Corrosion state determination method, corrosion state determination device, and computer program capable of executing the corrosion state determination method

Abstract

To provide a corrosion state determination method having more excellent determination accuracy.SOLUTION: A corrosion state determination method includes the steps of: acquiring a potential of a steel material 11b in the vicinity of each of a plurality of collation surfaces 11d for each of the plurality of collation surfaces 11d among surfaces of a concrete structure 11; calculating a gradient of the potential for each of the plurality of collation surfaces 11d; determining whether or not the gradient of the potential for each of the collation surfaces 11d is a predetermined threshold value or more; and determining that the collation surface 11d of which the gradient of the potential is determined to be the predetermined threshold value or more is a boundary area in which the possibility that the steel material 11b in the vicinity of the collation surface 11d is a boundary state between a corrosion state and a non-corrosion state is high.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a corrosion state determination method, a corrosion state determination device, and a computer program capable of executing a corrosion state determination method.

Background Art

[0002] In concrete structures in which steel materials are embedded, such as reinforced concrete, corrosion of the steel materials due to aging deterioration has become a problem. As a method for determining the corrosion state of steel materials embedded in a concrete structure, for example, Patent Document 1 discloses a method of measuring the natural potential of a steel material from the surface of the concrete structure and determining the corrosion state of the steel material based on the measured natural potential. In the method of determining the corrosion state of a steel material using the natural potential of the steel material, it is common to determine whether the steel material is corroded or not using the evaluation criteria defined as ASTM C876.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the evaluation criteria defined as ASTM C876, there is a wide range where the corrosion state is judged to be uncertain, in addition to the ranges judged to be in a corrosion state or a non-corrosion state. Therefore, even when actually measuring the natural potential of the steel in a concrete structure, there are many parts where the corrosion state is judged to be uncertain, and it is impossible to accurately judge the corrosion state of the steel. On the other hand, in Patent Document 1, attempts have been made to improve the accuracy of judgment by adopting other parameters such as the cover thickness and water content of the concrete in addition to the natural potential of the steel. However, parameters such as the cover thickness and water content do not directly represent the corrosion state of the steel, but only indirectly represent it. Therefore, sufficient judgment accuracy still cannot be obtained by the method of Patent Document 1.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a corrosion state determination method, a corrosion state determination device, and a computer program capable of executing the corrosion state determination method, which have more excellent determination accuracy.

Means for Solving the Problems

[0006] The corrosion state determination method of the present invention is a corrosion state determination method for determining the corrosion state of steel embedded in a concrete structure, including: for each of a plurality of reference surfaces on the surface of the concrete structure, obtaining the potential of the steel in the vicinity of each of the plurality of reference surfaces; calculating the gradient of the potential for each of the plurality of reference surfaces; determining whether the gradient of the potential for each of the reference surfaces is equal to or greater than a predetermined threshold; and determining the reference surface for which the gradient of the potential is determined to be equal to or greater than the predetermined threshold as a boundary region where the steel in the vicinity of the reference surface is likely to be in a boundary state between a corrosion state and a non-corrosion state.

[0007] Also, a step of determining whether the potential of the matching surface other than the matching surface determined to be the boundary region is less than the minimum potential among the potentials of the matching surface determined to be the boundary region; a step of determining the matching surface for which the potential is determined to be less than the minimum potential as a corrosion region where the steel material near the matching surface is likely to be in a corroded state; a step of determining whether the potential of the matching surface other than the matching surface determined to be the boundary region is greater than the maximum potential among the potentials of the matching surface determined to be the boundary region; and a step of determining the matching surface for which the potential is determined to be greater than the maximum potential as a non-corrosion region where the steel material near the matching surface is likely to be in a non-corroded state are preferably further included.

[0008] Also, the step of obtaining the potential includes, for each of a plurality of matching points arranged within the matching surface, obtaining the potential of the steel material near each of the plurality of matching points, and calculating an average value of the potentials of the steel material near the plurality of matching points as the potential for the matching surface. The step of calculating the gradient of the potential preferably includes calculating the gradient of the potential for the matching surface based on the difference in the potentials for the plurality of matching points within the matching surface and the distance between the plurality of matching points.

[0009] Also, the plurality of matching points are arranged side by side along a first direction and a second direction on the matching surface. The step of calculating the gradient of the potential includes calculating the gradient of the potential in the first direction as a first gradient based on the difference in the potentials for the plurality of matching points arranged side by side along the first direction and the distance between the plurality of matching points; calculating the gradient of the potential in the second direction as a second gradient based on the difference in the potentials for the plurality of matching points arranged side by side along the second direction and the distance between the plurality of matching points; and calculating the gradient of the potential for the matching surface based on the first and second gradients. This is preferably included.

[0010] It is also preferable to further include a step of displaying the potential and the gradient of the potential for each of the plurality of reference surfaces in a coordinate system in which one axis represents the potential and the other axis represents the gradient of the potential.

[0011] The corrosion state determination device of the present invention is a corrosion state determination device for determining the corrosion state of a steel material embedded in a concrete structure, and includes an acquisition unit that acquires the potential of the steel material in the vicinity of each of a plurality of reference surfaces on the surface of the concrete structure, and a calculation unit that calculates the gradient of the potential for each of the plurality of reference surfaces. The corrosion state determination device includes a determination unit that determines whether or not the gradient of the potential for each of the reference surfaces is equal to or greater than a predetermined threshold value, and configures the reference surface for which it is determined that the gradient of the potential is equal to or greater than the predetermined threshold value as a boundary region where the steel material in the vicinity of the reference surface is likely to be in a boundary state between a corroded state and a non-corroded state.

[0012] The determination unit further determines whether or not the potential of the reference surfaces other than the reference surface determined to be the boundary region is less than the minimum potential among the potentials of the reference surface determined to be the boundary region, determines the reference surface for which it is determined that the potential is less than the minimum potential as a corrosion region where the steel material in the vicinity of the reference surface is likely to be in a corroded state, determines whether or not the potential of the reference surfaces other than the reference surface determined to be the boundary region is greater than the maximum potential among the potentials of the reference surface determined to be the boundary region, and preferably configures the reference surface for which it is determined that the potential is greater than the maximum potential as a non-corrosion region where the steel material in the vicinity of the reference surface is likely to be in a non-corroded state.

[0013] Further, the acquisition unit is configured to acquire the potential of the steel material in the vicinity of each of the plurality of collation points arranged in the collation surface, and the calculation unit calculates the average value of the potentials of the plurality of collation points in the collation surface as the potential of the collation surface, and preferably, the calculation unit is configured to calculate the gradient of the potential of the collation surface based on the difference in potential of the plurality of collation points in the collation surface and the distance between the plurality of collation points.

[0014] Further, the plurality of collation points are arranged side by side along a first direction and a second direction on the collation surface, and the calculation unit calculates the difference in potential of the plurality of collation points arranged side by side along the first direction and the distance between the plurality of collation points, and calculates the gradient of the potential in the first direction as a first gradient, and calculates the difference in potential of the plurality of collation points arranged side by side along the second direction and the distance between the plurality of collation points, and calculates the gradient of the potential in the second direction as a second gradient, and preferably, the calculation unit is configured to calculate the gradient of the potential of the collation surface based on the first and second gradients.

[0015] Preferably, a display unit is further provided which is configured to display the potential and the potential gradient for each of the plurality of collation surfaces in a coordinate system in which one axis represents the potential and the other axis represents the potential gradient.

[0016] The computer program of the present invention includes computer-executable instructions that cause the computer to execute the corrosion state determination method when executed on a computer.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a corrosion state determination method, a corrosion state determination device, and a computer program capable of executing the corrosion state determination method, which have higher determination accuracy.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0019] Hereinafter, with reference to the accompanying drawings, a corrosion state determination method, a corrosion state determination device, and a computer program capable of executing the corrosion state determination method according to an embodiment of the present invention will be described. However, the embodiments shown below are examples, and the corrosion state determination method, device, and computer program of the present invention are not limited to the following embodiments.

[0020] A corrosion state determination method and device according to an embodiment of the present invention are a method and device for determining the corrosion state of a steel material embedded in a concrete structure, respectively. The concrete structure 11 to which the corrosion state determination method and device of the present embodiment are applied is a structure in which a steel material 11b is embedded in concrete 11a bonded by cement, as shown in FIG. 1. The concrete structure 11 is not particularly limited as long as it is a structure in which a steel material is embedded in concrete. For example, it includes bridge girders of bridges spanning rivers or the sea, bridge piers such as highways, large civil engineering structures such as dams, and buildings such as buildings. Further, as the steel material 11b embedded in the concrete 11a, in the present embodiment shown in FIG. 1, steel bars arranged in a lattice pattern are exemplified, but the type and size of the steel material and the arrangement method of the steel material are not particularly limited. Hereinafter, the corrosion state determination method and device of the present embodiment will be described based on an example in which the potential of the steel material (steel bar) 11b in the concrete structure (wall portion) 11 in which the steel material (steel bar) 11b is embedded at intervals d in the concrete 11a is measured to determine the corrosion state of the steel material 11b.

