Base material and method for adsorbing and immobilizing carbon dioxide using base material

Abstract

[Problem] To provide a base material and a method for adsorbing and immobilizing carbon dioxide using a base material that make it possible to semi-permanently adsorb and immobilize carbon dioxide in a base material in soil without using heat energy at all and solely by natural forces. [Solution] Provided is a base material 10 which is buried in soil and is used as a filler or a backfilling material for suppressing clogging. The base material 10 comprises: a hard aggregate body 20; a wet coating layer 30 which covers the surface of the aggregate body 20 and is composed of a naturally derived wetting substance 31 and an adhesion auxiliary material 32, the wetting substance 31 having an acidic functional group having at least a function of adsorbing and immobilizing carbon dioxide, a function of capturing an SS material, and a pH buffering action, and the adhesion auxiliary material 32 exhibiting viscosity when wetted and adhering the wetting substance 31 to the surface of the aggregate body 20; and a regenerated fine powder 33 of concrete that is a carbon dioxide carrier adhered to the surface of the aggregate body 20 or the wet coating layer 30.

Description

Base material and method for adsorbing and fixing carbon dioxide using the base material

[0001] The present invention is a carbon dioxide (CO ) containing material that can be used for sidewalks, parks, plazas, roadways, etc. ２ The present invention relates to a carbon dioxide adsorption technology, and in particular to a base material and a method for adsorbing and fixing carbon dioxide using the base material, which can adsorb and fix carbon dioxide over a long period of time while maintaining a good vegetation environment.

[0002] As one of the recent countermeasures against global warming, it is known to adsorb carbon dioxide in the air onto various carriers as follows, with the aim of reducing carbon dioxide emissions.

[0003] (1) Biochar Carrier Non-Patent Document 1 proposes that biochar produced by carbonizing trees at low temperatures can be buried in the soil as a soil conditioner to fix carbon dioxide semi-permanently.

[0004] (2) Limestone Carrier Non-Patent Document 2 proposes a system in which limestone is heated in a kiln to decompose it into calcium oxide and carbon dioxide, and the resulting calcium oxide is spread on a tray to adsorb carbon dioxide in the atmosphere.

[0005] On the other hand, it is known that aggregate extracted by crushing waste concrete materials is reused as recycled aggregate. If recycled aggregate with a large amount of concrete components adhering to its surface is used as aggregate for a concrete structure, it can cause a decrease in strength, so it is necessary to remove as much of the concrete adhering as possible. Patent Document 1 discloses a method of removing the concrete adhering by stirring and grinding the raw material of recycled aggregate heated to 100°C or higher in a dry kneading device.

[0006] Furthermore, high-quality natural aggregates such as crushed stone are used as base materials for the base directly under the sidewalk or for the vegetation base when constructing tree belts adjacent to sidewalks or roads (Patent Documents 2 and 3).

[0007] https: / / jp-gx.com / credits / nT1pyXumhttps: / / www.orix.co.jp / grp / move_on / entry / 2022 / 07 / 13 / 100000 JP Patent Publication No. 2023-182463 Registered Utility Model No. 3065278 JP Patent Publication No. 2005-133458

[0008] Conventional technologies for immobilizing carbon dioxide by adsorbing it onto various carriers have the following problems: <1> The carbon dioxide immobilization technology described in Non-Patent Document 1 is a match-and-pump technology, as it emits large amounts of carbon dioxide when carbonizing the wood that serves as the carrier. <2> The carbon dioxide immobilization technology described in Non-Patent Document 2 is also a match-and-pump technology, as it already emits a large amount of carbon dioxide during the heating stage, just like the cement manufacturing process. <3> Conventionally, large amounts of thermal energy are consumed when manufacturing various carriers, which increases the manufacturing costs of the carrier. <4> In order to adsorb carbon dioxide onto the carrier, carbon dioxide must be forcibly supplied to the carrier continuously, which increases the cost of carbon dioxide absorption.

[0009] Conventional technologies for using recycled or natural aggregates have the following problems: <1> It is technically difficult to completely remove the concrete components adhering to the surface of recycled aggregate, and trace amounts of concrete deposits remain on the surface of recycled aggregate. Because the concrete deposits are strongly alkaline, the use of recycled aggregate is limited to concrete aggregate, and proposals for new uses for recycled aggregate are desired. <2> Although technology for crushing waste concrete materials and recovering recycled aggregate has been established, no progress has been made in recycling the fine concrete powder (concrete filler) generated during the production of recycled aggregate, and proposals for new uses for concrete fine powder are desired.

