Admixture, cement composition, hardened cement, and method of producing hardened cement

Abstract

To provide an admixture for use in a cement composition including an organic polymer that can more efficiently be assimilated relative to a conventional one without significantly influencing the strength development.SOLUTION: The admixture to be used by mixing with cement, i.e., an admixture for being mixed with cement, includes an aerobic microbe and a polyhydroxyalkanoic acid (PHA) produced by a biological engineering method. Thereby, PHA produced by a biological engineering method, has a specific surface area larger than that of PLA formed by chemical synthesis and can more efficiently be assimilated by an aerobic microbe. PHA is free from a risk of being dissolved into water to elute and to decompose unlike glucose and does not substantially influence strength development of the hardened cement. Further, the present invention relates to a cement composition including an admixture, hardened cement, and a method of producing hardened cement.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an admixture, a cement composition, a hardened cement product, and a method for producing a hardened cement product, and in particular to an admixture to be used by mixing with cement, a cement composition containing an admixture, a hardened cement product obtained by hardening the cement composition, and a method for producing a hardened cement product in which corrosion of the steel material is inhibited by embedding the steel material in the cement composition. [Background technology]

[0002] Hardened cement products such as concrete and mortar are widely used for construction purposes, and in particular, reinforced concrete in which steel materials such as reinforcing bars are embedded in concrete is widely used as building structures.

[0003] Corrosion of steel in reinforced concrete is calculated by the following formula: Fe → Fe 2+ +2 e- ...Anode reaction 1 / 2O2+H2O+2 e- →2OH - ……Cathode reaction As shown in the figure, electrons are taken from the steel (iron) in the anodic reaction, and these electrons cause the cathodic reaction of oxygen dissolved in the water to proceed, resulting in the formation of OH - All you need to do is generate ions.

[0004] Therefore, in order to suppress corrosion of steel materials, measures to suppress the anodic reaction and / or the cathodic reaction can be considered.

[0005] Furthermore, cracks develop in the hardened cement over time, allowing water and oxygen to penetrate into the cracks, accelerating the anodic and cathodic reactions and accelerating the corrosion of the steel material. Therefore, repairing cracks in the hardened cement material is also important for suppressing corrosion of the steel material.

[0006] Patent Document 1 discloses a method for preventing corrosion of steel materials by utilizing the metabolism of aerobic microorganisms to consume dissolved oxygen in concrete and stagnate the cathodic reaction. At the same time, carbon dioxide is released by the microbial metabolism, which reacts with calcium dissolved in water from the hardened cement to precipitate carbonate, repairing cracks and preventing further penetration of water and air into the cracks, thereby indirectly preventing corrosion of steel materials.

[0007] In order to utilize the metabolism of such aerobic microorganisms to inhibit corrosion of steel materials and to improve the effectiveness of repairing cracks in hardened cement, it is important to increase the activity of the microorganisms.Therefore, it is effective to add a nutrient source for the microorganisms as an admixture together with the aerobic microorganisms.

[0008] In Patent Document 1, sugars, particularly glucose, are added as a nutrient source for microorganisms. However, adding large amounts of glucose inhibits the hydration reaction (hardening reaction) of cement, delaying the development of strength in the hardened cement product, and therefore it is not possible to add large amounts of glucose to the cement composition. Furthermore, there are problems with glucose dissolving in water, leaching out, and decomposing, and it is quickly assimilated and used up by microorganisms, making it less suitable as a long-term nutrient source.

[0009] Non-Patent Document 1 discloses a concrete healing agent (CHA-PLA) based cement admixture containing alkaline hydrophilic spore-forming Bacillus spores and polylactic acid (PLA) as a nutrient source. Adding CHA-PLA during the production of ready-mix concrete causes the polylactic acid to react with calcium in the cement composition in the mixing water and convert to calcium lactate. When cracks develop in the resulting hardened cement over time, the pH drops due to the infiltration of water and oxygen, and bacteria begin to become active. The bacteria then absorb oxygen and calcium lactate that have entered the cracks, and through metabolic activity, release calcium carbonate into the cracks, repairing the cracks and reducing the amount of oxygen in the hardened cement. Once the cracks are completely closed, the supply of water and oxygen is cut off, allowing the bacteria to once again remain dormant and prepare for the next crack to form.

[0010] As mentioned above, PLA (polylactic acid) exists in the hardened cement as calcium lactate, so adding large amounts of PLA does not have a noticeable adverse effect on the cement hydration reaction, and because lactic acid exists in the hardened cement as calcium lactate, there is little leaching out of the hardened cement.

