Liquid admixture for cement, cement composition, cement hardened body, and method for producing cement hardened body

Abstract

[Problem] To provide: an admixture which can uniformly impart crack self-repairing properties and resistance to sulfuric acid-induced deterioration to the whole of a cement-based material; a cement composition containing the admixture; a hardened body of the cement composition; and a method for producing a cement-based material using the admixture. [Solution] Provided is a liquid admixture for cement, which comprises: a first component including a microorganism capable of generating carbon dioxide through its metabolism; and a second component containing an inhibitor of the proliferation of a bacterium having a sulfur-oxidizing capability. According to the present invention, it becomes possible to uniformly impart crack self-repairing properties and resistance to sulfuric acid-induced deterioration to the whole of a hardened product of a cement composition. The present invention also provides: a cement composition which contains the liquid admixture for cement according to the present invention; a hardened body of the cement composition; and a method for producing a cement-based material using the liquid admixture for cement according to the present invention. [Selected drawing] FIG. 8

Description

Liquid cement admixture, cement composition, hardened cement product, and method for producing hardened cement product

[0001] The present invention relates to a liquid admixture for cement, a cement composition containing the same, a hardened cement product thereof, and a method for producing the hardened cement product, and in particular to a liquid admixture for cement containing a microorganism that generates carbon dioxide through metabolism, a cement composition containing the same, a hardened cement product obtained by hardening the same, and a method for producing the hardened cement product.

[0002] Hardened cement materials such as concrete and mortar will crack over time. Water and oxygen can penetrate these cracks, causing rust to form on the surface of the reinforcing bars. This rust causes the concrete on the surface of the reinforcing bars to peel off, resulting in deterioration.

[0003] Patent Document 1 (Japanese Patent No. 6716331) discloses that by adding aerobic microorganisms to a cement admixture, the aerobic microorganisms consume the oxygen in the resulting hardened cement product, thereby suppressing corrosion of steel materials in the hardened cement product, and further that if damage such as cracks occurs in the hardened cement product, the carbon dioxide emitted by the aerobic microorganisms can be expected to have the effect of sealing the cracks.

[0004] Apart from the problem of cracking over time in hardened cement, there is also the problem of early corrosion of concrete in concrete structures such as sewer pipes used in sewerage facilities, etc., due to sulfuric acid produced by sulfur-oxidizing bacteria.

[0005] Patent Document 2 (JP Patent Publication No. 2016-525879), Patent Document 3 (JP Patent No. 3044669), and Patent Document 4 (JP Patent No. 3320074) disclose the addition of a growth inhibitor to a cement composition that inhibits the activity of microorganisms that produce sulfuric acid (sulfur-oxidizing bacteria). This growth inhibitor can suppress corrosion of hardened cement such as concrete even in the presence of microorganisms that produce sulfuric acid.

[0006] Patent No. 6716331 Publication Special Publication No. 2016-525879 Publication Patent No. 3044669 Publication Patent No. 3320074

[0007] According to the invention disclosed in Patent Document 1 (Japanese Patent No. 6716331), cracks that occur in hardened cement are blocked, thereby inhibiting corrosion of steel materials in the hardened cement product. Furthermore, according to the growth inhibitors disclosed in Patent Documents 2 to 4 (Japanese Patent Publication Nos. 2016-525879, 3044669, and 3320074), as mentioned above, corrosion of hardened cement products such as concrete can be inhibited even in the presence of microorganisms that produce sulfuric acid.

[0008] However, although there have been technologies for self-repairing concrete and for making concrete resistant to sulfuric acid, there has been no technology that combines both.

[0009] Therefore, the inventors tried to create concrete by adding a commercially available "antibacterial agent" to a concrete composition containing a commercially available "microbial agent" that has the function of automatically repairing cracks, but they were unable to obtain the self-repairing effect of the concrete. This was thought to be due to the antibacterial agent suppressing the activity of the microorganisms in the microbial agent.

[0010] However, further investigation revealed that the inhibition of microbial activity was not caused by the antibacterial agent itself, but by the fine powder of the dispersant added to the antibacterial agent to improve the dispersibility of the admixture. However, simply removing the fine powder of the dispersant could worsen the dispersibility of the admixture, which could lead to variations in the activity of the antibacterial agent and microorganisms in the hardened cement paste.

[0011] The object of the present invention, made in view of the above problems, is to provide an admixture that can impart self-repairing properties to cracks and resistance to sulfuric acid degradation uniformly to the entire cement-based material, a cement composition containing the admixture, a hardened product thereof, and a method for producing a cement-based material using the admixture.

[0012] The present inventors have conducted extensive research to achieve the above object, and as a result have found that by adding water as a dispersant instead of a fine powder of dispersant, the inhibition of aerobic microorganism activity caused by the fine powder of dispersant is eliminated, and growth inhibitors that inhibit the activity of aerobic microorganisms and sulfur-oxidizing bacteria can be dispersed evenly throughout the cement-based material, thereby completing the present invention.

[0013] That is, it has been found that the above-mentioned object of the present invention can be achieved by a liquid admixture for cement, characterized by having a first component containing a microorganism that generates carbon dioxide through metabolism, and a second component containing an agent that inhibits the growth of bacteria having sulfur-oxidizing ability.

[0014] It is also preferable that the second component is a separate component from the first component, and that both the first component and the second component are liquid components, and that the first component and the second component are two-component admixtures that are mixed with cement immediately before use.

