JP7716066B2 - Corrosion state determination method, corrosion state determination device, and computer program capable of executing the corrosion state determination method - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. Publication name: Proceedings of the Japan Concrete Institute, Vol. 43, No. 1, 2021, pp. 1115-1120. Publisher: Japan Concrete Institute. Publication date: June 15, 2021.

Article 30, Paragraph 2 of the Patent Act applies. Publication name: Japan Concrete Institute Annual Conference 2021 (Nagoya), 43rd "Concrete Engineering Lecture" website (https://confit.atlas.jp/guide/event/jcinenji2021/subject/1183/advanced). Publisher: Japan Concrete Institute. Publication date: July 5, 2021.

Article 30, Paragraph 2 of the Patent Act applies. Name of the event: Japan Concrete Institute Annual Conference 2021 (Nagoya), 43rd "Concrete Institute Lecture Series" (held online). Organizer: Japan Concrete Institute (Public Interest Incorporated Association). Date: July 7, 2021 (July 7-9, 2021).

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

In concrete structures with buried steel, such as reinforced concrete, corrosion of the steel due to deterioration over time is a problem. Patent Document 1, for example, discloses a method for determining the state of corrosion of steel embedded in a concrete structure, in which the natural potential of the steel is measured from the surface of the concrete structure and the state of corrosion of the steel is determined based on the measured natural potential. Methods for determining the state of corrosion of steel using the natural potential of the steel typically use the evaluation criteria specified as ASTM C876 to determine whether the steel is corroded.

Japanese Patent Application Laid-Open No. 2018-17518

The evaluation standards specified in ASTM C876 include a wide range where the corrosion state is determined to be uncertain, in addition to the range where the corrosion state is determined to be either corroded or non-corroded. Therefore, even if the natural potential of the steel in a concrete structure is actually measured, there will be many areas where the corrosion state is determined to be uncertain, making it impossible to accurately determine the corrosion state of the steel. In response to this, Patent Document 1 attempts to improve the accuracy of the determination by adopting other parameters, such as the concrete cover thickness and moisture content, in addition to the natural potential of the steel. However, parameters such as cover thickness and moisture content do not directly indicate the corrosion state of the steel, but only indirectly, so the method in Patent Document 1 still does not provide sufficient accuracy in the determination.

The present invention has been developed in consideration of the above-mentioned problems, and aims to provide a corrosion state determination method, a corrosion state determination device, and a computer program capable of executing the corrosion state determination method with improved determination accuracy.

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, and is characterized by comprising the steps of: acquiring the potential of the steel near each of a plurality of reference surfaces among the surfaces of the concrete structure; calculating the potential gradient for each of the plurality of reference surfaces; determining whether the potential gradient for each of the reference surfaces is equal to or greater than a predetermined threshold; and determining a reference surface for which the potential gradient is determined to be equal to or greater than the predetermined threshold as a boundary region where the steel near the reference surface is likely to be in a boundary state between a corroded state and a non-corroded state.

It is preferable that the method further includes the steps of: determining whether the potential of the reference surfaces other than the reference surface determined to be the boundary region is less than the minimum potential of the potentials of the reference surfaces determined to be the boundary region; determining the reference surfaces determined to have the potential less than the minimum potential as corrosion regions where the steel near the reference surface is likely to be in a corroded state; determining whether the potential of the reference surfaces other than the reference surface determined to be the boundary region is greater than the maximum potential of the potentials of the reference surfaces determined to be the boundary region; and determining the reference surfaces determined to have the potential greater than the maximum potential as non-corrosion regions where the steel near the reference surface is likely to be in a non-corroded state.

Furthermore, it is preferable that the step of acquiring the potential includes a step of acquiring the potential of the steel material near each of a plurality of reference points arranged on the reference surface, and calculating the average value of the potential of the steel material near the plurality of reference points as the potential for the reference surface, and that the step of calculating the potential gradient includes a step of calculating the potential gradient for the reference surface based on the difference in potential for the plurality of reference points on the reference surface and the distance between the plurality of reference points.

Furthermore, it is preferable that the plurality of match points are arranged side by side along a first direction and a second direction on the match surface, and the step of calculating the potential gradient includes a step of calculating the potential gradient in the first direction as a first gradient based on the potential difference between the plurality of match points arranged side by side along the first direction and the distance between the plurality of match points, a step of calculating the potential gradient in the second direction as a second gradient based on the potential difference between the plurality of match points arranged side by side along the second direction and the distance between the plurality of match points, and a step of calculating the potential gradient on the match surface based on the first and second gradients.

It is also preferable that the method further includes a step of displaying the potential and the potential gradient 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 potential gradient.

The corrosion state determination device of the present invention is a corrosion state determination device for determining the corrosion state of steel materials embedded in a concrete structure, and includes: an acquisition unit that acquires, for each of a plurality of reference surfaces among the surfaces of the concrete structure, the electric potential of the steel materials in the vicinity of each of the plurality of reference surfaces; and a calculation unit that calculates the gradient of the electric potential for each of the plurality of reference surfaces.
and a judgment unit that judges the corrosion state of the steel material, wherein the judgment unit is configured to judge whether the potential gradient for each of the reference surfaces is equal to or greater than a predetermined threshold, and to judge a reference surface for which it is judged that the potential gradient is equal to or greater than the predetermined threshold as a boundary region in which the steel material near the reference surface is likely to be in a boundary state between a corroded state and a non-corroded state.

Furthermore, the determination unit is preferably configured to determine whether the potential of the reference surfaces other than the reference surface determined to be the boundary region is less than the minimum potential of the potentials of the reference surfaces determined to be the boundary region, determine the reference surfaces determined to have the potential less than the minimum potential as corrosion regions where the steel near the reference surface is likely to be in a corroded state, determine whether the potential of the reference surfaces other than the reference surface determined to be the boundary region is greater than the maximum potential of the potentials of the reference surfaces determined to be the boundary region, and determine the reference surfaces determined to have the potential greater than the maximum potential as non-corrosion regions where the steel near the reference surface is likely to be in a non-corroded state.

Furthermore, it is preferable that the acquisition unit is configured to acquire the electric potential of the steel material in the vicinity of each of a plurality of match points arranged on the match surface, and the calculation unit is configured to calculate the average value of the electric potentials for the plurality of match points on the match surface as the electric potential for the match surface, and to calculate the gradient of the electric potential for the match surface based on the difference in the electric potentials for the plurality of match points on the match surface and the distance between the plurality of match points.

Furthermore, it is preferable that the plurality of matching points are arranged in a row along a first direction and a second direction on the matching surface, and the calculation unit is configured to calculate the potential gradient in the first direction as a first gradient based on the potential difference between the plurality of matching points arranged in a row along the first direction and the distance between the plurality of matching points, calculate the potential gradient in the second direction as a second gradient based on the potential difference between the plurality of matching points arranged in a row along the second direction and the distance between the plurality of matching points, and calculate the potential gradient on the matching surface based on the first and second gradients.

It is also preferable that the device further comprises a display unit configured to display the potential and the potential gradient 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 potential gradient.

The computer program of the present invention is characterized by including computer-executable instructions that, when executed on a computer, cause the computer to execute the corrosion state determination method described above.

The present invention provides a corrosion state determination method, a corrosion state determination device, and a computer program capable of executing the corrosion state determination method with improved determination accuracy.

