VECD analysis to investigate the performance of long-term aged bio-asphalt mixtures compared to conventional asphalt mixtures

The road industry is seeking solutions to reduce its dependency on petroleum-based products and its carbon footprint. This is leading to increasing interest in the so-called bio-binders, i.e. binders in which bitumen is partially replaced with bio-oils from renewable sources. Fatigue cracking is a major distress for flexible pavements and therefore the fatigue behaviour of innovative road materials (such as bio-asphalt mixtures) must be characterised in a reliable way. Within this framework, this study aims at comparing the fatigue behaviour of a bio-asphalt mixture and the corresponding conventional asphalt mixture. The two mixtures were laboratory-mixed and laboratory-compacted, and the only difference between them was the binder (a bio-binder containing 10% of wood-based bio-oil vs. a conventional bitumen having physical and rheological properties similar to the bio-binder). The mixtures were short- and long-term aged in the laboratory and subjected to complex modulus tests and cyclic fatigue tests. The results, analysed according to the viscoelastic continuum damage (VECD) theory, showed that, after short-term aging, the bio-asphalt mixture may be slightly stiffer and thus more prone to cracking than the control mixture due to a possible over-aging caused by the effects of high temperatures. However, the long-term aging susceptibility of the bio-asphalt mix was found to be less severe as compared to the control mix, leading to fatigue performance benefits in the long term and corroborating the results of previous investigations at the binder level. Overall, these findings further encourage the use of bio-binders as an alternative to traditional asphalt binders.