Concrete structure

Abstract

To provide a method for efficiently fixing carbon dioxide in a concrete structure, so as to provide a high-strength concrete structure.SOLUTION: A concrete structure has a first concrete, a second concrete, and a porous body. The second concrete is located within the first concrete and is in contact with the first concrete. The porous body is located within the first concrete and is in contact with the second concrete. A concentration of calcium carbonate in the second concrete is higher than a concentration of calcium carbonate in the first concrete. The first concrete has a hole reaching the porous body from an outer surface. The porous body is spaced apart from the first concrete.SELECTED DRAWING: Figure 1C

Description

Technical Field

[0001] One embodiment of the present invention relates to a concrete structure and a method for manufacturing the same.

Background Art

[0002] Concrete is mainly composed of cement hydrates, aggregates, water, and additives, and is widely used in various fields as one of the important structural materials for creating social production bases and economic bases due to its excellent mechanical properties, weather resistance, ease of handling, and economy. Patent Documents 1 to 4 disclose that carbonation of concrete can be performed by bringing carbon dioxide into contact with the concrete, thereby increasing the strength of the concrete. However, a large amount of carbon dioxide is emitted during the production of cement, which is a raw material for concrete.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0004] One of the embodiments of the present invention aims to provide a concrete structure with a novel structure and a method for manufacturing the same. Alternatively, one of the embodiments of the present invention aims to provide a method for efficiently fixing carbon dioxide in a concrete structure to provide a high-strength concrete structure. Alternatively, one of the embodiments of the present invention aims to reduce the environmental load caused by carbon dioxide emissions during cement production by fixing carbon dioxide in a concrete structure.

Means for Solving the Problems

[0005] One of the embodiments of the present invention is a concrete structure. The concrete structure has a first concrete, a second concrete, and a porous body. The second concrete is located within the first concrete and is in contact with the first concrete. The porous body is located within the first concrete and is in contact with the second concrete. The calcium carbonate concentration in the second concrete is higher than the calcium carbonate concentration in the first concrete. The first concrete has pores reaching from the outer surface to the porous body. The porous body is separated from the first concrete.

[0006] One of the embodiments of the present invention is a method for manufacturing a concrete structure. This manufacturing method includes arranging a porous body inside ready-mixed concrete, curing the ready-mixed concrete, and supplying a gas containing carbon dioxide to the porous body. The arrangement and curing of the ready-mixed concrete are performed such that pores reaching from the outer surface of the cured ready-mixed concrete to the porous body are formed.

Brief Description of the Drawings

[0007]

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Mode for Carrying Out the Invention

[0008] Hereinafter, each embodiment of the present invention will be described with reference to the drawings and the like. However, the present invention can be implemented in various modes without departing from the gist thereof, and is not to be construed as being limited to the description of the embodiments exemplified below.

[0009] The drawings may be schematically represented in terms of the width, thickness, shape, etc. of each part compared to the actual aspect for the sake of clearer explanation, but this is merely an example and does not limit the interpretation of the present invention. In this specification and each figure, elements having the same functions as those described with respect to the previously shown figures may be denoted by the same reference numerals, and redundant explanations may be omitted.

[0010] In this specification, concrete refers to a cured product that does not exhibit fluidity, which is obtained by the hardening of a cement hydrate produced by the reaction of cement, which is one of the raw materials, with water. Therefore, mortar that does not contain aggregate is also included in the category of concrete. Concrete may contain fine aggregate with a diameter of 5 mm or less and coarse aggregate with a diameter exceeding 5 mm (for example, greater than 5 mm and 20 mm or less, or 10 mm or more and 20 mm or less). On the other hand, concrete before hardening, that is, a mixture containing cement and water and having fluidity without being completely hardened, is called ready-mixed concrete (also called fresh concrete). Ready-mixed concrete may contain additives such as AE agents (air-entraining agents), fluidizing agents, and thickeners in addition to cement, water, and aggregate.

[0011] In this specification and the claims, the expression "a certain structure is exposed from another structure" means a mode in which a part of a certain structure is not covered by another structure, and the part not covered by this other structure also includes a mode in which it is covered by yet another structure. Further, the mode represented by this expression also includes a mode in which a certain structure is not in contact with another structure.

