Method for measuring corrosion of reinforcing bar in concrete, conductive adhesive gel, and measuring probe

Abstract

To provide a technique capable of stably holding a measurement probe and reducing a workload in measurement work when measuring a corrosion state of a reinforcing bar inside a concrete structure.SOLUTION: In the method for measuring the corrosion of the reinforcing bar in the concrete, a measuring probe 20 having an electrode is bonded to the concrete structure C by a conductive adhesive gel applied to the electrode and held by the concrete structure C, and the corrosion state of the reinforcing bar in the concrete structure C is measured by energizing the reinforcing bar in the concrete structure C from the electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for measuring corrosion of reinforcing bars in concrete, a conductive adhesive gel, and a measurement probe for measuring the state of corrosion of reinforcing bars in concrete structures. [Background technology]

[0002] With the current trend of aging infrastructure in Japan, there is an urgent need to address the deterioration of structures in the maintenance of concrete structures. It is becoming increasingly recognized that preventative maintenance measures, which address deterioration-related defects before they become apparent, are effective in reducing the costs of maintaining concrete structures. Accordingly, since 2014, laws and regulations have required that personnel with the necessary knowledge and skills conduct inspections based on close visual inspections once every five years. While close visual inspections are effective in assessing the soundness of concrete structures where cracks and other defects have become apparent, diagnosis based on the results of close visual inspections may be too late if measures need to be taken before the defects become apparent.

[0003] Generally, the pore water in concrete is strongly alkaline, with a pH of 12 to 13, and iron forms a passive film on its surface, making it resistant to corrosion. However, when the corrosion rate of rebar increases due to the effects of chloride ions that penetrate from the outside due to neutralization of concrete or salt damage, the corrosion of the rebar causes cracks in the concrete (hereafter referred to as corrosion cracks). The more corrosion of the rebar progresses, the more time and money it takes to repair and reinforce, so for efficient maintenance, it is important to identify rebar corrosion before corrosion cracks occur.

[0004] Therefore, various non-destructive testing techniques have been developed that use alternating current to pass through reinforcing bars inside concrete to inspect the state of corrosion of the reinforcing bars inside the concrete structure without relying on corrosion cracks or destroying the concrete structure (see, for example, Patent Document 1). In such non-destructive testing, it is necessary to bring a measurement probe (electrode, sensor, etc.) into contact with the outer wall (surface) of a concrete structure using the worker's hand or a sensor support leg (see Non-Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 7113419 [Non-patent literature]

[0006] [Non-Patent Document 1] https: / / www.rex-rental.jp / large / 030 / middle / 090 / product / 20569

[0007] However, when inspecting the corrosion condition of rebar inside a concrete structure using non-destructive testing, it is necessary to keep the measurement probe (electrode, sensor, etc.) in stable contact with the concrete structure until the inspection is completed, and manually touching and holding the measurement probe is a heavy workload.

[0008] Furthermore, when the measurement probe is supported on the underside of a concrete structure by a sensor support leg for inspection, the sensor support leg must be installed in a stable location. Therefore, when inspecting the underside of a bridge from a rocking ship on the sea surface, it is difficult to stably hold the measurement sensor using the sensor support leg. Therefore, when measuring the corrosion state of reinforcing bars inside concrete structures, there is a need for a technology that can stably hold a measurement probe and reduce the workload involved in the measurement work. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention was devised based on the above-mentioned conventional problems and proposals, and aims to provide a technology that enables a measurement probe to be stably held on a concrete structure when measuring the corrosion condition of reinforcing bars inside a concrete structure, and that reduces the workload involved in the measurement work. [Means for solving the problem]

[0010] The present invention provides A method for measuring corrosion of rebar in concrete, comprising: A conductive adhesive gel containing a supporting electrolyte aqueous solution and a water-absorbent resin and having starch paste-like fluidity is applied to the electrodes of the measurement probe; Concrete structures a conductive adhesive gel is filled into the recess to adhere the electrode to the concrete structure and to adhere and hold the measurement probe to the concrete structure; measuring the corrosion state of the reinforcing steel in the concrete structure by passing an AC current through the electrodes to the reinforcing steel in the concrete structure; It is characterized by the fact that or A method for manufacturing a conductive adhesive gel used in a method for measuring corrosion of reinforcing bars in concrete, A water-absorbing resin, which acts as a gelling agent, is added to the aqueous solution of the supporting electrolyte. A conductive adhesive gel with starch paste-like fluidity is produced by stirring and kneading an aqueous solution of supporting electrolyte to which a water-absorbing resin has been added. It is characterized by the fact that or A conductive adhesive gel used in a method for measuring corrosion of rebar in concrete, The water-absorbing resin contains a modified acrylic crosslinked polymer and has starch paste-like fluidity. It is characterized by the fact that or The water-absorbing resin is AQUALIC CS-8S (registered trademark, manufactured by Nippon Shokubai Co., Ltd.) containing a modified acrylic crosslinked polymer. It is characterized by the fact that or The total weight of the measurement probe equipped with the electrodes is W (kg), and the contact area of ​​the electrodes with the concrete structure is S (mm 2 ), Strength T(N / mm 2 )≧9.8·(W(kg) / S(mm 2 )) is set to It is characterized by the fact that or The total weight of the measurement probe is 60 x 10 -3 kg, the electrode connection surface is a circle with a diameter of 50 (mm), Strength T(N / mm 2 ) ≥ 0.3 × 10 -3 (N / mm 2 ) is set to It is characterized by the fact that or A measurement probe for measuring a corrosion state of reinforcing bars in a concrete structure by passing an electric current through the concrete structure, An electrode; a conductive adhesive gel containing a modified acrylic crosslinked polymer and having starch paste-like fluidity; Equipped with The conductive adhesive gel is applied to the electrode, and the conductive adhesive gel penetrates into the recess of the concrete structure and adheres to the electrode, so that the electrode can be adhered to and held in place on the concrete structure. It is characterized by the following. [Effects of the Invention]

