Method for manufacturing concrete members and concrete members

Abstract

The present invention provides a method for manufacturing a concrete member and a concrete member that can be given different properties in the first concrete layer and the second concrete layer. [Solution] A method for manufacturing concrete members 1,1A, comprising: a first centrifugal molding step in which a first concrete is placed inside the formwork 3,3A and the formwork 3,3A is rotated to form a hollow first concrete layer 10,50 along the inner wall of the formwork 3,3A; and a second centrifugal molding step in which a second concrete with a different composition from the first concrete is placed inside the formwork 3,3A and the formwork 3,3A is rotated to form a second concrete layer 20,60 inside the first concrete layer 10,50.

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a concrete member and a technology of a concrete member.

Background Art

[0002] Conventionally, a method for manufacturing a concrete member has been known. For example, it is as described in Patent Document 1.

[0003] Patent Document 1 describes a method for manufacturing a hollow concrete member. In the above manufacturing method, with a spiral sheath tube installed inside a steel pipe, concrete is placed inside the steel pipe, and after the concrete is cured, the spiral sheath tube is removed to manufacture a hollow concrete member.

[0004] In such a concrete member, depending on the application, it may be desirable to impart different performances to the outer part and the inner part.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The present invention has been made in view of the above circumstances, and the problem to be solved is to provide a method for manufacturing a concrete member and a concrete member that can impart different performances to a first concrete layer and a second concrete layer.

Means for Solving the Problems

[0007] The problem to be solved by the present invention is as described above. Next, means for solving this problem will be described.

[0008] That is, claim 1 is a method for manufacturing a concrete member, comprising: a first centrifugal molding step of forming a hollow first concrete layer along the inner wall of the formwork by rotating the formwork with first concrete placed inside the formwork; and a second centrifugal molding step of forming a second concrete layer inside the first concrete layer by rotating the formwork with second concrete having a different composition from the first concrete placed inside the formwork.

[0009] In claim 2, the second concrete is made of a material with lower strength than the first concrete.

[0010] In claim 3, the second concrete is made of a material with a lower cement content than the first concrete.

[0011] Claim 4 includes a metal fiber placement step, which, prior to the second centrifugal molding step, involves rotating the formwork with metal fibers placed in the internal space covered by the first concrete layer, thereby arranging the metal fibers on the inner wall surface of the first concrete layer.

[0012] In claim 5, the metal fiber is formed such that its center of gravity is eccentric to one end in the longitudinal direction.

[0013] Claim 6 provides a columnar concrete member comprising a first concrete layer formed hollow by a first concrete, and a second concrete layer formed by a second concrete having a different composition from the first concrete, and provided inside the first concrete layer.

[0014] In claim 7, the second concrete is made of a material with lower strength than the first concrete.

[0015] In claim 8, the second concrete is made of a material with a lower cement content than the first concrete.

[0016] In claim 9, the second concrete is made of a material in which carbon dioxide is fixed.

Advantages of the Invention

[0017] As an effect of the present invention, the following effects are achieved.

[0018] In claim 1, different performances can be imparted to the first concrete layer and the second concrete layer.

[0019] In claim 2, it is possible to reduce the material cost while maintaining the strength required for the entire concrete member.

[0020] In claim 3, it is possible to reduce the amount of carbon dioxide generated during the production of cement while maintaining the strength required for the entire concrete member.

[0021] In claim 4, it is possible to facilitate the integration of the first concrete layer and the second concrete layer.

[0022] In claim 5, due to the centrifugal action, the longitudinal direction of the metal fibers tends to be oriented in the normal direction to the first concrete layer (the metal fibers tend to be erected with respect to the inner surface of the first concrete layer), and thus it is possible to more easily integrate the first concrete layer and the second concrete layer.

[0023] In claim 6, different performances can be imparted to the first concrete layer and the second concrete layer.

[0024] In claim 7, it is possible to reduce the material cost while maintaining the strength required for the entire concrete member.

[0025] In claim 8, while maintaining the strength required for the entire concrete member, it is possible to reduce the amount of carbon dioxide generated during the production of cement.

[0026] In claim 9, while suppressing an increase in the risk of neutralization of the concrete member, it can contribute to carbon dioxide reduction.

