JP7752500B2 - 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 is an important issue in order to curb global warming. One method known for reducing carbon dioxide emissions in the production of hardened cementitious materials is to absorb carbon dioxide during the curing process of the hardened cementitious material, thereby reducing the total amount of carbon dioxide emitted up to the time the hardened cementitious material is obtained.
For example, Patent Document 1 describes a precast concrete produced by hardening a concrete mixture containing one or both of γ- _C2S (symbol γ) and steelmaking slag powder (symbol B), and Portland cement (symbol C) as powder components, where the total of γ and B accounts for 25 to 95 mass% of the total content of γ, B, and C, and the water-cement ratio W/C is 80 to 250%, and the precast concrete undergoes _carbonation curing during the hardening process to form a carbonated region at a depth of 20 mm or more from the surface (but across the entire thickness of sections less than 20 mm thick). By utilizing the carbon dioxide absorption by carbonation curing, this precast concrete can significantly reduce the total amount of carbon dioxide emitted during the production of concrete products.

Furthermore, Patent Document 2 describes a cementitious hardened body _obtained by carbonating a hardened body of a cement mix containing: (A) a pulverized fired product containing 10 to 200 parts by mass of _C2AS per 100 parts by mass of _C2S and containing 20 parts by mass or less of C3A, a powdered cement composition containing Portland cement, (B) water, and (C) aggregate. This cementitious hardened body can significantly reduce carbon dioxide emissions by absorbing a large amount of carbon dioxide during the curing process, and, although it contains powdered materials other than Portland cement, can reduce the rate of decrease in compressive strength compared to a case in which all of the powdered materials are Portland cement.

JP 2011-168436 A JP 2016-047788 A

The present invention aims to provide a carbonated hardened body that contains powder materials other than Portland cement (especially those that emit less carbon dioxide during powder production than Portland cement), but that absorbs large amounts of carbon dioxide during the curing process, thereby significantly reducing the total amount of carbon dioxide emitted, has excellent dimensional stability and strength, and is easily reusable as a cement clinker raw material.

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 containing (A) a powdered hydraulic material containing C ₂ S and C ₂ AS and a pulverized product of a fired material that satisfies the following conditions (1) and (2), (B) water, and (C) an aggregate containing limestone aggregate, and have completed the present invention.
(1) When the fired product does not contain _C4AF , the amount of _C2AS is 10 to 2,000 parts by mass relative to 100 parts by mass of _C2S , and when the fired product contains _C4AF , the total amount of _C2AS and _C4AF is 10 to 2,000 parts by mass relative to 100 parts by mass of C2S, and the proportion of _C4AF in the total of _C2AS and _C4AF (100% by mass) is 70% by mass or less. (2 ₎ The fired product 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 . That is, the present invention provides the following [1] to [7].

[1] A carbonated hardened body obtained by carbonating a hardened body of a hydraulic composition including: (A) a powdered hydraulic material containing C ₂ S and C ₂ AS and a pulverized product of a fired material that satisfies the following conditions (1) to (2): (B) water; and (C) an aggregate containing limestone aggregate.
(1) When the burned product does not contain _C4AF , the amount of C2AS relative to ₁₀₀ parts by mass of _C2S is 10 to 2,000 parts by mass, and when the burned product contains _C4AF , the total amount of _C2AS and _C4AF relative to 100 parts by mass of _C2S is 10 to 2,000 parts by mass, and the proportion of _C4AF in the total of 100% by mass of _C2AS and _C4AF is 70% by mass or less. (2) The burned product 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. [2] The carbonated hardened body according to [1] above, wherein the proportion of limestone aggregate in the (C) aggregate is 20% by mass or more.
[3] The carbonated hardened body according to [1] or [2], wherein the powdery hydraulic material (A) contains gypsum powder.

