JP2017032515A - Corrosion sensor and corrosion detection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-precision, low-cost corrosion sensor which allows for monitoring risk of corrosion and progression of a corrosion environment.SOLUTION: A corrosion sensor is for detecting corrosion environment of concrete or steel, and comprises a detection portion comprising a corrosive metal formed into a plate, foil, or film, a counter electrode comprising a corrosion resistant metal formed into a plate, foil, or film and being disposed at a position opposite the detection portion, a dielectric material disposed between the detection portion and the counter electrode, first conductors connected to the detection portion, and a second conductor electrically connected to the counter electrode. The detection portion has an area of 300 nmto 20,000 nm, inclusive, and an electrical property thereof changes in response to reduction in area of the detection portion due to corrosion.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a technique for detecting a corrosive environment state of concrete or steel.

  Steel materials in concrete structures are protected from corrosion by forming a passive film on the steel material surface because the concrete maintains an alkaline environment. However, for example, if a corrosive factor such as carbon dioxide in the air, sulfuric acid in the sewerage facility, or chloride ions enters the concrete, the passive film is destroyed, and the steel and steel are corroded by water and oxygen in the concrete. Start. Moreover, in the structure using steel materials, such as an iron bridge and a plant, the protective coating is used so that rust may not arise in steel materials.

  When steel in a concrete structure is corroded, the steel expands in volume, and the expansion pressure causes cracks in the concrete. As it progresses, the function as a concrete structure can no longer be maintained.

  Therefore, before the corrosion of the steel material starts, the invasion of the corrosion factor and the start of corrosion of the steel material are detected. It is important to promote preventive maintenance of structures. Various corrosion diagnosis methods have been proposed for this problem. For example, a method of analyzing the corrosion factor by removing the core, a method of non-destructively measuring the natural potential and polarization resistance of the steel material, a method of detecting the corrosion factor by a chemical sensor or a gas sensor, a simulated corrosion member using a steel thin wire For example, a method of detecting corrosion when buried in concrete and the fine wire is broken is known.

  Among these corrosion diagnosis methods, the method of detecting corrosion by breaking a fine wire is: (a) the sensor is embedded in advance so that the core is not damaged, such as core removal, (b) the fine wire between the concrete surface and the steel material It is possible to monitor the time dependency of the invasion of corrosion factors from the surface by installing several depending on the depth, making it easy to make a maintenance plan. (C) Corrosion factors because iron corrosion is directly captured It is possible to detect the possibility of corrosion including not only the supply state of water and oxygen, but also (d) because it captures changes in electrical resistance, it can be detected with extremely low power consumption and is suitable for long-term monitoring. Various corrosion diagnosis methods by detecting fine wire cutting have been proposed (for example, Patent Documents 1 to 3). Also, a corrosion sensor using an iron foil material has been proposed in order to increase sensitivity and increase design freedom (Patent Document 4).

JP-A-8-0945557 JP-A-8-233896 Japanese Patent No. 3205291 JP 2012-145330 A

“Development research of non-destructive monitoring system for chloride infiltration process in concrete. Annual report of concrete engineering, Vol.23 NO.1, 2001”

  However, all conventional corrosion sensors capture electrical resistance. Iron with high conductivity has a problem that the resistance value hardly changes unless it breaks, and the sensitivity of the sensor tends to depend on the wire diameter, the wire width, and the like. Moreover, when evaluating the corrosion sensor alone, it is impossible to grasp how much the corrosion factor has developed in the concrete structure. Furthermore, if the detector is broken, the sensor function is lost.

  The present invention has been made in view of such circumstances, and it is possible to grasp the progress of a corrosive environment together with the risk of corrosion, and a capacitance type capable of achieving high accuracy and low cost. An object is to provide a corrosion sensor and a corrosion detection method.

(1) In order to achieve the above object, the present invention takes the following measures. That is, the corrosion sensor of the present invention is a corrosion sensor for detecting the corrosive environment of concrete or steel material, and has a detection part formed in a plate shape, a foil shape or a film shape with a corrosive metal, and has a corrosion resistance. A counter electrode provided at a position facing the detection unit, a dielectric provided between the detection unit and the counter electrode, and a plurality of first electrodes connected to the detection unit. And a second energization unit electrically connected to the counter electrode, wherein the detection unit has an area of 300 mm ² or more and 20,000 mm ² or less.

