Method for producing cement composition

Abstract

To provide a production method of a cement composition capable of fixing carbon oxide more into the cement composition without lowering air entrainment properties or flowability of the cement composition even if using dry ice.SOLUTION: A production method of a cement composition includes: a step (first mixing step) of mixing a part of cement, at least a part of fine aggregate, at least a part of water, and dry ice while agitating to obtain a cement-containing admixture; a step of standing the cement-containing admixture for 60 seconds or longer; and a step (second mixing step) of mixing the admixture after standing and the rest of respective materials constituting the cement composition while agitating to obtain the cement composition. In the first mixing step, a ratio of a partial amount of the cement to the total amount of the cement is 3-60 mass%, a ratio of at least a partial amount of the fine aggregate to the total amount of the fine aggregate is 80-100 mass%, and a ratio of at least a partial amount of the water to the total amount of the water is 80-100 mass%.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 curb global warming. In relation to this, technology is being considered to fix carbon dioxide captured from exhaust gases generated in cement manufacturing plants into concrete or the like. As a method for providing concrete in which carbon dioxide is efficiently immobilized, 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 adjusting the weight of the water so that the amount of unhydrated cement remaining in the concrete is between 0% and 50%. Furthermore, as a method for mixing and fixing carbon dioxide gas into concrete, Patent Document 2 describes a method for mixing carbon dioxide gas into concrete, which is characterized by controlling and reducing the pressure of liquefied carbon dioxide gas pumped from a carbon dioxide gas storage facility to turn it into powdered dry ice, and then spraying this powdered dry ice into the concrete and mixing it. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-37493 [Patent Document 2] Japanese Patent Application Publication No. 11-324324 Summary of the Invention [Problem to be solved by the invention]

[0004] When dry ice is used in the production of cement compositions such as concrete, the air entrainment and fluidity of the cement composition may be reduced. An object of the present invention is to provide a method for producing a cement composition that does not reduce the air entrainment and fluidity of the cement composition (e.g., concrete) despite the use of dry ice, and that can fix a larger amount of carbon dioxide in the cement composition. [Means for solving the problem]

[0005] As a result of intensive research into solving the above-mentioned problems, the present inventors have found that the above-mentioned objects can be achieved by a method for producing a cement composition, which includes the steps of: mixing, with stirring, cement in an amount that accounts for 3 to 60 mass% of the total amount of cement; fine aggregate in an amount that accounts for 80 to 100 mass% of the total amount of fine aggregate; water in an amount that accounts for 80 to 100 mass% of the total amount of water; and dry ice to obtain a cement-containing mixture; allowing the cement-containing mixture to stand for 60 seconds or more; and mixing, with stirring, the mixture that has been allowed to stand with the remainder of the materials that constitute the cement composition to obtain a cement composition, and have completed the present invention. That is, the present invention provides the following [1] to [6]. [1] A method for producing a cement composition containing cement, fine aggregate, and water, and in which carbon dioxide is fixed, comprising: a first mixing step of mixing, with stirring, a portion of the cement, at least a portion of the fine aggregate, at least a portion of the water, and dry ice to obtain a cement-containing mixture; a setting step of allowing the cement-containing mixture to stand for 60 seconds or more to obtain a mixture after setting; and a second mixing step of mixing, with stirring, the mixture after setting and the remainder of the materials constituting the cement composition to obtain the cement composition, wherein in the first mixing step, the proportion of the amount of the portion of the cement in the total amount of the cement is 3 to 60 mass %, the proportion of the amount of at least a portion of the fine aggregate in the total amount of the fine aggregate is 80 to 100 mass %, and the proportion of the amount of the at least a portion of the water in the total amount of the water is 80 to 100 mass %.

[0006] [2] The method for producing a cement composition according to [1], wherein the cement composition contains a cement admixture, and the cement admixture is supplied in the second mixing step. [3] The method for producing a cement composition according to [2], 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 cement composition contains coarse aggregate, and the coarse aggregate is supplied in the second mixing step. [5] The method for producing a cement composition according to [4] above, wherein the water-cement ratio of the cement composition is 30 to 65%. [6] The method for producing a cement composition according to any one of [1] to [5], wherein the amount of dry ice in the first mixing step is determined so that the carbon dioxide content in the mortar portion of the hardened product of the cement composition is 2.2 mass% or more. [Effects of the Invention]

