel with free radical interactions between the two reaction pathways. The same Arrhenius parameters are used for all 12 binders studied. The differences in asphalt binder oxidation rates can be explained with the use of only one adjustable parameter, the amount of reactive material available for the fast reaction. This result suggests that unmodified asphalt binders oxidize with essentially the same chemical mechanisms. Because the Arrhenius parameters apply universally, a simple test may be performed to characterize the oxidation kinetics for unmodified binders without expensive, long-term oxidation experiments at multiple temperatures. A rheological study of the materials generated in the aging of the 12 binders using dynamic shear rheometry was also performed to investigate the relationship of rheological changes with chemical changes as binders oxidize. The rheometry consisted of the generation of a series of isothermal frequency sweeps, followed by fitting the resulting master curve with the Christensen–Anderson model. Simple shifting cannot account for the master curve changes, but changes in the model parameters follow a log-linear relationship for oxidation chemical changes. These fits appear to be source dependent, suggesting that a method with two aging time conditions would be required to characterize the rheological property changes in an unmodified asphalt binder as it ages. Such a method would produce a complete master curve–shift function set at any extent of aging, suitable for input into rational performance models.