Cement composition, and method for manufacturing the cement composition

Abstract

To provide a cement composition that can reduce CO2 emissions and has sufficient strength development properties. [Solution] The cement composition comprises cement clinker, gypsum, and an admixture, the admixture containing limestone and carbonated cementitious hardened material. The calcium carbonate content in the admixture is 80% by mass or less, and the admixture content is 2 to 20% by mass based on the total amount of the cement composition.

Description

[Technical Field]

[0001] This disclosure relates to cement compositions and methods for producing cement compositions. [Background technology]

[0002] As part of efforts to promote decarbonization in the field of cement technology, cement compositions are being used in which a portion of ordinary Portland cement, which has a large carbon dioxide (CO2) emission during its production, is replaced with admixtures. Limestone is widely used as an admixture to replace ordinary Portland cement because it is readily available and inexpensive.

[0003] Current JIS standards stipulate that the amount of admixture that can be added to ordinary Portland cement is 5% by mass or less. On the other hand, as an attempt to promote decarbonization, for example, Non-Patent Document 1 investigates the possibility of adding admixture to ordinary Portland cement in amounts exceeding the 5% by mass specified in JIS standards. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Ayaka Nakaguchi et al., "Quality Evaluation of Cement with Increased Amount of Small Mixed Components," Cement Science & Concrete Technology, Cement Association, Vol. 72, pp. 389-395. [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] However, as described in Non-Patent Document 1, increasing the amount of admixture can affect various physical properties, such as reducing compressive strength.

[0006] This disclosure has been made in view of the above-mentioned problems and aims to provide a cement composition that can reduce CO2 emissions and has sufficient strength development. Furthermore, this disclosure aims to provide a method for manufacturing the said cement composition. [Means for solving the problem]

[0007] One aspect of this disclosure provides a cement composition comprising cement clinker, gypsum, and an admixture, wherein the admixture contains limestone and carbonated cementitious hardened material, the calcium carbonate content in the admixture is 80% by mass or less, and the admixture content is 2 to 20% by mass based on the total amount of the cement composition.

[0008] The above cement composition contains a mixture of limestone and carbonated cementitious material, thereby reducing CO2 emissions. Furthermore, because the calcium carbonate content in the mixture is within a predetermined range, it exhibits sufficient strength development.

[0009] Another aspect of this disclosure provides a method for producing a cement composition, comprising a mixing step of mixing a mixture containing limestone and a carbonated cementitious hardened body, cement clinker, and gypsum to obtain a cement composition, wherein the calcium carbonate content in the mixture is 80% by mass or less, and the content of the mixture in the cement composition is 2 to 20% by mass.

[0010] The above method for producing the cement composition uses a mixture containing limestone and carbonated cementitious hardened material, thereby reducing CO2 emissions. Furthermore, since the calcium carbonate content in the mixture is within a predetermined range, a cement composition with sufficient strength development can be produced. [Effects of the Invention]

[0011] This disclosure provides a cement composition that can reduce CO2 emissions and has sufficient strength development. This disclosure also provides a method for producing the cement composition. Brief Description of the Drawings

[0012] [Figure 1] Figure 1 is a diagram schematically showing an example of an apparatus used in the carbonation step. Modes for Carrying Out the Invention

[0013] Hereinafter, preferred embodiments of the present disclosure will be described in detail. However, the present disclosure is not limited to the following embodiments. In the following description, the expression "X to Y" (X and Y are arbitrary numbers) means "X or more and Y or less" unless otherwise specified. Unless otherwise specified, the materials exemplified in the present specification may be used singly or in combination of two or more kinds. The content of each component in the composition means the total amount of the plurality of corresponding substances present in the composition, unless otherwise specified, when a plurality of substances corresponding to each component are present in the composition.

[0014] <Cement Composition> The cement composition includes cement clinker, gypsum, and a admixture. The admixture contains limestone and a carbonated cementitious cured body. In addition, the content of calcium carbonate in the admixture is 80 mass% or less, and the content of the admixture is 2 to 20 mass% based on the total amount of the cement composition.

[0015] (Cement Clinker) Examples of the cement clinker include ordinary cement clinker, high-early-strength cement clinker, moderate-heat cement clinker, low-heat cement clinker, and oil well cement clinker.