[4] The (A) powdery hydraulic material contains cement, and the (A) powdery hydraulic material has a ratio of 5 to 90% by mass of the pulverized material and a ratio of 10 to 95% by mass of the cement. [1] to [3].
[5] The carbonated hardened body according to [4], wherein the ratio of the pulverized material in the powdered hydraulic material (A) is 40 to 85% by mass, the ratio of the cement is 15 to 60% by mass, and the cement is at least one of ordinary Portland cement and high-early-strength Portland cement.
[6] A method for producing the carbonated hardened body according to any one of [1] to [5] 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.
[7] The method for producing a carbonated hardened body according to [6], comprising a high-strength curing step for increasing the strength of the hardened body of the hydraulic composition between the demolding step and the carbonation curing step.

The carbonated hardened material of the present invention has excellent dimensional stability and strength.
Furthermore, the carbonated hardened material of the present invention can absorb a large amount of carbon dioxide during the curing process, thereby significantly reducing the total amount of carbon dioxide emitted.
Furthermore, since the carbonated hardened product of the present invention uses limestone aggregate as part of the aggregate, when the carbonated hardened product after use is reused as a raw material for cement clinker, separation and removal of aggregate, etc. is not required, and the amount of new raw material can be reduced, making it easy to reuse as a raw material for cement clinker.

The carbonated hardened product of the present invention is obtained by carbonating a hardened product of a hydraulic composition containing: (A) a powdered hydraulic material containing C ₂ S (2CaO·SiO ₂ : belite) and C ₂ AS (2CaO·Al ₂ O ₃ ·SiO ₂ : gehlenite) and a pulverized product of a fired product that satisfies the following conditions (1) and (2): (B) water; and (C) an aggregate containing limestone aggregate.
(1) When the fired product does not contain _C4AF ( _{4CaO.Al2O3.Fe2O3} : _{ferrite phase} ), the amount of C2AS is 10 to 2,000 parts by mass relative to ₁₀₀ parts by mass _{of C2S} , and when the fired product contains _C4AF , the total amount of _C2AS and _C4AF is 10 to 2,000 parts by mass relative to 100 parts by mass of _C2S , and the proportion of _C4AF in the total of _C2AS and _C4AF (100% by mass) is 70% by mass or less. (2) When the fired product does not contain _C3A ( _3CaO.Al2O3 : aluminate phase) or contains _C3A in an amount of 20 parts _by mass or less relative to 100 parts by mass of _C2S. 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.
The present invention will be described in detail below.

[(A) Powdered hydraulic material]
The powdered hydraulic material contains C ₂ S and C ₂ AS and also contains a pulverized product of the fired material that satisfies the above conditions (1) and (2).
Regarding the above condition (1), when the fired product does not contain _C4AF , the total amount of C2AS and _C4AF per ₁₀₀ parts by mass of _C2S is 10 to 2,000 parts by mass, preferably 15 to 1,000 parts by mass, more preferably 20 to 500 parts by mass, even more preferably 23 to 200 parts by mass, even more preferably 25 to 100 parts by mass, even more preferably 25 to 75 parts by mass, even more preferably 25 to 60 parts by mass, and particularly preferably 25 to 50 parts by mass. If the amount is less than 10 parts by mass, the amount of free lime (unreacted CaO) is difficult to reduce even when the firing temperature is increased, making firing difficult. If the amount exceeds 2,000 parts by mass, the amount of melt generated at high temperatures during production of the fired product increases, narrowing the firing temperature range. Furthermore, the relatively small amount of _C2S reduces the strength of the hardened body when demolding in the demolding step described below.

