JP7737280B2 - Carbonated hardened body and method for producing the same - Google Patents

Description

The present invention relates to a carbonated hardened body and a method for producing the same.

Currently, reducing carbon dioxide emissions has become an important issue in order to curb global warming.
As a method for reducing carbon dioxide emissions in the production of a cementitious hardened body, a method is known in which carbon dioxide is absorbed during the curing process of the cementitious hardened body, thereby reducing the total amount of carbon dioxide emitted until the hardened cementitious body is obtained.
Patent Document 1 describes a cementitious hardened body that can significantly reduce the total amount of carbon dioxide emitted by absorbing a large amount of carbon dioxide during the curing process, and is characterized by being obtained by carbonating a hardened body of a cement mixture that includes (A) a powder for cement mixing that includes either mullite or anorthite, or both, and a powdered cement composition that includes Portland cement, (B) water, and (C) aggregate.
Furthermore, Patent Document 2 describes a cementitious hardened body obtained by carbonating a hardened body of a cement mixture containing: (A) a pulverized fired product containing 10 to 200 parts by mass of _C2AS per 100 parts by mass of _C2S and having a _C3A content of 20 parts by mass or less; a powdered cement composition containing Portland cement; (B) water; and (C) aggregate.

Japanese Patent Application Laid-Open No. 2016-153357 JP 2016-47788 A

The object of the present invention is to provide a carbonated hardened body that can absorb and fix a larger amount of carbon dioxide during the curing process, thereby reducing the total amount of carbon dioxide emitted, and that has excellent strength, as well as a method for producing the same.

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 carbonated hardened body obtained by carbonating a hardened body of a _hydraulic composition comprising: (A) a hydraulic powder material containing clinker powder having a hydraulic modulus (H.M.) of 1.1 to 2.2, a silicate modulus (S.M.) of 1.9 to 6.0, and an iron modulus (I.M.) of 0.9 to 4.0, and gypsum in a content of _1.0 to _6.0 mass% calculated as _SO3 ; (B) a clinker aggregate containing _C2S and _C2AS , wherein the amount of _C2AS is 5 to 100 parts by mass per 100 parts by mass of _C2S , and the clinker aggregate contains no C3A or contains C3A in an amount of 20 parts by mass or less per 100 parts by mass of C2S; and (C) water, and have completed the present invention.
That is, the present invention provides the following [1] to [4].
[1] A carbonated hardened body obtained by carbonating a hardened body of a hydraulic composition comprising: (A) a hydraulic powder material containing clinker powder and gypsum, wherein the clinker powder has a hydraulic modulus (H.M.) of 1.1 to 2.2, a silicate modulus (S.M.) of 1.9 to 6.0, and an iron modulus (I.M.) of 0.9 to 4.0, and the gypsum content is 1.0 to 6.0 mass% in terms of _SO3 ; (B) a clinker aggregate containing _{C2S and C2AS} , wherein the amount of _C2AS is 5 to 100 parts by mass per 100 parts by mass _of the _C2S , and the clinker aggregate does not contain _C3A or contains the C3A in an amount of 20 parts by mass or less per 100 parts by mass of the C2S; and (C) water.

[2] A method for producing the carbonated hardened body described in [1] above, comprising: a kneaded mixture preparation step of kneading the materials (A) to (C) above to prepare a kneaded mixture of the hydraulic composition; a casting step of casting the kneaded mixture into a formwork; a demolding step of, after the kneaded mixture in the formwork has hardened, releasing from the formwork the hardened body of the hydraulic composition obtained by the hardening of the kneaded mixture; and a carbonation curing step of carbonating the hardened body of the hydraulic composition released from the formwork to obtain a carbonated hardened body.
[3] The method for producing a carbonated hardened body according to [2] above, wherein the hydraulic powder material is obtained by a clinker firing step of firing a clinker material to be fired, which contains one or more materials selected from industrial waste, general waste, and construction waste soil, at 1,250 to 1,500°C to obtain clinker, a clinker crushing step of crushing the clinker to obtain clinker powder, and a mixing step of mixing the clinker powder with gypsum to obtain the hydraulic powder material.
[4] The method for producing a carbonated hardened body according to [2] or [3], wherein the clinker aggregate is obtained by a calcination step of calcining an aggregate material containing at least one selected from industrial waste, general waste, and construction waste soil at 1,250 to 1,500°C to obtain a calcined product, a calcination crushing step of crushing the calcined product to obtain a crushed product, and a classification step of classifying the crushed product to obtain the clinker aggregate.

According to the present invention, more carbon dioxide can be absorbed and fixed during the curing process, thereby reducing the total amount of carbon dioxide emitted and producing a carbonated hardened body with excellent strength.

