JP6574331B2 - Corrosion sensor and corrosion detection method - Google Patents

Description

  The present invention relates to a technique for detecting a corrosive environment of a reinforced concrete structure.

  2. Description of the Related Art Conventionally, as a technique for detecting a corrosive environment, an electrical corrosion sensor that detects electrical characteristics that change when a fine wire such as iron corrodes is known (for example, Patent Document 1 and Patent Document 2). Moreover, as a method of detecting corrosion of a reinforcing bar, a strain gauge is attached to the reinforcing bar in the concrete structure, and the strain when the reinforcing bar is damaged is detected (Patent Document 3). On the other hand, an optical fiber has been conventionally used as a sensor for detecting strain generated in a structure. In Patent Document 4, a helically shaped optical fiber sensor is attached to a structure to be measured, and a change in light propagation characteristics of the optical fiber sensor is measured by an electro-optical measuring device. As a result, even if a large displacement occurs in the structure, it is possible to measure the displacement without breaking.

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

Japanese Patent Laid-Open No. 08-094557 JP 2012-145330 A Japanese Patent No. 4975420 JP 2000-097647 A Japanese Patent No. 4008623

  As a method for detecting corrosion in a reinforced concrete structure, the self-potential method has been conventionally known, but this method must be measured by connecting the cable and the internal rebar through the concrete surface. In addition, there is a problem that measurement cannot be performed unless the concrete surface is sufficiently wet. Furthermore, when the surface of the structure is a resin-based paint or tile finish, it cannot be measured.

  Conventionally known electrical corrosion sensors are affected by transmission loss, electromagnetic interference, etc. Furthermore, when monitoring is performed constantly, current flows at the time of measurement. is there. In addition, the detection due to corrosion breakage of these iron wires and iron foils cannot capture the electrical characteristics over time, and it is difficult to evaluate the degree of subsequent progress only by detecting that it has become a corrosive environment. It is.

  In addition, in order to measure the strain of a steel material due to corrosion, when a strain gauge is directly attached to the steel material or installed in the vicinity, the corrosive environment of the reinforcing bar cannot be detected in advance. Alternatively, the measuring instrument, adhesive, etc. cover the steel material, which affects the occurrence of corrosion and may not be able to accurately detect corrosion. Furthermore, if corrosion occurs in the portion, the strain gauge may be peeled off, and measurement may not be possible, or correct results may not be obtained even if measurement is possible.

  On the other hand, the method of directly winding an optical fiber around a reinforcing bar in a structure is to dispose the optical fiber over the entire structure and detect damage or deformation of the structure, and does not detect a corrosive environment. Even if the strain due to corrosion is detected, it is detected after the reinforcing bar is corroded.

  This invention is made in view of such a situation, and it aims at providing the corrosion sensor and corrosion detection method which can detect the corrosion environment of steel materials early and correctly using an optical fiber sensor. To do.

  (1) In order to achieve the above object, the present invention takes the following measures. That is, the corrosion sensor of the present invention is a corrosion sensor that detects the corrosive environment of a reinforced concrete structure, and includes an iron bar and an optical fiber sensor that is provided on the surface of the bar and detects strain. It is characterized by that.

  As described above, since the iron bar and the optical fiber sensor provided on the surface of the bar and detecting the strain are provided, an optical signal capable of long-distance transmission can be used, and multipoint measurement is performed. It becomes possible. In addition, since the change in the characteristics of the light wave propagating through the optical fiber sensor is detected by the strain caused by the corrosion of the rod material, the effects of transmission loss and electromagnetic interference, etc., when using an electrical corrosion sensor are detected. Since corrosion does not occur due to current flowing during measurement, it is possible to realize an accurate and convenient corrosion sensor. In addition, the degree of progress of the corrosive environment can be determined by continuously measuring the strain even after the corrosive environment is detected.

  (2) Moreover, the corrosion sensor of this invention WHEREIN: The said bar is a cylindrical form, It is characterized by the above-mentioned.

