Cement composition for fixing carbon dioxide, cement hardened body for fixing carbon dioxide, and method for fixing carbon dioxide

Abstract

This cement composition for fixing carbon dioxide contains a cement composition and a carbon dioxide absorption liquid containing a carbon dioxide absorbent. This cement hardened body for fixing carbon dioxide includes a cement hardened body and a carbonate carried on the cement hardened body. This method for fixing carbon dioxide has: a step for kneading a carbon dioxide absorption liquid containing a carbon dioxide absorbent into a cement composition; a step for hardening the cement composition containing the carbon dioxide absorbent to obtain a cement hardened body for fixing carbon dioxide; and a step for bringing the atmosphere into contact with the cement hardened body for fixing carbon dioxide, and fixing the carbon dioxide contained in the atmosphere to the cement hardened body for fixing carbon dioxide.

Description

Cement composition for carbon dioxide fixation, hardened cement product for carbon dioxide fixation, and carbon dioxide fixation method

[0001] The present invention relates to a cement composition for carbon dioxide fixation, a hardened cement product for carbon dioxide fixation, and a method for carbon dioxide fixation. This application claims priority to Japanese Patent Application No. 2023-110225, filed on July 4, 2023, the contents of which are incorporated herein by reference.

[0002] To prevent global warming, carbon dioxide (hereinafter referred to as CO ２ In the construction materials sector, reducing the amount of cement used will reduce CO emissions generated during concrete production. ２ How to reduce CO ２ A technique has been proposed for concrete that can fix (absorb) the above-mentioned substances (see, for example, Patent Document 1).

[0003] CO in new concrete ２ As a technique for promoting fixation of carbon dioxide, for example, the technique described in Patent Document 2 is known. The technique described in Patent Document 2 involves treating a concrete skeleton in which carbonation has not progressed, such as newly constructed concrete, with high-concentration CO ２ By placing it in a gas environment, carbonation is accelerated from the surface.

[0004] Japanese Patent No. 4822373 Japanese Patent Application Laid-Open No. 2014-51422

[0005] During the carbonation treatment, the concrete structure is covered with a sheet or other material to prevent CO ２ It is necessary to prevent the gas from leaking to the outside. This method is not always easy depending on the shape of the concrete structure, and CO ２ There is also the issue of the risk of gas leaking to the outside.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a cement composition for carbon dioxide fixation, a hardened cement product for carbon dioxide fixation, and a method for carbon dioxide fixation that can fix carbon dioxide without leaking the carbon dioxide to the outside.

[0007] In order to solve the above problems, the present invention has the following aspects. [1] A cement composition for carbon dioxide fixation, comprising a cement composition and a carbon dioxide absorbing liquid containing a carbon dioxide absorbent. [2] The cement composition for carbon dioxide fixation according to [1], wherein the carbon dioxide absorbing liquid has a pH of 8.0 or higher at 20°C. [3] The cement composition for carbon dioxide fixation according to [1] or [2], wherein the carbon dioxide absorbing liquid contains carbon dioxide. [4] The cement composition for carbon dioxide fixation according to any of [1] to [3], wherein the content of the carbon dioxide absorbing liquid is 0.01 parts by mass or more and 100 parts by mass or less per 100 parts by mass of cement contained in the cement composition. [5] The cement composition for carbon dioxide fixation according to any of [1] to [4], wherein the carbon dioxide absorbent is an alkaline compound. [6] The cement composition for carbon dioxide fixation according to any of [1] to [5], wherein the content of the carbon dioxide absorbent is 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the cement composition for carbon dioxide fixation. [6-1] The cement composition for carbon dioxide fixation according to any one of [1] to [6], wherein the content of the carbon dioxide absorbent is 0.1 parts by mass or more and 4 parts by mass or less, 0.2 parts by mass or more and 3.5 parts by mass or less, 0.3 parts by mass or more and 3 parts by mass or less, 0.4 parts by mass or more and 3 parts by mass or less, 0.45 parts by mass or more and 2.5 parts by mass or less, 0.45 parts by mass or more and 2.0 parts by mass or less, or 0.45 parts by mass or more and 1.5 parts by mass or less, relative to 100 parts by mass of the cement composition for carbon dioxide fixation. [7] The cement composition for carbon dioxide fixation according to any one of [1] to [6-1], wherein the content of the carbon dioxide absorbent is 0.1 parts by mass or more and less than 5 parts by mass, relative to 100 parts by mass of the cement composition for carbon dioxide fixation, and the carbon dioxide absorbing liquid contains carbon dioxide. [8] The cement composition for carbon dioxide fixation according to any one of [1] to [7], wherein the carbon dioxide absorbent is an amine compound, the content of the carbon dioxide absorbent is 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the cement composition for carbon dioxide fixation, and the carbon dioxide absorbing liquid contains carbon dioxide. [9] A hardened cement composition for carbon dioxide fixation, comprising a hardened cement product and a carbonate supported on the hardened cement product.

[10] The hardened cement for carbon dioxide fixation according to [9], wherein the content of the carbonate is 0 to 50 parts by mass per 100 parts by mass of the hardened cement.

[11] The hardened cement for carbon dioxide fixation according to [9] or

[10] , wherein the hardened cement is concrete.

[12] A method for carbon dioxide fixation, comprising the steps of kneading a carbon dioxide absorbing liquid containing a carbon dioxide absorbent into a cement composition, hardening the cement composition containing the carbon dioxide absorbent to obtain a hardened cement for carbon dioxide fixation, and bringing the hardened cement for carbon dioxide fixation into contact with atmospheric air to fix the carbon dioxide contained in the atmosphere in the hardened cement for carbon dioxide fixation.