[0011] Therefore, according to the alkali admixture in Non-Patent Document 1, even if added in large quantities, it does not have a significant effect on the strength development of cement, and furthermore, it contributes to reducing the amount of oxygen in the hardened cement and self-repairing of cracks while minimizing the risk of oxygen leakage from the hardened cement.In addition, since it contains a nutrient source, it can also maintain high microbial activity. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Patent No. 6716331 [Non-patent literature]

[0013] [Non-Patent Document 1] "Basilisk(R) HA Safety Data Sheet", [online], Aizawa High Pressure Concrete Co., Ltd., [Retrieved November 13, 2023], Internet <https: / / f.hubspotusercontent10.net / hubfs / 9396663 / Basilisk%E8%B3%87%E6%96%99 / HA_SafetyData_jpn.pdf?__hstc=251652889.029a8563d372cf90894ab300054a373e.1699841801638.1699841801638.1699841801638.1&__hssc=251652889.55.1699841801639&__hsfp=1696857715> Summary of the Invention [Problem to be solved by the invention]

[0014] As mentioned above, the alkali admixture in Non-Patent Document 1 does not significantly affect the strength of cement even when added in large quantities, and it contributes to reducing the amount of oxygen in the hardened cement and self-repairing cracks while minimizing the risk of oxygen leaking from the hardened cement. Furthermore, since it contains a nutrient source, it also helps maintain high microbial activity.

[0015] Thus, PLA (polylactic acid) is currently considered a good nutrient source. However, when PLA is extruded using existing chemical methods, the resulting particles are large, resulting in a small specific surface area and poor microbial assimilation. While it is possible to reduce the surface area by grinding, PLA resin is generally hard and difficult to grind. Furthermore, PLA generally has poor heat resistance. Therefore, when attempting to grind it using a ball mill, for example, the heat generated during grinding softens the PLA, potentially making it impossible to grind.

[0016] Therefore, there has been a demand for an admixture for cement compositions that contains an organic polymer that can be utilized more efficiently than conventional admixtures.

[0017] The present invention has been made in view of the above problems, and has an object to provide an admixture for cement compositions containing an organic polymer that does not significantly affect strength development and can be assimilated more efficiently than conventional admixtures. It is also an object of the present invention to provide a method for producing a hardened cement paste in which corrosion of steel is suppressed, using an admixture for cement compositions containing an organic polymer that does not significantly affect strength development and can be assimilated more efficiently than conventional admixtures. [Means for solving the problem]

[0018] The present inventors have conducted extensive research to achieve the above object, and as a result have discovered that adding bioengineered polyhydroxyalkanoates (PHA) to admixtures as a nutrient source for microorganisms does not significantly affect the strength development of hardened cement paste even when added in large amounts, and can be assimilated more efficiently than when PLA is used, thereby completing the present invention.

[0019] That is, it has been found that the above object can be achieved by an admixture for mixing with cement, which is characterized in that it contains aerobic microorganisms and polyhydroxyalkanoic acid (PHA) produced by biotechnological techniques.

[0020] It is also preferable that the polyhydroxyalkanoic acid (PHA) is marine degradable.

[0021] Furthermore, the aerobic microorganism is preferably a bacterium of the genus Bacillus, and it is particularly preferred that the aerobic microorganism is selected from the group consisting of Bacillus subtilis and Bacillus altitudinis.

[0022] Additionally, it is preferred that the admixture of the present invention further comprises a reducing agent.

[0023] The above object can also be achieved by a cement composition containing the admixture of the present invention, cement, and water, and further by a hardened cement body obtained by hardening the cement composition of the present invention while a steel material is embedded in the cement composition.

