JP7489047B2 - Equipment for detecting corrosion in rebars in concrete - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies Japan Concrete Institute Annual Proceedings of the Japan Concrete Institute, Vol. 43, No. 1, 2021 Published June 15, 2021

Article 30, paragraph 1 of the Patent Act applies Japan Concrete Institute Annual Meeting 2021 (Nagoya) held online (held via Zoom) Venue 4 [Non-destructive Inspection and Diagnosis 3] (lecture number 1199) (https://zoom.us/j/96900796974?pwd=bCt4MmtJbktZT01tejV1S1drUG9ZQT09#success) Held on July 8, 2021

The present invention relates to a device for detecting corroded portions of reinforcing bars in concrete, for example, in a concrete structure, using a non-destructive testing method.

Conventional natural potential methods for estimating the state of corrosion of rebars buried in concrete structures have the potential for erroneous judgment of corrosion, as the measured values change depending on the state of the concrete. Furthermore, conventional techniques for determining the corrosion rate of rebars in concrete require localized destruction, for example by drilling holes in the concrete structure, in order to establish electrical continuity with the buried rebars, which poses issues in terms of convenience, as it takes time and effort to perform corrosion diagnostic measurements of rebars in concrete.

The inventors have therefore invented a completely non-destructive method for evaluating the degree of corrosion of rebars in concrete, known as the DHz method, to solve the above problems (Patent Application No. 2020-83852). The DHz method evaluates the presence or absence of corrosion in a relative value within a certain measurement surface of a concrete structure. Therefore, the presence or absence of corrosion can only be evaluated within the area where the rebars embedded in the concrete structure are connected inside the concrete structure, and an issue is that it is not possible to evaluate in a different measurement range where the embedded rebars are not connected.

In the present invention, the impedance spectrum used to estimate the corrosion rate can be calculated by devising the arrangement of the electrode and the counter electrode on the measurement surface of the concrete structure, and the impedance spectrum of the reinforcing bar in the concrete can be obtained, making it possible to evaluate the presence or absence of corrosion in absolute values. As a result, even in a situation where the reinforcing bars embedded in the concrete structure are not connected inside the concrete structure, the presence or absence of corrosion of the reinforcing bars can be evaluated, and further, it becomes possible to compare and examine the corrosion states of the reinforcing bars embedded in, for example, two different concrete structures.

Patent Application No. 2020-83852 JP 2019-105513 A

Thus, the present invention has been devised to address the above-mentioned conventional problems, and aims to provide a corrosion detection device for reinforcing bars in concrete that makes it easy to estimate the locations of corrosion of reinforcing bars buried in a concrete structure even by non-destructive testing, is less likely to misjudge the presence or absence of reinforcing bar corrosion or the locations of corrosion depending on the state of the concrete, does not require locally destroying the concrete structure with a drill or the like to establish electrical continuity with the buried reinforcing bars, and can evaluate the presence or absence of reinforcing bar corrosion in absolute values based on the impedance spectrum of the reinforcing bars in concrete, and as a result, can evaluate the presence or absence of reinforcing bar corrosion even in situations where, for example, the buried reinforcing bars are not connected.

