JP2007177586A - Carbon dioxide fixing retaining wall - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carbon dioxide fixing retaining wall formed by effectively placing the surface capable of being easily formed in an optional slope and effectively fixing carbon dioxide in the atmosphere. <P>SOLUTION: In the retaining wall formed in the surface of the ground, it can be obtained by hardening a concrete composition containing water, cement, an admixture and aggregate, a weep hole provided so as to contact the upper surface layer with the atmosphere is formed in a structural body having the upper surface layer section formed by having a gap of a diameter 10 μm to 200 μm or a cavity hole having the same diameter of a cross section of 0.05 volume% to 10 volume%. Carbon dioxide is gradually infiltrated from an opening section of the gap in the surface layer section having such a gap, reaction is made to calcium hydroxide as a reaction product of hydration reaction of cement in the concrete composition to form calcium carbonate, and fixation of carbon dioxide is made. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a retaining wall structure used for protection and reinforcement of slopes and the like, and more specifically, carbon dioxide immobilization having a surface that efficiently immobilizes carbon dioxide in the atmosphere using the reaction of a cementitious material. Regarding retaining walls.

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 and building structures is gradually cured in the process where calcium hydroxide and calcium silicate hydrate, which are the main chemical components, react with CO ₂ in the atmosphere to produce 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 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 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 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 increase in concrete surface area was not sufficiently obtained, and carbon dioxide was not effectively fixed.
In addition, the explosion-resistant concrete composition contains pyrolytic organic fibers in addition to cement and aggregate (see, for example, Patent Document 5), but this composition is exposed to high temperatures. For the first time, fine voids for allowing air and water vapor to permeate are produced, and normally, it does not have a function of permeating and adsorbing carbon dioxide.
JP-A-8-105052 JP-A-9-205875 JP 11-268969 A JP 2003-277164 A JP 2000-143322 A

  The object of the present invention made in consideration of the above problems is to form carbon dioxide that can be easily formed on any slope and that effectively arranges a surface that can effectively fix carbon dioxide in the atmosphere. The purpose is to provide a fixed retaining wall.

The inventors of the present invention have made use of a concrete composition that greatly facilitates the carbonation reaction that can significantly immobilize carbon dioxide in the atmosphere and can efficiently fix carbon dioxide into mortar and concrete. It has been found that the above problems can be solved by giving a sufficient contact area with the atmosphere by utilizing the shape, and the present invention has been achieved.
That is, the present invention has the following configuration.
<1> A retaining wall formed for the purpose of protecting the surface of a slope, which is obtained by curing a concrete composition containing water, cement, an admixture, and an aggregate, and has a gap of 10 μm to 200 μm in diameter or the same diameter A structure having a surface layer portion provided with 0.05% by volume to 10% by volume of a hollow hole having a cross-section of the surface layer has a drain hole provided so that the surface layer portion is in contact with the atmosphere, and the surface layer portion Carbon dioxide retaining wall that immobilizes carbon dioxide in the atmosphere.
<2> The retaining wall is water, cement, an admixture, an aggregate, an alkali-decomposable resin fine particle, an organic fiber made of an alkali-decomposable resin, an ultraviolet-decomposable resin fine particle, and an organic fiber made of an ultraviolet-decomposable resin The carbon dioxide fixed retaining wall according to <1>, which is formed by placing and curing a carbon dioxide fixed concrete composition containing at least one of the above.
<3> The <1> or <2>, wherein the drainage hole is formed by removing the cylindrical member inserted into the mold when the concrete composition is placed after the concrete composition is cured. Carbon dioxide fixed retaining wall.
<4> The retaining wall is made of water, cement, admixture, aggregate, alkali-decomposable resin fine particles, organic fibers made of alkali-decomposable resin, ultraviolet-decomposable resin fine particles, and organic fibers made of ultraviolet-decomposable resin A retaining wall concrete block obtained by curing a carbon dioxide-fixed concrete composition containing at least one of the above is arranged and laminated so as to form a water drainage gap at least partially, The carbon dioxide fixed retaining wall according to <1>, wherein the carbon dioxide fixed retaining wall is formed by being fixed to.
<5> The carbon dioxide-fixed retaining wall according to <4>, wherein the retaining wall concrete block is fixed to the slope by filling back-ground crushed stone between the retaining wall concrete block and the slope.
<6> The carbon dioxide immobilization according to any one of <1> to <5>, wherein the carbon dioxide immobilization amount of the carbon dioxide immobilization retaining wall is 0.8 kg / m ² or more. Retaining wall.

