Manufacturing method for lightweight cellular cementitious hardened body

Abstract

To provide a method capable of manufacturing a lightweight cellular cementitious hardened body in which a larger amount of carbon dioxide is immobilized.SOLUTION: A manufacturing method for a lightweight cellular cementitious hardened body includes: a step of kneading a part of cement and water for a first cement-containing kneaded material to obtain the first cement-containing kneaded material; a step of supplying carbon dioxide gas into the first cement-containing kneaded material to obtain a carbonated kneaded material; a step of obtaining a second cement-containing kneaded material by kneading the carbonated kneaded material, a remainder of cement, and a part of water for the second cement-containing kneaded material, or the carbonated kneaded product and the remainder of cement; a step of obtaining air bubbles by mixing gas with foaming agent-containing water, which is obtained by mixing a foaming agent and water for foaming agent-containing water; a step of kneading air bubbles with the second cement-containing kneaded material to obtain an unhardened cement composition; and a step of curing an uncured cement composition to obtain a lightweight cellular cementitious hardened body.SELECTED DRAWING: None

Description

[Technical Field] 【0001】 This invention relates to a method for producing a lightweight cellular cementitious hardened body. [Background technology] 【0002】 In recent years, reducing carbon dioxide emissions has become a crucial issue in order to curb global warming. In this regard, technologies are being considered to fix carbon dioxide recovered from exhaust gases and other sources generated at cement manufacturing plants into concrete and other materials. As an example of a method that includes a step of fixing carbon dioxide in calcium-containing powder by blowing carbon dioxide-containing gas such as exhaust gas into a slurry containing 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, characterized by including a carbonation step of supplying carbon dioxide-containing gas to a slurry containing the calcium-containing powder and water before carbonation to obtain a carbonated slurry, and a grinding step of supplying cement clinker, gypsum, and the carbonated slurry to a finishing mill for cement production and grinding them to obtain the cement powder composition. Furthermore, as a foamed mortar that exhibits excellent carbon dioxide absorption capacity in a natural environment, Patent Document 2 describes a mortar mixture comprising water, powder, foam, and an admixture, wherein the volume unit amount of water is (L / m³). 3 ) and the volume unit amount of powder (L / m³ 3 Vp is the sum of ( ), and the volume of bubbles (L / m³) is the unit of volume of bubbles. 3 When Vso is used to represent the ratio of Vp to Vso, the foamed mortar mixture described has a ratio of 2:8 to 6:4, contains cement and γ-belite as powder components, and has a γ-belite content of 20 to 70% by mass in the powder. [Prior art documents] [Patent Documents] 【0003】 [Patent Document 1] Japanese Patent Application Laid-Open No. 2020-152631 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-188319 [Summary of the Invention] [Problems to be Solved by the Invention] 【0004】 An object of the present invention is to provide a method capable of producing a lightweight foamed cement hardened body in which a larger amount of carbon dioxide is immobilized. [Means for Solving the Problems] 【0005】 As a result of intensive studies to solve the above problems, the present inventor has obtained a first cement-containing kneaded material by kneading cement and water, supplied carbon dioxide gas into the first cement-containing kneaded material, and obtained a carbonated kneaded material. A step of kneading the carbonated kneaded material with cement and water, or kneading the carbonated kneaded material with cement to obtain a second cement-containing kneaded material, and a foaming agent and water for the foaming agent-containing water which is a part of the above water. A step of obtaining bubbles by mixing the foaming agent-containing water thus obtained with a gas, a step of kneading the second cement-containing kneaded material with the bubbles to obtain an uncured cement composition, and a step of curing the uncured cement composition to obtain a lightweight foamed cement hardened body. The inventors have found that the above object can be achieved by the method including the steps, and have completed the present invention. That is, the present invention provides the following [1] to [5]. [1] A method for producing a lightweight cellular cementitious hardened body comprising cement, a foaming agent, and water, and having carbon dioxide fixed, comprising: a first cement mixing step of mixing a portion of the cement with a portion of the water, which is water for a first cement-containing mixture, to obtain a first cement-containing mixture; a carbonated mixture preparation step of supplying carbon dioxide, which is the gaseous state of carbon dioxide to be fixed, to the first cement-containing mixture to obtain a carbonated mixture; and the carbonated mixture, the remainder of the cement, and a portion of the water, which is water for a second cement-containing mixture. A method for producing a lightweight foamed cement body, comprising: a second cement mixing step of mixing the above-mentioned carbonated mixture or mixing the remaining portion of the above-mentioned cement with the above-mentioned cement to obtain a second cement-containing mixture; a foam preparation step of mixing the above-mentioned foaming agent with a portion of the above-mentioned water, which is used for foaming agent-containing water, and gas to obtain bubbles; a cement composition preparation step of mixing the second cement-containing mixture with the bubbles to obtain an unhardened cement composition; and a hardening step of hardening the unhardened cement composition to obtain a lightweight foamed cement body. 