Method for producing cement-containing molded body and cement-containing molded body

Abstract

To provide a method for producing a cement-containing molded body, capable of easily reducing the amount of water permeated; and to provide the cement-containing molded body.SOLUTION: A method for producing a cement-containing molded body includes: a placing step of placing a cement-containing composition comprising a cement and water; and a hardening step of hardening the cement-containing composition to obtain the cement-containing molded body, wherein: the hardening step has a first hardening operation for hardening the cement-containing composition while contacting a chemical solution to a surface of the placed cement-containing composition; and the chemical solution contains an organic material and a micro-organism that generates carbon dioxide.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a cement-containing molded body and a cement-containing molded body.

Background Art

[0002] The construction of concrete, mortar, cement milk, etc. (hereinafter also referred to as "cement-containing composition") using microorganisms not only reduces the environmental load caused by the use of chemical substances, but also prevents the neutralization of the hardened product of the cement-containing composition (hereinafter also referred to as "cement-containing molded body") and may impart unprecedented properties such as self-healing function.

[0003] For example, Patent Document 1 proposes anti-neutralization concrete containing preferably alkaline microorganisms having a function of anti-neutralizing concrete. In the invention of Patent Document 1, by introducing and mixing a nutrient containing preferably alkaline microorganisms in the process of producing fresh concrete, it is intended to significantly suppress or prevent the neutralization phenomenon, which is one of the concrete deterioration factors, over a long period.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, although the invention of Patent Document 1 is a chemical agent that exerts an effect on the concrete surface, since it is kneaded into the whole concrete, the amount of the chemical agent used becomes extremely large. Since a cement-containing molded body such as a concrete structure uses a large amount of the cement-containing composition, the cost of the raw materials greatly affects the overall cost. In addition, it is required to reduce the water permeability of the cement-containing molded body in order to prevent carbonation due to the intrusion of air and moisture from the outside.

[0006] Therefore, the present invention aims at a method for producing a cement-containing molded body and a cement-containing molded body that can easily reduce the water permeability.

Means for Solving the Problems

[0007] In order to solve the above problems, the present invention has the following aspects. [1] A placing step of placing a cement-containing composition containing cement and water, and a curing step of curing the cement-containing composition to obtain a cement-containing molded body, wherein the curing step has a first curing operation of curing the cement-containing composition while bringing a chemical solution into contact with the surface of the placed cement-containing composition, and the chemical solution contains a microorganism that produces carbon dioxide and an organic substance. A method for producing a cement-containing molded body. [2] The method for producing a cement-containing molded body according to [1], wherein the organic substance is urea or a derivative of urea. [3] The method for producing a cement-containing molded body according to [1] or [2], wherein the first curing operation is to flood the chemical solution on the surface of the cement-containing composition.

[0008] [4] A cement-containing molded body having a base body that is a cured product containing cement and a coating layer located on the surface of the base body, wherein the base body contains carbonate in a surface layer portion having an arbitrary depth from the boundary with the coating layer, and the carbonate concentration in the surface layer portion is higher than the carbonate concentration in a central portion deeper than the arbitrary depth.

Effects of the Invention

[0009] According to the method for producing a cement-containing molded body and the cement-containing molded body of the present invention, the water permeability can be easily reduced.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0011] ≪Cement-containing Molded Body≫ The cement-containing molded body of the present invention has a base body which is a cured product containing cement, and a coating layer located on the surface of the base body. Hereinafter, the cement-containing molded body according to an embodiment of the present invention will be described in detail with reference to FIG. 1.

[0012] As shown in FIG. 1, the cement-containing molded body 1 of the present embodiment has a base body 10 and a coating layer 20 located on the surface of the base body 10. The base body 10 contains carbonate in the surface layer portion 14 at an arbitrary depth from the boundary with the coating layer 20, and the carbonate concentration in the surface layer portion 14 is higher than the carbonate concentration in the central portion 12 deeper than the arbitrary depth.

