Additive for ground improvement cement composition, ground improvement cement composition, ground improvement body, and ground improvement method

Abstract

To provide a ground improving material exhibiting excellent fluidity as slurry.SOLUTION: There is provided a ground improving cement-composition additive comprising a structural unit (A) derived from a carboxylic acid monomer represented by formula (1); -(-CR1(R2)-CR3(COOX1)-, (in the formula (1), R1, R3 each represent H, a methyl group, or an ethyl group, R2 represents H or -COOX2, and X1, X2 each represent H, a monovalent metal, a divalent metal, an ammonium group, or an organic amine group), and a structural unit (B) derived from an unsaturated polyalkylene glycol monomer represented by formula (2), (in the formula (2), R4, R5, and R6 each represent H, a methyl group, or an ethyl group, R7 represents an alkylene group, R8 represents H or a hydrocarbon group, P represents a number of from 0 to 2, and m represents a number of from 25 to 100).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to an additive for a soil improvement cement composition, a soil improvement cement composition, a soil improvement body, and a soil improvement method. More specifically, the present invention relates to an additive for a soil improvement cement composition, a soil improvement cement composition, a soil improvement body, and a soil improvement method, which are used for soil improvement for the purpose of strengthening the bearing capacity of the ground. [Background technology]

[0002] Ground improvement is the artificial improvement of the ground to increase its strength for the purpose of strengthening the bearing capacity of the foundations of buildings, countermeasures against liquefaction, etc. In recent years, the importance of ground improvement has increased due to the frequent occurrence of damage caused by earthquakes and heavy rains, and the government has also formulated the Basic Plan for National Resilience to promote disaster prevention measures. There are various methods for ground improvement, but the most widely used are those that use hardening agents containing cement because of their high cost-effectiveness. Examples of widely used methods include the consolidation method, in which a hardening agent such as a cement-based solidification material is mixed with the soil at the site to be improved to create an improved body, and the chemical injection method, in which a composition containing cement is injected into the ground. Among the ground improvement methods, those using cement-based solidification materials are classified into shallow layer improvement and deep layer improvement (including mid-layer improvement), of which about 90% are deep layer improvement. In deep layer improvement, a machine mixing method is often used, in which a hole is drilled deep into the ground with a construction machine equipped with a rod with a mixing blade at the tip, and a slurry of improvement material containing cement-based solidification material is injected into the hole, which is mixed and stirred with the on-site soil inside the hole, creating an improvement body underground. In recent years, there has been an increase in high-pressure injection mixing type ground improvement methods, in which a hole is drilled deep into the ground with a pipe equipped with a drilling tool at the tip, and then a slurry of improvement material containing cement-based solidification material is injected at high pressure from the tip of the pipe, cutting the soil underground and chemically solidifying it at the same time.

[0003] As a conventional composition used for ground improvement, a soil cement slurry containing a dispersant composition containing a water-soluble vinyl copolymer (polycarboxylic acid polymer) of a specific structure and an antifoaming agent, cement, and water in a specific ratio has been disclosed (see Patent Document 1). Also, a hydraulic cement composition for ground injection containing a blast furnace slag powder with a specific specific surface area and median diameter, classified cement satisfying specific conditions, and a polyacrylic acid dispersant in a specific ratio has been disclosed (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2013-1604 A [Patent Document 2] International Publication No. 2011 / 027890 Summary of the Invention [Problem to be solved by the invention]

[0005] The slurry of soil improvement materials used in soil improvement methods is required to have good fluidity and be easy to inject into holes. Polycarboxylic acid polymers are sometimes added, but although they have good cement dispersibility, there is an issue that their fluidity decreases when clayey soil is mixed in.

[0006] The present invention has been made in consideration of the above-mentioned current situation, and has an object to provide a ground improvement material having excellent fluidity in the form of a slurry of the ground improvement material. [Means for solving the problem]

[0007] The present inventors have investigated ground improvement materials that provide excellent slurry fluidity and have found that when a copolymer having a structural unit (A) derived from a carboxylic acid monomer of a specified structure and a structural unit (B) derived from an unsaturated polyalkylene glycol monomer of a specified structure is used as an additive for a cement-based solidification material, the resulting cement composition has excellent slurry fluidity, thereby arriving at the present invention.

