Capacitive corrosion sensor and its installation method

Abstract

To provide a capacitance-type corrosion sensor which can be set easily in a concrete structure and allows the progress of a corrosion to be known highly accurately, and a method for setting the same.SOLUTION: A capacitance type corrosion sensor 1 for detecting a corrosive environment of a steel material includes: a cylindrical detection unit 3 made of a corrosive metal; a bar-like counter electrode 9 made of an anti-corrosion metal, the counter electrode facing the inner surface of the detection unit 3; and a dielectric 7 provided between the detection unit 3 and the counter electrode 9. The capacitance changes according to reduction of the area of the detection unit 3 due to corrosion.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a capacitance-type corrosion sensor for detecting a corrosive environment of steel materials, and to an installation method thereof. [Background technology]

[0002] Steel in concrete structures is protected from corrosion by a passive film formed on the surface of the steel due to the alkaline environment of the concrete. However, when corrosive factors such as carbon dioxide in the air, sulfuric acid in sewerage facilities, or chloride ions penetrate the concrete, this passive film is destroyed, and the water and oxygen in the concrete begin to corrode the steel. Furthermore, protective paints are used in steel structures such as railway bridges and plants to prevent rust from forming on the steel.

[0003] When steel in a concrete structure corrodes, the volume of the steel expands, and the pressure of this expansion causes cracks in the concrete. The corrosion of the steel accelerates as corrosion factors penetrate through the cracks and water and oxygen are supplied from the outside, eventually causing the concrete structure to lose its functionality. In addition, when steel corrodes, the volume expansion of the steel causes the protective coating to lift or peel, losing its anti-corrosion effect.

[0004] Therefore, it is important to detect the intrusion of corrosion factors or the onset of corrosion before the corrosion of steel begins, and to protect the steel from corrosion by preventing further intrusion of corrosion factors, water, and oxygen through measures such as surface coating. To address this issue, various corrosion diagnosis methods and corrosion sensors have been proposed.

[0005] For example, Patent Document 1 describes a parallel-plate capacitance corrosion sensor that includes a detection unit made of a corroding metal, a counter electrode made of a corrosion-resistant metal and positioned opposite the detection unit, and a dielectric placed between the detection unit and the counter electrode. The capacitance corrosion sensor is embedded inside a concrete structure, and makes it possible to grasp the progress of corrosion inside the concrete structure based on the degree of corrosion of the iron foil material that serves as the detection unit. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 2017-032516 Summary of the Invention [Problem to be solved by the invention]

[0007] The larger the area of ​​the detection section of the capacitance-type corrosion sensor described above, the higher the measurement resolution, allowing for a more accurate understanding of the progression of corrosion. However, the larger the corrosion sensor, the more difficult it becomes to install it inside a concrete structure, especially in areas with dense reinforcement. Therefore, there is a demand for a corrosion sensor that is easy to install yet can accurately grasp the progression of corrosion.

[0008] Furthermore, to accurately grasp the progress of corrosion, it is necessary to consider various factors that affect corrosion to prevent discrepancies between the actual corrosion state of the steel and the detection results of the corrosion sensor. For example, the corrosion progress varies in the circumferential direction of the steel depending on the method of corrosion penetration. In addition, the void structure formed on the underside of the steel due to bleeding may accelerate the corrosion rate.

[0009] The present invention has been made in consideration of the above circumstances, and aims to provide a capacitance-type corrosion sensor that can be easily installed inside a concrete structure and that enables the progress of corrosion to be grasped with high accuracy, as well as a method for installing the same. [Means for solving the problem]

[0010] (1) In order to achieve the above object, the capacitance-type corrosion sensor of the present invention is a capacitance-type corrosion sensor that detects the corrosive environment of steel, and is characterized by comprising a cylindrical detection section formed of a corrosive metal, a rod-shaped counter electrode formed of a corrosion-resistant metal and arranged to face the inner surface of the detection section, and a dielectric arranged between the detection section and the counter electrode, and the capacitance changes in accordance with the reduction in area of ​​the detection section due to corrosion.

[0011] Because the detection unit is cylindrical, it is possible to ensure a large detection area while keeping the size of the sensor small, improving measurement resolution without sacrificing ease of installation. Furthermore, because the shape closely matches the shape of the steel, it is possible to reduce the error between the actual corrosion state and the detection results of the corrosion sensor, making it possible to grasp the progression of corrosion with high accuracy.

