Description:[TECHNICAL FIELD]
[0001]
An embodiment of the present invention relates to a concrete product and a manufacturing method thereof.

[BACKGROUND ART]
[0002]
Concrete is mainly composed of cement hydrate, aggregate, water, and additives and has been widely used in various fields as one of the important structural materials to create social production and economic infrastructure due to its excellent mechanical properties, weather resistance, ease of handling, and economic efficiency. Concrete without reinforcing steel has also been widely used not only as lining concrete but also as walls, curbs, slide blocks serving as pedestals of a variety of large equipment, small concrete products such as slide blocks, anchor blocks, drainage channels, safety blocks, parking blocks, and bricks, and the like.
[0003]
It has been known that cement serving as the raw material for concrete emits a large amount of carbon dioxide during its production, which has been represented as one of the causes of the greenhouse effect. In order to contribute to solving this problem, Patent Document 1 discloses a method of fixing carbon dioxide in concrete in which ready-mixed concrete is made to contact with carbon dioxide before the concrete is cured when a structure containing concrete is constructed, for example. Patent Document 2 discloses a design method of concrete structures which is effective in promoting the absorption of carbon dioxide into concrete. Similarly, Patent Document 3 discloses a method of fixing carbon dioxide in concrete products by placing the concrete products in a curing tank and introducing a gas containing carbon dioxide at a concentration higher than that of the atmosphere into the curing tank.

[CITATION LIST]
[PATENT LITERATURE]
[0004]
[Patent Document 1] Japanese Patent No. 5957283
[Patent Document 2] Japanese Patent No.4822373
[Patent Document 3] Japanese Patent Application Publication No. 2009-149456

[SUMMARY OF INVENTION]
[TECHNICAL PROBLEM]
[0005]
An object of an embodiment of the present invention is to provide carbonated concrete products having a novel structure and a method for manufacturing thereof. Alternatively, an embodiment of the invention is to provide a concrete product in which a large amount of carbon dioxide is fixed and a manufacturing method thereof. Alternatively, an object of an embodiment of the present invention is to provide a method for fixing carbon dioxide.

[SOLUTION TO PROBLEM]
[0006]
An embodiment of the present invention is a concrete block. The concrete block has a first concrete region and a second concrete region located inside the first concrete region. A part of a surface of the second concrete region exists in the same plane as a part of a surface of the first concrete region. A concentration of calcium carbonate of the first concrete region is higher than a concentration of calcium carbonate of the second concrete region.
[0007]
An embodiment of the present invention is a concrete block. The concrete block has a first concrete region and a second concrete region located inside the first concrete region. A part of a surface of the second concrete region exists in the same plane as a part of a surface of the first concrete region. A concentration of calcium hydroxide of the first concrete region is lower than a concentration of calcium hydroxide of the second concrete region.
[0008]
An embodiment of the present invention is a method for manufacturing a concrete block. The manufacturing method includes: injecting first ready-mixed concrete into a mold; forming an injection hole in the first ready-mixed concrete; introducing a gas containing carbon dioxide into the injection hole; curing the first ready-mixed concrete to form a first concrete region; injecting a second ready-mixed concrete into the injection hole; and curing the second ready-mixed concrete to form a second concrete region.
[0009]
An embodiment of the present invention is a method for fixing carbon dioxide. The method comprising: injecting first ready-mixed concrete into a mold; forming an injection hole in the first ready-mixed concrete; curing the first ready-mixed concrete while introducing a gas containing carbon dioxide into the injection hole to form a first concrete region; injecting second ready-mixed concrete into the injection hole; and curing the second ready-mixed concrete to form a second concrete region.

[BRIEF DESCRIPTION OF DRAWINGS]
[0010]
[FIG. 1A] A schematic perspective view of a concrete product according to an embodiment of the present invention.
[FIG. 1B] A schematic cross-sectional view of a concrete product according to an embodiment of the present invention.
[FIG. 1C] A schematic cross-sectional view of a concrete product according to an embodiment of the present invention.