【0006】 [2] The above lightweight cellular cementitious hardened body does not contain aggregate, and in the above cement composition preparation process, the density of the unhardened cement composition is 0.30 to 1.00 g / cm³. 3 A method for producing a lightweight cellular cementitious hardened body according to [1] above, wherein the amount of bubbles is adjusted to such an extent. [3] The above lightweight cellular cementitious hardened body contains aggregate, and the aggregate is supplied and mixed in either or both of the first cement mixing step and the second cement mixing step, and in the cement composition preparation step, the density of the unhardened cement composition is 0.70 to 2.50 g / cm³. 3 A method for producing a lightweight cellular cementitious hardened body according to [1] above, wherein the amount of bubbles is adjusted to such an extent. [4] A method for producing a lightweight foamed cementitious hardened body according to any one of [1] to [3], wherein the lightweight foamed cementitious hardened body contains a cement dispersant, and the cement dispersant is supplied and mixed in either or both of the first cement mixing step and the second cement mixing step. [5] A method for producing a lightweight cellular cementitious hardened body according to any one of [1] to [4], wherein the proportion of carbon dioxide in the lightweight cellular cementitious hardened body is 3.5 to 15.0% by mass. [Effects of the Invention] 【0007】 According to the manufacturing method of the present invention, a lightweight cellular cementitious hardened body with a larger amount of carbon dioxide fixed can be produced. [Modes for carrying out the invention] 【0008】 The present invention relates to a method for producing a lightweight cellular cementitious hardened body comprising cement, a foaming agent, and water, and having carbon dioxide fixed, comprising: a first cement mixing step of mixing a portion of the cement and a portion of the water, which is water for a first cement-containing mixture, to obtain a first cement-containing mixture; a carbonated mixture preparation step of supplying carbon dioxide, which is the gaseous state of carbon dioxide to be fixed, into the first cement-containing mixture to obtain a carbonated mixture; and the carbonated mixture, the remainder of the cement, and the above The method includes: a second cement mixing step of mixing a portion of the water for a second cement-containing mixture, or mixing a carbonated mixture with the remainder of the cement to obtain a second cement-containing mixture; a foam preparation step of mixing a foaming agent with a portion of the water for foaming agent-containing water and gas to obtain bubbles; a cement composition preparation step of mixing the second cement-containing mixture with the bubbles to obtain an unhardened cement composition; and a hardening step of hardening the unhardened cement composition to obtain a lightweight foamed cementite hardened body. The following explains each step in detail. 【0009】 [First cement mixing process] This process involves mixing a portion of the cement with a portion of the water, which is the water used for the first cement-containing mixture, to obtain the first cement-containing mixture. The above-mentioned cement is not particularly limited and includes, for example, various types of Portland cement such as ordinary Portland cement, rapid-hardening Portland cement, moderate-heat Portland cement, and low-heat Portland cement, as well as blended cements such as blast furnace cement and fly ash cement, and eco-cements. These may be used individually or in combination of two or more types. Among these, ordinary Portland cement is preferred from the standpoint of versatility and other factors. 【0010】 The proportion of the above-mentioned portion of the total amount of cement (the total amount of cement contained in the lightweight aerated cementitious cementitious hardened body) is preferably 1 to 50% by mass, more preferably 3 to 40% by mass, even more preferably 5 to 30% by mass, even more preferably 8 to 25% by mass, even more preferably 10 to 20% by mass, and particularly preferably 12 to 18% by mass. If the above proportion is 1% by mass or more, the amount of carbon dioxide immobilized in the lightweight aerated cementitious cementitious hardened body will be greater. If the above proportion is 50% by mass or less, the strength of the lightweight aerated cementitious hardened body will be greater. 【0011】 The type of water used is not particularly limited and includes, for example, tap water, sludge water, etc. The water for the first cement-containing mixture (hereinafter also referred to as "first mixing water") is a portion of the total amount of water contained in the lightweight cellular cementitious hardened body, and refers to the water supplied and mixed in this process (the water contained in the first cement-containing mixture). The proportion of the first mixing water in the total amount of water (total amount of water contained in the lightweight cellular cementitious hardened body) is preferably 50 to 99% by mass, more preferably 55 to 95% by mass, even more preferably 60 to 90% by mass, and particularly preferably 65 to 80% by mass. If the above proportion is 50% by mass or more, the fluidity of the first cement-containing mixture is improved, and workability is improved. In addition, in the carbonated mixture preparation process described later, it becomes easier to uniformly supply carbon dioxide to the first cement-containing mixture. If the above proportion is 99% by mass or less, the amount of water contained in the foaming agent-containing water is relatively large, and the amount of bubbles can be made larger. 【0012】 In this process, the water-cement ratio of the first cement-containing mixture is preferably 40-500%, more preferably 100-450%, even more preferably 150-400%, even more preferably 200-350%, and particularly preferably 250-330%. If the above ratio is 40% or higher, the fluidity of the first cement-containing mixture is further improved, and workability is enhanced. In addition, in the carbonated mixture preparation process described later, it becomes easier to uniformly supply carbon dioxide to the first cement-containing mixture. If the above ratio is 500% or lower, the amount of water contained in the foaming agent-containing water becomes relatively larger, and the amount of bubbles can be increased. The water-cement ratio is the mass ratio of water to cement (water / cement) expressed as a percentage (%). In this process, the method of mixing a portion of the cement with the first mixing water is not particularly limited. For example, a portion of the cement may be added to a stirring tank, then the first mixing water may be added and mixed, or a portion of the cement and the first mixing water may be added to a stirring tank simultaneously and then mixed. 