JP6626285B2 - Corrosion state prediction method - Google Patents

Description

  The present invention relates to a technique for predicting the progress of corrosion of steel.

  Rebar corrosion in a reinforced concrete structure significantly lowers the structural performance of the structure, and when corrosion cracking occurs, the cover concrete comes off, resulting in damage to third parties. Therefore, predicting the occurrence of corrosion cracks is extremely useful for the maintenance of reinforced concrete structures. Corrosion products generated due to the corrosion of reinforcing steel have a larger volume than iron, so that the volume near the corroded portion expands, which leads to the occurrence of corrosion cracks in concrete.

  2. Description of the Related Art Conventionally, as a technique for detecting a corrosive environment, an electric corrosion sensor that detects electric characteristics that change when a fine wire such as iron corrodes has been known (for example, Patent Literature 1 and Patent Literature 2). Further, as a method for detecting corrosion of a reinforcing bar, a strain gauge is attached to a reinforcing bar in a concrete structure to detect a strain when the reinforcing bar is damaged (Patent Document 3). On the other hand, conventionally, an optical fiber sensor for detecting a strain generated in a structure has been proposed. For example, in Patent Literature 4, a spirally 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 measurement device. Thus, when a displacement occurs in a structure, the displacement can be measured without destroying the structure.

  In Non-Patent Document 1, there is a method in which a corrosion product is sampled, a volume expansion coefficient of the corrosion product is estimated from a result of X-ray diffraction, a model is created, and a trial calculation of the occurrence of corrosion cracking is performed.

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

JP-A-8-09557 JP 2012-145330 A Patent No. 4975420 JP 2000-097647 A Japanese Patent No. 408623

Kumiko Suda, and 2 others, "Analytical Study on the Limit of Corrosion Crack Initiation Corrosion", Annual Journal of Concrete Engineering, Vol.14, 1992, No.1, 751-756

  Conventionally known electrical corrosion sensors suffer from transmission loss and the effects of electromagnetic interference.Furthermore, if monitoring is performed constantly, current will flow during measurement, which will lead to accelerated corrosion of the sensor itself. is there. In addition, the detection of these iron wires and iron foils due to corrosion breakage cannot detect the electrical characteristics over time, but only detects the corrosive environment, making it difficult to evaluate the degree of progress thereafter. It is.

  In addition, when a strain gauge is directly attached to a steel material or a strain gauge is installed near a steel material in order to measure the strain of the steel material due to corrosion, the measuring instrument or the adhesive covers the steel material. Therefore, it may affect the occurrence of corrosion and may not be able to detect corrosion accurately. Further, when corrosion occurs in that portion, the strain gauge may be peeled off, making it impossible to perform measurement, or may not be able to obtain correct results even though measurement is possible.

  Strictly speaking, it is difficult to grasp what kind of corrosion product has changed from iron depending on the location of the reinforcing bar, and how thick the iron has corroded. In addition, the corrosion products exposed to the atmosphere from the time of collecting the corrosion products to the time of analysis are changed from those in the environment in concrete under highly alkaline conditions, and the state of the corrosion products changes. Accurate volume expansion is difficult to achieve due to contamination products.

  On the other hand, the method of directly wrapping 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, but not to detect a corrosive environment.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a method for early and accurately detecting a corrosion environment of a steel material using an optical fiber sensor, and for predicting a corrosion progress state. Aim.

  (1) In order to achieve the above object, the present invention has taken the following measures. That is, the corrosion state prediction method of the present invention is a corrosion state prediction method for predicting the corrosion state of a steel material, and the light wave propagating in an optical fiber sensor fixed to directly or indirectly contact the steel material. Based on the property change, detecting the strain due to corrosion of the steel material, based on the relationship between the elapsed time and the detected strain, predicting the corrosion progress state of the steel material, at least including, I do.

  As described above, the strain due to corrosion of the steel material is detected based on the characteristic change of the light wave propagating in the optical fiber sensor, and the corrosion progress state of the steel material is predicted based on the relationship between the elapsed time and the detected strain. Thus, it is possible to easily detect corrosion of a steel material, predict the state of progress of corrosion, and predict the occurrence of cracks. Since the optical fiber is a thin wire, it does not block corrosion factors. Further, for example, a method of comparing the sensor measurement result of a concrete structure with an optical fiber sensor by previously obtaining the amount of expansion of a reinforcing bar that causes cracks up to the surface of the concrete structure can be adopted.

