# A Review on Bitumen Rejuvenation: Mechanisms, Materials, Methods and Perspectives
## 4 The State-Of-The-Art
### Images Techniques as Useful Complementary Tools  
[PERSON] et al. [62] have exploited the potential of FT-IR to investigate the effect of two different rejuvenators: a petroleum oil (called \"A\"), and a product derived from refined tall oil (called \"B\"). Rejuvenator \"A\" was added to 15% or 30% by weight on PAV, while the rejuvenator \"B\" was added to 10% or 20% by weight on PAV. These two dosage rates are the lower and upper limits of each rejuvenator type. Once the spectra were acquired, in order to determine if the use of the rejuvenators minimizes the oxidation, the I\({}_{\text{co}}\) and I\({}_{\text{so}}\) indices were calculated although the normalization seems to us to take place only over the C-H signal at 1459 cm\({}^{-1}\). As expected, PAV-aged samples show an increase in the I\({}_{\text{so}}\) value, as well as in the I\({}_{\text{co}}\) index. On the contrary, by perusal of Figure 14 it can be seen that both rejuvenators at both concentrations show a significant decrease in I\({}_{\text{so}}\) values, while the decrease with respect to the I\({}_{\text{co}}\) index is moderate. However, both additives have proved to be effective in counteracting the oxidation of the carbonyl groups, as well as the sulfoxide groups. The Authors also thought to compare the FT-IR results with a Cryo-Scanning Electron Microscopy (Cryo-SEM) investigation for evaluating fracture surface properties of rejuvenator-restored through a digital image processing technique to quantify cracks developed on the fractured surface, due to the aging process. The choice of this technique comes from the Authors' consideration that the evaluation of the microstructural assessment of asphalt with SEM would not be confident, due to presence of volatile components in asphalt and its susceptibility  
Figure 13: Total ion chromatogram for (**a**) unaged, (**b**) RTFOT-aged and (**c**) PAV-aged rejuvenated RAP (reprinted from Reference [61] with the permission of Elsevier). to electron beam damage. Instead, the use of Cryo attachment to SEM, implying a lowering of the samples' temperature well below the glass point, allows observing samples with greater beam and lower temperature sensitivity. They have acquired images with varying magnifications in different parts of the samples, to indicate the fracture surface characteristics of each sample. It is possible to notice that the asphalt sample has a rough and fractured surface with many fragments, due to the high stiffness caused by the aging process. Rejuvenator \"A\" makes the fracture surface of aged asphalt smoother with some remaining minor cracks or fragments. However, no further improvement of the surface texture can be observed when rejuvenator \"A\" amount was increased from 15 to 30%. Even adding rejuvenator \"B\" (10%) makes the fracture surface smoother, although at a minor extent, since significant amounts of fragments still holds. Instead, increasing the rejuvenator \"B\" amount from 10 to 20%, results in a significant improvement of the surface. An interesting aspect can be found in the work of [PERSON] et al., who notes that in order to identify the length and the gravity of the cracks, a digital analysis of the images was carried out using an edge detection technique. Briefly, various algorithms developed using MATLAB software DIP image toolbox were used to generate fracture models, including the crack propagation throughout the samples. Comparison with real samples allowed the selection of the best algorithm and a Fracture Index (F.I.) was defined in order to quantify the fracture capability of aged and restored asphalt samples. As expected, as it can be seen from Figure 15, PAV-aged asphalt has the highest F.I., confirming more pronounced brittleness of the aged asphalt with respect to the aged asphalt with rejuvenators. Figure 14: Calculated index values for various asphalt types (**a**) sulfoxide index, (**b**) carbonyl index (reprinted from Reference [62] with the permission of Elsevier).