[0021] First, a corrosion state determination system 1 in which the corrosion state determination device 6 of the present embodiment is incorporated and which is used to implement the corrosion state determination method of the present embodiment will be described. However, the corrosion state determination device of the present invention may be incorporated into a system other than the corrosion state determination system 1 described below, and the corrosion state determination method of the present invention can also be implemented using a system other than the corrosion state determination system 1 described below.

[0022] The corrosion state determination system 1 measures the potential of the steel material 11b embedded in the concrete structure 11 and determines the corrosion state of the steel material 11b. More specifically, the corrosion state determination system 1 measures the potential (natural potential or relative potential) of the steel material 11b embedded in the concrete structure 11 from the surface of the concrete structure 11, and determines the corrosion state of the steel material 11b from the measured potential of the steel material 11b.

[0023] As shown in FIG. 1, the corrosion state determination system 1 includes a reference contact portion 2 that contacts a reference position in the concrete structure 11, a verification electrode unit 3 that contacts a verification surface 11d on the surface of the concrete structure 11, and a potential difference measurement device 4 that is connected to the reference contact portion 2 and the verification electrode unit 3 and measures the potential difference between the reference contact portion 2 and the verification electrode unit 3. According to the corrosion state determination system 1, the potential difference between the potential at the reference position contacted by the reference contact portion 2 and the natural potential of the steel material 11b located in the vicinity of the verification surface 11d (substantially directly below in the cover thickness direction) contacted by the verification electrode unit 3 is measured by the potential difference measurement device 4.

[0024] When the reference position is the steel material 11b embedded in the concrete structure 11, the potential difference measured by the potential difference measuring device 4 indicates the natural potential of the steel material 11b in the vicinity of the verification surface 11d with which the verification electrode unit 3 comes into contact. When the reference position is the surface of the concrete structure 11 (reference surface 11c), the potential difference measured by the potential difference measuring device 4 indicates the difference (relative potential) between the natural potential of the steel material 11b in the vicinity of the reference surface 11c and the natural potential of the steel material 11b in the vicinity of the verification surface 11d. In the former case, for example, if the natural potential of the steel material 11b is equal to or lower than a predetermined potential value (the first threshold value, which is specified as -350 mV in ASTM C876, for example), it is determined that the steel material 11b at that position is corroded with a probability of 90% or more. If the natural potential of the steel material 11b is greater than a predetermined potential value (the second threshold value, which is specified as -200 mV in ASTM C876, for example), it is determined that the steel material 11b at that position is not corroded with a probability of 90% or more. In the latter case, for example, if the natural potential of the steel material 11b in the vicinity of the verification surface 11d is lower than a predetermined potential value compared to the natural potential of the steel material 11b in the vicinity of the reference surface 11c, it is determined that the steel material 11b in the vicinity of the surface of the verification surface 11d may be corroded. If it is greater than another predetermined potential value, it is determined that the steel material 11b in the vicinity of the verification surface 11d may not be corroded. The natural potential of the steel material 11b refers to the potential of the steel material 11b in a state where no potential is externally applied, and is the natural potential measured by a known natural potential measurement method.

[0025] The reference contact part 2 is an electrode member that is brought into contact with a reference position having a potential that serves as a reference for the natural potential of the steel material 11b measured on the reference surface 11d with which the verification electrode unit 3 comes into contact. The reference contact part 2 is electrically connected to one terminal of the potential difference measuring device 4 via a conducting wire 5 such as a lead wire. As the reference contact part 2, as shown in FIG. 1, when measuring the natural potential of the steel material 11b in the vicinity of the reference surface 11d, the reference terminal 21 that comes into contact with the steel material 11b serving as the reference position can be used. As the reference terminal 21, a known alligator clip or the like can be used. Further, when measuring the relative potential of the steel material 11b in the vicinity of the reference surface 11d, the reference electrode 22 that is located in the covering thickness direction (substantially directly above the vicinity of the region of the steel material 11b) in the vicinity of the region of the steel material 11b having the natural potential (reference potential) serving as a reference and that comes into contact with the surface (reference surface 11c) of the concrete structure 11 can be used as the reference contact part 2. As the reference electrode 22, known electrodes such as a copper / copper sulfate electrode, a silver / silver chloride electrode, and a calomel electrode can be adopted.

[0026] The verification electrode unit 3 is an electrode member that is brought into contact with the surface (verification surface 11d) of the concrete structure 11 that is located in the covering thickness direction (substantially directly above the vicinity of the region of the steel material 11b) in the vicinity of the region of the steel material 11b having a natural potential that is the object of measurement with respect to the reference potential. The verification electrode unit 3 is electrically connected to the other terminal of the potential difference measuring device 4 via a conducting wire 5 such as a lead wire. The verification electrode unit 3 is not particularly limited and is designed to correspond to the shape and size of the verification surface 11d.

[0027] The verification electrode unit 3 only needs to be able to measure the potential of the steel material 11b near the verification surface 11d, and its structure is not particularly limited. In the present embodiment, as shown in FIGS. 1 and 2, the verification electrode unit 3 includes a plurality of verification electrodes 31 and a verification electrode support portion 32 that is formed in a size corresponding to the size of the verification surface 11d and supports the plurality of verification electrodes 31. The plurality of verification electrodes 31 are configured to be simultaneously brought into contact with a plurality of verification points 11e (see FIG. 3(a)) within the verification surface 11d when the verification electrode unit 3 is disposed on the verification surface 11d. Thereby, since the potentials of a plurality of regions of the steel material 11b can be measured at the same timing, the potentials of a plurality of regions of the steel material 11b can be efficiently measured. Further, the plurality of verification electrodes 31 can measure the potentials of a plurality of regions of the steel material 11b without being affected by the temporal change of the plurality of verification points 11e at least within the same verification surface 11d. However, the verification electrode unit 3 may include a single verification electrode corresponding to the size of the verification surface 11d.

[0028] The reference electrode unit 3 only needs to be able to simultaneously measure the potentials of a plurality of regions of the steel material 11b, and the arrangement of the plurality of reference electrodes 31 is not particularly limited. In the present embodiment, the plurality of reference electrodes 31 are two-dimensionally arranged at intervals from each other within a plane including the first direction X and the second direction Y on the reference electrode support portion 32 so as to correspond to a plurality of reference points 11e within the reference surface 11d shown in FIG. 3. The interval between the reference electrodes 31 arranged closest to each other among the plurality of reference electrodes 31 (corresponding to the distances dx and dy between the reference points 11e) is preferably smaller than the distance d between two steel materials 11b buried separately in the concrete structure 11, and the interval between the reference electrodes 31 arranged most distantly from each other (corresponding to twice the distances dx and dy between the reference points 11e) is preferably larger than the distance d between two steel materials 11b buried separately in the concrete structure 11. By arranging the plurality of reference electrodes 31 in this way, when the reference electrode unit 3 is arranged on the reference surface 11d, the plurality of reference electrodes 31 come into contact with the surface within the reference surface 11d at an interval shorter than the distance d between the plurality of steel materials 11b. By using such a plurality of reference electrodes 31, it is possible to substantially simultaneously measure the potentials of a plurality of regions of the steel material 11b without having to confirm in advance the positions where the steel materials 11b are buried by means such as a rebar detector.

[0029] In the present embodiment, the plurality of reference electrodes 31 of the reference electrode unit 3 will be described with reference to the arrangement of the plurality of reference points 11e within the reference surface 11d shown in FIG. 3(a). They are arranged in a matrix (or lattice) pattern with substantially equal intervals along the first direction X (corresponding to the distance dx between the reference points 11e in the first direction X) and substantially equal intervals along the second direction Y (corresponding to the distance dy between the reference points 11e in the second direction Y). And the distance between the reference electrodes 31 in the first direction X is substantially equal to the distance between the reference electrodes 31 in the second direction Y. Note that in the present embodiment, the first and second directions X and Y are substantially orthogonal to each other, but they may have an angle other than orthogonal to each other.

