JP3326587B2 - Method for detecting corrosion points of steel 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 detecting corrosion of steel in concrete.

[0002]

2. Description of the Related Art Concrete is generally
Because of its strong resistance to various environments and strong alkalinity, the steel inside it is protected from corrosion by forming a passive film on the surface of the steel, so that the concrete structure is durable. It has been considered a permanent structure.

[0003] However, concrete structures which have been considered to be permanent structures are also made of carbon steel in the concrete due to neutralization in which the pH value of the concrete is lowered by carbon dioxide gas in the air, and penetration of chlorine ions into the concrete. Steel in concrete is corroded due to salt damage caused by corrosion, and the function of maintaining the strength of the concrete structure is lost, and the life of the structure is being questioned.

As a method of inspecting the corrosion state of steel in a deteriorated concrete structure, conventionally, a steel cover in concrete is removed and the state of corrosion of the steel is confirmed by exposing the steel in the concrete. Visual inspection methods have been used.

[0005] The concrete hanging work deteriorates the working environment and poses a problem from the viewpoint of safety. In addition, it reduces the strength of the concrete structure. Potential method, surface potential difference method, electric resistance method, polarization resistance method, AC impedance method and the like have been proposed [ASTM (American Society)
for Testing Materials) C876, JP-A-59-217147, JP-A-63-163266, Diagnosis of steel bar corrosion, published by Morikita Publishing Co., Ltd. on May 28, 1993].

The self-potential method is a method in which a conductive wire is connected to steel in concrete and the electrochemical activity of the steel inside the concrete is measured by measuring the surface of the concrete using a copper-copper sulfate electrode or the like. However, this method has a problem that the measurement error is large due to the influence of the water content of the concrete and the like, and is insufficient as a method for evaluating the corrosion of steel.

The surface potential difference method is an application of the natural potential method, in which two reference electrodes are used to determine the potential gradient of the natural potential by measurement on the concrete surface. Although there is no need to connect, there was a problem that the absolute value of the natural potential from which the degree of corrosion of the steel material could be estimated could not be obtained.

The electric resistance method is a method of measuring the electric resistance of concrete to know the ease of penetration of a corrosion factor in concrete and the state of penetration. However, even if the possibility of corrosion of steel material can be estimated, There was a problem that it was not enough to know the corrosion state of steel.

The polarization resistance method is a method in which a conducting wire is connected to a part of steel material in concrete, and a direct current is applied from the concrete surface to the steel material inside the concrete to measure the polarization resistance of the steel material surface. The method has a problem that it is difficult to apply the method to an actual concrete structure because the measurement is strict and the measurement takes time.

In the AC impedance method, a conductor is connected to a steel material in concrete, and the steel surface is changed from the concrete surface to the steel material.
An alternating current of 0.01 Hz to 100 KHz is applied at a voltage of 10 to 20 mV, the polarization resistance is measured, and the degree of corrosion of the steel material is estimated. The AC impedance method has recently attracted attention due to its high reliability and simplicity of measurement, and has been frequently used for measuring polarization resistance and concrete electric resistivity in a test room or on site.

However, in the AC impedance method, it is necessary to connect a lead wire to steel in concrete, and this connection is required in a measurement using a test body in a test room.
When preparing the specimen, expose the steel material in advance,
It is necessary to connect the conductor, and in the measurement of the concrete structure on site, except when the steel material inside the concrete is exposed, the steel material is exposed, so that the concrete work such as suspending the concrete to the steel material or There was a problem that coring work was required.

That is, although the AC impedance method is one of the non-destructive inspection methods, it requires destruction work for connecting the conductors, and the labor and the reliability of the structure due to the destruction may be reduced. There was a problem that there is. The present inventors have conducted various studies to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by adopting a specific method, and have completed the present invention.

[0013]

That is, according to the present invention, two or more steel corrosion detecting ends provided with electrodes are brought into contact with the concrete surface, an alternating current is passed between the electrodes, and the corrosion of the steel in the concrete is caused. In the method of detecting the three points A, B, C, and the reference point A on the concrete surface,
The impedance in three paths B, BC, and CA was measured, and a single polarization resistance at the reference point A or the reference point A was measured.
To measure a single concrete electric resistance in
Characterized by the method for detecting corrosion locations of steel in concrete
Yes, contact two or more steel corrosion detectors with electrodes
Contact with the surface of the REIT.
How to detect corrosion points of steel in concrete
And the points B, C and reference point A on the concrete surface
For the point, in the three routes AB, BC and CA,
Measure the impedance and determine the single polarization resistance at reference point A.
Or measure the electrical resistance of a single concrete at reference point A.
Corrosion of concrete in concrete characterized by
A single polarization resistance or reference at reference point A using the location detection method
A single concrete electric resistance at point A is measured, and an alternating current is applied to a path AD connecting the reference point A and the measurement point D.
And the polarization resistance or concrete electric resistance in the path AD.
This is a method for detecting a corrosion point of a steel material in concrete, wherein a resistance is measured and a single polarization resistance at a measurement point D or a single concrete electric resistance value at a measurement point D is calculated.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
According to the present invention, at least two steel corrosion detecting terminals provided with electrodes (hereinafter, referred to as main detecting terminals) are brought into contact with a concrete surface in the vicinity of a steel material to be measured in concrete, and measurement is performed by an AC impedance method in which an alternating current flows. Things.