【0013】 [Preparation process for carbonated compound] This process involves supplying carbon dioxide, which is the gaseous form of carbon dioxide that is to be fixed, to the first cement-containing mixture obtained in the first cement mixing process to obtain a carbonated mixture. In this process, from the viewpoint of uniformly supplying carbon dioxide to the first cement-containing mixture, it is preferable to supply carbon dioxide while the first cement-containing mixture (hereinafter also referred to as "the first mixture") is flowing. Methods for supplying carbon dioxide into the first mixture include, for example, the following methods (i) to (iii). (i) A method of supplying carbon dioxide gas into the first kneaded product, wherein a carbon dioxide gas supply means for supplying carbon dioxide gas into the first kneaded product is installed in a stirring tank for obtaining the first kneaded product. A more specific example is a method in which a carbon dioxide mixture is obtained by stirring and mixing a portion of cement and a first mixing water in a stirring tank for obtaining a first mixture, and in an apparatus equipped with a carbon dioxide supply means (e.g., a diffuser plate) disposed in the space for containing the mixture in the stirring tank, while stirring the first mixture, carbon dioxide is blown into the first mixture using the carbon dioxide supply means. 【0014】 (ii) A method of transferring the first kneaded material from a stirring tank for containing the first kneaded material into a device having carbon dioxide supply means (e.g., a diffuser plate) for supplying carbon dioxide gas, blowing carbon dioxide gas into the first kneaded material in the device to obtain a carbonated kneaded material, and then transferring the carbonated kneaded material to a carbonated kneaded material tank for containing the carbonated kneaded material. The stirring tank and the carbonation and kneading tank may be the same or different. 【0015】 A more specific example is a method in which a portion of cement and a first mixing water are stirred and mixed to obtain a first mixture, and the first mixture is placed in a stirring tank for obtaining a first mixture. The first mixture is then transferred to a device having a carbon dioxide supply means for supplying carbon dioxide gas, using a pump or the like, through a first flow passage for supplying the first mixture from the stirring tank to the device. Inside the device, carbon dioxide gas is supplied to the first mixture while stirring it. Subsequently, the first mixture after the carbon dioxide gas supply (carbonated mixture) is transferred to the stirring tank using a pump or the like through a second flow passage for supplying the carbonated mixture from the device to the stirring tank, thereby obtaining a carbonated mixture. Furthermore, the first kneaded material may be repeatedly circulated in the following order: the stirring tank, the first flow passage, the apparatus, and the second flow passage, until a sufficient amount of carbon dioxide is supplied. Furthermore, after obtaining the carbonated mixture, the carbonated mixture may be temporarily stored in a storage tank separate from the carbonated mixture tank, and then supplied from the storage tank to the carbonated mixture tank as needed. 【0016】 (iii) A method of transferring the first kneaded material from a stirring tank for containing the first kneaded material to a carbonated kneaded material tank for containing the carbonated kneaded material, by blowing carbon dioxide gas into the first kneaded material. A more specific example is a method in which a portion of cement and a first mixing water are stirred and kneaded together to obtain a first mixture, and the first mixture is placed in a stirring tank for the first mixture supplied from the stirring tank. While the first mixture is being circulated through a pipeline for the circulation of the first mixture, carbon dioxide gas is supplied to the first mixture and stirred to obtain a carbonated mixture, and then the carbonated mixture is transferred to the carbonated mixture tank. 【0017】 Examples of the above-mentioned pipeline include one having a carbon dioxide supply port for supplying the carbon dioxide gas to a first kneaded material circulating within the pipeline, and having a configuration that allows for stirring and mixing of the first kneaded material and the carbon dioxide gas. Specifically, examples include one in which aeration means (e.g., aeration plate) and stirring means (e.g., line mixer or static mixer) for supplying the carbon dioxide gas are arranged within the pipeline. Alternatively, after supplying carbon dioxide gas to the first mixture, the carbonated mixture may be returned to the stirring tank without being transferred to the carbonated mixture tank. Furthermore, the first mixture may be repeatedly circulated through the stirring tank and the pipeline in that order to supply a sufficient amount of carbon dioxide gas, and then the first mixture may be transferred to the carbonated mixture tank as a carbonated mixture. Furthermore, in the above method, after obtaining the carbonated kneaded product, it may be temporarily stored in a carbonated kneaded product storage tank for storing carbonated kneaded products, and the carbonated kneaded product may be supplied from the storage tank to the carbonated kneaded product tank as appropriate. 【0018】 From the viewpoint of increasing the amount of carbon dioxide fixed in the first compound, the supply of carbon dioxide may be carried out under pressurized conditions at the liquid surface of the first compound (for example, by increasing the internal pressure of the tank containing the first compound to 1,200 hPa or higher, which is above atmospheric pressure). Therefore, a carbon dioxide supply means for supplying carbon dioxide is preferably one that can be pressurized. 