Carbonation method for concrete structures

Abstract

To provide a new method for reinforcing or repairing concrete, and a concrete structure applied with the method.SOLUTION: The reinforcement method includes the steps of: forming a first injection hole at a concrete structure containing concrete; forming porous concrete at the inside of the first injection hole; and supplying a gas containing carbon dioxide or a medicine to the porous concrete. A porosity of the concrete is lower than a porosity of the porous concrete.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] One embodiment of the present invention relates to a method for reinforcing a concrete structure containing concrete, and a concrete structure to which this reinforcing method is applied. [Background technology]

[0002] Concrete is primarily composed of cement hydrate, aggregates such as fine and coarse aggregates, water, and additives. Due to its excellent mechanical properties, weather resistance, ease of handling, and cost-effectiveness, concrete is widely used in various fields as an important structural material for creating social production and economic infrastructure. One known method for reinforcing structures containing concrete (hereinafter, "concrete structures") is to introduce carbon dioxide into concrete. For example, Patent Document 1 discloses a method for contacting ready-mixed concrete with carbon dioxide before it hardens during construction of the concrete structure. Patent Document 2 discloses a method for designing a concrete structure that is effective in promoting carbon dioxide absorption 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 novel method for reinforcing or repairing concrete, and to provide a concrete structure to which this method is applied. [Means for solving the problem]

[0005] One embodiment of the present invention is a method for reinforcing a concrete structure. The method includes forming a first injection hole in a concrete structure containing concrete, forming porous concrete in the first injection hole, and supplying a gas or agent containing carbon dioxide to the porous concrete. The porosity of the concrete is smaller than the porosity of the porous concrete.

[0006] One embodiment of the present invention is a method for reinforcing a concrete structure. The method includes constructing a concrete structure having a first injection hole, forming porous concrete in the first injection hole, and supplying a gas or agent containing carbon dioxide to the porous concrete. The porosity of the concrete contained in the concrete structure is smaller than the porosity of the porous concrete.

[0007] One embodiment of the present invention is a concrete structure comprising a first concrete and a second concrete surrounded by the first concrete, wherein the first concrete has a lower calcium carbonate concentration than the second concrete.

[0008] One embodiment of the present invention is a concrete structure comprising a first concrete containing an agent and a second concrete containing the agent and surrounded by the first concrete, wherein the average concentration of the agent in the first concrete is lower than the average concentration of the agent in the second concrete. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic perspective view illustrating a method for reinforcing a concrete structure according to an embodiment of the present invention; [Figure 2] 1A and 1B are schematic perspective and end views illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention; [Figure 3]1 is a schematic end view illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention. FIG. [Figure 4] 1 is a schematic end view illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention. FIG. [Figure 5] 1A and 1B are schematic end and top views illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention; [Figure 6] 1A and 1B are schematic end and top views illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention; [Figure 7] 1 is a schematic end view illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention. FIG. [Figure 8] 1A and 1B are schematic perspective and end views illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention; [Figure 9] 1A and 1B are schematic perspective and side views illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention; [Figure 10] 1 is a schematic end view illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention. FIG. [Figure 11] 1A and 1B are schematic perspective and top views illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention; [Figure 12] 1 is a schematic side view illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention. FIG. [Figure 13] 1 is a schematic end view illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention. FIG. [Figure 14] 1A and 1B are schematic end views illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention, and a schematic diagram illustrating the composition of a concrete structure. [Figure 15] 1 is a schematic end view illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention. FIG. [Figure 16] 1A and 1B are schematic perspective and side views illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention; [Figure 17]1A and 1B are schematic perspective and side views illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention; [Figure 18] 1 is a schematic end view illustrating a method for reinforcing a concrete structure according to one embodiment of the present invention. FIG. [Figure 19] 1 is a schematic perspective view illustrating a method for reinforcing a concrete structure according to an embodiment of the present invention; [Figure 20] FIG. 2 is a schematic perspective view illustrating a method for producing a concrete test specimen according to an embodiment of the present invention. [Figure 21] FIG. 10 is a schematic perspective view illustrating a method for producing a concrete specimen of a comparative example. [Figure 22] FIG. 2 is a schematic diagram showing the results of carbonation of concrete test specimens of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, various embodiments of the present invention will be described with reference to the drawings. 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 construed as being limited to the description of the following exemplary embodiments.

[0011] In order to clarify the description, the drawings may show the width, thickness, shape, etc. of each part schematically 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 explanations may be omitted. In the attached drawings, for convenience, the xy plane is defined as the horizontal plane, and the z direction is defined as the vertical direction.

[0012] Hereinafter, the expression "a structure is exposed from another structure" means a state in which a part of a structure is not covered by another structure, and also includes a state in which this part not covered by another structure is covered by yet another structure.

[0013] Hereinafter, concrete, mortar, and porous concrete refer to hardened, non-fluid hydrates formed when cement, one of the raw materials, reacts with water. Concrete contains fine aggregates with diameters of 5 mm or less and coarse aggregates with diameters greater than 5 mm (e.g., greater than 5 mm but less than 20 mm, or greater than 10 mm but less than 20 mm). Mortar, on the other hand, refers to hardened products containing fine aggregate but without coarse aggregate, or with a coarse aggregate content of 10% or less by weight relative to the fine aggregate. In contrast to mortar, porous concrete refers to hardened products containing relatively large coarse aggregates, such as gravel, but without fine aggregate, or with a fine aggregate content of 10% or less by weight relative to the coarse aggregate. For this reason, porous concrete has more internal voids than concrete or mortar. Meanwhile, a mixture containing cement and water that remains fluid without being fully hardened is called ready-mix concrete (also known as ready-mix concrete). When ready-mixed concrete hardens, it will give concrete, mortar, or porous concrete, depending on the amount of coarse and fine aggregates used. Ready-mixed concrete contains cement, water, and aggregates, and may also contain additives such as air-entraining agents (AE agents), superplasticizers, viscosity improvers, and accelerators.

