Method for maintaining strength of concrete structures for buildings

Abstract

To provide a concrete structure that is easy to maintain and has dramatically improved durability, a method for strengthening the same, a method for manufacturing the same, and a method for maintaining the strength of the same. [Solution] The concrete structure 1 comprises a structure body 10 made of concrete with no reinforcing members extending in a predetermined direction arranged inside, and a shell 20 that surrounds the structure body 10 at a predetermined cross section, is integral with the structure body 10, has a tensile strength greater than that of the structure body 10, and has holes 21 that supply carbon dioxide from the outside air to the structure body 10, so that the strength of the structure is improved by carbonation of the concrete.

Description

[Technical field]

[0001] The present invention relates to a concrete structure which has significantly improved durability and is easy to maintain, a method for reinforcing the same, a method for manufacturing the same, and a method for maintaining the strength of the same. [Background technology]

[0002] Reinforced concrete is a type of structure that is extremely common in the fields of architecture and civil engineering, in which reinforcing bars are placed inside the concrete, making use of the mutual advantages of both concrete and reinforcing bars to improve their strength. Concrete contains calcium hydroxide and is strongly alkaline, so a passive film forms on the surface of the reinforcing bars, preventing them from oxidizing.

[0003] When reinforced concrete is exposed to the atmosphere, the calcium hydroxide in the concrete is carbonated by carbon dioxide. This reduces the alkalinity of the concrete, a process known as neutralization, which progresses from the surface of the reinforced concrete. When this neutralization region reaches the depth where the reinforcing bars are arranged, the reinforcing bars oxidize and rust. Then, the volume expansion caused by the rust causes cracks in the concrete, which reduces the durability of the reinforced concrete. In order to prevent the neutralization of concrete, a reinforced concrete has been proposed in which a multi-layer coating made of a specific resin and having specific physical properties is formed on the surface of the concrete (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-199350 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the reinforced concrete described in Patent Document 1 requires the formation of multiple layers of coating films, which makes post-treatment after the concrete hardens extremely troublesome. In addition, the carbonation of the concrete progresses as each coating film peels off due to deterioration, so the condition of each coating film must be constantly monitored, and the maintenance and management burden of structures using this reinforced concrete is also extremely heavy.

[0006] The present invention has been made in consideration of the above problems, and has an object to provide a concrete structure that is easy to maintain and has dramatically improved durability, a method for reinforcing the same, a method for manufacturing the same, and a method for maintaining the strength of the same. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides A structural body made of concrete, in which no reinforcing members extending in a predetermined direction are arranged, A concrete structure is provided which includes a shell which surrounds the structural body at a specified cross-section, is integral with the structural body, has a tensile stress greater than that of the structural body, and has holes for supplying carbon dioxide from the outside air to the structural body.

[0008] According to this concrete structure, the tensile stress of the shell is greater than that of the structure body, so the shell reinforces the tensile strength, bending strength, etc. of the concrete structure. Here, because the shell is disposed outside the structure body, the shell can bear a greater amount of the tensile stress acting on the concrete structure than when the reinforcing members are disposed inside the concrete. In addition, carbon dioxide from the outside air is supplied to the main body of the structure through the holes in the shell, which causes the concrete to carbonate from the surface side of the main body of the structure, and the concrete changes into stone material whose main component is calcium carbonate. In other words, the strength and durability of the main body of the structure improves over time.

[0009] In the above concrete structure, the structure body may have a lithified portion on at least the surface side where the concrete has been carbonated and transformed into stone.

[0010] This concrete structure has improved strength and durability of the structure body compared to structures that do not have a petrochemical portion.

[0011] In order to achieve the above object, the present invention provides The method for reinforcing a concrete structure, There is provided a method for strengthening a concrete structure, in which carbon dioxide is supplied from the outside to the structure body through the holes in the shell, and at least the surface side of the structure body is carbonated and transformed into a petrified portion.

[0012] According to this method for strengthening a concrete structure, carbon dioxide is supplied to the main body of the structure through the holes in the shell to form a petrified portion, thereby strengthening the concrete structure.

[0013] In order to achieve the above object, the present invention provides The method for producing a concrete structure, a shell forming step of forming the shell in a state where the concrete constituting the main body of the structure is not filled; a concrete filling step of filling the shell with fresh concrete without the reinforcing members being arranged; an excess water draining step of draining excess water from the fresh concrete to the outside through the holes of the shell by consolidation of the fresh concrete by its own weight; and a concrete hardening step of hardening the fresh concrete from which the excess water has been drained integrally with the shell to form the main body of the structure.

[0014] According to this method for manufacturing a concrete structure, the shell, which bears the tensile strength of the concrete structure, can be used as a form for hardening fresh concrete, eliminating the need to prepare a separate form. In addition, dismantling the form during manufacturing is no longer necessary, reducing the time and effort required for manufacturing the concrete structure. In addition, since no reinforcing members are placed inside the shell during the concrete filling process, the flow of fresh concrete inside the shell is not hindered by the reinforcing members, and the amount of vibrator used on the fresh concrete can be reduced or the vibrator work can be eliminated compared to when reinforcing members are placed. This reduces or eliminates the amount of slag that flows out of the holes in the shell when using a vibrator to fill the fresh concrete. In addition, in the excess water draining process, excess water not necessary for the hardening of the fresh concrete is drained, so the pressure applied from the fresh concrete to the shell is reduced. This allows the fresh concrete to be filled relatively high into the shell, which can increase the pouring efficiency per day and shorten the construction period. Furthermore, the water-cement ratio of the fresh concrete is reduced, which improves the density of the concrete and allows the production of high-quality concrete. Furthermore, the worker can check the condition of the fresh concrete through the holes in the shell, and even if an abnormality such as a cavity occurs in the fresh concrete, it can be quickly resolved.

