# A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives
## 7 Concluding Remarks  
1. Many materials are used for rejuvenating bitumen by lowering viscosity and stiffness. Since different physico-chemical mechanisms are involved in bitumen ageing (oxidation, evaporation, structural changes), different mechanisms of actions can be consequently exerted by the various rejuvenators (softening/fluxing, restoration of the pristine structure/properties). The distinction of the various mechanisms has been highlighted. These aspects have been shown in Sections 1-3.
2. The state-of-the-art constituted by the works carried out by several researchers in this field has been shown. Low-cost oils are generally added to increase the maltene fraction, but it should be noticed that an additive having complete rejuvenating function should also induce a reorganization of the chemical structure of asphaltenes and their assemblies. The restoring of the aged bitumen structure to the original conditions is not trivial, due to its complex organization at the supra-molecular scale. This has been extensively shown in Section 4.
3. Taking into account the complex chemistry involved in the bitumen rejuvenation, the additive performances can be improved by chemical manipulation/modification (paragraph 5.1). Some perspectives have been also presented (Section 5.2) considering for the complexity of the systems and suggesting the use of amphiphilic species as promising rejuvenator thanks to their simultaneous presence, within their molecular architecture of both polar and apolar moieties which permits their simultaneous interactions with polar (asphaltene clusters), apolar (maltene) and amphiphilic (resins) species of the bitumen.
4. Scattering techniques and nuclear magnetic relaxometry have been presented as vanguard and promising techniques deserving attention for deeper analyses in bitumen. In fact, they can probe the effectiveness of a rejuvenator in restoring the microstructure of bitumen after the aging process, whereas, mechanical properties, on their own, are not enough for investigating this aspect. A clear introduction to the physics of the techniques and applications to the study of bitumen has been presented.  
Figure 30: Inverse Laplace Transform (ILT) showing the Probability Density Function (PDF) of asphaltene and maltene aggregates of bitumen samples.  
With this work, we would like to share with the reader our belief that the detailed analysis of the physics of bitumen at the molecular basis extends the information taken from the commonly used empirical and quick tools. This allows to better understand the phenomena taking place in bitumen furnishing new tools for the piloted design of new and ever-performing rejuvenators.
6. We wanted to furnish a novel viewpoint for the study of bitumen based on the concepts of the complex systems in physics. According to this approach, the final behavior of the material is not only dictated by specific interactions, as usually assumed in most of the research papers, but also by collective contributions of many molecules interacting and aggregating themselves usually at different length scales in hierarchical structures generating emerging properties. We hope that this study can constitute a novel approach for the investigation of bitumen, and the improvements of its performances.  
P.C. ([PERSON]) conceptualization methodology and writing, P.C. ([PERSON]) conceptualization; M.P. editing correction and writing, V.L. conceptualization and research, R.A. conceptualization, and C.O.R. conceptualization and supervision.  
This research received no external funding.  
The authors declare no conflict of interest.