Cement hardened body for detecting carbon dioxide fixation and method for detecting carbon dioxide fixation range

Abstract

To provide a cement hardened body for detecting carbon dioxide fixation capable of detecting the progress of fixation of CO2 even in a pH range of 8-11, and a method for detecting a carbon dioxide fixation range using the same.SOLUTION: A cement hardened body for detecting carbon dioxide fixation comprises a cement hardened body and a carbon dioxide fixation range indicating solution which is carried on the cement hardened body and exhibits a color reaction in a pH range of 7-13.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a hardened cement material for detecting carbon dioxide fixation, and a method for detecting the extent of carbon dioxide fixation using the hardened cement material. [Background technology]

[0002] In order to prevent global warming, there is a worldwide demand for a reduction in carbon dioxide (hereinafter, also referred to as "CO2") emissions. In the field of construction materials, methods have been proposed for reducing the amount of CO2 generated during concrete production by reducing the amount of cement, as well as technologies related to concrete that can fix (absorb) CO2 (see, for example, Patent Document 1).

[0003] Although it is necessary to understand the progress of CO2 fixation in concrete, the appearance of the concrete does not change even when CO2 is fixed, so the progress of CO2 fixation cannot be grasped visually. The phenomenon in which concrete fixes CO2 is called "carbonation." The method for determining the depth of carbonation is specified in JIS A 1152:2018 "Method for measuring the carbonation depth of concrete" (hereinafter referred to as the "phenolphthalein method"). This method involves splitting the concrete, spraying the phenolphthalein solution specified in JA.5 of JIS K 8001 onto the split surface, and determining the areas that are not in contact as the neutralized areas. The phenolphthalein method uses the color reaction of phenolphthalein, and the areas where the pH of the pore solution in the concrete has dropped to about 8 due to the absorption of CO2 are determined to be the neutralized range. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4822373 Summary of the Invention [Problem to be solved by the invention]

[0005] When concrete is in the process of absorbing and fixing CO2, the pH of the pore solution in the concrete gradually decreases. The final pH value is generally around pH 8, but it varies depending on the composition of the concrete. In other words, for all concrete, the neutralization range determined by the phenolphthalein method and the absorption and fixation range of CO2 do not necessarily match, so the phenolphthalein method cannot determine the fixation range of CO2. In addition, the phenolphthalein method is a test method that involves slight destruction of the concrete structure, as cores taken from the concrete structure and drill powder from the holes are used as samples. Therefore, the phenolphthalein method damages the concrete structure for the test, and requires repairs to the concrete structure after the test is completed.

[0006] It is also possible to perform thermal analysis (TG-DTA) on a sample of crushed hardened cement to determine the presence of calcium carbonate in the sample, and to determine the amount of fixed CO2 based on the results. However, this method also requires obtaining samples from the concrete structure, which involves slight destruction of the concrete structure. In addition, analytical equipment cannot be used on-site, making it difficult to make an early determination on-site.

