JP7079051B2 - Corrosion estimation method and estimation method - Google Patents

Description

The present invention relates to a technique for estimating corrosion of steel materials.

In structures such as RC (Reinforced Concrete) and SRC (Steel Reinforced Concrete) structures, corrosion of reinforced concrete not only reduces the durability of concrete, but also adversely affects the structural performance of the structure. Conventionally, the natural potential method has been used for the occurrence of corrosion and the polarization resistance method for the progress of corrosion as a method for grasping the state of corrosion of reinforcing bars in an actual structure. However, since both methods measure through concrete, they are affected by the water content of concrete and chloride ions, and the measurement results vary, making it difficult to make a judgment. Therefore, a method for grasping the corroded state of reinforcing bars that is not affected by concrete is desired.

As conventionally used techniques, for example, Patent Document 1 and Patent Document 2 disclose an electrical corrosion sensor that detects electrical characteristics that change due to corrosion of thin wires such as iron. Further, Patent Document 3 discloses a technique of attaching a strain gauge to a reinforcing bar in a concrete structure and detecting the strain when the reinforcing bar is damaged, as a method of detecting corrosion of the reinforcing bar.

Further, the optical fiber has been conventionally used as a sensor for detecting strain generated in a structure. In Patent Document 4, a spirally shaped optical fiber sensor is attached to a structure to be measured, and changes in the optical propagation characteristics of the optical fiber sensor are measured by an electro-optical measuring device. This makes it possible to measure the displacement without breaking even if a large displacement occurs in the structure.

Further, in Patent Document 5, inside a concrete structure, a tape member that is hung on a spacer member and spirally wound, and an optical fiber that is wound along the tape member are used. This makes it possible to detect shear cracks in concrete members.

In addition, it is important to predict the progress of corrosion of steel materials in order to know the useful life of the structure. In particular, the amount of corrosion is important and is a factor that greatly affects the generated stress of concrete. In Non-Patent Document 1, a model is created based on the amount of corrosion and the coefficient of thermal expansion, and analysis is performed until corrosion cracks occur.

Japanese Unexamined Patent Publication No. 08-094557 Japanese Unexamined Patent Publication No. 2012-145330 Japanese Patent No. 4975420 Japanese Unexamined Patent Publication No. 2000-09767 Japanese Patent No. 408623

Mika Suzuki and 2 others, "Higher accuracy of durable / structural coupled analysis system based on quantification of crack generation limit corrosion amount and expansion rate of corrosive organisms", Annual Proceedings of Concrete Engineering, Vol.32, 2010, No.1, 773-778

The corroded area ratio and the amount of corrosion are used as quantitative indicators for grasping the corroded state of the reinforcing bar. The corroded area ratio is calculated by the following formula.

(Surface area of corroded rebar) / (Surface area of rebar) x 100 (%)
The amount of corrosion is calculated by the following formula.

(Mass of rebar before corrosion-Mass of rebar after removing corrosion products) / (Mass of rebar before corrosion) x 100 (%)
However, both the above-mentioned corrosion area ratio and corrosion amount are continuously measured or continuously corroded because it is necessary to take out the reinforcing bar and measure the corroded area or remove the corrosion product and then measure the mass of the reinforcing bar. It is difficult to grasp the state.

The present invention has been made in view of such circumstances, and it is possible to quantitatively grasp the corrosion area ratio or the amount of corrosion as the corrosion state of the reinforcing bar based on the behavior of the strain of the actual structure. It is intended to provide methods and estimation methods.

(1) In order to achieve the above object, the present invention has taken the following measures. That is, the corrosion estimation method of the present invention is a corrosion area ratio that indicates the ratio of the surface area of the corroded portion of the steel material to the surface area of the steel material or a corrosion estimation method that estimates the amount of corrosion of the steel material, and is an optical fiber on the surface of the steel material. Using a predetermined function, a step of fixing the sensor, a step of detecting the strain of the steel material due to the generation of a corrosion product by detecting a change in the characteristics of the light wave propagating in the optical fiber sensor, and a predetermined function are used. It is characterized by including a step of estimating a corrosion area ratio or a corrosion amount corresponding to the detected strain.

