JPH0796717B2 - Reference electrode for maintenance of cathodic protection and cathodic protection method using the same - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a reference electrode for favorably maintaining and controlling the cathodic protection state of a steel material in a reinforced concrete structure and a cathodic protection method using the same, and in particular, It is assumed that the reference electrode is limited to the same steel material as the corrosion-resistant steel material and that a current barrier cover for preventing the influence of the corrosion-resistant current is provided, and with reference to this, the potential of the corrosion-resistant steel material is a proper standard from its natural potential. The present invention relates to a reference electrode for maintenance and management of cathodic protection, which enables simple and economical maintenance and management by a shift value, and a cathodic protection method using the same.

[Prior Art] It was thought that the reinforcing bars in a concrete structure form a solid passive film on the reinforcing bar surface due to the alkalinity of the concrete itself, and corrosion cannot occur. However, in recent years, due to lack of cover thickness, deterioration of various environments, deterioration of quality of aggregate used, etc., the neutralization of concrete and the increase of salt concentration have progressed more than expected, causing corrosion of rebar and causing structural damage. It has been found to reduce function.

As measures against the corrosion of the reinforcing bars of such concrete structures, there are paints for the purpose of blocking from the bad environment, concrete coating method with resin, etc. Although the construction method or rebuilding to a new structure has been done, it is often impossible to rebuild it economically and physically, and both methods fundamentally prevent the corrosion of the reinforcing bar. Has not yet reached. Therefore, as a reinforcing bar anticorrosion method for concrete structures, an electrolytic protective method for supplying a corrosive protection current to the surface of the reinforcing bar has attracted attention.

In this cathodic protection method, conventionally, the following measurements have been performed in order to judge whether or not the reinforcing bars in the structure are in a corrosive protection state and perform maintenance management of the cathodic protection.

(1) Potential measurement and inflow current measurement of a concrete-embedded test piece that maintains electrical continuity with a reinforcing bar.

(2) Measurement of rebar potential with a reference electrode embedded in concrete.

(3) Measurement of rebar potential using a reference electrode provided on the outer surface of concrete.

(4) Measurement of corrosion resistance of the test piece of (1) above.

(5) Measurement of the resistance of the conducting wire when the test piece of (1) above is used as a wire.

Of the data obtained by these measurements, the most common and most reliable is the potential. Then, there are the following values as the reference value for controlling the corrosion prevention by this potential.

(1) Anticorrosion potential in the case of salt-containing concrete-420m
Vvs.SCE and −630 mVvs.SCE.

(2) Anticorrosion potential for concrete in general-770mVvs.SC
E.

(3) Potential that is baser than the pitting potential in the case of a healthy rebar.

(4) -100 mV shift value from the natural potential in the case of rusted reinforcing bars.

Based on these anticorrosion standard values, it is judged whether or not it is in an anticorrosion state, and maintenance and management of cathodic protection is performed. Of these, the most common and reliable one is the natural one shown in (4) above. It is said that the maintenance is based on the potential shifted by -100 mV from the potential.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional example, there is no established standard for knowing the anticorrosion effect, and there is a lack of data that is collated with the actual corrosion rate. That is,
It is difficult to determine which of the above potentials should be used as the anticorrosion standard because the reference electrodes used for the most frequently measured potentials are different and there are various potentials used as anticorrosion standards. Is. In addition, there is a problem that the galvanic protection circuit must be cut off for a long time in order to measure the polarization value of the reinforcing bar. Further, at the time of measuring the electric potential, it is necessary to embed the verification electrode in the concrete in advance at a place where it is difficult to measure from the concrete surface, for example, at a place where a person such as the back surface of the floorboard cannot enter. There is also a problem that there is no reference electrode that always maintains a stable potential in concrete.

The object of the present invention is to solve the problems of the conventional art.
Spontaneous potential of corrosion-resistant steel in reinforced concrete structures can be measured successively and continuously without interruption of corrosion current, and economically effective maintenance control of corrosion current within a certain range based on a reasonable reference shift value from the measured value. It is an object of the present invention to provide a reference electrode for maintenance and management of cathodic protection and a method of cathodic protection using the same.

[Means for Solving the Problems] In order to achieve the above object, a reference electrode for maintenance of cathodic protection of the present invention is a steel material electrode embedded in a reinforced concrete structure and a steel electrode covering the electrode in the reinforced concrete structure. It is provided with a current barrier cover for preventing the influence of the anticorrosion current provided to the anticorrosion steel material, and in the cathodic protection method of the present invention, refer to the reference electrode for cathodic maintenance control, and the potential of the anticorrosion steel material. Is polarized to be 50 mV or more lower than the potential of the reference electrode.

[Operation] In this configuration, the self-potential of the steel to be protected fluctuates with time due to changes in the environment, but the reference electrode buried in the environment in a concrete structure similar to the steel to be protected is the same as the steel to be protected. Since it is a steel material and is covered with a current barrier cover, the natural potential changes like the corrosion-resistant steel material.
Therefore, the natural potential of the reference electrode sequentially represents the natural potential of the corrosion-resistant steel material according to environmental changes, and the measurement is performed without interrupting the corrosion protection current. Furthermore, the present inventors have found that in making the present invention, if the corrosion-resistant steel material is cathodically polarized by at least 50 mV from its natural potential, the corrosion rate can be made substantially zero with respect to the actually assumed salt concentration. Therefore, economical electrocorrosion is performed by maintaining and controlling the potential of the steel to be protected against the potential of the reference electrode so as to be polarized with 50 mV as the minimum standard.

