Method for producing cement composition

Abstract

To provide a method for producing a cement composition capable of fixing carbon dioxide in the cement composition and having excellent fluidity and air entrainment.SOLUTION: A method for producing a cement composition includes the process of obtaining: a cement slurry by mixing a part of cement and a part of water; slurry containing carbon dioxide gas by supplying carbon dioxide gas into cement slurry; a high concentration cement containing composition by kneading the carbon dioxide gas containing slurry and the remainder of the cement (additional cement supply process); and a cement composition by kneading the high concentration cement containing composition and the remainder of the water (additional water supply process), the ratio of the amount of a part of cement in the total cement is 1 to 50 wt.%, the ratio of the amount of the remainder of cement is 50 to 99 wt.%, the amount of water in the total water 50 to 99 wt.%, the ratio of the remaining amount of water is 1 to 50 wt.%, an aggregate is supplied in either one or both of the additional cement supply process and the additional water supply process.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a cement composition. [Background technology]

[0002] In recent years, reducing carbon dioxide emissions has become an important issue in order to prevent global warming. In relation to this, technology is being considered for fixing carbon dioxide captured from exhaust gases generated in cement manufacturing plants into concrete, etc. As a method for providing concrete in which carbon dioxide is efficiently fixed, Patent Document 1 describes a method for producing concrete, which includes forming a first mixture containing cement and water, adding carbon dioxide to the first mixture to form a second mixture, and hardening the second mixture, and the weight of the water is adjusted so that the amount of unhydrated cement remaining in the concrete is between 0% and 50%. Patent Document 2 also describes a method for producing CO2-absorbing precast concrete, which contains one or two of γ-CS (symbol γ) and steel slag powder (symbol B) as powder components, and Portland cement (symbol C), and the total of γ and B in the total content of γ, B, and C is 25 to 95 mass%, and the water-cement ratio W / C is 80 to 250%, and is poured into a formwork. After demolding, one or more holes that allow ventilation are drilled in the solidified concrete, and the solidified concrete is carbonation-cured in an atmosphere with a CO2 concentration of 5 to 95%, forming a carbonation region from the surface (excluding the surface inside the hole) to a depth of 20 mm or more (however, in the entire thickness of the part with a thickness of less than 20 mm), and also forming a carbonation region from the surface inside the hole. In this method, combustion exhaust gas discharged from a factory or facility can be used in carbonation curing, and carbon dioxide emissions can be reduced. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-37493 A [Patent Document 2] JP 2011-168436 A Summary of the Invention [Problem to be solved by the invention]

[0004] When carbon dioxide gas is injected into a cement slurry prepared by mixing cement and water in the production of concrete or the like for the purpose of fixing carbon dioxide in the concrete, there is a problem that the fluidity and air entrainment property of the cement composition are significantly reduced. An object of the present invention is to provide a method capable of fixing carbon dioxide in a cement composition such as concrete and producing a cement composition having excellent fluidity and air entrainment properties. [Means for solving the problem]

[0005] As a result of intensive research into solving the above problems, the present inventors have found that the above objects can be achieved by a method for producing a cement composition including a cement slurry preparation step of mixing a part of cement and a part of water to obtain a cement slurry, a carbon dioxide gas supplying step of supplying carbon dioxide gas into the cement slurry to obtain a carbon dioxide gas-containing slurry, a cement additional supplying step of kneading the carbon dioxide gas-containing slurry with the remainder of the cement to obtain a high-concentration cement-containing composition, and a water additional supplying step of kneading the high-concentration cement-containing composition with the remainder of the water to obtain a cement composition, wherein the proportion of the part of the cement in the total amount of cement is 1 to 50 mass% and the proportion of the remainder of the cement is 50 to 99 mass%, the proportion of the part of the water in the total amount of water is 50 to 99 mass% and the proportion of the remainder of the water is 1 to 50 mass%, and aggregate is supplied in either one or both of the cement additional supplying step and the water additional supplying step, and have completed the present invention. That is, the present invention provides the following [1] to [4].

