JPS62263984A - Electrolytic protection method for concrete structure - Google Patents

Abstract

PURPOSE:To carry out the electrolytic protection of a structure extending over the air and an electrolyte at low current density by forming an electrically conductive coat on the surface of the structure so that part of electric current for electrolytic protection flowing in a reinforcing steel material in the electrolyte is allowed to flow in the steel material in the air through the coat. CONSTITUTION:An electrically conductive coat 2 is formed on the surface of a concrete pile 1 from the top to an average tide level. A galvanic anode 5 of an Al alloy or the like is fitted to the surface of the pile 1 in the sea with anchor bolts 6 so that the anode 5 is brought into electrical contact with an iron reinforcing rod 4. The coat 2 is coated with a sheathing material 8 having holes 7 through which electric current for electrolytic protection flows in the lower part. When the electrolytic protection of the iron reinforcing rods (reinforcing steel material) 4 in the pile 1 in the seawater (electrolyte) is carried out, part of electric current for electrolytic protection flowing in the rods 4 in the seawater is allowed to flow in the rods 4 in the air through the coat 2. By this method, the electrolytic protection of the rods 4 in the air can be uniformly carried out over a wide range.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention is applicable to concrete structures that use reinforcing bars or PCG materials as reinforcing steel materials that span the atmosphere and electrolyte, such as long bridges, bridges on coastal roads, and offshore plants. Concerning cathodic protection methods for forms, quays, piers, wave-dissipating facilities, etc.

(Conventional technology) Reinforced concrete structure (hereinafter referred to as RC structure)
Due to the combination of superior materials such as concrete and steel, it has been considered a semi-permanent structure that is structurally robust and requires no upkeep or maintenance. However, in RC structures in the marine environment, a large amount of salt contained in seawater spray and sea breeze comes flying in, and if it adheres to it, it can damage the concrete.
Internal: It has been found that it penetrates and corrodes internal reinforcing steel. In addition, even in RC structures in the atmospheric environment, the neutralization of concrete 1 is progressing due to the influence of exhaust gas from automobiles and factories, and furthermore, due to the increase in salt content in concrete 1 due to the use of sea sand. An accident occurred in which the reinforcing steel corroded and swelled, causing concrete to fall off, and was widely reported in the media.

Traditionally, anti-corrosion measures for such RC structures include hot-dip galvanizing the reinforcing bars, or adding anti-rust materials as an admixture when mixing concrete to create a strong oxide film on the reinforcing bars. For example, for RC structures in seawater, cathodic protection methods using a galvanic anode method or external power supply method are used, and for RC structures in the atmosphere, cathodic protection methods are used. It has been introduced in foreign literature that cathodic protection is effective, in which the surface of a material is coated with conductive paint and a platinum wire electrode connected to a DC power supply is embedded in the surface to supply a protective current.

[Problem that the invention seeks to solve]

However, although the above-mentioned galvanizing method has sufficient corrosion resistance in the presence of a low concentration of salt, there is a great risk that the reinforcing bars will corrode in the presence of a higher concentration of salt or in areas where cracks have been reached. In addition, the method using a rust preventive agent can be dangerous if the usage standards are not fully observed, such as pitting corrosion on reinforcing bars if the amount of the rust preventive agent added is less than the amount required for corrosion prevention. It turns out. Furthermore, the conventional cathodic protection method has the limitation that it can only be carried out in places where power is available for RC structures in the atmosphere.
It must be said that it is extremely uneconomical to install electrodes in the atmosphere and in seawater and design and construct corrosion protection separately for the same structure.

This invention solves the above-mentioned problems of the conventional ones, and allows concrete to be used in both the atmosphere and the electrolyte.
An object of the present invention is to provide a method for cathodic protection of a concrete structure, which enables economical cathodic protection by applying a low corrosion protection current density throughout the structure.

Means for Solving the Problem] To achieve this object, the present invention has the following configuration.

That is, the cathodic protection method for concrete 1/structures according to the present invention covers at least a part of the structure in the electrolyte and the surface of the structure in the atmosphere that is continuous with the electrolyte, and also coats the structure in the electrolyte with a conductive coating. By electrolytically protecting the reinforcing steel of the structure, a part of the corrosion protection current flowing into the reinforcing steel in the electrolyte flows into the reinforcing steel in the atmosphere via the conductive coating.

[For production]

In the cathodic protection method configured as described above, the corrosion protection current i due to cathodic protection directly passes through the concrete 1 layer in the electrolyte and flows into the reinforcing steel material, thereby maintaining the surface in a good corrosion protection state. In this case, it is known that the current density required for corrosion protection can be quite small, approximately one-tenth or less of that for bare steel in seawater, since the current is passed through the concrete layer. On the other hand, some anticorrosion current i,
Once it flows into the outer surface of the conductive coating in the electrolyte, it passes through the atmosphere and the concrete layer in the electrolyte in the vicinity and flows into the reinforcing steel material, giving a uniform potential distribution to the surface.

