JPS6324077B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an outer wall structure for an underground space that facilitates and completes corrosion prevention measures in soil.

Piping buried underground, basements, underground tanks, etc. require measures against soil corrosion so that they can withstand long-term use. In the soil, corrosion factors such as oxygen, moisture, and soluble salts are involved in a complex manner and change over time.
It is difficult to uniquely determine corrosivity. Furthermore, the environment in which the same structures come into contact is non-uniform, and as a result, localized corrosion such as pitting corrosion is likely to occur after a long period of time. Moreover, because it is difficult to predict, pitting corrosion may progress unexpectedly and penetrate in a short period of time even in soil that is considered to be of low corrosivity. Furthermore, it is difficult to test the degree of corrosion and repair techniques for underground structures, so underground structures that require particularly high safety require semi-permanent and maintenance-free anti-corrosion measures.

Conventionally, when constructing a steel structure underground, coating with paint or lining material and cathodic protection have been used as anti-corrosion measures. In case of painting,
If the paint film is damaged during civil engineering work, corrosion will concentrate in that area and cause pitting corrosion, so if cathodic protection is used in conjunction with this, even if a defect occurs, that area will be sufficiently protected. . When applying cathodic protection to underground structures, use a backing film 8 as shown in Figure 1.
The usual method is to embed a galvanic anode 3 wrapped in earth and sand 6 in earth and sand 6 in close proximity to a panel 1 of a structure covered with a coating film 2, and to establish continuity with a wire 5. The backing film 8 is normally used for corrosion prevention work in the soil in order to reduce the grounding resistance of the galvanic anode 3 and facilitate the generation of corrosion protection current, and is made of gypsum, bentonite, and copper sulfur in a ratio of 3:6:1. It is common to mix them in the following proportions.

In the above method, the construction work for cathodic protection is added to the construction work for burying the structure, which increases the scale of the work, and when adding a small underground space, there is not enough land, making it difficult to bury the galvanic anode. It is.
Therefore, the current method is to harden the exterior of unpainted or lightly painted steel panels with concrete. By the way, concrete is a corrosion-proof construction method that suppresses the elution of base metal due to its inherent alkalinity, and also suppresses the buoyancy of steel structures. However, during long-term use, cracks may form, corrosive groundwater may penetrate, and pitting corrosion may occur, so it is not a perfect anti-corrosion measure.

The present invention simplifies the above-mentioned corrosion protection specifications, compensates for the above-mentioned drawbacks, and provides an underground space outer wall structure with extremely high corrosion protection effects. That is, a galvanic anode made of a metal or alloy having a potential less base than steel is attached to a part of the steel member of the present invention to a panel while maintaining electrical continuity, and the part of the member other than the part where the galvanic anode is attached is covered with mortar or This is an exterior wall structure for an underground space with excellent corrosion resistance, which is characterized in that it is covered with concrete and the galvanic anode is covered with a backing film.

The present invention will be explained in detail below based on the drawings.

Fig. 2 shows a galvanic anode 3 made of a metal or alloy having a potential lower than that of steel to a steel panel 1 having an anticorrosive coating 2, and a connecting means 4 such as welding or bolts.
to ensure electrical continuity with the steel panel 1, and cover the steel panel portions other than the mounting portion of the galvanic anode 3 with mortar or concrete 7 to a desired thickness;
The galvanic anode 3 has a structure covered with the backing film 8 as described above, and FIG. 2 shows it buried in earth and sand 6. In this way, even if cracks occur in the mortar or concrete 7, local corrosion is suppressed by the action of the galvanic anode 3, thereby providing a complete anti-corrosion measure.

Above all, the most important feature of the structure of the present invention is that the galvanic anode 3 is covered only with the backing film 8 and not with mortar or concrete 7. Therefore, there is an advantage that there is no need to worry about the mortar or concrete 7 cracking due to the pressure of volumetric expansion due to the accumulation of reaction products as the galvanic anode is consumed. Furthermore, although it is possible to use unpainted steel panels for the structure of the present invention, steel panels with anti-corrosion coating are more suitable when used in harsh environments such as coastal landfills. There is. Furthermore, the structure of the present invention may be partially or entirely prefabricated in a factory, or the entire structure may be assembled on site.

The type, size, and quantity of galvanic anodes used in the structure of the present invention are determined in accordance with conventional cathodic protection design according to the grounded surface area and required life of the buried structure and the resistivity of the soil. The shape of the galvanic anode can be either with a core for welding installation or with bolt holes for bolt/nut installation, but a flat plate is suitable in cases where the unit member is a panel and has a shape suitable for transportation. .

