Method for producing cement composition

Abstract

To provide a manufacturing method capable of obtaining a cement composition that does not cause clogging in a device, can increase a fixing amount of carbon dioxide, and is hardly limited in its use.SOLUTION: A method for producing a cement composition including cement, aggregate, a cement dispersant, and water, and obtained by fixing carbon dioxide includes: a cement-containing kneaded product preparing step of mixing a part of the cement, a part or all of water, and the cement dispersant to obtain a cement-containing kneaded product having a water cement ratio of 30 to 100%; a carbonated kneaded product preparing step of supplying carbon dioxide, which is a gaseous state of carbon dioxide to be fixed, into the cement-containing kneaded product to obtain a carbonated kneaded product; a cement composition preparing step of kneading the carbonated kneaded product, the remainder of cement, the remainder of water, and the aggregate or kneading the carbonated kneaded product, the remainder of cement, and the aggregate to obtain the cement composition.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 an example of a method including a step of fixing carbon dioxide in a calcium-containing powder by injecting a carbon dioxide-containing gas such as exhaust gas into a slurry containing a calcium-containing powder, Patent Document 1 describes a method for producing a cement powder composition containing cement clinker powder, gypsum powder, and carbonated calcium-containing powder, which includes a carbonation step of supplying a carbon dioxide-containing gas into a slurry containing the calcium-containing powder and water before carbonation to obtain a carbonated slurry, and a grinding step of supplying the cement clinker, gypsum, and the carbonated slurry into a finishing mill for cement production and grinding them to obtain the cement powder composition. Furthermore, Patent Document 2 describes a method for producing a cement admixture, which includes a slurrying step in which fresh concrete sludge or fine waste concrete powder is heat-treated and then mixed with water to form a slurry, and a carbonation step in which carbon dioxide gas is passed through the slurry to carbonate it. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-152631 A [Patent Document 2] JP 2021-138574 A Summary of the Invention [Problem to be solved by the invention]

[0004] When carbon dioxide is fixed in cement by injecting a carbon dioxide-containing gas into a slurry containing cement (hereinafter also referred to as "carbonation treatment"), there is a problem that calcium carbonate precipitates and adheres in the carbon dioxide-containing gas outlet, inside a tank for performing the carbonation treatment, inside piping, etc., making it impossible to inject the carbon dioxide-containing gas or causing the device to become clogged. In order to prevent the above problems, a method of increasing the amount of water in the slurry containing cement and performing carbonation treatment can be considered. However, when the amount of water in the slurry is increased, the water-cement ratio of the cement composition (e.g., concrete) using the cement after carbonation treatment becomes large, which is a problem in that the applications of the cement composition are limited. An object of the present invention is to provide a method for producing a cement composition which can increase the amount of carbon dioxide fixed without causing blockage in the apparatus even if the amount of water in the cement-containing mixture into which a carbon dioxide-containing gas is injected is reduced, and which can obtain a cement composition which is not easily limited in its applications because the water-cement ratio of the resulting cement composition does not become excessively large. [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 including the steps of: mixing a part of the cement, a part or all of the water, and a cement dispersant to obtain a kneaded product having a water-cement ratio of 30 to 100%, supplying carbon dioxide gas into the kneaded product to obtain a carbonated kneaded product, and kneading the carbonated kneaded product with the remainder of the cement, the remainder of the water, and aggregate, or kneading the carbonated kneaded product with the remainder of the cement and aggregate to obtain a cement composition, and have completed the present invention. That is, the present invention provides the following [1] to [4]. [1] A method for producing a cement composition containing cement, aggregate, cement dispersant, and water, and having carbon dioxide fixed therein, comprising: a cement-containing kneaded product preparation step of mixing a part of the cement, a part or all of the water, and the cement dispersant to obtain a cement-containing kneaded product having a water-cement ratio of 30 to 100%; a carbonation kneaded product preparation step of supplying carbon dioxide, which is the gaseous state of the carbon dioxide to be fixed, into the cement-containing kneaded product to obtain a carbonated kneaded product; and a cement composition preparation step of kneading the carbonated kneaded product with the remainder of the cement, the remainder of the water, and the aggregate, or kneading the carbonated kneaded product with the remainder of the cement and the aggregate, to obtain the cement composition.