【0019】 Furthermore, carbon dioxide gas may be supplied to the first compound as a gas consisting solely of carbon dioxide, but from the viewpoint of ease of availability, etc., it may also be supplied to the first compound as a gas containing carbon dioxide. The proportion of carbon dioxide in the gas containing carbon dioxide 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 proportion is 5% by volume or more, the amount of carbon dioxide fixed in the first kneaded product can be increased. In addition, the time required to supply carbon dioxide 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 the thermal power generation process (carbon dioxide concentration: approximately 10% by volume), and gas separated and recovered from these exhaust gases (carbon dioxide concentration: approximately 100% by volume). 【0020】 The supply of carbon dioxide is carried out so that the pH of the first compound (carbonated compound) obtained by carbonation 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 carbon dioxide is supplied so that the pH is 5.0 or higher, the strength of the lightweight cellular cementitious hardened body is increased. In addition, the time required for carbon dioxide supply is shortened, and the manufacturing efficiency is further improved. When carbon dioxide is supplied so that the pH is 11.5 or lower, the amount of carbon dioxide fixed in the first compound is increased. Note that the pH of the first compound decreases when carbon dioxide is supplied. To ensure a sufficiently large amount of carbon dioxide is fixed in the first compound 、 The duration of carbon dioxide supply varies depending on the water-cement ratio, the carbon dioxide supply method, and the carbon dioxide concentration of the gas supplied using the method. Therefore, it is preferable to determine the timing of ending the carbon dioxide supply based on the measured pH value of the carbonated mixture. 【0021】 [Second cement mixing process] This process involves mixing the carbonated mixture obtained in the carbonated mixture preparation process with the remaining cement and a portion of the water (a portion of the water contained in the lightweight cellular cementitious hardened body) which is water for the second cement-containing mixture, or mixing the carbonated mixture with the remaining cement to obtain a second cement-containing mixture (hereinafter also referred to as the "second mixture"). The proportion of the remaining cement in the total amount of cement (the total amount of cement contained in the lightweight aerated cementitious cementate) is preferably 50-99% by mass, more preferably 60-97% by mass, even more preferably 70-95% by mass, even more preferably 75-92% by mass, even more preferably 80-90% by mass, and particularly preferably 82-88% by mass. If the above proportion is 50% by mass or more, the strength development of the cement composition is further improved. If the above proportion is 99% by mass or less, the amount of carbon dioxide immobilized in the lightweight aerated cementitious cementitious cementate becomes greater. 【0022】 The water for the second cement-containing mixture (hereinafter also referred to as "second mixing water") is a portion of the total amount of water contained in the lightweight cellular cementitious hardened body, and in this process, it refers to the water supplied and mixed (the water contained in the second cement-containing mixture minus the water contained in the first cement-containing mixture). In this process, when mixing the carbonated mixture, the remaining cement, and the second mixing water, the ratio of the amount of the second mixing water to the total amount of water (total amount of water contained in the lightweight cellular cementitious hardened body) is preferably 1 to 50% by mass, more preferably 2 to 40% by mass, even more preferably 3 to 30% by mass, and particularly preferably 4 to 25% by mass. If the above ratio is 1% by mass or more, the amount of air contained in the second mixture increases, and the fluidity of the second mixture improves. If the above ratio is 50% by mass or less, the fluidity of the first mixture is relatively improved, and it becomes easier to uniformly supply carbon dioxide to the first mixture. 【0023】 In this process, when mixing the carbonated mixture, the remaining cement, and the second mixing water, the order in which each material is mixed is not particularly limited. For example, (i) mixing the carbonated mixture and the remaining cement in a mixing tank, and then adding the second mixing water to the mixture and mixing; (ii) mixing the carbonated mixture and the second mixing water in a mixing tank, and then adding the remaining cement to the mixture and mixing; (iii) adding each material simultaneously in a mixing tank and mixing. Among these, from the viewpoint of improving the fluidity of the second mixture, (i) mixing the carbonated mixture and the remaining cement, and then adding the second mixing water to the mixture and mixing is preferred. 【0024】 [Bubble preparation process] This process involves mixing a foaming agent with a portion of the water contained in the lightweight foamed cementitious hardened body (which is used for the foaming agent-containing water), and then mixing this water with gas to obtain bubbles. The foaming agent is not particularly limited, and commercially available foaming agents for air mortar or air mortar can be used. Examples of foaming agents include surfactant-based foaming agents such as anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants, as well as protein-based foaming agents. In this process, the phrase "water for foaming agent-containing water, which is part of the water contained in the lightweight cellular cementitious hardened body" means a portion of the total amount of water mixed with the cement contained in the lightweight cellular cementitious hardened body (the total amount of water minus the water for the first cement-containing mixture and the water for the second cement-containing mixture). 