The carbonated hardened product of the present invention is obtained by carbonating a hardened product of a hydraulic composition comprising: (A) a hydraulic powder material containing clinker powder and gypsum, wherein the clinker powder has a hydraulic modulus (H.M.) of 1.1 to 2.2, a silicate modulus (S.M.) of 1.9 to 6.0, and an iron modulus (I.M.) of 0.9 to 4.0, and the gypsum content is 1.0 to 6.0 mass% calculated as _SO3 ; (B) a clinker aggregate containing _C2S and _C2AS , wherein the amount of _C2AS is 5 to 100 parts by mass per ₁₀₀ parts by mass _{of C2S} , and the clinker aggregate does not contain _C3A or contains C3A in an amount of 20 parts by mass or less per 100 parts by mass of C2S; and (C) water.
Here, "carbonation" refers to the reaction of an alkaline component in the set hydraulic composition with carbon dioxide to lower the pH of the alkaline component.

[(A) Hydraulic powder material]
The hydraulic powder material used in the present invention includes clinker powder and gypsum.
The hydraulic modulus (H.M.) of the clinker powder is 1.1 to 2.2, preferably 1.2 to 2.1, more preferably 1.3 to 2.0, and particularly preferably 1.4 to 1.8. If the hydraulic modulus is less than 1.1, the strength development of a hydraulic composition containing the clinker powder (containing a hydraulic powder material, clinker aggregate, and water) decreases. If the hydraulic modulus exceeds 2.2, the clinker's burnability decreases, free lime (f-CaO) tends to remain, and the burning temperature when producing the clinker must be increased.

The silicic acid ratio (S.M.) of the clinker powder is 1.9 to 6.0, preferably 2.0 to 5.8, more preferably 2.3 to 5.5, and particularly preferably 2.4 to 5.2. If the silicic acid ratio is less than 1.9, the fluidity of the hydraulic composition containing the clinker powder decreases. If the silicic acid ratio exceeds 6.0, the clinker's burnability decreases, and unreacted silica (SiO ₂ ) tends to remain, making it necessary to increase the burning temperature when producing the clinker.
The iron ratio (I.M.) of the clinker powder is 0.9 to 4.0, preferably 1.5 to 3.8, more preferably 2.0 to 3.7, and particularly preferably 2.4 to 3.6. If the iron ratio is less than 0.9, the strength development of the hydraulic composition containing the clinker powder decreases. If the iron ratio exceeds 4.0, the fluidity of the hydraulic composition containing the clinker powder decreases.

The hydraulic ratio, silica ratio, and iron ratio can be calculated using the following formulas.
Hydraulic ratio = CaO/(SiO ₂ + Al ₂ O ₃ + Fe ₂ O ₃ )
_Silicate ratio = _SiO2 / _{( Al2O3} + _Fe2O3 )
Iron ratio = Al ₂ O ₃ /Fe ₂ O ₃
(The chemical formula in the above formula represents the content (mass%) of the compound represented by the chemical formula in the clinker powder.)

The total content of aluminum oxide (Al ₂ O ₃ ) and iron oxide (Fe ₂ O ₃ ) in 100% by mass of clinker powder is preferably 4.0 to 14.0% by mass, more preferably 5.0 to 13.0% by mass, and particularly preferably 6.0 to 12.0% by mass. If the content is 4.0% by mass or more, carbonation will proceed more easily to the interior of the hardened hydraulic composition, further improving the efficiency of carbon dioxide absorption. If the content is 14.0% by mass or less, the amount of fixed carbon dioxide that can be absorbed by the hydraulic composition containing clinker powder will be greater.

From the viewpoints of ease of burning when producing clinker and the fluidity of the hydraulic composition, it is preferable that the clinker powder contains C ₂ S (2CaO.SiO ₂ : belite) and C ₂ AS (2CaO.Al ₂ O _{3.SiO 2} : gehlenite).
The amount of C ₂ AS per 100 parts by mass of C ₂ S is preferably 5 to 100 parts by mass, more preferably 6 to 75 parts by mass, more preferably 7 to 50 parts by mass, even more preferably 8 to 40 parts by mass, and particularly preferably 12 to 30 parts by mass. If the amount is 5 parts by mass or more, the amount of free lime (amount of unreacted CaO) is less likely to increase when the firing temperature is increased during firing, making firing easier. In addition, the amount of carbon dioxide absorption is greater. If the amount is 100 parts by mass or less, the amount of melt generated at high temperatures during production of the fired product is reduced, broadening the range of possible firing temperatures. In addition, since the amount of C ₂ S is relatively large, the strength of the hardened body when demolding in the demolding step described below is increased.

From the viewpoint of improving the fluidity of the hydraulic composition, the clinker powder preferably does not contain C ₃ A (3CaO·Al ₂ O ₃ : aluminate phase) or contains C ₃ A in an amount of 20 parts by mass or less per 100 parts by mass of C ₂ S.
When the clinker powder contains _C3A , the amount of _C3A per 100 parts by mass of _C2S is preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less. If the amount exceeds 20 parts by mass, the fluidity of the hydraulic composition decreases.

