JP4643374B2 - Concrete composition for forming carbon dioxide fixed molded body, carbon dioxide fixed molded body comprising the composition, and method for producing the same - Google Patents

Description

  The present invention relates to a concrete composition useful for forming a carbon dioxide-fixed molded body that efficiently fixes carbon dioxide in the atmosphere, carbon dioxide fixation obtained thereby, and a method for producing the molded body, The molded body is useful for civil engineering and building structures.

Japan's carbon dioxide emissions amount to about 1,250 million tons per year, accounting for about 5.1% of the world. Our target for reducing CO2 emissions in the 1997 Kyoto Protocol is 6% reduction compared to 1990, but the current measure is expected to increase 7%, and the global warming established in the Cabinet There is a need to implement effective measures as soon as possible in related fields centered on the headquarters for the promotion of industrialization.
On the other hand, “strengthening innovative technology development” is one of the pillars of carbon dioxide suppression measures, and it stores and immobilizes once released carbon dioxide, along with technologies such as energy saving and solar power generation. The development of technology is raised. As specific research subjects, marine organisms such as plankton, utilization technologies such as trees, electrochemical techniques, and technologies such as underground sequestration have been proposed, but how efficiently carbon dioxide is fixed at low cost. Kaga is in the process of research as a future issue.

  Cement concrete used for civil engineering and building structures is gradually cured in the process where calcium hydroxide and calcium silicate hydrate, the main chemical component, react with carbon dioxide in the atmosphere to generate calcium carbonate. Loss of alkalinity, so-called carbonation / neutralization. Since carbonation / neutralization phenomenon leads to rusting of reinforcing steel in concrete, many techniques for suppressing carbonation have been studied. On the contrary, the present invention proposes a technique for positively fixing carbon dioxide to a cement concrete molded body by utilizing this reaction.

In the general carbonation reaction of concrete, various cement hydrates react with carbon dioxide in the atmosphere to generate CaCO ₃ , decompose calcium silicate hydrate, and the like. The fastest reaction with CO _{2 in} cement hydrate is Ca (OH) ₂ , and the calcium hydroxide contained in the hardened cement hydrate reacts with carbon dioxide that has penetrated into the concrete from the atmosphere and carbonation. It can be represented by the following reaction formula that produces calcium.
Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O
By the above reaction, carbon dioxide in the atmosphere is fixed in the concrete as calcium carbonate, and carbon dioxide in the atmosphere is reduced by immobilization on the concrete molding. Since calcium carbonate in concrete exists as a stable reactant and is extremely difficult to decompose, carbon dioxide remains fixed in the concrete as it is. Such a reaction usually occurs and proceeds when carbon dioxide in the atmosphere gradually permeates and diffuses into the concrete molding and comes into contact with calcium hydroxide contained in the cement hydrate.

Conventionally, a concrete molded body generally used is expressed by the above formula because the microstructure of the concrete is dense, the diffusion coefficient of gas is small, and the penetration rate of carbon dioxide in the atmosphere is extremely slow. Such carbonation progresses very slowly, and it can be said that the characteristic of fixing carbon dioxide in the atmosphere is extremely weak. For example, in general civil engineering concrete, it takes about 50 years for the carbonation reaction to proceed from the surface layer to a depth of about 20 mm, and the amount of carbon dioxide fixed in the concrete is also limited. .
On the other hand, various porous concretes have been proposed for the purpose of imparting water permeability and air permeability to a concrete molded body or preventing explosion.

  For example, a method of entraining a large amount of air into the concrete, such as lightweight cellular concrete so-called ALC concrete, a method of mixing void forming material into the concrete composition, and shrinking or decomposing the void material after curing (for example, Patent Document 1) has been proposed. In this method, since the volume of voids formed is large, there is a drawback that mechanical properties such as compressive strength and bending strength of concrete are greatly impaired, and because the void area is large, the concrete surface area useful for adsorption of carbon dioxide. Is not sufficiently obtained, and carbon dioxide has not been effectively immobilized.

