JP7248509B2 - Cement additive, cement admixture, cement composition, molded article, and method for improving strength of molded article - Google Patents

Description

TECHNICAL FIELD The present invention relates to cement additives, cement admixtures, cement compositions, molded articles, and methods for improving the strength of molded articles.

Cement compositions such as cement paste obtained by adding water to cement, mortar obtained by mixing this with sand as a fine aggregate, and concrete obtained by mixing pebbles are used for various purposes such as structural materials, foundations, and fireproof walls. Quantity is also large. These cement compositions generate strength as molded bodies through aggregation and hardening due to hydration reaction between cement and water.

Cement additives are added to cement compositions for the purpose of improving various properties. A water absorbent resin is known as such an additive. For example, Patent Literature 1 discloses adding a water absorbent resin obtained by polymerizing a monomer component containing a sulfonic acid-based monomer to a cement composition. Addition of such a water-absorbent resin slows down the rate of evaporation of water from the cement composition in the initial stage of construction, preventing the occurrence of cracks.

In addition, in Patent Document 2, in adding a water-absorbent resin to a cement composition, it takes time to transport ready-mixed concrete before hardening from a ready-mixed concrete manufacturing factory to a construction site. In view of the problem that the resin reaches a saturated water absorption amount, a technology is disclosed in which a water-absorbing resin obtained by coating the surface of a water-absorbing resin with a slowly soluble/hydrolyzable resin is used as an additive for cement. there is

Furthermore, Patent Document 3 describes the use of a water-absorbing resin having anionic/cationic properties and a time-delayed swelling action in concrete and mortar.

JP-A-63-291840 JP-A-1-261250 Japanese Patent Publication No. 2011-525556

Strength is one of the most important properties of a molded article obtained by molding a cement composition. Strength is broadly classified into early strength and long-term strength. The early strength indicates the strength that the curing period is mainly about several days, and high early strength leads to shortening of the construction period and labor saving of construction. On the other hand, long-term strength indicates the strength after the curing period is mainly 28 days, and is directly linked to the durability of concrete, making it an indispensable performance for structures. Therefore, it is very important that the long-term strength of the molded article obtained by molding the cement composition is high.

In addition, ready-mixed concrete before hardening is transported from a factory for producing ready-mixed concrete to a construction site, pumped at a placement site, and filled in a mold. If the fluidity of the cement composition is too low or the viscosity of the cement composition is too high during pumping, it will take a long time to transport, and in the worst case, the cement composition will clog the pipes. Therefore, from the viewpoint of workability, it is preferable that the cement composition at the time of placement has low viscosity and high fluidity.

Therefore, the present invention provides an additive for concrete that has a low viscosity and high fluidity in the initial stage of addition, such as at the time of placing, and that can improve the long-term strength of molded bodies such as concrete when added. intended to

The present invention is a cement additive containing a water-absorbing resin, wherein the water-absorbing resin is obtained by polymerizing a monomer mixture containing 75 mol% or more of a nonionic monomer, and the monomer mixture is a cement additive containing 0.01 to 1 mol% of a non-hydrolyzable crosslinkable nonionic monomer and 25 mol% or more of a hydrolyzable crosslinkable nonionic monomer.

According to the cement additive of the present invention, the initial viscosity of the cement composition is less likely to change even when added. Therefore, the cement composition can be easily handled and pumped at the time of placing, improving workability. Moreover, according to the additive for cement of the present invention, the long-term strength of a molded body such as concrete after a long-term curing period (for example, after 28 days) is improved.

<Additives for cement>
A first embodiment of the present invention is a cement additive containing a water absorbent resin,
The water absorbent resin is obtained by polymerizing a monomer mixture containing 75 mol% or more of nonionic monomers,
The monomer mixture is a cement additive containing 0.01 to 1 mol% of a non-hydrolyzable crosslinkable nonionic monomer and 25 mol% or more of a hydrolyzable crosslinkable nonionic monomer. .

By using the cement additive of the present embodiment, the initial cement composition has high fluidity and low viscosity, while the long-term strength of the molded article is remarkably improved. Such an excellent effect is that the water-absorbing resin of the present invention does not exhibit high water-absorbing performance immediately after adding water (for example, up to about 2 hours), exhibits water-absorbing performance after the passage of time, and It is believed that this is later attributed to the expression of high water absorption performance.

The water absorbent resin used in the first embodiment is obtained by polymerizing a monomer mixture. The content of nonionic monomers in the monomer mixture is 75 mol % or more. Further, the monomer mixture contains 0.01 to 1 mol % of the non-hydrolyzable crosslinkable nonionic monomer and 25 mol% or more of the hydrolyzable crosslinkable nonionic monomer. That is, the monomer mixture contains two or more crosslinkable nonionic monomers, one of which is hydrolyzable and the other is non-hydrolyzable. If such a structure is deviated from, the water absorption performance begins to develop initially, for example, 5 minutes after the addition of water (see Comparative Production Examples 1 and 2 described below). However, as water is absorbed by the water-absorbing resin, the viscosity of the cement composition rises sharply, and it is necessary to significantly increase the amount of dispersant added in order to improve the fluidity of the cement composition. occur.

On the other hand, by adopting the configuration of this embodiment, the water absorption performance does not increase so much at the initial stage, for example, 5 minutes after the addition of water. In addition, even after 2 hours of addition, the rapid water absorption performance is not exhibited (see Examples below). Therefore, the amount of water absorbed by the water-absorbent resin in the cement composition is low, and the addition of a small amount of cement dispersant maintains the viscosity/fluidity of the cement composition at the initial stage of addition. Therefore, the working efficiency of the builder is improved, and the pump pressure feeding is performed smoothly. Although the detailed mechanism by which such an effect is exhibited by adopting the configuration of this embodiment is unknown, it is considered as follows. Under the alkaline environment of the cement composition, the structural unit portion of the hydrolyzable crosslinkable nonionic monomer undergoes hydrolysis. As a result, the crosslink density is reduced, the water absorption performance is improved, and the presence of structural units derived from non-hydrolyzable crosslinkable nonionic monomers can prevent the structure of the water-absorbent resin from collapsing. Conceivable.

On the other hand, the inventors have found that the long-term strength of the compact is improved by adopting the configuration of this embodiment. The water-absorbing resin of the present embodiment gently absorbs surrounding water during the period from the time of placement to the curing period in order to exhibit the water-absorbing performance gradually. This prevents moisture from escaping from the compact. In addition, since cement develops strength through a hydration reaction, when water is insufficient, sufficient reaction does not take place, and strength is not sufficiently developed as expected. By storing water in the water-absorbing resin after casting, water is supplied from the water-absorbing resin to the remaining unhydrated matter during the curing period, which improves the hydration rate of the cement and increases the strength of the concrete. be done.

For example, Patent Document 3 discloses a water absorbent resin having anionic properties. As in the present embodiment, the content of the anionic monomer is small, and the knowledge that even a polymer containing a nonionic monomer as a main component exhibits high water absorption performance constitutes a water absorbent resin. This is a very surprising fact in view of the conventional belief that the water absorption performance is exhibited by the repulsion of the anionic groups in the anionic monomer. The detailed mechanism as to why a polymer containing a nonionic monomer as a main component exhibits water absorption performance over time is unknown.

Patent Document 3 also discloses a polymer of a hydrolytically stable monomer and a hydrolyzable monomer in the presence of a cross-linking agent. Patent Document 3 describes that "only a hydrolytically stable cross-linking agent" is used as a cross-linking agent, and a hydrolyzable cross-linking agent (monomer) is not used as in the present embodiment.

The cement additive will be described in detail below.

In this specification, "X to Y" indicating a range means "X or more and Y or less".

As used herein, "acid (salt)" means "acid and/or its salt". "(Meth)acrylic" means "acrylic and/or methacrylic".