  (2) The corrosion state prediction method of the present invention is a corrosion state prediction method for predicting a corrosion state of a steel material, wherein the method is such that the steel rod and the iron rod are directly or indirectly contacted. Installing a corrosion sensor composed of a fixed optical fiber sensor at the same cover depth as the steel material to be detected, and based on the characteristic change of the light wave propagating in the optical fiber sensor, It is characterized by including at least a step of detecting a strain due to corrosion of a bar, and a step of predicting a corrosion progress state of a steel material based on a relationship between an elapsed time and the detected strain.

  As described above, the strain due to corrosion of the steel material is detected based on the characteristic change of the light wave propagating in the optical fiber sensor, and the corrosion progress state of the steel material is predicted based on the relationship between the elapsed time and the detected strain. Thus, it is possible to easily detect corrosion of a steel material, predict the state of progress of corrosion, and predict the occurrence of cracks. Since the optical fiber is a thin wire, it does not block corrosion factors. Further, for example, a method of comparing the sensor measurement result of a concrete structure with an optical fiber sensor by previously obtaining the amount of expansion of a reinforcing bar that causes cracks up to the surface of the concrete structure can be adopted.

  (3) In the corrosion state prediction method according to the present invention, the optical fiber sensor is wound around a surface of the steel material or the iron rod material.

  With this configuration, it is possible to accurately and easily detect the volume change due to the expansion of the reinforcing bar that causes the crack by the optical fiber sensor.

  (4) The corrosion state prediction method of the present invention is characterized by predicting the corrosion progress state of the steel material by fitting the relationship between the elapsed time and the detected strain to a prediction curve.

  As described above, since the relationship between the elapsed time and the detected strain is fitted to the prediction curve, it is possible to predict the timing of cracking due to the strain of the concrete structure and the progress of the strain.

  (5) In addition, the corrosion state prediction method of the present invention sets a threshold based on a predicted amount of strain of a steel material that causes cracks on the surface of a concrete structure, and the detected amount of strain determines the threshold value as the threshold value. It is characterized in that it is determined whether or not it has exceeded.

  As described above, the threshold is set based on the predicted amount of strain of the steel material that causes cracks on the surface of the concrete structure, and it is determined whether the amount of the detected strain exceeds the threshold. When the amount of strain exceeds the threshold value, it becomes possible to perform inspections such as a tap sound inspection and a non-destructive inspection. This makes it possible to repair or reinforce the concrete structure at an appropriate time.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to easily detect the corrosion of a steel material, predict the state of progress of corrosion, and predict the generation of cracks.

It is a figure showing Example 1 concerning the present invention. It is a figure showing Example 2 concerning the present invention. FIG. 9 is a view showing a third embodiment according to the present invention. FIG. 9 is a view showing a third embodiment according to the present invention. It is a figure showing Example 4 concerning the present invention. It is a figure showing Example 5 concerning the present invention. It is a figure showing Example 6 concerning the present invention. It is a figure showing Example 6 concerning the present invention. It is a figure showing Example 7 concerning the present invention. It is a figure showing Example 8 concerning the present invention. FIG. 2 is a diagram illustrating a schematic configuration of a test body according to Verification Example 1. FIG. 4 is a diagram illustrating a detection example of a corrosion sensor according to a first verification example. FIG. 4 is a diagram illustrating a detection example of a corrosion sensor according to a first verification example. It is a figure showing the schematic structure of the corrosion sensor concerning this embodiment. It is a figure showing typically signs that a corrosion sensor and a dummy sensor concerning this embodiment were installed in a reinforced concrete structure. It is a figure showing how to wind an optical fiber sensor to a polish bar. It is a figure which shows the outline of the test body which concerns on the verification example 2. It is a figure showing a measurement result.

  In the corrosion state prediction method according to the embodiment of the present invention, an optical fiber sensor is directly wound around a steel material such as a reinforcing bar in a structure, and expansion strain due to progress of corrosion is measured. In addition, a corrosion sensor is formed by winding an optical fiber sensor around a separately prepared bar such as a reinforcing bar or a polished bar, and the corrosion sensor is installed at the same cover depth as the reinforcing bar to be measured, and the progress of corrosion of the bar The expansion strain due to is measured.

  When measuring the expansion strain, a corrosion sensor made of a bar having an optical fiber sensor attached thereto may be provided at the same cover position as the reinforcing bar, or an optical fiber sensor may be attached directly to the steel material of the structure. When a corrosion sensor is installed, it is possible to measure a corrosion expansion strain closer to a real reinforcing bar by using a rod having a diameter and a material close to that of a reinforcing bar. When installing a corrosion sensor made of an iron bar, the corrosion sensor is fixed to a real reinforcing bar with a binding wire or the like so that the sensor does not move or fall off during construction.

