JPH0812168B2 - A method for measuring the polarization resistance of rebar in concrete. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to the polarization resistance of concrete, which is an important parameter for diagnosing corrosion due to salt damage of reinforcing bars in reinforced concrete (RC) structures. Regarding the measurement method,
Specifically, the absolute evaluation of the corrosion state and the corrosion rate is obtained by obtaining the measured polarization resistance value as a resistance value per unit area, which is measured by passing an electric current between the sensor installed on the concrete surface and the reinforcing bar. The present invention relates to a method for measuring polarization resistance in concrete, which enables the improvement of diagnostic accuracy.

[Prior Art] Conventionally, a method of using polarization resistance has been often used as a method of monitoring the corrosion rate of metals. Polarization resistance is used for diagnosing corrosion due to salt damage of reinforcing bars in a reinforced concrete structure. But it is an important parameter. As a method of measuring polarization resistance in concrete, for example, the 6th Annual Conference of Concrete Engineering Lecture Meeting No. 52 (1
(984), using a two-pole probe including a counter electrode and a reference electrode installed on the concrete surface and a polarization ohmmeter, and applying a current between the two-pole probe and the reinforcing bar in the concrete. There are known methods to do so. In the case of the measuring method shown here, the corrosion resistance of the reinforcing bar is diagnosed using the measured polarization resistance as it is without limiting the area to be measured.

[Problems to be Solved by the Invention] However, since the actual measured value of the polarization resistance is not the original value per unit area of the polarization resistance as described above, the measured actual value of the polarization resistance is used as it is to perform an absolute evaluation of the corrosion state. It was not possible, and only relative estimation under the same geometric boundary conditions was possible.

In view of such drawbacks of the prior art, the object of the present invention is to
It is an object of the present invention to provide a polarization resistance measuring method for reinforcing bars in concrete, which requires a normalized polarization resistance per unit area, which is indispensable for absolute evaluation of corrosion conditions.

[Means for Solving the Problems] FIG. 1 is a flow chart illustrating the procedure for measuring the polarization resistance of a reinforcing bar in concrete by the method of the present invention.

As shown in the figure, the method for measuring the polarization resistance of the present invention is such that an electric current is passed between a sensor including a counter electrode and a reference electrode installed on a concrete surface just above a surface reinforcing bar in concrete and the reinforcing bar in concrete. , The step of measuring the polarization resistance R _P and the environmental resistance R _S at that time (Step 1
And 2), and a predetermined ratio of the total current flowing between the sensor and the reinforcing bar, preferably 70%, is the cover thickness h from the center of the sensor.
As what flows to the surface rebar contained in the circle of radius of
Apparent polarization resistance per unit area from the measured polarization resistance R _P
Obtaining R _C 'and obtaining a (Step 3), and obtaining a resistivity ρ than the environmental resistance R _S (step 4), the polarization resistance R _C of the apparent' a and polarization parameters L _ap resistivity ρ Karamikake In the step (step 5), a predetermined ratio, preferably 70%, of the total current flowing between the sensor and the reinforcing bar is calculated as the reinforcing bar area calculation length as that which flows to the surface reinforcing bar included in the circle of radius X from the sensor center. Using an empirical formula that preliminarily obtained the relationship between the value l ^* / h divided by the cover thickness and the value h / L obtained by dividing the cover thickness h by the polarization parameter L, the apparent polarization was substituted for the polarization parameter L. A process of obtaining the polarization resistance R _C per unit area from the measured polarization resistance R _P using the parameter L _ap (step 6)
It has and.

Further, in the process of step 6, the distribution of the current flowing between the sensor and the reinforcing bar is regarded as the primary distribution depending on whether the value obtained by dividing the covering thickness h by the polarization parameter _Lap exceeds a predetermined value, preferably 5, or Two
The step of deciding whether to regard it as the secondary distribution (step 6a), and the step of setting the apparent polarization resistance R _C ′ as the true polarization resistance R _C per unit area when the current distribution is regarded as the primary distribution (step 6b). And when the current distribution is regarded as a quadratic distribution, a process of obtaining a true polarization resistance R _C per unit area using the empirical formula, the cover thickness h and the apparent polarization parameter L _ap (step
6c) and are preferably included.

Here, the primary current distribution is a current distribution that is determined only by the geometrical shape of the system. In this system, as a way of thinking for calculating the polarization resistance, almost 70% of the current flowing between the electrode and the reinforcing bar is used.
% Is a current distribution that flows to the surface rebar within the radius h (cover thickness) centered on the sensor. Also, 2
The secondary current distribution is a current distribution in which the polarization parameter L should be taken into consideration in addition to the geometrical condition of the system. The current distribution is such that 70% of the current flows to the surface rebar contained in the interior.