Thus, since the dielectric provided between the detection unit and the counter electrode is provided, the electrical characteristics such as dielectric loss tangent and capacitance change according to the decrease in the area of the detection unit due to corrosion. This makes it possible to capture the progress of the corrosive environment according to the area of the detection unit. The area of the detection unit can be measured as a sensor for a long time by having an area of 300 mm ² or more. Furthermore, it is possible to make it less susceptible to the effects when the aggregate contained in the concrete impedes the penetration of corrosion factors. In addition, by setting the sensor area to 20,000 mm ² or less, it can be formed in a size that does not affect the performance of the reinforcing bars and concrete in the structure, making it easy to manufacture and store, and to detect corrosion. It becomes easy to install in the place to do. Moreover, since the several 1st electricity supply part connected to the detection part is provided, it becomes possible to grasp | ascertain which part of the detection part corroded. In addition, since a plurality of first current-carrying parts are provided, even if any of the surroundings of the first current-carrying part is corroded and disconnected, other detection state and other connected state There is a high possibility that one energization part exists. Therefore, corrosion detection can be performed continuously for a long time.

  (2) Further, in the corrosion sensor of the present invention, the detection unit is provided with a plurality of through holes.

  As described above, since the detection unit has a plurality of through holes, corrosion factors stay, corrode the detection unit, and also cause a horizontal (lateral) corrosion reaction. Since it has the effect of accelerating the cross-sectional defect due to, it is possible to increase the sensitivity to the corrosion factor and to be easily corroded. Moreover, since the corrosion sensitivity of the part with the through hole of the detection part is high and the corrosion does not easily progress in the part without the through hole, this is selectively combined, for example, the vicinity of the first energization part It is possible to form a selectively corroding region if it is made of a flat metal having no through hole and the detection part has a through hole.

  (3) Moreover, the corrosion sensor of this invention WHEREIN: The planar shape of the said through-hole is a circle | round | yen, It is characterized by the above-mentioned.

  Thus, since the planar shape of the through hole is a circle, formation accuracy and yield are improved in formation by etching. When corners occur in the shape of the object to be formed, cracks occur in the corners due to the stress of metal dissolution during etching, or the etching solution stays in the corners and the metal dissolution proceeds locally. May not be formed. When the through-hole is circular, such stress is easily dispersed, and the corner portion does not stay. Therefore, the formation accuracy and the yield in the production of the through-hole of the detection portion are improved. As a result, it becomes possible to contribute to stabilization of quality and cost reduction.

  (4) Further, the corrosion sensor of the present invention is characterized in that the counter electrode is a metal bar.

  Thus, since the counter electrode is a metal bar, it is not necessary to create a thin counter electrode. Because it is rod-shaped, it is more robust and less susceptible to damage than a corrosion sensor that takes the form of a card or sheet. Moreover, it becomes possible to make a counter electrode compact with respect to the area of a detection part.

  (5) Moreover, in the corrosion detection method of the present invention, an alternating electric field is applied between the first energization part and the second energization part of the corrosion sensor according to any one of (1) to (4) above, It is characterized in that the progress of corrosion of the corrosion sensor is specified based on a change in electrical characteristic value caused by corrosion of the detection part of the corrosion sensor.

As described above, since the dielectric provided between the detection unit and the counter electrode is provided, the electrical characteristics such as dielectric loss tangent and capacitance change according to the decrease in the area of the detection unit due to corrosion. It is possible to capture the progress of the corrosive environment according to the area of the surface. The area of the detection unit can be measured as a sensor for a long time by having an area of 300 mm ² or more. Furthermore, it is possible to make it less susceptible to the effects when the aggregate contained in the concrete impedes the penetration of corrosion factors. In addition, by setting the sensor area to 20,000 mm ² or less, it can be formed in a size that does not affect the performance of the reinforcing bars and concrete in the structure, making it easy to manufacture and store, and to detect corrosion. It becomes easy to install in the place to do.

  (6) Moreover, the corrosion detection method of the present invention is a method for insulating the corrosion sensor according to any one of (1) to (4) above on a surface of a steel material of a concrete structure or a steel structure, A corrosion detection method for applying an AC electric field to a sensor to detect a corrosion progress state, wherein the corrosion progress state of the corrosion sensor is specified based on a change in an electrical characteristic value caused by corrosion of a detection portion of the corrosion sensor. It is characterized by that.

  Thus, since it sticks to a reinforcing bar or steel material, it is not necessary to ensure a large attachment space, it becomes possible to attach a corrosion sensor easily, and it becomes possible to avoid damage to a corrosion sensor.