[0015] Furthermore, in order to achieve the above object, the present invention provides The method for producing a concrete structure, a shell forming step of forming the shell in a state where the concrete constituting the main body of the structure is not filled; A concrete filling step of filling the shell with fresh concrete; an excess water draining step of draining excess water from the fresh concrete to the outside through the holes of the shell by consolidation of the fresh concrete by its own weight; a concrete hardening process in which the fresh concrete from which the excess water has been drained is hardened integrally with the shell to form a structure body; A method for manufacturing a concrete structure is provided, which includes a modification step of supplying carbon dioxide from outside to the structure body through the holes in the shell to carbonate at least the surface side of the structure body and modify it into a petrified portion.

[0016] In addition to the above effects, this method for manufacturing a concrete structure allows the stone-formed portion to be formed more easily by supplying carbon dioxide. At this time, the density of the concrete is improved, so that high-quality stone can be obtained.

[0017] Furthermore, in order to achieve the above object, the present invention provides The above-mentioned method for maintaining strength of a concrete structure comprises the steps of: a body strength increasing step of supplying carbon dioxide to the structure body through the holes in the shell, transforming the concrete on the surface side of the structure body into stone material to form a stone-formed portion, and increasing the bending strength of the structure body; A shell strength reducing step of allowing a reduction in the bending strength of the shell to the extent that the bending strength of the concrete structure as a whole is not reduced is provided.

[0018] According to this method for maintaining the strength of a concrete structure, the bending strength of the shell is allowed to decrease by the amount that the bending strength of the main body of the structure increases due to carbonation. Therefore, after the formation of the petrified portion, repair work due to deterioration or damage to the shell over time can be limited to a level that does not impair its strength, thereby reducing the burden of repair work.

[0019] In the above-mentioned method for maintaining the strength of a concrete structure, In the body strength increasing step, the surface side of the structure body is modified to stone material to a depth where the bending strength of the petrified portion exceeds the bending strength of the shell body, The shell strength reducing step may allow the shell to be removed from the structure body.

[0020] According to this method for maintaining the strength of a concrete structure, the shell is allowed to be removed from the main body of the structure after the bending strength of the main body of the structure has been sufficiently increased by carbonation. This not only eliminates the need to monitor the progress of neutralization of the concrete, but also obviates the need for maintenance of the shell, making it even easier to maintain the concrete structure.

[0021] In the above-mentioned method for maintaining the strength of a concrete structure, In the body strength increasing process, the entire structure body is transformed into stone material, The shell strength reducing step may allow the shell to be removed from the structure body.

[0022] According to this method for maintaining the strength of a concrete structure, after the entire structure body has been transformed into stone material, the shell body can be removed from the structure body, so there is no need to monitor the progress of neutralization of the concrete, and maintenance of the shell body is also unnecessary, making it easier to maintain the concrete structure. Also, since the entire structure body has been transformed into stone material, the concrete structure exhibits the same strength and durability as stone material. Effect of the Invention

[0023] According to the present invention, the maintenance and management of a concrete structure can be facilitated, and the durability of the concrete structure can be dramatically improved. [Brief description of the drawings]

[0024] [Figure 1] 1 is a schematic cross-sectional view of a concrete structure showing a first embodiment of the present invention. [Diagram 2] FIG. 1 is a front view of a concrete structure. [Diagram 3] FIG. [Figure 4] FIG. [Diagram 5] 1 is a flowchart showing a method for manufacturing a concrete structure. [Figure 6]FIG. 2 is a schematic cross-sectional view of the shell before concrete is filled. [Figure 7] FIG. 2 is a schematic cross-sectional view of a shell filled with fresh concrete. [Figure 8] FIG. 2 is a schematic cross-sectional view of a concrete structure in which the surface side of the structure body has been transformed into stone. [Figure 9] 1 is a flowchart showing a method for manufacturing a concrete structure having a petrified portion. [Figure 10] 1 is a flowchart showing a method for maintaining strength of a concrete structure. [Figure 11] FIG. 2 is a schematic cross-sectional view of a concrete structure in which the surface side of the structure body has been transformed into stone and the shell has been removed. [Figure 12] FIG. 2 is a schematic cross-sectional view of a concrete structure in which the entire body of the structure has been transformed into stone and the shell has been removed. [Figure 13] FIG. 11 is a partial plan view of a shell showing a modified example. [Figure 14] FIG. 11 is a partial plan view of a shell showing a modified example. [Figure 15] FIG. 11 is a partial cross-sectional view of a shell showing a modified example. [Figure 16] FIG. 11 is a partial plan view of a shell showing a modified example. [Figure 17] FIG. 11 is a partial cross-sectional view of a shell showing a modified example. [Figure 18] FIG. 11 is a partial plan view of a shell showing a modified example. [Figure 19] FIG. 11 is a partial cross-sectional view of a shell showing a modified example. [Figure 20] FIG. 11 is a partial plan view of a shell showing a modified example. [Figure 21] FIG. 11 is a partial cross-sectional view of a shell showing a modified example. [Figure 22] 5A, 5B, and 5C are a front view, a side view, and a plan view, respectively, of a concrete structure according to a second embodiment of the present invention. [Figure 23] FIG. 2 is an explanatory diagram showing the state in which fresh concrete is filled into the shell. [Figure 24] FIG. 13 is an explanatory diagram of a frame showing a modified example. [Diagram 25]FIG. 11 is a side view of a concrete structure showing a modified example. [Figure 26] 1A, 1B, and 1C are a front view, a side view, and a plan view, respectively, of a concrete structure showing a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Figures 1 to 12 show a first embodiment of the present invention, in which Figure 1 is a schematic cross-sectional view of a concrete structure, Figure 2 is a front view of a concrete structure, Figure 3 is a partial plan view of the shell, Figure 4 is a partial cross-sectional view of the shell, Figure 5 is a flow chart showing a method for manufacturing a concrete structure, Figure 6 is a schematic cross-sectional view of the shell before filling with concrete, Figure 7 is a schematic cross-sectional view of the shell filled with fresh concrete, Figure 8 is a schematic cross-sectional view of a concrete structure whose surface side of the structure body has degenerated into stone material, Figure 9 is a flow chart showing a method for manufacturing a concrete structure having a lithified part, Figure 10 is a flow chart showing a method for maintaining the strength of a concrete structure, Figure 11 is a schematic cross-sectional view of a concrete structure whose surface side of the structure body has degenerated into stone material and whose shell has been removed, and Figure 12 is a schematic cross-sectional view of a concrete structure whose entire structure body has degenerated into stone material and whose shell has been removed. Here, the schematic cross-sectional views of Figures 1, 6, 7, 8, 11 and 12 are for illustrative purposes only and differ from the dimensional ratios and shapes of each part of an actual concrete structure.