[13] A method for carbon dioxide fixation, comprising the steps of kneading a carbon dioxide absorbing liquid containing a carbon dioxide absorbent, in which carbon dioxide has been dissolved in advance, into a cement composition, hardening the cement composition containing the carbon dioxide absorbent to obtain a hardened cement for carbon dioxide fixation, and bringing the hardened cement for carbon dioxide fixation into contact with atmospheric air to fix the carbon dioxide contained in the atmosphere in the hardened cement for carbon dioxide fixation.

[0008] According to the present invention, it is possible to provide a cement composition for immobilizing carbon dioxide, a hardened cement product for immobilizing carbon dioxide, and a method for immobilizing carbon dioxide, which are capable of immobilizing carbon dioxide without leaking the carbon dioxide to the outside.

[0009] FIG. 10 is a graph showing the relationship between the amount of bleeding and the elapsed time (minutes) as a result of a bleeding test of a carbon dioxide fixation cement composition in Experimental Example 3. FIG. 11 is a graph showing the setting rate of a carbon dioxide fixation cement composition in Experimental Example 4. FIG. 12 is a graph showing the setting rate of a carbon dioxide fixation cement composition in Experimental Example 5. FIG. 13 is a graph showing the content of calcium carbonate in a carbon dioxide fixation hardened cement body in Experimental Example 6. FIG. 14 is a graph showing the content of calcium carbonate in a carbon dioxide fixation hardened cement body in Experimental Example 7. FIG. 15 is a graph showing the impedance of a carbon dioxide fixation hardened cement body in Experimental Example 8. FIG. 16 is a graph showing the compressive strength in a carbon dioxide fixation hardened cement body in Experimental Example 9.

[0010] [Cement Composition for Fixing Carbon Dioxide] A cement composition for fixing carbon dioxide according to one embodiment of the present invention contains a cement composition and a carbon dioxide absorbing liquid containing a carbon dioxide absorbent.

[0011] "Cement composition" A cement composition contains cement and water. Examples of cement compositions include concrete (ready-mixed concrete), mortar (paste mortar), and cement milk (cement paste). In this specification, concrete refers to a mixture of cement, fine aggregate (sand), and coarse aggregate (gravel (crushed stone)) and kneaded with water. In this specification, mortar refers to a mixture of cement and fine aggregate (sand) and kneaded with water. In this specification, cement milk refers to cement kneaded with water alone. In this specification, cement refers to a powder whose main ingredients are limestone, clay, silica, iron oxide raw materials, etc., which hardens through a chemical reaction with water. In this specification, fine aggregate refers to sand with a diameter of 5 mm or less. In this specification, coarse aggregate refers to gravel (crushed stone) with a diameter of more than 5 mm, and the diameter of the coarse aggregate is preferably 25 mm or less.

[0012] The mixing ratio of cement, fine aggregate, and coarse aggregate in concrete can be determined appropriately depending on the strength required for the concrete. The mixing ratio of cement, fine aggregate, and coarse aggregate, in mass ratio, is preferably, for example, 1 part cement to 2 to 3 parts fine aggregate and 4 to 6 parts coarse aggregate.

[0013] The mixing ratio of cement to fine aggregate in the mortar can be determined appropriately depending on the strength required for the mortar. The mixing ratio of cement to fine aggregate is preferably, for example, 1 part cement to 2 to 4 parts fine aggregate by mass.

[0014] "Carbon dioxide absorbing liquid" The carbon dioxide absorbing liquid is a liquid containing a carbon dioxide absorbent capable of absorbing carbon dioxide and a solvent. The carbon dioxide absorbing liquid has physical properties such as viscosity that allow it to be kneaded into a cement composition. When the carbon dioxide absorbent is liquid, the carbon dioxide absorbing liquid does not need to contain a solvent, which will be described later.

[0015] The content of the carbon dioxide absorbent in the carbon dioxide absorbing liquid is, for example, preferably 0.01% by mass or more, more preferably 1% by mass or more, and even more preferably 5% by mass or more, relative to the total mass of the carbon dioxide absorbing liquid. When the content of the carbon dioxide absorbent is equal to or more than the above-mentioned lower limit, the amount of carbon dioxide that can be fixed can be further increased. Furthermore, from the viewpoint of increasing the compressive strength of the carbon dioxide fixation hardened cement body obtained by hardening the carbon dioxide fixation cement composition, the concentration of the carbon dioxide absorbent in the carbon dioxide absorbing liquid is preferably 1% by mass or more and less than 5% by mass, relative to the total mass of the carbon dioxide absorbing liquid.

[0016] Examples of the solvent contained in the carbon dioxide absorbing liquid include water and organic solvents such as ethanol. As the solvent, water is preferred because it is less likely to volatilize at room temperature and easily dissolves the carbon dioxide absorbent. These solvents may be used alone or in combination of two or more.

[0017] The content of the solvent is, for example, preferably 25% by mass or more and 99.99% by mass or less, more preferably 50% by mass or more and 99% by mass or less, and even more preferably 75% by mass or more and 95% by mass or less, relative to the total mass of the carbon dioxide absorbing liquid. When the content of the solvent is equal to or more than the lower limit, the amount of carbon dioxide absorbing liquid impregnated into the cement composition can be further increased. When the content of the solvent is equal to or less than the upper limit, the content of the carbon dioxide absorbent can be further increased. Therefore, the amount of carbon dioxide that can be fixed can be further increased.

