Carbon dioxide fixation method and seaweed bed formation method using concrete substrate for seaweed bed growth reef

Abstract

To provide a carbon dioxide fixation method through the production of a porous concrete substrate for seaweed bed growth reef that allows absorption and retention of carbon dioxide for effectively promotion of seaweed growth, while effectively retaining blue carbon underwater to contribute to realization of carbon neutrality, and also to provide a seaweed bed formation method using the porous concrete substrate for seaweed bed growth reef.SOLUTION: A concrete composition is subjected to carbonation curing with carbon dioxide, wherein the concrete composition comprises 260 to 310 kg / m3 of early strength cement, with a water-to-cement ratio of 55 to 67, and an air content of 5.0 to 12.0 as measured according to JIS A 1128. This results in the preparation of a porous concrete body that retains 20 to 80 kg-CO2 / m3 of carbon dioxide and has a 28-day compressive strength of 30 to 43 N / mm2. Seaweed roots and / or spores are planted or sown into pores of the porous concrete body. The concrete body is installed on the seabed as a concrete growth reef substrate and the seaweeds absorb carbon dioxide in seawater.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for fixing carbon dioxide and a method for creating a seaweed bed using a concrete seaweed bed growth reef base material. In particular, the present invention relates to a method for fixing carbon dioxide and a method for creating a seaweed bed using a concrete seaweed bed growth reef base material that can effectively absorb and store carbon dioxide, effectively promote the growth of algae, and construct a seaweed bed that can contribute as a CO2 absorption source (blue carbon).

Background Art

[0002] In recent years, due to the influence of rising seawater temperature associated with climate change, conventional seaweed beds of seaweeds have been shrinking, and the so-called "coastal burning" areas due to predation by sea urchins and the like have been expanding. The expansion of such "coastal burning" not only results in the loss of maintained biodiversity, but also causes problems such as a decrease in the catch due to damage to the ecosystem, which affects the fishery.

[0003] In view of such a situation, in order to form a core seaweed bed for the regeneration of the seaweed bed in the surrounding sea area, a seaweed bed growth reef has been used and utilized for the formation of a seaweed bed. The basic configuration of a conventional seaweed bed growth reef is generally a base material such as concrete mainly using ordinary Portland cement, with seaweed seeds (zoospores, fertilized eggs) or roots installed and surrounded by a net as a countermeasure against predation by fish and the like.

[0004] However, in concrete using ordinary Portland cement, the water-cement ratio cannot be increased to obtain a certain level of strength, so the amount of air bubbles carried during concrete mixing decreases, and it is not sufficiently suitable for the absorption and storage of carbon dioxide (CO2). In addition, when the amount of air bubbles is increased, there are problems such as a decrease in the strength of the hardened concrete body and the occurrence of cracks and fractures.

[0005] As conventional concrete growth reef base materials, Japanese Patent Application Laid-Open No. 2011-229489 (Patent Document 1) discloses blocks formed using granulated fly ash as an aggregate and subjected to neutralization treatment with carbon dioxide gas. The granulated fly ash is formed from 100 parts by mass of fly ash generated in a coal-fired power plant and a raw material containing 3 to 7 parts by weight of blast furnace cement, and a fish reef and algal reef block is characterized by this.

[0006] Also, Japanese Patent Application Laid-Open No. 2006-081501 (Patent Document 2) describes a method for manufacturing a settlement base including a kneading step of kneading an aggregate, cement, and carbonated water to obtain a mixture, a molding step of injecting the mixture into a mold to obtain a molded body having at least an upper side with a porous property, and a carbonic acid treatment step of bringing the molded body into contact with carbonic acid, and is characterized by replacing a part of the cement with artificial zeolite.

[0007] Furthermore, Japanese Patent Application Laid-Open No. 2015-167524 (Patent Document 3) discloses an algal bed construction reef including a settlement part having a plurality of settlement blocks that promote the settlement of seaweed and a basket part that accommodates the settlement part so as to surround it. The settlement part is formed in a rectangular parallelepiped shape and is preferably a porous concrete block. The basket part is formed in a rectangular parallelepiped shape having an inclusion shape complementary to the settlement part, and further has a plurality of protrusions on at least one surface of the basket part for fixing to the seabed.

[0008] However, the conventional ones cannot fully exhibit carbon dioxide (CO2) absorption and storage performance, and in particular, carbon dioxide absorption and storage are not sufficiently considered as an algal bed growth reef base material.

