WO2022118731A1

WO2022118731A1 - Method for fixing carbon dioxide to concrete, and concrete structure including concrete

Info

Publication number: WO2022118731A1
Application number: PCT/JP2021/043177
Authority: WO
Inventors: 裕介藤倉; 智洋藤沼; サンジェイパリーク
Original assignee: 株式会社フジタ; 学校法人日本大学
Priority date: 2020-12-03
Filing date: 2021-11-25
Publication date: 2022-06-09
Also published as: JPWO2022118731A1

Abstract

Provided is a method for efficiently fixing carbon dioxide to concrete. The method includes: forming a gas injection hole in concrete included in a concrete structure; introducing a gas containing carbon dioxide into the gas injection hole; and after introducing the gas containing carbon dioxide, capping one end of the gas injection hole to seal the gas including carbon dioxide in the gas injection hole. The method may further include decompressing the gas injection hole before the introduction of the gas including carbon dioxide. The gas including carbon dioxide may further include water.

Description

How to fix carbon dioxide to concrete, and concrete structures containing concrete

One of the embodiments of the present invention relates to a method of fixing carbon dioxide to concrete contained in a concrete structure, and a concrete structure to which this method is applied.

Concrete is mainly composed of cement hydrate, aggregate, water, and additives, due to its excellent mechanical properties, weather resistance, ease of handling, economy, etc., social production base, economy. It is widely used in various fields as one of the important structural materials for creating a foundation. Cement is known to emit large amounts of carbon dioxide during its manufacture, which is cited as one of the causes of the greenhouse effect. Therefore, in order to contribute to solving this problem, for example, in Patent Document 1, when constructing a structure containing concrete (hereinafter referred to as a concrete structure), carbon dioxide is brought into contact with ready-mixed concrete before the concrete is hardened to form carbon dioxide. A method of fixing carbon to concrete is disclosed. Patent Document 2 discloses an effective method for designing a concrete structure for promoting the absorption of carbon dioxide into concrete.

Japanese Patent No. 5957283 Japanese Patent No. 4822373

One of the tasks of the embodiment of the present invention is to provide a method for efficiently fixing carbon dioxide to concrete. For example, one of the embodiments of the present invention is to provide a method for fixing carbon dioxide to concrete contained in an existing concrete structure. Alternatively, one of the embodiments of the present invention is to provide a concrete structure obtained by applying the above method.

One of the embodiments of the present invention is a method of fixing carbon dioxide to concrete. This method involves forming a gas injection hole in the concrete contained in the concrete structure, introducing a gas containing carbon dioxide into the gas injection hole, and capping one end of the gas injection hole after the gas introduction. Includes enclosing gas in gas inlets.

One of the embodiments of the present invention is a concrete structure. This structure includes a first concrete and a second concrete. The second concrete has a different composition from the first concrete, is surrounded by the first concrete, and extends in the first direction toward the inside of the first concrete. The first concrete includes a first zone in contact with the second concrete and a second zone surrounding the first zone. The concentration of calcium carbonate in the first zone decreases continuously as the distance from the interface between the first concrete and the second concrete increases in the second direction perpendicular to the first direction. The concentration of calcium carbonate in the second zone is constant in the second direction.

One of the embodiments of the present invention is a concrete structure. This structure includes concrete having a bottomed hole or a through hole extending in the first direction. The concrete includes a first zone that constitutes the side wall of the bottomed hole and the through hole, and a second zone that surrounds the first zone. The concentration of calcium carbonate in the first zone decreases continuously as the distance from the sidewall increases in the second direction perpendicular to the first direction. The concentration of calcium carbonate in the second zone is constant in the second direction.

The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The top view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The top view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. A side view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. A side view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. The schematic diagram which shows the composition in concrete obtained by the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The schematic diagram which shows the composition in concrete obtained by the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The top view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. The perspective view explaining the method of fixing carbon dioxide to concrete which is one of the embodiments of this invention. A side view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. A cross-sectional view illustrating a method of fixing carbon dioxide to concrete, which is one of the embodiments of the present invention. The perspective view of the concrete structure used in an Example. Sectional drawing of the concrete structure used in an Example.

Hereinafter, each embodiment of the present invention will be described with reference to drawings and the like. However, the present invention can be carried out in various embodiments without departing from the gist thereof, and is not construed as being limited to the description contents of the embodiments exemplified below.

In order to clarify the explanation, the drawings may schematically represent the width, thickness, shape, etc. of each part as compared with the actual embodiment, but the drawings are merely examples and limit the interpretation of the present invention. It's not something to do. In the present specification and each figure, elements having the same functions as those described with respect to the above-mentioned figures may be designated by the same reference numerals and duplicate description may be omitted.

Hereinafter, the expression "a structure is exposed from another structure" means an aspect in which a part of one structure is not covered by another structure, and is not covered by another structure. The portion also includes an embodiment covered by yet another structure.

Hereinafter, concrete refers to concrete that does not show fluidity because the hydrate produced by the reaction of cement, which is one of the raw materials, with water is hardened. On the other hand, the state in which the mixture containing cement and water does not completely harden and has fluidity is referred to as ready-mixed concrete (also called ready-mixed concrete).

Hereinafter, a method for fixing carbon dioxide using an existing concrete structure according to one of the embodiments of the present invention, and a concrete structure to which this method is applied will be described with reference to the attached drawings. .. In these figures, for convenience, the xy plane is a horizontal plane and the z direction is a vertical direction.