The proportion of C ₂ S in the clinker powder is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more, from the viewpoint of increasing the strength of the carbonated hardened body.
Furthermore, the proportion of C ₂ AS in the clinker powder is preferably 5 to 25% by mass, more preferably 6 to 20% by mass, and particularly preferably 7 to 15% by mass. If the proportion is 5% by mass or more, the amount of free lime (amount of unreacted CaO) is less likely to increase when the firing temperature is increased during firing, making firing easier. In addition, the amount of carbon dioxide absorbed increases. If the proportion is 25% by mass or less, the amount of molten liquid generated at high temperatures during production of the fired product decreases, broadening the range of possible firing temperatures. In addition, the strength of the carbonated hardened body increases.

The mineral composition of the clinker powder (the proportions of _C2S , _C2AS , and _C3A : mass %) can be quantified by Rietveld analysis by fitting the theoretical profile of each mineral to the powder X-ray diffraction chart (measured profile) of the clinker powder of the present invention, and commercially available analytical software can be used for this quantification.

The content of free lime in the clinker powder is preferably 2% by mass or less, more preferably 0.2 to 1.5% by mass, from the viewpoint of strength development in the carbonation curing step.
Furthermore, the clinker powder may contain other minerals in addition to the above-mentioned minerals such as _C2S . Examples of other minerals include _C4AF ( _{4CaO.Al2O3.Fe2O3} : _ferrite phase), _{C12A7 ( 12CaO.7Al2O3} ), mullite, anorthite, _an amorphous phase, _SiO2 , _cristobalite , rankinite, and wollastonite. These may be contained alone or in combination _of two or more.
The total content of the components other than the above-mentioned C ₂ S, C ₂ AS, and C ₃ A in the clinker powder is preferably 20% by mass or less, more preferably 15% by mass or less, and particularly preferably 10% by mass or less.

The Blaine specific surface area of the clinker powder is preferably 2,500 to 10,000 ^{cm 2} /g, more preferably 3,000 to 9,000 cm ² /g. If the Blaine specific surface area is 2,500 ^{cm 2} /g or more, the effect of reducing carbon dioxide emissions is greater. In addition, the strength of the resulting carbonated hardened body is greater. If the Blaine specific surface area is 10,000 cm ² /g or less, no grinding effort is required, and production costs can be reduced.

The gypsum content in 100% by mass of hydraulic powder material is 1.0 to 6.0% by mass, preferably 1.5 to 5.0% by mass, and more preferably 2.0 to 4.0% by mass, calculated as _SO3 . If the content is less than 1.0% by mass, the usable time before hardening of the hydraulic composition (the time during which good fluidity can be maintained) will decrease. If the content exceeds 5.0% by mass, the strength of the carbonated hardened product will decrease.
The gypsum is not particularly limited, and examples thereof include natural gypsum dihydrate, flue gas desulfurization gypsum, phosphate gypsum, titanic gypsum, and hydrofluoric gypsum. Examples of the form of gypsum include gypsum dihydrate, gypsum hemihydrate, and anhydrous gypsum. These may be used alone or in combination of two or more.

The hydraulic powder material may contain Portland cement clinker powder from the viewpoints of availability and improvement of strength development.
The Portland cement clinker powder is not particularly limited, and various types of Portland cement clinker powder such as ordinary Portland cement clinker, high-early-strength Portland cement clinker, moderate-heat Portland cement clinker, and low-heat Portland cement clinker can be used.
The proportion of Portland cement clinker powder in the hydraulic powder material is preferably 5 to 50% by mass, more preferably 10 to 40% by mass, and particularly preferably 15 to 30% by mass. If the proportion is 5% by mass or more, the strength of the hydraulic composition can be increased. If the proportion is 50% by mass or less, more carbon dioxide can be absorbed during the curing process.
The proportion of clinker powder in the hydraulic powder material is preferably 50 to 95% by mass, more preferably 60 to 90% by mass, and particularly preferably 70 to 85% by mass. If the proportion is 50% by mass or more, more carbon dioxide can be absorbed and fixed in the carbonation curing step. If the proportion is 95% by mass or less, the time for demolding can be shortened, improving the production efficiency of products made from carbonated hardened bodies.