  According to the present invention, it is possible to capture the progress of the corrosive environment according to the area of the detection unit. That is, it becomes possible to grasp the current state of corrosion more accurately by the area of the plate-like, foil-like, or film-like detection portion as compared with the method of detecting the resistance change due to the cutting of the iron foil or the thin wire. Moreover, since the detection part is provided with the area | region which has several through-holes, the sensitivity of a detection part can be improved and it can make it easy to corrode. As a result, it is possible to accurately associate the reduction in the area of the detection unit due to corrosion with the actual corrosion state, and it is possible to improve measurement sensitivity.

It is the figure which compared the existing resistance type corrosion sensor and the corrosion sensor of this invention. It is a figure which shows the concept of the corrosion sensor which concerns on this embodiment. It is a figure which shows schematic structure of the corrosion sensor which concerns on 1st Embodiment. It is a figure which shows schematic structure of the corrosion sensor which concerns on 2nd Embodiment. It is a figure which shows schematic structure of the corrosion sensor which concerns on 3rd Embodiment. It is a flowchart which shows the manufacturing method of the corrosion sensor which concerns on this embodiment. 1 is a diagram illustrating Example 1. FIG. FIG. 6 is a diagram showing Example 2. FIG. 6 is a diagram showing Example 3. It is a figure which shows the comparative example of the sensor of a mesh shape which concerns on this embodiment, and the sensor which does not have a through-hole. It is a figure which shows the comparative example of a sensor with a large area, and a sensor with a small area about a mesh-shaped sensor. It is a figure which shows the difference in the electrostatic capacitance value in each cycle by the measurement frequency at the time of salt water immersion of the capacitive corrosion sensor which concerns on this embodiment. It is the figure which showed the relationship between an area reduction rate and an electrostatic capacitance with the measured value of a theoretical value by making the electrostatic capacitance value after 1 cycle progress into the initial value of corrosion area rate 0%. It is a figure which shows the outline | summary of a test body. It is a figure which shows the outline | summary of the sensor embed | buried in a mortar test body. It is a figure which shows the result of the dielectric loss tangent measured in each cycle. It is a figure which shows the result of the electrostatic capacitance measured in each cycle.

[Outline of corrosion sensor]
FIG. 1 is a diagram comparing an existing resistance-type corrosion sensor and the corrosion sensor of the present invention, and FIG. 2 is a diagram showing a concept of the corrosion sensor according to the present embodiment. In FIG. 1, the existing resistance type corrosion sensor is shown on the left side of the paper (a). This existing resistance-type corrosion sensor detects electrical resistance that changes with the progress of corrosion, and is suitable for determining the presence or absence of a corrosion factor. However, the subsequent progress of corrosion cannot be detected.

  On the other hand, in FIG. 1, the corrosion sensor of the present invention is shown on the right side of the drawing (b). As shown in FIG. 2, the corrosion sensor includes a dielectric 5 formed of a resin film between a detection unit 1 formed of iron foil and a counter electrode 3 formed of a stable metal film, The lead wire 15a which comprises 1 energization part, and the lead wire 15b which comprises the 2nd electricity supply part are provided. In FIG. 2, the lead wire 15 a constituting the first energization unit is described as a single one, but the present invention is not limited to this. That is, a plurality of lead wires 15a constituting the first energization unit may be provided.

  Then, electrical characteristics such as capacitance, dielectric loss tangent, reactance, and parallel equivalent resistance that change with the progress of corrosion are detected. As shown in FIG. 1, (1) When the salt content penetrates into the concrete, (2) the corrosion factor reaches the detection part and the reaction starts. (3) A change in electrical characteristics is detected when a cross-sectional defect occurs in the detection unit. In order to detect changes in electrical characteristics, it is possible to evaluate not only the presence or absence of corrosion factors, but also the degree of subsequent corrosion development. In the present embodiment, an example is shown in which the shape and dimensions corresponding to the corrosion of reinforcing bars in concrete are specified, and the degree of freedom of the installation method of the corrosion sensor is increased to expand the application range and utilization method of the corrosion sensor.

[Measurement principle of corrosion sensor]
The dielectric loss tangent tanδ of the parallel plate conductor (detector) has the following relationship with ω: angular frequency, C: capacitance, and R: series equivalent resistance.
tanδ = ωCR (1)

The capacitance C of the parallel plate conductor (detecting unit) has the following relationship between the area S of the parallel plate conductor and the interval d between the parallel plate conductors.
C = Q / V = εS / d [F] (2)
Here, ε is a dielectric constant.

