## 3 Results and Discussion
### The Fourier Transform Infrared (FTIR) Test
#### 3.2.5 Quantification of Ageing Index  
Infrared spectroscopy was used to study the most interesting groups containing C-H, C=O and S=O, where determining the area of the peaks is very important for investigating the ageing effect. The area of the carbonyl (C=O) absorption was calculated in the range of 1752-1653 cm\({}^{-1}\), to cover the region that contained carboxylic acids, ketones and anhydrides. [PERSON] [8] stated that the reason behind considering the total carbonyl area is that the infrared spectra in the carbonyl region becomes more complicated for aged binders due to the intense ketone band appearance. Determining the anhydrides is also difficult because their absorption bands are overlapped by the strong ketone. Carboxylic acids are naturally present in bitumen and form extremely strong hydrogen bonds. Sulfoxide is important with regard to the determination of changes within functional groups due to ageing. The intense peak at 1027 cm\({}^{-1}\), assigned to the stretching vibration of sulfoxide (S=O), was also investigated. This is considered the functional group that is most formed in bitumen after the oxidation of sulfide moieties. The area of this band is determined to be in the range of 1065-1007 cm\({}^{-1}\) and is used for ageing investigation, as in the previous group. The changes in chemical bonding for the binders due to ageing can be determined by calculating the ratio changes of the chemical bonding. The ratio changes in the carbonyl band (I\({}_{\rm c=o}\)) and the sulfoxide band (I\({}_{\rm s=o}\)) for all the binders, before and after STA and LTA, are calculated using Equations (4) and (5) and are shown in Figures 8 and 9. \[\rm I_{C=O}=\frac{Area\ of\ the\ carbonyl\ band\ centered\ around\ 1694\ cm^{-1}}{\Sigma Area\ of\ the\ spectral\ bands\ between\ 2000\ and\ 600\ cm^{-1}} \tag{4}\](4)  
Based on previous studies [4; 8; 9; 31; 32; 41; 42], the formation and increase in the carbonyl index is observed after both STA and LTA for all binders. Formation of the carbonyl band centered around 1694 cm \({}^{-1}\) is calculated, and as can be seen in Figure 8, the oxidation due to STA and LTA leads to an increase in the functional carbonyl group. As stated previously, carboxylic acids and ketones are the main oxidation products for the carbonyl group, and they are responsible for the increase of asphaltenes that leads to bitumen hardness [4]. However, the values of the ratio of the carbonyl band showed that the formation of this band for the unaged binders was higher for 0 NCMB compared to 2 NCMB and 4 NCMB, while after STA, the ratio decreased after the addition of the NC particles. An unexpected  
Figure 7: (a) FTIR spectrum results of bands at wave number 1027 cm\({}^{-1}\); (b) absorbance value for sulfoxide at wave number 1027 cm\({}^{-1}\). result was noted after LTA, where the ratio of the carbonyl band showed a slight increase for 2 NCMB compared to 0 NCMB (4%), while 4 NCMB revealed the best result. Generally, it can be concluded that NC particles enhance resistance to ageing; this result is consistent with previous studies [18; 19; 20; 28; 40]. The ratio of the sulfoxide band was also calculated before and after ageing. Variation in the values of the ratio for unaged and STA did not give any clear information about whether NC particles improved resistance to ageing. The values showed that, when unaged, reduction in the ratio was noted for 2 NCMB and 4 NCMB compared with 0 NCMB, while after STA, the values were almost the same for all binders. The improvement in ageing resistance was only clear at the last stage of ageing, as can be seen in Figure 9, where 4 NCMB showed the least sensitivity to ageing, followed by 2 NC. Regarding the variation of the results for the ratio of the sulfoxide band for unaged and STA, the sulfoxide is thermally unstable [6], which is why the sulfoxide index was not considered as an ageing index in a previous study [43].