[0018] The viscosity of the carbon dioxide absorbing liquid at 25°C is, for example, preferably 1000 mPa·s or less, more preferably 50 mPa·s or less, and even more preferably 10 mPa·s or less. When the viscosity of the carbon dioxide absorbing liquid at 25°C is equal to or greater than the lower limit, the carbon dioxide absorbing liquid is more easily dispersed in the cement composition, facilitating the production of the cement composition. The viscosity of the carbon dioxide absorbing liquid at 25°C can be determined, for example, by setting the temperature of the object to be measured to 25°C, using the No. 2 rotor of a B-type viscometer, and reading the value 30 seconds after the rotor starts to rotate at a rotation speed of 60 rpm.

[0019] The pH of the carbon dioxide absorbing liquid at 20°C is, for example, preferably 7.0 or higher, more preferably 8.5 or higher, and even more preferably 10.0 or higher. When the pH of the carbon dioxide absorbing liquid at 20°C is equal to or higher than the lower limit, the rate of carbon dioxide absorption can be further increased. The upper limit of the pH of the carbon dioxide absorbing liquid at 20°C is not particularly limited, but is set to 14.0, for example, in consideration of ease of handling. Furthermore, from the viewpoint of increasing the compressive strength of a carbon dioxide fixation hardened cement body obtained by hardening the carbon dioxide fixation cement composition, the pH of the carbon dioxide absorbing liquid at 20°C is preferably 7 or higher and 10 or lower, more preferably 7 or higher and 9 or lower, and even more preferably 7 or higher and 8 or lower. The pH of the carbon dioxide absorbing liquid at 20°C can be measured by adjusting the measurement target to 20°C and using a pH meter (for example, a compact pH meter LAQUAtwin (registered trademark) pH-22B manufactured by Horiba, Ltd.).

[0020] The carbon dioxide absorbing liquid may contain carbon dioxide. The higher the carbon dioxide content, the more carbon dioxide can be fixed in the carbon dioxide fixing cement composition during production of the carbon dioxide fixing cement composition. The carbon dioxide content is, for example, preferably 1.0% mol or more, more preferably 10.0% mol or more, and even more preferably 50.0% mol or more, relative to the molar equivalent of nitrogen atoms in the carbon dioxide absorbent. The carbon dioxide content is preferably set to a value such that the pH of the carbon dioxide absorbing liquid at 20°C falls within the above range. When the carbon dioxide absorbing liquid contains carbon dioxide, the carbon dioxide exists in the carbon dioxide absorbing liquid as carbonate ions or bicarbonate ions. The method for adding carbon dioxide to the carbon dioxide absorbing liquid is not particularly limited, but examples thereof include bubbling carbon dioxide gas to dissolve it in the carbon dioxide absorbing liquid and adding dry ice (solid) to the carbon dioxide absorbing liquid.

[0021] The content of the carbon dioxide absorbing liquid is preferably 0.01 parts by mass or more and 100 parts by mass or less, and more preferably 30 parts by mass or more and 65 parts by mass or less, relative to 100 parts by mass of cement contained in the cement composition. When the content of the carbon dioxide absorbing liquid in the carbon dioxide fixation cement composition is equal to or more than the above-mentioned lower limit, the amount of carbon dioxide that can be fixed can be further increased. When the content of the carbon dioxide absorbing liquid in the carbon dioxide fixation cement composition is equal to or less than the above-mentioned upper limit, the amount of carbon dioxide absorbent attached to the carbon dioxide fixation hardened cement body obtained by hardening the carbon dioxide fixation cement composition can be maintained. The content of the carbon dioxide absorbing liquid in the carbon dioxide fixation cement composition can be adjusted by the type of cement composition, the type of carbon dioxide absorbent, and a combination thereof.

[0022] "Carbon dioxide absorbent" A carbon dioxide absorbent is contained in a cement composition and absorbs carbon dioxide in the atmosphere. As a result, the carbon dioxide in the atmosphere is captured in a hardened cement body for carbon dioxide fixation produced by hardening the carbon dioxide fixation cement composition, thereby reducing the carbon dioxide concentration in the atmosphere. In other words, carbon dioxide in the atmosphere can be fixed in the hardened cement body for carbon dioxide fixation. A carbon dioxide absorbent may be solid or liquid at room temperature and pressure. In this specification, "room temperature" refers to the standard temperature of the atmosphere, for example, 15°C to 25°C. "Normal pressure" refers to the standard pressure of the atmosphere, for example, 1 atmosphere (1013 hPa).

[0023] Examples of carbon dioxide absorbents include alkaline compounds. Here, "alkaline compound" refers to a compound that has a pH of more than 7 when dissolved in water. The alkaline compound may be an inorganic compound, an organic compound, or a mixture thereof. Examples of inorganic alkaline compounds include calcium hydroxide, magnesium hydroxide, sodium silicate, potassium silicate, lithium silicate, lithium nitrite, calcium nitrite, etc. Examples of organic alkaline compounds include arginine, lysine, urea, sodium acetate, potassium acetate, and amine compounds. The carbon dioxide absorbent is a CO ２It is preferable that the pH is not easily decreased during the reaction with the carbon dioxide absorbent. One carbon dioxide absorbent may be used alone, or two or more carbon dioxide absorbents may be used in combination.

[0024] Examples of amine compounds include aliphatic amines and aromatic amines. Of the amine compounds, aliphatic amines are preferred because they are easily soluble in water. Examples of aliphatic amines include alkylamines and alkanolamines. Examples of alkylamines include methylamine, dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine, propylamine, and butylamine. Examples of alkanolamines include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), monoisopropanolamine (MIPA), diisopropanolamine (DIPA), triisopropanolamine (TIPA), N-methylethanolamine (MMEA), and N-methyldiethanolamine (MDEA).