1. 1. Outline In the method for fixing carbon dioxide according to one of the embodiments of the present invention, a concrete structure containing hardened concrete is used as a substrate for fixing carbon dioxide. That is, carbon dioxide is brought into contact with the concrete contained in the concrete structure to fix carbon dioxide (carbonation of concrete). There are no restrictions on the type, shape, use, and installation location of the concrete structure, and any existing concrete structure can be used. The existing concrete structure may be, for example, a pillar or a foundation beam of a building, a pier or a pier of a bridge, a dike or a breakwater installed in a river or a harbor, a wave-dissipating block, or a lining concrete used for a road or a tunnel. good. Alternatively, it may be a movable property (concrete product) containing concrete such as a square or U-shaped concrete block or a gravel stone.

2. 2. Carbon dioxide fixation method 2-1. Formation of Gas Injection Hole FIG. 1A shows a schematic perspective view of the concrete structure 100. The concrete structure 100 shown here schematically represents all or part of various concrete structures, and as described above, the type, shape, and use of the concrete structure are not limited.

In the carbon dioxide fixation method according to one of the embodiments of the present invention, first, a gas injection hole 104 is formed in the concrete 102 constituting the concrete structure 100. As shown in a schematic cross-sectional view (FIG. 1B, FIG. 1C), the gas injection hole 104 may be a through hole penetrating the concrete structure 100 from the surface of the concrete 102 to the opposite surface (FIG. 1B), and one end thereof is closed. It may be a bottomed hole (Fig. 1C). The gas injection hole 104 may be formed so as to extend linearly, or may include a bent shape (not shown). Further, as shown in FIGS. 2A and 2B, a plurality of gas injection holes 104 may be provided. In this case, the extending directions of the plurality of gas injection holes 104 may be the same as each other, or the extension direction of at least one gas injection hole 104 may be different from that of the other gas injection holes 104. As shown in FIG. 2A, the stretching direction of all the gas injection holes 104 may be perpendicular to the outer surface of the concrete structure 100, or as shown in FIG. 2B, some or all of the gas injection holes 104 may have an extension direction. , May be stretched in a direction inclined with respect to the outer surface of the concrete structure 100. Although not shown, a plurality of gas injection holes 104 may intersect. That is, the gas injection holes 104 may be formed in a network in the concrete 102.

The surface on which the gas injection hole 104 is provided is not limited to the surface perpendicular to the horizontal plane, but may be a surface parallel to the horizontal plane (for example, the upper surface of the concrete structure 100), and the gas injection hole may be a surface inclined at an angle of less than 90 ° from the horizontal plane. 104 may be provided.

The cross-sectional area of the gas injection hole 104, that is, the opening area of the gas injection hole 104 on the outer surface of the concrete 102 can be arbitrarily set. For example, when the cross-sectional shape of the gas injection hole 104 (the shape on the outer surface of the concrete structure 100) is a circle, the diameter may be 1 mm or more and 100 mm or less or 2 mm or more and 150 mm or less, and the opening area is 0.785 mm ² or more 78. It may be 5 cm ² or less or 3.14 mm ² or more and 177 cm ² or less. By selecting the above range, the gas injection hole 104 can be formed without significantly impairing the strength and aesthetics of the concrete structure 100.

The gas injection hole 104 may be formed from the outer surface of the concrete 102 toward the inside by using a drill such as a vibration drill or a hammer drill.

Alternatively, the gas injection hole 104 may be formed at the same time as the concrete structure 100 is formed. Specifically, a formwork 150 for determining the shape of the concrete structure 100 is produced (FIG. 3A). At this time, one or more core materials (cores) 152 for forming a space corresponding to the gas injection hole 104 in the concrete 102 are arranged in the formwork 150 (FIGS. 3A and 3B). The core material 152 may be provided so that a part thereof is exposed from the mold 150. The shape of the core material 152 may be determined in consideration of the shape of the gas injection hole 104, may be a linear rod shape, or may be partially or wholly bent. Further, the core material 152 may be a hollow tube or may not be hollow (solid). The material contained in the core material 152 is not limited, and may be, for example, a metal material such as aluminum, iron, or stainless steel, wood, or resin. The resin may be a fiber reinforced plastic compounded with fibers such as glass fiber and carbon fiber. A release agent (release agent) or a curing retarder may be applied to the outer surface of the core material 152. By applying a mold release agent or a curing retarder, the core material 152 can be easily removed from the concrete 102 to form the gas injection hole 104, as will be described later.

Continue to place concrete 102. That is, the ready-mixed concrete 154 is placed in the formwork 150 (FIGS. 4A and 4B). At this time, the ready-mixed concrete 154 is poured so that at least a part of the core material 152 is embedded in the formwork 150 by the ready-mixed concrete 154. Ready-mixed concrete 154 contains at least water and cement, but aggregates such as sand, gravel, boulders, rocks, crushed stones, crushed sand, AE agents (bubble dispersants) fluidizers, thickeners, It may contain an additive such as a quick-setting agent.

The structure 100 is formed by hardening the ready-mixed concrete 154 and removing the formwork 150. Further, by removing the core material 152, the gas injection hole 104 can be formed in the concrete structure 100 (FIG. 5). The core material 152 does not necessarily have to be removed. For example, when the gas injection hole 104 is formed in a network shape, it may be difficult to remove the core material 152. In such a case, a porous material or a tubular core material 152 having a fine opening may be used, and carbon dioxide and the concrete 102 may be brought into contact with each other via the core material 152.

