JPH0454753B2 - - Google Patents

Description

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

[Conventional technology]

Reinforced concrete structures (hereinafter referred to as RC structures) have been regarded as semi-permanent structures that do not require upkeep or maintenance, in addition to being structurally robust due to the superior material combination of concrete and steel. However, it has been found that in RC structures in the marine environment, large amounts of salt contained in seawater spray and sea breeze are blown into the air, and when it adheres, it permeates into the concrete and corrodes the internal reinforcing steel. In addition, even in RC structures in atmospheric environments, the neutralization of concrete progresses due to the influence of exhaust gases from automobiles and factories, and the reinforcing bars corrode and swell due to the increase in salt content in concrete due to the use of sea sand. As a result, an accident occurred in which the concrete cover fell off, and it was widely covered by the media.

Conventional anti-corrosion measures for such RC structures include applying hot-dip galvanizing to 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 an external power source 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 supplying a corrosion protection current by covering the surface with conductive paint and embedding a platinum wire electrode connected to a DC power source on this surface.

[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 steel will corrode in the presence of a higher concentration of salt or at a location where cracks are reached. In addition, the method using rust preventive agents can be dangerous if the usage standards are not fully observed, such as pitting corrosion occurring in reinforcing bars if the amount of rust preventive agent added to the concrete is less than the amount required for corrosion prevention. . Furthermore, conventional cathodic protection methods have the limitation that they can only be applied to RC structures in the atmosphere where power is available, and electrodes are installed separately in the atmosphere and in seawater, even though the same structure is used. It must be said that it is extremely uneconomical to design and construct corrosion protection separately.

This invention solves the above-mentioned problems of conventional methods, and enables economical cathodic protection by consistently low corrosion protection current density for concrete structures that span both the atmosphere and electrolyte. The purpose of this invention is to provide a method for cathodic protection of concrete structures.

[Means for solving problems]

In order to achieve this object, the present invention has the following configuration.

That is, the cathodic protection method for concrete structures according to the invention covers the surface of the structure exposed to the atmosphere with a conductive coating, and the outside of this is held in an electrolyte with a water-absorbing and water-retaining current absorbing material. At the same time, by electrolytically protecting the reinforcing steel of the structure in the electrolyte, a part of the current flowing into the reinforcing steel in the electrolyte is transferred to the atmosphere through the current absorption material and the conductive coating. so that it flows into the reinforcing steel material.

[Effect]

In the cathodic protection method configured in this way,
The corrosion-protecting electricity i by cathodic protection directly passes through the concrete layer in the electrolyte and flows into the reinforcing steel material, keeping the surface in a good corrosion-protected state. In this case, it is known that because the current flows through the concrete layer, the current density required for corrosion protection can be quite small, approximately one-tenth or less of that for bare steel in seawater. On the other hand, a part of the anticorrosion current i flows into the current absorbing material in the electrolyte, passes through the conductive coating in the atmosphere and the concrete layer, and flows into the reinforcing steel material, creating a uniform potential distribution on the surface. give.

Since the conductive coating acts as a wide current distribution electrode, the anodic current density is low and the degree of consumption of the conductive coating is extremely low.

〔Example〕

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

FIG. 1 is a schematic vertical cross-sectional view of concrete piles on a pier. In Figure 1, the part of the concrete pile 1 to be coated, that is, the concrete surface in the atmosphere (above the high tide level), is coated with a conductive coating 2, for example, a conductive paint to a thickness of 300 to 500μ. . This conductive paint uses a highly weather-resistant paint made of urethane, epoxy, or acrylic resin binder mixed with graphite powder, carbon powder, nickel powder, lead peroxide powder, or zinc powder as a conductive filler. .

The conductive coating 2 is made of a conductive coating material other than conductive paint.
Zn spraying, Al spraying, conductive concrete, sheet-shaped conductive resin, corrosion-resistant metals, (Ti, Ta, Nb,
Cu, Cu alloy, Cr-Ni steel, etc.), Zn alloy, Al alloy, etc. can be used.

Next, a nonwoven fabric sheet containing an acrylic acid-based water-absorbing polymer as a current absorbing material 3 is held outside the conductive coating 2 so that its lower part is immersed in seawater. The current absorbing material 3 uses a material having water absorbing and water retaining properties, for example, in addition to the above-mentioned nonwoven fabric sheet, a polyethylene oxide water absorbing polymer blended with low density polyethylene or polypropylene is used in the form of a film or sheet.

In addition, in a marine environment as in this embodiment, an inflow hole 4 for anti-corrosion current is provided on the outside of the current absorption material 3 at the bottom.
Covering and reinforcing the exterior material 5 such as a fiber-reinforced plastic sheet provided with the current absorption material 3
This is extremely effective because it prevents deterioration or peeling off due to collision with floating objects.

This exterior material 5 is fixed to the concrete pile 1 with bolts and nuts using an angled tightening portion provided at the end. Further, it is preferable that the exterior material 5 and the current absorbing material 3 are bonded together in advance using an adhesive or the like.

On the other hand, a galvanic anode 6 made of Al alloy, Zn alloy, Mg alloy, etc. is placed on the surface of a concrete pile 1 in the sea.
are attached by anchor bolts 8 that have been brought into electrical contact with reinforcing bars 7 in advance. It goes without saying that in addition to this electrolytic anode type cathodic protection, an external power source type cathodic protection has the same effect.

Note that a backfill material may be interposed between the conductive covering 2 and the concrete surface.

〔Effect of the invention〕

As explained above, according to the cathodic protection method of the present invention, the conductive coating acts as a distributed electrode for cathodic protection and as a shield from the atmosphere, so that reinforcement steel materials in the atmosphere can be uniformly protected from corrosion over a wide range. be able to.

Therefore, for concrete structures that span both the atmosphere and the electrolyte, by simply applying cathodic protection to the reinforcing steel in the electrolyte, the effect of cathodic protection can be achieved on the reinforcing steel in the atmosphere, which eliminates the need for complicated electrode installation. This requires only in the electrolyte, and cathodic protection can be carried out in the atmosphere in areas where there is no power source.

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]

FIG. 1 is a schematic cross-sectional view showing one embodiment of the present invention. 1... Concrete pile, 2... Conductive coating,
3... Current absorption material, 6... Galvanic anode, 7... Reinforcing bar.

Claims (1)

[Claims] 1. A method for preventing corrosion of a concrete structure that spans both the atmosphere and an electrolyte, in which the surface of the structure that is exposed to the atmosphere is coated with a conductive coating, and the outside of the structure is covered with a conductive coating that absorbs water. In addition to retaining the current with a water-retaining current absorbing material, by electrolytically protecting the reinforcing steel of the structure in the electrolyte, a part of the anti-corrosion current flowing into the reinforcing steel in the electrolyte is absorbed by the current absorbing material and conductive. 1. A method for cathodic protection of concrete structures, characterized in that the atmosphere flows into the reinforcing steel material through a conductive coating. 2. The cathodic protection method for concrete structures according to claim 1, wherein the current absorbing material is a nonwoven fabric containing a water-absorbing polymer.