[0010] The present invention has been made in view of the above points, and its object is to provide a base material and a method for adsorbing and fixing carbon dioxide using the base material, which can adsorb and fix carbon dioxide semi-permanently to the base material in the soil using only natural forces, without using any thermal energy whatsoever.

[0011] The present invention provides a base material for use as a filler or backfill material buried in soil to prevent clogging. The base material comprises a hard aggregate body; a wet coating layer covering the surface of the aggregate body and including a naturally occurring wet substance having acidic functional groups that have at least the function of capturing SS substances and a pH buffering action; an adhesion aid that becomes viscous when wet and adheres the wet substance to the surface of the aggregate body; and recycled concrete fine powder that serves as a carbon dioxide carrier and is adhered to the surface of the aggregate body or the wet coating layer. In another aspect of the present invention, the recycled fine powder is untreated fine powder made from waste concrete. In another aspect of the present invention, the recycled fine powder is adhered to the surface of the aggregate body or the wet coating layer by utilizing the wettability of the adhesion aid. In another aspect of the present invention, the wet substance is allophane or humus. In another aspect of the present invention, the adhesion aid is at least one of water, a superabsorbent polymer, a polymer absorbent, a vinyl acetate resin, and polyvinyl alcohol. In another aspect of the present invention, the aggregate body is single-grained recycled aggregate produced from waste concrete. In another aspect of the present invention, it is used as a permeable base layer of a permeable roadbed structure. Furthermore, the present invention is a method for adsorbing and fixing carbon dioxide using a base material, in which the base material described in claim 1 is buried in soil as a filler or backfill material for preventing clogging, and when rainwater permeates into the soil, the concrete components of the base material react with the carbon dioxide contained in the rainwater as carbon dioxide to produce calcium carbonate, and the carbon dioxide is adsorbed and fixed on the surface of the base material in the form of calcium carbonate.

[0012] The present invention achieves at least one of the following effects. <1> By attaching recycled fine powder to a base material, the base material buried in the soil as a filler or backfill material to prevent clogging can also serve as a carbon dioxide carrier. In particular, carbon dioxide can be efficiently adsorbed into the base material buried in the soil without using any thermal energy, and the adsorbed carbon dioxide can be effectively fixed (retained). <2> The present invention utilizes the natural phenomenon of atmospheric carbon dioxide being naturally absorbed into rainwater and the natural phenomenon of rainwater permeating into the soil under its own weight to induce carbonation in the soil due to a reaction between carbon dioxide and concrete components, thereby adsorbing and fixing carbon dioxide in the base material. Therefore, the carbon dioxide adsorption and fixation function in the soil can be sustained semi-permanently. <3> In the present invention, by using recycled aggregate made from waste concrete as the aggregate main component of the base material and using fine powder from waste concrete that had previously been treated as industrial waste as the recycled fine powder, further effective utilization of industrial waste can be achieved. <4> In this invention, the aggregate itself and recycled fine powder are used as they are without heat treatment, so the base material doubles as a carbon dioxide carrier, eliminating the problems of mass consumption of fossil fuels and the generation of carbon dioxide due to heating. <5> Even if the base material contains concrete components, the naturally occurring moist substances contained in the wet coating layer act as a pH buffer, allowing the pH of the base material to be kept low. Therefore, even if vegetation or trees are planted on a permeable roadbed structure to which the base material is applied, the alkalinity caused by the concrete components can be alleviated, improving the vegetation environment. <6> Using the base material as a filler or backfill material to prevent clogging not only has the single effect of increasing carbon dioxide absorption, but also significantly contributes to the development of green infrastructure, such as landscape formation and microclimate improvement.

[0013] Model diagram of a permeable roadbed structure using base material. An explanatory diagram of the manufacturing method of the base material. (a) is an explanatory diagram of the process of covering the surface of the aggregate body with a wet coating layer, and (b) is an explanatory diagram of the process of attaching recycled fine powder to the surface of the aggregate body and the wet coating layer. Model diagram of the aggregate body covered with a wet coating layer. Model diagram of the base material manufactured by attaching recycled fine powder to the surface.