An example of a method for producing a hydraulic powder material includes a clinker firing step of firing a clinker material containing at least one material selected from industrial waste, general waste, and construction waste soil at 1,250 to 1,500°C to obtain clinker, a clinker crushing step of crushing the clinker to obtain clinker powder, and a mixing step of mixing the clinker powder with gypsum to obtain a hydraulic powder material.
Each step will be explained in detail below.
[Clinker burning process]
This process involves calcining a clinker material containing at least one material selected from industrial waste, general waste, and construction waste soil at 1,250 to 1,500°C to obtain clinker.
Here, industrial waste refers to waste generated as a result of business activities (excluding "construction soil," which will be described later). Examples of industrial waste include raw concrete sludge, various sludges (e.g., sewage sludge, water purification sludge, steelmaking sludge, etc.), construction waste, concrete waste, various incineration ashes (e.g., coal ash, chicken manure ash, livestock manure ash, biomass ash, sludge incineration ash), foundry sand, rock wool, waste glass, secondary blast furnace ash, various by-products, and unused resources (unused remaining materials, etc.).
Municipal waste refers to waste other than industrial waste (excluding "construction waste soil" described below). Examples of municipal waste include dried sewage sludge, municipal waste incineration ash, and shells.
Examples of construction waste soil include soil, earth and sand (e.g., waste soil from drilling resulting from excavation of the ground), residual soil, waste soil, and sludge (construction sludge; e.g., a mixture of cement milk and excavated soil resulting from ground improvement work) that are generated secondarily at construction sites and other work sites.

In addition to the above-mentioned industrial wastes, the clinker material for burning may also be made from common raw materials used in the _production of cement clinker, such as calcium-containing raw materials (CaO sources) such as limestone, quicklime, and slaked lime, silicon-containing raw materials ( _{SiO2 sources} ) such as silica stone and clay, aluminum-containing raw materials ( _Al2O3 sources) such as clay, and iron-containing raw materials ( _Fe2O3 sources) such as iron slag and iron cake.
These raw materials are mixed appropriately so that the hydraulic ratio, silica ratio, iron ratio, etc. of the resulting clinker powder fall within desired numerical ranges, thereby obtaining a clinker material for burning.
The firing temperature in this step is 1,250 to 1,500°C, preferably 1,260 to 1,400°C, and more preferably 1,280 to 1,350°C. If the temperature is below 1,260°C, the amount of free lime in the clinker powder increases, resulting in a decrease in the strength development of the hydraulic composition containing the clinker powder. If the temperature exceeds 1,500°C, the energy cost required for firing becomes excessive.
The method for mixing the raw materials is not particularly limited, and examples thereof include methods using conventional equipment. Furthermore, the equipment used for calcination is also not particularly limited, and for example, a rotary kiln can be used. When calcination is performed using a rotary kiln, waste oil, waste tires, waste plastics, and the like may be used as fuel substitute waste materials.

[Clinker crushing process]
This step is a step of pulverizing the clinker to obtain clinker powder. The method for pulverizing the clinker is not particularly limited, and may be a general method using, for example, a ball mill.
[Mixing process]
This process involves mixing clinker powder with gypsum to obtain a hydraulic powder material.
The gypsum may be a pre-pulverized gypsum powder. In addition, in the clinker pulverizing step, the clinker and the gypsum may be pulverized simultaneously. In this case, the clinker pulverizing step also serves as a mixing step.

Furthermore, two or more types of clinker powder may be mixed and used as the clinker powder contained in the hydraulic powder material.
An example of a method for producing clinker powder by mixing two or more types of clinker powder includes a clinker firing step in which each of two or more types of clinker materials for firing is fired at 1,250 to 1,500°C to obtain two or more types of clinker, a clinker crushing step in which two or more types of clinker are crushed to obtain two or more types of clinker powder for mixing, and a mixing step in which two or more types of clinker powder for mixing are mixed to obtain clinker powder.
Each of the two or more types of clinker materials for burning used in the clinker burning process can be obtained by appropriately mixing the above-mentioned raw materials so that the hydraulic ratio, silica ratio, iron ratio, etc. of the clinker powder obtained in the mixing process fall within the desired numerical range.
The calcination temperature is the same as the calcination temperature in the clinker calcination step of the method for producing a hydraulic powder material described above (however, the above temperatures for each of two or more types of clinker materials for calcination may be the same or different from each other).

Next, each of the two or more types of clinker obtained in the clinker burning process is crushed in a clinker crushing process to obtain two or more types of clinker powder for mixing. The two or more types of clinker powder for mixing are then mixed in a mixing process to obtain clinker powder. The mixing ratio of the clinker powder for mixing can be determined appropriately so that the hydraulic ratio, silica ratio, iron ratio, etc. of the clinker powder obtained in the mixing process fall within the desired numerical range.

[(B) Clinker Aggregate]
The clinker aggregate used in the present invention is a clinker aggregate containing _C2S and _C2AS , in which the amount of _C2AS is 5 to 100 parts by mass per 100 parts by mass of _C2S , and which does not contain _C3A or contains _C3A in an amount of 20 parts by mass or less per 100 parts by mass of _C2S .
The amount of C ₂ AS per 100 parts by mass of C ₂ S is preferably 5 to 100 parts by mass, more preferably 6 to 75 parts by mass, more preferably 7 to 50 parts by mass, even more preferably 8 to 40 parts by mass, and particularly preferably 12 to 30 parts by mass. If the amount is 5 parts by mass or more, the amount of free lime (amount of unreacted CaO) is less likely to increase when the firing temperature is increased during firing of the aggregate material, making firing easier. In addition, the amount of carbon dioxide absorption is greater. If the amount is 100 parts by mass or less, the amount of molten liquid generated at high temperatures during production of clinker aggregate is reduced, thereby broadening the range of possible firing temperatures. In addition, since the amount of C ₂ S is relatively large, the strength of the hardened body when demolding in the demolding step described below is increased.

