Cement admixture, cement composition, and carbonation-hardened body

Abstract

To provide a cement admixture that has enhanced capacity for CO2 absorption and can achieve high initial strength or long-term strength in cement compositions.SOLUTION: A cement admixture comprises γ-2CaO SiO2 and Merwinite as mineral compositions, and contains 2 mass% or more of γ-2CaO SiO2 and 40 mass% or less of Merwinite. It is preferable that the cement admixture has a particle size allowing at least 40 mass% to pass through a sieve with a 90 μm aperture, and that its Blaine specific surface area is 500 cm2 / g or more and 3000 cm2 / g or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention mainly relates to cement admixtures, cement compositions, and carbonated hardened bodies used in the civil engineering and construction industries.

Background Art

[0002] Great attention has been paid to the effective use of various slags that are by-products of the steel industry. In the steel industry, slags with various compositions and properties are by-produced depending on various processes, facilities, and steel grades to be melted. In addition, various cement admixtures are used in consideration of improving the performance of concrete, effectively utilizing resources, and reducing the environmental load, and studies on cement admixtures containing slag have been conducted.

[0003] For example, Patent Document 1 below describes a cement admixture and a cement composition containing γ-2CaO·SiO 2 (γ-C 2 S), and containing a non-hydraulic substance having a specific Blaine specific surface area and a specific content. According to the cement admixture of Patent Document 1, it is described that, compared with the conventional limestone fine powder admixture, the compressive strength of the cement composition is equivalent, the heat of hydration is small, and a high neutralization suppression effect can be obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In recent years, by carbonating concrete containing an admixture containing γ-C 2 S, CO 2There has been a study on the technology for obtaining a high-strength concrete product with a densified surface layer from absorption. In this case, by carbonating, the total CO 2 emission in obtaining the concrete product is reduced by the amount of CO 2 absorbed by the concrete. In the cement admixture and cement composition described in Patent Document 1, the neutralization suppression effect has been studied, but the CO 2 absorption amount has not been studied.

[0006] The present invention has been made in view of such circumstances, and an object thereof is to provide a cement admixture having a high CO 2 absorption amount and capable of obtaining a high initial strength or long-term strength of a cement composition, a cement composition containing the cement admixture, and a carbonated cured body.

Means for Solving the Problems

[0007] As a result of intensive studies to solve the above problems, the present inventor has conceived the following present invention and found that the problem can be solved. That is, the present invention is as follows. [1] As a mineral composition, γ-2CaO·SiO 2 , and melilite are contained, and the γ-2CaO·SiO 2 is contained in an amount of 2% by mass or more, and the melilite is contained in an amount of 40% by mass or less, a cement admixture. [2] The cement admixture according to [1], having a particle size that passes through a sieve with an opening of 90 μm in an amount of 40% by mass or more. [3] The Blaine specific surface area is 500 cm 2 / g or more and 3000 cm 2 / g or less, the cement admixture according to [1] or [2]. [4] The cement admixture according to any one of [1] to [3], containing an electric furnace reduction slag. [5] A cement composition containing the cement admixture according to any one of [1] to [4]. [6] A carbonated cured body comprising a carbonated cured product of the cement composition according to [5].

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a cement admixture having a high CO 2 absorption amount and capable of obtaining a high initial strength or long-term strength of a cured product produced therefrom, a cement composition containing the cement admixture, and a carbonated cured body.

Embodiments for Carrying Out the Invention

[0009] [Cement Admixture] The cement admixture of the present invention contains, as a mineral composition, γ-2CaO·SiO 2 and merwinite, and contains 2% by mass or more of γ-2CaO·SiO 2 and 40% by mass or less of merwinite.

[0010] (γ-2CaO·SiO 2 ) γ-2CaO·SiO 2 is represented by 2CaO·SiO 2 and is known as a low-temperature phase, which is completely different from the high-temperature phases α-2CaO·SiO 2 , α’-2CaO·SiO 2 , and β-2CaO·SiO 2 . Although all of these are represented by 2CaO·SiO 2 , their crystal structures and true densities are different. γ-2CaO·SiO 2 does not have hydraulicity, but γ-2CaO·SiO 2 has the property of absorbing carbon dioxide in the air and hardening, that is, it has air-hardening property.