In this way, since the corrosion area ratio or the corrosion amount corresponding to the detected strain is estimated based on the predetermined function, it is possible to obtain the corrosion area ratio or the corrosion amount by detecting the strain. This makes it possible to quantitatively grasp the corrosion area ratio or the amount of corrosion as the corrosion status of the steel material.

(2) Further, the corrosion estimation method of the present invention is characterized in that the corrosion area ratio is estimated by using a predetermined exponential function according to the number of laps of the optical fiber sensor with respect to the steel material.

With this configuration, it is possible to estimate the corrosion area ratio with respect to the strain of the steel material according to the number of laps. This makes it possible to quantitatively grasp the corroded area ratio as the corrosion status of the steel material.

(3) Further, the corrosion estimation method of the present invention is characterized in that the corrosion amount corresponding to the detected strain is estimated based on a predetermined linear function.

With this configuration, it is possible to determine the amount of corrosion by detecting the strain. This makes it possible to quantitatively grasp the amount of corrosion as the corrosion status of the steel material.

(4) Further, the corrosion estimation method of the present invention further includes a step of adhering an aqueous sodium chloride solution to the steel material to which the optical fiber sensor is fixed, and exposes the steel material to which the optical fiber sensor is fixed to the atmosphere. It is characterized in that the strain of the steel material due to the generation of corrosion products is detected in this state.

With this configuration, it is possible to estimate the corroded area ratio or the amount of corrosion in an unrestrained environment. That is, since the corrosion area ratio or the amount of corrosion differs between restrained and unrestrained, under unrestrained conditions, the corroded area ratio or amount of corrosion under unrestrained conditions when the steel material is exposed to the atmosphere, not in concrete. Can be estimated.

(5) Further, the corrosion estimation method of the present invention detects the strain of the steel material due to the generation of corrosion products in a state where the steel material to which the optical fiber sensor is fixed is immersed in a saturated calcium hydroxide solution. It is characterized by that.

This configuration makes it possible to estimate the corroded area ratio or the amount of corrosion in the same environment as unrestrained concrete. That is, since the corrosion area ratio or the amount of corrosion differs between restrained and unrestrained, for example, a saturated calcium hydroxide solution can reproduce the environment in concrete, not in concrete, under unrestrained conditions. By immersing in the concrete, it is possible to estimate the corrosion area ratio or the amount of corrosion under unrestrained conditions. It is also possible to estimate the corrosion area ratio or the corrosion amount ratio in a salt-damaged environment by mixing a salt in a saturated calcium hydroxide solution. The immersion also includes spraying the solution.

(6) Further, in the estimation method of the present invention, the corroded area ratio or the amount of corrosion corresponding to the detected strain obtained by the measurement method according to any one of (1) to (5) above is used for concrete. It is characterized by estimating the useful life of the structure.

With this configuration, a reinforced concrete model can be created using the corrosion area ratio or the amount of corrosion obtained here, and analysis such as FEM can be performed. As a result, the stress generated in the concrete due to corrosion and the time when cracks occur can be estimated, the useful life can be estimated with high accuracy, and the appropriate maintenance of the structure can be performed.

According to the present invention, since the corrosion area ratio corresponding to the detected strain is estimated based on a predetermined exponential function, it is possible to obtain the corrosion area ratio if the strain can be detected. Further, since the corrosion amount corresponding to the detected strain is estimated based on a predetermined linear function, it is possible to obtain the corrosion amount if the strain can be detected. This makes it possible to quantitatively grasp the corrosion area ratio or the amount of corrosion as the corrosion status of the steel material.

It is a figure which shows the schematic structure of the corrosion sensor which concerns on this embodiment. It is a figure which shows the winding method of the optical fiber sensor around the polishing steel bar. It is a figure which shows the relationship between the elapsed time after the start of measurement, and the strain of a polished steel bar detected by an optical fiber sensor. It is a figure which shows the relationship between a corrosion area ratio and a strain. It is a figure which shows the relationship between the corrosion amount and strain of a polishing steel bar. It is a figure which shows the result of converting the relationship between the elapsed time and the strain in the test body 1-2 into the strain in the radial direction of a reinforcing bar. It is a figure which shows the result of converting the relationship between the elapsed time and strain in the test body 1-2 into the displacement in the radial direction of a reinforcing bar.