From the viewpoint of improving the fluidity of the hydraulic composition, the clinker aggregate preferably does not contain C ₃ A (3CaO·Al ₂ O ₃ : aluminate phase) or contains C ₃ A in an amount of 20 parts by mass or less per 100 parts by mass of C ₂ S.
When the clinker powder contains _C3A , the amount of _C3A per 100 parts by mass of _C2S is preferably 20 parts by mass or less, preferably 15 parts by mass or less, more preferably 10 parts by mass or less, and particularly preferably 5 parts by mass or less. If the amount exceeds 20 parts by mass, the fluidity of the hydraulic composition decreases.

The proportion of C ₂ S in the clinker aggregate is preferably 50% by mass or more, more preferably 60% by mass or more, and particularly preferably 70% by mass or more, from the viewpoint of increasing the strength of the carbonated hardened body.
Furthermore, the proportion of C ₂ AS in the clinker aggregate is preferably 5 to 25% by mass, more preferably 6 to 20% by mass, and particularly preferably 7 to 15% by mass. If the proportion is 5% by mass or more, the amount of free lime (amount of unreacted CaO) is less likely to increase when the firing temperature is raised during firing of the aggregate material, making firing easier. Also, the amount of carbon dioxide absorbed increases. If the proportion is 25% by mass or less, the strength of the carbonated hardened body increases.
The mineral composition of the clinker aggregate (the proportions of C ₂ S, C ₂ AS, and C ₃ A: mass %) can be calculated in the same manner as for the mineral composition of the clinker powder.

The content of free lime in the clinker aggregate is preferably 2% by mass or less, more preferably 0.2 to 1.5% by mass, from the viewpoint of strength development in the carbonation curing step.
Furthermore, the clinker aggregate may contain other minerals in addition to the above-mentioned minerals such as _C2S . Examples of other minerals include _C4AF ( _{4CaO.Al2O3.Fe2O3} : _ferrite phase), _C12A7 ( _12CaO.7Al2O3 ), _mullite , anorthite, amorphous phase, _SiO2 , _cristobalite , rankinite, and _wollastonite . These may be contained alone or in combination _of two or more.
The total content of the components other than the above-mentioned C ₂ S, C ₂ AS, and C ₃ A in the clinker aggregate is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 5% by mass or less.

Furthermore, it is preferable that the hydraulic rate, silicate rate, and iron rate of the clinker aggregate, and the total content of aluminum oxide (Al ₂ O ₃ ) and iron oxide (Fe ₂ O ₃ ) in 100% by mass of the clinker aggregate, are within the same numerical ranges as the hydraulic rate, silicate rate, and iron rate of the above-mentioned clinker powder, and the total content of aluminum oxide (Al ₂ O ₃ ) and iron oxide (Fe ₂ O ₃ ) in 100% by mass of the clinker powder, for the same reasons.

An example of a method for producing clinker aggregate includes a fired product firing step of firing an aggregate material containing at least one material selected from industrial waste, general waste, and construction waste soil at 1,250 to 1,500°C to obtain a fired product, a fired product crushing step of crushing the fired product to obtain a crushed product, and a classification step of classifying the crushed product to obtain clinker aggregate.
The aggregate material for firing, the firing temperature and the firing method of the material in the firing step are the same as the clinker material for firing, the firing temperature and the firing method of the material in the method for producing a hydraulic powder material described above.
In the classification step, the particle size of the pulverized material is adjusted using a general classification method such as a sieve, and the clinker aggregate can be obtained as coarse aggregate or fine aggregate having a desired particle size distribution.
The clinker obtained in the clinker calcining step of the method for producing the hydraulic powder material described above may be used as the calcined material to be pulverized in the calcined material pulverizing step.

The hydraulic composition may also contain aggregates other than the above-mentioned clinker aggregates.
Examples of fine aggregates other than clinker aggregate include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag, lightweight fine aggregate, and mixtures thereof.
Examples of coarse aggregates other than clinker aggregate include river gravel, mountain gravel, land gravel, crushed stone, slag, lightweight coarse aggregate, and mixtures thereof.
When the hydraulic composition contains coarse aggregate, the fine aggregate ratio is preferably 5 to 70%, more preferably 10 to 60%. If the fine aggregate ratio is within the above range, the workability and ease of molding of the kneaded product are improved.
The amount of aggregate (the total amount when fine aggregate and coarse aggregate are used in combination) is preferably 200 to 700 parts by mass, more preferably 200 to 600 parts by mass, per 100 parts by mass of hydraulic powder material. If the amount is within this range, the strength of the carbonated hardened body will be increased and the shrinkage rate of the carbonated hardened body will be reduced.