[0011] (Merwinite) Merwinite is represented by 3CaO·MgO·2SiO 2 (C 3 MS 2 ), and according to merwinite, a large CO 2 absorption effect is achieved.

[0012] γ-2CaO·SiO 2A method for producing a cement admixture containing 2% by mass or more of melite and 40% by mass or less of melite is obtained by blending CaO raw material, SiO 2 raw material and MgO raw material in a predetermined molar ratio and heat-treating in a temperature range of 1000 ° C or higher. Examples of the CaO raw material include calcium carbonate such as limestone, calcium hydroxide such as slaked lime, by-product slaked lime such as acetylene by-product slaked lime, fine powder generated from waste concrete blocks, concrete sludge (dehydrated cake) generated in ready-mix concrete plants and concrete product plants, incineration ash (coal ash, woody biomass, municipal waste incineration ash, sewage sludge incineration ash, paper sludge, etc.), steel slag (converter slag, electric furnace slag, etc.). SiO 2 Examples of the raw material include quartz, clay, and various siliceous dusts generated as industrial by-products typified by silica fume and fly ash. Examples of the MgO raw material include magnesium hydroxide, basic calcium carbonate, dolomite, and the like.

[0013] The cement admixture of the present invention can use slag containing γ-2CaO·SiO 2 and melite, and for example, steel slag or stainless steel slag can be used. Among the slags, electric furnace reduction slag or stainless steel slag having a high content of γ-2CaO·SiO 2 is preferred.

[0014] The content of γ-2CaO·SiO in the cement admixture 2 is 2% by mass or more, preferably 10% by mass or more, and more preferably 15% by mass or more. Further, the content of γ-2CaO·SiO 2 is not particularly limited, but is preferably 95% by mass or less, and more preferably 90% by mass or less. When the content of γ-2CaO·SiO 2 is less than 2% by mass, a sufficient CO 2 absorption amount cannot be obtained.

[0015] In addition, the content of melvillite in the cement admixture is 40% by mass or less, preferably 37% by mass or less, and more preferably 35% by mass or less. Also, the content of melvillite is preferably 3% by mass or more, and more preferably 5% by mass or more. When the content of melvillite exceeds 40% by mass, the initial strength or long-term strength of the cement composition containing the cement admixture of the present invention decreases.

[0016] Each component of the slag is γ-2CaO·SiO 2 and is not particularly limited other than containing melvillite. Specifically, CaO, SiO 2 and MgO, etc. are the main chemical components, and in addition, Al 2 O 3 , S, Fe 2 O 3 , TiO 2 and MnO, etc. can be mentioned. Also, as the mineral composition other than γ-2CaO·SiO 2 and melvillite, gehlenite (2CaO·Al 2 O 3 ·SiO 2 ) is 30% by mass or less (preferably 5 - 30% by mass), periclase (MgO) is 15% by mass or less (preferably 2 - 15% by mass), larnite (β-2CaO·SiO 2 ) is 15% by mass or less (preferably 1 - 15% by mass), spinel (MgO·Al 2 O 3 ) is 25% by mass or less (preferably 10 - 25% by mass), stishovite (SiO 2 ) is 3% by mass or less, cristobalite (SiO 2 ) is 2% by mass or less, bredigite (7CaO·MgO·4SiO 2 ) is 25% by mass or less (preferably 5 - 20% by mass), and perovskite (CaO·TiO 2 ) may be contained in an amount of 2% by mass or less. γ-2CaO·SiO 2If the total of melvinite is less than 100%, these mineral compositions can be included.

[0017] The cement admixture may use slag itself alone as a cement admixture, or can be used in combination with other materials. Also, two or more kinds of slag can be used in combination.

[0018] Also, the particle size of the cement admixture of the present invention is preferably such that 40% by mass or more passes through a sieve with an opening of 90 μm, more preferably 80% by mass or more passes through, and even more preferably 90% by mass or more passes through. The particle size of the cement admixture can be adjusted by performing pulverization and classification. By setting the particle size of the cement admixture within the above range, the CO 2 absorption amount can be increased.

