JP2007177585A - Carbon dioxide fixing surface layer and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon dioxide fixing surface layer capable of easily being formed in a required domain and effectively fixing carbon dioxide in the atmosphere. <P>SOLUTION: The carbon dioxide fixing surface layer is constituted by spraying a concrete composition containing an organic fiber 14 consisting of water, cement, admixture, aggregate and alkali decomposite resin or ultraviolet ray decomposite resin on a slope 12 or the surface of a building, and it is characterized that the carbon dioxide fixing surface layer 10 formed by providing a cavity hole resulting from the organic fiber making three dimensional orientation in the concrete composition is formed and that carbon dioxide in the atmosphere can be fixed. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention provides a surface layer that can efficiently fix carbon dioxide in the atmosphere by utilizing a reaction of a cementitious material, which is disposed on the surface of an arbitrary building such as a slope, and such carbon dioxide fixing. The present invention relates to a production method capable of easily forming a surface layer.

Japan's CO ₂ emissions amount to about 1,250 million tons per year, accounting for about 5.1% of the world. The target for reducing CO ₂ emissions in the 1997 Kyoto Protocol is 6% reduction compared to 1990, but the current measure is expected to increase by 7%. 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 CO ₂ suppression measures, and it stores and immobilizes CO ₂ once exhausted 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 techniques such as trees, electrochemical techniques, and techniques such as underground sequestration have been proposed, but how efficiently CO ₂ is fixed at low cost. Kaga is in the process of research as a future issue.

Cement concrete used for civil engineering buildings is gradually cured in the process of calcium carbonate and calcium silicate hydrate, the main chemical component, reacting with CO ₂ in the atmosphere to generate calcium carbonate after hardening. 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 in the past. On the contrary, the present invention proposes a technique for positively fixing CO ₂ to a cement concrete molded body constituting the outer wall of a building by utilizing this reaction.

The carbonation reaction of general concrete can be expressed by the following reaction formula in which calcium hydroxide contained in the hardened cement hydrate reacts with carbon dioxide that has penetrated into the concrete from the atmosphere to generate calcium carbonate.
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 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 obtaining a porous concrete by adjusting the blending amount of aggregate and cement and maintaining a gap between the aggregates (for example, refer to Patent Documents 1 to 3), lightweight cellular concrete, so-called ALC concrete, etc. A method of entraining a large amount of air into the concrete, a method of mixing a void forming material into the concrete composition, and shrinking or decomposing the void material after curing (see, for example, Patent Document 4), etc. ing. However, in these methods, since the volume of voids formed is large, there is a disadvantage that mechanical properties such as compressive strength and bending strength of concrete are greatly impaired, and because the void area is large, it is useful for adsorption of carbon dioxide. The concrete surface area cannot be increased sufficiently, and carbon dioxide cannot be effectively fixed.
As described above, the formation of a surface layer that can be actively absorbed and immobilized on a slope or a building surface is generally eagerly desired from the viewpoint of suppressing the amount of carbon dioxide in the atmosphere. Currently.
JP-A-8-105052 JP-A-9-205875 JP 11-268969 A JP 2003-277164 A

  An object of the present invention made in consideration of the above problems is a surface layer that can be easily formed in an arbitrary region such as a slope and can effectively fix carbon dioxide in the atmosphere, and simple production thereof. It is to provide a method.

The inventors of the present invention use a concrete composition that greatly facilitates carbonation reaction that can significantly immobilize carbon dioxide in the atmosphere and can efficiently fix carbon dioxide into mortar and concrete, and by spraying method. It has been found that the above problems can be solved by forming a layer, and the present invention has been achieved.
That is, the present invention has the following configuration.
<1> A concrete composition containing water, cement, an admixture, an aggregate, and an organic fiber made of an alkali-decomposable resin or an ultraviolet-decomposable resin is sprayed on the slope, the inner wall of the tunnel or the surface of the building. A carbon dioxide-immobilized surface layer that is configured and has cavity holes due to the organic fibers that are three-dimensionally oriented in the concrete composition and immobilizes carbon dioxide in the atmosphere.
<2> The length of an organic fiber made of an alkali-decomposable resin or an ultraviolet-decomposable resin contained in the concrete composition is 20 mm or less, and the organic fiber is mixed in the concrete composition by a premix <1 > The carbon dioxide fixed surface layer described.
<3> The carbon dioxide-immobilized surface layer according to <1>, wherein the organic fiber is three-dimensionally oriented in the concrete composition when the concrete composition is sprayed on a building surface.
<4> The carbon dioxide according to any one of <1> to <3>, wherein the amount of carbon dioxide immobilized on the surface of the carbon dioxide-immobilized surface layer is 0.8 kg / m ² or more. Immobilized surface layer.