1 is a schematic diagram showing a corrosion state determination system incorporating a corrosion state determination device according to an embodiment of the present invention. 2 is a perspective view of the reference electrode unit of the corrosion state determination system of FIG. 1 as viewed from the reference electrode side. FIG. FIG. 1A is a front view of a reference surface to be measured by a corrosion state determination device and a corrosion state determination method according to an embodiment of the present invention, and FIG. 1B is an explanatory diagram showing the potential obtained for each of a plurality of reference points provided within the reference surface shown in FIG. 1A and the distance between the reference points. 1 is a diagram showing the distribution of the electric potential (natural potential) of steel material obtained at multiple matching points on the surface of a concrete structure by a corrosion state determination device and a corrosion state determination method according to one embodiment of the present invention. FIG. 1 is a diagram showing the distribution of the potential (natural potential) of steel material obtained for multiple reference surfaces within the surface of a concrete structure using a corrosion state determination device and corrosion state determination method according to one embodiment of the present invention. FIG. 1 is a graph showing the relationship between the potential (natural potential) of steel and the potential gradient obtained for multiple reference surfaces within the surface of a concrete structure using a corrosion state determination device and a corrosion state determination method according to one embodiment of the present invention. FIG. 10 is a diagram showing the distribution of the electric potential (natural potential) of steel material obtained at multiple matching points on the surface of another concrete structure using a corrosion state determination device and a corrosion state determination method according to one embodiment of the present invention. A figure showing the distribution of the potential (natural potential) of steel obtained for multiple reference surfaces within the surface of another concrete structure using a corrosion state determination device and corrosion state determination method according to one embodiment of the present invention. 1 is a graph showing the relationship between the potential (natural potential) of the steel material and the potential gradient obtained for multiple reference surfaces within the surface of another concrete structure using a corrosion state determination device and a corrosion state determination method according to one embodiment of the present invention.

The following describes a corrosion state determination method, corrosion state determination device, and computer program capable of executing the corrosion state determination method according to one embodiment of the present invention, with reference to the accompanying drawings. However, the embodiment described below is merely an example, and the corrosion state determination method, device, and computer program of the present invention are not limited to the following embodiment.

A corrosion state determination method and apparatus according to one embodiment of the present invention are a method and apparatus for determining the corrosion state of steel materials embedded in a concrete structure. The concrete structure 11 to which the corrosion state determination method and apparatus of this embodiment are applied is a structure in which steel materials 11b are embedded in concrete 11a bonded with cement, as shown in FIG. 1. The concrete structure 11 is not particularly limited as long as it is a structure in which steel materials are embedded in concrete, but examples include bridges spanning rivers or the sea, piers for highways, large civil engineering structures such as dams, and buildings. In addition, in this embodiment shown in FIG. 1, the steel materials 11b embedded in the concrete 11a are exemplified by rebars arranged in a grid pattern, but the type, size, and arrangement of the steel materials are not particularly limited. The corrosion state determination method and device of this embodiment will be described below based on an example in which they are used to measure the potential of steel material (reinforcing bars) 11b in a concrete structure (wall) 11 in which steel material (reinforcing bars) 11b are embedded in concrete 11a at intervals d, and determine the corrosion state of the steel material 11b.

First, we will describe a corrosion state determination system 1 that incorporates the corrosion state determination device 6 of this embodiment and is used to implement the corrosion state determination method of this embodiment. 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 may also be implemented using a system other than the corrosion state determination system 1 described below.

The corrosion state determination system 1 measures the potential of 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.

As shown in FIG. 1, the corrosion state determination system 1 comprises a reference contact part 2 that contacts a reference position on the concrete structure 11, a reference electrode unit 3 that contacts a reference surface 11d on the surface of the concrete structure 11, and a potential difference measuring device 4 that connects the reference contact part 2 and the reference electrode unit 3 and measures the potential difference between the reference contact part 2 and the reference electrode unit 3. According to the corrosion state determination system 1, the potential difference measuring device 4 measures the potential difference between the potential at the reference position where the reference contact part 2 contacts and the natural potential of the steel material 11b located near (approximately directly below in the cover thickness direction) the reference surface 11d where the reference electrode unit 3 contacts.

When the reference position is the steel material 11b buried 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 near the reference surface 11d with which the reference electrode unit 3 comes into contact. Furthermore, 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 near the reference surface 11c and the natural potential of the steel material 11b near the reference 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 (a first threshold value, e.g., −350 mV in ASTM C876), the steel material 11b at that position is determined to be corroded with a probability of 90% or higher. If the natural potential of the steel material 11b is higher than a predetermined potential value (a second threshold value, e.g., −200 mV in ASTM C876), the steel material 11b at that position is determined to be not corroded with a probability of 90% or higher. In the latter case, for example, if the natural potential of the steel material 11b near the reference surface 11d is lower than the natural potential of the steel material 11b near the reference surface 11d by a predetermined potential value, the steel material 11b near the reference surface 11d is determined to be corroded. If the natural potential is higher than another predetermined potential value, the steel material 11b near the reference surface 11d is determined to be not corroded. The natural potential of steel material 11b refers to the potential of steel material 11b when no external potential is applied, and is the natural potential measured using a known natural potential measurement method.

The reference contact 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 at the reference surface 11d that the reference electrode unit 3 contacts. The reference contact 2 is electrically connected to one terminal of the potential difference measuring device 4 via a conductor 5, such as a lead wire. As shown in FIG. 1, when measuring the natural potential of the steel material 11b near the reference surface 11d, a reference terminal 21 that is brought into contact with the steel material 11b serving as the reference position can be used as the reference contact 2. A well-known alligator clip or the like can be used as the reference terminal 21. Furthermore, when measuring the relative potential of the steel material 11b near the reference surface 11d, a reference electrode 22 that is brought into contact with the surface (reference surface 11c) of the concrete structure 11 located in the cover thickness direction near the area of the steel material 11b that has the reference natural potential (reference potential) (approximately directly above the area near the steel material 11b) can be used as the reference contact 2. The reference electrode 22 can be a known electrode such as a copper/copper sulfate electrode, a silver/silver chloride electrode, or a calomel electrode.

The reference electrode unit 3 is an electrode member that comes into contact with the surface (reference surface 11d) of the concrete structure 11, located in the cover thickness direction near the area of the steel material 11b that has a natural potential to be measured relative to the reference potential (substantially directly above the area near the steel material 11b). The reference electrode unit 3 is electrically connected to the other terminal of the potential difference measuring device 4 via a conductor 5 such as a lead wire. The reference electrode unit 3 is not particularly limited and is designed to correspond to the shape and size of the reference surface 11d.

The reference electrode unit 3 is not particularly limited in structure, as long as it can measure the potential of the steel material 11b near the reference surface 11d. In this embodiment, as shown in FIGS. 1 and 2, the reference electrode unit 3 includes multiple reference electrodes 31 and a reference electrode support portion 32 sized to correspond to the size of the reference surface 11d and supporting the multiple reference electrodes 31. When the reference electrode unit 3 is placed on the reference surface 11d, the multiple reference electrodes 31 are configured to simultaneously contact multiple reference points 11e (see FIG. 3(a)) within the reference surface 11d. This allows the potentials of multiple regions of the steel material 11b to be measured simultaneously, thereby enabling efficient measurement of the potentials of multiple regions of the steel material 11b. Furthermore, the multiple reference electrodes 31 can measure the potentials of multiple regions of the steel material 11b, at least within the same reference surface 11d, without being affected by changes in the multiple reference points 11e over time. However, the reference electrode unit 3 may also include a single reference electrode corresponding to the size of the reference surface 11d.