  The corrosion sensor according to the present embodiment uses this principle. That is, when the detection part of the sensor is corroded by a corrosive factor, the area of the opposing parallel plate conductors decreases, and the electrical characteristics change accordingly. By grasping the degree of change in the electrical characteristics, it is possible to grasp the reduction in the area of the detection unit, and thus the progress of corrosion.

  Further, the points to be noted in the corrosion sensor are as follows. That is, the detection unit needs to be a material that reacts with a corrosion factor. Next, in order to function as a corrosion sensor using capacitance as an electrical property, it is necessary to generate a cross-sectional defect, and thus it is necessary for the detection unit to disappear due to corrosion. In the present embodiment, these problems are solved by configuring the detection unit with a very thin iron foil. In addition, if the detection unit is totally corroded and disappears, it is impossible to evaluate the subsequent corrosion progress, and thus a size that requires a long period of time until the entire surface disappears is required. Furthermore, since it is used by being embedded in concrete, it is necessary to determine the attachment method and direction of the corrosion sensor. In addition, it is necessary to determine dimensions and shapes so as to eliminate the influence of aggregate used in concrete.

[First Embodiment]
FIG. 3 is a diagram illustrating a schematic configuration of the corrosion sensor according to the first embodiment. The corrosion sensor 20 is manufactured by rolling iron, and has an iron foil part 3 as a detection part having a thickness of 3 μm or more and 0.1 mm or less, a dielectric 7, and a lead wire connected to the iron foil part. 9, a counter electrode (not shown), and a lead wire connected to the counter electrode. The reason why the thickness of the iron foil portion is 3 μm or more and 0.1 mm or less is that if the thickness is too thin, the detection portion is liable to crack when the sensor is handled, and if the thickness is too thick, the sensitivity of the sensor may be lowered. Further, the area of the detection unit is 300 mm ² or more, preferably the area of the square of the maximum aggregate dimension Gmax in the concrete, more preferably 700 mm ² or more. By setting the area of the detection unit to 300 mm ² or more, it is possible to measure as a sensor for a long period of time by suppressing the rapid progress of the corrosion reaction of the detection unit.

In addition, the maximum size of aggregate used in concrete is often the size that passes through a 20 mm x 20 mm sieve or the one that passes through a 25 mm x 25 mm sieve, so the area of the detector is 300 mm. ^By setting it to ² or more, it can be made difficult to be affected by the aggregate such as an error factor caused by the aggregate coming directly above the detection unit. Moreover, it is preferable that the area of a detection part shall be 20,000 mm < ² > or less. By setting the area of the sensor to 20,000 mm ² or less, it can be formed in a size that does not affect the performance of the reinforcing bars and concrete in the structure, making it easy to manufacture and store, and to the place where corrosion is detected Installation is easy.

  An anticorrosion film made of a material that does not corrode may be provided on the iron foil portion 3 including the lead wire 9 or the entire outer edge portion.

[Second Embodiment]
FIG. 4 is a diagram illustrating a schematic configuration of a corrosion sensor according to the second embodiment. The corrosion sensor 10 is formed in a card shape (rectangular shape). The detection unit 11 includes a plurality of through holes, a first region formed in a mesh shape, and a second region having no through holes. A lead wire 15 is connected to the second region. The dimension of the corrosion sensor 10 is “50 mm × 70 mm”. Note that the planar shape of the plurality of through holes provided in the first region is a circle. This improves the sensor formation accuracy and yield.

[Third Embodiment]
FIG. 5 is a diagram showing a schematic configuration of a corrosion sensor according to the third embodiment. The corrosion sensor 13 is formed in a long-axis shape in which the card-shaped (rectangular) detection units shown in the first embodiment are continuously provided. The detection unit 14 is provided with a plurality of through holes, and a region formed in a mesh shape and a region having no through holes are alternately arranged. In addition, lead wires 15 are respectively provided at a plurality of locations in the region having no through hole. Thus, by providing a plurality of lead wires 15, it is possible to grasp how far the detection unit 14 has been corroded. Moreover, even if the periphery of some lead wires corrodes and breaks, it is possible to measure using other lead wires.