<5> A method for producing a carbon dioxide-immobilized surface layer that forms a surface layer capable of immobilizing carbon dioxide on a slope, an inner wall of a tunnel, or a surface of a building, the slope, an inner wall of a tunnel, or a surface of a building Protrusions for fiber orientation are provided on the surface, and then a concrete composition containing water, cement, an admixture, an aggregate, and an organic fiber made of an alkali-decomposable resin or an ultraviolet-degradable resin is laid by spraying. A method for producing a carbon dioxide-immobilized surface layer, wherein the organic fibers that are three-dimensionally oriented in the composition are decomposed and reduced in volume to provide a cavity hole in the surface layer portion of the concrete composition.
<6> The method for producing a carbon dioxide-immobilized surface layer according to <5>, wherein the fiber alignment protrusion is a solid having a rod shape, a plate shape, or a comb shape.
<7> A method for producing a carbon dioxide-immobilized surface layer that forms a surface layer capable of immobilizing carbon dioxide on a slope, an inner wall of a tunnel, or a surface of a building. A step of forming a protective wall for spraying the composition, and water, cement, an admixture, an aggregate, and an organic fiber made of an alkali-decomposable resin or an ultraviolet-decomposable resin toward the protective wall A step of laying the concrete composition by spraying, and a step of laying the concrete composition by spraying in the vicinity of the region where the concrete is hardened after the concrete composition is hardened. A method for producing a carbon dioxide-immobilized surface layer, which is repeated until a desired surface layer is formed.
<8> The length of the organic fiber made of an alkali-decomposable resin or an ultraviolet-decomposable resin contained in the concrete composition is 20 mm or less, and the organic fiber is mixed in the concrete composition by a premix <5 The manufacturing method of the carbon dioxide fixed surface layer of any one of> thru | or <7>.

The concrete composition for forming the carbon dioxide-fixed surface layer used in the present invention is water, cement, admixture, aggregate, organic fiber made of alkali-decomposable resin, and organic fiber made of UV-decomposable resin. This concrete composition is characterized by containing at least one, kneaded, applied by spraying to any slope or building surface, cured, and then contained in the concrete composition by alkali or ultraviolet light The organic fiber made of resin is decomposed, and a surface portion having voids useful for fixing carbon dioxide is formed.
In addition to the degradable organic fibers for forming voids, various compounds having carbon dioxide absorption can be added to the concrete composition having carbon dioxide fixing ability.

In addition, it is preferable that the carbon dioxide fixed amount in the surface of the carbon dioxide fixed surface layer of this invention is 0.8 kg / m < ² > or more as mentioned above. Considering that the carbon dioxide immobilization amount on the surface of a normal concrete structure is 0.30 to 0.40 kg / m ² , this carbon dioxide immobilization surface layer has an excellent carbon dioxide immobilization ability. I understand that.

Carbonation of cement mortar and concrete is caused by a reaction in which calcium hydroxide formed by cement hydration reacts with carbon dioxide that has penetrated into the concrete from the atmosphere to form calcium carbonate. 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.
Since the surface layer of the present invention accelerates the carbonation reaction of cement hydrate in mortar and concrete, decomposable fibers are added to mortar and concrete so that more carbon dioxide can penetrate into mortar and concrete. Many applied fine voids are formed, and such a surface layer can be easily formed by using a concrete spraying method. For this reason, by forming such a surface layer on the slope or the surface of the building, the slope, the inner wall of the tunnel and the surface of the building are protected, and excellent fixation of carbon dioxide in the air is secured to the surface. A chemical ability can be expressed.
Further, by using the spraying method, there is an advantage that a thin and large surface layer useful for fixing carbon dioxide can be easily formed.

  According to the present invention, it is possible to obtain a surface layer that can be easily formed in an arbitrary region such as a slope and can effectively immobilize carbon dioxide in the atmosphere, and the carbon dioxide-immobilized surface of the present invention. According to the method for producing a layer, a surface layer capable of effectively fixing carbon dioxide in the atmosphere can be easily formed in any region.

  The carbon dioxide-immobilized surface layer of the present invention has a concrete composition containing water, cement, an admixture, an aggregate, and an organic fiber made of an alkali-decomposable resin or an ultraviolet-decomposable resin on a slope or a building surface. It is obtained by spraying an object and curing, preferably 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, and carbon dioxide in the atmosphere. It can be effectively fixed.