[0011] According to the method for measuring corrosion of steel bars in concrete, the conductive adhesive gel, and the measurement probe of the present invention, the measurement probe is adhered and held to the concrete structure by the conductive adhesive gel, so that the measurement probe can be stably held to the concrete structure and the workload during the measurement work can be reduced. [Brief explanation of the drawings]

[0012] [Figure 1]1 is a conceptual diagram illustrating an outline of a method for measuring corrosion of rebar in concrete according to a first embodiment of the present invention. [Figure 2] 1 is a diagram illustrating a schematic configuration of a rebar corrosion measuring device in concrete according to a first embodiment. [Figure 3] FIG. 2 is a diagram illustrating a schematic configuration of a corrosion measuring instrument main body according to the first embodiment. [Figure 4] 1A to 1D are diagrams illustrating the schematic configuration of a measurement probe according to a first embodiment, in which (A) is a top view, (B) is a front view, (C) is a side view, and (D) is a bottom view. [Figure 5] 3 is a flowchart illustrating a method for producing a conductive adhesive gel according to the first embodiment. [Figure 6] 2A to 2C are diagrams illustrating an example of a conductive adhesive gel according to the first embodiment. [Figure 7] 3A to 3C are diagrams illustrating the properties of the conductive adhesive gel according to the first embodiment. [Figure 8] 4A to 4C are diagrams illustrating the adhesive strength of the conductive adhesive gel according to the first embodiment. [Figure 9] FIG. 1 is a conceptual diagram illustrating an example in which the in-concrete rebar corrosion measuring device according to the first embodiment is applied to a method for measuring in-concrete rebar corrosion (AC impedance method). [Figure 10] FIG. 2 is a conceptual diagram illustrating a current-carrying state in the AC impedance method according to the first embodiment. [Figure 11] 1A and 1B are conceptual diagrams showing the state in which a measurement probe in the method for measuring corrosion of steel bars in concrete according to the first embodiment is adhered (attached) to a concrete structure, where (A) is a conceptual diagram showing an example of measurement from the bottom surface, and (B) is a conceptual diagram showing an example of measurement from the side. [Figure 12] FIG. 2 is a conceptual diagram illustrating a connection state in a three-electrode method according to the first embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] [First embodiment] A first embodiment of the present invention will be described below with reference to FIGS. Fig. 1 is a conceptual diagram outlining a method for measuring corrosion of rebar in concrete according to a first embodiment of the present invention, Fig. 2 is a diagram outlining the general configuration of a rebar corrosion measuring device in concrete, and Fig. 3 is a diagram outlining the general configuration of the corrosion measuring device main body. Fig. 4 is a diagram outlining the general configuration of the measurement probe, with Fig. 4(A) showing a top view, Fig. 4(B) showing a front view, Fig. 4(C) showing a side view, and Fig. 4(D) showing a bottom view when no conductive adhesive gel has been applied. In the figure, symbol 1 indicates a corrosion measuring device for steel bars in concrete, symbol 10 indicates the corrosion measuring device body, symbol 20 indicates a measuring probe, symbol 22 indicates an electrode, symbol 26 indicates a conductive adhesive gel, and symbol C indicates a concrete structure. The corrosion measurement of rebar in concrete according to the first embodiment is performed by an AC impedance method.

[0014] 1, the method for measuring corrosion of rebars in concrete according to the first embodiment involves adhering a measurement probe 20 to the surface of a concrete structure C using the adhesive properties of a conductive adhesive gel, and then holding the measurement probe 20 on the concrete structure C until the measurement is completed (for example, for about 15 minutes) while passing an AC current, thereby measuring the corrosion state of the rebars embedded in the concrete structure C. Note that various methods can be applied to the measurement and determination methods (such as the frequency, current value, and change in current value of the AC current) in the AC impedance method.

[0015] Hereinafter, the schematic configuration of the in-concrete rebar corrosion measuring device 1 will be described with reference to FIG. As shown in Figure 2, the corrosion measuring device 1 for measuring steel bars in concrete includes, for example, a corrosion measuring device main body 10, three measuring probes (electrodes) 20, and cables (symbol 30 shown in Figure 1, not shown in Figure 2) connecting the corrosion measuring device main body 10 and each measuring probe (electrode) 20. The concrete rebar corrosion measuring device 1 is capable of measuring the corrosion state of the rebar by, for example, applying an alternating current from the surface of a concrete structure C to a rebar buried inside and calculating the impedance of the rebar surface.