[0014] First Embodiment In this embodiment, a method for reinforcing a concrete structure using carbon dioxide and a concrete structure to which this reinforcing method is applied will be described. There are no limitations on the type, shape, purpose, or installation location of the concrete structure to which this reinforcing method can be applied, and any new or existing concrete structure can be used. The concrete structure may be, for example, a building column or foundation beam, a bridge pier or abutment, a levee or breakwater installed in a river or port, a wave-dissipating block, or concrete lining used in a road or tunnel. Alternatively, it may be movable concrete (concrete product) such as a square or U-shaped concrete block or a stone sill.

[0015] 1. Reinforcement methods for concrete structures 1-1. Formation of the first injection hole 1(A) to 1(C) are schematic perspective views of a concrete structure 10. In this reinforcement method, first, a first injection hole 102 is formed in concrete 100 contained in the concrete structure 10 (FIG. 1(A)). The first injection hole 102 may be a through-hole that passes through the concrete structure 10, or, although not shown, may be a bottomed hole that does not pass through the concrete structure 10. The first injection hole 102 may be formed by drilling the concrete 100 using a drill such as a percussion drill, a hammer drill, or a diamond core drill.

[0016] The first injection holes 102 are preferably provided so as to extend linearly in one direction from the surface of the concrete structure 10, but may be curved within the concrete structure 10. There are no restrictions on the number of first injection holes 102, and the number may be determined appropriately depending on the shape, size, installation environment, strength, etc. of the concrete structure 10. When multiple first injection holes 102 are provided, the extension directions of the multiple first injection holes 102 may be the same as each other, or, as shown in FIG. 1(B), the extension direction of at least one first injection hole 102 may be different from that of the other first injection holes 102. As shown in FIGS. 1(A) and 1(B), the extension direction of all first injection holes 102 may be perpendicular to the outer surface of the concrete structure 10. Alternatively, as shown in FIG. 1(C), some or all of the first injection holes 102 may extend in a direction oblique to the outer surface of the concrete structure 10. Although not shown, multiple first injection holes 102 may intersect. That is, the first injection holes 102 may be formed in a network pattern within the concrete structure 10. The surface on which the first injection holes 102 are provided is not limited to a surface perpendicular to the horizontal plane, but may also be a surface parallel to the horizontal plane (for example, the top surface of the concrete structure 10), or the first injection holes 102 may be provided on a surface inclined at an angle of less than 90° from the horizontal plane.

[0017] The cross-sectional area of ​​the end of first injection hole 102, i.e., the opening area of ​​first injection hole 102 on the outer surface of concrete structure 10, can be set arbitrarily. For example, if the shape of the end of first injection hole 102 (the shape on the outer surface of concrete structure 10) is circular, its diameter D (see FIG. 1(A)) may be 15 mm or more and 200 mm or less, 20 mm or more and 150 mm or less, or 30 mm or more and 100 mm or less. The cross-sectional area of ​​the end of first injection hole 102 may be, for example, 176 mm 2 More than 314cm 2 Below, 314mm 2 over 176cm 2 or less, or 706mm 2 over 78cm 2 The following is also acceptable.

[0018] Alternatively, the first injection hole 102 may be formed when constructing the concrete structure 10. Specifically, one or more core materials (cores) 162 for forming a space corresponding to the first injection hole 102 are placed in a formwork 160 for pouring ready-mixed concrete to provide the concrete 100 ( FIG. 2(A) ). The core material 162 may be provided so that a portion thereof is exposed from the formwork 160. The shape of the core material 162 may be determined taking into account the shape of the first injection hole 102. It may be a straight rod, or may be partially or entirely bent. There are no restrictions on the material contained in the core material 162, 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 162. Applying a release agent or set retarder allows the core material 162 to be easily removed from the concrete 100 to form the first injection hole 102, as described below.

[0019] Next, concrete 100 is formed. That is, as shown in the schematic end view (FIG. 2(B)) along the dashed line CC' in FIG. 2(A), ready-mixed concrete 164 that will provide concrete 100 is poured into formwork 160. At this time, the ready-mixed concrete 164 is poured into formwork 160 so that the core material 162 is embedded by the ready-mixed concrete 164. The ready-mixed concrete 164 is hardened, and the formwork 160 and the core material 162 are removed, allowing the concrete structure 10 having the first pouring hole 102 to be constructed (see FIG. 1(A)).

[0020] The shape of the end of first injection hole 102, i.e., the opening shape of first injection hole 102 on the outer surface of concrete structure 10, can also be set as desired. When first injection hole 102 is formed using a drill, it will be circular, but when first injection hole 102 is formed during the construction of concrete structure 10, by appropriately selecting the shape of the cross section of core material 162 (a cross section perpendicular to the extension direction of core material 162), it is possible to form first injection hole 102 having, for example, a circle, a polygon such as a square or a star, an ellipse, or a shape whose periphery is made up of straight lines and curves.

[0021] 1-2. Formation of porous concrete Next, as shown in the schematic end views (FIGS. 3A and 3B) along the dashed lines AA' and BB' in FIG. 1A, porous concrete 104 is formed in the first injection hole 102. As described above, porous concrete is a hardened product that does not contain fine aggregate or has a significantly smaller amount of fine aggregate than coarse aggregate, and one of its characteristics is that its porosity is larger than that of the concrete 100 contained in the concrete structure 10. Ready-mixed concrete that provides the porous concrete 104 is poured into the first injection hole 102 and hardened, thereby filling the first injection hole 102 with the porous concrete 104. Therefore, even if a relatively large first injection hole 102 is formed, its effect on the strength of the concrete structure 10 can be ignored.

