# Electro-Thermal Properties of Carbon-Fiber-Reinforced Mortar Prisms
## 2 Experimental Samples and Experimental Set-Up
On the opposite surface of the piece, another electrode with the same dimension and direction as the first one is drawn. The electrode is located near the middle area of each piece. One of the electrodes is connected to the '+' terminal of the power supply and the other to the '-' terminal or ground terminal through electric wires. These wires are in contact parallel to the long side directions of their corresponding electrodes. The typical resistivity of the conductive glue is around 0.09 \(\Omega\)-cm to 0.0001 \begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **Sam. No.** & **Left (g)** & **Right (g)** & **Sum (g)** &
\begin{tabular}{c} **Weight (g)** \\ **(Average (g))** \\ \end{tabular} \\ \hline  & 1 & 216 & 248 & 464 & \\
0.0\% & 2 & 232 & 230 & 462 & 1386 (462) \\  & 3 & 225 & 235 & 460 & *0.93 \\ \hline  & 1 & 246 & 250 & 496 & \\
0.5\% & 2 & 248 & 247 & 495 & 1486 (495) \\  & 3 & 273 & 222 & 495 & *0.99 \\ \hline  & 1 & 203 & 294 & 497 & \\
1.0\% & 2 & 241 & 259 & 500 & 1497 (499) \\  & 3 & 241 & 259 & 500 & *1.0 \\ \hline  & 1 & 247 & 222 & 469 & \\
1.5\% & 2 & 227 & 235 & 462 & 1400 (467) \\  & 3 & 245 & 224 & 469 & *0.94 \\ \hline  & 1 & 195 & 241 & 436 & \\
2.0\% & 2 & 204 & 222 & 426 & 1296 (432) \\  & 3 & 212 & 222 & 434 & *0.87 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Weights of four different percentage prisms: Each percentage has 3 prism samples. \(\Omega\cdot\)cm [17]. The resistivity can go up several tens percent more when it is heated [17], but it is still very small compared with that of the dried prisms/concrete, which is in the range of 100 \(\Omega\cdot\)cm to 1,000,000 \(\Omega\cdot\)cm [18]. These rectangles are working as electrodes. However, the contact between these electrodes and the fibers in the prism piece can be hardly achieved due to mortars covering the fibers. This ill connection problem is worsened when the densities of fibers under the electrodes become lower. This ill connection and fiber density may be the decisive factors of determining the resistance values of different fibers percentage prisms and different prisms of the same fiber percentage. Hence, it is expected that the resistance values of the prisms will be reduced as the fiber percentage increases. This resistance decrease also reduces the resistance introduced by the ill connection, but it will still take the highest portion of the resistance in the higher fiber percentage prisms. It is also considered that the contact between electrodes and wires can also contribute some resistance because the wires cannot be fully in contact with the electrodes. The electrodes do not have a smooth surface because they are drawn on the prisms' rough surfaces. It is shown in the experiments that the resistance induced by the ill connection, lower density and unsmooth electrode surfaces is much larger than that of the fibers in the different percentage prisms. Since the resistance will induce heating near the surface of the prisms, a certain amount of electric power can be ineffectively consumed. To minimize this inefficient consumption of power, it is necessary to tighten the electric wires to the electrodes as much as possible. Figure 2 shows the experimental set-up. The set-up consists of a power supply for applying both voltage and current to the prism to be heated, a multimeter for measuring the resistance of the prism before applying power to determine the necessary current and voltage values for applying 30 W power, a bench wise for connecting the electric wires tightly to the gel electrodes, a thermal camera for photographing the thermal image, i.e., the prism's surface temperature variation with time, and a notebook for recording the thermal images as files. The prism's surface in the thermal image is one of the prism surfaces between the electrode surfaces. The thermal camera is fixed directly above the prism at a distance of 500 mm. Through the wires, 30 W of power was applied to each prism for up to five minutes.