JP6043591B2 - Cement additive and cement composition - Google Patents

Description

The present invention relates to a cement additive and its use. More specifically, the present invention relates to a cement additive containing a crosslinked product obtained by crosslinking a nonionic monomer unit as an essential constituent unit, and a cement composition containing the same.

In addition to cement, cement dispersants are added to cement compositions such as cement paste, mortar, and concrete used to construct civil engineering and building structures. Water has been added.

As a cement dispersant, a copolymer containing a structural unit derived from an unsaturated (poly) alkylene glycol ether monomer having an alkenyl group having 4 carbon atoms and a structural unit derived from an unsaturated monocarboxylic acid monomer is essential. A cement dispersant (see Patent Document 1) and the like have been developed, and the improvement of the delay in hardening of the cement composition and the development of early strength are realized along with exhibiting dispersibility.

JP 2002-121055 A

Christof Schrofl, Viktor Mechtcherine, Michaela Gorges, “Relation between the molecular structure and the efficiency of the super absorbent polymers (SAP) as concrete admixture to mitigate autogenous shrinkage”, Cement and Concrete Research 42 (2012) 865-873

In the cement composition, there is a phenomenon of self-shrinkage in which the inside is dried by cement hydration itself. If the distribution of water is biased inside the cement composition, the portion where water is unevenly distributed is largely self-shrinking, and the portion where water is not unevenly distributed is not self-shrinking (or the amount of shrinkage is small) Concrete cracks may occur or the strength of the concrete may decrease.

The copolymer for a cement dispersant described in Patent Document 1 is used for dispersing cement in water, and does not have an action of uniformly dispersing water in the cement composition. In addition, the problem of uneven self-shrinkage due to the uneven distribution of water described above is a problem that occurs even when a cement dispersant as described in Patent Document 1 is used.
Therefore, there has been a demand for a method for preventing cracks in concrete and a decrease in strength due to self-shrinkage.

Non-Patent Document 1 introduces the results of evaluating self-shrinkage characteristics by adding a superabsorbent resin composed of acrylic acid and acrylamide to a cement composition.

The present invention has been made in view of the above situation, and a cement additive capable of exhibiting an effect of uniformly dispersing water in a cement composition to cause uniform self-shrinkage, and such cement. It aims at providing the cement composition containing an additive.

The present inventors have intensively studied to solve the above problems. As a result, the crosslinked product having a nonionic monomer unit as an essential constituent unit has a highly water-absorbing action, and the crosslinked product that has absorbed water is dispersed in the cement composition. As a result, water was uniformly dispersed in the cement composition, and the hydration of the cement and water was found to occur uniformly in the cement composition, and the present invention was conceived.

That is, the present invention is a cement additive characterized by containing a crosslinked product having a nonionic monomer unit as an essential constituent unit.

The present invention is also a cement composition comprising the above cement additive, cement and water.
The present invention is described in detail below. In addition, what combined two or three or more of the preferable forms of this invention described in a paragraph below is also a preferable form of this invention.

[Cement additive]
The cement additive of the present invention contains a crosslinked product obtained by crosslinking a nonionic monomer unit as an essential constituent unit. As the monomer unit, in addition to the nonionic monomer unit which is an essential constituent unit, another monomer unit may be included.

[Nonionic monomer]
The nonionic monomer in the present invention is preferably an N-vinyl lactam monomer or a polyalkylene glycol monomer. Hereinafter, the cement additive having an N-vinyl lactam monomer as an essential constituent unit and the cement additive having a polyalkylene glycol monomer as an essential constituent unit will be described.
In the case where the N-vinyl lactam monomer is an essential constituent unit, the N-vinyl lactam monomer is included in the monomer component at a certain ratio as described later. Preferably, when the polyalkylene glycol monomer is an essential constituent unit, the polyalkylene glycol monomer is preferably contained in the monomer component at a certain ratio or more. Further, an N-vinyl lactam monomer and a polyalkylene glycol monomer may be mixed.

[Cement additive containing N-vinyl lactam monomer as an essential constituent unit]
[N-vinyl lactam monomer]
In the present invention, the N-vinyl lactam monomer is not limited as long as it is a monomer having an N-vinyl lactam structure, and examples thereof include N-vinyl pyrrolidone, N-vinyl caprolactam, and N-vinyl imidazoline. . These N-vinyl lactam monomers may be used alone or in combination of two or more. Among the N-vinyl lactam monomers, N-vinyl-2-pyrrolidone is particularly preferable from the viewpoint of the safety of the monomer and the resulting crosslinked product.

The method for producing the N-vinyl lactam monomer used in the present invention is not particularly limited. For example, when the N-vinyl lactam monomer is N-vinyl pyrrolidone, N-hydroxyethyl pyrrolidone is used. A method of vapor phase dehydration reaction is particularly preferable. There is no particular limitation on the specific method for vapor-phase dehydration reaction of N-hydroxyethylpyrrolidone. For example, the method reported in JP-A-8-141402 and JP-A-2939433 may be employed. In the above method, it is preferable to use γ-butyrolactone, which is a precursor of N-hydroxyethylpyrrolidone, derived from maleic anhydride.
However, the above monomers are N-vinylpyrrolidone obtained by vinylation of 2-pyrrolidone with acetylene, butyrolactone is reacted with ethanolamine to give 1- (β-oxyethyl) -2-pyrrolidone, and the hydroxyl group is converted to chlorine with thionyl chloride. N-vinylpyrrolidone obtained as a dehydrated salt, N-vinylpyrrolidone obtained by deaceticating an acetate ester intermediate obtained by reaction of N- (2-hydroxyethyl) -2-pyrrolidone and acetic anhydride, etc. There may be.

The N-vinyl lactam monomer produced by the above production method is usually used for polymerization through a purification step.

The monomer used for the production of the crosslinked product is not particularly limited as long as at least the N-vinyl lactam monomer is included. For example, only the N-vinyl lactam monomer is used. Alternatively, other polymerizable monomers copolymerizable with the N-vinyl lactam monomer may be used in combination. When monomers other than the N-vinyl lactam monomer are copolymerized, the content of the N-vinyl lactam monomer in 100% by mass (monomer component) of all monomers is particularly Although not limited, the N-vinyl lactam monomer is preferably 30% by mass or more, more preferably 40 to 90% by mass, and even more preferably 70 to 80% by mass. .
The term “100% by mass (monomer component)” as used herein refers to a concept that does not include a crosslinkable monomer but includes an N-vinyl lactam monomer and other monomers described later. is there.