  Once the expansion strain around the rebar due to rebar corrosion is obtained, analysis methods such as finite element method (FEM) analysis and finite covering method (FCM) analysis that input the rebar diameter, cover thickness, physical properties of concrete and rebar, etc. It can be used to predict the state of corrosion of reinforcing bars, the occurrence and progress of cracks, and the like. In this case, the amount of expansion of the reinforcing bar that causes cracks up to the concrete surface may be obtained by analysis such as the finite element method and compared with the sensor measurement result of the actual structure.

  In addition, even without analysis, we conducted experiments on several test specimens in the range of general fogging, grasped the general relationship between expansion strain due to corrosion and the occurrence of corrosion cracking, and about how much strain was If this occurs, it is predicted whether cracks will occur in the fogging part. In this case, the specimen is manufactured separately from the actual structure. Specimens shall have the same concrete composition, rebar cover, etc. as much as possible. An accelerated test or the like is performed using the test piece, and the amount of reinforcing bar expansion at which cracking occurs is determined by an optical fiber sensor. Then, the expansion amount obtained in advance is compared with the sensor measurement result of the actual structure. Hereinafter, embodiments of the present invention will be described.

[Mode of attaching optical fiber sensor directly to steel]
As a corrosion detection method according to the present embodiment, a case where an optical fiber sensor is wound around the outer periphery of a steel material in concrete will be exemplified. In this corrosion sensor, it is possible to detect the corrosive environment of the steel itself. When the steel material corrodes, a strain is generated due to volume expansion of the corrosion product. By detecting this strain with a measuring device such as a data logger via an optical fiber sensor, it is possible to diagnose whether or not the inside of concrete is in a corrosive environment and whether or not a corrosive factor has entered. .

  FIG. 1 is a diagram showing a first embodiment according to the present invention. In the first embodiment, an aspect in which the optical fiber sensor 62 is directly wound around the round bar 60 is adopted. Thereby, the optical fiber sensor 62 can be provided directly on the steel material without processing the steel material. As a result, early detection of a corrosive environment becomes possible. In addition, it becomes possible to accurately detect distortion due to corrosion.

  An FBG sensor or the like can be used as the optical fiber sensor. When the optical fiber sensor 62 is wound around the round steel 60, the optical fiber sensor 62 may be arranged in a straight line or may be arranged in a wavy shape, but is preferably spirally wound around, Or wrap it in a loop. As the number of rounds increases, the corroded portion and the optical fiber overlap with each other, the detection is performed early. However, when the number of rounds is too large, the corrosion factor is prevented from reaching the round bar 60. When the optical fiber sensor 62 is wound around the round bar 60, the optical fiber sensor 62 is wound tightly, preferably with a tensile force, and both ends are fixed with an adhesive. Thereby, it becomes possible to measure the strain on both the expansion side and the contraction side. After that, concrete is cast and the strain is measured by a data logger to detect the expansion due to corrosion of the reinforcing bars. Although the round bar 60 is used here, the above arrangement may be performed on the deformed reinforcing bar 65.

  FIG. 2 is a diagram showing a second embodiment according to the present invention. In the second embodiment, a deformed reinforcing bar 65 is used. In FIG. 2, the deformed reinforcing bar 65 is provided with ribs 66 at positions above and below the paper surface. In addition, the deformed reinforcing bar 65 is provided with a plurality of nodes 67 protruding from the surface and provided at predetermined intervals. In the second embodiment, the optical fiber sensor 62 is fixed to the top of the node 67. When fixing the optical fiber sensor 62, it is assumed that the optical fiber sensor 62 is fixed at two bonding points 69 as shown in FIG. In addition, the portion where the optical fiber sensor 62 is fixed is installed facing the surface of the concrete. As described above, since the optical fiber sensor 62 is fixed to the top of the node 67, it is possible to approach the concrete surface at a place where there is a concern about deterioration. This makes it possible to detect corrosion at a relatively early stage. In the second embodiment, since the optical fiber sensor 62 is arranged on the deformed reinforcing bar 65 as it is, the processing of the deformed reinforcing bar 65 becomes unnecessary. By removing the scale and rust of the joint 67, the portion of the deformed reinforcing bar 65 to which the optical fiber sensor 62 is fixed may be most easily rusted.