The present invention relates to
a measurement section including a measurement electrode disposed on a measurement surface of a concrete structure and a first counter electrode disposed on the measurement surface in contact with an outer peripheral surface of the measurement electrode, and capable of measuring the electric potential of the concrete structure;
a reference electrode that is installed at a predetermined distance in the horizontal direction from the measurement unit and that can measure a reference potential of the concrete structure;
A second counter electrode installed at a predetermined distance from the measurement unit in the horizontal direction;
an AC power source that is installed between the measurement unit and the second counter electrode and that has a high-frequency AC current and a low-frequency AC current that are applied between the first counter electrode and the second counter electrode;
a current measuring device for measuring a value of a current passed between the first counter electrode and the second counter electrode;
a potential difference meter that is installed between the measurement unit and the reference electrode and measures a potential difference between a measured potential substantially below the measurement unit and a reference potential of the concrete structure by the measurement electrode and the reference electrode;
The impedance approximately below the measurement portion is obtained from the current value and potential difference value measured by the current measuring device and potential difference measuring device when the AC current is passed through the measurement portion, and the corrosion location of the reinforcing steel embedded in the concrete structure can be detected from the obtained impedance.
It is characterized by:
or
a measurement section including a measurement electrode disposed on a measurement surface of a concrete structure and a first counter electrode disposed on the measurement surface in contact with an outer peripheral surface of the measurement electrode, and capable of measuring the electric potential of the concrete structure;
a reference electrode that is installed at a predetermined distance from the measurement unit on one side in the horizontal direction and that can measure a reference potential of the concrete structure;
A second counter electrode is installed at a predetermined interval from the measurement unit on the other side in the horizontal direction;
an AC power source that is installed between the measurement unit and the second counter electrode and that has a high-frequency AC current and a low-frequency AC current that are applied between the first counter electrode and the second counter electrode;
a current measuring device for measuring a value of a current passed between the first counter electrode and the second counter electrode;
a potential difference meter that is installed between the measurement unit and the reference electrode and measures a potential difference between a measured potential substantially below the measurement unit and a reference potential of the concrete structure by the measurement electrode and the reference electrode;
The impedance approximately below the measurement portion is obtained from the current value and potential difference value measured by the current measuring device and potential difference measuring device when the AC current is passed through the measurement portion, and the corrosion location of the reinforcing steel embedded in the concrete structure can be detected from the obtained impedance.
It is characterized by the above.

According to the present invention, even with non-destructive testing, it is easy to estimate the location of corrosion of reinforcing bars buried in a concrete structure, and it is less likely to misjudge the presence or absence of reinforcing bar corrosion or the location of corrosion depending on the state of the concrete. It is also not necessary to locally destroy the concrete structure with a drill or the like to establish electrical continuity with the buried reinforcing bars, and the presence or absence of corrosion of the reinforcing bars can be evaluated in absolute values based on the impedance spectrum of the reinforcing bars in the concrete. As a result, it is possible to evaluate the presence or absence of corrosion of the reinforcing bars even in situations where the buried reinforcing bars are not connected, for example.

FIG. 2 is an explanatory diagram illustrating the basic principle of measurement according to the present invention. FIG. 1 is an explanatory diagram for explaining an outline of measurement according to a conventional measurement method. FIG. 2 is an explanatory diagram illustrating the dimensions and reinforcement of the test specimen used in the experimental example. FIG. 1 is an explanatory diagram illustrating measurement results of a concrete test specimen performed using a conventional measurement method. FIG. 1 is an explanatory diagram (1) for explaining an outline of the measurement according to the measurement method of the present invention. FIG. 2 is an explanatory diagram illustrating the measurement results of a concrete test specimen performed using the measurement method of the present invention. FIG. 2 is an explanatory diagram (2) for explaining the measurement outline according to the measurement method of the present invention.

The present invention will now be described with reference to examples.
First, the basic principle of measurement according to the present invention will be described with reference to FIG.
Fig. 1(a) shows impedance spectra of iron immersed in an alkaline aqueous solution, and in this state, alternating currents of different frequencies from low to high were passed through the iron, and the electrical resistance of the iron was measured after 1 hour, 10 days, 12 days, 15 days, 20 days, and 30 days. Sodium chloride was added to the aqueous solution as needed to adjust the salt concentration to the values shown in Fig. 1(b) for each of the above-mentioned time periods, causing corrosion of the iron.

The relationship between frequency [Hz] and electrical resistance [Ω] associated with the corrosion state of iron will be explained with reference to Fig. 1(a), which is a double logarithmic graph with frequency [Hz] on the horizontal axis and electrical resistance [Ω] (impedance [kΩ· ^cm2 ]) on the vertical axis.

