JP6574356B2 - Capacitance type corrosion sensor and corrosion detection method - Google Patents

Description

  The present invention relates to a technique for detecting a corrosive environment 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 corrosion start of the steel material is detected, and the steel material is protected from corrosion by preventing further invasion of the corrosion factor and water and oxygen by measures such as surface coating, 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 is capable of grasping the progress of corrosion as well as the risk of corrosion, and is capable of achieving high precision, miniaturization, and cost reduction. It is an object of the present invention to provide a capacitive 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 capacitive corrosion sensor of the present invention is a capacitive corrosion sensor that detects the corrosive environment of concrete or steel, and is formed of a corrosive metal in the form of a plate, foil, or film. A detection unit, a counter electrode formed in a plate shape, a foil shape, or a film shape with a metal having corrosion resistance, provided at a position facing the detection unit, and provided between the detection unit and the counter electrode. A dielectric, and the capacitance changes in accordance with a decrease in the area of the detection unit due to corrosion.

  As described above, the dielectric provided between the detection unit and the counter electrode is provided, and the capacitance changes in accordance with the decrease in the area of the detection unit due to corrosion. Therefore, the corrosion environment progresses according to the area of the detection unit. It is possible to capture the situation. 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.

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

  Thus, since the detection part is provided with the several through-hole, the area of a detection part can be made small and it can make it easy to corrode. As a result, the corrosion in the detection part reaches the dielectric and can cause a change in capacitance. 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.

  (3) Moreover, the electrostatic capacitance type corrosion sensor of the present invention is characterized in that the detection section is formed in a mesh shape.

  As described above, since the detection unit is formed in a mesh shape, even when a part of the detection unit is corroded and lost in a limited manner, electrical conduction is ensured, and the amount of reduction in the detection unit area is reduced. Can be accurately captured by a change in capacitance. 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 increase measurement accuracy.

  (4) Further, the capacitance type corrosion sensor of the present invention corresponds to the corrosion prevention film provided in the second region surrounding the first region including the center of the detection unit, and the second region. And a second energization unit electrically connected to the counter electrode. The first energization unit electrically connected to the detecting unit and the second energization unit electrically connected to the counter electrode.

  As described above, since the corrosion prevention film is provided in the second region surrounding the first region including the center of the detection unit, the second region that does not corrode always remains. That is, when the vicinity of the place where the current-carrying part is connected corrodes, the remaining part without being corroded and the current-carrying part are electrically disconnected, and an erroneous detection result may be obtained. However, since the second region remains due to the corrosion-preventing film, the entire area of the remaining detection portion and the energization portion can always be electrically connected. Thereby, measurement accuracy can be maintained.

  (5) Further, in the capacitance type corrosion sensor of the present invention, the dielectric has a dielectric constant of 3 or more.

  As described above, since the dielectric has a dielectric constant of 3 or more, the decrease in the area of the detection unit can greatly contribute to the decrease in the capacitance. Thereby, the measurement sensitivity of the sensor can be improved.

  (6) Further, the corrosion detection method of the present invention is a corrosion detection method for detecting the progress of a corrosive environment of the concrete structure embedded in the concrete structure, and any one of the above (1) to (5) The electrostatic capacity type corrosion sensor is embedded in the concrete structure, and the electrostatic capacity type corrosion sensor is based on the change in the electrostatic capacity value due to the corrosion of the detection part of the electrostatic capacity type corrosion sensor. It is characterized by identifying the progress of corrosion of the sensor.

  With this configuration, it is possible to capture the progress of corrosion according to the area of the detection unit. That is, it is possible to more accurately grasp the current state of corrosion and the state of progress in the area of the plate-like, foil-like or film-like detector compared with the method of detecting resistance change due to cutting of iron foil or thin wire Become.

  (7) Moreover, the corrosion detection method of the present invention is a corrosion detection method that is embedded in a concrete structure and detects the progress of corrosion of the concrete structure, and is any one of the above (1) to (5) A plurality of capacitive corrosion sensors described in 1. are connected in parallel to form a continuous sensor, and the continuous sensor is embedded in the concrete structure, and the detection part of the capacitive corrosion sensor is corroded. The position of the corroded capacitive corrosion sensor is specified based on the change in the combined capacitance value of the continuous sensor.