2-2. Introduction of carbon dioxide Next, in order to fix carbon dioxide to the concrete 102, a gas containing carbon dioxide is supplied to the gas injection hole 104, and the carbon dioxide is brought into contact with the side wall of the gas injection hole 104. Specifically, a carbon dioxide supply source 120 is connected to one end (injection port) of the gas injection hole 104 via a carbon dioxide line 122, and a gas containing carbon dioxide is introduced into the gas injection hole 104 (FIG. 6A). .. Although not shown, when a plurality of gas injection holes 104 are provided, the same number of carbon dioxide supply sources 120 as the gas injection holes 104 may be used, and the carbon dioxide supply sources 120 corresponding to the respective gas injection holes 104 may be connected. A well or branched carbon dioxide line 122 may be used to connect a smaller number of carbon dioxide sources 120 to the gas injection holes 104 than the number of gas injection holes 104. The carbon dioxide line 122 is provided with a pressure gauge 124 and / or a flow meter 125 for measuring the pressure of the gas containing carbon dioxide introduced into the gas injection hole 104 (that is, the pressure in the gas injection hole 104). May be good.

The connection method between the carbon dioxide line 122 and the gas injection hole 104 can be arbitrarily selected, and the tip of the carbon dioxide line 122 may be simply inserted into the gas injection hole 104. Alternatively, in order to maintain a stable connection state, for example, as shown in FIG. 7A, an adapter 110 having an opening having a female screw structure is attached to the injection port, and the tip of the carbon dioxide line 122 has a male screw structure that meshes with the female screw structure. The joint 126 may be attached. By screwing the joint 126 into the adapter 110, the carbon dioxide line 122 can be reliably connected to the gas injection hole 104. As an optional configuration, a resin O-ring (or packing) 112 may be provided between the adapter 110 and the concrete 102 in order to prevent leakage of a gas containing carbon dioxide.

When the gas injection hole 104 is a through hole, the other end (exhaust port) is capped to contain the gas containing carbon dioxide, thereby preventing the leakage of the gas containing carbon dioxide and more effectively. Contact between the concrete 102 and carbon dioxide is possible. For example, the discharge port may be sealed with an adhesive tape, an elastic body such as rubber, or, as shown in FIGS. 6B and 7A, an acrylic resin, an epoxy resin, a polyester resin, a polyimide resin, or the like. The gas injection hole 104 may be sealed with a plate 106 containing the resin of the above or a metal material such as iron, stainless steel, or aluminum. Fiber reinforced plastic may be used as the resin. The plate 106 may be fixed by using bolts or screws, or simply a plate 106 that matches the shape of the discharge port may be inserted into the discharge port. Alternatively, the plate 106 may be fixed using an adhesive, an adhesive tape, or the like. Further, as shown in FIG. 8A, in order to improve the airtightness of the gas injection hole 104, the discharge port is closed with a packing 108 containing an elastic body such as rubber, and the plate 106 is sandwiched between the packing 108 and the concrete 102. May be provided.

The gas containing carbon dioxide may be pure carbon dioxide (for example, a purity of 99% or more) or a mixed gas of carbon dioxide and another gas. When a mixed gas is used, other gases include air, oxygen, nitrogen and the like. The concentration of carbon dioxide in the mixed gas can be arbitrarily set, but it is preferably higher than the concentration of carbon dioxide contained in the atmosphere (about 420 ppm) in order to efficiently bring the concrete 102 into contact with carbon dioxide. For example, the carbon dioxide concentration may be set from any concentration of 1% by volume or more and 100% by volume or less, 10% by volume or more and 50% by volume, or 10% by volume or more and 20% by volume or less.

The carbon dioxide supply source 120 may have a function of supplying a gas containing carbon dioxide to the gas injection hole 104, and examples thereof include a cylinder and a tank of the gas containing carbon dioxide as shown in FIG. 6A. The carbon dioxide supply source 120 is connected to a regulator (not shown), and the gas containing carbon dioxide is regulated. Alternatively, if facilities that emit a large amount of carbon dioxide (chemical plants, garbage incinerators, thermal power plants, other various factories, etc.) are already installed near the concrete structure 100, the gas emitted from these facilities, or Purified carbon dioxide obtained by performing dedusting, desulfurization, denitration, etc. on the exhaust gas may be used. In this case, since these facilities function as the carbon dioxide supply source 120, the cost for transporting carbon dioxide is reduced, and further emission of carbon dioxide due to the transport is prevented.

The gas containing carbon dioxide may be introduced so that the pressure in the gas injection hole 104 is higher than 0 MPa and lower than 2 MPa. When the pressure in the gas injection hole 104 is lower than the atmospheric pressure (for example, 1 atm or 0.101 MPa), a vacuum pump 130 such as a rotary oil pump or a dry pump is connected to the carbon dioxide line 122 to connect the gas injection hole. After reducing the pressure in 104, a gas containing carbon dioxide may be introduced. On the contrary, when boosting is required, a compressor or the like may be used.

