Method for fixing carbon dioxide to concrete

Abstract

To provide a method for efficiently fixing carbon dioxide in concrete.SOLUTION: A method for fixing carbon dioxide in concrete according to the present invention includes forming a gas injection hole in concrete contained 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 contain the gas containing carbon dioxide into the gas injection hole. The fixing method may further include decompressing the gas injection hole before introducing the gas containing carbon dioxide. The gas containing carbon dioxide may further include water.SELECTED DRAWING: Figure 7B

Description

[Technical field]

[0001] One embodiment of the present invention relates to a method for fixing carbon dioxide in concrete contained in a concrete structure, and a concrete structure to which this method is applied. [Background technology]

[0002] Concrete is mainly composed of cement hydrate, aggregate, water, and additives, and is widely used in various fields as one of the important structural materials for creating social production infrastructure and economic infrastructure due to its excellent mechanical properties, weather resistance, ease of handling, and economic efficiency. It is known that cement emits a large amount of carbon dioxide during its production, which is cited as one of the causes of the greenhouse effect. In order to contribute to solving this problem, for example, Patent Document 1 discloses a method for fixing carbon dioxide in concrete by contacting carbon dioxide with ready-mixed concrete before the concrete hardens when constructing a structure containing concrete (hereinafter, concrete structure). Patent Document 2 discloses a method for designing a concrete structure that is effective in promoting the absorption of carbon dioxide into concrete. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5957283 [Patent Document 2] Patent No. 4822373 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of one embodiment of the present invention is to provide a method for efficiently fixing carbon dioxide in concrete. For example, an object of one embodiment of the present invention is to provide a method for fixing carbon dioxide in concrete contained in an existing concrete structure. Alternatively, an object of one embodiment of the present invention is to provide a concrete structure obtained by applying the above method. [Means for solving the problem]

[0005] One embodiment of the present invention is a method for fixing carbon dioxide in concrete, the method including forming a gas injection hole in concrete contained in a concrete structure, introducing a gas including carbon dioxide into the gas injection hole, and, after the introduction of the gas, capping one end of the gas injection hole to contain the gas in the gas injection hole.

[0006] One embodiment of the present invention is a concrete structure. The structure includes a first concrete and a second concrete. The second concrete is different in composition from the first concrete, is surrounded by the first concrete, and extends in a 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 with increasing distance from the interface between the first concrete and the second concrete in a second direction perpendicular to the first direction. The concentration of calcium carbonate in the second zone is constant in the second direction.

[0007] One embodiment of the present invention is a concrete structure. The structure includes concrete having blind holes or through holes extending in a first direction. The concrete has blind holes or through holes. The through hole includes a first zone constituting a sidewall of the through hole and a second zone surrounding the first zone, the concentration of calcium carbonate in the first zone continuously decreasing with increasing distance from the sidewall in a second direction perpendicular to the first direction, and the concentration of calcium carbonate in the second zone being constant in the second direction. [Brief description of the drawings]

[0008] [Figure 1A] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 1B] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 1C] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 2A] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 2B] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 3A] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 3B] FIG. 2 is a top view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 4A] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 4B] FIG. 2 is a top view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Diagram 5] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 6A] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 6B]FIG. 2 is a side view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 7A] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 7B] FIG. 2 is a side view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 8A] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 8B] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 9A] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 9B] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 9C] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 10A] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 10B] FIG. 1 is a schematic diagram showing the composition in concrete obtained by a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 10C] FIG. 1 is a schematic diagram showing the composition in concrete obtained by a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 11A] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 11B] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 12A] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 12B] FIG. 2 is a top view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 13A] FIG. 1 is a perspective view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 13B] FIG. 2 is a side view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 14] FIG. 2 is a cross-sectional view illustrating a method for fixing carbon dioxide in concrete, which is one embodiment of the present invention. [Figure 15A] FIG. 2 is a perspective view of a concrete structure used in the examples. [Figure 15B] FIG. 2 is a cross-sectional view of a concrete structure used in the examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, each embodiment of the present invention will be described with reference to the drawings, etc. However, the present invention can be embodied in various forms without departing from the spirit of the present invention, and the present invention should not be interpreted as being limited to the description of the embodiments exemplified below.

[0010] In order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part in a schematic manner compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each drawing, elements having the same functions as those described in the previous drawings may be given the same reference numerals, and duplicated descriptions may be omitted.

[0011] Hereinafter, the expression "a structure is exposed from another structure" refers to a configuration in which a part of a structure is not covered by another structure, and also includes a configuration in which the part not covered by the other structure is covered by yet another structure.