[0014] The present invention will be described in detail below with reference to the drawings.

[0015] 1. Permeable roadbed structure <1> Overview of permeable roadbed structure A permeable roadbed structure using the base material 10 illustrated in Fig. 1 will be described. The permeable roadbed structure of this example is a laminated structure comprising a permeable base layer 41 mainly composed of the base material 10 laid on a roadbed 40, a permeable roadbed layer 42 laid on the permeable base layer 41, and a permeable pavement layer 43 laid on the permeable roadbed layer 42. Details of the base material 10 that constitutes the permeable base layer 41 will be described later.

[0016] <2> Permeable base layer, permeable base course layer The permeable base layer 41 and the permeable base course layer 42 as a whole have continuous pores that allow water to move by capillary rise. The permeable base layer 41 also functions as a rainwater storage and infiltration facility. The thickness of the permeable base layer 41 and the permeable base course layer 42 is selected appropriately depending on the site conditions, etc.

[0017] The grain size of the permeable roadbed structure is larger in the lower permeable base layer 41 than in the upper permeable base layer 42, and the permeability of the lower permeable base layer 41 is also larger than that of the upper permeable base layer 42.

[0018] <3> Examples of materials for the permeable base layer The permeable base layer 42 is made of mineral particles or artificial particles that are not deteriorated by rainfall or the like and can maintain a certain gap for a long period of time, such as granite or red clay. It is more preferable to use granite for the permeable base layer 42.

[0019] Generally, paved roads are subjected to repeated foot traffic, and so if ordinary soil or black soil is used as the permeable roadbed layer 42, a certain degree of permeability and capillary rise can be expected at the beginning of construction, but over time, the gaps between the soil particles will decrease due to repeated loads, and this performance will decline. In contrast, granite or red soil has fewer clay particles than ordinary soil or black soil, so the gaps between the soil particles are less likely to decrease even when subjected to repeated loads, making it possible to maintain permeability and capillary rise over a long period of time.

[0020] In this example, for ease of understanding, a form in which a permeable pavement layer 43 is formed on a permeable roadbed layer 42 is shown, but a known permeable base layer may also be provided between the permeable roadbed layer 42 and the permeable pavement layer 43.

[0021] <4> Permeable pavement layer The permeable pavement layer 43 is the uppermost layer having permeability, and may be made of, for example, hard blocks or permeable asphalt (open grain asphalt) having permeability and water retention.

[0022] 2. Base Material <1> Structure of Base Material The base material 10 is buried in the ground and used as a carrier for absorbing carbon dioxide, a filler or backfill material for preventing clogging, or the like.

[0023] The structure of the base material 10 will be described with reference to Figure 4. The base material 10 comprises an aggregate body 20 made of waste concrete, a wet coating layer 30 containing naturally occurring wet substances and attached to the surface of the aggregate body 20, and recycled concrete fine powder 33 that serves as a carbon dioxide carrier and is attached to the surface of the aggregate body 20 or the wet coating layer 30.

[0024] In the present invention, it is assumed that 100% recycled concrete materials are used for the aggregate body 20 and the recycled fine powder 33, so when manufacturing the base material 10, there are no problems such as the mass consumption of fossil fuels or the generation of carbon dioxide due to heating.

[0025] <2> Aggregate Body The aggregate body 20 includes, for example, hard recycled aggregate or natural aggregate. The particle size of the aggregate body 20 can be 10 mm to 20 mm, 20 mm to 30 mm, 30 mm to 40 mm, or 40 mm to 60 mm.

[0026] In this example, we will explain an embodiment in which recycled aggregate (recycled crushed stone) extracted from waste concrete is used as the aggregate body 20. When recycled aggregate is used for the aggregate body 20, for example, lumps of waste concrete are primarily crushed using a crushing device such as a jaw crusher, and the crushed concrete pieces are further crushed secondarily using a crushing device such as a centrifugal crusher, and then classified into a predetermined particle size range to produce the aggregate body 20. The aggregate body 20 may be of a single particle size or may have a predetermined particle size distribution.

[0027] <3> Wet Coating Layer The wet coating layer 30 comprises a naturally occurring wet substance 31 having an acidic functional group and an adhesion aid 32 having wettability.

