Cement admixture, cement composition, and cement hardened body

Abstract

Disclosed is a cement admixture which contains a calcium carbonate-containing powder and one or more non-hydraulic compounds that are selected from the group consisting of γ-2CaO∙SiO2, 3CaO∙2SiO2, α-CaO∙SiO2, and calcium magnesium silicate.

Description

Cement admixtures, cement compositions, hardened cement products

[0001] The present invention relates to a cement admixture, a cement composition, and a hardened cement product.

[0002] Concrete uses a large amount of cement as a raw material, so CO ２ This is mainly due to the large amount of fossil fuels used to generate combustion energy in the furnace during the cement production process, as well as the decarbonation reaction of limestone (CaCO ３ →CaO+CO ２ ) is generated. ２ Reducing emissions has become an important theme as part of measures to combat global warming.

[0003] CO emitted during the production of concrete products ２ In order to reduce the total amount of cement used, 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 being conducted on this topic.

[0004] On the other hand, γ-C ２ S(γ-2CaO・SiO ２ By forcibly carbonating (curing) concrete containing non-hydraulic compounds such as belite (also called gamma phase belite) as admixtures, CO ２ There is a known technique for obtaining a highly durable concrete product by densifying the surface layer through the absorption of γ-C (see, for example, Patent Document 1). ２ S does not undergo hydration reaction, and CO ２ Reacts with CaCO ３ and SiO ２ These products fill the voids in the cement matrix and dramatically improve the durability of the surface layer of the concrete product. In this case, the CO absorbed by the concrete during carbonation (salt) curing is ２ The total CO2 required to obtain concrete products is ２ Emissions will be reduced.

[0005] In addition, in Patent Document 2, γ-C is used as a powder component. ２ S, one or two types of steelmaking slag powder and Portland cement, and the proportion of γ-C in the total content ２ A concrete mix containing 25 to 95 mass% of the total of S and steelmaking slag powder and a water-cement ratio W / C of 80 to 250 mass% has been proposed. ２ CO emissions reduction and carbonation curing ２ By utilizing the absorption of CO, the total CO is reduced compared to conventional general concrete. ２ It states that it has become possible to create precast concrete products with significantly reduced emissions.

[0006] JP 2006-182583 A JP 2011-168436 A

[0007] However, γ-C ２ If a large amount of non-hydraulic materials such as S or industrial by-products is mixed and the amount of hydraulic cement used is reduced, strength development will decrease. Also, from the viewpoint of productivity, it is necessary to use more CO2 even in a short period of time. ２ It is required to fix the above.

[0008] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the problems can be solved by a cement admixture containing a specific non-hydraulic compound and a calcium carbonate-containing powder, and have arrived at the present invention. That is, the present invention is as follows.

[0009] [1] γ-2CaO・SiO ２ , 3CaO・2SiO ２ , α-CaO.SiO ２ [2] A cement admixture comprising one or more non-hydraulic compounds selected from the group consisting of γ-2CaO.SiO ２[3] The cement admixture according to [1] above, wherein the calcium carbonate content of the calcium carbonate-containing powder is 5% by mass or more. [4] The cement admixture according to any one of [1] to [3] above, wherein the mass ratio of the non-hydraulic compound to the calcium carbonate-containing powder is 1:6 to 3:1. [5] A cement composition comprising the cement admixture according to any one of [1] to [4] above and cement. [6] The cement composition according to [5] above, wherein the mass ratio of the cement admixture to the total mass of the cement admixture and the cement is 5 to 70% by mass. [7] A hardened cement product obtained by hardening the cement composition according to [5] or [6] above.

[0010] According to the present invention, strength development during carbonation curing is improved, and short-term CO ２ It is possible to provide a cement admixture that promotes fixation.

[0011] Hereinafter, one embodiment of the present invention (the present embodiment) will be described in detail, but the present invention is not limited to this embodiment. Note that "%" and "parts" in this specification are based on mass unless otherwise specified.

