## 4 Conclusions  
In this study, two recycling agents were studied to investigate their rejuvenating capabilities on bitumen binders subjected to multiple aging cycles. Rejuvenating agents and fluxing agents have different mechanisms of action on aged bitumen. A rejuvenator should be able to interact chemically with the components of bitumen to restore its properties. It should be also able to recover its physical rheological properties to guarantee the long-term performance of a recycled asphalt mixture. A fluxing agent is capable of only physically interacting with the aged bitumen by augmenting its maltenic fraction, thereby making it softer. Studies that distinguish between real rejuvenation and mere fluxing of aged bitumen will prove to be very important in the advancement of RAP technology. These studies couldhighlight pathways that will bring about an increase in the percentage of reclaimed asphalt that can be used in new road paving operations and, in the long run, facilitate recycling and resource conservation, thereby promoting a circular economy. The DSR, AFM, and optical microscopy findings of this study can be concluded thus:
* Dynamic shear rheology is fundamental in evaluating the mechanical properties of bitumen, and it often corroborates the results obtained from bitumen conventional tests. In fact, in this research, the conventional test results were also consistent with those of the DSR analysis. However, other techniques such as atomic force microscopy and light microscopy are very important in order to understand the mechanisms that govern the changes in bitumen's properties upon aging, and the recycling of bitumen with rejuvenators or mere fluxing agents.
* The DSR results show that both recycling agents used in this study reduced the stiffness of the aged bitumen, recovering its mechanical properties close to that of the reference virgin bitumen. This was observed via both complex modulus and the transition temperatures. As mentioned earlier, these results are consistent with those obtained from the conventional bitumen tests, as expected.
* Via AFM, the R1 recycling agent was observed to restore the internal structural components of the aged bitumen, bringing it back to a structure very similar to the reference virgin bitumen. R2 recycling agent was only able to augment the maltenic fraction of the aged bitumen, merely softening it.
* Via deasphaltenization and light microscopy of asphaltenes, it is observed that R1 effectively recovered the properties of the corresponding bitumen by restoring its property of change of state in relation to temperature. This was not observed with R2, meaning that it has little to no effect on the asphaltenes of aged bitumen. Since aging is said to have a major effect on the properties of asphaltenes, it can be said that R2, in the real sense, does not reverse the effects of oxidation.
* Adding up the test results of this study and comparing their implications with what is written in the scientific literature on this topic, recycling agent R1 can be said to be a rejuvenator, while recycling agent R2 can be said to be a fluxing/softening agent. Accordingly, the introduced methods could be efficient techniques to differentiate the recycling agents into fluxing (softening) agents and rejuvenators.  
Conceptualization, C.O.R. and L.V.; methodology, C.O.R., A.A.A., P.C., S.E. and M.P.; formal analysis, V.L., A.A.A. and S.E.; data curation, P.C., S.E., A.A.A. and V.L.; investigation, A.A.A., S.E., M.P., P.C. and E.G.; writing--original draft preparation, A.A.A. and S.E.; writing--review and editing, C.O.R., P.C. and L.V.; supervision, C.O.R. and L.V. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The authors declare no conflict of interest.