[0025] The amine compound may be any of a primary amine, a secondary amine, a tertiary amine, and a quaternary ammonium salt, and may have a cyclic structure. In addition to the above, examples of the amine compound include dicyclohexylamine (DCHA), dimethylcyclohexylamine (DMCHA), polyetheramine (PEA), diglycolamine (DGA), 2-amino-2-methyl-1-propanol (AMP90), n-methyl-2-pyrrolidone (NMP), N,N-dimethylformamide (DMF), pyrrolidine, piperidine, piperazine (PZ), and morpholine. These amine compounds may be used alone or in combination of two or more.

[0026] Amine compounds have the effect of inhibiting corrosion of steel materials such as carbon steel. Therefore, when the hardened cement body is reinforced concrete, amine compounds can inhibit corrosion of the reinforcing bars in the reinforced concrete. It is generally known that when reinforced concrete absorbs carbon dioxide, neutralization progresses and there is a risk of corrosion of the reinforcing bars due to a decrease in pH. By supporting an amine compound on the hardened cement body, this risk can be reduced. From the above perspectives, amine compounds are preferred as carbon dioxide absorbents.

[0027] The content of the carbon dioxide absorbent in the carbon dioxide fixation cement composition is preferably 1 part by mass or more, and more preferably 5 parts by mass or more, per 100 parts by mass of cement contained in the cement composition. When the content of the carbon dioxide absorbent in the carbon dioxide fixation cement composition is equal to or more than the above-mentioned lower limit, the amount of carbon dioxide that can be fixed can be further increased. Furthermore, from the viewpoint of increasing the compressive strength of a carbon dioxide fixation hardened cement body obtained by hardening the carbon dioxide fixation cement composition, the content of the carbon dioxide absorbent in the carbon dioxide fixation cement composition is preferably 0.1 part by mass or more and less than 5 parts by mass, more preferably 0.1 part by mass or more and less than 4 parts by mass, more preferably 0.2 part by mass or more and less than 3.5 parts by mass, more preferably 0.3 part by mass or more and less than 3 parts by mass, more preferably 0.4 part by mass or more and less than 3 parts by mass, more preferably 0.45 part by mass or more and less than 2.5 parts by mass, more preferably 0.45 part by mass or more and less than 2.0 parts by mass, and more preferably 0.45 part by mass or more and less than 1.5 parts by mass, per 100 parts by mass of the carbon dioxide fixation cement composition. Furthermore, from the viewpoint of increasing the compressive strength of a hardened cement body for carbon dioxide fixation obtained by hardening the cement composition for carbon dioxide fixation, it is preferable that the content of the carbon dioxide absorbent in the cement composition for carbon dioxide fixation be within the above range, and that the carbon dioxide absorbing liquid contain carbon dioxide, as described above. The content of the carbon dioxide absorbent in the cement composition for carbon dioxide fixation can be adjusted by the type of cement composition, the type of carbon dioxide absorbent, or a combination thereof.

[0028] [Method for producing a cement composition for immobilizing carbon dioxide] The cement composition for immobilizing carbon dioxide of this embodiment is obtained by kneading a cement composition with a carbon dioxide absorbing liquid. By kneading the carbon dioxide absorbing liquid into the cement composition, the carbon dioxide absorbing liquid is dispersed almost uniformly throughout the cement composition, and the carbon dioxide absorbent in the carbon dioxide absorbing liquid is supported by the cement composition. The method for kneading the cement composition and the carbon dioxide absorbing liquid is not particularly limited, but for example, a method of kneading using a twin-screw forced kneading mixer is used.

[0029] When the carbon dioxide absorbing liquid contains carbon dioxide, carbon dioxide is added to the carbon dioxide absorbing liquid in advance by the method described above, and then the cement composition and the carbon dioxide absorbing liquid are kneaded together.

[0030] [Hardened cement product for carbon dioxide fixation] The hardened cement product for carbon dioxide fixation according to one embodiment of the present invention includes a hardened cement product and a carbonate supported on the hardened cement product. In other words, the hardened cement product for carbon dioxide fixation according to this embodiment is a carbonate-supported product in which a carbonate is supported on the hardened cement product. In this specification, "supported" means that the carbonate is attached to both or either the interior and / or surface of the hardened cement product. In this specification, the hardened cement product functions as a so-called carrier.

[0031] "Hardened cement product" A hardened cement product is a hardened product of a cement composition containing cement and water. In this specification, the term "hardened product" refers to a product that has hardened to the extent that it does not deform when pressed with a finger. The cement composition used is the same as that used in the cement composition for carbon dioxide fixation in the above-mentioned embodiment. The hardened cement product is preferably concrete.

[0032] "Carbonate" Examples of carbonate include reaction products of the carbon dioxide absorbent with carbon dioxide and calcium ions in the cement composition or hardened cement body. Specifically, calcium carbonate (CaCO ３The content of carbonate in the hardened cement for fixation of carbon dioxide of this embodiment is preferably 0 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the hardened cement.

[0033] The hardened cement product for carbon dioxide fixation of this embodiment may contain the above-mentioned carbon dioxide absorbent in addition to the carbonate. The content of the carbon dioxide absorbent in the hardened cement product for carbon dioxide fixation is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 5 parts by mass or more, per 100 parts by mass of the hardened cement product serving as a carrier. When the content of the carbon dioxide absorbent in the hardened cement product for carbon dioxide fixation is equal to or greater than the above-mentioned lower limit, the amount of carbon dioxide that can be fixed can be further increased. Furthermore, from the viewpoint of increasing the compressive strength of the hardened cement body for carbon dioxide fixation, the content of the carbon dioxide absorbent in the hardened cement body for carbon dioxide fixation is preferably 0.1 parts by mass or more but less than 6.5 parts by mass, more preferably 0.1 parts by mass or more but less than 5.2 parts by mass, more preferably 0.2 parts by mass or more but less than 4.6 parts by mass, more preferably 0.3 parts by mass or more but less than 4 parts by mass, more preferably 0.5 parts by mass or more but less than 4 parts by mass, more preferably 0.6 parts by mass or more but less than 2.5 parts by mass, more preferably 0.6 parts by mass or more but less than 2.6 parts by mass, and more preferably 0.6 parts by mass or more but less than 2 parts by mass, per 100 parts by mass of the hardened cement body for carbon dioxide fixation. The content of the carbon dioxide absorbent in the hardened cement body for carbon dioxide fixation can be adjusted by the type of hardened cement body, the type of carbon dioxide absorbent, and a combination thereof.