[0022] Thereafter, a second injection hole 106 may be formed in the porous concrete 104, as shown in FIGS. 4(A) and 4(B), which correspond to FIGS. 3(A) and 3(B), respectively. The second injection hole 106 may be formed, for example, using a drill. The second injection hole 106 may penetrate both the concrete structure 10 and the porous concrete 104, or may be a bottomed hole that does not penetrate at least one of them. The cross-sectional area of ​​the second injection hole 106, i.e., the opening area of ​​the second injection hole 106 on the outer surface of the porous concrete 104, can also be set arbitrarily. For example, if the cross-sectional shape of the second injection hole 106 (the shape on the outer surface of the porous concrete 104) is circular, its diameter d may be 1 mm or more and 100 mm or less, or 2 mm or more and 150 mm or less. The cross-sectional area of ​​the second injection hole 106 is, for example, 0.785 mm. 2 More than 78.5cm 2 Less than or equal to 3.14mm 2 over 177cm 2 By selecting the above range, second injection hole 106 can be formed without significantly impairing the strength or appearance of concrete structure 10.

[0023] Like the first injection hole 102, the second injection hole 106 may also be formed during construction of the concrete structure 10. For example, as shown in a schematic end view (FIG. 5(A)) corresponding to FIG. 2(B), a core material 162 is placed in a formwork 160. The core material 162 corresponds to the space where the second injection hole 106 will be formed. Then, ready-mixed concrete 164, which will provide the concrete 100, is poured into the formwork 160. At this time, the ready-mixed concrete 164 is poured so that the core material 162 is not embedded. Then, a formwork 166 for forming the porous concrete 104 is placed on the ready-mixed concrete 164 (FIG. 5(B)). The formwork 166 may be installed before or after the ready-mixed concrete 164 hardens. Alternatively, the formwork 166 may be installed before pouring the ready-mixed concrete 164, although this is not shown. Porous concrete 104 is formed by pouring ready-mixed concrete that provides porous concrete 104 into formwork 166 and allowing it to harden (FIGS. 6(A) and 6(B)). After this, formwork 166 is removed, and ready-mixed concrete 164 that provides concrete 100 is poured into formwork 160 and allowed to harden (FIG. 7). By removing formwork 160 and core material 162, the concrete structure 10 having porous concrete 104 with second injection holes 106 can be constructed.

[0024] Alternatively, the porous concrete 104 having the second injection hole 106 may be prepared separately and embedded in the concrete 100 to construct the concrete structure 10. Specifically, a core material 162 is provided in a formwork 168 that determines the shape of the porous concrete 104 so as to occupy the space where the second injection hole 106 will be provided, and ready-mixed concrete that provides the porous concrete 104 is poured into the formwork 168 and hardened ( FIG. 8(A) ). Alternatively, the formwork 168 is filled with coarse aggregate, and ready-mixed concrete that does not contain coarse aggregate or has a small amount of coarse aggregate is poured into the formwork 168. Thereafter, the formwork 168 and the core material 162 are removed to obtain the porous concrete 104 having the second injection hole 106. On the other hand, as shown in FIG. 8(B), after partially pouring ready-mixed concrete 164 to provide concrete 100 into formwork 160, porous concrete 104 having second injection holes 106 is placed on top of the ready-mixed concrete 164. The ready-mixed concrete 164 is then poured again to embed the porous concrete 104 and allowed to harden. In this method, the shape of the porous concrete 104 can be controlled by appropriately adjusting the internal shape of the formwork 168. Although not shown, before pouring the ready-mixed concrete 164 to provide concrete 100, the porous concrete 104 having second injection holes 106 may be placed so that the extension direction of the second injection holes 106 is vertical, and then the ready-mixed concrete 164 to provide concrete 100 may be poured and allowed to harden.

[0025] 1-3. Carbon dioxide supply Next, carbon dioxide is supplied to the porous concrete 104. Specifically, as shown in FIG. 9(A), a carbon dioxide line 122 is connected to one end of the porous concrete 104 exposed from the concrete structure 10. When a second injection hole 106 is provided in the porous concrete 104, the carbon dioxide line 122 is connected to the second injection hole 106. A carbon dioxide supply source 120 is connected to the carbon dioxide line 122, and gas containing carbon dioxide supplied from the carbon dioxide supply source 120 is introduced into the porous concrete 104 via the carbon dioxide line 122. Although not shown, when the porous concrete 104 is provided in multiple first injection holes 102, the same number of carbon dioxide supply sources 120 as the number of first injection holes 102 may be used and connected to each of the porous concrete 104. Alternatively, branched carbon dioxide lines 122 may be used to connect fewer carbon dioxide supply sources 120 than the number of porous concrete 104 to the porous concrete 104. The carbon dioxide line 122 may be provided with a pressure gauge 126 and / or a flow meter 128 for measuring the pressure of the carbon dioxide-containing gas introduced into the porous concrete 104 .

[0026] Any method for connecting the carbon dioxide line 122 to the porous concrete 104 can be selected. For example, the carbon dioxide line 122 may be installed so that its tip covers the porous concrete 104. Alternatively, to maintain a stable connection, for example, as shown in FIG. 10(A), an adapter 110 having an opening with a female thread structure may be attached to the surface of the concrete structure 10 so as to surround or cover the porous concrete 104, and a joint 124 having a male thread structure that engages with the female thread structure may be attached to the tip of the carbon dioxide line 122. By screwing the joint 124 into the adapter 110, carbon dioxide-containing gas can be introduced into the porous concrete 104 while preventing carbon dioxide leakage from the carbon dioxide line 122. As an optional configuration, a resin O-ring (or packing) 112 may be installed between the adapter 110 and the concrete 100 to more effectively prevent leakage of carbon dioxide-containing gas. Preventing carbon dioxide leakage ensures work safety.

