JP2685358B2 - Corrosion diagnosis method for reinforcing bars in concrete - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for diagnosing corrosion of metal members (hereinafter referred to as reinforcing bars) embedded in concrete such as reinforcing bars and metal pipes in reinforced concrete structures.

[0002]

2. Description of the Related Art Reinforcing bars embedded in concrete are
It is known that corrosion occurs depending on the environmental conditions in which it is installed.

For example, when such corrosion occurs in a reinforcing bar,
It is desirable to detect the corrosion and repair it as soon as possible for maintenance of the reinforced structure. Then, in the inspection of the corrosion of the reinforcing bars embedded in the concrete, it is preferable that the existence of the corrosion is inspected and at the same time the amount of corrosion and the corrosion rate can be obtained to estimate the remaining life.

By the way, as a technique for nondestructively inspecting the corrosion of such a reinforcing bar, conventionally, the spontaneous potential of the reinforcing bar has been widely measured, but this method qualitatively determines the corrosion. Its presence can be detected, but no quantitative amount or rate of corrosion can be obtained.

In addition to this, it has been attempted to measure the polarization resistance by the AC impedance method. According to this method, the corrosion current corresponding to the corrosion rate can be obtained from the obtained polarization resistance, and the reinforcing bar can be obtained. It is considered possible to estimate the remaining life of a structure.

[0006]

However, in the measurement of the polarization resistance by this AC impedance method,
Since it is necessary to obtain AC impedance in a wide frequency range from extremely low frequency to high frequency,
Especially, it takes a long time to measure the AC impedance particularly in a low frequency region, and it is not yet widely used in practice. The present invention has been made based on such a background, and by quickly obtaining a polarization resistance capable of estimating the remaining life without degrading the measurement accuracy of AC impedance, it is possible to quickly perform corrosion diagnosis of reinforcing bars in concrete. In addition, it aims to be of high quality.

[0007]

In order to achieve this object, the invention according to claim 1 is an iron drawn on a complex plane.
From the AC impedance locus of concrete including streaks
Diagnosing the state of corrosion of rebar etc. using the calculated polarization resistance
In the method of diagnosing corrosion of reinforcing steel in concrete,
One or more pre-measured AC impedance loci
Peak in the imaginary part of the AC impedance locus based on
The low frequency range where points appear and the frequency side higher than the peak point
In advance, set the high frequency range where the minimum point appears,
Select the first frequency from the low frequency range in advance and
Select the second frequency in advance from the wave number range and
The real of a virtual circle passing through the peak and minimum points of the pedestal locus
Correspondence between diameters of several parts and polarization resistance is prepared in advance
The AC voltage of the first frequency added to the concrete,
AC current corresponding to the voltage of the first AC impedance
Second frequency added to concrete while calculating
From the alternating current voltage and the alternating current corresponding to this voltage
The AC impedance is calculated and these first AC impedances are calculated.
Of the virtual circle from the impedance and the second AC impedance
Calculate the diameter of several parts and calculate the polarization resistance corresponding to this diameter.
Characterized by using correspondences prepared in advance
This is a method for diagnosing corrosion of reinforcing bars in concrete.
Further, the invention of claim 2 is a reinforcing bar drawn on a complex plane.
Calculated from the AC impedance locus of concrete including
Diagnose the state of corrosion of rebar, etc. by using the generated polarization resistance.
In the method of diagnosing corrosion of steel bars in concrete,
One or more AC impedance loci measured in a random manner
Based on the imaginary part of the AC impedance locus
Preset the low frequency range where
Select the first frequency from the
The peak point that appears in the imaginary part of the resistance locus and the pair of polarization
First prepared by preparing the relationship and adding it to the concrete
Frequency alternating voltage and alternating current corresponding to this voltage
Calculate the first AC impedance from the
Calculate the peak point of the imaginary part of the pedestal and calculate the peak point
The polarization resistance corresponding to
This is a method for diagnosing corrosion of reinforcing steel in concrete, which is characterized by using it .