[0012] (2) In addition, the capacitance-type corrosion sensor of the present invention is characterized in that one end of the detection unit is hemispherical. This creates a curve at one end of the detection unit, making it possible to reproduce the effects of bleeding, particularly when the corrosion sensor is installed by hanging it from steel, and to grasp the progress of corrosion with greater accuracy.

[0013] (3) Furthermore, in the method for installing a capacitance-type corrosion sensor of the present invention, the detection unit is cylindrical, the outer diameter of the detection unit is 4 mm or more, and the diameter of the capacitance-type corrosion sensor is 50 mm or less. This improves measurement resolution without compromising ease of installation.

[0014] (4) A method for installing the capacitance-type corrosion sensor according to any one of (1) to (3) above, comprising the steps of fixing the capacitance-type corrosion sensor to one of two opposing steel members and embedding the capacitance-type corrosion sensor in a concrete structure having the steel members, wherein the capacitance-type corrosion sensor is located between the opposing steel members. This enables the capacitance-type corrosion sensor to sense the corrosion status of the steel members inside the concrete structure.

[0015] (5) Furthermore, the installation method of the capacitance-type corrosion sensor of the present invention is characterized in that the capacitance-type corrosion sensor is installed so that its longitudinal direction is aligned with the extension direction of the steel material to which the capacitance-type corrosion sensor is fixed. This makes it possible to align the extension direction of the corrosion sensor with the steel material whose corrosion progress is to be grasped. This reduces the error between the actual corrosion state and the detection result by the corrosion sensor, making it possible to grasp the corrosion progress state with high accuracy.

[0016] (6) Furthermore, the method for installing a capacitance-type corrosion sensor of the present invention is characterized in that the capacitance-type corrosion sensor is installed so that its longitudinal direction is aligned with the vertical direction. This allows the corrosion sensor to be installed by hanging it from a fixed steel material, making it easier to install the corrosion sensor.

[0017] (7) Furthermore, in the method for installing a capacitance-type corrosion sensor of the present invention, in a cross section of the concrete structure including the capacitance-type corrosion sensor perpendicular to the central axis of the capacitance-type corrosion sensor, the area of ​​the concrete constituting the concrete structure is larger than the area of ​​the capacitance-type corrosion sensor, thereby making it possible to prevent a decrease in durability of the concrete structure due to the installation of the corrosion sensor.

[0018] (8) Furthermore, in the method for installing a capacitance-type corrosion sensor of the present invention, in a region of the concrete structure sandwiched between cross sections perpendicular to the central axis of the capacitance-type corrosion sensor at both ends of the capacitance-type corrosion sensor, the volume of the concrete constituting the concrete structure is larger than the volume of the capacitance-type corrosion sensor. This makes it possible to further prevent a decrease in durability of the concrete structure due to the installation of the corrosion sensor.

[0019] (9) Furthermore, the method for installing a capacitance-type corrosion sensor of the present invention is characterized in that the capacitance-type corrosion sensor is positioned so that its longitudinal direction is along the extension direction of four surrounding steel members that extend in the same direction, is surrounded by the four steel members, and in a cross-sectional region perpendicular to the four steel members, the area of ​​the concrete that makes up the concrete structure is larger than the area of ​​the capacitance-type corrosion sensor. This makes it possible to further prevent the installation of a corrosion sensor from reducing the durability of the concrete structure. [Effects of the Invention]

[0020] According to the present invention, the device can be easily installed inside a concrete structure, and the progress of corrosion can be grasped with high accuracy. [Brief explanation of the drawings]

[0021] [Figure 1] FIG. 2 is a perspective view used to explain the principle of measuring capacitance according to the embodiment. [Figure 2] 1 is a perspective view showing a schematic configuration of a capacitance-type corrosion sensor according to an embodiment of the present invention. [Figure 3] 3 is a cross-sectional view taken along the line AA of the capacitance-type corrosion sensor shown in FIG. 2. [Figure 4] FIG. 10 is a perspective view showing a schematic configuration of a modified example of the capacitance-type corrosion sensor according to the present embodiment. [Figure 5] FIG. 10 is a perspective view showing a schematic configuration of a modified example of the capacitance-type corrosion sensor according to the present embodiment. [Figure 6]1 is a cross-sectional view showing a state in which a capacitance-type corrosion sensor is installed inside a concrete structure by the installation method of a capacitance-type corrosion sensor according to the present embodiment. FIG. [Figure 7] 10 is a cross-sectional view showing a state in which a capacitance-type corrosion sensor is installed inside a concrete structure according to a modified example of the installation method of the capacitance-type corrosion sensor in this embodiment. FIG. [Figure 8] FIG. 8 is a BB cross-sectional view of the concrete structure in which the capacitance-type corrosion sensor shown in FIG. 7 is installed. [Figure 9] 10 is a graph showing the results of a simulation of the corrosion area ratio and capacitance of the detection unit. DETAILED DESCRIPTION OF THE INVENTION

