Method for manufacturing cement hardened body having continuous voids and cement hardened body having continuous voids

Abstract

To provide a method for manufacturing a cement hardened body capable of fixing components in gas or aqueous solution at a higher level than conventionally, and to provide the cement hardened body.SOLUTION: A method for manufacturing a cement hardened body having continuous voids includes: a preparation step of preparing a cement composition containing a cement and a piece of an amphoteric metal; a hardening step of hardening the cement composition obtained in the preparation step to obtain a cement hardened body having continuous voids formed with a void region formed by dissolution of the piece of metal and a passageway through which hydrogen gas generated by the dissolution of the piece of metal moves to a surface of the cement hardened body and to a void region adjacent to the void region. The present invention also provides the cement hardened body having continuous voids.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a method for producing a cement hardened body having continuous voids and a cement hardened body having continuous voids, and particularly to a method for producing a cement hardened body having continuous voids for allowing gas and / or liquid to penetrate, and a cement hardened body having continuous voids.

Background Art

[0002] While a large amount of CO2 is emitted during the production stage of a cement hardened body, it has the effect of absorbing and fixing CO2 during the service stage, and there is a need as a storage site for CO2.

[0003] Also, there is a problem that Ca ions in the surface layer part of the cement hardened body are eluted and damaged by rainwater, seawater, groundwater, etc. 2+ ion is eluted and damaged by rainwater, seawater, groundwater, etc.

[0004] Therefore, in order to immobilize gas components such as CO2 and water-soluble components such as Ca ions in the cement hardened body, various components are physically permeated to the inside as a gas or aqueous solution and reacted with the cement hardened body, or the target ions are electrochemically permeated and adsorbed and reacted with the cement hardened body. There is a method. 2+ ion is adsorbed and reacted with the cement hardened body.

[0005] However, since the cement hardened body has a dense structure, it takes a long time to physically penetrate gas or an aqueous solution to the inside.

[0006] Patent Document 1 and Patent Document 2 disclose a cement hardened body in which alkali-decomposable resin fine particles or organic fibers made of an alkali-decomposable resin are contained in a cement composition, and the resin particles or organic fibers in the surface layer part are decomposed by acting alkali or ultraviolet rays on the cement hardened body obtained after curing. A surface layer part having voids useful for CO2 fixation is formed.

[0007] According to the cement hardened body having a surface layer portion with voids, the air permeability from the concrete surface to the deep part is improved, and since the surface area increases inside the concrete, CO2 in the air can be effectively immobilized.

[0008] Further, Patent Document 3 discloses that by kneading and mixing conductive fibers and reinforcing fibers in a cement composition, the resulting cement hardened body has increased strength and an effective reduction in surface resistance value.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0010] According to the inventions disclosed in Patent Documents 1 and 2, although CO2 in the air can be effectively immobilized in the cement hardened body, the need to reduce greenhouse gas emissions in the cement-concrete industry is increasing, and further improvement in the CO2 storage capacity of the cement hardened body is required.

[0011] In addition, in the cement hardened body containing the conductive fibers and reinforcing fibers described in Patent Document 3, since the surroundings of the fibers are covered with the cement hardened body, the surroundings of these fibers do not become waterlogged or airlogged, and therefore, the physical penetration of various components in the gas or aqueous solution requires the same long time as before.

[0012] In view of the above problems, an object of the present invention is to provide a method for manufacturing a cement hardened body capable of fixing components in a gas or aqueous solution at a higher level than before, and a cement hardened body.

Means for Solving the Problem

[0013] The inventors of the present invention have intensively studied to achieve the above object. As a result, by kneading metal pieces of amphoteric metal into a cement composition, the metal pieces dissolve in the alkaline cement hardened body, voids of a size caused by the shape of the metal pieces are generated, and hydrogen is generated as the metal pieces dissolve, so that these voids are connected to reach the surface of the cement hardened body, and it has been found that so-called continuous voids are generated, and the present invention has been completed.

