High resolution chemical fingerprinting and real-time oxidation dynamics of asphalt binders using Vocus Proton Transfer Reaction (PTR-TOF) mass spectrometry

Asphalt binders are complex mixtures with a molecular configuration that varies with source and its chemical composition is not fully understood. Understanding the building blocks of binders is critical to fully interpret important characteristics including oxidative transformations. This study explored the use of the Vocus proton transfer reaction time-of-flight (PTR-TOF) mass spectrometer for the high resolution chemical fingerprinting of asphalt binders along with the observation of their real time oxidation dynamics. Three different binders were selected to examine the sensitivity of this technique under different gas blankets namely nitrogen, volatile organic compounds (VOC) free air and ozone-enriched VOC free air. Hierarchical clustering revealed differences in the degree of chemical expression of various molecules in different binders, which could be attributed to their unique primary differences and chemical transformations. The results also indicated that even higher intensities of molecules could be observed under the ozone-enriched blanket and increased temperatures indicating that this environment contains reactive precursors which could promote oxidation. Finally, realtime oxidation characteristics of binders were explored through factor analysis (FA) which elucidated possible pathways for binder oxidation, for example, through benzylic routes. Overall, the work conducted in this study points to the remarkable potential of this novel analytical technique to fingerprint asphalt binders with a high time and chemical resolution. This work also sets the stage for further work in understanding asphalt binder composition and multi-scale transformations, inspiring a database of chemical fingerprints related to macro-level properties.