The clinker aggregate contained in the hydraulic composition may be contained as fine aggregate or coarse aggregate.
Alternatively, when the hydraulic composition contains coarse aggregate, the clinker aggregate may be contained in at least one of the fine aggregate and the coarse aggregate, but from the viewpoint of immobilizing a larger amount of carbon dioxide, it is preferable that the clinker aggregate be contained in the fine aggregate. Furthermore, when the fine aggregate contains clinker aggregate and aggregate other than clinker aggregate, the proportion of the clinker aggregate in the total amount of fine aggregate is preferably 40% by mass or more, more preferably 50% by mass or more, and particularly preferably 80% by mass or more. If the proportion is 40% by mass or more, a larger amount of carbon dioxide can be immobilized.

[Other ingredients]
The hydraulic composition may contain other materials as needed within the scope of not impairing the object of the present invention. Examples of other materials that may be contained as needed include various admixtures such as air-entraining agents, water-reducing agents, air-entraining water-reducing agents, high-performance water-reducing agents, antifoaming agents, and shrinkage-reducing agents, various admixtures such as fly ash, silica fume, ground granulated blast furnace slag, siliceous admixtures (excluding silica fume), and ground limestone, and fibers such as organic fibers and glass fibers.
The proportion of the other materials in the hydraulic composition varies depending on the type of the other materials, but is, for example, 20% by mass or less, preferably 10% by mass or less.

[(C) Water]
The water used in the present invention is not particularly limited, and examples thereof include tap water and sludge water.
The amount of water to be blended is not particularly limited, and may be any amount commonly used in paste, mortar, or concrete. For example, the amount of water to be blended is such that the mass ratio of water to hydraulic powder material (water/hydraulic powder material) is preferably 0.20 to 0.60, more preferably 0.23 to 0.50, and particularly preferably 0.23 to 0.40. If the ratio is 0.20 or more, workability is further improved. If the ratio is 0.60 or less, the strength development of the hydraulic composition is further improved.

An example of the method for producing a carbonated hardened body of the present invention includes a kneaded mixture preparation step of kneading the above-mentioned materials (A) to (C) to prepare a kneaded mixture of a hydraulic composition; a casting step of casting the kneaded mixture into a formwork; a demolding step of demolding the kneaded mixture in the formwork after it has hardened, from the formwork, a hardened body of the hydraulic composition obtained by the hardening of the kneaded mixture; and a carbonation curing step of carbonating the hardened body of the hydraulic composition demolded from the formwork to obtain a carbonated hardened body.
Each step will be explained in detail below.

[Kneaded material preparation step]
This step is a step of kneading the above-mentioned (A) hydraulic powder material, (B) clinker aggregate, and (C) water to prepare a kneaded product of the hydraulic composition.
The method for kneading the materials is not particularly limited, and the device used for kneading is also not particularly limited, and for example, a conventional mixer such as an omni mixer, a pan mixer, a twin-screw mixer, or a tilting mixer can be used.
[Pouring process]
This step is a step of casting the kneaded material obtained in the previous step into a formwork.
The casting method is not particularly limited, and a conventional method such as pouring can be used.
The curing method used after the kneaded material is poured into the formwork and before it is removed from the formwork is not particularly limited, and general curing methods such as air curing, moist air curing, underwater curing, and steam curing can be used.
[Demolding process]
This step is a step in which, after the kneaded material in the formwork has hardened, the hardened hydraulic composition obtained by the hardening of the kneaded material is removed from the formwork.

[Carbonation curing process]
This step is a step of carbonating and curing the hardened hydraulic composition released from the formwork to obtain a carbonated hardened body by carbonating the hardened hydraulic composition.
The concentration of carbon dioxide gas used for carbonation curing in this step is preferably 1% by volume or more, more preferably 3% by volume or more, even more preferably 10% by volume or more, still more preferably 50% by volume or more, and particularly preferably 60% by volume or more. If the concentration is 1% by volume or more, the amount of carbon dioxide absorbed in the carbonation curing step can be increased.
The upper limit of the carbon dioxide gas concentration is not particularly limited, and the higher the carbon dioxide gas concentration, the more the amount of carbon dioxide absorbed can be increased. However, from the viewpoint of reducing the cost of curing equipment and the like, the upper limit is preferably 90% by volume or less, more preferably 85% by volume or less, and particularly preferably 80% by volume or less.