As shown in Figure 1(a), it can be seen that the electrical resistance of iron [Ω] varies depending on the frequency [Hz] of the alternating current [A] that is passed through it. It can also be seen that the change in electrical resistance with frequency becomes smaller as the corrosion of the iron progresses. That is, the curves after 1 hour and 10 days, when no iron corrosion has occurred, have a steep slope, and it can be seen that the electrical resistance also changes significantly as the frequency is changed from low to high. On the other hand, in the case of a salinity of 1.0 M after 30 days, when the greatest amount of iron corrosion has occurred, the slope of the curve is the smallest, and it can be seen that the change in electrical resistance is small even when the frequency is changed from low to high.

From these results, it can be seen that when the iron is healthy and not corroded, the change in electrical resistance due to frequency is large, whereas when the iron is corroded, the change in electrical resistance due to frequency is small.

Therefore, as shown in Figure 1, by creating a graph plotting electrical resistance corresponding to alternating current of various frequencies and measuring the change in electrical resistance when the frequency is changed from low frequency to high frequency, it is possible to identify areas of iron corrosion.

The method for obtaining electrical resistance is to apply an alternating current of a specified frequency from the surface of the concrete into the reinforcing bar 5, obtain the change in potential difference between the reinforcing bar 5 and the surface of the concrete when the current is applied, and use Ohm's law to obtain the electrical resistance.

Here, when measuring the electrical resistance, the electrical resistance of the interface between the concrete covering the concrete surface and the buried rebar 5 is an important factor. Whether the electrical resistance of the interface is high or low can be used to determine whether the buried rebar 5 is corroded or not.

A method for obtaining the electrical resistance of the interface will be briefly described below.
First, the electrical resistance of the interface has a characteristic that the electrical resistance becomes zero when a high-frequency alternating current is applied. Therefore, when a high-frequency alternating current is applied, the electrical resistance of only the concrete of the cover portion can be obtained. Then, as the applied frequency is changed from high to low, the electrical resistance of the interface portion gradually appears, and finally, the sum of the electrical resistance of the concrete of the cover portion and the electrical resistance of the interface portion becomes the electrical resistance obtained when a low-frequency alternating current is applied. Therefore, by taking the difference between the electrical resistance when a low-frequency alternating current is applied and the electrical resistance when a high-frequency alternating current is applied, the electrical resistance of only the interface portion can be obtained.

This makes it possible to determine whether or not the buried rebar 5 is corroded, and in some cases even the state of corrosion of the buried rebar 5. Conventional methods require electrical continuity with the buried rebar 5 for these measurements, but this method is unique in that it does not require this.

Next, a conventional method for measuring electrical resistance will be described with reference to FIG.
The equipment used in the conventional measurement method includes a measurement electrode 7, which is a measurement reference electrode, and a first counter electrode 3 provided in contact with the outer peripheral surface of the measurement electrode 7. In addition, an AC power source 9 capable of supplying AC currents of different frequencies, such as high-frequency and low-frequency AC currents, a current measuring device 10 such as an ammeter, and a potential difference measuring device 11 such as a potentiometer are required.

The measurement electrode 7 is placed on the surface of the concrete structure 1, i.e., on the measurement surface 2, and the first counter electrode 3 is placed on the measurement surface 2 in contact with the outer peripheral surface of the measurement electrode 7. Measurements are performed by changing the measurement location of the measurement unit 6 composed of the measurement electrode 7 and the first counter electrode 3.

In the conventional measurement method, in order to obtain electrical continuity with the reinforcing bars 5 embedded in the concrete structure 1, it is necessary to locally drill holes from the surface of the concrete structure 1 toward the inside of the concrete. After drilling, a metal wire 12, such as a copper wire, is wired through the hole so as to be electrically connected to the reinforcing bars 5 inside the concrete.

