# Effect of Electrospun Nanofiber Additive on Selected Mechanical Properties of Hardened Cement Paste
## 2 Materials and Experimental Work
### A Method of Obtaining a Blend of Electrospun Nanofibers and Cement  
The chemicals and precursors used in this study include poly(hexamethylene adjamide) (Nylon 66, Sigma-Aldrich, Louis, Missouri, USA, density: 1.14 g/mL), formic acid (Daejung, Siheung-si, Gyeonggi-do, Korea, density: 1.22 g/mL), chloroform (Daejung, Korea, density: 1.492 g/mL), tetraethyl orthosilicate (TEOS, Alfa Aesar, Heysham, Lancashire, UK, density: 0.934 g/mL), polyvinylpyrrolidone (PVP, Sigma-Aldrich, USA, density: 1.2 g/mL), butanol (Sigma-Aldrich, USA, density: 0.81 g/mL), and multiwalled carbon nanotubes (97% purity, 10 nm outer diameter, 30 \(\upmu\)m length, Hanos, Jung-gu, Seoul, Korea). All chemicals were used as received. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**CaO** & **Al2O3** & **SiO2** & **SO3** & **MgO** & **Fe2O3** & **Ig. Loss** & **Specific Surface Area (cm2/g)** & **Compressive Strength, 28 Days (MPa)** \\ \hline
61.33 & 6.40 & 21.01 & 2.30 & 3.02 & 3.12 & 1.40 & 2800 & 36 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition and physical properties of the cement. Four polymer solutions were prepared in this study. To prepare the nylon 66 polymer solution, first of all, formic acid was diluted by chloroform with the volume proportion of 4:1 for forming the solvent. Then, nylon 66 was dispersed in this solvent with a weight proportion of 10%. To prepare the TEOS/PVP polymer solution, firstly, a solution was made by stirring TEOS and butanol with the volume proportion of 5:3, then merging PVP in this solution to yield a 10% polymer solution. The polymer solution containing CNTs and nylon 66 as well as the one containing CNTs and TEOS/PVP were prepared by the following steps: First, the solutions were prepared by adding CNTs into the presolution containing formic acid and chloroform, as well as the presolution containing TEOS and butanol, as mentioned above. It is worth mentioning that the added content of CNTs had to compensate for the content of nylon 66 or PVP that was taken out of the above solutions. In this work, the added CNT proportion of 0.4 wt % was chosen for the polymer solution. The polymer solution proportions are shown in Table 2. However, dispersing CNTs in a liquid solution is a complicated process due to its high aspect ratio, and the agglomeration phenomenon tends to occur under the strong van der Waals forces between CNT molecules [25]. Therefore, at this period, to obtain homogeneous solvents, an ultrasonication process was conducted to break the connection between CNT molecules [26; 27; 28]. Finally, nylon 66 and PVP were added into each solution with a consistent proportion of 9.6 wt % to obtain the final polymer solution containing CNTs and nylon 66, as well as the one containing CNTs and TEOS/PVP. The electrospinning process for fabricating nanofibers, as well as combining nanofibers with cement powders, was conducted according to the procedure presented in previous works [21; 22; 23]. The whole procedure is shown in Figure 1.  
The input parameters for the electrospinning process were set consistently for the four types of nanofiber-blended cementitious materials, as summarized in Table 3. To obtain good dispersion and \begin{table}
\begin{tabular}{c c c c c} \hline
**Polymer Solution** & **Presolution** & **N66** & **PVP** & **CNTs** \\ \hline N66 polymer solution & 90 (Formic acid + Chloroform) & 10 & - & - \\ \hline CNTs-N66 polymer solution & 90 (Formic acid + Chloroform) & 9.6 & - & 0.4 \\ \hline TEOS/PVP polymer solution & 90 (TEOS + Butanol) & - & 10 & - \\ \hline CNTs-TEOS/PVP polymer solution & 90 (TEOS + Butanol) & - & 9.6 & 0.4 \\ \hline \end{tabular}
\end{table} 
Table 2: Component proportions of polymer solutions by weight percent (%). Figure 1: The setup of the electrospinning process. OPC: ordinary Portland cement. avoid the gathering phenomenon of electrospun nanofibers in cement, the proportion of polymer solution of 5 wt % was chosen for the composite cementitious materials.