[0012] Hereinafter, a concrete structure according to one embodiment of the present invention and a method for manufacturing the same will be described.

[0013] 1. Structure of the concrete structure The concrete structure according to one embodiment of the present invention is not restricted in any way by its size, shape, installation location, etc. For this reason, the concrete structure may be, for example, columns, walls, beams of buildings or houses, or may be bridge piers, abutments of bridges, dam embankments, levees and breakwaters provided in rivers and harbors, wave-dissipating blocks, covering concrete used for roads and tunnels. Alternatively, it may be a movable property (concrete product) including concrete such as concrete blocks and paving stones having various shapes.

[0014] A schematic perspective view of the concrete structure 100 is shown in FIG. 1A, and schematic views of end faces along the chain lines A-A' and B-B' in FIG. 1A are shown in FIGS. 1B and 1C respectively. Here, a concrete structure 100 having generally an octahedral shape is illustrated. As shown in these figures, the concrete structure 100 has a first concrete 102, a second concrete 104, and a porous body 106. The concrete structure 100 may have a tube 108 as an optional configuration. Further, although not shown in FIGS. 1A to 1C, as will be described later, the concrete structure 100 may contain reinforcing bars or a third concrete inside. Hereinafter, these configurations will be described.

[0015] (1) First concrete and second concrete The first concrete 102 is located outermost in the concrete structure 100 and constitutes the outer surface of the concrete structure 100. Therefore, the shape of the first concrete 102 determines the shape of the concrete structure 100. The second concrete 104 is embedded in the first concrete 102 and is in contact with the first concrete 102. The second concrete 104 is sandwiched between the porous body 106 and the first concrete 102 and does not protrude from the outer surface of the first concrete 102.

[0016] Both the first concrete 102 and the second concrete 104 are hardened products of ready-mixed concrete and contain calcium carbonate together with calcium hydroxide which is a cement hydrate. The first concrete 102 and the second concrete 104 may further contain aggregates, iron oxide, fly ash, incineration ash such as biomass ash, industrial wastes such as sludge, and the like. Examples of the aggregates include sand, gravel, pumice, blast furnace slag, or recycled crushed stone obtained by crushing concrete.

[0017] Here, the concentration of calcium carbonate in the second concrete 104 is higher than the concentration of calcium carbonate in the first concrete 102. Conversely, the concentration of calcium hydroxide in the second concrete 104 is lower than the concentration of calcium hydroxide in the first concrete 102. The concentration of calcium carbonate in the second concrete 104 may decrease as the distance from the porous body 106 in contact therewith increases. Conversely, the concentration of calcium hydroxide in the second concrete 104 may increase as the distance from the porous body 106 in contact therewith increases. Therefore, the pH of the first concrete 102 is higher than the pH of the second concrete 104. The former may be alkaline with a pH of 8 or more, and the latter may have a pH of less than 8.

[0018] The first concrete 102 and the second concrete 104 are provided with holes (bottomed holes) 102a (see FIGS. 1A and 1C). The inner diameter of the hole 102a may be, for example, 1 mm or more and 5 mm or less. One end of the hole 102a inside reaches the porous body 106, and the other end reaches the outer surface of the first concrete 102. Further, the outer surface side of the inner wall of the hole 102a is constituted by the first concrete 102, and the porous body 106 side is constituted by the second concrete 104.

[0019] (2) Porous body The porous body 106 is a structure having a large number of pores inside and mainly composed of an inorganic compound. Examples of the inorganic compound constituting the main component include silicon oxide, magnesium oxide, iron oxide, aluminosilicate, and the like. Alternatively, the porous body 106 may contain an elastomer such as synthetic rubber or natural rubber, or a polymer such as a resin.

[0020] The diffusion coefficient of carbon dioxide in the porous body 106 is extremely large compared to that in the cement paste or aggregate in the first concrete 102 and the second concrete 104. Specifically, the diffusion coefficient of carbon dioxide in the porous body 106 is 10 2 or more. For example, the diffusion coefficient of carbon dioxide in the porous body 106 is 1 × 10 -5 m 2 / sec or more and 10 m 2 / sec or less. Alternatively, the porosity of the porous body 106 is extremely large compared to that in the cement paste or aggregate in the first concrete 102 and the second concrete 104, and is, for example, 50% or more and 80% or less.