[0027] Furthermore, capping the other end of the porous concrete 104 and sealing in the carbon dioxide-containing gas prevents leakage of the carbon dioxide-containing gas and allows for more effective contact between the porous concrete 104 and the carbon dioxide. For example, the outlet of the other end may be sealed using adhesive tape or an elastic material such as rubber. Alternatively, as shown in Figures 9(B) and 10(A), the other end of the porous concrete 104 may be covered with a plate 114 made of resin such as acrylic resin, epoxy resin, polyester resin, or polyimide resin, fiber-reinforced plastic containing these resins, or metal material such as iron, stainless steel, or aluminum, thereby sealing the porous concrete 104. The plate 114 may be fixed using bolts or screws. Alternatively, the plate 114 may be fixed using adhesive or adhesive tape. Furthermore, as shown in Figure 10(A), to improve airtightness, a gasket 116 made of an elastic material such as rubber may be placed between the porous concrete 104 and the plate 114 so as to cover the porous concrete 104.

[0028] The gas containing carbon dioxide may be pure carbon dioxide (e.g., 99% or higher purity) or a mixture 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 be set as desired, but in order to efficiently bring the porous concrete 104 into contact with the carbon dioxide, it is preferable that the concentration be higher than the concentration of carbon dioxide in the atmosphere (approximately 420 ppm). For example, the carbon dioxide concentration may be set at any concentration between 1% and 100% by volume.

[0029] The carbon dioxide supply source 120 may be any suitable device as long as it has the function of supplying carbon dioxide-containing gas to the porous concrete 104, such as a cylinder or tank for carbon dioxide-containing gas as shown in FIG. 9(A). The carbon dioxide supply source 120 is connected to a regulator (not shown) to adjust the pressure of the carbon dioxide-containing gas. Alternatively, if there are existing facilities (such as chemical plants, waste incineration facilities, thermal power plants, and various other factories) that emit large amounts of carbon dioxide near the concrete structure 10, the gas emitted by these facilities or purified carbon dioxide obtained by subjecting the exhaust gas to dedusting, desulfurization, denitrification, etc. may be used. In this case, the facility that emits carbon dioxide functions as the carbon dioxide supply source 120, thereby reducing the cost of transporting carbon dioxide and preventing carbon dioxide emissions associated with transportation.

[0030] The gas containing carbon dioxide may be introduced steadily (continuously) or intermittently. In the latter case, after the gas containing carbon dioxide is supplied, the carbon dioxide line 122 is removed and the porous concrete 104 is sealed. For example, the porous concrete 104 may be covered with adhesive tape. Alternatively, as shown in FIG. 10(B), the porous concrete 104 may be sealed using a cap 118 having a male thread structure that engages with the adapter 110.

[0031] As an optional configuration, a concentration meter 132 for measuring the carbon dioxide concentration may be provided inside the second injection hole 106 to measure the carbon dioxide concentration as needed or periodically. This makes it possible to monitor changes in the carbon dioxide concentration.

[0032] The gas containing carbon dioxide may be introduced so that the pressure inside the voids in the porous concrete 104 or the second injection hole 106 is higher than 0 MPa and lower than 1 MPa. If this pressure is lower than atmospheric pressure (for example, 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 pressure inside the voids in the porous concrete 104 or the second injection hole 106 may be reduced before the gas containing carbon dioxide is introduced (see FIG. 9(A)).

[0033] 1-4. Adjusting humidity When concrete comes into contact with carbon dioxide, calcium hydroxide and other substances contained in the concrete change to calcium carbonate (carbonation). The rate of carbonation also depends on humidity, and it is known that a high rate of carbonation is achieved when the humidity is approximately 50%. Therefore, in this reinforcement method, the humidity of the carbon dioxide-containing gas supplied may be adjusted. Specifically, a water supply source 140 may be provided, and water may be supplied to the porous concrete 104 via a carbon dioxide line 122 (FIG. 9(A)). Although not shown, the water supply source 140 may be equipped with a heating device or a cooling device to control the temperature of the supplied water. Alternatively, carbon dioxide-containing gas may be supplied from the carbon dioxide supply source 120 to the water supply source 140, and carbon dioxide-containing water may be supplied to the porous concrete 104.

[0034] As an optional configuration, a hygrometer 134 for measuring humidity may be provided in the second injection hole 106 to measure humidity as needed or periodically (FIG. 10(B)). This allows changes in humidity to be monitored.

[0035] On the other hand, if the humidity inside the second injection hole 106 is high, if the porous concrete 104 contains a large amount of water, or if the concrete 100 contains a large amount of water, the inside of the voids in the second injection hole 106 or the porous concrete 104 may be dried under reduced pressure using a vacuum pump 130 to remove some of the water. Then, a gas containing carbon dioxide may be supplied to the porous concrete 104.

[0036] The contact time between the porous concrete 104 and the gas containing carbon dioxide depends on the length and cross-sectional area of ​​the porous concrete 104 (i.e., the volume of the first injection hole 102), the volume of the concrete structure 10, 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.

[0037] The supply of carbon dioxide and water may be performed using a control device 142, as shown in FIG. 11(A). The control device 142 is supplied with carbon dioxide-containing gas and water from a carbon dioxide supply source 120 and a water supply source 140, respectively. The control device 142 is equipped with a mechanism (e.g., an air pump) for supplying the carbon dioxide-containing gas to the porous concrete 104. The control device 142 may further be configured to prepare a carbon dioxide-containing gas having an appropriate humidity using the supplied water and carbon dioxide and supply this gas to the porous concrete 104. Alternatively / in addition, the control device 142 may be configured to control the temperature of the carbon dioxide-containing gas supplied to the porous concrete 104. By providing the control device 142 with such a function, the carbon dioxide-containing gas can be supplied to the porous concrete 104 at an optimized temperature and humidity, enabling carbonation to be performed in a short period of time.

