## 4 Conclusions and Recommendations  
This study experimentally developed an understanding of the effect of adding carbon nanotubes in asphalt bitumen. Dynamic mechanical analysis and different performance tests were carried out. Different tests were performed on asphalt binder as well as asphalt mixtures. The following conclusions were drawn from the above research  
* Wet mixing techniques better helps in achieving homogeneous dispersion of CNTs in bitumen as compared to dry mixing.  
Figure 17: Loss of Coating at different durations with various CNTs percentages.  
Figure 18: Rut depth for unmodified and CNT-modified bitumen mix at 40 \({}^{\circ}\)C.  
* Sonication and magnetic stirring are necessary to improve the stability of CNTs in solvent.
* Introduction of CNTs in asphalt binder resulted in reduction in penetration value and ductility value, while it increased the softening point value of the bitumen, which means stiffness of the bitumen increased with the addition of CNTs.
* With the addition of CNTs, the PI value of bitumen increased, which means the bitumen temperature sensitivity decreased and thermal susceptibility also decreased.
* Complex shear modulus (G*) value increased and phase angle of the bitumen tended to decrease with increase in CNTs, which means the stiffness and elastic behavior of bitumen improved with the addition of CNTs in asphalt binder. Rut factor value also improved, which indicates the increase in resistance against permanent deformation.
* High Performance Grade (PG) of the bitumen increased with an increase in the CNTs dosage. PG 70 is recommended for most of the regions of Pakistan. This study aimed for achieving a PG 76 after a great bump in the required PG 70 to accommodate for the overloading on the highways of the country. The required PG 76 was achieved with 3% addition of CNTs in bitumen. Asphalt samples modified with 3% CNTs showed improved results for all parameters examined in this study. Hence, 3% CNTs dosage was selected as the optimum dosage.
* Bitumen bond strength value improved by adding CNTs in bitumen in both 24 h dry and 24 h moist conditions, while moisture susceptibility of bitumen decreased with addition of CNTs.
* From wheel tracker test results, it was concluded that the addition of 1% and 3% CNTs in bitumen reduced the rut depth by 25% and 37%, respectively, when tested at 40 \({}^{\circ}\)C. This is an indication of an increase in the resistance against permanent deformation at higher temperature for CNT-modified binder.
* Although wet mixing is a complicated process, it is preferred over the dry mixing technique because it ensures homogeneous dispersion of CNTs in the binder.  
Conceptualization, M.F.u.H. and N.A.; Data curation, M.Fu.H., Jamal, M.H., J.R. and S.B.A.Z.; Formal analysis, M.F.u.H., N.A. and Jamal; Investigation, M.Fu.H., Jamal, M.H. and J.R.; Methodology, M.Fu.H., N.A. and M.A.N.; Resources, M.Fu.H. and W.H.; Supervision, N.A.; Writing--original draft, M.Fu.H., and Writing--review and editing, N.A., M.A.N., S.B.A.Z. and W.H.  
The authors would like to acknowledge the support of the Civil Engineering department at The University of Lahore, Islamabad Campus in pursuit of this research work.  
The authors declare no conflict of interest.