[0021] The porous body 106 is embedded in the first concrete 102. The porous body 106 may be embedded in the second concrete 104. However, the porous body 106 is provided so as not to contact the first concrete 102 and to contact the second concrete 104. In other words, the porous body 106 is separated from the first concrete 102 and does not reach the outer surface of the first concrete 102. That is, the first concrete 102 covers the second concrete 104 and the entire porous body 106 and also functions as cover concrete for them.

[0022] The shape of the porous body 106 can also be arbitrarily determined. For example, the shape of the porous body 106 is not limited to a polyhedron including a hexahedron, and may be a sphere, an ellipsoid, a cylinder, a polygonal prism, a tubular shape, or the like. Alternatively, the entire surface of the porous body 106 may be composed of curved surfaces. It may be embedded in the first concrete 102 as a single mass having a fixed shape, or may be embedded in the first concrete 102 as a collection of a plurality of granular porous bodies. As understood from FIGS. 1B and 1C, the porous body 106 is not uniformly distributed within the concrete structure 100 but is localized. For example, the porous body 106 may be localized around the center or centroid of the concrete structure 100. Also, as shown in the schematic perspective view of FIG. 2A and the schematic views of the end faces along the chain lines C-C', D-D', and E-E' (FIGS. 2B to 3B, respectively), the concrete structure 100 may have a plurality of porous bodies 106 (here, the first porous body 106-1 and the second porous body 106-2). Even in this case, each of the plurality of porous bodies 106 may be a single mass or a collection of a plurality of granular porous bodies. Also, the same number of holes 102a as the plurality of porous bodies 106 may be provided so as to reach the individual porous bodies 106. Although not shown, branched holes 102a may be formed, and the porous bodies 106 may be arranged at the plurality of ends generated by the branching, respectively.

[0023] (3) Tube As shown in FIGS. 1A and 1C, for example, the concrete structure 100 may optionally include a tube 108 in the hole 102a. The diameter of the tube 108 may be, for example, 1 mm or more and 5 mm or less. By setting the inner diameter of the hole 102a and the diameter of the tube 108 within the above ranges, a path reaching the porous body 106 from the outer surface of the concrete structure 100 can be ensured over a long period without impairing the strength of the concrete structure 100. The tube 108 is a hollow member including, for example, a resin such as polyvinyl chloride, a fiber-reinforced plastic, or a metal such as iron or stainless steel. It covers the inner wall of the hole 102a, is arranged such that one end reaches the porous body 106, and the other end reaches the outer surface of the first concrete 102. Therefore, the outer surface side of the tube 108 is covered with the first concrete 102, and the porous body 106 side is covered with the second concrete 104.

[0024] (4) Third concrete As shown in FIG. 4A, for example, the concrete structure 100 may optionally include a third concrete 110 in the tube 108. In this case, the hole 102a is blocked by the tube 108 and the third concrete 110 filled in the tube 108. One end of the third concrete 110 reaches the outer surface of the first concrete 102, and the other end reaches the porous body 106. The third concrete 110, like the first concrete 102, contains a cement hydrate. The third concrete 110 may contain aggregates or may be a so-called mortar that does not contain aggregates (or contains a small amount of aggregates). The calcium carbonate concentration in the third concrete 110 is lower than that in the second concrete 104. However, the calcium carbonate concentration in the first concrete 102 may be higher or lower than that in the third concrete 110.

[0025] Alternatively, as shown in FIG. 4B, the concrete structure 100 may have a third concrete 110 that blocks the hole 102a without including the tube 108. In this case, the third concrete 110 contacts the first concrete 102 on the outer surface side and contacts the second concrete 104 and the porous body 106 on the porous body 106 side.

