JP4842103B2 - Additive for concrete - Google Patents

Description

  The present invention relates to a concrete additive and a concrete composition containing the same.

Conventionally, a polycarboxylic acid polymer has been used as a water reducing agent for concrete, and can be used for a wide range of concrete.

  Patent Document 1 discloses a concrete composition containing a specific cement dispersant for improving the bleaching of a highly fluid concrete composition having a large water / cement ratio.

  Patent Document 2 discloses a specific polyalkylene glycol mono (meth) acrylate monomer as a cement dispersant having excellent workability due to excellent gap-passability and high fluidity and strength. A cement dispersant having a weight average molecular weight of 5,000 to less than 10,000 obtained by reacting a specific carboxylic acid monomer and having a weight average molecular weight divided by a number average molecular weight of 1.0 to 1.5 is disclosed. ing.

However, these polymers are basically designed with an emphasis on imparting fluidity and reducing viscosity in the region of high strength (for example, water / cement ratio (W / C) is 0.40 or less). For example, workability at the time of placing poor blended concrete having a large water / cement ratio and a small amount of paste is not always good.
JP 11-79814 A JP 2005-281022 A

  The object of the present invention is to provide a concrete composition having a small amount of paste per unit volume and a large slump flow even at the same slump value, and an excellent feeling of smoothness and fluffiness during driving and kneading as an operator's sense. Is to provide an additive for concrete.

The present invention is an additive for concrete comprising a copolymer obtained by polymerizing the monomer 1 represented by the general formula (1) and the monomer 2 represented by the general formula (2). And
The weight average molecular weight of this copolymer is 15000-30000, The ratio (Mw / Mn) of a weight average molecular weight (Mw) and a number average molecular weight (Mn) is related with the additive for concrete which is 1.0-1.6. .

[In the formula, R ¹ and R ² are each a hydrogen atom or a methyl group, R ³ is a hydrogen atom, or — (CH ₂ ) q (CO) pO (AO) r—R ⁴ , and AO has 2 to 4 carbon atoms. An oxyalkylene group or an oxystyrene group, p is a number of 0 or 1, q is a number of 0 to 2, p and q are not simultaneously 0, r is an average added mole number of AO, a number of 3 to 150, R ⁴ represents a hydrogen atom or an alkyl group having 1 to 18 carbon atoms. ]

Wherein, R ¹¹ to R ¹³ are each a hydrogen atom, a methyl group or (CH ^₂₎ sCOOM _2, form a (CH ^₂₎ sCOOM ₂ is COOM ¹ or another (CH ^₂₎ sCOOM ₂ and anhydride In this case, M ¹ and M ² of these groups are not present. s represents the number of 0-2. M ¹ and M ² each represent a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group, an alkyl ammonium group, a substituted alkyl ammonium group, an alkyl group, a hydroxyalkyl group, or an alkenyl group. ]

Further, the present invention is a concrete composition containing the concrete additive, wherein the weight of water per 1 m ^{3 of} the concrete composition is 170 to 185 kg / m ³ , and the paste volume (water and hydraulic powder This relates to a concrete composition having a total volume of 250 to 320 L / m ³ .

  According to the present invention, regarding a concrete composition having a small amount of paste per unit volume, a slump flow is increased even at the same slump value, and a concrete composition excellent in a feeling of smoothness and fluffiness during driving and kneading as an operator's sense and A concrete additive for obtaining the composition is provided.