  In this way, since a plurality of capacitive corrosion sensors are connected in parallel to form a continuous sensor, the combined capacitance of the continuous sensors is determined by the sum of the capacitances of the capacitive corrosion sensors. Can be obtained. As a result, it is possible to calculate the decrease in the synthetic capacitance due to the reduction in the area due to corrosion of the detection unit by simple calculation, and it is possible to specify the position of the corrosive capacitance type corrosion sensor according to the synthetic capacitance. It becomes possible. Furthermore, because of the parallel connection, it is possible to easily increase or decrease the number of connected capacitive corrosion sensors.

  (8) Further, the corrosion detection method of the present invention is a corrosion detection method for detecting the progress of corrosion of the steel structure and the steel material by attaching to the surface of the steel structure and the steel material to be measured, The capacitance type corrosion sensor according to any one of 1) to (5) is affixed to the steel structure and the steel material surface, and the capacitance value due to corrosion of the detection part of the capacitance type corrosion sensor is measured. It is characterized in that the corrosion progress state of the capacitive corrosion sensor is specified based on the change.

  With this configuration, it is possible to capture the progress of corrosion according to the area of the detection unit. That is, it is possible to more accurately grasp the current state of corrosion and the state of progress in the area of the plate-like, foil-like or film-like detector compared with the method of detecting resistance change due to cutting of iron foil or thin wire Become.

  According to the present invention, it is possible to capture the progress of corrosion according to the area of the detection unit. That is, it is possible to more accurately grasp the current state of corrosion and the state of progress in the area of the plate-like, foil-like or film-like detector compared with the method of detecting resistance change due to cutting of iron foil or thin wire Become.

It is a top view which shows schematic structure of the electrostatic capacitance type corrosion sensor which concerns on this embodiment. It is sectional drawing of an electrostatic capacitance type sensor. It is a top view which shows schematic structure of the electrostatic capacitance type corrosion sensor which concerns on this embodiment. It is a top view which shows schematic structure of the 1st modification of the capacitive corrosion sensor which concerns on this embodiment. It is a top view which shows schematic structure of the 2nd modification of the capacitive corrosion sensor which concerns on this embodiment. It is a figure which shows the model of the evaluation result of the corrosion area rate by visual observation. 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 electrostatic capacitance measured in each cycle. It is a figure which shows a mode that the continuous sensor 50 was comprised by connecting three electrostatic capacitance type corrosion sensors in parallel. It is a figure which shows a mode that the connection sensor 51 was comprised by connecting three capacitive type corrosion sensors in parallel. It is a figure which shows the connection sensor 52 using three iron foil parts. It is a figure which shows the relationship between an electrostatic capacitance and the number of electrostatic capacitance type corrosion sensors.

[Measurement principle of capacitive corrosion sensor]
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] (1)
Here, ε is a dielectric constant.

  The capacitive corrosion sensor according to this 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 capacitance decreases accordingly. By grasping the degree of decrease in the capacitance, it is possible to grasp how the area of the detection unit is reduced, and thus the progress of the corrosive environment.

[First Embodiment]
[Configuration of Capacitive Corrosion Sensor]
FIG. 1 is a plan view showing a schematic configuration of a capacitive corrosion sensor according to the present embodiment. FIG. 2 is a cross-sectional view of the capacitive corrosion sensor 1 shown in FIG. 1 cut along AA. The capacitive corrosion sensor 1 is manufactured by rolling iron, and is provided in a mesh shape on the iron foil part 3 as a detection part having a thickness of 3 μm or more and 0.1 mm or less, and the iron foil part 3. A plurality of through holes 5, a dielectric 7, lead wires 9, and a counter electrode 10 are provided. The iron foil part 3 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. The area of the iron foil portion 3, so that it is possible to capture the corrosion progress stepwise, but it is preferably larger, is described herein as being a 3 cm ^2. Moreover, although the shape of the iron foil part 3 is circular, this invention is not necessarily 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.

  The iron foil part 3 is provided with a plurality of through holes 5 and is formed in a mesh shape. Since such a plurality of through-holes 5 are provided, the corrosion easily proceeds, and even when a portion of the corrosion is lost due to limited corrosion, the iron foil portion is rarely left in an island shape, Electrical continuity is ensured, and the reduction amount of the detection unit area can be accurately captured by the change in capacitance. In addition, in FIG. 1, although the shape of each through-hole 5 is made into the rectangle (square), this invention is not necessarily limited to this, It can also be set as circular and another shape. Further, the lead wire 9 constitutes a first energization part electrically connected to the iron foil part 3 and a second energization part electrically connected to the counter electrode 10.