[0008]

SUMMARY OF] According to the invention of claim 1, wherein, in the alternating current impedance locus viewed in Cole-Cole plot for reinforcing steel in concrete or the like, frequency range of the peak point of the imaginary part of the AC impedance takes a peak value is approximately 1
The frequency range is 00 mHZ to 5 mHZ, and the frequency range in which the AC impedance has a minimum value at a frequency higher than this frequency is approximately 100 to 1 HZ.

Therefore, the two points at which the AC impedance should be measured can be measured in a short time because they are relatively high frequency portions, and the number of measurement points is small, so that the measurement can be performed quickly. Then, it is possible to easily calculate the diameter of the virtual circle by using the AC impedance thus quickly obtained.

The diameter of this virtual circle and the Cole-Cole plot of the AC impedance of the reinforcing bars in concrete have a good correspondence with the minimum point intervals on both sides of the peak point. Can be accurately obtained, and by using this, an accurate polarization resistance can be calculated. Therefore, according to this method, the work of measuring the AC impedance to be measured can be performed in a short time, and since the number of measurement points is small, the measurement can be speeded up and there is a good correspondence, so that the accuracy is high. Polarization resistance can be obtained. Therefore, the corrosion diagnosis such as the estimation of the remaining life can be performed quickly and with high quality.

According to the second aspect of the invention, the concrete
Reinforcing bars in the car were displayed in a Cole-Cole plot
AC impedance in the AC impedance locus
The frequency range at the peak point where the imaginary part of
It is 100 mHZ to 5 mHZ. And of the peak point
The value of the imaginary part of the AC impedance obtained at the frequency
It can be used to calculate the polarization resistance. This imaginary part
Since there is a good correspondence between the value of
Use the value of the imaginary part of the AC impedance obtained in
Therefore, the accurate polarization resistance can be calculated.
Therefore, according to this method, the AC impedance to be measured is
In addition to performing the dance measurement work in a short time, the number of measurement points
Since there is only one point, it is said that the measurement can be done quickly.
However, since there is a good correspondence, a precise polarization resistance
Can be obtained. Therefore, corrosion diagnosis such as estimation of remaining life
Delivers fast and high quality.

[0012]

EXAMPLES First, the measurement principle of the present application will be described. In general, an electric system in which a corrosion reaction occurs can be represented by an electric equivalent circuit composed of resistors and capacitors as shown in FIG.
That is, Rsol is a solution resistance (concrete resistance) between the counter electrode and the sample electrode, and Cdl represents a capacitor capacity called an electric double layer capacity formed at the metal / solution interface. Further, Rct is called a charge transfer resistance, which is a resistance to a corrosion reaction and corresponds to a polarization resistance.

When minute AC voltages of various different frequencies are applied to such a circuit, a current of the same frequency with a phase advance of θ can be obtained due to the impedance of Cdl. The ratio of the applied AC voltage and the response AC current measured at each frequency, that is, the AC impedance is expressed as an absolute value and a phase difference with the frequency as a parameter, and the phase difference is used as a declination angle on a complex plane. cole-co
le) Generally displayed in the plot.

The AC impedance locus by the Cole-Cole plot corresponding to the equivalent circuit of FIG. 9 obtained in this way has an intersection (Rsol) with the real axis on the high frequency side as shown in FIG. Moreover, since the intersection with the real axis on the low frequency side is (Rct + Rsol), the polarization resistance R
ct is the diameter of the semicircular AC impedance locus, that is, the distance between the two intersections.

Therefore, the polarization resistance can be obtained from this AC impedance locus, and the corrosion rate can be estimated from the relationship that the reciprocal of the polarization resistance is proportional to the corrosion rate. By the way, the actual AC impedance locus of the reinforcing bar in concrete is shown in Figs.
As shown in the figure.

That is, these AC impedance loci are based on the research by the inventors of the present application, and are obtained by measuring and plotting the AC impedance over a wide range from high frequency to low frequency as is conventionally done. FIG. 7 is a Cole-Cole plot for a rebar that has not been corroded, and FIG. 8 is an example in which the progress of corrosion is observed.

When the reinforcing bar is not corroded as shown in FIG. 7, looking at the value of the imaginary part of the AC impedance, it is 10 KHZ or more.
It decreases monotonically in the range of 1HZ, takes a minimum value in the range of 10 to 1HZ, and thereafter sharply increases on the low frequency side, and the locus seems to indicate a part of a large circle.