When the fired product contains _C4AF , the total amount of C2AS and _C4AF per ₁₀₀ parts by mass of _C2S is 10 to 2,000 parts by mass, preferably 15 to 1,000 parts by mass, more preferably 20 to 500 parts by mass, even more preferably 23 to 200 parts by mass, even more preferably 23 to 100 parts by mass, even more preferably 23 to 75 parts by mass, and particularly preferably 23 to 60 parts by mass. If the amount is less than 10 parts by mass, the amount of free lime (unreacted CaO) is difficult to reduce even when the firing temperature is increased, making firing difficult. If the amount exceeds 2,000 parts by mass, the amount of melt generated at high temperatures during production of the fired product increases, narrowing the firing temperature range. Furthermore, because the amount of _C2S is relatively small, the strength of the hardened body when demolding in the demolding step described below is reduced, or it takes a long time to demold.
Furthermore, the proportion of _C4AF in the total of 100% by mass of _C2AS and _C4AF is 70% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass or less. If the proportion exceeds 70% by mass, the amount of _C2AS is relatively reduced, so that even if the firing temperature is increased during firing, the amount of free lime (amount of unreacted CaO) is difficult to reduce, making firing difficult.

Regarding the above condition (2), when the fired product contains _C3A , the amount of _C3A per 100 parts by mass of _C2S is 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 before hardening decreases.

The mineral composition of the fired product (the proportions of _C2S , _C2AS , _C4AF , and _C3A in mass%) can be calculated from the proportions (mass%) of CaO, _SiO2 , _Al2O3 , _{and Fe2O3} in the raw materials for the _fired product or in the fired product using the following formula.
C ₂ S=1.02×CaO+0.95×SiO ₂ −1.69×Al ₂ O ₃ −0.36×Fe ₂ O ₃
C ₂ AS=-1.63×CaO+3.04×SiO ₂ +2.69×Al ₂ O ₃ +0.57×Fe ₂ O _3
C4AF = _3.04 × _Fe2O3
C ₃ A = 1.61 × CaO - 3.00 × SiO ₂ - 2.26 × Fe ₂ O ₃ (However, if the value is negative, it is considered to be "0.")

As the raw material for the burned product, it is possible to use ordinary raw materials used in the production of cement clinker, such as calcium-containing raw materials ( _CaO sources) such as limestone, quicklime, slaked lime, etc., silicon _- containing raw materials ( _SiO2 sources) such as silica stone and clay, aluminum-containing raw materials ( _Al2O3 sources) such as clay, iron-containing raw materials ( _Fe2O3 sources) such as iron slag and iron cake, etc. In addition to the above-mentioned raw materials, it is also possible to use one or more selected from industrial waste, general waste, and construction waste soil.
After appropriately mixing the above-mentioned raw materials, the resulting mixture is preferably fired at a firing temperature of 1,000 to 1,450°C (more preferably 1,150 to 1,400°C), thereby obtaining the above-mentioned fired product.
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.

The form of the C ₂ S mineral in the fired product is not particularly limited and may be any of α-type, β-type, and γ-type. However, from the viewpoint of increasing the strength of the hardened body when demolding is performed or performing demolding early in the demolding step described below, it is preferable that the fired product contains at least one of α-type and β-type.
The morphology of the mineral can be measured using powder X-ray diffraction, electron backscatter diffraction (EBSD), or the like.

The proportion of C ₂ S in the fired product 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 fired product 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 amount of free lime (unreacted CaO) is less likely to remain when the firing temperature is increased during firing, making firing easier. Furthermore, the effect of reducing carbon dioxide emissions is greater. If the proportion is 50% by mass or less, the amount of molten liquid generated at high temperatures during production of the fired product is reduced, broadening the range of possible firing temperatures. Furthermore, the strength of the carbonated hardened body is greater.

The proportion of free lime in the burned product 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.
The fired product may contain other minerals in addition to the above-mentioned minerals such as C ₂ S. Examples of other minerals include mullite, anorthite, amorphous phase, quartz, cristobalite, rankinite, and wollastonite. These may be contained alone or in combination of two or more.
The total content of ingredients other than the above-mentioned C ₂ S, C ₂ AS, C ₄ AF, and C ₃ A in the fired product is preferably 20 mass % or less, more preferably 10 mass % or less, and particularly preferably 5 mass % or less.

The Blaine specific surface area of the pulverized product obtained by pulverizing the fired product 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, the energy required for pulverization can be kept low, and production costs can be reduced.

