JP7724683B2 - Soil cement additive, soil cement composition, and method for producing soil cement composition - Google Patents

Description

The present invention relates to a soil cement additive and a soil cement composition.

Soil cement is a mixture of soil and a cement-based solidification material (hydraulic powder) or water. Construction methods that use this soil cement include ground improvement, earth retaining, foundation piling, and backfilling. These methods typically involve adding cement milk, a premix of cement-based solidification material and water, to the soil. Examples of cement-based solidification materials include ordinary Portland cement, blast furnace cement, and blended cements made by mixing ordinary Portland cement with blast furnace slag, limestone powder, fly ash, fine silica powder, calcium carbonate, and gypsum. The amounts of solidification material and water added are determined by the physical properties of the soil being used to create the soil cement, such as its quality (sand, silt, clay, etc.) and its moisture content, as well as the construction method and purpose.

Construction methods using soil cement can be broadly divided into (1) methods that create soil cement in the original ground, i.e., underground, and (2) methods that create soil cement above ground. (1) Methods that create soil cement in the original ground include ground improvement methods, earth retaining methods, and foundation pile methods. In these methods, the soil cement, which is generally a mixture of cement slurry and the soil to be improved, is desired to have as low viscosity as possible, so that slime can be easily removed during drilling. (2) Methods that create soil cement above ground include the soil cement backfill method. This method makes effective use of excavated soil generated during construction work by adding and mixing cement milk above ground with the excavated soil and using it as backfill material or structural material. This method requires the soil cement to have extremely high fluidity and self-leveling properties.

As described above, the required properties of soil cement, such as viscosity and fluidity, vary depending on the construction method, etc. For this reason, various additives have traditionally been used to adjust the properties of soil cement.
Patent Document 1 discloses a fluidizer for soil cement comprising an acrylic acid (salt) polymer (I) containing acrylic acid (salt) as an essential constituent monomer, and an alkali metal hydroxide and/or alkali metal silicate (B). Patent Document 2 discloses a soil cement slurry containing cement, water, and a dispersant composition containing a water-soluble vinyl copolymer (polycarboxylic acid polymer) of a predetermined structure and an antifoaming agent in a predetermined ratio.

Japanese Patent Application Laid-Open No. 2006-232600 Japanese Patent Application Laid-Open No. 2013-1604

Conventional dispersants have the problem of not providing sufficient fluidity to soil cement slurries. The present invention provides a soil cement additive and soil cement composition with excellent fluidity.

In this specification, the range "X to Y" means "X or more and Y or less." In this specification, "~acid (salt)" means "~acid and/or its salt." "(Meth)acrylic" means "acrylic and/or methacrylic." "(Bi)carbonate" means "carbonate (salt) and/or bicarbonate (salt)."

The inventors of the present invention arrived at this invention as a result of extensive research aimed at solving the above-mentioned problems. Specifically, the soil cement additive of the present invention is a compound represented by the following general formula (1):

(in formula (1), R ¹ , R ² , and R ³ are the same or different and represent a hydrogen atom, a methyl group, or an ethyl group; and X ¹ represents a hydrogen atom, a monovalent metal, a divalent metal, an ammonium group, or an organic amine group), and a structural unit (A) derived from a carboxylic acid monomer represented by the following general formula (2);

(In formula (2), R4, R5, and R6 are the same or different and represent a hydrogen atom, a methyl group, or an ethyl group. R7 is the same or different and represents an alkylene group having 2 to 4 carbon atoms. R8 is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. p is a number from 0 to 2. m is a number from 0 to 1. n is a number from 10 to 100.) The present invention relates to a soil cement additive containing a poly(meth)acrylic acid polymer obtained by polymerizing (meth)acrylic acid or its alkali metal salt or alkaline earth metal salt with a polycarboxylic acid polymer having structural units (B) derived from an unsaturated (poly)alkylene glycol monomer represented by the following formula:

The present invention also relates to a soil cement composition containing the soil cement additive, hydraulic powder, soil, and water.

The present invention also relates to a method for producing a soil cement composition, which includes the steps of: mixing mixing water containing the soil cement additive and water with hydraulic powder to obtain a slurry; and mixing the slurry with soil.

The present invention provides a soil cement additive and soil cement composition with excellent fluidity.

The present invention will be described in detail below.
It should be noted that 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.
The additive of the present invention is intended for use in soil cement. The soil cement may include clay-containing soil. The soil cement may also contain hydraulic powder.
The soil cement in which the additive of the present invention is used may be for ground improvement or soil improvement.

(Soil cement additive)
The soil cement additive of the present invention is characterized by containing a polycarboxylic acid polymer and a poly(meth)acrylic acid polymer.