[FIG. 1D] A schematic cross-sectional view of a concrete product according to an embodiment of the present invention.
[FIG. 2] A flowchart showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 3A] A schematic perspective view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 3B] A schematic perspective view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 3C] A schematic perspective view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 4A] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 4B] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 4C] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 5A] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 5B] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 5C] A schematic top view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 6] A schematic view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 7A] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 7B] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 7C] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 8A] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.
[FIG. 8B] A schematic cross-sectional view showing a manufacturing method of a concrete product according to an embodiment of the present invention.

[DESCRIPTION OF EMBODIMENTS]
[0011]
Hereinafter, each embodiment of the present invention is explained with reference to the drawings. The invention can be implemented in a variety of different modes within its concept and should not be interpreted only within the disclosure of the embodiments exemplified below.
[0012]
The drawings may be illustrated so that the width, thickness, shape, and the like are illustrated more schematically compared with those of the actual modes in order to provide a clearer explanation. However, they are only an example, and do not limit the interpretation of the invention. In the specification and the drawings, the same reference number is provided to an element that is the same as that which appears in preceding drawings, and a detailed explanation may be omitted as appropriate.
[0013]
In the specification and the claims, an expression “a structure is exposed from another structure” means a mode in which a part of the structure is not covered by the other structure and includes a mode where the part uncovered by the other structure is further covered by another structure.
[0014]
In this specification, concrete refers to as a cured product that does not exhibit fluidity, which is obtained by curing cement hydrate formed by the reaction of cement, one of the raw materials, with water. Thus, cement paste without 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 greater than 5 mm (e.g., greater than 5 mm and equal to or less than 20 mm or equal to or more than 10 mm and equal to or less than 20 mm). On the other hand, pre-cured concrete, i.e., a mixture containing cement and water and having fluidity before completely being cured, is called ready-mixed concrete (also called fresh concrete). In addition to cement, water, and aggregate, ready-mixed concrete may contain additives such as AE agents (air bubble dispersants), fluidizers, and thickeners.
[0015]
In this specification, "curing" refers to as a process of curing ready-mixed concrete, and curing ready-mixed concrete forms cured ready-mixed concrete, i.e., concrete.
[0016]
Hereinafter, a concrete product, a manufacturing method thereof, and a method for fixing carbon dioxide utilizing the manufacturing method are explained using the accompanying drawings.
[0017]
1. Concrete Product
The carbonated concrete product according to an embodiment of the present invention is typically a concrete block. The concrete product may be, for example, concrete blocks laid on roads and slopes or concrete bricks used for walls and fences. Alternatively, the concrete product may be concrete blocks utilized for curbs, sliding blocks for various facilities, anchor blocks, safety blocks, parking blocks, wave dissipating blocks, or the like. Therefore, there are no restrictions on the shape and the size of the concrete product according to an embodiment of the present invention, and the shape and the size may be determined according to the application.
[0018]
FIG. 1A shows a schematic perspective view of a concrete block 100, which is an example of the concrete product according to an embodiment of the present invention. As described below, the concrete block 100 is produced by curing ready-mixed concrete and is therefore a sort of unfired brick. Although the concrete block 100 shown in FIG. 1A has a rectangular parallelepiped shape, there are no restrictions on the size or shape of the concrete block 100 as described above, and the concrete block 100 may have a polyhedral shape including a rectangular parallelepiped or cylindrical shape. Alternatively, ridges of adjacent planes may include a curve so as to be used for inter-blocks.
[0019]
The concrete block 100 is mainly composed of two parts. One is a first concrete region 102 serving as the primary component of the concrete block 100. The first concrete region 102 is the component determining the three-dimensional shape of the concrete block 100 and includes concrete that is cement hydrate. The first concrete region 102 may further include aggregate. The other part is at least one second concrete region 104. As shown in FIG. 1A, the at least one second concrete region 104 may include a plurality of second concrete regions 104. The second concrete region 104 also includes concrete and may further include aggregate. The composition ratio of concrete to aggregate may be the same or different between the first concrete region 102 and the second concrete region 104. The type of aggregate used may also be the same or different. The volume of the first concrete region 102 is greater than the total volume of the second concrete region 104.