Hereinafter, various aspects of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing an example of a first embodiment of a carbon dioxide-immobilized surface layer 10 of the present invention.
The carbon dioxide-immobilized surface layer 10 is formed by laying a concrete composition excellent in carbon dioxide-fixing ability on the slope of the natural ground 12 by a spraying method.
In the concrete composition excellent in carbon dioxide fixing ability, the degradable fibers 14 are dispersed so as to be three-dimensionally oriented, and these degradable fibers are alkalinized during curing after the concrete composition is cured. It is decomposed (reduced volume) by the components, or decomposed by ultraviolet rays to form minute hollow holes.
Thus, in order to efficiently impart the carbon dioxide fixing ability in the carbon dioxide fixed surface layer 10, it is important that the degradable fibers 14 are dispersed so as to be three-dimensionally oriented in the concrete composition. However, as one method for that purpose, an organic fiber 14 made of an alkali-decomposable resin or an ultraviolet-decomposable resin and having a length of 20 mm or less is mixed into the concrete composition by a premix, and this is used as a slope or the like. There is a method to apply by spraying method.

  Here, the premix method refers to mixing fibers at the time of mixing concrete. In addition, as another fiber mixing method, there is a method of mixing at the time of pumping the concrete composition (a method of spraying a hose with a fiber injection port), which is called a spray forming method.

  As the organic fiber used here, it is necessary to select a degradable fiber having a function of forming a void in the concrete composition by decomposing and reducing the volume after spraying the concrete composition. If the length of the organic fiber exceeds 20 mm, uniform dispersion by the premix becomes difficult. The organic fibers used here will be described in detail below, but when used in this embodiment, those having a diameter of 5 to 100 μm and a length of 50 μm to 20 mm are preferable, and more preferably a diameter of 10 to 50 μm and a length. It is 1-15 mm in thickness, More preferably, it is 10-25 micrometers in diameter, and 5-10 mm in length.

FIG. 2 is a schematic sectional view showing a second embodiment of the carbon dioxide-immobilized surface layer 20 of the present invention. The carbon dioxide-fixed surface layer 12 is laid by spraying a concrete composition excellent in carbon dioxide-fixing ability on the slope of the natural ground 12 in which protrusions 22 for orienting fibers are provided in advance at predetermined intervals. Is formed.
As shown in FIG. 2, when the concrete composition is applied by the spray forming method by providing the protrusions 22 at a predetermined interval on the surface of the natural ground 12, the concrete composition is the obstacle (projection) 22. By taking a more complicated flow path, organic fibers in the composition are three-dimensionally oriented, and pores useful for carbon dioxide fixation are uniformly formed. According to this method, since the organic fiber is three-dimensionally oriented regardless of its length and shape, the organic fiber can be suitably used over a wide range of 50 μm to 500 mm in length.

Next, the protrusion 22 in the second aspect will be described. The protrusions 22 have a shape that affects the flow direction of the sprayed concrete composition, and are formed at predetermined intervals. From the viewpoint of the effect, the thickness is preferably about 1 mm to 20 mm in diameter and more preferably 5 mm to 10 mm in terms of a cylinder. The length is appropriately determined depending on the thickness of the desired surface layer, preferably about 20 mm to 100 mm, and more preferably 40 mm to 80 mm.
Further, the arrangement density of the protrusions 22 is preferably about 4 to 400 per 1 m ² , and more preferably 25 to 45.
There are no particular restrictions on the material constituting the protrusion, and any material may be used as long as it does not cause large deformation or breakage due to spraying of the concrete composition. From the viewpoint of being excellent in durability with no deterioration, it is preferably made of a material such as steel, plastic, glass, carbon, rubber or the like. Moreover, when using a metal material, in order to suppress the influence of carbonation accompanying neutralization of a concrete composition, it is preferable to use what was rust-proofed.
As a method of fixing the protrusions to the slope or the building surface, depending on the material that composes the protrusions, it is possible to lay the protrusions individually one by one or in a net-like state. The method of doing is mentioned. In addition, sheet-like and net-like bodies such as lath nets with protrusions at predetermined intervals, non-woven fabrics and synthetic resin films with resin protrusions adhered to the entire slope It is also possible to take a method of fixing to
In this embodiment, the protrusions are rod-shaped, but the protrusions are not necessarily limited to this, and plate-like protrusions may be provided equally, or comb-like protrusions may be used.
By arranging the protrusions on the inner wall of the tunnel, particularly in the vicinity of the ceiling, the protrusions are not only useful for fiber orientation, but may have a function as a protective wall depending on the shape.

