Method for producing cement composition

Abstract

Provided is a method for manufacturing a cement composition in which carbon dioxide is immobilized. The method is capable of reducing the reaction time between cement and carbon dioxide and immobilizes a large amount of carbon dioxide. The method for manufacturing a cement composition uses cement, an aggregate, and water, and said method comprises: (A) a step of mixing a part of the cement and a part of the water to obtain a cement slurry in which the water-cement ratio is 250%; (B) a step of bringing the cement slurry into contact with carbonic acid gas to obtain a carbonized slurry; (C) a step of separating some water from the carbonized slurry to obtain a concentrated slurry with a liquid-solid ratio of 80% to 400%; (D) a step of mixing / kneading the concentrated slurry with the remainder of the cement to obtain a composition having a high concentration of cement; and (E) a step of mixing / kneading the composition containing a high concentration of cement with the remainder of the water to obtain the cement composition. The aggregate is supplied in step (D) or step (E).

Description

[Technical field]

[0001] The present invention relates to a method for producing a cement composition (for example, concrete in which carbon dioxide is fixed). [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 immobilizing carbon dioxide (carbonic acid gas) contained in exhaust gases and the like generated in cement manufacturing plants in cement compositions such as concrete. For example, Patent Document 1 describes a method for producing concrete in which carbon dioxide is efficiently fixed, which method 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, wherein the weight of the water is adjusted so that the amount of unhydrated cement remaining in the concrete is between 0% and 50%" (Claim 1).

[0003] Furthermore, Patent Document 2 describes a method for producing precast concrete that significantly reduces carbon dioxide emissions by absorbing a large amount of carbon dioxide during the curing process, as follows: "A method for producing carbon dioxide (CO2)-absorbing precast concrete, which comprises pouring a concrete mix into a formwork, and after demolding, subjecting the solidified concrete body to carbonation curing in an atmosphere with a carbon dioxide concentration of 5 to 95%, thereby forming a carbonation region at a depth of 20 mm or more from the surface" (claim 5). The concrete mixture used in the manufacturing method of Patent Document 2 is "a concrete mixture containing, as powder components, one or two of γ-C2S (symbol γ) and steel slag powder (symbol B), and Portland cement (symbol C), in which the total of γ and B in the total content of the above γ, B, and C is 25 to 95 mass %, and the water-cement ratio W / C is 80 to 250%" (Claim 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-37493 A [Patent Document 2] JP 2011-168436 A Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a method for producing a cement composition by immobilizing carbon dioxide, which can shorten the reaction time between cement and carbon dioxide and immobilize a large amount of carbon dioxide. [Means for solving the problem]

[0006] As a result of intensive research into solving the above problems, the present inventors have found that the above objects can be achieved by a method for producing a cement composition using cement, aggregate, and water, the method comprising: (A) a cement slurry preparation step of mixing a part of the cement with a part of the water to obtain a cement slurry having a water-cement ratio of 250% or more; (B) a carbonation step of contacting the cement slurry with carbon dioxide gas to obtain a carbonated slurry; (C) a concentration step of partially separating water from the carbonated slurry to obtain a concentrated slurry having a liquid-solid ratio of 80 to 400%; (D) a cement additional supply step of kneading the concentrated slurry with the remainder of the cement to obtain a high-concentration cement-containing composition; and (E) a water additional supply step of kneading the high-concentration cement-containing composition with the remainder of the water to obtain the cement composition, and the method has a configuration in which the aggregate is supplied in either one or both of the cement additional supply step and the water additional supply step, and thus the present invention has been completed. The present invention provides the following [1] to [8].