[0020]
A schematic view of a cross section along a chain line A-A' across the first concrete region 102 and the second concrete region 104 is shown in FIG. 1B. As can be understood from FIG. 1A and FIG. 1B, the second concrete region 104 is provided so as to be in contact with the first concrete region 102. More specifically, the side surfaces of the second concrete region 104 are entirely surrounded by the first concrete region 102, and its top surface 104a is exposed from a surface 102a of the first concrete region 102. In addition, the second concrete region 104 may be provided in the first concrete region 102 so that the top surface 104a of the second concrete region 104 and the surface 102a of the first concrete region 102 are in the same plane as each other. Thus, the top surface 104a of the second concrete region 104 constitutes a part of the three-dimensional shape of the concrete block 100.
[0021]
In the examples shown in FIG. 1A and FIG. 1B, the second concrete region 104 has a rod shape and its longitudinal direction (extending direction) is perpendicular to the top surface 104a and the surface 102a of the first concrete region 102. However, the longitudinal direction may be inclined from the top surface 104a of the second concrete region 104 or the surface 102a of the first concrete region as shown in Figure 1C. When a plurality of second concrete regions 104 is provided, the extending directions thereof may be parallel to each other, or the second concrete regions 104 may be configured such that the extending directions of arbitrarily selected two second concrete regions 104 do not intersect each other. Although not illustrated, the second concrete region 104 may be curved or bent within the first concrete region 102.
[0022]
In the examples shown in FIG. 1B and FIG. 1C, a bottom surface 104b facing the top surface 104a of the second concrete region 104 is also covered by the first concrete region 102 and is in contact with the first concrete region 102. However, all of or a part of the bottom surface 104b of the second concrete region 104 may be exposed from the surface of the first concrete region 102 (here, a surface 102b facing the surface 102a) as shown in FIG. 1D. In this case, the bottom surface 104b of the second concrete region 104 and the surface 102b of the first concrete region 102 may exist in the same plane as each other.
[0023]
There is no restriction on the shapes of the top surface 104a and the bottom surface 104b of the second concrete region 104 at the surfaces 102a and 102b of the first concrete region 102, and the shape may be circular, elliptical, or polyangular. Alternatively, the profiles of the top surface 104a and the bottom surface 104b of the second concrete region 104 each may consist of only straight lines or curves or may include both straight lines and curves. The areas of the top surface 104a and the bottom surface 104b of the second concrete region 104 are also not restricted and may be set according to the size of the concrete block 100. For example, the areas of the top surface 104a and the bottom surface 104b may be each selected from a range equal to or more than 1 cm2 and equal to or less than 500 cm2, equal to or more than 1 cm2 and equal to or less than 300 cm2, or equal to or more than 1 cm2 and equal to or less than 100 cm2.
[0024]
Here, the first concrete region 102 and the second concrete region 104 each contain calcium carbonate (CaCO3) along with calcium silicate hydrate (3CaO-2SiO2-3H2O) and calcium hydroxide (Ca(OH)2) formed by hydration of cement. In addition, an average concentration (composition) of calcium carbonate of the first concrete region 102 is higher than that of the second concrete region 104. Moreover, the concentration of calcium carbonate of the first concrete region 102 may decrease with increasing distance from the interface with the second concrete region 104. On the contrary, an average concentration (composition) of calcium hydroxide of the first concrete region 102 is lower than that of the second concrete region 104. Furthermore, the concentration of calcium hydroxide in the first concrete region 102 may decrease with increasing distance from the interface with the second concrete region 104.
[0025]
　As described above, because the first concrete region 102, which is the component determining the three-dimensional shape of the concrete block 100, has a high calcium carbonate concentration, the concrete block 100 exhibits high compressive strength. Therefore, the concrete product according to an embodiment of the present invention can be used as a concrete block with high strength.