[0014] That is, the above object of the present invention is achieved by a preparation step of preparing a cement composition containing cement and metal pieces of amphoteric metal, and hardening the cement composition obtained in the preparation step, and a void region formed by the dissolution of the metal pieces and hydrogen gas generated along with the dissolution of the metal pieces. It has been found that it is achieved by a manufacturing method of a cement hardened body having continuous voids, which comprises a hardening step of obtaining a cement hardened body having continuous voids formed by moving to the surface of the cement hardened body and to a void region adjacent to the void region.

[0015] Further, it is preferable that the metal pieces have a thickness in the range of 5 μm or more and 1 mm or less, a width in the range of 0.1 mm or more and 5 mm or less, and a length in the range of 0.5 mm or more and 50 mm or less.

[0016] Furthermore, it is preferable to add the metal pieces in an amount in the range of 0.05% by volume or more and 5% by volume or less with respect to the total volume of the cement composition excluding the metal pieces.

[0017] Moreover, the hardening step includes a curing operation of curing the cement composition obtained in the preparation step, and it is preferable that the curing of the curing operation includes curing under high-concentration CO2 conditions and / or underwater curing in an aqueous calcium hydroxide solution.

[0018] Further, the above object of the present invention is a cement hardened body having continuous voids, which is obtained by hardening a cement composition containing cement and metal pieces of an amphoteric metal, wherein the continuous voids are composed of a void region formed by the dissolution of the metal pieces and a migration path formed by the hydrogen gas generated upon the dissolution of the metal pieces migrating to the surface of the cement hardened body and to a void region adjacent to the void region. The object can also be achieved by a cement hardened body having continuous voids.

[0019] Furthermore, it is preferable that the cement hardened body having continuous voids has a water permeability coefficient in the range of 3.1×10 -4 or more and 8.1×10 -3 or less.

Advantages of the Invention

[0020] According to the method for producing a cement hardened body having continuous voids and the cement hardened body of the present invention, a cement hardened body having continuous voids composed of a void region formed by the dissolution of metal pieces in the cement composition and a migration path formed by the hydrogen gas generated upon the dissolution of the metal pieces migrating to the surface of the cement hardened body and to a void region adjacent to the void region can be obtained. Since the continuous voids of the cement hardened body are directly connected from the position of the metal pieces dispersed in the cement composition to the surface, or are connected via the position of the metal pieces adjacent to the position of the metal pieces, the continuous voids are not limited to the surface layer portion, but are also connected from the central portion to the surface of the cement hardened body. Therefore, the cement hardened body having continuous voids obtained by the present invention can fix components in a gas or an aqueous solution at a higher level than before.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0022] <Method for Producing Cement Hardened Body Having Continuous Void> Figure 1 is a flowchart showing the method for producing a cement hardened body having continuous voids of the present invention. As shown in the figure, the method for producing a cement hardened body having continuous voids of the present invention includes a preparation step (S110) and a hardening step (S120).

[0023] [Preparation Step (S110)] In this step, a cement composition containing cement and metal pieces of an amphoteric metal is prepared.

[0024] Cement is an inorganic binder that exhibits curability when kneaded with water. In the present invention, hydraulic cement is used. As the hydraulic cement, simple cements such as Portland cement (JIS R5210), hydraulic lime, Roman cement, and natural cement may be used, or mixed cements (JIS R5211, R5212, R5213) such as lime blended cement and blended Portland cement may also be used.

[0025] The water added to the above cement is not limited to pure water, and tap water, river water, lake water, and seawater can also be used.

[0026] The metal piece of the amphoteric metal is a metal piece that dissolves in an alkaline cement composition and is a metal piece of an amphoteric metal. The amphoteric metals are aluminum (Al), zinc (Zn), tin (Sn), and lead (Pb), and the simple substances react with both aqueous solutions of acids and aqueous solutions of strong bases to generate hydrogen (H2) gas.

[0027] Note that as amphoteric metals, metals in a state where the surface or part of the simple metal is oxidized are included, but metals in a state where they are oxidized to oxides even internally, such as alumina (Al2O3), are not included. This is because such oxides of amphoteric metals do not generate hydrogen gas when dissolved in an alkaline cement composition.