The powdered hydraulic material includes a pulverized product obtained by pulverizing the above-mentioned fired product. The method for pulverizing the fired product is not particularly limited, and examples thereof include a method using a conventional device such as a ball mill.
The powdered hydraulic material may contain gypsum powder from the viewpoint of the fluidity and workability of the hydraulic composition before hardening.
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 powdered hydraulic material may be produced by mixing gypsum powder obtained by crushing a calcined material with a crushed material obtained by crushing a calcined material, or by crushing the calcined material and gypsum simultaneously.
The proportion of gypsum powder in the powdered hydraulic material is preferably 5.0% by mass or less, more preferably 1.0 to 4.0% by mass, calculated as _SO3 . If the proportion is 5.0% by mass or less, the fluidity of the hydraulic composition before hardening is further improved. Note that when the powdered hydraulic material contains cement (described below), the proportion of gypsum powder includes the gypsum powder contained in the cement.

The powdered hydraulic material may contain cement from the viewpoint of strength development and the like.
The cement is not particularly limited, and examples thereof include various types of Portland cement such as ordinary Portland cement, high-early-strength Portland cement, moderate-heat Portland cement, and low-heat Portland cement, as well as ecocement, rapid-hardening cement, and ultra-rapid-hardening cement. These may be used alone or in combination of two or more.
Among these, ordinary Portland cement or high-early-strength Portland cement is preferred from the viewpoint of strength development and cost.

The proportion of the pulverized material in the powdered hydraulic material is preferably 5 to 90% by mass, more preferably 10 to 85% by mass, even more preferably 15 to 80% by mass, even more preferably 20 to 70% by mass, even more preferably 30 to 60% by mass, even more preferably 35 to 55% by mass, and particularly preferably 40 to 50% by mass. If the proportion is 5% by mass or more, the effect of reducing carbon dioxide emissions is greater. In addition, the strength of the resulting carbonated hardened body is increased. If the proportion is 90% by mass or less, the strength of the hardened body when demolded is greater or the demolding time is earlier, improving the production efficiency of products made from the carbonated hardened body.
Furthermore, when the powdered hydraulic material contains cement, the cement content in the powdered hydraulic material is preferably 5 to 95% by mass, more preferably 10 to 90% by mass, even more preferably 15 to 85% by mass, even more preferably 20 to 80% by mass, even more preferably 30 to 70% by mass, even more preferably 35 to 65% by mass, and particularly preferably 40 to 60% by mass. When the content is 5% by mass or more, the demolding time is accelerated, improving the production efficiency of products made from carbonated hardened bodies. When the content is 95% by mass or less, the effect of reducing carbon dioxide emissions is significant. Furthermore, the strength of the resulting carbonated hardened body is increased.

The content of free lime in the powdered hydraulic material 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.
The powdered hydraulic material may contain amines.
Amines are known to react with carbon dioxide to promote the production of carbonate ions, and the inclusion of amines can efficiently promote the carbonation of calcium components.
Amines are compounds having an amino group and a hydroxyl group in the molecule. Examples of amines include monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), diglycolamine (DGA), diisopropanolamine (DIPA), methyldiethanolamine (MDEA), and triisopropanolamine (TIPA). These amines are known as grinding aids.
Furthermore, used amines obtained from a carbon dioxide recovery unit may be used as the amines. In an amine-based carbon dioxide recovery unit for recovering carbon dioxide from exhaust gases from factories, etc., a liquid containing deteriorated amines is usually discarded. However, in the present invention, the waste liquid can be effectively utilized.
The amines may be used as grinding aids.
The amount of amines is preferably 0.002 to 1 part by mass, more preferably 0.01 to 0.1 part by mass, per 100 parts by mass of the powdery hydraulic material, from the viewpoint of accelerating the carbonation of the hardened body and enhancing the strength development in the carbonation curing step.