The measured polarization resistance R _P and the environmental resistance R _S in steps 1 and 2 are, for example, the impedance when a current of 0.01 Hz is applied between the sensor and the reinforcing bar, that is, the sum of the polarization resistance and the environmental resistance (R _P + R _S ) It can be obtained by measuring the impedance when a current of 10 KHz is applied, that is, the environmental resistance R _S.

The resistivity ρ in step 4 is determined by the environmental resistance R _S using, for example, the formula shown in Table 1 which is experimentally obtained in advance.
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In step 6 or step 6c, when obtaining the true polarization resistance R _C , it is necessary to know the polarization parameter L, but this value is known as the polarization resistance R _C to be originally obtained from the relationship of L = R _C / ρ. It is a value that cannot be obtained without it. Therefore, in the present invention, the apparent polarization parameter L _ap is obtained using the apparent polarization resistance R _C ′, and the true polarization resistance R _C is obtained using this. Therefore, when the polarization parameter L is large, the polarization resistance is evaluated to be small. However, this error increases in the environment of concrete almost corresponding to the increase of the polarization resistance R _C , and can be considered to be on a rust-free reinforcing bar with a low corrosion rate. If accuracy is particularly required in determining the corrosion state and the corrosion rate, it is a portion where the corrosion rate is large, and even if an error occurs in a portion where the corrosion rate is small and the corrosion rate is small, it does not cause much problem.

The reason why the polarization resistance is obtained by paying attention to the region in which approximately 70% of the total current flows in step 3 or 6 is as follows. That is, considering the homogeneity of the current distribution and the accuracy of the information, it is desirable to reduce the reinforcing bar area as much as possible, but if it is made extremely small, the current distribution has a direction dependency, making it difficult to evaluate the energizing current. Because,
This is because if the area is made large, the problem arises that the inhomogeneity of the current distribution increases.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

In order to obtain the empirical formula used in step 6 of FIG. 1 in advance, it is necessary to investigate the relationship between the polarization parameter L and the region where 70% of the total current flows. It can be examined using an experimental apparatus for carrying out the resistance measuring method.

In the figure, 8 is a water tank, 9 is an aqueous solution in the water tank 8 adjusted to have a predetermined resistivity ρ, and 10a and 10b are 16φ × arranged in the aqueous solution 9 in a grid pattern so as to have a constant water fog h.
950 mm upper and lower rebar (round steel). The water cover h is set based on the upper end of the upper reinforcing bar 10a. Reference numeral 11 is a 30φ disc electrode installed at a measurement point on the liquid surface just above the reinforcing bars 10a and 10b. As shown in FIG. 8, the disc electrode 11 includes a counter electrode 12 and a reference electrode 13, and the lower surface of the counter electrode 12 is a test surface 14.

In this configuration, low frequency (0.05Hz) and high frequency (1KHz) currents were passed between the disk electrode 11 and the reinforcing bars 10a and 10b to measure the polarization resistance R _P under the following experimental conditions. .

Water cover h: 10,8,6,4,2cm Rebar spacing l ₁ ＝ l ₂ : 10,20,30cm Resistivity of aqueous solution ρ: 150 to 1000Ω ・ cm 3 types from measurement point: Rebar intersection (x = 0), above the upper rebar (l ₁ /
2), also on the lower reinforcing bars (l _2/2), as shown in FIG. 9, instead of the disk electrode 11,
The mesh electrode 15 for homogenizing the current distribution is installed on the liquid surface, and under the same conditions as above, the matching electrode 16 is positioned near the reinforcing bar immediately below each of the above measurement points, which results in the polarization resistance at each measurement point. (R _P ′) was measured. Then, the value obtained by multiplying the polarization resistance value (R _P ′) at each of these measurement points by the total rebar area in the water tank 8 is taken as the true polarization resistance R _C at each measurement point and compared with the above-mentioned measured polarization resistance R _P. investigated.

Here, the comparative correspondence between R _P and R _C is handled as follows.

That is, the polarization resistance R _P measured by the disk electrode 11
In order to obtain the true polarization resistance value R _C per unit area from R _p , the reinforcing bar area S determined by the boundary conditions should be multiplied by R _P.
Therefore, the rebar area calculation length l ^* can be obtained by the following equation, where the rebar diameter is D.

The following data of l ^* thus obtained were excluded from the final analysis.