[0009] Also, these days, carbon neutrality with reduced greenhouse gas such as carbon dioxide has attracted attention, and strengthening of reduction of greenhouse gas emissions etc. is required. In particular, an algal bed is positioned as a CO2 absorption source (blue carbon) by photosynthesis, and the regeneration of an algal bed is regarded as an important issue in climate change countermeasures.

[0010] In view of such environmental protection, Japanese Patent Application Laid-Open No. 2023-110190 (Patent Document 4) discloses that dredged soil and a solidifying material are mixed, and a base material that exhibits a 28-day strength of 500 kN / m 2 or more and 9,800 kN / m 2 or less is put into water and installed, and it is a seaweed attachment base having a maximum porosity of 20% obtained from the following formula. The porosity formula is: Porosity % = (1 - the input amount m of the base material 3 / the volume m by the base material 3 ) × 100.

[0011] However, in conventional growth reefs for algal beds, it is common to use ordinary cement. Since the amount of air bubbles in the concrete body using ordinary cement is small, the amount of ordinary cement used increases. Furthermore, in order to obtain a certain strength, it is difficult to increase the water / ordinary cement ratio, and since the surface area of the obtained concrete is not sufficient, it is not a concrete growth reef base material that can sufficiently store carbon dioxide as an algal bed growth reef base material. Currently, there is an expectation for a base material that can effectively fix carbon dioxide, contribute to reducing the environmental load, and form an algal bed effective for the growth of algae.

Prior Art Documents

Patent Documents

[0012]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0013] An object of the present invention is to solve the above problems, be able to sufficiently absorb and store carbon dioxide, promote the growth of algae, and create a good algal bed, so that carbon dioxide can be effectively fixed, and blue carbon can be effectively stored even in water, contributing to the realization of carbon neutrality. It is to provide a good carbon dioxide fixation method using a porous concrete algal bed growth reef base material. Also, preferably, by using a concrete algal bed growth reef base material in which carbon dioxide is fixed by effectively utilizing the exhaust gas from a cement factory, it is possible to reduce the amount of carbon dioxide emissions and effectively fix carbon dioxide, and to provide a carbon dioxide fixation method.

[0014] Another object of the present invention is to provide a method for creating an algal bed using a concrete algal bed growth reef base material that is porous, can effectively promote the growth of algae, allows algae to effectively store blue carbon, and contributes to the realization of carbon neutrality.

Means for Solving the Problems

[0015] The inventors of the present invention have obtained a carbon dioxide fixation method and an algal bed creation method using a concrete algal bed growth reef base material, in which a concrete body having a specific air volume, in which carbon dioxide is effectively absorbed and stored by subjecting a concrete composition having a specific material and formulation to a neutralization curing treatment, is used as the algal bed growth reef base material, so that a rich algal bed can be formed and blue carbon can be effectively stored.

[0016] (1) The carbon dioxide fixation method using the concrete algal bed growth reef base material of the present invention is to neutralize and cure a concrete composition containing 260 to 310 kg / m of early-strength cement 3 , a water / cement ratio (mass%) of 55 to 67, and an air volume (volume%) of 5.0 to 12.0 according to JIS A 1128 with carbon dioxide-containing neutralization curing, so as to store 20 to 80 kg-CO2 / m of carbon dioxide 3 , and the 28-day compressive strength is 30 to 43 N / mm 2A porous concrete body is prepared, and the roots of algae are planted and / or spores are sown in the pores of the porous concrete body. The concrete body is installed on the seabed as a substrate for a concrete algae bed growth reef, and the algae absorb carbon dioxide in the sea. This is a method for carbon dioxide fixation using a concrete algae bed growth reef substrate.

[0017] (2) Preferably, in the carbon dioxide fixation method of (1) above, the concrete composition further contains an AE agent or a foaming agent. This is a method for carbon dioxide fixation using a concrete algae bed growth reef substrate.

[0018] (3) Preferably, in the carbon dioxide fixation method of (1) or (2) above, the concrete growth reef substrate has an air bubble amount of 3.0 to 8.9% by volume of 300 μm or more calculated using the linear traverse method (ASTM C 457). This is a method for carbon dioxide fixation using a concrete algae bed growth reef substrate.

[0019] (4) Also preferably, in the method for carbon dioxide fixation in the sea of (1) or (2) above, the neutralization curing is performed using the exhaust gas from a cement factory, and the porous concrete body is carbonated by the carbon dioxide in the exhaust gas, and the carbon dioxide is fixed. This is a method for carbon dioxide fixation using a concrete algae bed growth reef substrate.