[0028] From the perspective of ionization tendency, the metal piece of the amphoteric metal is preferably an aluminum piece.

[0029] When adopting an aluminum piece as the amphoteric metal, the oxide film of aluminum is stable in the range of pH 4 or more and 8 or less. Therefore, within this pH range, the dissolution of the aluminum piece does not occur. Thus, when adopting an aluminum piece as the amphoteric metal, the addition amounts of cement, water, and admixture should be selected so that the pH of the cement composition exceeds 8.

[0030] The size of the metal piece of the amphoteric metal can be any, but the thickness of the metal piece of the amphoteric metal is preferably in the range of 5 μm or more and 1 mm or less, and from the perspective of foamability (i.e., the generation of H2 gas), it is particularly preferably in the range of 10 μm or more and 300 μm or less. The width of the metal piece of the amphoteric metal is preferably in the range of 0.1 mm or more and 5 mm or less, and particularly preferably in the range of 1 mm or more and 5 mm or less. The length of the metal piece of the amphoteric metal is preferably in the range of 0.5 mm or more and 50 mm or less, and particularly preferably in the range of 5 mm or more and 30 mm or less.

[0031] Also, the blending amount of the metal pieces of the amphoteric metal can be any amount, but it is preferable to add the metal pieces of the amphoteric metal in an amount in the range of 0.05% by volume or more and 5% by volume or less with respect to the total volume of the cement composition excluding this metal piece, and it is particularly preferable to add in an amount in the range of 0.1% by volume or more and 5% by volume or less.

[0032] Also, the cement composition contains aggregate as an optional component. Aggregate is generally used in the production of concrete and is added to suppress heat generation due to the hydration reaction of the cement composition, suppress shrinkage, and reduce the amount of cement used to reduce costs. Aggregate is divided into coarse aggregate and fine aggregate. Coarse aggregate remains at 85% or more by mass on a 5 mm sieve, and fine aggregate passes through a 5 mm sieve and passes through a 10 mm sieve at 100% by mass.

[0033] Examples of the material of the aggregate include river sand, mountain sand, sea sand, blast furnace slag, and copper slag.

[0034] Also, it may optionally contain admixtures such as an AE agent (air-entraining agent), a water-reducing agent (AE water-reducing agent, water-reducing agent, high-performance AE water-reducing agent, etc.), a fluidizing agent, a setting / hardening regulator, a flash set retarder, a rust inhibitor, and a waterproof agent. In particular, from the viewpoint of improving the water permeability of the cement hardened body obtained after hardening, it is preferable to contain one or more of an AE agent, an AE water-reducing agent, and a high-performance AE water-reducing agent.

[0035] The cement composition can be prepared, for example, by powder-mixing cement and optionally other powder components, then adding water and optionally an admixture to this powder mixture and kneading it into a paste form, and if necessary, mixing fine aggregate and coarse aggregate, and then mixing the metal pieces of the amphoteric metal (the above is the preparation step (S110)).

[0036] [Hardening step (S120)] In this step, the cement composition obtained in the preparation step is hardened to obtain a cement hardened body having continuous voids composed of a void region formed by the dissolution of the metal pieces and a migration path through which hydrogen gas generated accompanying the dissolution of the metal pieces moves to the surface of the cement hardened body and to a void region adjacent to the void region.

[0037] The cement composition may be spread on an object with a trowel or the like and cured, or may be poured into a mold and cured.

[0038] When pouring the cement composition into a mold, it is preferably compacted to remove air bubbles. Compaction is performed by tapping the surface of the poured cement composition with a tamper or the like, piercing it with a rod, or by vibration of a vibrator. Here, since the dissolution of the metal piece of the amphoteric metal and the generation of hydrogen gas gradually start after the metal piece is mixed into the alkaline cement composition, it is preferable to perform the application of the cement composition or the pouring into the mold and the compaction at an early stage.

[0039] If the cement composition is prepared and compacted after being left for a long time, there is a risk that the hydrogen gas generated by the dissolution of the metal piece of the amphoteric metal in the cement composition is expelled from the cement composition by compaction and the continuous voids described later are impaired.

