Molded body for carbon dioxide fixation, method for using molded body, cement hardened body, and method for producing cement hardened body

Abstract

This method for producing a cement hardened body includes: a molding step for molding a molded body from a molding feedstock containing water and a fine powder of cement hydrate; and a carbonation step for carbonating a calcium-containing component contained in the fine powder of cement hydrate in an atmosphere that contains carbon dioxide, has a partial pressure of carbon dioxide of 3.0 MPa or less, and has a temperature of 80°C or less. The molded body for carbon dioxide fixation contains water and a fine powder of cement hydrate, and the particle diameter of the fine powder of the cement hydrate is 500 μm or less. The cement hardened body contains calcium carbonate, has a carbonation degree of 50% or more, and has a compressive strength of 17 N / mm 2 or more.

Description

Molded body for carbon dioxide fixation, method for using the molded body, hardened cement body, and method for manufacturing hardened cement body

[0001] The present disclosure relates to a molded body for carbon dioxide fixation, a method for using the molded body, a hardened cement body, and a method for producing the hardened cement body.

[0002] In order to achieve carbon neutrality, technological developments are underway to reduce carbon dioxide emissions. One such technology is the introduction of CO into materials containing a large amount of calcium, such as hardened cement paste. ２ CaCO ３ There is a known method for immobilizing CO ２ However, the amount of hardened cement that can be mixed with cement is limited, and the CO2 that is the raw material for the hardened cement is not available. ２ Therefore, a method for effectively utilizing cement paste in which the above-mentioned substances are immobilized is desired.

[0003] Known methods for effectively utilizing cement paste include treating the cement paste under high-temperature and high-pressure conditions or under high-pressure conditions and then forming a hardened cement body again. For example, Patent Document 1 proposes a method for producing a hardened cement body by carbonating a hydrated cement body in an open system under conditions of a pressure of 40 to 150 atmospheres and a temperature of 80 to 200°C for 15 to 60 minutes. Non-Patent Document 1 proposes a method for producing a molded body by compressing cement paste under pressure conditions of 50 to 200 MPa.

[0004] Japanese Patent Application Laid-Open No. 2000-86371

[0005] Yuya Sakai et al., "Regeneration of hardened cement paste by pressure and control of volume change," Journal of the Japan Society of Civil Engineers, E2 (Materials and Concrete Structures), Japan Society of Civil Engineers, 2016, Vol. 72, No. 1, p. 32

[0006] The methods described in Patent Document 1 and Non-Patent Document 1 are carried out under high-temperature and high-pressure conditions, and therefore require a large amount of energy and large-scale equipment. Therefore, the present disclosure provides a method for producing a hardened cement body that can produce a hardened cement body with sufficient compressive strength even under mild temperature and pressure conditions. It also provides a molded body for carbon dioxide fixation that can produce a hardened cement body with sufficient compressive strength even when carbonation is carried out under mild temperature and pressure conditions, and a method for using the same. It also provides a hardened cement body that has sufficient compressive strength and is useful for achieving carbon neutrality.

[0007] One aspect of the present disclosure provides a method for producing a hardened cement body, the method including: a molding step of molding a molding raw material containing cement hydrate fine powder and water to obtain a molded body; and a carbonation step of holding the molded body in an atmosphere containing carbon dioxide, where the carbon dioxide partial pressure is 3.0 MPa or less and the temperature is 80°C or less, to carbonate a calcium-containing component contained in the cement hydrate fine powder.

[0008] The method for producing a hardened cement product involves carbonating the calcium-containing component contained in the fine powder of cement hydrate in an atmosphere containing carbon dioxide, where the carbon dioxide partial pressure is 3.0 MPa or less and the temperature is 80° C. or less. This method allows for the carbonation of the calcium-containing component contained in the fine powder of cement hydrate to be carried out under mild temperature and pressure conditions, while still allowing for the production of a hardened cement product with sufficient compressive strength.

[0009] One aspect of the present disclosure provides a molded body for carbon dioxide fixation, which contains cement hydrate fine powder and water, where the cement hydrate fine powder has a particle size of 500 μm or less. This molded body for carbon dioxide fixation can fix a sufficient amount of carbon dioxide even when carbonation is performed under mild temperature and pressure conditions. This allows for the production of a hardened cement product with sufficient compressive strength.

[0010] One aspect of the present disclosure is a cement hydrate composition comprising fine powder of cement and water, and having an apparent density of 1.5 g / cm ３The present invention provides the following molded article for carbon dioxide fixation. This molded article for carbon dioxide fixation can fix a sufficient amount of carbon dioxide even when carbonation is carried out under mild conditions. As a result, a hardened cement product with sufficient compressive strength can be obtained.

[0011] One aspect of the present disclosure is a method for producing a calcium carbonate-containing powder having a carbonation degree of 50% or more and a compressive strength of 17 N / mm ２ The hardened cement product has sufficient compressive strength because the calcium-containing component is sufficiently carbonated. This makes it possible to use it in a variety of applications, and the amount of CO generated during the cement manufacturing process can be reduced. ２ This makes it possible to significantly reduce carbon emissions, making this hardened cement useful for achieving carbon neutrality.