[0026] As shown in FIG. 1, the concrete structure 1 includes a structure body 10 made of concrete and having a circular cross section, and a shell body 20 having a doughnut-shaped cross section that surrounds the structure body 10 in a planar cross section and is integral with the structure body 10. As shown in FIG. 2, the concrete structure 1 is formed into a cylindrical shape extending vertically as a whole, with the structure body 10 being cylindrical and the shell body 20 being cylindrical. In this embodiment, the size of the concrete structure 1 is 2000 mm in diameter and 7000 mm in height. As shown in FIG. 1, the concrete contains cement, water, coarse aggregate 11 and fine aggregate 12, and no reinforcing members such as reinforcing bars that extend in a predetermined direction are arranged inside the structure body 10. The type of cement is arbitrary, and in addition to Portland cement, mixed cements such as blast furnace cement, silica cement, and fly ash cement that are mainly mixed with Portland cement and other mixed materials, and special cements such as alumina cement can be used. Cement in which carbon dioxide is enclosed can also be used. Furthermore, in addition to hydraulic cement such as Portland cement, blast furnace cement, etc., air-setting cement can also be used. The material of the coarse aggregate 11 and the fine aggregate 12 in this embodiment is arbitrary, and various aggregates such as sand, gravel, crushed sand, crushed stone, slag aggregate, artificial lightweight aggregate, limestone aggregate, etc. can be used as appropriate. Also, the coarse aggregate 11 and the fine aggregate 12 in which carbon dioxide has been sealed can be used. Incidentally, the aggregates such as the coarse aggregate 11 and the fine aggregate 12 can be omitted as necessary.

[0027] The shell 20 has a higher tensile stress than the structure body 10, and has a plurality of holes 21 for supplying carbon dioxide in the outside air to the structure body 10, as shown in FIG. 1. Here, the tensile stress refers to the stress acting per unit area. The material of the shell 20 is arbitrary, and may be, for example, a rust-resistant metal, carbon fiber, aramid fiber, glass fiber, polymer resin, or a composite material of these. In this embodiment, the shell 20 is made of a rust-resistant metal. In addition, in this embodiment, the shell 20 has a higher tensile stress than the structure body 10, as well as a higher bending stress and shear stress.

[0028] In this embodiment, the shell 20 is composed of a plurality of split units 22. As shown in FIG. 3, the shell 20 is formed in a plate shape as a whole, and has a lattice portion 23 formed in a square lattice shape and forming the outer edge of each hole 21 when viewed from a direction perpendicular to the formation surface of the shell 20. In addition, the split unit 22 has a reinforcing rib 24 formed integrally with the lattice portion 23 and dividing the lattice portion 23 in the vertical and horizontal directions. In this embodiment, the reinforcing rib 24 is formed thicker than the lattice portion 23 and is arranged at equal intervals in the vertical and horizontal directions. That is, the reinforcing ribs 24 are arranged in a square lattice shape. The reinforcing ribs 24 located at the outermost positions in the vertical and horizontal directions form the outer frame of the split unit 22.

[0029] As shown in FIG. 4, the shell 20 is constructed by connecting the split units 22 to each other using the reinforcing ribs 24 that form the outer frame of each split unit 22. In this embodiment, connecting metal fittings 25 are used to connect the reinforcing ribs 24 to each other, and the reinforcing ribs 24 are welded together with the connecting metal fittings 25, and a welded portion 26 is formed on the surface side of the shell 20. Note that the method of connecting the reinforcing ribs 24 is arbitrary, and various connecting means can be used, such as welding, fastening the reinforcing ribs 24 using a fastener, providing the reinforcing ribs 24 with parts that fit together, and fitting the reinforcing ribs 24 together. Each split unit 22 is formed in a rectangular shape when viewed from a direction perpendicular to the formation surface of the shell 20. Specifically, the vertical dimension of each split unit 22 is set to the same dimension as the height dimension of the concrete structure 1, and a plurality of split units 22 are connected in the circumferential direction of the concrete structure 1. The thickness of the lattice portion 23 and the reinforcing ribs 24, the shape and size of the holes 21, the width of the portions of the lattice portion 23 separating the holes 21, etc. are appropriately set according to the application, purpose, required performance, etc.

