# A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives
## 2 Methods for Bitumen Characterizations
This is probably due, in our opinion, to the always-urgent need of improving performances for applicative purposes so that basic research, highlighting the specific intermolecular interactions and the molecular organization at the base of the observed behavior has been sometimes overlooked. Therefore, there is still a lack of information on how many additives affect the supra-molecular structure and the distribution of aggregates within the bituminous colloidal network and how this can reflect on the overall material properties. This makes the relationship between molecular interactions and the final material structure/properties (which is ultimately the final objective of physical chemistry) still quite vague. This problem was already faced recognizing that bitumen are characterized by intermolecular associations at different length-scales: asphaltene molecules are aggregated to form stacks by self-interactions and these aggregates are stabilized by polar resins, due to their amphiphilic chemical nature and the overall structures are then dispersed in a paraffin-like apolar matrix. These characteristics render the material a truly complex system, so an approach based on the complex systems theory is, therefore, necessary foreseeing different levels of complexity, each of them potentially showing emerging properties arising from the opportune organization of the molecules. It has been, in fact, recently highlighted that asphaltenes tend to form stacks of about 18 A, organized at higher levels of complexity in anisotropic aggregates of about 200 A \(\times\) 28 A, which, again, are assembled to form micrometer-size elongated aggregates characterized by the so-called \"bee-structure\" [24]. However, asphaltenes are unable to create a continuous network [25]. These recent findings opened the door to a better comprehension of the bitumen structure from X-ray scattering data, making this technique a method of election [26] for the structural investigation of such systems. In this context, it was shown that the influence of additives is exerted by their preferential localization in the maltene phase or close to the asphaltene clusters, depending on the additive chemical characteristics, thus, finally affecting the overall rheological properties. An additive can play, therefore, important roles: it can exert its effect at the inorganic/organic interface, or, at a lower level of complexity, within the maltene/asphaltene aggregates, whereas, a redox additive works at the chemical state of the single polar molecules, i.e., at an even lower level of complexity. Another mechanism exerted by the additive is the formation of a network inside the maltene giving elasticity to the bitumen [27] or a simple change of physical phase transition with fluxing at a higher temperature while conferring rigidity at lower ones [28]. The so-called \"antistripping agents\" act by stabilization of eventual supramolecular asphaltene aggregates in the maltene phase [8; 9]. As regards the additive chemical nature, selected polymers have been used (low-density polyethylene, ethylene-vinyl-acetate, SBS-polyphosphoric acid (PPA), Elvaloy, etc.) [29], as well as smaller molecules falling in the categories of organosilane and phospholipids [30] or paraffinic synthetic waves, derivate of fatty amines and surfactants [31], antioxidants [32], etc. Once introduced the chemical and the structural characteristics of a bitumen, the next paragraphs will highlight the modifications taking place during ageing and how the original state can be restored by the introduction of the concept of rejuvenator.