[0015] Furthermore, it is preferable that the microorganism is selected from alkaline-tolerant Bacillus bacteria, and it is particularly preferable that the alkaline-tolerant Bacillus bacteria is Bacillus subtilis var. natto, which further contains biotin as a coenzyme.

[0016] Furthermore, it is more preferable that the alkali-resistant Bacillus bacterium is Bacillus pumilus.

[0017] The growth inhibitor of bacteria having sulfur oxidizing ability is preferably selected from the group consisting of nickel and nickel compounds, tungsten and tungsten compounds, dicarboxylic acid compounds, and mixtures thereof.

[0018] Furthermore, the above-mentioned object of the present invention can also be achieved by a cement composition containing the liquid admixture for cement of the present invention and cement, and a hardened cement product obtained by hardening this cement composition.

[0019] Furthermore, the above-mentioned object of the present invention can also be achieved by a method for producing a hardened cement body, which comprises a mixing step of obtaining a cement composition by adding a liquid cement admixture having a first component containing a microorganism that generates carbon dioxide through metabolism and a second component containing a growth inhibitor of bacteria having sulfur oxidizing ability to cement or ready-mix concrete containing cement and mixing them, or, if the liquid cement admixture is a two-component admixture, adding a liquid first component containing a liquid microorganism that generates carbon dioxide through metabolism and a liquid second component containing a growth inhibitor of bacteria having sulfur oxidizing ability separately to cement or ready-mix concrete containing cement and mixing them, and a hardening step of hardening the cement composition to obtain the hardened body.

[0020] According to the present invention, by not adding a fine powder of dispersant, the activity of microorganisms that generate carbon dioxide through metabolism is not inhibited by the fine powder of dispersant. Furthermore, by using a liquid admixture, the dispersibility of growth inhibitors of microorganisms that generate carbon dioxide and bacteria with sulfur-oxidizing ability is improved when mixed with cement, allowing them to be present evenly throughout the hardened cement composition obtained.

[0021] Therefore, it is possible to impart crack self-repairing properties and resistance to sulfuric acid deterioration uniformly to the entire hardened cement composition.

[0022] FIG. 1 is a flow diagram showing a method for manufacturing a hardened cement body of the present invention. FIG. 2 is a schematic diagram showing a formwork for forming a hardened cement body used in a water leakage test of Example (Test 1). FIG. 3 is a schematic diagram showing a compression tester B for obtaining a cracked sample of a hardened cement body used in a water leakage test of Example (Test 1). FIG. 4 is a schematic diagram for explaining the water leakage test of Example (Test 1). FIG. 5 is a graph showing the results of the water leakage test of Example (Test 1). FIG. 6 is a flow diagram showing the flow of preparing a cracked sample of a hardened cement body for a water leakage test of Example (Test 2). FIG. 7 is a schematic diagram for explaining the water leakage test of Example Test 2. FIG. 8 is a graph showing the results of the water leakage test of Example Test 2.

[0023] <Liquid Admixture for Cement> The liquid admixture for cement of the present invention comprises a first component containing a microorganism that generates carbon dioxide through metabolism, and a second component containing a growth inhibitor of bacteria having sulfur oxidizing ability.

[0024] The microorganisms contained in the first component that generate carbon dioxide through metabolism are microorganisms that metabolize a nutrient source directly or indirectly to generate carbon dioxide. These microorganisms metabolize an organic carbon source (described below) in the presence or absence of oxygen to generate carbon dioxide.

[0025] This carbon dioxide reacts with water to produce carbonate ions, which then react with calcium ions derived from calcium hydroxide in the hardened cement body to precipitate calcium carbonate, which fills in cracks in the hardened cement body.This is the mechanism by which the hardened cement body self-repairs due to these microorganisms.

[0026] The microorganisms may be one or more selected from obligate (absolute) anaerobic microorganisms, facultative anaerobic microorganisms, obligate aerobic microorganisms, and microaerophilic microorganisms. From the viewpoint of consuming oxygen in the hardened cement body described below and preventing corrosion of steel materials embedded in this hardened body, facultative anaerobic microorganisms, obligate aerobic microorganisms, and microaerophilic microorganisms are preferred, with obligate aerobic microorganisms being particularly preferred.

[0027] Furthermore, from the viewpoint of oxygen consumption, microorganisms of the genus Bacillus are preferred, and since microorganisms that generate carbon dioxide through metabolism are mixed into the cement composition in an alkaline environment, it is particularly preferred that they be selected from alkaline-resistant Bacillus bacteria.