[0030] The size of the holes 21 of the shell 20 is set so as to suppress the outflow of the coarse aggregate 11 of the fresh concrete 13 described later. For example, the inscribed circle of the holes 21 can be set to a diameter of 30 mm, preferably 20 mm or less. In particular, if the inscribed circle of the holes 21 is set to a diameter of 20 mm or less, a sufficient outflow suppression effect can be obtained for the cement paste of the fresh concrete 13, and it is more preferable to set the diameter to 10 mm or less. In this embodiment, the diameter of the inscribed circle of the holes 21 is 10 mm. As shown in FIG. 1, in this embodiment, since the structure body 10 is cylindrical, the shell 20 is formed to be curved along the outer periphery of the structure body 10.

[0031] A method for manufacturing the concrete structure 1 configured as above will be described with reference to the flow chart of FIG. First, as shown in FIG. 6, the shell 20 is formed before being filled with concrete that constitutes the structure main body 10 (shell forming process: S1). In this embodiment, the shell 20 is formed by welding each divided unit 22 and assembling the cylindrical shell 20. The shell 20 may be assembled at the installation site of the concrete structure 1, or may be assembled in advance in a factory or the like and then transported to the installation site. It is of course possible to configure the shell 20 without dividing it, and in this case, the shell 20 may be manufactured at the installation site using a 3D printer, for example, or may be manufactured in advance in a factory or the like and then transported to the installation site.

[0032] Next, in the concrete filling step S3 described later, reinforcing members for the shell body 20 are installed as necessary so that the shell body 20 can withstand the pressure applied by the fresh concrete 13 (reinforcing member installation step: S2). Any reinforcing member may be used for the shell body 20, and examples of such reinforcing members include single pipes, supports, assembled scaffolding, and the like used in normal concrete formwork construction, as well as temporary reinforcing members such as lateral pressure reinforcing members that are matched to the shape of the shell body 20. If the shell body 20 can withstand the pressure of the fresh concrete 13, the reinforcing member installation step S2 can be omitted.

[0033] Next, as shown in FIG. 7, the shell 20 is filled with fresh concrete 13 (concrete filling step: S3). In this embodiment, since the upper end of the cylindrical shell 20 is open, the upper end of the shell 20 is used as a filling hole, and the fresh concrete 13 is filled therein. Then, due to the consolidation of the fresh concrete 13 by its own weight, excess water is discharged from the fresh concrete 13 to the outside through each hole 21 of the shell 20 (excess water discharge step: S4). After this, the fresh concrete 13 from which the excess water has been discharged is hardened together with the shell 20 to form the structure body 10 (concrete hardening step: S5). Then, when the concrete has a strength sufficient to be self-supporting, the reinforcing tool of the shell 20 is removed (reinforcing tool removal step: S6). If the reinforcing tool installation step S2 is omitted, the reinforcing tool removal step S6 is also omitted.

[0034] According to the manufacturing method of the concrete structure 1 of this embodiment, the shell 20, which bears the tensile strength of the concrete structure 1, can be used as a formwork to harden the fresh concrete 13, and there is no need to prepare a separate formwork. In addition, there is no need to dismantle the formwork during manufacturing, and the effort, time, etc. required for manufacturing the concrete structure 1 can be reduced.

[0035] Furthermore, since no reinforcing members are arranged inside the shell 20 in the concrete filling step S3, the flow of the fresh concrete 13 inside the shell 20 is not hindered by the reinforcing members, and the amount of vibrator used on the fresh concrete 13 can be reduced compared to when reinforcing members are arranged, or vibrator work can be made unnecessary. This makes it possible to reduce or eliminate the amount of slag that flows out from each hole 21 of the shell 20 due to the use of a vibrator when filling the fresh concrete.

[0036] In addition, in the excess water draining step S4, excess water unnecessary for the hardening of the fresh concrete 13 is drained, so that the pressure applied from the fresh concrete 13 to the shell 20 is reduced. This allows the fresh concrete 13 to be filled relatively high inside the shell 20, and for example, the pouring efficiency per day can be increased and the construction period can be shortened. Furthermore, since the water-cement ratio of the fresh concrete 13 is reduced, the density of the concrete can be improved and a high-quality structural body 10 can be obtained. Furthermore, the worker can check the condition of the fresh concrete 13 through each hole 21 of the shell 20, and even if an abnormality such as a cavity occurs in the fresh concrete 13, it can be quickly resolved.

[0037] Furthermore, since each hole 21 of the shell 20 is sized to suppress the outflow of the coarse aggregate 11 of the fresh concrete 13, the coarse aggregate 11 does not flow out when the excess water is drained. Furthermore, since the cement paste of the fresh concrete 13 is viscous, the cement paste does not flow out excessively. However, there are cases in which a small amount of cement paste flows out from each hole 21 and hardens both inside and outside the hole 21.

[0038] Furthermore, since the lattice portion 23 of the shell 20 is formed in a square lattice pattern, the shell 20 is not easily deformed in a specific direction within its formation surface, and can adequately resist pressure from the fresh concrete 13 while maintaining the shape of the shell 20. Furthermore, in this embodiment, since the lattice portion 23 is partitioned by reinforcing ribs 24 with relatively high rigidity, deformation of the lattice portion 23 in a direction perpendicular to the formation surface of the shell 20 due to the pressure of the fresh concrete 13 is suppressed.

[0039] According to the concrete structure 1 of this embodiment, the tensile stress of the shell body 20 is greater than that of the structure body 10, and the shell body 20 reinforces the tensile strength, bending strength, and the like of the concrete structure 1. Here, since the shell body 20 is disposed outside the structure body 10, the amount of tensile stress acting on the concrete structure 1 that is borne by the shell body 20 can be made greater than in the case where the reinforcing members are disposed inside the concrete. Furthermore, since the shell body 20 is filled with concrete, buckling of the shell body 20, which is a planar body, is suppressed. In particular, when the cement content of the concrete has hardened both inside and outside each hole 21, planar buckling of the shell body 20 can be effectively suppressed.