[Other monomers]
The monomer (other monomer) copolymerizable with the N-vinyl lactam monomer is not particularly limited (except for a monomer corresponding to the crosslinkable monomer). Specifically, for example, 1) unsaturated monocarboxylic acids such as partially neutralized or completely neutralized products of acrylic acid, methacrylic acid, crotonic acid or their monovalent metals, divalent metals, ammonia, organic amines, etc. Monomers; 2) Unsaturated dicarboxylic acids such as maleic acid, fumaric acid, itaconic acid, citraconic acid or their monovalent metals, divalent metals, ammonia, partially neutralized products or completely neutralized products with organic amines Monomer; 3) Vinylsulfonic acid, allylsulfonic acid, methallylsulfonic acid, styrenesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, sulfoethyl (meth) acrylate, sulfop Pyr (meth) acrylate, 2-hydroxysulfopropyl (meth) acrylate, sulfoethylmaleimide, 3-allyloxy-2-hydroxypropanesulfonic acid or partially neutralized products of these with monovalent metal, divalent metal, ammonia, organic amine And unsaturated sulfonic acid monomers such as completely neutralized products; 4) Amide monomers such as (meth) acrylamide, vinylacetamide, isopropylacrylamide, t-butyl (meth) acrylamide; 5) (meth) acrylic Hydrophobic monomers such as acid esters, styrene, 2-methylstyrene, vinyl acetate; 6) 2-hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, allyl alcohol, Polyethylene glycol Monoallyl ether, polypropylene glycol monoallyl ether, 3-methyl-2-buten-1-ol (prenol), polyethylene glycol monoprenol ether, polypropylene glycol monoprenol ether, 2-methyl-3-buten-2-ol Hydroxyl-containing unsaturated monomers such as (isoprene alcohol), polyethylene glycol monoisoprene alcohol ether, polypropylene glycol monomonoisoprene alcohol ether, N-methylol (meth) acrylamide, glycerol mono (meth) acrylate, glycerol monoallyl ether, vinyl alcohol 7) cationic monomers such as dimethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylamide; 8) (meth) acrylic acid Nitrile monomers such as rilonitrile; 9) phosphorus-containing monomers such as (meth) acrylamide methanephosphonic acid, (meth) acrylamide methanephosphonic acid methyl ester, 2- (meth) acrylamide-2-methylpropanephosphonic acid; Etc. Among these, 1) or 3) is preferable from the viewpoint of copolymerization with N-vinyl lactam monomer, and the unsaturated sulfonic acid monomer of 3) is particularly preferable. . These may use only 1 type and may mix 2 or more types and may make it copolymerize with a N-vinyl lactam-type monomer.

The content of the other monomer in 100% by mass (monomer component) of the total monomer is not particularly limited, but the other monomer is 0% by mass to 70% by mass. It is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 30% by mass or less.

When using an acidic group-containing monomer such as carboxylic acid or sulfonic acid as another monomer, or when using a basic group-containing monomer, the acidic group and the basic group are not neutralized. Either a neutralized product or a completely neutralized product can be used without any problem.

(Crosslinkable monomer)
In the present invention, it is particularly preferable to copolymerize a crosslinkable monomer having at least two polymerizable double bond groups per molecule with an N-vinyl lactam monomer. By polymerizing an appropriate amount of the crosslinkable monomer together with the N-vinyllactam monomer, an arbitrary crosslinked structure can be formed to obtain a crosslinked product.
Specific examples of the crosslinkable monomer include N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, Methylolpropane tri (meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipenta Erythritol hexa (meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, divinylben Zen, divinyltoluene, divinylxylene, divinylnaphthalene, divinyl ether, divinyl ketone, trivinylbenzene, tolylene diisocyanate, hexamethylene diisocyanate and the like. These may use only 1 type and may use 2 or more types together.

The usage-amount of the said crosslinkable monomer is not specifically limited, What is necessary is just to adjust suitably according to the intended purpose. For example, it is desirable to carry out copolymerization by containing 0.25 mol% or more of a crosslinkable monomer with respect to 100 mol% of the monomer component. Further, it is desirable that 0.15 mol% or less of a crosslinkable monomer is contained in 100 mol% of the monomer component for copolymerization.

[Crosslinked product]
The crosslinked product contained in the cement additive of the present invention has a water absorption capacity of 8 g / g or more after 24 hours with respect to an aqueous solution containing 0.6% by mass of calcium nitrate tetrahydrate and 0.089% by mass of potassium hydroxide. It is desirable.

The crosslinked product contained in the cement additive of the present invention is preferably obtained by polymerizing a monomer component containing 30% by mass or more of an N-vinyl lactam monomer.
The monomer component here is a concept that does not include a crosslinkable monomer but includes the above-described N-vinyl lactam monomer and other monomers.
And when calculating | requiring the ratio of a N-vinyl lactam monomer, the sum total of a N-vinyl lactam monomer and another monomer shall be 100 mass%, and the ratio of a N-vinyl lactam monomer Ask for.

The average particle size (average particle size) of the crosslinked product is not particularly limited, but is preferably 10 to 1000 μm, more preferably 50 to 600 μm.
When the average particle diameter is in such a small range, the crosslinked product is easily dispersed uniformly in the cement composition, so that the effects of the invention are easily exhibited.

[Method for producing crosslinked product]
The method for producing a crosslinked product contained in the cement additive of the present invention includes a polymerization step, but the method is not particularly limited, and examples thereof include a bulk polymerization method, a solution polymerization method, an emulsion polymerization method, and a suspension. Methods such as a polymerization method and a precipitation polymerization method can be employed. When a solvent is used in the polymerization reaction, the solvent is preferably water, but is selected from other solvents such as alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, n-butyl alcohol, diethylene glycol, and the like. It can also be used individually or in mixture of 2 or more types with water. The solvent may not be used.
When a solvent is used for the polymerization reaction, the concentration of the monomer component in the solution is preferably 25% by mass or more and 80% by mass or less. If the concentration of the monomer component is less than 25% by mass, it may be difficult to obtain a cross-linked product, or it may be difficult to crush the gel after polymerization. In addition, a long time is required for drying, and the resin may deteriorate during drying. On the other hand, when the concentration of the monomer component exceeds 80% by mass, it becomes difficult to control the polymerization and the residual monomer tends to increase.

