## 2 Materials and Methods
### CNT-Cement Composites Preparation and Electrical Characterization  
Cement pastes were produced using early strength development cement with a fixed water/cement (_w/c_) ratio of 0.50 and 0.60% of VMA by mass of cement to prevent water exudation. Samples were prepared by hand mixing the obtained dispersions with cement and VMA, which resulted in cement-based composites containing 0.10 and 0.40% CNT by mass of cement, as presented in Table 3. Cylinders (10 mm diameter and 20 mm height) were casted and cured at high relative humidity for 14 days. A total of 5 specimens were molded for each condition. After curing, all samples were dried in an oven at 40 \({}^{\circ}\)C for 24 h.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Code** & **Superplasticizer Name** & **Solids Content * & **Superplasticizer Type** \\ \hline A & Glenium 51 & 33\% & Ether polycarboxylate \\ B & ADI-SUPER H40 & 40\% & Ether polycarboxylate \\ C & MC-PowerFlow 1180 & 35\% & Ether polycarboxylate \\ D & Hormitec SP430 & 40\% & Naphthalene \\ \hline \hline \end{tabular}
\end{table}
Table 1: Nomenclature used for superplasticizers and their solid content. (* Informed by the manufacturer).  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Dispersion** & **SP Type** & **CNT (\%)** & **SP (\%)** & **Water (\%)** & **CNT:SP** &
\begin{tabular}{c} **Sonication Energy** \\ **(/gdispersion)** \\ \end{tabular} \\ \hline
0.25\%CNT/1.00\%SP A & A & & & & & 900 \\
0.25\%CNT/1.00\%SP B & B & & & & & 1000 \\
0.25\%CNT/1.00\%SP C & C & & & & & 1000 \\
0.25\%CNT/1.00\%SP D & D & & & & & 1000 \\ \hline \hline \end{tabular}
\end{table}
Table 2: CNTSP proportions and total sonication energy for each CNT dispersion.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Composite** & **CNT (\% *)** & **Cement (\%)** & **VMA (\% *)** & _w/c_ \\ \hline REF & - & & & & \\ \hline
0.10\% CNT-cement/SP A & & & & & \\
0.10\% CNT-cement/SP B & & & & & \\
0.10\% CNT-cement/SP C & & & & & \\
0.10\% CNT-cement/SP D & & & & & \\ \hline
0.40\% CNT-cement/SP A & & & & & \\
0.40\% CNT-cement/SP B & & & & & \\
0.40\% CNT-cement/SP C & 0.40 & & & & \\
0.40\% CNT-cement/SP D & & & & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: CNT–cement composites proportions adopted for electrical resistivity measurements. (* percentage by mass of cement).  
Copper sheets of a 0.1 mm thickness were glued to the end of the cylinders with silver conductive glue. A constant voltage of 5.0 V DC was applied to each sample for 20 min before measurement for signal stabilization [28]. The current (I) passing through the sample was measured using a 6 \(\frac{1}{2}\) digits resolution Keysight model 34461A multimeter. The applied voltage (V) was verified using a hand-held multimeter Hikari model HM-20230. Since the hand-held multimeter has an internal resistance of the same order of magnitude observed in the samples under test, the measurement setup, shown in Figure 1a, was adopted to mitigate its influence on the results. The electrical resistance of each sample was computed using [PERSON]'s law, according to Equation (1), and the electrical resistivity (\(\rho\)) of the material was obtained using the cross section area (A) and length (I) of the samples, according to Equation (2). An example of the cement paste specimens is presented in Figure 1b.  
\[\text{R}(\Omega)=\text{V}(\text{V})/\text{I}(\text{A}) \tag{1}\]  
\[\rho\]  
( \[\Omega\].cm ) \[=\text{R}(\Omega)\]  
.A(cm 2 ) \[/\text{I}(\text{cm})\] (2)