[0012] Hereinafter, concrete refers to a material that is made by reacting cement, one of the raw materials, with water to produce a hydrate that has hardened and no longer exhibits fluidity. On the other hand, a mixture containing cement and water that has not completely hardened and still retains fluidity will be referred to as ready-mixed concrete (also called ready-mix concrete).

[0013] Hereinafter, a method for fixing carbon dioxide using an existing concrete structure according to one embodiment of the present invention and a concrete structure to which this method is applied will be described with reference to the accompanying drawings. In these drawings, for convenience, the xy plane is taken as the horizontal plane and the z direction is taken as the vertical direction.

[0014] 1. Overview In a method for fixing carbon dioxide according to one embodiment of the present invention, a concrete structure containing hardened concrete is used as a substrate for fixing carbon dioxide. That is, carbon dioxide is fixed (carbonation of concrete) by contacting the concrete contained in the concrete structure with carbon dioxide. There are no limitations on the type, shape, use, or installation location of the concrete structure, and any existing concrete structure can be used. The existing concrete structure may be, for example, a building pillar or foundation beam, a bridge pier or abutment, a levee or breakwater installed in a river or harbor, a wave-dissipating block, or a concrete lining used in a road or tunnel. Alternatively, movable property (concrete product) containing concrete, such as a square or U-shaped concrete block or a footing stone, may be used.

[0015] 2. Methods for fixing carbon dioxide 2-1. Formation of gas injection holes 1A shows a schematic perspective view of a concrete structure 100. The concrete structure 100 shown here is a schematic representation of the whole or part of various concrete structures, and as described above, there is no limitation on the type, shape, or use of the concrete structure.

[0016] In a carbon dioxide fixation method according to one embodiment of the present invention, first, a gas injection hole 104 is formed in concrete 102 constituting a concrete structure 100. As shown in schematic cross-sectional views (FIGS. 1B and 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), or may be a bottomed hole with one end closed (FIG. 1C). The gas injection hole 104 may be formed to extend linearly, or may include a bent shape (not shown). In addition, as shown in FIGS. 2A and 2B, a plurality of gas injection holes 104 may be provided. In this case, the directions in which the plurality of gas injection holes 104 extend 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 extension 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 extend in a direction inclined to the outer surface of the concrete structure 100. Although not shown, multiple gas injection holes 104 may intersect. In other words, the gas injection holes 104 may be formed in a network shape within the concrete 102.

[0017] The surface on which the gas injection hole 104 is provided is not limited to a surface perpendicular to the horizontal plane, but may be a surface parallel to the horizontal plane (for example, the top surface of the concrete structure 100), or the gas injection hole 104 may be provided on a surface inclined at an angle of less than 90° from the horizontal plane.

[0018] The cross-sectional area of ​​the gas injection hole 104, i.e., the opening area of ​​the gas injection hole 104 on the outer surface of the concrete 102, can be set arbitrarily. For example, if the cross-sectional shape of the gas injection hole 104 (the shape on the outer surface of the concrete structure 100) is a circle, its 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 may be 0.785 mm 2 More than 78.5cm 2 Less than or equal to 3.14mm 2 over 177cm 2By selecting the above-mentioned range, the gas injection holes 104 can be formed without significantly impairing the strength and aesthetic appearance of the concrete structure 100.

[0019] The gas injection holes 104 may be formed from the outer surface of the concrete 102 toward the inside using a drill such as a vibratory drill or a hammer drill.

[0020] Alternatively, the gas injection hole 104 may be formed at the same time as the concrete structure 100 is formed. Specifically, a formwork 150 is prepared to determine the shape of the concrete structure 100 (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 placed in the formwork 150 (FIGS. 3A and 3B). The core material 152 may be provided so that a part of it is exposed from the formwork 150. The shape of the core material 152 may be determined in consideration of the shape of the gas injection hole 104, and may be a straight rod shape, or may be partially or entirely bent. In addition, the core material 152 may be a hollow tube or may not be hollow (solid). There is no restriction on the material contained in the core material 152, and it may be, for example, a metal material such as aluminum, iron, or stainless steel, wood, or resin. The resin may be, for example, a fiber-reinforced plastic composited with fibers such as glass fiber or carbon fiber. A release agent (mold release agent) or a hardening retarder may be applied to the outer surface of the core material 152. By applying the release agent or hardening retarder, the core material 152 can be easily removed from the concrete 102 to form the gas injection holes 104, as described below.