  In this way, since the bar is cylindrical, unlike deformed reinforcing bars with ribs and joints, when optical fibers are wound, they can be tightly wound without any gaps, making it easy to detect strain changes due to corrosion and winding. Sometimes optical fibers are not easily damaged.

  (3) Further, in the corrosion sensor of the present invention, the bar is a polished steel bar made of the same material as the reinforcing bar used in the reinforced concrete structure or a material more easily corroded.

  In this way, the corrosive environment can be detected earlier by making the material of the target concrete reinforcing bars the same as or more easily corroded. Furthermore, although the reinforcing bar is rust-proofed, it is easily corroded by using a polished steel bar that has not been rust-proofed, and the corrosive environment can be detected earlier.

  (4) Moreover, the corrosion sensor of this invention is further provided with the coating | coated part which coat | covers the said bar and the said optical fiber sensor.

  Thus, since the coating | coated part which coat | covers a rod and an optical fiber sensor is further provided, the expansion | swelling by a corrosion product can be caught. Moreover, it becomes possible to avoid that a steel bar will rust before installing in a reinforced concrete structure. Further, the steel bar and the optical fiber sensor are not damaged during construction such as when the sensor is installed or when concrete is placed.

  (5) Moreover, the corrosion sensor of this invention WHEREIN: The said optical fiber sensor is wound around the surface of the said rod.

  With this configuration, it is possible to detect the strain due to the volume change generated in the bar by the optical fiber sensor.

  (6) Moreover, the corrosion detection method of this invention installs the corrosion sensor in any one of said (1) to (5) in the surface layer side of the reinforcing bar in a reinforced concrete structure, It is characterized by detecting a change in characteristics of a light wave propagating through the.

  In this way, since the corrosion sensor is installed on the surface side of the reinforcing bar in the reinforced concrete structure, the bar of the corrosion sensor corrodes before the reinforcing bar in the reinforced concrete structure. It becomes possible.

  (7) Moreover, the corrosion detection method of this invention installs the corrosion sensor in any one of said (1) to (5) in a reinforced concrete structure, and is any of said (1) to (5) A dummy sensor that has been subjected to rust prevention treatment on the entire surface of the corrosion sensor, or a second bar that has a coefficient of linear expansion substantially equal to that of the iron bar and is less likely to corrode than a reinforcing bar, and A dummy sensor provided on the surface of the second bar and provided with an optical fiber sensor for detecting strain is installed in a reinforced concrete structure, and strain caused by factors other than corrosion is detected by the dummy sensor, The strain detected by the corrosion sensor according to any one of the above (1) to (5) is corrected using the strain detected by the dummy sensor.

  In this way, the strain generated by factors other than corrosion is detected using the dummy sensor, and the strain detected by the dummy sensor is detected by the corrosion sensor according to any one of (1) to (5) above. Since the distortion is corrected, it is possible to remove the influence of the distortion caused by factors other than corrosion such as temperature distortion.

  According to the present invention, an optical signal capable of long-distance transmission can be used, and multipoint measurement can be performed. In addition, it is not affected by transmission loss and electromagnetic interference as in the case of using an electrical corrosion sensor, and the corrosion does not progress due to current flowing during measurement. A sensor can be realized.

It is a figure which shows schematic structure of the corrosion sensor which concerns on this embodiment. It is a figure which shows typically a mode that the corrosion sensor and dummy sensor which concern on this embodiment were installed in the reinforced concrete structure. It is a figure which shows how to wind the optical fiber sensor around a polishing rod. It is a figure which shows schematic structure of the test body which concerns on a present Example. It is a figure which shows the example of a detection of the corrosion sensor which concerns on this embodiment.

