Rejuvenating Agents vs. Fluxing Agents: Their Respective Mechanisms of Action on Bitumen Subjected to Multiple Aging Cycles

Abstract

During the service life of road pavements, the asphalt, more specifically the surface layer, is susceptible to aging due to the oxidation phenomenon and the loss of the volatile compounds of bitumen, which functions as the binder in the asphalt conglomerate. Road pavements that undergo a significant level of oxidation become rigid and susceptible to cracking, and new paving operations will need to be carried out in order to make the road ideal for continued use. However, due to recent eco-friendly initiatives that have been put in place to promote a circular economy and also mitigate the problem of environmental pollution, the asphalt industry is currently devising means of safeguarding the environment while also minimizing the cost of the production of road pavements without compromising their quality. As a general solution to this issue, old asphalt pavements are removed and recycled as reclaimed asphalt (RA), with the aim of restoring the original properties of the binder in such a way that RA can be re-used in combination with virgin materials to produce new road pavements. In this research study, virgin bitumen is subjected to a cycle of aging, after which two recycling agents are used to modify the aged bitumen samples. These samples containing the different recycling agents were subjected to a second aging cycle, a second recycling agent treatment, and then again subjected to a final aging cycle. The two recycling agents have different compositions, and each one of them could be either a rejuvenating agent or a fluxing agent. This study investigates the effect of these recycling agents on aged bitumen, and how the addition of these recycling agents influences the changes observed between virgin, aged and recycled bitumen. This would enable an understanding of rejuvenation and fluxing mechanisms, which will help in the classification of the asphalt recycling agents as either rejuvenating or fluxing agents. Dynamic shear rheology, atomic force microscopy, and light microscopy to determine asphaltene melting point were the techniques used in this investigation. The results obtained demonstrate that rejuvenating agents are more effective in reversing the effects of oxidative aging on the bitumen binder than fluxing agents.