[Water absorbent resin]
As used herein, the term "water-absorbent resin" refers to a polymeric gelling polymer having a water swellability (CRC) of 5 g/g or more as defined by ERT441.2-02 and a soluble component of 50% by mass or less. It means drug. "ERT" is a European standard (substantial global standard) water absorbent resin measurement method (EDANA Recommended Test Methods) established by EDANA (European Disposables and Nonwovens Association). It is an abbreviation. In this specification, the physical properties of the water absorbent resin are measured according to the 2002 edition of ERT unless otherwise specified.

The water absorbent resin preferably has a water absorption capacity of less than 20 g/g, more preferably less than 18 g/g, and less than 15 g/g when immersed in 50 mL of an aqueous solution having a pH of 12.9 at 25°C for 2 hours. It is even more preferable to have By having such properties, the cement additive has low viscosity and high fluidity at the initial stage of addition, and is excellent in workability. It should be noted that the lower the water absorption capacity when immersed in an aqueous solution of pH 12.9 at 25° C. for 2 hours, the better.

In this specification, an aqueous solution of pH 12.9 is an aqueous solution obtained by mixing 1.72 g of CaSO ₄ .2H ₂ O, 6.96 g of Na ₂ SO ₄ , 4.76 g of K ₂ SO ₄ , 7.12 g of KOH and 979.4 g of deionized water. is. The pH 12.9 aqueous solution is a cement-simulating liquid that simulates becoming strongly alkaline when it contains cement. Therefore, the aqueous solution can mimic the behavior of the water absorbent resin when water is added to the cement composition containing the cement additive.

In addition, the water absorption capacity of the water-absorbing resin when immersed in an aqueous solution of pH 12.9 at 25° C. for 1 day is preferably 10 g/g or more, more preferably 15 g/g or more, from the viewpoint of improving long-term strength. is more preferable, and 20 g/g or more is even more preferable. It should be noted that the higher the water absorption ratio when immersed in an aqueous solution of pH 12.9 at 25° C. for 1 day, the better, and the upper limit is not particularly limited, but it is usually 50 g / g or less, and 45 g / g. The following are preferable.

The water-absorbent resin is preferably powder, and the shape of the powder may be spherical, aggregates thereof, or amorphous (crushed) obtained by pulverizing a hydrous gel or a dry polymer. It is preferably amorphous (pulverized).

The particle size distribution of the water absorbent resin (powder) is preferably in the range of 45 to 850 μm, more preferably in the range of 100 to 850 μm, more preferably in the range of 100 to 850 μm. Even more preferably in the range of ~850 μm. By increasing the average particle size of the water absorbent resin (powder), it is believed that the sustained release of water is enhanced and the long-term strength is further improved.

The mass average particle diameter (D50) of the water absorbent resin (powder) can be measured by a method similar to "Average Particle Diameter and Distribution of Particle Diameter" disclosed in EP 0349240. That is, using a JIS standard sieve (JIS Z8801-1 (2000)) having openings of 850 μm, 710 μm, 600 μm, 500 μm, 420 μm, 300 μm, 212 μm, 150 μm, 106 μm, and 45 μm or a corresponding sieve, 10 g of the particulate water absorbing agent are classified, and the mass of the water-absorbing resin remaining on each sieve and the mass of the water-absorbing resin that has passed through all the sieves are measured. Classification is performed for 5 minutes with a vibration classifier (IIDA SIEVE SHAKER, TYPE: ES-65, SER. No. 0501), and the residual percentage R is plotted on logarithmic probability paper. Then, the particle diameter corresponding to R=50% by mass can be used as the read average particle diameter as the mass average particle diameter (D50).

The amount of residual monomers in the water absorbent resin is preferably 1000 mass ppm or less, more preferably 500 mass ppm or less, and more preferably 400 mass ppm or less. When the amount of residual monomers is equal to or less than the above upper limit, the cement composition is highly safe. The amount of residual monomers is preferably as small as possible, but is usually 5 ppm by mass or more.

A conventionally known method can be used as a method for reducing the amount of residual monomers, and for example, a method such as adding a reducing substance after polymerization can be used. Here, the amount of residual monomer means the amount of monomer remaining in the water absorbent resin. Examples of reducing substances include inorganic reducing agents such as phosphorus reducing agents and sulfur reducing agents (especially oxygen-containing sulfur reducing agents); and organic reducing agents such as ascorbic acid.

According to ERT410.2-02, 1.0 g of a water-absorbent resin is added to 200 ml of a 0.9 wt% sodium chloride aqueous solution, and the amount of dissolved monomers after stirring for 1 hour at 500 rpm ( Unit: mass ppm) is measured using HPLC (high performance liquid chromatography).

The monomer mixture refers to all polymerizable monomers that form the polymer that is the main component of the water absorbent resin, and the total amount of the monomers that form the polymer is 100 mol %. The monomer mixture contains at least 75 mol % or more of nonionic monomers. Nonionic monomers are distinguished between non-crosslinking nonionic monomers and crosslinkable nonionic monomers. A crosslinkable nonionic monomer is, for example, a monomer having two or more unsaturated double bonds and serving to crosslink main chains. On the other hand, a non-crosslinkable nonionic monomer refers to a monomer having one unsaturated double bond.

Furthermore, crosslinkable nonionic monomers are distinguished between non-hydrolyzable crosslinkable nonionic monomers and hydrolyzable crosslinkable nonionic monomers.

In other words, the water absorbent resin contains 75 mol% or more of structural units derived from nonionic monomers, and 0.01 to 1 mol% of structural units derived from non-hydrolyzable crosslinkable nonionic monomers and water It contains 25 mol % or more of structural units derived from a degradable crosslinkable nonionic monomer. In addition, structural units derived from nonionic monomers, structural units derived from non-hydrolyzable crosslinkable nonionic monomers, and structural units derived from hydrolyzable crosslinkable nonionic monomers are It can be considered that the molar ratio coincides with that at the time of preparation.

(Crosslinkable nonionic monomer)
A crosslinkable nonionic monomer is a monomer having two or more polymerizable unsaturated groups. A crosslinked structure (crosslinked body) is formed by the crosslinkable nonionic monomer, and water absorption at the initial stage of addition can be suppressed.

The crosslinkable nonionic monomer is preferably water-soluble, since it can further exhibit the effects of the present invention. Hereinafter, the water-soluble crosslinkable nonionic monomer is also referred to as a water-soluble crosslinkable nonionic monomer. Here, "water-soluble" in the water-soluble crosslinkable nonionic monomer refers to a monomer that dissolves in 5 g or more in 100 g of water at 25°C. The water-soluble crosslinkable nonionic monomer preferably dissolves in an amount of 10 g or more, more preferably in an amount of 50 g or more, even more preferably in an amount of 100 g or more, in 100 g of water.

In the present embodiment, as the crosslinkable nonionic monomer, a hydrolyzable monomer (hydrolyzable crosslinkable nonionic monomer, hereinafter simply referred to as a hydrolyzable monomer) and a non-hydrolyzed Two kinds of monomers (non-hydrolyzable crosslinkable nonionic monomers, hereinafter simply referred to as non-hydrolyzable monomers) are used.

Here, the term "hydrolyzable" means that 80% or more of the monomer is decomposed when the monomer is immersed in an aqueous solution of pH 12.9 (25°C) for one day. Decomposition can be measured by analysis using techniques such as LC (liquid chromatography) and GC (gas chromatography).

The non-hydrolyzable monomer is not particularly limited as long as it is a compound having two or more polymerizable unsaturated groups. Meta) acrylamide-based monomers, polyfunctional vinyl ethers such as ethylene glycol divinyl ether, diethylene glycol divinyl ether, polyethylene glycol divinyl ether, propylene glycol divinyl ether, butylene glycol divinyl ether, hexanediol divinyl ether, polyfunctional aromatics such as divinylbenzene group vinyls. These can be used alone or in combination of two or more.

Among them, the non-hydrolyzable monomer preferably contains N,N'-methylenebisacrylamide. Furthermore, the non-hydrolyzable monomer may be only a (meth)acrylamide-based monomer, or only N,N'-methylenebis(meth)acrylamide.