[0028] Thank you for watching. The emotional feeling、. Thanksgiving、. The scientific feeling、. Thanksgiving feelings、. The emotional feeling、. Thanksgiving、. Feelings、. The sense of humor、. Emotional feelings、. The snow、. The sense of humor、. Thanksgiving、. Thanksgiving smile、. The heartbeat、. The snowflakes、. The snowflake snowflake、. The snowflakes、. The emotional feeling、. The snowflakes、M. snowflakes、M. The sense of humor、. Thanks、. Emotional emotions、. Thanksgiving 、. The emotions、M. scientifically based、. Thanksgiving、. Thanksgiving、. Thanksgiving、. Aesthetic emotions、. Aesthetic 、. Thanksgiving、. Thanks、. Thanksgiving、. Thanksgiving、. snowflakes、. scientific sentiment、. Thanksgiving、. Thanksgiving、. 2013、. Emotional fingers、. The emotions、. Ratings、. Thanksgiving、. The sense of humor、. Emotions、. Emotional feeling、. snowflakes、M. The snowflakes、. Emotional feeling、. The feeling of the snow、. snowflakes、M. Aesthetic 、. Thanksgiving smile、. The sense of humor、. Emotional snowflake、. Emotional snowflakes、. Feelings、. Thanksgiving feelings、. The snowflakes、M. The snowflakes、. Thanksgiving 、. Thanksgiving sentiment、. Happy、B. circulans, B. clarkii, B. clausii, B. coagulans, B. coahuilensis, B. cohnii, B. composti, B. curdlanolyticus, B. cycloheptanicus, B. cytotoxicus, B. daliensis, B. decisifrondis, B. decorationis, B. deserti, B. dipsosauri, B. drentensis, B. edaphicus, B. ehimensis, B. eiseniae, B. enclensis, B. endophyticus, B. endoradicis, B. farraginis, B. fastidiosus, B. fengqiensis, B. firmus, B. flexus, B. foraminis, B. fordii, B. formosus, B. fortis, B. fumarioli, B. funiculus, B. fusiformis, B. galactophilus, B. galactosidolyticus, B. galliciensis, B. gelatini, B. gibsonii, B. ginsengi, B. ginsengihumi, B. ginsengisoli, B. globisporus, B. glucanolyticus, B. gordonae, B. gottheilii, B. graminis, B. halmapalus, B. haloalkaliphilus, B. halochares, B. halodenitrificans, B. halodurans, B. halophilus, B. halosaccharovorans, B. hemicellulosilyticus, B. hemicentroti, B. herbersteinensis, B. horikoshii, B. horneckiae, B. horti, B. huizhouensis, B. humi, B. hwajinpoensis, B. idriensis, B. indicus, B. infantis, B. infernus, B. insolitus, B. invictae, B. iranensis,B. isabeliae, B. isronensis, B. jeotgali, B. kaustophilus, B. kobensis, B. kochii, B. kokeshiiformis, B. koreensis, B. korlensis, B. kribbensis, B. krulwichiae, B. laevolacticus, B. larvae, B. laterosporus, B. lautus, B. lehensis, B. lentimorbus, B. lentus, B. licheniformis, B. ligniniphilus, B. litoralis, B. locisalis, B. luciferensis, B. luteolus, B. luteus, B. macauensis, B. macerans, B. macquariensis, B. macyae, B. malacitensis, B. mannanilicus, B. marinus, B. marisflavi, B. marismortui, B. marmarensis, B. massiliensis, B. megaterium, B. mesonae, B. methanolicus, B. methylotrophicus, B. migulanus, B. mojavensis, B. mucilaginosus, B. muralis, B. murimartini, B. mycoides, B. naganoensis, B. nanhaiensis, B. nanhaiisediminis, B. nealsonii, B. neidei, B. neizhouensis, B. niabensis, B. niacini, B. novalis, B. oceanisediminis, B. odysseyi, B. okhensis, B. okuhidensis, B. oleronius, B. oryzaecocorticis, B. oshimensis, B. pabuli, B. pakistanensis, B. pallidus, B. pallidus, B. panacisoli, B. panaciterrae, B. pantothenticus, B. parabrevis, B. perfectB. pasteurii, B. patagoniensis, B. peoriae, B. persepolensis, B. persicus, B. pervagus, B. plakortidis, B. pocheonensis, B. polygoni, B. polymyxa, B. popilliae, B. pseudoalcaliphilu, B. pseudofirmus, B. pseudomycoides, B. psychodurans, B. psychophilus, B. psychrosaccharolyticus, B. psychrotolerantans, B. pulvifaciens, B. pumilus, B. purgationiresistens, B. pycnus, B. qingdaonensis, B. qingshengii, B. reuszeri, B. rhizosphereae, B. rigui, B. ruris, B. safensis, B. salarius, B. salexigens, B. saliphilus, B. schlegelii, B. sedimentis, B. selenatarsenatis, B. selenitereducens, B. seohaeanensis, B. shacheensis, B. shackletonii, B. siamensis, B. silvestris, B. simplex, B. siralis, B. smithii, B. soli, B. solimangrovi, B. solisalsi, B. songklensis, B. sonorensis, B. sphaericus, B. B. stearothermmophilus、B. stratospheric、B. underground、B. subtle、B. taenensis、B. tequilensis、B. thermantarctic, B. thermophilus、B. BNO thermocatenulatus、B. thermocloacaeB. B. thermogenicB. thermoglucosidasius, B. thermolactis, B. thermoleovorans, B. thermophilus, B. thermoruber, B. thermosphaericus, B. thiaminolyticus, B. thioparans, B. thuringiensis, B. tianshenii, B. trypoxylicola, B. tusciae, B. validus, B. valismortis, B. vedderi, B. velezensis, B. vietnamensis, B. Vireti, B. Vulcani, B. Examples include B. wakoensis, B. weihenstephanensis, B. xiamenensis, B. xiaoxiensis, and B. zhangjiangensis.

[0029] Among these, it is preferable that the alkali-tolerant Bacillus bacterium is B. pumilus. This is because B. pumilus spores are resistant to UV exposure, gamma-ray irradiation, desiccation, hydrogen peroxide, chemical disinfection, and the like, and are highly resistant to environmental stress, and therefore can germinate and be metabolized even after being maintained in a hardened cement body for a long period of time. Furthermore, it is particularly preferable that the alkali-tolerant Bacillus bacterium is Bacillus subtilis var. natto, which further contains biotin as a coenzyme.

[0030] In this specification, the term "microorganisms" refers to bacteria, yeast, fungi, protozoa, protozoa, and the like.

