The effects of environmental aging on Colombian asphalts

Abstract

Environmental exposure affects asphalt mixture performance. Using a Dynamic Shear Rheometer (DSR), we determined there was a correlation between the environmental aging of Colombian asphalt binders AC-20 and AC-30 and changes in their rheological properties. We aged asphalts using the Rolling Thin Film Oven (RTFO) test and the Pressure Aging Vessel (PAV), as well as an ultraviolet (UV) chamber designed especially for this project. This aging chamber generates UV radiation with radiation-condensation periods up to 500h. Physical properties were evaluated by penetration, ductility and softening point tests. Chemical evaluation was made through Fourier Transform Infra-Red (FTIR) Spectroscopy as a complement to Corbett SARA fractions. We then compared the physical, chemical and rheological aspects of the original and aged asphalt binders. On one hand, short-term aged asphalt binders showed a recuperation in ductility and |G∗| due to an increase in resin fractions. On the other hand, long-term aging produced by the PAV was similar to that of the RTFO treatment with an additional 500h of UV radiation. We carried out the dynamic evaluation of asphalts with Multiple Stress Creep Recovery (MSCR) tests. Taken together, these results show that AC-20 and AC-30 age differently based on their respective SARA fractions content: AC-30 displays higher levels of strain than AC-20 because of its increased levels of solid fractions. We found that RTFO treatment produced similar results in the asphalt binders after 100h of UV radiation. Additionally, chemical testing demonstrates that during short-term aging, saturates and naphthene aromatics convert into resins—the result of oxidation—until productions of these resins stops. Then, during the long-term resins are converted into asphaltenes.