[0021] Subsequently, concrete 102 is poured. That is, ready-mixed concrete 154 is poured into formwork 150 (FIGS. 4A and 4B). At this time, ready-mixed concrete 154 is poured so that at least a portion of core material 152 is embedded in formwork 150 by ready-mixed concrete 154. Ready-mixed concrete 154 contains at least water and cement, but may also contain aggregates such as sand, gravel, boulders, rocks, crushed stone, and crushed sand, as well as additives such as air-bubble dispersants, fluidizing agents, thickeners, and quick-setting agents.

[0022] The ready-mixed concrete 154 is hardened and the formwork 150 is removed to form the structure 100. Furthermore, by removing the core material 152, the gas injection holes 104 can be formed in the concrete structure 100 (FIG. 5). It is not necessary to remove the core material 152. For example, when the gas injection holes 104 are 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 fine openings may be used, and carbon dioxide may be brought into contact with the concrete 102 via the core material 152.

[0023] 2-2. Introduction of carbon dioxide Next, in order to fix the carbon dioxide in 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 (inlet) of the gas injection hole 104 via a carbon dioxide line 122, and the 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 number of gas injection holes 104 may be used and the carbon dioxide supply sources 120 corresponding to each gas injection hole 104 may be connected, or a branched carbon dioxide line 122 may be used to connect the carbon dioxide supply sources 120 to the gas injection holes 104, which are less than the number of the gas injection holes 104. The carbon dioxide line 122 may be 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 (i.e., the pressure inside the gas injection hole 104).

[0024] The method of connecting the carbon dioxide line 122 and the gas injection hole 104 can be selected arbitrarily, and the tip of the carbon dioxide line 122 may simply be inserted into the gas injection hole 104. Alternatively, in order to stably maintain the connection state, for example, as shown in FIG. 7A, an adapter 110 having an opening with a female thread structure may be attached to the injection port, and a joint 126 having a male thread structure that meshes with the female thread structure may be attached to the tip of the carbon dioxide line 122. 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 to prevent leakage of gas including carbon dioxide.

[0025] When the gas injection hole 104 is a through hole, the other end (exhaust port) is capped to seal the gas containing carbon dioxide, thereby preventing leakage of the gas containing carbon dioxide and enabling more effective contact between the concrete 102 and carbon dioxide. For example, the exhaust port may be sealed using adhesive tape, an elastic body such as rubber, or the like, or, as shown in Figs. 6B and 7A, the gas injection hole 104 may be sealed using a plate 106 containing a resin such as acrylic resin, epoxy resin, polyester resin, or polyimide resin, 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 using bolts or screws, or the plate 106 that matches the shape of the exhaust port may simply be inserted into the exhaust port. Alternatively, the plate 106 may be fixed using an adhesive or adhesive tape. Also, as shown in Fig. 8A, in order to improve the airtightness of the gas injection hole 104, the exhaust port may be closed with a packing 108 containing an elastic body such as rubber, and the plate 106 may be provided so as to sandwich the packing 108 between the concrete 102.

[0026] The gas containing carbon dioxide may be pure carbon dioxide (e.g., purity of 99% or more) or a mixed gas of carbon dioxide and other gases. When a mixed gas is used, the other gases may include air, oxygen, nitrogen, etc. The concentration of carbon dioxide in the mixed gas can also be set arbitrarily, but in order to efficiently bring the concrete 102 into contact with the carbon dioxide, it is preferable that the concentration is higher than the concentration of carbon dioxide contained in the atmosphere (approximately 420 ppm). For example, the carbon dioxide concentration may be set to any concentration between 1% by volume and 100% by volume, 10% by volume and 50% by volume, or 10% by volume and 20% by volume.

[0027] The carbon dioxide supply source 120 may have a function of supplying a gas containing carbon dioxide to the gas injection hole 104, and may be, for example, a cylinder or tank of a gas containing carbon dioxide as shown in FIG. 6A. The carbon dioxide supply source 120 is connected to a regulator (not shown) to adjust the pressure of the gas containing carbon dioxide. Alternatively, if facilities that emit a large amount of carbon dioxide (such as chemical plants, waste incineration facilities, thermal power plants, and various other factories) are already installed near the concrete structure 100, gases emitted by these facilities or purified carbon dioxide obtained by subjecting the exhaust gas to dedusting, desulfurization, denitrification, and the like may be used. In this case, these facilities function as the carbon dioxide supply source 120, so that the cost of transporting carbon dioxide is reduced and further emission of carbon dioxide associated with the transportation is prevented.