As described above, the material constituting the carbon dioxide-fixed retaining wall includes water, cement, admixture, aggregate, alkali-decomposable resin particles, organic fibers composed of alkali-decomposable resins, and UV-decomposable resin particles. And the concrete composition for carbon dioxide fixed molded object formation containing at least 1 sort (s) among the organic fiber which consists of ultraviolet-decomposable resin is mentioned. Such a concrete composition is kneaded and cured, and then the surface layer having voids useful for fixing carbon dioxide is decomposed by resin fine particles or resin contained in the concrete composition by alkali or ultraviolet rays. Part is formed, and high carbon dioxide fixation ability is expressed.
In addition to the decomposable organic material for forming the voids, various compounds having carbon dioxide absorption can be added to the concrete composition for forming a carbon dioxide-fixed molded body.

In order to form a retaining wall, a predetermined area of a natural ground that requires surface protection is excavated, a formwork that fits the slope (slope) to be formed is installed, and a carbon dioxide-fixed concrete composition is cast. In addition, the carbon dioxide-fixed concrete composition may be used to form a retaining wall concrete block that has been previously formed into a shape suitable for retaining wall formation and protect a predetermined area excavated from the natural ground. It can also be laminated and fixed so as to match the shape of the slope to be designed.
Here, the form of excavation and the manner in which the retaining wall is fixed differ depending on the situation of the site where the retaining wall is constructed, and various means such as embedding or using pile foundations can be applied depending on the situation. it can.
In addition, it is preferable that the carbon dioxide fixed amount of the carbon dioxide fixed retaining wall of the present invention is 0.8 kg / m ² or more as described above. Considering that the amount of carbon dioxide fixed on the surface of a normal concrete structure is 0.30 to 0.40 kg / m ² , this carbon dioxide fixed retaining wall has an excellent carbon dioxide fixing ability. I understand that.

  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.

  The retaining wall of the present invention promotes the carbonation reaction of cement hydrate in mortar and concrete, so that more carbon dioxide penetrates into the mortar and concrete so that a large number of fine layers are formed on the surface of the mortar and concrete. It is formed so that a vacant space is formed, and by arranging it on an arbitrary slope or the like, protection of the slope and excellent fixing ability of carbon dioxide in the air can be expressed.

  According to the present invention, it is possible to provide a carbon dioxide-immobilized retaining wall that can be easily formed on an arbitrary slope, and is effectively disposed on a surface capable of effectively immobilizing carbon dioxide in the atmosphere. it can