Brief Description of the Drawings

[0027] [Figure 1] Cross-sectional view schematically showing the concrete member according to the first embodiment of the present invention. [Figure 2] Flowchart showing the manufacturing method of the concrete member according to the first embodiment of the present invention. [Figure 3] (a) Schematic diagram showing a centrifuge. (b) Cross-sectional view schematically showing the state of the first centrifugal molding process. [Figure 4] (a) Cross-sectional view schematically showing the state of the metal fiber arrangement process. (b) Cross-sectional view schematically showing the state of the second centrifugal molding process. [Figure 5] Cross-sectional view schematically showing the concrete member according to the second embodiment of the present invention. [Figure 6] Flowchart showing the manufacturing method of the concrete member according to the second embodiment of the present invention. [Figure 7] (a) Cross-sectional view schematically showing the state of the reinforcing bar arrangement process. (b) Cross-sectional view schematically showing the state of the first centrifugal molding process. [Figure 8] (a) Cross-sectional view schematically showing the state of the second centrifugal molding process. (b) Cross-sectional view schematically showing the state of the pressing-in process.

Modes for Carrying Out the Invention

[0028] In the following description, according to the arrows shown in the drawings, the front-back direction and the left-right direction are defined respectively.

[0029] In the following, we will first describe the concrete member 1 according to the first embodiment of the present invention using Figure 1. Figure 1 is a cross-sectional view of the concrete member 1 taken from a plane perpendicular to the longitudinal direction.

[0030] The concrete member 1 shown in Figure 1 is a concrete member formed in a columnar shape. The concrete member 1 is formed in a cylindrical shape. The concrete member 1 is installed, for example, at a construction site to reach the supporting ground and is used as a precast pile to support the foundation of a building. The concrete member 1 is formed by multiple layers. In this embodiment, the concrete member 1 is mainly formed by a first concrete layer 10 and a second concrete layer 20.

[0031] The first concrete layer 10 constitutes the outer layer of the concrete member 1. The first concrete layer 10 is formed in a cylindrical shape by the first concrete. The second concrete layer 20 constitutes the inner layer of the concrete member 1. The second concrete layer 20 is provided inside the first concrete layer 10. The second concrete layer 20 is formed in a cylindrical shape so as to cover the inner circumferential surface 11 of the first concrete layer 10. The second concrete layer 20 is formed by the second concrete. The first and second concretes contain at least cement, water, fine aggregate, coarse aggregate, and admixtures as constituent materials. The second concrete may also contain admixtures as constituent materials.

[0032] Furthermore, concrete member 1 includes reinforcing bars that reinforce the first concrete layer 10 and the second concrete layer 20. Note that the reinforcing bars are not shown in the cross-sectional views of concrete member 1 shown in Figures 1, 3(b), 4(a), and 4(b). The reinforcing bars are formed in a roughly cylindrical cage shape. Concrete member 1 is constructed so that the reinforcing bars are covered by the first concrete layer 10 and the second concrete layer 20 in order to ensure the required concrete cover thickness.

[0033] The second concrete is formed to have a different composition from the first concrete. For example, the first and second concretes may have different mixing ratios of constituent materials such as cement, or they may have different types of constituent materials such as cement. By making the first concrete layer 10 and the second concrete layer 20 have appropriate compositions, different properties can be imparted to the first concrete layer 10 and the second concrete layer 20.

[0034] In general, the outer portion of concrete member 1 is often subjected to greater stress than the inner portion. Therefore, the outer portion of concrete member 1 may require relatively high strength, while the inner portion may not require relatively high strength.

[0035] Therefore, in this embodiment, the first concrete forming the outer first concrete layer 10 is made of a relatively strong material. As such a first concrete, for example, concrete containing ordinary Portland cement as cement is used.

[0036] On the other hand, as mentioned above, the inner portion of the concrete member 1 does not require relatively high strength. Therefore, even if a relatively weak material is used as the second concrete forming the second concrete layer 20 of the inner layer, it is easy to maintain the required strength for the concrete member 1 as a whole. Thus, in this embodiment, the second concrete is made of a material with a different composition from the first concrete, and is made of a material with lower strength than the first concrete. This makes it possible to reduce material costs while maintaining the required strength for the concrete member 1 as a whole.