[(B) Water]
In the hydraulic composition, the mass ratio of water to powdered hydraulic material (water/powdered hydraulic material) is preferably 0.3 to 1.0, more preferably 0.4 to 0.7. If the ratio is 0.3 or more, the effect of reducing carbon dioxide emissions is greater. In addition, the workability of the kneaded product of the hydraulic composition is improved. If the ratio is 1.0 or less, the strength of the carbonated hardened body is greater.

[(C) Aggregate containing limestone aggregate]
The aggregate used in the present invention includes limestone aggregate.
Examples of limestone aggregate include crushed limestone sand, crushed limestone stone, crushed dolomite sand, crushed dolomite stone, and recycled aggregates thereof.
The limestone aggregate may be contained in the fine aggregate, or in at least one of the fine aggregate and the coarse aggregate when the hydraulic composition contains coarse aggregate, but from the viewpoint of dimensional stability, it is preferable that the limestone aggregate be contained in both the fine aggregate and the coarse aggregate.
The proportion of limestone aggregate in the total amount of aggregate contained in the hydraulic composition is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, even more preferably 30% by mass or more, still more preferably 40% by mass or more, and particularly preferably 60% by mass or more. If the proportion is 5% by mass or more, shrinkage of the hardened body during carbonation curing and during the service life of the obtained hardened body can be reduced, and dimensional stability can be further improved.
Furthermore, when the limestone aggregate is a fine aggregate, the proportion of the limestone aggregate in the total amount of fine aggregate is preferably 5% by mass or more, more preferably 10% by mass or more, even more preferably 20% by mass or more, even more preferably 30% by mass or more, still more preferably 40% by mass or more, and particularly preferably 60% by mass or more. If the proportion is 5% by mass or more, shrinkage of the hardened body during carbonation curing and during the service life of the obtained hardened body can be reduced, and dimensional stability can be further improved.

By using limestone aggregate as the aggregate, the amount of shrinkage during carbonation curing and during the service period can be reduced, and dimensional stability can be further improved.
Furthermore, the carbonated hardened product of the present invention can be easily recovered after use and used as a cement clinker raw material.
For example, when only limestone aggregate is used as the aggregate, the carbonated hardened product of the present invention can be recovered after use and used entirely as a cement clinker raw material. In this case, cement clinker can be produced by simply adding a small amount of new raw material.

The aggregate may include aggregates other than limestone aggregate.
Examples of fine aggregates other than limestone aggregate include river sand, mountain sand, land sand, sea sand, crushed sand, silica sand, slag, recycled sand, lightweight fine aggregate, and mixtures thereof.
Examples of coarse aggregates other than limestone aggregate include river gravel, mountain gravel, land gravel, crushed stone, slag, recycled coarse aggregate, lightweight coarse aggregate, and mixtures thereof.
The amount of fine particles of limestone aggregate used as fine aggregate is preferably 15% by mass or less, more preferably 2 to 10% by mass, from the viewpoint of the fluidity of the hydraulic composition before hardening.
The amount of fine particles in the entire fine aggregate is preferably 10% by mass or less, more preferably 1 to 8% by mass, from the viewpoint of the fluidity of the hydraulic composition before hardening.

When the hydraulic composition contains coarse aggregate, the fine aggregate ratio is preferably 5 to 60%. If the fine aggregate ratio is within this 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 the powdered hydraulic material. When the amount is within the above range, the strength of the carbonated hardened body is increased and the shrinkage rate of the carbonated hardened body is reduced.
The coarseness ratio when the fine aggregate and the coarse aggregate are combined is preferably 1.0 to 7.0, more preferably 1.5 to 6.5.

[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 added as needed include various additives such as water-reducing agents, antifoaming agents, and shrinkage-reducing agents, and various admixtures such as fly ash, silica fume, ground granulated blast furnace slag, and ground limestone.
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.

[Method of manufacturing carbonated hardened body]
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 (A) powdered hydraulic material, (B) water, and (C) aggregate materials including limestone aggregate to prepare a kneaded mixture of a 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.
Each step will be explained in detail below.

[Kneaded material preparation step]
This step is a step of kneading the above-mentioned (A) powdery hydraulic material, (B) water, and (C) aggregate materials including limestone aggregate 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.
In this step, the components (A) to (C) may be kneaded with the amines.
[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.