[0016] The mineral composition of Portland cement clinker can be calculated by the Bogue equation. Here, the Bogue equation is an equation widely used as an equation for calculating the content ratio of main minerals in Portland cement clinker from the content ratio of chemical composition. By using the Bogue equation shown below, the contents of tricalcium silicate (3CaO·SiO₂, denoted as C₃S), dicalcium silicate (2CaO·SiO₂, denoted as C₂S), and tricalcium aluminate (3CaO·Al₂O₃, denoted as C₃A) in Portland cement clinker can be calculated. In addition, "%" in the following equations means "% by mass". The chemical formula represents the content ratio (% by mass) of each compound indicated by the chemical analysis value according to JIS R 5204:2019 "X-ray fluorescence analysis method for cement".

[0017] <Bogue equation> C3S[%]=(4.07×CaO[%])-(7.60×SiO2[%])-(6.72×Al2O3[%])-(1.43×Fe2O3[%])-(2.85×SO3[%]) C2S[%]=(2.87×SiO2[%])-(0.754×C3S[%]) C3A[%]=(2.65×Al2O3[%])-(1.69×Fe2O3[%]) C4AF[%]=3.04×Fe2O3[%]

[0018] As the cement clinker, Portland cement containing cement clinker, tricalcium silicate (3CaO·SiO₂, denoted as C₃S), slaked lime, and the like may be used. The Portland cement may be ordinary Portland cement, high-early-strength Portland cement, ultra-high-early-strength Portland cement, moderate-heat Portland cement, low-heat Portland cement, or sulfate-resistant Portland cement. From the viewpoint of further improving availability and early-age strength, the cement preferably contains at least one of ordinary Portland cement and high-early-strength Portland cement, and more preferably contains ordinary Portland cement.

[0019] The Blaine specific surface area of ​​cement clinker is, for example, 2500 cm². 2 / g or more, or 3000cm 2 It may be 10,000 cm² or more. Increasing the Blaine specific surface area of ​​the cement clinker tends to improve the strength development of the cement composition and reduce bleeding. The Blaine specific surface area of ​​the cement clinker is, for example, 10,000 cm². 2 / g or less, 8000cm 2 / g or less, or 5000cm 2 It may be less than / g. By reducing the Blaine specific surface area of ​​Portland cement, it is possible to further reduce CO2 emissions during cement production while lowering manufacturing costs.

[0020] In this specification, the Blaine specific surface area refers to the value measured in accordance with JIS R 5201:2015 "Physical Testing Methods for Cement".

[0021] The cement clinker content may be 50.0% by mass or more, 60.0% by mass or more, or 70.0% by mass or more, based on the total content of cement clinker and gypsum, from the viewpoint of further enhancing strength development, and may be 99.5% by mass or less, 99.0% by mass or less, or 98.5% by mass or less, from the viewpoint of sufficiently reducing CO2 emissions when manufacturing the cement composition. From the above viewpoint, the cement clinker content may be 50.0 to 99.5% by mass, 60.0 to 99.0% by mass, or 70.0 to 98.5% by mass, based on the total content of cement clinker and gypsum.

[0022] (plaster) For example, dihydrate gypsum, hemihydrate gypsum, and anhydrous gypsum can be used. One type of gypsum may be used alone, or multiple types may be used in combination. The gypsum content in the cement composition may be equivalent to that in general Portland cement.

[0023] The SO3 content of gypsum in the cement composition may be, for example, 0.5 to 3.0% by mass, 0.7 to 2.8% by mass, or 1.0 to 2.5% by mass, based on 100% by mass of the total amount of the cement composition.

[0024] The total content of cement clinker and gypsum in the cement composition may be 80% by mass or more, 83% by mass or more, 86% by mass or more, or 89% by mass or more, from the viewpoint of further enhancing strength development, and may be 98% by mass or less, 96% by mass or less, 94% by mass or less, or 92% by mass or less, from the viewpoint of sufficiently reducing CO2 emissions when manufacturing the cement composition.

[0025] (limestone) As limestone, for example, commercially available limestone, limestone powder, and powders mainly composed of calcium carbonate such as crushed limestone powder can be used. Preferably, the limestone contains those that conform to the small amount of mixed components described in JIS R 5210 "Portland Cement".

[0026] (Carbonated cementum hardened material) Carbonated cementitious body is a carbon dioxide of cementitious body. Cementitious body is a hardened body obtained by hardening a composition containing cement and water. The cementitious body may be a hardened cement paste, a hardened mortar, or a hardened concrete. Examples of cement include Portland cement, blended cement, eco-cement, and various other types of cement. The cementitious body may also include waste materials such as concrete or mortar building materials, waste cement paste, and sludge generated in ready-mixed concrete. The cementitious body may also include crushed concrete blocks. By using such waste materials, the effective utilization of resources can be achieved. The shape and size of the cementitious body are not particularly limited.