[0006] [2] The method for producing a cement composition according to the above [1], wherein the water-cement ratio of the cement composition is 30 to 65%. [3] The method for producing a cement composition according to [1] or [2], wherein in the cement-containing mixture preparation step, the proportion of the part of the cement in the total amount of the cement is 1 to 80 mass %. [4] The method for producing a cement composition according to any one of [1] to [3], wherein in the cement-containing mixture preparation step, a portion of the cement is mixed with a portion of the water, and the proportion of the amount of the portion of the water in the total amount of the water is 30 to 99 mass%. Effect of the Invention

[0007] According to the method for producing a cement composition of the present invention, even if the amount of water in the cement-containing mixture into which the carbon dioxide-containing gas is injected is reduced, no blockage occurs within the apparatus, and the amount of carbon dioxide fixed can be increased. Since the water-cement ratio of the resulting cement composition does not become excessively large, a cement composition that is not easily limited in its uses can be obtained. 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, a cement dispersant, and water, and having carbon dioxide fixed therein, and includes a cement-containing kneaded product preparation step of mixing a part of the cement, a part or all of the water, and the cement dispersant to obtain a cement-containing kneaded product having a water-cement ratio of 30 to 100%, a carbonation kneaded product preparation step of supplying carbon dioxide, which is the gaseous state of the carbon dioxide to be fixed, into the cement-containing kneaded product to obtain a carbonated kneaded product, and a cement composition preparation step of kneading the carbonated kneaded product, the remainder of the cement, the remainder of the water, and the aggregate, or kneading the carbonated kneaded product, the remainder of the cement, and the aggregate, to obtain a cement composition. Each step will be explained in detail below.

[0009] [Cement-containing mixture preparation process] This step is a step of mixing a part of cement, a part or all of water, and a cement dispersant to obtain a cement-containing kneaded material having a water-cement ratio of 30 to 100%. 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. Among these, ordinary Portland cement is preferred from the viewpoint of versatility and the like.

[0010] The proportion of the amount of the part of the cement in the total amount of cement (the total amount of cement contained in the cement composition) is preferably 1 to 80 mass%, more preferably 10 to 78 mass%, even more preferably 20 to 75 mass%, even more preferably 30 to 72 mass%, even more preferably 40 to 70 mass%, even more preferably 50 to 70 mass%, and particularly preferably 60 to 70 mass%. If the proportion is 1 mass% or more, the amount of carbon dioxide fixed in the cement composition is increased. If the proportion is 80 mass% or less, the strength development of the cement composition is further improved.

[0011] The water is not particularly limited, and examples thereof include tap water and sludge water. In this step, when a part of the water is mixed, the ratio of the amount of the part of the water in the total amount of water (total amount of water contained in the cement composition) is preferably 30 to 99 mass%, more preferably 32 to 90 mass%, even more preferably 35 to 80 mass%, even more preferably 38 to 70 mass%, even more preferably 40 to 60 mass%, and particularly preferably 40 to 50 mass%. If the above ratio is 30 mass% or more, the fluidity of the cement-containing kneaded product is further improved, and in the carbonation kneaded product preparation step described later, carbon dioxide gas is easily supplied uniformly to the cement-containing kneaded product. If the above ratio is 99 mass% or less, the amount of air contained in the cement composition is larger, and the fluidity of the cement composition is further improved.

