JP2015197307A - Corrosion detection sensor and evaluation method of corrosive environment of steel material in concrete - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sensor and the like allowing a corrosive environment of a steel material in concrete to be easily evaluated with high accuracy.SOLUTION: A corrosion detection sensor for detecting a corrosion progression state of a steel material in concrete is provided that is comprised of (C) a blocking material, and two or more sets of (A) corrosion detection members and (B) coating members. One surface of the corrosion detection member installed in the blocking material is covered with the coating member and the other surface of the coating member not covering the corrosion detection member is exposed. A water-cement ratio of at least one set of the coating members is different from water-cement ratios of the other sets of the coating members. (A) the corrosion detection member is formed from a thin steel sheet. (B) the coating member is comprised of a cement composition hardened body. (C) the blocking material blocks intrusion of corrosion factors.

Description

The present invention relates to a sensor for evaluating an environment in which a steel material in concrete corrodes, and a method for evaluating a corrosive environment of the steel material in concrete using the sensor.
Hereinafter, concrete is a concept including mortar in addition to concrete.

Steel materials such as rebars and PC steel materials in concrete are inherently covered with a passive film in an alkaline atmosphere and hardly corrode. However, if carbon dioxide permeates into the concrete and the concrete becomes neutral, or if corrosion factors such as chloride ions (hereinafter referred to as “salt content”) or sulfate ions penetrate and contact the steel, the surface of the steel will passivate. The coating is destroyed and the steel material is easily corroded. Among these ions, salt penetrates concrete quickly and has a high risk of corroding the reinforcing bars.
Therefore, reinforced concrete structures near the marine environment and coastline, and reinforced concrete structures such as areas where snow melting material is sprayed in the winter season, salt will permeate from the surface layer of the concrete, and in the long term corrosion of the steel in the concrete will occur. Concerned. If the steel in the concrete is corroded, performance such as durability of the reinforced concrete structure may be impaired, and serious defects may occur. Therefore, in the reinforced concrete structure, the position from the surface to the steel (cover), the concrete Quality (water / cement ratio) is defined to protect steel.
On the other hand, the location of reinforced concrete structures is diverse, and in addition to salt, environmental conditions such as temperature, solar radiation, and wind and rain affect the salt infiltration into concrete, so salt infiltration proceeds more than expected. In some cases, it is generally difficult to predict the corrosion time of steel in concrete for each reinforced concrete structure.

Therefore, Patent Document 1 considers the apparent diffusion coefficient D _t of the salinity in the depth direction of the concrete structure obtained by the survey at the time when t years have passed since the construction, and the secular change of the diffusion coefficient D _t. A method has been proposed for estimating the corrosion rate of reinforcing steel in a reinforced concrete structure subject to external salt damage from the salinity concentration C at the cover position of the reinforcing steel bar obtained by calculation and the temperature T. Patent Document 2 describes the corrosion status of steel in concrete, in which a fine wire made of the same material as the steel in a concrete structure is embedded in the concrete structure and the time when the fine wire is cut by corrosion is measured. A prediction method has been proposed. However, since the method requires prior investigation, its simplicity and estimation (prediction) accuracy are still not sufficient.

JP 2008-082449 A Japanese Patent Laid-Open No. 11-153568

  Therefore, an object of the present invention is to provide a sensor for easily and accurately evaluating a corrosive environment of a steel material in concrete and an evaluation method thereof.

The inventors of the present invention have examined a sensor or the like that meets the above object, and found that the following sensor and the evaluation method can achieve the above object, and have completed the following inventions [1] to [7].
[1] A corrosion detection sensor for detecting the progress of corrosion of a steel material in concrete, the sensor comprising:
It is composed of two or more sets of (A) corrosion detection member and (B) coating member. One surface of the corrosion detection member installed in the shielding material is covered with the coating member, and the corrosion detection member of the coating member is covered. A corrosion detection sensor in which the other surface that is not exposed is exposed and the water / cement ratio of at least one set of covering members is different from the water / cement ratio of the other set of covering members.
(A) Corrosion detection member formed of iron thin film (B) Cover member made of hardened cement composition (C) Barrier material that blocks intrusion of corrosion factors [2] The corrosion detection sensor is embedded in concrete In the above [1], the corrosion factor of the steel material in the concrete penetrates from the exposed surface of the covering member, and the electrical characteristics of the corrosion detecting member are changed by the corrosion factor to detect the progress of corrosion. The described corrosion detection sensor.
[3] The corrosion detection sensor according to [1] or [2], wherein the covering member has the following composition (a) to (d) and shape.
(A) Water / cement ratio (mass ratio × 100): 20 to 150%
(B) Water / powder ratio (mass ratio × 100): 15 to 120%
(C) Air volume: 5 to 35%
(D) Thickness of the covering member: 1 to 20 mm
[4] The [1] to [3], wherein the corrosion detection member is formed of a member that detects corrosion by a change in electrical resistance, a change in potential, or a change in current density due to a corrosion reaction caused by corrosion. The corrosion detection sensor according to any one of the above.
[5] The ratio of the distance from the concrete surface to the exposed surface of the covering member of the embedded corrosion detection sensor (hereinafter referred to as “embedding depth”) / (the thickness of the covering member) is 5 or more. Thus, the corrosion detection sensor according to any one of [1] to [4], which is used by being installed in concrete.

