# Performance Evaluation of Carbon Black Nano-Particle Reinforced Asphalt Mixture
## 4 Conclusions  
The following conclusions have been drawn through careful analysis of the test results:  
1. Addition of carbon black nano-particles has enhanced the conventional asphalt binder properties. For instance, 10% CBNPs content in conventional binder has reduced the penetration and ductility value by 24.5% and 40%, respectively. Furthermore, an elevation in softening point has been observed by the addition of CBNPs which leads to the reduction in high-temperature susceptibility of the asphalt binder. The large surface area of CBNPs and high degree of dispersion has contributed towards the change in the conventional asphalt binder properties, especially the stiffness of the binder. 2. A storage stability test has been used to check the permanence of the dispersion of CBNPs in the asphalt binder through identifying the difference in softening points of the samples obtained from the top and bottom sections of the test tube. The difference in softening point that has been obtained during the test is less than 2.5 \({}^{\circ}\)C i.e., 1 \({}^{\circ}\)C and 1.3 \({}^{\circ}\)C for 5% and 10% CBNPs-modified binder, respectively. This confirms that CBNPs-modified asphalt binder is a stable material and can be utilized by the pavement construction industry. 3. The complex shear modulus and performance grade of asphalt binder is significantly enhanced by incorporating CBNPs. Addition of 10% CBNPs has increased the complex shear modulus values from 8847 Pa to 34,679 Pa at 10 Hz frequency and 50 \({}^{\circ}\)C temperature. Also, 10% CBNPs addition has changed the PG 58 to PG 70 by improving the failure temperature from 62.5 \({}^{\circ}\)C to 70.9 \({}^{\circ}\)C. The large surface area of CBNPs and its homogenous dispersion influences the asphalt binder's rheology and helps achieve the desired stiffness improvement. Thus, it can be concluded that CBNPs is a promising modifier when it comes to improving resistance against permanent deformation. 4. Bitumen bond strength test results show significant improvement in the cohesive and adhesive bond strength of the binder through the incorporation of CBNPs. During 24 h of dry conditioning, and moisture conditioning, addition of 10% CBNPs has increased the POTS values from 7.5 MPa to 17 MPa and 6.55 MPa to 15.40 MPa respectively. The increase in adhesive and cohesive bond strength could be attributed to the electrostatic contribution in nano-modified material. The addition of nano material has increased the wetting potential of the modified binder promoting better wetting of the bitumen on to the aggregate surface thus enhancing the bitumen-aggregate bond strength. This could also be attributed to the increase in stiffness of the asphalt binder because of addition of nano particles [26]. 5. Bond strength is an important parameter in measuring the ability of asphalt binder to withstand moisture damage. Tests that are carried out directly on different bitumen-aggregate combinations after moisture conditioning can efficiently measure their moisture sensitivity [31]. Moisture sensitivity directly affects the durability of an asphalt mixture [32]. Significant improvement in POTS after 24 h of moisture conditioning shows that CBNPs have the potential to improve the durability of asphalt. 6. CBNPs have clearly shown potential for improving the permanent deformation resistance of the modified asphalt mixture. During a wheel tracking test, almost 37.8% reduction in rut depth at 55 \({}^{\circ}\)C, and 20% reduction in rut depth at 40 \({}^{\circ}\)C has been observed through the addition of 10% CBNPs in asphalt. Dynamic modulus values at 40 \({}^{\circ}\)C and 55 \({}^{\circ}\)C have been observed to be enhanced by introducing CBNPs. For instance, at 10 Hz and 55 \({}^{\circ}\)C, CBNPs have increased the dynamic modulus values from 664.4 MPa to 830.67 MPa. The improvement in dynamic modulus and improved rutting resistance is due to the fact that CBNPs-modified asphalt binder has higher stiffness and a better ability to bond with the aggregates.