# Electrical Characteristics of Ultra-High-Performance Concrete Containing Carbon-Based Materials
## 3 Results and Discussions
### Direct Current Measurements  
The DC measurements are summarized in Table 3, with the measurements at the ages of 3 and 28 days shown in Figures 7 and 8, respectively. All the specimens exhibited significantly higher conductivity than that of commonly known concrete (\(10^{-5}\) to \(10^{-12}\) S/m) [47];  
Figure 6: Tensile strengths of the different specimens. this could be due to the formation of a conductive path inside the concrete matrix by incorporating steel fibers into the UHPC formulation. The concrete conductivity on day 28 was significantly lower than that on day 3. Initially, the concrete showed relatively high conductivity due to the presence of residual water that did not contribute to hydration [48; 49]; on aging, this moisture was gradually removed by residual hydration and drying shrinkage. Here, the electrical conductivity was reduced according to the difference in the internal water content, even if there were no changes in the material properties of the concrete. The CNT specimen with a mixing content of 1.5% exhibited the highest conductivity at 3 days. The conductivity increased up to a mixing content of 1.5% at 28 days, with a slight decrease in conductivity observed for the specimen with 2.0% mixing content. Although the optimal CNT dispersion content was 1.5%, the conductivity of this specimen was not significantly higher than that of the 0.5% specimen. The CNT dispersion contained a small amount of mixed CNTs; thus, the CNT specimen exhibited low conductivity. Figure 7: Direct current measurements at the age of 3 days. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Carbon Materials**} & \multirow{2}{*}{**Concentration**} & \multicolumn{2}{c}{**At the Age of 3 Days**} & \multicolumn{2}{c}{**At the Age of 28 Days**} & \multicolumn{2}{c}{**Reduction Rate (\%)**} \\ \cline{3-7}  & & **Resistance** & **Conductivity** & **Resistance** & **Conductivity** & **(S/m \(\times\) 10\({}^{-3}\))-(\(\ddagger\))** & **(S/m \(\times\) 10\({}^{-3}\))-(\(\ddagger\))** & **(S/m \(\times\) 10\({}^{-3}\))-(\(\ddagger\))** & **(S/m \(\times\) 10\({}^{-3}\))-(\(\ddagger\))** \\ \hline \multirow{4}{*}{[CNT]} & 0.5 & 27,429 & 2.92 & 415,625 & 0.19 & 93.4\% \\  & 1.0 & 15,985 & 5.00 & 213,636 & 0.37 & 92.5\% \\  & 1.5 & 9242 & 8.66 & 133,000 & 0.60 & 93.1\% \\  & 2.0 & 11,561 & 6.92 & 123,182 & 0.65 & 90.6\% \\ \hline \multirow{4}{*}{[CF]} & 0.5 & 21,522 & 3.72 & 232,877 & 0.34 & 90.8\% \\  & 1.0 & 21,613 & 3.70 & 233,333 & 0.34 & 90.7\% \\  & 1.5 & 1788 & 44.75 & 14,297 & 5.60 & 87.5\% \\  & 2.0 & 1947 & 41.08 & 7644 & 10.47 & 74.5\% \\ \hline \multirow{4}{*}{[MF]} & 0.5 & 28,955 & 2.76 & 325,926 & 0.25 & 91.1\% \\  & 1.0 & 24,792 & 3.23 & 298,551 & 0.27 & 91.7\% \\  & 1.5 & 8880 & 9.01 & 77,857 & 1.03 & 88.6\% \\  & 2.0 & 5681 & 14.08 & 87,500 & 0.91 & 93.5\% \\ \hline \multirow{4}{*}{[GP]} & 0.5 & 8986 & 8.90 & 45,323 & 1.77 & 80.2\% \\  & 1.0 & 4870 & 16.43 & 76,674 & 1.04 & 93.6\% \\ \cline{1-1}  & 1.5 & 15,423 & 5.19 & 116,889 & 0.68 & 86.8\% \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Direct current measurements with reduction rates according to the age of concrete. The 12-mm-carbon-fiber specimen exhibited a high electrical conductivity; therefore, chopped fibers efficiently enhance the electrical conductivity of UHPC. Furthermore, the conductivity increased at mixing contents exceeding 1%; the millimeter-sized carbon fibers formed a conductive network in the concrete matrix. Additionally, a percolation zone was observed in the 1.5% specimen. This study could guide further research to develop a technology for imparting conductivity to UHPC, including the design of an optimized mix incorporating chopped fibers. The MF specimen containing 100 \(\upmu\)m carbon fibers exhibited lower conductivity than the specimen containing CF; therefore, micrometer-sized fibers formed a conductive network less efficiently than chopped fibers. However, a percolation zone was formed within the 1.5% mixing content specimen.