  FIG. 1 is a diagram showing a schematic configuration of a corrosion sensor according to the present embodiment. The corrosion sensor 11 includes a post-rolled steel bar 12 as an iron bar, and an optical fiber sensor 14 that is wound around the surface of the polished bar steel 12 and has a detection unit 13 that detects strain. Thereby, an optical signal capable of long-distance transmission can be used, and multipoint measurement can be performed. Further, the corrosion sensor 11 includes 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 with a cover of 10 mm. Since the covering portion 15 is provided, it is possible to avoid that the polished steel bar 12 is rusted before being installed in the reinforced concrete structure.

When steel materials corrode, corrosion products are generated and volume expansion occurs. When corrosion occurs in the steel material, some strain behavior occurs in addition to the influence of temperature, external force, etc., so that the corrosion can be detected by measuring the strain of the steel material. Since the behavior varies depending on 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 with a tensile force. Thereby, both the expansion side and the contraction side strain can be measured. 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 wave shape, but preferably spirals around. Wrap in a loop or loop. Since the corroded portion and the optical fiber overlap with each other as the number of turns increases, the detection is performed early. However, if the number of turns is too large, the corrosion factor is prevented from reaching the polished steel bar 12. As a guideline, the fiber length (mm) / steel bar surface area (mm ² ) is 0.01 to ² as a guide. Anyway, it is only necessary to detect the change in corrosion occurring in the polished steel bar 12 as strain. In the case where the optical fiber sensor 14 is wound around the polished steel bar 12, the polished steel bar 12 is preferably wound more uniformly as the surface is smoother and cylindrical, and the optical fiber sensor is less likely to be damaged. In addition, an FBG sensor or the like can be used as the detection unit 13, and the longer or more detection unit 13 is preferable.

  The mortar constituting the covering portion 15 has a water-cement ratio higher than that of the structural concrete so as not to prevent the invasion of the corrosion factor and so that the corrosion factor reaches the polished steel bar 12 at an early stage. The covering portion 15 preferably has a thickness of 3 to 15 mm so as to protect the polished steel bar 12 without cracking. Moreover, it is preferable to use an admixture so that separation and bleeding do not occur.

  Here, when repairing a reinforced concrete structure that has already deteriorated due to corrosion, internal salt is contained on the back side (inside) of the reinforced concrete structure. By installing the corrosion sensor 11 in the reinforced concrete structure as it is, the cover (surface ) Detect corrosion due to deterioration factors from all directions so that deterioration factor intrusion from the side and the influence of endogenous salinity are included. On the other hand, when detecting the deterioration factor only from the fogging (surface) side, the back side of the corrosion sensor 11 is covered with epoxy resin or the like to block the influence of the deterioration factor from the back side. Further, when repairing the repaired part with mortar, if the corrosion sensor is stored so as not to rust until installation, the corrosion sensor will not be damaged by the repair of the mortar, and therefore the covering part may be omitted.

Based on the theory of diffusion, it is possible to accurately predict the period from the depth of the embedded corrosion sensor 11 from the concrete surface and the depth of the reinforcing bar to the arrival of the corrosion factor on the steel material. Then it will be useful information. For example, if the corrosion factor penetrates from the concrete surface to the inside by diffusion, the distance from the concrete surface to the corrosion sensor 11 is A, the distance from the concrete surface to the reinforcing bar is B, and the corrosion sensor 11 from the construction of the concrete structure is the corrosion factor. TA is the time from when the concrete structure is constructed until corrosion of the steel material occurs, and the time TB can be predicted as TB = TA · (B ² / A ² ), and the information detected by the corrosion sensor 11 Therefore, it is possible to take measures to protect the concrete structure from deterioration before deterioration occurs. Further, by installing a plurality of corrosion sensors at different depths from the concrete surface, it is possible to more accurately determine the time until the reinforcing bars corrode.