[0012] In this step, the water-cement ratio of the cement-containing kneaded product is 30-100%, preferably 35-95%, more preferably 40-90%, further preferably 50-80%, and particularly preferably 55-70%. If the above ratio is 30% or more, the fluidity of the cement-containing kneaded product is further improved, and it becomes easy to uniformly supply carbon dioxide gas to the cement-containing kneaded product in the carbonation kneaded product preparation step described later. If the above ratio is 100% or less, the amount of carbon dioxide fixed in the cement composition becomes larger. In addition, since the water-cement ratio of the obtained cement composition does not become excessively large, the use of the cement composition is less likely to be limited. The water-cement ratio is the mass ratio (water / cement) of water (in this process, part or all of the water) to cement (in this process, part of the cement) expressed as a percentage (%). In this step, the method for mixing a portion of the cement and a portion or all of the water is not particularly limited. For example, a portion or all 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 or all of the water and a portion of the cement may be simultaneously added to a stirring tank or the like, and then mixed.

[0013] 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 amount of the cement dispersant is preferably 0.1 to 5.0 parts by mass, more preferably 0.3 to 4.0 parts by mass, even more preferably 0.5 to 3.0 parts by mass, even more preferably 0.8 to 2.5 parts by mass, and particularly preferably 1.0 to 2.0 parts by mass, relative to 100 parts by mass of the total amount of cement (total amount of cement contained in the cement composition). If the amount is 0.1 parts by mass or more, clogging inside the machine is less likely to occur in the cement-containing kneaded product preparation step and the carbonated kneaded product preparation step. In addition, the amount of carbon dioxide fixed can be increased. If the amount is 5.0 parts by mass or less, the cost of materials can be further reduced. In addition, in the cement-containing mixture preparation step, the entire amount of the cement dispersant is usually used. However, in the present invention, a part of the cement dispersant may be added in the cement composition preparation step described below. This embodiment is also included in the present invention. In this case, the proportion of the part of the amount of the cement dispersant in the total amount of the cement dispersant contained in the cement composition (100 mass%) is preferably 10 to 80 mass%, more preferably 20 to 70 mass%, and particularly preferably 30 to 60 mass%.

[0014] [Carbonated mixture preparation process] This process is carried out after the cement-containing kneaded material preparation process, and is a process in which carbon dioxide, which is the gaseous state of the carbon dioxide to be fixed, is supplied to the cement-containing kneaded material obtained in the previous process to obtain a carbonated kneaded material. In this step, from the viewpoint of uniformly supplying carbon dioxide gas to the cement-containing kneaded material, it is preferable to supply carbon dioxide gas while fluidizing the cement-containing kneaded material. Examples of the method for supplying carbon dioxide gas into the cement-containing mixture 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-containing kneaded mixture is installed in a stirring tank for obtaining the cement-containing kneaded mixture used in the cement-containing kneaded mixture preparation step, and carbon dioxide gas is supplied into the cement-containing kneaded mixture. 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-containing kneaded product, and a carbon dioxide gas supplying means (e.g., an air diffuser) disposed in a mixture storage space in the stirring tank, carbon dioxide gas is blown into the cement-containing kneaded product obtained in the above-mentioned cement-containing kneaded product preparation step while stirring the cement-containing kneaded product, to obtain a carbonated kneaded product.

[0015] (ii) A method in which the cement-containing kneaded material is transferred from a stirring tank for storing the cement-containing kneaded material 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-containing kneaded material in the apparatus to obtain a carbonated kneaded material, and then the carbonated kneaded material is transferred to a carbonation kneaded material tank for storing the carbonated kneaded material. The stirring tank and the carbonation kneaded material tank may be the same or different.

[0016] A more specific example is a method in which a mixture obtained by mixing part of the cement and part or all of the water (the cement-containing kneaded product obtained in the cement-containing kneaded product preparation step), which is contained in a stirring tank for stirring and mixing the cement and water to obtain a cement-containing kneaded product, 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 a carbon dioxide gas supplying 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 carbonated kneaded product. 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 carbonated kneaded material, the carbonated kneaded material may be temporarily stored in a storage tank for storing carbonated kneaded material, which is different from the carbonated kneaded material tank, and the carbonated kneaded material may be appropriately supplied from the storage tank to the carbonated kneaded material tank.