The present inventor, when a polycarboxylic acid-based dispersant having an alkylene oxide is added to a concrete composition containing cement and water, adsorbed density of alkylene oxide chains on the cement surface adsorbed by the dispersant (lines / m ² ) It was found that the effect of improving the fresh state of poor blended concrete with a small amount of paste is excellent by increasing the amount of paste. Here, the improvement of the fresh state means that a concrete with a feeling of smoothness and fluffiness that can be easily handled by an operator during driving and kneading can be obtained. That is, it is presumed that by uniformly distributing alkylene oxide chains with high density on the cement surface, the cement particles are prevented from agglomerating and a cement paste having a good dispersion state can be obtained. Since such a paste can uniformly coat the aggregate surface in the concrete, it is considered that a good concrete state can be created even with a small amount of paste. Therefore, in order to increase the adsorption density of alkylene oxide chains on the cement surface, it is important to (1) adsorb a large amount of dispersant on the cement particle surface, and (2) shorten the alkylene oxide chain in the dispersant molecule. Conceivable.

  In the civil engineering and construction fields, concrete is managed by slump (fluidity), and there is a standard value for fluidity. This fluidity is adjusted by the amount of dispersant added. Since the polycarboxylic acid-based dispersant optimized for dispersion performance (fluidity imparting effect, water reduction effect) is excellent in dispersion performance, a predetermined fluidity can be obtained with a small addition amount (and adsorption amount to cement). . That is, it is impossible to increase the adsorption density of the alkylene oxide chain on the cement surface by increasing the amount of addition while maintaining a predetermined fluidity. In the concrete additive of the present invention, the dispersibility is lowered to some extent, so that the amount of the dispersant added can be increased, the adsorption density of the alkylene oxide chain on the cement surface can be increased, and implantation is performed. In addition, it is possible to obtain a concrete that is easy to handle and easy to handle when kneading.

[Monomer 1]
In monomer 1, R ¹ and R ² in general formula (1) are each a hydrogen atom or a methyl group. R ³ is a hydrogen atom or — (CH ₂ ) q (CO) pO (AO) r—R ⁴ , preferably a hydrogen atom. When p is 0, AO forms an ether bond with (CH ₂ ) q, and when p is 1, it forms an ester bond. q is 0 to 2, preferably 0 or 1, and more preferably 0. AO is an oxyalkylene group having 2 to 4 carbon atoms or an oxystyrene group, and AO is preferably an oxyalkylene group having 2 to 4 carbon atoms, more preferably an oxyethylene group (hereinafter also referred to as an EO group). It is preferred that the EO group is 70 mol% or more, more preferably 80 mol% or more, further 90 mol% or more, and particularly, all AO are EO groups. r is the average added mole number of AO, and is a number of 3 to 150, preferably 4 to 50, more preferably 5 to 30, more preferably 5 to 25, and still more preferably 5 to 15. Moreover, AO is different in an average of r repeating units, and random addition, block addition, or a mixture thereof may be included. For example, AO can contain an oxypropylene group etc. besides EO group. Monomer 1 is preferably a compound with p = 1 and q = 0. Further, when p = 0, q = 1 is preferable.

R ⁴ is a hydrogen atom or an alkyl group having 1 to 18 carbon atoms, preferably 1 to 12, more preferably 1 to 4, and further preferably 1 or 2, and particularly preferably a methyl group.

  Monomer 1 includes a half-terminated alkyl-capped polyalkylene glycol such as methoxypolyethylene glycol, methoxypolypropylene glycol, methoxypolybutylene glycol, methoxypolystyrene glycol, ethoxypolyethylenepolypropyleneglycol, (meth) acrylic acid, maleic acid (half ) Esterified products, etherified products with (meth) allyl alcohol, and (meth) acrylic acid, maleic acid, and (meth) allyl alcohol adducts having 2 to 4 carbon atoms are preferably used.

  More preferred is an esterified product of alkoxy, polyethylene glycol, particularly methoxypolyethylene glycol and (meth) acrylic acid. Specific examples include ω-methoxypolyoxyalkylene methacrylate and ω-methoxypolyoxyalkylene acrylate, and ω-methoxypolyoxyalkylene methacrylate is more preferable.