[0020] (5) The method for creating an algae bed using the concrete algae bed growth reef substrate of the present invention uses a concrete composition containing 260 to 310 kg / m 3 of early-strength cement, a water / cement ratio (mass%) of 55 to 67, and an air content (volume%) of 5.0 to 12.0 according to JIS A 1128, and performs neutralization curing containing carbon dioxide, thereby storing 20 to 80 kg-CO2 / m 3 of carbon dioxide, and having a 28-day compressive strength of 30 to 43 N / mm 2A porous concrete body is prepared, algae roots are planted and / or spores are sown in the pores of the porous concrete body, and the concrete body is installed on the seabed as a concrete growth reef base material, and an algal bed is created in which the algae absorb carbon dioxide in the sea and grow. This is a method for creating an algal bed using a concrete algal bed growth reef base material.

Effects of the Invention

[0021] In the carbon dioxide fixation method using the concrete algal bed growth reef base material of the present invention, during the curing when preparing the concrete body that becomes the concrete algal bed growth reef base material, the amount of air bubbles entrained in the concrete base material is large, and the concrete base material becomes porous. Therefore, the structure is such that carbon dioxide can easily enter the inside of the concrete base material, carbonation is promoted, and carbon dioxide can be sufficiently absorbed and stored. In addition, algae roots and spores can easily adhere to the pores formed in the concrete base material, effectively promoting the growth of algae, and also effectively storing blue carbon in water, contributing to the realization of carbon neutrality. Preferably, by effectively using the exhaust gas from the cement factory to prepare the concrete algal bed growth reef base material, it is possible to reduce the amount of carbon dioxide emitted into the atmosphere and contribute to environmental protection.

[0022] In addition, the method for creating an algal bed using the concrete algal bed growth reef base material of the present invention can effectively promote the growth of algae by using the above-mentioned porous concrete algal bed growth reef base material, and can create an algal bed that can effectively store blue carbon and contribute to the realization of carbon neutrality.

Brief Description of the Drawings

[0023]

Figure 1

Embodiments for Carrying Out the Invention

[0024] The present invention will be described by the following preferred embodiments, but is not limited thereto. The method for carbon dioxide fixation using the porous concrete algal bed growth reef base material of the present invention comprises a concrete composition containing 260 to 310 kg / m of early-strength cement, a water / cement ratio (mass %) of 55 to 67, and an air content (volume %) of 5.0 to 12.0 according to JIS A 1128. By subjecting it to carbon dioxide-including neutral curing, 20 to 80 kg-CO 3 / m 2 is stored, and a porous concrete body having a 28-day compressive strength of 30 to 43 N / mm 3 is prepared. Algal roots are planted and / or spores are sown in the pores of the porous concrete body, and the concrete body is installed on the seabed as a concrete growth reef base material, and the algae absorb carbon dioxide in the sea and grow. This is a method for carbon dioxide fixation using a concrete algal bed growth reef base material. 2 Further, the method for creating an algal bed using the porous concrete algal bed growth reef base material of the present invention comprises using a concrete composition containing 260 to 310 kg / m of early-strength cement, a water / cement ratio (mass %) of 55 to 67, and an air content (volume %) of 5.0 to 12.0 according to JIS A 1128. By subjecting it to carbon dioxide-including neutral curing and hardening, 20 to 80 kg-CO2 / m

[0025] is stored, and a porous concrete body having a 28-day compressive strength of 30 to 43 N / mm 3 is prepared. Algal roots are planted and / or spores are sown in the pores of the porous concrete body, and the concrete body is installed on the seabed as a concrete growth reef base material, and an algal bed is created in which the algae absorb carbon dioxide in the sea and grow. This is a method for creating an algal bed using a concrete algal bed growth reef base material. 3 The porous (porous) concrete algal bed growth reef base material used in the method of the present invention will be described below. 2 The porous (porous) concrete algal bed growth reef base material used in the method of the present invention will be described below.

[0026] The porous (porous) concrete algal bed growth reef base material used in the method of the present invention will be described below. A concrete composition for preparing a porous (porous) concrete algae bed growth reef base material is prepared by mixing and kneading early-strength cement, water, fine aggregate, coarse aggregate, and preferably an AE agent or a foaming agent, and further an admixture or the like compounded as required, to produce the concrete composition (fresh concrete material) used in the present invention. In particular, by including an AE agent or a foaming agent, preferably by including a foaming agent instead of an AE agent, the resulting concrete body can more effectively have the above-described sufficient amount of air bubbles and CO2 absorption amount while maintaining a certain strength.

