# A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives
## 4 The State-Of-The-Art
### Thermal Stability Helps in Probing Rejuvenation  
By monitoring viscoelasticity, creep and response, FT-IR, Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC), [PERSON] and [PERSON] proved that successful rejuvenation takes place when these oils are added to the bitumen. It is interesting to notice that both oils have good thermostability performances. The virgin binder showed a visible mass loss at temperatures below 200 \({}^{\circ}\)C; instead, all the rejuvenated binders along with aged binder showed significant mass loss beyond 200 \({}^{\circ}\)C, but such temperatures are much higher than those typically adopted in hot mix asphalt preparation, rendering this difference not significant for practical purposes.  
Also, [PERSON] et al. [56] used thermal stability analysis to evaluate the effect of rejuvenating soybean oil on reclaimed asphalt pavement (RAP). Acknowledging the importance of studying thermal stability of rejuvenated binders to assure that eventual loss of rejuvenating additive (typically characterized by low molecular mass) does not modify asphalt performance, they carried out thermogravimetric analysis on the RAP, on the blend made by RAP and the pristine bitumen (PG58-28), and finally, on the mixture formed by RAP, soybean oil (12%) and the pristine bitumen. Coupled to Thermogravimetry (TG), an FT-IR spectrometric investigation on the gases produced by heating was also carried out. The Authors' results obtained by Thermogravimetry (TG) can be summarized in Table 1.  
Figure 4: FTIR spectrum for pongamia oil (reprinted from Reference [53] with the permission of [PERSON] and Francis).  
This table shows the Initial Decomposition Temperature (IDT), defined as the temperature where 2% mass loss occurs; the char yield percentage is the mass remaining at the temperature of 550 \({}^{\circ}\)C, and the percentage residue is the remaining percentage of asphalt material at the end of the analysis. From this table it is clear that the RAP binder shows the highest thermal stability, confirming that the stiffness is due to asphaltene amount that is more thermally stable, whereas, the other two binders show the same behavior, having an IDT few degrees lower. [PERSON] et al. also compared the spectra (at a temperature of 390 \({}^{\circ}\)C) of the gases evolved from the three different binders, taking into account for the blank constituted by the bare soybean oil. It turned out that the spectrum of the binder containing the rejuvenator shows a relatively intense peak typical of the rejuvenator itself. Although this observation can be thought as trivial, a pseudo-quantitative analysis, carried out at different temperatures by normalizing the FT-IR spectra at the same C-H stretching peak height (2930 cm\({}^{-1}\)), allowed the Authors to conclude that FT-IR spectrometry can be used as a tool to probe the rate of mass loss of the rejuvenator. In fact, a higher mass loss triggered by a temperature increase implies higher relative intensities of the characteristic functional groups of the rejuvenator itself (C=O stretching at 1736 cm\({}^{-1}\) and the two C-O stretching at 1015 and 1153 cm\({}^{-1}\)).