[0006] [1] A method for producing a cement composition containing cement, aggregate, and water, comprising: a cement slurry preparation step of mixing a part of the cement with a part of the water to obtain a cement slurry; a carbon dioxide gas supplying step of supplying carbon dioxide gas into the cement slurry to obtain a carbon dioxide gas-containing slurry; a cement additional supplying step of kneading the carbon dioxide gas-containing slurry with the remainder of the cement to obtain a high-concentration cement-containing composition; and a water additional supplying step of kneading the high-concentration cement-containing composition with the remainder of the water to obtain the cement composition, wherein the high-concentration cement-containing composition and the remainder of the water are kneaded to obtain the cement composition, and ... high-concentration cement-containing composition and the high-concentration cement-containing composition are kneaded to obtain the high-concentration cement-containing composition and the high-concentration cement-containing composition. A method for producing a cement composition, characterized in that the proportion of the portion of the cement used in the cement slurry preparation step is 1 to 50 mass % and the proportion of the remainder of the cement used in the cement additional supply step is 50 to 99 mass %, the proportion of the portion of the water used in the cement slurry preparation step is 50 to 99 mass % and the proportion of the remainder of the water used in the water additional supply step is 1 to 50 mass %, and the aggregate is supplied in either one or both of the cement additional supply step and the water additional supply step. [2] The method for producing a cement composition according to [1] above, wherein the cement composition contains a cement admixture, and the cement admixture is supplied in the additional water supply step. [3] The method for producing a cement composition according to [2] above, wherein the cement admixture comprises one or more cement dispersants selected from the group consisting of a water reducing agent, an air-entraining water reducing agent, a high-performance water reducing agent and a high-performance air-entraining water reducing agent, and an air-entraining agent. [4] The method for producing a cement composition according to any one of [1] to [3] above, wherein the aggregate comprises fine aggregate and coarse aggregate, and the water-cement ratio of the cement composition is 30 to 65%. Effect of the Invention

[0007] According to the method for producing a cement composition of the present invention, it is possible to fix carbon dioxide in a cement composition such as concrete, and to produce a cement composition having excellent fluidity and air entrainment properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] The method for producing a cement composition of the present invention is a method for producing a cement composition containing cement, aggregate, and water, and includes a cement slurry preparation step of mixing a part of the cement with a part of the water to obtain a cement slurry, a carbon dioxide gas supply step of supplying carbon dioxide gas (carbon dioxide in the form of a gas) into the cement slurry to obtain a carbon dioxide gas-containing slurry, a cement additional supply step of kneading the carbon dioxide gas-containing slurry with the remainder of the cement to obtain a high-concentration cement-containing composition, and a water additional supply step of kneading the high-concentration cement-containing composition with the remainder of the water to obtain a cement composition, wherein the proportion of the amount of the part of the cement used in the cement slurry preparation step is 1 to 50 mass%, and the proportion of the amount of the remainder of the cement used in the cement additional supply step is 50 to 99 mass%, the proportion of the amount of the part of the water used in the cement slurry preparation step is 50 to 99 mass%, and the proportion of the amount of the remainder of the water used in the water additional supply step is 1 to 50 mass%, and the aggregate is supplied in either one or both of the cement additional supply step and the water additional supply step. Each step will be explained in detail below.

[0009] [Cement slurry preparation process] This step involves mixing a portion of cement with a portion of water to obtain a cement slurry. The above cement is not particularly limited, and examples thereof include various Portland cements such as ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement, mixed cements such as blast-furnace cement and fly ash cement, and ecocement, etc. These may be used alone or in combination of two or more.

[0010] The proportion of the amount of the part of cement in the total amount of cement (the total amount of cement contained in the cement composition) is 1 to 50 mass%, preferably 3 to 40 mass%, more preferably 5 to 30 mass%, even more preferably 8 to 25 mass%, even more preferably 10 to 20 mass%, and particularly preferably 12 to 18 mass%. If the proportion is less than 1 mass%, the amount of carbon dioxide fixed in the cement composition will be small. If the proportion exceeds 50 mass%, the strength development of the cement composition will decrease.

[0011] The proportion of the amount of the part of water in the total amount of water (total amount of water contained in the cement composition) is 50 to 99 mass%, preferably 60 to 98 mass%, more preferably 70 to 97 mass%, and particularly preferably 75 to 96 mass%. If the proportion is less than 50 mass%, the fluidity of the cement slurry is significantly reduced, and it becomes difficult to uniformly supply carbon dioxide gas to the cement slurry in the carbon dioxide gas supplying step described below. If the proportion exceeds 99 mass%, the amount of air contained in the cement composition is reduced, and the fluidity of the cement composition is reduced.