[0038] Furthermore, as shown in Figure 11 (B), gas containing carbon dioxide may be circulated between the control device 142 and the porous concrete 104. In this case, the control device 142 is equipped with a mechanism, such as a circulation pump, for collecting the gas discharged from the other end of the porous concrete 104 and supplying it again to the porous concrete 104. Furthermore, the control device 142 may be configured to measure the concentration and humidity of carbon dioxide contained in the gas discharged from the other end of the porous concrete 104, and add carbon dioxide and water to the gas as appropriate based on the obtained data. This allows the porous concrete 104 to be constantly kept under conditions that will result in an optimal carbonation rate.

[0039] 1-5. Mortar formation in porous concrete As an optional step, after carbonation is completed, new mortar 165 may be applied to the second injection hole 106 and the porous concrete 104 as repair concrete. That is, ready-mixed concrete for providing mortar 165 is poured into the second injection hole 106 and the porous concrete 104 and allowed to harden ( FIG. 12 ). This allows the voids between the coarse aggregate 105 to be filled with mortar 165, and allows the porous concrete 104 to have a composition similar to that of the concrete 100 surrounding it. This reduces the difference in appearance between the area where the porous concrete 104 was provided and the concrete 100, thereby preventing damage to the aesthetics of the concrete structure 10.

[0040] 2. Composition of concrete structures to which this reinforcement method is applied When the concrete structure 10 is reinforced using the above-described reinforcement method, carbonation first occurs on the surface of the porous concrete 104 and in the voids between the coarse aggregate 105, and then progresses from the interface between the porous concrete 104 and the concrete 100 into the concrete 100 (FIG. 13). Therefore, as shown in a cross-sectional view (FIG. 14(A)) perpendicular to the extension direction of the first injection hole 102, carbonation in principle progresses isotropically in the direction perpendicular to the extension direction of the first injection hole 102 (i.e., in the xz plane) (see the arrows in FIG. 14(A)). The degree of carbonation is highest in the region 100a where the porous concrete 104 is provided (i.e., the region where the first injection hole 102 is provided), and decreases in the region 100b surrounding this region 100a (i.e., the region occupied by the concrete 100) as the distance from the interface between the region 100a and the region 100b increases (FIG. 14(B)). Since the porous concrete 104 with high porosity is provided in the region 100a, the calcium carbonate concentration in the region 100a is constant regardless of the distance from the center of the porous concrete 104, i.e., the center of the region 100a, or it gradually decreases as the distance from the center increases (FIG. 14(B)). In other words, the calcium carbonate concentration in the concrete contained in the region 100a is higher than the calcium carbonate concentration in the concrete contained in the region 100b surrounding the region 100a. Furthermore, the calcium carbonate concentration in the concrete contained in the region 100b decreases as the distance from the region 100a (i.e., the distance from the interface between the regions 100a and 100b) increases. The change in calcium carbonate concentration between the region 100a and the region 100b is continuous or discontinuous (FIGS. 14(B) and 14(C)).

[0041] On the other hand, because calcium hydroxide is consumed in carbonation, the calcium hydroxide concentration in the concrete contained in region 100a is lower than the calcium hydroxide concentration in the concrete contained in region 100b (FIG. 14(B)). Due to the high porosity of the porous concrete 104, the calcium hydroxide concentration in region 100a is constant regardless of the distance from the center of region 100a, or increases gradually as the distance from the center increases. Furthermore, the calcium hydroxide concentration in the concrete contained in region 100b increases as the distance from region 100a increases. The change in calcium hydroxide concentration between region 100a and region 100b is continuous or discontinuous (FIGS. 14(B) and 14(C)).

[0042] Known methods for carbonating concrete include placing hardened concrete in a curing tank filled with carbon dioxide, exposing the surface of hardened porous concrete to carbon dioxide, supplying carbon dioxide to the formwork used to pour ready-mixed concrete, and exposing the concrete structure to the atmosphere. However, the curing tank method requires a curing tank to contain the concrete for carbonation, making it unsuitable for structures such as buildings, columns, and tunnels. The method of exposing the porous concrete surface to carbon dioxide also requires a means to seal the concrete surface, making it unrealistic for use in large concrete structures. The method of supplying carbon dioxide to the formwork requires the formwork to be formed as a closed space, making it applicable to small structures but not to large structures. Furthermore, the method of using air contact does not allow for efficient carbonation due to the extremely low carbon dioxide concentration in the atmosphere.

[0043] On the other hand, in this reinforcement method, a first injection hole 102 is formed in the concrete structure 10, and gas containing carbon dioxide is supplied to the porous concrete 104 formed therein. Because the porous concrete 104 has a high porosity, not only does the porous concrete 104 carbonate quickly, but the carbon dioxide quickly reaches the interface between the porous concrete 104 and the concrete 100 (i.e., the inner wall of the first injection hole 102). Furthermore, due to the relatively large cross-sectional area of ​​the first injection hole 102, the area of ​​the concrete 100 that comes into contact with the carbon dioxide is large. This allows the concrete 100 surrounding the porous concrete 104 to carbonate at a high rate. When the concrete carbonates, its strength increases. In fact, the inventors have found that the carbon dioxide is released from approximately 20% of the cement (60 kg / m 3 It has been confirmed that when concrete is carbonated with carbon dioxide, the compressive strength of the concrete increases by approximately 8% to 10%. Therefore, by applying this reinforcement method, it is possible to increase the strength of the concrete structure 10 in a short period of time.

