Cement, cement composition, hardened cement product, and method for producing hardened cement product

Abstract

This cement is cured by a carbonation reaction, said cement comprising: a γ crystal phase constituted by γ-2CaO·SiO2(γ-C2S); a β crystal phase constituted by β-2CaO·SiO2(β-C2S); and 2CaO·Al2O3·SiO2(C2AS).

Description

[Technical Field]

[0001] The present invention relates to cement, a cement composition, a hardened cement product, and a method for producing the hardened cement product. [Background technology]

[0002] Various developments have been made in cement to date. One such technology is known from Patent Document 1. Patent Document 1 describes a technique for producing a hardened cement product with high flexural strength by kneading γ-2CaO·SiO2, a water-dispersible polymer, and water (claim 1). Patent Document 1 focuses on the characteristic of γ-2CaO·SiO2, which behaves as particles in an underwater environment, and describes that by using a water-dispersible polymer in combination with the γ-2CaO·SiO2 particles, lubrication or dispersion properties as well as plasticity are imparted (paragraph 0008), thereby achieving high flexural strength properties (paragraph 0005). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 04-214059 Summary of the Invention [Problem to be solved by the invention]

[0004] However, as a result of investigations by the present inventors, it was found that the γ-2CaO·SiO2 particles described in Patent Document 1 still have room for improvement in terms of workability, compressive strength, storage stability, and temperature dependency. [Means for solving the problem]

[0005] After further investigation, the inventors discovered that by using a cement containing a γ crystalline phase composed of γ-2CaO·SiO2, a β crystalline phase composed of β-2CaO·SiO2, and 2CaO·Al2O3·SiO2, it is possible to improve the workability, compressive strength, storage stability, and temperature dependency of such cement in a balanced manner, thereby completing the present invention.

[0006] According to one aspect of the present invention, there are provided the following cement, cement composition, hardened cement product, and method for producing the hardened cement product. 1. A cement that hardens by a carbonation reaction, The γ crystalline phase consists of γ-2CaO·SiO2 (γ-C2S) and The β crystalline phase consists of β-2CaO·SiO2 (β-C2S) and 2CaO·Al2O3·SiO2 (C2AS) and including, cement. 2. The cement according to 1., A cement having a γ-C2S content of 30% by mass or more and 98% by mass or less, based on 100% by mass of the cement. 3. The cement according to 1. or 2., A cement having a content of the C2AS of 0.5% by mass or more and 50% by mass or less relative to 100% by mass of the γ-C2S. 4. The cement according to any one of 1. to 3., A cement comprising a heterophase present in the gamma crystalline phase, the heterophase containing the C2AS. 5. The cement according to 4., A cement in which Al2O3 is not contained in the gamma crystalline phase. 6. The cement according to any one of 1. to 5., A cement comprising Al2O3 in the β crystalline phase. 7. The cement according to any one of 1. to 6., A cement having a content of the β-C2S of 1.0 mass% or more and 50 mass% or less relative to 100 mass% of the γ-C2S. 8. The cement according to any one of 1. to 7., Cement in powder form.

[0007] 9. A cement composition comprising the cement according to any one of 1. to 8., A cement composition which is either a cement paste, a cement mortar or a cement concrete. 10. The cement composition according to 9., A cement composition that does not contain Portland cement.

[0008] 11. A hardened cement product, which is a hardened product of the cement composition according to 9. or 10.

