# 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
In order to characterize the molecular mass distribution, the Authors used analysis of polydispersity, defined as the Mw-to-Mn ratio (Mw, weight average molecular weight; Mn, number-average molecular weight). The results are reported in Figure 11. Both Mw and polydispersity of the virgin asphalt were found to increase after PAV ageing, due to the various chemical reactions in the asphalt/polymer. On the other hand, the values of the PAV-aged virgin and SBS-modified bitumen show that the rejuvenation effect can be primarily attributed to the changes in the molecular polydispersity of the asphalt. Figure 9: Carbonyl and sulfoxide indexes of virgin, aged, and bio-rejuvenated asphalt (reprinted from Reference [60] with the permission of Elsevier). Conversely, for the PAV-aged SBS-modified asphalt, Mw decreases with the increase in the dosage of the bio-rejuvenator from 0 to 10%. Both the 5% and 10%-bio-rejuvenated asphalt exhibit lower PDs than the PAV-aged SBS-modified asphalt. However, there is no clear difference between the Mw values of the 5% and 10%-bio-rejuvenated asphalt. Figure 11: GPC Mw and PD results of virgin, aged, and bio-rejuvenated asphalt (for bio-rejuvenator: Mw = 861, PD = 1.0082) (reprinted from Reference [60] with the permission of Elsevier). Figure 10: GPC curves of bio-rejuvenator and virgin, aged, and bio-rejuvenated asphalt (reprinted from Reference [60] with the permission of Elsevier). In order to understand the role played by the rejuvenator on the RAP bitumen, [PERSON] et al. [61] used the GC-MS (Gas Chromatography-Mass Spectroscopy). They considered a rejuvenator produced from soybean oil, but they did not furnish further details. First, they analyzed the pure rejuvenator: its total ion chromatogram (see Figure 12a) shows five distinct and well-resolved peaks. The pure rejuvenator was then subjected to RTFOT-aging and PAV-aging following the same protocol as that used for asphalt binders aging to assess the chemical stability of the rejuvenator with aging. The total ion chromatogram for the RTFOT-aged and PAV-aged rejuvenator samples are shown in Figure 12 (panels b and c, respectively): they clearly show that the aged rejuvenator gives the same peaks at the same retention times and with similar relative intensity as the unaged rejuvenator. This indicates that the chemical composition of the rejuvenator is preserved during aging. Subsequently, they submitted rejuvenated RAP (unaged, RTFOT-aged and PAV-aged) to pyrolysis to analyze the evolved gases using Gas Chromatography coupled with Mass Spectrometry (GC-MS) (see Figure 13). The total ion chromatogram of the unaged rejuvenated binder shows the rejuvenator's peaks in addition to other smaller peaks attributed to the binder itself. However, the structure of the rejuvenator added to the binder appears to change with aging. It is, therefore, clear that the rejuvenator interacts with the RAP binder, with the consequent structure modification of the rejuvenator itself. Strikingly, the two peaks at 17.3 and 17.4 min are reduced in intensity with aging, and they entirely disappear in the PAV-aged binder. Figure 12: Total ion chromatogram for the used rejuvenator (**a**), the RTFOT-aged rejuvenator (**b**) and the pressure-aging-vessel (PAV)-aged rejuvenator (**c**) (reprinted from Reference [61] with the permission of Elsevier).