In the production of the cross-linked product, a method of polymerizing a monomer component having an N-vinyl lactam monomer as an essential component in the presence of a cross-linking agent may be employed, or a method of cross-linking treatment after polymerization may be employed. You may do it.

When performing the above polymerization reaction, for example, reaction conditions such as reaction temperature and pressure are not particularly limited. For example, the reaction temperature is preferably 20 to 150 ° C., and the pressure in the reaction system is preferably normal pressure or reduced pressure.

As a means for initiating polymerization of a monomer component mainly composed of an N-vinyl lactam monomer, a method of adding a polymerization initiator, a method of irradiating UV, a method of applying heat, in the presence of a photoinitiator For example, a method of irradiating light can be employed. Examples of the method of crosslinking after polymerization include, for example, (i) a method of irradiating UV to a N-vinyl lactam polymer, (ii) a method of applying heat to the N-vinyl lactam polymer, and self-crosslinking ( iii) A method in which a radical generator is contained in an N-vinyl lactam polymer and then self-crosslinked by applying heat, and (iv) a radical polymerizable crosslinking agent and a radical polymerization initiator are added to the N-vinyl lactam polymer. Examples of the method include heating and / or light irradiation after the inclusion.

When performing the said polymerization reaction, a polymerization initiator can be used. The polymerization initiator is not particularly limited as long as radicals are generated by heating or the like, but a water-soluble initiator that is uniformly dissolved in water at a concentration of 5% by mass or more at room temperature is preferable. Specifically, for example, peroxides such as hydrogen peroxide and t-butyl hydroperoxide; 2- (carbamoylazo) isobutyronitrile, 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis (2-methyl-N-phenylprolionamidine) dihydrochloride, 2,2′-azobis [2- (N-allylamidino) propane] dihydrochloride, 2,2′-azobis [ 2- (5-hydroxy-3,4,5,6-tetrahydropyrimidin-2-yl) propane] dihydrochloride, 2,2'-azobis [2- (2-imidazolin-2-yl) propane] 2 hydrochloric acid Salts, azo compounds such as 2,2′-azobis [2-methyl-N- (2-hydroxyethyl) propionamide]; persulfates such as potassium persulfate, ammonium persulfate and sodium persulfate; Redox initiators that generate radicals by combining an oxidizing agent and a reducing agent, such as acid and hydrogen peroxide, sodium sulfoxylate and t-butyl hydroperoxide, persulfate and metal salt, etc. . These may use only 1 type and may use 2 or more types together.

The amount of the polymerization initiator used is not particularly limited, but is 0.002 with respect to 100% by mass of all monomers (N-vinyl lactam monomer, other monomers, crosslinkable monomer). -15 mass% is preferable, and 0.01-5 mass% is further more preferable. In carrying out the above polymerization reaction, a conventionally known basic pH regulator can be used for the purpose of promoting the polymerization reaction or preventing hydrolysis of the N-vinyl lactam monomer. The pH regulator can be added by any method. For example, the pH regulator may be charged into the system from the initial stage of polymerization, or may be added successively during the polymerization. Specific examples of the pH regulator include ammonia, aliphatic amines, aromatic amines, sodium hydroxide, potassium hydroxide, and the like. Among these, ammonia is particularly preferable. These may use only 1 type and may use 2 or more types together. When using a pH adjuster, the amount of use is not particularly limited, but it is preferable to use it so that the solution at the time of polymerization is in the pH range of 5 to 10, preferably 7 to 9.

When the polymerization reaction is performed, a conventionally known transition metal salt can be used for the purpose of promoting the polymerization reaction. Specific examples of the transition metal salt include carboxylates and chlorides such as copper, iron, cobalt, and nickel. These may be used alone or in combination of two or more. May be. When the transition metal salt is used, the amount used is not particularly limited, but is preferably 0.1 to 20000 ppb, more preferably 1 to 5000 ppb in terms of weight ratio to the polymerizable monomer component. When performing the polymerization reaction, in addition to the polymerization initiator and, if necessary, the pH adjuster and the transition metal salt, any chain transfer agent, buffering agent, etc. can be used as necessary. .

When performing the above-mentioned polymerization reaction, the method of adding the above-mentioned charged components is not particularly limited, and can be performed by any method such as a batch method or a continuous method.

Hereinafter, the cement additive having a polyalkylene glycol monomer as an essential constituent unit will be described.
[Cement additive containing polyalkylene glycol monomer as essential constituent unit]
[Polyalkylene glycol monomer]
In the present invention, the polyalkylene glycol monomer is not particularly limited as long as it is a monomer having a polyalkylene glycol chain and a polymerizable group. For example, a monomer represented by the following general formula (1) is preferable.

However, R is hydrogen or a methyl group, X is the oxyalkylene group which may be same or different, Y is hydrogen, a C1-C5 alkoxy group, a phenoxy group, or a C1-C9 alkyl It is an oxyalkylphenyl group having 1 to 3 groups as a substituent, and n is 3 to 300.

The oxyalkylene group is preferably an oxyalkylene group having 2 to 4 carbon atoms. Moreover, it is desirable that the mole fraction of oxyethylene groups with respect to all oxyalkylene groups is 50 mol% or more.

Examples of the monomer represented by the general formula (1) include methoxypolyethylene glycol mono (meth) acrylate, methoxypolyethylene glycol / polypropylene glycol mono (meth) acrylate, and methoxypolyethylene glycol / polybutylene glycol mono (meth) acrylate. , Ethoxy polyethylene glycol / polypropylene glycol mono (meth) acrylate, ethoxy polyethylene glycol / polybutylene glycol mono (meth) acrylate, phenoxy polyethylene glycol mono (meth) acrylate, benzyloxypolyethylene glycol mono (meth) acrylate, etc. 1 type (s) or 2 or more types can be used.