[0007] The present invention has been made in consideration of the above circumstances, and aims to provide a hardened cement product for detecting carbon dioxide fixation that can detect the progress of CO2 fixation even in a pH range of 8 to 11, and a method for detecting the range of carbon dioxide fixation using the same. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention has the following aspects. [1] A hardened cement product for detecting carbon dioxide fixation, comprising: a hardened cement product; and a carbon dioxide fixation range indicator that exhibits a color reaction in the pH range of 7 to 13 and is supported on the hardened cement product. [2] The carbon dioxide fixation detection cement hardened body according to [1], wherein the content of the carbon dioxide fixation range indicator liquid is 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the cement hardened body. [3] The hardened cement body for detecting carbon dioxide fixation according to [1] or [2], which contains a carbon dioxide absorbent supported on the hardened cement body. [4] The hardened cement body for detecting carbon dioxide fixation according to [3], wherein the content of the carbon dioxide absorbent is 0 parts by mass or more and 20 parts by mass or less per 100 parts by mass of the hardened cement body. [5] The hardened cement body for detecting carbon dioxide fixation according to any one of [1] to [4], wherein the hardened cement body is concrete. [6] A step of forming the hardened cement body for detecting carbon dioxide fixation according to any one of [1] to [5] into a plate or column shape; a step of sealing the surfaces of the hardened cement body for detecting carbon dioxide fixation other than the two opposing end surfaces; and placing the carbon dioxide fixation detection hardened cement body so that one of the two end faces is flush with a carbon dioxide absorption surface of a target concrete structure, When the carbon dioxide fixation detection hardened cement body is in a plate shape, the two end faces are end faces along a short side direction or a long side direction of the carbon dioxide fixation detection hardened cement body, When the carbon dioxide fixation detection hardened cement body is columnar, the two end faces are the top and bottom faces of the carbon dioxide fixation detection hardened cement body. [7] The method for detecting the range of carbon dioxide fixation according to [6], wherein the cement hardened body constituting the carbon dioxide fixation detection cement hardened body has the same composition as that of the concrete structure. Effect of the Invention

[0009] According to the present invention, it is possible to provide a hardened cement product for detecting carbon dioxide fixation, which is capable of detecting the progress of CO2 fixation even in a pH range of 8 to 11, and a method for detecting the range of carbon dioxide fixation using the same. [Brief description of the drawings]

[0010] [Figure 1] FIG. 2 is a perspective view showing a method for detecting a carbon dioxide fixation range according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a perspective view showing a method for detecting a carbon dioxide fixation range according to an embodiment of the present invention. [Diagram 3] FIG. 2 is a diagram showing the color development state of hardened cement bodies in Examples and Comparative Examples. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] [Hardened cement body for detecting carbon dioxide fixation] The hardened cement product for detecting carbon dioxide fixation according to one embodiment of the present invention includes a hardened cement product and a carbon dioxide fixation range indicator that shows a color reaction in the pH range of 7 to 13 and is supported on the hardened cement product. In this specification, the term "supported" means that the carbon dioxide fixation range indicator is attached to both or either one of the inside and the surface of the hardened cement body. In this specification, the hardened cement body functions as a so-called carrier.

[0012] "Hardened cement body" The hardened cement product is a hardened product of a cement composition containing cement and water. In this specification, the term "cured product" refers to a product that has cured to the extent that it does not deform when pressed with a finger. The hardened cement material is preferably concrete.

[0013] "Cement Composition" The cement composition contains cement and water. Examples of the cement composition 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)), mixed with water. In this specification, mortar refers to a mixture of cement and fine aggregate (sand) kneaded with water. In this specification, cement milk refers to cement mixed with water only. In this specification, cement refers to a powder that is made primarily from limestone, clay, silica, iron oxide raw materials, etc., and 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) having a diameter of more than 5 mm, and the diameter of the coarse aggregate is preferably 25 mm or less.

[0014] The mixing ratio of cement, fine aggregate, and coarse aggregate in concrete can be appropriately determined depending on the strength required for the concrete. The mixing ratio of cement, fine aggregate, and coarse aggregate is preferably, for example, 1 part cement, 2 to 3 parts fine aggregate, and 4 to 6 parts coarse aggregate by mass ratio.

[0015] The mixing ratio of cement to fine aggregate in the mortar can be appropriately determined 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 ratio.

[0016] "Carbon dioxide fixed range indicator" The carbon dioxide fixation range indicator is a compound that shows a color reaction in the pH range of 7 to 13. Examples of the carbon dioxide fixation range indicator include a color indicator such as crystal violet, thymolphthalein, or alizarin yellow R, which is used alone or in a mixed solution of multiple indicators whose concentrations are adjusted so as to be visible, depending on the pH range corresponding to the CO2 fixation range according to the properties of the hardened cement body.