The present inventors focused on the relationship between the strain of the steel material due to corrosion and the corrosion area ratio and the amount of corrosion, fixed the optical fiber sensor to the steel material, and the strain and the corrosion area of the steel material obtained from the optical fiber sensor in a corroded environment. By formulating the relationship with the rate and the relationship between the strain of the steel material obtained from the optical fiber sensor and the amount of corrosion in a corroded environment, the strain obtained by the optical fiber sensor for the reinforcing bars in the actual structure is used. , It was found that the corroded state of the reinforcing bar can be grasped, and the present invention was reached.

That is, the corrosion estimation method of the present invention is a corrosion area ratio that indicates the ratio of the surface area of the corroded portion of the steel material to the surface area of the steel material or a corrosion estimation method that estimates the amount of corrosion of the steel material, and is an optical fiber on the surface of the steel material. Using a predetermined function, a step of fixing the sensor, a step of detecting the strain of the steel material due to the generation of a corrosion product by detecting a change in the characteristics of the light wave propagating in the optical fiber sensor, and a predetermined function are used. It is characterized by including a step of estimating a corrosion area ratio or a corrosion amount corresponding to the detected strain.

This made it possible for the present inventors to quantitatively grasp the corrosion area ratio or the amount of corrosion as the corrosion state of the steel material. Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

FIG. 1 is a diagram showing a schematic configuration of a corrosion sensor according to the present embodiment. The corrosion sensor 11 includes a polishing bar steel 12 as an iron bar, and an optical fiber sensor 14 having a detection unit 13 wound around the surface of the polishing bar steel 12 to detect strain. As a result, it is possible to use an optical signal capable of long-distance transmission, and it is possible to perform multipoint measurement. Further, the corrosion sensor 11 may include a covering portion 15 that covers the polished steel bar 12 and the optical fiber sensor 14. The covering portion 15 can be made of, for example, a mortar having a cover of 10 mm. Since the covering portion 15 is provided, it is possible to prevent the polished steel bar 12 from rusting before being installed in the reinforced concrete structure. Note that FIG. 1 shows the corrosion sensor 11 as an example, and does not specify the number of turns of the optical fiber sensor 14 with respect to the polished steel bar 12. That is, in the present embodiment, the number of turns of the optical fiber sensor 14 around the polished steel bar 12 is assumed to be several. Further, in the examples described later, an example in which the covering portion 15 is not provided is shown.

Corrosion of steel produces corrosion products and volume expansion. When the steel material is corroded, some strain behavior occurs in addition to the influence of temperature and external force. Therefore, the corrosion can be detected by measuring the strain of the steel material. Since the behavior differs depending on the environmental conditions and concrete, when the optical fiber sensor 14 is wound around the polished steel bar 12, it is wound so as to be in close contact with each other, preferably to apply a tensile force. This makes it possible to measure strain on both the expansion side and the contraction side.

Further, when the optical fiber sensor 14 is wound around the polished steel bar 12, the optical fiber sensor 14 may be attached in a straight line or bent in a wavy shape, but is preferably spirally rotated. Wrap in a shape or a loop. As the number of laps increases, the corroded portion and the optical fiber overlap with each other, so that the optical fiber is detected at an early stage. However, if the number of laps is too large, the corrosion factor does not reach the polished steel bar 12. As a guide, the number of laps is 0.01 to 2 for the fiber length (mm) / surface area of steel bar (mm ² ). In any case, it suffices if the change in corrosion that occurs in the polished steel bar 12 can be detected as a strain. When the optical fiber sensor 14 is wound around the polished steel bar 12, the polished steel bar 12 is preferably wound because it is columnar and the surface is smooth, so that the optical fiber sensor is not easily damaged. Further, the detection unit 13 can use an FBG sensor or the like, and it is preferable that the detection unit 13 is longer or larger.