The monomer used in the production of the crosslinked product is not particularly limited as long as at least the polyalkylene glycol monomer is included. For example, only the polyalkylene glycol monomer may be used. Alternatively, other polymerizable monomers copolymerizable with the polyalkylene glycol monomer may be used in combination. When monomers other than polyalkylene glycol monomers are copolymerized, the content of polyalkylene glycol monomers in 100% by mass (monomer component) of all monomers is particularly limited. Although not intended, the polyalkylene glycol monomer is preferably 70% by mass or more, and more preferably 85% by mass or more. Moreover, it is more preferable to set it as 85-100 mass%.
In addition, 100 mass% of all monomers here (monomer component) is a concept that does not include a crosslinkable monomer but includes a polyalkylene glycol monomer and other monomers described later. .

[Other monomers]
The monomer (other monomer) copolymerizable with the polyalkylene glycol monomer is not particularly limited (except for a monomer corresponding to the crosslinkable monomer), Specifically, for example, 1) unsaturated monocarboxylic acids such as partially neutralized products or completely neutralized products of acrylic acid, methacrylic acid, crotonic acid or their monovalent metals, divalent metals, ammonia, organic amines, etc. Monomers; 2) Unsaturated dicarboxylic acid-based monomers such as maleic acid, fumaric acid, itaconic acid, citraconic acid or their monovalent metals, divalent metals, ammonia, partially neutralized products or completely neutralized products with organic amines 3) Vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, sulfoethyl (meth) acrylate, Phopropyl (meth) acrylate, 2-hydroxysulfopropyl (meth) acrylate, sulfoethylmaleimide, 3-allyloxy-2-hydroxypropanesulfonic acid or partially neutralized products of these with monovalent metal, divalent metal, ammonia, and organic amine And unsaturated sulfonic acid monomers such as completely neutralized products; 4) Amide monomers such as (meth) acrylamide, vinylacetamide, isopropylacrylamide, t-butyl (meth) acrylamide; 5) (meth) acrylic Hydrophobic monomers such as acid esters, styrene, 2-methylstyrene, vinyl acetate; 6) 2-hydroxyethyl (meth) acrylate, polyethylene glycol mono (meth) acrylate, polypropylene glycol mono (meth) acrylate, allyl alcohol, Polyethylene Cole monoallyl ether, polypropylene glycol monoallyl ether, 3-methyl-2-buten-1-ol (prenol), polyethylene glycol monoprenol ether, polypropylene glycol monoprenol ether, 2-methyl-3-butene-2- Hydroxyl-containing unsaturated monomers such as all (isoprene alcohol), polyethylene glycol monoisoprene alcohol ether, polypropylene glycol monomonoisoprene alcohol ether, N-methylol (meth) acrylamide, glycerol mono (meth) acrylate, glycerol monoallyl ether, vinyl alcohol 7) Cationic monomers such as dimethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylamide; 8) (meta ) Nitrile monomers such as acrylonitrile; 9) Phosphorus-containing monomers such as (meth) acrylamide methanephosphonic acid, (meth) acrylamide methanephosphonic acid methyl ester, 2- (meth) acrylamide-2-methylpropanephosphonic acid And the like. Of these, 1) or 3) is preferable from the viewpoint of copolymerization with a polyalkylene glycol monomer, and the unsaturated sulfonic acid monomer 3) is particularly preferable. These may use only 1 type and may mix 2 or more types and may be copolymerized with a polyalkylene glycol-type monomer.

The content of the other monomer in 100% by mass (monomer component) of the total monomer is not particularly limited, but the other monomer is 0% by mass to 70% by mass. It is preferably 5% by mass or more and 40% by mass or less, more preferably 10% by mass or more and 30% by mass or less.

When using an acidic group-containing monomer such as carboxylic acid or sulfonic acid as another monomer, or when using a basic group-containing monomer, the acidic group and the basic group are not neutralized. Either a neutralized product or a completely neutralized product can be used without any problem.

(Crosslinkable monomer)
The crosslinkable monomer is the same as that in the case where the N-vinyl lactam monomer is an essential structural unit, and thus detailed description thereof is omitted.

[Crosslinked product]
As the cross-linked product, the water absorption after 24 hours with respect to an aqueous solution containing 0.6% by mass of calcium nitrate tetrahydrate and 0.089% by mass of potassium hydroxide is desirably 8 g / g or more.

The cross-linked product is preferably formed by polymerizing a monomer component containing 85% by mass or more of a polyalkylene glycol monomer.
The monomer component here is a concept that does not include a crosslinkable monomer but includes the above-described polyalkylene glycol monomer and other monomers.
And when calculating | requiring the ratio of a polyalkylene glycol type monomer, the ratio of a polyalkylene glycol type monomer is calculated | required by making the sum total of a polyalkylene glycol type monomer and another monomer into 100 mass%.

The average particle size (average particle size) of the crosslinked product is not particularly limited, but is preferably 10 to 1000 μm, more preferably 50 to 600 μm.
When the average particle diameter is in such a small range, the crosslinked product is easily dispersed uniformly in the cement composition, so that the effects of the invention are easily exhibited.

[Method for producing crosslinked product]
As a method for producing a crosslinked product, a polyalkylene glycol monomer is used instead of the N-vinyl lactam monomer, and a polyalkylene glycol polymer is used instead of the N-vinyl lactam polymer. Since it can be carried out similarly to the case where an N-vinyl lactam monomer is used as an essential structural unit, its detailed description is omitted.

Hereinafter, the cement composition using the cement additive of the present invention will be described.
[Cement composition]
The cement composition of the present invention includes the cement additive of the present invention, cement, and water.
Examples of cement include Portland cement (ordinary, early strength, very early strength, moderate heat, sulfate-resistant and low alkali types); various mixed cements (blast furnace cement, silica cement, fly ash cement); white Portland cement; alumina Cement; Super fast cement (1 clinker fast cement, 2 clinker fast cement, magnesium phosphate cement); Cement for grout; Oil well cement; Low exothermic cement (low exothermic blast furnace cement, fly ash mixed low exothermic blast furnace cement, Belite high-content cement); ultra-high-strength cement; cement-based solidified material; eco-cement (city waste incineration ash, cement produced from one or more of sewage sludge incineration ash), etc., as well as blast furnace slag, Fly ash, cinder ash, clinker assy , Husk ash, silica fume, silica powder, and a film obtained by adding a fine powder and gypsum limestone powder.

In addition to gravel, crushed stone, granulated slag, recycled aggregate, etc., aggregates such as siliceous, clay, zircon, high alumina, silicon carbide, graphite, chrome, chromic, magnesia, etc. Examples include fireproof aggregates.