[Monomer 2]
In the monomer 2, R ^{11 to} R ¹³ in the general formula (2) are each a hydrogen atom, a methyl group or (CH ₂ ) sCOOM ² , and (CH ₂ ) sCOOM ² is COOM ¹ or other (CH ₂₎ SCOOM may form a ² and anhydride. In that case, M ¹ and M ² of those groups do not exist. s represents the number of 0-2. R ₁₁ is preferably a hydrogen atom, and R ₁₂ is preferably a methyl group. R ₁₃ is preferably a hydrogen atom or (CH ₂ ) sCOOM ² .

M ¹ and M ² are each a hydrogen atom, an alkali metal, an alkaline earth metal, an ammonium group, an alkylammonium group, a substituted alkylammonium group, an alkyl group, a hydroxyalkyl group, or an alkenyl group. M ¹ and M ² are each preferably a hydrogen atom or an alkali metal.

  Specifically, monocarboxylic acid monomers such as (meth) acrylic acid and crotonic acid, dicarboxylic acid monomers such as maleic acid, itaconic acid and fumaric acid, or anhydrides or salts thereof (for example, alkalis) Metal salt, alkaline earth metal salt, ammonium salt, mono-, di-, trialkyl (carbon number 2 to 8) ammonium salt optionally substituted with hydroxyl group) or ester, preferably (meth) acrylic acid, Maleic acid, maleic anhydride, more preferably (meth) acrylic acid or an alkali metal salt thereof. In addition, (meth) acrylic acid means acrylic acid and / or methacrylic acid (hereinafter the same).

[Copolymer]
For example, the copolymer is charged with water in a reaction vessel and heated, and then the monomer 1 and the monomer 2 are reacted in the presence of a chain transfer agent and the like at a constant molar ratio and weight ratio to be aged. Can be manufactured. Neutralize after aging if necessary.

  The weight ratio (monomer 1 / monomer 2) of monomer 1 and monomer 2 used for the production of the copolymer is preferably 95/5 to 2/98, more preferably 80/20 to 5/95. 60/40 to 10/90 is more preferable, and 50/50 to 20/80 is more preferable.

  In the production of the copolymer, in addition to the monomer 1 and the monomer 2, one or more other copolymerizable monomers can be used. Examples of other copolymerizable monomers include allyl sulfonic acid, methallyl sulfonic acid, sulfoethyl methacrylate, alkali metal salts, alkaline earth metal salts, ammonium salts, or amine salts of any of these. (Meth) acrylamide, N-methyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2- (meth) acrylamide-2-metasulfonic acid, 2- (meth) acrylamide-2-ethanesulfonic acid, 2- (Meth) acrylamide-2-propanesulfonic acid, styrene, styrenesulfonic acid and the like. Further, as described in Japanese Patent No. 3336456, polyalkylene polyamine and dibasic acid or ester of dibasic acid and lower alcohol having 1 to 4 carbon atoms, acrylic acid or methacrylic acid or acrylic acid or methacrylic acid and carbon A polyamide polyamine monomer obtained by adding an alkylene oxide having 2 to 4 carbon atoms to an amino residue of a polyamide polyamine obtained by condensing an ester with a lower alcohol having 1 to 4 atoms; As described in JP-A-2004-2174, an ester of a polyalkylene polyamine and a dibasic acid and / or a dibasic acid and an alcohol having 1 to 4 carbon atoms, and (meth) acrylic acid and / or (meth) acrylic acid And an unsaturated bond obtained by reacting an ester of alcohol with 1 to 4 carbon atoms A polyamide polyamine monomer obtained by adding an alkylene oxide having 2 to 4 carbon atoms to the amino residue and imino group of a polyamide polyamine, as described in JP-A-2003-335563, a single amount of an amine alkylene oxide adduct And polyalkyleneimine alkylene oxide adduct monomers as described in JP-A No. 2004-342050, poly (polyoxyalkylene) unsaturated monomers as described in JP-A No. 2004-67934, and the like. It is done. The total ratio of the monomers 1 and 2 is preferably 30 to 100 mol%, more preferably 50 to 100 mol%, more preferably 75 to 100 mol%, and more preferably 90 to 100 mol% in all monomers. Preferably, substantially 100% is more preferable.