[0013] <Base body> The base body 10 is a cured product of a cement-containing composition containing cement and water. Examples of the cement-containing composition include concrete, mortar, cement milk, and the like. In this specification, concrete refers to a mixture of cement, fine aggregate (sand), and coarse aggregate (gravel (crushed stone)) kneaded with water. In this specification, mortar refers to a mixture of cement and fine aggregate (sand) kneaded with water. In this specification, cement milk refers to a product obtained by kneading cement with only water. In this specification, cement refers to a powder that is mainly composed of limestone, clay, silica, iron oxide raw materials, etc. and hardens through a chemical reaction with water. In this specification, fine aggregate refers to sand with a diameter of 5 mm or less. In this specification, coarse aggregate refers to gravel (crushed stone) with a diameter exceeding 5 mm, and the diameter of the coarse aggregate is preferably 25 mm or less.

[0014] The mixing ratio of cement, fine aggregate, and coarse aggregate in concrete can be appropriately determined according to the strength required for the concrete. The mixing ratio of cement, fine aggregate, and coarse aggregate is preferably, for example, 2 - 3 parts of fine aggregate and 4 - 6 parts of coarse aggregate with respect to 1 part of cement, by mass ratio.

[0015] The mixing ratio of cement and fine aggregate in mortar can be appropriately determined according to the strength required for the mortar. The mixing ratio of cement and fine aggregate is preferably, for example, 2 - 4 parts of fine aggregate with respect to 1 part of cement, by mass ratio.

[0016] The surface layer portion 14 is located at an arbitrary depth from the boundary with the coating layer 20 and contains carbonate. The surface layer portion 14 is formed by infiltration of a chemical solution described later into the cement-containing composition. The carbonate concentration in the surface layer portion 14 is higher than the carbonate concentration in the central portion 12 that is deeper than the arbitrary depth. That is, the carbonate concentration is high on the surface and in the vicinity of the surface of the substrate 10. This is due to the chemical solution described later producing carbonate.

[0017] The arbitrary depth in the substrate 10, that is, the thickness of the surface layer portion 14 is not particularly limited, but is preferably, for example, 0.1 - 50 mm, and more preferably 0.1 - 12.5 mm. When the thickness of the surface layer portion 14 is within the above numerical range, it is easy to maintain the strength of the substrate 10. The thickness of the surface layer portion 14 is preferably, for example, 0.1 - 20% of the thickness of the substrate 10, and more preferably 0.1 - 5%. When the thickness of the surface layer portion 14 is within the above numerical range, it is easy to maintain the strength of the substrate 10.

[0018] The carbonate concentration in the surface layer portion 14 is preferably, for example, 1 to 1000 mg / L, more preferably 10 to 1000 mg / L. When the carbonate concentration in the surface layer portion 14 is within the above numerical range, it is easy to maintain the strength of the substrate 10. The carbonate concentration in the surface layer portion 14 can be determined, for example, by dissolving a part of the surface layer portion 14 in an acid and measuring the gas generated at that time and the carbon dioxide contained in the aqueous solution with an infrared absorption detector. Alternatively, it can be determined by dissolving a part of the surface layer portion 14 in an acid and measuring the carbonate ions dissolved in the aqueous solution by ion chromatography. Examples of the carbonate in the surface layer portion 14 include calcium carbonate (excluding calcium carbonate in the coating layer 20 described later), sodium carbonate, potassium carbonate, magnesium carbonate, iron(II) carbonate, copper(II) carbonate, etc. These carbonates may be contained singly or in combination of two or more.

[0019] The central portion 12 is located at a position deeper than the surface layer portion 14 in the substrate 10. The central portion 12 is a portion of the cured product of the cement-containing composition where the chemical solution has not infiltrated. The carbonate concentration in the central portion 12 is lower than the carbonate concentration in the surface layer portion 14. The central portion 12 may or may not contain carbonate. The carbonate concentration in the central portion 12 is preferably, for example, 0.1 to 500 mg / L, more preferably 0.1 to 100 mg / L. When the carbonate concentration in the central portion 12 is below the above upper limit value, it is easy to maintain the strength of the substrate 10. The carbonate concentration in the central portion 12 is determined by the same method as the carbonate concentration in the surface layer portion 14. Examples of the carbonate in the central portion 12 include the same compounds as the carbonate in the surface layer portion 14. These carbonates may be contained singly or in combination of two or more.