[0028] The gas containing carbon dioxide may be introduced so that the pressure inside the gas injection hole 104 is higher than 0 MPa and equal to or lower than 2 MPa. When the pressure inside the gas injection hole 104 is lower than atmospheric pressure (e.g., 1 atmosphere or 0.101 MPa), a vacuum pump 130 such as a rotary oil pump or a dry pump may be connected to the carbon dioxide line 122, and the gas containing carbon dioxide may be introduced after reducing the pressure inside the gas injection hole 104. Conversely, when pressure increase is required, a compressor or the like may be used.

[0029] The gas containing carbon dioxide may be introduced steadily 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, and the injection hole may be closed to seal the gas injection hole 104. For example, the injection hole may be sealed with an adhesive tape, or an elastic body such as rubber may be inserted into the injection hole to seal it. Alternatively, as shown in FIG. 8B, the gas injection hole 104 may be sealed with 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 held in the gas injection hole 104 and leakage of carbon dioxide can be prevented.

[0030] As an optional configuration, a concentration meter 128 for measuring the carbon dioxide concentration may be provided inside the gas injection hole 104 (for example, in the side wall or cap 114 of the gas injection hole 104) to periodically measure the carbon dioxide concentration. This makes it possible to monitor changes in the carbon dioxide concentration.

[0031] 2-3. Adjusting humidity It is known that the rate at which carbon dioxide is fixed into concrete also depends on humidity, and that carbon dioxide is fixed at a high rate when the humidity is about 50%. For this reason, even in one embodiment of the present invention, the humidity inside 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 be equipped with a heating device or a cooling device for controlling the temperature of the water supplied. Alternatively, gas containing carbon dioxide may be supplied from the carbon dioxide supply source 120 to the water supply source 140, and water containing carbon dioxide may be supplied to the gas injection hole 104.

[0032] Optionally, a hygrometer 129 for measuring humidity may be provided inside gas injection hole 104 (e.g., in the side wall or cap 114 of gas injection hole 104) to periodically measure the humidity (FIG. 7B). This allows changes in humidity to be monitored.

[0033] On the other hand, when the humidity inside gas injection hole 104 is high, when a large amount of water is adsorbed on the side wall of gas injection hole 104, when the side wall of gas injection hole 104 is frozen, or when concrete 102 contains a large amount of water, the inside of gas injection hole 104 may be depressurized using vacuum pump 130 in order to remove some of the water inside gas injection hole 104. Then, gas containing carbon dioxide may be supplied into gas injection hole 104.

[0034] The contact time between the concrete 102 and the gas containing carbon dioxide depends on the length and cross-sectional area of ​​the gas injection hole 104 (i.e., the volume of the gas injection hole 104), the temperature, and the carbon dioxide concentration of the gas containing carbon dioxide, but may be, for example, from 1 hour to 20 years, from 1 day to 10 years, from 10 weeks to 5 years, or from 1 year to 3 years.

[0035] The supply of carbon dioxide and water may be performed using a control device 142 as shown in FIG. 7A. The control device 142 is supplied with carbon dioxide and water from the carbon dioxide supply source 120 and the water supply source 140, respectively. The control device 142 includes a mechanism (such as an air pump) for supplying a gas containing carbon dioxide to the gas injection hole 104. The control device 142 may further be configured to prepare a gas containing carbon dioxide having an appropriate humidity using the supplied water and carbon dioxide, and supply this gas to the gas injection hole 104. Alternatively / additionally, the control device 142 may be configured to control the temperature of the gas containing carbon dioxide to be supplied to the gas injection hole 104. By providing the control device 142 with such a function, the gas containing carbon dioxide can be supplied into the gas injection hole 104 at a temperature and humidity that provide a high carbon dioxide fixation rate.

[0036] 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, such as a circulation pump, for recovering the gas discharged from the gas injection hole 104 and supplying it again to the gas injection hole 104. The control device 142 may be configured to measure the concentration and humidity of carbon dioxide contained in the gas discharged from the gas injection hole 104 and add carbon dioxide and water to the gas as appropriate based on the obtained data. This allows the inside of the gas injection hole 104 to be constantly kept under conditions that provide an optimal carbon dioxide fixation rate.

[0037] Through the steps up to this point, carbon dioxide is fixed in the concrete 102.