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

FIG. 1 is a schematic sectional view showing the structure of a matching electrode according to an embodiment of the present invention. As shown in the figure, this reference electrode is provided with an iron electrode 1 and a current barrier cover 2 that covers the iron electrode 1 leaving a partially open portion, and the concrete electrode when viewed from a concrete surface (cathodic protection surface) 5. It is buried at a position shallower than the first reinforcing bar 4 in 3 or at the same level.
The iron electrode 1 and the current barrier cover 2 are insulated from each other by an insulating material 6, and the open portion of the barrier cover 2 is filled with mortar 7, which is in contact with the concrete 3. A lead wire 8 from outside the concrete is connected to one end of the iron electrode 1.

The iron electrode 1 is made of a steel material having a round bar shape, a disk shape, or the like, and a synthetic resin pipe such as vinyl chloride can be used as the current barrier cover 2. The mortar 7 may be concrete.

In this configuration, the reinforcing bar 4 is supplied with anticorrosion current by means (not shown) to perform galvanic protection, while the natural potential of the reinforcing bar 4 changes due to environmental changes such as salt concentration of the concrete 3. Further, since the iron electrode 1 is also filled with mortar 7 so as to be sensitive to salt intrusion and is located at a shallower level than the reinforcing bar 4, it is sensitive to environmental changes under the same conditions, and the natural potential is the same as that of the reinforcing bar 4. Fluctuates. Therefore,
By referring to the natural potential of the iron electrode 1 through the lead wire 7, and performing maintenance so as to polarize the potential of the reinforcing bar 4 to 50 mV or more, preferably about 100 mV from the natural potential, as will be described later, Effective cathodic protection is provided. In this case, since the iron electrode 1 is covered by the current barrier cover 2, the natural potential of the iron electrode 1 is not affected by the anticorrosion current, and therefore it is not necessary to interrupt the supply of the anticorrosion current to the rebar 4.

FIG. 2 is a graph showing the relationship between the shift value from the natural potential of the reinforcing bar and the corrosion rate at each salt concentration. The horizontal axis shows the corrosion rate (unit: mdd), and the vertical axis shows the shift value from the natural potential (unit: mV). However, a corrosion rate of 0 is 0.01m for convenience.
It is as dd.

The results of this graph were obtained by the present inventors for the first time in making the present invention, and sat.Ca (OH) ₂ aq. Was used as a concrete simulated aqueous solution, and the NaCl concentration was 0 to 30 Kg.
/ m ³ (0 to 1.4 wt%) in the range,
It was obtained by using two kinds of a round steel bar having a diameter of 13 mm and a length of 100 mm, a black-skin test piece (black-skin piece) and a pre-rusted test piece (corrosion streak).

From the graph in the figure, it can be seen that if the shift amount from the self-potential of the reinforcing bar is at least 50 mV in the base direction, the corrosion rate can be set to almost zero and a practically sufficient anticorrosion effect can be achieved. Also, considering the variation in the measured values, it can be seen that it is more perfect when shifting to the base method by 100 mV or more.

[Effect of the Invention] As described above, according to the present invention, the same material as the steel to be protected is used as the reference electrode, and a protective cover for the current barrier is provided on the reference electrode so as to be positioned in the cocrete in the same environment as the steel to be protected. Therefore, unlike the conventional case, it is possible to sequentially monitor the natural potential of the corrosion-resistant steel material with time and use it for maintenance management of the cathodic protection, without having to interrupt the cathodic protection circuit for a long time. Also, by adopting -50 mV as the reference shift value from the natural potential of the steel to be protected, it is not necessary for the reference electrode to always show a stable absolute value, and maintenance of economical cathodic protection based on the natural potential is not necessary. Can be managed.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of a reference electrode according to one embodiment of the present invention, and FIG. 2 is a shift from the self-potential of the reinforcing bar at each salinity concentration determined in the present invention. It is a graph which shows the relationship between a value and a corrosion rate. 1: Iron electrode, 2: Cover for current barrier, 3: Concrete, 4: Reinforcing bar, 5: Concrete surface, 6: Insulation material, 7: Mortar, 8: Lead wire.

Claims (2)

[Claims] 1. An electrode made of a steel material embedded in a reinforced concrete structure, and a current barrier cover for covering the electrode and for preventing an influence of an anticorrosion current supplied to an anticorrosion steel material in the reinforced concrete structure. , A reference electrode for maintenance and control of anticorrosion, which is used for maintenance and management of the potential of the steel to be protected under cathodic protection. 2. An electrocorrosion method for corroding an anticorrosion steel material by supplying an anticorrosion current to the anticorrosion steel material in a reinforced concrete structure, with reference to the reference electrode for maintenance of anticorrosion maintenance according to claim 1. An electrocorrosion method, characterized in that the electric potential of the anticorrosion steel material is made lower than the electric potential of the reference electrode and the minimum reference value is set to 50 mV to polarize.