[0012] [Cement admixture] The cement admixture according to this embodiment is a γ-2CaO.SiO ２ , 3CaO・2SiO ２ , α-CaO.SiO ２ and calcium magnesium silicate, and a calcium carbonate-containing powder. By containing the non-hydraulic compound and the calcium carbonate-containing powder, the cement admixture exhibits good strength development during carbonation curing and exhibits good short-term CO ２ This can promote immobilization.

[0013] <Non-hydraulic compound> The cement admixture of the present invention is a γ-2CaO.SiO ２ , 3CaO・2SiO ２ , α-CaO.SiO ２and calcium magnesium silicate.

[0014] (γ-2CaO・SiO ２ ) γ-2CaO.SiO is 2CaO.SiO ２ Among the compounds represented by the formula: ２ and α'-2CaO.SiO ２ , β-2CaO・SiO ２ These are completely different from 2CaO.SiO ２ However, the crystal structure and density are different. ２ is a non-hydraulic compound, and by carbonation curing mortar or concrete containing this compound as an admixture, ２ This allows the γ-2CaO.SiO2 to be absorbed, resulting in a highly durable product with a dense surface layer. ２ is CO ２ Reacts with CaCO ３ and SiO ２ This produces a gel rich in carbon dioxide, filling the voids in the cement matrix and dramatically improving the durability of the surface layer. ２ The total CO2 required to obtain the product is ２ This reduces emissions, making it a desirable compound from the standpoint of environmental protection.

[0015] (3CaO・2SiO ２ ) 3CaO・2SiO ２ Rankinite is a mineral that contains CaO in pseudowollastonite. It is a chemically stable mineral with no hydration activity, but carbonation has a significant effect on densification.

[0016] (α-CaO.SiO ２ ) α-CaO・SiO ２ (α-type wollastonite) is CaO.SiO ２ Among the compounds represented by the formula: ２These are completely different from CaO.SiO ２ However, the crystal structure and density are different. Naturally occurring wollastonite is a low-temperature phase of β-CaO.SiO ２ β-CaO.SiO ２ has needle-like crystals and is used as an inorganic fibrous material such as wollastonite fiber, but the α-CaO.SiO ２ The densification effect of carbonation is small.

[0017] (Calcium magnesium silicate) Calcium magnesium silicate is CaO—MgO—SiO ２ In this embodiment, 3CaO.MgO.2SiO ２ (C ３ MS ２ Merwinite represented by the formula (I) is preferred. By using merwinite, the densification effect due to carbonation is large.

[0018] The non-hydraulic compounds as described above may be one type or two or more types, but are preferably contained in the cement admixture at 15% by mass or more, and more preferably at 30% by mass or more. At 15% by mass or more, a sufficient densification effect can be obtained by carbonation curing. There is no particular upper limit, but from the viewpoint of storage stability, a content of 95% by mass or less is preferred. When two or more types of non-hydraulic compounds are used, the above content refers to the total amount of the two or more non-hydraulic compounds. The non-hydraulic compounds in the cement admixture can be analyzed and quantified, for example, by powder X-ray diffraction using a powder X-ray diffractometer (such as "SmartLab" manufactured by Rigaku Corporation).

[0019] Among the above non-hydraulic compounds, γ-2CaO.SiO ２ is preferred in that it requires less energy to grind than other compounds and has a large carbonation and densification effect over a long period of time, since it is accompanied by a powdering phenomenon called dusting during production. ２ In order to obtain the effect of the above, the amount of γ-2CaO.SiO relative to the total mass of the non-hydraulic compounds is ２is preferably 50% by mass or more, and more preferably 70% by mass or more. There is no particular upper limit. ２ may be 100% by mass.

[0020] The non-hydraulic compound in the present invention is a CaO raw material, SiO ２ It can be obtained by blending the raw material and the MgO raw material in a predetermined molar ratio and heat treating them in a rotary kiln, electric furnace, or the like. The temperature of the heat treatment is not particularly limited, but is usually in the range of about 1,000 to 1,800°C, and is often in the range of about 1,200 to 1,600°C. Examples of CaO raw materials include calcium carbonate such as limestone, calcium hydroxide such as slaked lime, by-product slaked lime such as acetylene by-product slaked lime, and fine powder generated from waste concrete blocks. SiO ２ Examples of raw materials include silica stone, clay, and various siliceous dusts generated as industrial by-products, such as silica fume and fly ash. Examples of MgO raw materials include magnesium hydroxide, basic magnesium carbonate, and dolomite. Non-energy-derived CO during heat treatment ２ In terms of reducing emissions, one or more types of industrial by-products containing CaO can be used, such as by-product slaked lime, fine powder generated from waste concrete blocks, municipal waste incineration ash, sewage sludge incineration ash, etc. Among these, the use of by-product slaked lime, which contains fewer impurities than other industrial by-products, is more preferable.