[0024] Furthermore, the above-mentioned object can also be achieved by a method for producing a hardened cement body in which corrosion of a steel material is inhibited, the method comprising: an embedding step of embedding a steel material in the cement composition of the present invention; and a curing step of curing the cement composition to obtain a hardened cement body. [Effects of the Invention]

[0025] According to the admixture used in combination with cement of the present invention and the method for producing a hardened cement product with reduced corrosion of steel materials of the present invention, bioengineered polyhydroxyalkanoate (PHA) is added as a nutrient source for aerobic microorganisms, resulting in a larger specific surface area than chemically synthesized PLA (polylactic acid), and therefore a higher utilization efficiency in the hardened cement composition (hardened cement product). Furthermore, unlike glucose, polyhydroxyalkanoate (PHA) does not dissolve in water and leach or decompose, nor does it inhibit the hydration reaction of cement, so it does not significantly affect the strength development of the hardened cement composition (hardened cement product) obtained. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a graph showing the change over time in the dissolved oxygen concentration in the sample solutions of Example 1 and Comparative Example 1-2 after microbial metabolism was suppressed in a high pH environment and then the pH was lowered to 9.0. [Figure 2] This is a graph of the same test as in Figure 1, but with the vertical axis converted to the respiration rate in the sample solution. [Figure 3] This is a graph of the same test as in Figure 1, with respiration rate on the vertical axis and pH on the horizontal axis. [Figure 4]1 is a flow diagram showing a method for producing a hardened cement product in which corrosion of a steel material is suppressed according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0027] <Mixed materials> The admixture of the present invention is an admixture to be mixed with cement and comprises aerobic microorganisms and biotechnologically produced polyhydroxyalkanoates (PHAs).

[0028] [Aerobic microorganisms] The aerobic microorganisms are not particularly limited as long as they consume oxygen and generate carbon dioxide, and include obligate aerobic microorganisms, facultative aerobic microorganisms, facultative anaerobic microorganisms, and microaerophilic microorganisms. A wide range of microorganisms can be used, including bacteria, yeasts, fungi, protozoa, and protozoa.

[0029] Among these, spore-forming microorganisms capable of forming spores (spores, particulates) are particularly preferred.

[0030] As the spore-forming microorganism, for example, one or more species of Bacillus subtilis (genus Bacillus), actinomycetes (genus Streptomyces, etc.), fungi (phyla Imperfectomycota, Ascomycota, Zygomycota, Basidiomycota, Chytridiomycota), etc. can be used. Among these, bacteria of the genus Bacillus (Bacillus subtilis) are preferred because they produce endospores (spores) and can survive in the highly alkaline and dry environments of cement compositions and hardened cement bodies.

[0031] Bacillus genus bacteria are not particularly limited, but include, for example, Bacillus subtilis (including Bacillus subtilis var. natto), Bacillus amyloliquefaciens, Bacillus lentus, Bacillus laterosporus, Bacillus alvei, Bacillus popilliae, Bacillus pumilus, Bacillus altitudinis, Bacillus licheniformis, Bacillus coagulans, Bacillus cereus, Bacillus halodurans, Bacillus acidicola, Bacillus acidopullulyticus, Bacillus acidovorans, Bacillus aeolius, Bacillus aestuarii, Bacillus garadhaerens, Bacillus akibai, Bacillus alcaliinulinus, Bacillus alcalophilus, Bacillus algicola, Bacillus alkalitolerans, Bacillus alkalogaya, Bacillus alveayuensis, Bacillus amiliensis, Bacillus aminovorans, Bacillus aquimaris, Bacillus arbutinivorans, Bacillus arenosi, Bacillus arseniciselenatis, Bacillus arsenicus, Bacillus arvi, Bacillus asahii, Bacillus atrophaeus, Bacillus axarquiensis, Bacillus azotoformans, Bacillus badius, Bacillus baekryungensis, Bacillus barbaricus, Bacillus bataviensis, Bacillus benzoevorans, Bacillus bogoriensis, Bacillus borophilicus, Bacillus borotolerans, BacillusOne or more species can be selected from the group consisting of Bacillus caldolyticus, Bacillus caldotenax, Bacillus caldovelox, Bacillus carboniphilus, Bacillus casamancensis, Bacillus catenulatus, Bacillus cellulosilyticus, Bacillus sphericus, Bacillus thuringiensis, Bacillus clausii, etc. Among these, aerobic microorganisms are preferably selected from the group consisting of Bacillus subtilis and Bacillus altitudinis because they are resistant to environmental stresses such as temperature and pH (Bacillus altitudinis is more preferred from the viewpoint of metabolic activity in a high pH environment), and natto bacteria (Bacillus subtilis var. natto) is particularly preferred in terms of heat resistance, economy, and safety (it is a microorganism that has been used in food and is therefore highly safe).

[0032] [Polyhydroxyalkanoates (PHAs) produced by bioengineering methods] The admixture of the present invention contains a nutrient source for aerobic microorganisms. By including the nutrient source in the admixture, it becomes possible to increase the activity of aerobic microorganisms when cracks or the like occur in the hardened cement body.

