Co2-fixing expanding agent, cement composition, and concrete composition

Abstract

To provide a CO2-fixing expanding agent capable of effectively fixing CO2 while exhibiting excellent expansibility.SOLUTION: The CO2-fixing expanding agent contains an ettringite-forming compound that forms ettringite, and the ettringite-forming compound preferably contains free lime in its mineral composition.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a CO2 immobilizing expansive material, a cement composition, and a concrete composition. [Background technology]

[0002] Reducing cracks in cement and concrete is important from the perspectives of reliability, durability, aesthetics, etc. of products and structures. Therefore, further technological advances in expansive additives that can improve these aspects are desired.

[0003] Furthermore, in order to reduce the total amount of CO2 emitted when manufacturing concrete products, it is effective to reduce the amount of cement used by incorporating large amounts of special additives or industrial by-products (ground granulated blast furnace slag, fly ash, etc.) as cement substitutes, and various research projects are currently underway.

[0004] Under these circumstances, research is also being conducted into technologies for absorbing (fixing) CO2 in hardened cement bodies. For example, Patent Document 1 discloses a method for forcibly absorbing or carbonating CO2 during production. Specifically, the method discloses a carbon dioxide fixation method that includes a contacting step of bringing a carbon dioxide-containing gas into contact with a cementitious hardened body and fixing the carbon dioxide contained in the carbon dioxide-containing gas in the cementitious hardened body. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-15659 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the fixation method in Patent Document 1 involves setting the moisture content in the carbon dioxide-containing gas to 1.5% or more and setting the temperature to 75 to 175°C, but does not disclose or suggest any material that can fix CO2, nor does it disclose any expanding material.

[0007] In view of the above, an object of the present invention is to provide a CO2 fixation expanding material having good expansion performance and CO2 fixation performance. [Means for solving the problem]

[0008] As a result of intensive research to solve the above problems, the present inventors have come up with the following invention and found that the above problems can be solved.

[0009] [1] A CO2 fixation expanding material containing an ettringite-forming compound that forms ettringite. [2] The CO2 fixation expansive material according to [1], wherein the ettringite-forming compound contains free lime as a mineral composition. [3] The CO2 immobilizing expansive material according to [2], containing 10 to 70 mass% of the free lime. [4] The CO2 fixation expansive material according to any one of [1] to [3], wherein the ettringite-forming compound contains auyne as a mineral composition. [5] The CO2 fixation expansive material according to any one of [1] to [4], wherein the ettringite-forming compound contains ternesite and / or gehlenite as a mineral composition. [6] The CO2 fixation expansive material according to [5], wherein the content (total content) of the ternesite and the gehlenite in the ettringite-forming compound is 2 to 15 mass%. [7] Blaine specific surface area is 2000-6000 cm 2 The CO2 fixation expanding material according to any one of [1] to [6], wherein the coefficient of friction is 1 / g. [8] The CO2 fixation expansive material according to any one of [1] to [7], which is mixed with cement. [9] A cement composition comprising a CO2 immobilizing expansive material according to any one of [1] to [8] and cement.

[10] A concrete composition comprising the CO2 immobilizing expansive material according to any one of [1] to [8], cement, and aggregate. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a CO2 fixation expanding material having good expansion performance and CO2 fixation performance. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, one embodiment of the present invention (the present embodiment) will be described in detail.

[0012] [CO2 fixation expanding material] The CO2-immobilizing expansive material of this embodiment contains an ettringite-forming compound that forms ettringite. In this embodiment, in a cement composition or concrete composition containing the CO2-immobilizing expansive material, ettringite forms as the composition solidifies, and the ettringite absorbs carbon dioxide (CO2) by capturing CO2 in its crystals. Furthermore, the expansion performance of the CO2-immobilizing expansive material provides a favorable expansion effect. Here, the above "solidification" refers to the time when the compressive strength is 2.5N / mm according to the method specified in JIS R 5201:2015 "Physical Test Methods for Cement". 2 This refers to a state in which:

[0013] Regarding the CO2 absorption already described, although it depends specifically on conditions such as humidity, it is expected that the generated ettringite will absorb a large amount of CO2 (1 mol to 3 mol, 4.2 mol, or 4.6 mol of ettringite) according to any of the following formulas (1) to (3). Formula (1): 3CaO・Al2O3・3CaSO4・32H2O+3CO2→3CaCO3+Al2O3(gel)+3CaSO4・2H2O+26H2O Formula (2): 3CaO Al2O3 3CaSO4 31.1H2O+4.6CO2→3CaCO3+Al2O3 10.4H2O 1.6CO2+3CaSO4 0.5H2O+19.2H2O Formula (3): 3CaO Al2O3 3CaSO4 30.9H2O+4.2CO2→3CaCO3+Al2O3 7.9H2O 1.2CO2+3CaSO4 2H2O+17.0H2O