[0022] [Measurement principle of capacitance type corrosion sensor] Capacitive corrosion sensors utilize the principle that as the sensor's detection part corrodes due to corrosion factors, the conductor area decreases, resulting in a corresponding decrease in capacitance, making it possible to grasp the progression of corrosion from the measured capacitance.

[0023] In the case of parallel plate conductors, it is known that the capacitance C can be calculated from the following formula (1) when the area of ​​the parallel plate is S, the distance between the parallel plate conductors is d, and ε is the dielectric constant. Therefore, the corrosion area of ​​the detection part can be easily calculated from the capacitance using formula (1).

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[0024] On the other hand, in the case of a concentric cylindrical conductor as shown in Figure 1, it is known that the capacitance C can be calculated using the following formula (2): In formula (2), a is the radius of the cylindrical electrode, b is the inner radius of the cylindrical electrode, L is the height of the concentric cylindrical conductor, ε0 is the dielectric constant of a vacuum, and ε ris the relative permittivity. However, in the case of a concentric cylindrical conductor, the area of ​​the conductor is not included in equation (2) for calculating the capacitance C. Therefore, it is difficult to calculate the corrosion area of ​​the detection part from the capacitance using equation (2).

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[0025] In contrast, regarding the relationship between the capacitance and area of ​​a concentric cylindrical conductor, assuming that the corroded portion of the detection part exists over the entire circumferential length, the corroded area can be found by calculating the height at which the corroded portion exists from the capacitance. That is, the radius of the cylindrical electrode is a, the inner radius of the cylindrical electrode is b, the height of the concentric cylindrical conductor is L, the permittivity of vacuum is ε0, and the relative permittivity is ε r Then, the height Lx of the concentric cylindrical conductor corroded in the circumferential direction is calculated using equation (3): From this, the corroded area of ​​the detection part can be calculated.

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[0026] The capacitance-type corrosion sensor operates on the principle that as the sensor's detection section corrodes due to corrosion factors, the area of ​​the opposing parallel plate conductors decreases, resulting in a corresponding decrease in capacitance. The capacitance-type corrosion sensor according to this embodiment utilizes this principle to detect the degree of decrease in capacitance, thereby making it possible to grasp the degree of decrease in the area of ​​the detection section and, ultimately, the progression of the corrosive environment.

[0027] [Configuration of capacitance type corrosion sensor] Fig. 2 is a perspective view showing a schematic configuration of a capacitance-type corrosion sensor according to this embodiment. Fig. 3 is a cross-sectional view taken along line AA of the capacitance-type corrosion sensor shown in Fig. 2. As shown in Figs. 2 and 3, the capacitance-type corrosion sensor 1 includes a detection unit 3, a dielectric 7, a counter electrode 9, lead wires 10, and a waterproof material 13.

[0028] The detection unit 3 is provided on the exposed side of the capacitance corrosion sensor 1 and is cylindrical with one end hemispherical. The detection unit 3 is made of a corrosive metal, such as iron, stainless steel, or aluminum. The material of the detection unit 3 is preferably the same as that of the measurement object whose corrosion state is to be determined, and when the measurement object is a steel material such as rebar, the material is preferably iron.

[0029] The thickness of the detection section 3 is preferably 0.001 μm or more and 1 mm or less. By making the thickness 1 mm or less, the sensitivity of the corrosion sensor 1 can be improved. The outer diameter of the detection section 3 is 4 mm or more, and the area of ​​the detection section 3 is 20,000 mm or less. 2 This provides a measurement resolution sufficient to grasp the progress of corrosion.

