# Electro-Thermal Properties of Carbon-Fiber-Reinforced Mortar Prisms
## 4 Experimental Results  
Before electrical heating, the resistances of the prisms were measured with a digital multimeter [23]. However, for the plane prisms, no heating was deposited to them because of their very high resistances. Since the plane prisms do not include any conductive material, their resistances cannot be measured with the multimeter. The resistance values of the fiber-reinforced prisms are summarized in Table 2. The resistance values of the front-back and top-bottom sides of the minimum volume specified in Figure 2 for three prisms of each fiber percentage are shown in Table 2. This table also presents the averaged resistance values of all three prisms specified as 1, 2 and 3, and the front-back and top-bottom sides specified by \"a\" and \"b\", respectively. In addition to the abovementioned values, the dynamic resistances of the different fiber percentage prisms under heating are also shown with the applied voltage, current and power. Table 2 informs about the following:  
1. The average resistance value of the same fiber percentage indicates that, as the fiber percentage increases, the resistance values decrease; the values are 21.1 \(\Omega\), 7.0 \(\Omega\), 5.3 \(\Omega\) and 4.4 \(\Omega\), for the 0.5%, 1.0%, 1.5% and 2.0% prisms, respectively;
2. The resistance values of \"a\" and \"b\" are not the same and the three prisms of the same fiber percentage numbered 1, 2 and 3 have slightly different resistance values even if they were made from the same batch mortar mix;
3. The difference between the lowest and the highest resistance values is 16 \(\Omega\), 2.5 \(\Omega\), 1.7 \(\Omega\) and 1.4 \(\Omega\) for the 0.5%, 1.0%, 1.5% and 2.0% prisms, respectively. However, the actual resistance values calculated from the voltage and current values (voltage/current) are 22.9 \(\Omega\), 6.2 \(\Omega\), 5.2 \(\Omega\) and 2.2 \(\Omega\) for the 0.5%, 1.0%, 1.5% and 2.0% prisms, respectively. These values are nearly the same as their corresponding average values, except for the 2.0% prisms. Item (1) confirms that the conductivity of the prisms is originated by the fibers. Otherwise, the fiber percentage increase does not induce the further increase in the conductivity values, i.e., decrease in the resistance values. In addition to this, Equations (1) and (2) inform that more power will be applied to the prism as the fiber percentage increases. Item (2) indicates that the fibers in the prisms are not uniformly distributed because the conductivities of the mortar prisms are brought by the fibers. As indicated in Item (3), the reducing resistance difference between prisms of the same fiber percentage tells that the fibers become more uniformly distributed in the prisms as the fiber percentage increases. Item (3) also shows that the actual resistances for the 0.5%, 1.0% and 1.5% prisms are slightly different from their corresponding average values, but for the 2.0% prism, the value is half of the measured resistance value. The reason is not completely clear, but it could be caused by the loosely contacted fibers, which become tightly connected to each other by the heat induced by the current flowing through the fiber. As shown in Equations (1) and (2), the resistance decrease will cause applying more power to the prism. This power increase will induce further increase in the temperature of the prism. This increase squeezes the fibers in the prism more due to the growing thermal expansion of the prism. The fibers squeezing will improve the connection between fibers, which, in turn, will cause the decrease of the resistance. The resistance decreases in the 2.0% prism when the power is applied will be the result of the improvement.