In addition, as a technique for actively adsorbing and fixing carbon dioxide, saturated lime water or a concentrated calcium hydroxide aqueous solution having a pH of about 9.5 or more is brought into contact with the air while being circulated and sprinkled. Although a method for collecting and absorbing carbon dioxide in the air has been proposed (see, for example, Patent Document 2), it is necessary to bring a strong alkaline aqueous solution into contact with air over a wide surface area. There are safety issues. Further, carbon dioxide or carbon dioxide-containing gas is mixed with alkali metal oxides (CaO, Na ₂ O, K ₂ O, etc.), alkaline earth metal oxides (MgO, etc.), coal containing heavy metal oxides, garbage A technique has been proposed in which carbon dioxide is carbonated by being reacted with combustion ash such as biomass, construction waste materials, etc., and fixed as carbonate (CaCO ₃ ) (see, for example, Patent Document 3). Then, a combustion furnace for pressurization and heating is necessary, and there is a problem that it is difficult to say that it is an efficient treatment method in consideration of necessary facilities and energy. Furthermore, in this method, it is necessary to guide the gas containing carbon dioxide into the apparatus. Therefore, under the conditions of use as civil engineering / building structures, etc., a sufficient carbon dioxide fixing function cannot be expressed. There was a problem.
JP 2003-277164 A JP-A-10-230131 JP-A-11-192416

The object of the present invention made in consideration of the above problems is to fix carbon dioxide having properties capable of effectively fixing carbon dioxide in the atmosphere without impairing the original mechanical properties such as compressive strength and bending strength of concrete. An object of the present invention is to provide a concrete composition for forming a molded article.
Another object of the present invention is to provide a carbon dioxide-immobilized molded body produced using such a concrete composition for forming a carbon dioxide-immobilized molded body, and production for efficiently obtaining the carbon dioxide-immobilized molded body. It is to provide a method.

The present inventors include an organic material capable of forming a void for making carbon dioxide in the atmosphere significantly permeate into the cement concrete composition, and specific fine particles for positively fixing carbon dioxide. It has been found that the above-mentioned problems can be solved by containing the present invention, and the present invention has been completed.
That is, the concrete composition for forming a carbon dioxide-fixed molded body of the present invention is a monomer selected from water, cement, admixture, aggregate, polylactic acid, polyglycolic acid, poly-3-hydroxybutyrate, or polycaprolactone. Containing an organic fiber composed of alkali-decomposable resin fine particles or alkali-decomposable resin, which is a homopolymerized aliphatic polyester resin containing a structural unit formed from an amount satisfying the following condition (A), and having a brain specific surface area of 3000 cm ² / g or more of a calcium oxide fine powder in an amount satisfying the following condition (B) , and by hardening the concrete composition, the surface layer portion has a void of 10 μm to 200 μm in diameter or It is possible to obtain a molded body provided with 0.05% by volume to 10% by volume of hollow holes having the same diameter cross section. And
Condition (A): Fine particles or organic fibers made of the alkali-decomposable resin are contained in an amount of 0.02 to 1.0% by volume based on the total amount of the concrete composition.
Condition (B): Calcium oxide fine powder having a Blaine specific surface area of 3000 cm ² / g or more is contained in the concrete composition in a range of 0.5% by volume to 2.0% by volume.

Examples of the fine powder of calcium oxide (CaO) contained in the concrete composition include fine powder of quick lime and lime-based expansion material. As such a fine powder, one containing CaO and having a brain specific surface area of 3000 cm ² / g or more is preferably mentioned. When such a fine powder is used, the content thereof is It is preferable that it is the range of 5-30 mass% with respect to content.
In such a concrete composition, the weight ratio of water and cement (binding material) is preferably 30% or more and 70% or less.

The carbon dioxide-immobilized molded body according to claim 4 of the present invention is formed from a monomer selected from water, cement, admixture, aggregate, polylactic acid, polyglycolic acid, poly-3-hydroxybutyrate or polycaprolactone. The organic fiber made of alkali decomposable resin fine particles or alkali decomposable resin, which is a homopolymerized aliphatic polyester resin containing a structural unit, is contained in an amount satisfying the following condition (A), and has a brain specific surface area of 3000 cm ² / 0 g of voids having a diameter of 10 μm to 200 μm or having a cross section of the same diameter are formed in the surface layer portion obtained by curing a concrete composition containing calcium oxide fine powder of g or more in an amount satisfying the following condition (B). 0.05 volume% to 10 volume% is provided.
Condition (A): Fine particles or organic fibers made of the alkali-decomposable resin are contained in an amount of 0.02 to 1.0% by volume based on the total amount of the concrete composition.
Condition (B): Calcium oxide fine powder having a Blaine specific surface area of 3000 cm ² / g or more is contained in the concrete composition in a range of 0.5% by volume to 2.0% by volume.
Region having a void of the carbon dioxide immobilization molded article, the range of 0~100mm in the depth direction from the surface of the concrete molded body, i.e., be present in the range of a depth of 100mm from the region exposed at least on the surface preferable.
Moreover, the method for producing a carbon dioxide-fixed molded body according to claim 6 of the present invention includes kneading, molding and curing any of the carbon dioxide-fixed molded body-forming concrete compositions of the present invention, Resin fine particles contained in the concrete composition or organic fibers made of resin are decomposed by alkali to form a surface layer portion having voids useful for fixing carbon dioxide.