[0021] Examples of by-product slaked lime include by-product slaked lime produced as a by-product in the acetylene gas production process using the calcium carbide method (there are wet and dry products depending on the acetylene gas production method), and by-product slaked lime for acetylene, such as by-product slaked lime contained in dust captured in the wet dust collection process of a calcium carbide electric furnace. By-product slaked lime contains, for example, 65 to 95 mass % (preferably 70 to 90 mass %) of calcium hydroxide, as well as 1 to 10 mass % of calcium carbonate and 0.1 to 6.0 mass % (preferably 0.1 to 3.0 mass %) of iron oxide. These proportions are determined by measuring the mass loss (Ca(OH)２ : Around 405 to 515 ° C, CaCO ３ The volume average particle size measured by laser diffraction / scattering method is about 50 to 100 μm. Furthermore, the moisture content measured by the loss on drying method specified in JIS K 0068:2001 "Method for measuring moisture content in chemical products" is preferably 10 mass % or less. In addition, CaS, Al ２ S ３ , and CaC ２ Sulfur compounds such as CaS may be contained, but the content is preferably 2% by mass or less.

[0022] CaO raw material, SiO ２ The raw materials may contain impurities, but this is not a problem as long as the effects of the present invention are not impaired. Specific examples of impurities include Al. ２ O ３ , Fe ２ O ３ , TiO ２ , MnO, Na ２ O.K. ２ O, S, P ２ O ５ , F, B ２ O ３ , chlorine, etc. Coexisting compounds include free calcium oxide, calcium hydroxide, calcium aluminate, calcium aluminosilicate, calcium ferrite, calcium aluminoferrite, calcium phosphate, calcium borate, magnesium silicate, leucite (K ２ O.Al ２ O ３ 4SiO ２ ), spinel (MgO.Al ２ O ３ ), magnetite (Fe ３ O ４ ), the aforementioned CaS, A1 ２ S ３ , and CaC ２ -Sulfur compounds such as CaS.

[0023] Among these impurities, the content of S (sulfur) in non-hydraulic compounds is ３The content is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, and even more preferably 0.5% by mass or less, calculated as 0.7% by mass or less. If the content is 1.0% by mass or less, a sufficient carbonation promotion effect is easily obtained, and the setting property and hardening property can be kept within an appropriate range. ３ The S content in terms of S (sulfur oxide) can be adjusted by adding, for example, calcium sulfate to the non-hydraulic compound, and can be confirmed by measuring by X-ray fluorescence analysis. Note that S (sulfur) may be present in the non-hydraulic compound in an amount of about 0.2 mass% in terms of oxide.

[0024] In addition, in order to make the effect of the non-hydraulic compound more easily manifest, the chemical composition is such that, per 100 parts by mass of the non-hydraulic compound, 45 to 70 parts by mass of CaO and SiO ２ 30 to 55 parts by mass of Al ２ O ３ 0 to 10 parts by mass of Li ２ It is preferable that the content of O is 0.001 to 1.0 part by mass, CaO is 60 to 70 parts by mass, and SiO ２ 30 to 45 parts by mass of Al ２ O ３ 0.5 to 5 parts by mass of Li ２ It is more preferable that the non-hydraulic compound contains 0.002 to 0.5 parts by mass of O. Furthermore, as chemical components, CaO, SiO ２ , Al ２ O ３ , and Li ２ The total amount of O is preferably 90 parts by mass or more, and more preferably 95 to 100 parts by mass. ２ , Al ２ O ３ , and Li ２ The O content can be measured by X-ray fluorescence analysis or ICP emission spectrometry.