[High strength curing process]
This step is optionally performed between the demolding step and the carbonation curing step, and is a step for increasing the strength of the hardened product of the hydraulic composition.
In this step, the hardened hydraulic composition released from the formwork is cured until its compressive strength reaches preferably 3 N/ ^mm2 or more, more preferably 5 N/ ^mm2 or more, and particularly preferably 10 N/ ^mm2 or more, thereby increasing the strength of the carbonated hardened body after carbonation curing (for example, the compressive strength of mortar or concrete).
The curing method is not particularly limited, and general curing methods such as air curing, moist air curing, underwater curing, and steam curing can be used. Note that the "curing" in the high-strength curing step does not include carbonation curing.

[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 concentration of carbon dioxide gas is not particularly limited, and the higher the concentration of carbon dioxide gas, 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 70% by volume or less, and particularly preferably 50% 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 50°C, and particularly preferably 15 to 35°C.
If the temperature during carbonation curing is within the above range, the productivity of products made from the carbonated hardened body can be improved, and the strength of the carbonated hardened body can be increased.
Furthermore, the carbonated hardened product of the present invention is highly effective in reducing carbon dioxide emissions even when carbonation curing is carried out at a relatively low temperature (for example, 5 to 30°C).
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.

In the carbonation curing step, it is preferable to carry out carbonation curing so that the carbonation depth from the surface of the carbonated hardened body is preferably 2 mm or more, more preferably 3 mm or more, even more preferably 4 mm or more, and particularly preferably 5 mm or more. By carrying out carbonation curing so that the carbonation depth is 2 mm or more, it is possible to allow the carbonated hardened body to absorb a larger amount of carbon dioxide. Specifically, the carbonation depth can be made 2 mm or more by appropriately adjusting the carbon dioxide gas concentration, temperature, and relative humidity values, as well as the curing time, in the carbonation curing step described above.
From the viewpoint of absorbing carbon dioxide in a short time, it is preferable to carry out carbonation curing so that the carbonation depth is 2 mm or more, preferably at an age of 1 day, more preferably at an age of 3 days.
The "carbonation depth from the surface of the carbonated hardened body" can be measured in accordance with "JIS A 1152:2018 (Method for measuring carbonation depth of concrete)".
The obtained carbonated hardened material can be used as a roadbed material, interlocking blocks, etc. Furthermore, even after being installed as a roadbed material, etc., it can continue to absorb and fix carbon dioxide.

In the present invention, the carbonated hardened product obtained by the above manufacturing method preferably emits at least 15% less carbon dioxide (more preferably at least 20%, even more preferably at least 30%, and particularly preferably at least 40%) during production than when the same Portland cement as that contained in the powdered cement composition is used instead of the pulverized burned product, and the strength (e.g., compressive strength) of the carbonated hardened product preferably decreases by no more than 50% (more preferably no more than 40%).

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.
[Preparation of powdered material A containing pulverized fired product]
Limestone, coal ash, construction waste soil, silica stone, and clay were used as raw materials for the calcined product. The raw material composition was adjusted so that the amount of _C2AS was 25 parts by mass, the amount of _C4AF was 10 parts by mass, and the amount of _C3A was 0 parts by mass per 100 parts by mass _of C2S in the resulting calcined product. The prepared raw materials were calcined using a small rotary kiln to obtain calcined product α1. The proportion of _C2S in the calcined product was 74.2% by mass, and the proportion of _C2AS was 18.8% by mass. The chemical composition and hydraulic ratio of calcined product α1 are shown in Tables 1 and 2.
The obtained calcined product α1 and gypsum dihydrate were simultaneously ground to produce powdered material A containing a ground calcined product having a Blaine specific surface area of 6,000 cm ² /g, a gypsum dihydrate content of 2.0 mass% in terms of SO ₃ , and a free lime content of 0.04 mass%.
During the grinding, triethanolamine was added as a grinding aid in an amount equivalent to 400 ppm by mass.