[0038] 2-4. Pouring concrete into the gas injection hole As an optional step, new repair concrete 103 may be poured into the gas injection hole 104 of the concrete structure 100 in which carbon dioxide has been fixed. Specifically, as shown in Figs. 9A to 9C, ready-mixed concrete is filled into the gas injection hole 104 and hardened. In the concrete structure 100, the repair concrete 103 extending into the concrete 102 is surrounded by the concrete 102. The area of ​​the cross section of the repair concrete 103 (cross section perpendicular to the direction in which the repair concrete 103 extends) is the same or substantially the same as the opening area of ​​the gas injection hole 104, and is, for example, 0.785 mm 2 over 177cm 2 The following is the result.

[0039] The repair concrete 103 may be poured over the entire gas injection hole 104, or, although not shown, may be poured over only a portion of the injection hole side. Pouring the repair concrete 103 makes it possible to compensate for the structural strength lost by forming the gas injection hole 104, and also makes it possible to maintain the aesthetic appearance of the concrete structure 100.

[0040] As will be described in detail later, the concrete 102 contained in the concrete structure 100 has an increased calcium carbonate composition due to carbon dioxide being fixed from the side walls of the gas injection holes 104. Therefore, the compositions of the concrete 102 and the repair concrete 103 may differ from each other. In this case, the former has a higher calcium carbonate concentration, and the latter has a higher calcium hydroxide concentration.

[0041] 2-5. Carbon dioxide-fixed concrete structure When carbon dioxide is brought into contact with the concrete 102 contained in the concrete structure 100 using the above-mentioned method, calcium hydroxide, calcium silicate (CSH), monosulfate, ettringite, unhydrated cement, and the like contained in the concrete 102 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 is also called carbonation, which first occurs from the side wall of the gas injection hole 104 and progresses 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 perpendicular to the extension direction of the gas injection hole 104 (FIG. 10A), carbonation in principle progresses isotropically in the direction perpendicular to the extension direction of the gas injection hole 104 (i.e., in the xz plane) (see the solid arrow in FIG. 10A). The degree of carbonation is higher closer to the gas injection hole 104. Therefore, the concrete 102 has a first zone 102a (a zone surrounded by a circle drawn with a chain line in FIG. 10A) in which the calcium carbonate concentration is relatively high and which constitutes the side wall of the gas injection hole 104, and a second zone 102b (a zone outside the circle) in which the calcium carbonate concentration is lower than that of the first zone 102a and which surrounds the first zone 102a. The first zone 102a and the second zone 102b are in contact with each other.

[0042] For this reason, as shown in FIG. 10B, in the first zone 102a, in a direction perpendicular to the y direction, i.e., in any direction in the xz plane (see, for example, the arrow a in FIG. 10A), the concentration of calcium carbonate in the concrete 102 decreases continuously as the distance from the side wall of the gas injection hole 104 increases. When the repair concrete 103 is filled, the concentration of calcium carbonate in the concrete 102 increases continuously as the distance from the interface between the repair concrete 103 and the concrete 102 increases. The zone where this increase stops and the concentration of calcium carbonate becomes 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.

[0043] 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 increases continuously in any direction in the xz plane as the distance from the side wall of the gas injection hole 104 increases. When filling the repair concrete 103, the concentration of calcium hydroxide in the concrete 102 decreases continuously as the distance from the interface between the repair concrete 103 and the concrete 102 increases. In the second zone 102b, an increase in the concentration of calcium hydroxide is not substantially observed, and the concentration of calcium hydroxide is constant or substantially constant. Although not shown, the concentration of calcium hydroxide in the repair concrete 103 is constant or substantially constant.

[0044] Similarly, in the direction from the outer surface of the concrete 102 to the opposite outer surface (see arrow b in FIG. 10A ), the plot of calcium carbonate concentration versus 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, where the concentrations of calcium carbonate and calcium hydroxide are constant or substantially constant. The second stage corresponds to the first zone 102a after passing the interface between the first zone 102a and the second zone 102b and back to the interface between the first zone 102a and the second zone 102b, where the concentration of calcium carbonate increases continuously and then decreases, and the concentration of calcium hydroxide decreases continuously and then increases. The third stage corresponds to the second zone 102b passing through the interface of the first zone 102a and the second zone 102b for the second time to the outer surface of the concrete structure 100, where the concentrations of calcium carbonate and calcium hydroxide are constant or substantially constant.

[0045] In the above-mentioned method for fixing carbon dioxide, the concrete 102 of the concrete structure 100 can come into contact with carbon dioxide in the gas injection hole 104 at a concentration that is extremely high compared to the carbon dioxide concentration in the atmosphere. Therefore, the carbon dioxide introduced into the gas injection hole 104 can efficiently come into contact with the concrete 102. Furthermore, by sealing the gas injection hole 104, leakage of carbon dioxide is prevented, and high safety during work can be ensured.