  The central portion of the right half of FIG. 5 is provided with a through hole in a part of the outer periphery that does not have the through hole of the detection unit made of metal, and a portion that is easily corroded in the vertical direction of the detection unit. Thus, by providing a through-hole in a part of the outer periphery that is difficult to corrode, the progress of the corrosion is accelerated at the part as compared with the other outer periphery. Therefore, when the location corrodes in the vertical direction, the current-carrying part in the central part and the current-carrying part on the right side will not be energized. Can be identified.

  In FIG. 5, the connection point 17 of the lead wire 15 is covered with a material that does not rust, such as resin. The dimension of the corrosion sensor 13 is “30 mm × 120 mm”. In the present embodiment, the planar shape of the plurality of through holes provided is a circle. This improves the sensor formation accuracy and yield.

[Method of manufacturing corrosion sensor]
FIG. 6 is a flowchart showing a method for manufacturing a corrosion sensor according to the present embodiment. First, iron is rolled to produce an iron foil (step S101). The iron foil has a thickness of 3 μm or more and 0.1 mm or less. Here, the iron foil may be a thin film formed by vapor deposition or plating, or may be formed in a plate shape. The reason why the thickness is set to 3 μm or more and 0.1 mm or less is that if the thickness is too small, the detection part is likely to crack when the sensor is handled, and if the thickness is too large, the sensitivity of the sensor may be lowered.

  Next, bonding of the iron foil material and the polyimide material is performed (step S102), and resist printing of the sensor pattern is performed (step S103). Next, chemical etching is performed (step S104). Here, a through hole is also formed. Next, a counter electrode plate as a counter electrode is formed (step S105). Here, for example, sputtering, metal vapor deposition, plating, metal paint, metal plate / metal foil sticking, and the like can be used. Next, the lead wire is connected and waterproofed (step S106), the exterior of the sensor is applied (step S107), and the process ends.

  The area of the iron foil serving as the detection unit is such that the progress of corrosion can be grasped in stages, and the shape of the iron foil is rectangular, but the present invention is not limited to this. The detection unit can be replaced with iron foil and replaced with the same material as the material whose corrosion state is to be measured, and may be a metal such as stainless steel or aluminum.

  A plurality of through holes are provided in the region of the iron foil as the detection unit, and are formed in a mesh shape. Since such a plurality of through-holes are provided, the corrosion easily proceeds, and even when a part of the corrosion is damaged due to limited corrosion, the iron foil is less likely to be left in the form of an island, and the electrical As a result, it is possible to ensure accurate continuity, and to accurately capture the amount of decrease in the area of the detection portion by a change in electrical characteristics. 4 and 5, the shape of each through-hole is circular from the viewpoint of yield, but the present invention is not limited to this, and can be rectangular or other shapes.

  Moreover, the detection part can also selectively combine the area | region which provided the through-hole, and the area | region without a through-hole in order to improve corrosion sensitivity according to the objective. By creating in combination as described above, it is possible to create a location where cross-sectional defects due to corrosion are unlikely to proceed, such as in the vicinity of a current-carrying portion, or a location where corrosion is caused early.

  As is clear from the equation (2), since the decrease in the dielectric constant and the reduction in the area of the iron foil are greatly involved in the decrease in the capacitance, the dielectric must be a dielectric having a dielectric constant of 3 or more. Desirably, the thickness is preferably 0.05 mm to 2 mm, and a dielectric that is less susceptible to temperature change is desirable. Thereby, the measurement sensitivity of the sensor can be improved. In this embodiment, the dielectric is made of a polyimide film, and the dielectric constant is 3.3.

  The counter electrode is preferably made of a metal having a high corrosion resistance. In order to capture the reduction due to the corrosion of the iron foil in terms of electrical characteristics, it is assumed that the area of the metal part does not change. The counter electrode includes a noble metal represented by gold, platinum, palladium, and the like, and is a metal having a lower ionization tendency than the target metal and having conductivity, and in the case of iron, palladium, copper, nickel, etc. Can be used. In addition to the rolled metal foil, there is a method of forming a film by sputtering, vapor deposition, plating, or the like. The thickness of the counter electrode is not limited.

  As shown in FIG. 5, a corrosion prevention film may be provided on the outer edge portion of the detection unit 14 including the lead wire 15 with a material that does not corrode. For example, a metal such as a resin or platinum can be used. . Among them, it is preferable to use an insulator such as a resin in order to grasp the progress of corrosion step by step. This resin may be applied or a seal may be attached. On the other hand, in the case of using a metal, in addition to gold or platinum, it is possible to use a noble metal from the detection part that is a material of the coating, such as palladium, copper, lead, tin, nickel, or an alloy thereof, and wet. The foil layer can be formed by a plating method, a dry plating method, or vapor deposition. In the case of using a metal, a potential difference with the detection unit is generated and corrosion progresses quickly, which is useful when it is desired to perform early corrosion detection.