[0040] The cement composition applied or poured into the mold is cured by curing until the required compressive strength is obtained, and a cement hardened body is obtained. Curing may be performed under conventionally known conditions such as air curing and water curing.

[0041] However, it is preferable that this step (S120) includes a curing operation for curing the cement composition obtained in the preparation step (S110), and the curing of the curing operation includes curing under high-concentration CO2 conditions and / or water curing in an aqueous calcium hydroxide solution.

[0042] Curing under high-concentration CO2 conditions may be air curing or water curing. The high-concentration CO2 condition means that if it is air curing, it may be a CO2 concentration higher than the CO2 concentration in the atmosphere. For example, it is 0.1% by volume or more, preferably 3% by volume or more, and particularly preferably 8% by volume or more.

[0043] The high-concentration CO2 condition means that, in the case of underwater curing, it is sufficient if the CO2 concentration is higher than the CO2 concentration in the natural environment. For example, it is 500 volume ppm or more, preferably when CO2 is in a saturated state in water. Saturated CO2 water can be prepared by bubbling CO2 gas into a water tank containing water to be used for underwater curing in advance. This bubbling may be carried out directly with a hose for the CO2 gas or by using a sintered nozzle or the like. However, from the viewpoint of the permeability of the CO2 gas into the continuous voids of the cement hardened body described later, it is preferable to introduce fine bubbles produced by introducing the CO2 gas into a fine bubble generator that generates fine bubbles with a bubble diameter of less than 100 μm into the above water tank. As the above fine bubble generator, a well-known one can be used. Note that the definition of the above fine bubbles shall be based on ISO 20480-1:2017.

[0044] The curing period under the high-concentration CO2 condition is, for example, 1 day or more, and the upper limit of the curing period is up to the period when the cement hardened body is not deteriorated by carbonation. Specifically, it is preferably 1 day or more and 1 month or less.

[0045] Regarding underwater curing in an aqueous calcium hydroxide solution, the concentration of calcium hydroxide in the aqueous solution is preferably 0.05 mass% or more, particularly preferably 0.1 mass% or more.

[0046] The curing period of underwater curing in an aqueous calcium hydroxide solution is, for example, 1 day or more, and the upper limit of the curing period is up to the period when the voids are filled by the calcium hydroxide hardened body. Also, considering the construction period as the upper limit of the curing period, it is preferably 1 day or more and 1 month or less.

[0047] Also, the curing operation may include water curing in an aqueous calcium hydroxide solution after curing under high-concentration CO2 conditions, or vice versa, may include curing under high-concentration CO2 conditions and normal air or water curing, may include water curing in an aqueous calcium hydroxide solution and normal air or water curing, may include only curing under high-concentration CO2 conditions, or may include only water curing in an aqueous calcium hydroxide solution. However, water curing under high-concentration CO2 conditions and in an aqueous calcium hydroxide solution should be avoided because calcium hydroxide and carbon dioxide react directly, and the components that react with the cement hardened body are impaired.

[0048] The cement hardened body obtained by the production method of the present invention has continuous voids composed of a void region formed by the dissolution of metal pieces of an amphoteric metal inside and a migration path through which hydrogen gas generated accompanying the dissolution of the metal pieces moves to the surface of the cement hardened body and to a void region adjacent to the void region.

[0049] That is, first, the metal pieces of the amphoteric metal start to dissolve from the time when they are mixed in the cement composition in the preparation step (S110), generate hydrogen gas, and after dissolution, the region where the metal pieces existed remains as a void region 12a (see FIG. 2 described later). Next, the generated hydrogen gas moves through the cement composition and communicates with the adjacent void region 12a, and further moves to form a migration path 12b (see FIG. 2) that communicates to the outside of the cement composition. When the cement composition is cured as it is to obtain a cement hardened body, the cement hardened body becomes a cement hardened body having continuous voids 12 composed of the void region 12a and the migration path 12b (the above is the curing step (S120)).