The gas containing carbon dioxide may be introduced constantly or intermittently during the period in which carbon dioxide is fixed. In the latter case, after supplying the gas containing carbon dioxide, the carbon dioxide line 122 may be removed from the gas injection hole 104, the injection port may be closed, and the gas injection hole 104 may be closed. For example, the injection port may be closed with an adhesive tape, or an elastic body such as rubber may be inserted into the injection port to seal the injection port. Alternatively, as shown in FIG. 8B, the gas injection hole 104 may be sealed by using a cap 114 having a male screw structure that meshes with the adapter 110. By sealing the gas injection hole 104, carbon dioxide can be reliably retained in the gas injection hole 104 and leakage of carbon dioxide can be prevented.

As an arbitrary configuration, a densitometer 128 for measuring the carbon dioxide concentration may be provided inside the gas injection hole 104 (for example, the side wall of the gas injection hole 104 or the cap 114), and the carbon dioxide concentration may be measured periodically. This makes it possible to monitor changes in carbon dioxide concentration.

2-3. Humidity adjustment The rate of fixing carbon dioxide to concrete depends on the humidity, and it is known that carbon dioxide is fixed at a high rate when the humidity is about 50%. Therefore, even in one of the embodiments of the present invention, the humidity in the gas injection hole 104 may be adjusted. Specifically, a water supply source 140 may be provided to supply water into the gas injection hole 104 via the carbon dioxide line 122 (FIG. 6A). Although not shown, the water supply source 140 may include a heating device and a cooling device for controlling the temperature of the supplied water. Alternatively, a gas containing carbon dioxide may be supplied from the carbon dioxide supply source 120 to the water supply source 140, and the water containing carbon dioxide may be supplied to the gas injection hole 104.

As an arbitrary configuration, a hygrometer 129 for measuring humidity may be provided inside the gas injection hole 104 (for example, the side wall of the gas injection hole 104 or the cap 114), and the humidity may be measured periodically (FIG. 7B). This makes it possible to monitor changes in humidity.

On the other hand, when the humidity in the gas injection hole 104 is high, a large amount of water is adsorbed on the side wall of the gas injection hole 104, the side wall of the gas injection hole 104 is frozen, or the concrete 102 contains a large amount of water. In such a case, the inside of the gas injection hole 104 may be depressurized by using a vacuum pump 130 in order to remove a part of the water in the gas injection hole 104. After that, the gas containing carbon dioxide may be supplied into the gas injection hole 104.

The contact time between the concrete 102 and the gas containing carbon dioxide depends on the length, cross-sectional area (that is, the volume of the gas injection hole 104) and temperature of the gas injection hole 104, and the concentration of carbon dioxide in the gas containing carbon dioxide. For example, it may be 1 hour or more and 20 years or less, 1 day or more and 10 years or less, 10 weeks or more and 5 years or less, and 1 year or more and 3 years or less.

As shown in FIG. 7A, the control device 142 may be used to supply carbon dioxide and water. Carbon dioxide and water are supplied to the control device 142 from the carbon dioxide supply source 120 and the water supply source 140, respectively. The control device 142 includes a mechanism (for example, a blower pump or the like) for supplying a gas containing carbon dioxide to the gas injection hole 104. The control device 142 may further prepare a gas containing carbon dioxide having an appropriate humidity by using the supplied water and carbon dioxide, and may be configured to supply this gas to the gas injection hole 104. Alternatively / Furthermore, the control device 142 may be configured so that the temperature of the gas containing carbon dioxide supplied to the gas injection hole 104 can be controlled. By imparting such a function to the control device 142, a gas containing carbon dioxide can be supplied into the gas injection hole 104 at a temperature and humidity at which a large carbon dioxide fixation rate can be obtained.

Further, as shown in FIG. 7B, a gas containing carbon dioxide may be circulated between the control device 142 and the gas injection hole 104. In this case, the control device 142 includes a mechanism for recovering the gas discharged from the gas injection hole 104, which is exemplified in a circulation pump or the like, and supplying the gas to the gas injection hole 104 again. Further, the control device 142 is configured to measure the concentration and humidity of carbon dioxide contained in the gas discharged from the gas injection hole 104, and appropriately add carbon dioxide or water to the gas based on the obtained data. May be. As a result, the inside of the gas injection hole 104 can be constantly placed under the condition that the optimum carbon dioxide fixation rate can be obtained.

By the process up to this point, carbon dioxide is fixed to the concrete 102.

2-4. Placing Concrete in Gas Injection Holes As an optional step, repair concrete 103 may be newly placed in the gas injection holes 104 of the concrete structure 100 in which carbon dioxide is fixed. Specifically, as shown in FIGS. 9A to 9C, the gas injection hole 104 is filled with ready-mixed concrete and hardened. In the concrete structure 100, the repair concrete 103 extending inside the concrete 102 is surrounded by the concrete 102. The area of the cross section of the repair concrete 103 (the cross section perpendicular to the direction in which the repair concrete 103 is stretched) is the same as or substantially the same as the opening area of the gas injection hole 104, for example, 0.785 mm ² or more and 177 cm ² or less. ..

The repair concrete 103 may be cast in the entire gas injection hole 104, or may be cast only in a part of the injection port side, although not shown. By placing the repair concrete 103, the structural strength lost by forming the gas injection hole 104 can be compensated, and the aesthetic appearance of the concrete structure 100 can be maintained.

Although the details will be described later, in the concrete 102 contained in the concrete structure 100, carbon dioxide is fixed from the side wall of the gas injection hole 104, so that the composition of calcium carbonate increases. Therefore, the compositions of the concrete 102 and the repair concrete 103 may differ from each other. In this case, the concentration of calcium carbonate is higher in the former, and conversely, the concentration of calcium hydroxide is higher in the latter.

