## 3 Results and Discussion
### FTIR Results  
The chemical characteristics of bitumen samples were measured by the FTIR analyses, which were carried out on samples from Experiment 6 (A2, B2, C1, D4), Experiment 13 (A4, B1, C4, D2), and Experiment 16 (A4, B4, C1, D3) mixtures and virgin bitumen. For Experiment 6 (A2, B2, C1, D4), modified bitumen was prepared using 0.30% Cecabase RT BIO10, a mixing temperature of 120 \({}^{\circ}\)C, a mixing time of 15 min, and a mixing speed of 4000 RPM.  
Spectra given in Figure 12 were recorded to identify critical functional groups in bitumen, covering wavelengths from 400 to 4000 cm\({}^{-1}\). The peaks at approximately 1030 cm\({}^{-1}\) indicate the presence of sulfoxides (S = O) [95]. The peaks at 1600 cm\({}^{-1}\) correspond to the C = C stretching, indicating the presence of aromaticity [96]. The peaks at 1700 cm\({}^{-1}\) indicate the presence of carbonyl compounds (C = O). The peaks around 2900 cm\({}^{-1}\) and 2850 cm\({}^{-1}\) indicate C-H alkane chains [97]. The peaks around 3421 cm\({}^{-1}\) represent the hydroxyl group (-OH) [98; 99]. These hydroxyl groups may form due to the oxidation of certain parts of the double bonds [100].  
In Experiment 6 and Experiment 16, peaks indicating the sulfoxide group (S = O) are observed around 1031 cm\({}^{-1}\). This chemical bond is produced by the absorption of oxygen by sulfur elements during aging [101]. Additionally, at high temperatures, asphalt's unsaturated chemical bonds break and form free radicals. These radicals combine with oxygen to form carbonyl and sulfoxide groups [94]. Sulfur atoms are more susceptible to thermal-oxidative aging [102]. Furthermore, the interaction between sulfur and oxygen atoms, resulting in sulfoxide bonds, can be beneficial for improving the mechanical properties of modified bitumen [103]. Mixing speeds of 3000 and 4000 rpm are thought to cause this situation. These peaks were not seen in virgin bitumen, and Experiment 13 did not exhibit these sulfoxide-related peaks due to the lower mixing speed, indicating a more effective anti-aging outcome [104].  
Around 1600 cm\({}^{-1}\), close-to-each-other peaks indicating C=C alkynes were observed. Variations around these peaks are related to the degradation of the polymer chain, resulting in high energy in the C-C bond, which contributes to the mechanical strength of bitumen [105]. In Experiment 6, the band's intensity at 1601 cm\({}^{-1}\) was stronger than that of the virgin bitumen and modified bitumen in Experiments 13 and 16. At -10 \({}^{\circ}\)C, Experiment 6's stiffness modulus is higher than that of virgin bitumen and Experiment 13, which might be attributed to this increased band intensity. The band at 1456 cm\({}^{-1}\) is attributed  
Figure 12: FTIR spectra.  
to the asymmetric bending vibration of the -CH\({}_{3}\) group, while the band at 1375 cm\({}^{-1}\) is assigned to the symmetric bending vibration of the -CH\({}_{3}\) group [106]. The symmetric and asymmetric stretching vibrations of the C-H bond in methylene result in characteristic bands at 2850 cm\({}^{-1}\) and 2920 cm\({}^{-1}\), respectively. In Experiment 13, the band intensities at 2850 cm\({}^{-1}\) and 2920 cm\({}^{-1}\) were significantly stronger compared to the virgin bitumen and modified bitumen of Experiments 6 and 16. This indicates that in Experiment 13, there was an increase in the methylene and saturated hydrocarbon content within the bituminous molecule. An increased level of saturated hydrocarbons enhances the resistance to putting of modified bitumen [106].