The detection end used in the present invention is not particularly limited as long as it has an electrode and an alternating current can easily flow on the concrete surface. It is preferable from the viewpoint of workability that a water retaining material such as absorbent cotton or sponge impregnated with an electrolyte solution such as calcium can be brought into contact with the concrete surface.

In order to prevent the water retention material from drying out, it is more effective to use a container that stores the electrolyte solution and can always supply the electrolyte solution to the water retention material. The shape and size of the detection end is such that the contact area with the concrete surface is 0.5 cm ²
There is no particular limitation as long as the above can be secured. Also,
When the applied voltage is measured on the basis of the natural potential, it is desirable to use an electrode provided with a reference electrode such as a lead electrode, a silver-silver chloride electrode, and a saturated calomel electrode. Without using a reference electrode,
Measurement is possible by measuring the potential difference between the electrodes.

The electrode used in the present invention is not particularly limited as long as a sufficient current flows, but an electrode processed with a material such as platinum or titanium is preferable from the viewpoint of durability and the like. Further, the shape of the electrode is not particularly limited, but it is preferable to use a linear or planar material that is electrochemically stable, and the surface area of the electrode is 1 mm ² or more for the purpose of improving the current flow. preferable. When inspecting the corrosion state of steel in concrete by using two or more main detecting ends, the distance between the main detecting ends is preferably 5 cm to 50 m, and 20 cm to 3 m.
0 m is more preferable. If the distance is less than 5 cm, the current that should originally flow between the concrete surface and the steel material does not pass through the steel material and may flow bypassing the concrete surface or the concrete surface layer. In some cases, the influence of the electrical resistance of the steel material is included in the measured value as an error, or the contact resistance between the steel materials is large, making the measurement impossible.

Next, the potentiostat and the galvanostat will be described. The detection end is connected to a potentiostat or a galvanostat by a conducting wire.
A potentiostat is a device that conducts electricity by voltage control, and a galvanostat is a device that is generally used as a device that conducts electricity by current control.When using these devices in the present invention, an AC output voltage, Alternatively, it can be used if the maximum value of the AC detection voltage is about 50 mV and the AC output current or the maximum value of the AC detection current is about 100 mA. When a reference electrode is used, it is desirable to use a four-electrode system, that is, an apparatus having two current supply terminals and two voltage detection terminals.

Next, the frequency analyzer will be described. The potentiostat or galvanostat is controlled by a frequency analyzer. A frequency analyzer is a device generally used as a device for giving an output command to a potentiostat or a galvanostat, and its AC output is a sine wave or a square wave having a control frequency of 1 Hz or less to 100 Hz or more. If possible, anything can be used.

Next, a measuring method will be described. At the time of measurement, in order to stabilize the electrical state of the concrete surface, it is preferable that the concrete surface is wetted with tap water or a calcium hydroxide solution before the measurement.
In this state, all the devices are connected, and the detection end is brought into contact with the concrete surface.
An AC voltage of 50 mV is applied. Compared with the conventional AC impedance method using a wire connection method to a reinforcing bar, when two measuring ends are used in the present invention, the current path is doubled, so that a voltage approximately twice as large as a normal voltage is applied. Need. Measurement is possible by using at least two types of frequencies.