[0037] Furthermore, a material with a lower cement content than the first concrete can be used as the second concrete. For example, concrete in which part of the cement is replaced with fly ash, or concrete in which part of the cement is replaced with blast furnace slag powder can be used as such a second concrete. Fly ash and blast furnace slag powder are typical industrial by-products. By using such environmentally friendly concrete as the second concrete, the amount of carbon dioxide emitted during cement production can be reduced. In addition, although the strength may decrease when using a material with a relatively low cement content, as mentioned above, the inner second concrete layer 20 does not require relatively high strength, so even if a material with a lower cement content than the first concrete is used as the second concrete, it is possible to maintain the necessary strength for the concrete member 1 as a whole.

[0038] Furthermore, a material with carbon dioxide fixed can be used as the second concrete layer. By using a material with carbon dioxide fixed, it is possible to contribute to the reduction of carbon dioxide emissions. Generally, fixing carbon dioxide in concrete increases the risk of material deterioration due to carbonation. In concrete member 1 (the reinforcing steel), the first concrete layer 10, which constitutes the outer layer, is more prone to rust than the second concrete layer 20, which constitutes the inner layer, due to the influence of the surrounding environment. If the first concrete layer 10, which is relatively prone to rust, undergoes carbonation, the risk of deterioration of the concrete member 1 as a whole is higher than if the second concrete layer 20, which is relatively less prone to rust, undergoes carbonation. Therefore, by making the part that fixes carbon dioxide the second concrete layer 20, which has a relatively low risk of deterioration due to carbonation, it is possible to contribute to the reduction of carbon dioxide emissions while reducing the risk of deterioration of the concrete member 1 as a whole.

[0039] Furthermore, metal fibers 30 are provided at the boundary between the first concrete layer 10 and the second concrete layer 20. The metal fibers 30 are, for example, steel fibers. The provision of metal fibers 30 makes it easier to integrate the first concrete layer 10 and the second concrete layer 20.

[0040] Next, the manufacturing method of the concrete member 1 will be described using Figures 2 to 4. As shown in Figure 2, the manufacturing method of the concrete member 1 includes a first centrifugal molding step (step S11), a metal fiber arrangement step (step S12), and a second centrifugal molding step (step S13). Each of the above steps is carried out in the factory where the concrete member 1 is manufactured.

[0041] The first centrifugal molding process (step S11) shown in Figure 3 is a process of forming the first concrete layer 10 using a centrifuge 2. The centrifuge 2 shown in Figure 3(a) comprises a hollow cylindrical formwork 3 rotatably supported on a frame 4, and a power source (not shown) for rotating the formwork 3 around its axis. As shown in Figure 3(b), in the first centrifugal molding process, the worker places the first concrete (fresh concrete), which is the material for the first concrete layer 10, inside the formwork 3 and seals it, then rotates the formwork 3. Due to the centrifugal force from the rotation of the formwork 3, the first concrete accumulates on the inner wall of the formwork 3 and is compacted. In this way, a cylindrical first concrete layer 10 is formed along the inner wall of the formwork 3. When the hardening of the first concrete layer 10 has progressed to a certain extent (before the first concrete layer 10 has completely hardened), the worker stops rotating the formwork 3. After performing the first centrifugal molding process, the worker performs the metal fiber placement process (step S12).

[0042] The metal fiber placement process (step S12) shown in Figure 4(a) is a process of placing metal fibers 30 in the first concrete layer 10. The metal fiber placement process (step S12) is performed when the first concrete layer 10 has hardened to a certain extent and before the second concrete layer 20 is formed. The worker puts an appropriate amount of metal fibers 30 into the internal space X covered by the first concrete layer 10 and rotates the formwork 3 in this state. As a result, due to centrifugal force, the metal fibers 30 are positioned on the inner surface 11 of the first concrete layer 10 such that a portion of them are embedded in the first concrete layer 10 (pierced into the first concrete layer 10).

[0043] Here, the metal fiber 30 is a longitudinal member, formed such that its center of gravity is eccentrically located at one end in the longitudinal direction. With the metal fiber 30 configured in this way, the centrifugal action caused by the rotation of the formwork 3 makes it easier for the longitudinal direction of the metal fiber 30 to orient itself in the direction normal to the first concrete layer 10 (the radial direction of the first concrete layer 10). In other words, the proportion of metal fiber 30 standing upright relative to the inner circumferential surface 11 of the first concrete layer 10 increases. Therefore, the second concrete layer 20, which is formed in the second centrifugal molding process (step S13) described later, can be easily integrated with the first concrete layer 10. After performing the metal fiber placement process, the worker performs the second centrifugal molding process (step S13).

