JPH06136573A - Corrosion preventive method for concrete structure by thermally sprayed film - Google Patents

Abstract

PURPOSE:To exhibit the corrosion preventive performance of a thermally sprayed film to the max. extent by bringing a metallic film for electric corrosion protection into tight contact with the surface of concrete confirmed to have prescribed pH and soluble chloride concn. and electrically connecting this film to the reinforcing bars, etc., in the concrete. CONSTITUTION:The surface of the concrete is confirmed to have <=pH11 and <=0.01wt.% (in terms of NaCl) soluble chloride concn. The thermally sprayed film of metal (high-purity Zn, Zn alloy, Zn-Al alloy, Al alloy or Mg alloy) baser than iron is brought into tight contact with the surface of this concrete by using an arc system or flame system. The thermally sprayed film and the reinforcing bars embedded into the concrete or steel structure are electrically connected.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a pier, a road bridge, a pier,
The present invention relates to a method of performing galvanic protection of a reinforcing bar or an iron-based structure such as a building structure with a metal spray coating.

[0002]

2. Description of the Related Art In recent years, there has been a problem that the reinforcing bars in a reinforced concrete structure are corroded by the intrusion of salt contained in fine aggregates or sea salt particles. As an anticorrosion measure, the electrocorrosion method has been attracting attention.A platinum-coated linear or mesh electrode is spread in or on a concrete structure, the positive electrode of a DC power supply device is connected to the electrode, and the negative electrode is made of concrete. An external power supply method for supplying a direct current from the electrode to the reinforcing bar or the like by connecting to the reinforcing bar or the like in the structure, or
There is a galvanic anode method in which a surface of a concrete structure is sprayed with a metal spray coating or a metal sheet having a lower electric potential than the reinforcing bars to electrically connect with the reinforcing bars in the concrete structure.

Further, a method described in Japanese Patent Application Laid-Open No. 2-282569, which is one method of galvanic anode method, is that a bolt is planted in a steel material in a concrete structure to project it out of the concrete, and the concrete, zinc, etc. With or without a water retention material between the galvanic anode sheets, the galvanic anode sheets such as zinc are attached to the bolts, and the nuts are tightened to fix the galvanic anode materials to the concrete surface. Is.

[0004]

However, in the conventional external power supply system, the platinum-coated linear or mesh electrode or the DC power supply device is expensive, and the construction is time-consuming and costly. Furthermore, a power generator is required in places where it is difficult to obtain power. Further, in the galvanic anode method, the metal sprayed coating or the metal sheet on the surface of the concrete is prematurely passivated by the alkali in the concrete, so that a sufficient anticorrosion effect may not be obtained.

Further, the method disclosed in Japanese Patent Laid-Open No. 2-282569, which is one of the galvanic anode methods, has the following problems. (1) It is necessary to attach a large number of Zn sheets in order to prevent corrosion of a wide concrete structure, and since many bolts are planted in the steel material in the concrete structure, attachment is troublesome. (2) Adhering a hard Zn sheet to the uneven surface of concrete requires time and labor for its processing and mounting. (3) High-concentration chloride in the viscous electrolyte may penetrate into the concrete and accelerate corrosion of the reinforcing bar. (4) Since the Zn sheet is attached by crimping with the plastic plate or the slate plate and fixing the bolt with the embedded nut, it takes time and labor, and particularly in a building structure, the aesthetic appearance may be impaired.

The present invention solves the above-mentioned problems and allows a metal film to be reliably adhered to the concrete surface,
It aims to provide a method of cathodic protection that is easy to construct even for wide concrete structures.

[0007]

According to the present invention, the concrete surface has a pH of 11 or less and a soluble chloride concentration of NaCl.
After confirming that the weight percentage is 0.01% or more,
Concrete that is characterized in that a metal spray coating having a potential lower than that of iron in concrete is adhered to the concrete surface, and the spray coating and the reinforcing bars or iron-based structures embedded in the concrete are electrically connected. It is a method of cathodic protection of structures.

The metal spray coating used in the present invention can be formed of high-purity Zn, Zn-based alloy, Zn-Al alloy, Al-based alloy or Mg-based alloy. Further, as the thermal spraying method, an arc method, a flame method or the like can be adopted.