[0028] <3.1> Naturally occurring moist material The naturally occurring moist material 31 is a naturally occurring material having an acidic functional group, such as allophane, humic substances, etc. The naturally occurring moist material 31 not only functions to capture SS substances, but also greatly contributes to increasing the height of water uptake by capillary action.

[0029] <3.1.1> Allophane Allophane is a type of clay mineral, a porous, amorphous silica-alumina mineral formed by the long-term weathering of volcanic ash-derived soil. Its component composition is Al ２ O ３ SiO ２ ・nH ２ O. Because it contains many very fine pores, it has a large specific surface area and is prone to physical adsorption and moisture absorption.

[0030] <3.1.2> Humus Humus is a naturally occurring humic substance with acidic functional groups that is produced during the decomposition process in which the remains of plants and animals in the soil are broken down by the action of microorganisms. It becomes a colloidal organic polymer compound that not only has the effect of being easily physically adsorbed, but also has a neutralizing effect on the alkalinity of recycled aggregate.

[0031] <3.2> Adhesion aid (means for adhering wet substance and recycled fine powder) It is difficult to inseparably adhere the wet substance 31 and recycled fine powder 33 to the aggregate body 20. Therefore, by using an adhesion aid 32 having wettability, the wet substance 31 and recycled fine powder 33 are adhered to the surface of the aggregate body 20.

[0032] The adhesion aid 32 is a wettable aid that exhibits viscosity when wet, and examples of suitable materials include water, a highly water-absorbent resin, a polymer absorbent (polyacrylic acid (salt)-based (sodium polyacrylate), starch graft polymerization-based, polyvinyl alcohol-based, and carboxymethyl cellulose (CMC)-based materials), vinyl acetate resin, and polyvinyl alcohol.

[0033] <4> Recycled Fine Powder In the present invention, after the surface of the aggregate body 20 is covered with the wet coating layer 30, recycled concrete fine powder 33 is further sprinkled on the surface to adhere in the form of a thin film. The particle size of the recycled fine powder 33 is selected appropriately. The recycled fine powder 33 refers to untreated concrete fine powder obtained by crushing concrete debris, etc. "Untreated" means that it has not been subjected to a heat treatment.

[0034] <4.1> Purpose of using recycled fine powder The recycled fine powder 33 is used for the following reasons: to utilize the carbonation phenomenon of concrete to continuously adsorb carbon dioxide, and to increase the surface area of ​​the aggregate body 20 to improve the function of capturing SS substances. "Continuously" means that carbon dioxide continues to be adsorbed semi-permanently without consuming thermal energy, etc.

[0035] When recycled aggregate is used as the aggregate body 20, the concrete components attached to the surface of the recycled aggregate can be used as a carrier of carbon dioxide, but since there is a large variation in the amount of concrete components attached, there is a limit to the stable adsorption of large amounts of carbon dioxide.

[0036] In the present invention, recycled concrete fine powder 33 is attached to the surface of the aggregate body 20 or the wet coating layer 30 in order to significantly increase the amount of concrete components attached to the base material 10 and the exposed area (surface area) of the concrete components, thereby stably adsorbing a large amount of carbon dioxide.

[0037] <4.2> Means for Adhering Recycled Fine Powder The recycled fine powder 33 is attached to the surface of the aggregate body 20 or the wet coating layer 30 by sprinkling it using the adhesion aid 32 having the wettability described above.

[0038] <4.3> Regarding the amount of coating of naturally occurring moist substances and the amount of recycled fine powder attached The amount (adherence area) of recycled fine powder 33 attached to the base material 10 affects the pH of the base material 10 and the amount of carbon dioxide adsorption. For example, increasing the amount of coating of recycled fine powder 33 increases the amount of carbon dioxide adsorption, while raising the pH of the base material 10, thereby worsening the planting environment. The amount (coverage area) of naturally occurring moist substances 31 attached to the base material 10 affects the pH of the base material 10. For example, increasing the amount of coating of naturally occurring moist substances 31 lowers the pH of the base material 10, improving the planting environment. This is because the naturally occurring moist substances 31 exert a pH buffering effect. Therefore, the amount of coating of naturally occurring moist substances 31 and the amount of coating of recycled fine powder 33 on the base material 10 should be selected appropriately, taking into account the pH of the base material 10, the amount of carbon dioxide adsorption, etc.