[0007] [1] A method for producing a cement composition using cement, aggregate, and water, comprising: a cement slurry preparation step of mixing a part of the cement with a part of the water to obtain a cement slurry having a water-cement ratio of 250% or more; a carbonation step of contacting the cement slurry with carbon dioxide gas to obtain a carbonated slurry; A concentration step of partially separating water from the carbonated slurry to obtain a concentrated slurry having a liquid-solid ratio of 80 to 400%; A cement additional supply step of kneading the concentrated slurry with the remainder of the cement to obtain a high-concentration cement-containing composition; and a water additional supply step of kneading the high-concentration cement-containing composition with the remainder of the water to obtain the cement composition, In the total amount of the cement, the proportion of the part of the cement used in the cement slurry preparation step is 1 to 50 mass%, and the proportion of the remaining amount of the cement used in the cement additional supply step is 50 to 99 mass%, A method for producing a cement composition, characterized in that the aggregate is supplied in either one or both of the cement additional supply step and the water additional supply step. [2] The method for producing a cement composition according to the above [1], wherein the proportion of the amount of water in the concentrated slurry obtained in the concentrating step is 50 to 99 mass% of the total amount of water contained in the cement composition, and the proportion of the remaining amount of water used in the additional water supply step is 1 to 50 mass%. [3] The method for producing a cement composition according to [1] or [2], wherein the difference (XY) between the water-cement ratio (X) of the cement slurry obtained in the cement slurry preparation step and the liquid-solid ratio (Y) of the concentrated slurry obtained in the concentration step is 50% or more. [4] The method for producing a cement composition according to any one of the above [1] to [3], wherein in the carbonation step, the carbon dioxide gas is supplied as a gas containing 5 volume % or more of carbon dioxide gas. [5] The method for producing a cement composition according to any one of [1] to [4], wherein in the carbonation step, the carbon dioxide gas is supplied until the pH of the carbonated slurry falls within the range of 5.0 to 11.5. [6] The method for producing a cement composition according to any one of [1] to [5] above, wherein the cement composition contains a cement admixture, and the cement admixture is supplied in the additional water supply step. [7] The method for producing a cement composition according to [6], 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. [8] The method for producing a cement composition according to any one of [1] to [7] above, wherein the aggregate comprises fine aggregate and coarse aggregate, and the liquid-solid ratio of the cement composition is 30 to 65%. Effect of the Invention

[0008] According to the method for producing a cement composition of the present invention, the reaction time between cement and carbon dioxide can be shortened. Furthermore, according to the method for producing a cement composition of the present invention, the amount of carbon dioxide fixed in the cement composition can be increased. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The method for producing a cement composition of the present invention is a method for producing a cement composition using cement, aggregate, and water, and includes the following steps: (A) a cement slurry preparation step of mixing a part of the cement with a part of the water to obtain a cement slurry having a water-cement ratio of 250% or more; (B) a carbonation step of contacting the cement slurry with carbon dioxide gas (carbon dioxide in the form of a gas) to obtain a carbonated slurry; (C) a concentration step of partially separating water from the carbonated slurry to obtain a concentrated slurry having a liquid-solid ratio of 80 to 400%; (D) a cement additional supply step of kneading the concentrated slurry with the remainder of the cement to obtain a high-concentration cement-containing composition; and (E) a water additional supply step of kneading the high-concentration cement-containing composition with the remainder of the water to obtain the cement composition. In the present invention, the proportion of the amount of cement (part) used in step (A) (cement slurry preparation step) is 1 to 50 mass% relative to the total amount of cement (100 mass%), and the proportion of the amount of cement (remainder) used in step (D) (cement additional supply step) is 50 to 99 mass%. In the present invention, aggregates (eg, coarse aggregates and fine aggregates) are supplied in either one or both of step (D) (additional cement supply step) and step (E) (additional water supply step). Each step will be explained in detail below.

[0010] [Step (A): Cement slurry preparation step] Step (A) is a step of mixing a part of the cement and a part of the water out of the total amount of cement and the total amount of water used in the production method of the present invention to obtain a cement slurry having a water-cement ratio of 250% or more. The 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.

[0011] The proportion of the amount of cement (part of cement) used in step (A) in the total amount (100% by mass) of cement contained in the cement composition of the present invention is 1 to 50% by mass, preferably 3 to 45% by mass, more preferably 5 to 40% by mass, even more preferably 8 to 35% by mass, even more preferably 10 to 32% by mass, and particularly preferably 12 to 30% by mass. If the proportion is less than 1% by mass, the amount of carbon dioxide fixed in the cement composition is reduced. If the proportion exceeds 50% by mass, the strength development of the cement composition is reduced.