[0027] The cement used in the above concrete composition is early-strength cement, and ordinary Portland cement or the like that has been conventionally used is not used. The blending amount of the early-strength cement is 260 to 310 kg / m 3 : per unit amount (kg / m 3 of the mass of the concrete composition 1 m 3 and preferably 260 to 290 kg / m 3 is desirably used. By using early-strength cement at such a content, while maintaining a certain strength, the water-cement ratio can be increased, so that the amount of air bubbles contained can be increased within the above range, and not only the surface but also the inside of the resulting concrete body can be made porous.

[0028] Also, the water to be blended is not particularly limited, and for example, tap water, industrial water, recycled water, groundwater, river water, rainwater, etc. can be used. The water / cement ratio (mass%) is 55 to 67 mass%, and preferably 60 to 65 mass%. As described above, by using early-strength cement, the water-cement ratio can be increased while maintaining a certain strength, the amount of air bubbles increases, carbonation is promoted, and the CO2 adsorption amount can be increased.

[0029] The fine aggregate is not particularly limited, and examples thereof include natural-derived sands such as mountain sand, river sand, land sand, sea sand, crushed sand, and limestone crushed sand defined in Aggregates for Ready Mixed Concrete in Appendix A of JIS A 5308, slag-derived sands such as blast furnace slag, electric furnace oxidized slag, and ferronickel slag, recycled aggregate, artificial lightweight aggregate, recovered aggregate, etc. One of these may be used alone, or two or more thereof may be used in combination.

[0030] The blending amount is not particularly limited as long as the resulting concrete body is within a range that does not substantially inhibit the object of the present invention. For example, in terms of the unit amount (kg / m 3 : mass per 1 m 3 of the concrete composition), it can be about 650 kg / m 3 to 1000 kg / m 3 can be used.

[0031] The coarse aggregate is not particularly limited, and examples thereof include natural aggregates such as river gravel, mountain gravel, and sea gravel defined in Aggregates for Ready Mixed Concrete in Appendix A of JIS A 5308, artificial aggregates such as crushed stones of sandstone, hard limestone, basalt, and andesite, recycled aggregate, etc. One of these may be used alone, or two or more thereof may be used in combination. The blending amount is not particularly limited as long as it is within a range that does not substantially inhibit the object of the present invention. For example, in terms of the unit amount (kg / m 3 : mass per 1 m 3 of the concrete composition), it can be about 800 kg / m 3 to 1250 kg / m 3 can be used.

[0032] Also, the AE agent or foaming agent is not particularly limited, and any known AE agent or foaming agent can be used. For example, as the AE agent, anionic, cationic, nonionic, and amphoteric surfactants can be exemplified, and anionic surfactants such as resin-based, alkylbenzene sulfonic acid-based, and alcohol ester-based surfactants can be preferably used. Further, as the foaming agent, for example, aluminum powder etc. can be used.

[0033] The compounding amount of the AE agent is preferably 0.001 to 0.01% by mass (C×%) with respect to the content of the above cement (C). Further, as the compounding amount of the foaming agent, it is 0.3 to 0.6 kg / m 3 (kg / m 3 : mass per 1 m of the concrete composition 3 , preferably 0.4 to 0.5 kg / m 3 is desirably set. By incorporating an AE agent or a foaming agent into the concrete composition, a concrete composition containing an air content (volume %) of 5.0 to 12.0 can be effectively obtained. Further, the concrete growth reef base material produced using the concrete composition can have a bubble amount of 300 μm or more of 3.0 to 8.9% by volume calculated using the linear traverse method (ASTM C 457).

[0034] Furthermore, if necessary, admixtures other than the above can be blended within a range that does not substantially inhibit the object of the present invention. Examples of the admixtures include AE water reducing agents, foaming agents, waterproof agents, etc., and one or more of these can be used. Also, within a range that does not substantially inhibit the object of the present invention, it is also possible to mix admixtures such as artificial calcium carbonate, steel slag, blast furnace slag, fly ash, etc.

[0035] The artificial calcium carbonate that is blended if necessary can preferably be artificial calcium carbonate synthesized using carbon dioxide contained in exhaust gas. Thereby, it is possible to protect the resources of limestone and to effectively utilize waste and the like. For example, carbon dioxide as an industrial product, air, exhaust gas containing carbon dioxide from a factory, such as exhaust gas containing carbon dioxide generated during the firing of cement clinker, is blown into the sludge water discharged from, for example, a cement factory, a ready-mixed concrete factory, a concrete product factory, etc., and reacted with the hydration products in the sludge water to produce calcium carbonate, and the sludge water is recovered to prepare artificial calcium carbonate, and the obtained artificial calcium carbonate can be used, but it is not limited to such a preparation method, and artificial calcium carbonate prepared by any known method can be used.