[0027] The cementitious material may be in the form of pulverized material (powder). The cementitious material may also be classified by a test sieve as specified in JIS Z 8801-1:2019, or by the average particle size (d50, etc., based on volume or number) measured by a laser particle size distribution analyzer. The particle size may be 40 mm or less, 10 mm or less, or 1 mm or less.

[0028] The bulk density of the cementitious hardened material may be 0.5 to 1.2 kg / L, 0.6 to 1.1 kg / L, or 0.7 to 1.0 kg / L. This can improve the efficiency of the carbonation reaction of the cementitious hardened material.

[0029] The age of the cementitious body is not particularly limited; for example, it may be 1 day or older, 7 days or older, 14 days or older, or 1 year or older.

[0030] The cementitious body may contain moisture. The moisture content in the cementitious body may be, for example, 15% by mass or more, or 20% by mass or more. The moisture content in the cementitious body may be, for example, 70% by mass or less, or 60% by mass or less.

[0031] The method for carbonating a cementitious hardened material is not particularly limited. For example, a cementitious hardened material can be carbonated by bringing a mixture containing cementitious hardened material and water into contact with a gas containing carbon dioxide. Alternatively, the cementitious hardened material can be carbonated by bubbling CO2 gas in water so that the ratio of water to cementitious hardened material (water-to-powder ratio) is 10 or more.

[0032] In carbonation, the calcium-containing components in the cementitious hardened material may react with carbon dioxide in the following reaction equations (1) and (2). Through these reactions, carbon dioxide is carbonated and fixed to the molded material. In reaction equation (2), x is any positive value, and z and t are any positive values ​​that satisfy z + t = 1. Note that the reaction that fixes carbon dioxide is not limited to the following two reactions. Ca(OH)2+CO2→CaCO3+H2O···(1) (CaO) x (SiO2)(H2O)+xCO2→xCaCO3+SiO2(H2O) t +(z-t)H2O···(2)

[0033] The gas containing carbon dioxide is not particularly limited, and may be an exhaust gas, which may be an exhaust gas discharged from a factory, or an exhaust gas discharged from equipment such as an incinerator or an electrostatic precipitator. When the carbonation apparatus is small-sized, the inflow rate of the gas may be, for example, 0.5 to 50 L / min, may be 1 to 30 L / min, may be 5 to 30 L / min, or may be 10 to 30 L / min. When the carbonation apparatus is large-sized, the inflow rate may be, for example, 50 to 1000 L / min, may be 100 to 900 L / min, or may be 200 to 800 L / min. The temperature of the gas may be 10 to 120°C. When the reaction is carried out in a container, the temperature of the gas may be the temperature at the inlet of the container.

[0034] The content of carbon dioxide in the gas may be 1 vol% or more, may be 5 to 50 vol%, or may be 10 to 30 vol%, relative to the total amount of the gas. The gas may contain nitrogen, oxygen, volatile organic substances, water (water vapor) and the like in addition to carbon dioxide.

[0035] From the viewpoint of increasing the amount of CO2 fixed in the cementitious cured body, the content of calcium carbonate in the carbonated cementitious cured body may be 20 mass% or more, 25 mass% or more, or 30 mass% or more.

[0036] In the present specification, the chemical composition is measured in accordance with the descriptions of JIS R 5202:2015 "Methods for chemical analysis of cement" or JIS R 5204:2019 "X-ray fluorescence analysis methods for cement".

[0037] From the viewpoint of further enhancing strength development, the Blaine specific surface area of the carbonated cementitious cured body is 3500 cm 2 / g or more, 4000 cm 2 / g or more, or 5000 cm2 It may be 1 / g or more. From the viewpoint of improving fluidity and handling properties, the Blaine specific surface area of ​​the carbonated cementitious hardened body should be, for example, 20,000 cm². 2 / g or less, 10000cm 2 / g or less, 8000cm 2 / g or less, or 6000cm 2 It may be less than or equal to / g.

[0038] The content of carbonated cementite in the cement composition may be 3% by mass or more, 4% by mass or more, or 5% by mass or more. This allows for further reduction of CO2 emissions while further improving short-term strength development. From the viewpoint of further improving strength development, the content of carbonated cementite in the cement composition may be 15% by mass or less, 10% by mass or less, or 8% by mass or less.

[0039] (mixed material) The mixture contains limestone and carbonated cementum hardened material, with a calcium carbonate content of 80% by mass or less. From the viewpoint of further enhancing strength development, the calcium carbonate content in the mixture may be 75% by mass or less, 70% by mass, or 65% by mass or less. The limestone and carbonated cementum hardened material in the mixture may each be in powder form.