2-5. Concrete structure in which carbon dioxide is fixed When carbon dioxide is brought into contact with the concrete 102 contained in the concrete structure 100 using the method described above, calcium hydroxide and calcium silicate (CSH) contained in the concrete 102 are brought into contact with the concrete 102. ), Monosulfate, ettringite, unhydrated cement, etc. react with carbon dioxide and change to calcium carbonate. As a result, the introduced carbon dioxide is fixed in the concrete 102 as calcium carbonate. This reaction, also called carbonation, first occurs from the side wall of the gas injection hole 104 and proceeds from the side wall to the inside of the concrete 102. Therefore, although it depends on the density and local composition of the concrete 102, as shown in the cross-sectional view (FIG. 10A) perpendicular to the stretching direction of the gas injection hole 104, the carbonation is perpendicular to the stretching direction of the gas injection hole 104. In principle (ie, in the xz plane), it travels isotropically (see the solid arrow in FIG. 10A). The degree of carbonation is higher as it is closer to the gas injection hole 104. Therefore, the concrete 102 has a relatively high calcium carbonate concentration, and has a first zone 102a (a zone surrounded by a chain line in FIG. 10A) constituting the side wall of the gas injection hole 104, and a calcium carbonate concentration. Is lower than that of the first zone 102a and will have a second zone 102b (the outer zone of the circle) surrounding the first zone 102a. The first zone 102a and the second zone 102b are in contact with each other.

Therefore, as schematically shown in FIG. 10B, in the first zone 102a, in the direction perpendicular to the y direction, that is, in any direction in the xz plane (see, for example, arrow a in FIG. 10A), the concrete 102. The concentration of calcium carbonate decreases continuously as the distance from the side wall of the gas injection hole 104 increases. When filling the repair concrete 103, the concentration of calcium carbonate in the concrete 102 continuously increases as the distance from the interface between the repair concrete 103 and the concrete 102 increases. The zone where this increase is stopped and the concentration of calcium carbonate is constant or substantially constant is the second zone 102b. Although not shown, the concentration of calcium carbonate in the repair concrete 103 is constant or substantially constant.

On the other hand, since calcium hydroxide is consumed in the reaction between concrete and carbon dioxide, in the first zone 102a, the concentration of calcium hydroxide in the concrete 102 in any direction in the xz plane is determined by the gas injection hole 104. It increases continuously as the distance from the side wall increases. When filling the repair concrete 103, the concentration of calcium hydroxide in the concrete 102 continuously decreases as the distance from the interface between the repair concrete 103 and the concrete 102 increases. In the second zone 102b, no increase in the concentration of calcium hydroxide is observed substantially, and the concentration of calcium hydroxide becomes constant or substantially constant. Although not shown, the concentration of calcium hydroxide in the repair concrete 103 is constant or substantially constant.

Similarly, in the direction from the outer surface of the concrete 102 to the opposite outer surface (see arrow b in FIG. 10A), the calcium carbonate concentration plot with respect to the distance from the outer surface can show three stages. Specifically, as shown in FIG. 10C, the first stage corresponds to the second zone 102b from the outer surface to the interface between the first zone 102a and the second zone 102b, here with calcium carbonate. The concentration of calcium hydroxide is constant or substantially constant. The second stage corresponds to the first zone 102a after passing through the interface between the first zone 102a and the second zone 102b and then reaching the interface between the first zone 102a and the second zone 102b again. Here, the concentration of calcium carbonate continuously increases and then decreases continuously, and the concentration of calcium hydroxide continuously decreases and then continuously increases. The third stage corresponds to the second zone 102b, which secondly passes through the interface between the first zone 102a and the second zone 102b and then reaches the outer surface of the concrete structure 100, here with calcium carbonate. The concentration of calcium hydroxide is constant or substantially constant.

In the carbon dioxide fixing method described above, the concrete 102 of the concrete structure 100 can come into contact with carbon dioxide at an extremely high concentration as compared with the carbon dioxide concentration in the atmosphere in the gas injection hole 104. Therefore, the carbon dioxide introduced into the gas injection hole 104 can efficiently come into contact with the concrete 102. Further, by sealing the gas injection hole 104, leakage of carbon dioxide is prevented, and high safety during work can be ensured.

Cement, which is the raw material of concrete 102, releases a large amount of carbon dioxide during its production. However, by applying this carbon dioxide fixing method, the concrete 102 fixes a large amount of carbon dioxide. Therefore, the method for fixing carbon dioxide according to the embodiment of the present invention can contribute to the reduction of carbon dioxide in the atmosphere and the suppression of global warming. Further, since the concrete 102 can have a high concentration of calcium carbonate produced by the reaction between calcium hydroxide generated by hydration of cement and carbon dioxide, the density of the concrete 102 increases by immobilizing carbon dioxide. As a result, the compression strength increases. In fact, the inventors have confirmed that when carbon dioxide of about 20% (60 kg / m ³ ) of cement is fixed, the compressive strength of concrete increases by about 8% to 10%. Therefore, by applying this carbon dioxide fixation method, it is possible to increase the strength of the existing concrete structure 100.