[0046] Cement, which is a raw material for concrete 102, releases a large amount of carbon dioxide during its production. However, by applying this carbon dioxide fixation method, concrete 102 will fix a large amount of carbon dioxide. Therefore, the carbon dioxide fixation method according to the embodiment of the present invention can contribute to reducing carbon dioxide in the atmosphere and curbing global warming. Furthermore, since concrete 102 can have a high concentration of calcium carbonate, which is produced by the reaction between carbon dioxide and calcium hydroxide produced by the hydration of cement, the density of concrete 102 increases by fixing carbon dioxide, and as a result, the compressive strength increases. In fact, the inventors have found that the carbon dioxide fixation method can fix a large amount of carbon dioxide in concrete 102 by approximately 20% (60 kg / m 3 It has been confirmed that when carbon dioxide is fixed, the compressive strength of the concrete increases by about 8% to 10%. Therefore, by applying this carbon dioxide fixation method, it is also possible to increase the strength of an existing concrete structure 100.

[0047] Known methods of fixing carbon dioxide in concrete include placing hardened concrete in a curing tank filled with carbon dioxide and contacting it, contacting the surface of hardened porous concrete with carbon dioxide, supplying carbon dioxide into a formwork for pouring ready-mixed concrete, and contacting a concrete structure with the atmosphere. However, the method using a curing tank requires a curing tank to contain the concrete for fixing carbon dioxide, and cannot be applied to buildings, such as buildings, columns, and tunnels. The method of contacting the surface of porous concrete with carbon dioxide also requires a means for sealing the concrete surface, so it is not practical to apply it to large concrete structures in particular. The method of supplying carbon dioxide into a formwork requires the formwork to be formed as a closed space, so it can be applied to small structures but cannot be applied to buildings. In addition, the method of using contact with the atmosphere does not allow efficient carbon dioxide fixation because the carbon dioxide concentration in the atmosphere is extremely low.

[0048] In contrast, the carbon dioxide fixation method according to one of the present embodiments can be applied to various existing concrete structures 100 without any particular restrictions on type, size, shape, use, or construction location, as long as the gas injection hole 104 can be formed. In addition, since there is no need to use new cement except for the step of filling the repair concrete 103, there is almost no need to directly or indirectly use the cement production step that generates a large amount of carbon dioxide. This means that not only is it not necessary to newly produce a reactive substrate for fixing carbon dioxide, but also that a huge amount of reactive substrate exists on the ground. Therefore, it can be said that the carbon dioxide fixation 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.

[0049] 3. Application Examples 3-1. Application to lining concrete As described above, the method for fixing carbon dioxide according to one embodiment of the present invention can be applied to various concrete structures 100. For example, as shown in FIG. 11A and its enlarged view in FIG. 11B, the method can be applied even if the concrete structure 100 is a tunnel, and carbon dioxide can be fixed by using the concrete (tunnel lining concrete) 102 that constitutes the inner wall of the tunnel. In this case, a plurality of gas injection holes 104 are formed in the concrete 102, and gas containing carbon dioxide is supplied to the gas injection holes 104. The extension direction of the gas injection holes 104 is arbitrary, and may be the vertical direction (z direction) or may be inclined from the vertical direction. For example, the gas injection holes 104 may be formed parallel to the normal line of the inner wall of the tunnel, or inclined from the normal line. In addition, the gas injection holes 104 may be through holes that penetrate the concrete 102, or may be bottomed holes. Even if the gas injection holes 104 are through holes, the exhaust outlet is a bedrock or ground that contacts the concrete 102, so that it is not necessary to close the exhaust outlet when supplying the gas containing carbon dioxide.

[0050] 3-2. Application to concrete structures containing reinforcing bars This carbon dioxide fixation method can also be applied to concrete structures containing reinforcing bars (reinforced concrete structures). For example, when fixing carbon dioxide to a concrete structure 100 having a plurality of reinforcing bars 160 and concrete 102 poured so as to embed the reinforcing bars 160 as shown in Fig. 12A, one or a plurality of gas injection holes 104 are formed so as to avoid the reinforcing bars 160. That is, each gas injection hole 104 is provided so that the reinforcing bars 160 are not exposed within 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.

[0051] When the concrete structure 100 is a building, the carbon dioxide fixation method can be applied to the reinforced concrete that constitutes the columns and beams. When applied to columns, the gas injection holes 104 are provided so as to avoid the reinforcing bars 160 (see FIG. 13A) that constitute the column main reinforcement and transverse reinforcement bars (FIG. 13B).