[0016] 3, the corrosion measuring device main body 10 is equipped with, for example, a CE terminal 11CE, an RE terminal 11RE, a WE(pot) terminal 11WEp, and a WE(cur) terminal 11WEc, each of which can be connected to a cable. The CE terminal 11CE and the WE(cur) terminal 11WEc are connected to, for example, a counter electrode, and the RE terminal 11RE and the WE(pot) terminal 11WEp are connected to, for example, a reference electrode. As shown in FIG. 3, corrosion measuring device main body 10 is equipped with AC power supply 10P, current measuring device (ammeter) 10A, and potential difference measuring device (potentiometer) 10V. The AC power supply 10P and the current measuring device (ammeter) 10A are arranged in series between the CE terminal 11CE and the WE (cur) terminal 11WEc, and the potential difference measuring device (potentiometer) 10V is arranged between the RE terminal 11RE and the WE (pot) terminal 11WEp. The AC power supply 10P is capable of applying AC currents of various frequencies to the CE terminal 11CE and the WE (cur) terminal 11WEc, and the current measuring device (ammeter) 10A measures the current passing between the CE terminal 11CE and the WE (cur) terminal 11WEc. The potential difference measuring device (potentiometer) 10V is arranged between the RE terminal 11RE and the WE (pot) terminal 11WEp, and is configured to measure the potential difference between the RE terminal 11RE and the WE (pot) terminal 11WEp. With this configuration, the potential difference between the potential of the concrete structure and the potential approximately below the counter electrode is measured at the RE terminal 11RE and the WE (pot) terminal 11WEp. In addition, it is preferable that the corrosion measuring device main body 10 is equipped with a detection means (not shown) that determines the degree of impedance from the current value and potential difference value measured when each AC current is passed, and detects corroded locations of the reinforcing bars in the concrete structure C based on the determined degree of impedance.

[0017] Furthermore, it is preferable that the corrosion measuring device main body 10 is powered by, for example, a PC (personal computer) or a mobile battery, and such a configuration eliminates the need for a large-scale power supply device and makes it possible to reduce power supply noise. The system is configured to apply an appropriate voltage to the structure using a unique voltage control system, making it possible to obtain polarization resistance with high accuracy. The calculation format of the corrosion measuring device main body 10 can be set arbitrarily, and it can be applied to various well-known rebar corrosion methods, for example, that determine the potential of the rebar and the potential in the concrete structure C to determine the state of corrosion of the rebar.

[0018] In addition, the corrosion measuring device main body 10 is preferably configured to calculate the polarization resistance by fitting an equivalent circuit through analysis of the measurement results, and to be able to calculate the corrosion rate per unit area by identifying the area to be measured using existing methods. If corrosion measuring device main body 10 can be directly connected to a reinforcing bar, WE(pot) terminal 11WEp and WE(cur) terminal 11WEc may be connected to the reinforcing bar and used for measurement by the three-electrode method.

[0019] As shown in FIG. 4, the measurement probe (electrode) 20 includes, for example, an electrode 22, a casing 24, and a conductive adhesive gel 26, and weighs, for example, 60 g (60×10 -3 kg). The electrode 22 is made of, for example, aluminum, and includes an inner electrode portion (reference electrode) 22A that serves as a reference electrode, and an outer electrode portion (counter electrode) 22B that serves as a counter electrode. The inner electrode portion (reference electrode) 22A is formed in a generally cylindrical shape with a flat tip. The outer electrode portion (counter electrode) 22B is substantially disk-shaped with a circular through-hole formed in the center, and the inner electrode portion (reference electrode) 22A is disposed in this circular through-hole with a radial gap therebetween. The tip surface of the inner electrode portion (reference electrode) 22A and the outer electrode portion (counter electrode) 22B are formed flush with each other. In this embodiment, the outer electrode portion (counter electrode) 22B is set to a circular shape with an outer diameter of, for example, 50 mm. Furthermore, a conductive adhesive gel 26, which will be described later, is applied to the tip surface of the inner electrode portion (reference electrode) 22A and the flat surface of the outer electrode portion (counter electrode) 22B.

[0020] The casing 24 is formed in a substantially rectangular parallelepiped shape, and the electrodes 22 are disposed on one longitudinal end face, and the terminals 25 for connecting the cables 30 are disposed on the other longitudinal end face. Inside the casing 24, wiring is provided that connects the electrodes 22 and the terminals 25. The side of the housing where the electrodes 22 and terminals 25 are not arranged is formed to a size that can be gripped during operation.

[0021] The terminal 25 includes a first terminal portion 25A and a second terminal portion 25B. For example, the first terminal 25A is connected to the inner electrode portion (reference electrode) 22A, and the second terminal 25B is connected to the outer electrode portion (counter electrode) 22B. Furthermore, the first terminal portion 25A and the second terminal portion 25B are connected to corresponding terminals of the cable 30.