[0007] According to the method for producing a cement composition of the present invention, even though dry ice is used, the air entrainment property and fluidity of the cement composition are not reduced, and a larger amount of carbon dioxide can be fixed in the cement composition. DETAILED DESCRIPTION OF THE INVENTION

[0008] The method for producing a cement composition of the present invention is a method for producing a cement composition that contains cement, fine aggregate, and water and that immobilizes carbon dioxide, and includes the following steps: a first mixing step in which a portion of the cement, at least a portion of the fine aggregate, at least a portion of the water, and dry ice are mixed with stirring to obtain a cement-containing mixture; a setting step in which the cement-containing mixture is allowed to stand for 60 seconds or more to obtain a mixture after setting; and a second mixing step in which the mixture after setting and the remainder of the materials that constitute the cement composition are mixed with stirring to obtain the cement composition, wherein in the first mixing step, the proportion of the amount of the portion of cement in the total amount of cement is 3 to 60 mass%, the proportion of the amount of at least a portion of the fine aggregate in the total amount of fine aggregate is 80 to 100 mass%, and the proportion of the amount of at least a portion of the water in the total amount of water is 80 to 100 mass%. Each step will be explained in detail below.

[0009] [First mixing process] This step is a step of mixing a portion of cement, at least a portion of fine aggregate, at least a portion of water, and dry ice with stirring to obtain a cement-containing mixture. The cement is not particularly limited, and examples thereof include various types of Portland cement 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. The proportion of the amount of the portion of cement in the total amount of cement (total amount of cement contained in the cement composition) is 3 to 60 mass%, preferably 4 to 55 mass%, more preferably 8 to 40 mass%, and particularly preferably 12 to 30 mass%. If the proportion is less than 3 mass%, the amount of carbon dioxide fixed in the cement composition will be small. If the proportion is more than 60 mass%, the strength development of the cement composition will be reduced.

[0010] 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 proportion of at least a portion of the fine aggregate in the total amount of fine aggregate (total amount of fine aggregate contained in the cement composition) is 80 to 100 mass%, preferably 90 to 100 mass%, more preferably 95 to 100 mass%, and from the viewpoint of production efficiency, particularly preferably 100 mass%. If the proportion is 80 mass% or more, the amount of carbon dioxide fixed in the cement composition will be greater. The amount of fine aggregate to be mixed is not particularly limited, and may be any amount generally used in mortar or concrete.

[0011] The water is not particularly limited, and examples thereof include tap water and sludge water. The proportion of at least a portion of the water in the total amount of water (total amount of water contained in the cement composition) is 80 to 100 mass%, preferably 90 to 100 mass%, more preferably 95 to 100 mass%, and from the viewpoint of production efficiency, particularly preferably 100 mass%. If the proportion is 80 mass% or more, the amount of carbon dioxide fixed in the cement composition will be greater. 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 40 to 60%. If the ratio is 30% or more, the mixing workability in the first mixing step and the second mixing step, and the workability when pouring the cement composition obtained in the second mixing step (fluidity of the cement composition) are further improved. If the ratio is 65% or less, the strength development of the cement composition is further improved.

[0012] The dry ice may be in any form of powder, granules, or blocks, but powdered dry ice is preferred from the viewpoint of immobilizing a larger amount of carbon dioxide in the cement composition in a shorter standing time in the standing step described below. In addition, in order to make it easier to add dry ice, powdered dry ice that has been compressed and molded may be used as the dry ice. Examples of methods for compressing powdered dry ice to form a shape include a method in which the pressure of powdered dry ice ejected from a liquefied carbon dioxide gas storage means such as a liquefied carbon dioxide gas cylinder or a liquefied carbon dioxide gas storage tank is used to pour the powdered dry ice into a molding container, and a method in which the powdered dry ice is compressed and molded in the container at the same time.

[0013] The amount of dry ice used in the first mixing step is preferably determined so that the carbon dioxide content in the mortar portion of the hardened cement composition obtained in the second mixing step described below is preferably 2.2% by mass or more, more preferably 2.3% by mass or more, even more preferably 2.4% by mass or more, even more preferably 2.5% by mass or more, and particularly preferably 2.6% by mass or more. The amount of dry ice determined in the first mixing step varies depending on the shape of the dry ice, the blending amounts of each material, etc., but is preferably 2 to 20 parts by mass, more preferably 3 to 15 parts by mass, even more preferably 4 to 10 parts by mass, and particularly preferably 5 to 8 parts by mass per 100 parts by mass of cement. If the amount is 2 parts by mass or more, the amount of carbon dioxide immobilized in the cement composition can be increased. If the amount is 20 parts by mass or less, a decrease in the strength development of the cement composition can be prevented.

