Method for producing cement hardened body

Abstract

To provide a method for producing a cement hardened body capable of efficiently fixing carbon dioxide.SOLUTION: A method for manufacturing a cement hardened body includes a placing step of placing a cement composition in a form, and a curing step of curing the cement composition placed in the placing step until it reaches a demolding strength, wherein the curing step includes a partial demolding step of forming a passage through which a gas can pass between the form and the cement composition when the compressive strength of the cement composition reaches a predetermined strength lower than the demolding strength.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a method for producing a hardened cement body. [Background technology]

[0002] For example, concrete, an example of a hardened cement product, is widely used in architectural and civil engineering structures. In the manufacturing process of typical cement used in concrete, a large amount of carbon dioxide is emitted due to high-temperature firing and decarbonation of limestone, a raw material. Meanwhile, in response to growing interest in the impact of climate change in recent years, attention has been focused on reducing the carbon dioxide emissions involved in concrete manufacturing to reduce the environmental impact. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-124416 Summary of the Invention [Problem to be solved by the invention]

[0004] For example, Patent Document 1 discloses that exhaust gas is supplied to concrete, causing the concrete to absorb the carbon dioxide in the exhaust gas, thereby preventing the carbon dioxide in the exhaust gas from being released into the atmosphere. However, in the conventional configuration, a long period of time is required for the carbon dioxide to be fixed in the concrete, and therefore there is room for improvement in terms of efficiently fixing the carbon dioxide.

[0005] Therefore, the present invention provides a method for producing a hardened cement product that can efficiently fix carbon dioxide. [Means for solving the problem]

[0006] A method for producing a hardened cement body according to an embodiment is a method for producing a hardened cement body using a cement composition, and includes a casting step of casting the cement composition into a formwork, and a curing step of curing the cement composition cast in the casting step until it hardens and reaches a demolding strength, and the curing step includes a partial demolding step of forming a passage between the formwork and the cement composition that allows gas to pass through when the compressive strength of the cement composition reaches a predetermined strength that is lower than the demolding strength. [Brief explanation of the drawings]

[0007] [Figure 1] A flowchart showing steps of a method for producing a hardened cement body according to one embodiment. [Figure 2] FIG. 10 is a diagram showing an example of a state in which a cement composition is poured into a formwork in a pouring step according to one embodiment. [Figure 3] Graph showing the relationship between accumulated temperature and compressive strength of cement composition [Figure 4] A flowchart showing an example of a curing process according to one embodiment. [Figure 5] Diagram showing the relationship between compressive strength and carbonation depth [Figure 6] FIG. 10 is a diagram illustrating an example of a state in which a part of the mold is removed in a partial demolding step according to one embodiment. [Figure 7] FIG. 10 is a diagram illustrating an example of a state in which carbon dioxide gas is supplied into a passage in a carbonation process according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, embodiments will be described with reference to the drawings. Note that the drawings used in the following description may be partially enlarged for convenience in order to make the features of the embodiments easier to understand, and the dimensional ratios of the components may not necessarily be the same as those in reality.

[0009] The method for producing a hardened cement product of this embodiment can be applied to the production of a hardened cement product using a cement composition 21 containing, for example, cement, coarse aggregate, fine aggregate, water, and admixtures. The hardened cement product produced by the method for producing a hardened cement product can be applied to various products used in civil engineering and construction work, such as precast retaining walls, box culverts, and gutters. In this embodiment, a case will be described in which the hardened cement product is applied to an L-shaped retaining wall, which is an example of a precast retaining wall produced in a factory.

[0010] 1, the method for producing a hardened cement body includes, for example, a casting step S11, a curing step S12, and a removal step S13. In this embodiment, the casting step S11, the curing step S12, and the removal step S13 are performed in this order in the method for producing a hardened cement body. The casting step S11 is a step of casting a cement composition 21 into a formwork 11 in which reinforcing bars (not shown) are placed, as shown in FIG.