  The weight average molecular weight (Mw) is 15000 or more from the viewpoint of the dispersion performance of the copolymer, and Mw is 30000 or less from the viewpoint of the number of adsorption onto the hydraulic powder such as cement. Therefore, Mw is 15000 to 30000, preferably 18000 to 25000, from the viewpoint of dispersion performance and easy handling feeling during kneading. Moreover, in order that a copolymer can adsorb | suck to the hydraulic powder surface densely, it is preferable that molecular weight distribution is narrow, and ratio (Mw / Mn) of Mw and number average molecular weight (Mn) is 1.0-1. From the viewpoint of easy handling during kneading, 1.0 to 1.4 is preferable.

  Mw and Mn of the copolymer are measured by gel permeation chromatography (GPC) method under the following conditions. Mw and Mn are calculated based on the peak of the polymer.

[GPC conditions]
Column: G4000PWXL + G2500PWXL (Tosoh)
Eluent: 0.2M phosphate buffer / CH ₃ CN = 9/1
Flow rate: 1.0mL / min
Column temperature: 40 ° C
Detection: RI
Sample size: 0.2mg / mL
Reference material: Polyethylene glycol equivalent

  Mw and Mw / Mn of a copolymer can be adjusted with the usage-amount of the chain transfer agent used at the time of superposition | polymerization, for example. As the number of chain transfer agents increases, the weight average molecular weight Mw decreases and Mw / Mn tends to decrease.

  The chain transfer agent has a function of causing a chain transfer reaction in radical polymerization (a reaction in which a growing polymer radical reacts with another molecule to move a radical active site). It is a substance to be added and is preferably used in the polymerization from the viewpoint of adjusting the suitable molecular weight and designing the performance of the dispersant for hydraulic composition.

  Examples of chain transfer agents include thiol chain transfer agents and halogenated hydrocarbon chain transfer agents, and thiol chain transfer agents are preferred.

As the thiol chain transfer agent, those having a —SH group are preferable, and in particular, the general formula HS—R—Eg (wherein R represents a hydrocarbon-derived group having 1 to 4 carbon atoms, and E is − OH, —COOM, —COOR ′ or —SO ₃ M group, M represents a hydrogen atom, monovalent metal, divalent metal, ammonium group or organic amine group, and R ′ represents an alkyl having 1 to 10 carbon atoms. In which g represents an integer of 1 to 2, for example, mercaptoethanol, thioglycerol, thioglycolic acid, 2-mercaptopropionic acid, 3-mercaptopropionic acid, thiomalic acid, Examples include octyl thioglycolate, octyl 3-mercaptopropionate, and the like from the viewpoint of chain transfer effect in a copolymerization reaction including monomers 1 to 3. Mercaptoethanol are preferable, more preferably mercaptopropionic acid. These 1 type (s) or 2 or more types can be used.

  Examples of the halogenated hydrocarbon chain transfer agent include carbon tetrachloride and carbon tetrabromide. Examples of other chain transfer agents include α-methylstyrene dimer, terpinolene, α-terpinene, γ-terpinene, dipentene, 2-aminopropan-1-ol and the like. A chain transfer agent can use 1 type (s) or 2 or more types.

  Further, from the viewpoint of reducing Mw / Mn, it is preferable to employ a combination of monomer 1 and monomer 2 having high copolymerizability. For example, the monomer 1 may be an esterified product of methoxypolyethylene glycol and methacrylic acid, and the monomer 2 may be a combination of methacrylic acid.

  The additive of the present invention is 0.05 to 2 parts by weight, more preferably 0.1 to 1.5 parts by weight, and further 0.2 to 1 by solid content concentration of the copolymer with respect to 100 parts by weight of the hydraulic powder. Use of parts by weight, and further 0.35 to 0.8 is preferable in terms of achieving both dispersibility and workability.