[0050] As described above, according to the method for producing a cement hardened body having continuous voids of the present invention, a void region formed by dissolution of metal pieces in the cement composition and a hydrogen gas generated accompanying the dissolution of the metal pieces move to the surface of the cement hardened body and to a void region adjacent to the void region, and a cement hardened body having continuous voids composed of the formed migration paths can be obtained. The continuous voids of the cement hardened body are directly connected from the position of the metal pieces dispersed in the cement composition to the surface, or are connected through the position of the metal pieces adjacent to the position of the metal pieces. Therefore, the continuous voids are not limited to the surface layer portion, but are also connected from the central portion to the surface of the cement hardened body.

[0051] Therefore, when curing is performed under high-concentration CO2 conditions in the curing process, CO2 penetrates into the continuous voids, so that the fixing efficiency of CO2 to the cement hardened body is greatly improved as compared with the conventional case. When water curing is performed in an aqueous calcium hydroxide solution in the curing process, the aqueous calcium hydroxide solution penetrates into the continuous voids, so that the fixing efficiency of calcium ions to the cement hardened body is greatly improved as compared with the conventional case.

[0052] <Cement hardened body having continuous voids> The cement hardened body having continuous voids of the present invention is a cement hardened body having continuous voids formed by curing a cement composition containing cement and metal pieces of an amphoteric metal, wherein the continuous voids are composed of a void region formed by dissolution of the metal pieces and a migration path formed by the hydrogen gas generated accompanying the dissolution of the metal pieces moving to the surface of the cement hardened body and to a void region adjacent to the void region.

[0053] The cement composition and its constituent components have already been described, so the description thereof is omitted here.

[0054] Then, as described above, the cement composition in which each component is mixed or the cement composition poured into a mold is cured by curing until the required compressive strength is obtained, and a cement hardened body is obtained.

[0055] Figure 2 is a schematic longitudinal sectional view of a cement hardened body 10 having continuous voids, which is obtained by injecting a cement composition in which each component is mixed into a cylindrical formwork and curing it.

[0056] As shown in the figure, the cement hardened body 10 has continuous voids 12. The continuous voids 12 are composed of a void region 12a formed by the dissolution of metal pieces of an amphoteric metal dispersed in the cement composition, and a migration path 12b formed by the hydrogen gas generated accompanying the dissolution of the metal pieces of the amphoteric metal moving to the surface of the cement hardened body 10 and to the void region 12a adjacent to the void region 12a.

[0057] By having such continuous voids 12, the water permeability and air permeability of the cement hardened body 10 are greatly improved as compared with the conventional ones. When the above curing is carried out under high-concentration CO2 conditions, a cement hardened body that fixes a larger amount of CO2 than the conventional one can be obtained. When the above curing is underwater curing in an aqueous calcium oxide solution, a cement hardened body that fixes a larger amount of calcium than the conventional one can be obtained.

[0058] Furthermore, the water permeability coefficient of the cement hardened body having continuous voids of the present invention may be any value, but from the viewpoint of improving the fixing efficiency of each component during curing, it is preferable that the water permeability and air permeability are higher than those of conventional concrete. And considering the applicability to structural members, it is preferable that the water permeability is smaller than that of porous concrete.

[0059] Considering such water permeability, air permeability, and applicability to structural members, the water permeability coefficient of the cement hardened body having continuous voids of the present invention is preferably in the range of 3.1×10 -4 or more and 8.1×10 -3 or less.

[0060] Furthermore, when the cement hardened body having continuous voids of the present invention is used as recycled aggregate, it is preferable that the cement hardened body having continuous voids of the present invention has a nominal strength in the range of 18 or more and 36 or less based on JIS A 5022:2018.

Example

[0061] Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited only to these examples.

[0062] <Test 1. Measurement of permeability coefficient> In Test 1, a cement hardened body having continuous voids and a cement hardened body having no continuous voids of the present invention were prepared as specimens, and the permeability coefficients of these specimens were measured and compared.