[0039] <5> Mixing means for base material In this example, a form of mixing using a mixing device 50 equipped with stirring blades in a storage tank will be described. There are no particular restrictions on the mixing means for the base material 10, and in addition to using the mixing device 50, mixing may also be performed using construction machinery such as a backhoe.

[0040] 3. Method for Manufacturing the Base Material A method for manufacturing the base material 10 will be described with reference to FIG.

[0041] <1> Dry mixing process of aggregate body As shown in Figure 2(a), first, the aggregate body 20 is charged into the kneading device 50 and then kneaded. Dry mixing means kneading only the aggregate body 20. At this time, water is sprayed inside the kneading device 50 to wet the surface of the aggregate body 20. Note that the dry mixing process of the aggregate body 20 is not essential and may be omitted.

[0042] <2> Step of Coating Aggregate Body with Wet Coating Layer Next, specified amounts of wet substance 31 and adhesion aid 32 are charged into the kneading device 50 and kneaded. By kneading the aggregate body 20, wet substance 31, and adhesion aid 32, a wet coating layer 30 is generated in the kneading device 50, and the wet coating layer 30 coats the surface of the aggregate body 20 ( FIG. 3 ). The adhesion aid 32 provides the wet coating layer 30 with adhesiveness, so that the wet coating layer 30 adheres to the surface of the aggregate body 20. The coating of the aggregate body 20 with the wet coating layer 30 may be either a coating of the entire surface of the aggregate body 20 or a partial (patchy) coating of the surface of the aggregate body 20.

[0043] <3> Recycled Fine Powder Adhesion Process The coating layer 30 covering the aggregate body 20 contains a small amount of moisture, giving it an appropriate degree of viscosity (adhesion). In this state, the measured recycled fine powder 33 is added to the kneading device 50 and kneaded. By adding the recycled fine powder 33 and kneading it, the recycled fine powder 33 adheres not only to the surface of the wet coating layer 30, which has wettability, but also to the exposed surface of the aggregate body 20 via the adhesion aid 32.

[0044] The recycled fine powder 33 is introduced and coated after the formation of the wet coating layer 30 in order to avoid the recycled fine powder 33 being buried deep in the wet coating layer 30, while allowing the recycled fine powder 33 to adhere to the surface of the wet coating layer 30 in an exposed state.

[0045] In this way, the base material 10 can be manufactured by a simple process of simply coating the surface of the aggregate body 20 with the wet coating layer 30 and the recycled fine powder 33.

[0046] It is also possible to manufacture the base material 10 by simultaneously adding the aggregate body 20, the wet substance 31, the adhesion aid 32 and the recycled fine powder 33.

[0047] <4> Heat Energy Required for Manufacturing Base Material As described above, the base material 10 according to the present invention uses 100% recycled concrete aggregate as the aggregate body 20, and further contains concrete filler that had been disposed of as industrial waste as recycled fine powder 33. Therefore, in manufacturing the base material 10, the concrete filler can be used as recycled fine powder 33 without heat treatment, and therefore, the problems of mass consumption of fossil fuels and generation of carbon dioxide due to heating are eliminated in manufacturing the base material 10 that also serves as a carrier.

[0048] [Functions of the Permeable Roadbed Structure] Hereinafter, a number of functions of the permeable roadbed structure will be described.

[0049] 1. Permeable roadbed structure allows rainwater to be stored and infiltrated, and cools the atmosphere

[0050] <1> Rainwater storage and infiltration function As shown in Figure 1, each layer 41 to 43 that constitutes the permeable roadbed structure has continuous water permeability, so rainwater etc. permeates downward and is finally stored in the permeable base layer 41. The function of capturing SS substances when rainwater infiltrates will be described later.

[0051] <2> Atmospheric cooling function When the surface temperature of the permeable pavement layer 43 rises with rising summer temperatures, the water stored in the permeable base layer 41 rises toward the permeable pavement layer 43 due to capillary action and evaporates into the atmosphere. As the water evaporates into the atmosphere, it absorbs the heat of vaporization, thereby lowering the temperature around the permeable pavement layer 43 and providing effective cooling. As a result, the cooling effect around the permeable pavement layer 43 can be maintained for a long period of time, making it extremely effective as a countermeasure against the urban heat island effect.