[0020] In this specification, the central portion 12 and the surface layer portion 14 are distinguished by the high or low carbonate concentration and the distance from the coating layer 20. That is, in the substrate 10, the portion where the chemical solution infiltrates and the carbonate concentration is high, or the portion within 50 mm from the coating layer 20 in the substrate 10 is referred to as the surface layer portion 14. The portion where the chemical solution does not infiltrate and the carbonate concentration is low, or the portion farther than 50 mm from the coating layer 20 is referred to as the central portion 12.

[0021] <coating layer> The coating layer 20 is located on the surface of the substrate 10. The coating layer 20 contains calcium carbonate. Since calcium carbonate is hardly soluble in water, the cement-containing molded body 1 is hardly absorbent of water. Therefore, the cement-containing molded body 1 can reduce the water permeability.

[0022] The content of calcium carbonate in the coating layer 20 is preferably 10% by mass or more, more preferably 30% by mass or more, still more preferably 50% by mass or more, and may even be 100% by mass with respect to the mass of the coating layer 20. When the content of calcium carbonate in the coating layer 20 is at the above lower limit value or more, the water permeability of the cement-containing molded body 1 can be further reduced. The content of calcium carbonate in the coating layer 20 can be determined, for example, by collecting a part of the coating layer 20, dissolving it in an acid, and measuring the gas generated at that time and the carbon dioxide contained in the aqueous solution with an infrared absorption detector. Alternatively, it can be determined by collecting a part of the coating layer 20, dissolving it in an acid, and measuring the carbonate ions dissolved in the aqueous solution by ion chromatography.

[0023] The coating layer 20 may contain other components in addition to calcium carbonate. Examples of other components in addition to calcium carbonate include calcium chloride, sodium chloride, microorganisms contained in the chemical solution, and the like.

[0024] The coating layer 20 may be formed on a part of the substrate 10 or may be formed on the entire surface of the substrate 10. Since the water permeability of the cement-containing molded body 1 can be further reduced, it is preferable that the coating layer 20 is formed on the entire surface of the base body 10.

[0025] The thickness of the coating layer 20 is not particularly limited. For example, 0.1 to 10 mm is preferable, and 1 to 10 mm is more preferable. When the thickness of the coating layer 20 is equal to or greater than the above lower limit value, the water permeability of the cement-containing molded body 1 can be further reduced. When the thickness of the coating layer 20 is equal to or less than the above upper limit value, it is easy to maintain the strength of the cement-containing molded body 1.

[0026] ≪Manufacturing method of cement-containing molded body≫ The manufacturing method of the cement-containing molded body of the present invention includes a placing step and a curing step. Each step will be described in more detail below.

[0027] <Placing step> The placing step is a step of placing a cement-containing composition containing cement and water. Examples of the cement-containing composition include the above-described concrete, mortar, cement milk, etc.

[0028] The method of placing the cement-containing composition is not particularly limited, and it can be placed by a conventional method. Examples of the method of placing the cement-containing composition include placing by a pump truck, bucket placing by a crane truck, manual shoot hopper placing, etc. When placing the cement-containing composition, a formwork may or may not be used. In the present embodiment, since it is easier to bring the chemical solution into contact with the surface of the cement-containing composition, it is preferable to use a formwork and place the cement-containing composition in the formwork.

[0029] <Curing step> The curing step is a step of curing the cement-containing composition to obtain a cement-containing molded body. The curing step includes a first curing operation.

[0030] (First curing operation) The first curing operation is an operation of curing the cement-containing composition while bringing a chemical solution into contact with the surface of the placed cement-containing composition. By having the first curing operation, the surface layer portion 14 is formed on the base body 10. In addition, by having the first curing operation, the coating layer 20 is formed on the surface of the base body 10. This is presumably because the microorganisms contained in the chemical solution produce carbon dioxide, dissolve in water to become carbonate ions, and the carbonate ions react with the calcium ions contained in the base body 10 and precipitate on the surface of the base body 10 as calcium carbonate. Since the cement-containing molded body 1 has the coating layer 20 on its surface, the water permeability can be easily reduced.