[6] The corrosion detection sensor is embedded in concrete,
The corrosion detection time is measured by the corrosion detection sensor,
Obtain corrosion evaluation parameters based on the corrosion relational expression including the corrosion occurrence time as a variable,
Evaluating the corrosive environment of steel in concrete using the corrosion evaluation parameters,
A method for evaluating the corrosive environment of steel in concrete.
[7] The above-mentioned corrosion relational expressions are the following formulas (1) and (2), and the corrosion evaluation parameters are the apparent diffusion coefficient and the surface salinity of concrete in the following formula (1). ] The evaluation method of the corrosive environment of the steel materials in concrete as described in the above.
C _CL = C ₀ × {1-erf [0.1 × S _cd / (2 × (D _d × t) ^0.5 )]} + C _i (1)
C _CL = a × (W / C) + b (2)
However, in _{(1), C CL} represents corroded salinity of steel in concrete _{^{(kg / m 3), C}} 0 represents the surface salinity of concrete _{^{(kg / m 3), S}} cd is buried Depth is expressed in mm, D _d is an apparent diffusion coefficient (cm ² / year), t is a time (year) until corrosion occurs, and C _i is an initial salinity. The equation (1) is an error function. Further, (2) _{wherein, C CL} represents corroded salinity of steel in concrete (kg / ^{m 3),} W / C represents the water / cement ratio, for each type of a and b below Cement Represents the material coefficient specified in.

  According to the corrosion detection sensor of the present invention and the method for evaluating the corrosive environment of steel in concrete using the same, the corrosive environment of steel in concrete can be evaluated easily and accurately.

It is a figure which shows an example of a corrosion detection member. It is a flowchart which shows an example of the manufacturing method of the corrosion detection member of this invention. It is a figure which shows an example of the block diagram of the corrosion detection sensor provided with the wireless communication module. (A) is BB 'sectional drawing of a corrosion detection sensor (an example) which has the coating | coated member shape | molded with the cement composition hardened | cured material of two types of water / cement ratio, (b) is A- of this sensor. It is A 'sectional drawing. It is a figure which shows the example of installation of the corrosion detection sensor in concrete, and positional relationship. It is a perspective view of a block-shaped corrosion detection sensor (an example). It is a perspective view of a disk-shaped corrosion detection sensor (an example). It is a perspective view of the corrosion detection sensor (an example) which has a covering member shape | molded with the cement composition hardened | cured material of three types of water / cement ratio. It is a figure which shows the calculation result of the salt content in concrete calculated | required with the evaluation method using the corrosion detection sensor of this invention.

1. The corrosion detection sensor used in the present invention is a sensor including (A) a corrosion detection member, (B) a covering member, and (C) a blocking material as essential constituent members as described in [1] above. . Further, in order to reinforce the strength of the sensor, reduce the size, eliminate an error factor, and the like, (D) an exterior material is included as an optional member as necessary.
Hereinafter, the present invention will be described in detail in the order of the components (A) to (D) with reference to the drawings.

(A) Corrosion detection member As shown in FIG. 1, the corrosion detection member 10 includes a conductor pattern portion 11, and the conductor pattern portion 11 is an iron thin film formed in the corrosion detection member 10. A measurement terminal 11 a is provided at the end of the pattern portion 11. The conductive pattern portion 11 changes in electrical characteristics such as a change in electrical resistance, a change in potential, and a change in current density due to the corrosion reaction of the metal due to salt. And since this iron thin film is excellent in the change of an electrical property, it is a foil material obtained by rolling iron.
The thickness of the iron thin film is preferably 0.1 to 100 μm. If the thickness is less than 0.1 μm, it is difficult to form a uniform thickness, and if it exceeds 100 μm, the sensitivity to changes in electrical characteristics tends to decrease. Further, the shape of the conductor pattern portion 11 is preferably a shape that has a high probability of contact with salinity and is likely to cause a corrosion reaction, and includes, for example, a zigzag shape as shown in FIG. Moreover, it is preferable that the area of the conductor pattern part has at least the length of one side constituting the area larger than the maximum aggregate size used for the concrete to be embedded in the corrosion detection sensor 100. If the length of the longest long side of the area is smaller than the maximum aggregate size, the corrosion detection sensor 100 is affected by the aggregate accidentally arranged immediately above the corrosion detection sensor 100, and the detection accuracy is lowered. there's a possibility that.

Next, a mechanism by which the conductor pattern portion 11 detects corrosion due to a change in electrical characteristics will be described.
A cell in which a battery is formed so that a metal anode part and a cathode part can be clearly distinguished is called a macro cell, and a current flowing between both electrodes is called a corrosion current (macro cell current). Then, a reaction in which the iron thin film is ionized by the corrosion reaction (anode reaction) and a reaction in which oxygen is reduced on the surface of the iron thin film (cathode reaction) proceed simultaneously, with the anode portion having a base potential and the cathode portion having a noble potential. As a result, a potential difference is generated, a corrosion current flows from the anode portion to the cathode portion, and the corrosion of the iron thin film proceeds.
Utilizing this principle, by providing a thin film portion 13 (cathode portion) formed of a noble metal such as gold at the end of the conductor pattern portion 11, the corrosion of the conductor pattern portion 11 proceeds and the corrosion is accelerated. I can grasp.