[0017] (iii) A method of blowing carbon dioxide gas into a cement-containing kneaded material when the cement-containing kneaded material is transferred from a stirring tank for accommodating the cement-containing kneaded material to a carbonation kneaded material tank for accommodating the carbonated kneaded material. A more specific example is a method in which a mixture obtained by mixing part of the cement and part or all of the water (the cement-containing kneaded product obtained in the above-mentioned cement-containing kneaded product preparation step) contained in a stirring tank for stirring and mixing the cement and water to obtain a cement-containing kneaded product is circulated through a pipeline for circulating the mixture supplied from the stirring tank, while supplying and stirring carbon dioxide gas into the mixture to obtain a carbonated kneaded product, and then the carbonated kneaded product is transferred to the above-mentioned carbonation kneaded product tank.

[0018] 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 the carbon dioxide gas is supplied into the mixture, the mixture may be returned to the stirring tank without being transferred to the carbonation kneaded material 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 the carbonation kneaded material tank as a carbonated kneaded material. In addition, in the above method, after the carbonated kneaded material is obtained, it may be temporarily stored in a kneaded material storage tank for storing the carbonated kneaded material, and the carbonated kneaded material may be appropriately supplied from the storage tank to the carbonated kneaded material tank.

[0019] From the viewpoint of increasing the amount of carbon dioxide fixed in the cement composition, the carbon dioxide gas may be supplied under pressure on the surface of the cement-containing mixture (for example, the internal pressure of the tank containing the cement-containing mixture may be increased 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.

[0020] In addition, carbon dioxide gas (carbon dioxide gas) may be supplied to the cement-containing mixture as a gas consisting of only carbon dioxide gas, but from the standpoint of ease of availability, etc., it may be supplied to the cement-containing mixture 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).

[0021] In this step, the carbon dioxide gas is supplied so that the pH of the carbonated kneaded product 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 carbonated kneaded product is lowered by supplying the carbon dioxide gas. The carbon dioxide gas supply time 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 to end the carbon dioxide gas supply is preferably determined based on the actual measured pH value of the carbonated kneaded product.

[0022] [Cement composition preparation process] This process is carried out after the carbonated kneaded product preparation process, and is a process for obtaining a cement composition by kneading the carbonated kneaded product obtained in the previous process with the remaining cement, the remaining water, and aggregate, or by kneading the carbonated kneaded product, the remaining cement, and aggregate. The proportion of the amount of the remainder of the above cement in the total amount of cement (total amount of cement contained in the cement composition) is preferably 20 to 99 mass%, more preferably 22 to 90 mass%, even more preferably 25 to 80 mass%, even more preferably 28 to 70 mass%, even more preferably 30 to 60 mass%, even more preferably 30 to 50 mass%, and particularly preferably 30 to 40 mass%. If the proportion is 20 mass% or more, the strength development of the cement composition is further improved. If the proportion is 99 mass% or less, the amount of carbon dioxide fixed in the cement composition can be increased.

[0023] 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 to be mixed (when fine aggregate and coarse aggregate are used in combination, the amount of each to be mixed) is not particularly limited, and may be any amount generally used in mortar or concrete.

[0024] In this step, when the carbonated kneaded product, the remainder of the cement, and the remainder of the water are kneaded, the ratio of the amount of the remainder of the water in the total amount of water (total amount of water contained in the cement composition) is preferably 1 to 70 mass%, more preferably 10 to 68 mass%, even more preferably 20 to 65 mass%, even more preferably 30 to 62 mass%, even more preferably 40 to 60 mass%, and particularly preferably 40 to 50 mass%. If the ratio is 1 mass% or more, the amount of air contained in the cement composition can be increased, and the fluidity of the cement composition is further improved. If the ratio is 70 mass% or less, the fluidity of the cement-containing kneaded product obtained in the cement-containing kneaded product preparation step is relatively improved, so that it becomes easier to supply carbon dioxide gas uniformly to the cement-containing kneaded product in the carbonated kneaded product preparation step.