As shown in FIG. 2, the measurement electrode 7 is connected to an RE (Reference Electrode) terminal, the first counter electrode 3 is connected to a CE (Counter Electrode) terminal, and the metal wire 12 electrically connected to the reinforcing bar 5 is connected to a WE (Working Electrode)_V terminal and a WE_I terminal.
Then, the RE terminal and the WE_V terminal are connected by a measurement cable or the like, that is, the measurement electrode 7 is connected to the metal wire 12 that is conductive with the buried rebar 5. In addition, a potential difference meter 11 is connected and installed between the RE terminal and the WE_V terminal.
Then, the CE terminal and the WE_I terminal are connected by a measurement cable or the like, that is, the first counter electrode 3 is connected to the metal wire 12 that is conductive with the buried rebar 5. An AC power source 9 and a current measuring device 10 are connected and installed between the CE terminal and the WE_I terminal.
Next, a low frequency current and a high frequency AC current, for example, in the frequency range of 0.01 Hz to 100 Hz, are continuously applied between the CE terminal and the WE_I terminal.

In the above-mentioned measurement, the current measuring device 10 obtains the current data flowing between the CE terminal and the WE_I terminal for each AC current (Iobs) of each frequency. It is preferable that the amplitude of the AC current is approximately 50 mV, which is the amplitude of the potential difference (Vobs) described below.

Next, while a low-frequency current or a high-frequency AC current is flowing between the CE terminal and the WE_I terminal, the potential difference between the RE terminal and the WE_V terminal is measured. The potential difference between the RE terminal and the WE_V terminal is measured by the potential difference meter 11, and the measured potential difference becomes the potential data near the measurement unit 6.

Here, the potential data is measured, but the potential of the buried rebar 5 does not change during the measurement. Therefore, the potential of the buried rebar 5 is used as a reference, and the measurement unit 6 installed on the measurement surface 2, i.e., the measurement electrode 7, measures the potential difference between the potential of the buried rebar 5 and the potential of the surface of the concrete structure 1 that is in contact with the measurement surface 2.

The potential difference (Vobs) obtained by the measurement is divided by the applied AC current (Iobs) according to the following formula (1), to obtain the measurement result (Zobs) which is the impedance.
Zobs = Vobs / Iobs ... (1)
For each frequency of AC current (Iobs), the measurement result (Zobs) is calculated to obtain the impedance spectrum.

Here, an example of an experiment based on the conventional measurement method procedure is shown. As an example of a concrete structure 1 for measuring corrosion of reinforcing bars in concrete, the one shown in Figure 6 is used as an experimental example. Figure 3(a) shows a plan view of the concrete specimen, Figure 3(b) shows a right side view of the concrete specimen, and Figure 3(c) shows a front view of the concrete specimen. The horizontal length of the concrete specimen is X, the horizontal length perpendicular to X is Y, and the vertical length perpendicular to X and Y is Z. In this experimental example, a concrete specimen with dimensions of X: 1600 mm x Y: 1600 mm x Z: 100 mm is used (see Figure 3).

The reinforcing bars 5 are arranged, for example, in a grid pattern, with 15 bars each in the vertical and horizontal directions, so that the cover of the first reinforcing bar is 50 mm and the cover of the second reinforcing bar is 69 mm. In this experimental example, reinforcing bars 5 measuring φ19 mm x 1600 mm are used.

In this experimental example, two types of concrete specimens were prepared: a corrosion test specimen in which the entire surface of the buried rebar 5 was corroded, and a non-corroded test specimen in which the entire surface of the buried rebar 5 was not corroded. The rebars 5 used in the corrosion test specimens were corroded by spraying them with 3% salt water in the atmosphere before being embedded in concrete. The rebars 5 were electrically shorted together by welding, and measurements were performed by connecting measurement lead wires (metal wires 12) to the ends of the rebars 5.