[0033] In the present invention, the admixture contains biotechnologically produced polyhydroxyalkanoates (PHAs) as a nutrient source for aerobic microorganisms. Examples of biotechnologically produced polyhydroxyalkanoates (PHAs) include, but are not limited to, polyhydroxybutanoic acid (PHB), poly(3-hydroxybutanoic acid / 3-hydroxyvaleric acid) (PHBV), and poly(3-hydroxybutanoic acid / 3-hydroxyhexanoic acid) (PHBH). In particular, considering that the polyhydroxyalkanoic acid (PHA) produced by bioengineering techniques is a polyhydroxyalkanoic acid (PHA) selected from the group consisting of poly(3-hydroxybutanoic acid / 3-hydroxyvaleric acid) (PHBV), poly(3-hydroxybutanoic acid / 3-hydroxyhexanoic acid) (PHBH), and mixtures thereof, it is preferable that the polyhydroxyalkanoic acid (PHA) produced by bioengineering techniques is a polyhydroxyalkanoic acid (PHA) selected from the group consisting of poly(3-hydroxybutanoic acid / 3-hydroxyhexanoic acid) (PHBH), and mixtures thereof.

[0034] Commercially available bioengineered PHAs are available from, for example, Kaneka (PHBH) and HighChem (PHBV).

[0035] Polyhydroxyalkanoates (PHAs) produced by bioengineering methods have smaller particle sizes than biodegradable plastics such as chemically synthesized polylactic acid (PLA). Therefore, polyhydroxyalkanoates (PHAs) produced by bioengineering methods have a relatively larger contact area with water that penetrates through cracks and other factors over time in hardened cement, making them more susceptible to initial decomposition and subsequent decomposition by aerobic microorganisms. This is thought to improve the efficiency of assimilation by aerobic microorganisms compared to chemically synthesized biodegradable plastics.

[0036] Furthermore, polyhydroxyalkanoates (PHAs) produced by bioengineering techniques are preferably marine degradable.Cement-based hardened bodies containing steel are often installed in the ocean's tidal zones, which not only provide a large amount of oxygen required for the cathodic reaction of the steel, but also create an extremely corrosive environment because the evaporation of seawater adhering to the surface of the hardened cement body causes chloride ions to condense.

[0037] In such an environment, the polyhydroxyalkanoic acid (PHA) produced by bioengineering techniques is marine degradable, which accelerates the decomposition of the polyhydroxyalkanoic acid (PHA) in hardened cement bodies containing the admixture of the present invention placed in marine tidal zones, etc., and improves the activity of aerobic microorganisms, making the admixture capable of providing hardened cement bodies that are more resistant to corrosion than conventional admixtures, even in severe corrosive environments.

[0038] Furthermore, from the viewpoint of assimilation efficiency, the particle size of polyhydroxyalkanoic acid (PHA) produced by bioengineering techniques is preferably 500 μm or less, more preferably 300 μm or less, and particularly preferably 100 μm or less.

[0039] Furthermore, the particle shape of the polyhydroxyalkanoic acid (PHA) produced by bioengineering techniques may be any, but spherical shape is preferable from the viewpoint of maintaining the fluidity of the cement composition when blended into the cement composition.

[0040] [Reducing agent] The admixture of the present invention preferably further contains a reducing agent. The reducing agent is not particularly limited as long as it is a substance that is stable in the alkaline environment of the cement paste and its hardened product and that reacts with the oxidizing substance in the hardened cement product to exhibit reducing ability. For example, a substance that is more easily oxidized than the metal (e.g., iron in reinforcing bars) used for corrosion prevention purposes is used.

[0041] Examples of such reducing agents include powdered iron and steel slag (blast furnace slag, steelmaking slag, electric furnace reduced slag), iron (II) ions, lithium aluminum hydride (LiAlH), sodium amalgam, sodium borohydride (NaBH), tin (II) ions, sulfite, hydrazine, zinc amalgam, diisobutylaluminum hydride (DIBAH), oxalic acid (CHO), formic acid (HCOOH), etc., which may be added alone or in combination of two or more.