  Moreover, it is preferable that an exterior material is formed with an insulator. For example, resin materials and ceramics. In the case of a conductive material, it is not preferable because it may be electrically connected to external concrete or the electrical characteristics of the detection unit may become unstable in AC measurement. When installing a corrosion sensor in concrete, fix it to the actual rebar with a cable tie, etc., and fix it so that the sensor does not move or fall off during construction. Moreover, you may affix on a reinforcing bar with an adhesive agent etc.

  FIG. 7A is a diagram illustrating the first embodiment. The card-shaped corrosion sensor 10 is installed in the cover of the concrete structure 60 so as to be parallel to the concrete surface.

  FIG. 7B is a diagram illustrating the second embodiment. The long-axis corrosion sensor 13 is installed along the reinforcing bar 62 in the concrete structure 61.

  FIG. 7C is a diagram illustrating the third embodiment. The long-axis corrosion sensor 13 is wound around a rod-shaped base 63 and used as a sensor unit. The base 63 is made of, for example, polished steel bar, and the long-axis corrosion sensor 13 is installed along the base 63. In this way, by adopting a rod-shaped sensor shape, it becomes possible to install along the reinforcing bars in the structure, so that the sensor is not easily damaged, and in addition to pouring concrete into the concrete formwork Since it does not hinder filling, it can be installed in a structure without special consideration. In this case, it is preferable to insulate the steel material from the counter electrode using an adhesive, a vinyl chloride coupler, or the like.

  A corrosion sensor can also be configured by forming a rod-like base material with a metal material, attaching a dielectric and a detection portion, and connecting a lead wire to the base material. In this case, since the rod-shaped base material also serves as the counter electrode, it is difficult to break and can be made compact even if the area of the detection unit is large.

  It is also possible to wrap the corrosion sensor 13 directly on a steel material such as a reinforcing bar. In this case, the sensor is not easily damaged, and filling of the concrete formwork is not hindered when pouring the concrete. In this case, since there is a risk of being affected by electricity in the structure, it is preferable to insulate the steel material and the counter electrode using an adhesive, a coupler made of vinyl chloride, or the like.

[Performance evaluation of corrosion sensors]
FIG. 8 is a diagram illustrating a comparative example of a mesh-shaped sensor according to the present embodiment and a sensor having no through hole. As shown in FIG. 8, the capacitance ratio changes according to the elapsed time (corrosion cycle), but the sensor that does not have a through-hole has a delayed reaction time due to a corrosion factor, and sensitivity is reduced. On the other hand, a mesh-shaped sensor has high sensitivity to corrosion factors, and the capacitance ratio decreases with the elapsed time, so the reaction time due to the corrosion factors is clear, the corrosion factors penetrate, and the sensor It is easy to grasp the time when it reached.

  FIG. 9 is a diagram illustrating a comparative example of a sensor having a large area and a sensor having a small area, with respect to a mesh-shaped sensor. As is clear from FIG. 9, the time when the capacitance ratio abruptly decreases according to the elapsed time is the same both by providing the through-holes. It is possible to grasp. Furthermore, when the elapsed time increases, a sensor with a small area shows a minimum value relatively quickly, whereas a sensor with a large area has a long measurable period. Therefore, it can be said that a sensor having a mesh shape preferably has a larger area of the detection unit when long-term monitoring is performed.

[Application to steel structures]
When applying protective paint to metal structures to be measured, such as steel bridges, plant equipment, street lamps, underground pipes, tanks, ships, etc., the surface of the metal material before application according to this embodiment Affix the sensor with an adhesive. When affixing, since it may be influenced by the electrical state of the structure, it is preferable to insulate with a resin tape, seal, or adhesive itself. The detection part of the sensor can be replaced with the same material as that whose corrosion state is desired to be measured, and may be made of a metal such as stainless steel or aluminum instead of the iron foil. Thereafter, a protective coating is applied in the same manner as the metal structure. The cable may or may not come out of the protective coating. When not using a cable, embed the sensor directly under the paint film. When measuring, peel off the paint film covering the sensor and connect a measuring instrument directly to measure the electrical signal associated with corrosion. To do. Alternatively, the measurement may be performed electromagnetically using a wireless method. Thus, the sensor can be installed without causing a coating film defect that occurs when the cable is pulled out.

