JP2023064566A - Tank made of pre-stressed concrete spray-coated with covering material - Google Patents

Abstract

To provide a tank made of pre-stressed concrete that can lower permeation speed of a storage liquid and secure durability.SOLUTION: A tank made of pre-stressed concrete has crack resistant property by controlling a pre-stress introduction amount to 5-10 kgf/cm2. The tank made of pre-stressed concrete has a spray coating film formed therein by spray-coating a metal or resin covering material at a surface of the tank.SELECTED DRAWING: None

Description

The present invention relates to a prestressed concrete tank in which a corrosion-resistant or permeation-resistant film is formed by spraying a metal or resin that is resistant to corrosive substances or permeable substances to the prestressed concrete tank.

Oils such as fuel oil and crude oil, which are liquids stored in concrete tanks, penetrate into the concrete and accelerate the rate of deterioration. It is common to prevent permeation.

In order to suppress water absorption and expansion of reactive aggregates mixed in concrete caused by alkali-silica reaction, which is a factor of concrete deterioration, it is common to take measures to suppress moisture intrusion by coating the surface of concrete.

Moreover, concrete is a strong alkali, and this alkali prevents corrosion of steel materials. On the other hand, calcium hydroxide in concrete reacts with carbon dioxide in the air to form calcium carbonate, and the concrete loses its alkaline state and becomes acidic, which is called neutralization. This corrodes steel materials such as rebar. Oxygen is chemisorbed on the surface of rebars in a highly alkaline environment, forming a dense oxide layer that forms a passive film, which protects rebars in concrete from corrosion. However, when chloride ions (Cl ⁻ ) exist in concrete in excess of the permissible concentration, the passive film on the surface of the reinforcement is destroyed and the reinforcement corrodes. Therefore, as a countermeasure against intrusion of deterioration factors such as carbon dioxide that causes neutralization and salt that causes salt damage, a protective layer is formed by a surface coating or the like.

Also, in order to improve fluidity and workability, the water-cement ratio of concrete is often increased, but this results in the generation of fine voids (porous portions). If such fine voids occur, in the case of a structure where the inner surface of the concrete is in direct contact with the storage liquid such as oil, the storage liquid penetrates into the concrete, accelerating the deterioration rate of the concrete, lowering the liquid tightness, and reducing the storage capacity. It may cause the liquid to leak.

In view of the above problems, as a measure to protect concrete from deterioration factors, there are measures such as coating applied to the concrete surface or coating with a metal material.

When a coating is used to cover the concrete surface, the penetration rate of the storage liquid into the concrete can be reduced and the deterioration rate can be suppressed, but the coating is eluted by the contents (especially oil). In addition, the coating that cannot follow the distortion and cracking of the concrete is peeled off, which shortens the useful life of the concrete.

In addition, as an example of using a metal material to cover the concrete surface, there is a PS type double shell low temperature tank in which a seal metal (steel lining material) with a thickness of about 3 mm is attached to the inner surface of the prestressed concrete outer tank. The construction is complicated, and there is a problem that the construction cost increases.

Furthermore, fuel storage facilities have a structure in which the outside of steel tanks is covered with concrete, which is highly liquid-tight, but has the problem of increasing construction costs.

By the way, as a conventional technique for improving durability, corrosion resistance, etc. of concrete, a technique of thermally spraying a concrete surface with a metal or the like is already known. By applying thermal spray coating such as metal to the concrete surface, the permeation rate of the storage liquid into the concrete is remarkably reduced. Patent Documents 1 and 2 are known as conventional techniques for spraying a metal or resin onto a concrete surface.

Patent Document 1 describes a galvanic anode method in the cathodic protection method, in which the surface of a reinforced concrete structure is blasted and then sprayed to a thickness of 270 (μm) to 330 (μm). A cathodic protection method for reinforced concrete structures is disclosed in which a thermally sprayed metal layer consisting of an anode of is formed.

In Patent Document 2, by applying a glossy glass layer uniformly fused to the required surface of a long prestressed concrete material reinforced by arranging metal wires, the concrete material is prevented from thermally deteriorating. to maintain the high strength of

The conventional techniques described in Patent Literatures 1 and 2 do not relate to techniques for preventing breakage and peeling of the thermal spray coating due to cracks during use of concrete.