[0031] The microorganisms that generate carbon dioxide through metabolism may be self-cultured or commercially available, such as pure culture Bacillus subtilis natto (volume 50 ml, manufactured by Miyagino Natto Seizosho).

[0032] The growth inhibitor of bacteria having sulfur oxidizing ability contained in the second component may be any substance as long as it is capable of inhibiting the growth of bacteria having sulfur oxidizing ability.

[0033] Examples of bacteria capable of oxidizing sulfur that affect the corrosion of hardened cement paste used in sewers include sulfur-oxidizing bacteria such as Acidithiobacillus albertensis, Acidithiobacillus thiooxidans, Halothiobacillus neapolitanus, Thiomonas sp., and Acidithiobacillus ferrooxidans. Note that bacteria capable of oxidizing sulfur are not limited to sulfur-oxidizing bacteria, but also include bacteria capable of oxidizing sulfur compounds, such as iron-oxidizing bacteria (Acidithiobacillus ferrooxidans).

[0034] Examples of growth inhibitors for bacteria having sulfur-oxidizing ability include nickel, tungsten, lead, zinc, cobalt, tin and compounds thereof, hydroxy acid compounds and dicarboxylic acid compounds.

[0035] However, from the viewpoint of maintaining the activity of microorganisms that generate carbon dioxide through metabolism, the growth inhibitor of bacteria having sulfur-oxidizing ability is preferably selected from the group consisting of nickel and nickel compounds, tungsten and tungsten compounds, dicarboxylic acid compounds, and mixtures thereof.

[0036] The nickel and tungsten are provided as fine powders of the metal (oxidation state zero).

[0037] Examples of nickel compounds include nickel oxide, nickel phthalocyanine powder, nickel phthalocyanine derivative powder, and water-soluble nickel compounds. Nickel phthalocyanine powder is a powder of a compound in which nickel atoms are coordinated to an unsubstituted phthalocyanine skeleton.

[0038] The nickel phthalocyanine derivative powder is a powder of a compound having a substituted atom other than a hydrogen atom or a substituent on the benzene ring of the nickel phthalocyanine skeleton molecule, and is usually a compound that is insoluble in water and hardly dissolves in acid.

[0039] The substituted atom or substituent of the nickel phthalocyanine derivative is as described in Japanese Patent No. 3320074, and specific examples thereof include a halogen atom, a substituted or unsubstituted alkyl group, a substituted or unsubstituted alkoxy group, a substituted or unsubstituted thioalkoxy group, an alkyl group-substituted amino group, a carbocyclic aromatic amino group, a mono- or di-substituted amino group, a substituted or unsubstituted aryloxy group, a substituted or unsubstituted arylthio group, and a substituted or unsubstituted aromatic ring group.

[0040] Examples of water-soluble nickel compounds include nickel sulfate, nickel nitrate, and nickel chloride, which exist in the hardened cement paste as sparingly soluble nickel hydroxide.

[0041] Examples of tungsten compounds include alkali metal salts of tungstic acid, hydrates of alkali metal salts of tungstic acid, and tungsten (VI) oxide (WO ３ ), tungsten(VI) oxide hydrate, etc. Specific examples of tungsten compounds include, for example, W ２８ O ５８ , Na ２ WO ４ , CaWO ４ , CaWO ４ ・H ２ O, CaWO ４ ・2H ２ O, or 5(NH ４ ) ２ O.12WO ３ ・nH ２ O (n=0 to 5).

[0042] The dicarboxylic acid compound can be provided in the form of an alkali metal salt of, for example, oxalic acid, succinic acid, malonic acid, glutaric acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, and itaconic acid.

[0043] From the viewpoint of resistance to sulfuric acid deterioration, the growth inhibitor of bacteria having sulfur-oxidizing ability is blended into the liquid admixture for cement at a ratio of 0.01 mass % or more, preferably 0.05 mass % or more, relative to the total cement composition.

[0044] Furthermore, from the viewpoint of maintaining the activity of microorganisms that generate carbon dioxide through metabolism, the growth inhibitor of bacteria having sulfur-oxidizing ability is blended into the liquid cement admixture in an amount of 100 mmol or less per CFU of microorganism (mmol / CFU), preferably 50 mmol / CFU or less.

[0045] The liquid cement admixture of the present invention contains a liquid dispersant. The liquid dispersant may be any liquid capable of dispersing the first and second components in the liquid cement admixture. Water is generally used, but to further improve dispersibility, it is preferable to add a nonionic water-soluble polymer (such as polyvinylpyrrolidone) as an auxiliary agent. The liquid dispersant is present in an amount of 50 to 95 parts by mass, preferably 70 to 90 parts by mass, per 100 parts by mass of the total liquid cement admixture.

[0046] Furthermore, when the liquid admixture for cement of the present invention is a two-component admixture in which the second component is a separate component from the first component and the first and second components are both liquid components, the liquid dispersant is present in an amount of 50 parts by mass or more and 90 parts by mass or less per 100 parts by mass of the first component, and 50 parts by mass or more and 90 parts by mass or less per 100 parts by mass of the second component.

[0047] Furthermore, the liquid admixture for cement of the present invention does not contain a dispersant for fine powder. An example of such a dispersant for fine powder is ground granulated blast furnace slag. In the present invention, ground granulated blast furnace slag refers to a granulated blast furnace slag having a specific surface area of ​​7000 cm2 as determined by the specific surface area test of JIS R 5201, 8.1. ２ This is because the use of a fine powder (ground granulated blast furnace slag) with a large specific surface area and therefore a small particle size as a dispersant increases the chances of contact with microorganisms that generate carbon dioxide through the metabolism described above, and is thought to inhibit the self-repairing ability of the hardened cement body due to these microorganisms.