[Preparation of powdered material B containing pulverized fired product]
The raw materials for the calcined product were limestone, coal ash, construction waste soil, silica stone, and clay. The raw material composition was adjusted so that _the resulting calcined product contained 40 parts by mass of _C2AS , 16 parts by mass of _C4AF , and 0 parts by mass of _C3A per 100 parts by mass of _C2S . The resulting raw materials were then calcined in a small rotary kiln to obtain calcined product α2. The calcined product contained 66.8% by mass of C2S and 26.9% by mass of _C2AS . The chemical composition and hydraulic ratio of calcined product α2 are shown in Tables 1 and 2.
The obtained calcined product α2 and gypsum dihydrate were simultaneously ground to produce powdered material B containing a ground calcined product having a Blaine specific surface area of 4,700 cm ² /g, a gypsum dihydrate content of 3.0 mass% in terms of SO ₃ , and a free lime content of 0.5 mass%.
During the grinding, a grinding aid (triethanolamine) was added in an amount equivalent to 400 ppm by mass.

The materials used other than the above powder materials A to B (a mixture of pulverized calcined material 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 (containing gypsum hemihydrate and gypsum dihydrate in a mass ratio of 62:38): 2.1 mass% (SO ₃ equivalent), grinding aid (triethanolamine): 400 ppm (mass equivalent), free lime: 0.4 mass%
(2) Fine aggregate A: crushed limestone sand, manufactured by Buko Mining Co., Ltd., bone dry density: 2.64 g/cm ³ , water absorption: 1.0%, FM 3.25, fine particle content: 5.4 mass%
(3) Fine aggregate B: mountain sand, manufactured by Abekawa Development Co., Ltd., bone dry density 2.54 g/cm ³ , water absorption rate: 2.1%, FM 3.25, fine particle content: 5.4 mass%
(4) Water: Tap water

[Examples 1 to 4, Comparative Example 1]
Powdered material A and ordinary Portland cement were mixed in a mixing ratio such that the ratio of powdered material A was 75 mass % and the ratio of ordinary Portland cement was 25 mass % in 100 mass % of a powdered hydraulic material obtained by mixing powdered material A and ordinary Portland cement, thereby obtaining a powdered hydraulic material.
The powdered hydraulic material and fine aggregate obtained by mixing crushed limestone sand and pit sand so that the blending ratios of crushed limestone sand and pit sand in 100% by mass of fine aggregate were shown in Table 3 were charged into a Hobart mixer in an amount of 225 parts by mass per 100 parts by mass of the powdered hydraulic material, and then dry-mixed to obtain a mixture. The obtained mixture was kneaded with water in an amount such that the mass ratio of water to the mixture (water/the mixture) was 0.5 to prepare mortar (a kneaded product of the hydraulic composition).
The obtained mortar was filled into a 4 x 4 x 16 cm formwork, and then subjected to moist air curing at a temperature of 20°C for 24 hours, followed by demolding. The demolded hardened mortar was then subjected to underwater curing at a temperature of 20°C until the material was 28 days old. After removing the hardened mortar from the water, it was left to stand in an accelerated carbonation tank at a temperature of 20°C and a relative humidity of 60°C until the material was 56 days old, whereby carbonation curing was performed.
The concentration of carbon dioxide gas in the carbonation curing was 5% by volume.