[0026]
2. Manufacturing Method of Concrete Product
FIG. 2 shows a flowchart of an example of the manufacturing method of the concrete block 100.
[0027]
(1) Preparation of Ready-Mixed Concrete
First, ready-mixed concrete is prepared. The ready-mixed concrete is prepared by mixing cement and water. At this time, aggregates such as sand, gravel, cobble, rock, crushed stone, and crushed sand and additives such as AE agents (bubble dispersants), fluidizing agents, thickening agents, and quickening agents may be further added. There are no restrictions on the type of cement, and it is possible to use ordinary Portland cement, white Portland cement containing iron oxide, alumina cement containing alumina, blast furnace cement added with blast furnace slag formed as a byproduct during the steel manufacturing process, fly ash cement added with a fly ash formed as a byproduct during coal ash combustion, eco cement containing waste materials such as incinerator ash and sludge, and the like. Sand, gravel, pumice stone, and the like may be used as aggregate, or recycled crushed stone obtained by crushing discarded concrete may also be used. The mass ratio of cement to aggregate may also be set appropriately in consideration of the characteristics required for the resulting concrete block, and aggregate with a weight of 3 to 10 times that of cement may be used, for example. The water-cement ratio is also not restricted and may be selected from a range of 10% to 100%. As additives, the various additives described above may be used as appropriate depending on the application of the concrete block and the like.
[0028]
Furthermore, fly ash, slag, ash such as biomass ash and incineration ash, silica fume, or the like may be added as admixture along with or instead of aggregate. The amount of admixture may be determined as appropriate and may be adjusted so that the water to binder ratio (W/B) is equal to or more than 35% and equal to or less than 70%. Here, the binder refers to cement and admixture, and the water-binder ratio is the mass of water with respect to the total mass of cement and admixture.
[0029]
Through the above process, ready-mixed concrete with fluidity can be obtained. Note that the ready-mixed concrete obtained here may have high fluidity so that it cannot free-stand or may have fluidity so that it can free-stand. In other words, the ready-mixed concrete obtained up to this process may have a solid state which easily deforms when an external force is applied. Here, free-standing means a state where the ready-mixed concrete does not readily deform but maintains a three-dimensional shape formed by a mold when an external force is applied even after being removed from the mold.
[0030]
(2) Molding
As shown in FIG. 3A and FIG. 3B, molding is performed by filling the mold 110 with the ready-mixed concrete 112 and applying a pressure from above the ready-mixed concrete 112. The pressure during pressurization may be selected from a range equal to or higher than 1 MPa and equal to or lower than 10 MPa, for example. Vibration may be applied before pressurization to remove air mixed into the mold 110 in order to entirely fill the interior of the mold 110 with the ready-mixed concrete 112 at a high density.
[0031]
(3) Primary Curing
Next, curing (primary curing process) is carried out. In the primary curing process, one or a plurality of injection holes (openings) 114 is first formed inside the ready-mixed concrete 112 in the mold 110. The injection holes 114 may be formed by, for example, piercing a rod (core material) made of wood, metal, or resin into the ready-mixed concrete 112 and pulling it out (FIG. 3C). When the ready-mixed concrete has high fluidity to the extent that it cannot free-stand, the injection hole 114 is formed by allowing the core material to stand still after piercing the core material until the ready-mixed concrete 112 is cured to the extent that the shape of the injection hole 114 can be maintained. A release agent (mold release agent) or curing retardant may be applied on the outer surface of the core material. As described below, the application of the release agent or curing retardant allows the core material to be easily removed from the ready-mixed concrete 112.
[0032]
As shown in FIG. 4A which is a schematic view of a cross section along a chain line B-B’ in FIG. 3C, the injection hole 114 may be a bottomed hole which does not pass through the ready-mixed concrete 112 or may be a through hole passing through the ready-mixed concrete 112 as shown in FIG. 4B. When the injection hole 114 is formed as a bottomed hole, the injection hole 114 is preferably formed so that its length (depth) is equal to or more than 50% and equal to or less than 80% of the height of the ready-mixed concrete 112 (length in the direction in which the injection hole 114 extends). In addition, one or a plurality of injection holes 114 may be formed to extend diagonally from the surface 112a of the ready-mixed concrete 112 as shown in FIG. 4C.