[0012] The water-cement ratio of the cement slurry prepared in step (A) is 250% or more, preferably 300 to 2,000%, more preferably 350 to 1,500%, further preferably 400 to 1,000%, and particularly preferably 450 to 700%. If the ratio is less than 250%, the object of the present invention, which is to shorten the reaction time between cement and carbon dioxide, cannot be fully achieved.If the ratio is 2,000% or less, the treatment efficiency of water separation (concentration of the carbonated slurry) in the subsequent step (C) (concentration step) can be further improved. "Water-cement ratio" is the mass ratio of water to cement (water / cement) expressed as a percentage (%) ([mass of water] × 100 ÷ [mass of cement]; unit: %). In step (A), the method of mixing cement and water is not particularly limited, and examples thereof include a method in which water is supplied into a storage and stirring means such as a stirring tank, and then cement is supplied and then stirred; and a method in which water and cement are simultaneously supplied into a storage and stirring means, and then stirred.

[0013] [Step (B): Carbonation step] Step (B) is a step of contacting the cement slurry obtained in step (A) with carbon dioxide gas to obtain a carbonated slurry. In the step (B), from the viewpoint of uniformly supplying carbon dioxide gas into the cement slurry, it is preferable to supply carbon dioxide gas while fluidizing the cement slurry. Examples of the method for supplying carbon dioxide gas into the cement slurry include the following methods (i) to (iii). (i) A method in which a carbon dioxide gas supplying means for supplying carbon dioxide gas into the cement slurry is installed in the stirring tank used in step (A) and carbon dioxide gas is supplied into the cement slurry in the stirring tank. A more specific example is a method in which, in an apparatus equipped with a stirring tank for stirring (mixing) cement and water to obtain a cement slurry and a carbon dioxide gas supplying means (e.g., an aeration plate) disposed in the stirring tank, carbon dioxide gas is blown into the cement slurry obtained in step (A) using the carbon dioxide gas supplying means while stirring the cement slurry, thereby obtaining a carbonated slurry.

[0014] (ii) A method in which the cement slurry in the stirring tank is introduced into an apparatus having a carbon dioxide gas supply means (e.g., an air diffuser), carbon dioxide gas is then blown into the cement slurry in the apparatus using the carbon dioxide gas supply means to obtain a carbonated slurry, and the carbonated slurry is then stored in a storage tank. The stirring tank and the storage tank may be the same or different.

[0015] A more specific example is a method in which the cement slurry contained in a stirring tank is introduced into an apparatus having a carbon dioxide gas supplying means (e.g., an air diffuser) through a first flow passage using a pump or the like, and then carbon dioxide gas is supplied into the cement slurry in the apparatus using the carbon dioxide gas supplying means while stirring the cement slurry, and then the resulting carbonated slurry is introduced into the stirring tank through a second flow passage using a pump or the like, and then the method includes a method in which the cement slurry is introduced into the stirring tank. An example of such an apparatus is one that includes a slurry storage tank for storing and stirring the cement slurry, and an aeration means (e.g., an aeration plate) for supplying carbon dioxide gas that is disposed in the slurry storage tank. Furthermore, the cement slurry 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 immobilized. Furthermore, after the carbonated slurry is obtained, the carbonated slurry may be temporarily stored in a storage tank different from the stirring tank, and then supplied from the storage tank to another storage tank.

[0016] (iii) A method of blowing carbon dioxide gas into the cement slurry in the mixing tank when the cement slurry is fed into a tank for storing the carbonated slurry. A more specific example is a method in which the cement slurry in a mixing tank is introduced into a pipeline connected to the mixing tank, and while circulating within the pipeline, carbon dioxide gas is supplied into the pipeline midway to obtain a carbonated slurry, and then the carbonated slurry is stored in a tank for storing carbonated slurry. The above-mentioned pipeline may, for example, have a carbon dioxide gas inlet and a mixing means for mixing the cement slurry and carbon dioxide gas inside. Specifically, the pipeline may have an aeration means (e.g., an aeration plate) for supplying carbon dioxide gas and a mixing means (e.g., a line mixer or a static mixer) disposed therein. In addition, after supplying carbon dioxide gas into the cement slurry, the obtained carbonated slurry may be returned to the stirring tank without being introduced into the tank for storing the carbonated slurry. Furthermore, the carbonated slurry may be repeatedly circulated through the stirring tank and the pipeline in this order to fix a sufficient amount of carbon dioxide gas, and then introduced into the tank for storing the carbonated slurry. Furthermore, after obtaining the carbonated slurry, the carbonated slurry may be temporarily stored in a storage tank different from the stirring tank, and then supplied from the storage tank to the tank for storing the carbonated slurry.