[0012] In this step, the water-cement ratio is preferably 100-500%, more preferably 150-450%, further preferably 200-400%, and particularly preferably 250-350%. If the ratio is 100% or more, the fluidity of the cement slurry is improved, and it becomes easier to uniformly supply carbon dioxide gas to the cement slurry in the carbon dioxide gas supplying step described below. If the ratio is 500% or less, the amount of carbon dioxide fixed in the cement composition is increased. The water-cement ratio is the mass ratio (water / cement) of water (in this process, a part of the water) to cement (in this process, a part of the cement) expressed as a percentage (%). In this step, the method of mixing a portion of the cement and a portion of the water is not particularly limited. For example, a portion of the water may be added to a stirring tank or the like, and then a portion of the cement may be added and then mixed; or a portion of the water and a portion of the cement may be simultaneously added to a stirring tank or the like, and then mixed.

[0013] [Carbon dioxide gas supply process] This step is a step of supplying carbon dioxide gas into the cement slurry obtained in the cement slurry preparation step to obtain a carbon dioxide gas-containing slurry. In this step, from the viewpoint of uniformly supplying carbon dioxide gas to the cement slurry, it is preferable to supply carbon dioxide gas while fluidizing the cement slurry. Examples of the method for supplying carbon dioxide gas into the cement slurry include the following methods (i) to (iii). (i) A method in which a carbon dioxide gas supplying means for supplying carbon dioxide gas into the cement slurry is installed in a stirring tank for obtaining the cement slurry used in the above-mentioned cement slurry preparation step, and carbon dioxide gas is supplied into the cement slurry. A more specific example is a method in which, in an apparatus equipped with a stirring tank for stirring and mixing cement and water to obtain a cement slurry, and a carbon dioxide gas supplying means (e.g., an aeration plate) disposed in a mixture storage space in the stirring tank, carbon dioxide gas is blown into the cement slurry obtained in the above-mentioned cement slurry preparation step using the above-mentioned carbon dioxide gas supplying means while stirring the cement slurry, thereby obtaining a carbon dioxide gas-containing slurry.

[0014] (ii) A method in which the cement slurry is transferred from a stirring tank for storing the cement slurry into an apparatus having a carbon dioxide gas supplying means (e.g., an air diffuser) for supplying carbon dioxide gas, and then carbon dioxide gas is blown into the cement slurry in the apparatus to obtain a carbon dioxide gas-containing slurry, and then the carbon dioxide gas-containing slurry is transferred to a carbon dioxide gas-containing slurry tank for storing the carbon dioxide gas-containing slurry. The stirring tank and the carbon dioxide-containing slurry tank may be the same or different.

[0015] A more specific example includes a method in which a mixture obtained by mixing a part of cement and a part of water (cement slurry obtained in the above-mentioned cement slurry preparation step) contained in a stirring tank for stirring and mixing cement and water to obtain a mixture is transferred using a pump or the like through a first flow passage for supplying the mixture in the stirring tank to the device having carbon dioxide gas supply means (e.g., an air diffuser) for supplying carbon dioxide gas, and then, while stirring the mixture in the device, carbon dioxide gas is supplied into the mixture, and then, the mixture after the carbon dioxide gas supply is transferred to the stirring tank using a pump or the like through a second flow passage for supplying the mixture in the device to the stirring tank, thereby obtaining a carbon dioxide gas-containing slurry. An example of the above-mentioned device is one that includes a mixture storage tank for storing and stirring the mixture, and an aeration means (e.g., an aeration plate) for supplying the carbon dioxide gas, which is disposed in the mixture storage space in the mixture storage tank. The mixture may be repeatedly circulated through the stirring tank, the first flow passage, the device, and the second flow passage in this order until a sufficient amount of carbon dioxide gas is supplied. Furthermore, after obtaining the carbon dioxide-containing slurry, the carbon dioxide-containing slurry may be temporarily stored in a storage tank for storing carbon dioxide-containing slurry, which is different from the carbon dioxide-containing slurry tank, and the carbon dioxide-containing slurry may be appropriately supplied from the storage tank to the carbon dioxide-containing slurry tank.