[0033]
After forming the injection holes 114, a gas containing carbon dioxide is injected into the injection holes 114. There is no restriction on the method of injecting the gas. For example, a carbon dioxide line 116 connected to a carbon dioxide source may be connected to the injection hole 114, and the gas containing carbon dioxide may be introduced from the carbon dioxide line 116 as shown in FIG. 5. At this time, the surface 112a of the ready-mixed concrete 112 may be exposed to the atmosphere. The gas containing carbon dioxide may be constantly supplied at a constant flow rate or may be intermittently supplied. In the latter case, the injection hole 114 may be sealed using a cap 118 when the gas containing carbon dioxide is not being supplied (FIG. 5B). By sealing the injection hole 114, carbon dioxide can be securely retained in the injection hole 114, and leakage of carbon dioxide can be prevented.
[0034]
A concentration of carbon dioxide in the gas containing carbon dioxide is higher than the concentration of carbon dioxide in the atmosphere. More specifically, the carbon dioxide concentration is selected from a concentration equal to or higher than 400 ppm and equal to or less than 100% as appropriate. The gas containing carbon dioxide may contain oxygen, nitrogen, argon, water, or the like. The gas containing carbon dioxide may be supplied from a cylinder filled with carbon dioxide. Alternatively, when there are existing facilities (chemical plants, waste incineration facilities, thermal power plants, various other plants, and the like) that emit large amounts of carbon dioxide near the site where secondary curing process is performed, the gas emitted from these facilities or purified carbon dioxide obtained by performing dust removal, desulfurization, denitrification, or the like on the emitted gas may be used as the gas containing carbon dioxide. In this case, these facilities serve as a source of the gas containing carbon dioxide, resulting in the reduction of the transporting cost of carbon dioxide and preventing further emissions of carbon dioxide associated with the transportation.
[0035]
In the primary curing process, the cement included in the ready-mixed concrete 112 reacts with water by which hydration proceeds. When Portland cement is used as the cement, for example, the contact of the minerals constituting the main components, namely alite (tricalcium silicate: 3CaO-SiO2) and belite (dicalcium silicate: 2CaO-SiO2), with water results in calcium silicate hydrate (3CaO-2SiO2-3H2O) and calcium hydroxide (Ca(OH)2). This calcium silicate hydrate and calcium hydroxide correspond to the cement paste of concrete. At this time, introduction of carbon dioxide from the injection hole 114 allows carbon dioxide to react with the calcium silicate hydrate and calcium hydroxide (carbonation) to form silicon dioxide and calcium carbonate. As this reaction proceeds, the calcium silicate hydrate grows calcium carbonate crystals to fill the voids in the ready-mixed concrete 112, forming a needle-like network. As a result, a strong cured product is produced in which silicon oxide is fixed within the network of the calcium carbonate crystals. That is, the ready-mixed concrete 112 is cured, and a first concrete region 102 with high compressive strength is obtained (FIG. 5C). Furthermore, when an admixture containing silicon oxide and aluminum oxide such as fly ash, blast furnace slag, and silica fume is used during the preparation of the ready-mixed concrete 112, a reaction with calcium hydroxide (pozzolanic reaction) also proceeds. Stable calcium silicate hydrate and calcium aluminate hydrate formed by the pozzolanic reaction fills the voids existing in the first concrete region 102, thereby increasing the density of the first concrete region 102.