  The hydraulic powder used in the hydraulic composition that is the target of the additive of the present invention is a powder having physical properties that is cured by a hydration reaction, and examples thereof include cement and gypsum. Preferred are ordinary Portland cement, Belite cement, moderate heat cement, early strong cement, super early strong cement, sulfuric acid resistant cement, etc., and blast furnace slag, fly ash, silica fume, stone powder (calcium carbonate powder), etc. May be added. In addition, the hydraulic composition finally obtained by adding sand, sand and gravel as aggregates to these powders is generally called mortar, concrete, etc., respectively.

  The additive of the present invention is particularly effective for poorly blended concrete having a large water / cement ratio and a small amount of paste, and is preferably applied to such concrete. A concrete composition that satisfies the following requirements is preferable.

The weight of water per 1 m ^{3 of the} concrete composition is preferably 170 to 185 kg / m ³ , more preferably 175 to 185 kg / m ³ . The paste volume (volume of water and hydraulic powder) per 1 m ³ is preferably 250 to 320 L / m ³ , more preferably 255 to 315 L / m ³ , and still more preferably 260 to 310 L / m ³ .

Therefore, the weight of water per 1 m ³ is 170 to 185 kg / m ³ as a concrete composition, and the paste volume (the sum of the volume of water and hydraulic powder) is 250 to 320 L / m ^3. preferable.

It is preferable that the weight of the hydraulic powder per concrete composition 1 m ³ is 190~420kg / m ^3, more preferably 200~410kg / m ^3, particularly preferably 210~400kg / m ^3. The water / hydraulic powder ratio (weight ratio) is preferably 0.40 to 0.70, more preferably 0.42 to 0.65, and particularly preferably 0.45 to 0.65.

  The aggregate of the concrete composition includes fine aggregate, coarse aggregate, etc., fine aggregate is preferably mountain sand, land sand, river sand, crushed sand, and coarse aggregate is mountain gravel, land gravel, river gravel, crushed stone. preferable. In particular, crushed sand has a large shape and a large specific surface area, which makes it difficult to knead with concrete having a small amount of paste. The additive of the present invention is more preferably used for a concrete composition containing aggregated sand in the aggregate in that the workability improving effect can be remarkably exhibited. The fine aggregate rate [s / a = fine aggregate volume / (fine aggregate volume + coarse aggregate volume) × 100 (%)] is preferably 40 to 60, and more preferably 45 to 55.

  Moreover, in manufacturing the concrete composition of the present invention, a known additive (material) can be used in addition to the additive of the present invention. For example, AE agent, fluidizing agent, retarder, early strengthening agent, accelerator, foaming agent, water retention agent, thickener, waterproofing agent, antifoaming agent, shrinkage reducing agent, water-soluble polymer, interface Various activators are listed.

Production Example 1
A glass reaction vessel (four-necked flask) with a stirrer was charged with 363 g of water, purged with nitrogen while stirring, and heated to 80 ° C. in a nitrogen atmosphere. ω-methoxypolyethyleneglycol monomethacrylate (average added mole number of ethylene oxide 9) 220 g (effective 99.9 wt%, moisture 0.1 wt%), methacrylic acid 56.9 g and 3-mercaptopropionic acid 2.3 g Two were added dropwise over a period of 1.5 hours, one mixed with 2.5 g ammonium persulfate dissolved in 45 g water. After aging at 80 ° C. for 1 hour, 0.75 g of ammonium persulfate dissolved in 15 g of water was added dropwise over 30 minutes, and then aging was carried out at 80 ° C. for 1.5 hours. After completion of aging, a 48% aqueous sodium hydroxide solution was added dropwise to neutralize to pH 6 to obtain a polymer A-1 having a weight average molecular weight of 46000. (Reaction rate 99.6%)

