# A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives
## 4 The State-Of-The-Art
### Rejuvenation May Be Uncorrelated with IR Functional Groups: Need of Chromatography  
[PERSON] et al. [57] found an interesting aspect. In fact, these Authors pointed out that, despite the addition of rejuvenators, the bitumen physico-chemical oxidation did not reverse: mechanical changes were not caused by chemical changes at functional groups level, but by a rearrangement of polar/nonpolar components. They took into account for three different commercial bio-based rejuvenators: a natural seed oil (called rejuvenator \"A\"), a cashew nut shell oil (called rejuvenator \"B\") and a rejuvenator based on tall oil (rejuvenator \"C\"). After highlighting by FT-IR that rejuvenator A and C have a rather similar chemical nature (see Figure 5 which reports the FT-IR spectra of the bare three rejuvenators), they performed FT-IR spectra on samples of RAP containing 5% of each rejuvenating and compared them to the spectrum of a virgin bitumen 50/70. The results are shown in Figure 6: the peaks corresponding to the ageing of binders, due to oxidation do not disappear although rejuvenators were added to the RAP binder. Chemical structures of RAP +5% C and RAP +5% A were found to be similar, suggesting that the chemical effect of rejuvenator C and A on RAP binder is similar. The Authors also determined the chemical ageing index (CAI). This is given by the sum of carbonyl index (CI) and sulfoxide index (SI) defined, as suggested in [PERSON] et al. [58], as the area of the carbonyl and sulphoxide signal, respectively, normalized, to the peaks related to the asymmetric vibration of CH\({}_{2}\) and CH\({}_{3}\) (around 1455 cm\({}^{-1}\)) and to the symmetric deformation vibration of CH\({}_{3}\) (around 1376 cm\({}^{-1}\)) as the latter areas do not change significantly. It must be noted that here the Authors use the same indices as [PERSON] and [PERSON], by considering the area of the FT-IR signals (and not the bare intensities) and normalizing them to signals related to the C-H functional group since they are expected to be hardly sensitive to the chemical environment. By using these indices, the Authors found that the unaged binders RAP + 5% A and RAP + 5% C have a higher CAI index than the plain RAP. Most probably due to the fact that seed oil and tall oil themselves contain carboxylic groups C=O, they found the same clues derived by [PERSON] and [PERSON] who found that the ketone group is present in their rejuvenator (pongamia oil) itself. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **IDT (\({}^{\circ}\)C)** & **Char Yield (\%)** & **Resolute (\%)** \\ \hline RAP & 316 & 30 & 7 \\ RAP + PG58-28 & 309 & 26 & 6 \\ RAP + 12\% Mod PG58-28 & 309 & 26 & 6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: TG results of the studied asphalt binders (reprinted from Reference [56] with the permission of Springer Nature). Figure 5: ATR-FT-IR spectra of the plain rejuvenators A, B and C before ageing) (reprinted from Reference [57] with the permission of Elsevier). Figure 6: ATR-FTIR spectra of the virgin binder 50/70, the RAP binder and the RAP binders with rejuvenators A, B and C (5% by mass of RAP binder each) (reprinted from Reference [57] with the permission of Elsevier). [PERSON] et al. [59] also used the FT-IR-ATR analysis to explore the effect of soybean-derived rejuvenator on two different kinds of performance grade bitumen. The types of bitumen, PG 64-28 and PG 58-28, were aged by Rolling Thin Film Oven Test (RTFOT, similar but slightly different in parameters values from TFOT technique) and pressure-aging-vessel (PAV) methods, and then they were doped with 0.75% of soybean-derived rejuvenator. Figure 7a shows the increase in the carbonyl index with ageing. The soybean additive does not influence the ageing behavior of the binder. Regarding the sulfoxide index, (shown in Figure 7b) it increases with the aging of PG 58-28. On the contrary, it decreases dramatically to the last step of PG 64-28 ageing (PAV). The drop is also present for the aged doped binder.