[0022] The conductive adhesive gel 26 is placed between the electrode 22 and the surface of the concrete structure to pass electricity from the electrode 22 to the concrete structure in order to measure the corrosion rate of the reinforcing steel buried inside the concrete structure. The conductive adhesive gel 26 also has the adhesiveness (adhesion) to adhere and hold the measurement probe 20 to the surface of the concrete structure. Here, adhesiveness means that the adhesiveness is maintained within the measurement time range, even if the gel hardens or hardens over the long term, and the probe can be attached and removed. In addition, the measurement probe 20 weighs 60g (60 x 10 -3 kg) and the measurement time is, for example, 15 minutes (for example, 20 minutes including a margin), the tensile strength T of the conductive adhesive gel 26, for example, 20 minutes after the electrode 20 is adhered to the concrete structure, is Since the electrode is circular with a diameter of 50 mm, the contact area (adhesion area) is (π x 25 x 25) (mm), Strength T(N / mm 2 )≧9.8·(W(kg) / S(mm 2 )) 9.8×60×10 -3 / (Connection area) = 9.8 x 60 x 10 -3 / (πx25x25)=0.3×10 -3 (N / mm 2 ) It is preferable to set it to

[0023] Next, the conductive adhesive gel 26 will be described with reference to FIGS. FIG. 5 is a flowchart illustrating an example of a method for producing (manufacturing) a conductive adhesive gel, and FIG. 6 is a diagram (photograph) illustrating an example of the conductive adhesive gel according to the first embodiment. The conductive adhesive gel 26 is produced by, for example, absorbing a 3.3 mol / L potassium chloride (KCl) aqueous solution, which is a supporting electrolyte aqueous solution, into a water-absorbing resin and kneading it.

[0024] Hereinafter, a method for producing (manufacturing) the conductive adhesive gel 26 will be described with reference to FIG. As shown in FIG. 5, the conductive adhesive gel 26 is produced by, for example, "preparing a potassium chloride (KCl) aqueous solution (aqueous supporting electrolyte solution) and a gelling agent" (S1), "adding the gelling agent to the potassium chloride (KCl) aqueous solution" (S2), and "stirring and kneading the potassium chloride (KCl) aqueous solution (aqueous supporting electrolyte solution) with the gelling agent added" (S3), which results in "the conductive adhesive gel being produced" (S4).

[0025] (1) Prepare a potassium chloride (KCl) aqueous solution (supporting electrolyte aqueous solution) and a gelling agent (S1). Prepare a potassium chloride (KCl) aqueous solution (aqueous supporting electrolyte solution) and a gelling agent. As the aqueous solution of the supporting electrolyte, for example, a 3.3 mol / L aqueous solution of potassium chloride (KCl) is suitable. Any gelling agent may be applied as long as practical adhesive strength can be ensured. Generally, a water-absorbing resin is less likely to absorb an aqueous solution containing salt, but it is desirable that the water-absorbing agent has salt resistance, can sufficiently absorb an aqueous solution of potassium chloride (KCl) (aqueous solution of a supporting electrolyte), and is less likely to form lumps (lumps of solid matter), and for example, it is preferable to apply a water-absorbing agent containing a modified acrylic crosslinked polymer. The type and concentration of the electrolyte used in the aqueous supporting electrolyte solution may be set arbitrarily.

[0026] Furthermore, when a salt-resistant water-absorbing resin (e.g., AQUALIC CS-8S (registered trademark, manufactured by Nippon Shokubai Co., Ltd.) is used, the amount of water absorbed in artificial seawater is about 1.5 times that of a general water-absorbing agent, and this is preferable in that sufficient water absorption is ensured. Aqualic CS-8S, for example, has an average particle size of approximately 15 μm, and is more prone to clumping than Aqualic CS-8HM, which has an average particle size of approximately 100 μm, but it can maintain strong adhesive strength (stickiness), and clumps of a size that are harmful to adhesion are less likely to form.

[0027] (2) Adding a gelling agent to potassium chloride (KCl) (aqueous supporting electrolyte solution) (S2) Next, a gelling agent is added to a potassium chloride (KCl) aqueous solution (aqueous supporting electrolyte solution). The amount of addition may be set arbitrarily after confirming the required adhesive strength. In this embodiment, for example, 15 g of AQUALIC CS-8S (registered trademark) was added to 100 g of a 3.3 mol / L potassium chloride (KCl) aqueous solution (aqueous supporting electrolyte solution).

[0028] (3) A potassium chloride (KCl) aqueous solution (aqueous supporting electrolyte solution) to which a gelling agent has been added is stirred and kneaded (S3). An aqueous solution of potassium chloride (KCl) (aqueous supporting electrolyte solution) to which a gelling agent has been added is stirred and kneaded to create viscosity so that lumps do not form. The stirring may be carried out manually or by using a mixer.

[0029] (4) Conductive adhesive gel is generated (S4) By carrying out the above steps S1 to S3, a conductive adhesive gel is produced.

[0030] The conductive adhesive gel 26 produced by the above manufacturing method has fluidity (viscosity) similar to that of starch paste used in crafts and office work, as shown in Figure 6, and can be free of lumps that would hinder the electrode 22 from adhering closely to the surface of the concrete structure 22. Furthermore, for example, after being adhered to the surface of the concrete structure C, the adhesiveness is maintained for at least until the measurement work is completed (for example, about 15 minutes), so that the measurement probe 20 can be adhered and held to the outer wall surface of the concrete structure C by the adhesiveness.