[0063] 1-1. Preparation of specimens (cement hardened bodies) Cement (ordinary Portland cement, manufactured by Sumitomo Osaka Cement Co., Ltd.), water (tap water), fine aggregate (mountain sand, produced in Kakegawa, Shizuoka Prefecture), coarse aggregate (crushed stone, produced in Sakakawa, Ibaraki Prefecture), AE water reducing agent (Yamaso 90SE, manufactured by Yamaso Chemical Co., Ltd.), air entraining agent (Vinsol, manufactured by Yamaso Chemical Co., Ltd.), polypropylene fiber (Mercury (registered trademark) C, manufactured by Daiwa Boushi Co., Ltd.), and aluminum pieces (manufactured by cutting aluminum foil with a thickness of 12 μm into pieces with a length of 25 mm and a width of 4 mm) were mixed and kneaded with a forced biaxial mixer for 2 minutes to prepare cement compositions (kneaded materials) of Comparative Examples 1 to 3 and Examples 1 to 2.

[0064] The formulations and qualities (slump, air content) of each cement composition are shown in Table 1. The slump was measured in accordance with JIS A 1101 for the cement composition (kneaded material) immediately after kneading, and the air content was measured in accordance with JIS A 1128 for the cement composition (kneaded material) immediately after kneading.

[0065]

Table 1

[0066] ※1: W / C is the percentage of the mass ratio of water (W) to cement (C). ※2: PP means polypropylene fiber. The mixing amount (Vol%) is the volume percentage with respect to the total volume of the cement composition excluding PP. ※3: Aluminum means aluminum pieces. The mixing amount (Vol%) is the volume percentage with respect to the total volume of the cement composition excluding the aluminum pieces.

[0067] Each of the obtained cement compositions was used to prepare cylindrical specimens (cement hardened bodies) with a diameter of 100 mm and a height of 100 mm according to the method for preparing specimens for the strength test of JIS A 1132 concrete. The curing condition was air curing, and the specimens at the age of 7 days were subjected to the following water permeability test.

[0068] 1-2. Water Permeability Test The water permeability test of each specimen will be described with reference to FIG. 3. FIG. 3 is a schematic diagram for explaining the water permeability test of the specimen in the example. As shown in the figure, a fine bubble generator 204 (fine bubble generator (FB-S15AI), manufactured by Sakamoto Giken Co., Ltd.) having a nozzle of a two-phase flow swirling type is provided at the tip of the water circulation path 202 in the water tank 200, and CO2 supplied from the CO2 cylinder 206 becomes fine bubbles and is supplied into the water tank 200.

[0069] And CO2 was dissolved in the water in the water tank 200 until it reached a saturated state until the start of the water permeability test.

[0070] In addition, an intake pipe 212 of a vacuum trap 210 (acrylic small vacuum container (type 300), manufactured by AS ONE Corporation) is inserted into the water tank 200, and the lower surface 220a of the specimen 220 is attached to the water tank side end of the intake pipe 212. The specimen 220 is inserted into a vinyl chloride pipe (inner diameter φ10 cm), and the two are joined with a waterproof adhesive. Therefore, the side peripheral surface 220b of the specimen 220 is the outer peripheral surface of the vinyl chloride pipe, and the lower surface 220a and the upper surface 220c of the specimen 220 are open surfaces.

[0071] An exhaust pipe 214 of the vacuum trap 210 is provided with a vacuum pump P (belt-driven oil rotary vacuum pump, manufactured by Yamato Scientific Co., Ltd.). Due to the suction pressure of the vacuum pump P, a negative pressure is generated in the space of the vacuum trap 210. As a result, water saturated with CO2 in the water tank 200 penetrates into the specimen 220 from the upper surface 220c of the specimen 220, and the water that has passed through the specimen 220 is trapped in the vacuum trap 210.

[0072] The water permeability test was carried out for 72 hours after attaching the specimen 220 to the water tank side end of the intake pipe 212 and starting the operation of the vacuum pump P. The suction pressure of the vacuum pump P was set to a maximum negative pressure of 0.08 MPa, and the pressure was adjusted according to the water permeability. The water permeability is the amount of water trapped in the vacuum trap 210 (the amount of water Q in Equation (2) described later). Then, the water permeability coefficient was determined as follows from the test results.