[0026] (5) Reinforcing bars When the concrete structure 100 includes reinforcing bars, the number, diameter, shape, arrangement, etc. thereof may be appropriately set according to the shape of the concrete structure 100 and the required strength. FIG. 5A is a schematic perspective view of the concrete structure 100 having the reinforcing bars 120, and FIG. 5B is a schematic view of the end face along the chain line F-F' of FIG. 5A. In addition, in FIG. 5A, for the sake of clarity, the second concrete 104, the tube 108, etc. are not shown. Here, an example in which three types of reinforcing bars (the first reinforcing bar 122, the second reinforcing bar 124, and the third reinforcing bar 126) are combined is shown. The first reinforcing bar 122 and the third reinforcing bar 126 extend such that the portions parallel to the upper surface of the first concrete 102 intersect each other, and extend along the side surface of the first concrete 102. On the other hand, the second reinforcing bar 124 extends parallel to the upper surface of the first concrete 102 so as to surround the first reinforcing bar 122 and the third reinforcing bar 126. These reinforcing bars 120 may be fixed to each other by a metal wire or the like (not shown).

[0027] As can be understood from FIG. 5B, the holes 102a and the tubes 108 are provided so as not to interfere with the reinforcing bars 120. Further, the reinforcing bars 120 do not contact the porous body 106 and the second concrete 104 and are separated from these. In other words, the reinforcing bars 120 are arranged so as to be selectively embedded in the first concrete 102. As described above, since the first concrete 102 is alkaline, by arranging the reinforcing bars 120 so as to be embedded in the first concrete 102, corrosion of the reinforcing bars 120 is prevented, and as a result, the concrete structure 100 can maintain the required strength over a long period of time.

[0028] When the reinforcing bar 120 is provided, the concrete structure 100 may be provided with a protective material 130 that covers a part of the porous body 106 and exposes the other part (FIG. 6A). The protective material 130 may be a sheet-like flexible cover, or may be a coating film formed on the surface of the porous body 106. The protective material 130 preferably has a low gas permeability, particularly for carbon dioxide. Examples of the material included in the protective material 130 include polymers with low gas permeability such as polyvinyl alcohol, polyacrylonitrile, ethylene-vinyl alcohol copolymer, polyvinylidene chloride, polyethylene terephthalate, nylon, polyvinyl chloride, polylactic acid, high-density (e.g., 0.96 g / cm 3 or higher density) polyethylene, and cellulose acetate. When the protective material 130 is formed by a coating film, a solution of the above-described polymer may be applied to the porous body 106, and the solvent may be distilled off to form a coating film of the above polymer.

[0029] As described above, the protective material 130 does not cover the entire porous body 106, and a part of the porous body 106 is exposed from the protective material 130. As shown in FIG. 6B, when the protective material 130 is used, the protective material 130 is located on the side of the reinforcing bar 120, and the porous body 106 is arranged such that the portion exposed from the protective material 130 is located on the side opposite to the reinforcing bar (or at a position farther from the closest reinforcing bar 120 to the porous body 106). As will be described later, a gas containing carbon dioxide is supplied to the porous body 106 using the holes 102a, and the second concrete 104 is formed by carbonation with carbon dioxide diffusing from the porous body 106. For this reason, the second concrete 104 is formed from the surface side not covered by the protective material 130 of the porous body 106. As a result, the protective material 130 is sandwiched between the porous body 106 and the first concrete 102, and the porous body 106 is embedded in the protective material 130 and the second concrete 104. Further, by providing the protective material 130 on the side of the reinforcing bar 120 of the porous body 106, the formation of the second concrete 104 with a high calcium carbonate concentration is suppressed on the side of the reinforcing bar 120. As a result, the first concrete 102 embedding the reinforcing bar 120 can maintain its alkalinity.

[0030] 2. Method for manufacturing a concrete structure Hereinafter, one of the methods for manufacturing the above-described concrete structure 100 will be described. Here, a method for manufacturing the concrete structure 100 including the reinforcing bars 120 will be described with reference to FIGS. 7A to 10B. FIGS. 7A to 10B are schematic end views corresponding to FIG. 4B.

[0031] First, considering the shape and required strength of the concrete structure 100, the reinforcing bars 120 (for example, the first reinforcing bar 122, the second reinforcing bar 124, and the third reinforcing bar 126) are arranged (FIG. 7A). Thereafter, the formwork 140 is arranged so as to surround the reinforcing bars 120.