[0025] The fineness of the non-hydraulic compound is not particularly limited, but the Blaine specific surface area (also called the Blaine value) is 1,500 to 8,000 cm ２ / g is preferred, and 2,000 to 6,000 cm ２ / g is more preferable, and 4,000 to 6,000 cm ２ / g is even more preferable. When the Blaine specific surface area is within the above range, good material separation resistance is obtained, the pulverization power required during pulverization is not large, which is economical, and weathering is suppressed, thereby suppressing deterioration of quality over time. In the present invention, the Blaine specific surface area is determined in accordance with the method specified in JIS R 5201:2015 "Physical Testing Methods for Cement."

[0026] <Calcium Carbonate-Containing Powder> The cement admixture of the present invention contains a calcium carbonate-containing powder. The calcium carbonate-containing powder is one that contains calcium carbonate in each particle, and examples thereof include commercially available limestone fine powder and synthetic calcium carbonate, artificial calcium carbonate obtained from raw materials such as concrete sludge, waste concrete, and paper sludge, and calcium carbonate obtained by processing waste materials containing calcium carbonate as a main component, such as eggshells and seashells.

[0027] The calcium carbonate content of the calcium carbonate-containing powder in the cement admixture of the present invention is preferably 5% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, and even more preferably 80% by mass or more. There is no particular upper limit, but it may be 100% by mass. When the calcium carbonate content is within the above range, strength development during carbonation curing is more likely to be improved. The calcium carbonate content of the calcium carbonate-containing powder can be measured by powder X-ray diffraction (powder X-ray diffractometer: "SmartLab" manufactured by Rigaku Corporation).

[0028] The fineness of the calcium carbonate-containing powder is 2,000 to 7,000 cm in terms of Blaine specific surface area. ２ / g, and 2,750 to 6,000 cm ２ / g, and more preferably 3,000 to 4,500 cm ２ It is more preferable that the SiO2 content is 1 / g.

[0029] The calcium carbonate-containing powder is contained in the cement admixture at a content of preferably 30 to 85 mass %, more preferably 35 to 80 mass %, and even more preferably 40 to 75 mass %.

[0030] The cement admixture of the present invention may contain a hydraulic compound in addition to the non-hydraulic compound and the calcium carbonate-containing powder. The hydraulic compound is not particularly limited as long as it is one that is commonly used in cement compositions, and may be 3CaO.SiO ２ , 2CaO.SiO ２ Calcium silicate represented by 3CaO·3Al ２ O ３ CaSO ４ Eelimite, represented by 4CaO.Al ２ O ３ Fe ２ O ３ and 6CaO.2Al ２ O ３ Fe ２ O ３ , 6CaO·Al ２ O ３ Fe ２ O ３ Calcium aluminoferrite, represented by 2CaO.Fe ２ O ３ These hydraulic compounds may be used alone or in combination of two or more.

[0031] The cement admixture of the present invention can be produced by mixing the non-hydraulic compound and the calcium carbonate-containing powder. Any existing mixer can be used as the mixer, such as a tilting mixer, an omni mixer, a Henschel mixer, a V-type mixer, or a Nauta mixer.

[0032] In the production of cement admixtures, industrial by-products containing the aforementioned non-hydraulic compounds can also be used. Examples of such industrial by-products include steelmaking slag. Among steelmaking slag, γ-2CaO.SiO ２ Electric furnace reduction slag or stainless steel slag with a high content is preferred.

[0033] In the cement admixture of the present invention, the mass ratio of the non-hydraulic compound to the calcium carbonate-containing powder is preferably 1:6 to 3:1, more preferably 1:5 to 5:2, and even more preferably 1:4 to 2:1. When the mass ratio of the non-hydraulic compound to the calcium carbonate-containing powder is within the above range, the short-term CO ２ This can further promote immobilization.

[0034] [Cement Composition] The cement composition according to this embodiment contains the cement admixture of the present invention and cement.