  The carbon dioxide fixed retaining wall of the present invention is formed and arranged to protect slopes of natural ground such as slopes, and hardens a concrete composition containing water, cement, admixture, and aggregate. Obtained and having a surface layer part provided with 0.05 to 10% by volume of voids having a diameter of 10 μm to 200 μm or a cross section having the same diameter, and fixing carbon dioxide in the atmosphere in the surface layer part To do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional view showing one embodiment of a carbon dioxide fixed retaining wall 10 of the present invention.
The carbon dioxide-fixed retaining wall 10 forms a formwork having a shape suitable for the retaining wall structure to be formed in a predetermined region formed by excavating a natural ground, and the carbon dioxide fixing ability is formed in the formwork. It is formed by casting an excellent concrete composition. In this case, the formed retaining wall 10 has a function of protecting the slope of the backside earth and sand 12 of the natural ground. In the embodiment shown in FIG. 1, the lower end of the retaining wall 10 is buried and held in the front earth and sand 14, but the lower end is not necessarily buried in the earth and sand 14.
Drain holes 16 are formed in the carbon dioxide fixed retaining wall 10 at a predetermined interval. The drain holes 16 are provided so that the inner surface layer portion is in direct contact with the atmosphere. Such drain holes 16 are formed by arranging, for example, cylindrical members penetrating the retaining wall structure at a predetermined interval in the raw material concrete composition when forming the carbon dioxide fixed retaining wall 10. A method of extracting the material after it has hardened, a method of placing a cylindrical mesh material that penetrates the retaining wall structure at predetermined intervals in the raw concrete composition, and then curing the concrete composition, water-soluble, biodegradable For example, a cylindrical member formed of a curable material may be disposed and an opening may be formed by melting or decomposing them.

A clogging prevention material (drain material) 18 made of a porous material that prevents clogging of the opening due to the inflow of earth and sand and does not hinder the outflow of water is disposed in the opening on the back side of the drainage hole 16 on the backside earth and sand 12. Is a preferred embodiment.
As the drain material that can be used here, the back opening hole is protected with a plastic net-like sheet (for example, Netron sheet, product name: Dainippon Plastic Co., Ltd.) or a non-woven water-permeable sandproof material, Examples of the method include putting a crushed stone, and a method of installing a mat having a three-dimensional network structure (for example, Hetimaron, trade name: manufactured by Shinko Nylon Co., Ltd.).

Normally, the drain hole is provided by disposing a hollow drain pipe in the retaining wall structure. In this way, by forming the drain hole 12 so that its inner surface is also in direct contact with the atmosphere. The carbon dioxide-fixed retaining wall 10 can adsorb and fix carbon dioxide not only from its surface but also from the inner surface of the drain hole 12, so that the carbon dioxide-fixing ability of the entire retaining wall 10 structure is improved. improves. In FIG. 1, the hatched area schematically shows the carbon dioxide fixing area, and it can be seen that the drain hole 16 is useful for improving the carbon dioxide fixing ability.
The opening shape of the drain hole 16 is not limited to a circular shape and an elliptical shape, and can take various shapes. 2A to 2D show examples of the opening shape of the drain hole. From the viewpoint of manufacturability, a shape such as a circle, a rectangular parallelepiped, or an ellipse shown in FIGS. 2A and 2B is preferable, but from the viewpoint of a large surface area in contact with the atmosphere, FIG. The shape shown in (D) is also preferable.
The opening diameter of the drain hole 16 is preferably 40 to 200 mm from the viewpoint of ensuring the original drainage performance.

The drain holes 16 are formed with a predetermined interval, and the interval or the number of units formed per unit area is appropriately selected in consideration of the characteristics of the backside soil, the environment to be formed, the size of the opening diameter, and the like. Generally, there are about 0.5 to 1 opening having a diameter of 100 mm per 2 m ² . Commercially available vinyl chloride pipes that can form this opening include VP40 (nominal diameter 40 mm), VP50 (nominal diameter 50 mm), VP75 (nominal diameter 75 mm), VP100 (nominal diameter 100 mm), VP125 (nominal diameter 125 mm), etc. The water drainage hole according to the present invention can be formed by fixing it in a formwork for forming the retaining wall and extracting it after hardening the concrete.
For example, even if one drain hole is formed per 2 m ² using VP100 and four drain holes per 2 m ² are formed using VP50, the amount of drainage obtained is almost the same. May be selected in consideration of the appearance and the like.
The installation location of the drain hole is arbitrary, but from the viewpoint of the drainage effect, it is preferable to install it about 30 cm above the top of the backfill earth and sand on the front surface.