[0040] In addition, carbon dioxide in the outside air is supplied to the structure body 10 through each hole 21 of the shell 20, so that the carbonation of the concrete progresses from the surface side of the structure body 10 to the inside of the structure body 10, and the concrete is transformed into stone material with the coarse aggregate 11 and the fine aggregate 12 as gravel. As a result, as shown in FIG. 8, the structure body 10 becomes a concrete structure 101 having a petrified portion 14 on the surface side. In this concrete structure 101, the strength and durability of the structure body 10 are improved compared to those without the petrified portion 14. That is, as time passes, the strength and durability of the structure body 10 of the concrete structure 1 improves. In addition, since the density of the concrete is improved in the excess water discharge process S4, a good quality petrified portion 14 can be obtained. When cement in which carbon dioxide is enclosed is used in fresh concrete, the concrete is carbonated at a predetermined rate, but even in this case, the non-carbonated part of the concrete is gradually carbonated from the surface side of the structure body 10. That is, even if the concrete is carbonated at a certain ratio, the strength and durability of the main body of the concrete structure improves over time.

[0041] To manufacture a concrete structure 101 having a petrification portion 14, as shown in Fig. 9, the above-mentioned shell formation step S1, concrete filling step S3, excess water draining step S4, and concrete hardening step S5 are followed by a modification step S7 in which carbon dioxide is supplied from the outside to the structure body 10 through each hole 21 of the shell 20 to carbonate at least the surface side of the structure body 10 and modify it to the petrification portion 14. In this embodiment, carbon dioxide is supplied to the structure body 10 by exposing the concrete structure 1 to the atmosphere. In order to promote carbonation, the concrete structure 1 may be placed in a space where the concentration of carbon dioxide is higher than that of the atmosphere, or carbon dioxide may be constantly sprayed onto the concrete structure 1.

[0042] According to the concrete structure 1 of this embodiment, if the strength of the shell 20 is continuously maintained, the strength of the concrete structure 1 will be improved, but if the strength of the concrete structure 1 satisfies a predetermined required performance, it is not necessarily necessary to continuously maintain the strength of the shell 20. Here, the method for maintaining the strength of the concrete structure of this embodiment will be described with reference to the flowchart of FIG.

[0043] Carbon dioxide is supplied to the structure body 10 of the concrete structure 1 through each hole 21 of the shell 20, and the concrete on the surface side of the structure body 10 is transformed into stone material to form the petrified portion 14 as shown in Fig. 8, thereby increasing the bending strength of the structure body 10 (body strength increasing step: S11). Then, a reduction in the bending strength of the shell 20 is permitted within a range in which the bending strength of the concrete structure 101 as a whole is not reduced (shell strength reducing step: S12).

[0044] According to this method for maintaining the strength of the concrete structure 101, the bending strength of the shell 20 is allowed to decrease by the amount that the bending strength of the structure main body 10 has increased due to carbonation, so that after the formation of the petrified portion 14, repair work due to deterioration over time, damage, etc. of the shell 20 can be limited to a range that does not impair the strength, thereby reducing the burden of the repair work. In addition to this embodiment, this strength maintaining method is effective for concrete structures in which tensile stress acts on the shell.

[0045] In addition, in the body strength increasing step S11, the surface side of the structure body 10 is transformed into stone material to a depth where the bending strength of the petrified portion 14 exceeds the bending strength of the shell 20, and in the shell strength reducing step S12, the shell 20 can be allowed to be removed from the structure body 10 as shown in FIG. 10. In this case, not only is there no need to monitor the progress of neutralization of the concrete, but the maintenance of the shell 20 is also unnecessary, making the maintenance of the concrete structure 101 even easier. The shell 20 after being allowed to be removed in the shell strength reducing step S12 can be handled freely. For example, the shell 20 may be actively dismantled, or the shell 20 may be left without monitoring for deterioration, etc. In the case where the shell 20 is left, since the outer surface of the shell 20 forms the design surface of the concrete structure 1, the surface of the shell 20 may be appropriately decorated.

[0046] Furthermore, in the main body strength increasing step S11, the entire structure main body 10 is transformed into stone material as shown in Fig. 11, and in the shell strength reducing step S12, the shell 20 can be allowed to be removed from the structure main body 10. In this case, since the entire structure main body 10 is transformed into stone material, the concrete structure 201 exhibits the same strength and durability as stone material. In other words, the concrete structure 201 in which the entire structure main body 10 is transformed into the petrified portion 14 is endowed with durability of 1000 years or more, similar to stone buildings such as ruins.

[0047] In the above embodiment, the concrete structure 1 is shown to be cylindrical, but it may also be, for example, rectangular or prismatic. The shape of the concrete structure is arbitrary as long as it comprises a structure body made of concrete and a shell that surrounds the structure body at a specified cross section, has a tensile stress at least greater than that of the structure body, and has holes for supplying carbon dioxide from the outside air to the structure body.

[0048] In the above embodiment, the shell 20 has the reinforcing ribs 24, but it may have no reinforcing ribs 24, as shown in Fig. 13. Furthermore, in the above embodiment, the shell 20 has the lattice portion 23 in a square lattice shape, but the lattice portion 23 may have a regular triangular lattice shape, which is also suitable for maintaining the shape of the shell 20. Furthermore, the shape of the holes 21 in each shell 20 is arbitrary, and may be, for example, a square, a polygonal shape other than an equilateral triangle, a circle, or the like, or may be a so-called irregular shape in which the shapes of the multiple holes 21 vary.