  3A and 3B are views showing a third embodiment according to the present invention. FIG. 3A is a diagram illustrating the deformed reinforcing bar 65 from a direction in which the rib 66 is located vertically with respect to the paper surface, and FIG. 3B is a diagram illustrating the deformed reinforcing bar 65 from any one of the ribs 66. In the third embodiment, the optical fiber sensors 62 are continuously arranged for the plurality of nodes 67. As shown in FIG. 3A, at each node 67, the optical fiber sensor 62 is bonded at two bonding points 69, respectively. As described above, by disposing the optical fiber sensor 62 in the plurality of nodes 67, a part where rust is generated and a part where rust is not generated are initially generated in a corrosive environment. Then, it is possible to distinguish between strain due to corrosion and strain not due to it, that is, strain due to temperature or external force, thereby removing the influence of strain due to temperature or external force. As a result, only distortion due to corrosion can be detected with high accuracy. Further, in the third embodiment, since the optical fiber sensor 62 is arranged on the deformed reinforcing bar 65 as it is, no processing is required. By removing the scale and rust of the joint 67, the portion of the deformed reinforcing bar 65 to which the optical fiber sensor 62 is fixed may be most easily rusted.

  FIG. 4 is a diagram showing a fourth embodiment according to the present invention. In the fourth embodiment, the cutting / polishing unit 70 is provided on the deformed reinforcing bar 65 by cutting or polishing a part of the rib 66. The optical fiber sensor 62 is arranged along the cutting / polishing unit 70, and the cutting / polishing unit 70 is placed facing the surface of the concrete. This makes it possible to detect the corrosion factor that has entered from the concrete surface at an early stage. In addition, by removing the scale and rust of the cutting / polishing unit 70, the cutting / polishing unit 70 among the deformed reinforcing bars 65 can be most easily rusted. In addition, by performing the rust prevention treatment on the bonding portion 69, the measurement period can be further lengthened.

  FIG. 5 is a diagram showing a fifth embodiment according to the present invention. A part of the deformed reinforcing bar 65 was formed by cutting or polishing a part of the deformed reinforcing bar 65 like a round bar, and a cutting / polishing unit 71 was provided. The optical fiber sensor 62 is installed on the cutting / polishing unit 71. Thereby, the optical fiber sensor 62 is easily wound, and the arrangement method can be the same as that of the first embodiment. By removing the scale and rust of the cutting / polishing unit 71, the cutting / polishing unit 71 among the deformed reinforcing bars 65 is most likely to rust, and thus the detection sensitivity can be increased. In addition, by performing the rust prevention treatment on the bonding portion 69, the measurement period can be further lengthened.

  6A and 6B are views showing a sixth embodiment according to the present invention. In the sixth embodiment, as shown in FIG. 6B, a cutting / polishing unit 73 is provided on a part of the deformed reinforcing bar 65 by continuously cutting or polishing any one of the plurality of nodes 67. Was. FIG. 6B shows an example in which three nodes 67 are continuously cut, for example. The cutting / polishing unit 73 may be provided along the rib 66 as shown in FIG. 6A. The optical fiber sensor 62 is attached along the cutting / polishing unit 73, and the cutting / polishing unit 73 is set to face the surface of the concrete. It becomes possible to detect the corrosion factor that has entered from the concrete surface at an early stage. In addition, by removing the scale and rust of the cutting / polishing unit 73, the cutting / polishing unit 73 among the deformed reinforcing bars 65 can be most easily rusted. Further, by performing the rust prevention treatment on the bonding portion 69, the measurement period can be further lengthened.

  FIG. 7 is a diagram showing a seventh embodiment according to the present invention. In Example 7, the coating layer 72 was provided between the deformed reinforcing bar 65 and the optical fiber sensor 62. The coating layer 72 is made of a hardened cement such as mortar. The mortar may be prepared with a water-cement ratio similar to that of concrete, or may be prepared with a more porous mixture. Preferably, the water cement ratio is 80% or less. This is because, when the coating layer 72 is provided between the deformed reinforcing bar 65 and the optical fiber sensor 62, the transmission of the expansion of the deformed reinforcing bar 65 due to corrosion to the optical fiber sensor 62 is delayed if the cement hardened material is soft.