[0031] (Chemical solution) The chemical solution in this specification contains microorganisms that produce carbon dioxide (hereinafter, also simply referred to as "microorganisms") and organic substances. By the chemical solution containing microorganisms, the carbonate concentration in the surface layer portion 14 can be increased. For this reason, more calcium carbonate can be formed in the coating layer 20. As a result, the water permeability of the cement-containing molded body 1 can be further reduced. Examples of the microorganisms include bacteria of the genus Bacillus and bacteria of the genus Transvalensis. From the viewpoint of having high alkali resistance and organic matter decomposing ability (especially urea decomposing ability), as the microorganisms, bacteria of the genus Bacillus are preferable, and among them, Sporosarcina Pasteurii ATCC11859 is more preferable. The microorganisms may be used alone or in combination of two or more.

[0032] Examples of the microorganisms include algae in addition to those described above. Examples of the algae include cyanobacteria, red algae, brown algae, green algae, etc. From the viewpoint of having high alkali resistance, cyanobacteria are preferable, and Arthrospira platensis NIES39 is more preferable.

[0033] The content of the microorganisms in the chemical solution is preferably 10 5 ~10 9 CFU / mL, and preferably 10 7 ~10 9CFU / mL is more preferable. When the content of microorganisms in the chemical solution is at least the above lower limit value, a sufficient amount of calcium carbonate can be produced. When the content of microorganisms in the chemical solution is at most the above upper limit value, the bad odor generated by the spoilage of excessive microorganisms can be suppressed.

[0034] Organic substances maintain the activity of microorganisms contained in the chemical solution. Examples of the organic substances include urea, derivatives of urea (such as phenylurea, benzylurea, N-benzoylurea, N,N-diphenylurea, etc.), acetic acid, lactic acid, methanol, ethanol, propanol, and the like. Since the organic substances also serve as a nitrogen source, urea and derivatives of urea are preferable, and urea is more preferable because it is easily available. When urea or a derivative of urea is used as the organic substance, ammonia is generated in addition to carbon dioxide. Since ammonia has a function of maintaining the alkalinity of the substrate 10, the neutralization of the cement-containing molded body 1 can be more suppressed. From the viewpoint that microorganisms can produce ammonia, urea or a derivative of urea is preferable as the organic substance. In this specification, the derivative of urea refers to a compound in which a hydrogen atom of urea is substituted with a hydrocarbon group. The organic substances may be used alone or in combination of two or more.

[0035] The content of the organic substance in the chemical solution is preferably 0.01 to 50 g / L, and more preferably 0.1 to 20 g / L. When the content of the organic substance in the chemical solution is at least the above lower limit value, it is easy to maintain the activity of microorganisms. When the content of the organic substance in the chemical solution is at most the above upper limit value, it is easy to maintain the strength of the cement-containing molded body 1.

[0036] The chemical solution may contain components other than the microorganisms that produce carbon dioxide and the organic substances (hereinafter also referred to as "optional components"). Examples of the optional components include a nitrogen source (excluding urea and derivatives of urea), a phosphorus source, a potassium source, other microorganisms, water, and the like. The optional components may be used alone or in combination of two or more.

[0037] Examples of the nitrogen source include corn gluten meal, yeast extract, meat extract, ammonium salts, nitric acid, amino acids, and the like.

[0038] Examples of the phosphorus source include phosphates such as sodium phosphate, sodium hydrogen phosphate, sodium dihydrogen phosphate, potassium phosphate, potassium hydrogen phosphate, potassium dihydrogen phosphate, magnesium phosphate, and calcium phosphate. As the phosphorus source, an organic phosphate compound may be used.

[0039] Examples of the potassium source include potassium salts excluding the above-mentioned potassium phosphate salts. Examples of the potassium salts include potassium chloride, potassium hydroxide, potassium nitrate, potassium sulfate, and the like.

[0040] Examples of other microorganisms include aerobic bacteria excluding the microorganisms that produce the above-mentioned carbon dioxide.

[0041] The content of the optional component in the chemical solution is preferably 0 to 10 g / L.

[0042] In the first curing operation, the temperature of the curing environment is preferably 5°C to 40°C, more preferably 10°C to 35°C, still more preferably 15°C to 35°C, and particularly preferably 20°C to 35°C. Also, in the first curing operation, the temperature of the curing environment is more preferably 10°C to 30°C, and still more preferably 15°C to 25°C. When the temperature of the curing environment is within the above numerical range, the microorganisms contained in the chemical solution are activated, and more carbon dioxide is produced. Therefore, more carbonate ions are produced, and more calcium carbonate in the coating layer 20 can be produced. As a result, the water permeability of the cement-containing molded body 1 can be further reduced.