In the cement composition, the unit water amount per 1 m ³ , the cement use amount, and the water / cement ratio are not particularly limited. For example, the unit water amount is 100 to 185 kg / m ³ , the cement amount used is 250 to 800 kg / m ³ , The water / cement ratio (mass ratio) is preferably 0.1 to 0.7. More preferably, the unit water amount is 120 to 175 kg / m ³ , the cement amount used is 270 to 800 kg / m ³ , and the water / cement ratio (mass ratio) = 0.15 to 0.65. As described above, the cement composition of the present invention can be used widely from poor blending to rich blending, and is effective for both high-strength concrete having a large unit cement amount and poor blending concrete having a unit cement amount of 300 kg / m ³ or less. It is. Further, the cement composition of the present invention has a relatively high water reduction rate region, that is, water / cement ratio (mass ratio) = 0.15 to 0.5 (preferably 0.15 to 0.4). Even in a low cement ratio region, it can be used satisfactorily.

In addition, the cement composition of the present invention can exhibit excellent performance even in a high water reduction rate region with high performance and has excellent workability. For example, for ready-mixed concrete and secondary concrete products (precast concrete) It can also be effectively applied to concrete, centrifugal concrete, vibration compaction concrete, steam-cured concrete, shotcrete, and the like. Also, medium-fluidity concrete (concrete with a slump value of 22-25 cm), high-fluidity concrete (concrete with a slump value of 25 cm or more and a slump flow value of 50-70 cm), self-filling concrete, self-leveling material It is also effective for mortar and concrete that require high fluidity.

In the cement composition, the blending ratio of the cement additive of the present invention is, for example, the total amount of cement mass in terms of solid content of the cement additive that is an essential component of the present invention. It is preferable to set so that it may be 0.01-1 mass% with respect to 100 mass%.

[Cement dispersant]
In addition to the cement additive of the present invention, the cement composition of the present invention preferably further contains a commonly used cement dispersant. A plurality of cement dispersants can be used in combination. The cement dispersant is not particularly limited. For example, polycarboxylic acid cement dispersant; carboxylate cement dispersant such as resin acid salt and oxycarboxylate; polyol complex; lignin sulfonate, melamine sulfonic acid Or a sulfonic acid such as a salt thereof (hereinafter referred to as an acid or a salt thereof), a formalin condensate, a creosote oil sulfonic acid (salt) formalin condensate, a naphthalene sulfonic acid (salt) formalin condensate, etc. Salt) -based cement dispersant and the like. These cement dispersants may be used alone or in combination of two or more.

Of the cement dispersants exemplified above, a polycarboxylic acid-based cement dispersant is particularly preferable because it has excellent water reduction performance and good slump retention performance. Thereby, a cement composition excellent in fluidity and excellent in strength, resistance to freezing and thawing, and the like can be obtained.

The polycarboxylic acid cement dispersant is a polymer obtained by polymerizing a monomer component containing an unsaturated carboxylic acid (salt). Examples of the polycarboxylic acid cement dispersant include, for example, a copolymer of polyethylene glycol monoallyl ether and maleic acid (salt); polyalkylene glycol (meth) allyl ether or polyalkylene glycol (meth) acrylate, and unsaturated. A copolymer formed by copolymerizing a monomer component comprising a sulfonate and a (meth) acrylate; a copolymer of (meth) acrylamide and (meth) acrylic acid (salt); a sulfonate group A copolymer obtained by copolymerizing a monomer component comprising (meth) acrylamide, (meth) acrylic acid ester, and (meth) acrylic acid (salt); polyalkylene glycol vinyl ether or polyalkylene glycol (meta ) Copolymer of allyl ether and (meth) acrylic acid (salt); polyalkylene A copolymer of glycol (meth) acrylate and (meth) acrylic acid (salt); a monomer component containing unsaturated carboxylic acid (salt) and a monomer having a polyalkylene glycol chain as essential components is polymerized. And the like.

Among the above examples, a copolymer obtained by polymerizing a monomer component containing an unsaturated carboxylic acid (salt) and a monomer having a polyalkylene glycol chain as essential components is preferable. Examples of the unsaturated carboxylic acid (salt) include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, citraconic acid, and the like, and neutralized products or partially neutralized products thereof. 1 type (s) or 2 or more types can be used. Examples of monomers having a polyalkylene glycol chain include hydroxyalkyl (meth) acrylates such as hydroxylethyl (meth) acrylate; ethylene glycol mono (meth) acrylate, polyethylene glycol / polypropylene glycol mono (meth) acrylate, etc. Polyalkylene glycol mono (meth) acrylates; alkoxypolyalkylene glycol mono (meth) acrylates such as methoxypolyethylene glycol mono (meth) acrylate and ethoxypolyethyleneglycol mono (meth) acrylate; polys such as ethylene glycol mono (meth) allyl ether Alkylene glycol mono (meth) allyl ether; alkoxypolyalkyl such as methoxypolyethylene glycol mono (meth) allyl ether A polyalkylene glycol monochloro ether such as ethylene glycol monochloro ether; an alkoxy polyalkylene glycol monochloro ether such as methoxy polyethylene glycol monochloro ether; Two or more kinds can be used. Further, these polycarboxylic acid cement dispersants may be used alone, or two or more kinds may be appropriately mixed and used.

In the cement composition, the blending ratio of the cement dispersant is preferably set to be 0.01 to 10% by mass with respect to 100% by mass of the total cement mass in terms of solid content, for example. If it is less than 0.01% by mass, the performance may not be sufficient. On the other hand, if it exceeds 10% by mass, the effect will substantially reach its peak, which may be disadvantageous in terms of economy. More preferably, it is 0.02-5 mass%, More preferably, it is 0.05-3 mass%. In the present specification, the solid content can be measured as follows.
(Solid content measurement method)
1. Weigh the aluminum dish.
The solid content to be measured is precisely weighed on the aluminum dish precisely weighed in 2.1.
3. A solid content measurement product precisely weighed in 2 is placed in a dryer adjusted to 130 ° C. in a nitrogen atmosphere for 1 hour.
4. After 1 hour, remove from the dryer and allow to cool in a desiccator at room temperature for 15 minutes.
5. After 15 minutes, remove from the desiccator and precisely weigh the aluminum dish and the measurement object.
The solid content is measured by subtracting the mass of the aluminum pan obtained in 1 from the mass obtained in 6.5 and dividing by the mass of the solid content measurement product obtained in 2.