[0017] The content of the carbon dioxide fixation range indicator in the carbon dioxide fixation detection hardened cement body is preferably 0.01 to 5 parts by mass, more preferably 0.01 to 1 part by mass, and even more preferably 0.01 to 0.1 parts by mass, relative to 100 parts by mass of the carrier hardened cement body. When the content of the carbon dioxide fixation range indicator in the carbon dioxide fixation detection hardened cement body is equal to or more than the lower limit, the coloring is clear and the judgment is easy. When the content of the carbon dioxide fixation range indicator in the carbon dioxide fixation detection hardened cement body is equal to or less than the upper limit, the cost of the reagent used can be suppressed.

[0018] "Carbon dioxide absorbent" The hardened cement body for detecting carbon dioxide fixation of this embodiment preferably contains a carbon dioxide absorbent. The carbon dioxide absorbent is contained in the hardened cement body for detecting carbon dioxide fixation and absorbs carbon dioxide in the atmosphere. Therefore, carbon dioxide in the atmosphere is taken in the hardened cement body for detecting carbon dioxide fixation formed by hardening the cement composition containing the carbon dioxide absorbent, and the carbon dioxide concentration in the atmosphere is reduced. In other words, carbon dioxide in the atmosphere can be fixed in the hardened cement body for detecting carbon dioxide fixation. The carbon dioxide absorbent may be a solid or a liquid at room temperature and pressure. In this specification, "normal 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).

[0019] The carbon dioxide absorbent may be, for example, an alkaline compound. Here, the term "alkaline compound" refers to a compound that has a pH of greater 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, and calcium nitrite. Examples of the organic alkaline compound include arginine, lysine, urea, sodium acetate, potassium acetate, and amine compounds. It is preferable that the carbon dioxide absorbent is one that is less likely to cause a decrease in pH when reacting with CO2. The carbon dioxide absorbent may be used alone or in combination of two or more kinds.

[0020] Examples of the amine compounds include aliphatic amines and aromatic amines. As the amine compound, an aliphatic amine is preferred since it is easily soluble in water. Examples of the aliphatic amine 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).

[0021] 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 amine compounds 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, morpholine, and the like. These amine compounds may be used alone or in combination of two or more.

[0022] 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 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, the risk can be reduced. From the above viewpoints, amine compounds are preferable as carbon dioxide absorbents.

[0023] The content of the carbon dioxide absorbent in the carbon dioxide fixation detection hardened cement body is preferably 0 to 20 parts by mass, more preferably 0.01 to 20 parts by mass, even more preferably 0.1 to 20 parts by mass, and most preferably 1 to 20 parts by mass. When the content of the carbon dioxide absorbent in the carbon dioxide fixation detection hardened cement body is equal to or more than the lower limit, the amount of carbon dioxide that can be fixed can be further increased. The content of the carbon dioxide absorbent in the hardened cement body for detecting carbon dioxide fixation can be adjusted by the type of hardened cement body, the type of carbon dioxide absorbent, or a combination thereof.

[0024] The hardened cement body for detecting carbon dioxide fixation of this embodiment may contain a carbonate which is a reaction product between a carbon dioxide absorbent and carbon dioxide or calcium ions in the hardened cement body. A specific example of the carbonate is calcium carbonate (CaCO3).

[0025] The hardened cement body for detecting carbon dioxide fixation of this embodiment may contain white cement in order to make it easier to distinguish the color state of the carbon dioxide fixation range indicator.

[0026] According to the present embodiment, the hardened cement body for detecting carbon dioxide fixation contains a hardened cement body and a carbon dioxide fixation range indicator liquid that shows a color reaction in the pH range of 7 to 13 supported on the hardened cement body, and therefore the color changes as the pH decreases in the CO2 fixation range, and the CO2 fixation range can be detected from the range where the color changes. Therefore, the progress of CO2 fixation can be detected even in the pH range of 8 to 11.

[0027] [Method of manufacturing hardened cement for detecting carbon dioxide fixation] As a method for producing the hardened cement body for detecting carbon dioxide fixation of this embodiment, for example, the following two production methods can be mentioned.