The content of the non-hydrolyzable monomer in the monomer mixture is 0.01-1 mol %. When the content of the non-hydrolyzable monomer is in such a range, it is possible to maintain the crosslinked structure in the water absorbent resin even in an alkaline environment after the addition of cement. The hydrate can be gradually watered. Therefore, long-term strength is improved. Since the effect of the present invention is further exhibited, the content of the non-hydrolyzable monomer in the monomer mixture is more preferably 0.05 to 0.5 mol%, and more preferably 0.1 to More preferably, it is 0.3 mol %.

The hydrolyzable monomer is not particularly limited as long as it is a compound having two or more polymerizable unsaturated groups. Examples include (poly)ethylene glycol di(meth)acrylate, (poly) Polyfunctional (meth)acrylates such as propylene glycol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, ethylene oxide-modified trimethylolpropane tri(meth)acrylate, pentaerythritol hexa(meth)acrylate; triallyl cyanurate, cyanuric acid such as triallyl isocyanurate or allyl ester of isocyanuric acid; These can be used alone or in combination of two or more. Among them, the hydrolyzable monomer preferably has an ester bond, more preferably a polyfunctional (meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol It is more preferably di(meth)acrylate, even more preferably (poly)ethylene glycol di(meth)acrylate, particularly preferably polyethylene glycol di(meth)acrylate, and polyethylene glycol diacrylate. is most preferred.

The content of the hydrolyzable monomer in the monomer mixture is 25 mol % or more. When the content of the hydrolyzable monomer is within such a range, the crosslink density is high in the initial stage of the alkaline environment after the addition of cement, so water absorption is suppressed. On the other hand, the hydrolyzable portion (eg, ester bond) of the hydrolyzable monomer is hydrolyzed over time, and the crosslink density becomes smaller, so that the water absorption performance is exhibited. Therefore, long-term strength is improved. The content of the hydrolyzable monomer in the monomer mixture is more preferably 45 mol % or more because the effects of the present invention are exhibited more effectively. The hydrolyzable monomer is preferably 25 to 99.9 mol%, more preferably 45 to 99.9 mol%, even more preferably 45 to 80 mol%, 45 to 60 mol % is particularly preferred.

A non-crosslinking monomer (non-crosslinking nonionic monomer) may be used as the nonionic monomer. A non-crosslinkable nonionic monomer refers to a monomer having one unsaturated double bond.

The non-crosslinkable nonionic monomer is preferably water-soluble, since it can further exhibit the effects of the present invention. Hereinafter, the water-soluble non-crosslinking nonionic monomer is also referred to as a water-soluble non-crosslinking nonionic monomer. Here, "water-soluble" in the water-soluble non-crosslinking nonionic monomer refers to dissolving 5 g or more in 100 g of water at 25°C. The water-soluble non-crosslinking nonionic monomer preferably dissolves in an amount of 10 g or more, more preferably 50 g or more, and even more preferably 100 g or more in 100 g of water.

The non-crosslinkable nonionic monomer is not particularly limited as long as it has one unsaturated double bond. Non-crosslinking nonionic monomers preferably exclude N-vinyl acylamides. Specific examples of non-crosslinking nonionic monomers include (meth)acrylamide, N-monomethyl(meth)acrylamide, N-monoethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide and the like (meth) ) acrylamide-based monomers; N-vinyllactam-based monomers such as N-vinylpyrrolidone; hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, hydroxybutyl (meth)acrylate, (meth)acryl Hydroxy(meth)acrylates such as hydroxypentyl acid; Unsaturated amines such as N-(2-dimethylaminoethyl)(meth)acrylamide, vinylpyridine and vinylimidazole; Vinyl cyanide monomers such as acrylonitrile and methacrylonitrile an unsaturated polyalkylene glycol alkenyl ether-based monomer represented by the following general formula (1);

(In general formula (1), R ¹ , R ² and R ³ each independently represent a hydrogen atom or a methyl group, and R ⁴ represents a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms. wherein R ^a O represents an oxyalkylene group having 2 to 18 carbon atoms, n represents the average number of added moles of the oxyalkylene group represented by R ^a O, and n is a number from 1 to 500. , x is an integer of 0 to 2, and y is 0 or 1.) and the like. These can be used alone or in combination of two or more.

In addition, since the water absorption performance after the passage of time is excellent, the non-crosslinkable nonionic monomer preferably contains a (meth) acrylamide-based monomer and/or a hydroxy (meth) acrylate, and (meth) It more preferably contains an acrylamide-based monomer, even more preferably contains (meth)acrylamide, and particularly preferably contains acrylamide. Furthermore, the non-crosslinking nonionic monomer may be only (meth)acrylamide, or may be only acrylamide.

The content of the non-crosslinking nonionic monomer in the monomer mixture is preferably 10 mol % or more. When the content of the non-crosslinking nonionic monomer is 10 mol% or more, the molded product is more excellent in long-term strength because it easily exhibits water absorption performance over time in an alkaline environment after cement is added. becomes. In the monomer mixture, the content of the non-crosslinking nonionic monomer is preferably 10 to 60 mol%, more preferably 25 to 50 mol%, 35 mol% or more and less than 50 mol% is even more preferred. As for the content of each monomer in the monomer mixture, the value obtained to the second decimal place is adopted.

In this embodiment, in addition to nonionic monomers, anionic monomers and/or cationic monomers may be included. An anionic monomer refers to a monomer having an anionic functional group or a salt group thereof in the monomer. The anionic functional group means a functional group that dissociates a counterion to become an anion (anionized). A cationic monomer refers to a monomer having a cationic functional group or a salt group thereof in the monomer. A cationic functional group means a functional group that dissociates a counter ion to become a cation (cationized).

In the present embodiment, the content of the anionic monomer and the cationic monomer in the monomer mixture is preferably 25 mol% or less, preferably 10 mol% or less, 5 mol% or less, 4 mol% or less, 3 mol% or less, 2 mol% or less, 1 mol% or less, 0.5 mol% or less, 0 mol% (i.e., not including anionic and cationic monomers) is most preferred.

A preferred embodiment of the present invention is that the water absorbent resin does not contain ionic monomers (anionic monomers and cationic monomers), that is, the water absorbent resin contains non-crosslinkable nonionic monomers and It is a form obtained by polymerizing a monomer mixture consisting only of crosslinkable nonionic monomers.

(Method for producing water absorbent resin)
The method for producing the water absorbent resin is not particularly limited, and it can be produced by a conventionally known method. Examples of the polymerization method for obtaining the water-absorbent resin include spray polymerization, droplet polymerization, bulk polymerization, precipitation polymerization, aqueous solution polymerization, reversed-phase suspension polymerization, and the like. I will list the manufacturing method used.

(1) Step of preparing a monomer mixture aqueous solution This step is a step of dissolving each monomer constituting the polymer in water as a solvent to prepare a monomer mixture aqueous solution.

Each monomer may be added all at once, or may be added in order. Here, the aqueous solution is a concept including an aqueous dispersion. If necessary, the aqueous monomer mixture solution may contain components constituting additives for cement such as trace components (chelating agents, surfactants, dispersants, etc.).

The "aqueous solution" in the monomer mixture aqueous solution is not limited to water in 100% by mass of the solvent, and a water-soluble organic solvent (e.g., alcohol, etc.) of 0 to 30% by mass, preferably 0 to 5% by mass. and these are treated as aqueous solutions in the present invention.

(2) Aqueous polymerization step Aqueous polymerization is a method of polymerizing an aqueous monomer solution without using a dispersion solvent. Disclosed in No. 4985518, No. 5124416, No. 5250640, No. 5264495, No. 5145906, No. 5380808, EP No. 0811636, No. 0955086, No. 0922717, etc. there is

The concentration of the aqueous monomer solution during the polymerization is not particularly limited, but is preferably from 20% by mass to a saturated concentration or less, more preferably from 25 to 80% by mass, and even more preferably from 30 to 70% by mass. A decrease in productivity can be suppressed when the concentration is 20% by mass or more. It should be noted that the polymerization in slurry (aqueous dispersion) of the monomers is found to lower the physical properties, so it is preferable to carry out the polymerization at a concentration below the saturation concentration.