Here, a method of pulling out the vinyl chloride tube is adopted for forming the drain hole, but the inner surface of the drain hole may be covered with a breathable material.
As a material for protecting the inner surface of the water drainage hole, from the viewpoint of achieving both air permeability and strength, foamed aluminum (a porous aluminum sheet, commercially available products such as Alporus, trade name: Shinko Steel) Wire industry, etc.), mesh aluminum (expanded metal) and perforated aluminum (punched metal), etc. are used. By making and installing a drain pipe with these materials, a vinyl chloride pipe is used. This is useful as a drain pipe with air permeability. In addition, a plastic net-like sheet or the like can be used as long as it has a strength that can be struck by impact at the time of placing, and a porous tube (a porous tube, a commercially available product that is often used for underground drainage, (Product name: Kanaflex Corporation, etc.) is also available.
It is more preferable to use a non-woven fabric wrapped around a pipe formed of these air-permeable materials because it can suppress outflow during construction of fine aggregate of concrete.

FIG. 3A is a cross-sectional view showing an example of a retaining wall 20 formed using a large concrete block 22 for retaining walls. Here, as shown in the front view of FIG. 3 (B), the drainage hole 24 uses a notch portion of the retaining wall concrete block 22, and there is a vinyl chloride pipe or a breathability as described above. It is formed by arranging pipes made of raw materials and performing stuffing. When a vinyl chloride tube is used, it is necessary to remove it after the filling has been cured. In the case of a large block, a drain hole may be formed in advance in the block itself.
A backfilling stone 26 is filled between the retaining wall concrete block 22 and the backside earth and sand 12, and the retaining wall concrete block 22 is fixed by the backfilling stone 26. Since voids are formed between the backfill stones 26 and have air permeability, carbon dioxide is not only the outer surface of the retaining wall concrete block 22 and the inner surface of the drain holes 24, but also the gaps of the backfill stones 26. It is also absorbed and fixed from the ground 12 side of the back surface in contact with. Normally, seal concrete 28 is provided at the top of the retaining wall concrete block 22 to stabilize these blocks and backfill stones, but this improves the ability to fix carbon dioxide from the back of the retaining wall concrete block. Therefore, it is also a preferable aspect to provide the seal concrete 28 with an opening (vent hole) as indicated by a broken line in FIG.
The shape of the drain hole 24 can be arbitrarily selected by changing the shape of the retaining wall concrete block 22. The opening area of the drain holes 24 of the retaining wall 20 shown in FIG. 3, the arrangement interval, and the like are the same as the ranges described in the embodiment described in FIG. 1.
The size of the retaining wall concrete block is appropriately selected according to the arrangement position and purpose of the retaining wall, but typical examples include a height of about 250 mm, a width of 400 mm, and a depth of about 350 mm. It is. Moreover, as a large sized thing, a thing about 1000 mm in height, width 2000mm, and depth 800mm is mentioned.
The use of the backfilling stone 26 for the retaining wall concrete block 22 is preferable from the viewpoint of the fixing ability and maintaining the gap, but the retaining wall concrete block 22 may be fixed using a material other than stone, For example, backfill concrete may be placed. It is preferable to construct with carbon dioxide-absorbing concrete as the backfilling concrete used here, and when using backside backcrushed crushed stone etc., if it is a material with air permeability, from the viewpoint of carbon dioxide absorption preferable.