[0016] (iii) A method of blowing carbon dioxide gas into a cement slurry when the cement slurry is transferred from a mixing tank for storing the cement slurry to a carbon dioxide gas-containing slurry tank for storing a carbon dioxide gas-containing slurry. A more specific example is a method in which a mixture of part of cement and part of water (cement slurry obtained in the above-mentioned cement slurry preparation step) is contained in a stirring tank for stirring and mixing cement and water to obtain a mixture, and while circulating the mixture supplied from the stirring tank through a pipeline for circulating the mixture, carbon dioxide gas is supplied into the mixture and stirred to obtain a carbon dioxide gas-containing slurry, and then the carbon dioxide gas-containing slurry is transferred to the carbon dioxide gas-containing slurry tank.

[0017] The above-mentioned pipeline may, for example, have a carbon dioxide gas supply port for supplying the carbon dioxide gas to the mixture flowing through the pipeline, and may have a form capable of stirring and mixing the mixture and the carbon dioxide gas. Specifically, the pipeline may include a diffuser means (e.g., a diffuser plate) for supplying the carbon dioxide gas, and a stirrer means (e.g., a line mixer or a static mixer) disposed in the pipeline. In addition, after carbon dioxide gas is supplied into the mixture, the mixture may be returned to the stirring tank without being transferred to a carbon dioxide-containing slurry tank. Furthermore, the mixture may be repeatedly circulated through the stirring tank and the pipeline in this order to supply a sufficient amount of carbon dioxide gas, and then the mixture may be transferred to a carbon dioxide-containing slurry tank as a carbon dioxide-containing slurry. In the above method, after the carbon dioxide-containing slurry is obtained, it may be temporarily stored in a slurry storage tank for storing carbon dioxide-containing slurry, and the carbon dioxide-containing slurry may be appropriately supplied from the storage tank to the carbon dioxide-containing slurry tank.

[0018] From the viewpoint of increasing the amount of carbon dioxide fixed in the cement composition, the carbon dioxide gas may be supplied under pressure at the liquid surface of the cement slurry (for example, by increasing the internal pressure of a tank containing the cement slurry to 1,200 hPa or more, which exceeds atmospheric pressure). For this reason, it is preferable that the carbon dioxide gas supplying means for supplying the carbon dioxide gas has a structure capable of applying pressure.

[0019] In addition, carbon dioxide gas may be supplied to the cement slurry as a gas consisting of carbon dioxide gas alone, but from the standpoint of ease of availability, etc., it may be supplied to the cement slurry as a gas containing carbon dioxide gas. The ratio of carbon dioxide gas in the gas containing carbon dioxide gas is preferably 5% by volume or more, more preferably 10% by volume or more, even more preferably 20% by volume or more, even more preferably 50% by volume or more, even more preferably 80% by volume or more, and particularly preferably 90% by volume or more. If the ratio is 5% by volume or more, the amount of carbon dioxide fixed in the cement composition can be increased. In addition, the time required for supplying carbon dioxide gas can be shortened. Examples of gases containing carbon dioxide include exhaust gas generated in the cement manufacturing process (carbon dioxide concentration: approximately 20% by volume), exhaust gas generated in the steelmaking process (carbon dioxide concentration: approximately 20% by volume), exhaust gas generated in thermal power generation processes (carbon dioxide concentration: approximately 10% by volume), and gas separated and recovered from these exhaust gases (carbon dioxide concentration: approximately 100% by volume).

[0020] In this step, the carbon dioxide gas is supplied so that the pH of the carbon dioxide gas-containing slurry is preferably within the range of 5.0 to 11.5, more preferably 5.5 to 11.0, even more preferably 6.0 to 10.0, and particularly preferably 6.5 to 9.5. When the carbon dioxide gas is supplied so that the pH is 5.0 or more, the strength development of the cement composition is further improved. In addition, the time required for supplying the carbon dioxide gas is shortened, and the production efficiency of the method of the present invention is further improved. When the carbon dioxide gas is supplied so that the pH is 11.5 or less, the amount of carbon dioxide fixed in the cement composition is increased. Incidentally, the pH of the carbon dioxide gas-containing slurry is lowered by supplying the carbon dioxide gas. The time for supplying carbon dioxide gas required to sufficiently increase the amount of carbon dioxide fixed in the cement composition varies depending on the water-cement ratio, the carbon dioxide gas supply means, the carbon dioxide gas concentration of the carbon dioxide gas-containing gas supplied using said means, etc. For this reason, in this step, the timing for terminating the supply of carbon dioxide gas is preferably determined based on the actual measured pH value of the carbon dioxide gas-containing slurry.

