JP3172748B2 - Cement admixture - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cement admixture having excellent performance as a dispersant, a water reducing agent, a superplasticizer and the like.

[0002]

2. Description of the Related Art In recent years, cement compounds such as cement paste, mortar and concrete have been used in large quantities in the fields of civil engineering, construction, secondary concrete products and the like. These cement compositions contain admixtures called dispersants, water reducing agents, fluidizers, and the like for the purpose of improving slump and workability.

Conventionally, as such an admixture, those mainly composed of lignin sulfonate and those mainly composed of formalin condensate of β-naphthalene sulfonate have been known, but each has advantages and disadvantages. There was no admixture showing good performance in any aspect of cement dispersion fluidity and hardening characteristics.

Japanese Patent Publication No. 2-16260 discloses an N-substituted-α, β-unsaturated monocarboxylic acid amide substituted with an N-substituted sulfonic acid group-containing residue, and an α, β-unsaturated monocarboxylic acid. It is described that a salt of the copolymer (1) is used as an admixture for cement. In addition, Japanese Patent Publication No. 1-55210
Japanese Patent Application Laid-Open Publication No. H11-163,199 proposes using a homopolymer of 2-acrylamido-2-methylpropanesulfonate or a copolymer of this monomer with acrylamide and / or acrylate as a hydraulic cement admixture. ing.

Further, Japanese Patent Publication No. 2-5701 discloses that
It is described that a copolymer of 2-acrylamide-2-methylpropanesulfonate, an unsaturated monocarboxylate, an unsaturated carboxylate and / or acrylonitrile, styrene, or vinyl acetate is used as a dispersant for cement. Have been. Also, Japanese Patent Application Laid-Open No. 62-21695
No. 0 discloses a copolymer of 2-acrylamido-2-methylpropanesulfonate, an unsaturated carboxylate, and an ethylene oxide and / or propylene oxide adduct of an unsaturated carboxylic acid with a dispersant for cement. It has been proposed to use as

[0006] However, these admixtures or dispersants all improve the slump loss, but require a large amount of addition in order to obtain initial fluidity (slump). Had to be increased.
As a result, the setting properties of the cement deteriorated, and the strength was remarkably reduced.

[0007]

DISCLOSURE OF THE INVENTION The present invention has an excellent initial fluidity, prevents a decrease in the fluidity, has a water reducing effect even with a small amount of addition, and has an effect of reducing air flow to cement. The present invention provides a cement admixture with little workability and excellent workability.

[0008]

The cement admixture of the present invention is characterized by containing the following copolymers (a) and (b).

(A): (A) an N-substituted-α, β-unsaturated monocarboxylic amide derivative represented by the following formula:

Embedded image (Wherein, R ₁ : hydrogen or a lower alkyl group R ₂ : a linear or branched alkylene group having 1 to 4 carbon atoms X: hydrogen, an alkali metal, an alkaline earth metal, ammonium, or an organic ammonium)

(B) A copolymer with an unsaturated carboxylic acid or a salt thereof, wherein the copolymerization ratio is (A) /
(B) = A copolymer in the range of 95/5 to 5/95 and having a weight average molecular weight of 750 to 300,000.

(B): (A) N-
A substituted-α, β-unsaturated monocarboxylic acid amide derivative;

(C) a copolymer with an unsaturated carboxylic acid ester or vinyl acetate, wherein the copolymerization ratio is in the range of (A) / (C) = 95/5 to 40/60 in a molar ratio;
And a copolymer having a weight average molecular weight of 10,000 to 300,000.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific examples of the N-substituted-.alpha.,. Beta.-unsaturated monocarboxylic amide derivative of the monomer component (A) include 2-acrylamido-2-methylpropanesulfonic acid and 2-acrylamidoethanesulfonic acid. Acid, 2-
Examples include methacrylamidoethanesulfonic acid, 3-methacrylamidopropanesulfonic acid or salts thereof.