[0008] That is, the present invention relates to a compound represented by the following general formula (1);

[0009] [ka] (In formula (1), R 1 , R 3 R may be the same or different and represents a hydrogen atom, a methyl group, or an ethyl group. 2 is a hydrogen atom or -COOX 2 Represents X. 1 , X 2 are the same or different and represent a hydrogen atom, a monovalent metal, a divalent metal, an ammonium group, or an organic amine group. 1 -COOX 2 may form an anhydride.) and a structural unit (A) derived from a carboxylic acid monomer represented by the following general formula (2);

[0010] [ka] (In formula (2), R 4 , R 5 and R 6 R may be the same or different and represents a hydrogen atom, a methyl group, or an ethyl group. 7 O may be the same or different and represents an oxyalkylene group having 2 to 4 carbon atoms. 8 represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. p represents a number from 0 to 2. m is R 7 represents the average added mole number of oxyalkylene groups represented by O, and is a number from 25 to 100. The additive for ground improvement cement composition is characterized by containing a copolymer having a structural unit (B) derived from an unsaturated polyalkylene glycol monomer represented by the formula (1).

[0011] In the above copolymer, the molar ratio of the structural unit (A) to the structural unit (B) (structural unit (A) / structural unit (B)) is preferably 50 / 50 to 95 / 5.

[0012] The copolymer preferably has a weight average molecular weight of 8,000 to 100,000.

[0013] The present invention also relates to a ground improvement cement composition comprising the additive for ground improvement cement compositions of the present invention and cement.

[0014] The present invention also relates to a ground improved structure which is constructed using the ground improvement cement composition of the present invention.

[0015] The present invention also relates to a ground improvement method comprising the step of injecting the ground improvement cement composition of the present invention into a hole formed in the ground. Effect of the Invention

[0016] The additive for ground improvement cement compositions of the present invention is a dispersant that provides excellent slurry fluidity to the cement composition, and therefore can be suitably used as a cement dispersant for preparing a cement composition to be used as a ground improvement material in ground improvement methods. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The present invention will be described in detail below. In addition, a combination of two or more of the individual preferred embodiments of the present invention described below is also a preferred embodiment of the present invention.

[0018] The dispersant for a ground improvement cement composition of the present invention has the following general formula (1):

[0019] [ka]

[0020] (In formula (1), R 1 , R 3 R may be the same or different and represents a hydrogen atom, a methyl group, or an ethyl group. 2 is a hydrogen atom or -COOX 2 Represents X. 1 , X 2 are the same or different and represent a hydrogen atom, a monovalent metal, a divalent metal, an ammonium group, or an organic amine group. 1 -COOX 2 may form an anhydride.) and a structural unit (A) derived from a carboxylic acid monomer represented by the following general formula (2);

[0021] [ka]

[0022] (In formula (2), R 4 , R 5 and R 6 R may be the same or different and represents a hydrogen atom, a methyl group, or an ethyl group. 7 O may be the same or different and represents an oxyalkylene group having 2 to 4 carbon atoms. 8 represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. p represents a number from 0 to 2. m represents R 7 represents the average added mole number of oxyalkylene groups represented by O, and is a number from 25 to 100. The copolymer may have one type of each of the structural unit (A) and the structural unit (B), or may have two or more types.

[0023] In the above general formula (1), examples of the monovalent metal include lithium, sodium, and potassium, and examples of the divalent metal include magnesium, calcium, strontium, and barium. Examples of the organic amine group include groups derived from primary amines such as methylamine, ethylamine, propylamine, n-butylamine, sec-butylamine, tert-butylamine, cyclohexylamine, benzylamine, and phenylamine; groups derived from secondary amines such as dimethylamine, diethylamine, dipropylamine, dibutylamine, diisobutylamine, di-sec-butylamine, di-tert-butylamine, dicyclohexylamine, dibenzylamine, and diphenylamine; groups derived from tertiary amines such as trimethylamine, triethylamine, tripropylamine, tributylamine, tricyclohexylamine, tribenzylamine, and triphenylamine; and groups derived from alkanolamines such as ethanolamine, diethanolamine, and triethanolamine. Among these, alkanolamine groups such as ethanolamine group, diethanolamine group, and triethanolamine group, and triethylamine group are preferred.