The reference electrode unit 3 is only required to be able to simultaneously measure the potential of multiple regions of the steel material 11b, and the arrangement of the multiple reference electrodes 31 is not particularly limited. In this embodiment, the multiple reference electrodes 31 are arranged two-dimensionally at intervals 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 the multiple reference points 11e within the reference surface 11d shown in FIG. 3. The spacing between the closest reference electrodes 31 (corresponding to the distance dx, dy between the reference points 11e) is preferably smaller than the distance d between two steel materials 11b embedded at a distance in the concrete structure 11, and the spacing between the furthest reference electrodes 31 (corresponding to twice the distance dx, dy between the reference points 11e) is preferably greater than the distance d between two steel materials 11b embedded at a distance in the concrete structure 11. By arranging the multiple reference electrodes 31 in this manner, when the reference electrode unit 3 is placed on the reference surface 11d, the multiple reference electrodes 31 come into contact with the surface of the reference surface 11d at intervals shorter than the distance d between the multiple steel materials 11b. By using such multiple reference electrodes 31, the potential of multiple areas of the steel material 11b can be measured simultaneously and virtually without omission, without the need to confirm the buried position of the steel material 11b in advance using a rebar detector or the like.

In this embodiment, the multiple reference electrodes 31 of the reference electrode unit 3 are arranged in a matrix (or lattice) at approximately equal intervals along the first direction X (corresponding to the distance dx between the reference points 11e in the first direction X) and at approximately equal intervals along the second direction Y (corresponding to the distance dy between the reference points 11e in the second direction Y), as described with reference to the arrangement of the multiple reference points 11e on the reference surface 11d shown in FIG. 3(a). The distance between the reference electrodes 31 in the first direction X is approximately equal to the distance between the reference electrodes 31 in the second direction Y. Note that although the first and second directions X and Y are approximately perpendicular to each other in this embodiment, they may also be at an angle other than perpendicular to each other.

In the example shown in FIG. 2, the reference electrode unit 3 is provided with 3 x 3 = 9 reference electrodes 31. However, the number of reference electrodes 31 can be set arbitrarily depending on the surface of the concrete structure 11 in question. The number of reference electrodes 31 may be, for example, one, in which case the reference electrode 31 can be formed to a size that covers the entire reference surface 11d. Alternatively, the number of reference electrodes 31 can be, for example, 2 x 2 = 4, 4 x 4 = 16, 5 x 5 = 25, 3 x 4 = 12, 3 x 5 = 15, etc. Known electrodes such as copper/copper sulfate electrodes, silver/silver chloride electrodes, and calomel electrodes can be used as the reference electrodes 31.

The reference surface 11d with which the reference electrode unit 3 contacts can be appropriately set on the surface of the concrete structure 11 in the cover thickness direction of the region of the steel material 11b (substantially directly above the region of the steel material 11b) depending on the region of the steel material 11b to be measured for potential. For example, if it is desired to examine the distribution of the corrosion state of the steel material 11b across part or all of the concrete structure 11, it is preferable to arrange multiple reference surfaces 11d adjacent to each other, for example, along the first direction X and/or the second direction Y, which are substantially perpendicular to each other. This allows the potential distribution of the steel material 11b to be measured seamlessly across the surface of the concrete structure 11, thereby examining the distribution of the corrosion state of the steel material 11b. The size of the reference surface 11d is not particularly limited, but is preferably set to a size that spans adjacent steel materials 11b, for example, when the reference surface 11d includes multiple reference points 11e, as shown in Figure 3(a). However, the reference surface 11d may be the entire object of measurement, without including multiple reference points 11e spaced apart from one another. In this case, the reference surface 11d may be sized to correspond to the width of the steel material 11b.

In this embodiment, as shown in FIG. 3(a), the reference surface 11d includes a plurality of reference points 11e. The plurality of reference points 11e are arranged two-dimensionally at intervals within a plane including the first direction X and the second direction Y, corresponding to the arrangement of the plurality of reference electrodes 31 of the reference electrode unit 3. By providing a plurality of reference points 11e within a single reference surface 11d in this manner, it is possible to examine the potential distribution in more detail than when a single reference point is provided. Furthermore, even if an abnormal value is accidentally measured at one of the plurality of reference points 11e, the influence of the abnormal value can be minimized by averaging it within the reference surface 11d, thereby enabling the potential on the reference surface 11d to be obtained with greater accuracy.

The matching surface 11d may include multiple matching points 11e, and the arrangement of the multiple matching points 11e is not particularly limited. In this embodiment, the multiple matching points 11e are arranged in a matrix (or lattice) at approximately equal intervals along the first direction X and at approximately equal intervals along the second direction Y, as shown in FIG. 3. The distance dx between the matching points 11e in the first direction X is approximately equal to the distance dy between the matching points 11e in the second direction Y. The distance dx, dy between the matching points 11e arranged closest to each other is preferably smaller than the distance d between two steel materials 11b embedded at a distance in the concrete structure 11. The distance between the matching points 11e arranged at the greatest distance (corresponding to twice the distance dx, dy between the matching points 11e in the illustrated example) is preferably larger than the distance d between two steel materials 11b embedded at a distance in the concrete structure 11. By arranging multiple reference points 11e in this manner, when the reference electrode unit 3 is placed on the reference surface 11d, the potential of multiple regions of the steel material 11b can be measured without any omissions, even without having to confirm the buried position of the steel material 11b in advance using a rebar detector or the like. Note that, as described above, the first and second directions X and Y are approximately perpendicular to each other in this embodiment, but they may also be at an angle other than perpendicular to each other.

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 multiple reference points 11e) where the reference electrode unit 3 (each of the multiple reference 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 conductor 5 such as a lead wire, and the other terminal of the potential difference measuring device 4 is electrically connected to the reference electrode unit 3 (each of the multiple reference electrodes 31) via a conductor 5 such as a lead wire. The potential difference measuring device 4 can be a potentiometer used in a known natural potential measurement method.

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 steel material 11b embedded in the concrete structure 11. In this embodiment, the corrosion state determination device 6 is connected to the potential difference measurement device 4 so as to be able to communicate data with the potential difference measurement device 4, and controls the potential difference measurement device 4 while acquiring the potential difference measured by the potential difference measurement device 4 from the potential difference measurement device 4. The corrosion state determination device 6 calibrates 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.

The corrosion state determination device 6 is connected to the potential difference measuring device 4 via, for example, a USB cable, a network cable, an internet line, or the like. In this 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 optionally, a display unit 64. The corrosion state determination device 6 is not particularly limited, and can be, for example, a well-known computing device such as a computer that includes internally or externally a processing unit such as a CPU that can mainly configure the acquisition unit 61, calculation unit 62, and determination unit 63, a storage device such as a memory or hard disk, a communication device such as a network interface, an input device such as a keyboard and mouse, and a display device such as a liquid crystal display that can mainly configure the display unit 64.

The acquisition unit 61 is configured to acquire the potential (natural potential or relative potential) of the steel material 11b near each of the multiple reference surfaces 11d on the surface of the concrete structure 11. In this embodiment, to acquire the potential of the steel material 11b near each of the multiple reference surfaces 11d, the acquisition unit 61 acquires the potential difference between a reference position on the concrete structure 11 and each of the multiple reference surfaces 11d on the surface of the concrete structure 11 from the potential difference measurement device 4. The potential difference acquired from the potential difference measurement device 4 is calibrated as necessary and processed as the potential (natural potential or relative potential) of the steel material 11b near the reference surface 11d. As described above, the potential of the reference surface 11d indicates the natural potential of the steel material 11b near the reference surface 11d when the reference position is the steel material 11b of the concrete structure 11. When the reference position is the reference surface 11c on the surface of the concrete structure 11, the potential indicates the relative potential of the steel material 11b near the reference surface 11d relative to the steel material 11b near the reference surface 11c. The potential of the reference surface 11d is stored, for example, in a storage device internal or external to the corrosion state determination device 6, in association with the position of the reference surface 11d. The corrosion state determination device 6 can investigate the potential distribution of the steel material 11b within the concrete structure 11 by acquiring the potentials of the reference 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).