[0014] The ettringite-forming compound according to this embodiment is not particularly limited as long as it is a compound that forms ettringite, and examples thereof include at least one selected from the group consisting of calcium sulfoaluminate, calcium aluminate, calcium fluoroaluminate, calcium chloroaluminate, alinite, NaO 8CaO 3AlO, alums, sulfates, and the like. Among these, from the viewpoint of exhibiting good strength and the amount of CO2 fixed, a combination of at least one of calcium sulfoaluminate and calcium aluminate with a sulfate is preferred.

[0015] Here, calcium aluminate (CA) according to this embodiment is a general term for compounds containing CaO and Al2O3 as main components, and specific examples thereof include amorphous compounds containing CaO and Al2O3 as main components, and crystalline calcium aluminates expressed as CaO·2Al2O3, CaO·Al2O3, 12CaO·7Al2O3, 11CaO·7Al2O3·CaF2, and 3CaO·3Al2O3·CaF2. Among these, the CaO / Al2O3 molar ratio of CA is preferably in the range of 0.45 to 3, and more preferably in the range of 0.8 to 2. When the CaO / Al2O3 molar ratio is 0.45 or more, sufficient early strength development is obtained. Furthermore, when the CaO / Al2O3 molar ratio is 3 or less, sufficient fluidity and usable life are obtained.

[0016] As mentioned above, calcium aluminate can be used in either crystalline or amorphous form, but amorphous form obtained by quenching the melt in an electric furnace or the like is preferred, and when the amorphous content is 60 mass% or more, excellent short-term strength development is achieved. The amorphous content (amorphous degree) can be determined by powder X-ray diffraction / Rietveld analysis.

[0017] The calcium sulfoaluminate (CSA) according to this embodiment is produced by firing raw materials such as lime, a calcareous raw material such as gypsum, and an alumina raw material such as bauxite at about 1300°C to 1600°C using a kiln or the like, and then pulverizing the raw materials. Although there is no particular limitation on CSA, for example, raw materials may be blended in a molar ratio of CaO:Al2O3:CaSO4 of 3:3:1, fired, and crushed, and this is called hauyne (3CaO 3Al2O3 CaSO4).

[0018] From the viewpoint of expansion coefficient, the ettringite-forming compound preferably contains free lime as a mineral composition. The ettringite-forming compound preferably contains 3 to 80 mass% of free lime, more preferably 15 to 65 mass%. By containing 3 to 80 mass% of free lime, excellent expansion performance can be ensured.

[0019] Furthermore, from the viewpoint of ensuring expansion coefficient and strength, the ettringite-forming compound preferably contains auyne as a mineral composition. The ettringite-forming compound preferably contains 1 to 30 mass% of auyne, more preferably 3 to 25 mass%. By containing 1 to 30 mass% of auyne, it is possible to achieve both excellent expansion performance and strength development.

[0020] From the viewpoint of efficient CO2 fixation, the ettringite-forming compound preferably contains ternesite and / or gehlenite as a mineral composition. The total amount of ternesite and gehlenite in the ettringite-forming compound is preferably 2 to 15 mass%, more preferably 3 to 10 mass%. By containing ternesite and gehlenite in a total amount of 2 to 15 mass%, CO2 can be fixed more efficiently. The ternesite content can be adjusted to the above range, for example, by mixing silicon dioxide as a reagent with the raw material.

[0021] The sulfates include alkali metal sulfates and alkaline earth metal sulfates. Examples of the alkali metal of the alkali metal sulfate include lithium, sodium, potassium, etc., and sodium is preferred. The alkali metal sulfate may be used alone or in combination of two or more.

[0022] Examples of the alkaline earth metal of the alkaline earth metal sulfate include magnesium and calcium, with calcium being preferred. The alkaline earth metal sulfate may be used alone or in combination of two or more. The particle size and grain size of the alkaline earth metal sulfate are not particularly limited. For example, the alkaline earth metal sulfate may be used in an amount of 1000 to 150 ... 2 / g. Here, the alkaline earth metal sulfate is preferably calcium sulfate, and examples thereof include anhydrous gypsum (anhydrous calcium sulfate), hemihydrate gypsum (calcium sulfate hemihydrate), and dihydrate gypsum (calcium sulfate dihydrate), etc. Among these, anhydrous gypsum is preferred.