[0044] The second centrifugal molding process (step S13) shown in Figure 4(b) is a process of forming the second concrete layer 20 using a centrifuge 2. In the second centrifugal molding process, the worker places the second concrete (fresh concrete), which is the material for the second concrete layer 20, into the internal space X (see Figure 4(a)) covered by the first concrete layer 10 and seals it, then rotates the formwork 3. Due to the centrifugal force from the rotation of the formwork 3, the second concrete accumulates on the inner surface 11 of the first concrete layer 10 and is compacted. In this way, a cylindrical second concrete layer 20 is formed inside the first concrete layer 10 so as to cover the inner surface 11 of the first concrete layer 10.

[0045] Here, in the metal fiber placement step (step S12), the metal fibers 30 are placed in the first concrete layer 10, making it easier for the second concrete layer 20 to integrate with the first concrete layer 10. The worker stops the rotation of the formwork 3 after a set amount of time has elapsed. In this way, the concrete member 1 is formed by performing the first centrifugal molding step (step S11), the metal fiber placement step (step S12), and the second centrifugal molding step (step S13).

[0046] Furthermore, the timing for pouring the second concrete in the second centrifugal molding process (step S13) may be set based on the hardness of the first concrete. Specifically, a sample of the first concrete may be taken when the first concrete is poured, and the hardness of the sample may be measured periodically using a hardness tester. Then, when the hardness of the sample reaches a level suitable for the first concrete layer 10 and the second concrete layer 20 to integrate, the second concrete may be poured. If the centrifugal force due to the rotation of the formwork 3 is too great, the metal fibers 30 may penetrate the first concrete layer 10 too deeply. Therefore, the rotation speed of the formwork 3 should be adjusted so that the metal fibers 30 do not penetrate the first concrete layer 10 too deeply.

[0047] As described above, by using a material with lower strength than the first concrete (step S13) that forms the first concrete layer 10 as the second concrete (step S11) that forms the second concrete layer 20, it is possible to reduce material costs while suppressing a decrease in the overall strength of the concrete member 1. Furthermore, by using a material with a lower cement content than the first concrete as the second concrete, it is possible to reduce the amount of carbon dioxide generated during cement production while maintaining the necessary strength for the concrete member 1 as a whole. In addition, by using a material with carbon dioxide fixed as the second concrete that forms the inner second concrete layer 20, it is possible to contribute to the reduction of carbon dioxide while reducing the risk of deterioration of the concrete member 1 as a whole. Alternatively, instead of using a material with carbon dioxide fixed in advance as the second concrete, a process of fixing carbon dioxide in the second concrete layer 20 may be performed after the second centrifugal molding process (step S13).

[0048] The concrete member 1A according to the second embodiment of the present invention will be described below with reference to Figure 5. Figure 5 is a cross-sectional view of the concrete member 1A cut by a plane perpendicular to the longitudinal direction. While the concrete member 1 according to the first embodiment is formed in a cylindrical shape, the concrete member 1A according to the second embodiment is formed in a columnar shape (prismatic shape) with a rectangular cross-section. In the illustrated example, the concrete member 1A is shown with the shorter side of the rectangle oriented left to right and the longer side of the rectangle oriented up to down. The concrete member 1A is used, for example, as a beam that constitutes the horizontal framework of a building. The concrete member 1A is mainly formed of a first concrete layer 50, a second concrete layer 60, a third concrete layer 70, and reinforcing bars 80.

[0049] The first concrete layer 50 is the outer layer of the concrete member 1A. The first concrete layer 50 is formed at the upper and lower ends of the concrete member 1A in a columnar shape (prismatic shape) with a rectangular cross-section. The first concrete layer 50 is formed of the same first concrete as the first concrete layer 10 according to the first embodiment.