[0019] The Blaine specific surface area of the cement admixture is preferably 500 cm 2 / g or more, more preferably 600 cm 2 / g or more, and even more preferably 700 cm 2 / g or more. Also, the upper limit is preferably 3000 cm 2 / g or less, more preferably 2500 cm 2 / g or less, and even more preferably 2000 cm 2 / g or less. The Blaine specific surface area of the cement admixture can be adjusted by performing pulverization and classification. By setting the Blaine specific surface area within the above range, the CO 2 absorption amount can be increased.

[0020] (Cement composition) The cement composition of the present invention contains the above cement admixture. The cement composition of the present invention also contains cement. Examples of cement that can be used in the cement composition of the present invention include various Portland cements such as normal, early strength, super early strength, low heat, and moderate heat, various mixed cements obtained by mixing blast furnace slag, fly ash, or silica with these Portland cements, waste-recycled cements produced using municipal waste incineration ash and sewage sludge incineration ash as raw materials, so-called Ecocement (R), and filler cements mixed with limestone powder, etc. In addition, compared to conventional cements, the present invention has a low CO 2 Geopolymer cement, sulfoaluminate cement, limestone-calcined clay cement (LC3), and CO 2 and carbonated cement which hardens by immobilizing the above. One or more of these can be used.

[0021] In the cement composition of the present invention, the amount of the cement admixture used is not particularly limited, but is usually preferably 5 parts by mass or more and 40 parts by mass or less, and more preferably 10 parts by mass or more and 40 parts by mass or less, relative to 100 parts by mass of the total of the cement and the cement admixture. 2 The amount of absorption can be increased, and the initial strength or long-term strength of the produced cement composition can be increased.

[0022] In addition, in the cement composition of the present invention, the amount of water used is not particularly limited, and is within the range of normal use. Specifically, the amount of water is preferably 10 parts by mass or more and 85 parts by mass or less per 100 parts by mass of cement and cement admixture. By making it 10 parts by mass or more, sufficient workability can be obtained, and by making it 85 parts by mass or less, sufficient strength expression can be obtained.

[0023] The particle size of the cement composition is not particularly limited because it depends on the purpose and application of the composition. However, it is usually 3,000 cm2 in terms of Blaine specific surface area. 2 / g or more 8,000cm 2 / g or less is preferable, and 4,000 cm 2 / g or more 6,000cm2 It is more preferable that it is below 3,000 cm 2 / g. By setting it to 8,000 cm 2 / g or more, sufficient strength expressivity can be obtained, and by setting it to 8,000 cm

[0024] In this specification, the cement composition is a general term for cement paste, mortar containing fine aggregate, and further concrete containing coarse aggregate.

[0025] In the cement composition of the present invention, in addition to cement and the present admixture, aggregates such as sand and gravel, blast furnace granulated slag fine powder, blast furnace slowly cooled slag powder, limestone fine powder, fly ash, and silica fume, admixture materials such as natural pozzolan such as volcanic ash, expansive agent, rapid hardening agent, water reducing agent, AE water reducing agent, high performance water reducing agent, high performance AE water reducing agent, defoaming agent, thickening agent, rust inhibitor, antifreeze agent, shrinkage reducing agent, polymer, setting regulator, clay minerals such as bentonite, and additives such as anion exchangers such as hydrotalcite, one or more known and commonly used additives and admixtures used in ordinary cement materials can be used within a range that does not substantially inhibit the object of the present invention.

[0026] The cement composition of the present invention may be produced by mixing each material during construction, or a part or all of them may be mixed in advance. Also, the mixing method of each material and water is not particularly limited, and each material may be mixed during construction, or a part or all of them may be mixed in advance. Also, after mixing a part of the materials with water, the remaining materials may be mixed.

[0027] As a mixing device for mixing each material, any existing device can be used. For example, a tilting drum mixer, an omnimixer, a Henschel mixer, a V-type mixer, and a Nauta mixer can be used.

[0028] (Carbonated hardened body) The carbonated cured body of the present invention is composed of the carbonated cured product of the above cement composition. The carbonated cured product is obtained by carbonating and curing the above cement composition. The carbonation curing in the present invention means subjecting the cured body prepared by mixing the present cement composition and water to carbonation treatment in a gas atmosphere containing carbon dioxide gas. The gas atmosphere is not particularly limited as long as it contains carbon dioxide gas, and may contain gases such as nitrogen, oxygen, hydrogen, argon, and water vapor.