[0035] The cement is not particularly limited, and examples thereof include various portland cements such as normal, early strength, extra early strength, low heat, and medium heat, various mixed cements obtained by mixing these portland cements with blast furnace slag, fly ash, silica, silica fume, metakaolin, allophane, etc., environmentally friendly cements (ecocement) manufactured using municipal waste incineration ash and sewage sludge incineration ash as raw materials, commercially available fine particle cements, white cements, filler cements obtained by mixing limestone fine powder, etc., and various cements can also be used in a fine powder form. ２ Low-emission geopolymer cement, sulfoaluminate cement, limestone-burned clay cement (LC3), CO ２ Examples include carbonated cement, which hardens by immobilizing . Also, cements prepared by increasing or decreasing the amount of components typically used in cement (e.g., gypsum) can be used. Furthermore, combinations of two or more of these can also be used.

[0036] From the viewpoint of manufacturing cost and strength development, the cement should have a Blaine specific surface area of ​​2,500 to 7,000 cm ２ / g, and 2,750 to 6,000 cm ２ / g, and more preferably 3,000 to 4,500 cm ２ It is more preferable that the SiO2 content is 1 / g.

[0037] In the cement composition of the present invention, the mass ratio of the cement admixture to the total mass of the cement admixture and cement of the present invention is preferably 5 to 70 mass%, more preferably 5 to 60 mass%, and even more preferably 10 to 50 mass%. When the mass ratio of the cement admixture is within the above range, good strength development is easily achieved, and short-term CO ２ This can facilitate the promotion of immobilization.

[0038] The cement composition of the present invention preferably contains aggregate. The aggregate is not particularly limited, and fine aggregates such as river sand, mountain sand, sea sand, lime sand, and silica sand, and coarse aggregates such as river gravel, mountain gravel, and lime gravel can be used.

[0039] The content of the aggregate is preferably 40 to 600 parts by mass, more preferably 50 to 500 parts by mass, and even more preferably 60 to 450 parts by mass, relative to 100 parts by mass of the total mass of the cement admixture and cement in the cement composition. By having the content of the aggregate within the above range, it is possible to improve fluidity retention and early strength development.

[0040] The calcium carbonate content of the cement composition is preferably 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. Having the calcium carbonate content within the above range facilitates better strength development during carbonation curing. The calcium carbonate content can be measured by powder X-ray diffraction (powder X-ray diffraction apparatus: Rigaku Corporation's "SmartLab").

[0041] Furthermore, the cement composition may contain one or more of the following known additives and admixtures used in ordinary cement materials, such as water reducing agents, air-entraining and entraining water reducing agents, high-performance water reducing agents, high-performance air-entraining and entraining water reducing agents, superplasticizers, antifoaming agents, thickeners, rust inhibitors, antifreeze agents, polymer dispersions for cement admixtures, shrinkage reducing agents, admixtures such as granulated blast furnace slag, slowly cooled blast furnace slag, sewage sludge incineration ash and its molten slag, municipal waste incineration ash and its molten slag, and pulp sludge incineration ash; fibrous substances such as polymers, vinylon fibers, acrylic fibers, and carbon fibers; setting modifiers; clay minerals such as bentonite; and anion exchangers such as hydrotalcite, within a range that does not adversely affect performance and does not substantially impair the objects of the present invention.

[0042] The cement composition of this embodiment may be prepared by mixing the respective materials at the time of application, or may be prepared by mixing some or all of the materials in advance. As the mixing device, the above-mentioned mixing devices can be used.

[0043] <Hardened cement product> The hardened cement product according to this embodiment is obtained by hardening the cement composition of the present invention.

[0044] The hardened cement product of the present invention can be obtained by kneading the cement composition of the present invention with water and subjecting it to carbonation curing. The amount of water mixed is preferably 10 to 70 mass %, more preferably 15 to 65 mass %, and even more preferably 20 to 60 mass %, based on the total mass of the cement admixture and cement in the cement composition. The mixing apparatus can be any of the above-mentioned mixing apparatuses. The water is not particularly limited, and examples thereof include tap water, groundwater, recycled water from ready-mix concrete plants, CO ２ Water containing the above may be used.

[0045] After mixing the cement composition with water and filling (casting) it into a formwork, and then typically demolding it and then carbonation curing. Mortar or concrete using the cement admixture of the present invention can be demolded about one day after casting.