[0052] Concrete is alkaline, but when it reacts with carbon dioxide to produce calcium carbonate, it gradually becomes acidic. When concrete becomes acidic, the reinforcing bars corrode, and the expansion of the reinforcing bars due to corrosion can induce deterioration such as cracking and breakage of the concrete. Therefore, when using a concrete structure 100 containing reinforcing bars, it is preferable that carbon dioxide is not fixed in the concrete located near the reinforcing bars.

[0053] In a concrete structure 100 including reinforcing bars, the reinforcing bars are not placed in the center of the concrete structure 100, but in a zone relatively close to the outer surface. For example, as shown in Fig. 12A, reinforcing bars 160 are placed to process the center of the concrete structure, and concrete 102 is constructed to embed the reinforcing bars 160. The same is true for columns made of reinforced concrete, where reinforcing bars 160 parallel to the extension direction of the column (column main reinforcement) are placed to surround the central axis of the column, and reinforcing bars extending horizontally, called lateral reinforcement bars, are placed to surround the column main reinforcement. Of the concrete 102, the portion outside the reinforcing bars is called cover concrete.

[0054] Therefore, in order to prevent carbon dioxide fixation in the concrete near the reinforcing bars, a protective tube 162 may be provided to cover the portion of the side wall of the gas injection hole 104 that is made of covering concrete, as shown in Fig. 14. The protective tube 162 may be provided on the injection port side and / or the exhaust port side of the gas injection hole 104, and its end reaches the outer surface of the concrete structure 100. Therefore, a part of the side wall covered by the protective tube 162 reaches one end (injection port or exhaust port) of the gas injection hole 104. Although not shown, a part of the protective tube 162 may protrude outward from the gas injection hole 104.

[0055] The length L of the protective tube 162 in the direction in which the gas injection holes 104 extend is preferably equal to or greater than the thickness of the covering concrete. More specifically, the length L of the protective tube 162 is preferably equal to or greater than the sum S of the shortest distance D from the reinforcing bar 160 located at 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 (e.g., the diameter d of the cross section). Alternatively, the length L is preferably selected from the range of 2 to 5 times the sum S, or 1.5 to 3 times the sum S.

[0056] There are no restrictions on the material contained in protective tube 162, and it may be, for example, a metal material such as iron, aluminum, or stainless steel, a resin such as epoxy resin, silicone resin, or acrylic resin, or wood. For example, protective tube 162 may be formed by applying an epoxy adhesive or an acrylic adhesive to the inlet and outlet sides of gas injection hole 104 to a length L and curing it.

[0057] By disposing the protective tube 162 and preventing the side wall of the length L from the inlet and outlet of the gas injection hole 104 from contacting with carbon dioxide, the side wall exposed from the protective tube 162 is selectively brought into contact with carbon dioxide. As a result, fixation (carbonation) of carbon dioxide starts from the side wall exposed from the protective tube 162, and then carbonation progresses 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 reinforcing bar 160 can be held in the second zone 102b in which carbon dioxide is not fixed (i.e., not carbonated). Since the reinforcing bar 160 is included in the second zone 102b, corrosion of the reinforcing bar 160 and deterioration of the concrete 102 caused by this can be prevented.

[0058] When the protective tube 162 is used, the repair concrete 103 may be cast after removing the protective tube 162, or may be cast while the protective tube 162 remains in the gas injection hole 104. In the latter case, the concrete structure 100 includes the protective tube 162, which covers at least a portion of the surface of the repair concrete 103. EXAMPLES

[0059] In this example, as a model experiment of a method for fixing carbon dioxide according to one embodiment of the present invention, carbon dioxide was supplied to a gas injection hole provided in a square prism-shaped concrete, and the carbonation of the concrete was evaluated.

[0060] 1. Example 1-1. Preparation of concrete with gas injection holes A formwork with an internal volume of 100mm x 100mm x 400mm was prepared, and a metal rod with a cross-sectional diameter of 9mm and length of 400mm was placed parallel to the longitudinal direction of the formwork. The metal rod was placed so as to pass through the centre of the cross section perpendicular to the longitudinal direction of the internal volume of the formwork. Ready-mixed concrete was poured into this formwork. The ready-mixed concrete used ordinary Portland cement manufactured by Taiheiyo Cement Corporation, with a unit water content of 170kg / m 3 , unit cement amount 340kg / m 3 (Water-cement ratio 50%). After 24 hours, the formwork and metal rods were removed to obtain concrete 102. A schematic perspective view of concrete 102 is shown in FIG. 15. As shown in FIG. 15, concrete 102 had a volume of 100 mm×100 mm×400 mm, and had through holes parallel to its longitudinal direction as gas injection holes 104.