  FIG. 2 is a diagram schematically illustrating a state in which the corrosion sensor and the dummy sensor according to the present embodiment are installed in a reinforced concrete structure. As shown in FIG. 2, the reinforced concrete structure 21 includes reinforcing bars 23 in the horizontal direction and the vertical direction. A dummy sensor 25 and corrosion sensors 26 and 27 are provided at positions closer to the surface than the reinforcing bar 23. A data logger 33 is also provided. The deterioration factor affects the corrosion sensors 26 and 27 before the reinforcing bar 23. Thus, when installing the corrosion sensor 11 in a reinforced concrete structure, it is desirable to install it on the surface layer side of the reinforcing bar in the reinforced concrete structure. By installing on the surface layer side, the bar of the corrosion sensor corrodes before the reinforcing bars in the reinforced concrete structure, so that early detection of corrosion becomes possible.

  When the corrosion sensor 11 is installed in a reinforced concrete structure and corrosion is detected, it is desirable to use a dummy sensor together. The dummy sensor may be a dummy sensor in which the entire surface of the corrosion sensor 11 is subjected to rust prevention treatment, or a second sensor that has substantially the same linear expansion coefficient as that of the polished steel bar 12 and is less susceptible to corrosion than the reinforcing bar. A dummy sensor provided with a bar and an optical fiber sensor that is provided on the surface of the second bar and detects strain may be used.

  Then, the corrosion sensor 11 and the dummy sensor are installed in the reinforced concrete structure, the strain caused by factors other than the corrosion is detected by the dummy sensor, and the strain detected by the corrosion sensor 11 is detected using the strain detected by the dummy sensor. It may be corrected. Thereby, for example, it becomes possible to eliminate the influence of strain caused by factors other than corrosion such as temperature strain.

  That is, various strains are generated in a reinforced concrete structure by temperature / humidity, concrete shrinkage, and external force. Therefore, at least a dummy sensor that is less likely to corrode than the corrosion sensor 11 is used, and the corrosion is determined in comparison with the strain behavior. The dummy sensor has a method in which the coating mortar is coated with an epoxy resin or the like to prevent the carbon steel inside from being corroded by preventing neutralization or deterioration factors from entering. Alternatively, stainless steel (for example, SUS410) having a linear expansion coefficient equivalent to that of carbon steel is used.

  Next, examples of the corrosion sensor will be described. Here, the case where corrosion is detected in salt water as a test will be described as an example. In this example, the outline of the corrosion sensor was as follows.

  The shape of the polished steel bar and the number of windings of the fiber are examples, and the present invention is not limited to these. As the polished steel bar, JISG 3108 SGD3M was used.

  In addition, it is preferable to detect corrosion based on the difference in strain behavior due to the dummy sensor, and it is expected that the effect of volume change and moisture content of the coated mortar will appear in the strain. A dummy sensor specimen was prepared.

  FIG. 3 is a diagram showing how the optical fiber sensor is wound around the polished steel bar. The method of winding the optical fiber around the polished steel bar is under a constant tension, for example, after confirming that some tensile strain has occurred at the time of winding, the winding work is performed, and the end is made of CN (manufactured by Tokyo Sokki) Fix it. FIG. 3B shows this embodiment.

  For example, optical fiber sensors (FBG sensors) having the following specifications are used.

  Next, the mortar as the covering portion will be described. The materials used for the mortar are as shown in the following table.

  Next, the composition of the mortar is as shown in the following table.

  In the above table, “B” is a mixture of “C” and “L”.

[Mortar mixing method]
The mortar used for the corrosion sensor was kneaded using “Maruto Seisakusho Co., Ltd. mortar mixer (2 L kneading)”. The mixing procedure is as follows. The mortar was kneaded in a constant temperature and humidity chamber at 20 ± 2 ° C. and a humidity of 50% or more.

  Put mortar into a vinyl mold (inner diameter φ 40 mm x height 50 mm), put a steel bar wrapped with optical fiber in the center, and after curing in the same constant temperature and humidity chamber for 3 hours, 20 ° C humidity 95 % Was cured for 7 days and demolded.