[0073] That is, when the length L of the saturated sample is constant, a proportional relationship (proportionality constant k) holds between the hydraulic gradient i and the flow velocity v, and this relationship is Darcy's law. The apparent flow velocity v of water flowing from a higher water level to a lower water level in the sample is given by Equation (1)

Number

Number

[0074] As shown in the figure, in Comparative Example 1 assuming general-purpose concrete, since it did not permeate water, the water permeability coefficient could not be calculated. In Comparative Example 2 where PP was mixed instead of aluminum pieces, water permeation was observed, and the water permeability coefficient was 2.62×10 -7 It was. The water permeability coefficient of Comparative Example 3, in which the air content in the cement composition was about three times that of Comparative Example 2 while mixing PP in the same manner as in Comparative Example 2, was about 1.25 times that of Comparative Example 2.

[0075] Also, in Example 1 in which aluminum pieces were mixed (mixing amount: 0.1% by volume), the water permeability coefficient was about 950 times that of Comparative Example 3 of the prior art. Furthermore, in Example 2 in which the mixing amount of aluminum pieces was increased to 0.4% by volume, the water permeability coefficient was about 26 times larger than that of Example 1.

[0076] From the above, it was found that by mixing metal pieces of amphoteric metal compared with the prior art, many continuous voids can be provided in the cement hardened body, and the permeability of gas and liquid containing components to be immobilized to the cement hardened body is improved.

[0077] <Test 2. Measurement of neutralization depth and CO2 fixation amount> 2-1. Preparation of test specimens (cement hardened bodies) A cement composition (kneaded material) was prepared using the same raw materials and preparation method as in the above "1-1. Preparation of test specimens (cement hardened bodies)", and a cement hardened body (test specimen) of Example 3 was prepared with the same shape and the same curing method. The water permeability test described in the above 1-2., that is, the suction test in CO2-saturated water, was performed to permeate CO2-saturated water into the test specimen (cement hardened body). Then, the neutralization depth and the CO2 fixation amount described later were measured together with the test specimens of Comparative Examples 1 to 3 prepared in the above 1-1. and used for the water permeability test in the above 1-2. The formulation and quality (slump, air content) of each cement composition are shown in Table 2. Note that the measurement of slump and air content was also as described above, and the description is omitted here.

[0078]

Table 2

[0079] 2 - 2. Confirmation of Neutralization Depth The specimen into which the above CO2-saturated water had penetrated was torn by applying a load from the width direction of the specimen using a compression testing machine, and a 1% phenolphthalein solution was sprayed onto the exposed water-permeable cross-section. The results are shown in Fig. 5. Fig. 5(a) shows the cross-section of the specimen of Comparative Example 1, and Fig. 5(b) is a substitute photograph of the drawing showing the cross-section of the specimen of Example 3.

[0080] As shown in the figure, almost the entire cross-section of the specimen of Comparative Example 1 reacted red, and while the part mixed with PP was slightly colorless, in the cross-section of the specimen of Example 3, a plurality of linear or reticular colorless regions were connected from the inside to the surface of the specimen among the red reaction regions. From this, it was confirmed that by using metal pieces of amphoteric metal, a region of continuous voids can be formed inside the specimen (cement hardened body), and thereby, it was possible to more efficiently immobilize CO2 compared to the case of using PP. 2 - 3. Measurement of CO2 Content in Specimen by Thermal Analysis (TG-DTA)

[0081] i. Preparation of Measurement Specimen For the specimen into which CO2-saturated water had penetrated, which was obtained in the above 2 - 1. Preparation of Specimen (Cement Hardened Body), a recycled coarse aggregate specimen reduced by quartering or a sample divider was used in an amount of about 2 kg so that the material composition ratio of the measurement specimen did not change, and the specimen was prepared according to the following procedure.