[0009] 12. A method for producing a hardened cement product, comprising a curing step of curing the cement composition according to 9. or 10. under environmental conditions of a temperature of 10°C to 150°C, a relative humidity of 10% to 80%, a CO2 concentration of 0.1% to 90%, and a water vapor pressure of 3.0 hPa to 300 hPa. 13. A method for producing a hardened cement product according to 12., The method for producing a hardened cement product, wherein the curing time in the curing step is 1 hour or more and 90 hours or less. 14. A method for producing a hardened cement product according to 12. or 13., In the curing step, the cement composition according to 9. or 10. is pressure-molded, or a water slurry containing the cement composition according to 9. or 10. is pressure-molded to obtain a pressure-molded product, and the pressure-molded product is then cured under the environmental conditions. [Effects of the Invention]

[0010] According to the present invention, there are provided a cement having excellent workability, compressive strength, storage stability, and temperature dependency, a cement composition using the same, a hardened cement product, and a method for producing the hardened cement product. [Brief explanation of the drawings]

[0011] [Figure 1] This is an SEM image of cement A. [Figure 2] This is an SEM image of cement B. DETAILED DESCRIPTION OF THE INVENTION

[0012] The cement of this embodiment will be outlined below.

[0013] The cement of this embodiment is a cement that hardens through a carbonation reaction and contains a γ crystalline phase composed of γ-2CaO·SiO2 (hereinafter sometimes abbreviated as γ-C2S), a β crystalline phase composed of β-2CaO·SiO2 (hereinafter sometimes abbreviated as β-C2S), and 2CaO·Al2O3·SiO2 (hereinafter sometimes abbreviated as C2AS).

[0014] According to the findings of the present inventors, by using cement containing γ-C2S, β-C2S, and C2AS, workability and compressive strength are improved, while a decrease in workability and compressive strength is suppressed even when the cement is stored under specified conditions, and a decrease in workability and compressive strength is suppressed even under fluctuating temperature conditions, preferably in a low-temperature environment. In other words, it has been found that the storage stability and temperature dependence of cement properties such as workability and compressive strength can be improved.

[0015] According to this embodiment, a cement having excellent workability, compressive strength, storage stability, and temperature dependency can be realized.

[0016] Furthermore, by appropriately controlling the CaO / SiO2 molar ratio according to the Al2O3 content in the raw materials, it is possible to achieve cement that is entirely powdered.

[0017] The cement of this embodiment will be described in detail below.

[0018] The cement includes an inorganic fired product containing at least γ-C2S and at least one of β-C2S and C2AS. The inorganic fired product refers to a molded or powdered product having a predetermined shape obtained by heating and firing inorganic raw materials.

[0019] γ-C2S is known to have α-type, β-type, and γ-type crystal forms. These differ in crystal structure and density. Among these, γ-C2S, which is γ-type, exhibits a carbonation inhibitory effect. Forced carbonation using γ-C2S can increase the densification of hardened cement.

[0020] γ-C2S constitutes the γ crystalline phase of cement, which may be included as an inorganic matrix in cement.

[0021] The lower limit of the γ-C2S content is, for example, 30 parts by mass or more, preferably 35 parts by mass or more, and more preferably 40 parts by mass or more, per 100 parts by mass of cement. On the other hand, the upper limit of the γ-C2S content is, for example, 98 parts by mass or less, preferably 95 parts by mass or less, and more preferably 93 parts by mass or less, per 100 parts by mass of cement. By ensuring that the content is not within this range, workability and compressive strength can be improved.

[0022] The cement may contain heterophases present in the gamma crystalline phase.

[0023] The heterogeneous phase is present inside the grains of the crystalline body made of the γ crystalline phase consisting of γ-C2S or along the grain interfaces in at least one SEM image of the fracture surface of the cement. In the SEM image, one or more heterogeneous phases may be contained in the crystal grains.

[0024] As a component constituting the heterogeneous phase, the cement preferably contains C2AS, which can further improve the carbonation rate. In addition, components other than C2AS may inevitably be present in the heterogeneous phase.

[0025] The lower limit of the C2AS content is, for example, 0.5% by mass or more, preferably 1.0% by mass or more, and more preferably 2.0% by mass or more, relative to 100% by mass of γ-C2S, which can improve workability, compressive strength, storage stability, and temperature dependency. On the other hand, the upper limit of the C2AS content is, for example, 50% by mass or less, preferably 40% by mass or less, and more preferably 30% by mass or less, relative to 100% by mass of γ-C2S, which allows for a balance of various properties.