<Polycarboxylic acid polymer>
The polycarboxylic acid polymer of the present invention is represented by the following general formula (1):

(in formula (1), R ¹ , R ² , and R ³ are the same or different and represent a hydrogen atom, a methyl group, or an ethyl group; and X ¹ represents a hydrogen atom, a monovalent metal, a divalent metal, an ammonium group, or an organic amine group), and a structural unit (A) derived from a carboxylic acid monomer represented by the following general formula (2);

(in formula (2), R ⁴ , R ⁵ and R ⁶ are the same or different and represent a hydrogen atom, a methyl group or an ethyl group; R ⁷ are the same or different and represent an alkylene group having 2 to 4 carbon atoms; R 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 a number of 0 or 1; and n represents a number from 10 to 100).

The copolymer may have one or more of the structural units (A) and (B). In the 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 the ethanolamine group, diethanolamine group, and triethanolamine group, and the triethylamine group are preferred.

Examples of the carboxylic acid monomer that can be used as a raw material for the structural unit (A) represented by the general formula (1) include unsaturated monocarboxylic acid monomers such as (meth)acrylic acid and crotonic acid; and their monovalent metal salts, divalent metal salts, ammonium salts, and organic amine salts, among which (meth)acrylic acid is preferred. When m in the structural unit (B) represented by the general formula (2) is 0, i.e., when it has an ether structure, acrylic acid is preferred from the viewpoint of copolymerizability.
In the above general formula (2), ^R8 represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. When ^R8 is a hydrocarbon group, it preferably has 1 to 18 carbon atoms, more preferably has 1 to 12 carbon atoms, and even more preferably has 1 to 8 carbon atoms.
Examples of hydrocarbon groups include methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl, isopentyl, neopentyl, 3-pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, isooctyl, 2,3,5-trimethylhexyl, 4-ethyl-5-methyloctyl, 2-ethylhexyl, tetradecyl, and octadecyl. 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. Of these, straight-chain, branched, or cyclic alkyl groups are preferred.

In the above general formula (2), n, representing the number of oxyalkylene groups, is a number between 10 and 100. Longer alkylene oxide chains suppress the aggregation of cement particles in the cement composition slurry, improving dispersibility and reducing the viscosity of the cement composition slurry. However, if the alkylene oxide chain is too long, the clay in the cement composition slurry will capture the alkylene oxide chain, causing cross-linking between the clay particles, which in turn has the effect of increasing viscosity. When the average number of added moles of oxyalkylene groups in the above general formula (2) is between 10 and 100, the effect of suppressing the aggregation of cement particles is achieved without being significantly affected by the clay. To achieve a better balance between these effects, the number n is preferably between 10 and 70, and more preferably between 10 and 50.

The unsaturated (poly)alkylene glycol monomers that are raw materials for the structural unit (B) represented by the general formula (2) include unsaturated (poly)alkylene glycol ester monomers in which m in the general formula (2) is 1, and unsaturated (poly)alkylene glycol ether monomers in which m in the general formula (2) is 0, and the unsaturated (poly)alkylene glycol ether monomers are preferred in that they are less susceptible to the weight average molecular weight of the polymer.
Examples of the unsaturated (poly)alkylene glycol ester monomer include (poly)alkylene glycol (meth)acrylates having an oxyalkylene group having 2 to 4 carbon atoms, such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, diethylene glycol (meth)acrylate, and dipropylene glycol (meth)acrylate; and (poly)alkylene glycol (meth)acrylates having an alkoxy group having 1 to 20 carbon atoms at the terminal and an oxyalkylene group having 2 to 4 carbon atoms, such as methoxyethyl (meth)acrylate, methoxypropyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, methoxydipropylene glycol (meth)acrylate, ethoxyethyl (meth)acrylate, ethoxypropyl (meth)acrylate, ethoxydiethylene glycol (meth)acrylate, and ethoxydipropylene glycol (meth)acrylate.

Examples of unsaturated (poly)alkylene glycol ether monomers include vinyl alcohols such as polyethylene glycol vinyl ether, polyethylene glycol (meth)allyl ether, polyethylene glycol 3-methyl-3-butenyl ether, methoxypolyethylene glycol vinyl ether, methoxypolyethylene glycol (meth)allyl ether, and methoxypolyethylene glycol 3-methyl-3-butenyl ether, (meth)allyl alcohol, and compounds in which 1 to 4 moles of alkylene oxide are added to unsaturated alcohols having 2 to 10 carbon atoms such as 3-methyl-3-buten-1-ol, 3-methyl-2-buten-1-ol, 2-methyl-3-buten-1-ol, and 2-methyl-2-buten-1-ol, as well as compounds in which a hydrocarbon group having 1 to 20 carbon atoms is bonded to the end of these. Preferred are compounds in which 10 to 100 moles of alkylene oxide having 2 to 3 carbon atoms are added to (meth)allyl alcohol or 3-methyl-3-buten-1-ol, and more preferred are compounds in which 10 to 100 moles of ethylene oxide are added to (meth)allyl alcohol or 3-methyl-3-buten-1-ol.