[CO2 fixed concrete composition]
Hereinafter, the concrete composition which has the carbon dioxide fixing ability used for formation of the retaining wall of this invention or the concrete block for retaining walls is demonstrated.
The carbon dioxide-fixed concrete composition that can be used to form the retaining wall of the present invention and that can fix carbon dioxide in the atmosphere is cured, and then the molded body has at least a gap of 10 μm to 200 μm in diameter in the surface layer portion. A hollow hole having a cross section of the same diameter is provided in a range of 0.05 volume% to 10 volume%. These voids include alkali-decomposable resin or UV-decomposable resin fine particles or organic fibers in the concrete composition, and after curing the concrete, exposed to an alkali atmosphere, natural light, or artificially irradiated with ultraviolet rays, etc. By means, these resins are decomposed and reduced in volume. 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 cavity holes formed in the surface layer portion of the molded body. The surface layer referred to in the present invention is a retaining wall structure or a range of depth from the surface to the depth of about 100 to 100 mm in the depth direction from the surface in the cross section of the drain hole, that is, from the outermost surface in contact with the atmosphere. In particular, the effect of the present invention can be achieved by having the above-mentioned voids and cavity holes in this region. The depth at which the air gap is formed is determined by the relationship with the thickness of the retaining wall of the present invention. The air gap may exist uniformly up to the deep part of the retaining wall, or may be formed only in the vicinity of the surface in the depth direction, but in consideration of fixation of carbon dioxide from the back surface of the retaining wall structure. For example, it is preferable that the voids exist up to the retaining wall or the deep part of the retaining wall concrete block.

The resin forming these voids is not particularly limited as long as it has a property of being reduced in volume or extinguished by irradiation under ultraviolet light or by irradiation with ultraviolet rays, but is an aliphatic polyester that is rapidly hydrolyzed by alkali. Preferred examples include biodegradable resins such as polyacrylic acid, polyethylene terephthalate that is hydrolyzed by alkali, polypropylene resins that are decomposed 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 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, for 4 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 shape of a diameter of 5 to 200 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.
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.

In the present invention, the carbon dioxide-fixed molded body applied to the surface of the concrete structure contains fine particles or organic fibers made of the aforementioned alkali-decomposable or ultraviolet-decomposable resin, water, cement, admixture, and aggregate. It is a molded article obtained by curing a concrete composition. The blending amount of the resin fine particles or organic fibers in the concrete composition is in the range of 0.02 to 1.0% by volume based on the total amount of the composition in consideration of the carbon dioxide fixation effect and the strength of the structure. It is preferably 0.05 to 0.5% by volume, more preferably 0.1 to 0.5% by volume.
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.

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 molded object in 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.

In the cement-based molded article of the present invention, various additives usually added to the cement-based molded article, for example, water reducing agents, air entraining agents, antifoaming agents, and the like can be appropriately mixed.
The weight ratio of water and cement in the cement molded body can be appropriately selected according to the use of the cement-based molded body to be formed. In order to promote the carbonation reaction with carbon dioxide in the atmosphere, The weight ratio of water to the binder is preferably 30% to 70%, more preferably 40% to 65%.

The carbon dioxide-fixed retaining wall or retaining wall concrete block of the present invention is prepared by kneading, molding and curing a carbon dioxide-fixing concrete composition containing fine particles or organic fibers made of a degradable resin for forming voids as described above. 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, a void can be formed only in the surface layer portion of the concrete molded body. 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 void formed in the surface layer portion can be detected by observing a cross section of the cured concrete body with an electron microscope. The porosity can be measured with a mercury intrusion porosimeter (automatic porosimeter Autopore III (trade name), manufactured by Micromeritex).
The carbon dioxide-fixed concrete composition used here has a faster carbonation reaction due to carbon dioxide in the atmosphere than conventional cement concrete compositions, and the amount fixed as calcium carbonate in the cement molded body is small. In addition to increasing effects, it is possible to obtain a molded body having the same mechanical properties as conventional ones.