  Carbonation of cement mortar and concrete is a reaction in which calcium hydroxide generated in the pores of cement hydrate by the hydration reaction of cement reacts with carbon dioxide that has penetrated into the concrete from the atmosphere to form calcium carbonate. Caused by. Since calcium carbonate is a chemically stable compound and is not easily decomposed in concrete under normal environmental conditions, carbon dioxide that has penetrated into the concrete is fixed in the concrete as calcium carbonate.

Although the operation of the present invention is not clear, it is estimated as follows. According to the concrete composition of the present invention, a large number of fine voids are formed in the surface layer portion of mortar and concrete by the alkali treatment after curing, and the air permeability from the concrete surface to the deep portion is improved.
Immobilization of carbon dioxide in the concrete proceeds according to the following reaction formula (1) as described above.
Ca (OH) ₂ + CO ₂ → CaCO ₃ + H ₂ O (1)
Here, when calcium oxide fine powder is added to the concrete composition, a reaction as represented by the following reaction formula (2) proceeds, so that in the fine voids, Ca ( OH) ₂ is produced. Therefore, it is presumed that the fixation of carbon dioxide gas by the reaction formula (1) is promoted.
CaO + H ₂ O → Ca (OH) ₂ + Q (2)

The ability to fix carbon dioxide by the carbonation reaction of cement hydrate inherent in concrete by generating Ca (OH) _{2 from} CaO exposed not only on the surface of the concrete compact but also on the surface of the formed void. Is carried out more efficiently, and carbon dioxide in the air can be effectively immobilized.
In the voids in the present invention, the volume of each void is fine, and there is no concern that the mechanical properties such as the compressive strength inherent in the concrete molded body will be greatly reduced. In addition, even if such voids are not necessarily present in the entire molded body, at least only in the surface layer portion of the molded body that easily comes into contact with carbon dioxide, the effect of the present invention can be obtained. By making this exist, it is possible to further suppress the decrease in strength.

  In the carbon dioxide-fixed molded article of the present invention, a void having a diameter of 10 μm to 200 μm or a hollow hole having a cross section of the same diameter is provided in the concrete in an amount of 0.05% to 10% with respect to the concrete volume in the surface layer portion. The presence of such fine voids can increase the amount of carbon dioxide permeated and immobilized without significantly reducing the amount of cement in the concrete and without damaging the mechanical properties of the concrete. It has become possible.

According to the present invention, a concrete composition for forming a carbon dioxide-fixed molded body having properties capable of effectively fixing carbon dioxide in the atmosphere without impairing the original mechanical properties such as compressive strength and bending strength of the concrete. Can be provided.
Moreover, according to the present invention, by using the above-described concrete composition for forming a carbon dioxide-fixed molded body, a carbon dioxide-fixed molded body having excellent strength and carbon dioxide-fixing ability can be provided. According to the production method of the present invention, the carbon dioxide-immobilized molded body of the present invention can be obtained efficiently.

  The concrete composition for forming a carbon dioxide-fixed molded body of the present invention comprises water, cement, an admixture, an aggregate, an organic fiber composed of alkali-decomposable resin fine particles or alkali-decomposable resin, and calcium oxide (CaO) fine powder. It is characterized by containing. By curing such a concrete composition, a molded body is obtained in which 0.05% to 10% by volume of voids having a diameter of 10 μm to 200 μm or hollow holes having a cross section of the same diameter are provided in the surface layer portion.