[Other materials contained in cement composition]
Examples of the cement composition of the present invention include water-soluble polymer substances, polymer emulsions, retarders, early strengthening agents / accelerators, mineral oil-based antifoaming agents, oil-based antifoaming agents, fatty acid-based antifoaming agents, fatty acids Ester defoamer, oxyalkylene defoamer, alcohol defoamer, amide defoamer, phosphate ester defoamer, metal soap defoamer, silicone defoamer, AE agent, interface Activating agent, waterproofing agent, cracking reducing agent, expansion agent, cement wetting agent, thickening agent, separation reducing agent, flocculant, drying shrinkage reducing agent, strength enhancer, self-leveling agent, rust inhibitor, coloring agent, mold prevention 1 type, or 2 or more types, such as an agent and blast furnace slag, may be included.
The blending ratio of these materials is not particularly limited, but is preferably set so as to be 10% by mass or less with respect to 100% by mass of the solid content of the cement dispersant.

In addition, when manufacturing the cement composition of this invention, a cement additive, cement, and water may be mixed at once, and a cement additive may be added after mixing cement and water. Further, the cement dispersant may be added together with the cement additive, cement and water, or may be added separately. Other materials included in the cement composition may be added together with the cement additive, cement, water, or may be added separately.

The cement additive of the present invention contains a cross-linked product having a nonionic monomer unit as an essential constituent unit and thus has a highly water-absorbing action and can absorb a large amount of water. it can. Then, the cement additive that has absorbed water is uniformly dispersed without being unevenly distributed in the cement composition, so that the water can be uniformly dispersed in the cement composition.
As a result, since hydration of cement and water occurs uniformly in the cement composition, self-shrinkage occurs uniformly in the cement composition, and cracking of concrete and a decrease in strength are prevented.
In addition, since water is uniformly dispersed in the cement composition, the distribution of pores remaining in the concrete after the water evaporates becomes uniform, so that the strength of the concrete does not become weak at a specific part. Can be demonstrated.
Therefore, the cement composition containing the cement additive of the present invention is suitably used in the civil engineering / architectural field.

FIG. 1 is a schematic diagram showing a method for measuring self-shrinkage strain.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples. Unless otherwise specified, “%” means “% by mass” excluding the yield.
In the following examples, the measurement conditions of the water content, the weight average particle diameter, and the water absorption ratio were as follows.

<Moisture content measurement conditions>
In the cross-linked product, the ratio of the component that does not volatilize at 180 ° C. is solid content, and the relationship with the water content is {solid content = 100−water content}.
The measurement method of solid content was performed as follows.
Weigh out about 2 g of the cross-linked product (weight W4 [g]) in an aluminum cup (weight W3 [g]) with a bottom diameter of about 5 cm and let it stand in an airless dryer at 180 ° C. for 3 hours to dry. It was. The total weight (W5 [g]) of the dried aluminum cup and the crosslinked product was measured, and the solid content was determined from the following formula (1).
Solid content (% by weight) = {(W5−W3) / W4} × 100 (1)

<Weight average particle size measurement conditions>
The weight average particle diameter (D50) of the crosslinked product according to the present invention was measured according to the measuring method disclosed in European Patent No. 0349240.
That is, using a sieve corresponding to a JIS standard sieve having a mesh opening of 300 μm, 212 μm, 150 μm, 106 μm, 75 μm, 45 μm (The IIDA TESTING SIEVE: inner diameter 80 mm; JIS Z8801-1 (2000)), 10 g of the crosslinked product was classified. After classification, the weight of each sieve was measured, and the weight percentage (% by weight) having a particle diameter of less than 150 μm was calculated.
The weight average particle diameter (D50) was obtained by plotting the residual percentage R of each particle size on a logarithmic probability paper, and reading the particle diameter corresponding to R = 50% by weight as the weight average particle diameter (D50). . In addition, a weight average particle diameter (D50) means the particle diameter of the standard sieve corresponding to 50 weight% of the whole particulate water absorbing agent.

<Measurement conditions of water absorption magnification suspended under no pressure>
The measurement of FSC (water absorption magnification suspended under no pressure) was performed according to ERT440.2-02.
0.2 g of the cross-linked product was weighed, uniformly put into a non-woven bag (60 × 85 mm), heat sealed, and then adjusted to 25 ± 3 ° C. calcium nitrate tetrahydrate (0.6 wt%) + hydroxylation It was immersed in 500 mL of potassium (0.089 wt%) aqueous solution.
After 24 hours, the bag was pulled up and suspended for 10 minutes for draining. Thereafter, the mass W3 [g] of the bag was measured.
The same operation was performed without adding the cross-linked product, and the mass W4 [g] of the bag at that time was measured. FSC (absorption capacity under no pressure) was calculated according to the following formula (2).
FSC (g / g) = (W3-W4) / (mass of crosslinked product (0.2 g))-1 (2)

[Production Example 1] Cross-linked product 1
An inner diameter of 85 mm, a cylindrical plastic container (capacity: 1000 mL), 94.2 g of N-vinyl-2-pyrrolidone, 130.3 g of sodium 2-acrylamido-2-methylpropanesulfonate (50 wt% aqueous solution), methylenebisacrylamide 965 g and 174.9 g of water were added and mixed well, then immersed in a hot water bath at 60 ° C., and nitrogen gas was blown in at 2 L / min for 20 minutes to remove dissolved oxygen in the aqueous solution.
Thereafter, 2.372 g of 2,2′-azobis [2- (2-imidazolin-2-yl) propane] dihydrochloride aqueous solution of 3% by mass with respect to 100% by mass of the total monomers was added and mixed. Static polymerization was carried out.
After the polymerization exotherm passed the peak, the warm water bath was heated to 80 ° C. and allowed to stand for 30 minutes.
The obtained gel was cut into a size of about 5 mm with scissors and then dried at 115 ° C. for 2 hours.
The obtained dried product is pulverized with a roll mill, classified using a JIS standard sieve having openings of 250 μm and 45 μm, a weight average particle size of 180 μm, and a 24-hour water absorption capacity in a calcium nitrate / potassium hydroxide aqueous solution. A crosslinked product 1 having a weight of 18 g / g and a water content of 5% by weight was obtained.