[0048] Therefore, the specific surface area is 7000 cm ２ / g or a blast furnace slag powder having a specific surface area of ​​7000 cm ２Particles with a particle size of less than 1 / g may be contained in the liquid admixture for cement of the present invention.

[0049] The liquid cement admixture of the present invention preferably contains a nutrient source for the microorganisms that generate carbon dioxide through the metabolism (hereinafter referred to as a microbial nutrient source).

[0050] The microbial nutrient source can be one or more of organic carbon sources (sugars, starch, lipids, etc.), inorganic carbon sources (sodium carbonate, etc.), organic nitrogen sources (amino acids, peptides, proteins, etc.), organic compounds other than organic carbon sources (vitamins, etc.), inorganic nitrogen sources (ammonia salts, nitrates, etc.), and inorganic nutrient sources (P, S, K, Na, etc.).

[0051] The liquid admixture for cement of the present invention may be a one-component admixture in which the first component and the second component are mixed, or may be a two-component admixture in which the first component and the second component are each formulated separately.

[0052] However, it is preferable that the second component is a separate agent from the first component, and that both the first and second components are liquid components, and that the first and second components are mixed with the cement immediately before use to form a two-component admixture. Because there is a possibility that the growth inhibitors of sulfur-oxidizing bacteria may inhibit the activity of microorganisms that generate carbon dioxide through their metabolism, by using a two-component admixture, contact between the microorganisms and high concentrations of the growth inhibitors can be avoided, improving the shelf life of the liquid admixture for cement.

[0053] When the liquid admixture for cement of the present invention is a two-component admixture, it is preferable that the microbial nutrient source be contained in the first component from the viewpoint of improving the preservation of microorganisms that generate carbon dioxide through metabolism.

[0054] <Cement Composition> The cement composition of the present invention contains the liquid admixture for cement of the present invention and cement.

[0055] There are no particular limitations on the cement that can be blended into the cement composition of the present invention, and for example, one or more of Portland cement (JIS R5210), blended cement (JIS R5211, R5212, R5213), ecocement, etc. can be used.

[0056] The liquid cement admixture is as described above, and a description thereof will be omitted here.

[0057] The cement composition of the present invention optionally contains fine aggregate (sand, etc.) or coarse aggregate (gravel, etc.) and may also optionally contain admixtures such as air-entraining agents, water-reducing agents (air-entraining water-reducing agents, water-reducing admixtures, high-performance air-entraining water-reducing agents, etc.), superplasticizers, setting / hardening regulators, accelerators, rust inhibitors, and waterproofing agents.

[0058] The cement composition of the present invention may also contain powders that undergo hydration under the alkaline condition of cement, such as silica powder, blast furnace slag powder, fly ash, and rice husk ash. However, the specific surface area of ​​these particles is less than 7000 cm. ２ / g and less than 5000 cm ２ It is preferable that the solubility is less than 1 / g.

[0059] Additionally, other admixtures such as cement admixture polymers and expansive agents may be included.

[0060] The cement composition of the present invention can be prepared, for example, by powder-mixing cement and, optionally, other powder components, adding water, the liquid admixture for cement of the present invention, and liquid components to the powder mixture, kneading the mixture to form a paste, and then mixing fine aggregate and coarse aggregate as necessary.

[0061] In addition, the cement composition of the present invention may be prepared by adding, mixing, and kneading materials other than the liquid admixture for cement of the present invention to obtain ready-mix concrete, and then adding and mixing the liquid admixture for cement of the present invention to this ready-mix concrete.

[0062] <Hardened Cement Product> The hardened cement product of the present invention can be obtained by applying the cement composition of the present invention to an object or by pouring it into a formwork and curing it for a predetermined period of time.

[0063] <Method for producing hardened cement product> Fig. 1 is a flow diagram showing a method for producing a hardened cement product of the present invention. As shown in the figure, the method for producing a hardened cement product of the present invention includes a mixing step and a hardening step.

[0064] [Mixing step (S110)] In this step, a liquid cement admixture having a first component containing a microorganism that generates carbon dioxide through metabolism and a second component containing a growth inhibitor of bacteria with sulfur-oxidizing ability is added to cement or ready-mix concrete containing cement, and mixed to obtain a cement composition.

[0065] The microorganisms that generate carbon dioxide through metabolism, the growth inhibitors of bacteria having sulfur-oxidizing ability, the liquid cement admixture, the cement, and the cement composition have already been explained, so their explanation will be omitted here.

[0066] The mixing of the cement composition can be carried out using a well-known method, for example, by powder-mixing cement and other powder components, and after the powder mixing, adding water, the liquid admixture for cement of the present invention, and liquid components, and kneading the mixture.

[0067] When the liquid admixture of the present invention is added to ready-mix concrete containing cement, the liquid admixture of the present invention is added to ready-mix concrete that has been prepared and kneaded, excluding the liquid admixture of the present invention. In this case, the liquid admixture of the present invention may be added to ready-mix concrete prepared in a batcher plant, or the liquid admixture of the present invention may be added to ready-mix concrete loaded on an agitator truck through its inlet.

[0068] Alternatively, in this process, if the liquid cement admixture is a two-component admixture, a liquid first component containing microorganisms that generate carbon dioxide through metabolism and a liquid second component containing a growth inhibitor of bacteria with sulfur-oxidizing ability are added separately to cement or ready-mix concrete containing cement, and then mixed to obtain a cement composition.