JP-A-2009-263739 JP-A-63-100085

Concrete such as reinforced concrete and unreinforced concrete has the property of being susceptible to cracking due to tensile load, sunlight, ultraviolet rays, and the like. Therefore, when thermal spraying is applied to the surface of reinforced concrete or the like, there is a high possibility that the thermal spray coating will be damaged or peeled off following cracks on the surface due to aged deterioration of the reinforced concrete.

In addition, when coating is applied to the wetted part of the inner surface of concrete, the coating film is eluted or peeled off by the storage liquid, and the storage liquid, which is one of the concrete deterioration factors such as oil, penetrates into the concrete from the exposed part. and the strength of the concrete itself decreases. Furthermore, when a concrete surface is painted, peeling of the paint film progresses due to changes in the environmental temperature, and the concrete portion from which the paint film has peeled off is directly exposed, causing accelerated partial deterioration.

The present invention is a prestressed concrete tank having a crack-resistant characteristic by controlling the prestress introduction amount to 5 to 10 kgf/cm ² , and thermally spraying a coating material of metal or resin on the surface of the tank to form a thermal spray coating. A formed prestressed concrete tank is provided.

The present invention also provides a prestressed concrete tank for storing oil, wherein the inner surface of the tank is thermally sprayed with aluminum, zinc, or lead having a relatively low melting point to form a thermal spray coating.

Further, the present invention provides a prestressed concrete tank for storing liquid ammonia, the tank being thermally sprayed with hard vinyl chloride resin to form a thermally sprayed coating on the inner surface of the tank.

The present invention provides a prestressed concrete tank which is located in a coastal area and has a thermal spray coating formed by thermal spraying aluminum bronze or zinc-aluminum alloy having seawater resistance on the surface of the tank.

In the present invention, different coating materials are thermally sprayed on the wetted surface of the inner surface of the tank, which is in contact with the stored liquid, and the gas phase portion exposed to the atmosphere, and the wetted surface is coated with the stored liquid. A tank made of prestressed concrete is provided by thermally spraying a coating material having corrosion resistance to the gas phase portion and thermally spraying the coating material having seawater resistance to the gas phase portion.

The prestressed concrete tank thermally sprayed with the coating material of the present invention combines the crack resistance of the prestressed concrete with the permeation resistance and durability of the thermal spray coating to prevent damage to the thermal spray coating due to cracks in the concrete. , it is possible to suppress peeling, reduce the permeation speed of the storage liquid into the prestressed concrete tank, and ensure durability.

In addition to the tensile strength of concrete being remarkably low at about one-tenth of its compressive strength, concrete is susceptible to cracking due to tensile stress other than load, such as drying shrinkage and changes in ambient temperature. Prestressed concrete (hereinafter referred to as PC) tank structures that store water supply and sewerage systems and low-temperature liquefied gas are subject to tensile stress generated by the action of loads, and the amount of prestress introduced is 5 to 10 kgf/cm ² based on past results. control to improve crack resistance. Prestress is generally applied in a horizontal direction parallel to the bottom surface (bottom plate) and in a vertical direction perpendicular to the bottom surface, but the present invention is not limited to this. If it is less than 5 kgf/cm ² , the effect of preventing cracks is small. If it is 10 kgf/cm ² , it has been found that it is sufficient to fill the tank with a storage material such as water or petroleum. However, the economic efficiency is inferior. PC tanks are more resistant to cracking than other reinforced concrete and the like, so even if thermal spraying is performed, the thermal spray layer is less likely to peel off.

A coating material is thermally sprayed on the surface of this PC tank to form a coating. As the coating material thermally sprayed on the tank surface, a metal or resin having a relatively low melting point and having excellent corrosion resistance in the alkaline environment of concrete can be used. A relatively low melting point means in this application that the melting point is 1100° C. or lower. Metals with a relatively low melting point can be used to increase the thickness of the thermally sprayed film to provide sufficient protection for the stored material as the concrete surface is porous. In addition, the surface temperature does not rise to the extent that causes thermal deterioration of the concrete base.