[0042] Among these, iron and steel slag powder is preferred because it has a high affinity with cement-based materials and does not inhibit the growth of aerobic microorganisms when used in combination with them. Among iron and steel slag powders, blast furnace slag powder contains a small amount of iron oxide (below the detection limit), but also contains zero to divalent iron (especially divalent iron) and other iron components (e.g., Fe3O4, i.e., triiron tetroxide), which function as reducing agents. Therefore, it has high reducing ability and is most suitable for the admixture of the present invention. The type of blast furnace slag powder is not particularly limited, and either air-cooled blast furnace slag or granulated blast furnace slag may be used, but powder (fine powder) is used in consideration of the dispersibility of the admixture.

[0043] Unlike aerobic microorganisms, reducing agents consume oxygen through chemical reactions, and therefore contribute particularly to oxygen consumption in sound concrete that is free of cracks and other damage. On the other hand, aerobic microorganisms are active when oxygen is supplied. Therefore, when an admixture contains both aerobic microorganisms and reducing agents, the corrosion inhibition effect is maintained for a longer period of time.

[0044] [Additives] The admixture of the present invention may contain additives other than the aerobic microorganisms and reducing agents.

[0045] The additives are not particularly limited as long as they do not inactivate the activity of aerobic microorganisms, and various additives can be used, such as fillers, dispersants, surfactants, pH adjusters, pH buffers, etc. One type of additive can be used alone, or two or more types can be used.

[0046] Nutrient sources for aerobic microorganisms other than bioengineered polyhydroxyalkanoates (PHAs) can also be added as additives. The nutrient sources are not particularly limited, and one or more of the following can be used: organic carbon sources (sugars, starch, etc.), inorganic carbon sources (sodium carbonate, etc.), organic nitrogen sources (amino acids, peptone, etc.), inorganic nitrogen sources (ammonium salts, nitrates, etc.), and inorganic nutrient sources (P, S, K, Mg, Fe, Na, etc.). However, inorganic nutrient sources such as calcium contained in cement do not need to be added separately.

[0047] The nutrient source is preferably one that does not release corrosive substances through the metabolism of aerobic microorganisms. If the carbon source (sugars, etc.) used as the nutrient source causes corrosive substances such as organic acids (acetic acid, pyruvic acid), a nitrogen source may be added to the nutrient source, and the organic acids may be masked by the ammonia produced by the microorganisms. This is particularly effective when using Bacillus bacteria.

[0048] When the aerobic microorganism is a spore-forming microorganism, a germination inducer can be added as a nutrient source. The germination inducer is not particularly limited, but for example, when the spore-forming microorganism is a Bacillus bacterium, amino acids such as L-alanine and L-valine can be used. Furthermore, when the Bacillus bacterium is Bacillus subtilis var. natto, a coenzyme such as biotin can be added as a nutrient source.

[0049] Nutrient sources for other aerobic microorganisms also include nutrient sources that affect the strength development of hardened cement bodies, so the mixing ratio thereof is, for example, 10% or less, and preferably 5% or less by mass, of the total mass of the admixture excluding water.

[0050] Therefore, according to the admixture of the present invention, polyhydroxyalkanoic acid (PHA) produced by biotechnology is added as a nutrient source for aerobic microorganisms, and therefore has a larger specific surface area than chemically synthesized PLA (polylactic acid), thereby increasing the assimilation efficiency of the hardened cement composition obtained. Furthermore, unlike glucose, polyhydroxyalkanoic acid (PHA) does not dissolve in water and leach or decompose, and there is no risk of inhibiting the hydration reaction of cement, so it does not significantly affect the strength development of the hardened cement composition obtained.

[0051] Therefore, by improving the efficiency of nutrient utilization compared to conventional methods, the corrosion prevention effect on steel materials based on the consumption of dissolved oxygen in the hardened cement body by the metabolism of aerobic microorganisms, and the crack repair effect due to the release of carbon dioxide by the metabolism of aerobic microorganisms and the precipitation of carbonates resulting from the reaction between this released carbon dioxide and calcium dissolved in water from the hardened cement body are further improved.

[0052] <Cement composition> The cement composition of the present invention contains the admixture of the present invention, cement, and water. The admixture is the same as the admixture described above, so a description thereof will be omitted here.

[0053] The amount of the admixture of the present invention in the cement composition is, for example, 3 The number of microbial cells per 10 ~10 15 / m 3 The amount of the mixture is 10 12 ~10 13 / m 3 It is preferable that the blending amount is such that:

[0054] The amount of the admixture of the present invention in the cement composition is, for example, 3 The amount of biotechnologically produced polyhydroxyalkanoates (PHA) per unit volume is 0.3-10 kg / m 3 The blending amount is 0.5 to 8 kg / m 3 It is preferable that the blending amount is such that:

[0055] [cement] Cement is an inorganic binder that hardens when mixed with water, and hydraulic cement is used in the present invention. As hydraulic cement, simple cement such as Portland cement (JIS R5210), hydraulic lime, Roman cement, or natural cement may be used, or mixed cement such as lime-blended cement or mixed Portland cement (JIS R5211, R5212, R5213) may be used.

