# A Review of Nanomaterials' Effect on Mechanical Performance and Aging of Asphal Mixtures
## Nanomaterials
### Modification of the Asphalt Binder with Nanomaterials
As it will be additive (nanomaterial) and neat asphalt binder dependent, several trials may be needed to determine the adequate combination of rotation speed and mixing time. In addition to the high-speed shear mixing, some authors also applied sonication. Table 4 presents the dry blending configuration used by several authors. The use of excessive rotational speed and prolonged mixing times can cause an undesired accelerated oxidation and consequent aging of the asphalt binder. The geometry of the mixing shaft head can also play an important role. The use of the most common shaft head geometries (such as blades, anchor, propeller, and Rushton) at high rotation speed can easily induce vortex effects that will potentiate the entrapment of air bubbles in the asphalt matrix. This effect, aggravated by the fact that the mixing occurs at high temperatures, may promote a significant premature oxidation of the asphalt. To mitigate this effect, the use of head geometries, such as the Jiffy head, that prevent vortex formation can be preferable. Other possibility to eliminate undesired oxidation could be to carry out the process of asphalt modification under controlled atmosphere conditions, for example using a nitrogen atmosphere furnace. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Modification** & **Neat Binder** & \begin{tabular}{c} **Temperature** \\ **(\({}^{\circ}\)C)** \\ \end{tabular} & \
\begin{tabular}{c} **Rotation** \\ **Speed (rpm)** \\ \end{tabular} &
\begin{tabular}{c} **Duration** \\ **(min.)** \\ \end{tabular} & **Reference** \\ \hline
2\%, 4\% SiO\({}_{2}\) & PG 76 PM & 160 & 1500 & 60 & [58] \\ \hline
3\% OMMT & PG 58-22 & 150 & 5000 & 100 & [35] \\ \hline
4\% SiO\({}_{2}\); 4\% ZVI\({}_{2}\) & 35/50 & 160 & 2000 & 60 & [25] \\ \hline
0.5\%, 1\% CNT\({}_{3}\) & PG 58-22 & 150 & 1550 & 90 & [59]1 \\ \hline
2\% CNT & PG 58-22 & 150 & 5000 & 100 & [60] \\ \hline
3\%, 5\%, 7\% NC; 3\%, 7\% NSF; 3\%, 5\%, 7\% NSF; 3\%, 5\%, 7\% NSFH & PG 52 (50/70) & 145 & 1500 & 60 & [27] \\ \hline
0.5\%, 1\% CNT\({}_{3}\) & 70/100 & 50/70 & 150 & 1550 & 90 & [61]1 \\ \hline
2\%, 4\% OMMT & PG 64-28 & 160 & 2500 & 180 & [55] \\ \hline
2\%, 4\% NMN; 2\% PMN\({}_{2}\) & PG 58-34 & 130 & 4000 & 120 & [38] \\ \hline
2\% to 8\% SiO\({}_{2}\) & 60/70 & 135 & 4000 & 120 & [19; 20] \\ \hline
0.5\% to 5\% SiO\({}_{2}\) & 70/100 & 160 & 4000 & 60 & [62] \\ \hline
1.5\% OMMT & PG 58-10 & 180 & 4000 & 45 & [39] \\ \hline
5\%, 10\% CSNP & PG 58-22 & 158 & 2800 & 45 & [63] \\ \hline
4\% SiO\({}_{2}\); 4\% & 60/70 & 160 & 6000 & 60 & [64] \\ \hline \multicolumn{5}{c}{\({}^{1}\) Using sonication.} \\ \end{tabular}
\end{table} 
Table 4: Dry blending configurations used by several authors. In the solvent blending method, the nanomaterial is initially dispersed in a compatible solvent (for example toluene or kerosene) that later will be mixed with the neat asphalt binder under medium to high temperature applying low speed stirring. The mixing process finishes when the evaporation of the solvent is complete. Some authors also applied sonication during the stirring time. The description of the solvent blending configurations can be found in the respective studies [65; 66; 67]. Due to several advantages, the dry blending method is the most widely used. Compared to the solvent blending method, the most important advantages of the dry blending method are that it is cheaper and easier to implement and does not require the use of high amount of solvents. For either method, the evaluation of the final modified binder properties will reveal if a homogeneous blend was achieved. To perform this evaluation, a procedure similar to the one stated by the CEN specification EN 13399--determination of storage stability of modified bitumen [68] or ASTM D5892-00 [69] can be used [63; 70]. As the used dosages of nanomaterials are typically low, under 6% of the mass of asphalt binder, and the individual mass of the nanoparticles is very small, sedimentation problems were not reported.