【0025】 The proportions of foaming agent and water are determined appropriately according to the target density and mass of the unhardened cement composition, the foaming ratio of the foaming agent, and the dilution ratio of the foaming agent. Specifically, it can be calculated by following the steps (i) to (ii) below. (i) The amount of unhardened cement composition obtained in the cement composition preparation process (described later) is 1 m 3When considering this, the volume (bubble volume) obtained by subtracting the volume of the second cement-containing kneaded material obtained in the second cement kneading step from the volume of the uncured cement composition (1 m 3 ) is calculated. (ii) From the bubble volume, the foaming ratio, and the dilution ratio of the foaming agent, the amount of the foaming agent can be calculated using the following formula. Amount of foaming agent (kg) = Bubble volume / Foaming ratio of foaming agent / Dilution ratio × 1000 Note that the amount of water can be calculated from the amount of the foaming agent and the dilution ratio. For example, when manufacturing 1 m of the uncured cement composition 3 , if the volume of the second cement-containing kneaded material is 0.34 m 3 , the bubble volume is 0.66 m 3 (660 liters). Here, when using a foaming agent with a foaming ratio of 20 times and a dilution ratio of 20 times, the amount of the foaming agent is 1.65 kg (0.66 / 20 / 20 × 1000 = 1.65 kg). 【0026】 As an example of a method for obtaining bubbles by mixing a foaming agent-containing water, which is obtained by mixing a part of the water contained in the foaming agent and the lightweight cellular cement hardened body and is water for the foaming agent-containing water, with gas, there is a method of preparing bubbles by mixing (kneading) water, a foaming agent, and gas (usually compressed gas) in a foaming device. Here, the compressed gas (usually compressed air) can be produced using a device capable of compressing gas such as a compressor. 【0027】 [Cement Composition Preparation Step] This step is a step of kneading the second cement-containing kneaded material obtained in the second cement kneading step and the bubbles obtained in the above-mentioned bubble preparation step to obtain an uncured cement composition. The second cement-containing kneaded material obtained in the second cement kneading step and the bubbles obtained in the bubble preparation step are usually prepared separately and then kneaded using kneading means such as a mixer. Alternatively, the cement composition preparation process may be carried out using an apparatus that combines a mixing means and a bubble dispensing device. Specifically, after the second cement mixing process, the second cement-containing mixture is mixed using the mixing means, and while mixing, a foaming agent and compressed air are added to the second cement-containing mixture from the bubble dispensing device, generating bubbles in the second cement-containing mixture during mixing. Such a configuration is also included in the present invention. In this case, the second cement mixing process, the bubble preparation process, and the cement composition preparation process are carried out continuously within the same apparatus. In this case, the water contained in the second cement-containing mixture is used as water for the foaming agent-containing water. 【0028】 When a lightweight cellular cementitious hardened body does not contain aggregate, the density of the unhardened cement composition is preferably 0.30 to 1.00 g / cm³. 3 , more preferably 0.34~0.95 g / cm³ 3 , more preferably 0.38~0.90 g / cm³ 3 More preferably 0.40 to 0.80 g / cm³ 3 More preferably 0.42 to 0.70 g / cm³ 3 Particularly preferred is 0.45 to 0.65 g / cm³. 3 The density is 0.30 g / cm³. 3 If the density is as described above, the strength of the lightweight cellular cementitious body can be increased. 3 The following conditions allow for a greater amount of carbon dioxide to be immobilized in the lightweight cellular cementitious material, and a smaller mass of the lightweight cellular cementitious material. 【0029】 Furthermore, when the lightweight cellular cementum hardened body does not contain aggregate, the amount of air in the unhardened cement composition is preferably 40 to 80 volume%, more preferably 42 to 78 volume%, even more preferably 45 to 75 volume%, even more preferably 55 to 72 volume%, and particularly preferably 62 to 70 volume%. If the amount of gas is 40 volume% or more, the amount of carbon dioxide immobilized in the lightweight cellular cementum hardened body can be increased. Also, the mass of the lightweight cellular cementum hardened body can be reduced. If the amount of gas is 80 volume% or less, the amount of foaming agent used can be reduced. 【0030】 When a lightweight cellular cementitious hardened body contains aggregate, the density of the unhardened cement composition is preferably 0.70 to 2.50 g / cm³. 3 , more preferably 1.00 to 2.30 g / cm³ 3 More preferably 1.20 to 2.10 g / cm³ 3 Particularly preferred is 1.50 to 2.00 g / cm³ 3 The density is 0.70 g / cm³. 3 If the above density is met, the strength of the lightweight cellular cementitious body can be increased. 3 The following conditions allow for a greater amount of carbon dioxide to be immobilized in the lightweight cellular cementitious material, and a smaller mass of the lightweight cellular cementitious material. 【0031】 Furthermore, when the lightweight cellular cementum hardened body contains aggregate, the amount of gas (usually air) in the unhardened cement composition is preferably 10 to 60 volume%, more preferably 12 to 50 volume%, even more preferably 15 to 40 volume%, even more preferably 16 to 30 volume%, and particularly preferably 17 to 25 volume%. If the amount of gas is 10 volume% or more, the amount of carbon dioxide immobilized in the lightweight cellular cementum hardened body can be increased. Also, the mass of the lightweight cellular cementum hardened body can be reduced. If the amount of gas is 60 volume% or less, the amount of foaming agent used can be reduced. By adjusting the amount of bubble-containing water mixed in this process, the density and gas content of the unhardened cement composition can be adjusted. 【0032】 The water-cement ratio of the cement composition (the ratio of the total amount of water in the cement composition to the amount of cement) is preferably 40-500%, more preferably 50-300%, even more preferably 60-200%, and particularly preferably 70-100%. If the above ratio is 40% or higher, the fluidity of the cement composition is further improved, and workability during placement and other processes is further improved. If the above ratio is 500% or lower, the strength of the lightweight cellular cementitious hardened body is increased. In addition, material segregation becomes less likely to occur. 