## 3 Results and Discussion  
### Differential Scanning Calorimetry (DSC)  
The present study was performed to check whether asphaltenes contained in bitumen could represent a probe to identify whether a recycled bitumen mixture has been rejuvenated or only fluxed by a softener agent. This hypothesis was based on the fact that upon oxidation of bitumen, the clusters of asphaltene molecules that contribute to the solid part of the bitumen tend to increase in size, thus stiffening the system [20; 21; 22; 23]. Asphaltenes are compounds with high molecular weights present in bitumens generally in 5% to 30% by weight and are insoluble in \(n\)-pentane, so that they can be isolated from the rest of bitumen by simple precipitation [43]. It has been furthermore observed that upon oxidation, their percentage in bitumen increases to the detriment of the maltene part. For these reasons, it seemed reasonable to forecast that the thermal properties of asphaltenes could be correlated to the historical background of bitumen. Indeed, if rejuvenation occurred, the asphaltenes may also have their initial thermal behavior restored. In Figure 1, the calorimetric analysis of all the samples obtained with both the bitumens utilized in this study are reported. Figure 1a shows the trend of the calorimetric curves relative to the asphaltene samples derived from the aged-by-RTFOT and non-aged Type 1 bitumen. RTFOT was carried out for 75 min in accordance to the standard procedure ASTM D2872-04 and for 225 min to obtain a bitumen (identified in the present work as \"RTFOT-225 min\") rigid enough to simulate a prolonged ageing process of 10-12 years, which is a period typical of recycled asphalts [47]. In all the samples, we found the presence of inflection points typical of glass transition [48; 49; 50; 51] (indicated in the graph segment enclosed between the two-colored vertical bars). The TG temperature of a material characterizes the temperature range over which this glass transition occurs. Firstly, it was observed that increasing the oxidation time, the inflection point moves towards higher temperatures. The same effect was observed for the first signal of the calorimetric curve (indicated in the graph with the X symbol). In particular, in the case of bitumen aged for 75 min, one remaining peak is also observed between the first signal of the calorimetric curve and the glass transition (indicated in the graph with a red arrow). This is because prior knowledge from scientific literature on this topic makes us understand that the asphaltenes form aggregated clusters [52; 53; 54; 55]. Some of these aggregated forms of clusters involve weaker interactions with a looser, longer range and self-assembly, and so are more exposed to oxidation, while those clusters in which the asphaltene molecules form a stuck structure (more tightly packed) are not as easily oxidized due to their compact structure. The addition of the regenerating additive TPI (green line) brings back the inflection point (in the figure represented by the segment enclosed between 2 beads on the curve) to values similar to those obtained for pristine bitumen while the addition of the fluxing additive commonly known as Soy Oil (purple line) shows a TG very similar to that observed for the bitumen aged by using RTFOT for 225 min. The chemical basis of their different effect has been clarified: the Soy Oil, due to its mostly apolar structure, is expected to be localized in the maltenic fraction, probably establishing basically apolar interactions. TPI, on the other hand, thanks to its phosphate group, can bind asphaltene clusters. The possibility of organophosphate to establish strong interactions was recently pointed out [57]. Parallel to this, the apolar molecular moiety renders TPI truly amphiphilic, the effect of which can be in synergy with the resins naturally present in the bitumens: If different amphiphiles are close together, they can give rise to peculiar self-assembly [58] with unexpected emerging properties and dynamics [59] up to the formation of ionic liquids [60,61].