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. To provide a cement composition slurry with excellent fluidity, it is necessary for the copolymer to fully exhibit the effect of dispersing the solids in the slurry. To this end, it is important that the effect of the copolymer adsorbing to cement via the acid groups and the effect of inhibiting cement particle aggregation via the oxyalkylene chains in the copolymer's side chains are exhibited in a balanced manner. When the molar ratio of the structural unit (A) to the structural unit (B) in the copolymer is within the above range, these effects are exhibited in a more balanced manner. The structural unit (A)/structural unit (B) ratio is more preferably 60/40 to 95/5, and even more preferably 65/35 to 95/5.
The copolymer may have a structural unit (C) other than the structural unit (A) and the 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; esters of unsaturated dicarboxylic acid monomers such as unsaturated dicarboxylic acid monomers and glycols having 2 to 18 carbon atoms or poly(alkylene glycols) having 2 to 18 carbon atoms and 2 to 500 moles of glycols added diesters and half esters with alkylene glycol; half amides of maleamic acid with 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;
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-hydroxypropyloxy sulfobenzoate, 4-(meth)acryloxybutyl sulfonate, (meth)acrylamidomethyl sulfonic acid, (meth)acrylamidoethyl sulfonic acid, 2-methylpropanesulfonic acid (meth)a Unsaturated sulfonic acids such as acrylamide and styrenesulfonic acid, and their monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts; amides of unsaturated monocarboxylic acids and amines having 1 to 30 carbon atoms, such as methyl(meth)acrylamide; 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; (meth)acrylamide, (meth)acrylalkylamide, N-methylol(meth)acrylamide, N, Unsaturated amides such as 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; polydimethylsiloxane propylaminomaleamic acid, polydimethylsiloxane Examples of the siloxane derivatives include aminopropylene aminomaleamic acid, polydimethylsiloxane-bis-(propylaminomaleamic acid), polydimethylsiloxane-bis-(dipropylene aminomaleamic 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 these can be used alone or in combination of two or more.

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.
The copolymer preferably has a weight-average molecular weight of 5,000 to 40,000. When the copolymer has such a weight-average molecular weight, the cement composition can exhibit a better balance between the effect of providing excellent slurry fluidity and the effect of preventing separation and sedimentation of solids. The weight-average molecular weight of the copolymer is more preferably 8,000 to 40,000, even more preferably 10,000 to 40,000, and particularly preferably 10,000 to 35,000.

When the structural unit (B) in the copolymer is derived from an unsaturated (poly)alkylene glycol ether monomer, that is, when m in general formula (2) is 0, the copolymer is less affected by molecular weight, and the upper limit of the weight average molecular weight is 100,000.
The copolymer preferably has a molecular weight distribution (weight average molecular weight Mw/number average molecular weight Mn) of 1.0 to 4.0. A copolymer with such a ratio can efficiently impart fluidity to the soil cement slurry. The molecular weight distribution is more preferably 1.5 to 3.5, even more preferably 1.5 to 3.0, and particularly preferably 1.5 to 2.5.

The weight average molecular weight Mw and number average molecular weight Mn of the copolymer can be measured by the molecular weight measurement method (1) described in the Examples below.
The copolymer can be produced by polymerizing a monomer component containing, as essential components, a carboxylic acid monomer serving as a raw material for the structural unit (A) and an unsaturated (poly)alkylene glycol monomer serving 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.

The soil cement dispersant of the present invention essentially contains the above copolymer, but may contain two or more of the above copolymers, or may contain one or more copolymers different from the above copolymers.

<Poly(meth)acrylic acid polymer>
The poly(meth)acrylic acid polymer of the present invention is a polymer of (meth)acrylic acid or its alkali metal salt or alkaline earth metal salt. The alkali metal salt refers to a salt of sodium, potassium, lithium, etc., and the alkaline earth metal salt refers to a salt of alkaline earth metal such as beryllium, magnesium, calcium, etc.