[0032] Thereafter, ready-mixed concrete 142 is placed in a part of the formwork 140 (FIG. 7B). The ready-mixed concrete 142 is prepared by mixing cement and water. At this time, in addition to aggregates, additives such as AE agents (air-entraining agents), fluidizing agents, and thickeners may be further added. There is no restriction on the type of cement, and ordinary Portland cement, white Portland cement containing iron oxide, alumina cement containing alumina, blast furnace cement added with blast furnace slag by-produced in the manufacturing process of steel materials, fly ash cement added with fly ash cement by-produced during the combustion of lime ash, eco-cement containing waste such as incineration ash and sludge, etc. can be used. As aggregates, sand, gravel, pumice, blast furnace slag, etc. may be used, or recycled crushed stone obtained by crushing discarded concrete may also be used. The weight ratio of cement to aggregates may be appropriately set in consideration of the characteristics required for the obtained concrete structure 100. For example, aggregates with a weight 3 times or more and 10 times or less that of the cement may be used. There is no restriction on the water / cement ratio either, but it may be selected from the range of 10% to 100%. As additives, the various additives described above may be appropriately used according to the use of the concrete block, etc. Further, ash such as fly ash, slag, biomass ash, and incineration ash, silica fume, carbides, etc. may be added as admixtures together with the aggregates or in place of the aggregates. The amount of the admixtures may be determined appropriately, but it may be adjusted so that the water-binder ratio (W / B) is 10% or more and 100% or less. Here, the binder refers to cement and admixtures, and the water-binder ratio is the mass of water relative to the total mass of cement and admixtures.

[0033] Thereafter, by disposing the porous body 106 and the tube 108 on the ready-mixed concrete 142, the porous body 106 is disposed inside the space formed by the reinforcing bars 120. The position of the porous body 106 may be determined by the height of the ready-mixed concrete 142 poured into the formwork 140 and its position within the upper surface thereof. The tube 108 is disposed such that one end reaches the porous body 106 and the other end contacts the formwork 140. When the porous body 106 is an aggregate of granular porous bodies, the tube 108 may be disposed, and then the granular porous bodies may be scattered so as to cover one end of the tube. Further, when providing the protective material 130, the porous body 106 having a coating film of the protective material 130 formed thereon in advance may be disposed, or the porous body 106 disposed on the ready-mixed concrete 142 may be covered with the protective material 130 (FIG. 8).

[0034] Thereafter, the porous body 106 and the tube 108 are embedded, and further, the ready-mixed concrete 142 is placed in the formwork 140 so as to cover the entire reinforcing bars 120 (FIG. 9A). Thereafter, the ready-mixed concrete is cured and the formwork 140 is removed.

[0035] Thereafter, as shown by the solid arrows in Fig. 9B, the carbon dioxide-containing gas is supplied to the porous body 106 through the hole 102a and the tube 108. The supply of the carbon dioxide-containing gas can be started at any time after the placement of the ready-mixed concrete 142. For example, it can be started several hours, one day, three days, one week, one month, one year, five years, ten years, or even 100 years or later after the placement of the ready-mixed concrete 142. For example, carbonation may be started before the concrete structure 100 is disassembled or discarded. The concentration of carbon dioxide contained in the carbon dioxide-containing gas only needs to be higher than the atmospheric carbon dioxide concentration, and can be arbitrarily selected, for example, from the range of 1% or more to 100% or less. Therefore, as a supply source of the carbon dioxide-containing gas, cylinders or tanks containing carbon dioxide can be used. Alternatively, if there are existing facilities (such as chemical plants, waste incineration facilities, thermal power plants, and various other factories) that emit a large amount of carbon dioxide near the production site of the concrete structure 100, the gas discharged from these facilities, or the purified gas obtained by performing dust removal, desulfurization, denitration, etc. on the discharged gas, may be used as the carbon dioxide-containing gas. In this case, these facilities function as a supply source of the carbon dioxide-containing gas, the cost for transporting carbon dioxide is reduced, and the emission of carbon dioxide during transportation is prevented.