Further, changes in the electrical characteristics (electric resistance, potential change, and current density) will be described below.
(I) Change in electrical resistance Since the cross-sectional area of iron decreases with the corrosion of the conductor pattern portion 11 and the electrical resistance increases thereby, the corrosion can be detected by the change in the electrical resistance.
(Ii) Potential change When the conductor pattern part 11 corrodes, when iron ionizes, the electron of a corrosion generation | occurrence | production location (anode) moves to an uncorroded location (cathode), and a potential difference arises. Corrosion current is continuously generated with this as a driving force, and corrosion progresses. For example, if the potential difference between metals is measured using electrodes, the occurrence of corrosion is known from the change in potential before and after the occurrence of the corrosion phenomenon. be able to.
(Iii) Change in current density Since corrosion is a phenomenon caused by the generation of a corrosion circuit, the corrosion phenomenon can be grasped by measuring the change in current density at the corrosion site caused by the corrosion current.

As shown in FIG. 1, the corrosion detection member 10 includes the conductor pattern portion 11, the measurement terminal 11 a, the base material 12, and the thin film portion 13. Among these, the base material 12 has a function of holding the conductor pattern portion 11 in the corrosion detection member 10.
The base material 12 is not particularly limited as long as it is a material having high electrical insulation, does not react with an alkali component contained in the cement composition cured body, and has high weather resistance and water resistance. And a glass composite material such as phenol resin, polyimide, polyethylene, polypropylene, vinyl chloride resin, fluororesin, or polycarbonate such as PET.
Moreover, since the thin film part 13 is a cathode part formed with noble metals, such as gold | metal | money, and the corrosion of the conductor pattern part 11 is accelerated | stimulated by the thin film part 13, corrosion can be grasped | ascertained earlier.

The manufacturing method of the corrosion detecting member 10 is as described in the following (i) to (v). A flowchart of the manufacturing method is shown in FIG.
(I) The base material 12 and the iron thin film which later comprises the conductor pattern part 11 are integrated, and an iron thin film sheet is produced. As the integration method, for example, an adhesive is applied to the base material 12, and the iron thin film and the base material 12 are bonded together using a roller or the like.
(Ii) On the iron thin film of the produced iron thin film sheet, a conductor pattern portion 11 and a resist film having a circuit shape are formed by screen printing or photo printing. In addition, after the resist film is printed, a guide for individually cutting and separating the corrosion detecting member 10 with a punching die is printed together.
(Iii) The iron thin film sheet on which the resist film is formed is etched in an etching tank. As a result, the exposed iron thin film not provided with the resist film is dissolved in the etching solution (for example, ferric chloride solution). After completion of the etching, the iron thin film sheet is taken out from the etching tank and the adhering liquid is washed.
(Vi) The resist film is removed with a solvent or the like to form the conductor pattern portion 11 and the outer shape of the circuit.
(V) The iron thin film sheet is divided, the masking is peeled off, and the conductor pattern portion 11 is formed. Then, the sensors subjected to the protection treatment using the punching die are individually cut and separated, and the cord 103 is attached.
Then, the completed corrosion detection member 10 is directly connected to an apparatus for detecting corrosion, and measures a change in electrical characteristics associated with the corrosion reaction of the conductor pattern portion or, as shown in FIG. You may connect to the radio | wireless apparatus which has and measure by radio | wireless.

(B) Coating member The coating member 101 is a hardened cement composition that covers the corrosion detection member 10 as shown in FIG. The covering member 101 is made of a hardened cement composition having two or more water / cement ratios, and the covering member 101 is blocked by a blocking material 102. One surface of the covering member 101 is an exposed surface, and the corrosion detection sensor 100 is embedded so that the exposed surface is parallel to the surface of the concrete to be embedded, and a corrosion factor in the concrete permeates from the exposed surface. Besides the exposed surface and the surface that covers the corrosion detecting member 10, the covering member 101 is covered with a blocking material 102 to prevent the penetration of the corrosion factor from the concrete.
After the corrosion factor that has entered from the outside penetrates into the concrete and reaches the corrosion detection sensor 100, it penetrates into the covering member 101, reaches the conductor pattern portion, and the iron forming the conductor pattern portion corrodes and Electrical characteristics change.

The said covering member 101 is a cement composition hardened | cured material, and this hardened | cured material is a mortar or cement cement paste hardened | cured material specifically ,. The cement composition refers to a composition containing at least one selected from the group consisting of cement alone or in addition to cement, blast furnace slag, fly ash, coal ash, limestone powder, silica fume, fine aggregate, and the like. .
From the viewpoint of evaluation accuracy, the cement is preferably the same as the cement in the concrete in which the sensor is embedded. The cement is not particularly limited, and ordinary Portland cement, early strength Portland cement, super early strength Portland cement, medium heat Portland cement, low heat Portland cement, sulfate resistant Portland cement, blast furnace cement, fly ash cement, coal ash-containing cement, One or more types selected from silica cement, white cement, eco-cement and the like can be mentioned.
The kneading water for the cement composition can be used as long as it does not adversely affect the evaluation of the corrosive environment, and is, for example, tap water or reclaimed water.

The water / cement ratio of the covering member 101 is preferably 20 to 150%. When the ratio is less than 20%, it is difficult to knead the cement composition, and it may be difficult to form the covering member 101 uniformly. In addition, if the ratio exceeds 150%, material separation may occur, and salt penetration may be uneven and evaluation accuracy may be reduced.
The water / powder ratio is preferably 15% to 120%. When the ratio is less than 15%, it is difficult to mix the cement composition, and it may be difficult to form the covering member 101. When the ratio exceeds 120%, material separation may occur when the covering member 101 is formed. There is.