In addition, such a metal or resin coating material is preferably a material having corrosion resistance to concrete deterioration factors such as storage liquid. Furthermore, it is preferable that the covering material be a material that can suppress the penetration of deterioration factors into the concrete and can follow the expansion and contraction caused by the environmental temperature.

The deterioration factor permeates into the concrete and becomes a factor that accelerates the deterioration rate of the concrete. For example, in the case of a PC tank that stores oil and that is in contact with the surface of concrete, the oil is a deterioration factor. In addition, sea water droplets, rainwater, etc., which come into contact with the surface of concrete, also become deterioration factors.

Also, when the water-cement ratio of the concrete is high, the unit water content is large, the fluidity is high, and the workability is good, but the compressive strength after hardening is low. Therefore, the upper limits of the water-cement ratio in civil engineering work are stipulated as 55% reinforced concrete and 60% unreinforced concrete. For PC tanks, admixtures that generate fine air bubbles (surfactants, etc.) or admixtures that are fine particles (fly ash, silica fume, ground granulated blast furnace slag) are added to increase fluidity during construction. By doing so, it is possible to control the water-cement ratio to 45% or less while ensuring the fluidity due to the ball bearing effect. By reducing the content to 45% or less, the neutralization depth of the PC tank can be reduced, and the useful life can be increased to a very long period (approximately 200 years). After the concrete hardens, the voids (porous parts) that occur when the water in the concrete dries up are reduced, so dense concrete can be produced and neutralization can be suppressed. In this way, fine air bubbles and voids on the concrete surface are reduced, the adhesiveness of the coating material is improved, peeling is prevented, and the life of the PC tank can be extended.

Admixtures are used in small amounts and their own volume is not included in the kneaded volume of concrete, etc. For the purpose of improving the fluidity of concrete and suppressing neutralization, AE agents, water reducing agents, A superplasticizer can be used. The amount of admixture used is relatively large, and its own volume is included in the kneading volume of concrete, etc., and it compensates for part of the drying shrinkage after hardening of ground granulated blast furnace slag, which has latent hydraulic properties. Intumescent materials can be used.

A coating material to be thermally sprayed on a PC tank for storing oil will be described below. For example, if the liquid stored in a PC tank is oil, the metal to be thermally sprayed on the wetted surface of the tank may be aluminum with a low melting point (melting point: about 660°C), zinc (melting point: about 420°C), or lead (melting point: about 420°C). melting point of about 328° C.) can be used. Aluminum includes pure aluminum (purity of 99% or more) and aluminum silicon mixed with 12% silicon. If Si is 18% or less, the melting point is lower than that of pure aluminum. As zinc, in addition to pure zinc, a zinc-aluminum alloy (melting point 440° C.) mixed with 15% aluminum is also used. Here, oil refers to general industrial oils including crude oil, petroleum, heavy oil, and the like.

In this way, by covering the wetted surface of the PC tank with a metal having corrosion resistance to the stored liquid, the stored liquid and PC do not come into direct contact, the thermal spray coating does not elute, and the liquid tightness is improved. It is possible to slow down the rate at which the storage liquid permeates into the PC, thereby suppressing deterioration in the strength and cracking of the PC.

In the case of PC tanks located in coastal areas, there is a concern that seawater splashes may come into the tank or airborne seawater splashes may be introduced into the tank through a ventilation system. Aluminum bronze (melting point about 1050° C.), which is an alloy of copper and aluminum, can be used, which has excellent seawater resistance. As the aluminum bronze, it is preferable to use, for example, a special aluminum bronze (Arms Bronze (registered trademark)) having remarkably improved seawater resistance. Special aluminum bronze is a copper alloy containing 5-12% aluminum with small additions of iron, nickel and manganese. Besides aluminum bronze, an aluminum-zinc alloy can also be used. Since the surface of the zinc-aluminum alloy thermal spray coating is harder than the coating film, it has wear resistance and exhibits excellent corrosion resistance especially in coastal environments. As this aluminum-zinc alloy, for example, a zinc-aluminum alloy wire for thermal spraying sold as Zn85Al15 can be used. A product consisting of 85% by weight zinc and 15% by weight aluminum, which is corrosion resistant to sodium chloride (salt), sulfur dioxide in marine environments. Suitable for arc and flame spray processes.

