## 4 Conclusions  
Nano-clay, also known as Halloysite nanotubes, which is a type of alumino-silicate clay, was added to bitumen at 0%, 2% and 4% by weight of bitumen for this study. The modified bitumen was aged, using STA and LTA, and then tested using consistency tests (to monitor the change in physical properties) and the FTIR method (to detect any chemical changes). Mixtures were also investigated using the ITS test, and any improvement in the modified bitumen after ageing was determined.  
The conclusion is that the physical and chemical properties of all the modified binders and the strength of their mixtures were affected by ageing. Ageing was dependent on NC percentage. However, the modified binders, including NC particles, showed a reduction in ageing sensitivity due to the absorption of heat from the NC. The conclusions may be summarized as follows:  
* Reduction in fluidity caused by mixing was observed in 0 NCMB. However, the penetration grade was still in the range of 60-70, which means only a slight impact from mixing.
* The addition of nano-clay particles caused an increase in the viscosity of the unaged 2 NCMB and 4 NCMB, which means an increase in stiffness and a reduction in temperature susceptibility.
* All modified nano-clay bitumens were affected by ageing. However, the results of the consistency tests and their ageing index showed that 2 NCMB and 4 NCMB had better resistance against ageing than 0 NCMB. The increase in PI for 2 NCMB and 4 NCMB indicates an improvement in temperature susceptibility.
* The FTIR test demonstrated that there are no newly created bands after adding nano-clay particles for unaged 0 NCMB, 2 NCMB and 4 NCMB. This suggests that there is no chemical activity between nano-clay and bitumen.
* The FTIR results showed that the absorbance peak was affected by ageing for all selected functional groups in this study. The selected groups were oxygen-containing compounds, aliphatic hydrocarbons, aromatic compounds, and sulfur compounds. Based on the absorbance peak, 2 NCMB and 4 NCMB were less sensitive to ageing.
* Quantification of the changes in chemical bonding for the carbonyl band and the sulfoxide band were calculated. The increase in the ratio of these bands indicates an increase in asphaltene content. Based on the results, 4 NCMB was the best modified binder, showing less ageing sensitivity.  
* The results of the ITS test were in line with previous results; STA and LTA resulted in increased ITS due to increased stiffness. The increase in the ITS of 2 NCMB and 4 NCMB indicates improved cohesion of the aged bitumen in the mixture, which could reflect improved resistance against cracking, leading to increased pavement durability.  
H.A.O.: Conceptualization, Writing--original draft, Methodology, Investigation, Formal analysis. H.Y.K.: Data curation, Funding acquisition. M.B.: Reviewing and Editing, Software. M.K.A.A.: Visualization, Data curation. A.M.: Reviewing and Editing, Validation. N.I.M.Y.: Supervision, Reviewing and Editing, Funding acquisition. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Universiti Kebangsaan Malaysia (Grant number DIP-2020-003) and Universiti Tenaga Nasional (J5100D4103-BOLDREFRESH2025-CENTRE OF EXCELLENCE)).  
Not applicable.  
**Data Availability Statement:** All data used in this research can be provided upon request.  
The authors would like to thank Universiti Tenaga Nasional for their financial support.  
The authors declare no conflict of interest.