[0028] (First manufacturing method) The method for producing a hardened cement body for detecting carbon dioxide fixation of this embodiment includes a step of applying a carbon dioxide fixation range indicating liquid to the surface of the hardened cement body to impregnate the hardened cement body with the carbon dioxide fixation range indicating liquid. The method for producing a hardened cement body for detecting carbon dioxide fixation of this embodiment may include a step of applying a carbon dioxide absorbing liquid containing a carbon dioxide absorbent to the surface of the hardened cement body to impregnate the hardened cement body with the carbon dioxide absorbing liquid containing a carbon dioxide absorbent.

[0029] The carbon dioxide absorbing liquid is a liquid containing a carbon dioxide absorbent capable of absorbing carbon dioxide and a solvent. When the carbon dioxide absorbent is a liquid, the carbon dioxide absorbing liquid does not need to contain a solvent described later.

[0030] 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, based on the total mass of the carbon dioxide absorbing liquid. When the content of the carbon dioxide absorbent is equal to or more than the lower limit, the amount of carbon dioxide that can be fixed can be further increased.

[0031] Examples of the solvent contained in the carbon dioxide absorbing liquid include water and organic solvents such as ethanol. As the solvent, water is preferable because it is difficult 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.

[0032] 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, based on 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 the carbon dioxide absorbing liquid impregnated into the cement composition can be 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 increased. Therefore, the amount of carbon dioxide that can be fixed can be increased.

[0033] The viscosity of the carbon dioxide absorbing liquid at 25°C is, for example, preferably 0.1 to 50 mPa·s, more preferably 0.5 to 25 mPa·s, and even more preferably 0.5 to 10 mPa·s. When the viscosity of the carbon dioxide absorbing liquid at 25°C is equal to or higher than the above lower limit, the amount of carbon dioxide absorbent supported in the hardened cement body can be further increased. When the viscosity of the carbon dioxide absorbing liquid at 25°C is equal to or lower than the above upper limit, the amount of carbon dioxide absorbing liquid impregnated in the hardened cement body can be further increased. The viscosity of the carbon dioxide absorbing liquid at 25°C can be obtained, for example, by setting the temperature of the measurement target to 25°C, using the No. 2 rotor of a B-type viscometer at a rotation speed of 60 rpm, and reading the value 30 seconds after the rotor starts to rotate.

[0034] The pH of the carbon dioxide absorbing liquid at 20° C. is, for example, preferably 7.0 or more, more preferably 8.5 or more, and even more preferably 10.0 or more. When the pH of the carbon dioxide absorbing liquid at 20° C. is equal to or more than the lower limit, the rate of absorbing carbon dioxide 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, for example, 14.0 in consideration of ease of handling. The pH of the carbon dioxide absorbing solution at 20°C can be measured by adjusting the measurement target to 20°C and using a pH meter (for example, compact pH meter LAQUAtwin (registered trademark) pH-22B manufactured by Horiba, Ltd.).

[0035] (Second manufacturing method) The method for producing a hardened cement product for detecting carbon dioxide fixation of this embodiment includes a kneading step of mixing a carbon dioxide fixation range indicator liquid with a cement composition to prepare a cement composition for carbon dioxide fixation, and a hardening step of hardening the cement composition for carbon dioxide fixation containing the carbon dioxide fixation range indicator liquid.

[0036] "Kneading process" The carbon dioxide fixation range indicator liquid is mixed with the cement composition to obtain the carbon dioxide fixation range indicator liquid. By mixing the carbon dioxide fixation range indicator with the cement composition, the carbon dioxide fixation range indicator liquid is dispersed almost uniformly throughout the cement composition, and the carbon dioxide fixation range indicator liquid is supported by the cement composition. The method for mixing the cement composition and the carbon dioxide fixation range indicator liquid is not particularly limited, but for example, a method of mixing them using a twin-shaft forced mixing mixer is used.