[0024] Examples of the carboxylic acid monomers that serve as raw materials for the structural unit (A) represented by the above general formula (1) include unsaturated monocarboxylic acid monomers such as (meth)acrylic acid and crotonic acid; unsaturated dicarboxylic acid monomers such as maleic acid, itaconic acid, mesaconic acid, citraconic acid and fumaric acid; and anhydrides of unsaturated dicarboxylic acid monomers such as their monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts. Among these, unsaturated monocarboxylic acid monomers such as (meth)acrylic acid and crotonic acid are preferred, and from an industrial viewpoint, (meth)acrylic acid is more preferred, and acrylic acid is even more preferred.

[0025] In the above general formula (2), R 8 R represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. 8 When is a hydrocarbon group, it is preferably one having 1 to 18 carbon atoms, more preferably one having 1 to 12 carbon atoms, and even more preferably one having 1 to 8 carbon atoms. Examples of the hydrocarbon group include a methyl group, an ethyl group, a propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, an isopentyl group, a neopentyl group, a 3-pentyl group, a hexyl group, a heptyl group, an octyl group, a nonyl group, a decyl group, an undecyl group, a dodecyl group, an isooctyl group, a 2,3,5-trimethylhexyl group, a 4-ethyl-5-methyloctyl group, a 2-ethylhexyl group, a tetradecyl group, an octadecyl group, and the like. straight-chain or branched-chain alkyl groups such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, and cyclooctyl; cyclic alkyl groups such as phenyl, benzyl, phenethyl, o-, m-, or p-tolyl, 2,3-, or 2,4-xylyl, mesityl, naphthyl, anthryl, phenanthryl, biphenylyl, benzhydryl, trityl, and pyrenyl. Among these, straight-chain, branched, or cyclic alkyl groups are preferred, and a methyl group is more preferred.

[0026] In the above general formula (2), m, which represents the average number of moles of oxyalkylene groups added, is a number from 25 to 100. The longer the alkylene oxide chain, the more effective it is in suppressing the aggregation of cement particles in the cement composition slurry, increasing dispersibility, and lowering the viscosity of the cement composition slurry. However, if the alkylene oxide chain is too long, the clay in the cement composition slurry captures the alkylene oxide chain, which causes crosslinking between the clay particles to proceed, thereby exerting the effect of increasing the viscosity. When the average number of moles of oxyalkylene groups added in the above general formula (2) is 25 to 100, the effect of suppressing the aggregation of cement particles is obtained without being affected much by the clay. The number of m, which is useful for further lowering the viscosity, is preferably 30 to 80, more preferably 35 to 70, and even more preferably 40 to 60.

[0027] Examples of the unsaturated polyalkylene glycol monomers that are the raw material for the structural unit (B) represented by the above general formula (2) include compounds in which 25 to 100 moles of an alkylene oxide having 2 to 4 carbon atoms are added to an unsaturated alcohol having 2 to 10 carbon atoms, such as vinyl alcohol, (meth)allyl alcohol, or 3-methyl-3-buten-1-ol, such as polyethylene glycol vinyl ether, polyethylene glycol (meth)allyl ether, polyethylene glycol 3-methyl-3-butenyl ether, (poly)ethylene (poly)propylene glycol (meth)allyl ether, or (poly)ethylene (poly)propylene glycol 3-methyl-3-butenyl ether, and compounds in which a hydrocarbon group having 1 to 20 carbon atoms is bonded to the end of these compounds. 7 The oxyalkylene groups represented by O may be the same or different, and when they are different, they may be added randomly or in blocks. However, they are preferably alkylene oxides having 2 to 3 carbon atoms, and more preferably all are ethylene oxide. As the unsaturated polyalkylene glycol monomer, in terms of further exerting the effects of the present invention, a compound in which 25 to 100 moles of an alkylene oxide having 2 to 3 carbon atoms is added to (meth)allyl alcohol or 3-methyl-3-buten-1-ol is preferable, and a compound in which 25 to 100 moles of ethylene oxide is added to (meth)allyl alcohol or 3-methyl-3-buten-1-ol is more preferable.

