## 2 Methodology
### Sample Preparation and Tests  
The samples of the soil chemically stabilized with Portland cement additivated or not with MWCNTs were prepared following the laboratory procedure presented in Figure 1.  
After the soil homogenization, a representative sample was collected (phase I). A slurry composed of Portland cement (phase II) plus MWCNTs dispersed with the aid of surfactant (phase II.C) or not (phase II.A) was prepared. The MWCNTs were dispersed with ultrasonic energy, using an ice bath with water flux to control the temperature, applied to an aqueous suspension of MWCNTs (phase II.A) or to an aqueous solution of surfactant with MWCNTs (phase II.C). The ultrasounds were applied using a probe-sonicator (Vibracell 501 from Sonics), during 5 min with a frequency of 20 Hz and power of 500 W. The quality of the MWCNTs dispersion was evaluated by the particle size distribution analysis obtained using DLS (the smaller the particle size, the better the quality of dispersion). As surfactants can also promote the dispersion of binder and/or soil particles, tests with only a surfactant solution, cement and soil (phase II.B) were prepared. The water present in  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline
**CaO** & **SiO2** & **Al2O3** & **Fe2O3** & **MgO** & **SO3** & **Cl**– & **S** & **Z** \\
**(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(\%)** & **(m2/kg)** & **(mV)** \\ \hline
62.8 & 19.2 & 4.9 & 3.2 & 2.5 & 3.4 & 0.01 & 349 & \(-\)2.14 \\ \hline \end{tabular} S = specific surface; Z = zeta potential (evaluated by electrophoretic light scattering).  
\end{table}
Table 2: Characteristics of cement particles (Portland cement type I 42.5 R).  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Surfactant** &
\begin{tabular}{c} **Market** \\ Condition** \\ \end{tabular} & **Charge (-)** & **Z (mV)** & **D2 (nm)** & **MW (kDa)** \\ \hline Viscocrete & commercial & nonionic & \(-\)2.8 & 4.65 & 242 \\ \hline Glycerox & commercial & nonionic & \(\sim\)0 & 41.93 & 4265 \\ \hline Amber 2001 & noncommercial & cationic & 66.7 & 170.84 & 1155 \\ \hline Amber 4001 & noncommercial & cationic & - & 5.65 & 54 \\ \hline \end{tabular} Z = zeta potential (evaluated by electrophoretic light scattering); Dz = hydrodynamic diameter (evaluated by dynamic light scattering); MW = molecular weight (evaluated by static light scattering).  
\end{table}
Table 3: Characteristics of surfactants [36; 37; 38].  
the slurry/aqueous suspension or solution increases the water content from the natural value (80.9%) to 113%. Afterward, the materials were mechanically mixed (phase III) and the paste produced was introduced in PVC molds in six layers (phase IV). Each layer was slightly compressed with a circular plate and vibrated with the help of a hand drill to remove possible air bubbles that may exist in the paste. Two geotextile filters were applied at the bottom and top of the sample. After curing under water for a period of 7 or 28 days (phase V) the samples were demolded and carefully cut to the final height of 76 mm (phase VI). Finally, the sample was placed on the compression load frame (Tristar 5000 from Wykeham Farrance) and the UCS test was performed at a constant strain rate of 0.76 mm/min (in agreement with BSI 1377-7 [40] and ASTM D2166 [41]). During the test, automatic readings were taken from the load cell and the vertical displacement transducer, allowing the definition of the stress-strain curve. All the tests were repeated twice to guarantee the reliability of the results. In order to assure that MWCNTs were not released from the chemically stabilized soil matrices, leaching tests were performed. More details can be found in [PERSON] [36], [PERSON] [37] and [PERSON] [38].  
Figure 1: Laboratory procedure for preparation of soil samples chemically stabilized with Portland cement additivated or not with MWCNTs.