Since the carbon dioxide-fixed concrete composition used in the present invention achieves efficient fixation of carbon dioxide mainly by promoting neutralization, it is more alkaline than ordinary concrete compacts. Because the atmosphere is neutralized quickly, when reinforcing bars, wire mesh, and steel frames are used as reinforcing materials in the retaining wall structure, materials that are difficult to oxidize and those that have been rust-proofed with excellent durability are used. It is preferable to select.
Examples of the rust prevention treatment of reinforcing bars used as the reinforcing material include known methods such as galvanization treatment. In place of steel materials, metal materials such as stainless steel that is not easily oxidized, FRP bars (composite reinforcing bars made of glass fiber or carbon fiber solidified with resin), ceramic materials, resin materials, etc. are embedded as reinforcing materials. It is also preferable to do.
Furthermore, it is possible to measure an increase in toughness due to mixing of non-steel fibers such as carbon fiber, vinylon fiber, polypropylene fiber, and aramid fiber.

The retaining wall of the present invention preferably has a carbon dioxide immobilization amount of 0.8 kg / m ² or more from the viewpoint of the effect, and more preferably 1.5 kg / m ² or more.

By disposing the retaining wall of the present invention on a slope of a natural mountain, it is possible to achieve a high carbon dioxide absorption capacity together with the protection of the slope. The retaining wall is made of residual concrete formwork (for example, Protelock Make, trade name: Takamura Co., Ltd.) made of carbon dioxide-fixed concrete and processed into a shape that can be detached from the retaining wall surface with bolts and nuts. By adopting a method or the like, it can be easily exchanged, and it has an advantage that it is easy to maintain the carbon dioxide fixing ability in a desired region at a predetermined level.
The retaining wall of the present invention can be formed by placing it on site, and when using a retaining wall concrete block, according to specifications designed in advance in consideration of carbon dioxide fixing ability, etc. Under high quality control, it can be manufactured in advance as a uniform product at the factory.

In the present invention, as a method for estimating the carbon dioxide fixing ability of the carbon dioxide fixing retaining wall, the method described in the specification of Japanese Patent Application No. 2005-145628 previously proposed by the present applicant can be applied.
That is, depending on the carbon dioxide fixing ability of the carbon dioxide-fixed molded body used for the concrete structure, 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 for the structure. 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 structure 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 immobilization ability on the retaining wall surface of the present invention (which naturally includes the inner surface of the drain hole) can be estimated and used for the design.

EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated further in detail, this invention is not restrict | limited to these description.
[Example 1]
(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 retaining wall]
About the concrete composition of the said Table 1, water, cement, sand, and an organic fiber or resin fine particles were thrown into a predetermined amount mixer (SD-100 mixer by a Pacific Kiko Co., Ltd., capacity | capacitance 100L), 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, it is molded in a mold suitable for a molded body as shown in FIG. 4 (A) imitating a retaining wall, subjected to air curing at a temperature of 20 ° C. and a humidity of 60% until the age of 8 weeks, A carbon dioxide fixed retaining wall 30 was obtained.

[Formation of drain holes]
The drainage holes 32 were formed by arranging two places on the specimen using a vinyl chloride pipe (VP100) defined by JIS K 6741, and removing the vinyl chloride pipe after the concrete was cured.
The side is covered with a non-breathable sheet to prevent carbonation, and Hettimaron (trade name: manufactured by Shinko Nylon Co., Ltd.) 34 is pasted on the entire back surface. Covered with sheet 36. In Example 1, the air on the back surface was configured to be able to vent to the surface through the gap of the hettimaron 34 and the drain hole 32. FIG. 4B shows a cross-sectional view thereof.

(Comparative Example 1)
Instead of the carbon dioxide-fixed concrete composition, a carbon dioxide-fixed retaining wall of Comparative Example 1 is obtained using a normal concrete composition having the same composition except that it does not contain a fiber obtained by melt spinning a polylactic acid resin. It was. Water drainage holes were formed by arranging two places on the specimen using a vinyl chloride pipe (VP100), and the vinyl chloride pipe was left after the concrete was cured. The back surface of the retaining wall of Comparative Example 1 was covered with a sheet having no air permeability assuming a backside earth and sand without attaching hetimalon.