[0030] In the matching electrode unit 3, in the example shown in FIG. 2, nine (3×3 = 9) matching electrodes 31 are provided. However, the number of the matching electrodes 31 can be arbitrarily set according to the surface of the concrete structure 11 to be targeted. The number of the matching electrodes 31 may be, for example, one, and in that case, the matching electrode 31 can be formed to have a size that covers the entire matching surface 11d. Alternatively, the number of the matching electrodes 31 can be, for example, 2×2 = 4, 4×4 = 16, 5×5 = 25, 3×4 = 12, 3×5 = 15, etc. As the matching electrode 31, known electrodes such as a copper / copper sulfate electrode, a silver / silver chloride electrode, and a calomel electrode can be employed.

[0031] The matching surface 11d that the matching electrode unit 3 contacts can be appropriately set on the surface of the concrete structure 11 in the covering thickness direction (substantially directly above the area of the steel material 11b) according to the area of the steel material 11b that is the object of potential measurement. For example, when it is desired to examine the distribution of the corrosion state of the steel material 11b over a part or all of the concrete structure 11, it is preferable that a plurality of matching surfaces 11d are arranged adjacent to each other. For example, it is preferable that they are arranged adjacent to each other along a first direction X and / or a second direction Y that are substantially orthogonal to each other. Thereby, the distribution of the potential of the steel material 11b can be measured without gaps over the surface of the concrete structure 11, and the distribution of the corrosion state of the steel material 11b can be examined. The size of the matching surface 11d is not particularly limited. However, when the matching surface 11d includes a plurality of matching points 11e as shown in FIG. 3(a), for example, it is preferably set to a size that straddles adjacent steel materials 11b. However, the matching surface 11d may be entirely the measurement object without including a plurality of matching points 11e arranged apart from each other. In that case, the matching surface 11d may have a size corresponding to the width of the steel material 11b or the like.

[0032] In this embodiment, as shown in FIG. 3(a), the matching surface 11d includes a plurality of matching points 11e. The plurality of matching points 11e are two-dimensionally arranged at intervals within a plane including the first direction X and the second direction Y corresponding to the arrangement of the plurality of matching electrodes 31 of the matching electrode unit 3. By providing a plurality of matching points 11e within one matching surface 11d in this way, a more detailed potential distribution can be examined compared to the case of providing a single matching point. Further, even if an abnormal value is accidentally measured at any of the plurality of matching points 11e, the influence of the abnormal value can be suppressed by averaging within the matching surface 11d, so that the potential of the matching surface 11d can be obtained with higher accuracy.

[0033] The matching surface 11d only needs to include a plurality of matching points 11e, and the arrangement of the plurality of matching points 11e is not particularly limited. In this embodiment, as shown in FIG. 3, the plurality of matching points 11e are arranged in a matrix (or lattice) pattern with substantially equal intervals along the first direction X and substantially equal intervals along the second direction Y. And the distance dx between the matching points 11e in the first direction X is substantially equal to the distance dy between the matching points 11e in the second direction Y. The distances dx and dy between the most closely arranged matching points 11e among the plurality of matching points 11e are preferably smaller than the distance d between the two steel materials 11b buried apart in the concrete structure 11, and the interval between the most distantly arranged matching points 11e (corresponding to twice the distances dx and dy between the matching points 11e in the illustrated example) is preferably larger than the distance d between the two steel materials 11b buried apart in the concrete structure 11. By arranging the plurality of matching points 11e in this way, when the matching electrode unit 3 is arranged on the matching surface 11d, the potentials of a plurality of regions of the steel material 11b can be measured substantially without leakage without having to confirm in advance the position where the steel material 11b is buried by a rebar detector or the like. Note that, as described above, in this embodiment, the first and second directions X and Y are substantially orthogonal to each other, but they may have an angle other than orthogonal to each other.

[0034] The potential difference measuring device 4 measures the potential difference between the reference position where the reference contact portion 2 (reference terminal 21 or reference electrode 22) contacts and the reference surface 11d (each of the plurality of reference points 11e) where the collating electrode unit 3 (each of the plurality of collating electrodes 31) contacts. As shown in FIG. 1, one terminal of the potential difference measuring device 4 is electrically connected to the reference contact portion 2 (reference terminal 21 or reference electrode 22) via a conducting wire 5 such as a lead wire, and the other terminal of the potential difference measuring device 4 is electrically connected to the collating electrode unit 3 (each of the plurality of collating electrodes 31) via a conducting wire 5 such as a lead wire. As the potential difference measuring device 4, a potential difference meter used in a known natural potential measurement method can be used.

[0035] As shown in FIG. 1, the corrosion state determination system 1 further includes a corrosion state determination device 6. The corrosion state determination device 6 is configured to determine the corrosion state of the steel material 11b embedded in the concrete structure 11. In this embodiment, the corrosion state determination device 6 is connected to the potential difference measuring device 4 so as to be capable of data communication, controls the potential difference measuring device 4, and acquires the potential difference measured by the potential difference measuring device 4 from the potential difference measuring device 4. The corrosion state determination device 6 performs a calibration process on the acquired potential difference as necessary, and processes the acquired potential difference as the potential (natural potential or relative potential) of the steel material 11b near the reference surface 11d or the reference point 11e. The corrosion state determination device 6 determines the corrosion state of the steel material 11b using the potential (natural potential or relative potential) of the steel material 11b near the reference surface 11d or the reference point 11e.

[0036] The corrosion state determination device 6 is connected to the potential difference measurement device 4 via, for example, a USB cable, a network cable, an Internet line, or the like. In the present embodiment, as shown in FIG. 1, the corrosion state determination device 6 includes an acquisition unit 61, a calculation unit 62, a determination unit 63, and an optional display unit 64. The corrosion state determination device 6 is not particularly limited. For example, a known computing device such as a computer having, internally or externally, an arithmetic processing device such as a CPU capable of mainly constituting the acquisition unit 61, the calculation unit 62, and the determination unit 63, a memory, a storage device such as a hard disk, a communication device such as a network interface, an input device such as a keyboard and a mouse, and a display device such as a liquid crystal display capable of mainly constituting the display unit 64 can be used.

[0037] The acquisition unit 61 is configured to acquire the potential (natural potential or relative potential) of the steel material 11b in the vicinity of each of the plurality of verification surfaces 11d on the surface of the concrete structure 11. In the present embodiment, the acquisition unit 61 acquires the potential difference between the reference position in the concrete structure 11 and each of the plurality of verification surfaces 11d on the surface of the concrete structure 11 from the potential difference measuring device 4 in order to acquire the potential of the steel material 11b in the vicinity of each of the plurality of verification surfaces 11d. The potential difference acquired from the potential difference measuring device 4 is subjected to calibration processing as necessary and processed as the potential (natural potential or relative potential) of the steel material 11b in the vicinity of the verification surface 11d. As described above, the potential for the verification surface 11d indicates the natural potential of the steel material 11b in the vicinity of the verification surface 11d when the reference position is the steel material 11b of the concrete structure 11, and indicates the relative potential of the steel material 11b in the vicinity of the verification surface 11d with respect to the steel material 11b in the vicinity of the reference surface 11c when the reference position is the reference surface 11c on the surface of the concrete structure 11. The potential for the verification surface 11d is stored, for example, in a storage device inside or outside the corrosion state determination device 6 in association with the position of the verification surface 11d. The corrosion state determination device 6 can examine the potential distribution of the steel material 11b in the concrete structure 11 by acquiring the potentials for the verification surfaces 11d arranged adjacent to each other (for example, adjacent to each other along the first direction X and / or the second direction Y) on the surface of the concrete structure 11.

[0038] The acquisition unit 61 may be configured to acquire the potential of the steel material 11b near each of the plurality of collating points 11e arranged in the collating surface 11d for each of the plurality of collating points 11e near the collating surface 11d in order to obtain the potential of the steel material 11b. In that case, the acquisition unit 61 acquires the potential difference between the reference position in the concrete structure 11 and each of the plurality of collating points 11e arranged in the collating surface 11d from the potential difference measuring device 4. The plurality of potential differences acquired for the plurality of collating points 11e are subjected to calibration processing as necessary, and are processed as the potential (natural potential or relative potential) of the steel material 11b near each collating point 11e, and are averaged within the same collating surface 11d as described later, and are processed as the potential (natural potential or relative potential) of the steel material 11b near the collating surface 11d. As described above, the potential of the collating point 11e indicates the natural potential of the steel material 11b near the collating point 11e when the reference position is the steel material 11b of the concrete structure 11, and indicates the relative potential of the steel material 11b near the collating point 11e with respect to the steel material 11b near the reference surface 11c when the reference position is the reference surface 11c on the surface of the concrete structure 11. The potential of the collating point 11e is stored, for example, in a storage device inside or outside the corrosion state determination device 6, in association with the position of the collating point 11e and the position of the collating surface 11d where the collating point 11e is arranged. The corrosion state determination device 6 can investigate the potential distribution of the steel material 11b in the concrete structure 11 in more detail by acquiring the potentials of the collating points 11e arranged at intervals from each other (for example, at substantially equal intervals along the first direction X and / or the second direction Y) within the collating surface 11d on the surface of the concrete structure 11.