Production Example 2
A polymer was produced in the same manner as in Production Example 1, except that the amount of water charged in a glass reaction vessel (four-necked flask) with a stirrer was 366 g and that 3-mercaptopropionic acid was 4.1 g. And the polymer A-2 of the weight average molecular weight 33000 was obtained. (Reaction rate 98.9%)

Production Example 3
Manufactured except that 375 g of water charged in a glass reaction vessel with a stirrer (four-necked flask), 5.8 g of 3-mercaptopropionic acid, and 5.0 g of ammonium persulfate dissolved in 45 g of water were used. A polymer was prepared as in Example 1. And polymer A-3 with a weight average molecular weight 25000 was obtained. (Reaction rate 99.5%)

Production Example 4
Manufactured except that the water charged in a glass reaction vessel (four-necked flask) with a stirrer was 386 g, 3-mercaptopropionic acid was 9.4 g, and ammonium persulfate 7.5 g was dissolved in 45 g of water. A polymer was prepared as in Example 1. And the polymer A-4 of the weight average molecular weight 19000 was obtained. (Reaction rate 100%)

Production Example 5
A glass reaction vessel (four-necked flask) with a stirrer was charged with 215 g of water, purged with nitrogen while stirring, and heated to 80 ° C. in a nitrogen atmosphere. 340 g of ω-methoxypolyethyleneglycol monomethacrylate (average added mole number of ethylene oxide 23) (effective content 64.5 wt%, moisture 35.5 wt%), methacrylic acid 40.5 g and 3-mercaptopropionic acid 1.4 g Two of the mixture and 1.5 g of ammonium persulfate dissolved in 45 g of water were added dropwise over 1.5 hours. After aging at 80 ° C. for 1 hour, 0.8 g of ammonium persulfate dissolved in 15 g of water was added dropwise over 30 minutes, and then aging was carried out at 80 ° C. for 1.5 hours. After completion of aging, a 48% aqueous sodium hydroxide solution was added dropwise to neutralize to PH6 to obtain a polymer B-1 having a weight average molecular weight of 57,000. (Reaction rate 99.7%)

Production Example 6
A polymer was produced in the same manner as in Production Example 5 except that the amount of water charged in a glass reaction vessel (four-necked flask) with a stirrer was 216 g and 3-mercaptopropionic acid was 2.5 g. And the polymer B-2 of the weight average molecular weight 38000 was obtained. (Reaction rate 99.2%)

Production Example 7
The water charged in a glass reaction vessel (four-necked flask) with a stirrer was 221 g, 3-mercaptopropionic acid was 3.6 g, and ammonium persulfate 3.1 g was dissolved in water 45 g. A polymer was produced in the same manner as in Production Example 5, except that 1.5 g of ammonium persulfate dissolved in 15 g of water was added dropwise over 30 minutes after aging. And the polymer B-3 of the weight average molecular weight 29000 was obtained. (Reaction rate 99.6%)

Production Example 8
The amount of water charged in a glass reaction vessel (four-necked flask) with a stirrer was 228 g, 3-mercaptopropionic acid was 5.7 g, and ammonium persulfate 4.6 g was dissolved in water 45 g. After aging for a time, a polymer was produced in the same manner as in Production Example 5, except that 2.3 g of ammonium persulfate dissolved in 15 g of water was added dropwise over 30 minutes. And the polymer B-4 of the weight average molecular weight 23000 was obtained. (Reaction rate 99.6%)

<Examples 1-4, Comparative Examples 1-4>
In order to quantify the fresh state of concrete with a smooth and fluffy feeling, the slump flow value when the slump value of the concrete was constant was used. That is, when the state is good, the mixing ability of the cement paste and the aggregate is good, so that the slump flow value tends to increase when the slump is the same because the paste layer wraps the entire aggregate uniformly. . On the other hand, when the state is bad, the coarse aggregate is blocked, so that the slump flow value tends to be small.