[0082] 1 Pulverize to about 5 mm or less 2 Immerse in acetone for 6 hours or more to remove free water 3 Leave in a vacuum desiccator for 6 hours or more 4 Grind finely with a ball mill to about 100 μm 5 Vacuum freeze-dry and store in a sealed container until analysis

[0083] ii. Measurement Weigh about 50 - 70 mg of the measurement sample prepared in i. into a platinum cell, and measure it with a differential thermal - thermogravimetric simultaneous analyzer TG - DTA (Hitachi High - Technologies TG / DTA7200) while flowing nitrogen gas at a flow rate of 70 mL / min and with a heating rate of 20 °C / min. From the relationship curve between the temperature and the mass reduction rate obtained by the measurement, assume that the range of mass reduction of carbon dioxide due to the decomposition of calcium carbonate is from 600 °C to 850 °C, and calculate the CO2 content (%) from the mass reduction amount in that temperature range.

[0084] iii. Calculation method of CO2 fixation amount Calculate the fixed amount of CO2 as the CO2 fixed per ton of the test specimen (cement hardened body) by Equation (3)

Equation

[0085] Note that by using the measured values before and after immobilizing CO2 in the carbonation test, the influence of the naturally - derived CO2 fixation amount is excluded. The test results are shown in Figure 6. Figure 6 is a bar graph showing the CO2 content in each test specimen by thermal analysis (TG - DTA) of the examples.

[0086] As shown in the figure, no CO2 immobilization by CO2 - saturated water was observed in the test specimen where water permeability was not observed (Comparative Example 1) and the test specimen with PP mixed in (Comparative Example 2). In the test specimen with PP mixed in and the air amount in the cement composition being about 20% (Comparative Example 3), a CO2 fixation amount of 0.46 mass% was observed, but this CO2 fixation amount was about half of the CO2 fixation amount of 1.09 mass% in the test specimen with aluminum pieces mixed in and the air amount in the cement composition being about 5% (Example 3).

[0087] As described above, compared with the prior art of mixing PP or increasing the air content in the cement composition with a chemical admixture, by mixing metal pieces of an amphoteric metal into the cement composition as in the present invention, continuous voids can be provided in the cement hardened body, and it has been found that more CO2 can be fixed more efficiently in the cement hardened body thereby.

Industrial Applicability

[0088] The cement hardened body having continuous voids obtained by the present invention can be used for recycled aggregates and the like.

Claims

1. A preparation step of preparing a cement composition containing cement and metal pieces of an amphoteric metal, a hardening step of hardening the cement composition obtained in the preparation step, and obtaining a cement hardened body having continuous voids composed of a void region formed by dissolution of the metal pieces and a migration path through which hydrogen gas generated along with the dissolution of the metal pieces moves to the surface of the cement hardened body and to a void region adjacent to the void region; A method for producing a cement hardened body having continuous voids, characterized by comprising the above.

2. The method for producing a cement hardened body having continuous voids according to claim 1, wherein the metal pieces have a thickness in the range of 5 μm or more and 1 mm or less, a width in the range of 0.1 mm or more and 5 mm or less, and a length in the range of 0.5 mm or more and 50 mm or less.

3. The method for producing a cement hardened body having continuous voids according to claim 1, wherein the metal pieces are added in an amount in the range of 0.05% by volume or more and 5% by volume or less based on the total volume of the cement composition excluding the metal pieces.

4. The hardening step includes a curing operation of curing the cement composition obtained in the preparation step, The curing in the curing operation includes curing under high-concentration CO ２ conditions and / or underwater curing in an aqueous calcium hydroxide solution. The method for producing a cement hardened body having continuous voids according to claim 1.

5. A cement hardened body having continuous voids, obtained by hardening a cement composition containing cement and metal pieces of an amphoteric metal, The continuous voids have continuous voids composed of a void region formed by dissolution of the metal pieces and a migration path through which hydrogen gas generated along with the dissolution of the metal pieces moves to the surface of the cement hardened body and to a void region adjacent to the void region. A cement hardened body having continuous voids, characterized by the above.

6. 3.1×10 －４ or more 8.1×10 －３ The cement hardened body having continuous voids according to claim 5, characterized by having a water permeability coefficient within the following range.

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