The temperature in the carbonation curing step is not particularly limited, but is preferably 5 to 100°C, more preferably 10 to 70°C, even more preferably 15 to 50°C, and particularly preferably 20 to 35°C. If the temperature is 5°C or higher, the productivity of the carbonated hardened body is further improved and the strength of the carbonated hardened body is further increased. If the temperature is 100°C or lower, the energy cost for carbonation curing can be reduced.
The relative humidity in this step is not particularly limited, but is preferably 20 to 90%, more preferably 30 to 80%, and particularly preferably 40 to 70%. If the relative humidity is 20% or higher, the productivity of the carbonated hardened body will be improved and the strength of the carbonated hardened body will be greater. It is difficult to increase the relative humidity above 90%, and the costs required for equipment, etc. will be excessive.
The obtained carbonated hardened material can be used as roadbed material, interlocking blocks, fish reefs, wave-dissipating blocks, planting blocks, manholes, pedestrian/vehicle boundary blocks, road gutters, high-strength external pressure pipes, buried formwork, precast panels, floorboards, wall parapets, soundproof walls, etc. Furthermore, even after installation as roadbed material, etc., it can continue to absorb and fix carbon dioxide.

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[Production of fired products 1 and 2]
Limestone, coal ash, construction soil, silica stone, and clay were prepared as raw materials for the fired products, and the prepared raw materials were fired in a small rotary kiln at 1,250°C for 30 minutes to obtain fired products 1 and 2. The chemical composition, mineral composition, hydraulic coefficient, etc. of fired products 1 and 2 are shown in Tables 1 and 2.
[Preparation of hydraulic powder material A]
The fired product 1 and gypsum dihydrate were simultaneously pulverized to produce hydraulic powder material A having a Blaine specific surface area of 6,000 cm ² /g and a gypsum dihydrate ratio of 2.0 mass % in the pulverized product in terms of SO ₃ .
[Preparation of hydraulic powder material B]
The fired product 2 and gypsum dihydrate were simultaneously pulverized to produce hydraulic powder material B having a Blaine specific surface area of 4,000 cm ² /g and a gypsum dihydrate ratio of 2.0 mass % in terms of SO ₃ in the pulverized product.

The materials used other than the above hydraulic powder materials 1 and 2 (a mixture of pulverized calcined material 1 or 2 and gypsum powder) are as follows:
[Materials used]
(1) Ordinary Portland cement; manufactured by Taiheiyo Cement Corporation; Blaine specific surface area: 3,240 cm ² /g; gypsum content: 2.1 mass % (SO ₃ equivalent); density: 3.16 g/cm ³ ; chemical composition, hydraulic hardness, etc. are shown in Tables 1 and 2.
(2) Fine aggregate A; mountain sand, density: 2.56 g/cm ³
(3) Fine aggregate B: obtained by pulverizing the fired product 1, density: 3.21 g/cm ³
(4) Fine aggregate C: obtained by pulverizing the fired material 2, density: 3.21 g/ ^cm3
(5) Coarse aggregate: crushed stone No. 7, density: 2.67 g/cm ³
(6) High-performance water reducer: manufactured by Pozzolith Solutions, trade name: Mastergranium 8000SM
(7) Water: tap water

[Examples 1 to 4]
The types and amounts of hydraulic powder material, fine aggregate, and coarse aggregate shown in Table 3 were added to an Einrich mixer and dry mixed. Next, while mixing the materials, water pre-mixed with a high-performance water-reducing agent was added over 30 seconds, and the mixture was further mixed for 60 seconds to prepare fresh concrete. The amount of high-performance water-reducing agent was set to 0.1 parts by mass per 100 parts by mass of hydraulic powder material. The fine aggregate ratio was 60%.
The resulting fresh concrete was placed in a high-vibration pressure molding machine (Gokosha, GK8-B model) and pressure molded to produce a test specimen. The test specimen dimensions were 200 mm length and 100 mm width, and the target height after molding was set at 80 mm.
Next, the specimen was subjected to moist air curing at a temperature of 20°C for 24 hours and then demolded. After demolding, the specimen, together with the bottom plate, was placed in a thermostatic chamber at 30°C, a relative humidity of 60%, and a carbon dioxide concentration of 80% by volume, and carbonation curing was carried out (shown as "carbonation curing" in Table 4).
The cured specimens (carbonated hardened specimens) were evaluated using the following methods. The results are shown in Table 3.

[Bending strength]
A bending strength test was conducted in accordance with "JIS A 5371:2016 (Precast Unreinforced Concrete Products, Appendix B (Regulations) Pavement and Boundary Blocks, Recommended Specifications B-3 Interlocking Blocks)," and the bending strength of specimens aged 1, 3, and 7 days was measured, starting from the day the form was removed. The loading span during measurement was 160 mm, and the loading rate was adjusted so that the increase in edge stress was 0.8 to 1.0 N/ ^mm2 per minute.
Three specimens were used for each age, and the average value was used as the measured value.