[0026] In this embodiment, it is possible to control the presence of the heterogeneous phases and the contents of the components that make up the heterogeneous phases by, for example, appropriately selecting the type and amount of each component contained in the cement, the cement preparation method, etc. Among these, factors that can be cited for achieving the desired presence of the heterogeneous phases and the desired contents of the components that make up the heterogeneous phases include, for example, using a raw material mixture containing a CaO raw material, a SiO2 raw material, and an Al2O3 raw material, using a rotary kiln lined with high-purity aluminum bricks, and / or applying a predetermined concentration of alumina mortar to the brick surfaces inside the kiln, and appropriately adjusting the conditions of the firing temperature, dry crushing, and granulation size.

[0027] The content of each mineral component in cement can be confirmed using common analytical methods. For example, the mineral composition of a crushed sample can be confirmed using powder X-ray diffraction, and the data can be analyzed using the Rietveld method to quantify the mineral composition. Furthermore, the mineral composition can be calculated based on the chemical components and the results of powder X-ray diffraction analysis.

[0028] The cement may be formulated to be free of Al2O3 in the gamma crystalline phase, which may improve workability, compressive strength, storage stability, and temperature dependency.

[0029] The cement may further be configured to include a β crystalline phase comprised of β-2CaO·SiO2.

[0030] The lower limit of the β-C2S content is, for example, 1.0 mass% or more, preferably 2.0 mass% or more, and more preferably 3.0 mass% or more, relative to 100 mass% of γ-C2S, which can improve the compressive strength. On the other hand, the upper limit of the β-C2S content is, for example, 50% by mass or less, preferably 30% by mass or less, and more preferably 20% by mass or less, relative to 100% by mass of γ-C2S. This can suppress a decrease in setting and hardening properties.

[0031] Cement containing β-C2S may be formulated to contain Al2O3 in the β crystalline phase, which can improve workability, compressive strength, storage stability, and temperature dependence.

[0032] The cement may contain a glass phase and / or CaO·2Al2O3 (hereinafter sometimes abbreviated as CA2).

[0033] The lower limit of the glass phase content is, for example, 20% by mass or more, preferably 30% by mass or more, and more preferably 40% by mass or more, relative to 100% by mass of γ-C2S. This makes it possible to realize a cement that is entirely powdered. On the other hand, the upper limit of the glass phase content is, for example, 120% by mass or less, preferably 100% by mass or less, and more preferably 90% by mass or less, relative to 100% by mass of γ-C2S. This makes it possible to realize a cement that is entirely powdered.

[0034] The lower limit of the CA2 content is, for example, 0.01% by mass or more, preferably 0.05% by mass or more, and more preferably 0.1% by mass or more, relative to 100% by mass of γ-C2S. This makes it possible to realize a cement that is entirely powdered. On the other hand, the upper limit of the CA2 content is, for example, 20% by mass or less, preferably 18% by mass or less, and more preferably 15% by mass or less, relative to 100% by mass of γ-C2S. This makes it possible to realize a cement that is entirely powdered.

[0035] The method for producing cement will be described.

[0036] The method for producing cement includes a step of firing a raw material mixture containing a CaO raw material, an SiO2 raw material, and an Al2O3 raw material, for example, in a kiln.

[0037] The CaO raw material may be commercially available industrial raw material, or may contain one or more selected from the group consisting of limestone, coal ash, quicklime, slaked lime, acetylene waste, steel slag (converter slag, electric furnace slag), coal ash, woody biomass combustion ash, fine powder generated from waste concrete blocks, industrial waste such as concrete sludge, and municipal waste incineration ash, and calcium carbonate obtained by refining these industrial wastes. Among these, slaked lime and by-product slaked lime may be used.