  As the slump flow value, an average value of the maximum value of the slump flow value and the slump flow value measured in the direction perpendicular to the length of ½ of the line segment giving the maximum value was adopted. The slump flow test of concrete is JIS A 1150 (coarse aggregate (G) maximum size 20mm, concrete temperature 20-22 ° C, how to pack samples: packed in 3 layers, uniformly with 25 striking rods for each layer) I followed).

The judgment of the state was such that the slump flow value was less than 310 mm: x, less than 310 to 330 mm: Δ, 330 to less than 350 mm: ◯, 350 mm or more: ◎.

(1) Concrete mix The concrete mix is shown in Table 1.

The materials used in Table 1 are as follows.
W: Tap water C: Ordinary Portland cement (Pacific Cement Co., Ltd.), density = 3.16 g / cm ³
S1: Sea sand from Setouchi, surface dry density = 2.54 g / cm ³
S2: Ibaraki crushed sand, surface dry density = 2.64 g / cm ³
G: Ibaraki crushed stone, surface dry density = 2.64 g / cm ³

(2) Preparation of Concrete Composition A 30-liter concrete composition was prepared using a forced biaxial mixer DAM60 manufactured by IHI. Adjustment was carried out at room temperature (about 20 ° C.) at a paddle rotation speed of 44 revolutions / minute. C, S1, S2 and G shown in Table 1 were added to the mixer, and kneaded for 10 seconds, and a mixed solution in which the polymer and W were mixed in advance was added. Thereafter, the mixture was kneaded for 90 seconds to obtain a concrete composition. At that time, the amount of the polymer added was adjusted so that the slump value was 20 cm.
The results are shown in Table 2.

  When the polymers A-1 to A-4 are compared, the smaller the weight average molecular weight, the greater the slump flow value and the better the state of the concrete, and the better the concrete state in the range of the weight average molecular weight of 15,000 to 30,000. . The same tendency is found in the polymers B-1 to B-4.

Claims (6)

The monomer 1 represented by the general formula (1) and the monomer 2 represented by the general formula (2) are weights of monomer 1 / monomer 2 = 95/5 to 2/98. An additive for concrete comprising a copolymer obtained by polymerization at a ratio ,
The concrete additive, wherein the copolymer has a weight average molecular weight of 15,000 to 30,000, and a ratio (Mw / Mn) of the weight average molecular weight (Mw) to the number average molecular weight (Mn) is 1.0 to 1.6.

[Wherein R ¹ is a hydrogen atom, R ² is a methyl group, R ³ is a hydrogen atom, AO is an oxyalkylene group having 2 carbon atoms, p is a number of 1, q is a number of 0, and r is an average addition of AO. It is the number of moles, the number of 5 to 15 , and R ⁴ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. ]

[Wherein, R ¹¹ represents a hydrogen atom, R ¹² represents a methyl group, R ¹³ represents a hydrogen atom, and M ¹ represents a hydrogen atom or an alkali metal. ]   The additive for concrete according to claim 1, wherein the total amount of monomer 1 and monomer 2 is 90 mol% or more in the monomers used for polymerization of the copolymer. A concrete composition containing the additive for concrete according to claim 1 or 2, a hydraulic powder, an aggregate, and water,
A concrete composition in which the weight of water per 1 m ^{3 of the} concrete composition is 170 to 185 kg / m ³ and the paste volume (the total volume of water and hydraulic powder) is 250 to 320 L / m ³ . The concrete according to claim ³ , wherein the weight of the hydraulic powder per 1 m ^{3 of the} concrete composition is 190 to 420 kg / m ³ and the water / hydraulic powder ratio (weight ratio) is 0.45 to 0.70. Composition.   The concrete composition according to claim 3 or 4, wherein the aggregate contains crushed sand. The concrete composition according to any one of claims 3 to 5, comprising 0.05 to 2 parts by weight of a concrete additive in a solid content concentration of the copolymer with respect to 100 parts by weight of the hydraulic powder.