3 and 4 are schematic cross-sectional views showing another method for forming the carbon dioxide-immobilized surface layer of the present invention. As another method of three-dimensionally orienting organic fibers by construction by the spraying method, it is preferable to perform the spraying direction from a direction that is nearly perpendicular to the slope or the surface of the building, and thus the cross-sectional shape becomes a rhombus Thus, a method of finishing as long as possible is mentioned.
That is, due to the nature of spraying, the concrete composition pumped by compressed air is placed so as to be pressed against the construction surface, so that the organic fibers are easily arranged in parallel to the spraying surface. When the fibers are two-dimensionally oriented along the slope, it becomes difficult to form a void from the outermost surface of the surface layer to the deep portion, and the carbon dioxide fixing ability may be lowered. However, the three-dimensional orientation of the fiber independent of the fiber length is realized by spraying locally from a certain direction and sequentially producing such diamond-shaped cured portions.
Here, the three-dimensional orientation refers to an orientation in which fibers are three-dimensionally present at random (an orientation in which fibers are present at random positions and directions in the X, Y, and Z spaces).
FIG. 3 shows a method of forming the surface layer 30 when the slope of the slope of the natural ground 12 forming the surface layer 30 is steep. When the slope is steep in this way, a protective wall 32 perpendicular to the ground is disposed at the top of the slope of the natural ground 12, and the concrete composition is sprayed from the direction indicated by the arrow in the figure. The region indicated by (1) is formed. After the area (1) is stabilized, this side surface is replaced with the protective wall 32 and the same spraying is performed to form the area (2). This is repeated sequentially toward the lower side to form a surface layer on the entire slope. In addition, a protective wall is installed for each area indicated by (1), (2), (3),..., And each area is sprayed sequentially before the upper area is stabilized and completely cured. You may go.

FIG. 4 shows a method of forming the surface layer 40 when the slope of the slope of the natural ground 42 forming the surface layer 40 is gentle. When the slope is gentle, the concrete composition is sprayed from the direction indicated by the arrow in the figure at the lower part of the slope of the natural ground 42, and first, the region indicated by (1), which is the lowest part of the surface layer, is formed. To do. In this case, since the ground and slope itself have a function as a protective wall, depending on the angle of the slope, the protective wall is not artificially provided and the unevenness formed on the ground, slope or building is protected. Can function as a wall. After stabilizing the concrete composition excellent in carbon dioxide fixing ability, the concrete composition is sprayed from the same direction on the upper surface of the region (1) to form the region shown in (2). The same process is sequentially repeated upward, and the surface layer 40 is formed on the entire slope.
As in the embodiment shown in FIGS. 3 and 4, the concrete composition is partially applied to the local region from a certain direction, that is, a direction that is perpendicular to the slope, that is, a direction that is almost horizontal to the ground. By spraying and forming a part of the surface layer, the orientation of the organic fibers can be made to the three-dimensional orientation as designed. In this case, the same effect can be obtained regardless of whether the organic fiber is blended by a premix method or by a method in which only the organic fiber is supplied and mixed at the time of spraying.
The carbon dioxide-immobilized surface of the present invention can be provided with a reinforcing material such as a metal material such as a reinforcing bar or inorganic fiber for the purpose of reinforcement.

  Hereinafter, the concrete composition excellent in the carbon dioxide fixing ability which comprises the carbon dioxide fixed surface of this invention is demonstrated.

[CO2 fixed concrete composition]
The carbon dioxide-immobilized molded body capable of immobilizing carbon dioxide in the atmosphere used for forming the surface layer of the present invention has a void having a diameter of 10 μm to 200 μm or a hollow hole having a cross section of the same diameter in at least the surface layer portion. It is provided in the range of 05 volume% to 10 volume%. These voids are made by, for example, containing an organic fiber of an alkali-decomposable resin or an ultraviolet-decomposable resin in a concrete composition, and exposing it to an alkali atmosphere after curing the concrete, or irradiating natural light or artificial ultraviolet rays. Thus, these resins are formed by decomposing and reducing the volume. The amount of voids and the space between the voids can be easily adjusted depending on the size of the organic fiber made of the resin to be contained, the amount added, and the like.
The effects of the present invention are achieved by the presence of voids and cavity holes formed in the surface layer of the hardened body of the concrete composition. The surface layer referred to in the present invention refers to a depth range from about 0 to 100 mm in the depth direction from the surface in the cross section of the surface layer made of a concrete hardened body, that is, from the outermost surface in contact with the atmosphere to 100 mm, The effect of the present invention can be achieved by having the voids and cavity holes as described above in this region. The depth at which the voids are formed is determined by the relationship with the thickness of the surface layer of the present invention. The air gap may exist uniformly up to the bottom, that is, the interface with the slope or the surface of the building, but may be formed only in the vicinity of the surface in the depth direction.

