# Oil Sludge as a Rejuvenator for Aged Bitumen: Structural and Thermal Effect
## 3 Results
### Analysis of the Impact of Oil Sludge on the Chemical Composition and Structure of Bitumen  
One of the most important tools for recording changes in the chemical composition of a bitumen sample is considered to be IR Fourier spectrum (FTIR). The FTIR spectrum of aged bitumen is shown in Figure 2.  
The main chemical functional groups for determining the class of bitumen binders are considered to be vibrations of aliphatic and aromatic bonds at wave numbers of about 3000-2880 cm\({}^{-1}\), 1350-1500 cm\({}^{-1}\), and 750-900 cm\({}^{-1}\)[38]. The authors of the work note that the most important are the bands in the range of 1800-900 cm\({}^{-1}\), which show chemical changes in functional groups based on heteroatoms. At the same time, in studies [39], the main signs of bitumen oxidation and the confirmation of the process of its aging have been directly associated with the formation of carbonyl (at 1700 cm\({}^{-1}\)) and sulfoxide (at 1030 cm\({}^{-1}\)) groups and aromatic groups. A number of scientists [38,40] confirm the successful use of peaks corresponding to sulfoxides and carbonyls to assess the degree of aging and their correlation with the physical and rheological properties of bitumen. At the same time, studies [41] have shown that changes in aromaticity depending on the source of bitumen and its state of aging are not convincing enough, since the evolution of aromatic bands with age is not always obvious, and therefore this parameter is less often used as an indicator of aging, despite the general recognition of an increase in aromaticity [42]. The FTIR spectra of aged bitumen showed the presence of absorption bands corresponding to the sulfoxide bond (S=O), detected at 1030 cm\({}^{-1}\). According to Figure 3, adding oil sludge to aged bitumen leads to a decrease in the sulfoxide bond values. To support this observation, a quantitative FTIR analysis was conducted by calculating the normalized absorbance ratios for the sulfoxide band (-1030 cm\({}^{-1}\)), using the aliphatic C-H deformation band at 1456 cm\({}^{-1}\) as an internal reference. Figure 2: FTIR spectrum of aged bitumen. As summarized in Table 4, the sulfoxide index (A\({}_{1030}\)/A\({}_{1456}\)) decreased with increasing oil sludge dosage (from 0.395 for aged bitumen to 0.259 for 5% OS), indicating a gradual reduction in sulfoxide group content. The carbonyl band at 1700 cm\({}^{-1}\), while present, exhibited only minor changes and was therefore excluded from the quantitative comparison at this stage. In [36], the decrease in sulfoxide and carbonyl bonds is associated with an increase in the ratio of maltenes to asphaltenes. It is important to point out that the symmetric and antisymmetric stretching bands of CH\({}_{2}\) and CH\({}_{3}\), occurring in the 2600-3000 cm \({}^{-1}\) region, are practically unchanged. Since the relative intensities of these contributions can be considered as indicators of the lateral packing of nearby alkyl chains in organic molecules [43], the unchanged intensity profile in this region suggests that no evident change in the short-range interactions of alkyls chains (mostly located within the maltene phase) takes place. The FTIR spectroscopy results confirmed the presence of oxygen-containing functional groups, such as carbonyl and sulfoxide, in the structure of RTFOT-aged bitumen, indicating oxidation and molecular degradation, while the maltenic alkylic region remained largely unaffected. These findings are supported by the SEM images shown in Figure 4. The aged bitumen (Figure 4a) exhibits a rough, irregular surface with microcracks and phase separation, reflecting the destruction of the colloidal structure due to oxidative aging. According to [44], bitumen-rich domains typically appear darker and more compact in SEM micrographs, but these features are largely diminished in aged samples. In contrast, Figure 4b-d depict the morphology of aged bitumen rejuvenated with 1%, 3%, and 5% oil sludge, respectively. With increasing sludge content, the surface becomes progressively smoother and more homogeneous.