【0033】 The cement composition may contain aggregate. The aggregate may consist of fine aggregate alone, or a combination of fine aggregate and coarse aggregate. Natural aggregate, artificial aggregate, or recycled aggregate can also be used. The fine aggregate is not particularly limited and includes, for example, river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag fine aggregate, and lightweight fine aggregate, or a mixture consisting of two or more types selected from these. The coarse aggregate is not particularly limited and may include, for example, river gravel, mountain gravel, land gravel, sea gravel, crushed stone, slag coarse aggregate, and lightweight coarse aggregate, or a mixture consisting of two or more types selected from these. The amount of aggregate is not particularly limited and can be any amount that is typical for lightweight cellular cementitious hardened bodies. For example, the amount of aggregate (total amount if fine aggregate and coarse aggregate are included) is preferably 10 to 350 parts by mass, more preferably 100 to 300 parts by mass, and particularly preferably 150 to 250 parts by mass, per 100 parts by mass of cement. If the above amount is 10 parts by mass or more, the strength of the lightweight cellular cementitious hardened body will be greater. 0 If the mass is below a certain limit, the mass of the lightweight cellular cementitious hardened body can be further reduced. When the cement composition contains aggregate, the aggregate may be supplied and mixed in any of the following steps: the first cement mixing step, the carbonated compound preparation step, the second cement mixing step, or the cement composition preparation step. However, from the viewpoint of manufacturing efficiency, it is preferable that the aggregate be supplied and mixed in either the first cement mixing step or the second cement mixing step, or both, and it is more preferable that it be supplied and mixed in the second cement mixing step. 【0034】 The cement composition may contain cement dispersants such as water-reducing agents, AE water-reducing agents, high-performance water-reducing agents, etc., from the viewpoint of improving the fluidity of the cement composition. In particular, when water is supplied but not mixed in the second cement mixing step, it is preferable that the cement composition contains cement dispersants from the viewpoint of improving the fluidity of the cement composition and preventing clogging in the equipment. If the cement composition contains a cement dispersant, the cement dispersant may be supplied and mixed in any of the following steps: the first cement mixing step, the carbonated compound preparation step, the second cement mixing step, or the cement composition preparation step. However, from the viewpoint of manufacturing efficiency, it is preferable that the cement dispersant be supplied and mixed in either the first cement mixing step or the second cement mixing step, or both, and it is more preferable that it be supplied and mixed in the second cement mixing step. The amount of cement dispersant added is preferably 0.1 to 5.0 parts by mass, more preferably 0.4 to 3.0 parts by mass, and particularly preferably 0.6 to 1.50 parts by mass, per 100 parts by mass of cement. 【0035】 The cement composition may optionally contain (i) various admixtures such as fly ash, silica fume, and blast furnace slag powder, (ii) various admixtures such as AE agents, defoamers, and fluidizers (excluding cement dispersants), and (iii) soil. The method of mixing the various admixtures, admixtures, and soil is not particularly limited, but from the viewpoint of manufacturing efficiency, it is preferable that they be supplied and mixed in the second cement mixing process. Furthermore, when using lightweight cellular cementitious material as a lightweight embankment, locally sourced soil obtained at the site where the lightweight embankment is formed can be used as the soil. The proportion of the above soil in the lightweight cellular cementitious material is preferably 60% by mass or less, more preferably 5 to 40% by mass, and particularly preferably 10 to 30% by mass, from the viewpoint of strength development of the lightweight cellular cementitious material. 【0036】 [Curing process] This process involves hardening an unhardened cement composition to obtain a lightweight, cellular cementitious hardened body. For example, a lightweight aerated cementitious hardened body can be obtained by pouring an unhardened cement composition into a mold, curing it using a general curing method, and then demolding it. When the lightweight cellular cementitious cementitious hardened body does not contain aggregate, the density of the lightweight cellular cementitious cementitious hardened body is preferably 0.30 to 1.00 g / cm³. 3 , more preferably 0.32~0.95 g / cm³ 3 , more preferably 0.38~0.90 g / cm³ 3 More preferably 0.40 to 0.80 g / cm³ 3 More preferably 0.42 to 0.70 g / cm³ 3 Particularly preferred is 0.45 to 0.65 g / cm³. 3 The density is 0.30 g / cm³. 3 If the density is as described above, the strength of the lightweight cellular cementitious body can be increased. 3 The following conditions allow for a greater amount of carbon dioxide to be immobilized in the lightweight cellular cementitious material, and a smaller mass of the lightweight cellular cementitious material. 【0037】 Furthermore, when the lightweight cellular cementitious cementitious hardened body contains aggregate, the density of the lightweight cellular cementitious cementitious hardened body is preferably 0.70 to 2.50 g / cm³. 3 , more preferably 1.00 to 2.30 g / cm³ 3 More preferably 1.20 to 2.10 g / cm³ 3 Particularly preferred is 1.50 to 2.00 g / cm³3 The density is 0.70 g / cm³. 3 If the above density is met, the strength of the lightweight cellular cementitious body can be increased. 3 The following conditions allow for a greater amount of carbon dioxide to be immobilized in the lightweight cellular cementitious material, and a smaller mass of the lightweight cellular cementitious material. Furthermore, the density of the lightweight cellular cementitious hardened material is lower than the density of the unhardened cement composition described above. 