Data measured within 10 cm from the insulating wall of the water tank 8 Data measured just above the lower rebar 10b
This is because the current distribution is affected by the insulation wall in the case of, and in the case of, the calculated length of the reinforcing bar area at the reinforcing bar intersection is
l _C ^*, rebar area calculating length just above one rebar and l _S ^*, as can be seen from the graph of FIG. 10 showing the relationship between the ^{_{(l S * -l C *)}} / h and h / D This is because, when the cover thickness h is small, the value measured on the lower reinforcing bar 10b is different from the value at other places (on the intersection or on the upper reinforcing bar).

In addition, the results shown in Fig. 10 are for the upper and lower rebar intersections.
It shows that there is no difference in the value of the rebar area calculation length l ^* on 10a and above, and from the viewpoint of rebar area calculation only the upper rebar should be considered as the measurement target.

FIG. 11 is a graph showing the relationship between l ^* / h and h / L in consideration of the above.

As shown in the figure, the value l ^* / h obtained by normalizing l ^* with h is
It can be neatly organized as a function of h / L.

Further, the regression function is G (x) = αx ^b , where G (x) = l ^* / hx: h / L a: 4.20906 b: −0.372397.

On the other hand, the same study was also conducted by an experiment using conductive paper. However, as shown in FIG. 2, the reinforcing bars 1 in the concrete are arranged in a grid pattern, and the sensor 2 is installed on the concrete surface directly above the reinforcing bar (surface reinforcing bar) closer to the surface. The analysis used was 2
Since it is treated as a dimensional problem, as shown in FIG. 3, a cross section cut in the longitudinal direction of the reinforcing bar immediately below the sensor in a plane including the center of the sensor 2 and perpendicular to the concrete surface is used as the geometric boundary condition for this conductive paper analysis. .

FIG. 4 shows boundary conditions on the conductive paper in which the polarization parameter L is also taken into consideration. However, considering the symmetry of the system, only the left half is treated. In the figure, 3 is a conductive paper simulating concrete, 4 is an electrode corresponding to a sensor (diameter a) installed on the concrete surface, and 5 is a reinforcing bar in the concrete. Reference numeral 6 is a constant voltage device for applying a constant voltage between the electrodes 4 and 5. The conductive paper 3 is provided with slits 7 having a constant width and length in a direction perpendicular to the reinforcing bar 5 as a portion corresponding to polarization resistance. If the resistivity of the concrete is ρ, the length L of the slit 7 corresponds to the polarization parameter L from the relationship of L = R _C / ρ. The dimension h in the figure corresponds to the cover thickness of the reinforcing bar.

In this configuration, the constant voltage device 6 is used to connect I and
Apply V voltage and examine the current distribution. If the distance from the right edge of the conductive paper is represented by X, and the value that normalizes the distance through which 70% of the total current flows by h is X / h (F = 70), X / h (F =
70) can be arranged as a function of h / L as shown in Fig. 5.

The curve in the figure is a curve showing the regression function f (t) = αt ^b where f (t): X / h (F = 70) t: h / L a: 1.53009 b: −0.32419.

On the other hand, the value X / (h + √L) (F = 70) obtained by normalizing the distance that 70% of the total current flows by (h + √L) is shown as a function of h / L. It becomes almost 1 regardless of the parameter, and it can be seen that the region where 70% of the total current flows is represented by h + √L.

Considering that the conductive paper analysis handles only half of the system, the regression function f (h / L) obtained by the conductive paper analysis is G (h
/ L) is very close. This shows that the rebar area to be considered when measuring the rebar polarization resistance inside the concrete can be approximated by the two-dimensional model as shown in Fig. 3 by the disc electrode placed on the concrete surface directly above the surface rebar.

Therefore, the rebar area evaluation range obtained from the conductive paper analysis results Think in It is also effective to use for calculating the polarization resistance.

FIG. 12 is a graph showing the results calculated using the regression function G (h / L) obtained in FIG. 11, and FIG. 13 is 8 is a graph showing the correspondence between the polarization resistance R _C ^ca1 calculated as and the measured value R _C ^obs . As can be seen from these figures, the degree of variation between the two data does not change much.

FIG. 14 is a graph showing the correspondence between the polarization resistance value obtained by the method described above and the actual corrosion state for an actual structure. As shown in the figure, the polarization resistance values were all 80 KΩ · cm ² or less at the places where some evidence of corrosion including slight corrosion was observed.

Fig. 15 shows the correspondence between the polarization resistance value measured by the above method and the finally rusted test piece for mild steel pieces (area determined) buried in various salt concentration mortars. It is a graph. Rust was observed on the test piece whose polarization resistance value was 80 KΩ · cm ² or less. This is in agreement with the threshold value for the presence or absence of rust in the actual structure, and indicates that there is no great error in the method of calculating the polarization resistance.