To obtain the potential of the steel material 11b near the reference surface 11d, the acquisition unit 61 may be configured to acquire the potential (natural potential or relative potential) of the steel material 11b near each of the multiple reference points 11e located within the reference surface 11d. In this case, the acquisition unit 61 acquires the potential difference between a reference position on the concrete structure 11 and each of the multiple reference points 11e located within the reference surface 11d from the potential difference measurement device 4. The multiple potential differences acquired for the multiple reference points 11e are calibrated as necessary and processed as the potential (natural potential or relative potential) of the steel material 11b near each reference point 11e, or are averaged within the same reference surface 11d as described below to obtain the potential (natural potential or relative potential) of the steel material 11b near the reference surface 11d. As described above, the potential at the reference point 11e indicates the natural potential of the steel material 11b near the reference point 11e when the reference position is the steel material 11b of the concrete structure 11. Alternatively, when the reference position is the reference surface 11c on the surface of the concrete structure 11, the potential indicates the relative potential of the steel material 11b near the reference point 11e relative to the steel material 11b near the reference surface 11c. The potential at the reference point 11e is stored in an internal or external storage device of the corrosion state determination device 6, for example, in association with the position of the reference point 11e and the position of the reference surface 11d on which the reference point 11e is located. The corrosion state determination device 6 can obtain the potentials at the reference points 11e that are spaced apart from one another within the reference surface 11d on the surface of the concrete structure 11 (e.g., at approximately equal intervals from one another along the first direction X and/or the second direction Y), thereby enabling a more detailed examination of the potential distribution of the steel material 11b within the concrete structure 11.

4 and 7 each show the distribution of the electrical potential (natural potential in the illustrated example) of the steel material 11b obtained for multiple reference points 11e provided on multiple reference surfaces 11d within the surface of a different concrete structure 11. The multiple reference surfaces 11d ((X1, Y1), (X2, Y1), ...) are arranged adjacent to each other along a first direction X (parallel to the horizontal sides in Figures 4 and 7) and a second direction Y (parallel to the vertical sides in Figures 4 and 7), which are substantially perpendicular to each other. Furthermore, the multiple reference points 11e ((1, 1), (2, 1), ...) within the multiple reference surfaces 11d are arranged at substantially equal intervals along the first direction X and the second direction Y, which are substantially perpendicular to each other. In Figures 4 and 7, the electrical potential of each reference point 11e is shown as a numerical value and as different shades of color, corresponding to the position of each reference point 11e and the position of the reference surface 11d on which each reference point 11e is located. In this way, the acquisition unit 61 acquires the potentials at multiple matching points 11e, making it possible to examine the potential distribution of the steel material 11b at each matching point 11e on the surface of the concrete structure 11.

In this embodiment, as described above, the corrosion state determination system 1 includes a reference electrode unit 3 having multiple reference electrodes 31. By using this reference electrode unit 3, the acquisition unit 61 can acquire multiple potentials for multiple reference points 11e within the same reference surface 11d at the same time. By acquiring multiple potentials for multiple reference points 11e at the same time, the effects of changes over time between the multiple reference points 11e can be suppressed. However, the acquisition unit 61 may also be configured to acquire the potential of the steel material 11b for multiple reference points 11e within the same reference surface 11d at different times rather than at the same time.

When multiple reference points 11e are arranged on the reference surface 11d, as in this embodiment, the calculation unit 62 may be configured to calculate the average value of the potentials of the multiple reference points 11e on the reference surface 11d as the potential of the reference surface 11d. This minimizes the impact of an abnormal value, even if an abnormal value due to noise in the electronic circuitry or the like occurs accidentally on one of the multiple reference electrodes 31, thereby enabling the potential of the reference surface 11d to be obtained with greater accuracy. In particular, when the reference electrode unit 3 is used, as in this embodiment, multiple potentials for the multiple reference points 11e are acquired at the same time, thereby minimizing the effects of changes over time and enabling the potential to be obtained with greater accuracy. However, the potential of the steel material 11b near the reference surface 11d may be acquired as a single potential rather than as the average value of the potentials of the steel material 11b near the multiple reference points 11e on the reference surface 11d.

5 and 8 show the distribution of the potential (natural potential in the illustrated example) of the steel material 11b near the reference surface 11d, calculated by averaging the potentials of the steel material 11b near multiple reference points 11e within the same reference surface 11d shown in Figures 4 and 7, respectively. In this way, the calculation unit 62 calculates the potential of the reference surface 11d by averaging the potentials at multiple reference points 11e, thereby enabling the potential distribution of the steel material 11b for each reference surface 11d within the surface of the concrete structure 11 to be examined. For example, referring to Figure 5, according to the conventional method standard (ASTM C876), the steel material 11b near the reference surface 11d located at (X1, Y3), (X2, Y3), ... (X5, Y5) has a potential greater than the second threshold (-200 mV), and is therefore determined to be non-corroded with a probability of 90% or more. In contrast, the potential of the steel material 11b near the reference surface 11d located at (X1, Y1), (X2, Y1), ... (X5, Y2) is greater than the first threshold (-350 mV) and less than the second threshold, so the corrosion state is determined to be uncertain.

The calculation unit 62 is configured to calculate the potential gradient for each of the multiple reference surfaces 11d. The potential gradient refers to the change in potential per unit length on the reference surface 11d. The greater the potential gradient for a given reference surface 11d, the greater the change in potential of the steel material 11b near that reference surface 11d; for example, the greater the difference in potential between the steel materials 11b near the reference surfaces 11d on either side of that reference surface 11d. Therefore, if the potential gradient for a given reference surface 11d is large, it can be estimated that the corrosion states of the steel materials 11b near the reference surfaces 11d on either side of that reference surface 11d are significantly different from each other.

The potential gradient for the reference surface 11d is not particularly limited and can be calculated using a variety of methods. For example, the calculation unit 62 may be configured to calculate the potential gradient for the reference surface 11d based on the potential differences for multiple reference points 11e on the reference surface 11d and the distances dx, dy between the multiple reference points 11e (see Figures 3(a) and 3(b)). In this embodiment, by calculating the potential gradient using multiple potentials acquired at the same time using the reference electrode unit 3, it is possible to at least suppress the effects of changes over time and calculate a more accurate potential gradient. In addition to the above, the potential gradient for the reference surface 11d can also be calculated based on the potential differences and distances between the reference surface 11d and other adjacent reference surfaces 11d.

In this embodiment, as shown in FIG. 3(a), multiple matching points 11e are arranged side by side on the matching surface 11d along the first direction X and the second direction Y. In the illustrated example, the multiple matching points 11e (nine in the illustrated example) are arranged in a matrix (or grid) at approximately equal intervals along the first direction X and the second direction Y, which are approximately perpendicular to each other. When the multiple matching 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 potential gradient in the first direction X as a first gradient Sx, calculate the potential gradient in the second direction Y as a second gradient Sy, and calculate the potential gradient S for the matching 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 potential gradient S on the reference surface 11d, as shown in the following equation (1):

Here, Sx and Sy represent the gradients of the electric potential in the first and second directions X and Y, respectively.