[0056] [water] The water to be mixed in the cement composition is not limited to pure water, but tap water, river water, lake water, and seawater can also be used.

[0057] [Optional ingredients] The cement composition also 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 is one that retains 85% or more by mass on a 5 mm mesh sieve, while fine aggregate is one that passes through a 5 mm mesh sieve and 100% by mass on a 10 mm mesh sieve.

[0058] It may also contain optional admixtures such as air entraining agents (air entraining agents), water reducing agents (air entraining water reducing agents, water reducing agents, high performance air entraining water reducing agents, etc.), superplasticizers, setting and hardening regulators, accelerators, rust inhibitors, waterproofing agents, etc.

[0059] The cement composition can be prepared, for example, by powder-mixing cement and, optionally, other powder components, adding water and the admixture of the present invention to the powder mixture, kneading the mixture to form a paste, and then mixing fine aggregate and coarse aggregate as necessary.

[0060] <Hardened cement> The hardened cement product of the present invention is obtained by hardening the cement composition of the present invention while a steel material is embedded in the cement composition.

[0061] [Steel] The steel material is not particularly limited, and includes, for example, a variety of steel materials such as reinforcing bars, steel frames, round steel bars, deformed steel bars, deformed reinforcing bars, PC steel materials, and molten wire mesh, and the material is also not particularly limited.

[0062] To embed steel materials in a cement composition, various methods can be used, such as a method of injecting the cement composition into a formwork in which the steel materials are placed, a method of applying the cement composition to the surface of the steel materials, or a method of spraying the cement composition onto the surface of the steel materials.

[0063] After the steel material is embedded in the cement composition, the cement composition is hardened through a process such as curing, and the hardened cement product of the present invention is obtained.

[0064] <Method of manufacturing hardened cement> As shown in FIG. 4, the method for producing corrosion-suppressed hardened cement body of the present invention includes an embedding step (S110) and a curing step (S120).

[0065] [Burial process (S110)] In this step, a steel material is embedded in the cement composition of the present invention. The cement composition and the steel material are the same as those described above, so a detailed description thereof will be omitted here.

[0066] For example, when the cement composition is poured into a formwork in which steel materials are placed, the formwork is first placed according to the desired shape of the hardened cement body, and reinforcing bars are laid inside the formwork, or the reinforcing bars are laid inside the formwork and then the formwork is placed around them. Then, the cement composition is poured into the formwork, and the reinforcing bars (steel materials) are embedded in the cement composition.

[0067] When applying the cement composition to the surface of a steel material, the cement composition is spread over the surface of a steel frame or wire mesh with a trowel or the like, and the steel frame or wire mesh is embedded in the cement composition. When spraying the cement composition onto the surface of a steel material, for example, the cement composition is sprayed onto the surface of a plate-shaped steel material or wire mesh, and the steel material or wire mesh is embedded in the cement composition (this is the embedding step (S110)).

[0068] [Curing process (S120)] In this step, the cement composition is cured to obtain a hardened cement body.

[0069] The cement composition applied or sprayed onto steel or injected into a formwork is cured until it attains the required compressive strength, thereby obtaining a hardened cement body. Curing can be carried out under conventionally known conditions, such as air curing or underwater curing (these are referred to as the curing step (S120)).

[0070] As described above, according to the method for producing corrosion-inhibited hardened cement body of the present invention, steel is embedded in the hardened cement body, which contains aerobic microorganisms and bioengineered polyhydroxyalkanoates (PHAs) as a nutrient source. This improves the efficiency of assimilation of the nutrient source compared to conventional methods, further improving the corrosion prevention effect of steel based on the consumption of dissolved oxygen in the hardened cement body by the metabolism of aerobic microorganisms, and the crack repair effect based on the release of carbon dioxide by the metabolism of aerobic microorganisms, which reacts with calcium dissolved in water from the hardened cement body to precipitate carbonates. [Example]

[0071] EXAMPLES The present invention will be specifically explained below by showing examples, but the present invention is not limited to these examples.