[0021] [Additional cement supply process] This step is a step of kneading the carbon dioxide gas-containing slurry obtained in the carbon dioxide gas supplying step with the remainder of the cement to obtain a high-concentration cement-containing composition. The proportion of the remainder of the cement in the total amount of cement (total amount of cement contained in the cement composition) is 50 to 99 mass%, preferably 60 to 97 mass%, more preferably 70 to 95 mass%, even more preferably 75 to 92 mass%, even more preferably 80 to 90 mass%, and particularly preferably 82 to 88 mass%. If the proportion is less than 50 mass%, the strength development of the cement composition decreases. If the proportion is more than 99 mass%, the amount of carbon dioxide fixed in the cement composition decreases.

[0022] [Additional water supply process] This step is a step of kneading the high-concentration cement-containing composition obtained in the cement additional supply step with the remainder of the water to obtain a cement composition. The proportion of the remaining amount of water in the total amount of water (total amount of water contained in the cement composition) is 1 to 50 mass%, preferably 2 to 40 mass%, more preferably 3 to 30 mass%, and particularly preferably 4 to 25 mass%. If the proportion is less than 1 mass%, the amount of air contained in the cement composition is small, and the fluidity of the cement composition is reduced. If the proportion exceeds 50 mass%, the fluidity of the cement slurry obtained in the cement slurry preparation step is relatively significantly reduced, and it becomes difficult to uniformly supply carbon dioxide gas to the cement slurry in the carbon dioxide gas supplying step.

[0023] In addition, the entire amount of water is usually used in the cement slurry preparation step and the additional water supply step. However, in the present invention, a portion of the remaining water used in the additional water supply step may be added to at least one of the carbon dioxide gas supply step and the additional cement supply step. This embodiment is also included in the present invention. In this case, the proportion of the amount of the portion of the remaining water in 100% by mass of the remaining water is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

[0024] In the present invention, the aggregate contained in the cement composition is supplied in either one or both of the cement additional supply step and the water additional supply step. Among them, it is preferable to supply the aggregate in the cement additional supply step from the viewpoint of production efficiency. The aggregate used in the present invention may be fine aggregate alone or a combination of fine and coarse aggregates. In addition, any of natural aggregates, artificial aggregates, and recycled aggregates may be used. The fine aggregate is not particularly limited, and examples thereof include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag fine aggregate, and lightweight fine aggregate, or a mixture of two or more types selected from these. The coarse aggregate is not particularly limited, and examples thereof include river gravel, mountain gravel, land gravel, sea gravel, crushed stone, slag coarse aggregate, and lightweight coarse aggregate, or a mixture of two or more types selected from these. The amount of aggregate mixed (when fine aggregate and coarse aggregate are used in combination, the amount of each) is not particularly limited, and may be any amount generally used in mortar or concrete.

[0025] The water-cement ratio of the cement composition (the mass ratio of the total amount of water to the total amount of cement contained in the cement composition [(total amount of water) / (total amount of cement)] expressed as a percentage (%)) is preferably 30 to 65%, and more preferably 40 to 60%. When the above ratio is 30% or more, the workability of mixing in the above-mentioned additional cement supplying step and additional water supplying step, and the workability (fluidity of the cement composition) when pouring the cement composition obtained in the additional water supplying step are further improved. When the above ratio is 65% or less, the strength development of the cement composition is further improved.