An example of how to give a frequency will be described. First, when the voltage VL is applied using the low frequency HL and the current IL flows, the electric double layer capacitance has a large value as an impedance in the equivalent circuit of FIG. 1, so that Rp and Rs act as an impedance. , IL flow through most of the paths. Next, the voltage VH is applied using the high frequency HH, and the current I
When H flows, since the electric double layer capacitance has a small value as impedance, only Rs acts as impedance, and IH flows through almost all paths. When a very small HL and a very large HH are used, the concrete electric resistance Rs [Ω] can be obtained as about EH / IH in FIG. 1, and the polarization resistance Rp [Ω] can be obtained as about EL / IL-EH /
It can be obtained as IH. By taking into account the diameter of the reinforcing bar and the thickness of the cover, the unit can be converted into concrete electric resistivity [Ω · cm] and polarization resistance [Ω · cm ² ]. Since the impedance due to the electric double layer capacitance is given by 1 / (2πfC), where f = frequency and C = electric double layer capacitance, if the frequency is low, it is better to use the lowest possible frequency Although the accuracy of the measurement is improved, the lower the frequency, the longer the measurement time is required. Therefore, practically, it is desirable to use about 0.01 to 1 Hz. As the high frequency, the higher the order of the frequency, the better the measurement accuracy. However, if the frequency is too high, radio wave leakage will occur.
0 kHz is practical.

In the present invention, when the measurement result is a two-point measurement,
The polarization resistance and the concrete electric resistance become the combined polarization resistance and the combined concrete electric resistance added as a series circuit.

Next, a method for obtaining the polarization resistance and the concrete electric resistance of each point will be described. The result obtained in claim 1 is that, in the case of two-point measurement, two-point polarization resistance,
This method is insufficient when the concrete electric resistance is a combined value and it is necessary to obtain the polarization resistance and the concrete electric resistivity at each measurement point. Therefore, in the present invention, the measurement is performed between arbitrary measurement points such as between point A and point B, between point B and point C, and between point C and point A by the method used in claim 1. Measured values between point A and point B are AB and point B
Assuming that the measured value between points C is BC and the measured value between points C and A is CA, the polarization resistance and concrete electric resistance at point A can be calculated as (AB-BC + CA) / 2. B,
The same applies to point C. Based on the measured value at point A obtained by the calculation, the composite polarization resistance and the synthetic concrete electrical resistance with any measurement object other than point A are measured, and the value at point A is subtracted from the measured value to obtain an arbitrary value. Point polarization resistance,
Find the electrical resistance of concrete. For example, when the polarization resistance and concrete electric resistance between points A and D are measured with reference to point A, simply subtract the polarization resistance and concrete electric resistance at point A, which is the reference point, from these measured values. D
Polarization resistance and concrete electric resistance of a point alone can be obtained. This series of operations and unit conversion can be automated by a computer.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments, but the present invention is not limited to these embodiments. Example 1 A detection end as shown in FIG. 2 was manufactured, and a measurement of a composite polarization resistance and a composite concrete electric resistance of a bottom portion of a reinforced concrete drainage treatment tank which is a single metal distribution having a depth of 2 m, a width of 5 m, and a depth of 7 m was made. Was done. In the measurement, the liquid in the wastewater treatment tank was drained immediately before the measurement, and the measurement was performed in a state where there was no pool water and the concrete surface was wet. Since the factory where this treatment tank is located uses industrial salt as a raw material for products, the wastewater contained chlorine. Therefore, the concrete contained salt, and the rebar was in a corrosive environment. First, in the measurement, the position of the reinforcing bar and the diameter of the reinforcing bar were measured using a reinforcing bar probe (Profometer 3 of Prosec, Switzerland). According to the result of the measurement, the diameter of the reinforcing bar and the cover thickness at each point described below were the same. As a detection end, a saturated solution of calcium hydroxide was used as an electrolyte solution, the material impregnated with a water retention material (gauze) was placed in a plastic cylinder, and a titanium mesh (Titanium mesh, type Elgard, type 210) was incorporated as an electrode. Were prepared. Using a saturated silver chloride inner electrode as a reference electrode (HS-205 manufactured by Toa Denpa Kogyo KK)
C) was placed on a water-retaining material (gauze) using two pieces, and used as a reference potential. A lead wire of a potentiostat (HA-150G, manufactured by Hokuto Denko KK) was connected to the electrode and the terminal of the reference electrode. The electrode of one detection end a and the reference electrode are C, R
Connect the E terminal, connect the WE1 and WE2 lead wires to the other electrode of the detection end b and the reference electrode with a lead wire with an alligator grip, and connect the detection ends to points A and B on the concrete surface 3 m away. installed. By operating a frequency analyzer (Hokuto Denko FRA 5080) connected to the potentiostat, first, a voltage 3 with a sine wave frequency of 0.001 Hz
0 mV was applied and the current was measured. According to the result of the measurement, the diameter of the reinforcing bar and the cover thickness at each point described below were the same. Next, a voltage 3 having a sine wave frequency of 1 kHz
0 mV was applied, and the synthetic concrete electric resistance and the synthetic polarization resistance were obtained as EH1 / IH1 and EL1 / IL1-EH1 / IH1, respectively. As a result, the synthetic polarization resistance and the synthetic concrete electric resistance were 1.0 kΩ and 2.0 kΩ, respectively.