[0050] The second concrete layer 60 is the inner layer of the concrete member 1A. More specifically, the second concrete layer 60 is formed between the upper first concrete layer 50 and the lower first concrete layer 50 (inside). The second concrete layer 60 is formed in a hollow, rectangular columnar shape (prismatic shape) so as to cover the inner wall surface 51 of the first concrete layer 50. The internal space of the second concrete layer 60 is formed in the center of the second concrete layer 60 in a plan view. The internal space of the second concrete layer 60 has a circular cross-section and is formed to penetrate the second concrete layer 60 from front to back (in the depth direction of the paper in Figure 5).

[0051] The second concrete layer 60 is formed of the same second concrete as the second concrete layer 20 in the first embodiment. In the second embodiment, the second concrete is made of a material with lower strength than the first concrete. Also, as in the first embodiment, the second concrete can be made of a material with a lower cement content than the first concrete. Furthermore, the second concrete can be made of a material in which carbon dioxide has been fixed.

[0052] The third concrete layer 70 is a portion formed to fill the internal space of the second concrete layer 60. The third concrete layer 70 is formed of third concrete. The third concrete is formed to have a different composition from the first and second concretes. In the second embodiment, the third concrete is made of a material with lower strength than the second concrete. Also, the third concrete can be made of a material with a lower cement content than the second concrete. Furthermore, the second concrete can be made of a material with fixed carbon dioxide, while the third concrete can be made of a material with fixed carbon dioxide.

[0053] The reinforcing bars 80 reinforce the concrete member 1A. The reinforcing bars 80 are formed in a cylindrical shape and are arranged along the longitudinal direction of the concrete member 1A. The reinforcing bars 80 are arranged to be embedded in each of the first concrete layers 50 on both sides. Multiple reinforcing bars 80 are provided at intervals along the short side of the concrete member 1A.

[0054] The method for manufacturing the concrete member 1A according to the second embodiment of the present invention will be described below with reference to Figures 6 to 8. The concrete member 1A is manufactured using a centrifuge 2A. The difference between the centrifuge 2A according to the second embodiment and the centrifuge 2 according to the first embodiment is that the internal space of the formwork 3 according to the second embodiment has a circular cross-section, whereas the internal space of the formwork 3A according to the first embodiment has a rectangular cross-section.

[0055] The manufacturing method for concrete member 1A includes a rebar placement step (step S21), a first centrifugal molding step (step S22), a second centrifugal molding step (step S23), and a press-fitting step (step S24), as shown in Figure 6. The press-fitting step (step S24) may be omitted.

[0056] The rebar placement process (step S21) shown in Figure 7(a) is the process of placing the reinforcing bars 80 inside the formwork 3A of the centrifuge 2A. In the rebar placement process, the worker places the reinforcing bars 80 at predetermined positions near both short sides of the internal space of the formwork 3A. After performing the rebar placement process, the worker performs the first centrifugal molding process (step S22).

[0057] The first centrifugal molding process (step S22) shown in Figure 7(b) is a process of forming the first concrete layer 50 using a centrifuge 2A. In the first centrifugal molding process, the worker places the first concrete (fresh concrete), which is the material for the first concrete layer 50, into the internal space of the formwork 3A and seals it, then rotates the formwork 3A. Due to the centrifugal force from the rotation of the formwork 3A, the first concrete accumulates near the short side of the internal space of the formwork 3A and is compacted. In this way, the first concrete layer 50, which has a rectangular cross-section (prismatic shape), is formed to cover the reinforcing bars 80. When the hardening of the first concrete layer 50 has progressed to a certain extent (before the first concrete layer 50 has completely hardened), the worker stops rotating the formwork 3A. After performing the first centrifugal molding process, the worker performs the second centrifugal molding process (step S23).

[0058] The second centrifugal molding process (step S23) shown in Figure 8(a) is a process of forming the second concrete layer 60 using a centrifuge 2A. In the second centrifugal molding process, the worker places the second concrete (fresh concrete), which is the material for the second concrete layer 60, into the internal space Xa (see Figure 7(b)) covered by the first concrete layer 50 and the formwork 3A, and seals it while rotating the formwork 3A. Due to the centrifugal force from the rotation of the formwork 3A, the second concrete accumulates and is compacted against the inner walls of the first concrete layer 50 and the formwork 3A. In this way, a hollow, prismatic second concrete layer 60 is formed, with an internal space that is cylindrical, so as to cover the inner wall surface 51 of the first concrete layer 50. When the hardening of the second concrete layer 60 has progressed to a certain extent (before the second concrete layer 60 has completely hardened), the worker stops rotating the formwork 3A. After performing the second centrifugal molding process, the worker performs the press-in process (step S24).