[0011] The formwork 11 has a foundation formwork 111, an inner formwork 112, and an outer formwork 113. The foundation formwork 111 is placed on the installation surface 91 on which the formwork 11 is to be installed. The inner formwork 112 and the outer formwork 113 are configured as separate bodies and are detachably attached to the foundation formwork 111. The inner formwork 112 is located inside the cement composition 21 to be poured into the formwork 11, and is arranged at a predetermined distance from the outer formwork 113. The outer formwork 113 is located outside the cement composition 21 to be poured into the formwork 11. The outer formwork 113 forms the side surface of the formwork 11.

[0012] In the casting process, the cement composition 21 is poured between the inner formwork 112 and the outer formwork 113. The cement composition 21 is, for example, a mixture of cement, coarse aggregate, fine aggregate, water, and admixtures. Examples of cement that can be used include ordinary Portland cement, high-early-strength Portland cement, low-heat Portland cement, moderate-heat Portland cement, extra-high-early-strength Portland cement, fly ash cement, and blast-furnace cement. Examples of coarse aggregate that can be used include river gravel, sea gravel, crushed stone, and CCU coarse aggregate. Examples of fine aggregate that can be used include river sand, sea sand, crushed sand, and CCU fine aggregate. Examples of admixtures that can be used include blast-furnace slag, fly ash, γ-belite, CCU material, and silica fume, as well as water-reducing agents, high-performance water-reducing agents, air-entraining water-reducing agents, and superplasticizers.

[0013] The curing step of step S12 is a step of curing the cement composition 21 cast in the casting step until it hardens and reaches a demolding strength. The demolding strength means a strength at which the hardened cement composition 21 can be lifted by a crane using a lifting jig or the like. The demolding strength is, for example, 12.0 N / mm 2 It is set to a high strength of at least 10 ...

[0014] The removal process in step S13 is a process of removing the formwork 11 from the intermediate product that has been formed into a predetermined shape, in this case an L-shape. The intermediate product is obtained during the manufacturing process of the hardened cement body, and becomes the final formed product, the hardened cement body, by undergoing specific processing. The specific processing can include, for example, repairing the exterior surface, as well as storing the intermediate product in a curing chamber (not shown) that can be filled with carbon dioxide gas and allowing the intermediate product to absorb the carbon dioxide gas.

[0015] The removal step is performed, for example, after the cumulative temperature M from when the cement composition 21 is mixed reaches 650°C·h or the compressive strength reaches 12.0 N / mm 2 In other words, the curing process is carried out after the accumulated temperature M reaches at least 650°C·h or the compressive strength reaches 12.0 N / mm 2The process is continued until the temperature reaches a value of 100°C. Note that "when the cement composition 21 is mixed" refers to when water is added to a mixture of raw materials for the hardened cement body other than water. The accumulated temperature M represents the strength of the cement composition 21 in terms of the temperature of the cement composition 21 and time. The accumulated temperature M can be calculated by multiplying the temperature θ of the cement composition 21 by the time T. The unit of the temperature θ is °C, and the unit of the time T is h.

[0016] FIG. 3 shows the results of a test conducted by the inventors of the present application regarding the relationship between the accumulated temperature M and the compressive strength of the cement composition 21, with the accumulated temperature M on the horizontal axis and the compressive strength on the vertical axis. As shown in FIG. 3, the accumulated temperature M and the compressive strength show a proportional relationship, and the larger the accumulated temperature M, the larger the compressive strength tends to be. In the test, for example, when the accumulated temperature M was about 170°C·h, the compressive strength was about 1.4 N / mm 2 It was confirmed that when the accumulated temperature M was approximately 650°C·h, the compressive strength was approximately 12.0 N / mm 2 was confirmed.

[0017] Next, the curing step will be described in detail. As shown in Fig. 4, the curing step includes a preparatory step of step A11, a partial demolding step of step A13, and a carbonation step of step A14. The preparatory step of step A11 is an early step in the curing step, in which the cement composition 21 is cured while covered with, for example, a vinyl sheet. The preparatory step is carried out, for example, at a temperature of 5°C to 60°C for 3 to 12 hours.