[0036] The flow rate of the carbon dioxide-containing gas may be adjusted so that the pressure in the hole 102a is 1 atm (0.1 MPa) or more and 20 atm (2 MPa) or less, or 1 atm (0.1 MPa) or more and 10 atm (1 MPa) or less. The carbon dioxide-containing gas may be continuously supplied to the hole 102a or intermittently supplied. In the latter case, after the carbon dioxide-containing gas is supplied to the hole 102a, the hole 102a may be closed using a cap (not shown). Preferably, an appropriate amount of moisture is added to the carbon dioxide-containing gas so that the humidity of the carbon dioxide-containing gas is 50% or more and 100% or less. Also, the temperature of the carbon dioxide-containing gas may be the outside air temperature, or a carbon dioxide-containing gas heated to, for example, 40°C or more and 60°C or less using a heating device (not shown) may be used.

[0037] As described above, one or more localized porous bodies 106 are provided inside the concrete structure 100. For this reason, a large amount of carbon dioxide can be supplied inside the concrete structure 100. As indicated by the dotted arrows in Fig. 9B, the supplied carbon dioxide diffuses almost isotropically from the surface of the porous body 106. As a result, carbonation proceeds three-dimensionally from the surface of the porous body 106. By this mechanism, the second concrete 104 is formed in the portion of the hardened ready-mixed concrete 142 that is in direct contact with the porous body 106 (Fig. 10A). On the other hand, the portion where carbon dioxide did not diffuse exists as the alkaline first concrete 102. As a result, the porous body 106 is separated from the first concrete 102 by the second concrete 104.

[0038] As described above, the porous body 106 is provided inside the space formed by the reinforcing bars 120 and does not contact the reinforcing bars 120. For this reason, although it also depends on the shape of the concrete structure 100, the arrangement of the reinforcing bars 120, the size of the porous body 106, the concentration of the carbon dioxide-containing gas, and the supply period, a certain distance can be ensured between the second concrete 104 and the reinforcing bars 120. Therefore, by appropriately controlling the progress state of carbonation, the reinforcing bars 120 can be surely arranged within the first concrete 102. Further, by providing the protective material 130, carbonation toward the reinforcing bars 120 can be suppressed. Therefore, even when the distance between the porous body 106 and the reinforcing bars 120 is small, it is also possible to prevent the reinforcing bars 120 from contacting the second concrete 104.

[0039] As an arbitrary step after the carbonation is completed, the tube 108 may be removed, and the third concrete 110 may be injected into the hole 102a and hardened (Fig. 10B). Alternatively, although not shown, the third concrete 110 may be injected into the tube 108 and hardened while the tube 108 remains.

[0040] Since the strength of concrete increases due to carbonation of the concrete, it becomes possible to provide a high-strength concrete structure by applying the embodiments of the present invention. Also, usually, in a large concrete structure, reinforcing bars are arranged under relatively thin cover concrete. Therefore, due to the need to prevent corrosion of the reinforcing bars due to acidification of the concrete, in the conventional method of supplying carbon dioxide-containing gas to the outer surface of the concrete structure, carbon dioxide can be used for fixation only in a part on the outside of the concrete structure. On the other hand, in the embodiments of the present invention, carbonation proceeds from the surface of the porous body 106 which is located inside the concrete structure 100 and can adsorb a large amount of carbon dioxide. For this reason, it is possible to arrange high-strength concrete inside the concrete structure, and at the same time, a large amount of carbon dioxide can be efficiently fixed. Such a feature can be said to greatly contribute to the fixation of carbon dioxide which is a greenhouse gas. Furthermore, by controlling the position of the porous body 106, it is also possible to selectively perform carbonation at an arbitrary location. Therefore, according to the embodiments of the present invention, it is possible to reduce the environmental load caused by a large amount of carbon dioxide emissions during cement production.

Example

[0041] In this example, an example will be described in which a concrete structure having a porous body disposed therein is fabricated, and a carbon dioxide-containing gas is supplied from a hole reaching the porous body to carbonate the concrete structure.

[0042] Ready-mixed concrete was prepared by mixing ordinary Portland cement (manufactured by Taiheiyo Cement Corporation) having a density of 3.16 g / cm 3 with water. At this time, the unit water amount was 170 kg / m 3 , and the unit cement amount was 340 kg / m 3, the water-cement ratio was 50%. This ready-mixed concrete was poured into a wooden formwork (200 mm × 200 mm × 200 mm). At this time, a 10 mm × 10 mm × 10 mm porous body was placed almost at the center of the formwork, and a tube (inner diameter 3 mm) was arranged such that one end reached the porous body and the other end reached the side surface of the poured ready-mixed concrete. As the porous body, an elastomer with a carbon dioxide diffusion coefficient of 0.01 - 0.1 (m 2 / sec) was used. A schematic perspective view of the fabricated concrete structure is shown in Fig. 11A, and a schematic view of the end face along the dashed line G-G' in Fig. 11A is shown in Fig. 11B.