That is, in the AC impedance locus of FIG. 7, there are 10 intersections with the real axis on the high frequency side (since they do not actually intersect and are minimum points, they are minimum points in this specification). It appears at a frequency of ~ 1HZ, and no intersection with the real axis is found on the low frequency side. On the other hand, as shown in FIG. 8, when there is corrosion in the reinforcing bar, it decreases monotonously over 10 KHZ to 1 HZ, takes a minimum value in the range of 100 to 1 HZ, and monotonically increases on the low frequency side thereafter, with 5 mHZ as the boundary. Is decreasing again. In this case, the AC impedance value is generally quite small, and the locus thereof has a semicircular shape crushed in the imaginary axis direction.

As is clear from FIG. 8, regarding the corrosion of the reinforcing bar in concrete, in order to clearly understand the shape of the AC impedance locus in such a Cole-Cole plot, a wide frequency range up to a low frequency of 1 mHZ or less is required. It can be seen that it is necessary to measure the AC impedance over the range, and the measurement requires a significant amount of time.

In the case of corroded rebar, the minimum point on the high frequency side (hereinafter referred to as the minimum point A, which is the intersection with the real axis) is generally affected by the corrosion rate of the reinforcing bar. It appears that the frequency appears in the range of 100 to 1HZ, the minimum point on the low frequency side (intersection with the real axis) appears at a frequency of 1mHZ or less, and the peak point of the semicircular AC impedance locus appears at 100mHZ to 5mHZ. Can be estimated.

Therefore, based on the characteristics of such an AC impedance locus for corrosion of reinforcing bars in concrete, in the first method of the present invention (hereinafter, referred to as a method of measuring two points), a high frequency side minimum point A appears. It is presumed that one frequency within the frequency range of 100 to 1 HZ, which is estimated to be 100 Hz, and a point (hereinafter, referred to as peak point B), which is a peak value of a semicircular AC impedance locus appear.
For one frequency in the frequency range of mHZ to 5 mHZ, the AC impedance value is measured using a measuring device (details of the measurement will be described later).

The absolute value of the AC impedance of the local minimum point A on the high frequency side thus obtained is ZH, and the phase angle is θH.
If the absolute value of the AC impedance at the peak point B is ZL and the phase angle is θL, the coordinates of these points A and B on the complex plane are A (ZH · cos θH, ZH · sin θH). ) B (ZL · cos θL, ZL · sineL).

These are A (RH, O) and B (R
L, CL) and the diameter of a circle (hereinafter referred to as a virtual circle) passing through these two points is RC ', this RC' is easily calculated from these A and B coordinates by the so-called Pythagorean theorem. Can be done (Fig. 1).

On the other hand, the polarization resistance theoretically corresponds to the diameter of the semicircular AC impedance locus, as described above with reference to FIG. 10. Therefore, in the actual AC impedance locus, the polarization resistance is on both sides of the peak point B. It can be considered that the interval between the high frequency side minimum point A and the low frequency side minimum point A ′ which are located represents the polarization resistance RC. And the polarization resistance R
The relationship between the distance between the high frequency side minimum point A and the low frequency side minimum point A'representing C and the RC 'is as shown in FIG. 2 according to the study by the present inventors. When obtained from a large number of samples, RC = 1.9RC 'is well established.

Therefore, the polarization resistance value RC is obtained from the coordinates A and B, and the electrochemical corrosion rate equation Icorr = RT / mFSRC (A / cm2) = 104RT / mFSRC (mm / y) The corrosion rate can be calculated. It is.

A method (hereinafter referred to as a one-point measurement method) which is simpler than the two-point measurement method and more quickly obtains the polarization resistance of the reinforcing bar in concrete is as follows. That is, in this case, the AC voltage E is applied at one frequency within the frequency range (100 to 5 mHZ) which is estimated to be the peak point of the AC impedance locus, and the current between the reinforcing bar and the sensor at this time is applied. Ratio of applied AC voltage and response AC current I measured from the response (Z = E /
AC impedance is obtained by setting I) as an absolute value and the phase shift θ between the two as a deviation angle (FIG. 3).