By covering the surface of a PC tank with a metal thermal spray coating that is resistant to seawater, deterioration of the tank in a corrosive environment containing salt can be suppressed, and reduction in strength and cracking of PC can be suppressed. It is also effective for snow melting and anti-freezing agent sprayed on PC structures on roads in snowy cold regions.

Forms of thermal spray materials include wire rods and powder materials.
As the aluminum wire for thermal spraying, it is possible to use a wire drawn for thermal spraying from an aluminum base metal of special type 2 (AI: 99.85 mass% or more).
The zinc wire for thermal spraying is drawn from the purest zinc ingot (Zn99.995 mass% or more, Fe0.001 mass% or less for corrosion prevention) as a welding wire rod (Zn99.9% mass% or more, Cu0.05 mass% or less). Lined ones can be used.
As the lead powder material for thermal spraying, one containing 99.5 mass % or more of Pb can be used.
The zinc-aluminum alloy wire for thermal spraying uses zinc of the purest zinc base metal or higher, aluminum of special type 2 or higher, and the mass ratio of zinc to aluminum is between 95:5 and 70:30. A wire drawn for thermal spraying can be used. In particular, alloy wire with a zinc to aluminum ratio of 85:15 exhibits optimum corrosion resistance to salt and marine environments.
An aluminum alloy wire containing 3% Ti in aluminum is also excellent in corrosion resistance in coastal areas.

Another coating material can be thermally sprayed depending on the corrosive environment of each part of the PC tank. For example, the wetted surface of the tank and the gas phase portion of the tank exposed to the outside air can be coated with different metals. For example, when the liquid stored in the PC tank is oil, the wetted surface may be coated with oil-resistant aluminum, and the gas phase portion may be coated with seawater-resistant aluminum bronze.

The base treatment for metal spraying is to prevent the effects of moisture, water, alkali, etc. from the base, improve the adhesion of the sprayed coating to the base, and use a special modified epoxy resin to ensure the required film thickness. A primer with silica sand incorporated as a fine powder can be used.

An appropriate thermal spraying method should be selected in consideration of each coating material and workability. Thermal spraying should be performed after removing the laitance from the surface of the PC tank and applying the above primer. can be done. Flame spraying, arc spraying, and cold spraying can be used as the spraying method.

Wire-type flame spraying is used for spraying metals and alloys such as aluminum and zinc. In wire flame spraying, a wire-shaped thermal spraying material continuously supplied from the center hole of a thermal spraying gun is melted by an oxygen-fuel mixed gas flame. In this thermal spraying method, a melted thermal spraying material is finely granulated by a jet of compressed air from the surroundings and sprayed onto the surface of a PC tank as a coating.

Arc spraying is often used for metal spraying such as aluminum and zinc, and because it melts materials with an arc, large-scale spraying and high-efficiency spraying are possible. Arc thermal spraying, also called wire arc thermal spraying, generates an arc between two metal wires, melts the wire by the heat of the arc, and feeds the wire according to the melting speed, while applying compressed air or the like. This is a thermal spraying method in which droplets are made finer by gas injection and sprayed onto the surface of a PC tank to form a coating.

Cold spray is used for lead spraying. Gas with a temperature lower than the melting point or softening temperature of the thermal spraying material is made supersonic, and the powdered thermal spraying material is injected into the flow and accelerated, and the solid state is collided with the surface of the PC tank to form a coating. is a method of forming

The film thickness of the coating material is adjusted and controlled so that there are no voids (porous portions) on the surface of the coating material. The thickness of the metal spray coating is preferably about 100-500 μm, more preferably 120-250 μm. By applying a metal thermal spray coating to the PC tank, it is possible to maintain permeation resistance and durability for at least the next few years. For example, if there is a lot of humidity inside the tank and the thickness of the aluminum or zinc spray coating is 150 μm, the service life of the spray coating (the number of years that repair is required first) is very long, 20 years or more. Are known. In addition, it is known that when a PC tank is located in a seawater-spraying zone or a place where salt is often splashed, and the thickness of the zinc thermal spray coating is 250 μm, the service life of the thermal spray coating is 10 to 20 years. In addition, since the PC tank has crack resistance, unlike the case of thermal spraying on other concrete, etc., it is possible to prevent damage and peeling of the metal spray coating due to cracks due to deterioration of concrete over time. The service life of the thermal spray coating itself can be reliably maintained.