The resin constituting the organic fibers forming these voids is not particularly limited as long as it has a characteristic of being reduced in volume or disappearing by being decomposed by irradiation with ultraviolet rays or by irradiation with ultraviolet rays. Preferable examples include aliphatic polyesters that decompose, biodegradable resins such as polyacrylic acid, polyethylene terephthalate that hydrolyzes with alkali, polypropylene resins that decompose by ultraviolet irradiation, and acrylic resins.
In particular, aliphatic polyester has sufficiently high fiber strength and good handling properties before being mixed into a concrete composition, but it is mixed into a concrete composition and cured to form a cement-based molded body. Is 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.

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 alone or in combination of two or more as the organic fiber material.

When forming voids, the aliphatic polyester resin is used after being formed into a fiber by a known method such as 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. The resin molded into a fiber form is preferable from the viewpoint of effect because it forms a long and narrow continuous void inside the concrete.
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, approximately 4 weeks.

In the case of blending an organic fiber made of an aliphatic polyester resin into a concrete composition, the organic fiber preferably has a shape having a diameter of 5 to 100 μm and a length of 50 μm to 20 mm, more preferably a diameter of 10 to 50 μm and a length. It is 1-15 mm, More preferably, it is 10-25 micrometers in diameter, and 5-10 mm in length.
As described above, when the organic fiber is premixed in the concrete composition and sprayed to achieve the three-dimensional orientation of the organic fiber, the length of the organic fiber is preferably 20 mm or less.
The shape of the organic fiber can be measured by an ordinary method using an image obtained with an electron microscope or a high-magnification optical microscope.

The concrete composition according to the present invention is characterized in that it contains organic fibers made of the aforementioned alkali-decomposable or ultraviolet-decomposable resin, water, cement, an admixture, and an aggregate. In the present invention, since the concrete composition is placed by the spraying method, the organic fiber does not necessarily have to be blended in the concrete composition. It is also possible to take.
As a compounding amount of the organic fiber in the concrete composition, in consideration of carbon dioxide fixing ability and strength of the surface layer to be formed, the total amount of the composition is in a range of 0.05 to 1.0% by volume. Is preferable, more preferably 0.05 to 0.5% by volume, and still more preferably 0.3 to 0.5% by volume. In addition, this content is in the formed surface layer, and it is preferable to appropriately select the supply conditions, the supply amount, and the like so as to be within the marked range even when organic fibers are added later.
The formed surface layer is made of a concrete composition composed of water, cement, an admixture, an aggregate, and a chemical admixture, and the weight ratio of various materials can be appropriately adjusted according to the application.

In the concrete composition, from the viewpoint of improving the carbon dioxide immobilization ability, fine powder or adsorbent that can adsorb carbon dioxide (hereinafter referred to as carbon dioxide adsorbing material as appropriate), calcium oxide (CaO) fine powder, etc. Additives can be included.
Here, as the fine powder or adsorbent capable of adsorbing carbon dioxide that can be blended in the concrete composition, slag containing γ-2CaO · SiO ₂ is preferably mentioned. Examples of such slag containing γ-2CaO · SiO ₂ include stainless steel slag and steelmaking slag. The slag is required to be Blaine specific surface area of 3000 cm ² / g or more, and more preferably in the range of 4000~10000cm ² / g. The specific surface area of slag can be measured by the brane method described in JIS R 5201 or by a method using a laser diffraction particle size meter.
When the slag is used as a carbon dioxide adsorbing substance, it is preferably in the range of 15 to 45% by mass with respect to the cement content contained in the concrete composition. Is expressed and has excellent mechanical properties.

Other preferable examples of the fine powder or adsorbent capable of adsorbing carbon dioxide include fine powder selected from the group consisting of zeolite fine powder, silica gel fine powder, alumina fine powder, and crustacean fine powder. Of these, zeolite fine powder and crustacean fine powder are preferable. Since crustaceans contain a large amount of calcium, when they are made fine powder, they exhibit excellent carbon dioxide adsorption ability.
The particle size of these fine powders is preferably about 1 μm to 3 mm, more preferably 10 μm to 1 mm.
When these fine powders are used as a carbon dioxide adsorbing substance, the content thereof is preferably in the range of 5 to 30% by mass with respect to the content of cement contained in the concrete composition. In this range, a remarkable carbon dioxide absorption effect is exhibited, and there is no concern of affecting the mechanical properties of the concrete molded body.