[0028] The copolymer preferably has a molar ratio of the structural unit (A) to the structural unit (B) (structural unit (A) / structural unit (B)) of 50 / 50 to 95 / 5. In order to make the cement composition slurry excellent in fluidity, it is necessary for the copolymer to fully exert the effect of dispersing the solid content in the slurry. For this purpose, it is important that the effect of the copolymer adsorbing to the cement by the acid group and the effect of suppressing the aggregation of cement particles by the effect of the oxyalkylene chain of the side chain of the copolymer are exerted in a balanced manner, and when the molar ratio of the structural unit (A) to the structural unit (B) in the copolymer is in the above range, these effects are exerted in a more balanced manner. Furthermore, if the proportion of the alkylene oxide chain is too high, the clay contained in the cement composition slurry captures the alkylene oxide chain, so that crosslinking between the clay proceeds and the viscosity increases. In view of this, the structural unit (A) / structural unit (B) is more preferably 50 / 50 to 90 / 10, and even more preferably 50 / 50 to 85 / 15.

[0029] The above copolymer may have a structural unit (C) other than the above structural unit (A) and structural unit (B). Other monomers that can be used as raw materials for the structural unit (C) include esters of unsaturated monocarboxylic acid monomers, such as (meth)acrylic acid, and alcohols having 1 to 30 carbon atoms; diesters and half esters of unsaturated dicarboxylic acid monomers, such as maleic acid, maleic anhydride, fumaric acid, itaconic acid, and citraconic acid, and alcohols having 1 to 30 carbon atoms; esters of alkyl (poly)alkylene glycols obtained by adding 1 to 500 moles of alkylene oxide having 2 to 18 carbon atoms to amines, and the above unsaturated monocarboxylic acid monomers; diesters and half esters of alkyl (poly)alkylene glycols obtained by adding 1 to 500 moles of alkylene oxide having 2 to 18 carbon atoms to the above alcohols or amines, and the above dicarboxylic acid monomers; diesters or half esters with real alkylene glycol; half amides of maleamic acid and glycols having 2 to 18 carbon atoms or polyalkylene glycols having 2 to 500 moles of these glycols added; (poly) alkylene glycol di(meth)acrylates such as triethylene glycol di(meth)acrylate, (poly) ethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, (poly) ethylene glycol (poly) propylene glycol di(meth)acrylate; polyfunctional (meth)acrylates such as hexanediol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, trimethylolpropane di(meth)acrylate; (poly) alkylene glycol dimaleates such as triethylene glycol dimaleate and polyethylene glycol dimaleate;

[0030] Unsaturated sulfonic acids such as vinyl sulfonate, (meth)allyl sulfonate, 2-(meth)acryloxyethyl sulfonate, 3-(meth)acryloxypropyl sulfonate, 3-(meth)acryloxy-2-hydroxypropyl sulfonate, 3-(meth)acryloxy-2-hydroxypropyl sulfophenyl ether, 3-(meth)acryloxy-2-hydroxypropyloxysulfobenzoate, 4-(meth)acryloxybutyl sulfonate, (meth)acrylamidomethyl sulfonic acid, (meth)acrylamidoethyl sulfonic acid, 2-methylpropanesulfonic acid (meth)acrylamide, and styrenesulfonic acid, as well as their monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts; unsaturated monocarboxylic acids and amines having 1 to 30 carbon atoms such as methyl(meth)acrylamide; Amides; vinyl aromatics such as styrene, α-methylstyrene, vinyltoluene, and p-methylstyrene; dienes such as butadiene, isoprene, 2-methyl-1,3-butadiene, and 2-chloro-1,3-butadiene; unsaturated amides such as (meth)acrylamide, (meth)acrylalkylamide, N-methylol (meth)acrylamide, and N,N-dimethyl (meth)acrylamide; unsaturated cyanides such as (meth)acrylonitrile and α-chloroacrylonitrile; unsaturated amines such as aminoethyl (meth)acrylate, methylaminoethyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, dibutylaminoethyl (meth)acrylate, and vinylpyridine; divinyl aromatics such as divinylbenzene; cyanurates such as triallyl cyanurate;Examples of the siloxane derivatives include polydimethylsiloxane propylaminomaleamic acid, polydimethylsiloxane aminopropylene aminomaleamic acid, polydimethylsiloxane-bis-(propylaminomaleamic acid), polydimethylsiloxane-bis-(dipropyleneaminomaleamic acid), polydimethylsiloxane-(1-propyl-3-acrylate), polydimethylsiloxane-(1-propyl-3-methacrylate), polydimethylsiloxane-bis-(1-propyl-3-acrylate), and polydimethylsiloxane-bis-(1-propyl-3-methacrylate), and one or more of these can be used.