[0026] In addition, from the viewpoint of further improving the air entrainment property and fluidity of the cement composition, it is preferable that the cement composition contains a cement admixture. Examples of the cement admixture include a cement dispersant and an AE agent. Although one of these may be used alone, it is preferable to use a cement dispersant and an AE agent in combination from the viewpoint of further improving the air entrainment and fluidity of the cement composition. Examples of the cement dispersant include water reducing agents, AE water reducing agents, high performance water reducing agents, and high performance AE water reducing agents, etc. Among them, from the viewpoint of improving the fluidity of the cement composition, delayed type water reducing agents, AE water reducing agents, or high performance AE water reducing agents are preferred. These may be used alone or in combination of two or more. The cement admixture is preferably supplied in the additional water supply step from the viewpoint of further improving the air entrainment and fluidity of the cement composition. Retarders such as gluconic acid, citric acid, and tartaric acid may also be used to delay and control the setting of the cement composition.

[0027] Furthermore, the cement composition may contain various admixtures such as fly ash, silica fume, ground granulated blast furnace slag, etc., as necessary. The method of mixing the various admixtures is not particularly limited, but it is preferable to mix them in at least one of the cement additional supply step and the water additional supply step from the viewpoints of production efficiency and not affecting the pH of the carbon dioxide gas-containing slurry in the carbon dioxide gas supply step. EXAMPLES

[0028] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Cement: ordinary Portland cement manufactured by Taiheiyo Cement Corporation (2) Fine aggregate: mountain sand (3) Coarse aggregate: crushed stone (4) Water; tap water (5) Air-entraining water-reducing agent; manufactured by Pozzolith Corporation, product name "Master Polyhede 15S" (6) Air entraining agent; product name "Master Air 303A" manufactured by Pozzolith Solutions Corporation

[0029] [Examples 1 to 3] A portion of the cement and a portion of the water in the unit amounts shown in Table 1 were mixed in a container for 60 seconds using a hand mixer to obtain a mixture (cement slurry, temperature: 23° C.) (cement slurry preparation step). The mixture in the container was transferred through a flow passage to a bubble-free dissolved water production device (manufactured by Tomoe Shoji Co., Ltd., product name "High concentration gas dissolving device") for supplying carbon dioxide gas to the mixture, and then carbon dioxide was supplied to the mixture in the device, and then the mixture was transferred through a flow passage different from the flow passage into the container, and the mixture was circulated for 8 hours to obtain a carbon dioxide gas-containing slurry (carbon dioxide gas supplying step). The pH of the obtained carbon dioxide gas-containing slurry was 8.56. The remainder of the cement, fine aggregate, and coarse aggregate in the unit amounts shown in Table 1 were added to the obtained carbon dioxide gas-containing slurry, and the mixture was kneaded for 30 seconds to obtain a high-concentration cement-containing composition (cement additional supply step). Next, the remaining amount of water in the unit amount shown in Table 1 and a liquid obtained by premixing the AE water reducing agent and AE agent in the amounts shown in Table 1 were added to the obtained high-concentration cement-containing composition and kneaded for 60 seconds. Next, the kneaded material adhering to the inner wall of the mixer was scraped off, and then kneaded for a further 60 seconds to obtain concrete (cement composition) (additional water supply process).

[0030] The slump of the obtained concrete was measured in accordance with "JIS A 1101:2020 (Concrete slump test method)". In addition, the compressive strength of the obtained concrete at ages of 1 day, 7 days, and 28 days was measured in accordance with "JIS A 1108:2018 (Test method for compressive strength of concrete)". Furthermore, the percentage of carbon dioxide (mass%) in the mortar of the 28-day-old concrete specimen used to measure the compressive strength was determined using thermogravimetry-differential thermal analysis (TG-DTA). Specifically, the specimen was crushed to remove the coarse aggregate, and then the sample (mortar portion) from which the coarse aggregate had been removed was subjected to thermogravimetry-differential thermal analysis (TG-DTA). From the measurement results, it was determined that the mass reduction in the endothermic peak range of about 550-800°C was due to the decarbonation of calcium carbonate contained in the mortar portion, and the percentage of carbon dioxide (mass%; value of calcium carbonate converted to carbon dioxide) in the mortar portion of the concrete specimen was calculated from the amount of reduction.