[0040] In this specification, the calcium carbonate content in the mixture may be the sum of the calcium carbonate content of each component contained in the mixture, or it may be the calcium carbonate content of the mixture as a whole. That is, the calcium carbonate content in the mixture may be a value calculated from the measured calcium carbonate content of each component contained in the mixture and the content ratio of each component in the mixture, or it may be a measured value of the calcium carbonate content of the mixture as a whole.

[0041] The content of the admixture in the cement composition may be 4% by mass or more, 6% by mass or more, or 8% by mass or more from the viewpoint of further reducing CO2 emissions, and may be 17% by mass or less, 14% by mass or less, or 11% by mass or less from the viewpoint of further enhancing strength development.

[0042] The mixture may contain aggregate components. In this specification, "aggregate components" means powder mainly composed of silica (SiO2). The silica content in the aggregate components is 70% by mass or more. The aggregate components may be aggregate components derived from cementitious material, which is the raw material for carbonated cementitious material (also called "raw aggregate"). The raw aggregate may be, for example, those listed in Annex A "Aggregates for Ready-Mixed Concrete" of JIS A 5308 "Ready-Mixed Concrete", or aggregates not listed in Annex A.

[0043] The cement composition may contain, in addition to cement clinker, gypsum, and admixtures, other components, to the extent that they do not impair the spirit of this disclosure. Examples of other components include calcium hydroxide, silica powder, other calcium-containing powders (excluding gypsum, limestone, and the above-mentioned carbonated cementitious hardened body), concrete water-reducing agents, accelerators, and retarders.

[0044] From the perspective of further enhancing strength development, the Blaine specific surface area of ​​the cement composition should be 3000-6000 cm². 2 / g, 3200~5800cm 2 / g, or 3500-5500cm 2 / g is acceptable.

[0045] <Method for manufacturing cement composition> The method for producing a cement composition includes a mixing step of mixing a mixture containing limestone and a carbonated cementitious hardened body, cement clinker, and gypsum to obtain a cement composition. In the method for producing a cement composition, the calcium carbonate content in the carbonated cementitious hardened body may be 20% by mass or more.

[0046] The cement composition produced by the above-described method for manufacturing the cement composition contains a mixture of limestone and carbonated cementitious hardened material, thereby reducing CO2 emissions, and also exhibits sufficient strength development because the calcium carbonate content in the mixture is within a predetermined range.

[0047] In the mixing process, a mixture containing carbonated cementitious body and limestone, cement clinker, and gypsum are mixed to obtain a mixture (cement composition). In the mixing process, the calcium carbonate content in the mixture containing carbonated cementitious body and limestone is 80% by mass or less. Furthermore, in the mixing process, the mixture containing carbonated cementitious body and limestone, cement clinker, and gypsum may be mixed so that, based on the total amount of the mixture (cement composition) obtained, the combined content of cement clinker and gypsum is 80-98% by mass, and the content of the mixture is 2-20% by mass.

[0048] The mixing of each material in the mixing process may be carried out using a mixer such as a pan mixer, a tilting drum mixer, or a ribbon mixer, or by mixing and grinding using a pulverizer such as a ball mill or a vertical roller mill and a roller press, or by grinding each of the main components separately and then mixing them in a mixer such as a mechanical mixer.

[0049] The process may include a first grinding step in which the carbonated cementitious hardened body is ground before the mixing step. Alternatively, the mixture may be used as is as the cement composition, or a second grinding step may be included in which the mixture is ground after the mixing step to obtain the cement composition. The grinding method in the first and second grinding steps is not particularly limited, and grinding may be performed using a grinder such as a ball mill, a vertical roller mill, or a roller press.

[0050] From the viewpoint of making the particle size of the cement composition uniform, the Blaine specific surface area of ​​the hardened carbonated cementitious material should be 2500 cm². 2 If the amount is less than / g, the method for producing the cement composition preferably has a first grinding step and a second grinding step. From the viewpoint of reducing the power required for grinding and from the viewpoint of work efficiency, the Blaine specific surface area of ​​the carbonated cementitious hardened body is 2500 cm². 2If the amount is greater than or equal to / g, the method for producing the cement composition may omit the first grinding step and perform only the second grinding step as the grinding step. In order to measure the Blaine specific surface area of ​​the carbonated cementitious hardened body, the method for producing the cement composition may further include a measurement step for measuring the Blaine specific surface area of ​​the carbonated cementitious hardened body. The Blaine specific surface area of ​​the carbonated cementitious hardened body can be measured in accordance with the method described in JIS R 5201:2015 "Physical Testing Methods for Cement".