[0012] One aspect of the present disclosure is a method for producing a granular material comprising calcium carbonate and sand, the method comprising: ２ The hardened cement product has sufficient compressive strength, making it suitable for a variety of uses, and is also suitable for reducing CO2 emissions during the cement manufacturing process. ２ This makes it possible to significantly reduce carbon emissions, making this hardened cement useful for achieving carbon neutrality.

[0013] One aspect of the present disclosure is to add carbon dioxide in the atmosphere to the molded body by adding CaCO ３ The present invention provides a method for using a molded body, which comprises a step of immobilizing carbon dioxide by heating the molded body to a temperature of 1000°C (2000°F). The molded body can immobilize a sufficient amount of carbon dioxide even when carbonation is carried out under mild conditions. Furthermore, a hardened cement product having sufficient compressive strength can be obtained from the molded body.

[0014] According to the present disclosure, it is possible to provide a method for producing a hardened cement body that has sufficient compressive strength even under mild temperature and pressure conditions. It is also possible to provide a molded body for carbon dioxide fixation that can produce a hardened cement body that has sufficient compressive strength even when carbonation is performed under mild temperature and pressure conditions, and a method for using the same. It is also possible to provide a hardened cement body that has sufficient compressive strength and is useful for achieving carbon neutrality.

[0015] FIG. 1(A) is a photograph of the cross section of the hardened cement body produced under the carbonation process conditions of Comparative Examples 1 to 4, and FIG. 1(B) is a photograph of the cross section of the hardened cement body produced under the carbonation process conditions of Comparative Example 5 (left column) and Comparative Example 6 (right column). FIG. 2 is a photograph of the cross section of the hardened cement body produced under the carbonation process conditions of Examples 1, 3, 6, and 9. FIG. 3 is a photograph of the cross section of the hardened cement body produced under the carbonation process conditions of Examples 2, 4, 7, and 10. FIG. 4(A) is a photograph of the cross section of the hardened cement body produced under the carbonation process conditions of Example 12 (left column) and Example 14 (right column). FIG. 4(B) is a photograph of the cross section of the hardened cement body produced under the carbonation process conditions of Example 13 (left column) and Example 15 (right column). FIG. 5 is a scatter plot showing the relationship between the ratio of the density of the hardened cement body to the density of the molded body (density ratio) and compressive strength.

[0016] Hereinafter, embodiments of the present disclosure will be described, possibly with reference to the drawings. However, the following embodiments are merely examples for explaining the present disclosure and are not intended to limit the present disclosure to the following content. The numerical ranges exemplified as "a to b" are numerical ranges inclusive of a and b, with a lower limit being a and an upper limit being b. Replacing the upper or lower limit of each numerical range with the numerical value of any of the examples is also included in the present disclosure. When multiple numerical ranges are exemplified in stages, the present disclosure also includes a numerical range in which the upper or lower limit of a first numerical range is replaced with the upper or lower limit of a second numerical range that is narrower than the first numerical range. When a numerical range is indicated by only an upper or lower limit, the present disclosure also includes a numerical range combining the upper and lower limits. When multiple materials are exemplified, one of the materials may be used alone, or multiple materials may be used in combination.

[0017] [Method for Producing Hardened Cement Product] A method for producing a hardened cement product according to one embodiment includes a molding step of molding a molding raw material containing cement hydrate fine powder and water to obtain a molded product, and a carbonation step of holding the molded product in an atmosphere containing carbon dioxide, where the carbon dioxide partial pressure is 3.0 MPa or less and the temperature is 80°C or less, to carbonate the calcium-containing component contained in the cement hydrate fine powder.

[0018] <Forming step> In the forming step, a forming raw material containing cement hydrate fine powder and water is formed to obtain a formed body. The cement hydrate fine powder is obtained by pulverizing cement hydrate obtained by hardening a composition containing cement and water. The cement hydrate may be any of hardened cement paste, hardened mortar, and hardened concrete. The cement may be various types of cement, such as Portland cement, blended cement, and ecocement.

[0019] The age of the cement hydrate is not particularly limited. For example, it may be one day or more, one year or more, or three years or more. The cement hydrate may be waste, such as waste building materials made of concrete or mortar, waste hardened cement paste, or sludge generated in ready-mix concrete. The use of such waste enables effective utilization of resources. Since the cement hydrate is used as a fine powder after being pulverized, there are no particular limitations on its shape or size.

[0020] The cement hydrate fine powder can be obtained by classifying the pulverized cement hydrate using a sieve. The number of times of classification may be one time or two or more times. The particle size of the cement hydrate fine powder in the present disclosure means the particle size of the cement hydrate that has passed through a sieve with a predetermined mesh size and been classified.

[0021] From the viewpoint of further increasing compressive strength, the particle size of the cement hydrate fine powder may be 500 μm or less, 400 μm or less, 350 μm or less, 300 μm or less, 250 μm or less, 200 μm or less, 150 μm or less, 100 μm or less, or 75 μm or less. From the viewpoint of handleability, the particle size of the cement hydrate fine powder may be 50 μm or more, 75 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, or 250 μm or more. The particle size of the cement hydrate fine powder may be, for example, 50 to 500 μm, 50 to 400 μm, 50 to 350 μm, 75 to 300 μm, 75 to 250 μm, 75 to 200 μm, or 75 to 150 μm.