  In addition, the water-cement ratio shall be equal to or higher than the concrete of the reinforced concrete structure so as not to hinder the passage of corrosion factors from the concrete surface to the reinforcing steel, and shall be the same as the concrete. Is preferred. When the water-cement ratio is equal to that of the concrete, the condition of the reinforcing bars in the reinforced concrete structure can be accurately grasped. Further, an admixture, a thickener, and a fiber may be blended in mortar or the like so that separation or bleeding does not occur. The coating layer 72 preferably has a thickness of 3 to 15 mm so that the irregularities on the surface of the deformed reinforcing bar 65 are eliminated and cracks do not occur. However, the present invention is not limited to these.

  As described above, since the coating layer 72 is provided and unevenness can be eliminated regardless of the location of the deformed reinforcing bar 65, the optical fiber sensor 62 can be disposed at any location. Further, since the deformed reinforcing bar 65 is corroded and the entire portion including the mortar expands, it becomes easy to detect the displacement due to the corrosion including the corroded portion.

  FIG. 8 is a view showing an eighth embodiment according to the present invention. In FIG. 8, the left side with respect to the paper surface employs a configuration in which a covering portion 74 is provided on a deformed reinforcing bar 65, and is characterized in that the optical fiber sensor 62 is wound in a state where the mortar is not cured. In this case, the optical fiber sensor 62 sinks into the mortar. Thus, the mortar can be made to function as an adhesive, and the adhesive point 69 may not be provided or may be temporarily fixed.

  On the other hand, in FIG. 8, the right side with respect to the paper surface is an aspect in which a portion to which the optical fiber sensor 62 is fixed is formed with a coating portion 74 with a hardened cement. The manner of fixing the optical fiber sensor 62 may be any of the embodiments 1 to 7 described above. The mortar can also function as an adhesive, and the adhesive points 69 may not be provided or may be temporarily fixed.

  As the cement hardened body of the present embodiment, a cement paste or mortar which is alkaline and becomes porous after solidification can be used. The hardened cement has a water-cement ratio equal to or higher than the concrete of the reinforced concrete structure, and preferably has a water-cement ratio equal to that of the concrete. As the cement material to be used, ordinary cement may be used, or fast-setting cement may be used. By appropriately blending the hardened cement and appropriately designing the cement material, the hardened cement can be made to have a property of penetrating corrosive factors such as chloride ions and allowing the corrosive factor to pass therethrough. Further, an admixture, a thickener, and a fiber may be blended in mortar or the like so that separation or bleeding does not occur. The coating layer 74 preferably has a thickness of 3 to 15 mm so as not to crack.

  As a result, the hardened cement constituting the covering portion 74 prevents corrosion of the reinforcing bar until the corrosion factor reaches, fixes the position of the optical fiber sensor 62 after manufacture, and protects the optical fiber sensor 62 at the time of casting. Perform the function of In addition, the hardened cement becomes porous, at least as high as the concrete of the reinforced concrete structure, and does not hinder the passage of corrosion factors from the concrete surface to the reinforcing steel. In the cutting or polishing in the above embodiment, the deformed reinforcing bar 65 is taken as an example, but the present invention is not limited to this, and a part of the round steel 60 may be cut or polished. Further, although the coating layer 72 and the coating portion 74 of the cement hardened body are exemplified by the deformed reinforcing bar 65, the present invention is not limited to this, and the coating layer 72 or the coating layer 72 is provided between the round steel 60 and the optical fiber sensor 62. A covering portion 74 may be provided.

  In all of the above embodiments, a dummy sensor can be used. That is, an optical fiber sensor is manufactured in the same manner as in the above-described embodiment, but a dummy sensor having a rust-preventive treatment applied to the entire surface is used. Then, the strain generated by a factor other than corrosion may be detected using the dummy sensor, and the strain detected by the optical fiber sensor may be corrected. Thereby, for example, it is possible to remove the influence of temperature distortion and the like. As the dummy sensor, there is a method in which a reinforcing bar or a covering portion on which the optical fiber sensor is disposed is covered with an epoxy resin or the like, thereby preventing neutralization and deterioration factors from entering and preventing corrosion of carbon steel inside. When a plurality of detection units are provided as in the third embodiment, a part of the detection units may be subjected to a rust prevention treatment.

[Mode in which an optical fiber sensor is attached to a polished bar steel to form a sensor]
FIG. 11 is a diagram illustrating a schematic configuration of the corrosion sensor according to the present embodiment. Although the above-described rebar or processed rebar can be used as a bar, here, a polished bar will be described as an example. The corrosion sensor 11 includes an iron bar 12 serving as an iron bar and an optical fiber sensor 14 wound around the surface of the polishing bar 12 and having a detection unit 13 for detecting strain. As a result, an optical signal that can be transmitted over a long distance can be used, and multipoint measurement can be performed. Further, the corrosion sensor 11 includes a coating portion 15 that covers the brushed steel bar 12 and the optical fiber sensor 14. The covering portion 15 can be made of, for example, mortar having a fog of 10 mm. Since the covering portion 15 is provided, it is possible to prevent the polished bar steel 12 from being rusted before being installed in the reinforced concrete structure.