The measurement position in this experimental example, that is, the installation position of the measuring unit 6, was X: 150 mm x Y: 150 mm x Z: 100 mm. The measurement results of each concrete specimen are shown in FIG.
Fig. 4 is a plot diagram showing the impedance spectrum obtained by obtaining the potential difference (Vobs) for each frequency of AC current (Iobs) and calculating the measurement result (Zobs), i.e., impedance, using formula (1). The vertical axis shows the imaginary part [Ω] and the horizontal axis shows the real part [Ω].

From Figure 4, the intersection of the spectrum obtained for each concrete test specimen (non-corroded and corroded test specimens) with the real part of the horizontal axis [Ω] represents the concrete resistance. It can be seen from the plot that the concrete resistance of the non-corroded test specimen is approximately 300 [Ω], while the concrete resistance of the corroded test specimen is approximately 550 [Ω]. Furthermore, the state of corrosion of the reinforcing bar 5 can be considered from the rise of the spectrum, and the rise of the spectrum of the corroded test specimen is smaller than that of the non-corroded test specimen (see Figure 4). Therefore, from the results in Figure 4, if the rise of the spectrum is small, it can be determined that the buried reinforcing bar 5 is corroded.

Next, an outline of the measurement according to the present invention will be described with reference to FIG.
The devices used in the measurement method of the present invention include a measurement electrode 7 which is a measurement reference electrode, a first counter electrode 3 provided in contact with the outer peripheral surface of the measurement electrode 7, a reference electrode 8 which is a reference electrode, and a second counter electrode 4. In addition, an AC power source 9 capable of supplying AC currents of different frequencies such as high and low frequency AC currents, a current measuring device 10 such as an ammeter, and a potential difference measuring device 11 such as a potentiometer are required.

The measurement electrode 7 is placed on the surface of the concrete structure 1, i.e., on the measurement surface 2, and the first counter electrode 3 is placed on the measurement surface 2 with the outer circumferential surface of the measurement electrode 7 in contact with it. Measurements are performed by changing the installation location of the measurement unit 6, which is composed of the measurement electrode 7 and the first counter electrode 3.

Next, the electrode arrangement of the present invention will be described.
First, a reference electrode 8 capable of measuring the reference potential of the concrete structure 1 is installed at a predetermined distance from the measuring unit 6. Then, a second counter electrode 4 is installed at a predetermined distance or more from the measuring unit 6 and the reference electrode 8. The reference electrode 8 needs to be installed at a position where it is not affected by the current flowing between the first counter electrode 3 and the second counter electrode 4 that constitute the measuring unit 6.

The measuring electrode 7 constituting the measuring section 6 measures the potential in the buried rebar 5 from the surface of the concrete structure 1, i.e., the measuring surface 2, when an alternating current is passed between the first counter electrode 3 and the second counter electrode 4. The reference electrode 8 measures the potential on the surface of the concrete structure 1. Here, when the electrode is installed in a position that is not affected at all by the current passing between the first counter electrode 3 and the second counter electrode 4, it can be considered to be the same potential as the potential in the buried rebar 5. Therefore, since the reference electrode 8 is installed in a position that is not affected by the current passing therethrough, it can be treated the same as the buried rebar 5. As a result, while conventional methods require electrical continuity with the buried rebar 5 for these measurements, the present invention does not require electrical continuity with the buried rebar 5.

Figure 5 shows an example of the electrode arrangement of the present invention. As can be seen from Figure 5, a reference electrode 8 capable of measuring the reference potential of the concrete structure 1 is installed on the measurement surface 2 at a predetermined distance on one side of the horizontal direction from the measurement unit 6. A second counter electrode 4 is installed at a predetermined distance from the measurement unit 6 on the other side of the horizontal direction from the measurement unit 6, that is, on the opposite side of the measurement unit 6 to the reference electrode 8. Note that in Figure 5, the reference electrode 8 is installed to the right of the measurement unit 6 and the second counter electrode 4 is installed to the left of the measurement unit 6, but there is no problem if the reference electrode 8 is installed on the left side and the second counter electrode 4 is installed on the right side.