[0031] Furthermore, before measurement, the conductive adhesive gel 26 is applied to the surface of the electrode 22 in a substantially flat manner. Note that the flatness means that when the electrode 22 is pressed against the concrete structure C, the conductive adhesive gel 26 is compressed and deformed so that the electrode 22 faces the surface of the concrete structure C with the conductive adhesive gel 26 sandwiched therebetween to an extent that electricity can be conducted therebetween. Furthermore, the thickness of the conductive adhesive gel 26 is preferably such that, if the surface of the concrete structure C is uneven, the conductive adhesive gel 26 can enter the recesses and the surface of the electrode 22 can face the concrete structure C approximately parallel to it.

[0032] Next, with reference to FIGS. 7 and 8, a suitable amount of additive when producing a conductive adhesive gel using AQUALIC CS-8S (registered trademark) will be described. To confirm the amount added, AQUALIC CS-8S (registered trademark) was added to 100 g of a 3.3 mol / L aqueous potassium chloride (KCl) solution (aqueous supporting electrolyte solution), and the potassium chloride (KCl) solution (aqueous supporting electrolyte solution) was stirred into AQUALIC CS-8S (registered trademark) to allow it to absorb water and knead to form a conductive adhesive gel. The properties of this gel were confirmed, and the adhesive strength was measured. The amounts of AQUALIC CS-8S (registered trademark) added were 5 g, 10 g, 15 g, 20 g, and 25 g.

[0033] The adhesive strength was measured by attaching a 50mm diameter electrode plate coated with conductive adhesive gel to a horizontal, flat surface of the concrete, and then pulling the electrode plate perpendicular to the adhesive surface (vertical direction) to measure the adhesive strength against tension in the direction perpendicular to the adhesive surface. Measurements were performed three times for each conductive adhesive gel. The results are shown in Figures 7 and 8.

[0034] The properties and adhesive strength of the conductive adhesive gel will be described below with reference to Fig. 7 and Fig. 8. Fig. 7 is a diagram for explaining the properties of the conductive adhesive gel according to the first embodiment, and Fig. 8 is a diagram for explaining the adhesive strength of the conductive adhesive gel. The conductive adhesive gel produced with an added amount of 5 g was thick and liquid-like, and as shown in Figure 8, the adhesive strength was approximately 0.4 × 10 -3 (N / mm 2 ) was. In addition, the conductive adhesive gel produced with an additive amount of 10 g was easy to apply and had an adhesive strength of approximately 1.30 to 1.79 × 10 -3 (N / mm 2 ) was. In addition, the conductive adhesive gel produced with an additive amount of 15 g was easy to apply and had an adhesive strength of approximately 1.34 to 1.68 × 10 -3 (N / mm 2 ) was. In addition, the conductive adhesive gel produced with an additive amount of 20 g was easy to apply and had an adhesive strength of approximately 1.34 to 1.60 × 10 -3 (N / mm 2 ) was. The conductive adhesive gel produced with an additive amount of 25 g was difficult to spread, but the adhesive strength was approximately 1.08 to 1.20 × 10 -3 (N / mm 2 ) was.

[0035] For example, if the total weight of the measurement probe is 60 g, the required adhesive strength is 0.3 × 10 -3 (N / mm 2 ) and it was confirmed that the adhesive strength was sufficient when the amount added was 10g, 15g, or 20g. It was also confirmed that a practical level of adhesive strength could be ensured even when the amount added was 25 g. On the other hand, it was found that an added amount of 5 g was not suitable.

[0036] Next, with reference to FIGS. 9 to 11, an example in which the in-concrete rebar corrosion measuring device 1 according to the first embodiment is applied to a method for measuring rebar corrosion in concrete (AC impedance method) will be described. FIG. 9 is a conceptual diagram illustrating an example in which the in-concrete rebar corrosion measuring device 1 and a conductive adhesive gel 26 according to the first embodiment are applied to measuring impedance in the method for measuring rebar corrosion in concrete (AC impedance method), and FIG. 10 is a conceptual diagram illustrating the current flow state in the AC impedance method according to the first embodiment. FIG. 11 is a conceptual diagram showing an example of the attachment (mounting) of a measurement probe. The AC impedance method is one of the methods for measuring rebar corrosion in concrete to determine the state of corrosion of the rebar. The conductive adhesive gel 26 is electrically attached to the surface of a concrete structure C, and then an AC current is passed through the rebar to obtain the potential, impedance, etc., used to determine the state of corrosion of the rebar.

[0037] In the method for measuring corrosion of rebars in concrete (AC impedance method) according to the first embodiment, an AC current is applied to rebars R in a concrete structure C, for example, from the surface of the concrete structure C using a rebar corrosion measuring device 1, and the polarization resistance (impedance) is calculated to measure the corrosion rate of the rebars. The conductive adhesive gel 26 may be applied to various measurement methods in which the measurement probe 20 is attached to the surface of the concrete structure C with the conductive adhesive gel 26 and an alternating current is applied.