In the polymerization step, a polymerization initiator is added to the aqueous monomer mixture solution obtained above.

The polymerization initiator to be used is appropriately determined depending on the form of polymerization, and is not particularly limited. Polymerization is initiated by these polymerization initiators.

Examples of the photolytic polymerization initiator include benzoin derivatives, benzyl derivatives, acetophenone derivatives, benzophenone derivatives, and azo compounds. Specifically, benzoin, benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether, α-methylbenzoin, α-phenylbenzoin, anthraquinone, methylanthraquinone, acetophenone, 2,2-diethoxyacetophenone, 2,2-dimethoxy-2 -phenylacetone, benzyldiacetylacetophenone, benzophenone, p-chlorobenzophenone, 2-hydroxy-2-methylpropiophenone, diphenyldisulfide, tetramethylthiuram sulfide, α-chloromethylnaphthalene, anthracene, hexachlorobutadiene, pentachlorobutadiene, Michler's ketone , 2-chlorothioxanthone, 2,4-diethylthioxanthone, benzyl dimethyl ketal, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2-methyl-1-[4-(methylthio)phenyl]-2 -morpholinopropanone-1,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propane -1-on and so on. Such photodegradable polymerization initiators may be commercially available products such as Irgacure (registered trademark) 184 (hydroxycyclohexyl-phenylketone), Irgacure (registered trademark) 2959 (1-[4-(2-hydroxy ethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one) and the like.

Examples of the thermal decomposition type polymerization initiator include persulfates such as sodium persulfate, potassium persulfate and ammonium persulfate; peroxides such as hydrogen peroxide, t-butyl peroxide and methyl ethyl ketone peroxide; , 2'-azobis(2-amidinopropane) dihydrochloride and 2,2'-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride.

Furthermore, examples of the redox polymerization initiator include a system in which the persulfate or peroxide is used in combination with a reducing compound such as L-ascorbic acid or sodium hydrogen sulfite.

Moreover, you may use together the said photodegradation-type polymerization initiator and the thermal decomposition-type polymerization initiator. Furthermore, active energy rays such as ultraviolet rays, electron beams and γ rays may be used alone or in combination with the polymerization initiator.

The amount of the polymerization initiator used is preferably 0.0001 to 1 mol %, more preferably 0.0005 to 0.5 mol %, relative to the monomer.

The polymerization step can be carried out under normal pressure, reduced pressure or increased pressure, preferably under normal pressure (or its vicinity, usually ±10 mmHg). The temperature at the start of polymerization is preferably 15 to 130°C, more preferably 20 to 120°C, although it depends on the type of polymerization initiator used.

Thus, a gel-like crosslinked polymer is obtained.

(3) Gel pulverization step In this step, the gel-like crosslinked polymer (hereinafter referred to as "water-containing gel") obtained through the above-mentioned polymerization step (especially aqueous solution polymerization) is gel-pulverized to form a particulate water-containing gel ( hereinafter referred to as "particulate hydrous gel").

The gel crusher that can be used is not particularly limited, but for example, a gel crusher equipped with a plurality of rotating stirring blades such as a batch or continuous double-arm kneader, a single-screw extruder, a twin-screw extruder, and a meat chopper. etc. Among them, a screw type extruder having a perforated plate at its tip is preferable, and examples thereof include the screw type extruder disclosed in JP-A-2000-063527.

(4) Drying step This step is a step of drying the hydrous gel obtained through the polymerization step and the like to obtain a dry polymer. When the polymerization step is aqueous solution polymerization, gel pulverization (fine granulation) is performed before and/or after drying the water-containing gel. Moreover, the dried polymer (aggregate) obtained in the drying step may be directly supplied to the pulverization step.

The drying method is not particularly limited, and various methods can be adopted. Specific examples include heat drying, hot air drying, reduced pressure drying, infrared drying, microwave drying, azeotropic dehydration drying with a hydrophobic organic solvent, and high humidity drying using high temperature water vapor. Or 2 types can also be used together. The drying temperature is preferably 100-300°C, more preferably 120-250°C. The drying time depends on the surface area and water content of the hydrous gel, the type of dryer, and the like, but is preferably 1 minute to 5 hours, for example.

(5) Pulverization/classification step In this step, the dried polymer obtained in the drying step is pulverized and/or classified, preferably to obtain a water absorbent resin having a specific particle size. It differs from the above (3) gel pulverization step in that the object to be pulverized has undergone a drying step. Moreover, the water-absorbing resin after the pulverization process may be called pulverized material.

Particle size control can be performed in the polymerization process, the gel pulverization process, or the pulverization/classification process in the drying process, but it is particularly preferably performed in the classification process after drying.

[Other ingredients]
Additives for cement contain a water absorbent resin as a main component. Here, the main component refers to 80% by mass or more of the cement additive, preferably 90% by mass or more, more preferably 95% by mass or more, and most preferably 98% by mass or more (the upper limit is 100% by mass, that is, a cement additive consisting only of a water-absorbing resin). In addition, the water absorbent resin as used in the present invention also includes a water absorbent resin obtained by chemically modifying the obtained polymer (such as surface modification). Preferably, the additive for cement is a water-absorbing resin composed only of a polymer obtained by polymerizing the above monomer mixture.

Additives for cement, in addition to the absorbent resin, for the purpose of stabilizing the water-absorbent resin, surfactants, anti-coloring agents, reducing agents, etc., each in an amount of 0 to 10% by mass, preferably 0.1 to 0.1%. You may contain 1 mass %.

<Cement admixture>
A second embodiment of the present invention is a cement admixture comprising the cement additive of the first embodiment and a cement dispersant. By using both in combination, when added to the cement composition, the dispersibility of the cement is ensured even in a region where the amount of the cement dispersant added is small, and the viscosity of the cement composition is maintained low. , the long-term strength of the compact is improved.

Conventionally known cement dispersants can be used as the cement dispersant. Cement dispersants include, for example, polyalkylarylsulfonate systems such as naphthalenesulfonic acid formaldehyde condensates; melamine formalin resin sulfonate systems such as melamine sulfonic acid formaldehyde condensates; aminoarylsulfonic acid-phenol-formaldehyde condensates. Aromatic aminosulfonate system such as; ligninsulfonate system such as ligninsulfonate and modified ligninsulfonate; various sulfonic acid dispersants having sulfonic acid groups in the molecule such as polystyrenesulfonate; JP-B-59-18338, polyalkylene glycol mono (meth) acrylic acid ester-based monomers, (meth) acrylic acid-based monomers such as those described in JP-A-7-223852, and these Copolymers obtained from monomers and copolymerizable monomers; A (poly)oxyalkylene group in the molecule of a copolymer obtained from an unsaturated (poly)alkylene glycol ether-based monomer, a maleic acid-based monomer, or a (meth)acrylic acid-based monomer as described and various polycarboxylic acid-based dispersants having a carboxyl group; (alkoxy) polyalkylene glycol mono (meth) acrylate, phosphoric acid monoester monomer, and phosphoric acid as described in JP-A-2006-52381 Various phosphoric acid-based dispersants having (poly)oxyalkylene groups and phosphoric acid groups in the molecule such as copolymers obtained from diester-based monomers, phosphoric acid-based dispersants described in Japanese Patent Application Publication No. 2008-517080 agents and the like. Among them, as the cement dispersant, it is preferable to use a polycarboxylic acid-based dispersant, since the effect of the present invention is exhibited more. Only one type of cement dispersant may be used, or two or more types may be used.

The mass ratio of the cement dispersant in the cement admixture to the cement additive is preferably 1:0.1-10, more preferably 1:0.5-5.

<Cement composition>
A third embodiment of the invention is a cement composition comprising the cement additive of the first embodiment and cement.

Another embodiment of the present invention is a cement composition containing a water absorbent resin and cement, wherein the water absorbent resin polymerizes a monomer mixture containing 75 mol% or more of a nonionic monomer. and the monomer mixture contains 0.01 to 1 mol% of a non-hydrolyzable crosslinkable nonionic monomer and 25 mol% or more of a hydrolyzable crosslinkable nonionic monomer, in a cement composition be.