In addition, in the structure of the present invention, the galvanic anodes are not necessarily attached to all the members, but the galvanic anodes are attached to only some of the members, and electrical continuity with other members is ensured using assembly bolts or the like. It is also possible to adopt a structure of

The coating thickness of mortar or concrete in the structure of the present invention is not particularly limited, but 50 to 200 mm is suitable based on the surface of the steel member. As mentioned above, the mortar or concrete coating in the present invention is provided for the purpose of corrosion prevention, but reinforcing materials, expansion agents, etc. may be added to the mortar or concrete as necessary, as long as the corrosion prevention effect is not impaired. It's fine.

By adopting the above structure, the present invention brings about the following effects. That is, although the anticorrosion effect of installing a galvanic anode is well known, the usual cathodic protection involves not only the above-mentioned problem of increased construction costs but also the following technical problems.

(1) Measurement of resistivity of buried soil and anode placement design based on this measurement.

(2) Design, construction, and management of current flow between the galvanic anode and target parts.

On the other hand, in the structure of the present invention, the anticorrosion current flows through the backfill and into the steel panel surface through the mortar or concrete, which has a relatively lower resistivity than the soil, so the distribution of the anticorrosion current is good. Therefore, the layout design of the galvanic anode can be done by applying a basic design with only the geometrical structure of the structure and the required life as the main prerequisites, and therefore can be easily designed without the help of experts. It can be carried out.

Furthermore, as calcium in the mortar or concrete precipitates on the surface of the steel panel, which is the object of corrosion protection, the necessary corrosion protection can be achieved with a smaller current than in the case of a bare surface, making it possible to create an economical and reliable corrosion protection design. be.

On the other hand, mortar or concrete are themselves protective against external soil corrosive environments, and a coating thickness of 50-200 mm can usually prevent corrosion of the underlying steel, but if a galvanic anode is present, even mortar or Even if cracks occur in the concrete, the cathodic protection will ensure corrosion protection.

Finally, the effects of the present invention will be explained in more detail with reference to the following examples.

Example A total surface area of approximately 60 m 2 was produced using 4 steel panels of 900 x 2700 mm on each side of the short side, 5 panels on both sides of the long side, and 5 panels of 900 x 3600 mm on the bottom ^. For the exterior wall structure of an underground space, panels measuring 900 x 2,700 mm were welded with magnesium-based plate-shaped galvanic anodes with a unit weight of 5.2 kg, each equipped with a steel core and welding terminal. A total of 18 galvanic anodes were installed. . This structure was installed on the long side 5 without attaching a galvanic anode to the bottom panel.
It is installed on the concrete base of the entire underground hole with a width of 4 m on the short side and a depth of 3 m, with a mortar layer for joining, and a 100 mm thick concrete covering layer is formed on the sides, excluding the area where the galvanic anode is installed. A structure of the present invention was fabricated by filling the space around the trailing anode with a commonly used backing film. After backfilling the entire structure with earth and sand and burying it for two years, we excavated it and investigated the underlying steel surface. As a result, no rust was observed on the side panels.
The bottom panel, to which no galvanic anode was attached, was also protected from corrosion by electrical continuity with the galvanic anode on the side panel, and no rust occurred.

Also, judging from the change in the steel surface potential over a two-year period, it was found that a corrosion protection life of more than 20 years can be expected.

As described above, the present invention has the advantage that corrosion protection work for underground structures can be carried out simply and completely without fear of unexpected local corrosion.
The service life of underground structures will also be extended and their reliability will be significantly improved. Particularly, in recent years, the use of basements has become more important due to housing conditions, and corrosion protection underground is of great significance for the future popularization.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional underground corrosion prevention means, and FIG. 2 is a schematic sectional view showing an embodiment of the structure of the present invention. 1 is a steel panel for an underground structure, 2 is an anti-corrosion coating, 3 is a galvanic anode for cathodic protection, 4 is a galvanic anode connection means, 5 is a galvanic anode connection connection, 6 is earth and sand,
7 is mortar or concrete, 8 is backfill.

Claims (1)

[Claims] 1. Attach a galvanic anode made of a metal or alloy with a potential lower than that of steel to a part of a steel member while maintaining electrical continuity, and cover the part of the member other than the part where the galvanic anode is attached with mortar or concrete. An exterior wall structure for an underground space with excellent corrosion resistance, characterized in that the galvanic anode is covered with a backing film.