[0025] In this step, when the carbonated kneaded product, the remainder of the cement, the remainder of the water, and the aggregate are kneaded, the order of kneading the materials is not particularly limited, and examples thereof include (i) a method of kneading the carbonated kneaded product, the remainder of the cement, and the aggregate, and then adding the remainder of the water to the kneaded product and kneading it, (ii) a method of kneading the carbonated kneaded product and the remainder of the water, and then adding the remainder of the cement and the aggregate to the kneaded product and kneading it, etc. Among them, from the viewpoint of improving the fluidity of the cement composition, the method of (i) kneading the carbonated kneaded product, the remainder of the cement, and the aggregate, and then adding the remainder of the water to the kneaded product and kneading it is preferable.

[0026] In addition, in the cement-containing kneaded product preparation step and the cement composition preparation step, the entire amount of water is usually used. However, in the present invention, a part of the water may be added in the above-mentioned carbonation kneaded product preparation step. This embodiment is also included in the present invention. In this case, the proportion of the amount of the part of the water in the total amount of water (100 mass%) is preferably 10 mass% or less, more preferably 8 mass% or less, and particularly preferably 5 mass% or less.

[0027] 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%, more preferably 35 to 60%, and particularly preferably 40 to 55%. When the above ratio is 30% or more, the workability of kneading in the above-mentioned cement composition preparation step and the workability when pouring the obtained cement composition (fluidity of the cement composition) are further improved. When the above ratio is 65% or less, the strength development of the cement composition is further improved. Also, the use of the cement composition is less likely to be limited.

[0028] In addition, the cement composition preferably contains an AE agent from the viewpoint of further improving the air entrainment and fluidity of the cement composition. The AE agent is usually supplied and mixed or kneaded in either one or both of the cement-containing mixture preparation step and the cement composition preparation step. Among them, in order to further improve the air entrainment and fluidity of the cement composition, it is preferable to supply and knead in the cement composition preparation step. In addition, the AE agent is usually supplied after being mixed with water in advance. The cement composition may also use retarders such as gluconic acid, citric acid, and tartaric acid to delay and control the setting of the cement composition. Furthermore, the cement composition may contain, as necessary, various admixtures such as fly ash, silica fume, ground granulated blast furnace slag, etc., antifoaming agent, fluidizing agent, etc. The method of mixing the various admixtures and admixtures is not particularly limited, but it is preferable to supply and knead them in the cement composition preparation step from the viewpoints of production efficiency and not affecting the pH of the carbonated kneaded product in the carbonated kneaded product preparation step. EXAMPLES

[0029] 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) Cement dispersant 1; AE water reducer, manufactured by Pozzolith Solutions, product name "Master Polyhede 15S" (5) Cement dispersant 2; high-performance AE water reducer, manufactured by Pozzolith Solutions, product name "Masterglenium SP8SV" (6) Air entraining agent; product name "Master Air 303A" manufactured by Pozzolith Solutions Corporation (7) Defoamer: Pozzolith Solutions, product name "Master Air 404" (8) Water; tap water

[0030] [Reference examples 1~2] Cement and water in amounts such that the water-cement ratio (mass ratio of water to cement expressed as a percentage) was the value shown in Table 1 were mixed in a container for 60 seconds using a hand mixer to obtain a mixture (cement-containing mixture, temperature: 23°C). The mixture in the container was transferred through a flow passage to a bubble-free dissolved water manufacturing device (manufactured by Tomoe Shoji Co., Ltd., product name "High Concentration Gas Dissolver") for supplying carbon dioxide gas to the mixture, and then carbon dioxide was supplied to the mixture in the device. The mixture was then repeatedly transferred into the container through a flow passage different from the flow passage, thereby circulating the mixture and obtaining a carbonated kneaded material. When the circulation was continued for 8 hours, no clogging occurred in the apparatus and a carbonated kneaded product was obtained, the result was evaluated as "good", and when clogging occurred in the apparatus during the circulation, the result was evaluated as "bad".