REFERENCE EXAMPLE 1 Only one detecting end a is used, and the reinforcing bar to be measured is
The measurement was carried out in the same manner as in Example 1 except that the WE1 and WE2 terminals of the potentiostat were connected in the range of 15 cm × 15 cm. First, when the polarization resistance and concrete electric resistance at point A were measured, the polarization resistance and concrete electric resistance were 0.5 kΩ and 0.9 kΩ, respectively.
Met. Next, when the polarization resistance and the concrete electric resistance at the point B were measured, the polarization resistance and the concrete electric resistance were 0.5 kΩ and 1.1 kΩ, respectively.

Example 2 In the method of Example 1, the point C, which is 3 m away from the point A and point B respectively, the point A and point B, the point B and point C, and the point C and point C, the combined polarization resistance and the combination Concrete electrical resistance was measured.
Table 1 shows the results.

[Table 1] The polarization resistance at each point is calculated as follows: [1.0 (between AB points)-1.1 (between BC points)
+1.1 (between CA points)] / 2 = 0.5 kΩ For point B, [1.1 (between BC points) -1.1 (between CA points)
+1.0 (between AB points)] / 2 = 0.5 kΩ For point C, [1.1 (between CA points) -1.0 (between AB points)
+1.1 (between BC points)] / 2 = 0.6 kΩ, and the concrete electric resistance of each point A was calculated as follows: [2.0 (between AB points)-2.0 (between BC points)
+1.8 (between CA points)] / 2 = 0.9 kΩ For point B, [2.0 (between BC points) -1.8 (between CA points)
+2.0 (between AB points)] / 2 = 1.1 kΩ For point C, [1.8 (between CA points)-2.0 (between AB points)
+2.0 (between BC points) /2=0.9 kΩ. Table 2 summarizes these results.

[Table 2] As a result, the corrosion state in the concrete from the polarization resistance value was large at points A, B and C. Also, the corrosion state in concrete from the concrete electric resistivity value is A,
Both points B and C were significantly corroded. This result is consistent with the result obtained by the conventional method, and the evaluation judgment is credible (see Reference Example 2).

REFERENCE EXAMPLE 2 The polarization resistance and concrete electric resistance at points A, B and C of Example 2 were measured by the method of Reference Example 1. Table 3 shows the results.

[Table 3]

[0028]

According to the present invention, in the AC impedance method, it is not necessary to connect a conducting wire to a part of the steel material in the concrete. Therefore, the hanging operation and the coring operation for exposing the steel material as in the conventional method are required. Can be omitted, and the corrosion state of the steel material in the concrete structure can be evaluated nondestructively. Therefore, there is an advantage that the labor can be reduced and the destruction of the concrete structure is not required.

[Brief description of the drawings]

FIG. 1 is an electric circuit of concrete electric resistance, polarization resistance, and electric double layer capacitance by an AC impedance method.

FIG. 2 shows a measuring device used in Examples 1 and 2.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 concrete 2 steel 3 polarization resistance R _p 4 concrete resistance R _s 5 electric double layer capacity C 6 electrode 7 reference electrode 8 water retention material 9 plastic cylinder 10 potentiostat or galvanostat 11 frequency analyzer

Continuation of the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) G01N 27/00-27/26 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A method of detecting corrosion of a steel material in concrete by contacting two or more steel material corrosion detection ends provided with electrodes to the concrete surface and passing an alternating current between the electrodes to detect a point of corrosion of the steel material in the concrete. For three points B, C, and reference point A, measure impedance in three paths of AB, BC, and CA, and measure single polarization resistance at reference point A or single concrete electric resistance at reference point A. A method for detecting a corroded portion of steel material in concrete, characterized in that: 2. At least two steel corrosion detecting terminals provided with electrodes.
Contact the concrete surface and apply an alternating current between the electrodes.
Method of detecting corrosion of steel in concrete
At point B, point C, and the reference point on the concrete surface
For three points A, three paths AB, BC, and CA
The impedance at the reference point A.
Pole resistance or single concrete electrical resistor at reference point A
Measuring the resistance of steel in concrete
Using the corrosion point detection method, a single polarization resistance or
Measures the electrical resistance of a single concrete at reference point A
An AC current is supplied to a path AD connecting the reference point A and the measurement point D.
Flushed, the polarization resistance or concrete electric resistance in the path AD is determined, the corrosion of steel in concrete, characterized in that to calculate the concrete electric resistance of the sole in the polarization resistance or measurement point D alone at the measurement point D Location detection method.