In addition to arranging the electrodes in a straight line as shown in FIG. 5, it is also possible to arrange the electrodes so that they are approximately L-shaped when viewed from above as shown in FIG. 7. This is an electrode arrangement in which a reference electrode 8 (or a second counter electrode 4) is arranged on the measurement surface 2 at a predetermined distance in the horizontal direction perpendicular to the measurement unit 6, and a second counter electrode 4 (or a reference electrode 8) is arranged at a predetermined distance in the horizontal direction from the measurement unit 6. Even when arranging the electrodes in the approximately L shape, the reference electrode 8 needs to be arranged at a position that is not affected by the current flowing between the first counter electrode 3 and the second counter electrode 4, so the reference electrode 8 and the second counter electrode 4 need to be arranged at a distance from each other.

The specified distance between the measuring unit 6 and the reference electrode 8, the so-called separation distance, is affected by the depth of the buried rebar 5 from the measuring surface 2, the concrete strength, the water content of the concrete, etc., which affect the current passing through the concrete. Therefore, accurate measurement results can be obtained by lengthening or shortening the separation distance between the measuring unit 6 and the reference electrode 8 depending on each concrete structure 1 being measured, and the corrosion of the buried rebar 5 can be determined. The same applies to the separation distance between the measuring unit 6 and the second counter electrode 4.

As a result, by placing the reference electrode 8 and the second counter electrode 4 at a predetermined distance from the measuring unit 6, it is no longer necessary to locally destroy the concrete structure 1, for example by drilling a hole, as in conventional measuring methods. In other words, the reference electrode 8 and the second counter electrode 4 serve as a substitute for electrical continuity with the buried rebar 5 in the conventional method. This is one of the features of the present invention.

Next, the measurement procedure of the present invention will be described.
5, the RE terminal is connected to the measurement electrode 7 constituting the measurement unit 6, and the CE terminal is connected to the first counter electrode 3. Furthermore, the WE_V terminal is connected to the reference electrode 8, and the WE_I terminal is connected to the second counter electrode 4.
Thereafter, the RE terminal and the WE_V terminal are connected by a measurement cable or the like, that is, the measurement electrode 7 is connected to the reference electrode 8. In addition, a potential difference meter 11 is connected and installed between the RE terminal and the WE_V terminal.
Then, the CE terminal and the WE_I terminal are connected by a measurement cable or the like, that is, the first counter electrode 3 and the second counter electrode 4 are connected. An AC power source 9 and a current measuring device 10 are connected and installed between the CE terminal and the WE_I terminal, respectively.
Next, a low frequency current and a high frequency AC current, for example, in the frequency range of 0.01 Hz to 100 Hz, are continuously applied between the CE terminal and the WE_I terminal.

In the above-mentioned measurement, the current measuring device 10 obtains the current data flowing between the CE terminal and the WE_I terminal for each AC current (Iobs) of each frequency. It is preferable that the amplitude of the AC current is approximately 50 mV, which is the amplitude of the potential difference (Vobs) described below.

Next, while a low-frequency current or a high-frequency AC current is flowing between the CE terminal and the WE_I terminal, the potential difference between the RE terminal and the WE_V terminal is measured. The potential difference between the RE terminal and the WE_V terminal is measured by the potential difference meter 11, and the measured potential difference becomes the potential data near the measurement unit 6.

Here, in measuring the potential data, the potential of the concrete surface to which the reference electrode 8 is in contact does not change during measurement, so the potential difference is measured from the potential of the concrete structure 1 surface to which the measurement electrode 7 is in contact with the measurement surface 2, using the potential of the reference electrode 8 as a reference.