  As is clear from the equation (1), the dielectric 7 is a dielectric having a dielectric constant of 3 or more because the decrease in the dielectric constant and the reduction in the area of the iron foil part 3 are greatly involved in the decrease in the capacitance. It is desirable that the thickness is 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 the present embodiment, the dielectric 7 is made of a polyimide film, and its dielectric constant is 3.3. In FIG. 1, the iron foil part 3 was formed with an iron foil having a diameter of 22 mm, adhered onto a polyimide film having a thickness of 0.105 mm, and the through hole 5 was formed by chemical etching. Also, gold was formed by sputtering on the surface of the polyimide film as the dielectric 7 opposite to the iron foil bonding surface.

  The counter electrode 10 is preferably a metal having a high corrosion resistance. In order to capture the decrease due to the corrosion of the iron foil part by the capacitance, it is premised that the area of the metal part does not change. In addition to noble metals such as gold, platinum, and palladium, titanium, nickel, or the like, which is a metal having a lower ionization tendency than a target metal and having conductivity, and the target is iron, 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.

  Further, as shown in FIG. 3, it is preferable to provide a corrosion prevention film 30 with a material that does not corrode on the outer edge portion of the iron foil portion 3 including the lead wire 9, for example, a metal such as a resin or platinum is used. Can do. 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, use a metal that is more precious than the detection part that is the material of the coating, such as gold, palladium, titanium, nickel, tin, lead, copper, stainless steel, or an alloy thereof. The foil layer can be formed by a wet 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.

  FIG. 4A is a plan view illustrating a schematic configuration of a first modification of the capacitive corrosion sensor according to the present embodiment, and FIG. 4B illustrates a second configuration of the capacitive corrosion sensor according to the present embodiment. It is a top view which shows schematic structure of a modification. The capacitive corrosion sensor 2 shown in FIG. 4A is manufactured by rolling iron, and has an iron foil part 4 having a thickness of 3 μm or more and 0.1 mm or less, and a plurality of slits provided in the iron foil part 4. 6, a dielectric 7, and a lead wire 9. 4B is produced by rolling iron, and has an iron foil portion 41 having a thickness of 3 μm or more and 0.1 mm or less, a dielectric 7, a lead wire 9, and the like. Is provided. There are no through holes or slits. Thus, this invention can also take the form shown to FIG. 4A and FIG. 4B. As shown in FIG. 3, the corrosion prevention film 30 may be provided with a non-corrosive material on the outer edge of the iron foil part 4 or 41 including the lead wire 9 in FIGS. 4A and 4B. .

[Performance evaluation of capacitive corrosion sensor]
The inventor confirmed the correlation between the reduction in area due to corrosion of the iron foil portion 3 of the capacitive corrosion sensor according to this embodiment and the capacitance. The present inventor immersed the electrostatic capacitance type corrosion sensor of FIG. 1 according to the present embodiment in a 3% NaCl aqueous solution, and visually observed the corrosion state every cycle with 7 days as one cycle. And the change of the corrosion area rate and the electrostatic capacitance was measured. The capacitance is measured by taking out the capacitance type corrosion sensor from the immersion liquid, removing the moisture adhering to the surface, and then using a tweezer-like probe between the end of the iron foil portion 3 and the noble metal 10. Capacitance was measured. 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.

  FIG. 5 is a diagram showing a model of the evaluation result of the corrosion area rate by visual observation. The visual corrosion evaluation method evaluated the location where the iron foil was missing due to corrosion as the corrosion area. FIG. 5A shows the corrosion state of the iron foil part in the first cycle, and the evaluation result of the corrosion area rate by visual observation is 0%. FIG.5 (b) shows the corrosion state of the iron foil part of the 2nd cycle, and the evaluation result of the corrosion area rate by visual observation is 20%. FIG.5 (c) shows the corrosion state of the iron foil part of the 3rd cycle, and the evaluation result of the corrosion area rate by visual observation is 60%. FIG.5 (d) shows the corrosion state of the iron foil part of the 4th cycle, and the evaluation result of the corrosion area rate by visual observation is 80%. Thus, it was confirmed that the corrosion of the iron foil part progressed and the corrosion area rate increased with the progress of the cycle.

  FIG. 6 is a diagram illustrating the difference in capacitance value in each cycle depending on the measurement frequency when the capacitive corrosion sensor according to the present embodiment is immersed in salt water. In FIG. 6, it can be seen that at any frequency, 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, the correlation between the corrosion area and the capacitance is increased, and the progress of corrosion can be grasped well, or the fluctuation factor due to the corrosion factor of the electrolyte typified by salt can be eliminated, so the measurement frequency is It is preferable to measure at 50 kHz or more, more preferably 100 kHz or more.