The first gradient Sx can be calculated based on the potential difference between the plurality of match points 11e arranged side by side along the first direction X and the distance dx between the plurality of match points 11e (see FIG. 3B). For example, the first gradient Sx can be calculated by dividing the potential difference (E ₁₁ -E 31 , E _{12 -E 32} , E 13 -E ₃₃ in FIG. 3B) obtained for the two most distant match points 11e among the plurality of match points _11e arranged side by side along the first direction X by the distance between the two most distant match points _11e (twice the distance dx between adjacent match points 11e). In this case, since there are three pairs of match points 11e arranged side by side, the first gradient Sx may be calculated by averaging the potential gradients for the three pairs of match points 11e. This calculation method is represented by the following equation (2).

Similarly to the first gradient Sx, the second gradient Sy can be calculated based on the potential difference between the plurality of match points 11e arranged side by side along the second direction Y and the distance dy between the plurality of match points 11e (see FIG. 3B). For example, the second gradient Sy can be calculated by dividing the potential difference (E11-E13, _E21 - _E23 , _E31 - _E33 in FIG. 3B) obtained for the two _most distant match points 11e among the plurality of match points 11e arranged side by side along the second direction Y by the distance between the two most distant match points 11e (twice _the distance dy between adjacent match points 11e). In this case, because there are three pairs of match points 11e arranged side by side, the second gradient Sy may be calculated by averaging the potential gradients for the three pairs of match points 11e. This calculation method is expressed by the following equation (3).

Here, E ₁₁ to E ₃₃ represent the electric potential (natural potential) for each of the multiple matching points 11 e, and dx and dy represent the distances between the matching points 11 e in the first and second directions X and Y, respectively (both 100 mm in the examples shown in Figures 3(a) and (b)).

The determination unit 63 is configured to determine the state of corrosion of the steel material 11b in the concrete structure 11 based on the potential and/or potential gradient for each reference surface 11d. For this purpose, the determination unit 63 is configured to determine whether the potential gradient for each reference surface 11d is equal to or greater than a predetermined threshold. The predetermined threshold can be set appropriately depending on the state of corrosion of the steel material 11b and the distribution of corroded areas. For example, the predetermined threshold can be set to a range greater than the reference potential gradient, based on the potential gradient for a reference surface 11d for which a relatively small change (gradient) in potential has been obtained within the surface of the concrete structure 11 being evaluated. The reference potential gradient can be, for example, the potential gradient obtained for a reference surface 11d near an area of steel material 11b that is not corroded or is likely to be not corroded, or the potential gradient obtained for a reference surface 11d near an area of steel material 11b that is corroded or is likely to be corroded. For example, referring to Figures 6 and 9 described below, the predetermined threshold value in each case can be set in the range of approximately 40 mV/100 mm or more and approximately 65 mV/100 mm or more. The predetermined threshold value can also be adopted based on the gradient of the potential obtained outside the surface of the concrete structure 11 being evaluated. In this case, it is preferable to verify that the gradient of the potential adopted can be applied within the surface of the concrete structure 11 being evaluated.

The determination unit 63 is configured to determine a reference surface 11d determined to have a potential gradient equal to or greater than a predetermined threshold as a boundary region, where the steel material 11b near the reference surface 11d is likely to be in a boundary state between a corroded state and a non-corroded state. By determining a reference surface 11d as a boundary region within the surface of the concrete structure 11 being determined, it is possible to recognize that the corrosion state of the steel material 11b near the reference surface 11d determined to be a boundary region has changed significantly. For example, by taking into account the magnitude of the acquired potential, it is possible to determine that the steel material 11b near the reference surface 11d on both sides of the reference surface 11d determined to be a boundary region is likely to be corroded or not corroded. Alternatively, it is possible to determine that the steel material 11b near the reference surface 11d outside the boundary region is likely to be corroded or not corroded depending on whether the potential is higher or lower than the potential of the reference surface 11d determined to be a boundary region. Therefore, as will be described in detail below, the corrosion state determination device 6 of this embodiment can determine whether an area of the steel material 11b where the corrosion state is determined to be uncertain using conventional methods is corroded or non-corroded, reducing the number of areas where the corrosion state is determined to be uncertain and achieving excellent determination accuracy.

As described above, the determination unit 63 is only required to be configured to determine whether at least 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 using various methods. The determination unit 63 may be configured, for example, to determine 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, 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, the determination unit 63 may be configured to determine 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. Furthermore, 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 determination unit 63 may be configured to determine that adjacent reference surface 11d is a non-corroded region where the steel material 11b near the adjacent reference surface 11d is likely to be in a non-corroded state.

Now, referring to Figures 5 and 8, the reference surface 11d determined to be a boundary area by the determination unit 63 is surrounded by a dotted line (the area (X1, Y2) to (X5, Y2) in Figure 5, and the area (X1, Y3) to (X5, Y3) in Figure 8). Of the reference surfaces 11d on either side of the reference surface 11d determined to be a boundary area, the reference surface 11d on one side (above the boundary area in Figures 5 and 8) has a relatively high potential of the steel material 11b, and the reference surface 11d on the other side (below the boundary area in Figures 5 and 8) has a relatively low potential of the steel material 11b. Taking these potential differences into account, the determination unit 63 can determine that the reference surface 11d on one side of the boundary region is a non-corroded region where the steel material 11b nearby is likely to be in a non-corroded state, and can determine that the reference surface 11d on the other side of the boundary region is a corroded region where the steel material 11b nearby is likely to be in a corroded state.

In particular, in the example shown in Figure 5, the steel material 11b near the reference surface 11d on the other side of the boundary region (below the boundary region in Figure 5) has a potential greater than the first threshold (-350 mV) and less than the second threshold (-200 mV) according to the standards of the conventional method (ASTM C876), and therefore is determined to have an uncertain corrosion state. However, the corrosion state determination device 6 of this embodiment can determine that even areas of the steel material 11b whose corrosion state is determined to be uncertain according to the standards of the conventional method are likely to be corroded, thereby achieving greater determination accuracy. Note that with respect to the examples shown in Figures 5 and 8, it has been confirmed by other methods that the steel material 11b near the corresponding reference surface 11d is in a corroded or non-corroded state, as determined by the corrosion state determination device 6 of this embodiment.

The determination unit 63 may also be configured to determine 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 to be a boundary region. Here, Figures 6 and 9 correspond to Figures 5 and 8, respectively, and show the relationship between the potential (natural potential in the illustrated example) and the potential gradient obtained for each of the multiple reference surfaces 11d. In Figures 6 and 9, the position information (e.g., (X1, Y1)) of the reference surface 11d is shown corresponding to the data point for each reference surface 11d, and the potential range of the steel material 11b near the reference surface 11d determined to be a boundary region is enclosed by a dotted line. Referring to Figures 6 and 9, the determination unit 63 may also be configured to determine whether the potential of the reference surface 11d other than the reference surface 11d determined to be a boundary region is less than the minimum potential of the potentials of the reference surface 11d determined to be a boundary region (the potential at the right end of the dotted line frame in Figures 6 and 9). The determination unit 63 may be configured to determine a reference surface 11d whose potential is determined to be less than the minimum potential (a reference surface 11d plotted to the right of the dotted frame in FIGS. 6 and 9 ) as a corroded region where the steel material 11b near the reference surface 11d is likely to be corroded. The determination unit 63 may also be configured to determine whether the potential of a reference surface 11d other than the reference surface 11d determined to be a 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 surfaces 11d determined to be boundary regions. The determination unit 63 may also be configured to determine a reference surface 11d whose potential is determined to be greater than the maximum potential (a reference surface 11d plotted to the left of the dotted frame in FIGS. 6 and 9 ) as a non-corrosion region where the steel material 11b near the reference surface 11d is likely to be non-corroded.