[0034] [Method for manufacturing hardened cement for carbon dioxide fixation] The hardened cement for carbon dioxide fixation of this embodiment is obtained by kneading the cement composition for carbon dioxide fixation of the above-mentioned embodiment with a carbon dioxide absorbing liquid containing a carbon dioxide absorbent containing carbon dioxide, and hardening the cement containing the carbon dioxide absorbent. As a result, carbonate, which is a reaction product of the carbon dioxide absorbent and carbon dioxide, permeates the interior (pores) of the hardened cement body, and the carbonate is supported in the hardened cement body. Note that after kneading the cement composition for carbon dioxide fixation and the carbon dioxide absorbing liquid, the solvent may be dried.

[0035] <<Carbon Dioxide Immobilization Method>> (First Embodiment) A carbon dioxide immobilization method according to one embodiment of the present invention includes a step of kneading a carbon dioxide absorbing liquid containing a carbon dioxide absorbent into a cement composition (hereinafter referred to as “Step 1A”), a step of hardening the cement composition containing the carbon dioxide absorbent to obtain a carbon dioxide immobilization hardened cement body (hereinafter referred to as “Step 2A”), and a step of bringing the carbon dioxide immobilization hardened cement body into contact with atmospheric air to immobilize carbon dioxide contained in the carbon dioxide immobilization hardened cement body (hereinafter referred to as “Step 3A”).

[0036] In step 1A, a carbon dioxide absorbing liquid containing a carbon dioxide absorbent is mixed with the cement composition to obtain a cement composition for carbon dioxide fixation. The method for mixing the carbon dioxide absorbing liquid with the cement composition is the same as the method described in the method for producing a cement composition for carbon dioxide fixation.

[0037] In step 2A, the carbon dioxide fixation cement composition obtained in step 1A is hardened to obtain a hardened cement product for carbon dioxide fixation. The method for hardening the carbon dioxide fixation cement composition is the same as the method described in the production method for the hardened cement product for carbon dioxide fixation.

[0038] In step 3A, the carbon dioxide contained in the air is absorbed by the carbon dioxide absorbent contained in the hardened cement body by bringing the hardened cement body into contact with the air, thereby enabling the carbon dioxide to be immobilized in the hardened cement body.

[0039] The method for bringing the hardened cement body for carbon dioxide fixation into contact with the atmosphere is not particularly limited, and for example, the hardened cement body for carbon dioxide fixation may be exposed to the atmosphere.

[0040] The time for which the hardened cement body for carbon dioxide fixation is brought into contact with the air is not particularly limited.

[0041] The amount of carbon dioxide fixed in the carbon dioxide fixation hardened cement product can be measured, for example, by pyrolysis gas chromatography mass spectrometry (pyrolysis GC / MS).

[0042] <<Carbon Dioxide Immobilization Method>> (Second Embodiment) A carbon dioxide immobilization method according to one embodiment of the present invention includes the steps of kneading a carbon dioxide absorbing liquid containing a carbon dioxide absorbent, in which carbon dioxide has been dissolved in advance, with a cement composition (hereinafter referred to as “Step 1B”), hardening the cement composition containing the carbon dioxide absorbent to obtain a hardened cement body for carbon dioxide immobilization (hereinafter referred to as “Step 2B”), and bringing the hardened cement body for carbon dioxide immobilization into contact with atmospheric air, thereby immobilizing the carbon dioxide contained in the atmosphere in the hardened cement body for carbon dioxide immobilization (hereinafter referred to as “Step 3B”).

[0043] In step 1B, a carbon dioxide absorbing liquid containing a carbon dioxide absorbent and in which carbon dioxide has been dissolved in advance is mixed with the cement composition to obtain a cement composition for carbon dioxide fixation. The method for dissolving carbon dioxide in the carbon dioxide absorbing liquid in advance is the same as the method explained in the method for producing a cement composition for carbon dioxide fixation. The method for mixing the carbon dioxide absorbing liquid with the cement composition is the same as the method explained in the method for producing a cement composition for carbon dioxide fixation.

[0044] In step 2B, the carbon dioxide fixation cement composition obtained in step 1B is hardened to obtain a hardened cement product for carbon dioxide fixation, similarly to step 2A. The method for hardening the carbon dioxide fixation cement composition is the same as the method described in the production method for the hardened cement product for carbon dioxide fixation.

[0045] In step 3B, similarly to step 3A, the carbon dioxide fixation hardened cement body is brought into contact with the air, whereby the carbon dioxide contained in the air is absorbed by the carbon dioxide absorbent contained in the carbon dioxide fixation hardened cement body, thereby enabling the carbon dioxide to be fixed in the carbon dioxide fixation hardened cement body.