[0022] The fine powder of cement hydrate contains calcium-containing components. The calcium-containing components contain Ca as a constituent element and carbon dioxide (CO ２ ) is the component to be immobilized. Examples of calcium-containing components include calcium hydroxide, calcium (alumino) silicate hydrate (C-(A-)S-H), ettringite (AFt), monosulfate (AFm), and unhydrated clinker minerals (e.g., alite, belite, and ferrite phases).

[0023] The content of the calcium-containing component in the fine powder of cement hydrate may be 20 to 80 mass %, 35 to 75 mass %, or 50 to 70 mass %.

[0024] The forming raw material contains cement hydrate fine powder and water. The ratio of water to cement hydrate fine powder in the forming raw material (also referred to as the "water / fine powder ratio") may be 1% by mass or more, 3% by mass or more, 5% by mass or more, or 10% by mass or more, from the viewpoint of facilitating the formation of a formed body. The ratio of water to cement hydrate fine powder in the forming raw material (water / fine powder ratio) may be 30% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less, from the viewpoint of facilitating the penetration of carbon dioxide into the hardened cement body and the fixation of carbon dioxide in the carbonation process. The water is not particularly limited, and tap water, distilled water, deionized water, etc. can be used, for example. The water / fine powder ratio may be, for example, 1 to 30% by mass, 3 to 20% by mass, 5 to 15% by mass, 5 to 10% by mass, or 10 to 15% by mass.

[0025] The forming raw material may contain sand. From the viewpoint of increasing the compressive strength of the hardened cement body, the content of sand in the forming raw material may be 5% by mass or more, 10% by mass or more, 20% by mass or more, 30% by mass or more, or 40% by mass or more of the total amount of the forming raw material. The content of sand in the forming raw material may be 80% by mass or less, 70% by mass or less, 60% by mass or less, 50% by mass or less, or 40% by mass or less of the total amount of the forming raw material. The content of sand in the forming raw material may be, for example, 5 to 80% by mass, 10 to 70% by mass, 20 to 60% by mass, 30 to 50% by mass, 40 to 50% by mass, or 30 to 40% by mass.

[0026] The particle size of the sand contained in the forming raw material may be 53 μm or more, 75 μm or more, 106 μm or more, 150 μm or more, 212 μm or more, 300 μm or more, 425 μm or more, or 600 μm or more from the viewpoint of ease of forming a green body. The particle size of the sand contained in the forming raw material may be 1180 μm or less, 850 μm or less, 600 μm or less, 425 μm or less, 300 μm or less, 212 μm or less, 150 μm or less, or 106 μm or less from the viewpoint of increasing the compressive strength of the hardened cement body.

[0027] The compact can be obtained, for example, by compression molding the raw material for molding. The compression molding may be performed by, for example, uniaxial compression, biaxial compression, hot isostatic pressing (HIP), or cold isostatic pressing.

[0028] The pressure when molding the molded body may be such that the molded body can be compressed to an extent that the shape can be maintained. From the viewpoint of obtaining a molded body without using a large amount of energy or a large device, the pressure when molding the molded body may be 5 MPa or less, 4 MPa or less, 3 MPa or less, 2 MPa or less, or 1 MPa or less. From the viewpoint of increasing the compressive strength of the molded body, the pressure when molding the molded body may be 0.3 MPa or more, 0.4 MPa or more, or 0.5 MPa or more. The pressure when molding the molded body may be, for example, 0.3 to 5 MPa, 0.4 to 4 MPa, 0.5 to 3 MPa, 0.5 to 2 MPa, or 0.5 to 1 MPa.

[0029] The atmosphere in the molding step is not particularly limited and may be, for example, air or an atmosphere containing an inert gas such as nitrogen gas or argon gas. The atmosphere in the molding step may also contain carbon dioxide. In this case, the calcium-containing component contained in the fine powder of cement hydrate may be carbonated even during the molding step.

[0030] The size and shape of the compact may be adjusted depending on the shape of the compression container. The apparent density of the compact is 1.5 g / cm ３ The apparent density of the molded body may be 1.5 g / cm or less. ３ By setting the temperature to 1.4 or less, carbonation will proceed sufficiently and a hardened cement body with sufficient compressive strength can be obtained. From the same viewpoint, the apparent density of the molded body is set to 1.4 g / cm ３ From the viewpoint of increasing the compressive strength of the molded body, the apparent density of the molded body may be 1.1 g / cm or less. ３ Above, 1.2g / cm ３ or more, or 1.3 g / cm ３ The apparent density of the molded body may be, for example, 1.1 to 1.5 g / cm ３ , 1.2-1.5g / cm ３ , 1.3-1.5g / cm ３ , or 1.3 to 1.4 g / cm３ It may be.

[0031] <Carbonation Step> In the carbonation step, the shaped body is held in an atmosphere containing carbon dioxide, where the carbon dioxide partial pressure is 3.0 MPa or less and the temperature is 80°C or less, to carbonate the calcium-containing component contained in the fine powder of cement hydrate, thereby obtaining a hardened cement body.