[0017] 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 liquid surface of the cement slurry (for example, by increasing the pressure of the gas phase above the liquid surface of a tank containing the cement slurry to 1,200 hPa or more, which exceeds atmospheric pressure). For this reason, it is preferable to use a carbon dioxide gas supplying means having a structure capable of applying pressure to supply carbon dioxide gas.

[0018] In the present invention, carbon dioxide gas may be supplied to the cement slurry as a gas consisting of carbon dioxide gas alone, but from the viewpoint of ease of availability, etc., carbon dioxide gas may be supplied to the cement slurry as a gas containing carbon dioxide gas. In this case, 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).

[0019] In step (B), carbon dioxide gas is supplied so that the pH of the carbonated slurry is preferably within the range of 5.0 to 11.5, more preferably 5.5 to 11.0, even more preferably 6.0 to 10.0, and particularly preferably 6.5 to 9.0. If the pH is 5.0 or higher, the strength development of the cement composition is further improved. In addition, the time required for supplying carbon dioxide gas is shortened, and the production efficiency of the cement composition is further improved. If the pH is 11.5 or lower, the amount of carbon dioxide fixed in the cement composition is increased. Incidentally, the pH of the carbonated slurry is lowered by supplying carbon dioxide gas. The time for supplying carbon dioxide gas varies depending on the water-cement ratio, the carbon dioxide gas supply means, the carbon dioxide gas concentration of the gas containing carbon dioxide gas, etc. For this reason, in step (B), the time for ending the supply of carbon dioxide gas is preferably determined based on the actual measured value of the pH of the carbonated slurry.

[0020] [Step (C): Concentration step] Step (C) is a step of partially separating water from the carbonated slurry obtained in step (B) (carbonation step) to obtain a concentrated slurry having a liquid-solid ratio of 80 to 400%. Here, "partially separating water from the carbonated slurry" means not completely separating the water contained in the carbonated slurry (in other words, dehydrating the carbonated slurry to leave only the solids), but separating only a portion of the water contained in the carbonated slurry (in other words, concentrating the carbonated slurry so that the amount of water in the slurry is reduced). "Liquid-solid ratio" is a term that corresponds to the "water-cement ratio" in step (A) (cement slurry preparation step), and means the mass ratio (water / [(uncarbonated cement) + (cement that is a material for carbonated cement)]) of the "liquid" water to the "solid" "uncarbonated cement (uncarbonated cement) and cement that is a material for the carbonated cement (carbonated cement)" expressed as a percentage (%) ([mass of water] × 100 ÷ [total mass of uncarbonated cement and cement that is a material for the carbonated cement]; unit: %). The term "concentrated slurry" refers to a product obtained by partially separating water from the cement slurry obtained in step (A) (cement slurry preparation step). The term "concentrated slurry" is not limited to a slurry-like product, but also includes a product that is not called a slurry (e.g., a mortar-like product).

[0021] In step (C), the liquid-solid ratio is 80 to 400%. If the liquid-solid ratio is less than 80%, the strength development of the cement composition after hardening decreases. If the liquid-solid ratio exceeds 400%, the amount of carbon dioxide fixed in the cement composition decreases. From the viewpoint of obtaining excellent strength development, the liquid-solid ratio is preferably 100% or more, more preferably 150% or more, further preferably 200% or more, and particularly preferably 250% or more. From the viewpoint of increasing the amount of fixed carbon dioxide, the liquid-solid ratio is preferably 300% or less, more preferably 250% or less, further preferably 200% or less, and particularly preferably 150% or less. In the present invention, the difference (XY) between the water-cement ratio (X) of the cement slurry obtained in step (A) (cement slurry preparation step) and the liquid-solid ratio (Y) of the concentrated slurry obtained in step (C) (concentration step) is preferably 50% or more, more preferably 100% or more, even more preferably 150% or more, and particularly preferably 200% or more. When the difference (XY) is 50% or more, the amount of carbon dioxide fixed in the cement composition can be increased. The upper limit of the difference (XY) is not particularly limited, but is, for example, 1,800% (usually, 1,200%).