[0059] The injection process (step S24) shown in Figure 8(b) is a process in which the third concrete layer 70 is formed by injection. In the injection process, the worker injects the third concrete into the internal space Xb (see Figure 8(a)) of the second concrete layer 60. As time passes, the third concrete hardens, forming the third concrete layer 70.

[0060] Thus, the concrete member 1A is formed by performing the rebar placement process (step S21), the first centrifugal molding process (step S22), the second centrifugal molding process (step S23), and the press-fitting process (step S24).

[0061] In this case, the prismatic concrete member 1A requires relatively high strength in the outer part, and the required strength decreases relatively as you move inward. That is, the second concrete layer 60 requires less strength than the first concrete layer 50, and the third concrete layer 70 requires less strength than the second concrete layer 60.

[0062] Therefore, in concrete member 1A, a material with lower strength is used as the second concrete (step S23) that forms the second concrete layer 60, and a material with lower strength is used as the third concrete (step S24) that forms the third concrete layer 70, and a material with lower strength is used as the third concrete (step S23) that forms the second concrete layer 60. Thus, it is possible to reduce material costs while maintaining the required strength for the concrete member 1A as a whole. In addition, by using a material with a lower cement content towards the inside of the concrete member 1A, it is possible to reduce the amount of carbon dioxide emitted during cement production while maintaining the required strength for the concrete member 1A as a whole.

[0063] As described above, the manufacturing methods for the concrete members 1 and 1A according to the first and second embodiments are as follows: A method for manufacturing concrete members 1,1A, The first centrifugal molding process (step S11 in Figure 2, step S22 in Figure 6) involves rotating the formwork 3,3A with the first concrete inside, thereby forming a hollow first concrete layer 10,50 along the inner wall of the formwork 3,3A. The second centrifugal molding process (step S13 in Figure 2, step S23 in Figure 6) involves rotating the formwork 3, 3A with a second concrete having a different composition from the first concrete inside, thereby forming the second concrete layer 20, 60 inside the first concrete layer 10, 50. It includes.

[0064] This configuration allows for different properties to be imparted to the first concrete layer 10,50 and the second concrete layer 20,60.

[0065] Furthermore, the second concrete is A material with lower strength than the aforementioned first concrete is used.

[0066] This configuration allows for a reduction in material costs while maintaining the necessary strength for the concrete members 1,1A as a whole.

[0067] Furthermore, the second concrete is A material with a lower cement content than the aforementioned first concrete is used.

[0068] This configuration allows for the maintenance of the necessary strength for the concrete members 1,1A as a whole, while reducing the amount of carbon dioxide emitted during cement production.

[0069] Furthermore, the method for manufacturing the concrete member 1 according to the first embodiment is as follows: Prior to the second centrifugal molding step (step S13 in Figure 2), the process includes a metal fiber placement step (step S12 in Figure 2) in which the metal fibers 30 are placed in the internal space covered by the first concrete layer 10, and the formwork 3 is rotated to position the metal fibers 30 on the inner circumferential surface 11 (inner wall surface) of the first concrete layer 10.

[0070] This configuration makes it easier to integrate the first concrete layer 10 and the second concrete layer 20.

[0071] Furthermore, the metal fiber 30 is It is formed such that the center of gravity is eccentrically shifted to one end in the longitudinal direction.

[0072] With this configuration, the longitudinal direction of the metal fibers 30 is more likely to be oriented in the direction normal to the first concrete layer 10 due to centrifugal force (making it easier for the metal fibers 30 to stand upright against the inner surface of the first concrete layer 10), and consequently, the first concrete layer 10 and the second concrete layer 20 can be more easily integrated.

[0073] Furthermore, the concrete members 1 and 1A according to the first and second embodiments are Concrete members 1,1A formed in a columnar shape, First concrete layers 10, 50 formed hollow by the first concrete, The second concrete layers 20, 60 are formed from a second concrete with a different composition from the first concrete, and are provided inside the first concrete layers 10, 50. It is equipped with the following features.