[0046] The atmosphere for carbonation curing is 15 to 60°C, 20 to 80% RH, CO ２It is preferable to carry out the process in an environment with a concentration of 1 to 95%, a temperature of 15 to 50°C, a humidity of 40 to 75% RH, and CO ２ It is more preferable to carry out the treatment in an environment with a concentration of 3 to 95%. The atmosphere may be atmospheric pressure, but may be pressurized as necessary.

[0047] CO fixed in the hardened cement body by carbonation curing ２ amount (CO ２ The fixed amount is the CO2 content measured by coulometric titration using a coulometer for the hardened cement body after carbonation curing and the cement composition before carbonation curing. ２ It is calculated from the amount of CO ２ The amount was determined by crushing the hardened cement or cement composition and placing it in an Erlenmeyer flask, adding hydrochloric acid (3 mol / L), stirring with a stirrer, and measuring the amount of CO generated. ２ The gas is introduced into the absorption solution with nitrogen, and the amount of carbon is measured from the amount of electricity required to maintain the transmittance of the absorption solution at a constant level. ２ Converted into CO content, ２ Content and CO of cement composition ２ From the difference in content, CO ２ The fixed amount can be calculated.

[0048] CO of hardened cement ２ The fixation rate can be calculated by the following formula: ２ The fixation rate is the same as that of the CO ２ The fixed amount and the CO of the cement composition described later ２ It can be calculated from the fixing ability and the content. ２ Immobilization rate) = (CO ２ fixed amount) / {(CO ２ Fixation ability) x (cement composition content)} x 100

[0049] CO of cement composition ２ The fixation capacity is a parameter value calculated by the following formula: (CO ２ Fixation capacity) = 0.785 (CaO - 0.56CaCO ３ -0.7SO ３ )+1.091MgO+1.42Na ２ O+0.935K ２O In the above formula, CaCO in the cement composition ３ The content of components other than CaCO can be measured in accordance with JIS R 5202:2015 "Methods for chemical analysis of cement." ３ The content of CO ２ CO2 of cement composition in measuring the fixed amount ２ From the content, (CaCO ３ Content) = (CO ２ content) / (CO ２ molecular weight)×(CaCO ３ Alternatively, in the case of simple measurement, the calculation may be performed using the following formula: (CO ２ Fixation capacity) = 0.785CaO

[0050] CO of cement composition ２ The fixing capacity is preferably 0.15 to 0.60, more preferably 0.20 to 0.50, and even more preferably 0.22 to 0.48. ２ When the fixing ability is within the above range, the strength development during carbonation curing is improved, and the short-term CO ２ This can further promote immobilization.

[0051] CO2 28 days after casting of hardened cement ２ The immobilization rate is preferably 55% or more, more preferably 58% or more, and even more preferably 60% or more.

[0052] The compressive strength of the hardened cement body 28 days after casting is 40 N / mm ２ It is preferable that the strength is 60 N / mm or more. ２ The upper limit is not particularly limited, but it is preferably 85 N / mm ２ It is preferable that the strength is 80 N / mm or less. ２ It is more preferable that:

[0053] The present invention will be further explained below based on experimental examples, but the present invention is not limited to these.

[0054] Experimental Example 1 A cement admixture was prepared by mixing the materials described below in the proportions shown in Table 1. The prepared cement admixture was mixed with cement and fine aggregate so that the cement admixture was 30 parts by mass and the fine aggregate was 300 parts by mass per 100 parts by mass of the cement and the prepared cement admixture, to prepare a cement composition. The prepared cement composition was used to prepare mortar by adding 50 parts by mass of water per 100 parts by mass of the cement and cement admixture, and kneading. The mortar was poured into a formwork (4 x 4 x 16 cm) and demolded after 1 day of age. The mortar was then stored at a temperature of 40°C, a relative humidity of 60% RH, and CO ２ The mixture was cured by carbonation in an environment with a concentration of 20% for up to 28 days to obtain a hardened cement product. As reference examples, a cement composition, mortar, and hardened cement product without any cement admixture were prepared in the same manner as above. The following measurements were carried out on the cement composition and hardened cement product. The results are shown in Table 1.