The covering member 101 is a hardened cement composition having two or more water / cement ratios. One of the two or more water / cement ratios is preferably the same as the water / cement ratio of the concrete to be embedded in the corrosion detection sensor 100.
If the water / cement ratio of the concrete and the covering member 101 is the same, the concentration of the corrosion factor at which the corrosion of the steel in the concrete begins to be the same, so that the evaluation error is reduced in evaluating the corrosion environment of the steel. it can. The other water / cement ratio different from the water / cement ratio is preferably set higher by about 5 to 30% than the water / cement ratio. If the water / cement ratio is high, the amount of salt that causes corrosion of the steel material is reduced, so that the corrosion becomes easy and the time for detecting the corrosion can be shortened.
Therefore, for example, in the corrosion detection sensor 100 having the two kinds of water / cement ratio coating members 101, the corrosion detection member 10 covered with the coating member 101 having a high water / cement ratio is more than the other corrosion detection member 10. It is possible to evaluate the corrosive environment of the steel material without delay when the corrosion detecting member 10 constituted by the covering member 101 using the same water / cement ratio as the target concrete reacts with a delay after reacting at an early stage. Become. For example, when the water cement / ratio of the target concrete is 50%, the water / cement ratios of the two types of hardened cement composition constituting the covering member 101 of the sensor may be 50% and 60%.
The water cement / ratio may be two or more, and the number of levels is not particularly limited. For example, as shown in FIG. 8, if the corrosion detection sensor 100 having the corrosion detection member 10 under the covering member 101 having three different types of water / cement ratios is used, the number of data is increased and the prediction accuracy is improved.

The amount of air contained in the covering member 101 is preferably 5 to 35%. If the amount of air is less than 5%, the cured cement composition constituting the covering member 101 becomes dense, and there is a possibility that the penetration of the corrosion factor may be slow, and there is a possibility that an error in the evaluation of the corrosive environment becomes large. When the amount of air exceeds 35%, the cement composition hardened body constituting the covering member 101 has excessive voids and the structure becomes non-uniform, so that the occurrence of corrosion tends to vary. The air amount can be adjusted using an air amount adjusting agent.
In addition, if the fluidity | liquidity of the cement composition which has the said air quantity is represented by the flow value (JISR5201-1997) of 15 strokes, it will be 105-250 mm.

The thickness of the covering member 101 is preferably 1 to 20 mm. If the value is less than 1 mm, molding is difficult, and defects such as cracks are likely to occur, and if it exceeds 20 mm, the penetration of the corrosion factor is delayed and the period required for evaluation becomes longer.
The thickness of the covering member 101 is selected so that the ratio of the thickness / embedding depth of the covering member 101 is 0.2 or less (see FIG. 5). If the thickness ratio exceeds 0.2, the influence of the covering member 101 is added as an error factor to the salt permeability of the concrete to be buried, which is not preferable. In other words, the corrosion detection sensor 100 of the present invention is used by being embedded in concrete so that the ratio of the embedded depth / the thickness of the covering member 101 is 5 or more.

  The area of the covering member 101 is an area that can completely cover the corrosion detecting member 10 disposed immediately below, and the length of one side is sand or gravel used for concrete to be embedded Be larger than the maximum diameter of the aggregate. For example, when the maximum diameter (maximum aggregate dimension) of the aggregate is 20 mm, a square having a side length of more than 20 mm, a rectangle, a circle having a diameter of more than 20 mm, or an ellipse having a major axis of more than 20 mm, etc. Select a shape. This is because, when the exposed surface of the covering member 101 of the corrosion detection sensor 100 is smaller than the aggregate used for the concrete to be embedded in the sensor, the exposure is accidentally caused by the largest aggregate contained in the concrete. This is to avoid a situation where the entire surface is covered and the penetration path of the corrosion factor from the concrete surface is blocked.

When the hardened cement composition forming the covering member 101 is mortar, examples of the fine aggregate to be used include one or more selected from the group consisting of river sand, land sand, silica sand, lightweight aggregate, and the like. The fine aggregate may be natural aggregate or recycled aggregate.
The maximum particle size of the fine aggregate is preferably 1 mm or less because the lower limit of the thickness of the sensor is limited by the particle size of the fine aggregate and the uneven distribution of the aggregate is prevented.
The blending amount of the fine aggregate is preferably 3 or less as a fine aggregate / powder ratio (mass ratio). When the value exceeds 3, since the amount of the powder paste is small, the moldability may be reduced and coarse voids may be generated. The unit volume ratio of the fine aggregate is preferably 60% by volume or less.

Further, the cured body may include an admixture in order to adjust the solidity of the cured body. The admixture is preferably a fine mineral powder not having latent hydraulic properties or pozzolanic activity, such as fine limestone powder or silica powder. Fineness of該混sum material is a Blaine specific surface area, preferably 2500~10000cm ² / g, more preferably 3000~8000cm ² / g. If the value is less than 2500 cm ² / g, the water retention and material separation resistance may decrease, and the quality of the corrosion detection sensor 100 may vary. If the value exceeds 10,000 cm ² / g, the viscosity increases and molding becomes difficult. There is a case. The substitution rate of the admixture is preferably 10 to 85% by mass. In addition, the said substitution rate is content rate (mass%) of an admixture when the sum total of the mass of an admixture and cement is set to 100. As shown in FIG.