[0018] Here, the inventors of the present application conducted a confirmation test on the relationship between compressive strength and carbonation depth, focusing on the fact that the lower the compressive strength at the start of carbonation in cement composition 21, the easier carbonation will proceed, i.e., the shorter the production time. In the confirmation test, a cylindrical specimen having a cross section of 10 cm x 10 cm was used, and a compressive strength of approximately 1.4 N / mm was used as σ1. 2 The specifications, σ2 compressive strength is approximately 6.0N / mm 2 The specifications, σ3 as compressive strength approximately 10.0N / mm 2Each specimen was placed in a curing room with an environment set to a temperature of 50°C, humidity of 50% RH, and a carbon dioxide concentration of 80 Vol% and then carbonation cured.

[0019] Figure 5 shows the relationship between compressive strength and carbonation depth in the confirmation test, with carbonation depth on the vertical axis. The greater the carbonation depth, the more advanced the carbonation. Carbonation depth was measured by cutting the test specimen longitudinally, spraying phenolphthalein solution onto the cut cross section, and then measuring the area of ​​the test specimen that was not discolored from the outside. As shown in Figure 5, it was confirmed that the lower the compressive strength, the greater the carbonation depth. This result was similar whether the carbonation period was one day or three days.

[0020] Therefore, in this embodiment, as shown in Fig. 4, when the compressive strength of the cement composition 21 reaches a predetermined strength σp, which is lower than the demolding strength, in the curing step (YES in step A12), the partial demolding step of step A13 is executed. The predetermined strength σp is 1.0 N / mm 2 More than 12.0N / mm 2 The predetermined strength σp is set within the following range: Preferably, the predetermined strength σp is 1.0 N / mm 2 More than 7.0N / mm 2 It is set within the following range. More preferably, the predetermined strength σp is 1.0 N / mm 2 More than 3.5N / mm 2 The range of the suitable predetermined strength σp is determined based on the results of the above-mentioned confirmation test and the fact that the compressive strength is generally 3.5 N / mm 2 ~7.0N / mm 2 This is based on the fact that the progress of carbonation tends to slow down when the compressive strength is 1.0 N / mm 2 If partial demolding is performed when the compressive strength is below 1.0 N / mm 2 If partial demolding is performed when the temperature is below this, the product after demolding may suffer from deformation of the partially demolded surface or poor skin release.

[0021] The partial demolding step is a step of forming a passage 30 through which gas can pass between the formwork 11 and the cement composition 21. In this embodiment, in the partial demolding step, the passage 30 is formed by removing a part of the outer formwork 113, as shown by the white arrow in Fig. 6. In the partial demolding step, the formwork 11 that can be removed is the formwork 11 that contacts a part of the cement composition 21 in the formwork 11 that is not bearing a load, for example, its own weight. In other words, after the partial demolding step, at least the part of the cement composition 21 in the formwork 11 that is bearing a load remains in contact with the formwork 11.

[0022] In the partial demolding step, at least a portion of the inner formwork 112 may be removed to form a passage 30 between the inner formwork 112 and the cement composition 21. In this case, as shown by the two-dot dash line and black arrow A in Fig. 6 , the formwork 11 may be configured so that the inner formwork 112 can rotate in a direction away from the cement composition 21, and the passage 30 may be formed between the inner formwork 112 and the cement composition 21 as the inner formwork 112 rotates. In addition, in the partial demolding step, the passage 30 may be formed by releasing the contact between the cement composition 21 and the formwork 11, so the mode of forming the passage 30 is not limited to the configuration in which a portion of the formwork 11 is removed.

[0023] Furthermore, the start condition of the partial demolding process may be determined not only by compressive strength but also by the cumulative temperature M. In this case, the range of the start condition of the partial demolding process based on the cumulative temperature M can be set to a range of 150°C·h or more and 650°C·h or less. This range is set to a value smaller than the lower limit of the cumulative temperature M of 650°C·h for executing the removal process. Note that the start point of the partial demolding process refers to the end point of the pre-loading process. Preferably, the range of the start condition of the partial demolding process based on the cumulative temperature M is set to a range of 170°C·h or more and 360°C·h or less. In this case, the partial demolding process is executed when the cumulative temperature M is in the range of 170°C·h or more and 360°C·h or less.