[0069] In this case, the mixing of the cement composition can be carried out, for example, by powder-mixing the cement and other powder components, and after the powder mixing, adding water and liquid components, and then separately adding the liquid first component and the liquid second component, and kneading the mixture.

[0070] When added to ready-mix concrete containing cement, for example, the liquid first component and the liquid second component are added separately to ready-mix concrete prepared in a batcher plant or ready-mix concrete loaded into an agitator vehicle that does not contain the liquid admixture for cement, which is the two-component admixture of the present invention.

[0071] The cement composition thus obtained is poured into a suitable formwork and compacted to remove air bubbles. Compaction is performed by hitting the surface of the poured cement composition with a tamper or the like, poking it with a stick, or vibrating it with a vibrator (the above is the mixing step (S110)).

[0072] [Hardening Step (S120)] In this step, the cement composition is hardened to obtain a hardened product. The cement composition may be spread on the target object with a trowel or the like and hardened, or may be poured into a formwork and hardened. When using reinforced concrete, reinforcing bars are placed in the formwork beforehand.

[0073] When the cement composition is poured into a formwork, it is preferably compacted to remove air bubbles. Compaction is performed by hitting the surface of the poured cement composition with a tamper or the like, poking it with a stick, or vibrating it with a vibrator.

[0074] The cement composition that has been applied or poured into the formwork is cured until it attains the required compressive strength, thereby obtaining a hardened cement body (this is the hardening step (S120)).

[0075] As described above, according to the liquid admixture for cement, cement composition, hardened cement product, and method for producing a hardened cement product of the present invention, by not adding a fine powder of dispersant, the activity of microorganisms that generate carbon dioxide through their metabolism is not inhibited by the fine powder of dispersant. Furthermore, by using a liquid admixture, the dispersibility of growth inhibitors of microorganisms that generate carbon dioxide and bacteria with sulfur-oxidizing ability is improved when mixed into cement, making it possible to ensure that they are present evenly throughout the hardened cement composition obtained.

[0076] Therefore, it is possible to impart self-repairing crack properties and resistance to sulfuric acid degradation uniformly throughout the hardened cement composition, which makes it possible to inhibit corrosion of the hardened cement body even in the presence of microorganisms that produce sulfuric acid, such as in sewerage facilities, and to enable self-repairing cracks even if they do occur. This reduces the cost and effort required to maintain the hardened cement body, and by extending the product life of the hardened cement body, it is possible to reduce the life cycle cost, including the manufacture and maintenance of the hardened cement body.

[0077] Furthermore, extending the product life of hardened cement paste can also have the effect of reducing environmental impact.

[0078] EXAMPLES The present invention will be specifically explained below by showing examples, but the present invention is not limited to these examples.

[0079] <1. Water Leakage Confirmation Test of Concrete (Hardened Cement Body)> A hardened cement body was prepared from a cement composition containing a cement admixture that includes a microorganism that generates carbon dioxide through metabolism and a growth inhibitor of bacteria having sulfur-oxidizing ability, and a water leakage test was conducted on the hardened cement body to confirm the self-repair performance of the hardened cement body.

[0080] 1-1. Test 1 First, we will explain the results of a water leakage test on hardened cement bodies made from cement compositions containing a powder cement admixture to which a fine powder dispersant (ground granulated blast furnace slag) has been added, rather than a liquid cement admixture.

[0081] i) Preparation of cement compositions of Comparative Examples 1 and 2 and Reference Example 1 Ordinary Portland cement, a microbial agent (CHA-PLA, manufactured by Basilisk Contracting BV), and a growth inhibitor 1 (Super Antibacterial Agent, manufactured by Ando Hazama Kogyo Co., Ltd.) were mixed and powder-mixed. The microbial agent was used as the outermost ingredient, i.e., 1 ml of the mixed powder of ordinary Portland cement, the microbial agent, and the growth inhibitor 1 was mixed. ３ It is added in an amount of 5 kg per unit.

[0082] Water (groundwater) was mixed with this mixed powder to prepare a cement paste, which was then mixed with fine aggregate 1, fine aggregate 2 and coarse aggregate and further kneaded to obtain a cement composition of Comparative Example 1 with a blend ratio of 30-18-20N.

[0083] Next, the materials were mixed and kneaded with the same composition and proportions as in Comparative Example 1, except that Growth Inhibitor 1 was replaced with Growth Inhibitor 2 (Celeb Antibacterial Agent, manufactured by Ando Hazama Kogyo Co., Ltd.), thereby obtaining the cement composition of Comparative Example 2.

[0084] In addition, the materials were mixed and kneaded in the same composition and proportions as in Comparative Example 1, except that no growth inhibitor was added, to obtain a cement composition of Reference Example 1.

[0085] The compositions of growth inhibitor 1 and growth inhibitor 2 are as shown in Table 1 below.

[0086]

[0087] ii) Preparation of cracked samples of hardened cement body for water leakage test Figure 2 is a schematic diagram showing a formwork for forming the hardened cement body used in the water leakage test of Example (Test 1). As shown in the figure, three formworks A were prepared, each consisting of a vinyl chloride pipe a with an inner diameter w of 100 mm and a height h of 80 mm, the bottom of which was sealed with an acrylic plate b. The gap between the vinyl chloride pipe and the acrylic plate was filled with caulking material c.

[0088] The cement compositions of Comparative Examples 1 and 2 and Reference Example 1 were filled in one layer into each of the vinyl chloride pipes a from the open top surface of form A, and the form A was poked appropriately with a ram and vibrated to remove air from the cement composition, and then the top surface was smoothed and flattened with a trowel.