Corrosion of steel produces corrosion products and volume expansion. When corrosion occurs in the steel material, some strain behavior occurs besides the influence of temperature, external force, and the like. Therefore, the corrosion can be detected by measuring the strain of the steel material. Since the behavior differs depending on environmental conditions and concrete, when the optical fiber sensor 14 is wound around the polishing rod 12, it is wound so as to be in close contact, preferably with a tensile force. Thereby, it becomes possible to measure the strain on both the expansion side and the contraction side. Further, when the optical fiber sensor 14 is wound around the polishing rod 12, the optical fiber sensor 14 may be stuck in a straight line or may be stuck in a wavy shape, but is preferably spirally wound. And wrap it in a loop. As the number of rounds increases, the corroded portion and the optical fiber overlap with each other, the detection is performed early. However, if the number of rounds is too large, the corrosion factor will not reach the polishing steel bar 12. The number of revolutions is, as a guide, fiber length (mm) / bar surface area (mm ² ) of 0.01 to ² . Anyway, any change in corrosion occurring in the polished bar 12 can be detected as strain. In addition, when the optical fiber sensor 14 is wound around the polishing rod 12, it is preferable that the polishing rod 12 is more uniformly wound as the columnar shape and the surface is smoother, and the optical fiber sensor is harder to break. 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 more.

  The mortar constituting the covering portion 15 has a water cement ratio equal to or higher than that of the structural concrete so as not to prevent the penetration of the corrosion factor. Above all, it is preferable that the water-cement ratio is equal to that of the concrete so that the condition of the reinforcing bars in the reinforced concrete structure can be accurately grasped. The coating 15 preferably has a thickness of 3 to 15 mm so as to protect the polished bar 12 without cracking. It is preferable to use an admixture so as not to cause separation or bleeding.

  FIG. 13 is a diagram showing how to wind the optical fiber sensor around the polishing bar. Regarding the manner of winding the optical fiber around the polishing rod, under a certain tension, for example, after confirming that some tensile strain is generated at the time of winding, the winding operation is performed, and the end is fixed with an adhesive.

  Here, when repairing a reinforced concrete structure that has already been corroded and deteriorated, the salt inside is included on the back side (inside) of the reinforcing bar. However, by installing the corrosion sensor 11 as it is in the reinforced concrete structure, the fog (surface) ) Detect corrosion due to the deterioration factor from all directions so that the deterioration factor intrusion from the side and the influence of the internal salt are included. Further, when the repaired part is repaired 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, so that the covering part may be omitted.

  FIG. 12 is a diagram schematically illustrating a state where the corrosion sensor and the dummy sensor according to the present embodiment are installed in a reinforced concrete structure. As shown in FIG. 12, the reinforced concrete structure 21 includes a reinforcing bar 23 in a horizontal direction or a vertical direction. A dummy sensor 25 and corrosion sensors 26 and 27 are provided at the same cover position as the reinforcing bar 23. Further, a data logger 33 is provided. As described above, when installing the corrosion sensor 11 in the reinforced concrete structure, it is desirable to install the corrosion sensor 11 so as to have the same cover as the reinforcing bar in the reinforced concrete structure. By installing at the same depth, the condition of the reinforcing bars in the reinforced concrete structure can be accurately grasped.

  When the corrosion sensor 11 is installed in a reinforced concrete structure 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 has been subjected to rust-prevention treatment may be used, or a second sensor having a linear expansion coefficient substantially equal to that of the polished bar steel 12 and less corrosive than a reinforcing bar. A dummy sensor including a bar and an optical fiber sensor provided on the surface of the second bar and detecting strain may be used.

  Then, the corrosion sensor 11 and the dummy sensor are installed in the reinforced concrete structure, the strain generated by a factor other than 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. As a result, for example, it is possible to remove the influence of strain caused by factors other than corrosion, such as temperature strain.