[0074] This configuration allows for different properties to be imparted to the first concrete layer 10,50 and the second concrete layer 20,60.

[0075] Furthermore, the second concrete is Materials that have had carbon dioxide fixed are used.

[0076] This configuration helps to reduce carbon dioxide emissions while suppressing the increased risk of carbonation in concrete members 1,1A.

[0077] Although embodiments of the present invention have been described above, the present invention is not limited to the above configuration, and various modifications are possible within the scope of the invention as described in the claims.

[0078] For example, the external shape of the concrete members 1 and 1A is not limited to those of each embodiment, but can be any shape. Also, although the concrete member 1 in the first embodiment is formed in a hollow shape, it may be formed in a solid shape. Also, although the concrete member 1A in the second embodiment is formed in a solid shape, it may be formed in a hollow shape (i.e., without the press-fitting process (step S24)).

[0079] Furthermore, in the first embodiment, a metal fiber placement step (step S12 in Figure 2) is performed to place metal fibers 30 on the inner circumferential surface 11 of the first concrete layer 10 before the second centrifugal molding step (step S13 in Figure 2) to form the second concrete layer 20. However, the second centrifugal molding step may be performed without performing the metal fiber placement step. Also, in the second embodiment, the metal fiber placement step may be performed between the first centrifugal molding step (step S22 in Figure 6) and the second centrifugal molding step (step S23 in Figure 6), so that the metal fibers 30 are placed on the inner wall surface 51 of the first concrete layer 50.

[0080] Furthermore, in the first and second embodiments, the second concrete forming the outer second concrete layer 20, 60 is made of a material with lower strength than the first concrete forming the inner first concrete layer 10, 50. However, depending on the shape of the concrete members 1, 1A, a material with lower strength than the second concrete may be used as the first concrete.

[0081] Furthermore, in the first embodiment, the structure is formed with two layers, a first concrete layer 10 and a second concrete layer 20, but it may be formed with three or more layers. That is, there may be other concrete layers besides the first concrete layer 10 and the second concrete layer 20, and at least one of the first concrete layer 10 and the second concrete layer 20 may contain multiple concrete layers.

[0082] Furthermore, in the first embodiment, the reinforcing bars are included in both the first concrete layer 10 and the second concrete layer 20, but they may be included only in the first concrete layer 10. [Explanation of symbols]

[0083] 1,1A Concrete Member 3,3A Formwork 10.50 First concrete layer 20,60 Second concrete layer 30 Metallic Fibers

Claims

1. A method for manufacturing concrete members, A first centrifugal molding step involves rotating the formwork while the first concrete is placed inside the formwork to form a hollow first concrete layer along the inner wall of the formwork, A second centrifugal molding step involves rotating the formwork while a second concrete, which has a different composition from the first concrete, is placed inside the formwork, thereby forming a second concrete layer inside the first concrete layer. A method for manufacturing concrete members including concrete members.

2. The aforementioned second concrete is A material with lower strength than the aforementioned first concrete is used. A method for manufacturing a concrete member according to claim 1.

3. The aforementioned second concrete is A material with a lower cement content than the aforementioned first concrete is used. A method for manufacturing a concrete member according to claim 1.

4. Prior to the second centrifugal molding step, the process includes a metal fiber placement step in which the metal fibers are placed in the internal space covered by the first concrete layer and the formwork is rotated to position the metal fibers on the inner wall surface of the first concrete layer. A method for manufacturing a concrete member according to claim 1.

5. The aforementioned metallic fiber is It is formed such that the center of gravity is eccentric to one end in the longitudinal direction. A method for manufacturing a concrete member according to claim 4.

6. A concrete member formed in a columnar shape, The first concrete layer is formed in the hollow by the first concrete, A second concrete layer is formed by a second concrete having a different composition from the first concrete, and is provided inside the first concrete layer. A concrete member having the following features.

7. The aforementioned second concrete is A material with lower strength than the aforementioned first concrete is used. The concrete member according to claim 6.

8. The aforementioned second concrete is A material with a lower cement content than the aforementioned first concrete is used. The concrete member according to claim 6.

9. The aforementioned second concrete is Materials that fix carbon dioxide are used. The concrete member according to any one of claims 6 to 8.

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