Since the conductive coating acts as a distributed current pole over a wide area, the anodic current density is low and the degree of depletion of the conductive coating is extremely low.

〔Example〕

Hereinafter, one embodiment of the present invention will be explained based on the drawings.

1 and 2 are schematic vertical cross-sectional views of concrete piles on a pier, respectively. In Fig. 1, the part of the concrete pile 1 to be coated, i.e., at least from the upper end up to the average tide level, remove marine organisms, algae, etc. from the concrete 1 surface with a wire brush, and apply a conductive coating to the surface. Applying material 2, for example, a conductive paint.

This conductive paint uses a highly weather-resistant paint made of urethane, epoxy, or acrylic resin binder mixed with gelafite powder, carbon powder, nickel powder, lead peroxide powder, or zinc powder as a conductive filler.

The film thickness of these paints is approximately 300 to 500 μm. When applying this paint, holes 3 for potential measurement are left unpainted at appropriate sizes and intervals, and a reference electrode is placed on the exposed concrete surface. The anticorrosion effect of the reinforcing bars 4 in the atmosphere is determined by pressing and measuring the potential.

The conductive coating 2 may be made of a conductive paint, a Zn-molten Zn alloy, an A1 alloy, or the like.

On the other hand, A1
A galvanic tXA pole 5 made of alloy, Zn alloy, Mg alloy, etc. is attached by an anchor bolt 6 that has been brought into electrical contact with the reinforcing bar 4 in advance. It goes without saying that in addition to this floating anode force type cathodic protection, an external power source type cathodic protection has the same effect.

In addition, covering the outside of the conductive paint 2 with an exterior material made of ##4 fiber-reinforced plastic with anti-corrosion current inflow holes 7 at the bottom to strengthen it will prevent deterioration of the conductive paint and prevent floating This is effective because it prevents the paint film from peeling off due to collisions with objects.

2 is the same as FIG. 1 except that the conductive coating 2 is a two-layered conductive composite coating with different natural potentials. This conductive composite coating includes a corrosion-resistant metal sheet coated with conductive paint, a corrosion-resistant metal sheet 1
A material made of Zn melted and a material made of a conductive resin seal and a corrosion-resistant metal sheet are used.

This conductive composite coating has a conductive coating 2 with a lower natural potential (for example, Zn) on the concrete 1 side, and a conductive coating 2 with a more negative potential (for example, Cu) on the outside. Attach it so that it looks like this. When installed in this way, the cathodic protection anode/Cu galvanic.

Electrolytic protection is performed by adding the electromotive force of the Zn/Fc system to the electromotive force of the Zn/Fc system, which increases the electromotive force, making it ideal for use in a high resistance environment.

Further, a backfill material may be present between the conductive coating 2 and the surface of the concrete 1.

〔Effect of the invention〕

As explained above, according to the cathodic protection method of this invention,
Since the conductive coating acts as a distributed electrode for cathodic protection and as a shield from the atmosphere, the reinforcing steel material in the atmosphere can be uniformly protected from corrosion over a wide range.

Therefore, for concrete structures that span both the atmosphere and the electrolyte, it is possible to consistently provide cathodic protection to the reinforcing steel in the atmosphere by simply applying cathodic protection to the reinforcing steel in the atmosphere. It only needs to be installed in an electrolyte, and it is possible to perform cathodic corrosion protection in the atmosphere in areas where there is no power supply.Furthermore, after installation, it is easy to check whether corrosion protection is being maintained by simply measuring the electrical potential.

Furthermore, since oxygen and the like are blocked by the concrete layer and the conductive coating, the corrosion protection current density of the reinforcing steel material is significantly reduced.

[Brief explanation of drawings]

1- Concrete I-Pile 2------- Conductive coating 3 - Measurement hole 4　　　　　−　Rebar 5 Galvanic anode

Claims (2)

[Claims] (1) A corrosion prevention method for a concrete structure that spans both the atmosphere and an electrolyte, the method comprising coating at least a part of the electrolyte and the surface of the structure in the atmosphere that is continuous with the electrolyte with a conductive coating; , by applying cathodic protection to the reinforcing steel of the structure in the electrolyte, a part of the anti-corrosion current flowing into the reinforcing steel in the electrolyte flows into the reinforcing steel in the atmosphere via the conductive coating. A cathodic protection method for concrete structures that is characterized by: (2) The method for cathodic protection of concrete structures according to claim 1, wherein the conductive coating is a two-layer conductive composite coating having different natural potentials.