Polymers of acrylic acid or its alkali metal salts or alkaline earth metal salts are particularly preferred, with polymers of acrylic acid or its alkali metal salts being preferred, and polymers of acrylic acid being most preferred. Poly(meth)acrylic acid polymers can contain other vinyl monomers (salts) as constituent monomers in addition to (meth)acrylic acid or its alkali metal salts or alkaline earth metal salts. Examples include hydroxyl group-containing alkyl (meth)acrylates, alkyl (meth)acrylates, amino group-containing acrylates, amide group-containing monomers, vinyl esters, alkenes, aromatic vinyl monomers, maleimide derivatives, nitrile group-containing vinyl monomers, monomers containing phosphonic acid groups, monomers containing sulfonic groups, aldehyde group-containing vinyl monomers, alkyl vinyl ethers, vinyl chloride, vinylidene chloride, allyl alcohol, vinylpyrrolidone, and other functional group-containing monomers.

When other vinyl monomers are contained as constituent monomers, the content (mol %) of the other vinyl monomer units, based on the total number of moles of the constituent monomers of the poly(meth)acrylic acid polymer, is preferably 0.1 to 50, more preferably 0.3 to 40, and particularly preferably 0.5 to 30. Within this range, the fluidity of the soil cement will be even better.

Poly(meth)acrylic acid polymers can be obtained using known vinyl monomer polymerization methods that have already been reported, such as the method described in JP-A-2006-347784.

The weight-average molecular weight (Mw) of the poly(meth)acrylic acid polymer is preferably 1,000 to 100,000, more preferably 2,000 to 50,000, particularly preferably 2,000 to 30,000, and most preferably 2,000 to 20,000. The molecular weight distribution (weight-average molecular weight Mw/number-average molecular weight Mn) is preferably 1.2 to 3.0, more preferably 1.3 to 2.5, and particularly preferably 1.4 to 2.0. Within this range, the fluidity of the soil cement will be even better. The molecular weight of the poly(meth)acrylic acid polymer is measured according to the molecular weight measurement method (2) described in the Examples.

The mass ratio of the polycarboxylic acid polymer to the poly(meth)acrylic acid polymer is preferably polycarboxylic acid polymer/poly(meth)acrylic acid polymer = 5/95 to 95/5, more preferably 10/90 to 90/10, and particularly preferably 20/80 to 80/20, in order to ensure the fluidity of the soil cement composition while improving the viscosity reduction of specific clayey materials containing a large amount of bentonite, and to make the soil cement slurry less susceptible to material separation.
The proportion of alkali metal salt or alkaline earth metal salt contained in the polycarboxylic acid polymer and the poly(meth)acrylic acid polymer, i.e., the degree of neutralization of the carboxylic acid-derived monomer portion, is preferably low. Specifically, if 100 mol% is when all carboxylic acid-derived monomer portions are neutralized and 0 mol% is when no neutralization occurs, then 80 mol% or less is preferred, and 60 mol% or less is more preferred. Furthermore, a low degree of neutralization of the poly(meth)acrylic acid polymer is suitable for achieving both improved dispersibility and improved viscosity reduction of specific clayey materials, and is preferably 30 mol% or less, more preferably 20 mol% or less, and most preferably 10 mol% or less. 0 mol% (no alkali metal salt or alkaline earth metal salt at all) is also one of the most preferred forms.

For soil cement additives containing polycarboxylic acid polymers, poly(meth)acrylic acid polymers, and poly(meth)acrylic acid polymers, the lower the degree of neutralization of the carboxylic acid-derived monomer moieties contained in the composition, the more preferable. Specifically, if 100 mol% is when all carboxylic acid-derived monomer moieties are neutralized and 0 mol% is when none are neutralized, the degree of neutralization is preferably 0 mol% to 50 mol%, more preferably 0 to 30 mol%, particularly preferably 0 to 25 mol%, and most particularly preferably 0 to 20 mol%.

In addition to polycarboxylic acid polymers and poly(meth)acrylic acid polymers, soil cement additives may contain one or more additives such as antifoaming agents, water-soluble polymers, polymer emulsions, retarders, early-strengthening agents/accelerators, air-enhancing agents, surfactants, waterproofing agents, rust inhibitors, crack-reducing agents, expansion agents, thickeners, separation-reducing agents, flocculants, drying shrinkage-reducing agents, strength enhancers, and self-leveling agents.

(Soil cement composition)
The present invention provides a soil cement composition containing soil, hydraulic powder, and the soil cement additive of the present invention. That is, the present invention provides a soil cement composition containing soil, hydraulic powder, a polycarboxylic acid polymer, and a poly(meth)acrylic acid polymer.
The present invention also provides a method for producing soil cement by mixing soil, hydraulic powder, water, and the soil cement additive of the present invention, i.e., by mixing soil, hydraulic powder, water, a polycarboxylic acid polymer, and a poly(meth)acrylic acid polymer.

The polycarboxylic acid polymer and poly(meth)acrylic acid polymer in these compositions can be one or more embodiments selected from the polycarboxylic acid polymer and poly(meth)acrylic acid polymer embodiments described above. Furthermore, the matters described in relation to the soil cement additive of the present invention can be applied as appropriate to these soil cements and their manufacturing methods.