[0046] The carbon dioxide fixation cement composition of this embodiment contains a cement composition and a carbon dioxide absorbing liquid containing a carbon dioxide absorbent, and therefore can absorb (fix) atmospheric carbon dioxide. As a result, the concentration of carbon dioxide in the atmosphere can be reduced. The carbon dioxide fixation hardened cement body of this embodiment supports carbonate, and therefore can absorb (fix) atmospheric carbon dioxide. As a result, the concentration of carbon dioxide in the atmosphere can be reduced. The carbon dioxide fixation method of this embodiment can be applied to hardened cement bodies, rather than to cement-containing compositions in the middle of their production. Therefore, it can be applied to existing hardened cement bodies, and can contribute to reducing the concentration of carbon dioxide in the atmosphere. The carbon dioxide fixation method of this embodiment can fix carbon dioxide using the simple method of impregnation, and therefore does not require large-scale equipment or construction. The carbon dioxide fixation method of this embodiment can fix carbon dioxide using a simple method, and therefore can be repeatedly applied to existing hardened cement bodies.

[0047] The carbon dioxide fixation cement composition, carbon dioxide fixation hardened cement body, and carbon dioxide fixation method of the present invention have been described above. However, the present invention is not limited to the above embodiments and can be modified as appropriate without departing from the spirit of the present invention. For example, the carbon dioxide fixation hardened cement body may be dried, followed by drying the carbon dioxide absorbing liquid. However, in the carbon dioxide fixation method, it is preferable not to dry the carbon dioxide absorbing liquid, as this further increases the carbon dioxide absorption efficiency. For example, if the carbon dioxide absorption effect decreases, the carbon dioxide absorption effect can be restored by re-impregnating the hardened cement body with the carbon dioxide absorbing liquid. The carbon dioxide absorption effect can be determined by measuring the carbon dioxide concentration in the atmosphere surrounding the carbon dioxide fixation hardened cement body. Alternatively, the carbon dioxide fixation hardened cement body can be determined by placing a sample of the carbon dioxide fixation hardened cement body in a container such as a sample bag filled with carbon dioxide and observing the decrease in volume of the container as the sample absorbs carbon dioxide.

[0048] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0049] Experimental Example 1 A cement composition for carbon dioxide fixation was obtained according to the formulation shown in Table 1. Cement (C) and fine aggregate (S) were charged into a twin-screw forced mixer (manufactured by Pacific Engineering Corporation) and dry-mixed. After that, a carbon dioxide absorbing solution to which a lignin-based air-entraining (AE) water-reducing agent had been added was charged and mixed to form a mortar. Next, coarse aggregate (G) was charged and mixed to form a cement composition for carbon dioxide fixation. N-methyldiethanolamine (MDEA) or a secondary amine (MAE) was used as the carbon dioxide absorbent, and a carbon dioxide absorbing solution was prepared in which the concentrations of MDEA and MAE were 0% by mass (water), the MDEA concentration was 5% by mass, the MDEA concentration was 10% by mass, and the MAE concentration was 5% by mass.

[0050]

[0051] <Evaluation> For each of the carbon dioxide fixation cement compositions, the air content was measured according to JIS A 1128:2014 "Pressure-based test method for air content in fresh concrete - Air chamber pressure method," and the slump was measured according to JIS A 1101:2014 "Test method for slump of concrete." The results are shown in Table 2.

[0052]

[0053] The results shown in Table 2 show that when a lignin-based admixture was used, the slump was lower with MDEA than with Control.

[0054] [Experimental Example 2] A cement composition for fixation of carbon dioxide was obtained with the formulation shown in Table 3. The method of mixing the cement composition was the same as in Example 1, except for the chemical admixture used. In Example 2, a polycarboxylic acid-based chemical admixture was used as the chemical admixture.

[0055]

[0056] <Evaluation> For each of the carbon dioxide fixation cement compositions, the air content was measured according to JIS A 1128:2014 "Pressure-based test method for air content in fresh concrete - Air chamber pressure method," and the slump was measured according to JIS A 1101:2014 "Test method for slump of concrete." The results are shown in Table 3.

[0057]

[0058] From the results shown in Table 3, it was found that when a polycarboxylic acid-based admixture was used, the slump increased in MAE compared to Control 1. It was also found that when a polycarboxylic acid-based admixture was used, the change in slump was smaller than when a lignin-based admixture was used.

[0059] [Experimental Example 3] A cement composition was prepared according to the formulation shown in Table 5, and a carbon dioxide absorbing liquid containing a carbon dioxide absorbent was added to the cement composition to obtain a cement composition for carbon dioxide fixation. The cement composition was mixed in the same manner as in Example 1. N-methyldiethanolamine (MDEA) or a secondary amine (MAE) was used as the carbon dioxide absorbent, and a carbon dioxide absorbing liquid was prepared in which the concentrations of MDEA and MAE were 0 mass% (water), the MDEA concentration was 5 mass%, and the MAE concentration was 5 mass%.

[0060]

[0061] <Evaluation> A bleeding test was conducted on each of the above cement compositions for carbon dioxide fixation according to the Japan Concrete Institute's "Method for testing concrete bleeding using a small container" (JCI-S-015-2018). The results are shown in Figure 1. In Figure 1, the vertical axis represents the amount of bleeding, and the horizontal axis represents the elapsed time (minutes). The results shown in Figure 1 show that the amount of bleeding decreased when MDEA was used, but increased when MAE was used.

[0062] [Experimental Example 4] In the same manner as in Experimental Example 1, four types of cement compositions for fixing carbon dioxide were obtained.

[0063] <Evaluation> The setting rate of each of the carbon dioxide fixation cement compositions was measured according to JIS A 1147:2019 "Test method for setting time of concrete." The results are shown in Figure 2. From the results shown in Figure 2, it was found that the setting rate tends to be delayed both when MDEA and when MAE were used. When MDEA was used, it was found that the setting rate was significantly delayed at 10% by mass. When MAE was used, it was found that the setting rate was delayed even at 5% by mass.