[0036]
The rate of carbonation Is affected not only by the concentration of carbon dioxide but also by temperature and humidity. Thus, a humidifier 122 may be connected between the carbon dioxide source 120 and the carbon dioxide line 116, and water vapor may be added to the gas containing carbon dioxide using the humidifier 122 to adjust the rate of carbonation (FIG. 6). For example, water vapor may be added so that the humidity of the gas containing carbon dioxide is adjusted to be equal to or higher than 40% and equal to or lower than 100%. The temperature of the gas containing carbon dioxide may be the same as room temperature or ambient air temperature. However, a temperature controller 124 for controlling the temperature of the gas containing carbon dioxide may be installed between the carbon dioxide source 120 and the carbon dioxide line 116, and the gas containing carbon dioxide above room temperature may be supplied. In this case, the temperature of the gas containing carbon dioxide may be adjusted in a range of, for example, equal to or higher than 40 °C and equal to or lower than 60 °C.
[0037]
The pressure of the introduced gas containing carbon dioxide is preferred to be equal to or higher than 1 atm (0.10 mPa) and equal to or lower than 1.3 atm (0.13 mPa) to prevent deformation of the uncured ready-mixed concrete 112. A pressure gauge or a flow meter 126 for monitoring the pressure may be installed in the carbon dioxide line 116 (FIG. 6), the humidifier 122, or the temperature controller 124.
[0038]
Since carbonation is generally an exothermic reaction, the part in which carbonation is taking place in the secondary curing process has a higher temperature than the rest of the ready-mixed concrete 112. Therefore, the progress of carbonation can be monitored by monitoring the temperature of the ready-mixed concrete 112. For example, a plurality of contact-type temperature sensors equipped with thermocouples, resistance thermometers, thermistors, bimetals, charging thermometers, or the like may be placed on the surface of the ready-mixed concrete 112, and information from the temperature sensors may be collected. Alternatively, the temperature of the ready-mixed concrete 112 may be monitored using a non-contact temperature sensor such as a thermographic camera. By using non-contact temperature sensors, the surface temperature of the ready-mixed concrete 112 can be easily visualized.
[0039]
As shown in FIG. 5A, the carbonation proceeds from the sidewalls of the injection holes 114 in contact with the gas containing carbon dioxide toward the interior. Thus, at the start of the secondary curing process, the temperature around the injection hole 114 is high, and the high temperature area is gradually separated from the injection hole 114. Thereafter, when the curing and carbonation of the ready-mixed concrete 112 are completed, the temperature of the surface 102a of the resulting first concrete region 102 is approximately uniform. Therefore, the time when the temperature of the surface 102a becomes substantially uniform may be recognized as the time when the primary curing process, i.e., the curing of the ready-mixed concrete 112 and the carbonation of the concrete produced by the curing are completed.
[0040]
The mass of the ready-mixed concrete 112 increases because calcium hydroxide is converted to calcium carbonate during the carbonation of concrete as described above. Thus, in addition to or instead of monitoring the temperature as described above, the mass of the ready-mixed concrete 112 may be monitored, and the change in mass may be used to monitor the progress of curing and carbonation. Since water is also evaporated from the ready-mixed concrete 112 during the secondary curing process, the mass increase due to the carbonation and the evaporation of water affect the mass change. Therefore, the time when the mass of the ready-mixed concrete 112 becomes constant or substantially constant may be recognized as the time when the curing of the ready-mixed concrete 112 and the carbonation of the concrete produced by the curing are completed.
[0041]
(4) Filling of Injection Holes
Next, the injection hole 114 in the first concrete region 102 is filled. Specifically, after the primary curing process is completed, ready-mixed concrete 128 is injected into the injection holes 114 (FIG. 7A). The composition of the ready-mixed concrete 128 may be the same as or different from that of the ready-mixed concrete 112 providing the first concrete region 102. At this time, vibration may be applied to remove air mixed into the ready-mixed concrete 128 so that the ready-mixed concrete 128 is densely filled throughout the interior of the injection hole 114. Moreover, the top surface 128a of the ready-mixed concrete 128 may be levelled so that the surface 128a of the ready-mixed concrete 128 and the surface 102a of the first concrete region 102 are in the same plane in order to flatten the surface of the resulting concrete block. In addition, pressure may be applied to the first concrete region 102 and the ready-mixed concrete 128 injected in the injection hole 114 using a pressure jig 130 (FIG. 7B). The applied pressure may be selected from a range equal to or higher than 1 mPa and equal to or lower than 10 mPa, for example.