[0043] After 24 hours had passed since the ready-mixed concrete was poured, the form was removed, and carbon dioxide with a purity of 99.999% was injected from a cylinder through the tube 108. The pressure of the carbon dioxide was 0.4 MPa. The concrete structure was cut 24 hours and 72 hours after the start of the injection of the carbon dioxide-containing gas, and a 1% ethanol solution of phenolphthalein was sprayed on the cross section to measure the carbonation depth. When carbonation has not progressed, the concrete shows alkalinity, so the cross section turns red. On the other hand, as carbonation progresses, the pH decreases, so color development by phenolphthalein is not observed. Therefore, the region where color development by phenolphthalein is not observed corresponds to the porous body 106 and the second concrete 104 generated by carbonation, and the region where color development is observed corresponds to the first concrete 102. The carbonation depth was evaluated as the distance D from the center of the cross section (see Fig. 12).

[0044] As a result, 24 hours after the start of the supply of the carbon dioxide-containing gas, the distance D was about 50 mm, and 72 hours after, the distance D was about 100 mm, indicating that almost the entire part had carbonated. This result suggests that by applying the embodiment of the present invention, carbonation of concrete can be extremely efficiently carried out even using a carbon dioxide-containing gas at a relatively low pressure.

[0045] As long as the above-described embodiments as the embodiments of the present invention do not conflict with each other, they can be implemented in appropriate combination. Based on each embodiment, those in which a person skilled in the art appropriately adds, deletes, or changes the design of components are also included in the scope of the present invention as long as they have the gist of the present invention.

[0046] Even other operational effects different from the operational effects brought about by the above-described embodiments are understood to be naturally brought about by the present invention as long as they are obvious from the description in this specification or can be easily predicted by a person skilled in the art.

Explanation of Signs

[0047] 100: Concrete structure, 102: First concrete, 102a: Hole, 104: Second concrete, 106: Porous body, 106-1: First porous body, 106-2: Second porous body, 108: Tube, 110: Third concrete, 120: Reinforcing bar, 122: First reinforcing bar, 124: Second reinforcing bar, 126: Third reinforcing bar, 130: Protective material, 140: Formwork, 142: Ready-mixed concrete

Claims

1. a first concrete, a second concrete located within the first concrete and in contact with the first concrete, and a porous body located within the first concrete and in contact with the second concrete, wherein the calcium carbonate concentration in the second concrete is higher than the calcium carbonate concentration in the first concrete, the first concrete has pores reaching the porous body from an outer surface, and the porous body is a concrete structure separated from the first concrete.

2. The concrete structure according to claim 1, wherein an outer surface side of an inner wall of the pores is formed by the first concrete, and a porous body side is formed by the second concrete.

3. The concrete structure according to claim 1, further comprising a tube within the pores.

4. The concrete structure according to claim 1, further comprising a protective material covering a part of the porous body between the porous body and the first concrete, wherein the porous body is embedded in the second concrete and the protective material.

5. The concrete structure according to claim 1, wherein the calcium carbonate concentration in the second concrete decreases as a distance from the porous body increases.

6. The concrete structure according to claim 1, wherein at least one of the first concrete and the second concrete includes an aggregate having a specific surface area lower than a specific surface area of the porous body.

7. The concrete structure according to claim 1, wherein the porous body is locally present within the first concrete.

8. The concrete structure according to claim 1, further comprising steel bars in the first concrete.

9. The concrete structure according to claim 8, wherein the steel bars are separated from the second concrete and the porous body.

10. The concrete structure according to claim 1, wherein the porous body and the second concrete are entirely covered by the first concrete.

11. The concrete structure according to claim 1, further comprising a third concrete within the pores.

12. The concrete structure according to claim 3, further comprising a third concrete within the tube.

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