As a method of fixing carbon dioxide to concrete, a method of placing and contacting hardened concrete in a curing tank filled with carbon dioxide, a method of bringing carbon dioxide into contact with the surface of hardened porous concrete, and ready-mixed concrete. There are known methods such as supplying carbon dioxide into a mold for pouring concrete structure and contacting the concrete structure with the atmosphere. However, the method using a curing tank requires a curing tank for accommodating concrete for fixing carbon dioxide, and cannot be applied to buildings such as buildings, pillars, and tunnels. Even in the method of contacting carbon dioxide with the porous concrete surface, a means for sealing the concrete surface is required, so that it is not realistic to apply it particularly to a large concrete structure. In the method of supplying carbon dioxide into the formwork, it is necessary to form the formwork as a closed space, so that it can be applied to a small structure, but it cannot be applied to a building. In addition, the method using contact with the atmosphere cannot efficiently fix carbon dioxide because the concentration of carbon dioxide in the atmosphere is extremely low.

On the other hand, in the carbon dioxide fixation method according to one of the present embodiments, as long as the gas injection hole 104 can be formed, the type, size, shape, use, and construction site are not particularly restricted. It can be applied to various existing concrete structures 100. Further, since it is not necessary to use new cement except for the step of filling the repair concrete 103, there is almost no need to directly or indirectly utilize the step of producing cement that generates a large amount of carbon dioxide. This means that not only does it not need to create a new reaction substrate to fix carbon dioxide, but there is a huge amount of reaction substrate on the ground. Therefore, it can be said that the carbon dioxide fixing method according to one of the present embodiments can fix an extremely large amount of carbon dioxide and is useful as an effective tool for suppressing global warming.

3. 3. Application example 3-1. Application to lining concrete As described above, the method for fixing carbon dioxide according to one of the embodiments of the present invention can be applied to various concrete structures 100. For example, as shown in FIG. 11A and FIG. 11B, which is an enlarged view thereof, the concrete structure 100 can be applied even if it is a tunnel, and carbon dioxide is used by using the concrete (tunnel lining concrete) 102 constituting the inner wall of the tunnel. Carbon can be fixed. In this case, a plurality of gas injection holes 104 are formed in the concrete 102, and a gas containing carbon dioxide is supplied to the gas injection holes 104. The stretching direction of the gas injection hole 104 is arbitrary, and may be a vertical direction (z direction) or may be inclined from the vertical direction. For example, the gas injection hole 104 may be formed so as to be parallel to the normal of the inner wall of the tunnel or to be inclined from the normal. Further, the gas injection hole 104 may be a through hole penetrating the concrete 102 or a bottomed hole. Even if the gas injection hole 104 is a through hole, the discharge port is a bedrock or ground in contact with the concrete 102, so that the discharge port does not have to be closed when supplying gas containing carbon dioxide.

3-2. Application to concrete structures containing reinforcing bars This method of fixing carbon dioxide can also be applied to concrete structures containing reinforcing bars (reinforced concrete structures). For example, when carbon dioxide is fixed to a concrete structure 100 having a plurality of reinforcing bars 160 and a concrete 102 placed so as to embed the reinforcing bars 160 as shown in FIG. 12A, the reinforcing bars 160 should be avoided. Form one or more gas injection holes 104. That is, each gas injection hole 104 is provided so that the reinforcing bar 160 is not exposed in the gas injection hole 104. In the example shown in FIG. 12B, a plurality of linear gas injection holes 104 are provided so as to extend in the y direction between adjacent reinforcing bars 160.

When the concrete structure 100 is a building, the method for fixing this carbon dioxide can be applied to the reinforced concrete constituting columns and beams. When applied to columns, a gas injection hole 104 is provided so as to avoid reinforcing bars 160 (see FIG. 13A) constituting column main bars, lateral reinforcing bars, and the like (FIG. 13B).

Concrete is alkaline, but when it reacts with carbon dioxide to produce calcium carbonate, it gradually acidifies. When concrete is acidic, the reinforcing bars are corroded, and the expansion of the reinforcing bars due to the corrosion may induce deterioration such as cracking or breakage of the concrete. Therefore, when the concrete structure 100 including the reinforcing bar is used, it is preferable that carbon dioxide is not fixed to the concrete located in the vicinity of the reinforcing bar.

In the concrete structure 100 including the reinforcing bar, the reinforcing bar is not arranged in the center of the concrete structure 100, but is arranged in a zone relatively close to the outer surface. For example, as shown in FIG. 12A, the reinforcing bar 160 is arranged so as to cut off the central portion of the concrete structure, and the concrete 102 is constructed so as to embed the reinforcing bar 160. The same applies to columns made of reinforced concrete. Of the reinforcing bars 160, the reinforcing bars (column main bars) parallel to the extending direction of the columns are arranged so as to surround the central axis of the columns, and the reinforcing bars extending in the horizontal direction called lateral reinforcing bars are the columns. Arranged so as to surround the main bar. Of the concrete 102, the portion outside the reinforcing bar is called cover concrete.

Therefore, in order to prevent carbon dioxide from being fixed to the concrete in the vicinity of the reinforcing bar, as shown in FIG. 14, a protective tube 162 may be provided to cover the portion of the side wall of the gas injection hole 104 made of the cover concrete. The protective tube 162 can be provided on the inlet side and / or the outlet side of the gas injection hole 104, and its end reaches the outer surface of the concrete structure 100. Therefore, a portion of the side wall covered by the protective tube 162 reaches one end (inlet or outlet) of the gas inlet 104. Although not shown, a portion of the protective tube 162 may protrude outward from the gas injection hole 104.