[0072] In this example, we used Bacillus subtilis natto as the aerobic microorganism, and used conventional polylactic acid (PLA) and poly(3-hydroxybutyrate / 3-hydroxyvalerate) copolymer (PHBV, a bioengineered PHA) as its nutrient sources. We then examined the change in Bacillus subtilis natto activity after its microbial metabolism was suppressed in a high-pH environment and the pH was lowered to approximately 9.0 using hydrochloric acid. The operation of suppressing microbial metabolism in a high-pH environment and then lowering the pH to approximately 9.0 using hydrochloric acid or other methods was intended to monitor changes in microbial activity over time as the surface of the hardened cement body was neutralized or water infiltrated through cracks that developed after the hardened cement body was placed in a high-pH environment immediately after pouring the cement composition.

[0073] 1. Cultivation of Bacillus subtilis natto For pre-culture, 0.8 mL of stock solution of Bacillus subtilis natto (product name: pure culture Bacillus subtilis natto, manufactured by Miyagino Natto Seizosho), 0.5 g of LB medium, and 20 mL of distilled water were placed in a test tube, the surface was covered with commercially available food wrap film, and shake culture was carried out at a temperature of 20°C for 24 hours or more. Note that 50 mL of the stock solution of Bacillus subtilis natto contains 300 to 400 million Bacillus subtilis natto.

[0074] For the main culture, S7 medium was dissolved in 500 mL of distilled water in order from top to bottom, and the mixture was brought up to 1000 mL by measuring and stirring. 1 mL of the pre-culture solution was then inoculated into the mixture, and the mixture was cultured for 24 hours in a constant temperature room at 20°C while aerating using an air pump and air tube. The composition of the S7 medium is as follows: S7 Base (※1) 85.5ml 1M MOPS(3-(N-morpholino)propanesulfonic acid)pH7.0 10ml 1M L-sodium glutamate 2ml MT mix (※2) 1ml 25% (W / V) glucose 4ml (※1 Breakdown of S7 Base K2HPO40.17g 0.13g KH2PO4 (NH4)2SO4 0.27g / 200ml) (※2 Breakdown of MT mix 2 ml of 1M HCl 40.6g MgCl2·6H2O CaCl2·2H2O 10.29g MnCl₂·4H₂O 0.99g ZnCl2 13.6mg FeCl3·6H2O 135mg Thiamine·HCl 67.5mg / 1L (filter sterilized)

[0075] 2. Observation of changes in microbial activity after lowering pH from high to pH 9.0 30 mL of the culture solution of Bacillus subtilis natto after main culture was added to a test tube, and calcium hydroxide was added to adjust the pH to 11.81. 1.0 g of PHBV (product name: PHBV powder, manufacturer: HighChem Co., Ltd., particle size: 0.5 μm to 30 μm) was then added as a PHA produced by bioengineering. This sample is designated as Example 1. Hydrochloric acid was then added to adjust the pH to 9.0, and the dissolved oxygen concentration in the test tube was measured up to 900 hours after the addition of hydrochloric acid, with the time being set as 0 hours.

[0076] Furthermore, a sample was prepared as Comparative Example 1, which was subjected to the same test as in Example 1, except that 1.0 g of polylactic acid (PLA) (product name: PLA (polylactic acid), manufacturer: HighChem Co., Ltd., particle size: approximately 3.5 mm) was added instead of PHBV. Another sample was prepared as Comparative Example 2, which was subjected to the same test as in Example 1, except that PHBV and its substitute were not added. Note that the test tubes for both samples contained glucose derived from the culture medium during the main culture.

[0077] Dissolved oxygen concentration was measured using an optical oxygen sensor (product name: OXY-1 ST / ST trace, manufacturer: PreSens).

[0078] The results are shown in Figure 1. Figure 1 is a graph showing the change over time in the dissolved oxygen concentration in the sample solutions of Example 1 and Comparative Example 1-2 after the microbial metabolism was suppressed in a high pH environment and the pH was then lowered to 9.0.