[0051] From the perspective of further enhancing strength development, the Blaine specific surface area of ​​the carbonated cementitious hardened material included in the mixture is 3500 cm². 2 / g or more, 4000cm 2 / g or more, or 5000cm 2 It may be 1 / g or more. From the viewpoint of improving fluidity and handling, the Blaine specific surface area of ​​the carbonated cementitious hardened material contained in the mixture should be, for example, 20,000 cm². 2 / g or less, 10000cm 2 / g or less, 8000cm 2 / g or less, or 6000cm 2 It may be less than or equal to / g.

[0052] From the perspective of further enhancing strength development, the Blaine specific surface area of ​​the cement composition should be 3000-6000 cm². 2 / g, 3200~5800cm 2 / g, or 3500-5500cm 2 / g is acceptable.

[0053] The second crushing step may be performed after the mixing step, or simultaneously with the mixing step. In other words, in the method for producing the cement composition, crushing may be performed after mixing each material, or the materials may be mixed after crushing each material, or the mixing and crushing of each material may be performed simultaneously.

[0054] From the viewpoint of further enhancing the strength development of the cement composition, the method for producing the cement composition may include both a first grinding step and a second grinding step.

[0055] A method for producing a cement composition may further include a carbonation step in which a mixture containing a cementitious hardened body and water is brought into contact with a gas containing carbon dioxide to obtain a carbonated cementitious hardened body. In the method for producing a cement composition, the carbonated cementitious hardened body obtained in the carbonation step can be used in the mixing step described above.

[0056] Figure 1 shows a schematic diagram of an example of an apparatus used in the carbonation process (hereinafter also referred to as the "carbonation apparatus"). The carbonation apparatus 10 comprises a container 1 configured to contain a mixture, a temperature detector 2 for detecting the temperature inside the container, a gas supply unit 3 for supplying gas containing carbon dioxide into the container 1, and adjustment units 4A and 4B for adjusting the amount of gas supplied from the gas supply unit 3 based on the measurement data of the temperature detector 2. The carbonation process described above can be carried out, for example, by using the carbonation apparatus 10.

[0057] The shape of container 1 is not particularly limited as long as it can contain the mixture. To reduce the influence of outside air and other factors on the temperature measurement inside the container, it is preferable that container 1 be airtight in all parts except for the gas supply path such as piping.

[0058] Container 1 may be equipped with a stirrer. By stirring the mixture inside the container using the stirrer, the carbonation reaction of the cementitious hardened material can be accelerated.

[0059] Container 1 may be configured to be rotatable or oscillating in order to promote the carbonation reaction of the cementitious hardened body. Container 1 may be rotated or oscillated by a drive unit provided within Container 1, or by equipment other than Container 1, such as an oscillating platform.

[0060] The gas supply unit 3 is connected to the container 1, and the gas supply unit 3 can introduce gas containing carbon dioxide into the container 1. The gas supply unit 3 may also supply gases other than carbon dioxide. Examples of gases other than carbon dioxide include nitrogen and air. The gas supply unit 3 may have cylinders such as a carbon dioxide (CO2) cylinder and a nitrogen (N2) cylinder. In Figure 1, the gas supply unit 3 has a carbon dioxide cylinder 3A and a nitrogen cylinder 3B, but the gas supply unit of the carbonation device does not have to have a carbon dioxide cylinder 3A and a nitrogen cylinder 3B; it is sufficient if it can supply gas containing carbon dioxide.

[0061] The flow rate control units 4A and 4B are installed in the piping connecting the gas supply unit 3 and the container 1. The signals from the temperature detector 2 are input to each of the flow rate control units 4A and 4B. These gas control units 4A and 4B may adjust the amount of gas supplied from the gas supply unit 3 to the container 1 based on the measurement data from the temperature detector 2. This allows for an efficient carbonation reaction. Although Figure 1 shows two control units 4A and 4B, the number of control units is not limited to this and may be changed depending on, for example, the number of different types of gas used.

[0062] The carbonation apparatus 10 shown in Figure 1 is equipped with a thermocouple 5 attached to a container 1. The thermocouple 5 is connected to a temperature detector 2, and the temperature inside the container 1 can be measured by the thermocouple 5. Note that the temperature measuring unit for measuring the temperature inside the container 1 is not limited to a thermocouple, and the temperature inside the container 1 may be measured by a temperature measuring unit other than a thermocouple.