[0043] In the first curing operation, the humidity of the curing environment is preferably 50%RH or more, more preferably 60%RH or more, still more preferably 70%RH or more, and may be 100%RH. When the humidity of the curing environment is equal to or higher than the above lower limit value, volatilization of the moisture in the chemical solution can be suppressed, and the activity of the microorganisms contained in the chemical solution can be easily maintained.

[0044] The curing time in the first curing operation is preferably 1 to 14 days, more preferably 2 to 12 days, and even more preferably 3 to 10 days. When the curing time in the first curing operation is at least the above lower limit value, the carbonate concentration in the surface layer portion 14 can be increased more. When the curing time in the first curing operation is at most the above upper limit value, the carbonate concentration in the surface layer portion 14 is saturated, and the productivity of the cement-containing molded body 1 can be increased more.

[0045] The method of bringing the chemical solution into contact with the surface of the cement-containing composition is not particularly limited. For example, there are a method of spraying the chemical solution on the surface of the cement-containing composition, a method of applying the chemical solution on the surface of the cement-containing composition, a method of attaching a water-retaining mat impregnated with the chemical solution on the surface of the cement-containing composition, a method of flooding the chemical solution on the surface of the cement-containing composition, and the like. From the viewpoint of easily making the distribution of carbonate in the surface layer portion 14 uniform, as the method of bringing the chemical solution into contact with the surface of the cement-containing composition, a method of flooding the chemical solution on the surface of the cement-containing composition is preferable. When applying the cement-containing molded body 1 to the wall surface of a structure or the like, from the viewpoint that the chemical solution can be brought into contact with the surface of the cement-containing composition for a long time, a method of attaching a water-retaining mat impregnated with the chemical solution on the surface of the cement-containing composition is preferable.

[0046] As the method of bringing the chemical solution into contact with the surface of the cement-containing composition, in addition to the methods described above, there is a method of spraying the chemical solution on the surface of the cement-containing composition and covering the surface on which the chemical solution is sprayed with a protective material. By covering the surface on which the chemical solution is sprayed with a protective material, evaporation of moisture from the surface can be prevented, formation of the coating layer 20 by microorganisms (improvement of water resistance) and the self-healing function of microorganisms can be promoted. For this reason, the water resistance of the surface (treated surface) on which the chemical solution is sprayed is improved, and the cement-containing molded body 1 in which self-healing of microorganisms is performed can be obtained. As a result, the water permeability of the cement-containing molded body 1 can be reduced more.

[0047] The method of spraying the chemical solution only needs to be able to spray it uniformly on the surface of the cement-containing composition. For example, there are a method of spraying with a spray or a spray gun, a method of applying with a brush, and the like. The protective material only needs to be able to prevent the drying of the treated surface. For example, a resin film, a water-retaining mat, etc. can be mentioned. Examples of the resin film include a polyethylene film, a polypropylene film, a polyester film, etc. Since it can be easily worked, a polypropylene film is preferred. The resin film may be a packaging film or a film containing air bubbles for heat preservation. Examples of the water-retaining mat include a concrete curing mat containing water, and a chemical solution may be contained instead of water. As a method of covering the treated surface with a protective material, it only needs to be able to protect at least the treated surface. Examples include a method of attaching the protective material to the surface to be protected, a method of wrapping the entire cement-containing composition with the protective material, etc.

[0048] (Second curing operation) The curing process may have a second curing operation. The second curing operation is an operation of removing the chemical solution and curing the cement-containing composition. By having the second curing operation, the cement-containing composition cures more efficiently, and the productivity of the cement molded body 1 can be further increased.

[0049] In the second curing operation, the temperature of the curing environment is preferably 5°C to 40°C, more preferably 10°C to 35°C, still more preferably 15°C to 35°C, and particularly preferably 20°C to 35°C. Also, in the second curing operation, the temperature of the curing environment is more preferably 10°C to 30°C, and still more preferably 15°C to 25°C. When the temperature of the curing environment is within the above numerical range, the curing of the cement-containing composition is further promoted. Therefore, the productivity of the cement molded body 1 can be further increased.