[0089] The cement composition filled in form A was cured in air at room temperature for 28 days to obtain hardened cement bodies of Comparative Examples 1 and 2 and Reference Example 1.

[0090] After 28 days, the acrylic plate of the formwork A was removed, and as shown in Fig. 3, a load was applied to the hardened cement body Z from both sides in the width direction of the hardened cement body Z using a compression testing machine B, forcibly generating cracks 12 in the hardened cement body Z. The crack widths of the hardened cement body Z were measured with a crack gauge and were 0.4 mm for the hardened cement body Z of Reference Example 1 and Comparative Example 2, and 0.35 mm for the hardened cement body Z of Comparative Example 1.

[0091] iii) Water leakage test (evaluation of self-repair performance) Next, as shown in Figure 4, formwork a' and a'' of the same diameter as formwork a were connected above and below formwork a with caulking material, and a constricted portion d of a smaller diameter than formwork a'' was provided below formwork a''. The bottom of constricted portion d was open, and a container f was provided below constricted portion d.

[0092] A hole e having a diameter of about 10 mm is provided on the side of the form a' at a position 50 mm above the joint with the form a.

[0093] The hole e is provided to allow water poured from the form a' to drain through the hole e, thereby maintaining a constant head pressure of the hardened body Z within the form a.

[0094] Water was then poured into form a' from the top of form a' at a rate such that the water level in form a' remained constant at the height of hole e, i.e., such that the poured water was allowed to drain through hole e to maintain a constant head pressure on the hardened body Z within form a. Water g leaking through cracks 12 in the hardened body Z was collected in container f, and the amount of water leakage per day was measured. The results are shown in Figure 5. In Figure 5, the vertical axis represents the amount of water leakage (ml / day) for each hardened cement body from the start date to the final date of the water leakage test, and the horizontal axis represents the test date (day) of the water leakage test.

[0095] As shown in the figure, the hardened cement body of Reference Example 1, to which only the microbial agent was added, stopped leaking water approximately 40 days after the start of the test, while the hardened bodies of Comparative Examples 1 and 2 continued to leak water even after approximately 45 days had passed since the start of the test, and the amount of water leaked was extremely large, at approximately 40% compared to the start of the test, as of the final day, March 14th.

[0096] This is thought to be because the activity of the microorganisms in the microbial preparation was inhibited by the fine powder dispersant (ground granulated blast furnace slag) contained in the growth inhibitors 3 and 4 contained in the cement compositions of Comparative Examples 1 and 2, resulting in a decrease in self-repair performance.

[0097] 1-2. Test 2 Next, the results of a water leakage test of hardened cement bodies made from cement compositions containing liquid admixtures for cement that use a liquid as a dispersant instead of a fine powder dispersant will be described.

[0098] i) Preparation of cement compositions of Examples 1 to 4, Reference Example 2, and Comparative Examples 3 and 4 Ordinary Portland cement (manufactured by Ube Mitsubishi Cement Co., Ltd.), fine aggregate (Kakegawa sand) (trade name: sand, manufactured by Abekawa Development Co., Ltd.), and coarse aggregate (Satsukime crushed stone) (trade name: crushed stone, manufactured by Satsukime Mining Co., Ltd.) were mixed in the unit cement amounts shown in Table 2, and dry-mixed in a mixer for 15 seconds to obtain dry-mixed concrete. To this was added various admixtures and water in the amounts shown in Table 2, and the mixture was further mixed in the mixer for 30 seconds. Any materials adhering to the walls and blades of the mixer were scraped off, and then the mixture was further mixed for 90 seconds and discharged from the mixer to obtain the cement compositions of Examples 1 to 4, Reference Example 2, and Comparative Examples 3 and 4.

[0099] The blending conditions for these cement compositions are as follows:

[0100] Water-cement ratio: 55%, fine aggregate ratio: 43.5%, target slump value: 12.5±2.5 cm, target air content: 4.5±0.5%

[0101] Among the various admixtures, the natto bacteria culture solution was prepared by inoculating 100 μl of natto bacteria (manufactured by Miyagino Natto Seizosho) into a test tube containing 5 ml of liquid medium, and then culturing the test tube in a warm bath at 37° C. with shaking at 100 rpm for 24 hours.

[0102]

[0103] The fresh properties of the obtained cement compositions of Examples 1 to 4, Reference Example 2, and Comparative Examples 3 and 4, and the compressive strength of their hardened bodies (hardened cement bodies) are shown in Table 4. The compressive strength was measured on hardened cement bodies cured in water at 20°C on the 1st, 5th, and 28th day.

[0104] The conditions for measuring the fresh properties of the cement compositions in Table 4 and the compressive strength of their hardened bodies are as follows.

[0105] The slump value was measured in accordance with JIS A 1101, a concrete slump test method.

[0106] The air content was measured in accordance with JIS A 1128, Test method for air content of fresh concrete by pressure - Air chamber pressure method.

[0107] The concrete temperature (temperature of fresh concrete) was measured in accordance with JIS A 1156, Method for measuring temperature of fresh concrete.

[0108] The compressive strength of the obtained hardened cement paste was measured in accordance with JIS A 1108, a test method for compressive strength of concrete, and the average value of the compressive strengths of three test specimens at each age was used.

[0109] The shape, manufacturing method, and curing conditions of the hardened cement paste used in the compressive strength test were in accordance with JIS A 1132, Method of making specimens for concrete strength tests. That is, the shape of the hardened cement paste was in accordance with 4.1 Specimen dimensions, i.e., a cylindrical specimen with a diameter of 100 mm and a height of 200 mm, the manufacturing method was in accordance with 4.3 Concrete packing method, and the curing conditions were in accordance with 7 Formwork removal and curing, i.e., underwater curing at 20°C.