[0063] The carbonation apparatus 10 shown in Figure 1 includes a rocking platform 6. The rocking platform 6 allows the container 1 to be rocked. The means for rocking the container 1 are not limited to the rocking platform; the container 1 may be rocked by means other than the rocking platform. In a modified example, the apparatus 10 may also include a drive unit for rotating the container 1.

[0064] Note that the carbonation apparatus 10 shown in Figure 1 is merely one example of a carbonation apparatus. A carbonation apparatus only needs to have the function of carbonating cementitious hardened material, and does not need to be equipped with a temperature detector, flow rate control unit, thermocouple, and rocking platform. For example, the cementitious hardened material may be carbonized by stirring while supplying CO2 gas into a mortar mixer.

[0065] The manufacturing method described above may include other steps besides those described above. Examples of other steps include a sorting step for selecting raw materials, and a modification step for washing raw materials or removing repellent components.

[0066] The cement composition produced by the above-described manufacturing method may be mixed with fine aggregate, coarse aggregate, water, admixtures, etc., and used as a mortar composition or concrete composition.

[0067] Fine aggregate can be any fine aggregate specified in JIS A 5005:2020 "Crushed stone and crushed sand for concrete". Examples of fine aggregate include river sand, land sand, sea sand, crushed sand, silica sand, copper slag fine aggregate, and electric furnace oxidized slag fine aggregate. When using fine aggregate, the amount used may be, for example, 50 to 500 parts by mass, 100 to 300 parts by mass, or 200 to 250 parts by mass per 100 parts by mass of the cement composition described above.

[0068] For coarse aggregate, the coarse aggregate specified in JIS A 5005:2020 "Crushed stone and crushed sand for concrete" can be used. Examples of coarse aggregate include gravel and crushed stone. When using coarse aggregate, the amount used may be, for example, 50 to 500 parts by mass, 100 to 300 parts by mass, or 200 to 250 parts by mass per 100 parts by mass of the cement composition described above.

[0069] Fine aggregate and coarse aggregate can be used in combination, in which case the total amount of fine aggregate and coarse aggregate used may be 100 to 300 parts by mass, or 200 to 250 parts by mass, per 100 parts by mass of the cement composition described above.

[0070] Examples of water include tap water, distilled water, and deionized water. The amount of water used may be 20 to 100 parts by mass, or 40 to 70 parts by mass, per 100 parts by mass of the cement composition described above.

[0071] Examples of admixtures include air-entraining agents, water-reducing agents, high-performance water-reducing agents, high-performance air-entraining agents, fluidizers, defoamers, shrinkage reducers, setting accelerators, setting retarders, and thickeners. The amount of admixture used may be, for example, 0.01 to 2 parts by mass per 100 parts by mass of the cement composition described above.

[0072] Although several embodiments have been described above, this disclosure is not limited in any way to the embodiments described above. Furthermore, the descriptions of the embodiments described above are applicable to each other.

[0073] The above-described embodiment includes the following: [1] A cement composition comprising cement clinker, gypsum, and an admixture, The aforementioned mixture contains limestone and a carbonated cementum hardened body. The calcium carbonate content in the aforementioned mixture is 80% by mass or less. A cement composition in which the content of the admixture is 2 to 20% by mass, based on the total amount of the cement composition. [2] The cement composition according to [1], wherein the calcium carbonate content in the carbonated cementitious hardened body is 20% by mass or more. [3] The Blaine specific surface area of ​​the aforementioned carbonated cementitious hardened material is 3500 cm². 2 A cement composition according to [1] or [2], wherein the amount is 1 / g or more. [4] The cement composition according to any one of [1] to [3], wherein the mixed material contains aggregate components. [5] The cement composition according to any one of [1] to [4], wherein the SO3 equivalent content of the gypsum is 0.5 to 3.0% by mass, based on the total amount of the cement composition. [6] The Braine specific surface area of ​​the cement composition is 3000 to 6000 cm². 2 A cement composition according to any one of [1] to [5], wherein the amount is / g. [7] The process includes a mixing step of mixing limestone, a carbonated cementitious hardened body, a mixed material containing cement clinker, and gypsum to obtain a cement composition. The calcium carbonate content in the aforementioned mixture is 80% by mass or less. A method for producing a cement composition, wherein the content of the admixture in the cement composition is 2 to 20% by mass. [8] A method for producing a cement composition according to [7], further comprising at least one step of: a first grinding step of grinding the carbonated cementitious hardened body before the mixing step; and a second grinding step of grinding a mixture obtained by mixing the admixture, the cement clinker, and the gypsum to obtain the cement composition. [9] A method for producing a cement composition according to [7] or [8], further comprising a carbonation step of contacting a mixture containing a cementitious hardened body and water with a gas containing carbon dioxide to obtain a carbonated cementitious hardened body. [Examples]

[0074] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0075] [Raw materials for cement composition] The following materials were used as raw materials for the cement composition.

