Bitumen ageing – Impact of reactive oxygen species. (December 2020)

• Record Type: Journal Article
• Authors: Hofko, Bernhard; Maschauer, Daniel; Steiner, Daniel; Mirwald, Johannes; Grothe, Hinrich
• Is Part Of: Case studies in construction materials. Volume 13(2020)
• Publication Date: 2020-12
• Subjects: Asphalt mixture -- Bitumen -- Ageing -- Reactive oxygen species -- Nitrogen oxides -- Ozone -- Dynamic shear rheometer -- Air void content; Building materials -- Case studies -- Periodicals; 691.05
• DOI: 10.1016/j.cscm.2020.e00390
• Languages: English
• ISSNs: 2214-5095

Abstract

Highlights: Lab ageing methods for asphalt consider molecular oxygen (O2 ) as an oxidant. Its reactivity is low at ambient temperatures. Atmospheric chemistry shows that other reactive oxygen species (ROS) with high reactivity interact with asphalt in the field. Ageing experiments with different gaseous atmospheres were conducted. The results show that a combination of O3 and NOx induce significant oxidative ageing at ambient temperatures and pressures. Abstract: Bitumen from crude oil refinery is an important construction material as the binding component for asphalt mixes in road construction. Due to its organic composition, it is susceptible to oxidation when being exposed to reactive oxygen species (ROS). Oxidation is the main factor driving long-term ageing of the bitumen, which leads to an increase of brittleness and stiffness at lower temperatures and thus, makes road constructions more prone to cracking. Ageing is therefore a limiting factor for the service life of road infrastructure. In the presented study, the impact of different ROS on oxidative ageing of bitumen is studied. Asphalt mix specimens are aged in a specially designed device (VAPro) by leading different gases through the specimen, i.e. pressurized air, O2, O3 enriched O2 and dried air enriched with O3 and NOx . The flow rate is 1.0 L/min and the conditioning time is set to 7 days for air and 3 days for all other gases, respectively. Temperature (+60 °C) and pressure are set to simulate realistic field conditions. Bitumen is extracted and recovered from the specimens after ageing and assessed rheologically by DSR analysis. It was found that neither ambient atmosphere, nor pure O2 or O3 enriched O2 by themselves induce relevant oxidative ageing. By combining air, O3 and NOx, high oxidative ageing levels comparable to RTFOT + PAV can be achieved. Thus, realistic, yet efficient laboratory ageing methods for bitumen and asphalt mixtures need to take all ROS, especially NOx, into account.