[0030] 4, one end of detection unit 3 may be flat instead of hemispherical, but considering the effects of bleeding, a hemispherical shape is preferable. When one end of detection unit 3 is hemispherical, it is possible to reproduce the formation of a void structure formed by bleeding and its effect on corrosion, particularly when corrosion sensor 1 is installed by hanging it from steel, making it possible to grasp the progress of corrosion with high accuracy.

[0031] Furthermore, instead of being cylindrical with a bottom, the inner surface may penetrate the bottom, but in that case, it is necessary to cover the end with a waterproof material 13 to prevent water from entering, as shown in Figure 5. Furthermore, the shape of the detection unit 3 is preferably the same as the shape of the object whose corrosion state is to be determined, and the cross-sectional shape may be rectangular or triangular.

[0032] The counter electrode 9 is a cylindrical electrode that shares the same central axis as the detection unit 3. The counter electrode 9 is preferably made of a metal with high corrosion resistance. To capture the corrosion-induced decrease in the detection unit 3 through electrical characteristics, it is necessary that the area of ​​the counter electrode 9 does not change. The counter electrode 9 can be made of a metal that has a lower ionization tendency and is more conductive than the target metal, such as a precious metal such as gold, platinum, or palladium. For example, if iron is the target to be detected, palladium, copper, nickel, or the like can be used. The shape of the counter electrode 9 does not have to be cylindrical; it can also be a polygonal shape such as a square prism or a triangular prism. The diameter of the counter electrode 9 is not important.

[0033] Furthermore, the lead wire 10 constitutes a first current-carrying part electrically connected to the detection part 3 and a second current-carrying part electrically connected to the counter electrode 9.

[0034] The dielectric 7 is filled between the detection unit 3 and the counter electrode 9. As is clear from formula (3), the magnitude of the dielectric constant and the reduction in the area of ​​the detection unit 3 are greatly involved in the reduction in capacitance, so the dielectric 7 preferably has a dielectric constant of 3 or more. The thickness of the dielectric 7 is preferably 1 nm to 5 mm. It is desirable to use a material that changes little with temperature. This makes it possible to improve the measurement sensitivity of the sensor. The dielectric 7 is preferably a polyimide film with a dielectric constant of 3.3.

[0035] Furthermore, multiple through holes may be formed in the detection unit 3 and the dielectric 7 by chemical etching or the like. By forming the through holes, corrosion progresses easily, and even if a limited portion corrodes and is lost, the detection unit 3 is less likely to be left behind as islands, ensuring electrical continuity. The shape of each through hole is not particularly limited, but is preferably circular from the viewpoint of formation accuracy and yield. Furthermore, the multiple through holes may be mesh-shaped or slit-shaped.

[0036] Waterproofing material 13 is provided to prevent water from entering corrosion sensor 1. Waterproofing material 13 is made of a waterproof material, such as epoxy resin. Because corrosion sensor 1 is provided with waterproofing material 13, waterproofing is improved and insulation between detection unit 3 and counter electrode 9 can be ensured.

[0037] Furthermore, the diameter of the corrosion sensor 1 is preferably 50 mm or less. This is because, when the lattice-pattern reinforcement 20 is densely arranged, the length of one side of a cross-sectional area 40, which is surrounded by four main reinforcements (described later) and perpendicular to the four main reinforcements, is typically 30 mm to 200 mm. Therefore, by setting the diameter of the corrosion sensor 1 within the above range, it becomes easy to place the corrosion sensor 1 in this area 40. However, the diameter of the sensor is not limited to this and can be set appropriately according to the size of the area 40. Note that, although the cross-sectional shape of the corrosion sensor 1 in FIG. 2 is circular, it is not limited to this and may be polygonal, such as rectangular or triangular.

[0038] [Installation method of capacitance type corrosion sensor] Next, a method for installing a capacitance-type corrosion sensor will be described. Figure 6 is a cross-sectional view of a concrete structure in which a corrosion sensor is installed. A lattice-shaped reinforcement 20 is assembled by arranging rebars crosswise, and a lead wire 10 is wound around the upper lattice-shaped reinforcement 20, and a corrosion sensor 1 is hung perpendicular to the lattice-shaped reinforcement 20. At this time, the corrosion sensor 1 is fixed to the lattice-shaped reinforcement 20 so that it is positioned between the upper and lower lattice-shaped reinforcement 20. The lattice-shaped reinforcement 20 with the corrosion sensor 1 fixed thereto is placed in a formwork, and concrete is poured.