[0036] The above-mentioned early-strength cement, fine aggregate, coarse aggregate, AE agent or foaming agent, and water are mixed and kneaded at the above specific mixing ratios, and the admixtures and admixture materials to be blended as necessary, and a concrete composition containing an air content (volume %) measured by JIS A 1128 of 5.0 to 12.0 volume %, preferably 5 to 11 volume %, is prepared. The preparation procedure is not particularly limited as long as it is a method capable of uniformly kneading even if the early-strength cement, fine aggregate, coarse aggregate, etc. are prepared in advance and water is mixed therewith, or all the raw materials are mixed at once. Also, there is no limitation on the type of kneader, etc., and a conventional kneader can be used, but a kneader that can be sufficiently stirred and kneaded so that the air content becomes 5.0 to 12.0 volume % is used.

[0037] The reason for setting the air content in the above range, especially 5.0 volume % or more, is to suppress the decrease in frost resistance (as specified in the Concrete Standard Specification), and when the air content exceeds a certain amount, the 28-day compressive strength of the hardened concrete body rapidly decreases and the durability is impaired. Therefore, the air content is maintained at 20 N / mm 2 or less so as to be maintained at 12 volume %.

[0038] Next, the obtained concrete composition can be cured using known curing methods such as steam curing, sealed curing, carbonation curing, autoclave curing, etc., and it is possible to cure and harden by combining these curing methods to obtain a molded body. However, carbonation curing using a gas containing at least carbon dioxide is carried out to produce a hardened concrete body by hardening while promoting carbonation by the carbonation curing. The shape of the concrete body to be obtained is not particularly limited as long as it is a molded body that does not move in water due to ocean currents or the like. For example, it can be cured and hardened in the shape of a rectangular parallelepiped or a quadrangular prism to produce a hardened concrete body.

[0039] The gas containing carbon dioxide that promotes carbonation curing is not particularly limited as long as it can promote the carbonation of the obtained concrete body, and a gas adjusted to contain, for example, about 10 to about 30% by volume of carbon dioxide can be used. Preferably, for example, exhaust gas discharged from cement plants and other exhaust gas can be effectively used. Such exhaust gas generally contains 10 to 30% by volume of carbon dioxide, and by using the exhaust gas during carbonation curing that promotes carbonation, it is possible to effectively carry out the carbonation of the concrete body.

[0040] Specifically, in order to promote the carbonation of concrete, autoclave curing (high-temperature and high-pressure steam curing) (JIS A 0203) is utilized, and at that time, the exhaust gas containing carbon dioxide discharged from a cement plant is introduced at 180 to 190 °C and within 10 to 11 atmospheres as an example to illustrate a method for promoting carbonation.

[0041] Thus, in the present invention, since exhaust gas containing carbon dioxide is preferably used, not only in cement plants, but also in various facilities such as power plants, incinerators, steel mills, and factory facilities, the amount of exhaust gas containing carbon dioxide generated during operation discharged into the atmosphere can be reduced, carbon dioxide can be fixed, and it becomes possible to contribute to the realization of carbon neutrality.

[0042] Since the above concrete composition for manufacturing a concrete body contains an air amount at the above ratio, the concrete body obtained by curing and hardening becomes porous (porous state), and not only the surface of the concrete body but also the inside thereof becomes porous (porous state), and the air voids in the concrete body are formed not only as independent voids but also as continuous voids in which further pores exist in the voids. As a result, carbon dioxide can be introduced to the inside of the concrete body, and carbonation is promoted. An example of the state of the formed bubbles (voids) is schematically shown in FIG. 1.

[0043] Preferably, the amount of air bubbles contained in the concrete body is such that, for example, using the linear traverse method (ASTM C 457) for obtaining the area ratio of air bubbles by calculation, the amount of air bubbles of 300 μm or more from the obtained data is 3.0 to 8.9% by volume. By setting the amount of air bubbles (≧300 μm) to 3.0% by volume or more, the CO2 absorption amount of the concrete base material can be 20 kg-CO2 / m 3 or more as described below, and it becomes possible to exhibit excellent CO2 absorption ability.

[0044] Since it is such an extremely porous concrete body in this way, the gas containing carbon dioxide at the time of carbonation curing enters not only the pores on the surface of the concrete body but also the voids (pores) formed inside, and carbonation can be promoted not only on the surface of the concrete body but also inside the concrete body, and effective immobilization of carbon dioxide can be realized.

[0045] The amount of carbon dioxide absorbed by the concrete body is measured by the method described in the following test example, and is 20 to 80 kg-CO2 / m 3 (carbon dioxide absorption amount per 1 m of concrete body 3 (kg)), and a large amount of carbon dioxide can be fixed.