The mortar constituting the covering portion 15 has a water-cement ratio equal to or higher than that of the structure concrete so as not to prevent the invasion of the corrosive factor and to allow the corrosive factor to reach the polished steel bar 12 at an early stage. The covering portion 15 preferably has a thickness of 3 to 15 mm so that the polished steel bar 12 can be protected without cracking. Further, it is preferable to use an admixture so that separation and bleeding do not occur.

When the corrosion sensor 11 is installed in concrete to detect corrosion, it is desirable to use a dummy sensor together. As the dummy sensor, a dummy sensor in which the entire surface of the corrosion sensor 11 is subjected to rust prevention treatment may be used, or a second dummy sensor having substantially the same linear expansion coefficient as the polished steel bar 12 and less likely to corrode than the reinforcing bar. A dummy sensor provided on the surface of the bar material and the second bar material and provided with an optical fiber sensor for detecting strain may be used.

Then, the corrosion sensor 11 and the dummy sensor are installed in the same environment, the strain generated by a factor other than corrosion is detected by the dummy sensor, and the strain detected by the dummy sensor is used to correct the strain detected by the corrosion sensor 11. May be. This makes it possible to remove the influence of strain caused by factors other than corrosion, such as temperature strain.

That is, various strains occur in concrete due to temperature / humidity, shrinkage of concrete, and external force. Therefore, at least a dummy sensor that is less likely to corrode than the corrosion sensor 11 is used, and corrosion is determined by comparing with the strain behavior thereof. As a dummy sensor, there is a method in which a coated mortar is coated with an epoxy resin or the like to prevent neutralization and invasion of deterioration factors and prevent corrosion of carbon steel inside. Alternatively, use stainless steel (for example, SUS410) having a coefficient of linear expansion equivalent to that of carbon steel.

[Example]
Next, an embodiment will be described. FIG. 2 is a diagram showing how an optical fiber sensor is wound around a polished steel bar. The method of winding the optical fiber cable 42 around the polished steel bar 41 is to perform the winding work under a certain tension, for example, after confirming that some tensile strain is generated at the time of winding, and fix the end portion with an adhesive. ..

In this embodiment, the optical fiber cable 42 (φ150 μm) is spirally wound around the central section 25 mm in the axial height direction of the polished steel bar 41 (JIS G3108, φ20 × h50 mm) so that the FBG sensor portion is located in the center. Both ends of the optical fiber cable 42 were fixed to the polished steel bar 41 by adhesion. Three test pieces were prepared for each of the three levels of the number of laps of the optical fiber cable 42 of 1, 2, and 3, and a 10% NaCl aqueous solution was prepared with respect to the side surfaces other than the upper and lower end surfaces of the polished steel bar 41. Adhere salt water with absorbent cotton soaked in, and 30 ° C. 90% R. H. The strain of the polished steel bar due to corrosion was measured by placing it in a constant temperature and humidity chamber.

As the optical fiber sensor (FBG sensor), for example, the one having the specifications shown in the following table was used.

ここで、ε：ひずみ（μ）、λ：測定時の波長（ｎｍ）、λ^*：初期波長（ｎｍ）である。 In the optical fiber sensor, the wavelength was converted to strain by the following equation, and the change in strain due to corrosion was confirmed.

Here, ε: strain (μ), λ: wavelength at the time of measurement (nm), λ ^* : initial wavelength (nm).

[Corrosion test]
The corroded state of the test piece was photographed at 0.7 days, 3 days, 7 days, 10 days, and 14 days after the elapsed days from the start of measurement, and the corroded area ratio was calculated. The corroded area ratio indicates the ratio of the surface area of the corroded portion of the steel material to the surface area of the steel material. The measurement is terminated when the wavelength of the optical fiber sensor exceeds the permissible value or on the 14th day, whichever comes first, and after removing the optical fiber cable 42 installed on the polished steel bar 41, 10% ammonium hydrogen citrate is used. It was immersed in an aqueous ammonium solution (60 ° C.) to remove rust, and the amount of corrosion was measured.