[0050] In the second curing operation, the humidity of the curing environment is preferably 20%RH or more, more preferably 40%RH or more, still more preferably 60%RH or more, and may be 100%RH. When the humidity of the curing environment is above the above lower limit value, the curing of the cement-containing composition is further promoted, and a cement molded body 1 with excellent strength can be obtained. Note that as a curing environment, curing may be performed in water (relative humidity: 100% RH).

[0051] The curing time in the second curing operation is preferably 7 to 200 days, more preferably 14 to 180 days, and even more preferably 30 to 120 days. Also, the curing time in the second curing operation is preferably 1 to 14 days, more preferably 2 to 12 days, and even more preferably 3 to 10 days. When the curing time in the second curing operation is at least the above lower limit value, the curing reaction of the cement-containing composition proceeds sufficiently, and the cement-containing molded body 1 having excellent strength can be obtained. When the curing time in the second curing operation is at most the above upper limit value, the productivity of the cement-containing molded body 1 can be further enhanced.

[0052] The method for removing the chemical solution can be appropriately determined according to the method of bringing the chemical solution into contact with the surface of the cement-containing composition. For example, when the chemical solution is sprayed or applied onto the surface of the cement-containing composition, it can be removed by gently wiping with a clean cloth or the like, or by natural drying or the like. When a water-retaining mat or the like impregnated with the chemical solution is attached onto the surface of the cement-containing composition, after peeling off the water-retaining mat or the like, it can be removed by gently wiping with a clean cloth or the like, or by natural drying or the like. When the chemical solution is flooded onto the surface of the cement-containing composition, the chemical solution can be removed by demolding the mold used during casting, or by draining the flooded chemical solution using a pump or the like.

[0053] By undergoing the second curing operation, the thickness of the surface layer portion 14 can be controlled, and the substrate 10 having sufficient strength can be obtained. In addition, by undergoing the second curing operation, the thickness of the coating layer 20 can be controlled, and the cement-containing molded body 1 having sufficient strength can be obtained. Note that even if the chemical solution is removed during the second curing operation, it is considered that microorganisms are attached to the coating layer 20 and the surface layer portion 14. For this reason, it is considered that carbon dioxide is also generated during the second curing operation, and the coating layer is further formed by precipitation of calcium carbonate.

[0054] The cement-containing molded body of the present invention can reduce the water permeability without changing the composition of the cement-containing composition. If the water permeability can be reduced, the application range of the cement-containing molded body can be expanded to underground structures, water storage facilities, etc., and the neutralization of the cement-containing molded body due to water intrusion can be suppressed. Therefore, an improvement in the durability of the cement-containing molded body can also be expected. The manufacturing method of the cement-containing molded body of the present invention only needs to treat the surface of the cement-containing composition, so the amount of the chemical solution containing microorganisms used can be significantly reduced compared with the conventional method of kneading microorganisms into the whole cement-containing composition. Since the cement-containing molded body of the present invention is obtained without kneading a chemical solution containing microorganisms into the whole cement-containing composition, the strength of the substrate can be maintained. Therefore, the cement-containing molded body of the present invention can be used in various applications where strength is required. The manufacturing method of the cement-containing molded body of the present invention can supply stable moisture to microorganisms by using the moisture in the curing process. Therefore, the reaction of microorganisms can be more reliably controlled, and the water permeability of the cement-containing molded body can be more easily reduced compared with the conventional technology in which the reaction of microorganisms depends on the external environment.

[0055] As described above, the manufacturing method and the cement-containing molded body of the present invention have been described. However, the present invention is not limited to the above-described embodiments and can be appropriately changed without departing from the gist thereof. In the above-described embodiment, the curing process has the second curing operation. However, the curing process may only have the first curing operation without the second curing operation. In the above-described embodiment, the number of times of bringing the chemical solution into contact with the surface of the cement-containing composition is not particularly mentioned. However, the number of times of bringing the chemical solution into contact with the surface of the cement-containing composition may be once or two or more times. In the above-described embodiment, the coating layer 20 is located on the outermost layer of the cement-containing molded body 1. However, the cement-containing molded body may have other layers such as a waterproof layer on the surface of the coating layer.