[0079] As shown in the figure, the dissolved oxygen concentration in the solution of Example 1 (PHBV) dropped significantly to 3.40 mg / L after 48 hours, while the dissolved oxygen concentration in the solution of Comparative Example 1 (PLA) remained high at 5.17 mg / L even after 120 hours, and the dissolved oxygen concentration in the solution of Comparative Example 2 (none) remained high at 8.40 mg / L even after 216 hours. The drop in the dissolved oxygen concentrations in the solutions of Example 1 and Comparative Example 1 is thought to be due to the initiation of re-metabolism by Bacillus subtilis natto due to the pH being lowered using hydrochloric acid. However, the dissolved oxygen concentration in the solution of Example 1 dropped more than in Comparative Example 1 at an elapsed time that was half that of Comparative Example 1, indicating that PHA (PHBV) produced by bioengineering techniques has a higher assimilation efficiency than chemically synthesized polylactic acid (PLA).

[0080] Aeration was performed in each sample solution after 48 hours in Example 1, after 120 hours in Comparative Example 1, and after 216 hours in Comparative Example 2, and the dissolved oxygen concentration rose temporarily by dissolving gaseous oxygen from the atmosphere. However, when aeration was stopped, the dissolved oxygen concentration began to decrease due to aerobic respiration.

[0081] FIG. 2 is a graph of the same test as FIG. 1, but with the vertical axis converted to the respiration rate in the sample solution.

[0082] Here, in the present invention, the respiration rate refers to the value obtained by calculating the amount of dissolved oxygen consumed by microorganisms per second using the change in dissolved oxygen concentration over time measured for 5 minutes at a sampling rate of once per second, and then calculating the average value for the 5 minutes.

[0083] As shown in the figure, in Comparative Example 2, an increase in respiration rate was confirmed after 216 hours, then reached a maximum value after 288 hours, after which the respiration rate decreased and showed a low value of 0.002 mg / L·s or less. In Comparative Example 1, the respiration rate began to increase after 48 hours, reached a maximum value after 120 hours, and thereafter showed a value of around 0.004 mg / L·s. In Example 1, the respiration rate began to increase from 0 hours, continued to rise, peaked after 216 hours, reached a value of around 0.006, and then further increased after 900 hours.

[0084] This result indicates that Example 1, in which PHBV was added as a PHA produced by bioengineering techniques, had higher microbial activity than Comparative Example 1, in which polylactic acid (PLA) was added. This is thought to be because PHBV produced by bioengineering techniques has a smaller particle size than polylactic acid (PLA) produced by chemical synthesis, which increases the contact area with the solution and makes it easier for primary decomposition to proceed, and then it is more easily decomposed by Bacillus subtilis natto.

[0085] Figure 3 is a graph of the same test as Figure 1, with respiration rate on the vertical axis and pH on the horizontal axis.

[0086] As shown in the figure, in both the samples of Example 1 and Comparative Examples 1 and 2, the respiration rate increases as the pH decreases. Furthermore, the respiration rates of Comparative Example 1 and Example 1, which each contain biodegradable plastics (PLA, PHBV), tend to be higher than those of Comparative Example 2. In particular, Example 1 tends to have a higher respiration rate than Comparative Example 1.

[0087] This is thought to be due to the difference in particle size between PHBV (particle size 0.5 μm to 30 μm) and PLA (particle size approximately 3.5 mm). [Industrial Applicability]

[0088] The admixture of the present invention can be used for mixing with cement. Furthermore, hardened cement products obtained by hardening a cement composition containing the admixture of the present invention, and hardened cement products obtained by the manufacturing method of the present invention, can be widely used as architectural structures. In particular, when the admixture of the present invention contains a marine-degradable PHA produced by bioengineering techniques, the hardened cement products can be suitably used for floating marine structures and architectural structures built in the marine tidal zone.

Claims

1. An admixture used by mixing with cement, Aerobic microorganisms, a bioengineered polyhydroxyalkanoic acid (PHA); An admixture for mixing with cement, comprising:

2. 2. The admixture according to claim 1, wherein the polyhydroxyalkanoic acid (PHA) is marine degradable.

3. 2. The admixture according to claim 1, wherein the aerobic microorganism is a bacillus bacterium.

4. 4. The admixture of claim 3, wherein the aerobic microorganism is selected from the group consisting of Bacillus subtilis and Bacillus altitudinis.

5. 10. The admixture of claim 1 further comprising a reducing agent.

6. A cement composition comprising the admixture of claim 1, cement, and water.

7. A hardened cement product obtained by hardening the cement composition according to claim 6 while a steel material is embedded in the cement composition.

8. An embedding step of embedding a steel material in the cement composition according to claim 6; a curing step of curing the cement composition to obtain a hardened cement body; 1. A method for producing a hardened cement product in which corrosion of steel material is inhibited, comprising:

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