【0038】 The proportion of carbon dioxide in the lightweight cellular cementitious hardened body (the proportion of carbon dioxide immobilized in the lightweight cellular cementitious hardened body) is preferably 3.5 to 15.0% by mass, more preferably The percentage is 4.0 to 14.0% by mass, more preferably 5.0 to 13.0% by mass, even more preferably 6.0 to 12.0% by mass, even more preferably 7.0 to 11.0% by mass, and particularly preferably 8.0 to 10.0% by mass. If the above percentage is 5.0% by mass or more, more carbon dioxide can be fixed, and carbon dioxide emissions can be further reduced. Lightweight cellular cementitious hardened bodies with a percentage exceeding 15.0% by mass may be difficult to manufacture. The compressive strength of a lightweight cellular cementitious hardened body, measured in accordance with "JIS A 1108:2018 (Compression Test Method for Concrete)" at 7 days of age, is preferably 50 to 12,000 kN / m². 2 More preferably 60 to 10,000 kN / m 2 More preferably 100 to 3,000 kN / m 2 More preferably 200-2,900 kN / m 2 More preferably 400 to 2,800 kN / m 2 Particularly preferred is 600 to 2,700 kN / m 2 That is the case. The resulting lightweight aerated cementitious hardened material can be used as lightweight embankment, lightweight embankment structure, lightweight aerated concrete, insulation material, etc. [Examples] 【0039】 The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. [Materials used] (1) Cement; manufactured by Taiheiyo Cement Corporation, ordinary Portland cement (2) Foaming agent; anionic surfactant, manufactured by Onoda Chemico Co., Ltd., product name: "OFA-S" (3) AE water-reducing agent; manufactured by Pozzolith Solutions, product name "Master Polyheed 15S" (4) Fine aggregate; Density: 2.57g / cm 3 (5) Coarse aggregate; density: 2.65g / cm 3 (6) Water; tap water 【0040】 [Examples 1-5] In the first cement mixing step, a portion of the cement and the water for the first cement-containing mixture were mixed in a container using a hand mixer for 60 seconds to obtain a mixture (first cement-containing mixture, temperature: 23°C). The amount of cement and water for the first cement-containing mixture was such that the water-cement ratio was 300% (the unit amount of the above cement portion was 60.5 kg / m³). 3 For example, the unit amount of water used in cement-containing mixtures is 181.6 kg / m³. 3 ) As part of the carbonation preparation process, carbon dioxide-containing gas (temperature: 20°C) with a carbon dioxide concentration of 99.6% by volume was supplied to the mixture (pH: 11.5) in the container using an air pump at a rate of 30 liters / minute. The supply of carbon dioxide-containing gas was continued until the pH of the mixture reached 9.0, thereby obtaining the carbonation mixture. In the second cement mixing step, the remaining cement was added to the carbonated mixture in the container and mixed for 60 seconds using a hand mixer to obtain the mixture. Next, after scraping off the mixture adhering to the inner wall of the mixer, the water for the second cement-containing mixture and a liquid mixture of the amount of AE water-reducing agent shown in Table 1 were added and mixed for 60 seconds using a hand mixer to obtain the second cement-containing mixture. The amounts of the remaining cement and the water for the second cement-containing mixture were such that the water-cement ratio of the second cement-containing mixture was 64% (the unit amount of the remaining cement was 292.5 kg / m³). 3 The unit volume of the remaining water for the cement-containing mixture is 45.4 kg / m³. 3 ) Note that "unit quantity" refers to the unit volume of 1 m³ of hardened lightweight cellular cementitious material. 3 This refers to the amount of ingredients mixed per unit by mass. 【0041】 On the other hand, in the process of preparing bubble-containing water, a foaming agent and water for foaming agent-containing water were mixed to obtain foaming agent-containing water, and then bubbles were prepared by kneading the foaming agent-containing water while supplying compressed air using a foaming machine. The amounts of foaming agent and foaming agent-containing water are 1.65 kg / m³ each. 3 , 31.35 kg / m 3 ) was established. Next, as a cement composition preparation step, air bubbles were mixed into the second cement-containing mixture in an amount such that the density of the unhardened cement composition (indicated as "unhardened" in Table 1) became the value shown in Table 1, thereby obtaining an unhardened cement composition. The following evaluations were performed using the obtained unhardened cement composition. 【0042】 [Evaluation of handling performance] After placing the unhardened cement composition into a cup, the cup was tilted. A "○" was given if the unhardened cement composition flowed continuously, and a "×" was given if it flowed discontinuously or not at all. [Calculation of the density of an unhardened cement composition] Unhardened cement composition, in a volume of 1 liter (1,000 cm³) 3The material is filled into a mass of 1 liter, the surface is leveled, the mass is measured, and the density (g / cm³) is calculated by dividing the obtained mass by the volume (1 liter). 3 ) was calculated. [Measurement of air content in unhardened cement composition] The air content of the unhardened cement composition was measured in accordance with the Japan Highway Public Corporation standard "Test Methods for Air Mortar and Air Milk (JHS A 313-1992)". 【0043】 [Measurement of compressive strength] After pouring the unhardened cement composition into a formwork, a 20cm × 40cm × 8cm lightweight cellular cementitious cementitious hardened body was prepared by leaving it undisturbed at room temperature (approximately 20-25°C). The compressive strength of the obtained lightweight cellular cementitious hardened body at 7 days was measured in accordance with "JIS A 1108:2018 (Test method for compressive strength of concrete)". [Calculation of density of lightweight cellular cementitious material] The density of the lightweight cellular cementitious hardened material used for measuring compressive strength (indicated as "hardened material" in Table 1) was calculated. [Calculation of the percentage of carbon dioxide in hardened lightweight cellular cementitious material] The percentage of carbon dioxide (mass%) in the mortar portion of the lightweight aerated cementitious hardened material used to measure compressive strength was determined using thermogravimetric differential thermal analysis (TG-DTA). Specifically, after crushing the lightweight aerated cementitious hardened material, thermogravimetric differential thermal analysis (TG-DTA) was performed on the sample (mortar portion). From the measurement results, the decrease in mass in the endothermic peak range of approximately 550-800°C was determined to be due to the decarboxylation of calcium carbonate contained in the mortar portion. From the amount of this decrease, the percentage of carbon dioxide in the mortar portion (mass%) (value equivalent to carbon dioxide of calcium carbonate) was calculated. 