[0042]
(5) Secondary Curing
Next, the secondary curing process is performed to cure the ready-mixed concrete 128. The secondary curing process may be performed in the air or in a gas atmosphere containing carbon dioxide. In the former case, the secondary curing process may be performed outdoors or indoors, such as in a curing room. In the case of performing the secondary curing process under an atmosphere of a gas containing carbon dioxide, the secondary curing process may be performed in a curing room, and a gas containing carbon dioxide may be introduced into the curing room, for example. When the secondary curing process is performed under an atmosphere of a gas containing carbon dioxide, the same conditions as those for the primary curing process described above may be used.
[0043]
Similar to the primary curing process, the temperature of the top surface 128a of the ready-mixed concrete 128 and/or the change in the total mass of the first concrete region 102 and the ready-mixed concrete 128 may be monitored during the secondary curing process to monitor the progress of the secondary curing process. The secondary curing process allows the ready-mixed concrete 128 to provide the second concrete region 104, thereby providing the concrete block 100 (FIG. 7C).
[0044]
As mentioned above, carbonation is performed on the ready-mixed concrete 112 providing the first concrete region 102 using the injection hole 114. Thus, the ready-mixed concrete 112 is able to contact with the gas containing carbon dioxide over a relatively large area so that carbonation proceeds efficiently. On the other hand, even if the secondary curing process is performed on the ready-mixed concrete 128 providing the second concrete region 104 in an atmosphere of a gas containing carbon dioxide, carbonation proceeds only at the vicinity of the top surface 128a because the contact surface with the gas containing carbon dioxide is limited to the top surface 128a. Therefore, the average concentration of calcium carbonate in the first concrete region 102 is higher than that in the second concrete region 104. In addition, the concentration of calcium carbonate in the first concrete region 102 decreases with increasing distance from the second concrete region 104 depending on the degree of carbonation. On the contrary, the average concentration of calcium hydroxide in the first concrete region 102 is lower than the average concentration of calcium hydroxide in the second concrete region 104. The concentration of calcium hydroxide in the first concrete region 102 also increases with increasing distance from the second concrete region 104 depending on the degree of carbonation.
[0045]
(6) Demolding
The concrete block 100 is then isolated by ejecting the concrete block 100 from the mold 110 (demolding). Note that it is not always necessary to perform the demolding after the secondary curing process is completed. For example, in the case where the ready-mixed concrete 112 before forming the injection holes 114 has sufficiently low fluidity to free-stand, the ready-mixed concrete 112 may be demolded, and then the formation of the injection hole 114, the primary curing process, the filling of the injection hole 114, and the secondary curing process may be performed. Alternatively, the ready-mixed concrete 112 in which the injection hole 114 is formed may be demolded after the primary curing process, followed by the filling of injection hole 114 and the secondary curing process. In the case where the primary curing process is performed after demolding the ready-mixed concrete 112 in which the injection hole 114 is formed as a through hole, it is preferred that the carbon dioxide line 116 be connected to one end of the injection hole 114 and the other end be plugged with a cap 118 or the like to prevent leakage of the gas containing carbon dioxide.
[0046]
Moreover, as shown in FIG. 8A and FIG. 8B, the injection hole 114 may be formed using a perforated tube 132 composed of a metal or a resin and having a plurality of openings on a side surface thereof, and the carbon dioxide line 116 may be connected to the perforated tube 132 while the perforated tube 132 is located in the ready-mixed concrete 112. The perforated tube 132 and the carbon dioxide line 116 may be integrated. The use of the perforated tube 132 allows for efficient formation of the injection hole 114 and the introduction of carbon dioxide.