[0044] Furthermore, as described above, in this reinforcement method, a relatively large first injection hole 102 is formed in the concrete structure 10, and porous concrete 104 is placed in the first injection hole 102. Also, by pouring ready-mixed concrete that adds mortar 165 to the porous concrete 104, it is possible to form concrete having a composition similar to that of concrete 100 in the first injection hole 102. Therefore, the formation of the first injection hole 102 does not affect the strength of the concrete structure 10, which constitutes the main part of the concrete structure 10, and does not detract from the aesthetic appearance of the concrete structure 10.

[0045] Furthermore, this reinforcement method allows for rapid carbonation, making it possible to fix large amounts of carbon dioxide in the concrete structure 10. As described above, this reinforcement method can be applied to a variety of existing concrete structures 10 without any particular restrictions on type, size, shape, purpose, or construction location, as long as the first injection holes 102 can be formed. This means that not only is it not necessary to create a new reactive substrate for fixing carbon dioxide, but also that a huge amount of reactive substrate exists on the ground. Therefore, this reinforcement method not only can reinforce the concrete structure 10, but can also fix an extremely large amount of carbon dioxide, making it an effective tool for curbing global warming.

[0046] 3. Application Examples 3-1. Application to lining concrete This reinforcement method can be applied to various concrete structures 10. For example, as shown in FIG. 15, this reinforcement method can be applied even when the concrete structure 10 is a tunnel, allowing carbon dioxide to be fixed while reinforcing the tunnel's inner wall. In this case, one or more first injection holes 102 are formed in the lining concrete of the concrete structure 10, and porous concrete 104 is poured into the first injection holes 102. A gas containing carbon dioxide is then supplied to the porous concrete 104. The extension direction of the first injection hole 102 is arbitrary, and may be vertical (z direction) or tilted from the vertical direction. For example, the first injection hole 102 may be parallel to the normal to the tunnel's inner wall, or, although not shown, the first injection hole 102 may be formed so as to be tilted from the normal. The first injection hole 102 may be a through hole penetrating the concrete 100 or a blind hole. Even when the first injection hole 102 is a through hole, one end of the first injection hole 102 is closed by bedrock or the ground, so there is no need to seal the end of the porous concrete 104 when supplying the gas containing carbon dioxide. As described above, after carbonation is completed, ready-mixed concrete that provides mortar 165 may be poured into the porous concrete 104.

[0047] 3-2. Application to concrete structures containing reinforcing bars This reinforcing method can also be applied to concrete structures containing reinforcing bars (reinforced concrete structures). For example, in a concrete structure 10 having multiple reinforcing bars 150 and concrete 100 poured to embed the reinforcing bars 150 as shown in FIG. 16(A), one or more first injection holes 102 are formed to avoid the reinforcing bars 150 (FIG. 15(B)). That is, each first injection hole 102 is provided so that the reinforcing bars 150 are not exposed within the first injection hole 102. In the example shown in FIG. 15(B), multiple linear first injection holes 102 are provided to extend in the y direction between adjacent reinforcing bars 150.

[0048] If the concrete structure 10 is a building, this reinforcing method can be applied to the reinforced concrete that makes up the columns and beams. When applied to columns, the first injection holes 102 are provided (FIG. 17(B)) so as to avoid the reinforcing bars 150 (see FIG. 17(A)) that make up the column main reinforcement and transverse reinforcement.

[0049] Concrete is alkaline, but as carbonation progresses, it gradually becomes acidic. When concrete becomes acidic, 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 10 containing reinforcing bars, it is preferable that carbon dioxide is not fixed in the concrete located near the reinforcing bars.

[0050] In a concrete structure 10 that includes reinforcing bars, the reinforcing bars are not placed in the center of the concrete structure 10, but in a zone relatively close to the outer surface. For example, as shown in Figure 16(A), reinforcing bars 150 are placed so as to surround the center of the concrete structure, and concrete 100 is constructed so as to embed the reinforcing bars 150. The same is true for reinforced concrete columns, where the reinforcing bars 150 that are parallel to the extension direction of the column (column main reinforcement) are placed so as to surround the central axis of the column, and reinforcing bars that extend horizontally, called transverse reinforcement bars, are placed so as to surround the column main reinforcement (Figure 17(A)). The part of the concrete 100 outside the reinforcing bars is called cover concrete.

[0051] Therefore, to prevent carbonation of the concrete near the reinforcing bars, a protective tube 108 may be provided to cover the portion of the inner wall of the first injection hole 102 that is made of cover concrete, as shown in FIG. 18. The protective tube 108 may be provided at one end and / or the other end of the first injection hole 102, and the end reaches the outer surface of the concrete structure 10. Therefore, the portion of the inner wall covered by the protective tube 108 reaches one end of the first injection hole 102. Although not shown, a portion of the protective tube 108 may protrude outward from the first injection hole 102.

[0052] The length L of the protective tube 108 in the direction in which the first injection hole 102 extends is preferably equal to or greater than the thickness of the concrete cover. More specifically, the length L of the protective tube 108 is preferably equal to or greater than the shortest distance D from the reinforcing bar 150 located at the innermost position of the concrete structure 10 to the outer surface of the concrete 100. min and the maximum cross-sectional length (e.g., cross-sectional diameter d') of the reinforcing bar 150. 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.

[0053] There are no restrictions on the material contained in protective tube 108, 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 108 may be formed by applying an epoxy adhesive or an acrylic adhesive to the inner wall of first injection hole 102 on the injection inlet and outlet sides of first injection hole 102 to a length L and then curing it.

[0054] By placing the protective tube 108 and preventing carbon dioxide from contacting the inner wall of the first injection hole 102 up to a length L, the porous concrete 104 and the inner wall exposed by the protective tube 108 are selectively brought into contact with carbon dioxide. As a result, in the concrete 100 surrounding the porous concrete 104, carbonation begins at the inner wall exposed by the protective tube 108, and then carbonation progresses from the inner wall to the interior of the concrete. As a result, as shown in FIG. 18, the carbonated region 100c does not extend to the reinforcing bar 150, preventing corrosion of the reinforcing bar 150 and the resulting deterioration of the concrete 100.