[Evaluation of carbon dioxide fixation capacity]
The amount of carbon dioxide fixed was 50 cm apart by drilling through the retaining walls of Example 1 and Comparative Example 1, and the resulting concrete powder was collected and neutralized in a 1% phenolphthalein ethanol solution. Was measured. Next, the concrete powder when the neutral depth is reached is collected, and the carbon dioxide weight contained in the calcium carbonate is determined by thermal analysis using a thermogravimetric measuring device (TG8110C, manufactured by Rigaku Corporation). It was calculated by measuring.
The result of neutralization promoting material age 13 days was measured. The results are shown in Table 2 below.

  As is clear from the results in Table 2, the carbon dioxide-fixed retaining wall of the present invention was formed using a normal concrete composition, and compared with the retaining wall of Comparative Example 1 that did not consider ventilation, The amount of carbon dioxide immobilized was 10 times or more, and the configuration of the present invention was confirmed to be effective.

It is sectional drawing which shows the one aspect | mode of the carbon dioxide fixed retaining wall of this invention formed by casting a carbon dioxide fixed concrete composition. (A)-(D) are schematic which shows the example of the opening shape of the drain hole formed in the carbon dioxide fixed retaining wall. (A) It is sectional drawing which shows the one aspect | mode of the carbon dioxide fixed retaining wall of this invention formed of the concrete block for retaining walls, FIG.3 (B) is a part of the state which laminated | stacked the concrete block for retaining walls. FIG. (A) It is a perspective view which shows the one aspect | mode of the carbon dioxide fixed retaining wall of Example 1 formed by casting a carbon dioxide fixed concrete composition, (B) is the sectional drawing.

Explanation of symbols

10, 20, 30 Carbon dioxide fixed retaining wall 12 Backside earth and sand (natural ground)
16, 24 Drain hole 22 Concrete block for carbon dioxide fixed retaining wall

Claims (6)

  A retaining wall formed for the purpose of protecting the surface of a slope, obtained by curing a concrete composition containing water, cement, an admixture, and an aggregate, and having a void having a diameter of 10 μm to 200 μm or a cross section having the same diameter. The structure having a surface layer portion provided with 0.05% by volume to 10% by volume of hollow holes has drain holes provided so that the atmosphere contacts the surface layer portion, and the surface layer portion is in the atmosphere. Carbon dioxide retaining wall to immobilize carbon dioxide.   The retaining wall is at least one of water, cement, admixture, aggregate, alkali-decomposable resin fine particles, organic fibers made of alkali-decomposable resin, ultraviolet-decomposable resin fine particles, and organic fibers made of ultraviolet-decomposable resin The carbon dioxide-fixed retaining wall according to claim 1, wherein the carbon dioxide-fixed concrete composition containing one kind is casted and cured.   The carbon dioxide according to claim 1 or 2, wherein the drainage hole is formed by removing a cylindrical member inserted into a mold when the concrete composition is placed, after the concrete composition is cured. Fixed retaining wall.   The retaining wall is at least one of water, cement, admixture, aggregate, alkali-decomposable resin fine particles, organic fibers made of alkali-decomposable resin, ultraviolet-decomposable resin fine particles, and organic fibers made of ultraviolet-decomposable resin A retaining wall concrete block obtained by curing a carbon dioxide-fixed concrete composition containing one type is arranged and laminated so as to form a void for draining at least partially, and is fixed to a slope. The carbon dioxide-immobilized retaining wall according to claim 1, wherein the carbon dioxide-immobilized retaining wall is formed.   5. The carbon dioxide-fixed retaining wall according to claim 4, wherein the retaining wall concrete block is fixed to the slope by filling back-filled crushed stone or back-filled concrete between the retaining wall concrete block and the slope. The carbon dioxide-immobilized retaining wall according to any one of claims 1 to 5, wherein a carbon dioxide-immobilized amount of the carbon dioxide-immobilized retaining wall is 0.8 kg / m ² or more.

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