[0032] The partial pressure of carbon dioxide in the atmosphere during the carbonation step may be 2.5 MPa or less, 2.0 MPa or less, 1.5 MPa or less, or 1.0 MPa or less. By lowering the partial pressure of carbon dioxide, carbonation of the hardened cement body can be sufficiently promoted without using a container or device that can withstand high pressure. From the viewpoint of promoting fixation of carbon dioxide, the partial pressure of carbon dioxide in the atmosphere during the carbonation step may be 0.01 MPa or more, 0.1 MPa or more, 0.5 MPa or more, or 0.8 MPa or more. The partial pressure of carbon dioxide in the atmosphere during the carbonation step may be, for example, 0.01 to 3.0 MPa, 0.1 to 2.5 MPa, 0.5 to 2.0 MPa, or 0.8 to 1.0 MPa. The total pressure during the carbonation step may also be within the above-mentioned range.

[0033] Carbon dioxide may be gas, liquid, supercritical, or subcritical. The partial pressure of carbon dioxide in the atmosphere of the carbonation step can be adjusted by a known method. For example, the partial pressure of carbon dioxide may be adjusted by storing dry ice in the same container as the molded body, or by injecting carbon dioxide gas into the container holding the molded body.

[0034] The atmosphere in the carbonation step may contain substantially only carbon dioxide, or may contain a gas other than carbon dioxide. The atmosphere in the carbonation step may be, for example, air or a mixed gas of air and carbon dioxide, or an atmosphere containing carbon dioxide and an inert gas such as nitrogen gas and argon gas. From the viewpoint of reducing the pressure of the atmosphere in the carbonation step, the concentration of carbon dioxide in the atmosphere may be 80% by volume or more, 90% by volume or more, 95% by volume or more, or 99% by volume or more.

[0035] The total pressure of the atmosphere in the carbonation step may be 8 MPa or less, 7 MPa or less, 6 MPa or less, 5 MPa or less, 4 MPa or less, or 3 MPa or less from the viewpoint of further reducing the load on the equipment and further reducing energy consumption. From the viewpoint of sufficiently immobilizing carbon dioxide, the pressure may be 0.2 MPa or more, 0.5 MPa or more, 1 MPa or more, or 1.5 MPa or more.

[0036] The temperature of the atmosphere in the carbonation step may be 80°C or lower, 70°C or lower, 65°C or lower, 60°C or lower, 50°C or lower, or 40°C or lower, from the viewpoint of reducing the load on the equipment and reducing energy consumption. From the viewpoint of sufficiently immobilizing carbon dioxide, the temperature may be 5°C or higher, 10°C or higher, 20°C or higher, 25°C or higher, 30°C or higher, 40°C or higher, or 50°C or higher. The temperature may be, for example, 5 to 80°C, 10 to 70°C, 20 to 65°C, 30 to 60°C, 30 to 50°C, or 40 to 60°C.

[0037] In the carbonation step, the molded body is kept in the above-mentioned atmosphere for a predetermined period of time (e.g., 1 minute or more, 3 hours or more, 1 hour or more, 3 hours or more, 6 hours or more, 12 hours or more, 1 day or more, 3 days or more, or 5 days or more). This allows carbonation to proceed, and a hardened cement body with sufficient compressive strength can be obtained. The period for keeping the molded body in the above-mentioned atmosphere may be 30 days or less, 20 days or less, or 10 days or less.

[0038] The ratio of the density of the hardened cement body after the carbonation process (after being held in a carbon dioxide atmosphere) to the density of the shaped body before the carbonation process (before being held in a carbon dioxide atmosphere) may be 1.15 or more, 1.20 or more, 1.25 or more, or 1.30 or more. This allows for a hardened cement body with sufficiently high compressive strength to be obtained. The ratio of the density of the hardened cement body after the carbonation process (after being held in a carbon dioxide atmosphere) to the density of the shaped body before the carbonation process (before being held in a carbon dioxide atmosphere) may be 1.40 or less, 1.35 or less, or 1.30 or less. This allows for sufficiently mild conditions in the carbonation process to reduce the load on the equipment used in the carbonation process. The density ratio may be, for example, 1.15 to 1.40, 1.20 to 1.35, or 1.25 to 1.30.

[0039] The compressive strength of the hardened cement is 10 N / mm ２ Above, 17N / mm ２ or more, or 20 N / mm ２ Such hardened cement products can be used for various purposes, such as concrete aggregates and processed products such as secondary products. The compressive strength of the hardened cement products may be, for example, 10 to 60 N / mm ２ , 17-60N / mm ２ , 20-60N / mm ２ , or 20 to 50 N / mm ２ It may be.

[0040] In the carbonation process, the calcium-containing component contained in the fine powder of cement hydrate reacts with carbon dioxide, for example, according to the following reaction formulas (1) and (2). Through these reactions, carbon dioxide is carbonated and fixed in the molded body. In reaction formula (2), x is any positive number, and z and t are any positive numbers that satisfy z + t = 1. Note that the reaction for fixing carbon dioxide is not limited to the following two reactions. Ca(OH) ２ +CO ２ → CaCO ３ +H ２ O... (1) (CaO) ｘ (SiO ２ ) (H ２ O) + xCO ２ → xCaCO３ +SiO ２ (H ２ O) ｔ +(z-t)H ２ O... (2)

[0041] The degree to which carbon dioxide has been fixed in the molded body (carbonation degree of the hardened cement body) can be calculated based on the amount of carbon dioxide fixed in the calcium-containing component contained in the fine powder of cement hydrate, which is the raw material for the hardened cement body.