[0046] Although the concrete body is porous (porous state), the compressive strength (JIS A 1108) after 28 days of age is 30 to 43 N / mm 2It has excellent strength expression. When the concrete body is installed as an algal bed growth reef, it will not be destroyed by ocean currents or the like, cracks or fractures will not occur, and it will not move in water, making it excellent for use as an algal bed growth reef.

[0047] Such a concrete body is used as a concrete algal bed growth reef base material for creating an algal bed, especially a core algal bed. Since such a concrete algal bed growth reef base material is porous, the roots of algae can be planted and / or spores can be sown in the pores, and it can be used as the concrete growth reef base material and installed on the seabed. Such a concrete algal bed growth reef base material has a weight and strength such that it will not move due to ocean currents or the like when installed on the seabed.

[0048] When using the concrete algal bed growth reef base material as an algal bed for growing algae, it is desirable to adopt any known method, such as fixing the roots of algae to the concrete growth reef base material with a string or the like, or winding and fixing a seed thread with spores of algae, to plant the roots of algae and / or sow and fix the spores. If necessary, a separate seed germination plate, for example, the seed germination plate described in JP-A-2016-19469, etc., can be installed on the concrete growth reef base material to plant the roots of algae and / or sow the spores to form an algal bed growth reef.

[0049] The algae are not particularly limited, and any algae can be targeted. For example, seaweeds such as Anthocerotophyceae seaweeds or Sargassum seaweeds, Zostera seaweeds, Enhalus seaweeds, and Laminariaceae seaweeds can be exemplified.

[0050] Since the concrete algal bed growth reef base material has a large number of concave and convex pores, seeds and spores are released from the algae grown from the concrete algal bed growth reef base material, and the seeds and spores further adhere to the pores of the concrete algal bed growth reef base material, facilitating the establishment of the roots of algae, enabling the cultivation of algae, forming a core algal bed, and effectively growing algae.

[0051] Through photosynthesis by algae that form a nuclear algal bed, CO2 in seawater is taken into the interior of the algal bed's seaweed chloroplasts and absorbed and stored. As the amount of CO2 in seawater decreases due to this, CO2 in the atmosphere is absorbed by the seawater, and marine plants such as algae in the water absorb carbon dioxide dissolved from the atmosphere into the seawater and accumulate it as organic carbon compounds in the seaweed through photosynthesis reactions. This organic carbon compound is stored in the mud on the shallow seabed and is not easily decomposed by bacteria due to the oxygen-free state, enabling CO2 to be stored in the seabed over a long period of time, and thus achieving carbon dioxide fixation.

[0052] Preferably, in order to protect the algae growing on the concrete algal bed growth reef base material from being damaged by marine organisms, around the algal bed growth reef base material, or when a separate seed attachment plate body is installed as necessary, around the concrete algal bed growth reef base material including the seed attachment plate body, it is also possible to install an enclosure that does not obstruct the sea current, for example, a net-like enclosure.

[0053] As described above, the concrete algal bed growth reef base material for forming an algal bed absorbs CO2 in the exhaust gas from a cement factory or the like or in the atmosphere, and while also absorbing CO2 in seawater by algae, it contributes to carbon neutrality, forms a nuclear algal bed, and can also contribute to the cultivation and productivity improvement of fisheries.

Example

[0054] The present invention will be described by the following examples and comparative examples, but is not limited thereto. Materials Used When preparing and testing a concrete growth reef base material effective for algal bed construction using the carbon dioxide fixation method of the present invention, the materials shown in Table 1 below were used.

[0055]

Table 1

[0056] (Examples 1 to 4, Comparative Examples 1 and 2) Using each of the materials in Table 1 above, each material was uniformly kneaded in a constant temperature chamber at 20°C using a forced kneading pan mixer at the blending ratios shown in Table 2 below to prepare a concrete composition (fresh concrete material). Specifically, the cement, fine aggregate, and coarse aggregate in Table 1 above were blended and dry-kneaded for about 30 seconds, and then the AE agent, foaming agent, and water were blended and kneaded for an additional 90 seconds to prepare each concrete composition (fresh concrete material).

[0057] Each of the concrete compositions (fresh concrete materials) prepared as described above was poured into a cylindrical mold of φ10×20 cm, demolded at an age of 1 day, and then sealed and cured at room temperature until an age of 7 days. After that, air was replaced with a gas adjusted to have a carbon dioxide content of 10% by volume (corresponding to the amount of carbon dioxide contained in the exhaust gas), and the samples were further cured in a carbonation curing tank at a temperature of 20°C and a humidity of 60% for 7 days to obtain each cylindrical concrete specimen of φ10×20 cm.