[0039] Figures 4 and 7 each show the distribution of the potential (natural potential in the illustrated example) of the steel material 11b obtained for a plurality of collating points 11e provided on a plurality of collating surfaces 11d within the surface of different concrete structures 11. The plurality of collating surfaces 11d ((X1, Y1), (X2, Y1), ···) are arranged adjacent to each other along a first direction X (parallel to the side extending in the horizontal direction in FIGS. 4 and 7) and a second direction Y (parallel to the side extending in the vertical direction in FIGS. 4 and 7) that are substantially orthogonal to each other. Also, the plurality of collating points 11e ((1, 1), (2, 1), ···) within the plurality of collating surfaces 11d are arranged at substantially equal intervals along the first direction X and the second direction Y that are substantially orthogonal to each other. In FIGS. 4 and 7, the potential for each collating point 11e is associated with the position of each collating point 11e and the position of the collating surface 11d on which each collating point 11e is arranged, and is shown as a numerical value and also as a difference in color shading. In this way, by the acquisition unit 61 acquiring the potential for the plurality of collating points 11e, it is possible to examine the potential distribution of the steel material 11b for each collating point 11e within the surface of the concrete structure 11.

[0040] In the present embodiment, as described above, the corrosion state determination system 1 includes the collating electrode unit 3 having a plurality of collating electrodes 31. By using this collating electrode unit 3, the acquisition unit 61 can acquire a plurality of potentials for a plurality of collating points 11e within the same collating surface 11d at the same timing. By acquiring the plurality of potentials for the plurality of collating points 11e at the same timing, it is possible to suppress the influence of the change over time between the plurality of collating points 11e. However, the acquisition unit 61 may be configured to acquire the potential of the steel material 11b at different timings instead of the same timing for the plurality of collating points 11e within the same collating surface 11d.

[0041] When a plurality of collation points 11e are arranged within the collation surface 11d as in the present embodiment, the calculation unit 62 may be configured to calculate the average value of the potentials for the plurality of collation points 11e within the collation surface 11d as the potential for the collation surface 11d. Thereby, even if an abnormal value due to noise in the electronic circuit or the like accidentally occurs in any one of the plurality of collation electrodes 31, the influence of the abnormal value can be suppressed to a small extent, so that the potential for the collation surface 11d can be obtained with higher accuracy. In particular, when the collation electrode unit 3 is used as in the present embodiment, since the plurality of potentials for the plurality of collation points 11e are acquired at the same timing, at least the influence of changes over time is suppressed, and a more accurate potential can be obtained. However, the potential of the steel material 11b near the collation surface 11d may be acquired as a single potential instead of as the average value of the potentials of the steel material 11b near the plurality of collation points 11e within the collation surface 11d.

[0042] FIG. 5 and FIG. 8 respectively show the distribution of the potential (natural potential in the illustrated example) of the steel material 11b near the collation surface 11d calculated by averaging the potentials of the steel material 11b near the plurality of collation points 11e within the same collation surface 11d shown in FIGS. 4 and 7 respectively. In this way, by the calculation unit 62 averaging the potentials for the plurality of collation points 11e to calculate the potential for the collation surface 11d, the potential distribution of the steel material 11b for each collation surface 11d within the surface of the concrete structure 11 can be examined. For example, referring to FIG. 5, according to the standard (ASTM C876) of the conventional method, the steel material 11b near the collation surface 11d located at (X1, Y3), (X2, Y3), ··· (X5, Y5) has a potential greater than the second threshold value (-200 mV), so it is determined that there is no corrosion with a probability of 90% or more. On the other hand, the steel material 11b near the collation surface 11d located at (X1, Y1), (X2, Y1), ··· (X5, Y2) has a potential greater than the first threshold value (-350 mV) and less than or equal to the second threshold value, so the corrosion state is determined to be uncertain.

[0043] The calculation unit 62 is configured to calculate the potential gradient for each of the plurality of matching surfaces 11d. The potential gradient means the change in potential per unit length on the matching surface 11d. The larger the potential gradient for a certain matching surface 11d, the greater the change in the potential of the steel material 11b in the vicinity of that matching surface 11d. For example, the potential difference between the steel materials 11b in the vicinity of the matching surfaces 11d on both sides sandwiching that matching surface 11d is large. Therefore, if the potential gradient for a certain matching surface 11d is large, it can be estimated that the corrosion states of the steel materials 11b in the vicinity of the matching surfaces 11d on both sides sandwiching that matching surface 11d are significantly different from each other.

[0044] The potential gradient for the matching surface 11d is not particularly limited and can be calculated by various methods. For example, the calculation unit 62 may be configured to calculate the potential gradient for the matching surface 11d based on the potential differences for a plurality of matching points 11e within the matching surface 11d and the distances dx, dy (see FIGS. 3(a) and 3(b)) between the plurality of matching points 11e. In the present embodiment, by calculating the potential gradient using a plurality of potentials acquired at the same timing using the matching electrode unit 3, at least the influence of changes over time can be suppressed, and a more accurate potential gradient can be calculated. Note that the potential gradient for the matching surface 11d can also be calculated based on the potential difference and the distance between the matching surface 11d and another adjacent matching surface 11d, in addition to the above.

[0045] Here, in the present embodiment, as shown in FIG. 3(a), a plurality of collation points 11e are arranged side by side along a first direction X and a second direction Y on a collation surface 11d. In the illustrated example, a plurality (nine in the illustrated example) of collation points 11e are arranged in a matrix (or grid) at substantially equal intervals along each of the first direction X and the second direction Y that are substantially orthogonal to each other. When a plurality of collation points 11e are arranged side by side along the first direction X and the second direction Y, the calculation unit 62 may be configured to calculate the gradient of the potential in the first direction X as a first gradient Sx, calculate the gradient of the potential in the second direction Y as a second gradient Sy, and calculate the gradient S of the potential for the collation surface 11d based on the first and second gradients Sx and Sy. For example, the calculation unit 62 can calculate the square root of the sum of the squares of the first and second gradients Sx and Sy as the gradient S of the potential for the collation surface 11d, as shown by the following formula (1).

[0046] TIFF0007716066000001.tif1070However, Sx and Sy represent the gradients of the potential in the first and second directions X and Y, respectively.

[0047] The first gradient Sx can be calculated based on the potential difference between a plurality of collation points 11e arranged side by side along the first direction X and the distance dx between the plurality of collation points 11e (see FIG. 3(b)). For example, the first gradient Sx is the potential difference (in FIG. 3(b), E 11 -E 31 、E 12 -E 32 、E 13 -E 33 ) obtained for the two most separated collation points 11e among the plurality of collation points 11e arranged side by side along the first direction X, divided by the distance between the two most separated collation points 11e (twice the distance dx between adjacent collation points 11e). At this time, since there are three pairs of collation points 11e arranged most distantly, the first gradient Sx may be obtained by averaging the gradients of the potential for the three pairs of collation points 11e. This calculation method is represented by the following formula (2).

[0048] Also, similar to the first gradient Sx, the second gradient Sy can be calculated based on the potential difference between a plurality of collation points 11e arranged side by side along the second direction Y and the distance dy between the plurality of collation points 11e (see Fig. 3(b)). For example, the second gradient Sy is the potential difference obtained for the two most separated collation points 11e among the plurality of collation points 11e arranged side by side along the second direction Y (in Fig. 3(b), E 11 -E 13 、E 21 -E 23 、E 31 -E 33 ). It can be obtained by dividing the potential difference by the distance between the two most separated collation points 11e (twice the distance dy between adjacent collation points 11e). At this time, since there are three pairs of collation points 11e arranged most separated from each other, the second gradient Sy may be obtained by averaging the potential gradients for the three pairs of collation points 11e. This calculation method is represented by the following formula (3).

[0049] TIFF0007716066000002.tif32105However, E 11 ~E 33 represent the potential (natural potential) for each of the plurality of collation points 11e, and dx and dy respectively represent the distances between the collation points 11e in the first and second directions X and Y (in the examples shown in Figs. 3(a) and (b), both are 100 mm).