As the CaO fine powder that can be used in the present invention, one containing CaO and having a brain specific surface area of 2000 cm ² / g or more is used.
As the fine powder mainly composed of CaO, a powder obtained by pulverizing quick lime, lime-based expansion material, or the like into a fine powder having a Blaine specific surface area of 2,000 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.
The CaO fine powder is preferably contained in the concrete composition in the range of 0.5 to 2.0% by volume. In this range, excellent carbon dioxide adsorption ability is expressed, and the mechanical properties of the molded article are also excellent. .

There is no restriction | limiting in particular as a cement used for the concrete composition which is a raw material of a surface layer in this invention, According to the use of the cement-type molded object formed, it can select from various cements suitably. 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 surface layer 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.

In the concrete composition forming the surface layer of the present invention, various additives usually added to cement, for example, a water reducing agent, an air entraining agent, an antifoaming agent and the like can be appropriately added.
The weight ratio of water and cement in the concrete composition used in the present invention can be appropriately selected according to the installation location and application of the surface layer to be formed, but promotes the carbonation reaction with carbon dioxide in the atmosphere. For this purpose, the weight ratio of water to the binder is preferably 30% or more and 70% or less, more preferably 40% or more and 65% or less.

The carbon dioxide-immobilized surface layer of the present invention is kneaded with a carbon dioxide-immobilized concrete composition containing organic fibers made of a degradable resin for forming voids as described above, and is placed in a desired region by a spraying method and cured. Then, it can be produced by decomposing the resin fine particles or the organic fibers made of the resin contained in the concrete composition with alkali or ultraviolet rays 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, voids can be formed only in the surface layer portion of the surface layer. In addition, by spraying a concrete composition that does not contain a decomposable resin for forming voids first, placing concrete containing a decomposable resin for forming voids on the surface, and curing to form a void, the surface layer portion It is also possible to form a surface layer having voids only.
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.

  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.

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 concrete composition for forming a carbon dioxide-fixed molded body used here has a faster carbonation reaction with carbon dioxide in the atmosphere than conventional cement-concrete compositions, and is fixed as calcium carbonate in the cement molded body. In addition to the effect of increasing the amount to be formed, it is possible to obtain a molded product having the same mechanical properties as the conventional one.

Next, the details of the spraying method will be described.
As a device for placing a concrete composition on a slope or the surface of a building by a spraying method, a device generally used for spraying concrete, for example, an air compressor, a meter, a sprayer, a mixer, etc., is used. A squeeze type or piston type pump pressure sprayer is preferable from the viewpoint of material separation and rebound during spraying. Also,
The spraying conditions are preferably a pumping distance of 200 m or less and a direct height of 50 m or less.

In the surface layer of the present invention, it is also possible to improve the strength by arranging a reinforcing material such as a reinforcing bar or a frame material therein.
Since the carbon dioxide-immobilized surface layer used in the present invention achieves efficient fixation of carbon dioxide mainly by promoting neutralization, it is compared with a surface layer made of ordinary concrete. Since the neutralization of the alkaline atmosphere is quick, it is preferable to select a reinforcing bar used as a reinforcing material or a steel frame using a material that is not easily oxidized, or a material that has been subjected to a rust prevention process that is excellent in durability.
That is, when a reinforcing bar or a steel frame is used as a reinforcing material in the molded body, it is preferable to use a rust-proof surface. Examples of the rust prevention treatment include known methods such as surface coating with a resin material such as galvanization treatment and epoxy resin. Also, instead of iron materials, embed metal materials such as stainless steel, titanium and nickel that are not easily oxidized, and FRP bars (composite reinforcing bars made of glass fiber and carbon fiber solidified with resin) that do not rust as reinforcements. Is also preferable. Furthermore, it is also possible to make the structure streaky by measuring the toughness increase due to mixing of non-steel fibers such as carbon fiber, vinylon fiber, polypropylene fiber, and aramid fiber.
Furthermore, it is also a preferable aspect that a reinforcing fiber selected from the group consisting of carbon fiber, stainless steel fiber, and vinylon fiber is dispersed and mixed in the concrete composition.

The amount of carbon dioxide immobilized in the carbon dioxide-immobilized surface layer of the present invention is preferably 0.8 g / m ² or more from the viewpoint of the effect, and more preferably 1.5 kg / m ² or more.
The thickness of the surface layer of the present invention is appropriately selected according to the state and purpose of use on the slope of the natural ground on which the surface layer is formed or the surface of the building, but generally in the range of 3 cm to 15 cm. Preferably there is.