  FIG. 7 is a graph showing the relationship between the area reduction rate and the capacitance, together with the actual measured value, with the capacitance value after one cycle elapses as the initial value of the corrosion area rate of 0%. FIG. 7 shows both a type having a plurality of through holes (mesh type) and a type having a plurality of slits (line type) among the capacitive corrosion sensors according to the present embodiment. Two solid lines indicate the theoretical values of the mesh type and the line 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 line type. As shown in FIG. 7, the measured value of the capacitance of the capacitive corrosion sensor according to the present embodiment has a correlation between the corrosion area ratio and the capacitance, although there is a deviation from the theoretical value. In particular, a corrosion area ratio of 60% or more closely approximates the theoretical relationship between the corrosion area ratio and the capacitance, and can be said to be accurately grasped by measuring the capacitance.

  In addition, it is thought that the mesh type sensor shown in FIG. 1 can catch progress of corrosion more easily than the line type sensor shown in FIG. This is because, in the case of a line-type sensor, depending on the site where corrosion occurs, the decrease in electrode area due to corrosion may not correspond to the decrease in electrode area calculated backward from the capacitance.

[Second Embodiment]
[Performance evaluation of capacitive corrosion sensor by accelerated test using mortar specimen]
For the purpose of confirming the performance of the capacitive 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. 8 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 (FIG. 8 (b)) in which a capacitive corrosion sensor was buried at a position of 15 mm in fog and a level (FIG. 8 (a)) in which a polished steel bar of φ20 mm × 130 mm was buried for corrosion area measurement 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. 9 is a diagram showing an outline of a sensor embedded in a mortar specimen. As shown in FIG. 9, the capacitance type corrosion sensor 1 is provided with a space between the O-ring 15 and the acrylic case 13 and is bonded to the acrylic case 13 with an epoxy resin 17. Since this capacitance type corrosion sensor 1 measures the capacitance from the outside of the specimen, only the iron foil portion 3 is placed on the surface so that the lead wire 9 is soldered and the connection portion of the lead wire 9 is not corroded. The case is covered with an acrylic case 13 so as to be exposed, and the inside of the case is filled with a resin 21. 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 13 is used. However, this is not always necessary, and if the above purpose can be achieved, the acrylic case 13 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. FIG. 10 is a diagram showing the results of capacitance measured in each cycle for two identical sensors M-1 and M-2. The initial value was the result measured after demolding the test specimen and before immersing it in salt water. Up to 3 cycles each, there is a slight downward trend from the initial value, but thereafter M-1 slightly increases to 4 cycles. Moreover, regarding M-2, there is almost no change until 6 cycles.

  It can be seen that a decrease in capacitance was observed from 6 cycles for M-1 and a decrease from 5 cycles for M-2, and M-1 was decreased stepwise. When M-2 is 7 cycles and M-1 is 8 cycles and the capacitance is 20 pF or less, no subsequent change is observed. In the sensor shown in FIG. 9, the lead wire connecting portion is protected with resin as compared with the state shown in FIG. 1, and an area of about 20% of the iron foil portion 3 does not act as a detecting portion. When evaluated by the electrostatic capacity obtained from the area acting as the detection part, when it reaches 20 pF, almost the entire exposed iron foil part 3 is missing. For this reason, it is thought that further corrosion progress cannot be grasped. That is, it can be said that the detection parts of all the sensors are lost in 6 to 8 cycles.

  The capacitance type corrosion sensor according to the present embodiment has a high correlation between the corrosion area ratio of the iron foil portion 3 as the detection portion and the capacitance, and has a basic performance capable of grasping the progress of corrosion. Yes. Moreover, in the accelerated test in the mortar containing salt content, it has been evaluated that the decrease in the capacitance of the capacitance type corrosion sensor according to the present embodiment has a function of capturing the occurrence of corrosion. Further, since the change in capacitance shows a step change before all the detection units are lost, the progress of corrosion can be evaluated by the capacitance type corrosion sensor according to the present embodiment.

  FIG. 11 is a diagram showing a state in which the continuous sensor 50 is configured by connecting three of the above-described capacitive corrosion sensors in parallel. The continuous sensor 50 has three capacitance type corrosion sensors 1 and 2 arranged in a staircase pattern in the cover depth direction.

  FIG. 12 is a diagram showing a state in which the above-described capacitance type corrosion sensor is connected in parallel to form a continuous sensor 51. The continuous sensor 51 is arranged obliquely so that the three capacitive corrosion sensors 1 and 2 are placed on a slope.