Any appropriate content can be adopted as the content of the cement additive (or water-absorbing resin) in the cement composition, depending on the purpose. As such a content ratio, when used in mortar or concrete using hydraulic cement, the content ratio of the cement additive (or water absorbent resin) to 100 parts by mass of cement is preferably 0.01 to It is 10 parts by mass, more preferably 0.02 to 5 parts by mass, still more preferably 0.05 to 3 parts by mass. By setting such a content ratio, various favorable effects such as low viscosity, high fluidity, and increased strength are brought about.

The cement composition preferably contains water. The cement composition preferably contains aggregate.

Any appropriate cement can be adopted as the cement. Such cements include, for example, Portland cement (ordinary, early strength, ultra-early strength, moderate heat, sulfate-resistant and low alkaline forms thereof), various mixed cements (blast furnace cement, silica cement, fly ash cement), White Portland cement, alumina cement, ultra fast hardening cement (1 clinker fast hardening cement, 2 clinker fast hardening cement, magnesium phosphate cement), grouting cement, oil well cement, low heat cement (low heat blast furnace cement, low fly ash mixture) exothermic blast-furnace cement, belite-rich cement), ultra-high-strength cement, cement-based solidifying material, eco-cement (cement manufactured from one or more of municipal waste incineration ash and sewage sludge incineration ash), and the like. Furthermore, fine powders such as blast furnace slag, fly ash, cinder ash, clinker ash, husk ash, silica powder, limestone powder, and gypsum may be added to the cement composition. The cement contained in the cement composition of the present invention may be of one kind or may be of two or more kinds.

In the cement composition, any appropriate values can be set for the unit water amount per 1 m ³ of the cement composition, the amount of cement used, and the water/cement ratio. As such values, the unit water amount is preferably 100 kg/m ³ to 185 kg/m ³ , the cement amount used is preferably 250 kg/m ³ to 800 kg/m ³ , and the water/cement ratio (mass ratio) = 0.1 to 0.7, more preferably, the unit water amount is 120 kg/m ³ to 180 kg/m ³ , the cement amount used is 270 kg/m ³ to 800 kg/m ³ , and the water/cement ratio ( mass ratio) = 0.12 to 0.65.

Any appropriate aggregate such as fine aggregate (such as sand) and coarse aggregate (such as crushed stone) can be used as the aggregate. Examples of such aggregate include sand (land sand, etc.), crushed stone, water granulated slag, and recycled aggregate. Examples of such aggregates include refractory aggregates such as silicatic, clay, zircon, high alumina, silicon carbide, graphite, chromium, chromamag, and magnesia.

The cement composition preferably contains a cement dispersant. That is, a preferred embodiment of the present invention is a cement composition comprising the cement additive of the first embodiment, cement, and a cement dispersant. Cement dispersants are the same as those described in the section of the second embodiment.

The mass ratio of the cement dispersant to the cement additive in the cement composition is preferably 1:0.1-10, more preferably 1:0.5-5. The content ratio of the cement dispersant in the cement composition may be any appropriate content ratio depending on the purpose.

The cement composition can contain any other appropriate cement additive within a range that does not impair the effects of the present invention. Such other cement additives include, for example, other cement additives exemplified in (1) to (12) below. (1) Water-soluble polymer substances: nonionic cellulose ethers such as methyl cellulose, ethyl cellulose, carboxymethyl cellulose; polysaccharides produced by microbial fermentation such as yeast glucan, xanthan gum, β-1,3 glucans; polyacrylamide, etc. . (2) Polymer emulsions: copolymers of various vinyl monomers such as alkyl (meth)acrylates. (3) Hardening retardant: oxycarboxylic acids such as gluconic acid, glucoheptonic acid, arabonic acid, malic acid, citric acid, or salts thereof; Saccharides; Disaccharides such as maltose, sucrose and lactose; Trisaccharides such as raffinose; - sugars or sugar alcohols such as threitol, L-threitol, D-iditol, D-glycidol, D-erythro-D-galacto-octitol; polyhydric alcohols such as glycerin; phosphonic acids such as aminotri(methylenephosphonic acid); Derivatives thereof and the like. (4) early strengthening agent/accelerator: soluble calcium salts such as calcium chloride, calcium nitrite, calcium nitrate, calcium bromide and calcium iodide; chlorides such as iron chloride and magnesium chloride; sulfate; potassium hydroxide; carbonates; thiosulfates; formic acid and formates such as calcium formate; alkanolamines; alumina cements; calcium aluminate silicates and the like. (5) Oxyalkylene antifoaming agents: polyoxyalkylene alkyl ethers such as diethylene glycol heptyl ether; polyoxyalkylene acetylene ethers; (poly)oxyalkylene fatty acid esters; polyoxyalkylene sorbitan fatty acid esters; (Aryl) ether sulfate ester salts; polyoxyalkylene alkyl phosphate esters; polyoxypropylene polyoxyethylene laurylamine (propylene oxide 1 to 20 mol adduct, ethylene oxide 1 to 20 mol adduct, etc.), alkylene oxide added polyoxyalkylenealkylamines such as amines derived from fatty acids obtained from cured beef tallow (1 to 20 mol of propylene oxide, 1 to 20 mol of ethylene oxide, etc.); polyoxyalkyleneamides; (6) Antifoaming agent other than oxyalkylene type: Mineral oil type, oil type, fatty acid type, fatty acid ester type, alcohol type, amide type, phosphate ester type, metal soap type, silicone type antifoaming agent. (7) AE agent: resin soap, saturated or unsaturated fatty acid, sodium hydroxystearate, lauryl sulfate, ABS (alkylbenzenesulfonic acid), alkanesulfonate, polyoxyethylene alkyl (phenyl) ether, polyoxyethylene alkyl (phenyl) ether Sulfuric acid esters or salts thereof, polyoxyethylene alkyl (phenyl) ether phosphates or salts thereof, protein materials, alkenylsulfosuccinic acid, α-olefin sulfonates and the like. (8) Other surfactants: various anionic surfactants; various cationic surfactants such as alkyltrimethylammonium chloride; various nonionic surfactants; various amphoteric surfactants. (9) Waterproof agents: fatty acids (salts), fatty acid esters, fats and oils, silicon, paraffin, asphalt, wax and the like. (10) Rust preventives: nitrites, phosphates, zinc oxide and the like. (11) Crack reducing agents: polyoxyalkyl ethers and the like. (12) Expansive material; ettringite-based, coal-based, etc.;

Other known cement additives include cement wetting agents, thickeners, segregation reducing agents, flocculants, drying shrinkage reducing agents, strength enhancers, self-leveling agents, rust inhibitors, colorants, antifungal agents, and the like. can be mentioned. These known cement additives (materials) may be used alone or in combination of two or more. In addition, other cement additives are blended into the cement composition in appropriate amounts in consideration of the purpose of addition.

The cement composition can be useful for ready-mixed concrete, concrete for secondary concrete products, centrifugal molding concrete, vibration compaction concrete, steam cured concrete, shotcrete, and the like. Cement compositions include medium-flow concrete (concrete with a slump value of 22 to 25 cm), high-flow concrete (concrete with a slump value of 25 cm or more and a slump flow value of 50 to 70 cm), self-compacting concrete, self-leveling materials, etc. It can also be effective for mortar and concrete that require high fluidity.

The cement composition may be prepared by blending the components in any suitable manner. For example, a method of kneading the constituent components in a mixer can be used.

<Molded body>
A fourth embodiment of the present invention is a molded article obtained by molding the cement composition of the third embodiment.

Formation of the molded body is carried out by a conventionally known method without any particular limitation. As a molding method, for example, a method of pouring the cement composition into the mold, curing the whole mold, and then demolding, or pouring the cement composition into the mold and then demolding the molded product from the mold. and the like.

The curing method is not particularly limited, and any of underwater curing, sealing curing, and air curing may be used. Moreover, you may cure by applying a curing agent.