[0058] Separately, each of the concrete compositions (fresh concrete materials) prepared as described above was poured into a rectangular parallelepiped mold of 30 cm×30 cm×30 cm, demolded at an age of 1 day, and then sealed and cured at room temperature until an age of 7 days. After that, air was replaced with a gas adjusted to have a carbon dioxide content of 10% by volume (corresponding to the amount of carbon dioxide contained in the exhaust gas), and the samples were further cured in a carbonation curing tank at a temperature of 20°C and a humidity of 60% for 7 days to obtain each rectangular parallelepiped concrete specimen of 30 cm×30 cm×30 cm.

[0059] Test Examples (Test Example 1) Air content in the concrete composition (fresh concrete material) The air content in the concrete composition (fresh concrete material) was measured according to JIS A 1128, and the results are shown in Table 2 below.

[0060] (Test Example 2) Bubble content of the concrete specimen The above rectangular parallelepiped hardened concrete specimens each with dimensions of 30 cm × 30 cm × 30 cm were sliced to cut out specimens with dimensions of 10 cm × 10 cm × 10 cm. Using the linear traverse method (ASTM C 457) to calculate the area ratio of air bubbles in each specimen, the amount of air bubbles of 300 μm or more was calculated from the obtained data. Specifically, the cut surface of each cut concrete specimen was polished, and the polished surface was scanned with an optical microscope. From the length of the line segment crossing the air bubbles with respect to the total scanning length, assuming the air bubbles as a single unit system, the air void spacing factor of the concrete was estimated from the number and length of the air bubbles, and the amount of air bubbles with an average of 300 μm or more was calculated. The results are shown in Table 2 below.

[0061] (Test Example 3) Compressive Strength In preparing the above cylindrical concrete specimens each with dimensions of φ10 × 20 cm, they were poured into a cylindrical formwork with dimensions of φ10 × 20 cm, demolded at an age of 1 day, and then sealed and cured at room temperature until an age of 7 days. After that, curing was carried out in the above neutralization curing tank for 7 days, and further sealed and cured at room temperature for 14 days (total curing of 28 days). The 28-day compressive strength of each obtained concrete specimen was measured according to JIS A 1108, and the results are shown in Table 2 below.

[0062] (Test Example 4) Carbon Dioxide (CO2) Absorption Amount During the curing for preparing the above cylindrical concrete specimens each with dimensions of φ10 × 20 cm, the amount of calcium carbonate (CaCO3) at the time of charging into the above neutralization curing tank and after 7 days of the neutralization curing (14 days after the age) was quantified by performing TG-DTA reactivity analysis using a TG-DTA apparatus. Using the following formula, the difference in the carbon dioxide absorption amount was calculated to obtain the carbon dioxide absorption amount per 7 days of the neutralization curing. Absorbed CO2 amount (kg-CO2 / m 3 ) = (CaCO3 quantified after 7 days of the neutralization curing (kg / m 3 ) × CO2 molecular weight / CaCO3 molecular weight) - ((CaCO3 quantified at the start of the neutralization curing (kg / m 3 ) × CO2 molecular weight / CaCO3 molecular weight)

[0063] (Test Example 5) Substrate for Seaweed Bed Growth Reef On each of the above rectangular concrete specimens with dimensions of 30 cm × 30 cm × 30 cm, seaweed roots were wound around the upper surface of each concrete specimen in the same amount (area) and fixed. Each concrete specimen was installed on the seabed as a substrate for seaweed bed growth reef, and the growth status of seaweed on each growth reef substrate after 20 days was observed.

[0064] The growth status of each growth reef substrate was evaluated according to the "Method for Grasping Degree" described in P26 of the Guide for J-Blue Credit (Registered Trademark) Certification Application (Ver. 2.2.1) by the Japan Blue Economy Technology Research Consortium (March 2023). Specifically, the area ratio of seaweed occupying the upper surface of each growth reef substrate after 20 days of installation on the seabed was evaluated in five levels as the landscape coverage degree according to the following evaluation criteria. In addition, the situation when each growth reef substrate with roots wound around was installed on the seabed was in the state of "1" according to the following evaluation criteria. Coverage Class 5 (Dense Growth) ··· Coverage 75% or more 4 (Thick Growth) ··· Coverage 50% or more and less than 75% 3 (Sparse Growth) ··· Coverage 25% or more and less than 50% 2 (Spot Growth) ··· Coverage 5% or more and less than 25% 1 (Extremely Spotty Growth) ··· Coverage less than 5% The results are shown in Table 2 below.