[0037] In the mixing step, the cement composition may be mixed with a carbon dioxide absorbent and a carbon dioxide fixation range indicator. In order to knead the carbon dioxide absorbent into the cement composition, the carbon dioxide absorbing liquid may be used. The carbon dioxide absorbing liquid has physical properties such as viscosity that allow it to be kneaded into the cement composition.

[0038] "Curing process" In the hardening step, the cement composition for carbon dioxide fixation containing the carbon dioxide fixation range indicator liquid is hardened to obtain a hardened cement body for detecting carbon dioxide fixation. As a result, the carbon dioxide fixation range indicator liquid permeates into the inside (pores) of the hardened cement body and is supported in the hardened cement body. When the cement composition also contains a carbon dioxide absorbent, carbonate, which is a reaction product between the carbon dioxide absorbent and carbon dioxide or calcium ions in the hardened cement body, permeates into the inside (pores) of the hardened cement body and is supported in the hardened cement body.

[0039] [Method of detecting the range of carbon dioxide fixation] A method for detecting the range of carbon dioxide fixation according to one embodiment of the present invention includes a step of forming the cement hardened body for carbon dioxide fixation detection of the above-described embodiment into a plate shape (hereinafter referred to as the "first step"), a step of sealing the faces of the cement hardened body for carbon dioxide fixation detection other than the two opposing end faces (hereinafter referred to as the "second step"), and a step of positioning the cement hardened body for carbon dioxide fixation detection so that one of the two end faces is on the same plane as the carbon dioxide absorption surface of a target concrete structure (hereinafter referred to as the "third step").

[0040] Hereinafter, the method for detecting the carbon dioxide fixation range of this embodiment will be described with reference to FIG. 1 and FIG.

[0041] "First step" In the first step, the hardened cement body for detecting carbon dioxide fixation is formed into, for example, a plate-like hardened cement body for detecting carbon dioxide fixation 1 as shown in Fig. 1. In Fig. 1, the shape of the hardened cement body for detecting carbon dioxide fixation 1 in a plan view is rectangular. The hardened cement body for carbon dioxide fixation detection 1 is obtained by machining or otherwise processing the hardened cement body for carbon dioxide fixation detection obtained by the above-mentioned manufacturing method for a hardened cement body for carbon dioxide fixation detection to a predetermined size and shape. Alternatively, the hardened cement body for carbon dioxide fixation detection 1 may be obtained by the above-mentioned manufacturing method for a hardened cement body for carbon dioxide fixation detection, and the hardened cement body for carbon dioxide fixation detection may be used as the hardened cement body for carbon dioxide fixation detection 1.

[0042] In the first step, the carbon dioxide fixation detection hardened cement body may be a square-shaped carbon dioxide fixation detection hardened cement body in a plan view, or a columnar carbon dioxide fixation detection hardened cement body.

[0043] In addition, the hardened cement body constituting the carbon dioxide fixation detection hardened cement body preferably has the same composition as that of the concrete skeleton described below.

[0044] "Second step" In the second step, for example, as shown in Fig. 1, faces 1c, 1d, 1e, and 1f other than two end faces 1a and 1b facing each other along the short side of the hardened cement body 1 for carbon dioxide fixation detection are sealed with a sealant 10. This results in a state in which only the two end faces 1a and 1b facing each other along the short side of the hardened cement body 1 for carbon dioxide fixation detection are exposed as shown in Fig. 1. These two end faces 1a and 1b become CO2 absorption faces of the hardened cement body 1 for carbon dioxide fixation detection.

[0045] The sealing material 10 is not particularly limited as long as it is transparent and prevents the transmission of gas and water, but examples thereof include glass, acrylic resin, polyvinylidene chloride resin, vinyl fluoride resin, polyethylene resin, polypropylene resin, PET resin, etc.