There is no restriction | limiting in particular in the cement used for the concrete composition of this invention, According to the use of the cement-type molded object formed, it can select suitably from various cements. As the cement, ordinary Portland cement, moderately hot Portland cement, low heat Portland cement, blast furnace cement, fly ash cement, and the like can be used.
There is no restriction | limiting in particular as said admixture, According to the use of the cement-type molded object formed, a kind and usage-amount can be suitably selected from various cement and the admixture for concrete. As the admixture, blast furnace slag fine powder, fly ash, silica fume and the like can be generally used.
Moreover, there is no restriction | limiting in particular in the kind and quantity of aggregate, According to the use of the molded object formed, the kind and mixing ratio of aggregate can be selected suitably.

The concrete composition of the present invention contains organic fibers composed of alkali-decomposable resin fine particles or alkali-decomposable resin in order to form suitable voids as described in detail below. The alkali-decomposable resin used as the raw material for the fine particles or organic fibers is not particularly limited as long as it has the property of being decomposed and reduced or extinguished in an alkaline atmosphere, but fat that hydrolyzes quickly with alkali. family polyesters, biodegradable trees such as polyacrylic acid butter, and the like preferably.
That is, the aliphatic polyester has sufficiently high fiber strength and good handleability before being mixed into the concrete composition. However , the aliphatic polyester is mixed into the concrete composition and cured to obtain a cement-based molded body. When formed, it is particularly preferable from the viewpoint that the resin constituting the fiber is hydrolyzed and reduced in molecular weight, gasified, and forms good voids in the molded body by being exposed to an alkaline atmosphere.

First, an aliphatic polyester resin will be described as an example of the resin having hydrolyzability in such an alkaline atmosphere.
The aliphatic polyester resin used in the present invention may be either a homopolymer resin or a copolymer resin, but is preferably a homopolymer resin obtained by self-condensation polymerization and / or ring-opening polymerization. As such a homopolymerized aliphatic polyester resin, various known resins can be used, and more specifically, selected from the group consisting of polylactic acid, polyglycolic acid, poly-3-hydroxybutyrate and polycaprolactone. At least one is preferred.
Any of the above exemplified homopolymerized aliphatic polyester resins is known as a biodegradable resin, but is preferably used in the present invention because it is easily hydrolyzed and reduced in molecular weight under an alkaline atmosphere.

Further, in the present invention, a copolymerized aliphatic polyester resin having two or more structural units of each resin in a polymer molecule, or a copolymerized aliphatic polyester resin having a structural unit of each resin and other structural units. Can also be used.
Among these resins, polylactic acid using lactic acid obtained by fermentation as a raw material is particularly preferable from the viewpoints of economy, carbon neutrality, and effects.
In the present invention, these aliphatic polyester resins may be used singly or in combination of two or more kinds as resin fine particles and organic fiber materials.

In the case of forming voids, the aliphatic polyester resin is used after being formed into a fiber shape or a fine particle shape by a known method such as emulsion polymerization, granulation or spinning. In the case of forming into an organic fiber, the spinning method is not particularly limited, and an arbitrary method can be appropriately selected from known methods conventionally used in spinning thermoplastic resins. Moreover, you may extend | stretch a spinning fiber by a well-known method as needed. A resin molded into a fiber form is preferable because it forms a long and narrow continuous void inside the concrete, so that the effect of the present invention is improved as compared with an indeterminate or fine particle resin.
In addition, the aliphatic polyester resin has other properties within the range in which the object of the present invention is not impaired in order to improve moldability, spinnability, and physical properties other than alkali hydrolyzability in the case of fibers. These thermoplastic resins such as polyethylene, polypropylene, polyvinyl alcohol, polyacetal, aromatic polyester, polystyrene, polyamide, etc. may be used in combination, and known additives such as plasticizers may be added as appropriate.

The organic fiber for a cement-based molded body of the present invention made of such a material has hydrolyzability in an alkaline atmosphere. Therefore, when mixed with a cement compound to form a cement-based molded body, The resin constituting the fiber is hydrolyzed by exposure to an alkali atmosphere inherent in cement hydrate. For example, when polylactic acid fibers are used, the volume is reduced and voids are formed by leaving the cement hydrate for a certain period, specifically, 9 weeks or more.
When blending an aliphatic polyester resin into a concrete composition, from the viewpoint of effects, the fine particles preferably have an average particle size in the range of 10 to 500 μm, more preferably 20 to 200 μm.

