# 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
Ageing was probed by FT-IR-ATR in both the control and modified asphalt binders. As a result, the carbonyl and sulfoxide functional groups increase with ageing. The time evolution of these two functional groups, leads to the conclusion that the modification does not cause any significant influence on the ageing behavior of the asphalt binders. [PERSON] et al. also investigated the molecular size distribution with Gel Permeation Chromatography (GPC) in order to evaluate if the rejuvenator modified molecular properties of RAP binder. They used two kinds of detector: one is the refractive index (RI) detector, and the second one is a variable wavelength detector with UV signal (UV). From RI detector, RAP + 5% A and RAP + 5% C (see Figure 8) displayed a shift from the large to the middle size as compared to RAP binder. Comparing the FT-IR spectra and the results obtained with GPC they hypothesized the presence of an ether group (C-O-C) in the RAP modified with A and C, whereas, from UV detector a shift towards the smaller molecular sizes has been observed in RAP + 5% B. In summary rejuvenators could partially change the molecular size distribution of the RAP binders. Figure 8: GPC spectra with UV (**left**) and RI-signals (**right**) of the RAP binder and the RAP binder with rejuvenator A, B and C (5% by mass of RAP binder each) (reprinted from Reference [57] with the permission of Elsevier). Figure 7: Carbonyl index (**a**) and sulfoxide index (**b**) (data taken from Reference [59]). The idea of combining FT-IR to obtain information on functional groups and GPC test to obtain information on molecular weight distribution was also exploited by [PERSON] et al. [60] who studied the effect of a bio-rejuvenator made by a by-product in cotton-oil production and dibutyl phthalate (7.5 wt% in the bio-rejuvenator) as plasticizer. In fact, they carried out a comparison between the FT-IR spectra of pure bio-rejuvenator; pristine bitumen; bitumen aged by Thin Film Oven Test (TFOT - 5 h, 163 \({}^{\circ}\)C) followed by a pressure-aging-vessel (PAV) test (aging temperature in the PAV test 90 \({}^{\circ}\)C, pressure 2.1 MPa, duration of the test 20 h); PAV was added with 5% or 10% bio-rejuvenator. Moreover, they carried out FT-IR spectra on an asphalt modified with styrene-butadiene-styrene (SBS); SBS-modified PAV, and 5% or 10% bio-rejuvenator on SBS-modified PAV. The peak-area intensity of the oxygenated groups (CO and SO) was used to probe the degree of aging and rejuvenation of the asphalt. Here, again, the Authors calculated the I\({}_{\text{co}}\) and the I\({}_{\text{so}}\) indexes. As expected, for pristine bitumen and SBS-modified asphalt, the carbonyl and sulfoxide indexes increase after aging. As it can be seen by a perusal of Figure 9, both indexes decrease with the addition of the bio-rejuvenator. However, the carbonyl and sulfoxide indexes of the PAV-aged asphalt cannot be restored to their original levels. The Authors applied the GPC to the system under consideration to shed light on the effect of the rejuvenator on the molecular size distribution. The chromatogram reported in Figure 10a shows that the dw/dlogM versus Mw (weight-average molecular weight) curves for the bio-rejuvenator. Mw of the bio-rejuvenator is about 1000 g/mol, and the narrow and sharp peak indicates that the molecular-distribution dispersity of the bio-rejuvenator is low. Figure 10b shows that the PAV-aging process causes a decrease in the low and medium-weight molecular content of the pristine bitumen while increasing its high-weight molecular content. Adding the rejuvenator helps in improving the properties of the PAV-aged bitumen by increasing the medium-weight molecular content and decreasing the low-weight molecular content. Figure 10c shows a similar phenomenon with the single-peak in the PAV-aged SBS-modified asphalt splitting into two peaks after bio-rejuvenation.