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 below the minimum potential is determined to be indeterminate according to the standards of the conventional method (ASTM C876) because its potential is greater than the first threshold (-350 mV) and less than the second threshold (-200 mV). However, the corrosion state determination device 6 of this embodiment can determine that even areas of the steel material 11b whose corrosion state is determined to be indeterminate according to the standards of the conventional method are likely to be in a corroded state, thereby achieving greater determination accuracy. Note that, with respect to the examples shown in Figures 6 and 9, as described above with reference to Figures 5 and 8, it has been confirmed by other methods that the steel material 11b near the corresponding reference surface 11d is in a corroded or non-corroded state, as determined by the corrosion state determination device 6 of this embodiment.

The display unit 64 displays the potential and/or potential gradient of the steel material 11b obtained for the multiple reference points 11e and/or multiple reference surfaces 11d. In this embodiment, as shown in Figures 6 and 9, the display unit 64 is configured to display the potential and potential gradient for each of the multiple reference surfaces 11d in a coordinate system in which one axis (the horizontal axis in the illustrated example) represents the potential and the other axis (the vertical axis in the illustrated example) represents the potential gradient. According to the corrosion state determination device 6 of this embodiment, the display unit 64 is configured to graphically display the relationship between the potential and potential gradient for the reference surfaces 11d, allowing for a clear understanding of the distribution of the potential gradient relative to the potential of the steel material 11b. Therefore, compared to when the potential of the steel material 11b is displayed using color shading, as shown in Figures 4-5 and 7-8, for example, the boundary region can be clearly identified, allowing for a clearer understanding of the corrosion state of the steel material 11b.

Next, the corrosion state determination method of this embodiment will be described using an example in which it is implemented using the corrosion state determination system 1 of this embodiment. However, the corrosion state determination method of the present invention is not limited to the example below, and can also be implemented using systems other than the corrosion state determination system 1 of this embodiment. Furthermore, the corrosion state determination method of this embodiment is not particularly limited, and can be executed by a person, or by a computer program containing computer-executable instructions that, when executed on a computer, causes the computer to execute the corrosion state determination method of this embodiment. Note that, although several steps will be described below, the order of the steps is not limited to the order described below.

The corrosion state determination method of this embodiment is a method for determining the corrosion state of steel material 11b embedded in a concrete structure 11. The corrosion state determination method includes a step of acquiring the potential of steel material 11b near each of a plurality of reference surfaces 11d among the surfaces of the concrete structure 11. In this embodiment, to acquire the potential of steel material 11b near each of the plurality of reference surfaces 11d, the potential difference between a reference position on the concrete structure 11 and each of the plurality of reference surfaces 11d on the surface of the concrete structure 11 is acquired. The acquired potential difference is calibrated as necessary and processed as the potential (natural potential or relative potential) of steel material 11b near the reference surface 11d. As described above, the potential of the reference surface 11d indicates the natural potential of the steel material 11b near the reference surface 11d when the reference position is the steel material 11b of the concrete structure 11. When the reference position is the reference surface 11c on the surface of the concrete structure 11, the potential indicates the relative potential of the steel material 11b near the reference surface 11d relative to the steel material 11b near the reference surface 11c. The potential of the reference surface 11d may be stored in a storage device internal or external to the corrosion state determination device 6, for example, in association with the position of the reference surface 11d. By obtaining the potentials of the reference surfaces 11d arranged adjacent to each other on the surface of the concrete structure 11 (e.g., adjacent to each other along the first direction X and/or the second direction Y), the potential distribution of the steel material 11b within the concrete structure 11 can be investigated, as shown in FIGS. 5 and 8 .

The step of acquiring the potential of the steel material 11b near each of the plurality of reference surfaces 11d may include acquiring the potential of the steel material 11b near each of the plurality of reference points 11e located within the reference surface 11d. In this embodiment, to acquire the potential of the steel material 11b near each of the plurality of reference points 11e, the potential difference between a reference position on the concrete structure 11 and each of the plurality of reference points 11e located within the reference surface 11d is acquired. The potential differences acquired for the plurality of reference points 11e are calibrated as necessary to determine the potential (natural potential or relative potential) of the steel material 11b near each reference point 11e, or are averaged within the same reference surface 11d as described below to determine the potential (natural potential or relative potential) of the steel material 11b near the reference surface 11d. As described above, the potential at the reference point 11e indicates the natural potential of the steel material 11b near the reference point 11e when the reference position is the steel material 11b of the concrete structure 11. Alternatively, when the reference position is the reference surface 11c on the surface of the concrete structure 11, the potential indicates the relative potential of the steel material 11b near the reference point 11e relative to the steel material 11b near the reference surface 11c. The potential at the reference point 11e may be stored in a storage device internal or external to the corrosion state determination device 6, for example, in association with the position of the reference point 11e and the position of the reference surface 11d on which the reference point 11e is located. By acquiring the potentials at the reference points 11e that are spaced apart from each other within the reference surface 11d on the surface of the concrete structure 11 (e.g., approximately equally spaced from each other along the first direction X and/or the second direction Y), the potential distribution of the steel material 11b within the concrete structure 11 can be examined in more detail, as shown in FIGS. 4 and 7 .

When acquiring the potential of the steel material 11b near each of the multiple matching points 11e, the multiple potentials for the multiple matching points 11e within the same matching surface 11d may be acquired at the same time. By acquiring the multiple potentials for the multiple matching points 11e at the same time, the effects of changes over time at the multiple matching points 11e can be suppressed. However, the potential of the steel material 11b for the multiple matching points 11e within the same matching surface 11d may be acquired at different times rather than at the same time.

The process of acquiring the potential of the steel material 11b near each of the multiple reference surfaces 11d may include a process of calculating the average value of the potential of the steel material 11b near the multiple reference points 11e as the potential for the reference surface 11d. By averaging the potentials for the multiple reference points 11e to calculate the potential for the reference surface 11d, the potential distribution of the steel material 11b for each reference surface 11d within the surface of the concrete structure 11 can be examined, as shown in Figures 5 and 8. Furthermore, even if an abnormal value due to noise or other factors is accidentally acquired for one of the multiple reference points 11e, the influence of the abnormal value can be minimized by averaging, thereby enabling the potential for the reference surface 11d to be obtained with greater accuracy. In particular, acquiring multiple potentials for the multiple reference points 11e at the same time can at least suppress the influence of changes over time, thereby obtaining a more accurate potential. However, the potential of the steel material 11b near the reference surface 11d may be obtained as a single potential rather than as the average value of the potentials of the steel material 11b near multiple reference points 11e within the reference surface 11d.

The corrosion state determination method of this embodiment includes a step of calculating the potential gradient for each of multiple reference surfaces 11d. The potential gradient refers to the change in potential per unit length on the reference surface 11d. The greater the potential gradient for a given reference surface 11d, the greater the change in potential of the steel material 11b near that reference surface 11d; for example, the greater the difference in potential between the steel materials 11b near the reference surfaces 11d on either side of that reference surface 11d. Therefore, if the potential gradient for a given reference surface 11d is large, it can be estimated that the corrosion states of the steel materials 11b near the reference surfaces 11d on either side of that reference surface 11d are significantly different from each other.