[Calculation of shrinkage strain ratio]
At the age of 28 days, the length of the hardened mortar was measured immediately after it was removed from the water, and this length was determined as the base length. Next, the length of the hardened mortar was measured immediately after the completion of carbonation curing, and the amount of shrinkage strain of the hardened mortar was calculated by subtracting this length from the base length.
The length of the hardened mortar was measured using a contact gauge in accordance with "JIS A 1129-2:2010 (Method for measuring change in length of mortar and concrete - Part 2: Contact gauge method)".
The shrinkage strain ratio of the hardened mortar was calculated using the following formula, assuming that the shrinkage strain amount in Comparative Example 1 described below was 100%. Note that a smaller shrinkage strain ratio indicates better dimensional stability.
Shrinkage strain ratio = shrinkage strain of hardened mortar / shrinkage strain of Comparative Example 1 × 100%
In addition, the compressive strength of the mortar was measured using the hardened mortar after carbonation curing in accordance with "JIS R 5201:2015 (Physical testing methods for cement)."
The compressive strength ratio (%) was then calculated using the following formula:
Compressive strength ratio (%) = compressive strength after carbonation curing of Example / compressive strength after carbonation curing of Comparative Example × 100
The results are shown in Table 3.

[Example 2]
A hardened mortar was obtained in the same manner as in Experimental Example 1, except that powdered material B was used instead of powdered material A, and the proportion of powdered material B was 50% by mass and the proportion of ordinary Portland cement was 50% by mass out of 100% by mass of powdered hydraulic material obtained by mixing powdered material A and ordinary Portland cement.
The shrinkage strain ratio and compressive strength ratio of the obtained hardened mortar were calculated in the same manner as in Experimental Example 1. The results are shown in Table 4.

From Table 3, it can be seen that the shrinkage strain ratios of Examples 1 to 4 (56 to 96%) are smaller than the shrinkage strain ratio of Comparative Example 1 (100%), and the amount of shrinkage strain after carbonation curing is small.
Furthermore, the compressive strength ratios of Examples 1 to 4 (102 to 107%) are greater than the compressive strength ratio of Comparative Example 1 (100%), indicating that they are superior in strength.
From Table 4, it can be seen that the shrinkage strain ratios of Examples 5 and 6 (60 to 81%) are smaller than the shrinkage strain ratio of Comparative Example 2 (100%), and the amount of shrinkage strain after carbonation curing is small.
Furthermore, the compressive strength ratios of Examples 5 and 6 (101 to 104%) are greater than the compressive strength ratio of Comparative Example 2 (100%), demonstrating that they are superior in strength.

Claims (5)

A carbonated hardened body obtained by carbonating a hardened body of a hydraulic composition comprising (A) a powdered hydraulic material containing cement and a pulverized product of a fired material containing C ₂ S and C ₂ AS and satisfying the following conditions (1) and (2): (B) water; and (C) an aggregate containing limestone aggregate,
The proportion of the pulverized material in the (A) powdery hydraulic material is 40 to 85% by mass, the proportion of the cement is 15 to 60% by mass, and the cement is at least one of ordinary Portland cement and high-early-strength Portland cement,
A carbonated hardened body characterized in that the proportion of the limestone aggregate in the aggregate (C) is 100 mass% .
(1) When the fired product does not contain _C4AF , the amount of _C2AS is 10 to 100 parts by mass relative to 100 parts by mass of _C2S , and when the fired product contains _C4AF , the total amount of _C2AS and _C4AF is 10 to 100 parts by mass relative to 100 parts by mass of C2S, and the proportion of _C4AF in the total of 100% by mass of _C2AS and _C4AF is 70% by mass or less. ( ₂ ) The fired product 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. The carbonated hardened body according to claim 1 , wherein the powdery hydraulic material (A) contains gypsum powder. The powdery hydraulic material (A) contains an amine,
2. The carbonated hardened material according to claim 1, wherein the amount of the amines is 0.002 to 1 part by mass per 100 parts by mass of the powdery hydraulic material (A). A method for producing the carbonated hardened body according to any one of claims 1 to 3 , 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 the hydraulic composition obtained by hardening the kneaded material in the formwork after the kneaded material in the formwork has hardened;
a carbonation curing step of carbonating the set body of the hydraulic composition released from the form to obtain a carbonated set body of the hydraulic composition;
A method for producing a carbonated hardened body, comprising: The method for producing a carbonated hardened body according to claim 4 , further comprising a high-strength curing step for increasing strength of the hardened body of the hydraulic composition between the demolding step and the carbonation curing step.