[0009]

In the present invention, since the metal film for cathodic protection formed by the thermal spraying method is used, the metal film can be adhered easily and surely without being influenced by the irregularities on the concrete surface. In addition, even when corrosion protection is applied to a wide concrete structure, there is only one place to electrically connect the thermal spray coating and the reinforcing bar or iron-based structure embedded in the concrete, so there are many Zn coats on the concrete surface. Compared with the conventional method of attachment, it can be installed with very little effort.

On the other hand, in the conventional thermal spraying method, the thermal spray coating may be passivated by the alkali content in the concrete, and the anticorrosive effect may not be obtained. Then, the inventors of the present invention studied the environmental conditions under which the thermal sprayed coating was not passivated for coatings having different compositions and thermal spraying methods, and found that the pH was 11 or less and the salt concentration was 0.01% or more as a solution. In each case, it was found that the noble potential of the film was suppressed. When the chloride concentration in concrete is expressed by NaCl, if the specific gravity of concrete is 2.3, it is 0.00
Equivalent to 4%. In the present invention, it is not necessary to interpose a viscous electrolyte between the concrete surface and the sprayed coating in this way, and the construction becomes simple, and high concentration chloride in the viscous electrolyte permeates into the concrete, resulting in corrosion of the rebar. There is no fear of promoting.

When the thermal spray coating formed as described above and the reinforcing bars in the concrete are electrically connected by an electric wire or the like, an anticorrosive current flows from the thermal spray coating to the reinforcing bars through the concrete.
The magnitude of this anticorrosion current is a value obtained by dividing (EL-ER) by the resistance R of the concrete, where EL is the potential of the sprayed coating and ER is the potential of the reinforcing bar, that is, (EL-ER) / R.
The electric potential of the reinforcing bar in healthy concrete is -100 to -2.
Although it shows 00 mV, the electric potential of the reinforcing bar corroded by salt damage shows about -500 mV. Therefore, when the potential of the thermal spray coating is close to the potential of the above electrode, the anticorrosion current becomes difficult to flow, and the anticorrosion effect is impaired. Therefore, the potential of the thermal spray coating is preferably close to the potential in seawater of −1000 to −1100 mV.
If it is −920 mV or less, the anticorrosion effect can be sufficiently exhibited.

[0012]

[Examples] Pure Zn (99.995%) thermal spray coating by the arc method, Al-Zn formed by the arc method (capacity ratio A
1 / Zn: 50/50, weight ratio Al / Zn: 72/2
8) Pseudo-alloy film (Zn and Al wires with the same diameter are used one by one, and the Zn particles and A
(a coating formed by laminating 1 particle) and a concrete test piece having a pure Zn (99.995%) sprayed coating by the flame method, respectively, were Ca (OH) ₂
And the negative polarization potential (mV) was measured by immersing in various solutions whose pH and chloride concentration were adjusted with NaCl and NaCl, and the results shown in Table 1 were obtained. The values in the table are average potentials of the respective coatings when an anticorrosion current in a practical range is flown out from the coatings. Normally, concrete absorbs carbon dioxide gas in the air to gradually lose alkali content, and the pH drops from 12. As is clear from Table 1, in the range where the chloride concentration is 0.01% or more while the pH shifts to 11 or less, the potential of the thermal spray coating is all -920 mV or less, and the potential in seawater is It was found that the anticorrosion effect can be fully exerted because it is close to.

[0013]

[Table 1]

[0014]

EFFECTS OF THE INVENTION The present invention employs the above-mentioned constitution, and after confirming that the pH and chloride concentration of the surface of the concrete structure satisfy the above-mentioned ranges, a thermal spray coating is formed on the concrete surface, thereby performing thermal spraying. It is possible to suppress the noble potential of the coating and maximize the anticorrosion performance of the thermal spray coating.

Claims (3)

[Claims] 1. The pH of the concrete surface is 11 or less,
After confirming that the concentration of soluble chloride is 0.01% or more in terms of NaCl weight percentage, a metal spray coating having a potential lower than that of iron in concrete is adhered to the concrete surface. A method for galvanic protection of a concrete structure, comprising electrically connecting reinforcing bars or iron-based structures embedded in the structure. 2. A high-purity Zn, Zn-based alloy, Z
The cathodic protection method according to claim 1, which is an n-Al alloy, an Al alloy, or a Mg alloy. 3. The cathodic protection method according to claim 1, wherein a thermal spray coating formed by an arc method or a flame method is used.