The potential gradient for the reference surface 11d is not particularly limited and can be calculated using a variety of methods. For example, the step of calculating the potential gradient for the reference surface 11d may include a step of calculating the potential gradient for the reference surface 11d based on the potential differences for multiple reference points 11e within the reference surface 11d and the distances dx, dy between the multiple reference points 11e (see Figures 3(a) and 3(b)). For example, by calculating the potential gradient for the reference surface 11d using multiple potentials for multiple reference points 11e acquired at the same time, it is possible to at least suppress the effects of changes over time and calculate a more accurate potential gradient. In addition to the above, the potential gradient for the reference surface 11d can also be calculated based on the potential differences and distances between the reference surface 11d and other adjacent reference surfaces 11d.

In this embodiment, as shown in FIG. 3(a), multiple matching points 11e are arranged side by side on the matching surface 11d along the first direction X and the second direction Y. In the illustrated example, the multiple matching points 11e (nine in the illustrated example) are arranged in a matrix (or grid) at approximately equal intervals along the first direction X and the second direction Y, which are approximately perpendicular to each other. When the multiple 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 for the matching surface 11d may include the steps of calculating the potential gradient in the first direction X as a first gradient Sx, calculating the potential gradient in the second direction Y as a second gradient Sy, and calculating the potential gradient S for the matching surface 11d based on the first and second gradients Sx and Sy. For example, the potential gradient S for the reference surface 11d can be calculated as the square root of the sum of the squares of the first and second gradients Sx and Sy, as shown in the following equation (1):

Here, Sx and Sy represent the gradients of the electric potential in the first and second directions X and Y, respectively.

The first gradient Sx can be calculated based on the potential difference between the plurality of match points 11e arranged side by side along the first direction X and the distance dx between the plurality of match points 11e (see FIG. 3B). For example, the first gradient Sx can be calculated by dividing the potential difference (E ₁₁ -E 31 , E _{12 -E 32} , E 13 -E ₃₃ in FIG. 3B) obtained for the two most distant match points 11e among the plurality of match points _11e arranged side by side along the first direction X by the distance between the two most distant match points _11e (twice the distance dx between adjacent match points 11e). In this case, since there are three pairs of match points 11e arranged side by side, the first gradient Sx may be calculated by averaging the potential gradients for the three pairs of match points 11e. This calculation method is represented by the following equation (2).

Similarly to the first gradient Sx, the second gradient Sy can be calculated based on the potential difference between the plurality of match points 11e arranged side by side along the second direction Y and the distance dy between the plurality of match points 11e (see FIG. 3B). For example, the second gradient Sy can be calculated by dividing the potential difference (E11-E13, _E21 - _E23 , _E31 - _E33 in FIG. 3B) obtained for the two _most distant match points 11e among the plurality of match points 11e arranged side by side along the second direction Y by the distance between the two most distant match points 11e (twice _the distance dy between adjacent match points 11e). In this case, because there are three pairs of match points 11e arranged side by side, the second gradient Sy may be calculated by averaging the potential gradients for the three pairs of match points 11e. This calculation method is expressed by the following equation (3).

Here, E ₁₁ to E ₃₃ represent the electric potential (natural potential) for each of the multiple matching points 11 e, and dx and dy represent the distances between the matching points 11 e in the first and second directions X and Y, respectively (both 100 mm in the examples shown in Figures 3(a) and (b)).

The corrosion state determination method of this embodiment includes a step of determining whether the potential gradient for each reference surface 11d is equal to or greater than a predetermined threshold. The predetermined threshold can be set appropriately depending on the corrosion state of the steel material 11b and the distribution of corroded areas. For example, the predetermined threshold can be set in a range greater than the reference potential gradient, using the potential gradient for a reference surface 11d for which a relatively small change (gradient) in potential has been obtained within the surface of the concrete structure 11 being determined as a reference. The reference potential gradient can be, for example, the potential gradient obtained for a reference surface 11d near an area of steel material 11b that is not corroded or is likely to be not corroded, or the potential gradient obtained for a reference surface 11d near an area of steel material 11b that is corroded or is likely to be corroded.

The corrosion state determination method of this embodiment includes a step of determining a reference surface 11d determined to have a potential gradient equal to or greater than a predetermined threshold as a boundary region where the steel material 11b near the reference surface 11d is likely to be in a boundary state between a corroded state and a non-corroded state. By determining a reference surface 11d as a boundary region within the surface of the concrete structure 11 being determined, it is possible to recognize that the corrosion state of the steel material 11b has changed significantly near the reference surface 11d determined to be a boundary region. For example, by taking into account the magnitude of the acquired potential, it is possible to determine that the steel material 11b near the reference surface 11d on both sides of the reference surface 11d determined to be a boundary region is likely to be corroded or not corroded. Alternatively, it is possible to determine that the steel material 11b near the reference surface 11d other than the boundary region is likely to be corroded or not corroded depending on whether the potential is higher or lower than the potential of the reference surface 11d determined to be a boundary region. Therefore, as will be described in detail below, the corrosion state determination method of this embodiment makes it possible to determine whether an area of steel material 11b where the corrosion state is determined to be uncertain using conventional methods is in a corroded or non-corroded state, reducing the number of areas where the corrosion state is determined to be uncertain and achieving excellent determination accuracy.

As described above, the corrosion state determination method of this embodiment may include at least a step of determining whether 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 using 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, if the potential of a reference surface 11d adjacent to a 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, the adjacent reference surface 11d may be determined to be a corrosion region where the steel material 11b near the adjacent reference surface 11d is likely to be corroded. The corrosion state determination method may also 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, that adjacent reference surface 11d is 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.

Referring now to Figures 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 Figure 5, and the region (X1, Y3) to (X5, Y3) in Figure 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 Figures 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 Figures 5 and 8) has a relatively low potential of the steel material 11b. Taking these potential differences into account, 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.

In particular, in the example shown in Figure 5, the steel material 11b near the reference surface 11d on the other side of the boundary region (below the boundary region in Figure 5) has a potential greater than the first threshold (-350 mV) and less than the second threshold (-200 mV) according to the standards of the conventional method (ASTM C876), and therefore is judged to have an uncertain corrosion state. However, according to the corrosion state judgment method of this embodiment, it is possible to judge that the region of the steel material 11b whose corrosion state is judged to be uncertain according to the standards of the conventional method is highly likely to be in a corroded state, thereby achieving greater judgment accuracy.

The corrosion state determination method of this embodiment may also 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 to be a boundary region. For example, referring to FIGS. 6 and 9, the corrosion state determination method of this embodiment may also include a step of determining whether the potential of the reference surface 11d other than the reference surface 11d determined to be a boundary region is less than the minimum potential of the potentials of the reference surfaces 11d determined to be a boundary region (the potential at the right end of the dotted line frame in FIGS. 6 and 9). The corrosion state determination method of this embodiment may also include a step of determining the reference surface 11d determined to have a potential less than the minimum potential (the reference surface 11d plotted to the right of the dotted line frame in FIGS. 6 and 9) as a corrosion region where the steel material 11b near the reference surface 11d is likely to be corroded. The corrosion state determination method of this embodiment may also include a step of determining whether the potential of a reference surface 11d other than the reference surface 11d determined to be a boundary region is greater than the maximum potential of the potentials of the reference surfaces 11d determined to be a boundary region (the potential at the left end of the dotted line frame in Figures 6 and 9).The corrosion state determination method of this embodiment may also include a step of determining a reference surface 11d determined to have a potential greater than the maximum potential (a reference surface 11d plotted to the left of the dotted line frame in Figures 6 and 9) as a non-corrosion region in which the steel material 11b near the reference surface 11d is likely to be in a non-corroded state.