[0031] The content of the structural unit (C) other than the structural unit (A) and the structural unit (B) in the copolymer is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, of the entire copolymer.

[0032] The copolymer preferably has a weight average molecular weight of 8000 to 100000. When the copolymer has such a weight average molecular weight, the effect of providing excellent fluidity to the cement composition slurry and the effect of preventing separation and sedimentation of the solid content can be more well-balanced. The weight average molecular weight of the copolymer is more preferably 10000 to 80000, further preferably 20000 to 60000, and particularly preferably 25000 to 50000. The weight average molecular weight of the copolymer can be measured by the method described in the Examples below.

[0033] The copolymer can be produced by polymerizing a monomer component including, as essential components, a carboxylic acid monomer as a raw material for the structural unit (A) and an unsaturated polyalkylene glycol monomer as a raw material for the structural unit (B). The copolymer can be produced in the same manner as described in JP-A-2017-222553 and JP-A-2019-81692 for producing a polymer.

[0034] The dispersant for ground improvement cement compositions of the present invention essentially contains the above-mentioned copolymer, but may contain two or more of the above-mentioned copolymers, or may contain one or more copolymers different from the above-mentioned copolymers. The content of the copolymer in the dispersant for ground improvement cement composition of the present invention (when two or more kinds of copolymers are contained, the total content) is not particularly limited, but is preferably 20 to 100 mass% relative to 100 mass% of the solid content (i.e., non-volatile content) in the dispersant, more preferably 50 to 100 mass%, and even more preferably 80 to 100 mass%.

[0035] As described above, by adding the additive for a ground improvement cement composition of the present invention to cement, the slurry of the cement composition can be made excellent in fluidity. Such a ground improvement cement composition containing the additive for a ground improvement cement composition of the present invention and cement is also one of the present inventions, and a ground improvement body constructed using the ground improvement cement composition is also one of the present inventions.

[0036] The ground improvement cement composition of the present invention preferably contains 0.01 to 10 mass% of the additive for the ground improvement cement composition of the present invention relative to 100 mass% of the solid content of the composition. By containing it in such a ratio, the slurry of the cement composition can be made more excellent in fluidity and the separation and settling of the solid content can be more sufficiently suppressed. The content of the dispersant for the ground improvement cement composition of the present invention is more preferably 0.02 to 5 mass%, and even more preferably 0.05 to 3 mass%, relative to 100 mass% of the solid content of the composition.

[0037] The cement contained in the ground improvement cement composition of the present invention includes Portland cement (normal, early strength, super early strength, moderate heat, sulfate resistance and each low alkali form); various mixed cements (blast furnace cement, silica cement, fly ash cement); white Portland cement; alumina cement; ultra-fast hardening cement (1 clinker fast hardening cement, 2 clinker fast hardening cement, magnesium phosphate cement); grout cement; oil well cement; low heat cement (low heat type blast furnace cement, fly ash mixed low heat type blast furnace cement, belite high content cement); ultra-high strength cement; cement-based solidification material; ecocement (cement manufactured using one or more of urban waste incineration ash and sewage sludge incineration ash as raw materials), as well as those containing fine powders such as blast furnace slag, fly ash, cinder ash, clinker ash, husk ash, silica fume, silica powder, limestone powder, and gypsum. The cement contained in the ground improvement cement composition of the present invention may be only one type, or two or more types.