[0031] [Reference examples 3~5] Cement and water in amounts that yielded a water-cement ratio as shown in Table 1, and an AE water-reducing agent in an amount shown in Table 1 were mixed in a container for 60 seconds using a hand mixer to obtain a mixture (cement-containing kneaded product, temperature: 23°C) (corresponding to the cement-containing kneaded product preparation step of the present invention). A carbonated kneaded product was obtained in the same manner as in Reference Example 1, except that the above mixture was used (corresponding to the carbonated kneaded product preparation step of the present invention). When the circulation was continued for 8 hours, no clogging occurred in the apparatus and a carbonated kneaded product was obtained, the result was evaluated as "good", and when clogging occurred in the apparatus during the circulation, the result was evaluated as "bad". The results are shown in Table 1.

[0032] [Table 1]

[0033] [Examples 1-2] In the cement-containing mixture preparation process, part of the cement, part of the water, and the AE water reducer in the unit amounts shown in Table 2 were mixed in a container using a hand mixer for 60 seconds to obtain a mixture (cement-containing mixture, temperature: 23°C). As the carbonated kneaded material preparation process, the mixture in the above container was circulated for 8 hours using a bubble-free dissolved water manufacturing device (manufactured by Tomoe Shoji, product name ``High Concentration Gas Dissolver'') in the same manner as in Reference Example 1 to obtain a carbonated kneaded material. In the cement composition preparation step, the remaining part of the cement in the unit amount shown in Table 2, the fine aggregate, and the coarse aggregate were dry-mixed for 30 seconds, and the above-mentioned carbonated mixture was mixed for 60 seconds using a twin-axis forced mixer to obtain a mixture. Next, the mixture adhering to the inner wall of the mixer was scraped off, and then a liquid obtained by mixing the remaining part of the water in the unit amount shown in Table 2 and the amount of the AE agent shown in Table 2 was added, and the mixture was mixed for 60 seconds to obtain a cement composition. The unit amounts shown in Tables 2 and 4 are per 1 m of the final cement composition. 3 The quantity (mass) of each material is shown.

[0034] The slump of the obtained concrete (cement composition) 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 7 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.

[0035] [Comparative Example 1] Cement, fine aggregate, and coarse aggregate in the unit amounts shown in Table 2 were dry mixed for 30 seconds using a twin-axis forced mixer. Next, a liquid obtained by mixing the unit amount of water shown in Table 2 and the amount of AE water-reducing agent and AE agent shown in Table 2 was added and mixed for 60 seconds. After scraping off the mixed material adhering to the inner wall of the mixer, the mixture was further mixed for 60 seconds to obtain a cement composition. The slump and other properties of the resulting concrete (cement composition) were measured in the same manner as in Example 1. [Comparative Example 2] A cement composition was obtained in the same manner as in Example 1, except that no AE water-reducing agent was used in the cement-containing mixture preparation step, and a liquid obtained by mixing the remainder of the unit amount of water shown in Table 2 with the AE agent and AE water-reducing agent in the amounts shown in Table 2 was added in the cement composition preparation step (cement composition preparation step). The slump and other properties of the resulting concrete (cement composition) were measured in the same manner as in Example 1. The results are shown in Table 3.