[0050] The determination unit 63 is configured to determine the corrosion state of the steel material 11b in the concrete structure 11 based on the potential and / or the gradient of the potential for each of the reference surfaces 11d. For this purpose, the determination unit 63 is configured to determine whether the gradient of the potential for each of the reference surfaces 11d is equal to or greater than a predetermined threshold value. The predetermined threshold value can be appropriately set according to the corrosion state of the steel material 11b and the distribution of the corrosion regions. For example, the predetermined threshold value can be set in a range greater than the gradient of the potential for the reference surface 11d where a potential with a relatively small change (gradient) is obtained within the surface of the concrete structure 11 to be determined. As the gradient of the potential serving as a reference, for example, the gradient of the potential obtained for the reference surface 11d in the vicinity of the region of the steel material 11b that is not corroded or is highly likely not to be corroded, or the gradient of the potential obtained for the reference surface 11d in the vicinity of the region of the steel material 11b that is corroded or is highly likely to be corroded can be selected. For example, referring to FIGS. 6 and 9 described below, the predetermined threshold value in each case can be set in a range of about 40 mV / 100 mm or more and about 65 mV / 100 mm or more. Note that the predetermined threshold value can also be adopted based on the gradient of the potential obtained outside the surface of the concrete structure 11 to be determined. In this case, it is preferable to verify that the gradient of the potential to be adopted is applicable within the surface of the concrete structure 11 to be determined.

[0051] The determination unit 63 is configured to determine a matching surface 11d for which it is determined that the potential gradient is equal to or greater than a predetermined threshold value as a boundary region where the steel material 11b in the vicinity of the matching surface 11d is likely to be in a boundary state between a corroded state and a non-corroded state. Within the surface of the concrete structure 11 to be determined, when a certain matching surface 11d is determined to be a boundary region, it can be recognized that the corrosion state of the steel material 11b changes significantly in the vicinity of the matching surface 11d determined to be the boundary region. Thereby, for example, the steel materials 11b in the vicinity of the matching surfaces 11d located on both sides sandwiching the matching surface 11d determined to be the boundary region can be determined to be highly likely to be either corroded or non-corroded by also considering the magnitude of the acquired potential. Alternatively, depending on whether the potential is greater or smaller compared to the potential for the matching surface 11d determined to be the boundary region, it can be determined that the steel material 11b in the vicinity of the matching surface 11d outside the boundary region is highly likely to be either corroded or non-corroded. Therefore, according to the corrosion state determination device 6 of the present embodiment, as will be described in detail below, even in a region of the steel material 11b where the corrosion state is determined to be uncertain by the conventional method, it is possible to determine whether it is in a corroded state or a non-corroded state, the region where the corrosion state is determined to be uncertain is reduced, and excellent determination accuracy can be obtained.

[0052] As described above, the determination unit 63 only needs to be configured to determine whether at least the matching surface 11d is a boundary region. There is no particular limitation on the corrosion state of the steel material 11b near the matching surface 11d outside the boundary region, and it can be determined by various methods. For example, the determination unit 63 may be configured to determine the corrosion state of the steel material 11b near the matching surface 11d outside the boundary region based on the spatial distribution of the matching surface 11d determined to be the boundary region. More specifically, when the potential of the matching surface 11d adjacent to the matching surface 11d determined to be the boundary region is lower than the potential of the matching surface 11d determined to be the boundary region, the determination unit 63 may be configured to determine the adjacent matching surface 11d as a corrosion region where the steel material 11b near the adjacent matching surface 11d is likely to be in a corroded state. Further, when the potential of the matching surface 11d adjacent to the matching surface 11d determined to be the boundary region is higher than the potential of the matching surface 11d determined to be the boundary region, the determination unit 63 may be configured to determine the adjacent matching surface 11d as a non-corrosion region where the steel material 11b near the adjacent matching surface 11d is likely to be in a non-corroded state.

[0053] Here, referring to FIGS. 5 and 8, the matching surface 11d determined to be the boundary region by the determination unit 63 is surrounded by a dotted line (in FIG. 5, the region from (X1, Y2) to (X5, Y2); in FIG. 8, the region from (X1, Y3) to (X5, Y3)). Among the matching surfaces on both sides sandwiching the matching surface 11d determined to be the boundary region, for the matching surface 11d on one side (above the boundary region in FIGS. 5 and 8), the potential of the steel material 11b is relatively high, and for the matching surface 11d on the other side (below the boundary region in FIGS. 5 and 8), the potential of the steel material 11b is relatively low. Considering such a potential difference, the determination unit 63 can determine the matching surface 11d on one side of the boundary region as a non-corrosion region where the steel material 11b in its vicinity is likely to be in a non-corroded state, and can determine the matching surface 11d on the other side of the boundary region as a corrosion region where the steel material 11b in its vicinity is likely to be in a corroded state.

[0054] In particular, in the example shown in FIG. 5, the steel material 11b near the collating surface 11d on the other side of the boundary region (the lower side than the boundary region in FIG. 5) has a potential greater than the first threshold value (-350 mV) and equal to or less than the second threshold value (-200 mV) according to the standard of the conventional method (ASTM C876), so the corrosion state is determined to be uncertain. However, according to the corrosion state determination device 6 of the present embodiment, it is possible to determine that the region of the steel material 11b, for which the corrosion state is determined to be uncertain according to the standard of the conventional method, is highly likely to be in a corrosion state, so that more excellent determination accuracy can be obtained. Regarding the examples shown in FIGS. 5 and 8, it has been confirmed by other methods that the steel material 11b near the corresponding collating surface 11d is in a corrosion state or a non-corrosion state as determined by the corrosion state determination device 6 of the present embodiment.

[0055] Further, the determination unit 63 may be configured to determine the corrosion state of the steel material 11b near the matching surface 11d other than the boundary region based on the potential of the matching surface 11d determined as the boundary region. Here, FIGS. 6 and 9 respectively correspond to FIGS. 5 and 8, and show the relationship between the potential (natural potential in the illustrated example) and the potential gradient obtained for each of the plurality of matching surfaces 11d. In FIGS. 6 and 9, the position information ((X1, Y1), etc.) of the matching surface 11d is described corresponding to the data points for each matching surface 11d, and the potential range of the steel material 11b near the matching surface 11d determined as the boundary region is surrounded by a dotted line. Referring to FIGS. 6 and 9 for explanation, the determination unit 63 may be configured to determine whether the potential of the matching surface 11d other than the matching surface 11d determined as the boundary region is less than the minimum potential (the potential at the right end of the dotted frame in FIGS. 6 and 9) among the potentials of the matching surface 11d determined as the boundary region. Then, the determination unit 63 may be configured to determine the matching surface 11d (the matching surface 11d plotted to the right of the dotted frame in FIGS. 6 and 9) for which the potential is determined to be less than the minimum potential as a corrosion region where the steel material 11b near the matching surface 11d is likely to be in a corroded state. Further, the determination unit 63 may be configured to determine whether the potential of the matching surface 11d other than the matching surface 11d determined as the boundary region is greater than the maximum potential (the potential at the left end of the dotted frame in FIGS. 6 and 9) among the potentials of the matching surface 11d determined as the boundary region. Then, the determination unit 63 may be configured to determine the matching surface 11d (the matching surface 11d plotted to the left of the dotted frame in FIGS. 6 and 9) for which the potential is determined to be greater than the maximum potential as a non-corrosion region where the steel material 11b near the matching surface 11d is likely to be in a non-corroded state.

[0056] In particular, in the example shown in FIG. 6, for the steel material 11b in the vicinity of the matching surface 11d (the matching surface 11d plotted to the right of the dotted line frame in FIG. 6) where the potential is determined to be less than the minimum potential, according to the standard of the conventional method (ASTM C876), since its potential is greater than the first threshold value (-350 mV) and less than or equal to the second threshold value (-200 mV), the corrosion state is determined to be uncertain. However, according to the corrosion state determination device 6 of the present embodiment, it is possible to determine that there is a high possibility of corrosion even in the region of the steel material 11b where the corrosion state is determined to be uncertain according to the standard of the conventional method, so that more excellent determination accuracy can be obtained. Regarding the examples shown in FIGS. 6 and 9 as well, similar to what was described above with respect to FIGS. 5 and 8, it has been confirmed by other methods that the steel material 11b in the vicinity of the corresponding matching surface 11d is in a corrosion state or a non-corrosion state according to the determination result of the corrosion state determination device 6 of the present embodiment.