[Performance evaluation of corrosion sensors]
The present inventors have confirmed the difference in capacitance value depending on the measurement frequency of the corrosion sensor according to the present embodiment. In this embodiment, an iron foil part was formed with an iron foil having a diameter of 22 mm, adhered onto a 0.105 mm thick polyimide film (dielectric constant 3.3), and a through hole was formed by chemical etching. Also, gold was deposited as a counter electrode on the surface opposite to the iron foil bonding surface of the polyimide film as the dielectric by sputtering. The through hole has a mesh type and a plurality of slits. The present inventors dipped the corrosion sensor according to the present embodiment in a 3% NaCl aqueous solution, and visually observed the corrosion state for each cycle, with 7 days as one cycle. Capacitance is measured by taking out the corrosion sensor from the immersion liquid, removing the water adhering to the surface, and then measuring the capacitance between the end of the iron foil and the counter electrode with a tweezer probe. did. Measurement conditions were carried out under an alternating electric field of 1 V from 100 Hz to 100 kHz using an LCR meter. The apparatus used in the experiment is shown in the following table. The corrosion area of each cycle by visual observation was 0% in the first cycle, 20% in the second cycle, 60% in the third cycle, and 80% in the fourth cycle.

  FIG. 10 is a diagram illustrating the difference in capacitance value in each cycle depending on the measurement frequency when the corrosion sensor according to this embodiment is immersed in salt water. In FIG. 10, at any frequency, it can be seen that the capacitance increases in the first cycle from before the test, and thereafter the capacitance decreases. Moreover, the difference between the cycles tended to be slightly smaller as the measurement frequency was higher. Moreover, in any cycle, the capacitance tends to decrease as the measurement frequency increases. Therefore, since the correlation between the corrosion area and the capacitance is increased, the progress of the corrosion can be grasped well, and the variation factor due to the corrosion factor of the electrolyte represented by the salinity can be eliminated, so the measurement frequency is 50 kHz. In addition, it is preferable to measure at 100 kHz or more.

  FIG. 11 is a diagram showing the relationship between the area reduction rate and the capacitance, together with the actual measured value, with the capacitance value after one cycle elapsed as the initial value of the corrosion area rate of 0%. FIG. 11 shows both a mesh type and a slit type detection unit among the corrosion sensors according to the present embodiment. Two solid lines indicate the theoretical values of the mesh type and the slit type, respectively. The quadrangular plot shows the actual measurement value of the mesh type, and the triangular plot shows the actual measurement value of the slit type. As shown in FIG. 11, although the measured value of the capacitance of the corrosion sensor according to the present embodiment is different from the theoretical value, the correlation between the corrosion area ratio and the capacitance is high. In particular, the corrosion area ratio of 60% or more closely approximates the theoretical relationship between the corrosion area ratio and the capacitance, and it can be said that the corrosion area can be accurately grasped by measuring the capacitance. Therefore, among the electrical characteristics, it is preferable to use a capacitance that can accurately grasp the progress of the corrosive environment.

[Performance evaluation of corrosion sensor by accelerated test using mortar specimen]
For the purpose of confirming the performance of the corrosion sensor according to the present embodiment in mortar, evaluation was made by an accelerated test using a test body kneaded with salt.

[Outline of specimen]
The mortar specimen was a 1: 3 mortar with a water cement ratio of 65%, and NaCl was added so that the amount of chloride ions was 4.8 kg / m ³ . FIG. 12 is a diagram showing an outline of the test specimen. Here, the test body was 100 mm × 100 mm × 100 mm in size. A level in which a corrosion sensor was embedded at a position of 15 mm (FIG. 12B) and a level in which a polished steel bar of φ20 mm × 130 mm was embedded for measurement of the corrosion area (FIG. 12A) were prepared. In addition, the surface of the test body was left only on one surface where salt water permeation was performed, and the other surface was covered with an epoxy resin.