[0036] [Table 2]

[0037] [Table 3]

[0038] [Example 3] As the cement-containing mixture preparation process, a portion of the cement, a portion of the water, and an AE water reducer in the unit amounts shown in Table 4 were mixed in a container using a hand mixer for 60 seconds to obtain a mixture (cement-containing mixture, temperature: 23°C). As the carbonated kneaded material preparation process, the mixture in the above container was circulated for 8 hours using a bubble-free dissolved water manufacturing device (manufactured by Tomoe Shoji, product name ``High Concentration Gas Dissolver'') in the same manner as in Reference Example 1 to obtain a carbonated kneaded material. In the cement composition preparation step, the remaining unit amount of cement shown in Table 4, fine aggregate, and coarse aggregate were dry-mixed for 30 seconds, and the above-mentioned carbonated mixture was mixed for 60 seconds using a twin-shaft forced mixer to obtain a mixture. Next, the mixture adhering to the inner wall of the mixer was scraped off, and then the remaining unit amount of water shown in Table 4 and a liquid mixture of the defoaming agent and high-performance AE water-reducing agent in the amounts shown in Table 4 were added, and mixed for 60 seconds to obtain a cement composition. The slump flow of the obtained concrete (cement composition) was measured in accordance with "JIS A 1150:2020 (Concrete Slump Flow Test Method)". In addition, the compressive strength of the obtained concrete at ages of 7 days and 28 days was measured, and the proportion of carbon dioxide (mass %) in the mortar portion of the 28-day concrete specimen was calculated in the same manner as in Example 1.

[0039] [Comparative Example 3] Cement, fine aggregate, and coarse aggregate in the unit amounts shown in Table 4 were dry mixed for 30 seconds using a twin-axis forced mixer. Next, a liquid obtained by mixing the unit amounts of water shown in Table 4 with the amounts of an antifoaming agent and a high-performance AE water-reducing agent shown in Table 4 was added and mixed for 60 seconds. After scraping off the mixed material adhering to the inner wall of the mixer, the mixture was further mixed for 60 seconds to obtain a cement composition. The slump flow of the obtained concrete (cement composition) was measured in the same manner as in Example 3. [Comparative Example 4] A cement composition was obtained in the same manner as in Example 3, except that no AE water-reducing agent was used in the cement-containing mixture preparation step, and a liquid obtained by mixing the remainder of the unit amount of water shown in Table 4 with the amounts of an antifoaming agent and a high-performance AE water-reducing agent shown in Table 4 was added in the cement composition preparation step (cement composition preparation step). The slump flow of the obtained concrete (cement composition) was measured in the same manner as in Example 3.

[0040] [Table 4]

[0041] [Table 5]

[0042] From Reference Examples 3 to 5 in Table 1, it can be seen that by using an AE water reducer in the cement-containing kneaded material preparation step, clogging of the inside of the equipment does not occur in the carbonated kneaded material preparation step even if the water-cement ratio is 40 to 80%. Furthermore, from Tables 3 and 5, it can be seen that the carbon dioxide content in the mortar portions of Examples 1 to 3 (6.83 to 11.29% by mass) is greater than the carbon dioxide content in the mortar portions of Comparative Examples 1 to 4 (1.89 to 3.14% by mass), indicating that more carbon dioxide can be fixed according to the present invention.

Claims

1. A method for producing a cement composition comprising cement, aggregate, a cement dispersant, and water, and fixing carbon dioxide, comprising the steps of: a cement-containing kneaded product preparation step of mixing a part of the cement, a part or all of the water, and the cement dispersant to obtain a cement-containing kneaded product having a water-cement ratio of 50 to 90%; A carbonation kneaded product preparation step of supplying carbon dioxide, which is a gaseous state of the carbon dioxide to be fixed, into the cement-containing kneaded product to obtain a carbonated kneaded product; a cement composition preparation step of kneading the carbonated kneaded product, the remainder of the cement, the remainder of the water, and the aggregate, or kneading the carbonated kneaded product, the remainder of the cement, and the aggregate, to obtain the cement composition; The water-cement ratio of the cement composition is 30 to 65%, A method for producing a cement composition, characterized in that in the cement-containing mixture preparation step, the proportion of the part of cement in the total amount of cement is 40 to 70 mass %.

2. 2. The method for producing a cement composition according to claim 1, wherein in the cement-containing kneaded product preparation step, a portion of the cement and a portion of the water are mixed, and the proportion of the amount of the portion of the water in the total amount of the water is 30 to 99 mass%.

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