[Production Example 2] Cross-linked product 2
A reactor equipped with a stirring blade, a reflux condenser, a thermometer, a nitrogen gas introduction tube, and a dropping funnel was prepared in a four-neck separable flask having a capacity of 2000 mL.
After adding 800 g of cyclohexane and 4.5 g of sucrose fatty acid ester (Daiichi Kogyo Seiyaku Co., Ltd., DK Ester (registered trademark) F-50) as a dispersant to the separable flask, put it in a hot water bath up to 75 ° C. Mixing while raising the temperature, the sucrose fatty acid ester was dissolved. Thereafter, nitrogen gas was blown at 2 L / min for 20 minutes to remove dissolved oxygen in the solution.
Separately, a sufficiently mixed polymerization monomer aqueous solution (94.9 g of N-vinyl-2-pyrrolidone, 130.3 g of sodium 2-acrylamido-2-methylpropanesulfonate (50 wt% aqueous solution), 0. 228 g and water (174.9 g) were put into a 500 ml dropping funnel, nitrogen gas was blown at 2 L / min for 20 minutes to remove dissolved oxygen in the aqueous solution, and 3% by weight of 2,2′-azobis [ 2- (2-Imidazolin-2-yl) propane] dihydrochloride 2.372 g was added and mixed uniformly. This was dropped into the cyclohexane heated to 75 ° C. and dispersed.
After completion of the dropwise addition, the polymerization reaction was completed by maintaining the liquid temperature in the separable flask at 75 ° C. for 60 minutes.
Subsequently, the hot water bath was set to 90 ° C. or higher and azeotropic dehydration was performed to a solid content of 85%, followed by filtration.
After completion of filtration, the solution was left to stand for 16 hours in a dryer at 80 ° C. Thereafter, classification was performed using JIS standard sieves having openings of 250 μm and 45 μm, the weight average particle size was 149 μm, the 24-hour water absorption in calcium nitrate / potassium hydroxide aqueous solution was 26 g / g, and the water content was 5% by weight. A crosslinked product 2 was obtained.

[Production Example 3] Cross-linked product 3
By carrying out the same method except that the amount of methylene bisacrylamide of Production Example 2 was changed to 1.755 g, the weight average particle size was 148 μm, the 24-hour water absorption in a calcium nitrate / potassium hydroxide aqueous solution was 15 g / g, and the water content was A crosslinked product 3 having a rate of 5% by weight was obtained.

[Comparative Production Example 1] Comparative crosslinked product 1
To an 85 mm inner diameter, cylindrical plastic container (capacity 1000 mL), add 39.75 g of acrylic acid, 379.07 g of 37 wt% sodium acrylate aqueous solution, 0.551 g of polyethylene glycol diacrylate (molecular weight 522), and 69.387 g of water. Then, the mixture was immersed in a hot water bath at 60 ° C., and nitrogen gas was blown in at 2 L / min for 20 minutes to remove dissolved oxygen in the aqueous solution. Thereafter, 2.372 g of a 3% by weight aqueous sodium persulfate solution was added and mixed, and then allowed to stand for polymerization. After the polymerization exotherm passed the peak, the warm water bath was heated to 80 ° C. and allowed to stand for 30 minutes. The obtained gel was cut into a size of about 5 mm with scissors and then dried at 180 ° C. for 30 minutes. The obtained dried product is pulverized by a roll mill, classified using a JIS standard sieve having openings of 850 μm and 45 μm, a weight average particle size of 429 μm, and a 24-hour water absorption capacity in a calcium nitrate / potassium hydroxide aqueous solution. A comparative crosslinked product 1 having 5 g / g and a water content of 5% by weight was obtained.

A mortar test was performed on the crosslinked products 1 to 3 and the comparative crosslinked product 1 prepared in Production Examples 1 to 3 and Comparative Production Example 1.

<Self-shrinkage strain measurement method>
(1) Mortar preparation method The mortar which added the crosslinked products 1-3 and the comparative crosslinked product 1 prepared by the manufacture examples 1-3 and the comparative manufacture example 1 as a crosslinked material, and the mortar which does not add a crosslinked material were prepared.
An example in which the crosslinked products 1 to 3 prepared in Production Examples 1 to 3 were added to Examples 1 to 3, and an example in which the comparative crosslinked product 1 prepared in the Comparative Production Example was added to Comparative Example 1, and no crosslinked product was added. Was referred to as Comparative Example 2.
The formulation without adding a cross-linked product (Mortar formulation A) and the formulation with a cross-linked product added (Mortar formulation B) were as shown in Table 1 below.

セメント：普通ポルトランドセメント（太平洋セメント社製）
水 ：イオン交換水
砂 ：ＪＩＳ Ｒ ５２０１ セメント強さ試験用標準砂（セメント協会）
ポリカルボン酸系高性能減水剤：すべての試験において、セメントに対して０．０８質量％（固形分）の減水剤を添加した。上記の水量は、本減水剤込みの重量である。
消泡剤：セメント１ｋｇあたり１％消泡剤水溶液を２０ｇ添加した。
モルタル配合Ｂにおける架橋物の添加量は、モルタルフロー値が約２００ｍｍとなるように調整した。 (Contains mortar)

Cement: Ordinary Portland cement (manufactured by Taiheiyo Cement)
Water: Ion-exchanged sand: JIS R 5201 Standard sand for cement strength test (Cement Association)
Polycarboxylic acid-based high-performance water reducing agent: In all tests, 0.08% by mass (solid content) water reducing agent was added to cement. The above water amount is the weight including the water reducing agent.
Antifoaming agent: 20 g of 1% antifoaming agent aqueous solution was added per 1 kg of cement.
The addition amount of the cross-linked product in the mortar formulation B was adjusted so that the mortar flow value was about 200 mm.

(Mortar kneading method)
The kneading was carried out at room temperature 20 ± 3 ° C. and humidity 60 ± 5%.
For kneading mortar, Hobart type mortar mixer: Model No. N-50 (trade name, manufactured by Hobart) was used. The kneading speed was all low (first speed).
The procedure of mortar kneading was as follows.
(1) After the cement is kneaded for 5 seconds (in the case of adding a cross-linked product, it was added to the cement before the actual kneading), water containing a water reducing agent and an antifoaming agent was added over 15 seconds, and further 10 seconds. Stop after kneading. In addition, the water injection end time was confirmed and used as the water injection time.
(2) Sand was thrown in for 30 seconds and kneaded again for 60 seconds.
(3) Kneading was stopped and scraped off for 20 seconds.
(4) After scraping, the mixture was kneaded again for 120 seconds and then stopped, the mortar was taken out, and the flow value and the amount of air were confirmed.