[0049] Also, for example, as shown in Figs. 14 and 15, the shape of each hole 21 of the shell may be a rhombus. The shell of Figs. 14 and 15 is made of a metal plate, and each hole 21 is formed into a rhombus by making cuts in a zigzag pattern and expanding it. The lattice portion 23 is composed of a first inclined portion 23a that extends in one vertical direction (upper in Fig. 14) and in one horizontal direction (rightward in Fig. 14), and a second inclined portion 23b that extends in one vertical direction and in the other horizontal direction (leftward in Fig. 14). In this shell, the reinforcing rib of the above embodiment is not formed, and the outer edge of the lattice portion 23 forms the outer edge of the split unit. In the shell of Figs. 14 and 15, each split unit is connected at the horizontal end of the lattice portion 23. Specifically, one lateral vertex 23c formed by the first inclined portion 23a and the second inclined portion 23b and the other lateral vertex 23d formed by the first inclined portion 23a and the second inclined portion 23b are connected by spot welding to form a welded portion 26 on the shell body.

[0050] Also, for example, as shown in Figs. 15 and 16, each hole 21a, 21b may be slit-shaped. The shell of Figs. 15 and 16 is made of a metal plate, and each hole 21a, 21b is formed by using a punching press die. In the shell of Figs. 15 and 16, holes 21a extending in the vertical direction (up and down direction in Fig. 15) and holes 21b extending in the horizontal direction (left and right direction in Fig. 15) are arranged alternately in the vertical direction and the horizontal direction. Around each hole 21a, 21b, an inclined surface 21c formed during punching is formed. By forming the inclined surface 21c in this way to thicken the shell, the section modulus of the shell can be increased. In addition, in the shell produced by such a punching press, the shape of the holes 21a, 21b can be arbitrarily changed, and further strengthening can be achieved by press bending reinforcement.

[0051] Also, for example, as shown in Figs. 18 and 19, the shell may have a planar carbon cloth 123 with holes 121 formed therein and a skeletal member 124 formed thicker than the carbon cloth 123. As shown in Fig. 18, the skeletal members 124 are arranged at equal intervals in the vertical and horizontal directions in a square lattice pattern. In this embodiment, as shown in Fig. 19, the skeletal members 124 are divided and arranged on the front and back sides of the carbon cloth 323, sandwiching the carbon cloth 123. The skeletal members 124 are fixed at intersections in the vertical and horizontal directions with screws 127. Similarly to the above embodiment, the skeletal members 124 forming the outer frame of the split unit are connected to each other using connectors 125, and a welded portion 126 is formed on the front side of the shell. The material of the skeletal member 124 is arbitrary, and it may be, for example, plastic.

[0052] Also, for example, as shown in Figures 20 and 21, carbon cloth 123 may be adhered and fixed to skeletal member 124 of the shell. In the shell of Figures 20 and 21, skeletal member 124 is disposed on the back side of carbon cloth 123, extension portion 123a extending toward the back side is formed on carbon cloth 123, and extension portion 123a is adhered and fixed to the entire surface of skeletal member 124. Also, skeletal members 124 forming the outer frame of the split unit are connected and fixed by wrapping connecting carbon cloth 123b around them. The material of skeletal member 124 is arbitrary, and may be, for example, a specified alloy.

[0053] In the above embodiment, the upper surface of the concrete structure 1 is not covered by the shell 20, but as shown in Fig. 22, the upper surface of a concrete structure 301 can be covered by a shell 320. Fig. 22 shows a concrete structure according to a second embodiment of the present invention, where (a) is a front view, (b) is a side view, and (c) is a plan view.

[0054] As shown in FIG. 22(a), the concrete structure 301 is composed of an upper horizontal extension 302, a lower horizontal extension 303, and a vertical extension 304 connecting the upper horizontal extension 302 and the lower horizontal extension 303. In this embodiment, the concrete structure 301 is a pier structure, and the upper horizontal extension 302 forms a girder support, the lower horizontal extension 303 forms a foundation, and the vertical extension 304 forms a column base. The lower horizontal extension 303 is formed in a rectangular parallelepiped shape with a partially cut-out upper side, and as shown in FIG. 22(c), the vertical extension 304 is disposed in the center of the lower horizontal extension 303 in a plan view. As shown in FIG. 22(a), the lower horizontal extension 303 is formed such that the inner side of the upper surface in the left-right direction is inclined downward toward the outside from the connection part with the vertical extension 304, and the outer side in the left-right direction is formed horizontally. In this embodiment, the vertical extension portion 304 is formed in a cylindrical shape. The upper horizontal extension portion 302 is formed in a flat rectangular parallelepiped shape with the lower side partially cut out. Specifically, as shown in FIG. 22(b), the front-rear dimension of the upper horizontal extension portion 302 is the same as the diameter of the vertical extension portion 304, and as shown in FIG. 22(c), the upper horizontal extension portion 302 is formed in a rectangular shape protruding in the left-right direction from the vertical extension portion 304 in a plan view, as shown in FIG. 22(c). Also, as shown in FIG. 22(a), the bottom surface of the upper horizontal extension portion 302 is formed so as to be inclined upward from the connection portion with the vertical extension portion 304 toward the outside in the left-right direction, and the vertical dimension is formed so as to gradually shorten from the left-right center toward the left-right outside. In this embodiment, the size of the concrete structure 301 is 10,725 mm in the front-to-back direction, 2,500 mm in the left-to-right direction, and 2,250 mm in the height direction for the outer shape of the upper horizontal extension part 302, 7,500 mm in the front-to-back direction, 7,500 mm in the left-to-right direction, and 2,000 mm in the height direction for the lower horizontal extension part 303, and the vertical extension part 304 has a diameter of 2,500 mm and a height of 7,250 mm.