The soil cement composition of the present invention will now be described. The soil cement composition of the present invention can be used, for example, in ground improvement methods, earth retaining methods, foundation piling methods, and backfilling methods.

The soil cement composition of the present invention includes a soil cement composition containing the soil cement dispersant of the present invention, soil, hydraulic powder, and water.

Hydraulic powders are powders that harden when mixed with water. Examples include Portland cement (normal, early-strength, extra-early-strength, moderate-heat, sulfate-resistant, and each low-alkali form); various blended cements (blast-furnace cement, silica cement, fly ash cement); white Portland cement; alumina cement; ultra-rapid-hardening cements (1-clinker rapid-hardening cement, 2-clinker rapid-hardening cement, magnesium phosphate cement); cement for grout; oil well cement; low-heat cement (low-heat blast-furnace cement, low-heat blast-furnace cement mixed with fly ash, high-belite cement); ultra-high-strength cement; cement-based solidifying materials; ecocement (cement made from one or more of municipal waste incineration ash and sewage sludge incineration ash), as well as those made by adding fine powders such as blast-furnace slag, fly ash, cinder ash, clinker ash, husk ash, silica fume, silica powder, limestone powder, and gypsum. The soil improvement cement composition of the present invention may contain only one type of cement, or two or more types of cement.

Examples of soil include sand, silt, and clay. These soils may contain organic matter, such as humus. Soil generated at construction sites can be used. Furthermore, soil cement can be produced by injecting a composition containing components other than soil of the soil cement into the ground as a high-pressure jet for the purpose of ground improvement, etc., and entraining the soil in the ground in the jet.

The content of the soil cement additive in the soil cement composition of the present invention is preferably 0.001% by mass or more, more preferably 0.005% by mass or more, even more preferably 0.01% by mass or more, even more preferably 0.05% by mass or more, even more preferably 0.1% by mass or more, and most preferably 0.2% by mass or more, and preferably 40% by mass or less, more preferably 30% by mass or less, and even more preferably 20% by mass or less, relative to the hydraulic powder. When the soil cement additive of the present invention is used, it is preferably used so that the content of the soil cement additive in the soil cement composition is within this range.

In the soil cement composition of the present invention, the soil content relative to the hydraulic powder is preferably 200% by mass or more, more preferably 300% by mass or more, and preferably 1500% by mass or less, more preferably 1200% by mass or less.

The soil cement composition of the present invention has a water/hydraulic powder ratio of preferably 30% by mass or more, more preferably 50% by mass or more, even more preferably 70% by mass or more, and preferably 500% by mass or less, more preferably 400% by mass or less, even more preferably 300% by mass or less.

(Method for producing soil cement composition)
The present invention also provides a method for producing soil cement by mixing soil, hydraulic powder, water, and the soil cement additive of the present invention, i.e., by mixing soil, hydraulic powder, water, a polycarboxylic acid polymer, and a poly(meth)acrylic acid polymer.

A method for producing a soil cement composition includes, for example, mixing hydraulic powder with the soil cement additive of the present invention and water to obtain a slurry, and mixing the slurry with soil. The mixer used in the slurry-obtaining step is not particularly limited as long as it can achieve uniform mixing, but mechanical impeller mixers are commonly used. The soil cement additive of the present invention, water, and hydraulic powder are added to the mixer while stirring, and the mixture is kneaded for, for example, 1 minute to 15 minutes to obtain a slurry. The soil cement additive of the present invention is preferably premixed with water and used as the mixing water, or added to cement milk (a mixture of hydraulic powder and water) after its production. When adding soil cement additives, the polycarboxylic acid polymer may be pre-mixed with water and used as mixing water, and the poly(meth)acrylic acid polymer may be mixed in after producing cement milk containing the polycarboxylic acid polymer. However, it is preferable to pre-mix the soil cement additives (polycarboxylic acid polymer and poly(meth)acrylic acid polymer) with water and use the mixing water as mixing water.

Next, the process of mixing the slurry and soil can be specifically classified based on the mixing mechanism: (1) a method typified by the CDM method in which prepared slurry is discharged underground while being stirred with mechanical stirring blades; (2) a method typified by the jet mixing method in which prepared slurry is sent underground as a high-pressure jet, scraping away and mixing the surrounding soil; and (3) a method in which prepared slurry is discharged and stirred and mixed with the soil in situ, such as a multi-axis auger in underground diaphragm wall construction, e.g., the SMW method, or a vertical mixing horizontal drag method, e.g., the TRD method. Soil cement compositions are produced by these methods.
In this manufacturing method, the polycarboxylic acid polymer, poly(meth)acrylic acid polymer, soil, water, and hydraulic powder can be used so as to satisfy the quantitative relationships described for the soil cement composition of the present invention.