Moreover, in order to prevent cracks due to drying shrinkage, the cured cement composition forming the covering member 101 is made of organic fibers such as vinylon fibers, polyethylene fibers, and polypropylene fibers, inorganic fibers such as steel fibers and glass fibers, Further, it may contain a shrinkage reducing agent, a humectant and the like. The amount of the fiber added is preferably 0.02 or less by mass ratio with respect to the amount of powder in the cement composition.
Moreover, in order to improve the fluidity | liquidity of a cement composition, you may add water reducing agents, such as a water reducing agent, AE water reducing agent, and a high performance AE water reducing agent. The addition rate of the water reducing agent is preferably 0.05 or less in terms of mass ratio with respect to the amount of powder in the cement composition.

  The covering member 101 can be manufactured by casting molding into a mold, extrusion molding, press molding, vibration pressure molding or the like. For example, the corrosion detection member 10 is installed on the bottom side of an acrylic or high-strength mortar mold (exterior material 102), and the cement composition is placed on the exposed surface side. And after shaping | molding, a molded object may perform wet curing, underwater curing, steam curing, autoclave curing, etc.

  In the above-described configuration, the corrosion detecting member 10 may be individually disposed immediately below the covering member 101 for each covering member 101 having a different water / cement ratio, or by electrically connecting the corrosion detecting member, It is good also as a circuit structure that an electrical characteristic changes for every location of the covering member 101. FIG. For example, one corrosion detection member and one fixed resistor are assembled in series, and this is combined into one unit for each covering member 101 and connected in parallel, and the fixed resistors have different resistances. If the circuit is selected and configured by a circuit, a change in the electrical characteristics of the individual corrosion detection members 10 arranged immediately below the respective covering members 101 can be measured by one measurement circuit. The measurement circuit of the corrosion detection member 10 is not limited to the circuit configuration as long as the change in the electrical characteristics of the corrosion detection member 10 can be detected.

(C) Barrier Material In the corrosion detection sensor 100 of the present invention, the distance from the surface of the concrete to the exposed surface of the covering member 101 of the sensor and the change in the electrical characteristics of the conductor pattern portion from the point of embedding in the concrete occur. The corrosive environment is evaluated based on the time required for the process. Therefore, it is necessary to prevent penetration of the corrosion factor from other surfaces except the exposed surface of the coating member 101 into which the corrosion factor enters and the surface of the corrosion detection member 10 to which the corrosion factor reaches. As shown in FIG. 4, the surfaces other than the surface and the surface of the corrosion detection member 10 are blocked by a blocking material 102 (if the exterior material 102 also has a blocking effect, it can be the blocking material 102). Further, the boundary between the covering members 101 having different water / cement ratios arranged adjacent to each other is also blocked by the blocking material 102 in order to prevent the movement of the corrosion factors. Accordingly, the blocking material 102 is not particularly limited as long as it can prevent the invasion of corrosion factors. For example, the cement composition cured body such as mortar, ceramics, resin molded product, film, sheet, coating film, and 1 or more types chosen from a board etc. are mentioned. These blocking materials 102 can be applied to the corrosion detection member 10 and the covering member 101 via an adhesive, an adhesive, or the like. Therefore, the blocking material 102 does not penetrate the corrosion factor or is significantly lower than the covering member 101.

(D) Exterior Material The exterior material 102 is an arbitrary component used as necessary for reinforcing the strength of the corrosion detection sensor 100, reducing the size, avoiding an error factor, and the like. Cement composition hardened bodies, ceramic fired products and molded products having similar physical properties such as expansion coefficients are preferred. When the exterior material 102 has a function as the shielding material 102, the exterior material 102 is also included in the shielding material 102.

2. Next, a method for evaluating the corrosive environment of steel in concrete according to the present invention (hereinafter referred to as “corrosive environment evaluating method”) will be described.
(1) Outline of Corrosion Environment Evaluation Method In general, the corrosion environment of steel in concrete is affected by material factors such as the type and composition of cement and the environmental conditions around the concrete. Therefore, since the corrosive environment varies from concrete to concrete, the corrosive environment evaluation method of the present invention employs a method in which the corrosion detection sensor 100 is embedded in the concrete to actually grasp the corrosive environment in the concrete.
That is, the corrosion environment evaluation method of the present invention is based on a corrosion relational expression in which the corrosion detection sensor 100 is embedded in concrete, the corrosion occurrence time is measured by the corrosion detection sensor 100, and the corrosion occurrence time is included as a variable. In this method, a parameter for evaluating corrosion (hereinafter referred to as “corrosion evaluation parameter”) is obtained and the corrosive environment of the steel material in the concrete is evaluated using the parameter.

(2) Corrosion relational expression Specifically, the corrosion relational expression includes the following formula (1) which is Fick's second diffusion equation representing the diffusion phenomenon of the substance, the amount of corrosion generated salt of steel in concrete, and the cement composition. It is the following formula (2) representing the relationship between the water / cement ratio of the cured product.
C _CL = C ₀ × {1-erf [0.1 × S _cd / (2 × (D _d × t) ^0.5 )]} + C _i (1)
C _CL = a × (W / C) + b (2)
However, in _{(1), C CL} represents corroded salinity of steel in concrete _{^{(kg / m 3), C}} 0 represents the surface salinity of concrete _{^{(kg / m 3), S}} cd is buried Depth is expressed in mm, D _d is an apparent diffusion coefficient (cm ² / year), t is a time (year) until corrosion occurs, and C _i is an initial salinity. The equation (1) is an error function. Further, in _{(2), C CL} represents corroded salinity of steel in concrete (kg / ^{m 3),} W / C represents the water / cement ratio, a and b are determined for each type of cement Represents material coefficient.