[0038] The method for measuring rebar corrosion in concrete (AC impedance method) shown in Figures 9 to 11 involves applying AC currents of various frequencies using a rebar corrosion measuring device 1 in concrete, measuring the impedance, analyzing the obtained impedance spectrum, and calculating the polarization resistance, which is an indicator of rebar corrosion.

[0039] Various methods, such as the three-electrode method, can be used to obtain the impedance spectrum of reinforcing bars in concrete. With the three-electrode method, the measuring device is connected directly to the rebar, so all of the applied current flows through the rebar and measurement results can be handled quantitatively, but it is necessary to remove part of the concrete structure to expose the rebar when making measurements.On the other hand, with this method of measuring rebar corrosion in concrete, the current flowing through the rebar becomes unclear, making interpretation of the measurement results difficult, but there is no need to expose the rebar, and measurements can be made non-destructively.

[0040] An example of a method for measuring corrosion of reinforcing bars in concrete will be described below with reference to FIGS. [Measurement probe installation] First, as shown in FIG. 9, the measurement probe 20A, the measurement probe 20B, and the measurement probe 20C are placed on the surface of the concrete structure C corresponding to the reinforcing bar R. At this time, the measurement probes 20A, 20B, and 20C are placed at an appropriate distance (for example, 130 cm or more) from one another so that electricity does not flow through the concrete structure C to one another. Furthermore, it is desirable to wet the concrete structure C for, for example, 15 minutes or more before adhering the measurement probes 20 (20A, 20B, 20C).

[0041] Furthermore, the measurement probes 20A, 20B, and 20C are connected to the measuring device main body 10 of the in-concrete rebar corrosion measuring device 1, as shown in FIGS. Specifically, the measurement probe 20A is connected to the CE terminal 11CE and the RE terminal 11RE. At this time, as shown in Fig. 10, the outer electrode portion (counter electrode) 22B is connected to the CE terminal 11CE, and the inner electrode portion (reference electrode) 22A is connected to the RE terminal 11RE.

[0042] 9 and 10, the measurement probe 20B is connected to the RE terminal 11RE and the corresponding WE (pot) terminal WE p As a result, the inner electrode portion (reference electrode) 22A of the measurement probe 20B is connected to the inner electrode portion (reference electrode) 22A of the measurement probe 20A, which is the reference electrode, via the potentiometer 10A.

[0043] 9 and 10, the measurement probe 20C is connected to the CE terminal 11CE and the corresponding WE (cur) terminal 11WE. C As a result, the outer electrode portion (counter electrode) 22B of the measurement probe 20C is connected to the outer electrode portion (counter electrode) 22B of the measurement probe 20A via the AC power supply 10P and the current measuring device 10A.

[0044] In addition, Figure 9 shows an example in which the reinforcing bar R is buried on the upper side (near the upper surface) of the concrete structure C, but if the reinforcing bar R to be measured is buried on the lower side (near the lower surface) of a bridge or the like, the measurement probe 20 is adhered to the lower side of the concrete structure C as shown in Figure 11 (A). Furthermore, when the reinforcing bar R to be measured is buried in the side (near the side) of a vertical wall of a bridge pier, embankment, etc., the measurement probe 20 is adhered to the side of the concrete structure C as shown in FIG. 11(B).

[0045] [Measurement method] Hereinafter, polarization resistance measurement by this method will be described with reference to FIG. In Figure 10, symbols Z1, Z2, and Z3 are the impedances from measurement probes 20A, 20B, and 20C to the rebar, respectively, and impedances Z1, Z2, and Z3 are composed of the resistance of the conductive adhesive gel 26 at each position and the resistance due to the concrete (hereinafter referred to as concrete resistance) R11, R21, and R31, the electrical resistance R12, R22, and R32 on the surface of the rebar R, and the capacitors C1, C2, and C3 at the interface between the concrete and the rebar. Furthermore, by placing each measurement probe 20 (20A, 20B, 20C) at a position sufficiently far apart, no current flows directly through the surface of the concrete structure C and the cover of the concrete structure C, and all current passing through the interior of the concrete structure passes through the reinforcing bars R. Specifically, between measurement probe 20A and measurement probe C, an alternating current passes through the path of outer electrode portion (counter electrode) 22B of measurement probe 20A, the inside of concrete structure C, reinforcing bar R, the inside of concrete structure C, and outer electrode portion (counter electrode) 22B of measurement probe 20C.

[0046] The specific steps will be explained below. (1) Alternating currents of various frequencies are applied between the inner electrode portion (reference electrode) 22A of measurement probe 20A and the inner electrode portion (reference electrode) 22A of measurement probe 20B. When the probes are sufficiently separated, no current flows from measurement probe 20A to measurement probe 20B, regardless of the frequency. Here, the dashed arrow with an x ​​in Figure 10 indicates that no current flows. As a result, the change in the potential difference between the inner electrode portion (reference electrode) 22A of measurement probe 20B and the inner electrode portion (reference electrode) 22A of measurement probe 20A becomes equal to the potential difference applied to impedance Z1. At this time, measurement probe 20A outputs an electric signal so that the potential difference between measurement probe 20A and measurement probe 20B becomes a sine wave, and measurement probe 20C monitors the generated current, thereby determining impedance Z1. (2) Next, in the equivalent circuit for impedance Z1, the capacitor C1 exists in parallel with the electrical resistance R12 at the concrete-rebar interface, so in the high-frequency range, only the concrete resistance R11 is measured, and in the low-frequency range, the impedance of the concrete resistance R11 + electrical resistance R12 is measured. Therefore, by measuring Z1 at various frequencies and fitting it to the equivalent circuit, the electrical resistance R12 can be calculated. (3) Next, for example, the cover thickness CL, the diameter of the rebar R, the rebar spacing, etc. shown in Figure 9 are input to estimate the polarization resistance and corrosion rate. In healthy rebars, the electrical resistance R12 is large, while in rebars with advanced corrosion, the electrical resistance R12 is small.