[0064] [Experimental Example 5] In the same manner as in Experimental Example 2, four types of cement compositions for fixing carbon dioxide were obtained.

[0065] <Evaluation> The setting rate of each of the carbon dioxide fixation cement compositions was measured according to JIS A 1147:2019 "Test method for setting time of concrete." The results are shown in Figure 3. From the results shown in Figure 3, it was found that the setting rate tends to be delayed both when MDEA and when MAE were used. When MDEA was used, it was found that a significant delay occurred at 10% by mass. When MAE was used, it was found that a delay occurred even at 5% by mass. It was also found that when a lignin-based admixture was used, the setting rate tended to be significantly delayed.

[0066] Experimental Example 6 A cement composition was prepared according to the formulation shown in Table 6, and a carbon dioxide absorbing liquid containing a carbon dioxide absorbent was added to the cement composition to obtain a cement composition for carbon dioxide fixation. A Hobart mixer was used to mix the cement composition. Cement (C) was added, and then water (W) and the carbon dioxide absorbent were added and kneaded to obtain a cement paste. The cement composition for carbon dioxide fixation was then hardened to obtain a hardened cement product for carbon dioxide fixation. N-methyldiethanolamine (MDEA) was used as the carbon dioxide absorbent, and carbon dioxide absorbing liquids were prepared with MDEA concentrations of 0 mass% (water) and 5 mass%, 10 mass%, 20 mass%, and 30 mass%.

[0067]

[0068] <Evaluation> The hardened cement for carbon dioxide fixation was sealed and cured for 28 days, crushed to a size of about 10 mm, and then left in the air. After 4 months and 10 months, a randomly selected sample was crushed from each hardened cement for carbon dioxide fixation and 10 mg of the sample was taken out and analyzed for calcium carbonate (CaCO ) in the hardened cement for carbon dioxide fixation using a thermogravimetric and differential thermal analyzer (TG / DTA). ３ The results are shown in Figure 4. From the results shown in Figure 4, it can be seen that the higher the concentration of MDEA, the lower the amount of CaCO in the hardened cement paste for carbon dioxide fixation. ３ The amount of calcium carbonate produced is given by the mass difference (mass loss) between the mass at 500°C and the mass at 800°C in TG / DTA.

[0069] [Experimental Example 7] A cement composition for carbon dioxide fixation was obtained according to the formulation shown in Table 7. Using a Hobart mixer, cement (C) and a carbon dioxide absorbing liquid were mixed to obtain a cement composition for carbon dioxide fixation. The cement composition for carbon dioxide fixation was then hardened to obtain a hardened cement for carbon dioxide fixation. N-methyldiethanolamine (MDEA) was used as the carbon dioxide absorbent, and carbon dioxide absorbing liquids were prepared with MDEA concentrations of 0 mass % (water as a control) and 10 mass %. Carbon dioxide was also dissolved in the carbon dioxide absorbing liquid by bubbling. The amount of carbon dioxide dissolved was 0.6 mol (CO ２ / mdea mol).

[0070]

[0071] <Evaluation> The hardened cement for carbon dioxide fixation was sealed and cured for 7 days, then crushed and 10 mg of each was taken out. The calcium carbonate (CaCO ) in the hardened cement for carbon dioxide fixation was measured using TG / DTA. ３ ) content was measured. The evaluation method was the same as in Example 6. The results are shown in Figure 5. From the results shown in Figure 5, it can be seen that by using a carbon dioxide absorbing solution in which carbon dioxide is dissolved, a larger amount of carbon dioxide is fixed. In other words, the amount of carbon dioxide fixed changes depending on the amount of carbon dioxide dissolved.

[0072] [Experimental Example 8] A cement composition for carbon dioxide fixation was obtained according to the formulation shown in Table 8. Cement (C) and a carbon dioxide absorbing liquid were mixed using a Hobart mixer to obtain a cement composition for carbon dioxide fixation. An SS400 steel material with an outer diameter of 25 mm and a thickness of 2.5 mm was set in the sample holder of the measuring jig, and the exposed surface of the steel material (1 cm ２ ), and the carbon dioxide fixation cement composition was hardened to provide a hardened cement body for carbon dioxide fixation on the surface of the steel material. N-methyldiethanolamine (MDEA) was used as the carbon dioxide absorbent, and a carbon dioxide absorbing solution was prepared with an MDEA concentration of 10 mass %. Carbon dioxide was also dissolved in the carbon dioxide absorbing solution by bubbling. The amount of carbon dioxide dissolved was 0.6 mol (CO ２ / mdea mol).

[0073]

[0074] <Evaluation> After the hardened cement body for carbon dioxide fixation was sealed and cured for seven days, the polarization resistance of the steel material in contact with the hardened cement body for carbon dioxide fixation was measured using a potentiostat (HZ-PRO, manufactured by Hokuto Denko Corporation). The measurement was performed by immersing the hardened cement body in the same solution as the carbon dioxide absorption solution used for mixing, and using a platinum rod as the counter electrode and a silver-silver chloride electrode as the reference electrode, by the electrochemical impedance method. The results are shown in Figure 6. From the results shown in Figure 6, it was confirmed that the polarization resistance exceeded 130 kΩ, and that the internal steel material was passivated even when carbon dioxide was fixed in the initial stage.