[0038] The content of cement in the ground improvement cement composition of the present invention is preferably 20-100% by mass relative to 100% by mass of the solid content of the composition. By using a ground improvement cement composition containing cement in such a ratio, the ground improved body obtained by using the composition can be made to have better strength. The content of cement is more preferably 40-100% by mass, and even more preferably 60-100% by mass relative to 100% by mass of the solid content of the composition.

[0039] The ground improvement cement composition of the present invention preferably contains water. In this case, the content of water is preferably 40 to 120 mass% relative to 100 mass% of the solid content of the composition. By containing water in such a ratio, the slurry of the ground improvement cement composition has better fluidity and the separation and settling of the solid content is more sufficiently suppressed. The content of water is more preferably 40 to 100 mass%, and even more preferably 40 to 80 mass%, relative to 100 mass% of the solid content of the composition.

[0040] The ground improvement cement composition of the present invention may further contain other admixtures, so long as it contains the dispersant for a ground improvement cement composition of the present invention and cement. In particular, when the dispersant of the present invention is used in combination with an antifoaming agent, the antifoaming agent can reduce the viscosity of the slurry by defoaming the air bubbles in the cement composition slurry, and therefore, in one preferred embodiment of the present invention, the ground improvement cement composition of the present invention contains the dispersant for ground improvement cement compositions of the present invention and an antifoaming agent. As the defoaming agent, one or more of various defoaming agents such as mineral oil-based defoaming agents, oil-based defoaming agents, fatty acid-based defoaming agents, fatty acid ester-based defoaming agents, oxyalkylene-based defoaming agents, alcohol-based defoaming agents, amide-based defoaming agents, phosphate ester-based defoaming agents, metal soap-based defoaming agents, and silicone-based defoaming agents can be used.

[0041] When the ground improvement cement composition of the present invention contains an antifoaming agent, the content of the antifoaming agent is preferably 5 to 50 mass %, more preferably 5 to 40 mass %, based on 100 mass % of the dispersant for ground improvement cement composition of the present invention.

[0042] The ground improvement cement composition of the present invention may contain other admixtures in addition to the defoaming agent. Examples of admixtures other than antifoaming agents include various sulfonic acid-based dispersants (water-reducing agents) having sulfonic acid groups in the molecule, various polycarboxylic acid-based dispersants (water-reducing agents) having polyoxyalkylene chains and carboxyl groups in the molecule other than the above-mentioned copolymers, and various phosphate-based dispersants (water-reducing agents) having phosphate groups in the molecule. The ground improvement cement composition of the present invention may also contain one or more types of cement additives (materials), such as water-soluble polymer substances, polymer emulsions, retarders, early strength agents / accelerators, air-enhancing agents, surfactants, waterproofing agents, rust inhibitors, crack reducing agents, expansive agents, cement wetting agents, thickeners, separation reducing agents, flocculants, drying shrinkage reducing agents, strength enhancing agents, self-leveling agents, rust inhibitors, colorants, mold inhibitors, blast furnace slag, fly ash, cinder ash, clinker ash, husk ash, silica fume, silica powder, and gypsum. The ground improvement cement composition of the present invention may also contain one or more fluidity imparting agents, such as carbonates, bicarbonates, phosphates, sulfates, etc. Examples of metal carbonates include alkali metal carbonates such as sodium carbonate and potassium carbonate, and examples of metal bicarbonates include alkali metal bicarbonates such as sodium hydrogen carbonate and potassium hydrogen carbonate.

[0043] The ground improvement cement composition of the present invention has excellent fluidity when in a slurry state, and therefore can be suitably used in a ground improvement method in which a cement composition for ground improvement is injected into a hole formed in the ground to create a ground improvement body. Such a ground improvement method, that is, a ground improvement method comprising a step of injecting the ground improvement cement composition of the present invention into a hole formed in the ground, also constitutes one aspect of the present invention.

