# Electro-Thermal Properties of Carbon-Fiber-Reinforced Mortar Prisms
## 1 Introduction  
The interest in developing conductive concrete increases with the growth of the number of traffic accidents incurred by black ice, which is known as the thin layer of ice on the surfaces of roads/airfield runways [1]. The conventional method of deicing roads is spraying various chloride products to roads/airfield runways [2]. It is effective but it damages cars/planes, roads, driveways and environments surrounding the roads/airfields in the long run. Hence, as an alternative method to the spraying, melting the ice by heating the road with electric power has been developed. However, the electric power can only be delivered by the electric current because it is linearly proportional to the square of the current. However, the concrete itself cannot flow electrical current because it is an electrical insulating material. To make the road able to flow the current, it should be made to have a certain electrical conductivity. There are two known ways of making a road electrically conductive: one of them is embedded heat-generating electric wires underneath the surface, and the other is making the road itself to be a conductive material by mixing the concrete with materials that conduct electricity. However, since it has been known that the former is more costly and less reliable than the latter [3], more research has been done to develop conductive materials to be mixed with the concrete. Typical conductive materials are electrically conductive particles such as carbon black and steel powders, and carbon fibers (hereafter abbreviated as fibers in this paper) [4; 5; 6; 7]. The conductive particles and the fibers differ in their mixability with the concrete. The particle form can be uniformly mixed with the concrete, but the fibers cannot. This is why the fibers are made to have a wire form and they are embedded into the concrete [6; 7]. However, this is not a good method because it can reduce the physical strength of the concrete instead of reinforcing it. Nevertheless, since a certain amount of short fibers has often been mixed to reinforce the physical strength of the cement mortar due to their much higher tensile strength compared with the concrete [8; 9; 10], their electrical conductivity transforms the fiber-reinforced concrete into a conductive material. The electric conductivity of the fibers is in the range of 5 \(\times\) 10\({}^{4}\)-5 \(\times\) 10\({}^{5}\) S (ampere/volt)/m (length) [11]. This conductivity value is much lower than that of metal. Hence, it can be used as a heat-generating electric wire, i.e., a heater that will generate enough heat to melt the ice and keep the road surface ice-free. The conductivity of conductive concrete is estimated with embedded mesh-type wire grid electrodes placed at a fixed distance apart from each other. The resistance value between two electrodes is measured [12; 13] because the conductivity is obtained by inverting the resistivity value, which is linearly proportional to the resistance value. The resistance is defined as the resistivity of the fiber/conductive particles multiplied by the distance between electrodes and divided by the electrode area. To heat the concrete, it is necessary to attach the electrodes to the concrete. Since the mesh-type embedded electrodes are just a wire grid formed by thin copper wires, each of these wires is localized, i.e., isolated by the surrounding cement/concrete in the concrete. Due to this isolation, the electric current will be confined within the area occupied by the wires. Since the area will be much smaller than that of the concrete cross-section holding the electrode, the resistance of the current will be very high. Hence, the large portion of the heat induced by the current will be dissipated near the electrodes. Therefore, heating the concrete by flowing current through the embedded wire grids will not be efficient. It is possible to replace the wire grid with an electrically conductive glue. It can be painted on the surface of the concrete to be used as an electrode.