The organic fibers preferably have a diameter of 5 to 100 μm and a length of 50 μm to 500 mm, more preferably a diameter of 10 to 50 μm and a length of 1 to 15 mm, and still more preferably a length of 5 to 10 mm. It is.
The particle diameter of the fine particles and the shape of the organic fiber can be measured by a conventional method using an image taken with an electron microscope or a high magnification optical microscope.
The amount of resin fine particles or organic fibers in the concrete composition is in the range of 0.02 to 1.0% by volume with respect to the total amount of the concrete composition, considering the carbon dioxide fixing ability and the strength of the structure. required that this is, more preferably 0.05 to 0.5 vol%, more preferably from 0.1 to 0.3% by volume.

The concrete composition of the present invention further contains calcium oxide (CaO) fine powder.
As the CaO fine powder that can be used in the present invention, one containing CaO and having a Blaine specific surface area of 3000 cm ² / g or more is used.
As the fine powder mainly composed of CaO, a powder obtained by pulverizing quick lime, a lime-based expansion material, or the like into a fine powder having a Blaine specific surface area of 3000 cm ² / g or more can be used. Such a fine powder can be used as an admixture as well as a lime-based admixture.
Blaine specific surface area of fine powder required to be at 3000 cm ² / g or more, and more preferably in the range of 3000~4000cm ² / g. In addition, the brane specific surface area of the fine powder can be measured by a brane method described in JIS R 5201 or by a method using a laser diffraction particle size meter.

The CaO fine powder is preferably contained in the concrete composition in the range of 0.5 % by volume to 2.0% by volume. In this range, excellent carbon dioxide adsorbing ability is expressed, and the mechanical properties of the molded body are improved. Also excellent. If the content is too high, excessive volume increase of the product due to the hydration reaction will cause cracks and deformation in the resulting concrete molded body, and mechanical properties such as compressive strength and elastic modulus will decrease, resulting in the function of the structure. There is a risk of damage.

In addition to the above essential components, various additives that are usually blended in cementitious compositions such as water reducing agents, air entraining agents, antifoaming agents, and the like can be blended in the concrete composition of the present invention as appropriate.
The weight ratio of water and cement in the concrete composition can be appropriately selected according to the use of the molded body made of the concrete composition to be formed, but in order to promote the carbonation reaction with carbon dioxide in the atmosphere. In this case, the weight ratio of water to the binder is preferably 30% to 70%, and more preferably 40% to 65%.

Next, the carbon dioxide fixed molded body of the present invention will be described.
The molded product obtained by curing the concrete composition of the present invention has voids having a diameter of 10 μm to 200 μm or hollow holes having a cross section of the same diameter in the surface layer portion in a range of 0.05 volume% to 10 volume%. . This void is formed by decomposing and reducing the volume of these resins by means of exposing the alkali-decomposable resin particles contained in the concrete composition or organic fibers made of the resin to an alkaline atmosphere after the concrete is cured. can do. The size and density (abundance) of the voids can be easily adjusted by the size of the resin fine particles to be contained or the organic fibers made of the resin, the added amount, and the like.

The effect of the present invention is achieved by the presence of voids and voids in the surface layer portion of the molded body and the presence of an adsorbent of carbon dioxide contained in the concrete composition. In the present invention , the region having voids is in the surface layer portion , in other words, in the cross-section of the concrete molded body, it is in the range of about 0 to 100 mm in the depth direction from the surface. The effect of the present invention can be achieved by having such voids and hollow holes. When the thickness in the depth direction of the molded body exceeds 100 mm , the voids may exist uniformly up to a further depth of the molded body, but exist in a deep portion other than the region defined in the depth direction. Since the voids that do not easily participate in the fixation of carbon dioxide gas, the effect of improving the fixation of carbon dioxide by the voids existing in a deep region exceeding 100 mm in the depth direction other than the surface layer portion is small.

The carbon dioxide fixed molded body of the present invention is a molded body obtained by curing the above-described concrete composition of the present invention.
The cement molded body is a concrete composition comprising water, cement, an admixture, an aggregate, and a chemical admixture, and the weight ratio of various materials is appropriately adjusted according to the intended use of the formed cement-based molded body. be able to.