  In other words, various distortions occur in the reinforced concrete structure due to temperature / humidity, contraction of the concrete, and external force. Therefore, at least a dummy sensor that is less susceptible to corrosion than the corrosion sensor 11 is used, and the corrosion is determined by comparing it with its strain behavior. As a dummy sensor, there is a method in which a coating mortar is coated with an epoxy resin or the like to prevent neutralization and deterioration factors from entering, thereby preventing corrosion of carbon steel inside. Alternatively, stainless steel (for example, SUS410 or the like) having a linear expansion coefficient equivalent to that of carbon steel is used.

[Example of verification]
FIG. 9 is a diagram illustrating the concept of the corrosion detection method according to the present embodiment using a test body. As shown in FIG. 9, the test body 40 is configured by winding an optical fiber sensor 51 around a steel bar 50 and covering with a cement hardened body 52 such as mortar. The vertical fog is 20 mm and the horizontal fog is 10 mm with respect to the test body 40. FIG. 9 shows an example in which the optical fiber sensor 51 has one turn with respect to the steel bar 50. However, the case where the optical fiber sensor 51 has three turns will also be verified. Next, a specific verification example of the test body 40 will be described.

  JIS G 3108 SGD3M was used as the polishing bar. The winding of the optical fiber around the polishing rod is performed under a certain tension, for example, after confirming that a certain tensile strain is generated at the time of winding, performing the winding operation, and then using CN (manufactured by Tokyo Sokki) Fixed. An optical fiber sensor (FBG sensor) having the specifications shown in Table 2 was used. In addition, it is preferable to detect corrosion based on the difference in the strain behavior of the dummy sensor, and it is expected that the influence of the volume change and the moisture content of the coated mortar will appear in the strain. The body was made.

次に、被覆モルタルについて説明する。モルタルの使用材料は、次の表に示す通りである。

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

次に、モルタルの配合は、次の表に示す通りである。

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

なお、上記の表中、「Ｂ」とは、「Ｃ」と「Ｌ」とを混合したものである。

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

[Method of mixing mortar]
The mortar used for the test specimen was kneaded using a “mortar mixer (2L kneading) manufactured by Maruto Co., Ltd.”. The kneading procedure is as follows. The kneading of the mortar was performed in a constant temperature and humidity room at 20 ± 2 ° C. and a humidity of 50% or more.

  Mortar is driven into a PVC mold (inner diameter φ40 mm × height 50 mm, or inner diameter φ40 mm × height 65 mm), and a steel bar with an optical fiber wound in the center, and then placed in the same temperature and humidity chamber. After curing for 3 hours, the mixture was cured for 7 days at 20 ° C. and 95% or more humidity, and was demolded.

  The test specimen 40 was placed in a corrosive environment (under a temperature of 40 ° C., immersed in a 10% aqueous solution of NaCl for 1 day, dried at 60% humidity for 3 days, immersed again in a 10% aqueous solution of NaCl for 1 day, and then dried at 60% humidity). The change in wavelength was measured with a measuring instrument (manufactured by Watanabe Seisakusho Co., Ltd.). In the immersion of the NaCl: 10% aqueous solution, a portion 30 mm from the lower end of the specimen (45 mm from the lower end of the specimen in the case of three turns) was immersed so that the NaCl aqueous solution did not enter from the optical fiber drawer. . The dummy specimen used here was the same specimen as the corrosion sensor without using a steel bar that did not corrode experimentally, and was immersed in pure water that did not corrode instead of using an aqueous NaCl solution.

  The wavelength was converted into strain by the following equation, 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), λ *: initial wavelength (nm).

  FIG. 10A is a graph showing the relationship between elapsed time and strain in a corrosive environment. In the verification example shown in FIG. 10A with one roll, the strain temporarily changed due to temperature change and water absorption of the mortar due to immersion in salt water or water on the 1st and 4th. It was not due to corrosion. On the 16th, the strain amount between the test specimen and the dummy test specimen deviated. Then, when the coating mortar of the specimen was removed, it was confirmed that the steel bar was corroded.

  In the verification example of three windings shown in FIG. 10B, the measurement is started after the temperature becomes constant, and the measurement is continued after the corrosion. Corrosion cracks occurred on the 45th measurement day. It has been proved that it is possible to continuously capture expansion due to corrosion until cracks occur.

[Monitoring of corrosion progress after detection]
As described above, the optical fiber sensor is directly wound around the steel material in the structure to measure the expansion strain due to the progress of corrosion.Also, the corrosion sensor is formed by winding the optical fiber sensor around the rod, A corrosion sensor is installed at the same cover depth as the reinforcing bar to measure the expansion strain due to the progress of corrosion of the bar, and then the progress of corrosion is monitored.

