# Performance Evaluation of Carbon Black Nano-Particle Reinforced Asphalt Mixture
## 2 Experimental Work
### Preparation of CBNPs Modified Bitumen  
Two percentages of CBNPs were used in this study i.e., 5% and 10% by weight of asphalt binder The maximum CBNPs content of 10% was selected, as performance grade (PG) 70 was achieved at this dosage. PG 70 is the desired performance grade of binder in Pakistan as per the temperature zoning [17]. PG 70-10 asphalt binder covers almost 70% areas of Pakistan. Asphalt binder (60/70) procured from Attock Oil Refinery has PG 58-22, therefore CBNPs were mixed with the asphalt binder to achieve the desired performance grade. All modified binders were prepared using a high shear mixer. Asphalt binder was heated to 158 \(\pm\) 5 \({}^{\circ}\)C until it became fluid. Then CBNPs were added steadily into the asphalt binder and the mixture was stirred at 2800 rpm for 45 min to ensure homogenous dispersion of nanoparticles. Scanning electron microscopy (SEM) was used to check the homogenous dispersion of CBNPs in the asphalt binder. Figure 1a shows the spherical shape of CBNPs used in this study whereas homogenous dispersion of CBNPs in the asphalt binder is displayed in Figure 1b. Figure 1b depicts that the mixing operation of applying 2800 rpm for 45 min to disperse CBNPs in the asphalt binder is acceptable.  
Homogenous dispersion was further ensured by storage stability analysis and repeatable results of PG during trial blending techniques. The storage stability analysis (BS EN 13399-2017) of CBNPs modified samples showed less than 2.5 \({}^{\circ}\)C difference in softening point among the top and bottom portions of the sample, which is proof of stable and homogenous CBNPs-modified asphalt binder.  
\begin{table}
\begin{tabular}{c c} \hline
**Morphology** & **Spherical** \\ \hline
**Colour** & Black \\
**Purity** & Greater than 95\% \\
**Average particle size (APS)** & 150 nm \\
**H\({}_{2}\)O** & Less than 5\% \\
**Ash** & Less than 3.2\% \\
**PH** & 9.8 \\
**Density** & 0.38 g/mL \\
**Electrical Resistivity** & 0.30 \(\Omega\)-cm \\ \hline \end{tabular}
\end{table}
Table 2: Carbon black nano-particles (CBNPs) feature.  
Figure 1: (a) Scanning electron microscope (SEM) image of carbon black nano-particles (CBNPs); (b) SEM image of carbon black nano-particles in asphalt binder.  
A number of CBNPs-modified binder samples were prepared by using different mixing durations and blending techniques (hand mixing, and shear mixing utilizing different blender RPMs). All these samples were tested under dynamic shear rheometer (DSR) and their high PG temperatures were determined. Mixing duration of 45 min and 2800 blender RPMs were finally selected as these two conditions provided with a homogeneous sample with repeatable results. DSR test results for the samples that were taken from three different portions of the sample container (top, bottom, and middle) during PG test also provides proof of homogenous dispersion of CBNPs in the asphalt binder. Results are presented in Table 3.  
The traceability of particles through SEM is largely related to the size of the particles. As the utilized CBNPs had an average diameter of 150 nm, they were relatively easily traceable. However, some trials were still required to be carried out, and it was necessary to zoom-in to the required resolution to study the dispersion of CBNPs in bitumen. SEM is generally sufficient to study the dispersion of particles [19], however, for more in depth analysis into the size and internal structure of the particles, transmission electron microscopy (TEM) may be preferred.