[0023] The amount of sulfate is preferably 7 to 60 parts by mass, more preferably 15 to 58 parts by mass, and even more preferably 20 to 57 parts by mass, calculated as an anhydride, relative to 100 parts by mass of calcium sulfoaluminate. Furthermore, the content of the alkaline earth metal sulfate in anhydrous terms is preferably 40 to 160 parts by mass, more preferably 42 to 157 parts by mass, and even more preferably 45 to 155 parts by mass, relative to 100 parts by mass of calcium aluminate. If the content of the alkaline earth metal sulfate is within the above range, it is likely to exhibit excellent long-term strength development.

[0024] From the viewpoint of the development of good strength and the amount of CO2 fixation, it is preferable that the ettringite-forming compound is calcium sulfoaluminate and / or calcium aluminate and contains auyne as a mineral composition. The ettringite-forming compound preferably contains 10 mass% or more of auyne, more preferably 15 mass% or more. The amount of auyne can be adjusted by changing the component ratio of CaO, Al2O3, and SO3 in the raw materials. There is no particular upper limit, but in practice it is 80 mass%.

[0025] Furthermore, from the viewpoint of the development of good strength and the amount of CO2 fixation, the calcium sulfate as a mineral composition in the ettringite forming compound is preferably 2 to 75 mass %, more preferably 10 to 70 mass %. The mineral compositions of free lime, auyne, ternesite, gehlenite, calcium sulfate, etc. in the ettringite-forming compound can be measured by the XRD / Rietveld method.

[0026] The Blaine specific surface area of ​​the ettringite forming compound is 1,500 to 8,000 cm in order to fully demonstrate its function. 2 / g, and 2,000 to 7,000 cm 2 / g is more preferred.

[0027] In order to fully demonstrate its function, the CO2 fixation expansion material of this embodiment has a Blaine specific surface area of ​​1,500 to 8,000 cm 2 / g, and 2,000 to 7,000 cm 2 / g, and more preferably 2,000 to 6,000 cm 2 / g is more preferred.

[0028] In order to fully exert its function, the ettringite-forming compound is contained in the CO2 fixation expansive material at a content of preferably 80 mass % or more, and more preferably 90 mass % or more.

[0029] Furthermore, when the solidified material obtained by mixing 100 parts by mass of CO2 fixation expanding material with 50 parts by mass of water and curing for 24 hours is left to stand for 24 hours in an environment of 20°C, 60% RH and a CO2 concentration of 5%, the CO2 fixation rate is preferably 9% or more, and more preferably 10% or more. Here, the fixation rate can be determined by the ratio of the number of moles of reacted CaO to the number of moles of CaO before the reaction (mol of reacted CaO / mol of CaO before the reaction).

[0030] The CO2 fixation expansive material described above can be used for a variety of purposes as is or mixed with other materials. However, taking into consideration the long-term durability of the solidified material when it is in use and the application of existing technologies related to maintenance and management, it is preferable that it be used as a mixture with cement or concrete.

[0031] [Cement composition and concrete composition] The cement composition according to this embodiment contains the CO2-immobilizing expansive material of the present invention and cement, as described above. Also, the concrete composition according to this embodiment contains the CO2-immobilizing expansive material of the present invention and cement, as described above. The cement composition in this embodiment is a general term for cement, cement paste, and mortar.

[0032] The content of the CO2 fixation expanding material is preferably in the range of 5 to 90 parts by mass, more preferably 30 to 80 parts by mass, per 100 parts by mass of cement, from the viewpoint of improving the expansiveness and CO2 fixation.

[0033] The cement used in this embodiment is not particularly limited, and examples include various cements such as ordinary, early-strength, extra-early-strength, low-heat, and medium-heat cements; various blended cements obtained by blending these cements with blast furnace slag, fly ash, or silica fume; environmentally friendly cements (ecocements) produced using municipal waste incineration ash or sewage sludge incineration ash as raw materials; siliceous materials such as metakaolin and clay calcined ash; and commercially available fine particle cements. Various cements and blended cements can also be finely powdered and used. Furthermore, cements containing components (e.g., gypsum) typically found in ordinary cements can also be used. In this embodiment, ordinary Portland cement or early-strength Portland cement is preferably selected from the viewpoints of heat of hydration, drying shrinkage, and packing properties.

[0034] In addition, from the viewpoint of manufacturing costs and strength development, the Blaine specific surface area of ​​cement is 2,500 to 7,000 cm 2 / g, and 2,750 to 6,000 cm2 It is more preferable that it is / g. In this specification, the Blaine specific surface area is determined in accordance with JIS R 5201 (Physical test methods for cement).

[0035] Examples of the fine aggregate used in this embodiment include river sand, mountain sand, land sand, sea sand, silica sand, crushed sand, lime crushed sand, blast furnace slag fine aggregate, recycled fine aggregate, etc. The type and content of the fine aggregate may be selected according to the target mechanical strength of the hardened concrete.