【0044】 [Example 6] To the carbonated compound prepared in the same manner as in Example 1, fine aggregate was added at a rate of 725 kg / m³. 3 , coarse aggregate 877 kg / m 3An unhardened cement composition was obtained by following the same procedure as in Example 1, except that the air bubbles were added and mixed in such an amount that the density of the unhardened cement composition reached the values ​​shown in Table 1. The obtained uncured cement composition was used to evaluate its handling properties and other aspects in the same manner as in Example 1. The percentage of carbon dioxide in the lightweight cellular cementitious cementitious hardened body of Example 6 was calculated using a sample (mortar portion) obtained by crushing the lightweight cellular cementitious cementitious hardened body (concrete), removing the coarse aggregate, and then grinding it. 【0045】 [Comparative Example 1] Cement and water were mixed in a container using a hand mixer for 60 seconds to obtain a mixture (temperature: 23°C). The amount of cement and water used was such that the water-cement ratio was 64% (the unit amount of cement was 353 kg / m³). 3 The unit volume of water is 227 kg / m³. 3 ) On the other hand, after mixing a foaming agent with water for foaming agent-containing water to obtain foaming agent-containing water, bubbles were prepared by kneading the foaming agent-containing water while supplying compressed air using a foaming machine. The amounts of foaming agent and water for containing the foaming agent are 1.65 kg / m³ each. 3 , 31.35 kg / m 3 ) was established. Next, air bubbles were mixed into the above mixture in an amount such that the density of the unhardened cement composition became the value shown in Table 1, thereby obtaining an unhardened cement composition. The obtained uncured cement composition was used to evaluate its handling properties and other aspects in the same manner as in Example 1. 【0046】 [Comparative Example 2] An unhardened cement composition was obtained in the same manner as in Comparative Example 1, except that compressed carbon dioxide was introduced instead of compressed air using a foaming machine during mixing. The obtained uncured cement composition was used to evaluate its handling properties and other aspects in the same manner as in Example 1. 【0047】 [Table 1] 【0048】 Table 1 shows that when comparing Examples 1-6 with Comparative Examples 1-2, the proportion of carbon dioxide in Examples 1-6 (3.86-9.05% by mass) is greater than that in Comparative Examples 1-2 (3.28-3.45% by mass). This indicates that, according to the present invention, a lightweight cellular cementitious hardened body with more carbon dioxide fixed can be obtained.

Claims

[Claim 1] A method for producing a lightweight cellular cementitious hardened body comprising cement, a foaming agent, and water, and wherein carbon dioxide is fixed, A first cement mixing step involves mixing a portion of the above-mentioned cement with a portion of the above-mentioned water, which is water for the first cement-containing mixture, to obtain the first cement-containing mixture. A carbonated mixture preparation step is performed by supplying carbon dioxide, which is the gaseous state of carbon dioxide that is to be fixed, to the first cement-containing mixture described above to obtain a carbonated mixture. A second cement mixing step to obtain a second cement-containing mixture by mixing the above-mentioned carbonated mixture, the remainder of the above-mentioned cement, and a portion of the above-mentioned water for a second cement-containing mixture, or by mixing the above-mentioned carbonated mixture and the remainder of the above-mentioned cement. A foam preparation step involves mixing the above-mentioned foaming agent with a portion of the above-mentioned water, which is used for foaming agent-containing water, and gas to obtain bubbles. A cement composition preparation step involves mixing the above-mentioned second cement-containing mixture with the above-mentioned air bubbles to obtain an unhardened cement composition. A curing step in which the above uncured cement composition is cured to obtain a lightweight cellular cementitious hardened body. Includes, A method for producing a lightweight aerated cementitious hardened body, characterized in that the proportion of a portion of the cement used in the first cement mixing step is 8 to 25% by mass of the total amount of cement, and the water-cement ratio of the first cement-containing mixture is 150 to 400%. [Claim 2] The above lightweight cellular cementitious hardened body does not contain aggregate, and In the cement composition preparation step described above, the density of the unhardened cement composition is 0.30 to 1.00 g / cm³. ３ A method for producing a lightweight cellular cementitious hardened body according to claim 1, wherein the amount of air bubbles is adjusted to achieve the above-mentioned result. [Claim 3] The above lightweight cellular cementitious body contains aggregate, and The above aggregate is supplied and mixed in either or both of the first cement mixing process and the second cement mixing process. In the cement composition preparation step described above, the density of the unhardened cement composition is 0.70 to 2.50 g / cm³. ３ A method for producing a lightweight cellular cementitious hardened body according to claim 1, wherein the amount of air bubbles is adjusted to achieve the above-mentioned result. [Claim 4] The above lightweight cellular cementitious hardened body contains a cement dispersant, and A method for producing a lightweight cellular cementitious hardened body according to any one of claims 1 to 3, wherein the cement dispersant is supplied and mixed in either or both of the first cement mixing step and the second cement mixing step. [Claim 5] A method for producing a lightweight cellular cementitious hardened body according to any one of claims 1 to 4, wherein the proportion of carbon dioxide in the above-mentioned lightweight cellular cementitious hardened body is 3.5 to 15.0% by mass.

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