[0047] From the above, in polarization resistance measurement, the potential difference across Z1 is measured based on the voltage value at the reference electrode from the inner electrode portion (reference electrode) 22A of the measurement probe 20A via the conductive adhesive gel 26, and electricity is passed through the concrete structure C from the outer electrode portion (counter electrode) 22B of the measurement probe 20A via the conductive adhesive gel 26 to measure the current flowing through Z1 based on the current value at the counter electrode.The impedance Z1 is calculated by taking the ratio of these values, and the electrical resistance R12 is calculated by analyzing Z1 to determine the corrosion condition of the reinforcing bar R.

[0048] Any method may be used to estimate the corrosion state, and when calculating the electrical resistance R12, it is preferable to refer to, for example, the concrete cover of the reinforcing bar to be measured, the diameter of the reinforcing bar to be measured, and the spacing between the reinforcing bars. stomach. Note that (1) and (2) above are usually measured from high frequencies. The corrosion state of the reinforcing bar R may be measured at a plurality of measurement points by moving the measurement probe 20 (changing the position).

[0049] According to the method for measuring corrosion of steel bars in concrete, the conductive adhesive gel 26, and the measurement probe 20 of the first embodiment, the measurement probe 20 is adhered and held to the concrete structure C by the conductive adhesive gel 26, so that the measurement probe 20 can be stably adhered and held to the concrete structure C, and manual holding is not required during the measurement work, thereby reducing the workload. Furthermore, since the measurement probe 20 is adhered to the concrete structure C by its adhesiveness, the measurement probe 20 can be easily removed after the measurement work is completed.

[0050] Furthermore, the measuring probe 20 is adhered and held to the concrete structure C due to its adhesiveness, and there is no need to support and hold the measuring probe 20 to the concrete structure C using a support member (rigid body) or manually.The measuring probe 20 is connected to the corrosion measuring device main body 10 by a cable 30, which improves the freedom of positioning of the measuring probe 20.Therefore, the corrosion condition of reinforcing bars R buried under and near the sides of a bridge can be stably measured, for example, from a ship rocking on the sea surface or river surface.

[0051] Furthermore, since the conductive adhesive gel (conductive adhesive gel) 26 can be deformed to fit the unevenness of the concrete structure C, the electrode 22 adheres closely to the concrete structure C, reducing electrical resistance and allowing electricity to flow efficiently. Furthermore, since the measurement probe 20 can be stably held on the concrete structure C, the measurement accuracy can be improved.

[0052] Next, a method for measuring corrosion of rebar in concrete using a three-electrode method according to a modified example of the first embodiment will be described with reference to Fig. 12. Fig. 12 is a conceptual diagram illustrating a connection state applied to the three-electrode method according to the modified example of the first embodiment. In measuring rebar corrosion in concrete using the three-electrode method, as shown in Fig. 12, the WE(pot) terminal WEp and the WE(cur) terminal WEc of the corrosion measuring device main body 10 are directly connected to the rebar R exposed from the concrete structure C. The rebar R is exposed in advance by, for example, removing (screwing) the concrete structure C.

[0053] As shown in Figure 12, the corrosion measuring device main body 10 has the RE terminal 11RE and the WE (pot) terminal WEp connected via a potential difference meter, and the CE terminal 11CE and the WE (cur) terminal WEc connected via an AC power supply 10P and a current meter 10A. Then, the measurement probe 20A (20) is placed on the surface (measurement surface) of the concrete structure C at a position corresponding to the reinforcing bar R to be measured. At this time, the inner electrode portion (reference electrode) 22A and the outer electrode portion (counter electrode) 22B of the measurement probe 20A are connected to the surface of the concrete structure C via the conductive adhesive gel 26. Furthermore, the inner electrode portion (reference electrode) 22A of the measurement probe 20A (20) is connected to the RE terminal 11RE, and the outer electrode portion (counter electrode) 22B is connected to the CE terminal 11CE.

[0054] Then, an AC current in the low frequency range of, for example, 0.01 Hz to 100 Hz and an AC current in the high frequency range are continuously applied between the CE terminal 11CE and the WE (cur) terminal WEc to obtain AC currents of the respective frequencies. Next, while a low-frequency current or a high-frequency AC current is being passed between the CE terminal and the WE(cur) terminal, the potential difference between the RE terminal 11RE and the WE(pot) and WEp terminals is measured. The potential difference between the RE terminal 11RE and the WE(cur) terminal is measured by a potentiometer 10V, and the measured potential difference becomes potential data near the measurement probe 20A, which is the measurement unit. Here, when measuring the potential data, the potential difference is measured between the potential of the reinforcing bar R as a reference and the potential of the surface of the concrete structure C that is in contact with the measuring part of the concrete structure C, i.e., the inner electrode part (reference electrode) 22A of the measurement probe 20A.