[0024] The lower limit of 170°C·h corresponds to a compressive strength of 1.4 N / mm in the test results shown in Figure 3. 2The upper limit of 360°C·h is based on the cumulative temperature M of 170°C·h, where the temperature was confirmed to be 170°C·h. The upper limit of 360°C·h is also based on the working environment. Specifically, it is preferable that the process from the pouring process to the partial demolding process be completed within one working day, with the maximum working time expected to be 9 hours. Therefore, assuming a working time of 9 hours in an environment with an outside temperature of 40°C, which corresponds to a scorching hot summer day, the upper limit of 360°C·h is set as the starting condition for the partial demolding process. Note that the outside temperature and working time used to calculate the upper limit of 360°C·h are not limited to these.

[0025] The carbonation process of step A14 in FIG. 4 is a process in which carbon dioxide gas is supplied to the passage 30 formed in the partial demolding process, thereby causing the cement composition 21 to absorb the carbon dioxide gas. In the carbonation process, as shown in FIG. 7, the formwork 11 and the cement composition 21 are surrounded by an enclosing member 41, which is configured, for example, as a bellows tent, and carbon dioxide gas is supplied to the internal space of the enclosing member 41 using a pipe 42 connected to an external carbon dioxide gas supply source. For example, the enclosing member 41 can be configured to surround the formwork 11 and the cement composition 21 by covering them from above. In this way, carbon dioxide gas can be supplied to the passage 30, as indicated by the black arrow in FIG. 7.

[0026] According to the embodiment described above, the method for producing a hardened cement body is a method for producing a hardened cement body using the cement composition 21. The method for producing a hardened cement body includes a casting step and a curing step. The casting step is a step of casting the cement composition 21 into a formwork 11. The curing step is a step of curing the cement composition 21 cast in the casting step until it hardens and reaches a form-removal strength. The curing step also includes a partial form-removal step. The partial form-removal step is a step of forming a passage 30 between the formwork 11 and the cement composition 21 through which gas can pass when the compressive strength of the cement composition 21 reaches a predetermined strength σp that is lower than the form-removal strength.

[0027] According to this, by partially demolding the formwork 11 at a stage before the cement composition 21 exhibits its demolding strength, it is possible to promote the carbonation of the cement composition 21. This allows carbon dioxide to be efficiently fixed in the cement composition 21. In addition, it is possible to return a portion of the carbon dioxide emitted during the production of cement, which is the main raw material of the hardened cement body, to the hardened cement body. This reduces the total amount of carbon dioxide emitted during the production process of the hardened cement body, and as a result, it is possible to reduce the environmental load.

[0028] The specified strength σp is 1.0N / mm 2 More than 12.0N / mm 2 The content is set within the following range: This allows carbon dioxide to be effectively fixed in the cement composition 21. Therefore, carbonation of the cement composition 21 can be promoted.

[0029] The partial demolding step is performed when the accumulated temperature M from the time the cement composition 21 is mixed is in the range of 150°C·h to 650°C·h. By using the accumulated temperature M to manage the timing of performing the partial demolding step, it is possible to promote carbonation of the cement composition 21 while suppressing an increase in workload.

[0030] The above describes an embodiment of the present invention, but this embodiment is presented as an example and is not limited to the above-mentioned aspects and the aspects shown in the drawings, and various modifications and extensions can be made without departing from the spirit of the present invention. [Explanation of symbols]

[0031] 11...formwork, 21...cement composition, 30...passageway

Claims

1. A method for producing a hardened cement body using a cement composition, comprising: A casting step of casting the cement composition into a formwork; A curing process in which the cement composition cast in the casting process is cured until it hardens and reaches a demolding strength, The curing step includes a partial demolding step of forming a gas-permeable passage between the formwork and the cement composition when the compressive strength of the cement composition reaches a predetermined strength lower than the demolding strength. Method for manufacturing hardened cement.

2. The predetermined strength is 1.0 N / mm ２ 12.0N / mm or more ２ Set within the following range: The method for producing the hardened cement product according to claim 1.

3. The partial demolding step is carried out in a range of an accumulated temperature from the time when the cement composition is mixed to 150°C·h or more and 650°C·h or less. The method for producing the hardened cement product according to claim 1.

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