FIG. 3 is a diagram showing the relationship between the elapsed time after the start of measurement and the strain of the polished steel bar detected by the optical fiber sensor. In the legend shown in FIG. 3, (number of laps of the optical fiber)-(No) is shown. For example, in "1-1", the number of laps of the optical fiber is 1, and No. It shows that it is a test piece of 1. As shown in FIG. 3, it can be seen that the volume expansion strain due to corrosion is measured with the passage of time.

[Relationship between corrosion area rate and strain]
Next, in order to examine the relationship between the corrosion area ratio and the strain, which is a guideline for grasping the corrosion state, the corrosion area ratio was calculated for each body whose strain could be measured until the 14th day, and the relationship with the strain was determined. It is shown in FIG. The corrosion area ratio 0.7 days from the start of measurement is about 20% in each case, and the corrosion has progressed, but the strain is about several tens of μ at most, which is not a large value. Focusing on the test piece 3-2 with 3 laps of the optical fiber cable, the strain tends to increase even if the corrosion area ratio is smaller than that of other test pieces, and increases exponentially when it exceeds about 30%. did. The longer the number of laps of the optical fiber cable, the longer the contact length with the steel surface, and the higher the probability of contact with the corroded part, the faster the corrosion can be detected. It is expected to prevent arrival.

As shown in FIG. 4, an exponential function of "y = 11.546e ^0.0657x , R ² = 0.995" (R ² is the contribution ratio) was obtained from the measurement results of the test body 1-2. Further, from the measurement results of the test body 2-2, an exponential function of "y = 2.0314e ^0.0794x , R ² = 0.9537" was obtained. Further, from the measurement results of the test body 3-2, an exponential function of "y = 0.2209e ^0.1616x , R ² = 0.877" was obtained. As is clear from this result, it was possible to formulate the relationship between the strain of the polished steel bar obtained from the optical fiber sensor in each test piece and the corrosion area ratio.

[Relationship between corrosion amount and strain]
FIG. 5 is a diagram showing the relationship between the amount of corrosion and strain of the polished steel bar. As is clear from FIG. 5, a positive correlation is observed between the amount of corrosion and the strain regardless of the number of laps of the optical fiber cable, and when the corrosion is considerably advanced, the volume expands as the amount of corrosion increases. It was found that the strain was also large, and it was found that the amount of corrosion could be estimated from the strain. As shown in FIG. 5, a linear function of "y = 891.7x, R ² = 0.4103" was obtained from the relationship between the amount of corrosion and the strain for each of the number of laps 1 to 3. As is clear from this result, it was possible to formulate the relationship between the strain and the amount of corrosion of the polished steel bar obtained from the optical fiber sensor in each test piece.

By conducting the above-mentioned tests in various environments, it is possible to estimate the corrosion area ratio and the corrosion amount of the reinforcing bar from the strain amount of the polished steel bar.

[Modeling of reinforcing bars in corroded state]
FIG. 6 is a diagram showing the result of converting the relationship between the elapsed time and the strain in the test piece 1-2 shown in FIG. 3 into the strain in the radial direction of the reinforcing bar. FIG. 7 is a diagram showing the result of converting the relationship between the elapsed time and the strain in the test piece 1-2 shown in FIG. 3 into the radial displacement of the reinforcing bar. These make it possible to model the reinforcing bar in a corroded state.

In order to reproduce the above-mentioned test in a strong alkaline environment of concrete, a reinforcing bar around which an optical fiber sensor is wound is immersed in a saturated calcium hydroxide solution, and the corrosion product is elastic so as not to diffuse into water. It is also possible to cover the reinforcing bar with a fiber or sponge having a small modulus and measure the strain in the same environment as concrete under conditions close to unrestrained. By mixing a salt with a saturated calcium hydroxide solution, it is possible to perform measurements in a salt-damaged environment.