The potential difference (Vobs) obtained by the measurement is divided by the applied AC current (Iobs) to obtain the measurement result (Zobs) of impedance according to the following formula (1). Note that the impedance calculated by formula (1) is an absolute value.
Zobs = Vobs / Iobs ... (1)
For each frequency of AC current (Iobs), the measurement result (Zobs) is calculated to obtain the impedance spectrum.

Here, we present an example of an experiment based on the measurement method of the present invention. Note that the dimensions and reinforcement conditions of the two types of test specimens used in this example are the same as those in the example of an experiment based on the conventional measurement method described above.

In other words, as an example of a concrete structure 1 for measuring corrosion of reinforcing bars in concrete, the one shown in Figure 3 can be used as an experimental example. As can be seen from Figure 3, the horizontal length of the concrete specimen is X, the horizontal length perpendicular to X is Y, and the vertical length perpendicular to X and Y is Z. In this experimental example, a concrete specimen with dimensions of X: 1600 mm x Y: 1600 mm x Z: 100 mm is used (see Figure 3).

The reinforcing bars 5 are arranged, for example, in a grid pattern, with 15 bars each in the vertical and horizontal directions, so that the cover of the first reinforcing bar is 50 mm and the cover of the second reinforcing bar is 69 mm. In this experimental example, reinforcing bars 5 measuring φ19 mm x 1600 mm are used.

In this experimental example, two types of concrete specimens were prepared: a corrosion test specimen in which the entire surface of the buried rebar 5 was corroded, and a non-corroded test specimen in which the entire surface of the buried rebar 5 was not corroded. Note that the rebar 5 used in the corrosion test specimen was corroded by spraying it with 3% salt water in the atmosphere before being embedded in concrete. Furthermore, the rebars 5 were electrically short-circuited by welding.

The measurement position in this experimental example, i.e., the installation position of the measurement unit 6, was X: 150 mm x Y: 150 mm x Z: 100 mm, and the second counter electrode 4 was installed at a position of X: 150 mm x Y: 1450 mm x Z: 100 mm. The reference electrode 8 was installed at a position of X: 1450 mm x Y: 150 mm x Z: 100 mm. The arrangement of these electrodes is as shown in Figure 7.

In the conditions of this experimental example, the predetermined distance between the measuring unit 6 and the second counter electrode 4, i.e., the separation distance, was set to 1300 mm, and the predetermined distance between the measuring unit 6 and the reference electrode 8, i.e., the separation distance, was set to 1300 mm. This separation distance is appropriately determined taking into consideration the size and thickness of the concrete structure 1, the number of reinforcing bars, the covering position of the reinforcing bars 5, the concrete strength, the elastic modulus of the concrete, etc.

Then, the RE terminal is connected to the measurement electrode 7 constituting the measurement unit 6, the CE terminal is connected to the first counter electrode 3, the WE_V terminal is connected to the reference electrode 8, and the WE_I terminal is connected to the second counter electrode 4. After that, the RE terminal and the WE_V terminal are connected, i.e., the measurement electrode 7 and the reference electrode 8 are connected. The CE terminal and the WE_I terminal are also connected, i.e., the first counter electrode 3 and the second counter electrode 4 are connected. The AC power source 9 and the current meter 10 are then installed between the CE terminal and the WE_I terminal, and the potential difference meter 11 is connected between the RE terminal and the WE_V terminal.

Figure 6 shows the measurement results of each concrete specimen obtained according to the electrode arrangement of the experimental example described above. Note that Figure 6 shows both the measurement results according to the present invention and the measurement results according to the conventional method.

In Fig. 6, the potential difference (Vobs) between the measurement electrode 7 and the reference electrode 8 is obtained each time an AC current (Iobs) of each frequency is applied between the first counter electrode 3 and the second counter electrode 4, and the measurement result (Zobs), i.e., the impedance, is calculated using formula (1). This is a plot diagram in which an impedance spectrum is plotted based on the calculated impedance. The vertical axis indicates the imaginary part [Ω], and the horizontal axis indicates the real part [Ω].

