The role of polymer modification in mitigating 'sunburn' damage on asphalt roads

Asphalt roads suffer from ageing throughout their service life due to exposure to ultraviolet light (UV). The aim of this study is to determine the role of polymers such as ethylene vinyl acetate (EVA), styrene butadiene styrene (SBS) and crumb rubber from end-of-life tyres (CR) in protecting bitumen against the damage caused by UV radiations when roads are exposed to sunlight. One unmodified bitumen and four polymer-modified commercial binders were exposed to a filtered xenon-arc light for 10, 20 and 30 days before being tested. Overall, SBS modified binders were less damaged by UV exposure, followed by CR and EVA modified binders. More specifically, SBS provided the best cracking resistance to the binder after ageing compared to conventional unmodified bitumen, followed by CR. EVA did not improve the cracking resistance of the binder. A deep chemical analysis of the photo-oxidation mechanism of polymer-modified binders revealed that SBS is more effective in reducing the formation of carbonyls and aromatics in aged bitumen compared to CR and EVA. The 3D network formed by SBS polymer chains in bitumen was found to be more resistant to oxidation than CR and EVA chains, hence providing a superior UV resistance to SBS-modified binders. Overall, CR seems to provide a sustainable alternative to conventional polymers since using CR for bitumen modification would reduce landfilling of tyres while increasing roads service life and reducing maintenance costs.