[0036] Examples of the coarse aggregate used in this embodiment include crushed stones obtained by crushing andesite, rhyolite, hard sandstone, limestone, etc., river gravel, mountain gravel, land gravel, blast furnace slag coarse aggregate, recycled coarse aggregate. The rock type, size and content of the coarse aggregate may be selected according to the target mechanical strength of the hardened concrete.

[0037] In this embodiment, various additives may be contained. For example, water reducing agents, AE agents, foaming agents, shrinkage reducing agents, waterproof agents, rust preventives, thickening agents, polymers, water retaining agents, pigments, water repellents, white efflorescence preventives, etc. can be mentioned.

Examples

[0038] The present invention will be specifically described by the following examples, but the present invention is not limited thereto.

[0039] [Experimental Example 1] <Preparation of CO2 immobilizing expansive material> Calcium carbonate reagent, aluminum hydroxide reagent, calcium sulfate reagent, and silicon dioxide reagent were mixed so as to have the composition shown in Table 1 below, and heat-treated at 1350 °C for 3 hours to adjust the Blaine specific surface area to 3500 cm 2 / g to prepare an ettringite-forming compound, which was used as a CO2 immobilizing expansive material.

[0040] (Evaluation) <Strength> A composition with a water / powder mass ratio of 0.5 and a fine aggregate / powder mass ratio of 3.0 was molded into specimens of 40×40×160 mm, and the strengths at ages of 1, 3, and 7 days (JIS R 5201:2015 "Physical Test Methods for Cement") were measured. The ettringite-forming compound was mixed at 5% by mass based on the powder. Note that the above "powder" refers to the total of the ettringite-forming compound and cement (ordinary Portland cement). Also, silica sand was used as the fine aggregate. After demolding at 1 day of age, carbonation curing was carried out under the conditions of temperature: 20°C, humidity: 60%RH, and CO2 concentration: 5%.

[0041] <CO2 absorption amount (CO2 content, CO2 immobilization rate)> A paste with a water / powder mass ratio of 0.5 was molded into specimens of 20×20×80 mm. After demolding at 1 day of age, carbonation curing was carried out under the conditions of temperature: 20°C, humidity: 60%RH, and CO2 concentration: 5%. The ettringite-forming compound was mixed at 6.7% by mass based on the powder. After that, the specimens were crushed to less than 90 μm at a predetermined age, and then the CO2 content was measured by the coulometer method. Note that the above "powder" refers to the total of the ettringite-forming compound and cement (ordinary Portland cement).

[0042] <Expansibility> A composition with a water / powder mass ratio of 0.5 and a fine aggregate / powder mass ratio of 3.0 was molded into specimens of 40×40×160 mm, and the length change rates at ages of 7 and 28 days (JIS A 6202:2*017 "Expansion Materials for Concrete") were measured. After demolding at 1 day of age, carbonation curing was carried out under the conditions of temperature: 20°C, humidity: 60%RH, and CO2 concentration: 5%. Note that the above "powder" refers to the total of the ettringite-forming compound and cement (ordinary Portland cement). The ettringite-forming compound was mixed at 6.7% by mass based on the powder. Also, silica sand was used as the fine aggregate.

[0043]

Table 1

Claims

[Request 1] CO containing ettringite-forming compounds that form ettringite ２ Fixed expansion material. Request 2 2. The CO composition according to claim 1, wherein the ettringite-forming compound contains free lime as a mineral composition. ２ Fixed expansion material. Request 3 3. The CO according to claim 2, wherein the free lime is contained in an amount of 10 to 70 mass %. ２ Fixed expansion material. Request 4 2. The CO composition according to claim 1, wherein the ettringite-forming compound contains auyne as a mineral component. ２ Fixed expansion material. Request 5 2. The CO composition according to claim 1, wherein the ettringite-forming compound contains ternesite and / or gehlenite as a mineral composition. ２ Fixed expansion material. [Request 6] 6. The CO composition according to claim 5, wherein the content of the ternesite and the gehlenite in the ettringite-forming compound is 2 to 15 mass%. ２ Fixed expansion material. Request 7 Blaine specific surface area is 2000 to 6000 cm ２ / g of CO ２ Fixed expansion material. Request 8 The CO of claim 1 mixed with cement. ２ Fixed expansion material. [Request 9] The CO according to any one of claims 1 to 8 ２ A cement composition comprising a fixed expansive material and cement. Request 10 The CO according to any one of claims 1 to 8 ２ A concrete composition comprising a fixed expansive material, cement, and aggregate.

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