  FIG. 13 is a diagram showing a continuous sensor 52 using three iron foil portions 3. In the continuous sensor 52, the three iron foil portions 3 are arranged obliquely with the dielectric 7 and the counter electrode 10 in common.

  In the first to third embodiments, assuming that the capacitance of each capacitance type corrosion sensor is Q, in the initial state, the combined capacitance of the continuous sensors 50 to 52 is Q + Q + Q = 3Q.

  The continuous sensors 50 to 52 are embedded in the concrete structure. Thereafter, the detection portion of the capacitive corrosion sensor is corroded from the direction of the progress of the corrosion factor, and the area of the iron foil portion is reduced. Along with this, the combined capacitance value of the continuous sensors 50 to 52 also decreases. FIG. 14 is a diagram illustrating the relationship between the capacitance and the number of capacitance-type corrosion sensors. In the initial state, the combined capacitance value of the capacitive corrosion sensors connected in parallel is 3Q. Thereafter, when the detection portion of each capacitance type corrosion sensor is corroded sequentially and the area decreases, the combined capacitance value of the connection sensors 50 to 52 also decreases. In FIG. 14, the solid line portion is the combined capacitance value shown as a model.

  For example, a change in the combined capacitance value of the continuous sensors 50 to 52 due to the corrosion of the detection unit of the electrostatic capacitance type corrosion sensor of the continuous sensors 50 to 52 embedded in the concrete structure is, for example, This is grasped by the solid line shown in FIG. Depending on the combined capacitance value, it is possible to grasp which capacitance type corrosion sensor is corroded at the present time.

[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.

  As described above, according to the present embodiment, the dielectric is provided between the detection unit and the counter electrode, and the capacitance changes according to the decrease in the area of the detection unit due to corrosion. It is possible to grasp the progress of corrosion by 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 body as compared with the method of detecting the resistance change due to the cutting of the iron foil or the thin wire.

1, 2, 40 Capacitance type corrosion sensor 3, 4, 41 Iron foil part 5 Through-hole 6 Slit 7 Dielectric 9 Lead wire 10 Counter electrode 13 Acrylic case 15 O-ring 17 Epoxy resin 21 Resin 30 Corrosion prevention film 32, 34 Lead wire 50, 51, 52 Continuous sensor

Claims (8)

A capacitive corrosion sensor for detecting the corrosive environment of concrete or steel,
A detector formed of a corrosive metal plate, foil or film;
A counter electrode formed in a plate shape, foil shape or film shape with 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 capacitance-type corrosion sensor that detects the progress of corrosion based on a correlation between a decrease in the area of the detection unit due to corrosion and a decrease in capacitance .   The capacitive 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 1, wherein the detection unit is formed in a mesh shape. A corrosion prevention film provided in a second region surrounding the first region including the center of the detection unit;
A first energization unit electrically connected to a detection unit corresponding to the second region;
The capacitive corrosion sensor according to claim 1, further comprising a second energization unit electrically connected to the counter electrode.   The capacitance-type corrosion sensor according to any one of claims 1 to 4, wherein the dielectric has a dielectric constant of 3 or more. A corrosion detection method embedded in a concrete structure and detecting the progress of the corrosion environment of the concrete structure,
The capacitive corrosion sensor according to any one of claims 1 to 5 is embedded in the concrete structure,
A corrosion detection method characterized by identifying a corrosion progress state of a capacitance type corrosion sensor based on a change in capacitance value caused by corrosion of a detection part of the capacitance type corrosion sensor. A corrosion detection method embedded in a concrete structure and detecting the progress of the corrosion environment of the concrete structure,
A plurality of capacitive corrosion sensors according to any one of claims 1 to 5 are connected in parallel to form a continuous sensor,
The continuous sensor is embedded in the concrete structure,
The position of the corroded capacitive corrosion sensor is specified based on a change in the combined capacitance value of the continuous sensor caused by corrosion of the detection unit of any one of the capacitive corrosion sensors. Corrosion detection method. It is a corrosion detection method for sticking to the surface of a steel structure and steel material to be measured, and detecting the progress of the corrosion environment of the steel structure and steel material,
The capacitance value by sticking the capacitance type corrosion sensor in any one of Claims 1-5 to the steel structure and the steel material surface, and the detection part of the capacitance type corrosion sensor corroding A corrosion detection method characterized by identifying a corrosion progress state of a capacitive corrosion sensor based on a change in the capacitance.

Images