  As a monitoring method, for example, when 30% of the strain value of the optical fiber, which is predicted to cause corrosion cracking, is measured by an analysis or a specimen test, inspection is performed by a known method such as a tapping inspection or a nondestructive inspection. carry out. The reason for setting it to 30% is that, as shown in FIG. 10B, the corrosion expansion rapidly progresses after reaching 30%. In other words, up to that point, the state can be grasped without requiring large manuals and devices. In subsequent inspections, if it is judged that the deterioration has progressed and it is dangerous, repair and reinforcement will be performed by a known method.

Further, as shown in FIG. 10B, since the slope of the curve sharply increases from the 25th day, this is approximated by “y = ax (straight line)” or “y = ax ² (quadratic curve)”. It is also possible. That is, in FIG. 10B, it is possible to predict the amount of strain corresponding to the number of elapsed days by selecting and fitting a prediction curve with a strain between 0 and 2000 (× 10 ⁻⁶ ). Then, when corrosion cracking occurs by analysis or test specimen, it can be compared with the amount of strain to obtain an indication of the subsequent service life.

[Verification Example 2]
In order to confirm whether the strain increases in accordance with the state of corrosion, we checked the state of corrosion and measured the strain with an optical fiber in the case of air in which an optical fiber was wound around a steel material. As shown in FIG. 14, the test piece was made of a 20 mm-diameter steel bar and one turn of an optical fiber sensor in a range of a measurement area height of 25 mm at the center. FIG. 15 is a diagram showing the measurement results. Since the sample was in the air at 20 ° C. until the second day of the measurement, there was almost no corrosion as indicated by circle 1. Immediately after that, salt water was applied to the central part of the test piece of one fiber. Thereafter, the strain rapidly increased, and the circle 2 showed a corrosion range of 10% as judged visually, and the circle 3 showed a corrosion range of 35% as judged visually. From the above results, it can be seen that the strain increases in accordance with the degree of corrosion.

DESCRIPTION OF SYMBOLS 11 Corrosion sensor 12 Polished bar 13 Detection part 14 Optical fiber sensor 15 Covering part 21 Reinforced concrete structure 23 Reinforcing bar 25 Dummy sensor 26 Corrosion sensor 40 Specimen 50 Steel bar 51 Optical fiber sensor 52 Mortar 60 Round steel 62 Optical fiber sensor 65 Deformed reinforcing bar 66 Rib 67 Section 69 Adhesion points 70, 71, 73 Cutting / polishing unit 72 Coating layer 74 Coating unit

Claims (5)

A corrosion state prediction method for predicting a corrosion state of a steel material in a concrete structure ,
Detecting strain associated with volume expansion due to corrosion of the steel material based on a change in characteristics of the light wave propagating through the optical fiber sensor fixed to directly or indirectly contact the steel material;
Determining whether or not the detected strain has reached a certain ratio with respect to the strain at the time when corrosion cracking occurs in the concrete . A corrosion state prediction method for predicting a corrosion state of a steel material in a concrete structure ,
Installing a corrosion sensor composed of an iron bar and an optical fiber sensor fixed so as to directly or indirectly contact the iron bar at the same cover depth as the steel to be detected; When,
Based on a change in the characteristics of the light wave propagating in the optical fiber sensor, detecting a strain due to volume expansion due to corrosion of the iron bar,
Determining whether or not the detected strain has reached a certain ratio with respect to the strain at the time when corrosion cracking occurs in the concrete .   The corrosion state prediction method according to claim 1 or 2, wherein the optical fiber sensor is wound around a surface of the steel material or the iron bar. A corrosion state prediction method for predicting a corrosion state of a steel material in a concrete structure,
Detecting strain associated with volume expansion due to corrosion of the steel material based on a change in characteristics of the light wave propagating through the optical fiber sensor fixed to directly or indirectly contact the steel material;
A corrosion state prediction method, wherein a corrosion progress state of a steel material is predicted by fitting a relationship between an elapsed time and the detected strain to a prediction curve. A corrosion state prediction method for predicting a corrosion state of a steel material in a concrete structure,
A step of installing a corrosion sensor composed of an iron bar and an optical fiber sensor fixed to directly or indirectly contact the iron bar at the same cover depth as the steel to be detected. When,
Based on a change in the characteristics of the light wave propagating in the optical fiber sensor, detecting a strain due to volume expansion due to corrosion of the iron bar,
A corrosion state prediction method, wherein a corrosion progress state of a steel material is predicted by fitting a relationship between an elapsed time and the detected strain to a prediction curve .

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