[0057] The display unit 64 displays the potential and / or the gradient of the potential of the steel material 11b acquired for a plurality of matching points 11e and / or a plurality of matching surfaces 11d. In the present embodiment, as shown in FIGS. 6 and 9, the display unit 64 displays the potential and the gradient of the potential for each of the plurality of matching surfaces 11d in a coordinate system in which one axis (the horizontal axis in the illustrated example) indicates the potential and the other axis (the vertical axis in the illustrated example) indicates the gradient of the potential. According to the corrosion state determination device 6 of the present embodiment, since the display unit 64 is configured to graphically display the relationship between the potential and the gradient of the potential for the matching surface 11d, the distribution of the gradient of the potential with respect to the potential of the steel material 11b can be clearly grasped. Therefore, for example, compared with the case where the potential of the steel material 11b is displayed in shades of color as shown in FIGS. 4 to 5 and FIGS. 7 to 8, the boundary region can be clearly grasped, and the corrosion state of the steel material 11b can be more clearly grasped.

[0058] Next, an example of implementing the corrosion state determination method of the present embodiment using the corrosion state determination system 1 of the present embodiment will be described. However, the corrosion state determination method of the present invention is not limited to the following example, and can also be implemented using a system other than the corrosion state determination system 1 of the present embodiment. Further, the corrosion state determination method of the present embodiment is not particularly limited, and can be executed by a human, or can also be executed by a computer program including computer-executable instructions for causing a computer to execute the corrosion state determination method of the present embodiment when executed on a computer. Note that several steps will be described below, but the order of the steps is not limited to the order of the following description.

[0059] The corrosion state determination method of the present embodiment is a method for determining the corrosion state of the steel material 11b embedded in the concrete structure 11. The corrosion state determination method includes a step of obtaining the potential of the steel material 11b in the vicinity of each of the plurality of verification surfaces 11d on the surface of the concrete structure 11. In the present embodiment, in order to obtain the potential of the steel material 11b in the vicinity of each of the plurality of verification surfaces 11d, the potential difference between the reference position in the concrete structure 11 and each of the plurality of verification surfaces 11d on the surface of the concrete structure 11 is obtained. The obtained potential difference is subjected to calibration processing as necessary and processed as the potential (natural potential or relative potential) of the steel material 11b in the vicinity of the verification surface 11d. As described above, the potential for the verification surface 11d indicates the natural potential of the steel material 11b in the vicinity of the verification surface 11d when the reference position is the steel material 11b of the concrete structure 11, and indicates the relative potential of the steel material 11b in the vicinity of the verification surface 11d with respect to the steel material 11b in the vicinity of the reference surface 11c when the reference position is the reference surface 11c on the surface of the concrete structure 11. The potential for the verification surface 11d may be stored, for example, in a storage device inside or outside the corrosion state determination device 6 in association with the position of the verification surface 11d. By obtaining the potentials for the verification surfaces 11d arranged adjacent to each other on the surface of the concrete structure 11 (for example, adjacent to each other along the first direction X and / or the second direction Y), as shown in FIGS. 5 and 8, the potential distribution of the steel material 11b in the concrete structure 11 can be examined.

[0060] The step of obtaining the potential of the steel material 11b in the vicinity of each of the plurality of collating surfaces 11d may include the step of obtaining the potential of the steel material 11b in the vicinity of each of the plurality of collating points 11e arranged in the collating surface 11d. In the present embodiment, in order to obtain the potential of the steel material 11b in the vicinity of each of the plurality of collating points 11e, the potential difference between the reference position in the concrete structure 11 and each of the plurality of collating points 11e arranged in the collating surface 11d is obtained. The plurality of potential differences obtained for the plurality of collating points 11e are subjected to calibration processing as necessary, and are used as the potential (natural potential or relative potential) of the steel material 11b in the vicinity of each collating point 11e. Further, as described below, by averaging within the same collating surface 11d, it is processed as the potential (natural potential or relative potential) of the steel material 11b in the vicinity of the collating surface 11d. As described above, the potential for the collating point 11e indicates the natural potential of the steel material 11b in the vicinity of the collating point 11e when the reference position is the steel material 11b of the concrete structure 11, and indicates the relative potential of the steel material 11b in the vicinity of the collating point 11e with respect to the steel material 11b in the vicinity of the reference surface 11c when the reference position is the reference surface 11c on the surface of the concrete structure 11. The potential for the collating point 11e may be stored, for example, in a storage device inside or outside the corrosion state determination device 6, in association with the position of the collating point 11e and the position of the collating surface 11d on which the collating point 11e is arranged. By obtaining the potential for the collating points 11e arranged at intervals from each other (for example, at substantially equal intervals along the first direction X and / or the second direction Y) within the collating surface 11d on the surface of the concrete structure 11, as shown in FIGS. 4 and 7, the potential distribution of the steel material 11b in the concrete structure 11 can be examined in more detail.

[0061] When obtaining the potential of the steel material 11b in the vicinity of each of the plurality of collating points 11e, the plurality of potentials for the plurality of collating points 11e within the same collating surface 11d may be obtained at the same timing. By obtaining the plurality of potentials for the plurality of collating points 11e at the same timing, the influence of the change over time of the plurality of collating points 11e can be suppressed. However, for the plurality of collating points 11e within the same collating surface 11d, the potential of the steel material 11b may be obtained at different timings instead of the same timing.

[0062] The step of obtaining the potential of the steel material 11b in the vicinity of each of the plurality of collating surfaces 11d may include a step of calculating the average value of the potentials of the steel material 11b in the vicinity of the plurality of collating points 11e as the potential for the collating surface 11d. By averaging the potentials for the plurality of collating points 11e to calculate the potential for the collating surface 11d, as shown in FIGS. 5 and 8, the potential distribution of the steel material 11b for each collating surface 11d within the surface of the concrete structure 11 can be examined. Also, even if an abnormal value due to noise or the like is accidentally obtained for any of the plurality of collating points 11e, the influence of the abnormal value can be suppressed to a small extent by averaging, so that the potential for the collating surface 11d can be obtained with higher accuracy. In particular, if the plurality of potentials for the plurality of collating points 11e are obtained at the same timing, at least the influence of the change over time can be suppressed, so that a more accurate potential can be obtained. However, the potential of the steel material 11b in the vicinity of the collating surface 11d may be obtained as a single potential instead of as the average value of the potentials of the steel material 11b in the vicinity of the plurality of collating points 11e within the collating surface 11d.

[0063] The corrosion state determination method of the present embodiment includes a step of calculating the potential gradient for each of the plurality of comparison surfaces 11d. The potential gradient means the change in potential per unit length on the comparison surface 11d. The larger the potential gradient for a certain comparison surface 11d, the greater the change in the potential of the steel material 11b near that comparison surface 11d. For example, the potential difference between the steel materials 11b near the comparison surfaces 11d on both sides sandwiching that comparison surface 11d is large. Therefore, if the potential gradient for a certain comparison surface 11d is large, it can be estimated that the corrosion states of the steel materials 11b near the comparison surfaces 11d on both sides sandwiching that comparison surface 11d are significantly different from each other.

[0064] The potential gradient for the comparison surface 11d is not particularly limited and can be calculated by various methods. For example, the step of calculating the potential gradient for the comparison surface 11d may include a step of calculating the potential gradient for the comparison surface 11d based on the potential differences for a plurality of comparison points 11e within the comparison surface 11d and the distances dx, dy (see FIGS. 3(a) and (b)) between the plurality of comparison points 11e. For example, by calculating the potential gradient for the comparison surface 11d using the plurality of potentials for the plurality of comparison points 11e acquired at the same timing, at least the influence of the change over time can be suppressed, and a more accurate potential gradient can be calculated. Note that the potential gradient for the comparison surface 11d can also be calculated based on the potential difference and the distance between the comparison surface 11d and another adjacent comparison surface 11d in addition to the above.

[0065] Here, in the present embodiment, as shown in FIG. 3(a), a plurality of matching points 11e are arranged side by side along a first direction X and a second direction Y on a matching surface 11d. In the illustrated example, a plurality (nine in the illustrated example) of matching points 11e are arranged in a matrix (or lattice) pattern at substantially equal intervals along each of the first direction X and the second direction Y that are substantially orthogonal to each other. When a plurality of matching points 11e are arranged side by side along the first direction X and the second direction Y, the step of calculating the potential gradient of the matching surface 11d may include a step of calculating the potential gradient in the first direction X as a first gradient Sx, a step of calculating the potential gradient in the second direction Y as a second gradient Sy, and a step of calculating a potential gradient S of the matching surface 11d based on the first and second gradients Sx and Sy. For example, the potential gradient S of the matching surface 11d can be calculated by the square root of the sum of the squares of the first and second gradients Sx and Sy, as shown by the following formula (1).

[0066] TIFF0007716066000003.tif1070However, Sx and Sy respectively represent the potential gradients in the first and second directions X and Y.