[0038] The SiO2 raw material may be commercially available as an industrial raw material, such as silica stone, silica sand, quartz, or diatomaceous earth. These may be used alone or in combination of two or more. However, these may not be used if the CaO raw material or Al2O3 raw material contains the necessary amount of SiO2. For example, when coal ash containing SiO2 is used as the CaO raw material, the above SiO2 raw material does not need to be added.

[0039] Here, coal ash (fly ash, etc.) is a general term for combustion ash obtained by burning coal, such as coal combustion ash discharged from the boiler of a thermal power plant. Examples of coal ash include ash generated in a coal-fired power plant by pulverized coal combustion and coal ash that falls and is collected from the combustion gas of the combustion boiler as it passes through an air preheater or a coal economizer, coal ash collected by an electrostatic precipitator, and coal ash that falls to the bottom of the combustion boiler furnace.

[0040] The Al2O3 raw material may be commercially available as an industrial raw material, or may contain, for example, one or more selected from the group consisting of bauxite, aluminum hydroxide, and aluminum ash. The aluminum ash may be mainly composed of aluminum hydroxide. Among these, bauxite may be used.

[0041] These raw materials are mixed and crushed to obtain a raw material mixture after firing, so that the mineral composition ratio is predetermined.

[0042] The method of mixing and grinding is not particularly limited, and either a dry grinding method or a wet grinding method can be applied. In the case of the wet grinding method, a dehydration treatment is required for subsequent granulation. In addition, when quicklime is used as the raw material, a dry grinding method is preferable. In addition, the γ-C2S / C2AS ratio in cement can be controlled by adjusting the ratio of raw materials used.

[0043] The raw material mixture may be granulated before firing. The granules are adjusted to an appropriate size, for example, 0.5 to 20.0 cm.

[0044] The firing temperature may be, for example, 1,200°C to 1,600°C, preferably 1,300°C to 1,550°C, and more preferably 1,400°C to 1,450°C.

[0045] For firing, a kiln such as a rotary kiln can be used. For example, a rotary kiln may be used in which the bricks in the firing zone are made of high-purity alumina bricks with an Al2O3 content of 99% or more by mass, and / or alumina mortar adjusted to an appropriate concentration may be applied to the inner surface of the bricks in the firing zone of the rotary kiln before firing.

[0046] Cement may be obtained as an inorganic burned product (clinker) obtained by burning inorganic raw materials, or may be obtained as a powdered inorganic burned product by pulverizing the clinker.

[0047] The cement composition of the present embodiment contains at least the above-described cement, and may contain water and sand as necessary. This cement composition is any of cement paste, cement mortar, and cement concrete. In this specification, cement paste can be defined as containing cement and water, cement mortar as containing cement, water, and sand (fine aggregate), and cement concrete as containing cement, water, and aggregate (fine aggregate, coarse aggregate).

[0048] The amount of cement used varies depending on the purpose of use, but may usually be, for example, 1 to 90 parts by mass, preferably 2 to 80 parts by mass, more preferably 3 to 70 parts by mass, per 100 parts by mass of the cement composition. In this specification, unless otherwise specified, the symbol "to" indicates that the upper and lower limits are included.

[0049] The cement composition may be configured not to contain Portland cement such as normal, early strength, extra early strength, low heat, or medium heat cement. In other words, the cement of this embodiment can be used alone without being used in combination with Portland cement.

[0050] The amount of water used is not particularly limited, but the water / cement ratio in the cement composition is usually, for example, about 25 to 70 mass %, and may be 30 to 60 mass %.

[0051] Furthermore, the cement composition may contain, as necessary, one or more of aggregates such as sand (fine aggregate) and gravel (coarse aggregate), expansive additives, rapid hardening agents, set adjusters, water reducing agents, high-performance water reducing agents, air entraining agents, air entraining water reducing agents, high-performance air entraining water reducing agents, thickeners, rust inhibitors, antifreeze agents, hydration heat inhibitors, polymer emulsions, clay minerals such as bentonite and montmorillonite, ion exchangers such as zeolite, hydrotalcite, and hydrocalumite, sulfates such as aluminum sulfate and sodium sulfate, phosphates, and boric acid, within a range that does not substantially impair the objects of the present invention.

