# A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives
## 4 The State-Of-The-Art
### Images Techniques as Useful Complementary Tools
[23] to discriminate the effect of Dodecyl Benzene Sulfonic Acid (DBSA) as a solubilizer together with conventional rejuvenator (a blend of fluid catalytic cracking slurry--FCC--and bitumen with penetration of 70 grade) in two different aged (TFOT and PAV) bitumen. [PERSON] et al. compared first the effect of aging on the virgin bitumen, whose clues are reported in Figure 17. This figure shows the AFM images of virgin bitumen, Thin Film Oven Test (TFOT) aged bitumen and PAV aged bitumen. The Authors have observed that the aging of the bitumen leads to a decrease in the aging of the bitumen. The authors have observed that the aging of the bitumen leads to a decrease in aging of the bitumen. Figure 16: Topographic images of virgin (**top row**), aged (**2 nd row**), aromatic extract (**3 rd row**), and WV oil rejuvenated (**4 th row**) ABD (left, \(20\times 20~{}\upmu\)m\({}^{2}\)) and AAD (right, \(40\times 40~{}\upmu\)m\({}^{2}\)) measured at room temperature (\(\sim\)20 \({}^{\circ}\)C). The colour scales range over 10 nm and 60 nm for ABD and AAD based samples, respectively (reprinted from Reference [5] with the permission of Elsevier). to a change in the colloidal structure, and differently from [PERSON] et al., an increase in the size of the bee-structures (see Figure 17). Then, they compared the effect of adding the conventional rejuvenating (CR) and the solubilised rejuvenating (SR) on the aged bitumen TFOT and PAV. The comparison in TFOT-aged bitumen and PAV-aged bitumen are reported in Figure 17. They found that in any case the surface of both TFOT and PAV bitumen become smoother with the introduction of CR or SR. However, in the case of TFOT there is no evident difference between the effect of CR and SR showing that, in this case, DBSA does not affect much the surface smoothing action exerted by the rejuvenator. On the other hand, an evident effect can be detected in the case of PAV. By inspection of Figure 18 (lower panel) and comparison with Figure 17, it is possible to notice how the addition of CR on the aged PAV bitumen does not bring marked morphological changes, just a slight reduction in the size of the bee-structures. On the contrary, the addition of SR helps asphaltenes of PAV aged bitumen to be re-dispersed, and this contributes to the performance improvement. For the Authors DBSA (1.5% by weight of rejuvenator) can react with asphaltenes via its sulfonic group to form a solvation layer covering on the surface of asphaltenes clusters, thus, interfering with the colloidal structure transformation of aged bitumen. Therefore, PAV aged bitumen can be recovered  
Figure 17: Atomic Force Microscopy (AFM) images of virgin bitumen, TFOT aged bitumen and PAV aged bitumen: (**a**) Virgin bitumen, (**b**) TFOT aged bitumen, (**c**) PAV aged bitumen (reprinted from Reference [23] with the permission of MDPI open access journal). Figure 18: Upper panel: (**a**) Regenerated TFOT aged bitumen with 10 wt% CR, (**b**) regenerated TFOT aged bitumen with 10 wt% SR; lower panel: (**c**) Regenerated PAV aged bitumen with 10 wt% CR, (**d**) regenerated PAV aged bitumen with 10 wt% SR (reprinted from Reference [23] with the permission of MDPI open access journal). from Gel to Sol-Gel by 10 wt% SR, and the dimension of a bee-like structure formed by asphaltenes can be approximately that of virgin bitumen. Also, [PERSON] et al. [63] have explored the potentiality of AFM techniques to investigate the effect of rejuvenator on the aged bitumen. They used a bitumen aged through Rotational Cylinder Ageing Tester (RCAT) for testing two types of rejuvenators, namely, BM1 and CM1. They analyzed the pristine, aged and doped aged bitumen by means rheology and AFM. From the rheological analysis, they were able to observe that the aged bitumen P1 shows higher complex shear modulus and lower phase angle compared to the pristine bitumen. Obviously, ageing makes the bitumen stiffer (Figure 19a) and less viscous (Figure 19b). The neat rejuvenators show very distinct behaviors.