[0067] The first gradient Sx can be calculated based on the potential difference between a plurality of matching points 11e arranged side by side along the first direction X and the distance dx between the plurality of matching points 11e (see FIG. 3(b)). For example, the first gradient Sx is the potential difference (in FIG. 3(b), E 11 -E 31 、E 12 -E 32 、E 13 -E 33) can be obtained by dividing it by the distance between the two most separated matching points 11e (twice the distance dx between adjacent matching points 11e). At this time, since there are three pairs of the most separated matching points 11e, the first gradient Sx may be obtained by averaging the potential gradients for the three pairs of matching points 11e. This calculation method is represented by the following formula (2).

[0068] Also, similar to the first gradient Sx, the second gradient Sy can be calculated based on the potential difference between a plurality of matching points 11e arranged along the second direction Y and the distance dy between the plurality of matching points 11e (see Fig. 3(b)). For example, the second gradient Sy is the potential difference obtained for the two most separated matching points 11e among the plurality of matching points 11e arranged along the second direction Y (in Fig. 3(b), E 11 -E 13 、E 21 -E 23 、E 31 -E 33 ). It can be obtained by dividing it by the distance between the two most separated matching points 11e (twice the distance dy between adjacent matching points 11e). At this time, since there are three pairs of the most separated matching points 11e, the second gradient Sy may be obtained by averaging the potential gradients for the three pairs of matching points 11e. This calculation method is represented by the following formula (3).

[0069] TIFF0007716066000004.tif32105However, E 11 ~E 33 represents the potential (natural potential) for each of the plurality of matching points 11e, and dx and dy respectively represent the distances between the matching points 11e in the first and second directions X and Y (in the examples shown in Figs. 3(a) and (b), both are 100 mm).

[0070] The corrosion state determination method of this embodiment includes a step of determining whether or not the potential gradient for each of the reference surfaces 11d is equal to or greater than a predetermined threshold value. The predetermined threshold value can be appropriately set according to the corrosion state of the steel material 11b and the distribution of the corrosion regions. For example, the predetermined threshold value can be set in a range greater than the potential gradient of the reference surface 11d for which a potential with relatively small change (gradient) is obtained within the surface of the concrete structure 11 to be determined. As the potential gradient serving as a reference, for example, the potential gradient obtained for the reference surface 11d in the vicinity of the region of the steel material 11b that is not corroded or is highly likely not to be corroded, or the potential gradient obtained for the reference surface 11d in the vicinity of the region of the steel material 11b that is corroded or is highly likely to be corroded can be selected.

[0071] The corrosion state determination method of the present embodiment includes a step of determining a comparison surface 11d for which the potential gradient is determined to be equal to or greater than a predetermined threshold value as a boundary region where the steel material 11b in the vicinity of the comparison surface 11d is likely to be in a boundary state between a corroded state and a non-corroded state. Within the surface of the concrete structure 11 to be determined, when a certain comparison surface 11d is determined to be a boundary region, it can be recognized that the corrosion state of the steel material 11b changes significantly in the vicinity of the comparison surface 11d determined to be the boundary region. Thereby, for example, the steel materials 11b in the vicinity of the comparison surfaces 11d located on both sides of the comparison surface 11d determined to be the boundary region can be determined to be highly likely to be either corroded or non-corroded by also considering the magnitude of the acquired potential. Alternatively, depending on whether the potential is greater or smaller compared to the potential of the comparison surface 11d determined to be the boundary region, it can be determined that the steel material 11b in the vicinity of the comparison surface 11d other than the boundary region is highly likely to be either corroded or non-corroded. Therefore, according to the corrosion state determination method of the present embodiment, as will be described in detail below, even in a region of the steel material 11b where the corrosion state is determined to be uncertain by the conventional method, it is possible to determine whether it is in a corroded state or a non-corroded state, the region where the corrosion state is determined to be uncertain is reduced, and excellent determination accuracy can be obtained.

[0072] As described above, the corrosion state determination method of this embodiment only needs to include a step of determining whether or not the reference surface 11d is a boundary region. The corrosion state of the steel material 11b near the reference surface 11d other than the boundary region is not particularly limited and can be determined by various methods. For example, the corrosion state determination method of this embodiment may include a step of determining the corrosion state of the steel material 11b near the reference surface 11d other than the boundary region based on the spatial distribution of the reference surface 11d determined to be a boundary region. More specifically, the corrosion state determination method of this embodiment may include a step of determining, if the potential of a reference surface 11d adjacent to the reference surface 11d determined to be a boundary region is lower than the potential of the reference surface 11d determined to be a boundary region, determining the adjacent reference surface 11d as a corrosion region where the steel material 11b near the adjacent reference surface 11d is likely to be corroded. In addition, the corrosion state determination method may include a step of determining, if the potential of a reference surface 11d adjacent to a reference surface 11d determined to be a boundary region is higher than the potential of a reference surface 11d determined to be a boundary region, the adjacent reference surface 11d as a non-corroded region in which the steel material 11b near the adjacent reference surface 11d is likely to be in a non-corroded state.

[0073] 5 and 8, the reference surface 11d determined to be a boundary region according to the above method is surrounded by a dotted line (the region (X1, Y2) to (X5, Y2) in FIG. 5, and the region (X1, Y3) to (X5, Y3) in FIG. 8). Of the reference surfaces 11d on either side of the reference surface 11d determined to be a boundary region, the reference surface 11d on one side (above the boundary region in FIGS. 5 and 8) has a relatively high potential of the steel material 11b, while the reference surface 11d on the other side (below the boundary region in FIGS. 5 and 8) has a relatively low potential of the steel material 11b. Taking such a difference in potential into consideration, the reference surface 11d on one side of the boundary region can be determined to be a non-corrosion region where the steel material 11b nearby is likely to be non-corroded, and the reference surface 11d on the other side of the boundary region can be determined to be a corrosion region where the steel material 11b nearby is likely to be corroded.

[0074] In particular, in the example shown in FIG. 5, for the steel material 11b near the reference surface 11d on the other side of the boundary region (below the boundary region in FIG. 5), according to the standard (ASTM C876) of the conventional method, its potential is greater than the first threshold value (-350 mV) and less than or equal to the second threshold value (-200 mV), so the corrosion state is determined to be uncertain. However, according to the corrosion state determination method of the present embodiment, for the region of the steel material 11b where the corrosion state is determined to be uncertain according to the standard of the conventional method, it can be determined that there is a high possibility that it is in a corrosion state, so more excellent determination accuracy can be obtained.

[0075] Further, the corrosion state determination method of the present embodiment may include a step of determining the corrosion state of the steel material 11b near the reference surface 11d other than the boundary region based on the potential of the reference surface 11d determined as the boundary region. For example, referring to FIGS. 6 and 9 for description, the corrosion state determination method of the present embodiment may include a step of determining whether the potential of the reference surface 11d other than the reference surface 11d determined as the boundary region is less than the minimum potential (the potential at the right end of the dotted frame in FIGS. 6 and 9) among the potentials of the reference surface 11d determined as the boundary region. Then, the corrosion state determination method of the present embodiment may include a step of determining the reference surface 11d (the reference surface 11d plotted on the right side of the dotted frame in FIGS. 6 and 9) for which the potential is determined to be less than the minimum potential as a corrosion region where the steel material 11b near the reference surface 11d is highly likely to be in a corrosion state. Further, the corrosion state determination method of the present embodiment may include a step of determining whether the potential of the reference surface 11d other than the reference surface 11d determined as the boundary region is greater than the maximum potential (the potential at the left end of the dotted frame in FIGS. 6 and 9) among the potentials of the reference surface 11d determined as the boundary region. Then, the corrosion state determination method of the present embodiment may include a step of determining the reference surface 11d (the reference surface 11d plotted on the left side of the dotted frame in FIGS. 6 and 9) for which the potential is determined to be greater than the maximum potential as a non-corrosion region where the steel material 11b near the reference surface 11d is highly likely to be in a non-corrosion state.

[0076] In particular, in the example shown in Figure 6, the steel material 11b near the reference surface 11d (the reference surface 11d plotted to the right of the dotted frame in Figure 6) whose potential is determined to be less than the minimum potential has a potential greater than the first threshold (-350mV) and less than the second threshold (-200mV) according to the standard of the conventional method (ASTM C876), and therefore is determined to have an uncertain corrosion state. However, according to the corrosion state determination method of this embodiment, it is possible to determine that the region of the steel material 11b whose corrosion state is determined to be uncertain according to the standard of the conventional method is also highly likely to be corroded, thereby achieving greater determination accuracy.