[0055] The concrete structure 301 of this embodiment includes a structure body made of concrete and a shell 320 that covers the structure body. In this embodiment, the shell 320 surrounds the upper horizontal extension portion 302, the lower horizontal extension portion 303, and the vertical extension portion 304 in all cross sections of the concrete structure 301, such as the front cross section, the plan cross section, and the side cross section, and surrounds the upper horizontal extension portion 302. No reinforcing members such as reinforcing bars that extend in a predetermined direction are arranged inside the structure body of the concrete structure 301. The shell 320 has a higher tensile stress than the structure body, and has a plurality of holes that supply carbon dioxide from the outside air to the structure body. In this embodiment, the shell 320 is also higher than the structure body in not only tensile stress but also bending stress and shear stress.

[0056] In this embodiment, as in the first embodiment, the shell 320 is composed of a plurality of divided units. In this embodiment, two types of lattice parts with different hole sizes are used in the shell 320. As in the above embodiment, the hole size of the first lattice part is set so as to suppress the outflow of coarse aggregate of fresh concrete. The hole size of the first lattice part can be set arbitrarily, but for example, the inscribed circle of the hole can be set to a diameter of 20 mm or less. On the other hand, the hole size of the second lattice part is set so that the hose 330 for delivering fresh concrete can be inserted. The first lattice part and the second lattice part of the shell 320 each have a higher tensile stress than the structure body. The hole size of the second lattice part can be set arbitrarily, but for example, the inscribed circle of the hole can be set to a diameter of 50 mm or more and 150 mm or more. The second lattice part is used in the shell 320 for the part covering the entire upper surface of the upper horizontal extension part 302 and the horizontal part on the upper surface of the lower horizontal extension part 303, and the first lattice part is used in the other parts.

[0057] The concrete structure 301 configured as above is also manufactured through the same steps as those in the first embodiment. The manufacturing method of the concrete structure 301 will be described with reference to the flowchart of FIG. First, the shell 320 is formed without being filled with concrete that constitutes the main body of the structure (shell forming step: S1). In this embodiment, too, the shell 320 is assembled by combining the divided units. The shell 320 may be assembled at the installation site of the concrete structure 1, or may be assembled in advance at a factory or the like and then transported to the installation site. It is of course possible to configure the shell 320 without dividing it. In this case, too, the shell 320 may be manufactured at the installation site using a 3D printer, or may be manufactured in advance at a factory or the like and then transported to the installation site. Then, reinforcing members for the shell are installed as necessary (reinforcing member installation step: S2).

[0058] Next, the shell 320 is filled with fresh concrete (concrete filling step: S3). Specifically, the hose 330 is inserted into the hole on the upper surface of the upper horizontal extension 302 of the shell 320, which is composed of the second lattice part, and the fresh concrete is fed into the shell 320 using the multiple hoses 330, thereby filling the shell 320 with fresh concrete. The hose 330 may be one. In this embodiment, the multiple hoses 330 are used to fill the shell 320 from the lower side. If necessary, the fresh concrete may be fed into the shell 320 from the horizontal part of the upper surface of the lower horizontal extension 303, which is composed of the second lattice part, in addition to the upper surface of the upper horizontal extension 302. Furthermore, an opening may be provided in the first lattice part to be used for feeding the fresh concrete, and the opening may be closed after the feeding of the fresh concrete from the opening is completed.

[0059] In this embodiment, the part of the shell 320 corresponding to the lower horizontal extension 303 is formed with the inside of the left and right direction of the upper surface inclined downward from the connection part with the vertical extension 304 toward the outside, so that fresh concrete can be filled more accurately along the surface shape of the shell 320 than when the upper surface of the lower horizontal extension 303 is formed perpendicular to the vertical extension 304. Also, the part of the shell 320 corresponding to the upper horizontal extension 302 is formed with the inside of the left and right direction of the bottom surface inclined upward from the connection part with the vertical extension 304 toward the outside, so that fresh concrete can be filled more accurately along the surface shape of the shell 320 than when the bottom surface of the upper horizontal extension 302 is formed perpendicular to the vertical extension 304. Also in this embodiment, since no reinforcing member is arranged inside the shell 320, the amount of slag flowing out from each hole of the shell 320 due to the use of a vibrator when filling fresh concrete can be reduced or eliminated.

[0060] Then, due to the consolidation of the fresh concrete by its own weight, excess water is discharged from the fresh concrete to the outside through each hole of the shell 320 (excess water discharge step: S4). In this embodiment, each hole of the first lattice part is sized to suppress the outflow of the coarse aggregate of the fresh concrete, so that the coarse aggregate does not flow out to the outside. Furthermore, the fresh concrete can be filled relatively high inside the shell 320, and for example, the pouring efficiency per day can be increased and the construction period can be shortened. Furthermore, since the water-cement ratio of the fresh concrete is reduced, the concrete can be made more dense and high quality concrete can be obtained. Furthermore, the worker can check the condition of the fresh concrete through each hole of the shell 320, and even if an abnormality such as a cavity occurs in the fresh concrete, it can be quickly eliminated. In particular, since each hole of the part covering the entire upper surface of the upper horizontal extension part 302 and the horizontal part of the upper surface of the lower horizontal extension part 303 is formed large, each hole can be used as an inspection hatch when an abnormality occurs in these upper surface parts. In addition to each hole, a larger inspection hatch may be formed separately. Furthermore, since the lattice portion of the shell 320 is formed in a square lattice pattern, it is possible to adequately resist the pressure from the fresh concrete while maintaining the shape of the shell 320. Furthermore, since the lattice portion is supported by an outer frame portion having a relatively high rigidity, deformation of the lattice portion in a direction perpendicular to the formation surface of the shell 320 due to the pressure of the fresh concrete is suppressed.