In this case, Zsin θ = CL, and CL
Is an approximate value of the peak value of the AC impedance locus. In addition, the polarization resistance R of the AC impedance locus
The relationship between C and CL is as shown in FIG. 4 according to the study by the inventors of the present application, and RC = 4.0CL is well established when it is obtained from a large number of samples by experiments.

Therefore, if the CL thus obtained is regarded as the peak value of the AC impedance locus, the polarization resistance RC can be calculated by measuring only one AC impedance corresponding to the frequency of the peak value. it can. Next, a measuring device for measuring the AC impedance of the reinforcing bar in concrete used for carrying out the method of the present application will be described.

In FIG. 5, 1 is concrete and 2 is rebar. 3 is a terminal connected to the reinforcing bar 2, 4 is a counter electrode having a solid electrolyte therein, and 5 is a reference electrode. 6
Is an AC voltage applying device for measuring the potential between the reinforcing bar 2 and the counter electrode 4 and applying an AC voltage of various different frequencies therebetween, 7 is a phase of the applied AC voltage and the response AC current. A frequency response analyzer for obtaining the deviation amplitude ratio, and 8 is a control computer for automatically performing a series of measurement operations.

AC impedance measurement using such a measuring device is performed as follows. That is, first, the counter electrode 4 is arranged on the surface of the concrete 1, the terminal 3 is connected to the reinforcing bar 2 exposed from the concrete 1, and the potential between the surface of the concrete 1 and the reinforcing bar 2 is measured.

Next, while controlling the electric potential of the reinforcing bar 2 in the concrete 1 to this electric potential, the AC voltage applying device 6
An alternating voltage having a required frequency is applied at a voltage of about 10 mV. At the same time, the current response between the reinforcing bar 2 and the counter electrode 4 is analyzed by the frequency response analysis device 7, the AC impedance is measured, and the measured value of the AC impedance obtained by this is transmitted to the computer 8. At 8, the required calculation is performed to estimate the polarization resistance and the remaining life.

In order to confirm how the measured value of the corrosion rate based on the above-mentioned measuring principle matches the measured value and what the measuring time is, the present inventors The following confirmation test was performed using the apparatus. In this confirmation test, sample S shown in FIG.
Was prepared and subjected to a dry and wet repeated corrosion test every 6 hours in a 3% Nacl solution at 35 ° C for 1 year, and then the AC impedance was measured as described above, and the concrete was destroyed to determine the corrosion rate of the rebar. Actually measured.

The results are shown in Table. As shown in 1.
Samples 1 to 6 in the table show the case of two-point measurement of the present invention,
Samples 7 to 9 show the case of the one-point measurement of the present invention. Also,
In the table, Samples 10 to 13 are comparative examples.

[Table 1]

In the case of the two-point measurement of the present invention shown in Samples 1 to 6, the error between the estimated value obtained and the measured value is within about 50%, and sufficient reliability is obtained. The measurement time is within 3 minutes. In addition, samples 7 to 9
In the case of the one-point measurement of the present invention shown in, the ratio of the obtained estimated value and the actually measured value is almost the same as in the case of the two-point measurement,
It can be seen that the measurement time is further shortened with sufficient reliability.

On the other hand, in the case of the samples 10 to 12 of the comparative example, since they are out of the frequency range of the present invention, the measurement time is short, but the measurement error is extremely large and the reliability is poor. The sample 13 as a comparative example was measured over all frequencies as in the conventional case, and the reliability of the measured value was the same as in the case of the present invention, but the measurement required a long time. I understand.

As is clear from the above comparison, the estimated value of the corrosion rate obtained by the method according to the present invention has sufficient reliability, the measurement time is short, and the estimated value of the corrosion rate is high. It withstands practical applications such as life prediction.

[0037]

As described above, according to the first aspect of the invention, the work of measuring the AC impedance to be measured can be performed in a short time, and the number of measurement points is as small as two .
Since the measurement can be performed quickly and there is a good correspondence, it is possible to obtain the polarization resistance with high accuracy.