[Fixed carbon dioxide amount]
Seven-day-old specimens were cut perpendicular to the long sides with a concrete cutter and processed into plates about 10 mm thick. The plate-shaped specimens were dried under atmospheric pressure until the surface was dry, then transferred to a vacuum dryer and dried under reduced pressure for at least 24 hours. The entire specimen was then finely pulverized using a vibrating disk mill, after which thermogravimetric analysis was performed using a TG-DTA device. As a result of the analysis, the weight loss observed within the range of 600-800°C was considered to be due to the decarbonation of _CO2 , and the amount of carbon dioxide fixation (kg/ton) was calculated by dividing this by the amount of binder used in the specimen.
The results are shown in Table 4.

[Comparative Example 1]
The demolded specimen, together with its bottom plate, was placed on a metal tray placed in a dryer, filled with water to a depth of about 3 cm, and cured in air by leaving the tray to stand without turning on the dryer (shown as "air curing" in Table 4). Except for this, a cured specimen was obtained in the same manner as in Example 1. Using this specimen, bending strength was measured and the amount of carbon dioxide fixation was calculated in the same manner as in Example 1.
[Comparative Examples 2 to 3]
A cured test specimen was obtained in the same manner as in Example 1. Using the test specimen, bending strength was measured and the amount of fixed carbon dioxide was calculated in the same manner as in Example 1.
[Comparative Example 4]
A cured test specimen was obtained in the same manner as in Comparative Example 1. Using the test specimen, bending strength was measured and the amount of fixed carbon dioxide was calculated in the same manner as in Example 1.
[Comparative Example 5]
A cured specimen was obtained in the same manner as in Example 1. Using the specimen, bending strength was measured in the same manner as in Example 1. The amount of fixed carbon dioxide was not calculated.

Table 4 shows that the flexural strength of the carbonated hardened bodies of Examples 1 to 4 was 3.0 N/mm ² or more (1-day age: 5.0-6.4 N/mm ² , 3-day age: 6.3-8.5 N/mm 2 , 7-day age: 7.1-8.8 N/mm ² ). This shows that the carbonated hardened bodies satisfy the flexural strength (3.0 N/mm ² ) of ordinary block N (mainly used for sidewalks) specified in JIS A 5371: ²⁰¹⁰ (precast unreinforced concrete products) recommended specification B-3 interlocking block. In particular, the flexural strength at 3 and 7 days is greater than the flexural strength at 3 and 7 days of Comparative Examples 1 to 5 (3-day age: 1.6-5.6 N/mm ² , 7-day age: 1.8-6.5 N/mm ² ).
Furthermore, the amount of carbon dioxide fixed in Examples 1 to 4 at an age of 7 days (121 to 152 kg/ton) was greater than the amount of carbon dioxide fixed in Comparative Examples 1 to 4 at an age of 7 days (10 to 83 kg/ton), indicating that the carbonated hardened body absorbed and fixed more carbon dioxide.

Claims (4)

(A) A hydraulic powder material containing clinker powder and gypsum, wherein the clinker powder has a hydraulic modulus (H.M.) of 1.1 to 2.0 , a silicate modulus (S.M.) of 2.4 to 5.2 , and an iron modulus (I.M.) of 2.0 to 4.0, and the gypsum content is 1.0 to 6.0 mass% in terms of _SO3 ;
(B) a clinker aggregate containing _C2S and _C2AS , wherein the amount of _C2AS is 5 to 100 parts by mass relative to 100 parts by mass of _C2S , and the clinker aggregate does not contain _C3A or contains _C3A in an amount of 20 parts by mass or less relative to 100 parts by mass _{of C2S} ;
(C) water;
A carbonated hardened product obtained by carbonating a hardened product of a hydraulic composition comprising the above-mentioned formula (1). A method for producing the carbonated hardened body of claim 1, comprising:
a kneaded mixture preparation step of kneading the materials (A) to (C) to prepare a kneaded mixture of the hydraulic composition;
A casting step of casting the kneaded material into a formwork;
a demolding step of demolding a hardened body of hydraulic composition obtained by hardening the kneaded material in the formwork after the kneaded material in the formwork has hardened from the formwork; and a carbonation curing step of carbonating the hardened body of hydraulic composition demolded from the formwork to obtain a carbonated hardened body of the hardened body of hydraulic composition.
A method for producing a carbonated hardened body, comprising: a clinker calcination step of calcining the calcined clinker material, the hydraulic powder material being one or more selected from industrial waste, general waste, and construction waste soil, at 1,250 to 1,500°C to obtain clinker;
a clinker grinding step of grinding the clinker to obtain the clinker powder;
3. The method for producing a carbonated hardened product according to claim 2, wherein the hydraulic powder material is obtained by a mixing step of mixing the clinker powder with gypsum to obtain the hydraulic powder material. a calcination step of calcining the clinker aggregate, which contains at least one material selected from industrial waste, general waste, and construction waste soil, at 1,250 to 1,500°C to obtain a calcined product;
A pulverization step of pulverizing the sintered product to obtain a pulverized product;
4. The method for producing a carbonated hardened product according to claim 2, wherein the clinker aggregate is obtained by a classification step in which the pulverized material is classified.