[0022] The proportion of the amount of water in the concentrated slurry obtained in step (C) (concentrating step) is preferably 50 to 99 mass % relative to the total amount of water (100 mass %) contained in the cement composition which is the target product of the present invention. When the ratio is 50% by mass or more, the strength development after hardening of the cement composition can be further improved, and when the ratio is 99% by mass or less, the amount of carbon dioxide fixed in the cement composition can be further increased. From the viewpoint of obtaining excellent strength expression, the proportion is preferably 60 mass % or more, more preferably 70 mass % or more, further preferably 75 mass % or more, and particularly preferably 80 mass % or more. From the viewpoint of increasing the amount of fixed carbon dioxide, the proportion is preferably 90% by mass or less, more preferably 80% by mass or less, further preferably 70% by mass or less, and particularly preferably 65% ​​by mass or less. In step (C) (concentration step), a known solid-liquid separator such as a sedimentation separator, a vacuum dehydrator, or a pressure dehydrator can be used as a means for separating water.

[0023] [Process (D): Cement additional supply process] Step (D) is a step of kneading the concentrated slurry obtained in step (C) (concentration step) with the remainder of the cement to obtain a high-concentration cement-containing composition (a composition containing cement at a higher concentration than the concentrated slurry obtained in step (C) by adding cement). The proportion of the amount of cement used in step (D) (the remainder of the cement) in the total amount of cement contained in the cement composition of the present invention (100% by mass) is 50 to 99% by mass, preferably 55 to 97% by mass, more preferably 60 to 95% by mass, even more preferably 65 to 92% by mass, even more preferably 68 to 90% by mass, and particularly preferably 70 to 88% by mass. If the proportion is less than 50% by mass, the strength development after hardening of the cement composition decreases. If the proportion exceeds 99% by mass, the amount of carbon dioxide fixed in the cement composition decreases.

[0024] [Process (E): Additional water supply process] Step (E) is a step of kneading the high-concentration cement-containing composition obtained in step (D) with the remainder of the water to obtain a cement composition (a composition containing cement at a lower concentration than the high-concentration cement-containing composition obtained in step (D) by adding water). In the total amount (100 mass%) of water contained in the cement composition which is the target product of the present invention, the amount of water (the remainder) supplied in step (E) is preferably 1 to 50 mass%. When the ratio is 1 mass% or more, the amount of carbon dioxide fixed in the cement composition can be increased, and when the ratio is 50 mass% or less, the strength development after hardening of the cement composition can be increased. From the viewpoint of increasing the amount of fixed carbon dioxide, the proportion is preferably 10% by mass or more, more preferably 20% by mass or more, further preferably 30% by mass or more, and particularly preferably 35% by mass or more. From the viewpoint of obtaining excellent strength expression, the proportion is preferably 40 mass % or less, more preferably 30 mass % or less, further preferably 25 mass % or less, and particularly preferably 20 mass % or less.

[0025] In the present invention, aggregate is supplied in either one or both of step (D) (additional cement supply step) and step (E) (additional water supply step). From the viewpoint of efficiency in producing the cement composition, it is preferable to supply the aggregate in step (D) (cement additional supply step). The aggregate used in the present invention may be fine aggregate alone or a combination of fine and coarse aggregates. The aggregate may be any of natural aggregate, artificial aggregate, and recycled aggregate. The fine aggregate is not particularly limited, and examples thereof include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag fine aggregate, and lightweight fine aggregate, or a mixture of two or more types selected from these. The coarse aggregate is not particularly limited, and examples thereof include river gravel, mountain gravel, land gravel, sea gravel, crushed stone, slag coarse aggregate, and lightweight coarse aggregate, or a mixture of two or more types selected from these. The amount of aggregate mixed (the amount of each mixed when fine aggregate and coarse aggregate are used in combination) is not particularly limited, and may be a general amount used in mortar or concrete. When fine aggregate and coarse aggregate are used together, for example, the unit weight of fine aggregate is 600 to 1,100 kg / m 3 , the unit weight of coarse aggregate is 800-1,500 kg / m 3 The fine aggregate ratio can be set at 30 to 60%. The "fine aggregate ratio" is the percentage (%) of the mass of fine aggregate (A) out of the total mass of fine aggregate (A) and coarse aggregate (B) (A × 100 ÷ (A + B); unit: %).