[0052] The kneading method is not particularly limited and may be a commonly used method. As a mixing device, any existing stirring device can be used, such as a tilting mixer, an omni mixer, a V-type mixer, a Henschel mixer, or a Nauta mixer.

[0053] The cement and water may be mixed at the time of construction, or some or all of the materials may be mixed in advance.

[0054] The cement of this embodiment and the cement composition containing the cement have air-hardening properties, that is, they harden by a carbonation reaction using a CO2-containing gas, etc. By hardening the cement composition, a hardened cement product is obtained.

[0055] An example of a method for producing a hardened cement product may involve curing the composition under environmental conditions containing a CO2-containing gas, and may include a curing step of curing the composition under environmental conditions of a temperature of 10°C to 150°C, a relative humidity of 10% to 80%, a CO2 concentration of 0.1% to 90%, and a water vapor pressure of 3.0 hPa to 300 hPa, more preferably a temperature of 15°C to 130°C, a relative humidity of 20% to 70%, a CO2 concentration of 0.5% to 80%, and a water vapor pressure of 5.0 hPa to 250 hPa.

[0056] The curing time in the curing step can be changed appropriately depending on the application, but may be, for example, from 1 hour to 90 hours, more preferably from 3 hours to 80 hours.

[0057] The curing method is not particularly limited, and any of the commonly used curing methods such as room temperature and normal pressure curing, steam curing, high temperature and high pressure steam curing, and pressurized curing can be applied.

[0058] In addition, the method for producing a hardened cement product may involve pressure-molding the above-mentioned cement composition or pressure-molding a water slurry containing the above-mentioned cement composition to obtain a pressure-molded product during the curing step, and then curing the pressure-molded product under the above-mentioned environmental conditions.

[0059] Although the embodiments of the present invention have been described above, these are merely examples of the present invention, and various other configurations may be adopted. Furthermore, the present invention is not limited to the above-described embodiments, and modifications and improvements within the scope of achieving the object of the present invention are included in the present invention. Below, examples of reference forms are given. The first example cement is an air-setting cement containing a gamma crystalline phase composed of gamma-2CaO·SiO2 (gamma-C2S), a beta crystalline phase composed of beta-2CaO·SiO2 (beta-C2S), and 2CaO·Al2O3·SiO2 (C2AS). The second example cement is an air-setting cement containing a gamma crystalline phase composed of gamma-2CaO·SiO2 (gamma-C2S) and 2CaO·Al2O3·SiO2 (C2AS). The third example cement is an air-hardening cement containing a gamma crystalline phase composed of gamma-2CaO·SiO2 (gamma-C2S) and a beta crystalline phase composed of beta-2CaO·SiO2 (beta-C2S). [Example]

[0060] The present invention will be described in detail below with reference to examples, but the present invention is not limited to the descriptions of these examples.

[0061] <Cement Preparation> (Raw materials used) By-product slaked lime: slaked lime produced as a by-product after the reaction of calcium carbide with water to generate acetylene. Contains 0.8% by mass of SiO2, 0.6% by mass of Al2O3, 0.3% by mass of Fe2O3, 68.5% by mass of CaO, 0.02% by mass of MgO, 0.01% by mass of Na2O, 0.01% by mass of K2O, and 0.5% by mass of SO3. Loss on ignition (LOI) is 24.1% by mass.

[0062] Silica: Fine silica powder, 99.3 mass% SiO2, 0.01 mass% Al2O3, 0.0 mass% Fe2O3, 0.0 mass% CaO, 0.04 mass% MgO, 0.02 mass% Na2O, 0.3 mass% K2O, 0.04 mass% SO3, and 0.6 mass% loss on ignition (LOI).

