The rheological transformation of bitumen during the recycling of repetitively aged asphalt pavement

Abstract

This article explores changes in bitumen during the recycling of asphalt pavement and what consequences the observed rheology has on pavement performance in the short and long term in the Nordic environment. As the existing environment dictates the state of performance, this research focuses on the intermediate and cold temperature performance and requirements, especially transformation from ductile to brittle behaviour. An asphalt pavement, originally constructed by using conventional paving grade bitumen 70/100 and 50/70, was rehabilitated by hot in-place recycling (HIR) for the first, second and third time. The HIR yields the pavement surface consisting of more than 70% of the in situ recycled asphalt. Samples were taken prior to, during construction and in the service. The rheological evaluation of ageing and rejuvenation of bitumen was conducted to investigate the effect of repetitive recycling on bitumen properties. Contractors used soft bitumen 650/900 as a rejuvenator and admixture with the virgin penetration grade 70/100 bitumen. Extracted binders were analysed by means of Penetration, Fraass breaking point and Dynamic Shear Rheometer. The typical rheological analysis was extended by comparing the Glover–Rowe parameter with the Damage Zone, and a good correlation between field performance and material properties was found. Such field sample analysis was complimented by the laboratory simulation of repetitive ageing and rejuvenation of penetration grade 70/100 bitumen. Although the stiffness of the binder could be restored by using the fresh admixture and rejuvenator, the treatment could not recover the original balance between the viscous and elastic response of the bitumen. The criterion given by this Damage Zone was evaluated. A second provisional zone (Insufficient Binder Ductility Zone), now providing the means to evaluate binder properties capable of withstanding the cold Nordic climate conditions, is proposed.