[0044] In the ground improvement method of the present invention, the method of forming holes in the ground is not particularly limited, but a method of forming holes by drilling the ground is preferred because it allows holes to be formed efficiently. Examples of ground improvement methods in which holes are formed by drilling the ground include a high-pressure injection and mixing type ground improvement method in which a pipe is inserted into the formed hole and a slurried ground improvement cement composition is injected from the pipe into the ground at high pressure to cut the soil underground and chemically solidify it at the same time; a mechanical mixing method in which a cement composition is mixed with soil in a hole to create a ground improvement body; and an underground continuous wall method. The ground improvement cement composition of the present invention can be suitably used in any of these methods. Therefore, the above-mentioned ground improvement method includes a step of drilling the ground to form a hole, and a step of cutting the soil in the ground and chemically solidifying it at the same time by high-pressure injection of the ground improvement cement composition of the present invention in the hole, and a step of drilling the ground to form a hole and mixing the ground improvement cement composition of the present invention with the soil in the hole, which are all suitable embodiments of the ground improvement method of the present invention. Among the above-mentioned mechanical mixing methods, a particularly suitable embodiment of the ground improvement method of the present invention is a mechanical mixing method in which a construction machine equipped with a rod having an agitating blade at the tip is used to drill a deep layer of the ground, while stirring and mixing with the on-site soil in the formed hole, and creating an improved body in the ground.

[0045] The ground improvement method of the present invention may include steps other than the steps described above. The ground improvement method of the present invention may be a method other than the above-mentioned one, such as a high-pressure jet combined mechanical mixing method.

[0046] The ground improved body of the present invention is a ground improved body obtained by hardening a mixture containing the ground improvement cement composition of the present invention and soil. The ground improved body of the present invention is also ground improved by the ground improvement method of the present invention. The matters described in the ground improvement cement composition and ground improvement method of the present invention can be appropriately applied to the ground improved body of the present invention. The ground improved body of the present invention contains the additive for the ground improvement cement composition of the present invention, soil, and cement. This ground improved body may be a ground improved body obtained by hardening a slurry containing soil, water, and cement. EXAMPLES

[0047] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. In addition, unless otherwise specified, "parts" means "parts by mass" and "%" means "% by mass".

[0048] <Weight average molecular weight measurement conditions> Equipment: Waters Alliance (2695) Analysis software: Waters, Empower2 Professional + GPC option Columns used: Tosoh Corporation, TSKguard columns SWXL + TSKgel G4000SWXL + G3000SWXL + G2000SWXL Detector: Refractometer (RI) detector (Waters 2414), multi-wavelength visible-ultraviolet (PDA) detector (Waters 2996) Eluent: 115.6 g of sodium acetate trihydrate dissolved in a mixed solvent of 10,999 g of water and 6,001 g of acetonitrile, and the pH was adjusted to 6.0 with acetic acid. Standard material for creating calibration curve: polyethylene glycol (peak top molecular weight (Mp) 272500, 219300, 107000, 50000, 24000, 12600, 7100, 4250, 1470) Calibration curve: A cubic equation was prepared based on the Mp values ​​and elution times of the above standard substances. Flow rate: 1mL / min Column temperature: 40℃ Measurement time: 45 minutes Amount of standard sample solution injected: 100 μL (eluent solution with polymer concentration of 0.1% by mass) Polymer sample solution injection volume: 100 μL (eluent solution with polymer concentration of 0.5% by mass) Molecular weights were recorded to two significant figures.

[0049] (Example of copolymer production) Copolymer 1 was synthesized by the following method. The other copolymers in the table were synthesized in the same manner. In a glass reaction vessel equipped with a thermometer, a stirrer, a dropping funnel, a nitrogen inlet tube, and a reflux condenser, 360.1 g of water and 518.2 g of an ethylene oxide adduct of 3-methyl-3-buten-1-ol as an unsaturated polyalkylene glycol ether monomer (average number of moles of ethylene oxide added: 50 moles) were charged, and the inside of the reaction vessel was replaced with nitrogen under stirring, and the temperature was raised to 74°C under a nitrogen atmosphere, and then an unsaturated carboxylic acid monomer aqueous solution in which 29.9 g of acrylic acid was dissolved in 28.4 g of water was dropped over 5 hours, and at the same time as the drop of the acrylic acid aqueous solution was started, an initiator aqueous solution in which 1.9 g of ammonium persulfate was dissolved in 61.5 g of water was dropped over 5 hours and 10 minutes. After that, the temperature was maintained at 74°C for 20 minutes, and the polymerization reaction was completed. Then, after cooling to 30°C, the mixture was neutralized to pH 5.5 with a 30% aqueous sodium hydroxide solution to obtain a copolymer 1 having a weight average molecular weight of 63,000.