The molded article of the fourth embodiment can be used for various purposes because it can be used for a long period of time. Specific examples include structures such as buildings; concrete structures such as columns, piles, and gutters.

<Method for improving strength of compact>
A fifth embodiment of the present invention is a method for improving the strength of a molded body obtained by molding a cement composition containing cement, comprising adding the cement additive of the first embodiment to the cement composition. This is a method for improving the strength of a compact.

The strength of the molded body may exceed 100%, preferably 105% or more, and more preferably 110% or more, compared to the strength of the molded body before adding the cement additive. For the strength of the molded body, the value measured by the method described in Examples below is adopted.

The effects of the present invention will be described using the following examples and comparative examples. Although "parts" or "%" may be used in the examples, "parts by mass" or "% by mass" are indicated unless otherwise specified. Moreover, unless otherwise specified, each operation is performed at room temperature (25° C.) and normal pressure.

[Production Example 1]
A 1000 ml cylindrical separable flask was charged with 3.7 g of acrylamide, 26.27 g of diacrylate of polyethylene glycol (to which 9 mol of ethylene oxide was added) (hereinafter abbreviated as PEG9DA), 0.0241 g of N,N-methylenebisacrylamide and 60 g of water. 93 g was charged and uniformly dissolved. Here, in the monomer mixture consisting of acrylamide, PEG9DA and N,N-methylenebisacrylamide, 49.9 mol% acrylamide, 49.9 mol% PEG9DA, and 0.15 mol% N,N-methylenebisacrylamide. After replacing the inside of the flask with nitrogen, the flask was heated to 45° C. on a hot water bath, 4.656 g of a 1% sodium persulfate aqueous solution and 4.464 g of a 0.1% L-ascorbic acid aqueous solution were added, and the stirring was stopped to polymerize. let me Heat was generated after the polymerization started, and the temperature rose to 80°C after 10 minutes. When the liquid temperature stopped rising, the bath temperature was raised to 80° C., and aging was carried out for 30 minutes. The resulting gel-like polymer (water-containing gel) was finely divided using a cutter, dried with hot air at 130° C. for 3 hours, pulverized with a mixer, and sieved using JIS standard sieves with openings of 500 μm and 250 μm. Then, it passed through a sieve with an opening of 500 μm, and the powdery water absorbent resin remaining on the sieve with an opening of 250 μm was collected. 90% by mass or more of the powdery water-absorbing resin was in the range of 45 to 850 μm. This powdery water absorbent resin was used as an additive for cement.

[Production Example 2]
A 1000 ml cylindrical separable flask was charged with 1.71 g of acrylamide, 28.27 g of diacrylate of polyethylene glycol (with 9 mol of ethylene oxide added) (hereinafter abbreviated as PEG9DA), 0.0185 g of N,N-methylenebisacrylamide and 62 g of water. 1 g was prepared and uniformly dissolved. Here, in the monomer mixture consisting of acrylamide, PEG9DA and N,N-methylenebisacrylamide, 30.0 mol% acrylamide, 69.9 mol% PEG9DA, and 0.15 mol% N,N-methylenebisacrylamide. After replacing the inside of the flask with nitrogen, the flask was heated to 45° C. on a hot water bath, 4.056 g of a 1% sodium persulfate aqueous solution and 3.888 g of a 0.1% L-ascorbic acid aqueous solution were added, stirring was stopped, and polymerization was performed. let me Heat was generated after the polymerization started, and the temperature rose to 80°C after 10 minutes. When the liquid temperature stopped rising, the bath temperature was raised to 80° C., and aging was carried out for 30 minutes. The resulting gel-like polymer (water-containing gel) was finely divided using a cutter, dried with hot air at 130° C. for 3 hours, pulverized with a mixer, and sieved using JIS standard sieves with openings of 500 μm and 250 μm. Then, it passed through a sieve with an opening of 500 μm, and the powdery water absorbent resin remaining on the sieve with an opening of 250 μm was collected. 90% by mass or more of the powdery water-absorbing resin was in the range of 45 to 850 μm. This powdery water absorbent resin was used as an additive for cement.

[Production Example 3]
A 1000 ml cylindrical separable flask was charged with 29.99 g of diacrylate (hereinafter abbreviated as PEG9DA) of polyethylene glycol (with 9 mol of ethylene oxide added), 0.0138 g of N,N-methylenebisacrylamide and 63.1 g of water. was dissolved in Here, 99.9 mol % of PEG9DA and 0.15 mol % of N,N-methylenebisacrylamide in the monomer mixture consisting of PEG9DA and N,N-methylenebisacrylamide. After replacing the inside of the flask with nitrogen, the flask was heated to 45° C. on a hot water bath, 3.542 g of a 1% sodium persulfate aqueous solution and 3.396 g of a 0.1% L-ascorbic acid aqueous solution were added, stirring was stopped, and polymerization was performed. let me Heat was generated after the polymerization started, and the temperature rose to 80°C after 10 minutes. When the liquid temperature stopped rising, the bath temperature was raised to 80° C., and aging was carried out for 30 minutes. The resulting gel-like polymer (water-containing gel) was finely divided using a cutter, dried with hot air at 130° C. for 3 hours, pulverized with a mixer, and sieved using JIS standard sieves with openings of 500 μm and 250 μm. Then, it passed through a sieve with an opening of 500 μm, and the powdery water absorbent resin remaining on the sieve with an opening of 250 μm was collected. 90% by mass or more of the powdery water-absorbing resin was in the range of 45 to 850 μm. This powdery water absorbent resin was used as an additive for cement.

[Comparative Production Example 1]
A 1000 ml cylindrical separable flask was charged with 19.69 g of acrylamide, 8.23 g of acrylic acid, 1.99 g of diacrylate of polyethylene glycol (with 9 moles of ethylene oxide added) (hereinafter abbreviated as PEG9DA), and 0 of N,N-methylenebisacrylamide. 0.0915 g and 46.76 g of water were charged and dissolved uniformly. Here, in a monomer mixture consisting of acrylamide, acrylic acid, PEG9DA and N,N-methylenebisacrylamide, 70.0 mol% acrylamide, 28.9 mol% acrylic acid, 1 mol% PEG9DA, N,N-methylenebisacrylamide Acrylamide is 0.15 mol %. After replacing the inside of the flask with nitrogen, the flask was heated to 45° C. on a hot water bath, 11.934 g of a 1% sodium persulfate aqueous solution and 11.441 g of a 0.1% L-ascorbic acid aqueous solution were added, stirring was stopped, and polymerization was performed. let me Heat was generated after the polymerization started, and the temperature rose to 80°C after 10 minutes. When the liquid temperature stopped rising, the bath temperature was raised to 80° C., and aging was carried out for 30 minutes. The resulting gel-like polymer (water-containing gel) was finely divided using a cutter, dried with hot air at 130° C. for 3 hours, pulverized with a mixer, and sieved using JIS standard sieves with openings of 500 μm and 250 μm. Then, it passed through a sieve with an opening of 500 μm, and the powdery water absorbent resin remaining on the sieve with an opening of 250 μm was collected. 90% by mass or more of the powdery water-absorbing resin was in the range of 45 to 850 μm. This powdery water absorbent resin was used as an additive for cement.

