# Electro-Thermal Properties of Carbon-Fiber-Reinforced Mortar Prisms
## 2 Experimental Samples and Experimental Set-Up  
Three mortar prisms reinforced with each of the four volume percentages of fibers, namely, 0.5%, 1.0%, 1.5% and 2.0%, are prepared according to the Korean Standard [14]. The fibers are bundled to have a diameter of 7 \(\pm\) 2 \(\upmu\)m and then cut into 6 mm in length before being added to the mortar mixture. The preparation details of the fiber to mix with the mortar are described in [15]. The prism dimensions are 40 mm \(\times\) 40 mm \(\times\) 160 mm and their designed weight is 500 g [15]. They were kept in a water reservoir for 28 days for curing. Three samples for each fiber percentage were prepared. Each of these prisms was broken into two parts due to the flexural strength test undertaken [16]. Thus, six pieces for each fiber percentage were obtained. These pieces are not of same size because each sample is broken into two pieces by the crack induced by the test. Hence, the length of each piece is either slightly longer or shorter than 80 mm, i.e., a half of the prism's length of 160 mm. These broken sample pieces had been kept in laboratory condition for almost three years. They were expected to be nearly dried because the plane mortar prisms that were stored together with the samples revealed that their resistances far exceed the Fluke's handheld multimeter's measuring range and their weights do not have the designed value. All of them have lower values than the designed value due to the presence of fibers. Table 1 shows the sample weight measured with a precision scale (Cas: cas-USA.com). It includes the weight of plane prisms. The weights of two broken left and right pieces of each sample and the sum and average of the same percentage prisms are also shown. The table shows that the same percentage prisms have almost the same weight, though between different percentage prisms, the weight differences are prominent. Only 1.0% prisms are near 500 g while other percentage samples are much lighter than the 1.0%. The average weight of the 1.0% prisms is 499 g. The weight is reduced to 495 g, 467 g, 462 g and 432 g for the 0.5%, 1.5%, 0.0% and 2.0% prisms, respectively. When the average weights of other percentage prisms are normalized by that of the 1.0% prisms, the values are given as 0.99, 0.94, 1.0, 0.93 and 0.87 for 0.0%, 0.5%, 1.0% 1.5% and 2.0%, respectively. These values are also specified in Table 1. The 2.0% prism reveals the smallest value. The highest weight recorded by 1.0% prism implicitly informs that the number of air pockets in the prisms is the smallest. The number of air pockets decreases as the fiber percentage increases [15]. This is why the weight of the plane prism is slightly greater than that of the 2.0% prism. The increasing fiber percentage reduces the prism's weight, but the decreasing rate in the number of the air pockets is greater than the weight reduction rate due to the growth of the fibers volume. The weight of the plane prisms allows estimating the density of the plane prisms. It is calculated as 1804.69 kg/m\({}^{3}\). This density value is almost the same as that of the fiber (Toray (Japan)'s intermediate modulus type T1100G), which is specified as 1800 kg/m\({}^{3}\). The density value of the plane prisms also implicitly indicates that they lost most of their moisture. To heat the prisms, the DC (Direct Current) power supply should be able to regulate current up to 5 A and voltage to 30 V for electrical heating. For electrical heating, a conductive gel is painted on one surface of each piece and its opposite side along the bisecting line of the piece in its length direction in order to have the shape of a rectangle with dimensions of 40 mm \(\times\) 5 mm. The rectangle shape is selected to observe the heat diffusion to its two sides. Figure 1 shows the electrode preparation in each prism piece; the electrode connection is also shown. A conductive gel electrode with a thickness of 5 mm is drawn on one surface of each piece.