[0055] (Material used) Non-hydraulic compound (γ-2CaO・SiO ２ ): First-grade reagent calcium carbonate and first-grade reagent silicon dioxide were mixed in a molar ratio of 2:1, heat-treated in an electric furnace at 1,400 ° C for 2 hours, and allowed to cool to room temperature. After that, the Blaine specific surface area was 4,000 cm ２ The obtained sample was analyzed by powder X-ray diffraction (powder X-ray diffractometer: "SmartLab" manufactured by Rigaku Corporation) and found to be γ-2CaO.SiO ２ It was confirmed that the powder contained 81% by mass of calcium carbonate. Calcium carbonate-containing powder A: limestone pulverized product, calcium carbonate content 95%, Blaine specific surface area 3,200 cm ２ / g. Cement: Ordinary Portland cement (commercial product), Blaine specific surface area 3,300 cm ２ / g, specific gravity 3.15g / cm ３ Water: Tap water. Fine aggregate: Sand from the Himekawa River system in Itoigawa City, Niigata Prefecture, maximum size 5 mm or less, density 2.62 g / cm ３ .

[0056] (Measurement items) Compressive strength: In accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement," the compressive strength was measured at ages of 3 days, 7 days, and 28 days, with the age at the time of pouring being considered as 0 days.

[0057] Flow: The flow value of the mortar was measured in accordance with the method specified in JIS R 5201:2015 "Physical testing methods for cement."

[0058] CO ２ Immobilization amount: For each of the cement composition and the hardened cement body, a coulometer (2000S-CAT model, manufactured by Nippon Ansu Co., Ltd.) was used. The hardened cement body or the cement composition was pulverized and placed in an Erlenmeyer flask. Hydrochloric acid (3 mol / L) was added and the mixture was stirred with a stirrer. The generated CO ２ The gas is introduced into the absorption solution with nitrogen, and the amount of carbon is measured from the amount of electricity required to maintain the transmittance of the absorption solution at a constant level. ２ Converted into CO content, ２ Content and CO of cement composition ２ From the difference in content, CO ２ The fixed amount was calculated.

[0059] CO ２ Fixation rate: CO expressed by the following formula ２ Regarding the fixing ability, in accordance with JIS R 5202:2015 "Chemical analysis method of cement", CaCO ３ The contents of components other than CaCO were measured. ３ The content of CO ２ CO2 of cement composition in measuring the fixed amount ２ From the content, (CaCO ３ Content) = (CO ２ content) / (CO ２ molecular weight)×(CaCO ３ The molecular weight was calculated as (CO ２ Fixation capacity) = 0.785 (CaO - 0.56CaCO ３ -0.7SO ３ )+1.091MgO+1.42Na ２ O+0.935K ２ O Calculated CO ２Using the fixing ability, the CO of the hardened cement body is calculated from the following formula: ２ The fixation rate was calculated. ２ Immobilization rate) = (CO ２ fixed amount) / {(CO ２ Fixation ability) x (cement composition content)} x 100

[0060]

[0061] The cement admixture of the present invention is useful as a cement admixture particularly for use in the fields of civil engineering and construction, and can be suitably used as a cement composition.

Claims

1. γ-2CaO・SiO ２ , 3CaO・2SiO ２ , α-CaO.SiO ２ and calcium magnesium silicate, and a calcium carbonate-containing powder.

2. The non-hydraulic compound is γ-2CaO・SiO ２ The cement admixture according to claim 1, 3. The cement admixture according to claim 1 or 2, wherein the calcium carbonate content of the calcium carbonate-containing powder is 5% by mass or more.

4. The cement admixture according to claim 1 or 2, wherein the mass ratio of the non-hydraulic compound to the calcium carbonate-containing powder is 1:6 to 3:

1.

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

6. The cement composition according to claim 5, wherein the mass ratio of the cement admixture to the total mass of the cement admixture and the cement is 5 to 70 mass %.

7. A hardened cement product obtained by hardening the cement composition according to claim 5.

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