# Electro-Thermal Properties of Carbon-Fiber-Reinforced Mortar Prisms
## 4 Experimental Results
As shown in the 240 sec images, the radii of the circles increase as the fiber percentage increases, though the difference between 0.5% and 1.0% is not prominent. This means that the prisms with higher fiber percentage will be heated more. The amount of the diffused heat reduces as the radius of the circle increases and the area between these two half circles, i.e., the middle part of the prism is heated less due to its smaller resistance compared with the near-electrode parts. This makes the temperature of the middle part much lower than the electrode side. However, as the heating time increases, a clearly visible heated corridor having a width comparable to the dotted rectangle in each image appears between these two circles, as shown in the 270 sec image of 0.5%, 240 sec images of both 1.0% and 1.5%, and 180 sec image of 2.0%. These corridors identify the presence of the minimum volume. The further increase in the heating time induces the circles to contact and overlap with each other, as shown in the 300 sec image of 1.5% and the 240 sec and 300 sec images of 2.0%. Figure 5 also shows that the circles have bigger radii as the fiber percentage increases. Figure 6 shows thermal images for different pieces of the percentage prisms, different from Figure 5.  
Only three thermal images at 1, 3 and 5 min of heating for each percentage prism are combined to show the temperature distribution changes in the prism surface with the  
Figure 5: Heat/Temperature distribution patterns of a prism set. The dotted vertical rectangle and the time in each temperature distribution represent the surface area of the minimum volume and the heating time, respectively. Figure 6: Heat/Temperature distribution patterns of another prism set. The numbers represent average temperatures of the prism surface (**top left** corner of each image) and the minimum volume surface (**middle**). The dotted vertical rectangle and the solid line in each temperature distribution represent the surface area of the minimum volume and the bisect line of the rectangle, respectively. heating time. The dotted rectangle in each image represents the surface area corresponding to the minimum volume. Each image corresponds to the surface area of 57.66 mm \(\times\) 40 mm specified in Figure 4. The numbers in the left corner and the center of each image indicate the average temperatures of the surface area and the dotted rectangle, respectively, during the initial temperature, i.e., the temperature before heating, which is 24\({}^{\circ}\). Thus, the actual temperature increment by the electric power will be the numbers minus 24\({}^{\circ}\), i.e., 8.6\({}^{\circ}\) (32.6-24\({}^{\circ}\)) for the 1 min case of the 0.5% prism in Figure 6.  
The temperature range of each thermal image is normalized from 22.8\({}^{\circ}\) to 80\({}^{\circ}\) for comparison. The color bar is the same as in Figure 5. The color changes from black, purple, blue, green, red and yellow to white, corresponding to the lowest to the highest temperature. Therefore, as the time increases, more surface areas of each prism turn red, yellow and white. The temperature distribution patterns are very similar to the images in Figure 5, except for the 1.5% prism. For the 1.5% prism, the bottom electrode pattern is the same as the 1.5% patterns in Figure 5, but the top electrode pattern has a cucumber shape that almost fits inside of the rectangle. This identifies the presence of the minimum volume and indicates that the resistance value of the minimum volume under the cucumber-shaped area is almost the same as that of the interface between the electrode and fibers. This part of the minimum volume is almost equally heated by the electric power. The images for the 3 and 5 min durations show that the top and bottom patterns overlap each other and extend outside the rectangle. Figure 6 reveals the following:  
1. The waveforms of the temperature distributions are somewhat smoothly varying with their peaks near the left and right edges, and their minimum is at their middle parts.