[0042] For example, the carbonation degree (%) of the hardened cement paste can be calculated using the following formula (3): Carbonation degree (%) = Carbon dioxide (CO ２ ) Fixed amount (g) / maximum CO ２ Fixed amount x 100... (3)

[0043] Carbon dioxide (CO ２ The fixed amount of CO is calculated as the difference between the weight of the hardened cement body after the carbonation process and the weight of the molded body before the carbonation process. ２ The fixed amount is the theoretical maximum amount of carbon dioxide that can be fixed relative to the total amount of calcium-containing components contained in the molded body before the carbonation step. ２ The fixed amount is the amount of CO that reacts with calcium oxide (CaO) when the content of the calcium-containing component is converted to the content of calcium oxide (CaO) and the calcium oxide (CaO) reacts in its entirety according to the following reaction formula (4). ２ That is, the maximum CO ２ The fixed amount is calculated based on the weight of CaO when the content of the calcium-containing component is converted into CaO. ２ → CaCO ３ (4)

[0044] From the viewpoint of providing a hardened cement body with sufficient compressive strength, the carbonation degree (%) of the hardened cement body may be 50% or more, 55% or more, 60% or more, 65% or more, or 70% or more. The carbonation degree (%) of the hardened cement body may be, for example, 50 to 95%, 55 to 90%, 60 to 85%, 65 to 80%, or 70 to 80%.

[0045] According to the above-mentioned production method, a sufficient amount of carbon dioxide can be fixed even when carbonation is carried out under milder temperature and pressure conditions than conventional methods, thereby making it possible to obtain a hardened cement product with sufficient compressive strength.

[0046] [Molded body for carbon dioxide fixation] The molded body for carbon dioxide fixation according to one embodiment contains cement hydrate fine powder and water, and the particle size of the cement hydrate fine powder is 500 μm or less. This molded body for carbon dioxide fixation may be the same as the molded body described in the embodiment of the method for producing a hardened cement body. Therefore, the contents described in the embodiment of the method for producing a hardened cement body also apply to this embodiment.

[0047] A molded body for carbon dioxide fixation according to another embodiment contains cement hydrate fine powder and water, and has an apparent density of 1.5 g / cm ３ The molded body for carbon dioxide fixation may be the same as the molded body described in the embodiment of the method for producing a hardened cement body. Therefore, the contents described in the embodiment of the method for producing a hardened cement body also apply to this embodiment.

[0048] The molded body for carbon dioxide fixation according to each of the above embodiments can fix a sufficient amount of carbon dioxide even when carbonation is carried out under mild conditions as explained in the embodiment of the method for producing a hardened cement body. Therefore, a hardened cement body having sufficient compressive strength can be obtained. Such a molded body can fix a sufficient amount of carbon dioxide generated during the cement production process. ２ Since cement can be obtained by immobilizing CO in the cement manufacturing process, ２ This allows for a significant reduction in carbon dioxide emissions, making this molded product useful for achieving carbon neutrality.

[0049] [Hardened cement body] The hardened cement body according to one embodiment contains calcium carbonate, has a carbonation degree of 50% or more, and a compressive strength of 17 N / mm ２This hardened cement product may be the same as the hardened cement product described in the embodiment of the method for manufacturing a hardened cement product described above. Therefore, the contents described in the embodiment of the method for manufacturing a hardened cement product also apply to this embodiment.

[0050] A hardened cement product according to another embodiment contains calcium carbonate and sand and has a compressive strength of 10 N / mm ２ The compressive strength is, for example, 10 to 60 N / mm ２ , 12~40N / mm ２ , 15-30N / mm ２ , or 20 to 25 N / mm ２ This hardened cement body may be manufactured by the above-mentioned embodiment of the manufacturing method for a hardened cement body. This hardened cement body can be obtained by using a molding raw material containing sand among the embodiments of the manufacturing method for a hardened cement body. The sand may also be the same as that described in the embodiment. Therefore, the contents described in the embodiment of the manufacturing method for a hardened cement body also apply to this embodiment.

[0051] The hardened cement product according to each of the above embodiments has sufficient compressive strength because the calcium-containing component is sufficiently carbonated. This makes it possible to use it for various purposes, and the amount of CO generated during the cement manufacturing process is small. ２ This makes it possible to significantly reduce carbon emissions, making this hardened cement useful for achieving carbon neutrality.

[0052] [Method of Using the Molded Article] A method of using the molded article according to one embodiment is to add carbon dioxide in the atmosphere to the molded article by adding CaCO ３ CO2 is fixed as ２ The molded body may be obtained by the molding step described in the embodiment of the method for producing a hardened cement body. ２ The fixation step may be the carbonation step described in the embodiment of the method for producing a hardened cement body. The contents described in the embodiments of the method for producing a hardened cement body and the molded body for carbon dioxide fixation also apply to this embodiment. The method of use of this embodiment is to convert carbon dioxide in the atmosphere into CaCO 3 . ３ This can also be said to be the use of the molded body for immobilizing it as a substance.