[0014] In this step, the method of stirring and mixing the materials is not particularly limited. Examples include a method in which the materials are all put into a mixer or the like at once and mixed while stirring, or a method in which a powdered or granular material (a material in the form of a powder or granules) other than water and dry ice, such as cement, is mixed, and then the resulting mixture is mixed with water and dry ice while stirring. The stirring time varies depending on the stirring means, the amount of each material, the shape of the dry ice, etc., but is preferably 45 to 240 seconds, more preferably 60 to 180 seconds, and particularly preferably 90 to 150 seconds. If the above time is 45 seconds or more, the amount of carbon dioxide fixed in the cement composition can be increased. If the above time is 240 seconds or less, the time required for production can be shortened, thereby improving productivity. The start point (0 seconds) of the above mixing time is the time when mixing starts after all of the materials used in the first mixing step, such as cement, water, and dry ice, have been supplied. The first mixing step and the second mixing step (described later) may be performed in the same container, or may be performed in different containers. Examples of the container include a pail can and a mixer having a stirring means. When a container without a stirring means, such as a pail can, is used, a hand mixer or the like can be used as the stirring means.

[0015] [Standing process] This step is a step of leaving the cement-containing mixture obtained in the first mixing step to stand for 60 seconds or more to obtain a mixture after standing. The standing time is 60 seconds or more, preferably 75 to 360 seconds, more preferably 90 to 240 seconds, and particularly preferably 105 to 180 seconds. If the time is 60 seconds or more, the amount of carbon dioxide fixed in the cement composition can be increased. If the time is 360 seconds or less, the time required for production can be shortened, thereby improving productivity. The standing of the cement-containing mixture may be carried out while the cement-containing mixture is contained in the container in which the first mixing step was carried out, or may be carried out after the cement-containing mixture is transferred from the container to another container (e.g., a mixer, etc.). When the cement-containing mixture is allowed to stand in the container in which the first mixing step was performed, the start of the standing time (0 seconds) is the time when the stirring in the first mixing step is completed. When the cement-containing mixture is allowed to stand after being transferred from the container in which the first mixing step was performed to another container (such as a container for the second mixing step), the start of the standing time (0 seconds) is the time when the transfer of the cement-containing mixture to the other container is completed.

[0016] [Second mixing process] This step is a step of mixing the mixture after standing with the remaining components of the cement composition while stirring to obtain a cement composition. The remainder of each material constituting the cement composition is the remainder of each of the cement, the fine aggregate, and the water (the remainder not mixed in the first mixing step). The stirring time varies depending on the stirring means, the amount of each material, etc., but is preferably 45 to 240 seconds, more preferably 60 to 180 seconds, and particularly preferably 90 to 150 seconds. If the above time is 45 seconds or more, the materials can be mixed more uniformly. If the above time is 240 seconds or less, the time required for production can be shortened, thereby improving productivity. The start point (0 seconds) of the above mixing time is the time when mixing starts after the remaining part of the cement is supplied.

[0017] The cement composition may contain coarse aggregate. The coarse aggregate may be supplied in either or both of the first mixing step and the second mixing step, but is preferably supplied in the second mixing step from the viewpoint of production efficiency. 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 coarse aggregate to be mixed is not particularly limited, and may be any amount generally used in concrete.

[0018] The cement composition preferably contains a cement admixture from the viewpoint of further improving the air entrainment property and fluidity of the cement composition. Examples of cement admixtures include cement dispersants, air-entraining agents, etc. Although one of these may be used alone, it is preferable to use a cement dispersant and an air-entraining agent in combination from the viewpoint of further improving the air entrainment property and fluidity of the cement composition. Examples of cement dispersants include water reducing agents, air-entraining water reducing agents, high-performance water reducing agents, and super-adjustable air-entraining water reducing agents. Among these, retarded water reducing agents, air-entraining water reducing agents, and super-adjustable air-entraining water reducing agents are preferred from the viewpoint of improving the fluidity of the cement composition. These may be used alone or in combination of two or more. The cement admixture may be supplied in at least one of the first mixing step and the second mixing step, but is preferably supplied in the second mixing step from the viewpoint of further improving the air entrainment and fluidity of the cement composition. Furthermore, gluconic acid, citric acid, tartaric acid, and the like may be used as a retarder to delay the setting of the cement composition.