[Comparative Production Example 2]
A 1000 ml cylindrical separable flask was charged with 9.45 g of acrylamide, 1.35 g of acrylic acid, 19.15 g of diacrylate of polyethylene glycol (with 9 moles of ethylene oxide added) (hereinafter abbreviated as PEG9DA), and 0 of N,N-methylenebisacrylamide. 0.0439 g and 56.78 g of water were charged and dissolved uniformly. Here, in a monomer mixture consisting of acrylamide, acrylic acid, PEG9DA and N,N-methylenebisacrylamide, 70 mol% acrylamide, 9.9 mol% acrylic acid, 20 mol% PEG9DA, 0 N,N-methylenebisacrylamide .15 mol %. After replacing the inside of the flask with nitrogen, the flask was heated to 45° C. on a hot water bath, 6.79 g of a 1% sodium persulfate aqueous solution and 6.509 g of a 0.1% L-ascorbic acid aqueous solution were added, stirring was stopped, and polymerization was performed. let me Heat was generated after the polymerization started, and the temperature rose to 80°C after 10 minutes. When the liquid temperature stopped rising, the bath temperature was raised to 80° C., and aging was carried out for 30 minutes. The resulting gel-like polymer (water-containing gel) was finely divided using a cutter, dried with hot air at 130° C. for 3 hours, pulverized with a mixer, and sieved using JIS standard sieves with openings of 500 μm and 250 μm. Then, it passed through a sieve with an opening of 500 μm, and the powdery water absorbent resin remaining on the sieve with an opening of 250 μm was collected. 90% by mass or more of the powdery water-absorbing resin was in the range of 45 to 850 μm. This powdery water absorbent resin was used as an additive for cement.

[Water absorption test method]
1.72 g of CaSO ₄ .2H ₂ O, 6.96 g of Na ₂ SO ₄ , 4.76 g of K ₂ SO ₄ , 7.12 g of KOH and 979.4 g of deionized water were mixed to obtain a solution for water absorption test. was prepared (pH 12.9).

About 0.2 g of the powdery water absorbent resin was accurately weighed (mass W1 (g)), placed in a 4 cm×5 cm non-woven fabric tea bag, and sealed by heat sealing. This tea bag is placed in a glass screw tube with a specified volume of 50 mL, and placed in 50 mL of a water absorption test solution at room temperature (25 ° C.) and normal pressure for a predetermined time (5 minutes, 30 minutes, 2 hours, 1 day). ). Then, the edge of the tea bag was grasped with tweezers and the tea bag was pulled up, placed on a Kimtowel (manufactured by Nippon Paper Crecia Co., Ltd.) with one side of the tea bag facing down, and allowed to stand for 5 seconds. Next, the liquid was drained off by putting the opposite side down on a kimtowel and allowing it to stand still for 5 seconds, and then the mass (W2 (g)) of the tea bag was measured. Separately, the same operation was performed without using the water absorbent resin, and the mass of the tea bag (W3 (g)) at that time was obtained as a blank. The water absorption capacity calculated according to the following formula was defined as the liquid absorption capacity.

Table 1 below shows the water absorption capacity of each powdery water absorbent resin.

From the above results, the powdery water absorbent resins of Production Examples 1 to 3 had a water absorption capacity of less than 15 g/g after 5 minutes, and less than 15 g/g even after 2 hours. On the other hand, it had a high water absorption capacity of 10 g/g or more after 1 day. On the other hand, the powdery water-absorbent resins of Comparative Production Examples 1 and 2 already had a water absorption capacity of 10 g/g or more after 5 minutes. From this result, it can be seen that the powdery water absorbent resins of Production Examples 1 to 3 exhibit high water absorption performance over time, while the water absorption performance is not very high at the beginning of the addition of water (up to about 2 hours). .

It is more preferable that the powdery water absorbent resin has a water absorption capacity of less than 10 g/g after being immersed for 5 minutes according to the above water absorption test method.

[Production Example A: Production of Cement Dispersant]
A glass reactor equipped with a Dimroth condenser, a Teflon (registered trademark) stirring blade and a stirrer with a stirring seal, a nitrogen introduction tube, and a temperature sensor was charged with 80.0 parts of ion-exchanged water and stirred at 250 rpm. It was heated to 70° C. while introducing nitrogen at 200 mL/min. Next, a mixed solution of 133.4 parts of methoxypolyethylene glycol monomethacrylate (average number of added moles of ethylene oxide: 9), 26.6 parts of methacrylic acid, 1.53 parts of mercaptopropionic acid and 106.7 parts of deionized water was added dropwise over 4 hours, and at the same time, a mixed solution of 1.19 parts of ammonium persulfate and 50.6 parts of ion-exchanged water was added dropwise over 5 hours. After completion of dropping, the temperature was maintained at 70° C. for 1 hour to complete the polymerization reaction. Then, it was neutralized with an aqueous sodium hydroxide solution to obtain an aqueous polycarboxylic acid-based copolymer solution containing a polymer as a cement dispersant (solid content: about 46.0% by mass).

[Evaluation method 1: Mortar test and strength test method]
A kneader for mechanical kneading, a spoon, a flow table, a flow cone and a plunging rod according to JIS-R5201-1997 were used. At this time, mortar tests were conducted in accordance with JIS-R5201-1997 unless otherwise specified.

The mortar (cement composition) was mixed with 587 g of ordinary Portland cement manufactured by Taiheiyo Cement Co., Ltd., 1350 g of standard sand for cement strength test according to JIS-R5201-1997, and the aqueous copolymer solution obtained in Production Example A (cement dispersant ) and an antifoaming agent (copolymer solid content is 0.11 to 0.19 parts by mass per 100 parts by mass of cement, Table 2 below). 0.3 parts by mass of the powdery water-absorbent resins of Production Examples 1-3 and Comparative Production Examples 1-2 were added in advance to 100 parts by mass of cement and mixed with the cement. The antifoaming agent was added for the purpose of avoiding the influence of air bubbles on the dispersibility of the mortar composition, and the air content was adjusted to 4.0% or less. Specifically, an oxyalkylene antifoaming agent was used in an amount of 0.1% relative to the copolymer. When the amount of air in the mortar was greater than 4.0%, the amount of antifoaming agent added was adjusted so that the amount of air was 4.0% or less.

The mortar was prepared at room temperature (20±2° C.) for 4 minutes and 30 seconds using a Hobart-type mortar mixer (model number N-50, manufactured by Hobart). Specifically, specified amounts of cement and powdered water-absorbing resin were placed in a kneader, and the kneader was attached to the kneader and started at a low speed. Fifteen seconds after starting the paddle, water containing a specified amount of cement dispersant and defoamer was added for 15 seconds. After that, sand was added and kneaded at low speed for 30 seconds, then at high speed and kneading was continued for 30 seconds. After removing the kneading bowl from the kneader and stopping kneading for 120 seconds, reattaching the kneading bowl to the kneader and kneading at high speed for 60 seconds (4 minutes and 30 minutes after starting at low speed at the beginning) seconds later), and stirred with a spoon 10 times on each side. Fill the flow cone placed on the flow table with the kneaded mortar in two layers. Each layer was poked 15 times over the entire surface so that the tip of the shovel penetrated about half the depth of the layer. 6 minutes later, after lifting the flow cone vertically, the diameter of the mortar spread on the table was measured in two directions, and the average value was taken as the flow value.

To measure the mortar air content, put mortar into a 500 ml graduated cylinder, measure the weight and volume, and measure the difference between the measured volume and the volume when the mortar has an air content of 0% of the weight of the charged weight. calculated as

After measuring the flow value and the amount of air, a sample for compressive strength test was prepared, and the compressive strength after 28 days was measured under the following conditions.

Specimen preparation: 50 mm × 100 mm
Specimen curing (28 days): After curing for 24 hours at a temperature of about 20°C, humidity of 60%, and constant temperature and humidity air, the specimen was wrapped in a polyethylene film to prevent water exchange between the mortar surface and the outside. After that, it was placed in a plastic bag, sealed, and sealed for 27 days.

Specimen polishing: Specimen surface polishing (specimen polishing finishing machine used)
Compressive strength measurement: Automatic compressive strength measuring instrument (Mayekawa Seisakusho)
[Evaluation method 2: funnel flow down test method]
A funnel flow test of mortar was carried out as an evaluation of pipe passageability during pumping. If the mortar did not clog in the middle and flowed down in a short period of time, it was judged that the passage through the pipe was good. A specific method of the funnel flow test is as follows.

A J14 funnel (upper end inner diameter 70 mm, lower end inner diameter 14 mm, height 392 mm) defined by the Japan Society of Civil Engineers standard JSCE-F541 was fitted with a rubber stopper at the lower end and vertically supported on a stand. Next, an electronic scale was installed below the lower end of the J14 funnel for measuring the amount of mortar that flowed out.