[0046] "The third step" In the third step, as shown in Fig. 2, the hardened cement body 1 for carbon dioxide fixation detection is arranged so that one of the two end faces 1a, 1b (end face 1a in Fig. 2) is flush with the surface (carbon dioxide absorption surface) 100a of the target concrete skeleton 100. In Fig. 3, the hardened cement body 1 for carbon dioxide fixation detection is attached to the side surface 100b of the concrete skeleton 100, and the hardened cement body 1 for carbon dioxide fixation detection is arranged so that the end face 1a is flush with the carbon dioxide absorption surface 100a of the concrete skeleton 100.

[0047] The concrete structure 100 is a concrete structure in which it is desired to detect the fixation status of CO2.

[0048] According to the method for detecting the carbon dioxide fixation range of this embodiment, the hardened cement body 1 for carbon dioxide fixation detection absorbs CO2 from the end face 1a toward the end face 1b along the longitudinal direction of the hardened cement body 1 for carbon dioxide fixation detection, so that the fixed range of CO2 can be detected by observing the faces 1c, 1d, 1e, and 1f other than the end faces 1a and 1b of the hardened cement body 1 for carbon dioxide fixation detection. In detail, in the fixed range of CO2, the pH of the hardened cement body 1 for carbon dioxide fixation detection decreases, so that the color of the carbon dioxide fixation range indicator changes, so that the fixed range of CO2 can be detected from the changed range.

[0049] When the concrete structure 100 in which the CO2 fixation range is to be detected is newly constructed, the hardened cement body 1 for carbon dioxide fixation detection is separately manufactured at the time of construction of the concrete structure 100. Then, as described above, the hardened cement body 1 for carbon dioxide fixation detection is arranged so that the end face 1a is on the same plane as the carbon dioxide absorption face 100a of the concrete structure 100.

[0050] On the other hand, when the concrete body 100 for which the CO2 fixation range is to be detected is already installed, a part of the existing concrete body 100 is cut to obtain a concrete core. The concrete core is then impregnated with a carbon dioxide fixation range indicator liquid to obtain a hardened cement body 1 for carbon dioxide fixation detection. Next, the faces 1c, 1d, 1e, and 1f other than the two end faces 1a and 1b facing each other along the short side direction of the hardened cement body 1 for carbon dioxide fixation detection are sealed with a sealant 10. Next, the hardened cement body 1 for carbon dioxide fixation detection is placed in the cut portion of the concrete body 100 so that the end face 1a is on the same plane as the carbon dioxide absorption face 100a of the concrete body 100.

[0051] In this embodiment, the carbon dioxide fixation detection hardened cement body is plate-shaped, but this embodiment is not limited to this. In this embodiment, when the carbon dioxide fixation detection hardened cement body is columnar, the two end faces are the top and bottom faces of the carbon dioxide fixation detection hardened cement body.

[0052] According to the method for detecting the range of carbon dioxide fixation of this embodiment, the color of the hardened cement body for detecting carbon dioxide fixation changes as the pH decreases in the range of CO2 fixation, so the range of CO2 fixation can be detected from the range where the color changes. Therefore, the progress of CO2 fixation can be detected even in the pH range of 8 to 11.

[0053] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims. EXAMPLES

[0054] The present invention will be described in more detail below using examples and comparative examples, but the present invention is not limited to these examples.

[0055] [Example 1] 0.3 g of crystal violet was dissolved in 20 mL of ethanol, and 80 mL of distilled water was added to prepare 100 mL of solution. 50 mL of the above solution was weighed out, and the solution was mixed with 100 g of white cement and N-methyldiethanolamine (MDEA) as a carbon dioxide absorbent to prepare a cement composition. The content of N-methyldiethanolamine was 5% by mass of the total mass of the cement composition. After the bleeding of the water was stopped, the obtained cement composition was poured into a form and allowed to harden, thereby obtaining a hardened cement body. The hardened cement was placed in an environment with a CO2 concentration of 5%, at 20°C and 60% RH to accelerate carbonation, and the color change was confirmed. The results are shown in Fig. 3. In Fig. 3, the hardened cement body of Example 1 is shown second from the right.