[0026] The liquid-solid ratio of the cement composition is preferably 30 to 65%, and more preferably 40 to 60%. When the ratio is 30% or more, the fluidity of the cement composition is further improved, and when the ratio is 65% or less, the strength development of the cement composition is further improved.

[0027] From the viewpoint of further improving air entrainment and fluidity, the cement composition preferably contains a cement admixture. Examples of the cement admixture include cement dispersants, AE agents, etc. In particular, from the viewpoint of further improving air entrainment and fluidity, it is preferable to use a cement dispersant and an AE agent in combination. Examples of cement dispersants include water reducing agents, air-entraining water reducing agents, high-performance water reducing agents, and high-performance air-entraining water reducing agents. The amount of the cement dispersant is, for example, 0.5 to 3 parts by mass (preferably 1.0 to 2.0 parts by mass) relative to 100 parts by mass of cement. The cement dispersant is preferably supplied in step (E) (additional water supply step) from the viewpoint of further improving the air entrainment property and fluidity of the cement composition. The amount of the AE agent is, for example, 0.001 to 0.03 parts by mass (preferably 0.003 to 0.02 parts by mass) relative to 100 parts by mass of cement.

[0028] The cement composition may contain various admixtures such as fly ash, silica fume, and ground granulated blast furnace slag, as required. The amount of the admixture is preferably 30 parts by mass or less, more preferably 20 parts by mass or less, further preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less, based on 100 parts by mass of cement. In the manufacturing method of the present invention, the step of using various admixtures is not particularly limited, but from the viewpoints of efficiency in manufacturing the cement composition and not affecting the pH of the carbonated slurry in step (B) (carbonation step), it is preferable that the step be at least one of step (D) (additional cement supply step) and step (E) (additional water supply 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) Water: Tap water (5) AE water reducing agent: Product name "Master Polyhede 15S" (manufactured by Pozzoliss Corporation) (6) Air entraining agent: Trade name "Master Air 303A" (manufactured by Pozzolith Solutions)

[0030] [A. Experiment on water-cement ratio in cement slurry preparation process] [Examples 1 to 4, Comparative Example 1] Cement and water in the amounts shown in Table 1 were mixed in a container for 60 seconds using a hand mixer to obtain a cement slurry (liquid temperature: 23°C). Carbon dioxide gas (concentration: 100%) was blown into the cement slurry in the container through a carbon dioxide gas supply pipe at a rate of 20 liters / minute to obtain a carbonated slurry (end of the carbonation process). The time from the start of blowing carbon dioxide gas to the time when the pH of the carbonated slurry reached equilibrium within the range of 6 to 7 (end of reaction) was defined as the "reaction time (min)". The reaction times are shown in Table 1. From Table 1, it can be seen that the higher the water-cement ratio, the shorter the reaction time.

[0031] [Table 1]

[0032] [B. Experiment on liquid-solid ratio in concentration process] [Examples 5 to 7, Comparative Example 2] The carbonated slurry obtained in Example 2 (water-cement ratio: 500%) was left to stand to allow the solids (cement and carbonated cement) to settle, and then the water was removed using a submersible pump to adjust the liquid-solid ratio as shown in Table 2 (end of the concentration process). However, in Comparative Example 2, water was not removed. The remaining part of the cement, the fine aggregate, and the coarse aggregate were added to the obtained concentrated slurry, and the mixture was kneaded for 60 seconds to obtain a high-concentration cement-containing composition (completion of the cement additional supply step). Next, water and admixtures (AE water-reducing agent and AE agent) in the amounts shown in Table 2 were added to the obtained high-concentration cement-containing composition and mixed for 60 seconds. Next, the mixed material adhering to the inner wall of the mixer was scraped off, and then the mixture was mixed for an additional 60 seconds to obtain concrete (cement composition) (end of the water addition supply process).

