## 3 Results and Discussion
### Effect of MWCNTs
A similar observation can be made for the nonionic surfactant \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Surfactant** & \multicolumn{2}{c}{\(\mathbf{D_{k}}\) **(for MWCNTs = 0.001\%/0.01\%)**} \\ \hline
**Name** & **Conc. (\%)** & **(nm)** \\ \hline Viscocrete & 3 & 155.1/119.5 \\ \hline \multirow{4}{*}{Glycerox} & 0.5 & -/197.2 \\ \cline{2-3}  & 1 & -/167.6 \\ \cline{2-3}  & 3 & -/175.2 \\ \hline \multirow{4}{*}{Amber 2001} & 0.1 & -/- \\ \cline{2-3}  & 0.5 & 548.0/684.5 \\ \cline{2-3}  & 1 & -/718.2 \\ \cline{2-3}  & 2 & -/954.2 \\ \hline \multirow{4}{*}{Amber 4001} & 0.5 & -/521.5 \\ \cline{2-3}  & 1 & -/322.9 \\ \cline{1-1} \cline{2-3}  & 3 & -/316.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Dispersion characterization of MWCNTs suspensions. Figure 9: Strength improvement factor (for samples with 7 curing days) for the stabilized soil with MWCNT suspensions for the surfactants studied, applied in different concentrations. Viscocrete, where the IF decreases from 1.63 at 7 days to 1.36 at 28 days. Even though there is a decrease, in the case of the surfactant Viscocrete, the effect at 28 days is still positive contrary to what is observed for the Amber 2001, which may be related to the size of surfactant molecules. Indeed, Viscocrete is characterized by molecules of smaller hydrodynamic diameter than Amber 2001 (Table 3); thus, Viscocrete is less likely to form micelles that may hinder the occurrence of cementitious reactions and at the same time the smaller size of the Viscocrete molecules allow the bonding of the cementitious products to the surface of the solid particles (MWCNTs and soil), thus promoting a denser and stronger solid matrix. The relative decrease of the effect of MWCNTs with time is explained by the development over time of the physicochemical reactions of the Portland cement producing a greater quantity of cementitious products. Thus, with time the matrix becomes denser and stronger and, as a consequence, the relative impact of MWCNTs presence decreases. One important issue related with the application of CNTs is their impact on environment if CNTs are released, namely, on human life, animals and plants. In order to investigate a possible release of MWCNTs from the stabilized soil matrices, leaching tests on chemically stabilized soil samples additivated with MWCNTs dispersed in a surfactant solution were done at 1, 4, 7 and 14 curing days. These tests were complemented with optical microscope images and SEM images of the leachate. Tests were performed for the \"worst scenario\", i.e., adding the highest quantity of MWCNTs (0.01%) dispersed in an Amber 2001 solution (conc. = 0.1%). As seen in Figure 11, two kinds of materials were identified in the SEM images: needle-shaped materials are calcium silicate associated with the Portland cement reactions with water, and materials in the form of irregular polyhedrons are soil particles. By analysis of Figure 11, it can be concluded that there are no traces of MWCNTs in the leachate, proving that the MWCNTs are entrapped in the stabilized soil matrix. In summary, the analyses from the leachate resulting from leaching tests, it is concluded that the amount of material released is not significant and does not contain traces of MWCNTs. Figure 10: Stress–strain normalized curves (for samples with 28 curing days) for the stabilized soil with MWCNTs suspensions of the surfactant Amber 2001 (conc. of 0.1% and 1%) and Viscocrete (conc. of 3%).