As there are millions of such constituents within the bitumen, its chemical analysis is usually performed based on the molecular structure type, not by studying the constituents individually [16]. Any technique, therefore, that differentiates the types of molecules or fractions within narrower properties would be a more effective form of analysis. The stiffness and viscosity of asphalt pavement and its corresponding bitumen increase with time while it is in service; this is called the ageing phenomenon. As this phenomenon is responsible for the chemical modifications occurring in each fraction of bitumen, it is one of the most important factors impacting the bitumen structure. Asphalt research is currently directed towards the construction of new road pavements using milled reclaimed asphalt pavement (RAP) with consequent advantages both economically and environmentally. To use RAP in a bituminous conglomerate, it is necessary to add additives termed \"Rejuvenating\". The search for these additives is simply based on the evaluation of their effect on the mechanical performance of the final conglomerate. Having more information on the effect of the bitumen ageing process will make it possible to design these additives by identifying molecules containing functional groups which can interact in a targeted manner with aged bitumen components, thus regenerating them. Generally, the ageing process is divided into two stages: short-term ageing and long-term ageing [17]. The former results from the loss of volatile components from the bitumen's maltene due to mixing at high temperature in the pristine paving process or during asphalt construction. The latter, in turn, occurs in the field, owing to the following factors: oxidation of bitumen components by atmospheric oxygen, evaporation of low-molecular-weight components of maltene, and polymerization between the bitumen's components. These processes induce greater stiffness and viscosity of the bitumen, which ultimately hardens the material, causing potential cracking and loss of its binding efficiency [16]. In the laboratory, different artificial standard methods for simulating the ageing phenomenon have been introduced. The Rolling Thin-Film Oven Test (RTFOT) and Thin-Film Oven Test (TFOT) techniques are considered short-term ageing as they simulate bitumen ageing during storage, mixing, transport, and placing as pavement. Meanwhile, to simulate long-term ageing, ultraviolet testing (UV) and Pressure Ageing Vessel (PAV) are employed. In this study, RTFOT and PAV are used as short- and long-term ageing simulation techniques, respectively [18]. As the outcome of ageing is crucial, a vast number of studies, using various perspectives and theories, have explored a range of parameters or factors relating to this phenomenon. Different in situ techniques have been used in the laboratory to evaluate, analyze, and identify what actually occurs inside bitumen during the ageing process [9]. These studies or techniques, however, are mainly measuring a specific factor of a material; this raises a challenge to identify all the feasible variables and forms of the material to study the bitumen ageing process, for either short-term ageing or long-term ageing. The ageing phenomenon impacts not only the rheology of binders but also the structural chemistry; thus, there are numerous techniques to characterize this phenomenon, such as softening point (EN 1427 [19]), penetration test (EN 1426 [20]), and viscosity (EN 13302 [21]). As explained above, the process of ageing causes an increase in stiffness and viscosity but reduces the bitumen penetration grade. Thus, from this point of view, it is feasible to establish an ageing index by measuring the variation of the abovementioned physical properties (before and after ageing). This parameter has proven to be the most exemplary measure with regard to the results observed in the field [22]. It is important to note that assessing bitumen's physical and mechanical properties allows indirect macro-structural analysis of the binder.