Because the soil cement composition of the present invention has excellent soil cement fluidity, it can be suitably used in a ground improvement method in which a cement composition for ground improvement is injected into holes formed in the ground to create a ground improvement body. This type of ground improvement method, i.e., a ground improvement method that includes a step of injecting a composition of the present invention containing components other than soil into holes formed in the ground, also constitutes one aspect of the present invention.

The present invention provides a ground improvement method in which a soil cement composition containing the additive of the present invention is mixed with soil. That is, the present invention provides a ground improvement method in which a soil cement composition containing a polycarboxylic acid polymer and a poly(meth)acrylic acid polymer as essential components is mixed with ground. In the ground improvement method of the present invention, the soil cement composition and soil are mixed at a volume ratio of (the soil cement composition)/(soil) of preferably 0.1 or more, more preferably 0.2 or more, and preferably 1.5 or less, more preferably 1.0 or less.

The present invention will be described in more detail below using examples, but the present invention is not limited to these examples. Unless otherwise specified, all parts mean parts by mass, and all percentages mean % by mass.

The molecular weight was measured by one of the following methods determined depending on the substance.
<Method for measuring molecular weight (1)>
Columns used: TSKguard column α + TSKgel α-5000 + TSKgel α-4000 + TSKgel α-3000, manufactured by Tosoh Corporation, were connected together and used.
Eluent: A solution prepared by dissolving 62.4 g of sodium dihydrogen phosphate·2H ₂ O and 143.3 g of disodium hydrogen phosphate·12H ₂ O in 7794.3 g of ion-exchanged water and mixing this with 2000 g of acetonitrile was used.
Detector: Viscotek triple detector "Model 302 Light Scattering Detector", 90° scattering angle for right-angle light scattering, 7° scattering angle for low-angle light scattering, 18 μL cell volume, 670 nm wavelength.
Standard sample: Polyethylene glycol SE-8 (Mw=107000) manufactured by Tosoh Corporation was used, and the instrument constants were determined with its dn/dC set to 0.135 ml/g and the refractive index of the eluent set to 1.333.
Injection amount: Standard sample: 100 μL of a solution prepared by dissolving the polymer in the eluent so that the polymer concentration was 0.2 vol % was injected.
Sample: 100 μL of a solution prepared by dissolving the polymer in the eluent so that the polymer concentration was 1.0 vol % was injected.
Flow rate: 0.8ml/ml
Column temperature: 40°C

<Method for measuring molecular weight (2)>
The molecular weight was measured by gel permeation chromatography (GPC) using polyacrylic acid of known molecular weight as a standard substance. The detailed conditions are as follows:
Equipment: Waters Alliance (e2695)
Analysis software: Empower2 Professional + GPC option, manufactured by Waters Columns used: GF-310HQ, GF-710-HQ, GF-1G-7B, manufactured by Shodex
Detector: differential refractometer (RI) detector (Waters 2414)
Eluent: 0.1 mol/L aqueous sodium acetate solution. Standard material for creating calibration curve: Polyacrylic acid manufactured by American Polymer Standards (peak top molecular weight (Mp) 131,000, 750,000, 589,700, 193,800, 115,000, 62,900, 47,500, 28,000, 7,500, 2,925, 1,250).
Calibration curve: A cubic equation was prepared based on the Mp values and elution times of the above standard substances.
Injection volume of standard sample solution: 50 μL (eluent solution with polymer concentration of 0.1% by mass)
Amount of polymer sample solution injected: 50 μL (eluent solution with a polymer concentration of 0.5% by mass)
Flow rate: 0.5 mL/min Column temperature: 40°C
Measurement time: 90 minutes

<Production of copolymer>
A glass reaction vessel equipped with a thermometer, a spreader, a dropping funnel, a nitrogen inlet tube, and a reflux condenser was charged with 304.5 g of ion-exchanged water and 249.1 g of an unsaturated polyalkylene glycol ether (IPN-50) in which an average of 50 moles of ethylene oxide (EO) was added to isoprenol, and the temperature was raised to 60°C, after which 26.0 g of a 4% aqueous hydrogen peroxide solution was added thereto.
An aqueous solution prepared by diluting 23.6 g of acrylic acid with 5.9 g of ion-exchanged water, and IPN-50
An aqueous solution prepared by dissolving 747.3 g of the compound in 320.3 g of ion-exchanged water was added dropwise over 4 hours.
At the same time, an aqueous solution prepared by dissolving 1.3 g of L-ascorbic acid and 3.2 g of 3-mercaptopropionic acid in 318.8 g of ion-exchanged water was added dropwise over 4.5 hours. After the completion of the dropwise addition, stirring was continued for 1 hour to terminate the polymerization reaction. Thereafter, the reaction solution was adjusted to pH 6 using a 30% aqueous solution of sodium hydroxide at a temperature below the polymerization reaction temperature, yielding an aqueous solution of copolymer (1) having a weight-average molecular weight (Mw) of 17,500. The weight-average molecular weight was measured using the molecular weight measurement method (1).