The carbon dioxide-fixed molded article of the present invention is kneaded with a concrete composition for forming a carbon dioxide-fixed molded article containing fine particles or organic fibers made of a degradable resin for forming voids, molded, cured, It can be produced by decomposing resin fine particles or resin-containing organic fibers contained in the concrete composition by alkali treatment to form a surface layer portion having voids useful for fixing carbon dioxide.
When exposed in an alkaline atmosphere, the resin gradually decomposes (/ volume reduction) from the surface area of the molded body in contact with the alkali, and voids are formed. By controlling the characteristics of the alkaline atmosphere and the contact conditions with the alkaline atmosphere, a void can be formed only in the surface layer portion of the concrete molded body. In addition, by placing concrete containing void-decomposable resin on the surface of a molded body made of a concrete composition that does not contain void-decomposable resin and curing it to form voids, only on the surface layer A molded body having voids can also be formed.
Thus, although the space | gap should just be formed in the surface layer part which is concerned with fixation of a carbon dioxide at least, it may be uniformly formed to the further deep part of concrete. However, as described above, voids existing in the deep portion are less useful from the viewpoint of fixing carbon dioxide.

  Carbon dioxide gradually permeates from the openings in the surface layer having such voids, and reacts with calcium hydroxide, which is a reaction product of cement hydration in the concrete composition, to form calcium carbonate. Carbon dioxide is fixed. At this time, due to the function of the CaO fine powder contained in the concrete composition, the fixation of carbon dioxide is promoted on the surface of the molded body or the surface of the fine voids formed therein, and the carbon dioxide is more efficient. Immobilization is achieved.

The size and shape of the gap formed in the surface layer portion can be detected by observing the cross section of the molded body with an electron microscope. The porosity can be measured with a mercury intrusion porosimeter or the like.
The carbon dioxide-fixed molded body made of the concrete composition of the present invention has a carbonation reaction by carbon dioxide in the atmosphere accelerated compared to a molded body made of a conventional cement concrete composition, and carbon dioxide is contained in the cement molded body. While being fixed efficiently and having the effect of increasing the amount of immobilization, its mechanical properties can be maintained at the same level as that of a molded body made of a conventional concrete composition.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not restrict | limited to these description.
(Experimental example: Formulation of concrete composition)
In 100 parts by mass of cement composition containing normal Portland cement, water and sand (aggregate), organic fiber and calcium oxide fine powder of the amount shown in Table 1 below are blended, and water / cement A concrete composition was prepared by preparing a mortar having a composition ratio (W / C ratio) of 50% and a cement composition / sand ratio of 1/3.

[Materials used]
Cement: Normal Portland cement (manufactured by Taiheiyo Cement) 3.15 specific gravity
Water: tap water Sand: Kisarazu mountain sand, surface dry density 2.65 g / cm ³ , water absorption 0.46%, actual volume ratio 60.4%, coarse grain rate 6.70
AE water reducing agent: Tupole EX20 (manufactured by Takemoto Yushi Co., Ltd.)
Antifoaming agent: AFK-2 (manufactured by Takemoto Yushi Co., Ltd.)

Organic fiber: Polylactic acid short fiber, fiber diameter 48μm, length 10.0mm
Calcium oxide fine powder: lime-based expansion material (manufactured by Taiheiyo Cement Co., Ltd., Expand: CaO is the main component, Blaine specific surface area is about 3500 cm ² / g fine powder: In Table 1, “CaO fine powder” )

[Concrete composition]
Table 1 shows the composition of the concrete composition. Details of each material used in the table are as described above. In Table 1 below, W / C represents the water / binder ratio.

[Production method of cement molding]
About the concrete composition of the said Table 1, water, cement, sand, organic fiber, or resin fine particles were thrown into a predetermined amount mixer (SK-30S mixer by Hobart, capacity 30L), and it kneaded for 3 minutes. At this time, an appropriate amount of AE water reducing agent and antifoaming agent was added and adjusted so that the amount of air in the mortar after kneading became a constant value (5.0 vol%). After kneading, it was molded into a mold and cured to obtain a carbon dioxide fixed molded body. Each test shown below was done about these molded objects. These results are shown in Table 2 below. The polylactic acid fiber is reduced in volume by being left in the cement hydrate for a certain period, specifically 9 weeks or more, and a void is formed.