[0055] The potential difference obtained by measurement is then divided by the applied AC current to obtain the impedance expressed as (potential difference / applied AC current), which is then repeated for each frequency and plotted on a block diagram with the horizontal axis representing the real part (Ω) and the vertical axis representing the imaginary part (Ω) to obtain an impedance spectrum.The corrosion rate of the rebar can be determined by analyzing the impedance spectrum thus created.

[0056] According to the method for measuring corrosion of rebar in concrete according to the modified example of the first embodiment, the measurement probe 20 is stably adhered, bonded and held in close contact with the concrete structure C, thereby reducing the workload during the measurement work. Furthermore, the corrosion condition of reinforcing steel R near the underside and sides of a bridge can be stably measured, even from a ship on the sea or river surface.

[0057] The present invention is not limited to the above-described embodiment, and various modifications can be made thereto. For example, in the above embodiment, a case has been described in which a 3.3 mol / L potassium chloride (KCl) aqueous solution is used as the supporting electrolyte aqueous solution to generate the conductive adhesive gel 26, but the present invention is not limited to a 3.3 mol / L potassium chloride (KCl) aqueous solution, and any supporting electrolyte aqueous solution applicable to the method for measuring corrosion of rebar in concrete, such as sodium hydroxide, calcium hydroxide, or sodium sulfate, may be used, and the concentration is not limited to 3.33.3 mol / L and may be set arbitrarily.

[0058] Furthermore, in the above embodiment, a case has been described in which AQUALIC CS-8S (registered trademark, manufactured by Nippon Shokubai Co., Ltd.), which contains a modified acrylic cross-linked polymer, is used as the water absorbent for producing the conductive adhesive gel 26. However, the present invention is not limited to AQUALIC CS-8S (registered trademark, manufactured by Nippon Shokubai Co., Ltd.), and other water absorbents containing a modified acrylic cross-linked polymer or other water absorbents not containing a modified acrylic cross-linked polymer may also be used.

[0059] Furthermore, in the above embodiment, the case where the conductive adhesive gel 26 and the measurement probe 20 are applied to a method for measuring rebar corrosion in concrete, which is an AC impedance method, has been described. However, the present invention is not limited to these measurement methods, and other methods for measuring rebar corrosion in concrete may be used, such as applying an AC current to a concrete structural part C via the conductive adhesive gel 26 to measure the state of corrosion of the rebar R inside. For example, the conductive adhesive gel 26 may be applied to a reference electrode in a method in which a terminal is connected directly to the rebar, a reference electrode is placed on the concrete surface, and the potential (natural potential) from the rebar R to the concrete surface is measured to determine corrosion. [Explanation of symbols]

[0060] 1. Steel bar corrosion measuring device in concrete 10 Corrosion measuring instrument body 20 Measuring Probes 22 electrodes 22A Inner electrode (reference electrode) 22B Outer electrode part (counter electrode) 24 Casing 26 Conductive adhesive gel 30 Cable

Claims

1. A measurement probe having electrodes is adhered to the concrete structure by a conductive adhesive gel applied to the electrodes and is held by the concrete structure; measuring the corrosion state of the reinforcing steel in the concrete structure by passing a current through the electrodes to the reinforcing steel in the concrete structure; A method for measuring corrosion of rebar in concrete.

2. A conductive adhesive gel used in the method for measuring corrosion of reinforcing bars in concrete according to claim 1, The electrode is formed by absorbing an aqueous solution of a supporting electrolyte into a water-absorbing resin and kneading the resin, and is configured to have an adhesive strength capable of adhering and holding the electrode to the concrete structure. A conductive adhesive gel characterized by:

3. The water-absorbing resin contains a modified acrylic crosslinked polymer. The conductive adhesive gel according to claim 2 .

4. The water-absorbing resin is AQUALIC CS-8S (registered trademark, manufactured by Nippon Shokubai Co., Ltd.), which contains a modified acrylic crosslinked polymer. The conductive adhesive gel according to claim 2 .

5. The total weight of the measurement probe equipped with the electrode is W (kg), and the contact area of ​​the electrode with the concrete structure is S (mm ２ ), then Strength T (N / mm ２ )≧9.8・(W(kg) / S(mm ２ )) is set to The conductive adhesive gel according to claim 2 .

6. The total weight of the measurement probe is 60 x 10 －３ kg, and the electrode connection surface is a circle with a diameter of 50 (mm), Strength T (N / mm ２ ) ≧0.3×10 －３ (N / mm ２ ) is set to The conductive adhesive gel according to claim 2 .

7. A measurement probe for measuring a corrosion state of reinforcing bars in a concrete structure by passing an electric current through the concrete structure, An electrode; The conductive adhesive gel according to any one of claims 2 to 6, Equipped with The conductive adhesive gel is applied to the electrode, and the electrode can be adhered and held to the concrete structure by the conductive adhesive gel. A measurement probe characterized by:

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