[0076] (Cement clinker) As the cement clinker, the following ordinary Portland cement containing cement clinker was used. • Ordinary Portland cement (cement clinker content: 94.1% by mass, gypsum content: 1.8% by mass, gypsum content in SO3 equivalent: 1.46% by mass, limestone content: 4.1% by mass, manufactured by UBE Mitsubishi Cement Corporation)

[0077] (plaster) The gypsum used was one that met the requirements specified in JIS R 9151:2009 "Natural gypsum for cement."

[0078] (mixed material) As the mixture, a powder containing limestone and carbonated cementitious hardened material, as described later, was used. The mixture was prepared by weighing and then mixing the limestone and carbonated cementitious hardened material in a bag. The mixing ratios of limestone and carbonated cementitious hardened material in the mixture are shown in Table 2.

[0079] ·Limestone The limestone (CC) used had a calcium carbonate content of 90% by mass or more and an aluminum oxide content of 1.0% by mass or less, meeting the requirements for small amounts of mixed components described in JIS R 5210:2019 "Portland cement". The calcium carbonate content of the limestone was 98.58% by mass, and the Blaine specific surface area was 3530 cm². 2 It was / g.

[0080] • Carbonated cementum hardened body As the hardened carbonated cementum, a material prepared according to the following procedure was used.

[0081] <Preparation Procedure for Hardened Carbonated Cementaceous Body> First, ordinary Portland cement (cement clinker content: 94.1% by mass, gypsum content: 1.8% by mass, gypsum content in SO3 equivalent: 1.46% by mass, limestone content: 4.1% by mass, manufactured by UBE Mitsubishi Cement Corporation), water, fine aggregate A (crushed sand), fine aggregate B (sand), coarse aggregate (crushed stone), and admixture (AE damping agent delayed type I) are mixed in the amounts shown in Table 1 (kg / cm³). 3 The raw concrete (water-cement ratio [W / C]: 52.9%) was prepared by mixing the ingredients as follows.

[0082] [Table 1]

[0083] Next, the prepared raw concrete was sealed and cured for 7 days after placement, then demolded and cured outdoors for 127 days until the test date to obtain a simulated concrete block. Subsequently, the simulated concrete block was roughly crushed to a diameter of approximately 200 mm using heavy machinery, and the roughly crushed simulated concrete was finely crushed with a jaw crusher and passed through an electric sieve with a mesh size of 40 mm to prepare concrete lumps. These were then processed in a grinder, and the fine powder generated during grinding was collected with a dust collector to obtain a powdery cementitious hardened material with a particle size of 0.3 mm or less.

[0084] Next, the powdered cementitious body prepared using the following procedure was carbonated. First, 200g of the prepared cementitious body and 50g of water were placed in a mortar mixer conforming to JIS R 5201. Subsequently, carbon dioxide gas (concentration: 20%) was passed through the container at a flow rate of 2 L / min for 4 hours, bringing the mixture containing the cementitious body and water into contact with the carbon dioxide gas. The carbonation reaction of the cementitious body was carried out while stirring at a low speed, and carbonated cementitious body was prepared. The Blaine specific surface area of ​​the carbonated cementitious body was 5370 cm². 2 It was / g.

[0085] The obtained carbonated cementum hardened material was heated under the following conditions using a thermogravimetric differential thermal analyzer (TG-DTA), and the weight loss (in mass %) between 600°C and 800°C during the heating process was measured to determine the calcium carbonate content in the carbonated cementum hardened material. As a result, the calcium carbonate content in the obtained carbonated cementum hardened material was 36.4% by mass. [Thermogravimetric differential thermal analysis conditions] The temperature was raised from room temperature to 1000°C at a rate of 10°C / min. After that, heating was stopped and the temperature was lowered to 40°C.

[0086] (Examples 1-2, Comparative Examples 1-2, and Reference Example 1) Cement compositions were prepared by mixing cement clinker, gypsum, limestone, and a powder containing carbonated cementum hardened material in the proportions (mass%) shown in Table 2. Specifically, first, the cement composition of Reference Example 1 was prepared by mixing and grinding cement clinker, gypsum, and limestone in a ball mill. Then, the cement compositions of the Examples and Comparative Examples were obtained by mixing the cement composition of Reference Example 1 with a mixture containing limestone and carbonated cementum hardened material, which was prepared separately by grinding, in predetermined proportions.