[0056] [Example 2] A hardened cement body was obtained in the same manner as in Example 1, except that the content of N-methyldiethanolamine in the cement composition was 10 mass %. This hardened cement body was carbonated in the same manner as in Example 1, and the color change was confirmed. The results are shown in Fig. 3. In Fig. 3, the hardened cement body of Example 2 is shown first from the right.

[0057] [Comparative Example 1] A hardened cement material was obtained in the same manner as in Example 1, except that N-methyldiethanolamine was not included. This hardened cement body was carbonated in the same manner as in Example 1, and the color change was confirmed. The results are shown in Fig. 3. In Fig. 3, the hardened cement body of Comparative Example 1 is shown in the third from the right.

[0058] [Comparative Example 2] A hardened cement body was obtained in the same manner as in Example 1, except that the aqueous crystal violet solution was not used. This hardened cement body was carbonated in the same manner as in Example 1, and the color change was confirmed. The results are shown in Fig. 3. In Fig. 3, the hardened cement body of Comparative Example 2 is shown in the fifth column from the right.

[0059] [Comparative Example 3] A hardened cement body was obtained in the same manner as in Example 2, except that the aqueous crystal violet solution was not used. This hardened cement body was carbonated in the same manner as in Example 1, and the color change was confirmed. The results are shown in Fig. 3. In Fig. 3, the hardened cement body of Comparative Example 3 is shown in the fourth column from the right.

[0060] [Comparative Example 4] A hardened cement material was obtained in the same manner as in Example 1, except that neither N-methyldiethanolamine nor the aqueous solution of crystal violet was used. This hardened cement body was carbonated in the same manner as in Example 1, and the color change was confirmed. The results are shown in Fig. 3. In Fig. 3, the sixth from the right shows the hardened cement body of Comparative Example 4.

[0061] From the results shown in FIG. 3, it was found that in Examples 1 and 2, the range of CO2 fixation could be detected from the range where the color change occurred. [Explanation of symbols]

[0062] 1. Hardened cement for detecting carbon dioxide fixation 10. Encapsulating material 100 Concrete structure

Claims

1. A hardened cement body for detecting carbon dioxide fixation, comprising: a hardened cement body; and a carbon dioxide fixation range indicator liquid that exhibits a color reaction in the pH range of 7 to 13 and is supported on the hardened cement body.

2. 2. The carbon dioxide fixation detection method according to claim 1, wherein the carbon dioxide fixation range indicator liquid is contained in an amount of 0.01 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the hardened cement body.

3. 2. The hardened cement body for detecting carbon dioxide fixation according to claim 1, further comprising a carbon dioxide absorbent supported on the hardened cement body.

4. 4. The carbon dioxide fixation detection method according to claim 3, wherein the carbon dioxide absorbent is contained in an amount of 0 to 20 parts by mass based on 100 parts by mass of the hardened cement body.

5. 2. The carbon dioxide fixation detection method according to claim 1, wherein the hardened cement body is concrete.

6. A step of forming the hardened cement body for detecting carbon dioxide fixation according to any one of claims 1 to 5 into a plate or column shape; a step of sealing the surfaces of the hardened cement body for detecting carbon dioxide fixation other than the two opposing end surfaces; and placing the carbon dioxide fixation detection hardened cement body so that one of the two end faces is flush with a carbon dioxide absorption surface of a target concrete structure, When the carbon dioxide fixation detection hardened cement body is in a plate shape, the two end faces are end faces along a short side direction or a long side direction of the carbon dioxide fixation detection hardened cement body, When the carbon dioxide fixation detection hardened cement body is columnar, the two end faces are the top and bottom faces of the carbon dioxide fixation detection hardened cement body.

7. 7. The method for detecting a carbon dioxide fixation range according to claim 6, wherein the hardened cement body constituting the carbon dioxide fixation detection hardened cement body has the same composition as that of the concrete structure.

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