[0061] 1-2. Carbon dioxide fixation A carbon dioxide cylinder was connected to one end (inlet) of the 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 supplying carbon dioxide, the concrete was cut and the liquid properties of the pore solution in a cross section perpendicular to the longitudinal direction were evaluated. The liquid properties were evaluated by spraying a 1% ethanol solution of phenolphthalein as an indicator onto the cross section and checking whether the indicator changed color.

[0062] 15B, a circular region of about 60 mm in diameter centered on gas injection hole 104 (a through hole) was colorless and did not show any coloring due to the indicator, whereas a red coloring due to the indicator was observed outside this region. 72 hours after the start of carbon dioxide supply, the entire cross section was colorless and did not show any coloring due to the indicator.

[0063] 2. Comparative Example Meanwhile, as a comparative example, concrete of the same size without gas injection holes 104 was prepared and left to stand in a thermo-hygrostat in an environment of 60% relative humidity and 5% carbon dioxide concentration to evaluate carbonation. Carbonation was evaluated in the same manner as above, and as a result, after 4 weeks from the start of carbonation, an area 12.8 mm from the outer surface and after 8 weeks, an area 18 mm from the outer surface showed no coloring due to the indicator, while red coloring due to the indicator was observed in the other areas.

[0064] 3. Discussion When the pH of the concrete pore solution is above about 10, the indicator turns red, and when the pH is below 8.3, the indicator remains colorless. Thus, in areas where red coloring is observed, the pH of the pore solution is above 10, indicating that carbonation, i.e., carbon dioxide fixation, is not progressing or that a sufficient amount of carbon dioxide has not been fixed. On the other hand, in areas where no coloring is observed, the pH of the pore solution is below 8.3, indicating that carbonation is progressing sufficiently.

[0065] 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 carbon dioxide supply, and carbon dioxide is fixed in the entire concrete after 72 hours. On the other hand, in the comparative example, about 45% is carbonated in 4 weeks (i.e., about 672 hours), but even after 8 weeks (about 1344 hours), carbonation remains at 59%. From the above results, it was confirmed that carbon dioxide can be efficiently fixed 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, without using a device for containing the entire concrete, such as a thermostatic chamber. This shows that the carbon dioxide fixation method according to one embodiment of the present invention is an extremely useful method for carbon dioxide fixation using concrete structures, especially large concrete structures.

[0066] The above-described embodiments of the present invention may be combined as appropriate as long as they are not mutually inconsistent. Any embodiment in which a person skilled in the art appropriately adds or deletes components or modifies the design based on each embodiment is also included in the scope of the present invention as long as it includes the gist of the present invention.

[0067] Even if there are other effects and advantages different from those brought about by the respective embodiments described above, those which are clear from the description in this specification or which can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention. [Explanation of symbols]

[0068] 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: O-ring, 114: cap, 120: carbon dioxide supply source, 122: carbon dioxide line, 124: pressure gauge, 125: flow meter, 126: joint, 128: concentration meter, 129: humidity meter, 130: vacuum pump, 140: water supply source, 142: control device, 150: formwork, 152: core material, 154: ready mixed concrete, 160: reinforcing bar, 162: protective tube

Claims

1. forming gas injection holes in the concrete structure; introducing a gas comprising carbon dioxide into the gas injection hole; recovering the gas discharged from the gas injection hole with a control device; and supplying the recovered gas to the gas injection hole.

2. The method further includes adding at least one of carbon dioxide and water to the recovered gas in the control device; The method of claim 1 , comprising supplying the gas to which at least one of the carbon dioxide and water has been added to the gas injection hole.

3. measuring the carbon dioxide concentration and humidity of the gas discharged from the gas injection hole; The method of claim 2 , wherein the controller is configured to add at least one of the carbon dioxide and water to the gas discharged from the gas injection hole based on the carbon dioxide concentration and the humidity.

4. The method of claim 1 , wherein the gas injection holes extend through the concrete structure.

5. The method of claim 3 further comprising measuring a carbon dioxide concentration and a humidity of the gas provided from the controller to the gas injection hole.

6. 10. The method of claim 1, further comprising pouring concrete into the gas injection hole after delivering the recovered gas to the gas injection hole.

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