[0047]
As described above, in the manufacturing method of the concrete product according to an embodiment of the present invention, calcium hydroxide in the concrete paste reacts with carbon dioxide during the primary curing process to provide calcium carbonate. That is, carbon dioxide is fixed in the concrete product as calcium carbonate. Hence, this manufacturing method can be recognized as a fixing method of carbon dioxide. Therefore, the manufacturing method of the concrete product according to an embodiment of the present invention is able to contribute to the reduction of carbon dioxide in the atmosphere and the control of global warming. In addition, since the first concrete region 102 of the concrete product has a high concentration of calcium carbonate, fixing carbon dioxide increases the density of the first concrete region 102, which in turn increases its compressive strength. Indeed, the inventors have confirmed that fixing carbon dioxide of approximately 20% of the cement (60 kg/m3) results in an increase in compressive strength of the concrete by 8% to 10%. Therefore, it is possible to provide concrete products with superior strength by applying this manufacturing method.
[0048]
Furthermore, in the manufacturing method of the concrete product according to an embodiment of the present invention, the injection hole 114 is formed in the ready-mixed concrete 112 before the curing, and the curing (primary curing process) of the ready-mixed concrete 112 is performed while introducing the gas containing carbon dioxide into the injection hole 114. Therefore, no container to seal the ready-mixed concrete 112 is required, and the carbonation can be performed in a state where the surfaces of the ready-mixed concrete 112 are exposed to the outside air. Thus, it is possible to more conveniently provide concrete products at a lower cost.
[0049]
The aforementioned modes described as the embodiments of the present invention can be implemented by appropriately combining with each other as long as no contradiction is caused. Furthermore, any mode which is realized by persons ordinarily skilled in the art through the appropriate addition, deletion, or design change of elements or through the addition, deletion, or condition change of a process is included in the scope of the present invention as long as they possess the concept of the present invention.
[0050]
It is understood that another effect different from that provided by each of the aforementioned embodiments is achieved by the present invention if the effect is obvious from the description in the specification or readily conceived by persons ordinarily skilled in the art.

[REFERENCE SIGNS LIST]
[0051]
100: Concrete block, 102: First concrete region, 102a: Surface, 102b: Surface, 104: Second concrete region, 104a: Top surface, 104b: Bottom surface, 110: Mold, 110a: Top surface, 112: Ready-mixed concrete, 112a: Surface, 114: Injection hole, 114: Injection hole, 116: Carbon dioxide line, 118: Cap, 120: Carbon dioxide source, 122: Humidifier, 124: Temperature controller, 126: Flow meter, 128: Ready-mixed Concrete, 128a: Top surface, 130: Pressure jig, 132: Perforated Tube
 
, Claims:[Claim 1]
A concrete block having:
a first concrete region; and
at least one second concrete region located inside the first concrete region,
wherein a part of a surface of the at least one second concrete region exists in the same plane as a part of a surface of the first concrete region, and
wherein a concentration of calcium carbonate of the first concrete region is higher than a concentration of calcium carbonate of the at least one second concrete region.

[Claim 2]
A concrete block having:
a first concrete region; and
a second concrete region located inside the first concrete region,
wherein a part of a surface of the second concrete region exists in the same plane as a part of a surface of the first concrete region, and
wherein a concentration of calcium hydroxide of the first concrete region is lower than a concentration of calcium hydroxide of the second concrete region.

[Claim 3]
The concrete block according to claim 1 or 2,
wherein a side surface of the second concrete region is entirely surrounded by the first concrete region.

[Claim 4]
The concrete block according to claim 1,
wherein the at least one second concrete region includes a plurality of second concrete regions in the first concrete region.

[Claim 5]
A method for producing a concrete block, the method comprising:
injecting first ready-mixed concrete into a mold;
forming an injection hole in the first ready-mixed concrete;
introducing a gas containing carbon dioxide into the injection hole;
curing the first ready-mixed concrete to form a first concrete region;
injecting a second ready-mixed concrete into the injection hole; and
curing the second ready-mixed concrete to form a second concrete region.