[0052] 2. Carbon dioxide fixation and storage function of the base material

[0053] <1> Dissolution of carbon dioxide into rainwater Carbon dioxide present in the atmosphere dissolves in carbon dioxide (H ２ CO ３ ) and dissolves in rainwater. Rainwater with dissolved carbon dioxide is slightly acidic. ２ O+CO ２ →H ２ CO ３

[0054] <2> Carbonation phenomenon caused by concrete components and carbon dioxide The base material 10 is buried in the ground as a permeable base layer 41 containing aggregate bodies 20 made from waste concrete and recycled fine powder 33 made from waste concrete. Therefore, when rainwater containing carbon dioxide permeates the permeable pavement layer 43, the concrete components of the base material 10 (aggregate bodies 20 and recycled fine powder 33) react with the carbon dioxide contained in the rainwater, causing carbonation.

[0055] Carbonation is the process by which calcium compounds in cement hydrate into calcium hydroxide (Ca(OH) ２ ) reacts with carbon dioxide to form calcium carbonate.

[0056] That is, the carbon dioxide (H ２ CO ３ ) reacts with the concrete components of the base material 10 to form calcium carbonate (CaCO ３ ) is precipitated. Ca(OH) ２ +2H ２ CO ３ →CaCO ３ ↓+2H ２ O

[0057] <2.1> Fixation and accumulation of carbon dioxide (calcium carbonate) In this way, carbon dioxide in the atmosphere permeates into the soil via rainwater, and then becomes carbonated in the permeation base layer 41 in the soil, eventually becoming calcium carbonate (CaCO ３ ) and accumulates on the surface of the substrate 10.

[0058] The carbon dioxide absorption phenomenon caused by carbonation in concrete is well known, but the present invention does not simply absorb carbon dioxide. The base material 10 according to the present invention is designed to continuously absorb carbon dioxide into the base material 10 in the soil and to fix (retain) carbon dioxide.

[0059] <2.2> Carbon dioxide accumulation period The surface of the base material 10 in the soil is always wet, and the base material 10 is maintained alkaline, so that the base material 10 can continue to adsorb carbon dioxide. ３The time it takes for carbon dioxide to accumulate in the permeation base layer 41 in the soil is roughly the time it takes for the pH to drop from around 12.6 to around 8.6, and it is possible for carbon dioxide to be continuously adsorbed and fixed, albeit in small amounts, for hundreds of years. In other words, the carbonation phenomenon caused by the base material 10 that constitutes the permeation base layer 41 can continue for hundreds of years.

[0060] <2.3> Quantification of carbon dioxide As mentioned above, the permeable base layer 41 formed from the base material 10 functions as a carbon dioxide adsorption and fixation layer, so by selecting the thickness and volume of the permeable base layer 41, it is possible to quantify the fixation of carbon dioxide.

[0061] <2.4> Natural absorption of carbon dioxide As mentioned above, the carbon dioxide absorption function of the base material 10 is achieved naturally through the infiltration phenomenon of rainwater containing carbon dioxide and the carbonation reaction. Therefore, in the present invention, no external energy such as thermal energy is used to absorb carbon dioxide, and the absorption and fixation of carbon dioxide can be continued semi-permanently using only natural forces.

[0062] 3. Other Functions of the Base Material In addition to the functions already described, the base material 10 also exhibits the following functions.

[0063] <1> Function of capturing SS substances and function of preventing clogging For example, if the permeable base layer 41 is constructed using only ordinary aggregate bodies 20, SS substances that seep in with rainwater will remain between the aggregate bodies 20 and cause clogging. Therefore, when a planting strip is provided adjacent to a sidewalk or road, it becomes difficult for the root systems of plants and trees to extend between the aggregate bodies 20, which are the base material, and there is room for improvement in the growing environment.

[0064] In contrast, the base material 10 has a coating structure in which the entire surface of the aggregate body 20 is covered with a wet coating layer 30 containing naturally occurring wet substances 31, and the coating layer 30 has a moderate viscosity due to the small amount of moisture it contains. Therefore, when rainwater containing SS substances flows down the wet coating layer 30 on the surface of the base material 10, the floating SS substances are easily attached and captured simply by coming into contact with the naturally occurring wet substances 31. Because the captured SS substances are moist and of nearly the same quality as the naturally occurring wet substances 31, new SS substances are captured by the captured SS substances. Because the infiltration rate of rainwater is extremely slow, the captured SS substances do not separate from the base material 10 and flow out, and the captured state is maintained for a long period of time.