[0019] Furthermore, the cement composition may contain various cement admixtures such as fly ash, silica fume, ground granulated blast furnace slag, etc., as needed. The cement admixture may be supplied in either or both of the first mixing step and the second mixing step, but is preferably supplied in the second mixing step from the viewpoint of preventing adverse effects on carbon dioxide fixation due to, for example, fluctuations in the pH of the cement-containing mixture. [Example]

[0020] The present invention will be specifically described 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: pit sand (3) Coarse aggregate: crushed stone (4) Water; tap water (5) Dry ice: Powdered dry ice is sprayed from a nozzle connected to a liquefied carbon dioxide gas cylinder, the dry ice is poured into a container, and the pressure of the spray from the nozzle simultaneously compresses and shapes the dry ice. (6) AE water reducer; manufactured by Pozzolith, product name "Master Polyhed 15S" (7) Air-entraining agent: manufactured by Pozzolith Solutions, trade name "Master Air 303A"

[0021] [Examples 1 to 4] Cement (part of cement) in an amount corresponding to the unit amount shown in Table 2, and water, fine aggregate, and dry ice in an amount corresponding to the unit amount shown in Table 1 were simultaneously charged into a forced twin-shaft mixer, and mixed while stirring for 120 seconds, with the time when charging was completed being the starting point (0 seconds) (first mixing step). Thereafter, the resulting mixture was allowed to stand for 120 seconds, with the time when stirring was completed being the starting point (0 seconds) (standing step). Next, the mixture in the mixer was mixed with the total amount of part of the cement and the remainder of the cement in a unit amount (336 kg / m) shown in Table 1. 3 ) in an amount of cement (the remainder of the cement; in Example 1, 319.2 kg / m 3 ) and the unit amount in Table 1 (1,004 kg / m 3 ) of coarse aggregate, an air-entraining water-reducing agent, and an air-entraining agent were mixed in advance, and the mixture was stirred for 60 seconds, starting from the time when the mixing was completed (0 seconds). After scraping off any mixture adhering to the inner wall of the mixer, the mixture was stirred for another 60 seconds to obtain concrete (cement composition) (second mixing step). The temperature of the concrete immediately after mixing was 22°C, as measured in accordance with JIS A 1156:2006 (Method for measuring the temperature of fresh concrete). The amount of the AE water-reducing agent was set to 1.4 parts by mass per 100 parts by mass of cement, and the amount of the AE agent was set to 0.006 parts by mass per 100 parts by mass of cement.

[0022] The slump of the obtained concrete was measured in accordance with "JIS A 1101:2020 (Concrete slump test method)". In addition, the air content of the above concrete was measured in accordance with "JIS A 1128:2019 (Test method for air content of fresh concrete by pressure - Air chamber pressure method)". In addition, the compressive strength of the obtained concrete was measured at ages of 1 day, 7 days, and 28 days 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 a 28-day-old concrete specimen used to measure 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, the mass loss in the endothermic peak range around 550–800°C was determined to be due to decarbonation of calcium carbonate contained in the mortar portion. Based on this mass loss, the percentage of carbon dioxide (mass%; the value of calcium carbonate converted to carbon dioxide) in the mortar portion of the concrete specimen was calculated.

[0023] [Comparative Example 1] Cement, fine aggregate, and coarse aggregate in the amounts shown in Table 1 were simultaneously added to a forced twin-shaft mixer and dry-mixed for 15 seconds, after which a premixed mixture of water, an air-entraining water-reducing agent, and an air-entraining agent was added and mixed for 60 seconds while stirring. Any material adhering to the inner wall of the mixer was then scraped off, and the mixture was further mixed for an additional 60 seconds while stirring to obtain concrete. The temperature of the concrete immediately after mixing was 22°C, as measured in the same manner as in Example 1. The amount of the AE water-reducing agent was set to 1.4 parts by mass per 100 parts by mass of cement, and the amount of the AE agent was set to 0.004 parts by mass per 100 parts by mass of cement. The slump and other properties of the resulting concrete were measured in the same manner as in Example 1.

