# Performance Evaluation of Carbon Black Nano-Particle Reinforced Asphalt Mixture
## 3 Results and Discussion
### Effect of CBNPs on Bitumen Aggregate Bond Strength  
The effect of CBNPs on bitumen aggregate bond strength was studied using a pneumatic adhesion tensile testing instrument (PATTI) and the results are displayed in Table 8a,b. Figure 4 shows the comparison of POTS after 24 h of dry and moisture conditioning in the form of a bar chart. Samples modified with CBNPs have higher POTS values than the base asphalt binder after 24 h of dry and moisture conditioning. The addition of CBNPs has increased the POTS value from 7.5 MPa to 17 MPa after 24 h of dry conditioning. The mode of failure is cohesive (breakage of bond at bitumen-bitumen interface) post 24 h of dry conditioning and changed to adhesive failure (breakage of bond at bitumen-aggregate interface) after 24 h of moisture conditioning. The change of failure mode could be attributed to water penetration through the aggregate (porous material) which weakens  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Sample** & **Failure Temperatures (\({}^{\circ}\)C)** \\ \hline
**Base Asphalt Binder** & 62.5 (PG 58) \\
**5\% CBNPs** & 64.5(PG 64) \\
**10\% CBNPs** & 70.9(PG 70) \\ \hline \hline \end{tabular}
\end{table}
Table 7: Effect of CBNPs on the performance grade (PG).  
Figure 3: **(a)** Graphical representation of \(G^{\star}\) and reduced frequency; **(b)** graph of reduced frequency and phase angle; **(c)** graph of \(G^{\star}\)/sin\(\delta\) versus reduced frequency.  
the bond at the bitumen-aggregate interface and results in low pull-off tensile strength values [25]. After 24 h of moisture conditioning, modified binders performed better than the base binder and 10% CBNPs-modified binder has shown the highest POTS values. Addition of nano material has increased the wetting potential of the modified binder promoting better wetting of the bitumen onto 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 the addition of nano particles [26]. Moreover, significant improvement in bond strength of a nano-hybrid material could be attributed to hydrogen bonds and van der Waals interaction [27].  
According to these results, it can be concluded that CBNPs have the potential to improve the adhesive/cohesive bond strength of asphalt.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Replicates**} & \multicolumn{3}{c}{**24 h Dry Conditioning**} \\ \cline{2-4}  & **Base Asphalt Binder** & **5\% CBNPs** & **10\% CBNPs** \\ \hline
**1** & 7.67 (C) & 11.80 (C) & 16.54 (\(C/A\)) \\
**2** & 8.00 (C) & 11.80 (C) & 16.50 (C) \\
**3** & 7.67 (C) & 12.00 (C) & 16.73 (C) \\
**4** & 7.11 (C) & 12.00 (C) & 17.34 (C) \\
**5** & 6.82 (C) & 11.80 (C) & 17.80 (C) \\
**Average** & 7.50 & 11.90 & 17.00 \\ \hline \hline \end{tabular} \(C\) = Cohesive failure and \(C/A\) = 50% Cohesive and 50% Adhesive failure.  
\end{table}
Table 8: **(a)** Pull-off tensile strength (POTS) values (MPa) and failure modes after 24 h of dry conditioning. (b) POTS values (MPa) and failure modes after 24 h of moisture conditioning.  
Figure 4: POTS of dry and moisture-conditioned samples.