The intersection of the spectrum obtained for each concrete test specimen (non-corroded and corroded test specimens) with the real part of the horizontal axis [Ω] represents the concrete resistance, and in both results, the concrete resistance of the non-corroded test specimen was approximately 300 [Ω], while the concrete resistance of the corroded test specimen was approximately 550 [Ω]. In addition, the state of corrosion of the reinforcing bar 5, which can be inferred from the rise of the spectrum, is such that in both results the rise of the spectrum of the corroded test specimen is smaller than that of the non-corroded test specimen (see Figure 6).

From the above, the spectrum obtained based on the measurement method of the present invention is roughly consistent with the spectrum obtained by the conventional method, i.e., by connecting the buried rebar 5, and it is possible to evaluate the presence or absence of corrosion of the rebar 5 in concrete buried in a concrete structure in a non-conductive manner without connecting the rebar 5 in concrete. Furthermore, since the impedance obtained by the measurement method of the present invention is calculated as an absolute value, it is possible to evaluate the presence or absence of rebar corrosion for each measurement position even in a situation where the rebar 5 buried in the concrete structure 1 is not connected.

Reference Signs List 1 Concrete structure 2 Measurement surface 3 First counter electrode 4 Second counter electrode 5 Reinforcing bar 6 Measurement unit 7 Measurement electrode 8 Reference electrode 9 AC power source 10 Current meter 11 Potential difference meter 12 Metal wire

Claims (2)

a measurement section including a measurement electrode disposed on a measurement surface of a concrete structure and a first counter electrode disposed on the measurement surface in contact with an outer peripheral surface of the measurement electrode, and capable of measuring the electric potential of the concrete structure;
a reference electrode that is installed at a predetermined distance in the horizontal direction from the measurement unit and that can measure a reference potential of the concrete structure;
A second counter electrode installed at a predetermined distance from the measurement unit in the horizontal direction;
an AC power source that is installed between the measurement unit and the second counter electrode and that has a high-frequency AC current and a low-frequency AC current that are applied between the first counter electrode and the second counter electrode;
a current measuring device for measuring a value of a current passed between the first counter electrode and the second counter electrode;
a potential difference meter that is installed between the measurement unit and the reference electrode and measures a potential difference between a measured potential substantially below the measurement unit and a reference potential of the concrete structure by the measurement electrode and the reference electrode;
The impedance approximately below the measurement portion is obtained from the current value and potential difference value measured by the current measuring device and potential difference measuring device when the AC current is passed through the measurement portion, and the corrosion location of the reinforcing steel embedded in the concrete structure can be detected from the obtained impedance.
A corrosion detection device for reinforcing bars in concrete.
a measurement section including a measurement electrode disposed on a measurement surface of a concrete structure and a first counter electrode disposed on the measurement surface in contact with an outer peripheral surface of the measurement electrode, and capable of measuring the electric potential of the concrete structure;
a reference electrode that is installed at a predetermined distance from the measurement unit on one side in the horizontal direction and that can measure a reference potential of the concrete structure;
A second counter electrode is installed at a predetermined interval from the measurement unit on the other side in the horizontal direction;
an AC power source that is installed between the measurement unit and the second counter electrode and that has a high-frequency AC current and a low-frequency AC current that are applied between the first counter electrode and the second counter electrode;
a current measuring device for measuring a value of a current passed between the first counter electrode and the second counter electrode;
a potential difference meter that is installed between the measurement unit and the reference electrode and measures a potential difference between a measured potential substantially below the measurement unit and a reference potential of the concrete structure by the measurement electrode and the reference electrode;
The impedance approximately below the measurement portion is obtained from the current value and potential difference value measured by the current measuring device and potential difference measuring device when the AC current is passed through the measurement portion, and the corrosion location of the reinforcing steel embedded in the concrete structure can be detected from the obtained impedance.
A corrosion detection device for reinforcing bars in concrete.

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