[0033] The slump of the obtained concrete was measured in accordance with "JIS A 1101:2020 (Concrete slump test method)". In addition, the compressive strength of the resulting concrete was measured at 7 and 28 days after construction in accordance with JIS A 1108:2018 (Test method for compressive strength of concrete). Furthermore, the percentage of carbon dioxide (mass%) in the 7-day-old specimens used to measure the compressive strength was determined using thermogravimetry-differential thermal analysis (TG-DTA). Specifically, thermogravimetry-differential thermal analysis (TG-DTA) was performed, and the mass loss in the endothermic peak range of approximately 550-800°C was determined to be due to decarbonation of calcium carbonate contained in the mortar portion of the concrete from the amount of mass loss. The percentage of carbon dioxide in the mortar portion (mass%; the value of calcium carbonate converted to carbon dioxide) was calculated from the amount of mass loss, and the amount of fixed carbon dioxide per ton of cement was determined.

[0034] [C. Experiment without carbonation] [Comparative Example 3] Unit weight is 336kg / m 3 The amount of cement is 840 kg / m 3 The amount of fine aggregate is 938 kg / m 3 The amount of coarse aggregate was charged into a 55-liter forced pan mixer, mixed dry for 30 seconds, and then the unit weight was 168 kg / m 3 The mixture was then mixed for 60 seconds after scraping off the mixture adhering to the inner wall of the mixer. The mixture was then mixed for another 60 seconds to obtain a concrete (cement composition). The above results are shown in Table 3. From Table 3, it can be seen that the amount of carbon dioxide fixed in the mortar portion in Examples 5-7 is larger than that in Comparative Examples 2-3.

[0035] [Table 2]

[0036] [Table 3]

Claims

1. A method for producing a cement composition using cement, aggregate, and water, comprising the steps of: a cement slurry preparation step of mixing a part of the cement with a part of the water to obtain a cement slurry having a water-cement ratio of 250% or more; a carbonation step of contacting the cement slurry with carbon dioxide gas to obtain a carbonated slurry; A concentration step of partially separating water from the carbonated slurry to obtain a concentrated slurry having a liquid-solid ratio of 80 to 400%; A cement additional supply step of kneading the concentrated slurry with the remainder of the cement to obtain a high-concentration cement-containing composition; and a water additional supply step of kneading the high-concentration cement-containing composition with the remainder of the water to obtain the cement composition, In the total amount of the cement, the proportion of the part of the cement used in the cement slurry preparation step is 1 to 50 mass%, and the proportion of the remaining amount of the cement used in the cement additional supply step is 50 to 99 mass%, The aggregate is supplied in either one or both of the cement additional supply step and the water additional supply step, The ratio of the amount of water in the concentrated slurry obtained in the concentrating step to the total amount of water contained in the cement composition is 50 to 99 mass%, and the ratio of the amount of the remaining water used in the additional water supply step is 1 to 50 mass%, The method for producing a cement composition, characterized in that the difference (X-Y) between the water-cement ratio (X) of the cement slurry obtained in the cement slurry preparation step and the liquid-solid ratio (Y) of the concentrated slurry obtained in the concentration step is 50% or more.

2. The method for producing a cement composition according to claim 1, wherein in the carbonation step, the carbon dioxide gas is supplied as a gas containing 5 volume % or more of carbon dioxide gas.

3. 2. The method for producing a cement composition according to claim 1, wherein in the carbonation step, the carbon dioxide gas is supplied until the pH of the carbonated slurry falls within the range of 5.0 to 11.

5.

4. The cement composition includes a cement admixture, The method for producing a cement composition according to claim 1, wherein the cement admixture is supplied in the additional water supply step.

5. The method for producing a cement composition according to claim 4, 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.

6. The aggregate includes fine aggregate and coarse aggregate, The method for producing a cement composition according to any one of claims 1 to 5, wherein the liquid-solid ratio of the cement composition is 30 to 65%.

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