# A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives
## 2 Methods for Bitumen Characterizations  
The characteristics of bitumen are not trivial at all: it is an organic high-viscosity viscoelastic binding agent which is itself a composite system constituted by nano-meter sized aggregates of polar molecules (asphaltenes) dispersed in a more apolar continuous phase of saturated paraffins, aromatic oils and resins called maltene [2; 3]. Usually, these fractions can be determined by the so-called S.A.R.A. determination (Saturates, Aromatics, Resins and Asphaltenes) [10]. In this method, the sample of bitumen is dissolved in peroxide-free tetrahydrofuran solvent (usually to reach a 2% (_w/v_) solution). Saturated components of the sample are developed in _n_-heptane solvent while the aromatics in a 4:1 mixture of toluene and \(n\)-heptane. Afterwards, the rods are dipped into a third tank, (usually 95 to 5% mixture of dichloromethane and methanol). This organic medium proved suitable to develop the resin fraction, whereas, the asphaltene fraction is left on the lower end of the rods. However, it must also be pointed out that asphaltenes are not classified using their molecular structure, but they are defined traditionally on the basis of the procedure required to extract them from heavy oils [11]. Bitumen are a not well-defined mixture of constituents so different methods of analysis exist where solvents are added to bitumen to determine its chemical properties. For example, [PERSON] [12] offered a method for not only determining the number of maltenes and asphaltenes of bitumen, but also distinguishing light-, middle-, and high-solubility of asphaltenes. However, for an effective study, the general viewpoint of their overall assembly becomes more important than the detailed chemical speciation of the various molecules involved. Based on this, a testing method for determination of the quality of bitumen, called \"simplified laboratory method\", was developed in order to gain fast and easy information. S.A.R.A. determination and the attempts by [PERSON] are examples of this approach to gain chemical information. Bitumen are also regarded in terms of their performances, for which a rheological description of the materials is often given. Empirical approaches are always followed to determine the performances within a chosen temperature range [13; 14] for convenient use [15; 16]. Due to the general description of the bitumen performances in rheological terms (penetration index, softening point, ductility, viscosity), and due to the need of quick, easy and low-cost methods to characterize the bitumen, the lack of detailed knowledge of the supramolecular assembly characterizing the bitumen structure at the various levels of complexity caused the fact that a rational correlation of the bitumen structure with its performances is actually missing. Attempts at more sophisticated investigative tools are present. Scattering experiments, and in particular X-ray scattering ones, would be advisable to probe the structure from the A to the meso-scale. As a matter of fact, remarkable attempts have been made since the '60s [17], but the bitumen complex organization has hindered the development of such structural study in details. The structural investigation has been, therefore, generally carried out by Atomic Force Microscopy (AFM) [18], by Confocal Laser Scanning Microscopy [19], by Optical Microscopy [20], and Fluorescence Microscopy [21], but all these methods were used to probe the micro-scale (not going deeper to the nano-scale) and the surface. Attempts at gaining information on the nano-scale structure of the bulk have been limited, and the results remained quite hypothetical [22]. Even the \"colloidal structure\" is just empirically derived by the contents of aromatics, resins, asphaltenes and saturates [23].