(3) Corrosion evaluation parameter The corrosion evaluation parameters are the apparent diffusion coefficient of concrete and the surface salt content of concrete in the following formula (1). The diffusion coefficient is affected by material characteristics such as the type of cement constituting the concrete, the amount of unit cement in the concrete, and the water / cement ratio of the concrete, but the influence of the water / cement ratio is particularly large. In addition, the surface salinity of concrete is strongly influenced by the environment of the area where the concrete structure is constructed. Conventionally, the environment in which a concrete structure is constructed is quite different, so it is difficult to predict the surface salinity, and in reality, other than chemical analysis of concrete specimens taken from the structure by boring. There was no means to know the surface salinity. However, according to the evaluation method using the corrosion detection sensor 100 of the present invention, the apparent diffusion coefficient and the surface salinity of the concrete can be obtained simultaneously based on the equation (1).

(4) Method for calculating corrosion evaluation parameter Next, a method for calculating the corrosion evaluation parameter will be described.
If the water / cement ratio or the kind of cement of the covering member 101 is different, the amount of salt (corrosion generated salt amount) that causes corrosion in the iron forming the conductor pattern portion under it is different, but the cement in the covering member 101 is different. Are the same, only the water / cement ratio is related to the amount of corrosion generated salinity. Formula (2) is a formula derived based on this idea, and represents a linear relationship between the amount of iron corrosion generated salinity and the water / cement ratio. The material coefficients a and b in the formula (2) may be obtained in advance by experiments, or the coefficients described in the Japan Society of Civil Engineers Concrete Standard Specification (Design Standard Specification for Concrete Established in 2012: Standard, p. 149 p). May be used.
Corrosion-generating salinity of corrosion detection members under two or more coating members 101 having two or more different water / cement ratios is different as described above, and penetration of corrosion factors from the concrete surface is diffused. Therefore, there is a time difference until the salt content at the depth position where the corrosion detection sensor 100 is installed reaches two different corrosion-generated salt concentrations.
Therefore, for example, if the corrosion detection sensor 100 including the two covering members 101 having two different water / cement ratios is used, two sets of the two corrosion-generated salinities in the equation (1) The time (t) until the occurrence of corrosion and the embedding depth (S _cd ) are obtained. Based on the two sets of time and depth values, the surface salinity of the concrete and the apparent diffusion coefficient of the concrete can be calculated using equation (1).
Note that the value on the left side of (1) is the amount of salt generated by corrosion of the steel in the concrete, and is obtained from the water / cement ratio of the concrete by the formula (2).

On the contrary, if the surface salinity and the apparent diffusion coefficient of the concrete are obtained, the depth position of the reinforcing bar of the concrete structure can be known from the design drawing. Therefore, the corrosion occurrence time of the reinforcing bar in the concrete structure (t ) Becomes an unknown, and if the equation (1) is solved for t, the corrosion occurrence time of the reinforcing bars in the concrete structure can be predicted.
However, in the corrosive environment evaluation method of the present invention, it is necessary that the time for the corrosion factor to penetrate (pass) through the covering member 101 is short. However, as described in paragraphs 0020 and 0021, the air amount is set large. Therefore, the permeability of the corrosion factor is high, the thickness of the covering member 101 is as thin as 1 to 20 mm, and the ratio of the thickness of the covering member 101 of the corrosion detection sensor 100 to the embedding depth of the corrosion detection sensor 100 is 0. .2 or less, the corrosion factor penetrates the covering member 101 in a short time compared to a concrete structure.
In addition, as can be seen from the equation (1), the amount of penetration of the corrosion factor in the concrete structure is drastically reduced in the depth direction. Therefore, if a plurality of sensors are installed at different depths and the corrosion occurrence time is calculated using the equation (1), there is a high possibility that a time difference of several decades will occur and the error will increase. On the other hand, since the corrosion detection sensor 100 having a plurality of water / cement ratios of the present invention can be installed at the same depth position and can determine the amount of salinity occurring at a plurality of locations, there are few errors, Evaluation time can be shortened.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.
1. Materials used (1) Cement: Ordinary Portland cement (manufactured by Taiheiyo Cement)
(2) Fine aggregate: Silica sand (fine sand) that has passed through a JIS standard sieve with a nominal size of 850 μm
(3) Admixture: fine limestone powder, Blaine specific surface area of 6000 cm ² / g
(4) Water: tap water (5) AE water reducing agent: Pozzolith no. 70 (registered trademark, manufactured by BASF Japan)
(6) Air amount adjusting agent: Microair 303A (registered trademark, manufactured by BASF Japan)
(7) Corrosion detection member: Iron