[0053] Although several embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments. For example, the contents described in each embodiment may also be applied to other embodiments.

[0054] Some embodiments of the present disclosure described above include the following: [1] A method for producing a hardened cement body, comprising: a molding step of molding a molding raw material containing cement hydrate fine powder and water to obtain a molded body; and a carbonation step of holding the molded body in an atmosphere containing carbon dioxide, where the carbon dioxide partial pressure is 3.0 MPa or less and the temperature is 80°C or less, to carbonate the calcium-containing component contained in the cement hydrate fine powder. [2] A method for producing a hardened cement body according to [1], wherein the ratio of the water to the cement hydrate fine powder is 20 mass% or less. [3] A method for producing a hardened cement body according to [1] or [2], wherein the particle size of the cement hydrate fine powder is 500 μm or less. [4] A method for producing a hardened cement body according to any one of [1] to [3], wherein the pressure when molding the molding raw material is 5 MPa or less. [5] A method for producing a hardened cement body according to any one of [1] to [4], wherein the molding raw material contains sand, and the sand content in the molding raw material is 80 mass% or less. [6] The method for producing a hardened cement body according to any one of [1] to [5], wherein the ratio of the density of the hardened cement body to the density of the molded body is 1.15 or more. [7] The hardened cement body has a compressive strength of 10 N / mm ２ [8] A molded body for carbon dioxide fixation, comprising fine powder of cement hydrate and water, wherein the particle size of the fine powder of cement hydrate is 500 μm or less. [9] An apparent density of 1.5 g / cm ３

[10] The molded body for carbon dioxide fixation according to [8], which contains fine powder of cement hydrate and water and has an apparent density of 1.5 g / cm or less. ３

[11] A molded body for carbon dioxide fixation according to any one of [8] to

[10] , which contains carbon dioxide and has a carbon dioxide partial pressure of 3.0 MPa or less and a temperature of 80°C or less, and when the molded body is kept for 1 hour in an atmosphere, the density of the molded body becomes 1.15 or more compared to before the keeping.

[12] A molded body for carbon dioxide fixation according to any one of [8] to

[10] , which contains calcium carbonate and has a carbonation degree of 50% or more and a compressive strength of 17 N / mm ２

[13] A hardened cement product containing calcium carbonate and sand, and having a compressive strength of 10 N / mm ２

[14] The hardened cement body according to

[12] or

[13] , which is obtained by carbonating a calcium-containing component contained in the cement hydrate fine powder in an atmosphere containing carbon dioxide, in which the carbon dioxide partial pressure is 3.0 MPa or less and the temperature is 80°C or less, of a formed body of a forming raw material containing cement hydrate fine powder and water.

[15] The hardened cement body according to any one of [8] to

[11] above, in which carbon dioxide in the atmosphere is added to the formed body by carbonating a calcium-containing component contained in the cement hydrate fine powder. ３

[16] A method for using a molded article, comprising a step of converting carbon dioxide in an atmosphere into CaCO3 and fixing the carbon dioxide in the atmosphere as CaCO3. ３

[17] A hardened cement product obtained by fixing carbon dioxide in the molded product according to any one of [8] to

[11] above.

[0055] The present disclosure will be described in more detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0056] [Comparative Examples 1 to 6, Examples 1 to 15] In each comparative example and example, early-high-strength Portland cement having the chemical composition shown in Table 1 below was used. A cement paste was prepared by blending this early-high-strength Portland cement with water so that the ratio of water to this early-high-strength Portland cement (water / cement ratio) was 0.4. The water content in the cement paste, including the water contained in the hydrates and pores, was 28.6% by mass, and the content of cement components in the cement paste (excluding water in the hydrates) was 71.4% by mass. The calcium oxide (CaO) content in the cement paste was 71.4 x 65.09 / 100 = 46.5% by mass. The chemical composition was measured in accordance with JIS R 5204, "Method for X-ray fluorescence analysis of cement."

[0057]

[0058] (Cement hydrate pulverization) A hardened paste (3-year-old) was prepared using the above cement paste. This was coarsely pulverized to 5 mm or less using a vibration mill (manufactured by Kawasaki Heavy Industries, Ltd.). The mixture was then further pulverized using a vibration mill, and sieved using sieves with openings of 300 μm, 250 μm, 150 μm, and 75 μm to obtain the following four types of cement hydrate fine powders with different particle sizes. The types of fine powder used in each comparative example and each example are shown in Tables 2 and 4. Cement hydrate fine powder (A): particle size 250 to 300 μm Cement hydrate fine powder (B): particle size 150 to 250 μm Cement hydrate fine powder (C): particle size 75 to 150 μm Cement hydrate fine powder (D): particle size 75 μm or less

[0059] (Compression molding of cement hydrate fine powder) 25 g of each of the fine powders (A) to (D) shown in Tables 2 and 4 was weighed out, and distilled water was mixed with each fine powder so that the ratio of water to cement hydrate (water / fine powder ratio) was the value shown in Tables 2 and 4 to obtain a mixture. The mixture was compressed at 0.7 MPa for 3 minutes using a compression molding machine (manufactured by Riken Seiki Co., Ltd.) to obtain a cylindrical molded body with a diameter of approximately 34 mm and a height of approximately 20 mm. The volume and mass of the molded body were then measured, and the apparent density of the molded body was calculated. The calculated apparent densities (densities) of the molded bodies of each Comparative Example and each Example are shown in Tables 3 and 5, respectively.