[0039] The corrosion sensor 1 embedded in the concrete structure 100 can measure the capacitance corresponding to the corrosion of the detection unit 3, and the measured capacitance can be used to detect the current corrosion area ratio of the detection unit 3. A high correlation is observed between the corrosion area ratio of the detection unit 3 and the capacitance, and the capacitance shows a gradual change according to the corrosion of the detection unit 3, making it possible to evaluate the degree of corrosion progression.

[0040] The capacitance corrosion sensor 1 may be installed so as to be parallel to the lattice-patterned reinforcement 20, as shown in Fig. 7. In this case, the corrosion sensor 1 may be fixed to the lattice-patterned reinforcement 20 with adhesive, a cable tie, or the like. The corrosion sensor 1 may also be fixed during pouring, or may be installed parallel to the lattice-patterned reinforcement 20 by laying the corrosion sensor 1 on the concrete 30 that is being poured.

[0041] The diameter of the corrosion sensor 1 is preferably smaller than the distance between the rebars that make up the grid-pattern reinforcement 20. As shown in Fig. 8, the corrosion sensor 1 is preferably installed so that the area of ​​the concrete 30 that makes up the concrete structure 100 is larger than the area of ​​the corrosion sensor 1 in a cross section perpendicular to the central axis of the corrosion sensor 1, and more preferably, the corrosion sensor 1 is installed so that the volume of the concrete 30 that makes up the concrete structure 100 is larger than the volume of the corrosion sensor 1 in the region of the concrete structure 100 sandwiched between the cross sections perpendicular to the central axis of the corrosion sensor 1 at both ends of the corrosion sensor 1.

[0042] Furthermore, the corrosion sensor 1 is preferably surrounded by four steel members and disposed so that in a cross-sectional area 40 perpendicular to the four steel members, the area of ​​the concrete constituting the concrete structure 100 is larger than the area of ​​the corrosion sensor 1. FIG. 8 is a vertical cross-sectional view of the concrete structure shown in FIG. 7. The concrete structure shown in FIG. 8 has four main reinforcements constituting a lattice-pattern reinforcement arrangement 20. The corrosion sensor 1 is surrounded by the four main reinforcements, is located within the cross-sectional area 40 perpendicular to the four main reinforcements, and is disposed along the extension direction of the four main reinforcements. The cross-sectional area 40 surrounded by the four main reinforcements and perpendicular to the four main reinforcements refers to a rectangular area that includes the outer surfaces of the four main reinforcements in a cross section whose longitudinal direction is perpendicular to the four main reinforcements extending in the same direction around the periphery.

[0043] In particular, when the corrosion sensor 1 is installed between densely arranged lattice-patterned reinforcement bars 20, concrete 30 may not be sufficiently filled between the surface of the steel material and the outer periphery of the corrosion sensor 1, and the unfilled area may become a void. If voids are formed inside the concrete structure 100, this may cause uneven strength and reduced durability. Therefore, by arranging the concrete so that the area of ​​the concrete constituting the concrete structure 100 is larger than the area of ​​the corrosion sensor 1 in the cross-sectional area 40 surrounded by four main reinforcements and perpendicular to the four main reinforcements, the formation of voids can be suppressed, and the reduction in durability caused by uneven strength due to voids can be suppressed.

[0044] [Application to steel structures] The capacitance-type corrosion sensor according to this embodiment can also be applied to steel structures. When a protective coating is applied to a metal structure to be measured, such as a steel bridge, plant equipment, streetlight, underground pipe, tank, or ship, the sensor according to this embodiment is attached to the surface of the metal material using an adhesive or the like before coating. Since the electrical condition of the structure may be affected during application, it is preferable to insulate the sensor with resin tape, sealant, or the adhesive itself. A protective coating is then applied, similar to that for metal structures. The cable may or may not be exposed to the outside of the protective coating. If the cable is not exposed, the sensor is buried under the coating, and when measurement is required, the coating covering the sensor is peeled off and a measuring instrument is directly connected to measure the electrical signal associated with corrosion. Alternatively, measurements may be performed electromagnetically using a wireless method. This allows the sensor to be installed without causing defects in the coating that would occur if the cable were pulled out.