2. Test method (1) Preparation of corrosion detection sensor and concrete test specimen Using a mortar with a water / cement ratio of 30% and a fine aggregate volume ratio of 40%, the outer dimensions of corrosion are 90mm in length, 50mm in width, and 15mm in thickness. The exterior material 102 of the detection sensor 100 was produced. Next, a recess having a depth of 2 mm, a size of 55 mm, and a width of 25 mm is formed in a flat portion of 90 mm in length and 50 mm in width of the exterior material 102, and a width of 5 mm, a length of 25 mm, and a thickness is formed in the central portion of the recess. A blocking member 102 having a thickness of 2 mm was installed vertically to divide the recess into two locations.
Furthermore, the corrosion detection member 10 having a length of 25 mm, a width of 20 mm, and a thickness of 0.02 mm was installed in the two recesses, and a cable was connected thereto.
Next, according to the blending conditions and blending shown in Table 1, mortars having different water / cement ratios were kneaded, and the mortars were respectively placed in the two recesses to form the surface. Sealed and cured for 7 days. In addition, the said mortar was adjusted using the said AE water reducing agent and the said air amount adjusting agent so that it might become the air amount and flow value which are shown in Table 1, respectively.
Then, as shown in FIG. 4, one of the exposed surfaces of the covering member 101 is left and the other five surfaces are covered with a mortar exterior material 102 (blocking material 102). A corrosion detection sensor 100 was produced, in which the coating member 101 and the corrosion detection member 10 were arranged directly below each other.

Then, after the sensor is installed in a 100 mm × 100 mm × 200 mm mold so as to be 20 mm from the surface of the prismatic concrete, the water / cement ratio is 50% in the mold, and the maximum coarse aggregate size Was filled with 20 mm of concrete.
Also, as a reference example, a rebar (SD295A, D10) with a length of 120 mm is installed at a position 35 mm deep from the surface inside the formwork, imitating a concrete structure, and filled with the same concrete as the concrete did. In addition, the lead wire was connected to the reinforcing bar so that the presence or absence of corrosion of the reinforcing bar could be determined by measuring the natural potential of the reinforcing bar.
Each of the five concrete pieces prepared above was sealed and cured until the age of 26 days, and then five specimens other than the permeation face were coated with a resin to prepare a test specimen.

(2) Corrosion promotion test From the age of 28 days, the specimen was immersed in an aqueous solution of sodium chloride at 60 ° C. and 10% by mass for 72 hours, and further dried at 60 ° C. and 60% humidity for 72 hours. This immersion and drying was repeated as one cycle to perform corrosion promotion curing.
Then, each time one cycle was passed, the electrical resistance of the corrosion detecting member 10 was measured with a high precision tester, and the natural potential of the reinforcing bar was measured with a high precision tester using a reference electrode (lead electrode).

  As a result of the test, the corrosion detection member 10 of the covering member 101 formed at a water / cement ratio of 60% increases four resistance values after the elapse of 4 cycles, and increases the remaining one resistance value after the elapse of 5 cycles. Reactions were observed, and the average number of cycles in which the reactions of the five corrosion detection sensors 100 were recognized was 4.2 cycles. Further, in the corrosion detecting member 10 covered with the covering member 101 having a water / cement ratio of 50%, one resistance value increases after four cycles, and the remaining four resistance values increase after five cycles. The average value of the cycles in which the reactions of the five corrosion detection sensors 100 were recognized was 4.8 cycles.

  Moreover, in the specimen of the reference example in which the reinforcing bar is embedded at a position 35 mm from the surface, the natural potential of one reinforcing bar decreases to −350 mV or less after 14 cycles, and the natural potential of the two reinforcing bars decreases after 15 cycles. It decreased to −350 mV or less, and the natural potential of the remaining two reinforcing bars decreased to −350 mV or less after 16 cycles. As a criterion for reinforcing bar corrosion, if the natural potential of the reinforcing bar drops below -350 mV, it can be determined that corrosion has occurred with a probability of 90% or more. Therefore, one reinforcing bar in the specimen of the reference example is one after 14 cycles. It is expected that two after 15 cycles and 2 after 16 cycles corroded.

(3) Calculation of corrosion evaluation parameters
Since the covering member 101 in the corrosion detection sensor 100 is manufactured using ordinary Portland cement, the material coefficient and the equation (2) described on page 149 of the concrete standard specification [design: standard] established in 2012 are obtained. The following equation (3) was derived by using this method. Then, in the following equation (3), the water / cement ratio is 50% and the value of 60% is substituted for 0.5 and 0.6 for the variable W / C, respectively, and the steel corrosion occurs for each water / cement ratio. When the amount of generated salt (C _lim , the unit is kg / m ³ ) was obtained, 1.9 and 1.6 were obtained, respectively. The value was used as Cl _max (that is, C _lim = Cl _max ) in the formula (1).
C _lim = −3.0 (W / C) +3.4 (3)

Here, since the accelerated test was used, the number of cycles was regarded as time, and when the corrosion occurrence time t in the equation (1) was used, a sensor incorporating a mortar (coating member 101) having a water / cement ratio of 60% was used. Substituting Cl _max = 1.6, S _cd = 20, t = 4.2, and C _i = 0.3 into the equation (1), the amount of salt on the exposed surface of the covering member 101 (C ₀ ) And the following equation (4) using the apparent diffusion coefficient (D _dt ) in the accelerated test as a variable (unknown number). Further, when a sensor containing a mortar with a water / cement ratio of 50% is used, Cl _max = 1.9, S _cd = 20, t = 4.8, and C _i = 0. By substituting 3, the following equation (5) was obtained with the salt content (C ₀ ) and the diffusion coefficient (D _dt ) as variables.
1.6 = C ₀ × {1-erf [0.1 × 20 / (2 × (D _dt × 4.2) ^0.5 )]} + 0.3 (4)
1.9 = C ₀ × {1-erf [0.1 × 20 / (2 × (D _dt × 4.8) ^0.5 )]} + 0.3 (5)
Then, from the binary simultaneous equations of the equations (4) and (5), C ₀ = 11 kg / m ³ as the surface salinity of the concrete, and the apparent diffusion coefficient D _dt = 0.195 cm ² / cycle in the acceleration test I wanted. Based on these two corrosion evaluation parameters, the corrosive environment of the steel material in the concrete could be evaluated. For example, the amount of salt at a depth of 35 mm from the concrete surface was calculated using the surface salinity of the concrete and the diffusion coefficient. FIG. 9 shows a graph showing the calculation result (curve) of the depth position and the steel material corrosion-generated salt content of 1.9 kg / m ³ with a water / cement ratio of 50%.

