## 2 Materials and Methods
### Mix Proportions  
The mix proportions are provided in Table 2. The binders used consisted of 80% OPC and 20% FA. Poly-carboxylate based superplasticizer, with a binder ratio of up to 0.4% by weight, was utilized to improve the workability of the cement paste and mortar specimens due to the low water-to-binder ratio (0.28).  
The proportion of binder to aggregate was 0.5 for the mortar mixtures. The aggregate used in this study, ISO standard sand, were natural and fine, and consisted of round particles with more than 98% silica contents. As shown in Table 2, the paste mixtures were named as \"PC-\" with various amounts of MWCNT contents, ranging from 0 to 0.5% to binder mass. \"PC00\" is the paste label of OPC and FA without MWCNT, and \"PC05\" indicates 0.5 mass% of MWCNT were added in binders to cast paste specimens for the experiments. In order for water-to-binder ratio to be 0.28, extra water was added in  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Materials**} & \multicolumn{8}{c}{**Chemical Compositions (wt\%)**} & \multirow{2}{*}{**Density**} & **Blaine** \\ \cline{2-3}  & **CaO** & **SiO2** & **Al2O3** & **Fe2O3** & **MgO** & **K2O** & **Na2O** & **SO3** & **(kg/m3)** & **(m2/kg)** \\ \hline OPC & 57.9 & 20.5 & 4.4 & 3.9 & 2.0 & 1.1 & 0.1 & 1.0 & 3.15 & 358 \\ FA & 1.7 & 64.3 & 20.6 & 7.5 & 0.9 & 1.1 & 0.3 & 0.1 & 2.29 & 410 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical and physical properties of raw materials used.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Specimens**} & **OPC (g)** & **FA (g)** & **Water (g)** & **MWCNT** & **ISO Standard** \\ \cline{2-6}  & **PC00** & & & 28.0 & - & \\ \hline PC01 & & & & 23.1 & 5 & \\ \hline PC02 & & & 18.2 & 10 & \\ \hline PC03 & & & 13.3 & 15 & \\ \hline PC04 & & & 8.4 & 20 & \\ \hline PC05 & & & 3.5 & 25 & \\ \hline MC00 & & & 28.0 & - & \\ \hline MC01 & & & 23.1 & 5 & \\ \hline MC02 & & & 18.2 & 10 & \\ \hline MC03 & & & 13.3 & 15 & \\ \hline MC04 & & & & 8.4 & 20 & \\ \hline MC05 & & & 3.5 & 25 & \\ \hline \hline \end{tabular}
\end{table}
Table 2: Mix proportions of paste and mortar samples containing multi-walled carbon nanotubes (MWCNTs).  
Figure 2: Particle size distribution of the ordinary Portland cement and fly ash.  
the mixture. This is because MWCNT solution contained 2 wt% of solid contents. The \"MC-\" mixtures were identical with the \"PC-\" mixtures, except for the additions of ISO sand.  
The mixing procedures for the production of paste and mortar specimens were similar to that specified by ISO 679. All binders were placed and pre-mixed in a 5-L bowl for 30 s with the automatic mortar mixer. Then, MWCNT solution and additional water were applied and mixed in the bowl for an additional 30 s at a low speed, 140 RPM for rotating and 65 RPM for revolving.  
Subsequently, 120 s of high-speed mixing, 285 RPM for rotating and 125 RPM for revolving, was performed to produce paste specimens for microstructure analysis. In order to evaluate mechanical properties, durability, and thermal conductivity of the mixtures, ISO sand was added to the fresh paste specimens by mixing at high speed for another 120 seconds.