[0055] When the protective tube 108 is used, the ready-mixed concrete that provides the repair concrete mortar 165 may be poured after removing the protective tube 108, or may be poured while the protective tube 108 remains in the first pouring hole 102. In the latter case, the concrete structure 10 includes the protective tube 108, which is positioned between the concrete 100 and the porous concrete 104.

[0056] Second Embodiment In this embodiment, a method for reinforcing a concrete structure 10 that is different from the reinforcing method described in the first embodiment will be described. One of the differences between the reinforcing method according to this embodiment and the reinforcing method described in the first embodiment is that the reinforcing method according to this embodiment uses an agent instead of or in addition to the gas containing carbon dioxide. Descriptions of configurations that are the same as or similar to those described in the first embodiment may be omitted.

[0057] In the reinforcement method according to this embodiment, similar to the reinforcement method described in the first embodiment, a first injection hole 102 is formed in a concrete structure 10, or a concrete structure 10 provided with a first injection hole 102 is constructed, and porous concrete 104 is poured into the first injection hole 102 (see FIGS. 1(A) to 8(B)). Then, a chemical is injected into the porous concrete 104 using, for example, a syringe 170 (FIG. 19). The chemical may be, for example, a curable resin, or a chemical solution containing a compound capable of forming a passivation state on the surface of reinforcing bars, such as lithium nitrite. Examples of the curable resin include epoxy resins, such as two-component epoxy resins, and silicone resins.

[0058] When chlorides caused by salt damage penetrate concrete and reach the rebars, the passive state of the rebar surface is destroyed, causing corrosion. This phenomenon is also caused by the neutralization of concrete, and the corrosion of the rebars causes them to expand, inducing cracks in the concrete. Generally, when repairing cracked concrete, chemicals are injected from the surface of the concrete. However, even if chemicals are injected from the surface of the concrete, it is difficult to ensure that they penetrate into the concrete quickly and reliably.

[0059] However, in the reinforcement method according to the present embodiment, a first injection hole 102 having a relatively large cross-sectional area is formed in the concrete structure 10, and an agent is supplied to the porous concrete 104 provided within the first injection hole 102. Because the porous concrete 104 has many voids, the agent quickly penetrates the voids in the porous concrete 104 and reaches the inner wall of the concrete 100 surrounding the porous concrete 104. Once the agent reaches the inner wall of the concrete 100, it penetrates further into the concrete 100 or into cracks. Therefore, similar to the reinforcement method described in the first embodiment, the degree of penetration of the agent is highest in the region 100a where the porous concrete 104 is provided, and decreases in the region 100b surrounding the region 100a as the distance from the interface of the region 100b increases compared to the region 100a (see FIG. 14(A)). Because region 100a contains porous concrete 104 with a high porosity, the average concentration of the chemical agent in region 100a is constant regardless of the distance from the center of porous concrete 104, i.e., the center of region 100a, or gradually decreases as the distance from the center increases. In other words, the average concentration of the chemical agent in the concrete contained in region 100a is higher than the average concentration of the chemical agent in the concrete contained in region 100b surrounding region 100a. Furthermore, the concentration of the chemical agent in the concrete contained in region 100b decreases as the distance from region 100a (i.e., the distance from the interface between region 100a and region 100b) increases. The change in chemical agent concentration between region 100a and region 100b may be continuous or discontinuous.

[0060] The first injection hole 102 has a relatively large cross-sectional area, ensuring a large contact area between the concrete 100 and the agent. This allows a sufficient amount of agent to be supplied to the interior of the concrete structure 10. As a result, cracks that have occurred not only on the surface of the concrete structure 10 but also inside the structure can be filled with resin. Furthermore, when a chemical solution containing lithium nitrite is used as the agent, the agent can be supplied to the rebar surface from inside the concrete 100 through the cracks, effectively regenerating the passive film on the rebar surface and inhibiting corrosion of the rebar.

[0061] It is also possible to inject a chemical solution containing a compound capable of regenerating passivation, such as lithium nitrite, and then inject the resin into the porous concrete 104. Furthermore, after the injection of the chemical, a gas containing carbon dioxide may be further injected into the porous concrete 104. Alternatively, the chemical may be injected into the porous concrete 104 after the gas containing carbon dioxide has been injected. [Example]

[0062] In this example, the results of carbonation of concrete specimens containing porous concrete are described.

[0063] 1. Preparation of Concrete Specimens 1-1.Example As shown in Figure 20(A), a cylindrical formwork 168 measuring φ100 mm and height 400 mm was used, and a metal rod measuring φ9 mm and length 400 mm was placed in the center as the core material 162. Coarse aggregate (maximum diameter approximately 20 mm) was spread around the metal rod, and ready-mixed concrete was poured. The ready-mixed concrete used ordinary Portland cement manufactured by Taiheiyo Cement Corporation, with a unit water content of 170 kg / m 3 , unit cement amount 340kg / m 3The ready-mixed concrete was allowed to harden at room temperature for 24 hours, then demolded, and the resulting porous concrete 104 was placed in a 400 mm x 400 mm x 400 mm formwork 160 (Fig. 20(B)). Normal Portland cement manufactured by Taiheiyo Cement Corporation was used, with a unit water content of 170 kg / m 3 , unit cement amount 340kg / m 3 Ready-mixed concrete prepared to have a water-cement ratio of 50% was poured into formwork 160, allowed to harden at room temperature for 24 hours, and then formwork 160 and core material 162 were removed to obtain a concrete specimen having an injection hole in porous concrete 104.