  The surface layer of the present invention. By arranging it on the outer wall of a building such as a building, or a slope such as a natural mountain or embankment, the surface strength can be improved, and a surface having a high carbon dioxide absorption capacity can be formed in an arbitrary region.

As a method for estimating the carbon dioxide fixing ability of the carbon dioxide fixing surface layer in the present invention, the method described in the specification of Japanese Patent Application No. 2005-145628 previously proposed by the applicant of the present application can be applied.
That is, according to the carbon dioxide fixing ability of the carbon dioxide-fixed molded body used in the concrete building, the time when the molded body is in contact with the atmosphere is from T ₀ at the time of occurrence to T _S at the end of fixation such as at the time of dismantling. More specifically, the carbonation depth c of the concrete gas-absorbing material at the elapsed time t from the time T ₀ is expressed as the carbonation rate equation c = Further, carbon dioxide is expressed as dc (depth from the surface), where S is the area of the boundary surface s between the already carbonized region and the non-carbonized region in the carbon dioxide fixed molded body used in the building. A) The density of carbon contained in the volume portion when it has progressed by a is defined as a, and the gas absorption amount W when the carbonation depth c is reached is expressed as W (c) = ∫ (a × S) dc. Greenhouse gas absorption within a specified time from both methods It is intended to estimate the amount.

Carbonation of concrete is also commonly referred to as neutralization reaction but, as its carbonation (neutralization) rate equation can be used c = A × t ^n, called the root law. Here, c is the reaction amount, A is the carbonation rate coefficient, and t is the elapsed time. N is a constant determined experimentally, and generally n = 0.5.

The carbonation rate coefficient A in the carbonation rate equation c = A × t ^0.5 has been studied variously in the past, but simply, A _Q depending on the water cement ratio (W / C), A constant R depending on other factors, which can be expressed as A = A _Q × R, where R is a constant called a carbonation rate, A _{P is} a coefficient due to the attribute of concrete, and A is a coefficient due to the finishing material. _{If the} coefficient according to the classification of _S and the environment (temperature and humidity, carbon dioxide concentration) is A _E , R = A _P × A _S × A _E.

For the A _Q, for example, the following formula 1 are known when experimentally a W / C ≧ 0.6, also Equation 2 is known when a W / C ≦ 0.6 (Kishitani, “Durability of Reinforced Concrete” published by Kashima Construction Technology Research Institute, 1963).

[Formula 1]
A _Q = {(W / C) −0.25} / [0.3 × {1.15 + 3 (W / C)}] ^0.5

[Formula 2]
A _Q = {4.6 × (W / C) −1.76} / √ (7.2)
In addition, if the above-mentioned W (c) = ∫ (a × S) dc is used, it is possible to measure the amount of greenhouse gas absorbed in a concrete building of an arbitrary shape. The absorption amount per unit surface area can also be obtained by setting / S = ∫abc.
In this way, the carbon dioxide fixing ability in the surface layer of the present invention can be estimated and used for the design.
By installing the surface layer of the present invention at an arbitrary position so as to be in contact with the atmosphere, a region having carbon dioxide fixing ability can be formed. Specifically, for example, the surface of a building such as a detached house or a building, the surface of a bridge pier, a bridge deck, a retaining wall, a civil engineering structure such as a dam or a tunnel, a natural ground, a seawall, etc. And the inner wall of the tunnel.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not restrict | limited to these description.
(Concrete composition mix)
An organic fiber composed of degradable resin in the amount shown in Table 1 below is blended in 100 parts by mass of cement composition containing ordinary Portland cement, water and sand (aggregate), and the water / cement composition ratio (W A concrete composition was prepared by preparing a mortar having a / C ratio of 55% and a cement composition to sand ratio of 1/3.
For comparison, instead of alkali-decomposable organic fibers, general building materials are blended with non-degradable organic fibers used as reinforcing materials, and concrete compositions are prepared with the same mixing amount for comparison. As an example.

[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 ratio 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 resin melt-spun fiber (described as PLA fiber in the table, hereinafter the same), fiber diameter 20 μm, length 5.0 mm

[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, and S / C represents the sand / cement ratio.

[Production of carbon dioxide fixed surface layer]
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% by volume).
After kneading, the mixture is pumped with a mortar pump (MM-105HA manufactured by Shin Meiwa Kogyo Co., Ltd.) and an air compressor (G-75K manufactured by MEIJI) and sprayed on a slope with an angle of 45 degrees to form a surface layer. A carbon-immobilized surface layer was formed.