[0060] (Treatment conditions for carbonation step) The obtained molded bodies of each comparative example and each example were placed in a pressure vessel, and carbon dioxide gas was filled into the pressure vessel using dry ice. ２ The partial pressure was adjusted to the conditions shown in Tables 2 and 4. In both cases, the gas composition was almost CO ２ Only CO ２ The partial pressure was approximately equal to the total pressure. The time maintained under these conditions is shown in Tables 2 and 4. The temperature inside the pressure vessel was adjusted using a water bath. After maintaining the time shown in Tables 2 and 4, the hardened cement body was removed from the pressure vessel. The volume and mass of the hardened cement body were measured, and the apparent density of the hardened cement body was calculated. The calculated apparent densities (densities) of the hardened cement body are shown in Tables 3 and 5, respectively.

[0061] (Calculation of Density Change) The ratio of the density of the hardened cement body to the density of the molded body was calculated as the “density ratio.” The results are shown in Tables 3 and 5.

[0062] (Compressive strength test) The compressive strength of the hardened cement paste was measured in accordance with JIS R 5201:2015 "Physical testing methods for cement." The results are shown in Tables 3 and 5.

[0063] (Evaluation of carbonation progress of molded body using phenolphthalein solution) The carbonation progress of the obtained hardened cement body was evaluated by staining the hardened cement body with phenolphthalein solution. Phenolphthalein solution was dropped onto the cross section of the hardened cement body, and the carbonation progress was evaluated based on whether or not the hardened cement body turned reddish purple. Phenolphthalein solution reacts with alkaline solution to turn reddish purple. That is, the non-carbonated parts of the cross section of the hardened cement body turned reddish purple.

[0064] Figure 1(A) is a photograph of the cross section of the hardened cement body produced under the carbonation process conditions of Comparative Examples 1 to 4. The upper left of Figure 1(A) is a photograph of Comparative Example 1, the upper right is a photograph of Comparative Example 2, the lower left is a photograph of Comparative Example 3, and the lower right is a photograph of Comparative Example 4.

[0065] FIG. 1(B) is a photograph of the cross section of the hardened cement body produced under the carbonation process conditions of Comparative Example 5 (left) and Comparative Example 6 (right).

[0066] Figure 2 shows photographs of the cross sections of hardened cement bodies produced under the carbonation process conditions of Examples 1, 3, 6, and 9. The upper left of Figure 2 is a photograph of Example 1, the upper right is a photograph of Example 3, the lower left is a photograph of Example 6, and the lower right is a photograph of Example 9.

[0067] Fig. 3 shows photographs of the cross sections of hardened cement bodies produced under the carbonation process conditions of Examples 2, 4, 7, and 10. The upper left of Fig. 3 is a photograph of Example 2, the upper right is a photograph of Example 4, the lower left is a photograph of Example 7, and the lower right is a photograph of Example 10.

[0068] Fig. 4(A) is a photograph of a cross section of the hardened cement body produced under the carbonation process conditions of Examples 12 and 14. Fig. 4(B) is a photograph of a cross section of the hardened cement body produced under the carbonation process conditions of Examples 13 and 15.

[0069] 2, 3, and 4, most of the cross section of the hardened cement body was not reddish purple. From these results, it can be seen that the low temperature and low CO ２ It was confirmed that carbonation of the molded body proceeded sufficiently even when carbonation was carried out under relatively mild partial pressure conditions.

[0070] (Calculation of carbonation degree of hardened cement body) The carbonation degree (%) of the hardened cement body was calculated using the above-mentioned formula (3). ２ The amount of carbon dioxide (CO) fixed was calculated using the following formula (5). ２ ) Fixed amount (g) = Weight (g) of hardened cement body after carbonation - Weight (g) of molded body before carbonation (5)

[0071] The CaO content of the cement hydrate fine powder used in each Comparative Example and each Example was 46.5 mass % as described above. Therefore, 25 g of the cement hydrate fine powder contained 11.62 g of CaO (molecular weight 56). All of the CaO contained in the cement hydrate fine powder was carbonated to calcium carbonate (CaCO ) as shown in the above formula (4). ３ : molecular weight 100) ２ The amount of immobilized CO (molecular weight 44) is 9.13 (g). This value corresponds to the maximum CO ２ The carbon dioxide (CO ２ ) fixed amount and this maximum CO ２ The carbonation degree of the hardened cement body of each Comparative Example and each Example was calculated using the fixed amount. The results are shown in Tables 3 and 5.

[0072]

[0073]

[0074]

[0075]

[0076] Fig. 5 is a scatter plot showing the relationship between the compressive strength of the hardened cement products of Examples 1 to 11 and the ratio of the density of the hardened cement product to the density of the molded product before carbonation (density ratio). Fig. 5 shows that the higher the density ratio of the hardened cement product, the higher the compressive strength. Furthermore, the hardened cement products produced using cement hydrate fine powder (D) or (C) with a particle size of 75 μm or less or 75 to 150 μm tended to have particularly high density ratios and high compressive strengths.

