# A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives
## 4 The State-Of-The-Art
### Rejuvenation Probed by [PERSON] et al. in 2012 [52] explored the possibility of using a waste cooking oil (WCO) as rejuvenator in the aged bitumen, in order to reduce the expense of highway renovation. They added various amounts of a WCO mainly composed by Oleic acid (C18:2n9c, 43.7%), Palmitic acid (C16:0, 38.4%) and Linoleic acid (C18:2n6c, 11.4%) to an aged bitumen monitoring the changes in standard parameters like penetration index, softening point, Brookfield viscosity and dynamic shear viscosity. The comparison among pristine, aged and rejuvenated bitumen gave self-consistent results furnishing clear clues: the aged bitumen, which is stiffer than the virgin one as result of oxidation processes, can be substantially driven to the performances typical of the virgin bitumen by progressive addition of waste cooking oil. The restoring of the virgin performances takes place at WCO content of 3%, but they can even be improved (n penetration index, softening point and viscosity) by further addition of WCO up to 5%. See, for example, Figure 2 where the penetration value versus various rejuvenator amounts is reported. These results were interpreted at the molecular basis with the aid of Fourier transform infrared spectroscopy (FT-IR) which probes the amount of oxidized functional groups, and specifically C=O and S=O. The increase of polar functional group signal intensity, and specifically C=O and S=O ones, in FT-IR spectra when the bitumen is aged correlates with its stiffness increase. This suggests that the loss in bitumen performances is due to the oxidation process. Even, this increase correlates with an increase in asphaltenes fraction, i.e., the most polar component of the bitumen. On the other hand, the addition of WCO implies a substantial restoring of the pristine C=O and S=O signal, together with the pristine asphaltene/maltene ratio, although the process seems not to be complete/quantitative. Typical IR spectra, together with the most important band attributions, are reported in Figure 3. In conclusion, WCO appears to have a rejuvenating effect because it reduces the oxidation (asphaltene content) compared to an aged bitumen, even if it is not capable of restoring the correct ratio maltene asphaltenes. However, it is interesting to point out that the rejuvenated bitumen has less tendency to ageing compared to original bitumen and has lower volatility than the virgin bitumen reasonably, due to the lower volatility of bio-oil as a consequence of its high content in saturated hydrocarbons. Unfortunately, the Authors do not give details on the FT-IR experiments. To avoid FT-IR artefacts, due to differences in the optical path (different thickness of samples) or in experimental procedures, [PERSON] and [PERSON] [53] wasiely consider the relative amount of ketonic bond with respect to the signals of functional groups which are not expected to change, like the bending of C-H bonds. This peak is pointed out in Figure 4.  
Figure 3: FTIR analysis of virgin aged and rejuvenated bitumen (VB, virgin bitumen; AB, aged bitumen; RB, rejuvenated bitumen) (reprinted from Reference [52] with the permission of Elsevier). Figure 2: Penetration value versus different rejuvenated waste cooking oil (WCO) bitumen’s (AB, aged bitumen) (reprinted from Reference [52] with the permission of Elsevier). This criterion of using a relative intensity was proposed by [PERSON] et al. [54], but the use of the relative area is consistent with the consideration by [PERSON] et al. [55]. In any case, [PERSON] and [PERSON] studied the rejuvenating effect of two different types of oils (the pongamia oil and a composite castor oil made of 70% castor oil and 30% coke-oven gas condensate). The results confirm the clues by [PERSON] et al. showing an increase of the C=O relative signal when the bitumen is aged. Moreover, they found that the C=O relative signal slightly tends to decrease when the composite oil is added, but more markedly increases when pongamia oil is added.