[Evaluation of carbon dioxide fixation capacity]
After accelerated neutralization, the formed surface layer was cored with a core cutter of φ10 cm, and it was split to measure the amount of carbon dioxide fixed.
For measurement of carbon dioxide fixed amount, a piece of concrete composition is collected from the cross section of the broken mass, ground with a ball mill, screened through a # 200 sieve, and a thermogravimetric measurement device (TG8110C, manufactured by Rigaku Corporation) is used. Thus, the weight of carbon dioxide contained in the calcium carbonate in the powder sample was measured. As a result, the carbon dioxide immobilization amount was 1.92 kg / m ² .
When a surface layer was formed with a normal concrete composition and evaluated in the same manner, the amount of carbon dioxide immobilized was 0.34 kg / m ² , and the surface layer of the present invention was converted into a surface layer with a normal concrete composition. In comparison, it was confirmed that carbon dioxide was immobilized at a high efficiency of 5 times or more.

It is sectional drawing which shows the example of the 1st aspect of the carbon dioxide fixed surface layer of this invention obtained by the method of premixing organic fiber. It is sectional drawing which shows the one aspect | mode which formed the carbon dioxide fixed surface layer in the slope of the natural ground provided with the protrusion for orientating a fiber. It is a schematic sectional drawing which shows the method of forming a carbon dioxide fixed surface layer on the slope with a steep slope. It is a schematic sectional drawing which shows the method of forming a carbon dioxide fixed surface layer in the slope with a gentle gradient.

Explanation of symbols

10, 20, 30, 40 Carbon dioxide fixed surface 12, 42 Ground mountain 14 Organic fiber 22 Projection

Claims (8)

  It is constructed by spraying a concrete composition containing water, cement, an admixture, an aggregate, and an organic fiber made of an alkali-decomposable resin or an ultraviolet-decomposable resin on the slope, the inner wall of the tunnel or the surface of the building, A carbon dioxide-immobilized surface layer that has voids due to the organic fibers that are three-dimensionally oriented in a concrete composition and immobilizes carbon dioxide in the atmosphere.   The length of the organic fiber which consists of alkali-decomposable resin or ultraviolet-decomposable resin contained in the concrete composition is 20 mm or less, and the organic fiber is mixed in the concrete composition by a premix. Carbon dioxide fixed surface layer.   The carbon dioxide-immobilized surface layer according to claim 1, wherein the organic fibers are three-dimensionally oriented in the concrete composition when the concrete composition is sprayed on a slope, an inner wall of a tunnel or a surface of a building. The carbon dioxide fixed surface according to any one of claims 1 to 3, wherein the carbon dioxide fixed amount on the surface of the carbon dioxide fixed surface layer is 0.8 kg / m ² or more. layer.   A method of manufacturing a carbon dioxide-immobilized surface layer that forms a surface layer capable of immobilizing carbon dioxide on a slope, an inner wall of a tunnel, or a surface of a building, and fiber orientation on the slope, the inner wall of a tunnel, or the surface of a building After that, a concrete composition containing water, cement, an admixture, an aggregate, and an organic fiber made of an alkali-decomposable resin or an ultraviolet-decomposable resin is laid by spraying. A method for producing a carbon dioxide-immobilized surface layer, wherein the organic fibers that are three-dimensionally oriented are decomposed and reduced in volume to provide cavity holes in the surface layer portion of the concrete composition.   6. The method for producing a carbon dioxide-immobilized surface layer according to claim 5, wherein the fiber alignment protrusion is a solid having a rod shape, a plate shape, or a comb shape.   A method for producing a carbon dioxide-immobilized surface layer that forms a surface layer capable of immobilizing carbon dioxide on a slope, an inner wall of a tunnel, or a surface of a building, wherein a concrete composition is blown onto the slope, the inner wall of a tunnel, or a structure. A step of forming a protective wall for attachment, and a concrete composition containing water, cement, an admixture, an aggregate, and an organic fiber made of an alkali-decomposable resin or an ultraviolet-decomposable resin toward the protective wall A step of laying an object by spraying, and a step of laying the concrete composition by spraying in the vicinity of a region where the concrete is stabilized after the concrete composition is stabilized, and each step is performed on a desired surface. A method for producing a carbon dioxide-immobilized surface layer, which is repeated until a layer is formed.   The length of the organic fiber which consists of alkali-decomposable resin or ultraviolet-decomposable resin contained in the said concrete composition is 20 mm or less, and this organic fiber is mixed by the premix in the concrete composition. Item 8. A method for producing a carbon dioxide-immobilized surface layer according to any one of Items 7 to 8.

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