## 1 Introduction  
The use of Reclaimed asphalt pavement (RAP) for the production of new road pavements is at the center of research in the bituminous conglomerates sector [1, 2, 3, 4, 5, 6, 7]. The use of chemical additives is intended to increase the percentage of RAP in the production of bituminous conglomerates. However, through this strategy, both the performance and the life span of the road is mainly unchanged [8, 9, 10, 11]. The most common problem faced by technicians who carry out quality control on bituminous conglomerates and researchers looking for new rejuvenating additives for bitumen is the capability to distinguish the fluxing effect from the rejuvenating effect that the various additives available on the market might possess [12, 13, 14]. Indeed, when a mere softening agent is added to a bituminous mixture that in part contains RAP, its overall viscosity will be lowered, thus improving workability. However, in this case, even if the laying of the road pavement can be done without problems, the pavement will be fragile and its lifespan will be shortened, owing to the presence of the oxidized parts of the bitumen coming from the RAP constituent. Identical rheological effect will be obtained using a regenerative agent, but in this specific case, both resistance and lifespan will be on the increase. Indeed, contrary to a mere fluxing agent, a rejuvenating additive will chemically interact with the oxidized parts of the bitumen, bringing their physico-chemical characteristics back to their initial state before the oxidation phenomena [15, 16, 17]. This restores elasticity to the bitumen binder besides simply lowering its viscosity. For this reason, it is therefore highly important to be able to distinguish, for a given unknown bituminous mixture, which of these additives, i.e., fluxing agent vs. regenerative agent, has indeed been employed. To face this problem, some considerations are useful: literature studies have shown that during the oxidation phenomenon, the clusters of asphaltene molecules that make up the solid part of the bitumen tend to increase their size, stiffening the system [18; 19; 20; 21]. This phenomenon was mainly observed by atomic force microscopy (AFM) and scanning electron microscope (SEM) analyses [22; 23; 24; 25]. Asphaltenes are compounds with high molecular weights present, in bitumen typically in 5% to 30% by weight, and are insoluble in \(n\)-pentane, and therefore they can be isolated from the rest of the bitumen by simple precipitation [26]. It has been observed that their percentage in bitumen increases to the detriment of the maltene part after oxidation. In this study, to simulate the aging process occurring during the lifespan of road pavements, 2 methods were used: Rolling Thin Film Oven Test (RTFOT) [27; 28] and Pressure Aging Vessel (PAV) [29; 30; 31]. These 2 types of aging processes were chosen as they are the most commonly used in research in this field. Furthermore, PAV is the methodology used in the UNI EN 14769 Regulation for simulating the aging of road bitumens. Four different recycling agents (either softening or rejuvenating agents) were mixed to two different types of bitumen. In each case, the asphaltene fractions were extracted and analyzed by Differential Scanning Calorimetry (DSC) [32; 33; 34], a routinely used method for the characterization of the thermal properties of materials. DSC is a technique that enables the characterization of several physico-chemical characteristics of materials. It is used to evaluate and determine phenomena such as crystallization, melting, characterization of glass transition, mesomorphic transition temperatures and the corresponding enthalpy and entropy changes. It is also used to characterize and quantify other effects that evidence changes in latent heat or heat capacity. A major advantage of this technique is its simplicity and ability to be applied over a diverse range of samples (solids, gels and even powder form).