[0065] Focusing on the fact that allophane, humus, etc. that make up the naturally occurring wet material 31 have properties and compositions that are very similar to those of the kibushi clay, red clay, etc. that make up the SS material, the surface of the aggregate body 20 is coated with a wet coating layer 30 that contains the naturally occurring wet material 31 that is almost the same quality as the SS material, thereby forming the base material 10.

[0066] In this way, by capturing the SS substances on the surface of the base material 10, it is possible to effectively suppress the settling and accumulation of the SS substances, which are the cause of the formation of an impermeable layer at the bottom of the permeable base layer 41, which is an aggregate of the base materials 10. Therefore, the excellent clogging prevention effect of the base material 10 can be maintained for a long period of time.

[0067] <2> Buffering Action of Naturally Occurring Moisture Substances The moist coating layer 30 covering the surface of the base material 10 contains naturally occurring moisture substances 31, which exert a pH buffering action.

[0068] For example, when the naturally occurring wet substance 31 is humus, the reaction can be described as a deprotonation reaction of the carboxyl group and the phenolic hydroxyl group, which are acidic functional groups contained in humic acid (humic acid) and fulvic acid that constitute the humus (H ＋ is called a proton.) >COOH⇔>COO － +H ＋ >OH⇔>O － +H ＋H dissociated from the acidic functional groups contained in humic acid and fulvic acid ＋ is an alkaline component (OH － ) reacts with H ２ O, which lowers the pH.

[0069] The fact that the aggregate body 20 constituting the base material 10 is made of recycled aggregate made from concrete and that the recycled fine powder 33 coated on its surface is made from concrete are factors that increase the pH of the base material 10, but by utilizing the buffering action of the naturally occurring moist substance 31 contained in the wet coating layer 30, it is possible to keep the pH of the base material 10 at a low value. Therefore, even if vegetation or trees are planted on a permeable roadbed structure to which the base material 10 is applied, the alkalinity caused by the concrete components can be alleviated, improving the vegetation environment.

[0070] 10... Base material 20... Aggregate body (recycled aggregate) 30... Wet coating layer 31... Wet substance 32... Adhesion aid 35... Recycled fine powder 40... Subgrade 41... Permeable base layer 42... Permeable roadbed layer 43... Permeable pavement 50... Mixing device

Claims

1. A base material to be buried in the ground and used as a filler or backfill material to prevent clogging, characterized by comprising: a hard aggregate body; a wet coating layer covering the surface of the aggregate body and comprising a naturally occurring moist substance having an acidic functional group that has at least the function of capturing SS substances and a pH buffering action; and an adhesion aid that becomes viscous when wet and causes the moist substance to adhere to the surface of the aggregate body; and recycled concrete fine powder that serves as a carbon dioxide carrier and is attached to the surface of the aggregate body or the wet coating layer.

2. The base material according to claim 1, wherein the recycled fine powder is untreated fine powder made from waste concrete.

3. The base material according to claim 1 or 2, characterized in that the recycled fine powder is adhered to the surface of the aggregate body or wet coating layer by utilizing the wettability of the adhesion aid.

4. The base material according to claim 1, characterized in that the moist substance is allophane or humus.

5. The base material according to claim 1, wherein the adhesion aid is at least one of water, a superabsorbent resin, a polymeric absorbent, a vinyl acetate resin, and polyvinyl alcohol.

6. The base material according to claim 1, wherein the aggregate body is a single-grain recycled aggregate produced from waste concrete.

7. The base material according to claim 1, characterized in that it is used as a permeable base layer of a permeable roadbed structure.

8. A method for adsorbing and fixing carbon dioxide using a base material, comprising: burying the base material according to claim 1 in the ground as a filler or backfill material for preventing clogging; when rainwater seeps into the ground, the concrete components of the base material react with the carbon dioxide contained in the rainwater as carbon dioxide to produce calcium carbonate; and adsorbing and fixing the carbon dioxide in the form of calcium carbonate on the surface of the base material.

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