Therefore, the corrosion diagnosis such as the estimation of the remaining life can be performed quickly and with high quality. Further, according to the second aspect of the present invention,
In this way, the measurement work of AC impedance to be measured can be done in a short time.
It can be done in the meantime, and the number of measurement points is as small as 1
You can be quick and have a good correspondence
Therefore, it is possible to obtain an accurate polarization resistance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a principle of measuring a polarization resistance value according to the present invention.

FIG. 2 is a graph showing the relationship between RC and RC ′.

FIG. 3 is an explanatory view of the principle of a simple method for measuring the polarization resistance value according to the present invention.

FIG. 4 is a graph showing the relationship between RC and CL.

FIG. 5 is an overall schematic explanatory view of a measuring apparatus used for carrying out the method of the present application.

FIG. 6 is an explanatory diagram of a sample used in an experiment for confirming the effect of the method of the present application.

FIG. 7 is an AC impedance locus by Cole-Cole plot, which is a specific example of a reinforcing bar having no corrosion in concrete.

FIG. 8 is an AC impedance locus based on a Cole-Cole plot, which is a specific example of a reinforcing bar corroded in concrete.

FIG. 9 is an electrical equivalent circuit of an electrode system undergoing a corrosion reaction.

FIG. 10 is an explanatory diagram of a Cole-Cole plot.

[Explanation of symbols]

 A high frequency side minimum point A'low frequency side minimum point B peak point RC polarization resistance RC 'virtual circle diameter 1 concrete 2 rebar

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yu Yokota 5467 Fuchu-cho, Sakaide City, Kagawa Prefecture (72) Inventor Hideaki Aki 4-53-3 Kitahama, Chuo-ku, Osaka City, Osaka Prefecture Sumitomo Metal Industries Co., Ltd. (56) References JP-A 63-149549 (JP, A) JP-A 63-259456 (JP, A) JP-A 2-8733 (JP, A) JP-A 61-111401 (JP, A) JP-A 60 -200153 (JP, A)

Claims (2)

(57) [Claims] 1. A coil including a reinforcing bar and the like drawn on a complex plane.
Polarization calculated from the AC impedance locus of the Nuclet
Concrete that uses resistance to diagnose the state of corrosion of rebar etc.
One or more AC impedance loci measured in advance in the method for diagnosing corrosion of reinforcing bars in
Peak in the imaginary part of the AC impedance locus based on
The low frequency range where points appear and the frequency side higher than the peak point
In advance, set the high frequency range where the minimum point appears and select the first frequency from the low frequency range beforehand.
A second frequency is selected in advance from the wave number range, and it passes through the peak point and the minimum point of the AC impedance locus.
Show the correspondence between the diameter of the real part of the imaginary circle and the polarization resistance.
First, prepare the AC voltage of the first frequency added to the concrete, and
The first AC impedance from the AC current corresponding to the pressure
Calculate and calculate the frequency of the second frequency added to the concrete.
The second alternating current from the flowing voltage and the alternating current corresponding to this voltage.
Impedance is calculated, and these first AC impedance and second AC impedance
And the diameter of the real part of the imaginary circle, and the polarization resistance corresponding to this diameter is
A method for diagnosing corrosion of reinforcing steel in concrete, which is characterized by using correspondence. 2. A coil including a reinforcing bar and the like drawn on a complex plane.
Polarization calculated from the AC impedance locus of the Nuclet
Concrete that uses resistance to diagnose the state of corrosion of rebar etc.
One or more AC impedance loci measured in advance in the method for diagnosing corrosion of reinforcing bars in
Peak in the imaginary part of the AC impedance locus based on
Set the low frequency range where the points will appear in advance
The first frequency is selected in advance from the range, and the peak point that appears in the imaginary part of the AC impedance locus,
Prepare the correspondence with the polarization resistance in advance, and compare this voltage with the AC voltage of the first frequency applied to the concrete.
The first AC impedance from the AC current corresponding to the pressure
Calculate and calculate the peak point of the imaginary part of this first AC impedance
Then, prepare the polarization resistance corresponding to this peak point in advance.
Corrosion diagnosis method for reinforcing bars in concrete , characterized by investigating using the correspondence relationship .