[0065]

Table 2

[0066] From the results in Table 2 above, the concrete growth reef substrate according to the present invention uses early-strength cement (HC), so that when maintaining a certain strength, the water-cement ratio becomes larger, and at the same time, the CO2 absorption amount becomes larger, and it has good strength. That is, the concrete growth reef substrate according to the present invention has an enhanced CO2 absorption and storage function. In addition, in Examples 2 to 4, the amount of air, particularly the amount of bubbles of 300 μm or more, is increased compared to Example 1, and it can be seen that as the amount of air increases, the amount of CO2 absorption also increases.

[0067] In Comparative Example 1, early-strength cement (HC) is used and the air content is also increased. However, since the air content is outside the scope of the present invention and excessive, strength reduction has occurred, and it cannot withstand practical use as a growth reef base material on the seabed. In Comparative Example 2, ordinary Portland cement (NC), which is a general concrete used for conventional algal bed growth reefs, is used. Therefore, in order to maintain a certain level of strength, compared with the concrete growth reef base material used in the present invention, the water-cement ratio becomes smaller, and carbonation progresses with difficulty, so it can be seen that the amount of CO2 absorption becomes smaller.

[0068] Thus, by using a concrete composition using early-strength cement and having an air content of 5.0 to 12.0% by volume, etc., and making a concrete algal bed growth reef body having an air bubble amount of 3.0 to 8.9% by volume, etc. of 300 μm or more, a method for fixing carbon dioxide and a method for creating an algal bed using a concrete algal bed growth reef base material capable of effectively absorbing and storing CO2 can be obtained.

Industrial Applicability

[0069] The method for fixing carbon dioxide and the method for creating an algal bed using the concrete algal bed growth reef base material of the present invention can absorb and store carbon dioxide when preparing the concrete growth reef base material, enable the creation of an algal bed where algae can be effectively grown, and contribute to the realization of carbon neutrality by effectively storing blue carbon. By further installing the concrete algal bed growth reef base material inside or outside the wind turbine rows of floating or fixed offshore wind power generation, it can be used not only for the formation of fish reefs and algal bed growth reefs in the coastal area but also in the open sea.

Claims

Claim 1 Use 260 to 310 kg / m of early-strength cement ３ , a concrete composition containing a water / cement ratio (mass %) of 55 to 67 and an air content (volume %) of 5.0 to 12.0 according to JIS A 1128 is subjected to carbon dioxide-containing neutralization curing, whereby 20 to 80 kg-CO ２ / m ３ is stored, and a porous concrete body having a 28-day compressive strength of 30 to 43 N / mm ２ is prepared. Roots of algae are planted and / or spores are sown in the pores of the porous concrete body, and the concrete body is installed on the seabed as a concrete growth reef base material, and the algae absorb carbon dioxide in the sea. A method for fixing carbon dioxide using a concrete algae bed growth reef base material, characterized in that Claim 2 In the carbon dioxide fixation method according to Claim 1, the concrete composition further contains an AE agent or a foaming agent, and is a carbon dioxide fixation method using a concrete algal bed growth reef base material, characterized in that. Claim 3 In the carbon dioxide fixation method according to Claim 1 or 2, the concrete growth reef base material is a carbon dioxide fixation method using a concrete algal bed growth reef base material, characterized in that the amount of air bubbles of 300 μm or more calculated by the linear traverse method (ASTM C 457) is 3.0 to 8.9% by volume. Claim 4 In the method for fixing carbon dioxide in the sea according to Claim 1 or 2, the neutralization curing is carried out using the exhaust gas from a cement factory, and the porous concrete body is carbonated by the carbon dioxide in the exhaust gas, so that the carbon dioxide is fixed, and is a carbon dioxide fixation method using a concrete algal bed growth reef base material, characterized in that. Claim 5 Use 260 to 310 kg / m of early-strength cement ３ , a concrete composition containing a water / cement ratio (mass %) of 55 to 67 and an air content (volume %) of 5.0 to 12.0 according to JIS A 1128, and perform carbonation curing containing carbon dioxide to store 20 to 80 kg-CO ２ / m ３ . Prepare a porous concrete body with a 28-day compressive strength of 30 to 43 N / mm ２ . Plant the roots of algae and / or sow spores in the pores of the porous concrete body, install the concrete body on the seabed as a concrete growth reef base material, and create an algal bed where the algae absorb carbon dioxide in the sea and grow. A method for creating an algal bed using a concrete algal bed growth reef base material, characterized by the above steps.

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