[0063] Alumina: 99.03% by weight Al2O3, 0.14% by weight SiO2, <0.01% by weight Fe2O3, <0.01% by weight CaO, 0.06% by weight TiO2, loss on ignition (LOI) 0.82% by weight.

[0064] (Cement A) As a raw material containing CaO and SiO2, the above-mentioned by-product slaked lime and silica stone were blended to obtain the CaO / SiO2 molar ratio shown in Table 1, and then dry mixed and pulverized to obtain a mixed raw material. The obtained mixed raw material was granulated to produce granules with a diameter of approximately 1 cm to 2.5 cm. The resulting granulated material was placed in a rotary kiln whose firing zone consisted of high-purity alumina bricks (with an Al2O3 content of 99% or more by mass), fired at a firing point of 1,400°C, and powdered clinker was synthesized during the cooling process to room temperature. The resulting powdered clinker was used as Cement A.

[0065] (Cement B, C) Clinker powders with the mineral proportions shown in Table 1 were synthesized in the same manner as cement A, except that the above-mentioned alumina was used instead of silica stone and the CaO / SiO2 molar ratio and Al2O3 content shown in Table 1 were adopted. These were used as cements B and C.

[0066] (Cement D) Calcium carbonate powder with a purity of 99.0% by mass or higher and silicon oxide powder with a purity of 99.0% by mass or higher were mixed so that the molar ratio of CaO / SiO2 was 2.0, and the mixture was heat-treated at 1,400°C for 2 hours and slowly cooled in an electric furnace to synthesize γ-C2S powder. The resulting γ-C2S powder was used as cement D. The γ-C2S powder obtained here contains C2AS and C 12 A7 was not included as it was not dissolved.

[0067] The obtained SEM images and elemental surface analysis using an energy dispersive X-ray analyzer (EDS) confirmed that C2AS is present in the γ crystalline phase composed of γ-C2S in cements A to C, and that Al2O3 is not contained in this γ crystalline phase. Furthermore, β-C2S was confirmed in cements A to C, and it was confirmed that Al2O3 is contained in the β crystalline phase composed of β-C2S. Furthermore, the fracture surfaces of the resulting clinker powders of cements A to C were observed using an SEM, and it was confirmed that C2AS was present in the γ crystalline phase composed of γ-C2S. Figure 1 shows an SEM image of the fracture surface of clinker from cement A, and Figure 2 shows an SEM image of the fracture surface of clinker from cement B. In Figures 1 and 2, arrow A (white area) represents C2AS, and arrow B (gray area) represents γ-C2S.

[0068] [Table 1]

[0069] In Table 1, γ-C2S:γ-2CaO·SiO2, β-C2S:β-2CaO·SiO2, and C2AS:2CaO·Al2O3·SiO2 are represented. In Table 1, the proportions of mineral composition were calculated based on the results of chemical composition quantified using fluorescent X-rays and the results of identification by powder X-ray diffraction.

[0070] The resulting cement was evaluated based on the following evaluation items.

[0071] <Workability, compressive strength, storage stability, temperature dependency> (Preparation of mortar) Cement (any of Examples 1 to 3 or Cement A to D of the Comparative Example), water (tap water), and sand (JIS standard sand) were mixed in a room at 20°C to prepare a mortar with a water / cement ratio of 1 / 1 (by mass) and a cement / sand ratio of 1 / 3 (by mass).

[0072] Using the mortar (sample A) immediately after preparation, workability, compressive strength (strength), storage stability, and temperature dependency were measured as follows. (Test Method) Workability: Using Sample A immediately after preparation (storage 0 months), the flow value was measured in a 20°C environment in accordance with the flow test of JIS R 5201. Compressive strength (strength): Using Sample A immediately after preparation (storage period 0 months), the compressive strength was measured at 28 days old in accordance with JIS R 5201 in an environment of 20°C temperature, 60% relative humidity, 5% CO2 concentration, and 9.2 hPa water vapor pressure.