[0087] The calcium carbonate content in the mixed material shown in Table 2 was calculated by measuring the calcium carbonate content of each component (limestone and carbonated cementitious hardened material) contained in the mixed material, and then using the measured values ​​and the content ratio of each component in the mixed material.

[0088] <Measurement of compressive strength> Using the cement compositions prepared in Examples 1-2, Comparative Examples 1-2, and Reference Example 1, the compressive strength was measured in accordance with the description in JIS R 5201:2015 "Physical Testing Methods for Cemeteries," and the compressive strength ratio, based on the compressive strength of Reference Example 1, was determined from the measured values.

[0089] Specifically, first, 100 parts by mass of each cement composition was mixed with 300 parts by mass of standard cement strength testing sand obtained from the Cement Association as fine aggregate, and 50 parts by mass of water to prepare a mortar composition. The mortar composition was mixed and then filled into a mold. Next, the mold was placed in a humid chamber with a relative humidity of 90% or higher and cured at 20°C for 24 hours. After that, the mold was removed to obtain the hardened mortar bodies of Examples 1-2, Comparative Examples 1-2, and Reference Example 1.

[0090] Next, each mortar cured underwater in a constant temperature chamber at 20°C. On the 7th day of underwater curing, each mortar cured was removed from the water, and its compressive strength was measured. The ratio of the compressive strength of each example and comparative example to the compressive strength of the mortar cured in Reference Example 1 was calculated as ((compressive strength of each example and comparative example's mortar cured at 7 days / compressive strength of Reference Example 1's mortar cured at 7 days) × 100). The compressive strength of the mortar cured after 28 days of underwater curing was also measured using the same procedure, and the ratio of the compressive strength of each example and comparative example's mortar cured at Reference Example 1 to the compressive strength of the mortar cured in Reference Example 1 was calculated. The results are shown in Table 2.

[0091] [Table 2]

[0092] As shown in Table 2, the cement compositions of Examples 1 and 2 had a higher compressive strength ratio than Comparative Examples 1 and 2 and Reference Example 1. The cement compositions of Examples 1 and 2 were confirmed to have particularly excellent initial strength development. [Explanation of Symbols]

[0093] 10...device, 1...container, 2...temperature detector, 3...gas supply unit, 3A...carbon dioxide cylinder, 3B...nitrogen cylinder, 4A,4B...adjustment unit, 5...thermocouple, 6...rocking platform.

Claims

1. A cement composition comprising cement clinker, gypsum, and an admixture, The aforementioned mixture contains limestone and a carbonated cementum hardened body. The calcium carbonate content in the aforementioned mixture is 80% by mass or less. A cement composition in which the content of the admixture is 2 to 20% by mass, based on the total amount of the cement composition.

2. The cement composition according to claim 1, wherein the calcium carbonate content in the carbonated cementitious hardened body is 20% by mass or more.

3. The Blaine specific surface area of ​​the aforementioned carbonated cementitious hardened material is 3500 cm². ２ The cement composition according to claim 1 or 2, wherein the amount is 1 / g or more.

4. The cement composition according to claim 1 or 2, wherein the mixed material contains an aggregate component.

5. Based on the total amount of the cement composition, the SO of the gypsum ３ The cement composition according to claim 1 or 2, wherein the converted content is 0.5 to 3.0% by mass.

6. The Braine specific surface area of ​​the cement composition is 3,000 to 6,000 cm². ２ The cement composition according to claim 1 or 2, wherein the amount is / g.

7. The process includes a mixing step of mixing a mixture containing limestone and carbonated cementitious hardened material, cement clinker, and gypsum to obtain a cement composition. The calcium carbonate content in the aforementioned mixture is 80% by mass or less. A method for producing a cement composition, wherein the content of the admixture in the cement composition is 2 to 20% by mass.

8. A method for producing a cement composition according to claim 7, further comprising at least one step of: a first grinding step of grinding the carbonated cementitious hardened body before the mixing step; and a second grinding step of grinding a mixture obtained by mixing the admixture, the cement clinker, and the gypsum to obtain the cement composition.

9. A method for producing a cement composition according to claim 7 or 8, further comprising a carbonation step of contacting a mixture containing a cementitious hardened body and water with a gas containing carbon dioxide to obtain the carbonated cementitious hardened body.

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