The length L of the protective tube 162 in the direction in which the gas injection hole 104 extends is preferably equal to or larger than the thickness of the cover concrete. More specifically, the length L of the protective tube 162 is the shortest distance D from the reinforcing bar 160 located inside the innermost part of the concrete structure 100 to the outer surface of the concrete 102, and the maximum length of the cross section of the reinforcing bar 160. It is preferably the same as or more than the sum S of (for example, the diameter d of the cross section). Alternatively, the length L is preferably selected from the range of 2 times or more and 5 times or less or 1.5 times or more and 3 times or less of the sum S.

There are no restrictions on the material contained in the protective tube 162, and for example, metal materials such as iron, aluminum, and stainless steel, resins such as epoxy resin, silicone resin, and acrylic resin, and wood may be used. For example, an epoxy-based adhesive or an acrylic-based adhesive may be applied to the injection port and the discharge port side of the gas injection hole 104 so as to have a length of L, and cured to form a protective tube 162.

By arranging the protective tube 162 and preventing contact between the side wall having a length L from the inlet and the discharge port of the gas injection hole 104 and carbon dioxide, the side wall exposed from the protective tube 162 selectively contacts carbon dioxide. Will be done. As a result, carbon dioxide fixation (carbonation) is started from the side wall exposed from the protective tube 162, and then carbonation proceeds from the side wall to the inside of the concrete 102. As a result, as shown in FIG. 14, it is possible to prevent the first zone 102a in which carbon dioxide is fixed from expanding to the reinforcing bar 160, and the second zone in which carbon dioxide is not fixed (that is, not carbonated) can be prevented. Reinforcing bar 160 can be held in the zone 102b of. Since the reinforcing bar 160 is included in the second zone 102b, it is possible to prevent corrosion of the reinforcing bar 160 and deterioration of the concrete 102 due to the corrosion.

When the protective tube 162 is used, the repair concrete 103 may be placed after the protective tube 162 is removed, or the protective tube 162 may be placed while remaining in the gas injection hole 104. In the latter case, the concrete structure 100 includes a protective tube 162, which covers at least a portion of the surface of the repair concrete 103.

In this embodiment, as a model experiment of a method for fixing carbon dioxide according to one of the embodiments of the present invention, carbon dioxide was supplied to a gas injection hole provided in a square columnar concrete, and carbonation of the concrete was evaluated. ..

1. 1. Example 1-1. Fabrication of Concrete with Gas Injection Hole A formwork with an internal volume of 100 mm × 100 mm × 400 mm was prepared, and a metal rod having a cross section diameter of 9 mm and a length of 400 mm was arranged parallel to the longitudinal direction of the formwork. The metal rod was placed so as to pass through the center of the cross section perpendicular to the longitudinal direction of the internal volume of the formwork. Ready-mixed concrete was placed in this formwork. Ready-mixed concrete was prepared by using ordinary Portland cement manufactured by Taiheiyo Cement Co., Ltd. so that the unit water amount was 170 kg / m ³ and the unit cement amount was 340 kg / m ³ (water cement ratio 50%). After 24 hours, the formwork and metal rods were removed to give concrete 102. A schematic perspective view of the concrete 102 is shown in FIG. As shown in FIG. 15, the concrete 102 had a volume of 100 mm × 100 mm × 400 mm, and had a through hole parallel to the longitudinal direction as a gas injection hole 104.

1-2. A carbon dioxide cylinder was connected to one end (injection port) of the carbon dioxide fixation gas injection hole 104 via a rubber hose, and carbon dioxide was continuously supplied to the gas injection hole 104 at a pressure of 0.1 MPa. After the supply of carbon dioxide, the concrete was cut and the liquid property of the pore solution having a cross section perpendicular to the longitudinal direction was evaluated. The liquid property was evaluated by spraying a cross section with a 1% ethanol solution of phenolphthalein as an indicator and confirming the presence or absence of coloration of the indicator.

Twenty-four hours after the start of carbon dioxide supply, as schematically shown in FIG. 15B, the circular region having a diameter of about 60 mm centered on the gas injection hole 104, which is a through hole, was colorless without showing coloration by the indicator. On the other hand, red coloration due to the indicator was observed on the outside of this area. 72 hours after the start of carbon dioxide supply, the entire cross section did not show coloration by the indicator and was colorless.

2. 2. Comparative Example On the other hand, as a comparative example, concrete of the same size without a gas injection hole 104 was prepared and placed in a constant temperature and humidity chamber in an environment with a relative humidity of 60% and a carbon dioxide concentration of 5% to evaluate carbonation. did. As a result of evaluating carbonation in the same manner as the above-mentioned method, the region 12.8 mm from the outer surface after 4 weeks from the start of carbonation and the region 18 mm from the outer surface did not show coloration by the indicator after 8 weeks. In the other areas, red coloration due to the indicator was observed.

3. 3. Discussion When the pH of the concrete pore solution exceeds about 10, the indicator turns red, and when the pH falls below 8.3, it does not show color and remains colorless. Therefore, in the region where red coloration is observed, the pH of the pore solution exceeds 10, and carbonation, that is, carbon dioxide fixation has not progressed, or a sufficient amount of carbon dioxide has not been fixed. Is shown. On the other hand, in the region where no coloration was observed, the pH of the pore solution was below 8.3, indicating that carbonation was sufficiently progressing.