According to the above calculation, the amount of corrosion generated salt was 1.9 kg / m ³ when 15 cycles of the accelerated test passed. On the other hand, in the test results using the test specimen of the reference example, the corrosion time of the reinforcing bars installed at a position where the depth from the concrete surface was 35 mm was almost the same as the calculation results. Therefore, according to the experimental result and the evaluation method, it is possible to predict the corrosion time of the reinforcing bars in the concrete structure or to calculate the progress in the depth direction of the corrosion environment of the steel material by calculation.

  As described above, the apparent diffusion coefficient and the surface salinity can be obtained by using the corrosion detection sensor 100 having the coating member 101 and the corrosion detection member constituted by two or more different water / cement ratios. Moreover, according to the evaluation method using the corrosion detection sensor 100 of the present invention, not only the location environment of the concrete structure but also the time until the reinforcing bars of the concrete structure reach corrosion for each installation position of the corrosion detection sensor 100. Can be predicted. This makes it possible to take planned preventive maintenance measures, such as determining the priority of repairing the structure and treating with a salt penetration inhibitor.

DESCRIPTION OF SYMBOLS 10 Corrosion detection member 11 Conductive pattern part 11a Measurement terminal 12 Base material 13 Thin film part 100 Corrosion detection sensor 101 Cover member 102 Exterior material, blocking material 103 Code

Claims (7)

A corrosion detection sensor for detecting the progress of corrosion of steel in concrete, the sensor comprising the following (C) blocking material,
It is composed of two or more sets of (A) corrosion detection member and (B) coating member. One surface of the corrosion detection member installed in the shielding material is covered with the coating member, and the corrosion detection member of the coating member is covered. A corrosion detection sensor in which the other surface that is not exposed is exposed and the water / cement ratio of at least one set of covering members is different from the water / cement ratio of the other set of covering members.
(A) Corrosion detection member formed of an iron thin film (B) Covering member made of a hardened cement composition (C) Blocking material for blocking invasion of corrosion factors   The corrosion detection sensor is used by being embedded in concrete, and the corrosion factor of the steel material in the concrete penetrates from the exposed surface of the covering member, and the electrical characteristics of the corrosion detection member change due to the corrosion factor to cause corrosion. The corrosion detection sensor according to claim 1, which detects a progress state. The corrosion detection sensor according to [1] or [2], wherein the covering member has the following composition (a) to (d).
(A) Water / cement ratio (mass ratio × 100): 20 to 150%
(B) Water / powder ratio (mass ratio × 100): 15 to 120%
(C) Air volume: 5 to 35%
(D) Thickness of the covering member: 1 to 20 mm   The said corrosion detection member is formed by the member which detects corrosion by the change of the electrical resistance by the corrosion reaction resulting from corrosion, the change of an electric potential, or the change of an electric current density. The described corrosion detection sensor.   (Distance from the surface of the concrete to the exposed surface of the covering member of the embedded corrosion detection sensor) / (thickness of the covering member) / installed in the concrete so that the ratio is 5 or more. Item 5. The corrosion detection sensor according to any one of items 1 to 4. The corrosion detection sensor is embedded in concrete,
The corrosion detection time is measured by the corrosion detection sensor,
Obtain corrosion evaluation parameters based on the corrosion relational expression including the corrosion occurrence time as a variable,
Evaluating the corrosive environment of steel in concrete using the corrosion evaluation parameters,
A method for evaluating the corrosive environment of steel in concrete. The said corrosion relational expression is following (1) Formula and following (2) Formula, The said corrosion evaluation parameter is the apparent diffusion coefficient in the following (1) Formula, and the surface salinity of concrete, It is Claim 6. A method for evaluating the corrosive environment of steel in concrete.
C _CL = C ₀ × {1-erf [0.1 × S _cd / (2 × (D _d × t) ^0.5 )]} + C _i (1)
C _CL = a × (W / C) + b (2)
However, in the formula (1), _CCL represents the corrosion-induced salt content (kg / m ³ ) of the steel material, C ₀ represents the surface salt content (kg / m ³ ) of the concrete, and S _cd represents the surface of the concrete. Represents the distance (mm) to the exposed surface of the covering member of the embedded corrosion detection sensor, D _d represents the apparent diffusion coefficient (cm ² / year), and t represents the time (year) until corrosion occurs. C _i represents the initial salinity. The equation (1) is an error function. In the formula (2), _CCL represents the corrosion-generated salt content (kg / m ³ ) of the steel material, W / C represents the water / cement mass ratio (%), and a and b are the following types of cement. It represents the material coefficient determined for each.

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