[0075] [Experimental Example 9] A cement composition for carbon dioxide fixation was obtained with the formulation shown in Table 9. Using a Hobart mixer, cement (C) and a carbon dioxide absorbing liquid were mixed to obtain a cement composition for carbon dioxide fixation. The cement composition for carbon dioxide fixation was then hardened to obtain a hardened cement body for carbon dioxide fixation. Using 1-(2-hydroxyethyl)piperazine (HEPZ) as the carbon dioxide absorbent, carbon dioxide absorbing liquids were prepared with HEPZ concentrations of 0 mass % (water as a control), 2 mass %, and 10 mass %. Carbon dioxide was also dissolved by bubbling into the carbon dioxide absorbing liquids with formulation names PC2 and P10C. The amount of carbon dioxide dissolved was 1.5 mol (CO ２ / HEPZ mol).

[0076]

[0077] <Evaluation> After the hardened cement for carbon dioxide fixation was sealed and cured for 14 days, the compressive strength of the hardened cement for carbon dioxide fixation was measured using a method conforming to JIS A 1108:2018 "Testing Method for Compressive Strength of Concrete." Measurements were performed using a SHIMADZU UH-X. The results are shown in Figure 7. The results shown in Figure 7 indicate that the compressive strength of the hardened cement for carbon dioxide fixation can be increased by reducing the amine concentration in the cement composition. It was also found that the compressive strength of the hardened cement for carbon dioxide fixation can be increased by using a carbon dioxide absorbing solution in which carbon dioxide has been dissolved. In addition, X-ray diffraction (XRD) measurements were performed on the hardened cement for carbon dioxide fixation of Blend Examples P2 and P2C. X-ray diffraction measurements were performed using a Rigaku Smart Lab. The results of the X-ray analysis are shown in Table 10.

[0078]

[0079] From the results shown in Table 10, it can be seen that by using a carbon dioxide absorbing solution in which carbon dioxide is dissolved, C, the main component of cement in the hardened cement for carbon dioxide fixation, can be reduced. ３It was found that S decreased. In other words, by using a carbon dioxide absorbing liquid in which carbon dioxide is dissolved, the progress of the cement hydration reaction is less likely to be hindered. Furthermore, it was found that by using a carbon dioxide absorbing liquid in which carbon dioxide is dissolved, calcite (calcium carbonate) increased. In other words, by using a carbon dioxide absorbing liquid in which carbon dioxide is dissolved, the amount of carbon dioxide adsorbed by the hardened cement body for carbon dioxide fixation increases.

[0080] From the above, it was found that the carbon dioxide fixation method of the present invention can fix carbon dioxide in a hardened cement body for carbon dioxide fixation. In addition, it was found that the carbon dioxide absorbing liquid used in the carbon dioxide fixation method of the present invention can further enhance the anticorrosion effect of the hardened cement body for carbon dioxide fixation. Furthermore, it was found that by adding carbon dioxide to the carbon dioxide absorbing liquid used in the carbon dioxide fixation method of the present invention, the compressive strength of the hardened cement body for carbon dioxide fixation can be further increased.

Claims

1. A cement composition for fixing carbon dioxide, comprising a cement composition and a carbon dioxide absorbing liquid containing a carbon dioxide absorbent.

2. The cement composition for fixing carbon dioxide according to claim 1, wherein the carbon dioxide absorbing liquid has a pH of 8.0 or more at 20°C.

3. The cement composition for fixing carbon dioxide according to claim 1, wherein the carbon dioxide absorbing liquid contains carbon dioxide.

4. A cement composition for fixing carbon dioxide as described in claim 1, wherein the content of the carbon dioxide absorbing liquid is 0.01 parts by mass or more and 100 parts by mass or less per 100 parts by mass of cement contained in the cement composition.

5. The cement composition for fixing carbon dioxide according to claim 1, wherein the carbon dioxide absorbent is an alkaline compound.

6. The cement composition for fixing carbon dioxide according to claim 1, wherein the content of the carbon dioxide absorbent is 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the cement composition for fixing carbon dioxide.

7. The cement composition for fixation of carbon dioxide according to claim 1, wherein the content of the carbon dioxide absorbent is 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the cement composition for fixation of carbon dioxide, and the carbon dioxide absorbing liquid contains carbon dioxide.

8. The cement composition for fixation of carbon dioxide according to claim 1, wherein the carbon dioxide absorbent is an amine compound, the content of the carbon dioxide absorbent is 0.1 parts by mass or more and less than 5 parts by mass per 100 parts by mass of the cement composition for fixation of carbon dioxide, and the carbon dioxide absorbing liquid contains carbon dioxide.

9. A hardened cement product for fixing carbon dioxide, comprising: a hardened cement product; and a carbonate supported on the hardened cement product.

10. The hardened cement body for carbon dioxide fixation according to claim 9, wherein the content of the carbonate is from 0 to 50 parts by mass per 100 parts by mass of the hardened cement body.

11. The hardened cement material for carbon dioxide fixation according to claim 9, wherein the hardened cement material is concrete.

12. A method for fixing carbon dioxide, comprising the steps of: mixing a carbon dioxide absorbing liquid containing a carbon dioxide absorbent with a cement composition; hardening the cement composition containing the carbon dioxide absorbent to obtain a hardened cement body for fixing carbon dioxide; and bringing the hardened cement body for fixing carbon dioxide into contact with atmospheric air, thereby fixing the carbon dioxide contained in the atmosphere in the hardened cement body for fixing carbon dioxide.

13. A method for fixing carbon dioxide, comprising the steps of: kneading a carbon dioxide absorbing liquid containing a carbon dioxide absorbent, in which carbon dioxide has been dissolved in advance, into a cement composition; hardening the cement composition containing the carbon dioxide absorbent to obtain a hardened cement body for fixing carbon dioxide; and bringing the hardened cement body for fixing carbon dioxide into contact with atmospheric air, thereby fixing the carbon dioxide contained in the atmosphere in the hardened cement body for fixing carbon dioxide.

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