(Self-shrinkage strain measurement method)
The self-shrinkage strain was measured using a strain gauge (model: KMC-70-120-H3 (manufactured by Kyowa Denki Co., Ltd.)) and a data logger (model: UCAM-65a (manufactured by Kyowa Denshi Co., Ltd.)).
FIG. 1 is a schematic diagram showing a method for measuring self-shrinkage strain.
Five hours after the water pouring time at the time of mortar kneading was used as the starting point of the shrinkage strain measurement.
The procedure for strain measurement was as follows.
(1) It was confirmed that the flow value and air amount of the prepared mortar were predetermined values.
(2) As shown in FIG. 1, a polypropylene container (caliber × lower diameter × height = 91 × 84 × 127 mm) equipped with a strain gauge was filled with mortar in two portions from the bottom to about 100 mm. After each filling, it was struck 15 times using a steel stick (φ9 × 300 mm), and then the container was lightly tapped several times with a mallet to uniformly fill the mortar.
(3) After filling with mortar, it was covered with a polyvinylidene chloride sheet, stored at 20 ± 2 ° C., and strain values were measured at intervals of 15 to 30 minutes for about 7 days.

(Calculation of shrinkage strain)
The amount of shrinkage strain was measured by the following equation (1) using the strain values at each measurement time and the starting point (after 5 hours from the water injection).
[Shrinkage strain (× 10 ⁻⁶ )] = [Strain value at each measurement time] − [Strain value at the starting point] (1)

(Measurement of mortar flow value)
The mortar flow value was measured using a flow table, a flow cone, and a stick described in JIS R 5201 (Cement physical test method), item 11 (Flow test).
The flow value measurement procedure was as follows.
(1) A flow cone was installed at the center on the flow table.
(2) The mortar was filled up to half the height of the flow cone and pierced 10 times over the entire surface with a stick.
(3) The mortar was filled up to the upper part of the flow cone, and after piercing the entire surface 10 times with the stick as in (2), when the filling was not sufficient, the mortar was supplemented to smooth the surface.
(4) The flow cone was raised right above.
(5) After confirming that the flow of the mortar stopped, the maximum direction in which the mortar spread and the length in the direction perpendicular thereto were measured, and the average value was taken as the mortar flow value.

(Measurement of mortar air volume)
The mortar air amount was measured using a 500 ml graduated cylinder according to JIS A 1174 (unit volume mass test method of polymer cement mortar not yet solidified and test method based on mass of air amount (mass method)).

Table 2 shows the results of the mortar test and the shrinkage strain.
In Table 2, the added amount of the cross-linked product indicates the added amount (% by mass) of the cross-linked product with respect to 100% by mass of the total cement mass.
Also, the amount of air in the mortar was less than 2% in all examples.

In Examples 1 to 3 to which crosslinked products 1 to 3 were added, the shrinkage strain after 7 days was smaller in all cases than that in Comparative Example 2, and the cement additive of the present invention was effective in reducing self-shrinkage. It has been found.
Further, in Comparative Example 1 using the comparative cross-linked product 1, the water absorption ratio is low, so that it is necessary to add 1.4% by mass of the cross-linked product with respect to the total amount of cement mass of 100% by mass in order to obtain the same mortar flow. was there. Further, the obtained mortar became very hard after several minutes of kneading and lost fluidity.

Claims (10)

A cement additive containing a crosslinked product obtained by crosslinking a nonionic monomer unit as an essential constituent unit,
The nonionic monomer contains an N-vinyl lactam monomer ,
The cross-linked product includes N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, and trimethylolpropane. Di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa (meth) acrylate, triallyl cyanurate , Triallyl isocyanurate, triallyl phosphate, triallylamine, poly (meth) allyloxyalkane, divinylbenzene, divinyltoluene, divinylalkyl Polymerizing at least one crosslinkable monomer selected from the group consisting of silene, divinylnaphthalene, divinyl ether, divinyl ketone, trivinylbenzene, tolylene diisocyanate and hexamethylene diisocyanate together with an N-vinyl lactam monomer. features and to Rousset instrument additive to become Te. The cement additive according to claim 1 , wherein the crosslinked product is obtained by polymerizing a monomer component containing 30% by mass or more of the N-vinyl lactam monomer. A cement additive containing a crosslinked product obtained by crosslinking a nonionic monomer unit as an essential constituent unit,
The nonionic monomer contains a polyalkylene glycol monomer ,
The crosslinked product is obtained by polymerizing only a polyalkylene glycol monomer, or is obtained by polymerizing only a polyalkylene glycol monomer and another polymerizable monomer,
The other polymerizable monomers are: unsaturated dicarboxylic acid monomer; unsaturated sulfonic acid monomer; amide monomer; hydrophobic monomer; hydroxyl group-containing unsaturated monomer; monomer; nitrile monomer; at least Tanedea features and to Rousset instrument additive Rukoto selected from the group consisting of phosphorous monomer. The cement additive according to claim 3 , wherein the crosslinked product is obtained by polymerizing a monomer component containing 85 mass% or more of the polyalkylene glycol monomer. The cross-linked product has a water absorption capacity of 8 g / g or more after 24 hours with respect to an aqueous solution containing 0.6% by mass of calcium nitrate tetrahydrate and 0.089% by mass of potassium hydroxide. To 4. The cement additive according to any one of 1 to 4 . The cement additive according to any one of claims 1 to 5 , wherein the crosslinked product is polymerized by containing 0.25 mol% or more of a crosslinking agent with respect to 100 mol% of the monomer component. The cement additive according to any one of claims 1 to 5 , wherein the crosslinked product is polymerized by adding 0.15 mol% or less of a crosslinking agent to 100 mol% of the monomer component. The cement additive according to any one of claims 1 to 7 , which is used as a self-shrinkage reducing agent. Cement additive according to any one of claims 1 to 8, cement, and cement composition comprising water. The cement composition according to claim 9 , further comprising a cement dispersant for dispersing the cement.

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