[0077] The corrosion state determination method of this embodiment may further include a step of displaying the potential and potential gradient for each of the multiple reference surfaces 11d in a coordinate system in which one axis represents the potential and the other axis represents the potential gradient, as shown in Figures 6 and 9. According to the corrosion state determination method of this embodiment, by graphically displaying the relationship between the potential and the potential gradient for the reference surfaces 11d, the distribution of the potential gradient relative to the potential of the steel material 11b can be clearly understood. Therefore, compared to when the potential of the steel material 11b is displayed using color shading, as shown in Figures 4 to 5 and 7 to 8, for example, the boundary region can be clearly identified, and the corrosion state of the steel material 11b can be more clearly understood. [Explanation of symbols]

[0078] 1. Corrosion condition determination system 2 Reference contact part 21 Reference terminal 22 Reference electrode 3 Reference electrode unit 31 Reference electrode 32 Reference electrode support part 4 Potential difference measuring device 5 conductor 6. Corrosion condition determination device 61 Acquisition Department 62 Arithmetic section 63 Judgment section 64 Display section 11 Concrete structures 11a Concrete 11b Steel material (reinforcing bar) 11c Reference surface 11d Matching surface 11e Matching point d Distance between steel materials dx Distance between matching points in the first direction dy Distance between matching points in the second direction X First direction [[ID=

Claims

1. A method for determining the corrosion state of steel embedded in a concrete structure, comprising: for each of a plurality of reference surfaces on the surface of the concrete structure, obtaining the potential of the steel in the vicinity of each of the plurality of reference surfaces; calculating the gradient of the potential for each of the plurality of reference surfaces; determining whether the gradient of the potential for each of the reference surfaces is equal to or greater than a predetermined threshold value; determining the reference surface for which it is determined that the gradient of the potential is equal to or greater than the predetermined threshold value as a boundary region where the steel in the vicinity of the reference surface is likely to be in a boundary state between a corroded state and a non-corroded state; and including: the step of obtaining the potential includes obtaining the potential of the steel in the vicinity of each of a plurality of reference points arranged in the reference surface, and calculating an average value of the potentials of the steel in the vicinity of the plurality of reference points as the potential for the reference surface; the step of calculating the gradient of the potential includes calculating the gradient of the potential for the reference surface based on the difference in potential and the distance between the plurality of reference points in the reference surface. A method for determining the corrosion state.

2. A method for determining the corrosion state of steel embedded in a concrete structure, comprising: for each of a plurality of reference surfaces on the surface of the concrete structure, obtaining the potential of the steel in the vicinity of each of the plurality of reference surfaces; calculating the gradient of the potential for each of the plurality of reference surfaces; determining whether the gradient of the potential for each of the reference surfaces is equal to or greater than a predetermined threshold value; determining the reference surface for which it is determined that the gradient of the potential is equal to or greater than the predetermined threshold value as a boundary region where the steel in the vicinity of the reference surface is likely to be in a boundary state between a corroded state and a non-corroded state; and including: the step of obtaining the potential includes obtaining the potential of the steel in the vicinity of another reference surface adjacent to each of the reference surfaces; the step of calculating the gradient of the potential includes calculating the gradient of the potential for each of the reference surfaces based on the difference in potential and the distance between each of the reference surfaces and the other reference surfaces. A method for determining the corrosion state.

3. a step of determining whether the potential of the matching surface other than the matching surface determined to be the boundary region is less than the minimum potential among the potentials of the matching surface determined to be the boundary region; a step of determining the matching surface for which the potential is determined to be less than the minimum potential as a corrosion region where the steel material near the matching surface is highly likely to be in a corroded state; a step of determining whether the potential of the matching surface other than the matching surface determined to be the boundary region is greater than the maximum potential among the potentials of the matching surface determined to be the boundary region; a step of determining the matching surface for which the potential is determined to be greater than the maximum potential as a non-corrosion region where the steel material near the matching surface is highly likely to be in a non-corroded state; The corrosion state determination method according to claim 1 or 2, further comprising:

4. the plurality of matching points are arranged side by side along a first direction and a second direction on the matching surface; the step of calculating the gradient of the potential includes: a step of calculating, as a first gradient, the gradient of the potential in the first direction based on the difference in potential between a plurality of matching points arranged side by side along the first direction and the distance between the plurality of matching points; a step of calculating, as a second gradient, the gradient of the potential in the second direction based on the difference in potential between a plurality of matching points arranged side by side along the second direction and the distance between the plurality of matching points; a step of calculating the gradient of the potential for the matching surface based on the first and second gradients; The corrosion state determination method according to claim 1, comprising:

5. The corrosion state determination method according to any one of claims 1 to 4, further comprising a step of displaying the potential and the potential gradient for each of the plurality of matching surfaces in a coordinate system in which one axis represents the potential and the other axis represents the potential gradient.

6. A corrosion state determination device for determining the corrosion state of a steel material embedded in a concrete structure, comprising: an acquisition unit that acquires the potential of the steel material near each of the plurality of matching surfaces on the surface of the concrete structure for each of the plurality of matching surfaces; a calculation unit that calculates the potential gradient for each of the plurality of matching surfaces; a determination unit that determines the corrosion state of the steel material; and the determination unit: determines whether the potential gradient for each of the matching surfaces is equal to or greater than a predetermined threshold; Determine the matching surface for which it is determined that the gradient of the potential is equal to or greater than the predetermined threshold value as a boundary region where the steel material in the vicinity of the matching surface is likely to be in a boundary state between a corroded state and a non-corroded state. It is configured as follows. The acquisition unit is configured to acquire the potential of the steel material in the vicinity of each of the plurality of matching points arranged in the matching surface for each of the plurality of matching points. The calculation unit calculates the average value of the potentials for the plurality of matching points in the matching surface as the potential for the matching surface. Based on the difference in potential for the plurality of matching points in the matching surface and the distances between the plurality of matching points, calculate the gradient of the potential for the matching surface. A corrosion state determination device configured as described above. **Claim 7**: A corrosion state determination device for determining the corrosion state of a steel material embedded in a concrete structure, an acquisition unit that acquires the potential of the steel material in the vicinity of each of a plurality of matching surfaces among the surfaces of the concrete structure for each of the plurality of matching surfaces; a calculation unit that calculates the gradient of the potential for each of the plurality of matching surfaces; a determination unit that determines the corrosion state of the steel material and is provided with The determination unit determines whether or not the gradient of the potential for each of the matching surfaces is equal to or greater than a predetermined threshold value, and determines the matching surface for which it is determined that the gradient of the potential is equal to or greater than the predetermined threshold value as a boundary region where the steel material in the vicinity of the matching surface is likely to be in a boundary state between a corroded state and a non-corroded state. It is configured as follows. The acquisition unit is configured to acquire the potential of the steel material in the vicinity of the other matching surfaces adjacent to each of the matching surfaces for the other matching surfaces adjacent to each of the matching surfaces, and the calculation unit is configured to calculate the gradient of the potential for each of the matching surfaces based on the difference in potential and the distance between each of the matching surfaces and the other matching surfaces. A corrosion state determination device. **Claim 8** The determination unit determines whether or not the potential for the matching surfaces other than the matching surface determined to be the boundary region is less than the minimum potential among the potentials for the matching surface determined to be the boundary region, and determines the matching surface for which it is determined that the potential is less than the minimum potential as a corrosion region where the steel material in the vicinity of the matching surface is likely to be in a corroded state. Determine whether the potential for the collating surface other than the collating surface determined to be the boundary region is greater than the maximum potential among the potentials for the collating surface determined to be the boundary region. Determine the collating surface for which it is determined that the potential is greater than the maximum potential as a non-corrosion region where the steel material near the collating surface is highly likely to be in a non-corroded state. The corrosion state determination device according to claim 6 or 7, which is configured as described above.

9. The plurality of collating points are arranged side by side along a first direction and a second direction on the collating surface. The calculation unit Based on the difference in potential for the plurality of collating points arranged side by side along the first direction and the distance between the plurality of collating points, calculate the gradient of the potential in the first direction as a first gradient. Based on the difference in potential for the plurality of collating points arranged side by side along the second direction and the distance between the plurality of collating points, calculate the gradient of the potential in the second direction as a second gradient. Calculate the gradient of the potential for the collating surface based on the first and second gradients. The corrosion state determination device according to claim 6, which is configured as described above.

10. The corrosion state determination device according to any one of claims 6 to 9, further comprising a display unit configured to display the potential and the potential gradient for each of the plurality of collating surfaces in a coordinate system in which one axis represents the potential and the other axis represents the potential gradient.

11. A computer program including computer-executable instructions that cause a computer to execute the corrosion state determination method according to any one of claims 1 to 5 when executed on the computer.

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