[0045] [Example] Next, we simulated the relationship between the capacitance measured by the capacitance-type corrosion sensor and the corrosion area at the detection part. The simulation conditions, including the various conditions required to calculate the capacitance C and the materials of each component, are shown below. (Simulation conditions) Counter electrode radius a: 12 mm Inner radius b of the detection part: 13 mm Corrosion sensor length L: 200 mm Detector material: Fe Dielectric material: Alumina Counter electrode material: Cu

[0046] The simulation was performed using a capacitance-type corrosion sensor with the same shape as that shown in Fig. 4. The simulation did not take into account the waterproofing material.

[0047] The simulation results are shown in Figure 9. Figure 9 shows the capacitance C at the detection section when the corrosion area ratio is 0 to 100% using equation (3). As shown in Figure 8, the corrosion area ratio and capacitance are proportional to each other. This makes it possible to calculate the corrosion area ratio using equation (3) from the capacitance measured by the corrosion sensor.

[0048] As described above, the capacitance-type corrosion sensor according to this embodiment can grasp the progress of corrosion based on the area of ​​the detection part, even if it is a concentric conductor, because the capacitance changes according to the reduction in the area of ​​the detection part due to corrosion. Furthermore, it can be easily installed inside a concrete structure, making it possible to grasp the progress of corrosion with high accuracy. [Explanation of symbols]

[0049] 1. Capacitive corrosion sensor 3. Detection unit 7 Dielectrics 9 Counter electrode 10 Lead Wire 13 Waterproof material 20 Lattice reinforcement 30 Concrete 40 Cross-sectional area enclosed by and perpendicular to the four main bars 100 Concrete Structures

Claims

1. A capacitance-type corrosion sensor for detecting a corrosive environment of a steel material, a cylindrical detection unit formed of a corrosive metal; a rod-shaped counter electrode formed of a corrosion-resistant metal and provided so as to face the inner surface of the detection unit; a dielectric provided between the detection unit and the counter electrode, A capacitance-type corrosion sensor characterized in that the capacitance changes in accordance with a reduction in the area of ​​the detection part due to corrosion.

2. 2. The capacitance-type corrosion sensor according to claim 1, wherein one end of the detection portion is hemispherical.

3. the detection unit is cylindrical, The outer diameter of the detection unit is 4 mm or more, 3. The capacitance-type corrosion sensor according to claim 1, wherein the capacitance-type corrosion sensor has a diameter of 50 mm or less.

4. The method for installing the capacitance type corrosion sensor according to any one of claims 1 to 3, a step of fixing the capacitance-type corrosion sensor to one of the steel materials facing each other; and embedding the capacitance-type corrosion sensor in the concrete structure having the steel material, A method for installing a capacitance type corrosion sensor, characterized in that the capacitance type corrosion sensor is positioned between the opposing steel materials.

5. 5. A method for installing a capacitance-type corrosion sensor as described in claim 4, characterized in that the capacitance-type corrosion sensor is arranged so that its longitudinal direction is along the direction in which the steel material to which the capacitance-type corrosion sensor is fixed extends.

6. 5. The method for installing a capacitance-type corrosion sensor according to claim 4, wherein the capacitance-type corrosion sensor is installed so that the longitudinal direction of the capacitance-type corrosion sensor is aligned vertically.

7. A method for installing a capacitance type corrosion sensor as described in any one of claims 4 to 6, characterized in that in a cross section of the concrete structure including the capacitance type corrosion sensor perpendicular to the central axis of the capacitance type corrosion sensor, the area of ​​the concrete that constitutes the concrete structure is larger than the area of ​​the capacitance type corrosion sensor.

8. A method for installing a capacitance-type corrosion sensor as described in any one of claims 4 to 7, characterized in that in the region of the concrete structure sandwiched between cross sections perpendicular to the central axis of the capacitance-type corrosion sensor at both end positions of the capacitance-type corrosion sensor, the volume of the concrete that constitutes the concrete structure is larger than the volume of the capacitance-type corrosion sensor.

9. The capacitance-type corrosion sensor is positioned so that its longitudinal direction is along the extending direction of four surrounding steel materials that extend in the same direction, A method for installing a capacitance-type corrosion sensor as described in any one of claims 4 to 8, characterized in that in a cross-sectional region surrounded by the four steel materials and perpendicular to the four steel materials, the area of ​​the concrete that constitutes the concrete structure is larger than the area of ​​the capacitance-type corrosion sensor.

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