The obtained mortar was poured up to the upper surface of a J14 funnel, and the upper surface was leveled. Next, the rubber plug was removed to allow the mortar to flow out, and the time from the start of the mortar flow until 1200 g flowed down was measured with a stopwatch, and this was defined as the funnel flow down time.

The results of each example and comparative example are shown in Table 2 below. The % in the 28-day strength column is the % of each strength when the numerical value of Comparative Example 1 is taken as 100%.

From the above results, the cement composition using the additive for cement of Example obtained the same flow value with the same amount of dispersant as Comparative Example 1. Further, in the cement composition having the same flow value (fluidity), the cement composition using the cement additive of the example is compared with the cement composition using the cement additive of Comparative Examples 2 and 3. The amount of cement dispersant was relatively small. In addition, it was found that the cement composition using the additive for cement of the example had a short flow-down time, and thus had a low viscosity and excellent pumpability. In addition, the cement composition using the cement additive of the example had improved strength after 28 days of sealed curing compared to Comparative Example 1 in which no cement additive was added.

On the other hand, in Comparative Examples 2 and 3 using the powdery water-absorbing resin which does not employ the constitution of the present invention, it was necessary to add a large amount of dispersant in order to obtain the same flow value (fluidity). In addition, the cement compositions of Comparative Examples 2 and 3 had a long flow-down time, resulting in high viscosity and poor workability.

[Evaluation Method 3: Concrete Test and Strength Test Method]
Ordinary Portland cement (manufactured by Taiheiyo Cement Co., Ltd.) was used as cement, land sand from the Oi River water system was used as fine aggregate, crushed stone from Omi was used as coarse aggregate, and tap water was used as kneading water. Cement: 382 kg/m ³ Water: 172 kg/m ³ , fine aggregate: 796 kg/m ³ , coarse aggregate: 930 kg/m ³ , fine aggregate rate (fine aggregate/fine coarse aggregate + coarse aggregate) (volume ratio): 47%, cement dispersant and Water Absorbent Resin Powder A cement composition was prepared at a water/cement ratio (mass ratio) of 0.45 as shown in Table 3 below. 0.3 parts by mass of the powdery water-absorbent resins of Production Examples 1 to 3 and Comparative Production Examples 1 to 2 were added in advance to 100 parts by mass of cement and mixed with the cement.

In addition, the materials used for measurement, the forced kneading mixer, and the measuring instruments were adjusted under the atmosphere of the above measurement temperature so that the temperature of the cement composition reached the measurement temperature of 20 ° C., and kneading and each measurement were performed as described above. It was carried out under the atmosphere of the measurement temperature. In addition, in order to avoid the influence of air bubbles in the cement composition on the fluidity of the cement composition, an oxyalkylene antifoaming agent is used as necessary so that the air content is 4.5 ± 0.5%. adjusted to

Under the above conditions, concrete was produced using a forced kneading mixer with a kneading time of 90 seconds, and the flow value and air content were measured. The flow value and air content were measured in accordance with Japanese Industrial Standards (JIS-A-1101:2014, 1128:2014). The amount of cement dispersant added was such that the flow value was 375 mm to 425 mm.

After measuring the flow value and the amount of air, a sample for compressive strength test was prepared, and the compressive strength after 28 days was measured under the following conditions. Specimen preparation: 100 mm x 200 mm Specimen curing (28 days): Temperature of about 20°C, humidity of 60%, constant temperature and humidity air curing for 24 hours. After wrapping the sample with a polyethylene film, it was placed in a plastic bag, sealed, and sealed for 27 days.

Specimen polishing: Specimen surface polishing (specimen polishing finishing machine used)
Compressive strength measurement: Automatic compressive strength measuring instrument (Mayekawa Seisakusho)
The results are shown in Table 3 below.

From the above results, the cement composition using the additive for cement of the example obtained the same flow value with the same amount of dispersant as the comparative example. In addition, in the cement composition having the same flow value (fluidity), the cement composition using the cement additive of the example is compared with the cement composition using the cement additive of the comparative example. The amount of cement dispersant was small. In addition, the cement composition using the cement additive of the example had improved strength after 28 days of sealed curing compared to Comparative Example 1 in which no cement additive was added.

On the other hand, in Comparative Examples 2 and 3 using the powdery water-absorbing resin which does not employ the constitution of the present invention, it was necessary to add a large amount of dispersant in order to obtain the same flow value (fluidity).

Claims (14)

A cement additive containing a water absorbent resin,
The water absorbent resin is obtained by polymerizing a monomer mixture containing 75 mol% or more of nonionic monomers,
The monomer mixture contains 0.01 to 1 mol% of a non-hydrolyzable crosslinkable nonionic monomer and 25 mol% or more of a hydrolyzable crosslinkable nonionic monomer,
The water-absorbent resin was added to an aqueous solution of pH 12.9 (here, the aqueous solution of pH 12.9 is CaSO ₄ .2H ₂ O 1.72 g, Na ₂ SO ₄ 6.96 g, K ₂ SO ₄ 4.76 g, KOH 7.12 g and 979.4 g of deionized water). A cement additive containing a water absorbent resin,
The water absorbent resin is obtained by polymerizing a monomer mixture containing 75 mol% or more of nonionic monomers,
The monomer mixture contains 0.01 to 1 mol% of a non-hydrolyzable crosslinkable nonionic monomer and 25 mol% or more of a hydrolyzable crosslinkable nonionic monomer,
A cement additive , wherein the content of the anionic monomer and the cationic monomer in the monomer mixture is 5 mol % or less. 3. The additive for cement according to claim 1, wherein said water absorbent resin has a water absorption capacity of 10 g/g or more when immersed in said aqueous solution of pH 12.9 at 25[deg.] C. for 1 day. The cement additive according to any one of claims 1 to 3, wherein the content of the hydrolyzable crosslinkable nonionic monomer in the monomer mixture is 45 mol% or more. The cement additive according to any one of claims 1 to 4, wherein the hydrolyzable crosslinkable nonionic monomer has an ester bond. The cement additive according to any one of claims 1 to 5, wherein the monomer mixture contains 10 mol% or more of non-crosslinkable nonionic monomers. 7. The cement additive according to claim 6, wherein said non-crosslinkable nonionic monomer comprises a (meth)acrylamide-based monomer. A cement admixture comprising the cement additive according to any one of claims 1 to 7 and a cement dispersant. A cement composition comprising the additive for cement according to any one of claims 1 to 7 and cement. 10. The cement composition of claim 9, further comprising a cement dispersant. A cement composition comprising a water absorbent resin and cement,
The water absorbent resin is obtained by polymerizing a monomer mixture containing 75 mol% or more of nonionic monomers,
The monomer mixture contains 0.01 to 1 mol% of a non-hydrolyzable crosslinkable nonionic monomer and 25 mol% or more of a hydrolyzable crosslinkable nonionic monomer,
The water-absorbent resin was added to an aqueous solution of pH 12.9 (here, the aqueous solution of pH 12.9 is CaSO ₄ .2H ₂ O 1.72 g, Na ₂ SO ₄ 6.96 g, K ₂ SO ₄ 4.76 g, KOH 7.12 g and 979.4 g of deionized water). A cement composition comprising a water absorbent resin and cement,
The water absorbent resin is obtained by polymerizing a monomer mixture containing 75 mol% or more of nonionic monomers,
The monomer mixture contains 0.01 to 1 mol% of a non-hydrolyzable crosslinkable nonionic monomer and 25 mol% or more of a hydrolyzable crosslinkable nonionic monomer,
A cement composition, wherein the content of the anionic monomer and the cationic monomer in the monomer mixture is 5 mol% or less. A molded article obtained by molding the cement composition according to any one of claims 9 to 12 . A method for improving the strength of a molded body obtained by molding a cement composition containing cement,
A method for improving the strength of a molded body, comprising incorporating the cement additive according to any one of claims 1 to 7 or the cement admixture according to claim 8 into the cement composition.