Copolymer (2) and copolymers (4), (5), and (6) were synthesized in the same manner as copolymer (1). The weight average molecular weights were measured by the molecular weight measurement method (1).
A reactor equipped with a thermometer, stirrer, dropping device, nitrogen inlet tube, and condenser was charged with 273 g of distilled water and heated to 80°C. Subsequently, a solution containing 375 g of methoxypolyethylene glycol monomethacrylate (average number of moles of ethylene oxide added: 25), 75 g of methacrylic acid, 3.3 g of 3-mercaptopropionic acid, and 100 g of distilled water was added dropwise over 4 hours, and 50 g of a 10% aqueous solution of ammonium persulfate was added dropwise over 5 hours. After the dropwise addition of the solution was completed, the reaction mixture was maintained at 80°C for 1 hour. After cooling, the pH was adjusted to 6 with the addition of a 30% aqueous solution of sodium hydroxide, yielding an aqueous solution of copolymer (3) with a weight-average molecular weight of 20,000. The weight-average molecular weight was measured using the molecular weight measurement method (1).

Copolymers (7), (8), and (9) and comparative copolymers (1) and (2) were synthesized in the same manner as copolymer (3). The weight-average molecular weights were measured using the molecular weight measurement method (1).

<Production of Poly(meth)acrylic Acid Polymer>
A 2.5 L stainless steel separable flask equipped with a stirrer, reflux condenser, and dropping device was charged with 373 g of deionized water and heated to a boiling reflux temperature while stirring to form a polymerization reaction system. Next, 132.2 g of a 35% aqueous solution of sodium hydrogen sulfite (hereinafter referred to as 35% SBS) was added dropwise to the polymerization reaction system under boiling reflux conditions. Five minutes after the start of the 35% SBS addition, 810 g of an 80% aqueous solution of acrylic acid (hereinafter referred to as 80% AA) and 390 g of a 15% aqueous solution of sodium peroxodisulfate (hereinafter referred to as 15% NaPS) were added dropwise from separate nozzles. The addition time for each aqueous solution was 120 minutes, and the addition rate for each solution was constant and continuous. After the dropwise addition of the 15% NaPS was completed, the reaction solution was maintained at a boiling point reflux state (aged) for an additional 30 minutes to complete the polymerization reaction, thereby obtaining an aqueous solution of poly(meth)acrylic acid polymer (1) having a weight-average molecular weight of 10,000. The weight-average molecular weight was measured by the molecular weight measurement method (2).

Poly(meth)acrylic acid polymers (2) to (6) are the same as poly(meth)acrylic acid polymer (1).
was produced in the same manner as

<Soil cement preparation and flow measurement>
Under the test conditions described below, the materials, mixer, and measuring instruments used in the test were all regulated to a test temperature of 20°C under the above test temperature atmosphere, and kneading and physical property measurements were also carried out under the above test temperature atmosphere.
Before preparing the soil cement, 5000 g of Motoyama Kibushi clay (clay powder A, manufactured by Seto Ceramic Materials Co., Ltd.) and 3000 g of water were placed in a plastic bag, mixed by hand for 10 minutes, and left to stand at 20°C for at least one day to prepare a hydrated Kibushi clay with a moisture content of 60%.
In a polypropylene cup (product number: New Disposable Cup 1000 mL; manufactured by AS ONE),
An additive solution was prepared by adding 200 g of water containing a polycarboxylic acid polymer and a poly(meth)acrylic acid polymer (the total amount of the polycarboxylic acid polymer and the poly(meth)acrylic acid polymer added was specified to be 3.0% relative to the cement-based solidification material), and sodium carbonate as a polyvalent ion insolubilizer in an amount of 2.0% relative to the cement-based solidification material, and stirring the mixture.
200 g of cement-based solidification material (Geoset 200, manufactured by Taiheiyo Cement) was added to the prepared additive solution and stirred at 300 rpm for 4 minutes using a Three-One motor to prepare a cement slurry. The prepared cement slurry and 600 g of hydrated wood-bushi clay with a moisture content of 60% were added to the kettle of a Hobart mixer (model number N-50; manufactured by Hobart Co.), and stirring was initiated with the Hobart mixer to prepare the soil cement. Two minutes after the start of stirring, stirring was stopped, and the clay on the side of the kettle was scraped off for 30 seconds. Stirring was then resumed and continued for 10 minutes from the start of stirring to prepare the soil cement. The prepared soil cement was subjected to flow measurement using a truncated cone-shaped flow cone (lower diameter 100 mm, upper diameter 70 mm, height 60 mm). Detailed conditions for the flow measurement are described below.
Installation of the cone and flat plate: Before use, the cone was visually inspected to ensure there were no stains, scratches, or dents. The inner surface of the cone and the top surface of the flat plate were wiped clean with a wet cloth or similar.
Sample filling method: The cone was placed on a horizontally placed flat plate, and the sample was packed in two layers of approximately equal volume. Each layer was leveled with a poker, and then poked evenly 25 times to ensure no bias. The poker was inserted deep enough to reach almost the previous layer.
Flow measurement: After the sample was filled, the cone was lifted horizontally and then it was waited until the soil cement stopped flowing. The maximum diameter and the diameter perpendicular to that were then measured with a vernier caliper, and the average value was calculated and recorded as the flow.