Example

[0056] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0057] [Example 1, Comparative Example 1] A cement composition (concrete composition) was prepared by mixing 7.3% by mass of water, 15.4% by mass of cement, 35.0% by mass of fine aggregate (sand), and 42.3% by mass of coarse aggregate (gravel). This concrete composition was poured into a mold to produce a specimen with a length of 300 mm, a width of 300 mm, and a height of 100 mm (casting process). 0.9 L of the chemical solution having the chemical solution composition shown in Table 1 was poured over the surface of this specimen and cured for 7 days in a thermostatic chamber at 20 °C and 100% RH (first curing operation). Ultra-pure water was used as the solvent for the chemical solution. In Table 1, "bacterial suspension" indicates a suspension of "Sporosarcina Pasteurii ATCC11859". In Table 1, "K2HPO4" indicates dipotassium hydrogen phosphate. In Table 1, "Yeast Extract" indicates yeast extract. The chemical solution after pouring was collected, and the ammonium ion concentration was measured by ion chromatography. As a comparative example, a specimen cured by pouring water instead of the chemical solution was also produced (Comparative Example 1), and the ammonium ion concentration of this water was measured in the same manner. The results are shown in Figure 2.

[0058]

Table 1

[0059] As shown in Figure 2, in Example 1, it was confirmed that ammonium ions were generated. This is presumably because the urea in the chemical solution was decomposed by microorganisms. It should be noted that the reason why the ammonium ion concentration is maximum on the second day of curing is presumably because the activity of the microorganisms in the chemical solution is highest on the second day of curing.

[0060] After curing the specimen for 7 days, the chemical solution was removed, and then the mold was demolded. The specimen was dried in a constant temperature room at 20°C and 40% RH for 2 months to obtain a cement molded body (concrete molded body) (second curing operation). Using the obtained concrete molded body, a water permeability test was conducted according to the surface water absorption test described in the Proceedings of the Concrete Engineering Annual Conference, Vol. 34, No. 1, 2012, "Proposal of Measurement Method and Data Processing Method in the Surface Water Absorption Test of Concrete". Specifically, using a surface water absorption test device composed of a water absorption cup part with an inner diameter of 80 mm where the concrete molded body contacts water and a vertical cylinder part (inner diameter 8 mm) for reading the change in water absorption as a change in water level, under the environment of 20°C, water injection was started from the lower part of the water absorption cup, and the time when the initial water level reached 300 mm was set as time 0. Visually, the height of the water surface was measured after 10 minutes, 480 minutes, and 1440 minutes. Regarding the measured height of the water surface at each elapsed time as h (mm), the water absorption A (mL) was calculated by the following formula (1). Note that 1 mL = 1000 mm 3 was used. π represents the pi. Water absorption A (mL) = (300 - h) × π × 4 × 4 × 1000 ··· (1)

[0061] The results of the water permeability test are shown in Table 2. As shown in Table 2, in Example 1, the water absorption (water permeability) was less than that in Comparative Example 1, and the water permeability after 1440 minutes (24 hours) had decreased by 10% or more.

[0062]

Table 2

[0063] [Example 2, Comparative Example 2] A concrete composition with the same composition as in Example 1 was prepared, and a specimen with a simulated crack provided by sandwiching a 1-mm-thick Teflon (registered trademark) sheet was produced under the same conditions as in Example 1 (first curing operation). Then, after removing the chemical solution, the mold was demolded, and the specimen was cured in water at 20°C for 3 months to obtain a concrete molded body (second curing operation). As a comparative example, a specimen cured by immersing it in water instead of the chemical solution was also produced (Comparative Example 2).

[0064] The surface of the obtained concrete molded body was observed with an optical microscope. The results are shown in FIGS. 3 and 4. As shown in FIGS. 3 and 4, it can be seen that more coating layers are formed on the surface of Example 2 than on the surface of Comparative Example 2. Therefore, in Example 2, the size of the simulated crack was smaller than that in Comparative Example 2. This means that Example 2 is superior in the self-healing function of cracks compared to Comparative Example 2. Note that the line segments in the lower right corners of FIGS. 3 and 4 are line segments indicating that FIGS. 3 and 4 have the same scale.