[0024] Comparative Example 2 Cement, fine aggregate, and coarse aggregate in the amounts shown in Table 1 were simultaneously added to a forced twin-shaft mixer and dry-mixed for 15 seconds. After that, a premixed mixture of water, an air-entraining water-reducing agent, and an air-entraining agent was added and mixed for 60 seconds. Any kneaded material adhering to the inner wall of the mixer was then scraped off, and the mixture was mixed for 60 seconds while stirring. Dry ice in the amount shown in Table 1 was then added, and the mixture was mixed for an additional 120 seconds while stirring to obtain concrete. The temperature of the concrete immediately after mixing was 21°C, as measured in the same manner as in Example 1. The amount of the AE water-reducing agent was set to 1.8 parts by mass per 100 parts by mass of cement, and the amount of the AE agent was set to 0.010 parts by mass per 100 parts by mass of cement. The slump and other properties of the resulting concrete were measured in the same manner as in Example 1.

[0025] [Comparative Examples 3 to 4] Cement (a portion of the cement) corresponding to the unit amount shown in the column for the first mixing step in Table 2, and water, fine aggregate, and dry ice corresponding to the unit amounts shown in Table 1 were simultaneously charged into a forced twin-shaft mixer and mixed while stirring for 120 seconds. Next, cement (the remainder of the cement) in an amount such that the total amount of the portion of the cement and the remainder of the cement was the unit amount shown in Table 1, coarse aggregate in an amount such that the unit amount shown in Table 1, and a pre-mixed mixture of an air-entraining water-reducing agent and an air-entraining agent were charged into the mixer and mixed while stirring for 60 seconds. Next, any kneaded material adhering to the inner wall of the mixer was scraped off, and the mixture was further mixed while stirring for 60 seconds to obtain concrete. The temperature of the concrete immediately after mixing was 22°C, as measured in the same manner as in Example 1. The amount of the AE water-reducing agent was set to 1.4 parts by mass per 100 parts by mass of cement, and the amount of the AE agent was set to 0.006 parts by mass per 100 parts by mass of cement. The slump and other properties of the resulting concrete were measured in the same manner as in Example 1. The results are shown in Table 2.

[0026] [Table 1]

[0027] [Table 2]

[0028] From Table 2, it can be seen that the proportions of carbon dioxide in the mortar portions of Examples 1 to 4 (2.48 to 2.65 mass%) are greater than the proportions (1.75 to 2.39 mass%) of Comparative Examples 1 to 4, and therefore a greater amount of carbon dioxide was fixed in the cement compositions of Examples 1 to 4. In particular, a comparison of Examples 1 to 4 with Comparative Examples 3 to 4 (which were the same as Examples 1 to 4 except that the standing step was not performed) shows that a greater amount of carbon dioxide can be fixed by performing the standing step. Furthermore, the slump (18.5-20.0 cm) and air content (4.4-4.7%) of Examples 1-4 are larger than the slump (4.0 cm) and air content (1.6%) of Comparative Example 2 (materials other than dry ice were mixed, and then dry ice was added and stirred and mixed). This shows that, although dry ice was used in Examples 1-4, there was no decrease in air entrainment and fluidity.

Claims

1. A method for producing a cement composition containing cement, fine aggregate, and water, and having carbon dioxide fixed therein, comprising: a first mixing step of mixing a portion of the cement, at least a portion of the fine aggregate, at least a portion of the water, and dry ice under stirring to obtain a cement-containing mixture; a step of leaving the cement-containing mixture for 90 to 360 seconds to obtain a mixture after leaving; a second mixing step of mixing the mixture after standing with the remaining components of the cement composition while stirring to obtain the cement composition; In the first mixing step, the amount of dry ice is determined so that the proportion of the amount of the portion of cement in the total amount of cement is 3 to 60 mass %, the proportion of the amount of at least a portion of the fine aggregate in the total amount of the fine aggregate is 80 to 100 mass %, the proportion of the amount of at least a portion of the water in the total amount of the water is 80 to 100 mass %, and the carbon dioxide content in the mortar portion of the hardened body of the cement composition is 2.48 mass % or more; A method for producing a cement composition, wherein the dry ice is formed by compressing powdered dry ice.

2. The method for producing a cement composition according to claim 1, wherein the cement composition contains a cement admixture, and the cement admixture is supplied in the second mixing step.

3. 3. The method for producing a cement composition according to claim 2, 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 claims 1 to 3, wherein the cement composition contains a coarse aggregate, and the coarse aggregate is supplied in the second mixing step.

5. The method for producing a cement composition according to claim 4, wherein the water-cement ratio of the cement composition is 30 to 65%.

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