Since the true polarization parameter L is unknown in the measurement of the polarization resistance in the actual structure, the polarization resistance R _C ′ in the primary current distribution is taken as the apparent polarization resistance and R _C ′ is obtained from the environmental resistance measurement value. The polarization resistance was calculated using the value L _ap (apparent polarization parameter) divided by ρ.

[Effects of the Invention] As described above, according to the present invention, since the polarization resistance as a resistance value per unit area is obtained based on the actual measurement value of the polarization resistance, the absolute value of the corrosion state and the corrosion rate is used by using this value. The evaluation can be performed and the evaluation accuracy is improved.

[Brief description of drawings]

FIG. 1 is a flow chart illustrating a procedure for measuring polarization resistance of reinforcing bars in concrete by the method of the present invention, FIG. 2 is a plan view showing arrangement of reinforcing bars in concrete, and FIG. 3 is a sensor center. Cross-sectional view cut in the longitudinal direction of the reinforcing bar immediately below the sensor in a plane perpendicular to the surface of the concrete including the surface, Fig. 4 is a schematic diagram showing the boundary conditions on the conductive paper considering the polarization parameter L, and Fig. 5 is X / h. A graph showing (F = 70) as a function of h / L, and FIG. As a function of h / L, FIG. 7 is a schematic diagram showing an experimental apparatus for carrying out the method for measuring polarization resistance according to one embodiment of the present invention, and FIG. 8 is the apparatus shown in FIG. FIG. 9 is a perspective view showing a configuration of a disc electrode used, FIG. 9 is a schematic diagram showing a state in which a mesh electrode for homogenizing a current distribution is installed on the liquid surface in place of the disc electrode of FIG. Fig. 10 is a graph showing the relationship between the calculated length of the reinforcing bar area at the intersection of the reinforcing bars, the calculated length of the reinforcing bar area directly above one reinforcing bar, the cover thickness and the diameter of the reinforcing bar, and Fig. 11 shows l ^* / h and h / L Fig. 12 is a graph showing the result of polarization resistance obtained by using the regression function G (h / L) obtained in Fig. 11, Fig. 13 is a rebar calculation length. A graph showing the correspondence between the polarization resistance R _C ^ca1 calculated as and the measured value R _C ^obs, and FIG. 14 shows the correspondence between the polarization resistance measured by the method of the present invention and the actual corrosion state for the actual structure. The graphs shown in FIG. 15 and FIG. 15 are graphs showing the correspondence between the polarization resistance values measured using test pieces of known area and the test pieces that finally rusted. 1: Reinforcing bar, 2: Sensor, 3: Conductive paper, 4,5: Electrode, 6: Constant voltage device, 7: Slit, 8: Water tank, 9: Aqueous solution, 10a: Upper rebar, 10
b: Lower rebar, 11: Disc electrode, 12: Counter electrode, 13: Reference electrode, 14:
Test surface, 15: mesh electrode, 16: reference electrode.

Claims (2)

[Claims] 1. A current is passed between a sensor including a counter electrode and a reference electrode installed on a concrete surface directly above a surface reinforcing bar in concrete and the reinforcing bar in the concrete, and polarization resistance and environmental resistance at that time are measured. The process, the current of a predetermined ratio of the total current flowing between the sensor and the reinforcing bar, as flowing from the sensor center to the surface reinforcing bar contained in the circle of the covering thickness radius, from the measured value of the polarization resistance unit area The step of obtaining the apparent polarization resistance per hit, the step of obtaining the resistivity from the environmental resistance, the step of obtaining the apparent polarization parameter from the apparent polarization resistance and the resistivity, of the total current flowing between the sensor and the reinforcing bar. The predetermined proportion of the current was calculated as the current flowing through the surface rebar contained within the predetermined radius from the sensor center, and the rebar area calculation length was divided by the cover thickness. By using an empirical formula in which the relationship between the value and the value obtained by dividing the fog thickness by the polarization parameter was obtained in advance, the apparent polarization parameter was used in place of the polarization parameter, and the polarization per unit area was calculated from the measured polarization resistance value. A method for measuring polarization resistance of reinforcing bars in concrete, the method comprising: determining resistance. 2. The step of obtaining the polarization resistance per unit area determines the distribution of the current flowing between the sensor and the reinforcing bar as 1 depending on whether the value obtained by dividing the cover thickness by the apparent polarization parameter exceeds a predetermined value. The process of determining whether it is considered to be the secondary distribution or the secondary distribution; the process of determining the apparent polarization resistance as the true polarization resistance per unit area when the current distribution is considered to be the primary distribution; The method of determining the polarization resistance per unit area using the empirical formula, the cover thickness and the apparent polarization parameter when regarded as a quadratic distribution. Method.