[0031] [Comparative Example 1] Unit weight is 336kg / m 3 The amount of cement is 840 kg / m 3 The amount of fine aggregate is 938 kg / m 3 The amount of coarse aggregate was mixed dry for 30 seconds using a Hobart mixer, and then the unit weight was 168 kg / m 3 A liquid mixture of water in an amount of 1.4 parts by mass of AE water reducing agent and 0.006 parts by mass of AE agent per 100 parts by mass of cement was poured in and mixed for 60 seconds. Next, the mixture adhering to the inner wall of the mixer was scraped off, and the mixture was mixed for another 60 seconds to obtain a concrete (cement composition). The pH of the water was 7.4. Measurement of the slump of the obtained concrete was carried out in the same manner as in Example 1.

[0032] [Comparative Example 2] Unit weight is 56.0kg / m 3 The amount of cement is 168 kg / m 3 The mixture was mixed in a container for 60 seconds using a hand mixer to obtain a mixture (cement slurry, temperature: 23°C). The mixture in the container was transferred through a flow passage to a bubble-free dissolved water production device (manufactured by Tomoe Shoji Co., Ltd., product name "High concentration gas dissolving device") for supplying carbon dioxide gas to the mixture, and then carbon dioxide was supplied to the mixture in the device, and then the mixture was transferred through a flow passage different from the flow passage into the container, and the mixture was circulated for 8 hours to obtain a carbon dioxide gas-containing slurry. The pH of the carbon dioxide gas-containing slurry obtained was 8.56. The obtained carbon dioxide-containing slurry was mixed with a mixture of 1.6 parts by mass of AE water reducing agent and 0.012 parts by mass of AE agent per 100 parts by mass of cement, with a unit amount of 840 kg / m 3 The amount of fine aggregate is 938 kg / m 3 The amount of coarse aggregate was added and mixed to obtain a concrete (cement composition). The slump of the obtained concrete was measured in the same manner as in Example 1. The results are shown in Table 2.

[0033] [Table 1]

[0034] [Table 2]

[0035] From Table 2, it can be seen that the proportion of carbon dioxide in the mortar portion of the concrete specimens in Examples 1 to 3 (2.79 to 2.92 mass%) is greater than the above proportion (1.89 mass%) in Comparative Example 1, and therefore carbon dioxide was fixed in the cement composition in Examples 1 to 3. Moreover, the above ratio in Comparative Example 2 was 2.81 mass %, and it is understood that in Comparative Example 2 as well, carbon dioxide was fixed to the same extent as in Examples 1 to 3. Here, from a comparison between Examples 1 to 3 and Comparative Example 2, the slump (18.0 to 19.0 cm) and air content (4.4 to 5.1%) of Examples 1 to 3 are greater than the slump (4.0 cm) and air content (2.3%) of Comparative Example 2, and therefore it is understood that the fluidity and air entrainment of the cement composition are improved according to the present invention.

Claims

1. 1. A method for producing a cement composition comprising cement, aggregate, water, and a cement admixture, comprising: a cement slurry preparation step of mixing a portion of the cement with a portion of the water to obtain a cement slurry; a carbon dioxide gas supplying step of supplying carbon dioxide gas into the cement slurry to obtain a carbon dioxide gas-containing slurry; A cement additional supply step of kneading the carbon dioxide gas-containing slurry with the remainder of the cement to obtain a high-concentration cement-containing composition; and a water addition step of kneading the high-concentration cement-containing composition, the remainder of the water, and the cement admixture to obtain the cement composition, In the total amount of the cement, the proportion of the part of the cement used in the cement slurry preparation step is 1 to 50 mass%, and the proportion of the remaining amount of the cement used in the cement additional supply step is 50 to 99 mass%, In the total amount of the water, the proportion of the part of the water used in the cement slurry preparation step is 50 to 99 mass%, and the proportion of the remaining amount of the water used in the water additional supply step is 1 to 50 mass%, The aggregate is supplied in either one or both of the cement additional supply step and the water additional supply step, A method for producing a cement composition, characterized in that the cement admixture contains one or more cement dispersants selected from the group consisting of water reducing agents, air-entraining water reducing agents, high-performance water reducing agents and high-performance air-entraining water reducing agents, and an air-entraining agent.

2. The aggregate includes fine aggregate and coarse aggregate, 2. The method for producing a cement composition according to claim 1, wherein the water-cement ratio of the cement composition is 30 to 65%.

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