[0061] Thereafter, the fresh concrete from which excess water has been drained is hardened together with the shell 320 to form the main body of the structure (concrete hardening step: S5). Then, when the concrete has enough strength to stand on its own, if reinforcements were used, the reinforcements of the shell 320 are removed (reinforcement removal step: S6). In this embodiment, it is possible to pour concrete with the horizontal extensions 302, 303 and the vertical extension 304 as one unit, which allows the construction period of the pier structure to be significantly shortened.

[0062] According to the concrete structure 301 of this embodiment, the tensile stress of the shell 320 is greater than that of the structure body, and therefore the shell 320 reinforces the tensile strength, bending strength, etc. of the concrete structure 301. Since the shell 320 is disposed outside the structure body, the shell 320 can bear a greater amount of the tensile stress acting on the concrete structure 301 than when the reinforcing members are disposed inside the concrete. Furthermore, since the upper horizontal extension 302, the lower horizontal extension 303, and the vertical extension 304 can be formed without jointing, there is no need to consider the weak joints when designing the structure, as in the conventional structure having joints, and the degree of freedom in design is dramatically improved.

[0063] In addition, carbon dioxide in the outside air is supplied to the structure body 310 through each hole of each shell 320, so that the carbonation of the concrete progresses from the surface side of the structure body 310, and the concrete is transformed into stone material with aggregate as gravel. In other words, the strength and durability of the concrete structure 301 as a pier structure improves over time. In this embodiment, the density of the concrete is improved in the excess water discharge process S4, so that a good quality petrified part is formed.

[0064] Alternatively, the surface side of each structure body may be transformed into stone material to a depth where the tensile strength of the petrified portion exceeds the tensile strength of the shell 320, and the shell 320 may be removed from the structure body. In this case, not only is there no need to monitor the progress of neutralization of the concrete, but maintenance of the shell 320 is also unnecessary, making maintenance of the pier structure even easier. Furthermore, by transforming the entire structure body into stone material, it is possible to achieve the same strength and durability as stone material, and the pier structure can be used for more than 1,000 years, just like stone buildings such as ruins.

[0065] In the second embodiment, as shown in FIG. 24, the portion corresponding to the vertical extension portion 304 of the shell 320 may be extended upward and downward to form an extension portion 320a. In this case, as shown in FIG. 24, it is preferable that the upper extension portion 320a is connected to the portion corresponding to the upper surface of the upper horizontal extension portion 305, and the lower extension portion 320a is connected to the portion corresponding to the bottom surface of the lower horizontal extension portion 303, in terms of strength of the concrete structure 301. It is also preferable to increase the hole diameter of each extension portion 320a so that the flow of fresh concrete is not hindered by each extension portion 320a. It is also preferable to form the bottom surface of the upper horizontal extension portion 302 into a circular curved surface or a parabolic shape in a side view, as shown in FIG. 25, in terms of strength and economy of the concrete structure 301.

[0066] In the second embodiment, the present invention is applied to a pier structure, but it can also be applied to other buildings in which horizontal and vertical extensions are connected as shown in Fig. 26, and the shape of the concrete structure can be changed as desired. The concrete structure 401 in Fig. 26 is a pier structure that also serves as a retaining wall, and is composed of an upper horizontal extension 402, a lower horizontal extension 403, and seven vertical extensions 404 that connect the upper horizontal extension 402 and the lower horizontal extension 403, and is completely covered by a shell 420.

[0067] In the second embodiment, the upper horizontal extension portion 302, the lower horizontal extension portion 303, and the vertical extension portion 304 are integrally cast on site, but they may be divided and cast in order from the bottom by the manufacturing method of the above embodiment. Also, for example, the upper horizontal extension portion 302 may be cast in advance at a factory by the manufacturing method of the above embodiment, and the transported upper horizontal extension portion 302 may be assembled to the lower horizontal extension portion 303 and vertical extension portion 304 cast on site.

[0068] Although the embodiments of the present invention have been described above, the invention according to the claims is not limited to the embodiments described above. It should be noted that not all of the combinations of features described in the embodiments are essential to the means for solving the problems of the invention. [Explanation of symbols]

[0069] 1. Concrete Structure 10 Structure body 11 Coarse aggregate 12 Fine aggregate 13 Fresh Concrete 14 Petrification Department 20 Shell 21 holes 21a hole 21b hole 101 Concrete Structure 121 holes 201 Concrete Structure 301 Concrete Structure 320 Shell 401 Concrete Structure 420 Shell S1 Shell formation process S2 Reinforcement installation process S3 Concrete filling process S4 Surplus water discharge process S5 Concrete hardening process S6 Reinforcement removal process S7 Denaturation step S11 Body strength increase process S12 Shell strength reduction process

Claims

[Claim 1] A structural body made of concrete, in which no reinforcing members extending in a predetermined direction are arranged, A method for maintaining strength of a concrete structure for construction, comprising: a shell that surrounds the main body of the structure at a predetermined cross section, is integral with the main body of the structure, has a tensile stress greater than that of the main body of the structure, and has a hole for supplying carbon dioxide from outside air to the main body of the structure, a body strength increasing step of supplying carbon dioxide to the structure body through the holes in the shell, transforming the concrete on the surface side of the structure body into stone material to form a lithified portion, and increasing the bending strength of the structure body; A shell strength reduction step of allowing the bending strength of the shell to be reduced to a degree that does not result in a decrease in the bending strength of the concrete structure as a whole; After the bending strength of the shell is allowed to be reduced in the shell strength reduction step, the shell is left in place, After the bending strength of the shell is allowed to be reduced in the shell strength reduction process, the shell forms a design surface of the concrete structure, A method for maintaining strength of a concrete structure for construction, wherein the supply of carbon dioxide to the structure body is carried out by exposing it to the atmosphere.

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