[0029] The carbonated cured body in the present invention refers to a cured body obtained by hydrating and curing the present cement composition and then further subjecting it to carbonation curing.

Examples

[0030] Hereinafter, the present invention will be described in more detail using examples and comparative examples. However, the present invention is not limited to the following examples and comparative examples as long as it does not deviate from the gist thereof.

[0031] <Experimental Example 1> Using the electric furnace reducing slag with the content of γ-2CaO·SiO shown in Table 1 2 and melilite, a cement admixture was prepared. Commercially available products were used for the electric furnace reducing slag. The mineral composition of the slowly cooled product of the used electric furnace reducing slag is shown in Table 1. Each sample was pulverized to obtain the Blaine specific surface area shown in Table 2. Also, the passing fraction through a sieve with an aperture of 90 μm at that time is shown in Table 2.

[0032]

Table 1

[0033] Regarding the mineral components of this cement admixture, they were quantified by mineral composition analysis using powder XRD (manufactured by Rigaku Corporation, SmartLab Studio II).

[0034] (CO 2 content rate) Using the cement admixtures of Test Nos. 1-1 to 1-12, CO 2The content ratio was measured. Each cement admixture was prepared to have a median diameter of 15 μm so as not to be affected by the particle size. 5 g of each cement admixture was packed into a styrene bottle with a body diameter of 30 mm and a height of 60 mm, and left standing in a curing tank under the conditions of 40 °C, 60% RH, and a carbon dioxide concentration of 20% by volume. Appropriately, 2.5 g of water of equal amount was added for carbonation. After carbonating for 3 days, the sample was pulverized to pass through a sieve with an aperture of 150 μm to obtain a cement admixture for measurement. For this, hydration was stopped with acetone and dried at 40 °C, and the CO 2 content ratio was measured. A coulometer (manufactured by Nippon Rans Corporation, model 2000S - CAT) was used. Hydrochloric acid (hydrochloric acid concentration: 3 mol / L) was added to each cement material placed in an Erlenmeyer flask, stirred with a stirrer, and the generated CO 2 gas was introduced into the absorbent solution with nitrogen, and the carbon amount was measured from the amount of electricity required to keep the transmittance of the absorbent solution constant, and converted to the CO 2 content ratio. The results are shown in Table 2. Note that the preferable CO 2 content ratio is 2.8% or more.

[0035] (Compressive strength) Also, a cement composition was prepared using the cement admixture prepared in Experimental Example 1 and the following materials. Cement: Ordinary Portland cement (commercial product), 20 parts by mass Cement admixture: 10, 30, or 50 parts by mass were taken out of 100 parts by mass of cement, and a predetermined amount was replaced by mass Water: Tap water, 50 parts by mass with respect to a total of 100 parts by mass of cement and cement admixture Sand: Standard sand for cement strength test (commercial product), 67 parts by mass The prepared cement composition was poured into a mold of 4 cm×4 cm×16 cm, and steam curing was carried out under the conditions of 20 °C and 60% RH. After steam curing, it was demolded immediately, and carbonation curing was carried out under the conditions of 40 °C, 60% RH, and a carbon dioxide gas concentration of 20% by volume. The compressive strength (initial strength) after 3 days from placing and the compressive strength (long - term strength) after 28 days from placing were measured. The compressive strength was measured according to JIS R 5201. The results are shown in Table 2.

[0036]

Table 2

Industrial Applicability

[0037] The cement admixture of the present invention has a high CO 2 content and can obtain a high initial strength or long-term strength of the cement composition, so it can be effectively used in the civil engineering and construction industries.

Claims

1. As a mineral composition, γ-2CaO·SiO ２ , and contains melvinite, The above γ-2CaO·SiO ２ A cement admixture containing 2% by mass or more of the above and 40% by mass or less of the melilite.

2. The cement admixture according to claim 1, having a particle size that allows 40% by mass or more of a sieve with an opening of 90 μm to pass through.

3. The brain specific surface area is 500 cm ２ / g or more and 3000 cm ２ / g or less, the cement admixture according to claim 1 or 2.

4. The cement admixture according to claim 1 or 2, containing an electric furnace reduction slag.

5. A cement composition containing the cement admixture according to claim 1 or 2.

6. A carbonated cured body composed of a carbonated cured product of the cement composition according to claim 5.

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