  FIG. 4 is a diagram illustrating a schematic configuration of a test body according to the present example. As shown in FIG. 4, the specimen 40 has a vertical fog of 20 mm and a horizontal fog of 10 mm with respect to the corrosion sensor 11. The following table gives an overview of the specimens.

  Measure the specimen in a corrosive environment (at a temperature of 40 ° C., immersed in a 10% NaCl aqueous solution for 1 day, dried for 60% humidity for 3 days, again immersed in a 10% aqueous NaCl: 1 day, and then dried for 60% humidity). The change in wavelength was measured with an instrument (manufactured by Watanabe Seisakusho Co., Ltd.). In the immersion of the NaCl: 10% aqueous solution, a portion of 30 mm from the lower end of the test specimen was immersed so that the NaCl aqueous solution did not enter from the optical fiber lead-out portion. The dummy specimen used here was the same specimen as the corrosion sensor without using a steel bar that does not corrode experimentally, and was immersed in pure water that does not corrode instead of using the NaCl aqueous solution.

  Using the following equation, the wavelength was converted to strain, and the change in strain due to corrosion was confirmed.

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。

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

  FIG. 5 is a graph showing the relationship between elapsed time and strain in a corrosive environment. In this embodiment, since the samples were immersed in salt water or water on the 1st and 4th, the strain temporarily changed due to temperature change, water absorption by the mortar, etc., but the dummy sensor also changed in the same way, so it was not caused by corrosion. On the 16th, the amount of strain between the corrosion sensor and the dummy sensor deviated. Then, when the covering mortar of the corrosion sensor was removed, it was confirmed that the steel bar was corroded.

  As described above, according to the present embodiment, since the optical fiber sensors 13 and 14 that are provided on the surface of the polished steel bar 12 and detect strain are provided, an optical signal capable of long-distance transmission is used. It is possible to perform multipoint measurement. In addition, it is not affected by transmission loss and electromagnetic interference as in the case of using an electrical corrosion sensor, and the corrosion does not progress due to current flowing during measurement. A sensor can be realized.

DESCRIPTION OF SYMBOLS 11 Corrosion sensor 12 Polishing steel bar 13 Detection part 14 Optical fiber sensor 15 Covering part 21 Reinforced concrete structure 23 Reinforcement 25 Dummy sensor 26 Corrosion sensor 40 Specimen 41 Polishing steel bar 42 Optical fiber sensor

Claims (6)

A corrosion sensor comprising: an iron bar separate from the reinforcing bars constituting the reinforced concrete structure ; and an optical fiber sensor that is provided on the surface of the bar and detects strain caused by volume expansion due to corrosion of the bar. In the reinforced concrete structure,
A dummy sensor in which the entire surface of the corrosion sensor has been subjected to rust prevention treatment, or a second bar having a linear expansion coefficient substantially equal to that of the iron bar and less susceptible to corrosion than a reinforcing bar, and the second A dummy sensor provided on the surface of the bar and including an optical fiber sensor for detecting strain is installed in the reinforced concrete structure,
The strain caused by factors other than corrosion is detected by the dummy sensor, and the strain detected by the corrosion sensor is used to correct the strain accompanying volume expansion due to corrosion of the bar material detected by the corrosion sensor. Corrosion detection method . The corrosion detection method according to claim 1, wherein the bar is cylindrical. The corrosion detection method according to claim 1, wherein the bar is a polished steel bar made of the same material as the reinforcing bar used in the reinforced concrete structure or a material more easily corroded. The corrosion detection method according to any one of claims 1 to 3, further comprising a covering portion that covers the rod member and the optical fiber sensor. The corrosion detection method according to claim 1, wherein the optical fiber sensor is wound around a surface of the bar. The said corrosion sensor is installed in the surface layer side of the reinforcing bar in a reinforced concrete structure, The characteristic change of the light wave which propagates in the said optical fiber sensor is detected , The any one of Claims 1-5 characterized by the above-mentioned. The described corrosion detection method.

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