[Sensor embedded in mortar specimen]
FIG. 13 is a diagram showing an outline of a sensor embedded in a mortar specimen. As shown in FIG. 13, the corrosion sensor 100 is spaced from the acrylic case 113 by an O-ring 115 and bonded to the acrylic case 113 by an epoxy resin 117. Since this corrosion sensor 100 measures the dielectric loss tangent and capacitance from the outside of the test body, only the iron foil portion 103 is exposed on the surface so that the lead wire 109 is soldered and the connection portion of the lead wire 109 is not corroded. As shown, the outer case is covered with an acrylic case 113 and the inside of the case is filled with a resin 121. The reason for this construction is to prevent the rust of the lead wires and to avoid the influence of the concrete itself filled with the dielectric itself due to the dielectric and the dielectric constant fluctuating depending on the water content. It also has the meaning of protecting the sensor from impact when filling concrete. In the present embodiment, the acrylic case 113 is used. However, this is not always necessary, and if the above purpose can be achieved, the acrylic case 113 is not used, for example, only the resin. I do not care.

[Conditions for accelerated testing of mortar specimens]
The conditions of the acceleration test were immersed in a 10% NaCl aqueous solution at 40 ° C. for 2 days and dried for 5 days in a 60% RH environment, and one cycle was performed, and a total of 10 cycles of the acceleration test was performed. The capacitance and dielectric loss tangent of the corrosion sensor were measured using an LCR meter at the end of each cycle. The measurement condition was an AC voltage of 1 V, and the measurement frequency was fixed at 100 kHz with reference to the measurement result of the salt water immersion experiment. FIG. 14 is a diagram showing the results of dielectric loss tangent measured in each cycle for three identical sensors M-1, M-2, and M-3. FIG. 15 is a diagram illustrating the results of capacitance measured in each cycle for three identical sensors M-1, M-2, and M-3. The initial value was the result measured after demolding the test specimen and before immersing it in salt water.

  The dielectric loss tangent increased gradually from 3 cycles for M-2 and M-3, and gradually increased from 6 cycles for M-1. On the other hand, the capacitance is found to decrease from 6 cycles for M-2 and M-3, from 7 cycles for M-1, and to decrease in stages for M-1 and M-2. .

  As described above, according to the present embodiment, it is possible to capture the progress of corrosion according to the area of the detection unit. That is, it becomes possible to grasp the current state of corrosion more accurately by the area of the plate-like, foil-like, or film-like detection portion as compared with the method of detecting the resistance change due to the cutting of the iron foil or the thin wire. Moreover, since the area | region which has a some through-hole is provided in the detection part, the detection sensitivity of corrosive environment can be improved and it can make it easy to corrode. As a result, corrosion in the detection unit can cause a change in electrical characteristics. As a result, it is possible to accurately associate the reduction in the area of the detection unit due to corrosion with the actual corrosion state, and it is possible to improve measurement sensitivity.

DESCRIPTION OF SYMBOLS 1 Detection part 3 Counter electrode 5, 7 Dielectric 9 Lead wire 10, 13, 20, 100 Corrosion sensor 11 Detection part 14 Detection part 15 Lead wire 15a Detection part lead wire 15b Counter electrode lead wire 17 Connection point 60 Concrete structure Object 61 Concrete structure 62 Reinforcing bar 63 Base material 103 Iron foil part 109 Lead wire 113 Acrylic case 115 O-ring 117 Epoxy resin 121 Resin

Claims (6)

A corrosion sensor that detects the corrosive environment of concrete or steel,
A detector formed of a corrosive metal plate, foil or film;
A counter electrode formed of a metal having corrosion resistance and provided at a position facing the detection unit;
A dielectric provided between the detection unit and the counter electrode;
A plurality of first energization units connected to the detection unit;
A second energization part electrically connected to the counter electrode,
The corrosion sensor is characterized in that the detection section has an area of 300 mm ² or more and 20,000 mm ² or less.   The corrosion sensor according to claim 1, wherein the detection unit is provided with a plurality of through holes.   The capacitive corrosion sensor according to claim 2, wherein the planar shape of the through hole is a circle.   The corrosion sensor according to claim 1, wherein the counter electrode is a metal bar. An AC electric field is applied between the first energization part and the second energization part of the corrosion sensor according to any one of claims 1 to 4,
A corrosion detection method characterized in that the progress of corrosion of a corrosion sensor is specified based on a change in electrical characteristic value caused by corrosion of a detection portion of the corrosion sensor.   The corrosion sensor according to any one of claims 1 to 4 is insulated and attached to a surface of a steel material of a concrete structure or a steel structure, an AC electric field is applied to the corrosion sensor, and a corrosion progress state is detected. A corrosion detection method, wherein a corrosion progress state of a corrosion sensor is specified based on a change in an electrical characteristic value caused by corrosion of a detection portion of the corrosion sensor.

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