# Effect of Electrospun Nanofiber Additive on Selected Mechanical Properties of Hardened Cement Paste
## 3 Results and Discussion  
### Mechanical Strength  
The influence of electrospun nanofibers on the 28-day mechanical properties is shown in Figure 3 (where \"MCP\" means \"modified cement paste\"). From an overall perspective, it is evident that the mechanical strength rose significantly in most cases of electrospun-nanofiber-modified cement pastes. As is illustrated in Figure 3a,b, the increase in compressive strength of the hardened pastes containing TEOS/PVP-based nanofibers was stronger than that of the pastes containing nylon-66-based nanofibers. For instance, compared with the compressive strength of the hardened plain cement paste, the compressive strength of the hardened pastes containing TEOS/PVP NFs and the hybrid CNTs-TEOS/PVP NFs increased 27.3% and 33.4%, respectively, and that of the hardened pastes containing N66 NFs and the hybrid CNTs-N66 NFs increased 6.9% and 14.8%, respectively. These observations show the effectiveness of TEOS/PVP-based nanofibers at increasing the compressive strength of cement materials. Figure 3c shows the toughness results calculated from the stress-strain curves in Figure 3a. Theoretically, the material toughness can be calculated by the area under the stress-strain curve [31]. The observation from Figure 3c shows a significant increase in the toughness of 16.0%, 18.2%, 47.3%, and 61.7% of the pastes containing N66 NFs, CNTs-N66 NFs, TEOS/PVP NFs, and CNTs-TEOS/PVP NFs, in that order, compared with the toughness of the hardened plain cement paste. In addition, [PERSON]'s modulus can be observed from the slope of the stress-strain curve. It is worth mentioning that despite changing the composition of the material, [PERSON]'s modulus remained unchanged, as shown in Figure 3a. Furthermore, there was an increase in the ductile deformation of the nanofiber-blended cement pastes compared with that of the plain paste, namely, increases of 10%, 13.3%, 26.7%, and 30% when introducing N66 NFs, CNTs-N66 NFs, TEOS/PVP NFs, and CNTs-TEOS/PVP NFs into the cement pastes, respectively. Table 4 summarizes the ductile deformation ratio of the blended paste to the plain paste. In contrast, the observations from the tensile strength tests show the effectiveness of nylon-66-based nanofibers at enhancing the tensile characteristics of Portland cement (see Figure 3d). There was a sharp increase in tensile strength in the hardened cement pastes containing N66 NFs and CNTs-N66 NFs of 25.7% and 54.3%, respectively, compared with that of the plain paste, while the tensile strength of the hardened cement pastes containing TEOS/PVP NFs and CNTs-TEOS/PVP NFs rose slightly, with an average increase of 5.7% and 17.1%, respectively. These observations show an important role of nylon-based nanofibers in increasing the tensile strength of Portland cement. In addition, the role of CNTs in reinforcing the nanofibers is clarified through these results. As mentioned above, the proportion of CNTs can be relatively estimated to be 0.02 wt % of the blended cementitious materials. In the literature, [PERSON] et al. [19] reported an increase of 19% in compressive strength when adding 0.5 wt % treated CNTs into the paste, and [PERSON] et al. [20] reported an increase of 45% in tensile strength when adding 0.1 wt % CNTs into the paste. This present work reports an increase of 33.4% in compressive strength and 54.3% in tensile strength when adding CNTs-TEOS/PVP NFs and CNTs-N66 NFs into the paste (0.02 wt % CNTs), respectively, which shows the feasibility of an indirect approach of using CNTs in enhancing the mechanical properties of cementitious materials. \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Fracture Strain** & **Ductile Deformation Ratio** \\ \hline Plain paste & 0.003 & 1.00 \\ \hline N66 NFs MCP & 0.0033 & 1.10 \\ \hline CNT-N66 NFs MCP & 0.0034 & 1.13 \\ \hline TEOS/PVP NFs MCP & 0.0038 & 1.27 \\ \hline CNTs-TEOS/PVP NFs MCP & 0.0039 & 1.30 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Ductile deformation ratio.