If the liquid stored in a PC tank is liquid ammonia, the coating material to be thermally sprayed on the wetted surface of the tank should be a rigid vinyl chloride resin (melting point about 85 to 210° C.) can be used. Thermal spraying of hard vinyl chloride can be carried out by flame spraying, in which powder of vinyl chloride resin is thermally melted with a flame, sprayed, and sprayed to a thickness of 500 μm or more on the surface of a PC tank to form a film. The thickness of the sprayed film can be 0.5 mm to 7.0 mm. Other resin materials are also available. In water supply, ultraviolet rays are irradiated as a countermeasure against cryptosporidium. Therefore, for tap water tanks, it is preferable to use a material that is weather resistant against temperature changes and that does not deteriorate due to ultraviolet rays.

Metal spraying can be used when the stock is a gas such as propane, ethylene or methane.

The present invention combines the crack resistance of PC with the penetration resistance and durability of the thermal spray coating to suppress damage and peeling of the thermal spray coating due to cracks in concrete. It is possible to reduce the permeation speed of the storage liquid into the tank and ensure durability.

Furthermore, the present invention also has the following effects as compared with the prior art. That is, it is possible to suppress aged deterioration due to neutralization of concrete structures, measures against salt damage, ASR (alkali-aggregate reaction), etc., which have hitherto been a concern. Compared to conventional PC tanks coated with paint, the thermal spray coating is less likely to be peeled off and damaged, and the service life of the PC tank is longer than before, making it possible to use it for a long time. Furthermore, compared with the case of thermal spraying on ordinary reinforced concrete or the like, it is possible to reduce the film thickness of the coating material necessary to resist cracks in the base, which facilitates construction and management. Construction costs can be greatly reduced compared to the case of covering with conventional steel lining materials.

By replacing the seal metal (steel lining material) on the inner surface of the PC outer tank of the conventional PS type double shell low temperature tank with a thermal spray coating made of a coating material such as metal, the construction period and cost can be reduced.
In addition, instead of covering the outside of the conventional steel tank with PC, the construction period and cost can be reduced by replacing the inner surface of the PC tank with a coating made of a coating material such as metal.
Furthermore, by applying it to seawater and wastewater treatment equipment, etc., it is possible to improve corrosion resistance, permeation resistance, and the like.

Claims (5)

A tank made of prestressed concrete having crack resistance properties by controlling the amount of prestress introduced to 5 to 10 kgf/cm ² , and prestressed concrete in which a coating material of metal or resin is thermally sprayed on the surface of the tank to form a thermal spray coating. made tank. 2. The prestressed concrete tank according to claim 1, which stores oil and has a thermal spray coating formed by spraying aluminum, zinc, or lead on the inner surface of the tank. 2. The prestressed concrete tank according to claim 1, which is for storing liquid ammonia and has a thermally sprayed coating formed on the inner surface of the tank by thermally spraying a rigid vinyl chloride resin. 4. The tank according to any one of claims 1 to 3, which is located in a coastal area and has a thermal spray coating formed by thermal spraying aluminum bronze or zinc-aluminum alloy having seawater resistance on the surface of the tank. Prestressed concrete tank. It is located in a coastal area, and different coating materials are thermally sprayed on the wetted surface of the inner surface of the tank, which is in contact with the stored liquid, and the gas phase portion exposed to the atmosphere, and the wetted surface is coated with the stored liquid. 2. A tank made of prestressed concrete according to claim 1, wherein a coating material having corrosion resistance against water is thermally sprayed, and said coating material having seawater resistance is thermally sprayed on said gas phase portion.