[0077] When the Examples were compared with the Comparative Examples, which used the same type of cement hydrate and underwent the same carbonation process for the same time, the hardened cement bodies of the Examples all had compressive strengths comparable to those of the Comparative Examples, which underwent the carbonation process at high temperature and high pressure.

[0078] (Examples 16 to 20) In the same manner as in Example 1, hardened paste of ordinary Portland cement (aged 3 years) was coarsely pulverized to 5 mm or less. It was then further pulverized using a vibration mill, and sieved using sieves with openings of 150 μm and 75 μm to obtain two types of fine cement hydrate powder with different particle sizes as follows. The types of fine powder used in each example are shown in Table 7. Fine cement hydrate powder (E): particle size 150 μm or less Fine cement hydrate powder (F): particle size 75 μm or less

[0079] Sand (N40, N50, N80) manufactured by Nippyo Mining Co., Ltd. was prepared. The particle size distribution of each sand is shown in Table 6. The particle size distribution was determined by sieving sand starting with a sieve with a larger mesh size and then sorting the undersize sand obtained by sieving through a sieve with the next larger mesh size. Each value in Table 6 indicates the proportion (mass%) remaining on the sieve. In Table 6, Pan refers to sand that passed through a sieve with a mesh size of 53 μm and has a particle size smaller than 53 μm.

[0080]

[0081] A forming raw material was prepared by mixing cement hydrate fine powder and sand so that the sand content in the forming raw material would be the value shown in Table 7. Except for using this forming raw material, a formed body was produced in the same manner as in Examples 1 to 15, and a carbonation step was carried out to produce a hardened cement body. The ratio of water to cement hydrate fine powder (water / fine powder ratio), carbonation step conditions, and compressive strength of the hardened cement body were as shown in Tables 7 and 8. As shown in Table 8, even when sand was included in the forming raw material, a hardened cement body with sufficient compressive strength could be obtained, as in Examples 1 to 15.

[0082]

[0083]

[0084] These results confirmed that the method for producing a hardened cement body of the present disclosure can produce hardened cement bodies with sufficient compressive strength not only from cement paste but also when aggregate is included.

[0085] The present disclosure can provide a method for producing a hardened cement body that has sufficient compressive strength even under mild temperature and pressure conditions. It can also provide a molded body for carbon dioxide fixation that can produce a hardened cement body that has sufficient compressive strength even when carbonation is performed under mild temperature and pressure conditions. It can also provide a hardened cement body that has sufficient compressive strength and is useful for achieving carbon neutrality.

Claims

1. A method for producing a hardened cement body, comprising: a molding step of molding a molding raw material containing cement hydrate fine powder and water to obtain a molded body; and a carbonation step of holding the molded body in an atmosphere containing carbon dioxide, the carbon dioxide partial pressure being 3.0 MPa or less and the temperature being 80°C or less, to carbonate the calcium-containing components contained in the cement hydrate fine powder.

2. The method for producing a hardened cement body according to claim 1, wherein the ratio of the water to the fine powder of the cement hydrate is 20 mass% or less.

3. A method for producing a hardened cement body as described in claim 1 or 2, wherein the particle size of the fine powder of cement hydrate is 500 μm or less.

4. A method for producing a hardened cement body according to claim 1 or 2, wherein the pressure when molding the molding raw material is 5 MPa or less.

5. A method for producing a hardened cement body as described in claim 1 or 2, wherein the forming raw material contains sand, and the sand content in the forming raw material is 80 mass% or less.

6. A method for producing a hardened cement body as described in claim 1 or 2, wherein the ratio of the density of the hardened cement body to the density of the molded body is 1.15 or more.

7. The compressive strength of the hardened cement body is 10 N / mm ２ The method for producing a hardened cement body according to claim 1 or 2, wherein the hardened cement body is a hardener.

8. A molded body for carbon dioxide fixation, comprising fine powder of cement hydrate and water, the fine powder of cement hydrate having a particle size of 500 μm or less.

9. Apparent density is 1.5 g / cm ３ The molded article for carbon dioxide fixation according to claim 8, wherein:

10. A cement hydrate powder containing water and an apparent density of 1.5 g / cm ３ The following molded body for carbon dioxide fixation:

11. A molded body for carbon dioxide fixation according to any one of claims 8 to 10, wherein when the molded body is held for one hour in an atmosphere containing carbon dioxide, in which the partial pressure of carbon dioxide is 3.0 MPa or less and the temperature is 80°C or less, the density of the molded body becomes 1.15 or more compared to the density before the holding.

12. Contains calcium carbonate, has a carbonation level of 50% or more, and a compressive strength of 17N / mm ２ The above is the hardened cement body.

13. A concrete mixture containing calcium carbonate and sand with a compressive strength of 10 N / mm ２ The above is the hardened cement body.

14. A hardened cement body as described in claim 12 or 13, obtained by carbonating a calcium-containing component contained in a formed body of a forming raw material containing cement hydrate fine powder and water in an atmosphere containing carbon dioxide, the carbon dioxide partial pressure being 3.0 MPa or less and the temperature being 80°C or less.

15. The molded body according to claim 8 or 9 is treated with carbon dioxide in an atmosphere by adding CaCO ３ and fixing the molded article as a molded article.

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