[0110]

[0111] ii) Preparation of Cracked Hardened Cement Body Samples for Water Leakage Tests Figure 6 is a flow diagram showing the process for preparing cracked hardened cement body samples for water leakage tests in Example Test 2. First, the cement compositions of Examples 1 to 4, Reference Example 2, and Comparative Examples 3 and 4 were each poured into a cylindrical formwork F with an inner diameter of 100 mm and a height of 200 mm to a height of 100 mm. They were then subjected to moist air curing at 20°C and 90% RH (step i). After demolding, they were subjected to standard underwater curing for 26 days (step ii). They were then subjected to air curing for 7 days in a high-temperature, constant-humidity chamber at 20°C and 60% RH (step iii). Finally, at the final stage of air curing, the periphery of the hardened cement body was reinforced with tape T (step iv), and a load was applied to both sides of the reinforced hardened cement body in the width direction to forcibly generate cracks in the hardened cement body (step v).

[0112] The cracked sample thus obtained was returned to the formwork F, and the bottom peripheral surface was fixed to the lower edge of the formwork F with a sealant to prepare a specimen S for use in a water leakage test (step vi).

[0113] iii) Water Leak Test (Evaluation of Self-Repair Performance) Fig. 7 is a schematic diagram for explaining the water leakage test for Example Test 2. As shown in the figure, the specimen S obtained in step vi above was fixed and placed using a clamp (not shown) or the like, and a water receiving container V was placed below it. Then, 700 ml of water was poured from the top of the formwork F onto the top of the cracked sample of the hardened cement body, and the amount of water dripping into the water receiving container V after 10 minutes was measured using an electronic balance M.

[0114] The water leakage test was performed the day after the 7-day air curing in step iii above (measurement day = 1 day). From the day after the measurement, air curing was performed for 3 days in a high-temperature, constant-humidity chamber at 20°C and 60% RH (air curing = 3 days), followed by standard underwater curing for 3 days (standard underwater curing = 3 days). This test cycle of 1 week was repeated 12 times, and the amount of dripped water in each water leakage test was added up to obtain the cumulative water permeability (mL) of the specimen. The results are shown in Figure 8. In Figure 8, the vertical axis shows the cumulative water permeability (mL) of each specimen, and the horizontal axis shows the crack width (mm) of each specimen.

[0115] As shown in the figure, compared to Reference Example 2, which does not contain both an antibacterial agent and microorganisms that generate carbon dioxide through metabolism, Comparative Examples 3 and 4, which contain only microorganisms that generate carbon dioxide through metabolism, are confirmed to have a high self-repair effect on cracks, and therefore have a low cumulative water permeability.

[0116] Similarly, in Examples 1 to 4, which contain both an antibacterial agent and microorganisms that generate carbon dioxide through metabolism, the cumulative water permeability was low, confirming that when water is used as a dispersant instead of a fine powder dispersant (ground granulated blast furnace slag), the antibacterial agent does not have an effect of inhibiting the growth of microorganisms that generate carbon dioxide through metabolism.

[0117] In addition, when Examples 1 and 2, in which CHA-PLA was used as a microorganism that generates carbon dioxide through metabolism, were compared with Examples 3 and 4, in which Bacillus subtilis natto was used as the microorganism, the cumulative water permeation amount was lower in Examples 3 and 4. This shows that Bacillus subtilis natto has a higher self-repair effect than CHA-PLA in the presence of an antibacterial agent.

Claims

1. A liquid admixture for cement comprising: a first component containing a microorganism that generates carbon dioxide through metabolism; and a second component containing a growth inhibitor of bacteria having sulfur-oxidizing ability.

2. The liquid admixture for cement according to claim 1, wherein the second component is a separate component from the first component, and both the first component and the second component are liquid components, and the first component and the second component are two-component admixtures that are mixed with cement immediately before use.

3. The liquid cement admixture according to claim 1, wherein the microorganism is selected from alkaline-tolerant bacteria of the genus Bacillus.

4. The liquid cement admixture according to claim 3, wherein the alkali-resistant Bacillus bacterium is Bacillus subtilis var. natto, and further contains biotin as a coenzyme.

5. The liquid admixture for cement according to claim 3, wherein the alkali-resistant Bacillus bacterium is Bacillus pumilus.

6. The liquid cement admixture according to claim 1, wherein the growth inhibitor of sulfur-oxidizing bacteria is selected from the group consisting of nickel and nickel compounds, tungsten and tungsten compounds, dicarboxylic acid compounds, and mixtures thereof.

7. A cement composition comprising the liquid admixture for cement according to any one of claims 1 to 6 and cement.

8. A hardened cement product obtained by hardening the cement composition according to claim 7.

9. A method for producing a hardened cement body, comprising: a mixing step of adding a liquid cement admixture having a first component containing a microorganism that generates carbon dioxide through metabolism and a second component containing a growth inhibitor of bacteria having sulfur oxidizing ability to cement or ready-mix concrete containing cement and mixing them, or, if the liquid cement admixture is a two-component admixture, adding a liquid first component containing a microorganism that generates carbon dioxide through metabolism and a liquid second component containing a growth inhibitor of bacteria having sulfur oxidizing ability separately to cement or ready-mix concrete containing cement and mixing them, to obtain a cement composition; and a hardening step of hardening the cement composition to obtain a hardened cement body.

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