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 is determined to be in an uncertain state of corrosion according to the standards of the conventional method (ASTM C876) because its potential is greater than the first threshold (-350 mV) and less than the second threshold (-200 mV). However, according to the corrosion state determination method of this embodiment, it is possible to determine that even areas of the steel material 11b whose corrosion state is determined to be in an uncertain state according to the standards of the conventional method are highly likely to be in a corroded state, thereby achieving greater determination accuracy.

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

REFERENCE SIGNS LIST 1 Corrosion state 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 state determination device 61 Acquisition part 62 Calculation part 63 Determination part 64 Display part 11 Concrete structure 11a Concrete 11b Steel material (reinforcing bar)
11c Reference surface 11d Reference surface 11e Reference point d Distance between steel members dx Distance between reference points in the first direction dy Distance between reference points in the second direction X First direction Y Second direction

Claims (11)

A corrosion state determination method for determining the corrosion state of a steel material embedded in a concrete structure, comprising:
acquiring, for each of a plurality of reference surfaces among the surfaces of the concrete structure, the electric potential of the steel material in the vicinity of each of the plurality of reference surfaces;
calculating a gradient of the potential for each of the plurality of reference surfaces;
determining whether the gradient of the electric potential for each of the reference surfaces is greater than or equal to a predetermined threshold;
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 in which 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 ,
the step of acquiring the potential includes a step of acquiring, for each of a plurality of reference points arranged on the reference surface, the potential of the steel material in the vicinity of each of the plurality of reference points, and calculating an average value of the potentials of the steel material in the vicinity of the plurality of reference points as the potential of the reference surface;
a step of calculating the potential gradient for the reference surface based on the potential differences for the plurality of reference points within the reference surface and the distances between the plurality of reference points; A corrosion state determination method for determining the corrosion state of a steel material embedded in a concrete structure, comprising:
acquiring, for each of a plurality of reference surfaces among the surfaces of the concrete structure, the electric potential of the steel material in the vicinity of each of the plurality of reference surfaces;
calculating a gradient of the potential for each of the plurality of reference surfaces;
determining whether the gradient of the electric potential for each of the reference surfaces is greater than or equal to a predetermined threshold;
determining that the reference surface, for which the gradient of the potential is determined to be equal to or greater than the predetermined threshold, is a boundary region in which it is highly likely that the steel material in the vicinity of the reference surface is in a boundary state between a corroded state and a non-corroded state;
Including,
the step of acquiring the potential includes a step of acquiring, for each of the reference surfaces adjacent to another reference surface, the potential of the steel material in the vicinity of the other reference surface;
A corrosion state determination method, wherein the step of calculating the potential gradient includes a step of calculating the potential gradient for each of the reference surfaces based on the potential difference and distance between each of the reference surfaces and the other reference surfaces. determining whether the potential of the reference surface other than the reference surface determined to be the boundary region is less than a minimum potential of the potentials of the reference surface determined to be the boundary region;
a step of determining that the reference surface whose potential is determined to be less than the minimum potential is a corrosion area in which the steel material near the reference surface is likely to be in a corroded state;
determining whether the potential on the reference surface other than the reference surface determined to be the boundary region is greater than a maximum potential among the potentials on the reference surface determined to be the boundary region;
3. The corrosion state determination method according to claim 1, further comprising a step of determining that the reference surface, for which the potential is determined to be greater than the maximum potential, is a non-corroded region in which the steel material in the vicinity of the reference surface is likely to be in a non-corroded state. the plurality of reference points are arranged side by side on the reference surface along a first direction and a second direction;
The step of calculating the gradient of the potential comprises:
calculating a gradient of the potential in the first direction as a first gradient based on the potential differences for a plurality of matching points arranged side by side along the first direction and distances between the plurality of matching points;
calculating a gradient of the potential in the second direction as a second gradient based on the potential differences for a plurality of matching points arranged side by side along the second direction and distances between the plurality of matching points;
2. The corrosion state determination method according to claim 1 , further comprising the step of: calculating the gradient of the potential on the reference surface based on the first and second gradients. 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 reference surfaces in a coordinate system in which one axis represents the potential and the other axis represents the potential gradient. 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, for each of a plurality of reference surfaces among the surfaces of the concrete structure, the electric potential of the steel material in the vicinity of the plurality of reference surfaces;
a calculation unit that calculates the gradient of the potential for each of the plurality of reference surfaces;
a determination unit for determining a corrosion state of the steel material,
The determination unit
determining whether the gradient of the electric potential for each of the reference surfaces is greater than or equal to a predetermined threshold;
The reference surface for which it has been determined that the gradient of the potential is equal to or greater than the predetermined threshold is determined to be a boundary region in which it is highly likely that the steel material in the vicinity of the reference surface is in a boundary state between a corroded state and a non-corroded state ,
the acquisition unit is configured to acquire, for each of a plurality of reference points arranged on the reference surface, an electric potential of the steel material in the vicinity of the plurality of reference points;
The calculation unit
calculating an average value of the potentials for the plurality of reference points within the reference surface as a potential for the reference surface;
Calculating a gradient of the potential on the reference surface based on the potential differences for the plurality of reference points within the reference surface and the distances between the plurality of reference points.
The corrosion state determination device is configured as follows . 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, for each of a plurality of reference surfaces among the surfaces of the concrete structure, the electric potential of the steel material in the vicinity of the plurality of reference surfaces;
a calculation unit that calculates the gradient of the potential for each of the plurality of reference surfaces;
a determination unit for determining a corrosion state of the steel material;
Equipped with
The determination unit
determining whether the gradient of the electric potential for each of the reference surfaces is greater than or equal to a predetermined threshold;
The reference surface for which it is determined that the gradient of the potential is equal to or greater than the predetermined threshold is determined to be a boundary region in which it is highly likely that the steel material in the vicinity of the reference surface is in a boundary state between a corroded state and a non-corroded state.
It is structured as follows:
the acquisition unit is configured to acquire, for each of the reference surfaces adjacent to another reference surface, the electric potential of the steel material in the vicinity of the other reference surface;
The corrosion state determination device, wherein the calculation unit is configured to calculate the potential gradient for each of the reference surfaces based on the potential difference and distance between each of the reference surfaces and the other reference surfaces. The determination unit
determining whether the potential of the reference surface other than the reference surface determined to be the boundary region is less than a minimum potential of the potentials of the reference surface determined to be the boundary region;
The reference surface determined to have the potential less than the minimum potential is determined to be a corrosion area in which the steel material near the reference surface is likely to be in a corroded state;
determining whether the potential on the reference surface other than the reference surface determined to be the boundary area is greater than a maximum potential among the potentials on the reference surface determined to be the boundary area;
8. The corrosion state determination device according to claim 6 or 7, wherein the reference surface determined to have a potential greater than the maximum potential is determined to be a non-corroded area in which the steel material in the vicinity of the reference surface is likely to be in a non -corroded state. the plurality of reference points are arranged side by side on the reference surface along a first direction and a second direction;
The calculation unit
calculating a gradient of the potential in the first direction as a first gradient based on the potential differences for a plurality of matching points arranged side by side along the first direction and distances between the plurality of matching points;
calculating a gradient of the potential in the second direction as a second gradient based on the potential differences for a plurality of matching points arranged side by side along the second direction and distances between the plurality of matching points;
The corrosion state determination device according to claim 6 , further comprising: a step of calculating a gradient of the potential on the reference surface based on the first and second gradients. 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 reference surfaces in a coordinate system in which one axis represents the potential and the other axis represents the potential gradient. A computer program comprising computer-executable instructions that, when executed on a computer, causes the computer to execute the corrosion state determination method described in any one of claims 1 to 5.