Differential effects of ultraviolet radiation and oxidative aging on bio-modified binders

This paper investigates how ultraviolet and oxidative aging affects physiochemical and rheological properties of bio-modified binders containing different bio-oils extracted from biomass (wood pellet, miscanthus, corn stover, and animal waste). Oxidative aging was done in a rolling thin-film oven followed by a pressurized aging vessel; UV aging was performed under an ultraviolet irradiation machine that simulates the effect of sunlight. The extent of aging in each specimen was reported based on the changes in select material properties as measured by UV-Vis, Differential Scanning Calorimetry, Rheometry, Thin-Layer Chromatography with Flame-Ionization Detection, Gel Permeation Chromatography (GPC), and Fourier Transform Infrared Spectroscopy. The results showed that the aging process leads to the shift of the UV-vis absorption to a higher wavelength for all tested binders indicating the formation of conjugated structures and nano-aggregates. This was in-line with binder's fractional characterization showing an increase in the content of fused polyaromatics hydrocarbons (resin and asphaltene) after aging. This was also evidenced in an increase of average molecular weight after aging mainly due to formation of asphaltene nano-aggregates driven by increased polarity of molecules during oxidation as carbonyl and sulfoxides formed. The formation of carbonyl functional groups was more pronounced after UV aging while oxidative aging gave rise to the formation of sulfoxide groups more than carbonyl. Bio-modified binders’ aging resistance varied based on the biomass resources used; however, all of them had higher resistance to UV aging than petroleum-based binders. The outcome of this study provides an insight to differentiate the aging behavior of bio-modified asphalt binder from a petroleum-based binder.