[Method of evaluating molded product]
1. Compressive strength Compressive strength was measured according to JIS R5201.
2. Neutralization depth After subjecting to 20 ° C. water curing until the age of 9 weeks, the sample was allowed to stand for 4 weeks in an environment of 20 ° C., relative humidity 60%, and carbon dioxide concentration 5% for accelerated neutralization. After accelerated neutralization, a phenolphthalein 1% alcohol solution was applied to the mortar cross section to confirm the neutralization depth. The deeper the neutralization depth, the more carbon dioxide is fixed by neutralization, which is preferable.
3. Carbonation amount As with the neutralization depth test, after curing at 20 ° C until the age of 9 weeks, it is promoted by standing for 4 weeks in an environment of 20 ° C, relative humidity 60% and carbon dioxide concentration 5%. Sexification was performed. After standing, the specimen is pulverized with a ball mill, the one passing through the # 200 sieve is screened, and the carbon mass in the powder sample is measured using a total carbon analyzer (TOC-SSM5000A manufactured by Shimadzu Corporation). Converted from carbon mass to carbon dioxide mass, the CO ₂ immobilization amount was determined as the carbon dioxide mass relative to the total volume of the sample. The larger the numerical value, the more carbon dioxide is immobilized, which is preferable.

  From Table 2, the molded bodies of Examples 1 to 4 of the present invention have a carbon dioxide content fixed by a carbonation reaction as large as about 5 to 15 times that of Comparative Example 1 having no voids. In comparison with Comparative Example 2 having only voids, the ratio is 1.1 to 1.6 times, and the carbonation reaction of the cement molded body and the adsorption of carbon dioxide proceed efficiently, and a large amount of carbon dioxide is immobilized. You can see that Further, the compressive strength is 95% or more of Comparative Example 1, and even if it has a surface layer portion having voids, almost the same strength as Comparative Example 1 with no fiber added is obtained. I understand that.

Claims (5)

Alkaline degradation which is a homopolymerized aliphatic polyester resin containing structural units formed from monomers selected from water, cement, admixtures, aggregates, polylactic acid, polyglycolic acid, poly-3-hydroxybutyrate or polycaprolactone Calcium oxide fine powder containing organic fiber made of fine resin particles or alkali-decomposable resin in an amount satisfying the following condition (A) and having a Blaine specific surface area of 3000 cm ² / g or more satisfies the following condition (B): It is a concrete composition contained in an amount , and by hardening the concrete composition, 0.05 to 10 volume% of voids having a diameter of 10 μm to 200 μm or cavity holes having a cross section of the same diameter are formed in the surface layer portion. A concrete composition for forming a carbon dioxide-fixed molded body, wherein a molded body is provided.
Condition (A): Fine particles or organic fibers made of the alkali-decomposable resin are contained in an amount of 0.02 to 1.0% by volume based on the total amount of the concrete composition.
Condition (B): Calcium oxide fine powder having a Blaine specific surface area of 3000 cm ² / g or more is contained in the concrete composition in a range of 0.5% by volume to 2.0% by volume. The concrete composition according to claim 1, wherein a mass ratio of the water to the cement is 30% or more and 70% or less. Homopolymerized aliphatic polyester resin or copolymerized fat containing structural units formed from monomers selected from water, cement, admixture, aggregate, polylactic acid, polyglycolic acid, poly-3-hydroxybutyrate or polycaprolactone Calcium oxide fine powder containing alkali-decomposable resin fine particles or organic fibers composed of alkali-decomposable resin, which is an aromatic polyester resin, in an amount satisfying the following condition (A) and having a Blaine specific surface area of 3000 cm ² / g or more 0.05% by volume to 10% by volume of voids having a diameter of 10 μm to 200 μm or a cross section having the same diameter are provided in the surface layer portion obtained by curing the concrete composition contained in an amount satisfying the following condition (B). A carbon dioxide-immobilized molded article characterized by comprising
Condition (A): Fine particles or organic fibers made of the alkali-decomposable resin are contained in an amount of 0.02 to 1.0% by volume based on the total amount of the concrete composition.
Condition (B): Calcium oxide fine powder having a Blaine specific surface area of 3000 cm ² / g or more is contained in the concrete composition in a range of 0.5% by volume to 2.0% by volume. The carbon dioxide-immobilized molded article according to claim 3 , wherein the region having voids of the carbon dioxide-immobilized molded article exists in a range of 0 to 100 mm in the depth direction from the surface of the concrete molded article. After the concrete composition for forming a carbon dioxide-fixed molded body according to claim 1 or 2 is kneaded, molded and cured, an organic fiber made of resin fine particles or resin contained in the concrete composition by alkali is obtained. A method for producing a carbon dioxide-immobilized molded article, which is decomposed to form a surface layer portion having voids useful for immobilizing carbon dioxide.