## 3 Results and Discussion  
### Consistency Tests  
Various physical properties--penetration, penetration ageing index, softening point, softening point index and penetration index (PI) of the unaged and aged modified binders are detailed in Table 1. Based on the results obtained for modified binders, it can be concluded that NC had a considerable effect on the stiffness of the modified binders before ageing. It was notable that mixing had little influence on the stiffness of the modified binder with no NC particles, where the penetration reduced from 68 (0.1 dmm) for the unmodified bitumen 60/70 penetration grade to 64.6 (0.1 dmm) for 0 NCMB (still in the same penetration grade). However, the addition of NC for 2 NCMB and 4 NCMB led to an increase in stiffness of the modified bitumen. The penetration values decreased, while the softening point increased, indicating the effect of NC particles on the bulk of the modified bitumen. The increase in the stiffness was expected and could be explained by the absorption of the maltenes phase by NC, leading to an increase in asphaltene content. Applying STA and LTA led to an increase in stiffness of the modified bitumen. To check which binder was more sensitive, penetration ageing index and softening point index were determined. Based on the results in Table 1, the 0 NCMB was more sensitive for both STA and LTA compared to 2 NCMB and 4 NCMB. The sensitivity of the 0 NCMB indicates that its temperature susceptibility that makes it more susceptible to thermal cracking. NC reduced the sensitivity of 2 NCMB and 4 NCMB to ageing; these particles absorb the heat, preventing the increase of the asphaltene formation by absorbing some of the maltenes [28]. The change in the consistency parameter as a function of temperature is a sign of the temperature susceptibility and can be obtained by determination of the PI. The PI values for the binders increased after the addition of NC. In addition, the increase in PI extended after STA and LTA for all modified binders, as can be seen in Table 1. Comparing PI values between modified binders, it can be seen that for all ageing stages (unaged, STA and LTA) the PI was highest for 4 NCMB and lowest for 0 NCMB. This result is in good agreement \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Ageing**} & **Penetration** & **Penetration** & **Softening** & **Softening** & **PI** \\  & & **(0.1 mm)** & **Ageing Index** & **Point (\({}^{\circ}\)C)** & **Point Index** & **PI** \\ \hline \multirow{3}{*}{0 NCMB} & unaged & 64.6 & - & 47.5 & - & \(-\)1.3 \\  & STA & 52.3 & 0.81 & 52.2 & 1.10 & \(-\)0.6 \\  & LTA & 42.1 & 0.65 & 58.1 & 1.22 & 0.2 \\  & unaged & 54.0 & - & 53.4 & - & \(-\)0.2 \\
2 NCMB & STA & 48.3 & 0.89 & 59.0 & 1.10 & 0.7 \\  & LTA & 39.8 & 0.74 & 62.3 & 1.16 & 0.9 \\  & unaged & 49.2 & - & 59.0 & - & 0.8 \\
4 NCMB & STA & 43.2 & 0.88 & 61.6 & 1.04 & 1.0 \\  & LTA & 38.9 & 0.79 & 64.7 & 1.09 & 1.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Penetration, penetration ageing index, softening point, softening point index and penetration index (PI). with the penetration ageing index and softening point index data. The higher PI values for 2 NCMB and 4 NCMB indicate that these binders are less susceptible to temperature and more elastic [14]. Table 2 details the viscosity ageing index (VAI) data. All NCMB was mixed and prepared in the same condition. The viscosity at 135 \({}^{\circ}\)C was evaluated for unaged and aged modified bitumen. Ageing increases the viscosity for modified bitumen, but responses were varied. All samples showed an increase in viscosity after both STA and LTA. After STA, VAI was highest for 0 NCMB and less, and almost the same for 2 NCMB and 4 NCMB. After LTA, VAI was highest for 0 NCMB and reduced for 2 NCMB and 4 NCMB. When VAI reduces from 0 NCMB to 2 NCMB and 4 NCMB, this means that the sensitivity is reduced. The addition of NC reduced the effect of temperature and improved the ageing resistance.