<Examples 1 to 18 and Comparative Examples 1 to 4>
Using the copolymers (1) to (9) shown in Table 1 and the poly(meth)acrylic acid polymers (1) to (6) shown in Table 2, the soil cement preparation and flow measurement tests described above were carried out with the formulations shown in Tables 3 to 5. The results are shown in Tables 3 to 5.

As shown in Table 3, good flow results were observed when a copolymer with a molecular weight of 40,000 or less was blended, or when m in the copolymer structural unit (B) was 0.

As shown in Table 4, good flow results were observed when using various poly(meth)acrylic acid polymers.

As shown in Table 5, good flow results were observed when the weight ratio of copolymer to poly(meth)acrylic acid polymer was used within an appropriate range.

Claims (4)

The following general formula (1):
(in formula (1), R ¹ , R ² , and R ³ are the same or different and represent a hydrogen atom, a methyl group, or an ethyl group; and X ¹ represents a hydrogen atom, a monovalent metal, a divalent metal, an ammonium group, or an organic amine group), and a structural unit (A) derived from a carboxylic acid monomer represented by the following general formula (2);
(In formula (2), R4, R5, and R6 are the same or different and represent a hydrogen atom, a methyl group, or an ethyl group. R7 is the same or different and represents an alkylene group having 2 to 4 carbon atoms. R8 represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. p represents a number from 0 to 2. m represents a number from 0 to 1, and n represents a number from 10 to 100.) A soil cement additive comprising a poly(meth)acrylic acid polymer obtained by polymerizing a polycarboxylic acid polymer having a weight average molecular weight of 5,000 to 40,000 and having a structural unit (B) derived from an unsaturated (poly)alkylene glycol monomer represented by the following formula (2): (In formula (2), R4, R5, and R6 are the same or different and represent a hydrogen atom, a methyl group, or an ethyl group . R7 is the same or different and represents an alkylene group having 2 to 4 carbon atoms. R8 represents a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. p represents a number from 0 to 2. m represents a number from 0 to 1, and n represents a number from 10 to 100.) The following general formula (1):
(in formula (1), R ¹ , R ² , and R ³ are the same or different and represent a hydrogen atom, a methyl group, or an ethyl group; and X ¹ represents a hydrogen atom, a monovalent metal, a divalent metal, an ammonium group, or an organic amine group), and a structural unit (A) derived from a carboxylic acid monomer represented by the following general formula (2);
(In formula (2), R4, R5, and R6 are the same or different and represent a hydrogen atom, a methyl group, or an ethyl group. R7 is the same or different and represents an alkylene group having 2 to 4 carbon atoms. R8 is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. p is a number from 0 to 2. m is a number from 0, and n is a number from 10 to 100.) A soil cement additive comprising a poly(meth)acrylic acid polymer obtained by polymerizing a polycarboxylic acid polymer having a structural unit (B) derived from an unsaturated (poly)alkylene glycol monomer represented by the following formula (2): (In formula (2), R4, R5, and R6 are the same or different and represent a hydrogen atom, a methyl group, or an ethyl group . R7 is the same or different and represents an alkylene group having 2 to 4 carbon atoms. R8 is a hydrogen atom or a hydrocarbon group having 1 to 20 carbon atoms. p is a number from 0 to 2. m is a number from 0, and n is a number from 10 to 100.) A soil cement composition comprising the soil cement additive according to claim 1 or 2, hydraulic powder, soil, and water. A method for producing a soil cement composition, comprising the steps of: mixing hydraulic powder with mixing water containing the soil cement additive according to claim 1 or 2 and water to obtain a slurry; and mixing the slurry with soil.