As described above, according to the present embodiment, the corrosion area ratio or the amount of corrosion corresponding to the detected strain is estimated based on a predetermined function. Therefore, the corrosion area ratio or corrosion is detected by detecting the strain. It is possible to determine the quantity. This makes it possible to quantitatively grasp the corrosion area ratio or the amount of corrosion as the corrosion status of the steel material.

11 Corrosion sensor 12 Polished steel bar 13 Detection unit 14 Optical fiber sensor 15 Coating unit 41 Polished steel rod 42 Optical fiber cable

Claims (6)

A corrosion area ratio indicating the ratio of the surface area of the corroded portion of the steel material to the surface area of the steel material or a corrosion estimation method for estimating the amount of corrosion of the steel material.
The process of fixing the optical fiber sensor to the surface of the steel material and
A step of detecting the strain of the steel material due to the generation of a corrosion product by detecting a change in the characteristics of the light wave propagating in the optical fiber sensor, and a step of detecting the strain of the steel material.
Including a step of estimating the corrosion area ratio or the amount of corrosion corresponding to the detected strain using a predetermined function.
A corrosion estimation method, characterized in that the corrosion area ratio is estimated by using a predetermined exponential function according to the number of laps of the optical fiber sensor with respect to a steel material. A corrosion area ratio indicating the ratio of the surface area of the corroded portion of the steel material to the surface area of the steel material or a corrosion estimation method for estimating the amount of corrosion of the steel material.
The process of winding the optical fiber sensor so that it is in close contact with the surface of the steel material, and
The process of fixing the wound optical fiber sensor and
A step of detecting the strain of the steel material due to the generation of a corrosion product by detecting a change in the characteristics of the light wave propagating in the optical fiber sensor, and a step of detecting the strain of the steel material.
A corrosion estimation method comprising a step of estimating a corrosion area ratio or a corrosion amount corresponding to the detected strain using a predetermined function. The corrosion estimation method according to claim 2, wherein the amount of corrosion corresponding to the detected strain is estimated based on a predetermined linear function. A corrosion area ratio indicating the ratio of the surface area of the corroded portion of the steel material to the surface area of the steel material or a corrosion estimation method for estimating the amount of corrosion of the steel material.
A process of winding the optical fiber sensor so as to be in close contact with the surface of the steel material in an unrestrained environment.
The process of fixing the wound optical fiber sensor and
The step of adhering the sodium chloride aqueous solution to the steel material to which the optical fiber sensor is fixed, and
A step of detecting strain of the steel material due to the generation of a corrosion product by detecting a change in the characteristics of a light wave propagating in the optical fiber sensor in a state where the steel material to which the optical fiber sensor is fixed is exposed to the atmosphere. When,
Including a step of estimating the corrosion area ratio or the amount of corrosion corresponding to the detected strain using a predetermined function.
The detected strain is converted into the radial strain and the radial displacement of the reinforcing bar, and the converted radial strain and the radial displacement are modeled as the corrosion state of the reinforcing bar without restraint. Corrosion estimation method. A corrosion area ratio indicating the ratio of the surface area of the corroded portion of the steel material to the surface area of the steel material or a corrosion estimation method for estimating the amount of corrosion of the steel material.
A process of winding the optical fiber sensor so as to be in close contact with the surface of the steel material in an unrestrained environment.
The process of fixing the wound optical fiber sensor and
The steel material to which the optical fiber sensor is fixed is immersed in a saturated calcium hydroxide solution, and by detecting a change in the characteristics of the light wave propagating in the optical fiber sensor, the steel material is generated due to the generation of corrosion products. And the process of detecting the strain of
Including a step of estimating the corrosion area ratio or the amount of corrosion corresponding to the detected strain using a predetermined function.
The detected strain is converted into the radial strain and the radial displacement of the reinforcing bar, and the converted radial strain and the radial displacement are modeled as the corrosion state of the reinforcing bar without restraint. Corrosion estimation method. It is characterized in that the useful life of a concrete structure is estimated by using the corrosion area ratio or the amount of corrosion corresponding to the detected strain obtained by the corrosion estimation method according to any one of claims 1 to 5. Estimating method to do.

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