[0065] [Examples 3-4, Comparative Examples 3-4] A cement composition (concrete composition) was prepared by mixing 6.3% by mass of water, 11.9% by mass of cement, 38.2% by mass of fine aggregate (sand), and 43.6% by mass of coarse aggregate (gravel). This concrete composition was poured into a mold, and a specimen with a width (L W ) of 400 mm, a thickness (L L ) of 100 mm, and a height (L H ) of 400 mm was produced (casting process). After leaving this specimen to stand in a thermostatic chamber at 20°C and 100% RH for 2 days, it was demolded, and 100 mL of the chemical solution with the chemical solution composition shown in Table 1 was sprayed onto the E surface of the specimen in FIG. 5 using a spray. In Table 1, "bacterial suspension" indicates a suspension of "Sporosarcina Pasteurii ATCC11859" or "Arthrospira platensis NIES39". Then, the entire specimen was wrapped with a packaging polypropylene film to suppress the evaporation of moisture from the treated surface. In this state, the specimen was cured in a thermostatic chamber at 20°C and 100% RH for 5 days (the first curing operation). Then, the above polypropylene film was removed, and the specimen was dried in a thermostatic chamber at 20°C and 40% RH for 28 days to obtain a cement molded body (concrete molded body) 3 (the second curing operation). Using the obtained concrete molded body 3, a surface water absorption test was performed using the surface water absorption test device 30 shown in FIG. 5.

[0066] Here, as shown in FIG. 5, the surface water absorption test apparatus 30 has a measurement unit F and an analysis unit J, and the measurement unit F and the analysis unit J are connected by a wiring I. The measurement unit F is connected to a support unit H, and the support unit H is connected to two fixing jigs G. The fixing jig G is fixed to the E surface of the concrete molded body 3, and the measurement unit F is in close contact with the E surface of the concrete molded body 3. The inner diameter (L F ) of the measurement unit F is 50 mm, and the analysis unit J is configured to measure the surface water absorption amount of the measurement unit F.

[0067] In the surface water absorption test, the surface water absorption amount in the measurement unit F for 10 minutes was measured. The results are shown in FIG. 6. In FIG. 6, the symbols A, B, C, and D represent A: no spraying (Comparative Example 3), B: spraying only water (Comparative Example 4), C: spraying a chemical solution containing Sporosarcina Pasteurii ATCC11859 (Example 3), D: spraying a chemical solution containing Arthrospira platensis NIES39 (Example 4). As shown in FIG. 6, in Example 3, the surface water absorption amount is 1.16 mL, and in Example 4, the surface water absorption amount is 1.01 mL. Compared with Comparative Example 3 (surface water absorption amount 1.31 mL) and Comparative Example 4 (surface water absorption amount 1.21 mL), it was found that the surface water absorption amount is less and the water repellency of the concrete surface is improved.

[0068] As is clear from the above-described examples, it was found that the cement-containing molded body of the present invention can easily reduce the water permeability.

Explanation of symbols

[0069] 1... Cement-containing molded body, 3... Cement-containing molded body (concrete molded body), 10... Substrate, 12... Central part, 14... Surface layer part, 20... Coating layer, 30... Surface water absorption test apparatus

Claims

1. A method for manufacturing a cement-containing molded body, comprising a substrate that is a cured product containing cement and a coating layer located on the surface of the substrate, the method comprising: a placing step of placing a cement-containing composition containing cement and water; a curing step of curing the cement-containing composition to obtain a cement-containing molded body, wherein the curing step includes a first curing operation of curing the cement-containing composition while bringing a chemical solution into contact with the surface of the placed cement-containing composition to form a surface layer portion containing carbonate from the boundary between the substrate and the coating layer to an arbitrary depth of the substrate; the chemical solution contains a microorganism that produces carbon dioxide and an organic substance, a method for manufacturing a cement-containing molded body.

2. The method for manufacturing a cement-containing molded body according to claim 1, wherein the organic substance is urea or a derivative of urea.

3. The method for manufacturing a cement-containing molded body according to claim 1 or 2, wherein the first curing operation is to flood the chemical solution on the surface of the cement-containing composition.

4. A cement-containing molded body manufactured by the manufacturing method according to any one of claims 1 to 3, comprising a substrate that is a cured product containing cement and a coating layer located on the surface of the substrate, wherein the substrate contains carbonate in a surface layer portion at an arbitrary depth from the boundary with the coating layer, and the carbonate concentration in the surface layer portion is higher than the carbonate concentration in a central portion deeper than the arbitrary depth, a cement-containing molded body.

Images