[0051] (Characteristics evaluation) For the copolymers 1 to 5 produced by the methods of the above Production Examples and the comparative copolymers 1 and 2, the viscosity of the cement composition slurry was evaluated by the following method. <Measurement of viscosity of cement composition slurry> 133.3g of cement (ordinary Portland cement, Taiheiyo Cement) and 66.7g of water containing 0.3% by weight of copolymer were added to a PP container (Pack Ace 600mL, Teraoka Corporation; mouth diameter 91mm, bottom diameter 84mm, height 127mm), and the mixture was stirred at 300rpm for 3 minutes with a SUS blade (six paddles without inclination, length of each paddle 20mm, height 10mm) using a three-one motor (BL600, Shinto Scientific Co., Ltd.) to prepare a cement composition slurry. The viscosity of the cement composition slurry was then measured by changing the amplitude of the vibrator from 1.2mm to 0.1mm using a tuning fork vibration rheometer (RV-10000A, A&D Co., Ltd.), and the viscosity at the same shear rate (shear rate = 200s-1) was calculated. In the clay-added condition, 2.0 g of bentonite (Kunigel V1, Kunimine Kogyo Co., Ltd.) was added to 133.3 g of the above cement, and the mixture was stirred before the above measurements.

[0052] [Table 2]

[0053] The viscosity ratio (clay added / clay not added) is the value obtained by dividing the viscosity under the clay added condition by the viscosity under the clay not added condition, and is a value that indicates the susceptibility of the viscosity of the cement composition slurry to the presence or absence of clay. The higher this value, the more difficult it becomes to handle in actual construction due to the influence of the clay contained in the clayey soil, such as by reducing the fluidity of the cement composition slurry. From Table 2, it can be seen that the viscosity ratio is smaller when the additive for the ground improvement cement composition of the present invention is used than when the additive for the ground improvement cement composition of the present invention is used, and it is clear that when the additive for the cement composition of the present invention is used, the decrease in the fluidity of the cement composition slurry when clay is contained is small, and the fluidity of the slurry is excellent.

Claims

1. The following general formula (1): 【Chemistry 1】 (In formula (1), R1 and R3 each represent a hydrogen atom. R2 represents a hydrogen atom. X １ , X ２ and each independently represent a hydrogen atom, a monovalent metal, a divalent metal, an ammonium group, or an organic amine group. 【Chemistry 2】 (In formula (2), R ４ and R ５ is a hydrogen atom, and R ６ R represents a methyl group. ７ O represents an oxyalkylene group having 2 carbon atoms. ８ represents a hydrogen atom; p represents the number 1 or 2; m represents R ７ represents the average added mole number of oxyalkylene groups represented by O, and is a number from 25 to 100.) and a structural unit (B) derived from an unsaturated polyalkylene glycol monomer represented by the formula (I) and wherein the molar ratio of the structural unit (A) to the structural unit (B) (structural unit (A) / structural unit (B)) is 50 / 50 to 85 / 15 (excluding cases where the molar ratio is 2.5 or more).

2. The additive for a ground improvement cement composition according to claim 1, characterized in that the copolymer has a weight average molecular weight of 10,000 to 80,000.

3. A ground improvement cement composition comprising the additive for ground improvement cement compositions according to claim 1 or 2 and cement (excluding ultrafine cement containing blast furnace slag and gypsum and having a particle size of 16 μm or more of 10 volume % or less).

4. A ground improvement structure which is constructed using the ground improvement cement composition according to claim 3.

5. A ground improvement method comprising the step of injecting the ground improvement cement composition according to claim 3 into a hole formed in the ground.

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