[0073] Storage stability: Immediately after preparation, cements A to D were each placed in a sealed plastic bag and stored for 3 months at a temperature of 20°C and a humidity of 60%. Mortar (sample B) was prepared in the same manner as above (preparation of mortar), except that cements A to D stored for 3 months were used. Using Sample B immediately after preparation (stored for 3 months), workability (flow value) and compressive strength were measured under the same conditions as Sample A above. The relative ratio of each test result of Sample B stored for 3 months to each test result of Sample A stored for 0 months was then calculated.

[0074] Temperature dependency: Using Sample A immediately after preparation (storage 0 months), workability and compressive strength were measured under the same conditions except for changing the test temperature to 5°C, and the relative ratio of each test result at 5°C to each test result at 20°C was calculated.

[0075] In Table 1, in the tests for workability, compressive strength, storage stability, and temperature dependency, if the material can be used without any problems in practical use it is marked as "good," and if there is a possibility that problems may arise in practical use it is marked as "poor."

[0076] Furthermore, the cements from Examples 1 to 3 were mixed with sand (JIS standard sand) and 5% water in a room at 20°C, and the resulting mixture was pressure-molded at 30 MPa to prepare mortar pellets (pressure-molded products) measuring 4 cm x 4 cm x 16 cm. The pressure-molded products were cured in an environment with a temperature of 20°C, a relative humidity of 60% RH, a CO2 concentration of 5%, and a water vapor pressure of 9.2 hPa, yielding hardened cement products with practical compressive strength.

[0077] The cements of Examples 1 to 3 were excellent in workability and compressive strength, and were shown to have high storage stability and low temperature dependency compared to Comparative Example 1. Such cements of each Example can be suitably used as cements that harden by a carbonation reaction.

[0078] This application claims priority based on Japanese Patent Application No. 2022-019299, filed February 10, 2022, the disclosure of which is incorporated herein in its entirety.

Claims

1. A cement that hardens by a carbonation reaction, γ-2CaO.SiO ２ (γ-C ２ S), and a γ crystalline phase composed of β-2CaO.SiO ２ (β-C ２ S), and a β crystalline phase composed of 2 CaO・Al ２ O ３ • SiO ２ (C) ２ AS)と、 Including, The content of the γ-C 2 S is 30% by mass or more and 98% by mass or less in 100% by mass of the cement, the content of the C 2 AS is 0.5% by mass or more and 50% by mass or less relative to 100% by mass of the γ-C 2 S; the content of the β-C 2 S is 1.0 mass% or more and 50 mass% or less relative to 100 mass% of the γ-C 2 S, The γ crystalline phase does not contain Al 2 O 3 , A cement comprising Al 2 O 3 in the β crystalline phase.

2. 10. The cement of claim 1, The heterogeneous phase is present in the γ crystalline phase, and the heterogeneous phase contains the C ２ Cement containing AS.

3. 3. The cement according to claim 1 or 2, Cement in powder form.

4. A cement composition comprising the cement of claim 1, A cement composition which is either a cement paste, a cement mortar or a cement concrete.

5. 5. The cement composition of claim 4, A cement composition that does not contain Portland cement.

6. A hardened cement product which is a hardened product of the cement composition according to claim 4.

7. The cement composition according to claim 4 is heated at a temperature of 10°C to 150°C, a relative humidity of 10% to 80%, and CO ２ A method for producing a hardened cement product, comprising a curing step of curing under environmental conditions of a concentration of 0.1% or more and 90% or less and a water vapor pressure of 3.0 hPa or more and 300 hPa or less.

8. The method for producing a hardened cement product according to claim 7, The method for producing a hardened cement product, wherein the curing time in the curing step is 1 hour or more and 90 hours or less.

9. The method for producing a hardened cement product according to claim 7, In the curing step, the cement composition according to claim 4 is pressure-molded, or a water slurry containing the cement composition according to claim 4 is pressure-molded to obtain a pressure-molded product, and the pressure-molded product is then cured under the environmental conditions.

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