## 1 Introduction
In contrast, dielectric heating can achieve uniform internal heating and, if necessary, the location of the electric field can be specified [36, 37]. However, the dielectric constant of a heated object may vary significantly during heating. Further, because dielectric heating requires a higher frequency power supply than induction heating, power converters such as inverters are required [38]. Therefore, dielectric heating systems are expensive, and there is a risk of inductive and radio wave interferences due to the harmonic waves generated by power converters. To avoid the inductive failure of the power supply system, the supply line providing power to the dielectric heating furnace and other power supply systems are kept independent, and an active filter is also used [39]. Furthermore, to overcome the possible interference with other radio devices, a power source in a frequency band provided exclusively for dielectric heating is used. However, owing to problems associated with high frequencies (short wavelengths) and the required equipment, the efficiency of use for dismantling structures is relatively poor compared to induction heating methods [40]. In this study, a general-purpose reinforcement utilized for reinforced concrete among metal materials was employed as a conductive resistor for high-frequency induction heating, and was used as a mechanism to weaken concrete via thermal conduction of heated reinforcing steel. In the case of high-frequency induction heating, the internal reinforcement, that is, the heated object, generates heat by itself and thus increases the energy density of the reinforcement inside the reinforced concrete much more effectively than indirect heating using hydrogen. Further, for reinforced concrete members, the surface temperature of reinforced concrete increases owing to heat-sensitive conductive resistance to high-frequency induction heating, resulting in increased heat being applied to the surface temperature of the reinforced concrete. In addition, separation of concrete enclosing reinforcing bars by heating concrete on the surface of the reinforcing bar and dehydrating and weakening the cement paste (the main component of concrete) is possible. Furthermore, in induction heating, local heating is possible. Moreover, increasing the temperature of cement-based substances is comparatively economical because of their excellent thermal efficiency. However, as mentioned in the previous paragraphs, various variables related to the maximum power cost exist, such as the surface area and heating distance of the reinforcing steel, and the concrete is expected to undergo various internal structural changes such as changes in density due to temperature variations. In this study, we examine the characteristics of concrete using temperature distributions and trends consistent with those applied in previous research to the same type of reinforcement, arrangement of reinforcing bars, and heating distances. For a particular reinforced concrete specimen featuring a single reinforced bar, the basic characteristics were examined using high-frequency induction heating. In high-frequency induction heating, the increase of temperature with time depends on the changes in eddy current and current density caused by the joining method and bar arrangement. Furthermore, the mechanical, physical, and chemical properties of concrete against the actual fragility of reinforced concrete members due to high-frequency induction heating were examined to determine the fragility properties of heated concrete.