[0064] 1-2.Comparative example The concrete specimen for the comparative example was prepared as follows. As shown in Figure 21, a formwork 160 with an internal volume of 400 mm x 400 mm x 400 mm was prepared, and a metal rod with a cross-sectional diameter of 9 mm and a length of 400 mm was placed vertically as a core material 162. The metal rod was placed so as to pass through the center of the formwork 160. Ready-mixed concrete was poured into this formwork 160. The ready-mixed concrete used ordinary Portland cement manufactured by Taiheiyo Cement Corporation, with a unit water content of 170 kg / m 3 , unit cement amount 340kg / m 3 The ready-mixed concrete was allowed to harden at room temperature for 24 hours, after which the formwork 160 and core material 162 were removed to obtain a concrete specimen having an injection hole.

[0065] 2. Carbon dioxide supply A carbon dioxide cylinder was connected to the injection hole of the concrete specimens of the example and comparative examples via a high-pressure rubber hose, and carbon dioxide was supplied at a pressure of 0.1 MPa. 24 hours and 72 hours after the start of injection, the center of the concrete specimen was cut with a diamond cutter and carbonation was evaluated. Carbonation was evaluated by spraying a 1% ethanol solution of phenolphthalein as an indicator onto the cross section of the concrete specimen and checking whether the indicator changed color.

[0066] The results are shown in Figures 21(A) and 21(B). Figures 21(A) and 21(B) are cross-sectional schematic diagrams of concrete specimens of the Example and Comparative Example, respectively. Reflecting the above-mentioned fabrication method, the concrete specimen of the Example has a second injection hole 106 located approximately in the center of the 400 mm x 400 mm cross section, surrounded by porous concrete 104 with a diameter of 100 mm. Similarly, the cross section of the concrete specimen of the Comparative Example is a square with each side measuring 400 mm, and a first injection hole 102 is located approximately in the center.

[0067] When an indicator was sprayed onto the cross sections of these specimens, the outside of the region 180 surrounded by the dotted circle turned red, while the inside of the region 180 was colorless. This means that carbonation had progressed within the region 180, and the concrete within the region 180 had become neutral. In the concrete structure of the example, it was confirmed that carbonation had progressed to a distance of approximately 30 mm from the outer interface of the porous concrete 104. Similarly, carbonation in the concrete structure of the comparative example also progressed to a distance of approximately 30 mm from the inner wall of the first injection hole 102. However, the carbonated region was larger in the concrete specimen of the example. Specifically, the area of ​​the region 180 in the concrete specimen of the example was 2.00 × 10, which is the area of ​​a circle with a diameter of approximately 160 mm minus the area of ​​a circle with a diameter of 9 mm. 4 mm 2 Even if porous concrete 104 is excluded, the 4 mm 2 In contrast, in the concrete structure of the comparative example, the carbonated area was 3.67 × 10, which is the area of ​​the circle with a diameter of 69 mm minus the area of ​​the circle with a diameter of 9 mm. 3 mm 2 The above results show that by applying the reinforcement method according to the embodiment of the present invention, it is possible to increase the strength of a concrete structure in a short period of time and to fix a large amount of carbon dioxide.

[0068] The above-described embodiments of the present invention can be combined as appropriate as long as they are not mutually inconsistent. A product in which a person skilled in the art appropriately adds or deletes components or modifies the design based on each embodiment is also included within the scope of the present invention as long as it includes the gist of the present invention.

[0069] Even if there are other effects and advantages different from those brought about by the above-described embodiments, those that are clear from the description in this specification or that 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]

[0070] 10: concrete structure, 100: concrete, 100a: area, 100b: area, 100c: area, 102: first injection hole, 104: porous concrete, 105: coarse aggregate, 106: second injection hole, 108: protective tube, 110: adapter, 112: packing, 114: plate, 116: packing, 118: cap, 120: carbon dioxide supply source, 122: carbon dioxide line, 124: joint, 126: pressure gauge, 128: flow meter, 130: vacuum pump, 132: concentration meter, 134: humidity meter, 140: water supply source, 142: control device, 150: reinforcing bar, 160: formwork, 162: core material, 164: ready-mixed concrete, 165: mortar, 166: formwork, 168: formwork, 170: syringe

Claims

1. providing a concrete structure having one or more injection holes formed therein, extending from the surface into or through the structure by drilling or by removing a core material during construction; Filling or burying porous concrete inside the injection hole from one end to the other end in the extension direction of the injection hole; supplying a gas containing carbon dioxide to the porous concrete exposed from the concrete structure; A method for carbonating a concrete structure, wherein the porosity of the concrete structure is smaller than the porosity of the porous concrete.

2. The carbonation method according to claim 1 , wherein a hardening resin is injected into the porous concrete before or after the supply of the gas containing carbon dioxide.

3. providing a concrete structure having one or more first injection holes formed therein by drilling or by removing a core material during construction, the first injection holes extending from the surface into or through the structure; Filling or burying porous concrete inside the first injection hole from one end to the other end in the extension direction of the first injection hole; forming a second injection hole extending along the extension direction inside the porous concrete; and supplying a gas containing carbon dioxide to the second injection hole; A method for carbonating a concrete structure, wherein the porosity of the concrete contained in the concrete structure is smaller than the porosity of the porous concrete.

4. The carbonation method according to claim 3 , wherein a hardening resin is injected into the porous concrete or the second injection hole before or after the supply of the gas containing carbon dioxide.

5. The carbonation method according to claim 1 or 2, further comprising pouring ready-mixed concrete into the voids of the porous concrete.

6. 5. The carbonation method of claim 3 or 4, further comprising pouring ready-mixed concrete into the second injection hole.

7. The carbonation method according to claim 1 , further comprising supplying water to the porous concrete when the gas is supplied to the porous concrete.

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