From the results of the examples, it can be seen that carbon dioxide is fixed in about 30% of the concrete 24 hours after the start of supply of carbon dioxide, and carbon dioxide is fixed in the entire concrete 72 hours later. On the other hand, in the comparative example, about 45% was carbonated in 4 weeks (that is, about 672 hours), but only 59% was carbonated in 8 weeks (about 1344 hours). From the above results, by providing a gas injection hole in the concrete and supplying a gas containing a high concentration of carbon dioxide from the gas injection hole, efficiency is achieved without using a device for accommodating the entire concrete such as a constant temperature bath. It was confirmed that carbon dioxide can be fixed well. This indicates that the method for fixing carbon dioxide according to one of the embodiments of the present invention is an extremely useful method for fixing carbon dioxide using a concrete structure, particularly a large concrete structure.

Each of the above-described embodiments of the present invention can be appropriately combined and implemented as long as they do not contradict each other. Those skilled in the art who appropriately add, delete, or change the design based on each embodiment are also included in the scope of the present invention as long as the gist of the present invention is provided.

Of course, other effects different from those brought about by each of the above-described embodiments, which are obvious from the description of the present specification or which can be easily predicted by those skilled in the art, are of course the present invention. It is understood that it is brought about by.

100: Concrete structure, 102: Concrete, 102a: First zone, 102b: Second zone, 103: Repair concrete, 104: Gas injection hole, 106: Plate, 108: Packing, 110: Adapter, 112: О Ring, 114: Cap, 120: Carbon dioxide source, 122: Carbon dioxide line, 124: Pressure gauge, 125: Flow meter, 126: Joint, 128: Densitometer, 129: Humidity gauge, 130: Vacuum pump, 140: Water source, 142: Control device, 150: Formwork, 152: Core material, 154: Ready-mixed concrete, 160: Reinforcing bar, 162: Protective tube

Claims

Forming gas injection holes in the concrete contained in the concrete structure,
Immobilization of carbon dioxide, including introducing a gas containing carbon dioxide into the gas injection hole, and after introducing the gas, capping one end of the gas injection hole to contain the gas in the gas injection hole. how to.
The method of claim 1, further comprising depressurizing the gas injection hole prior to the introduction of the gas.
The method according to claim 1, wherein the gas further contains water.
The gas injection hole is a through hole and is
The method of claim 1, wherein the method further comprises capping the other end of the gas injection hole prior to the introduction of the gas.
The method according to claim 1, wherein the gas injection hole is a bottomed hole.
The method according to claim 1, wherein the opening area of the one end of the gas injection hole is 0.785 mm 2 or more and 177 cm 2 or less.
The method according to claim 1, wherein the gas injection hole extends perpendicularly to the outer surface of the concrete structure.
The method according to claim 1, wherein the gas injection hole extends in a direction inclined with respect to the outer surface of the concrete structure.
Further including covering a part of the side wall of the gas injection hole with a protective tube, the part reaches the one end of the gas injection hole and
The concrete structure contains reinforcing bars and contains
The method according to claim 1, wherein the length of the protective tube in the direction in which the gas injection hole extends is larger than the sum of the shortest distance from the outer surface of the concrete structure to the reinforcing bar and the diameter of the reinforcing bar.
The method according to claim 1, further comprising placing concrete in the gas injection hole after the introduction of the gas.
The method according to claim 1, wherein the gas injection hole is formed by using a drill.
The formation of the concrete structure is
It is performed by pouring ready-mixed concrete so as to embed at least a part of the core material in the formwork in which the core material is arranged, and by hardening the ready-mixed concrete.
The method according to claim 1, wherein the formation of the gas injection hole is performed by removing the core material.
A second concrete, which is different in composition from the first concrete and the first concrete, is surrounded by the first concrete and extends in a first direction toward the inside of the first concrete, and includes a second concrete.
The first concrete includes a first zone in contact with the second concrete and a second zone surrounding the first zone.
The concentration of calcium carbonate in the first zone decreases continuously as the distance from the interface between the first concrete and the second concrete increases in the second direction perpendicular to the first direction. death,
A concrete structure in which the concentration of calcium carbonate in the second zone is constant in the second direction.
The concrete structure according to claim 13, wherein the second zone includes reinforcing bars.
The concrete structure according to claim 13, wherein the area of the cross section of the first concrete parallel to the second direction is 0.785 mm 2 or more and 177 cm 2 or less.
The concrete structure according to claim 13, further comprising a protective tube that is in contact with the first concrete and covers at least a part of the surface of the second concrete.
Includes concrete with bottomed or through holes extending in the first direction,
The concrete includes a first zone constituting the bottomed hole or the side wall of the through hole, and a second zone surrounding the first zone.
The concentration of calcium carbonate in the first zone decreases continuously as the distance from the sidewall increases in the second direction perpendicular to the first direction.
A concrete structure in which the concentration of calcium carbonate in the second zone is constant in the second direction.
The concrete structure according to claim 17, wherein the second zone includes reinforcing bars.
The concrete structure according to claim 17, wherein the area of the cross section of the bottom hole or the through hole parallel to the second direction is 0.785 mm 2 or more and 177 cm 2 or less.
The concrete structure according to claim 17, further including a protective tube in contact with a part of the side wall on the outer surface side of the concrete.