Further, specific examples of the monomer component (B) of the copolymer include acrylic acid, methacrylic acid, maleic acid, crotonic acid, fumaric acid, citraconic acid, itaconic acid and salts thereof.

As the salt (X) in these monomer components (A) and (B), organic ammonium salts such as alkali metal salts, alkaline earth metal salts, ammonium salts, amine salts and alkanolamine salts are used.

The copolymer (a) of the present invention comprises the above (A),
The copolymerization ratio of the copolymerization component (B) is (A) /
(B) = 95/5 to 5/95, preferably 55/45 to 85/15, more preferably 60/40 to 80/20. When the copolymerization ratio exceeds 95/5, the initial fluidity is significantly deteriorated.
On the other hand, when the copolymerization ratio is less than 5/95, the properties of the cured product deteriorate.

Further, the copolymer (a) of the present invention needs to have a weight average molecular weight in the range of 750 to 300,000, preferably 40,000 to 300,000, and more preferably 90,000 to 230,000.
If the weight-average molecular weight exceeds 300,000, the viscosity of the aqueous solution increases, making it difficult to handle, and the initial fluidity is significantly deteriorated. Conversely, when the molecular weight is less than 750, the slump holding power is deteriorated.

The unsaturated carboxylic acid ester or vinyl acetate (C) which is a copolymer component in the copolymer (b) of the present invention includes methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, and acrylic acid. Examples include methyl, ethyl acrylate, propyl acrylate, butyl acrylate, dimethyl maleate, diethyl maleate, methyl crotonate, ethyl crotonate, propyl crotonate, butyl crotonate, and vinyl acetate.

The copolymer (b) of the present invention comprises the above (A),
The copolymerization ratio of the copolymerization component (C) is (A) /
(C) = 95/5 to 40/60, preferably 80/20
It needs to be in the range of 〜50 / 50. When the copolymerization ratio exceeds 95/5, the holding power of the slump deteriorates remarkably. On the contrary, when the copolymerization ratio is less than 40/60, the air amount increases and the cement strength is inferior.

The copolymer (b) of the present invention needs to have a weight average molecular weight in the range of 10,000 to 300,000, preferably 70,000 to 300,000.
If the weight average molecular weight exceeds 300,000, the viscosity of the aqueous solution becomes high, handling becomes difficult, and the deterioration of slump holding power is remarkable. Conversely, if the molecular weight is less than 10,000, the amount of air increases and the slump holding power also deteriorates.

The copolymers (a) and (b) of the present invention are:
For example, it can be synthesized by radical polymerization or the like, but using a redox initiator obtained by combining a persulfate as a radical initiator and a reducing agent selected from sulfite, bisulfite and pyrosulfite, aqueous solution polymerization or suspension By the polymerization, the monomer components (A) and (B), or
Those obtained by copolymerizing (A) and (C) monomer components are preferred. As a result, the intended effects of the present invention are further achieved.

As the persulfate, sodium persulfate, ammonium persulfate, potassium persulfate and the like are used. Further, as the reducing agent to be used, sodium sulfite,
Potassium sulfite, ammonium sulfite, sodium bisulfite, potassium bisulfite, ammonium bisulfite, sodium pyrosulfite, potassium pyrosulfite, ammonium pyrosulfite and the like are used. In particular, a redox polymerization initiator obtained by combining ammonium persulfate and potassium bisulfite is preferable.

(A) In the copolymerization reaction of the copolymer,
The components (A) and (B) may be added simultaneously to the reaction system, or the component (A) may be added to the component (B). (B) In the copolymerization reaction of the copolymer,
It is preferable to add both components (A) and (C) simultaneously to the reaction system.

The concentration of the persulfate is preferably from 0.003 to 0.2 mol, and more preferably from 0.007 to 0.1 mol, per mol of the vinyl monomer. The persulfate concentration is 0.
If it exceeds 2 moles, the weight average molecular weight of the obtained copolymer decreases, and the slump holding power also deteriorates. Conversely, 0.00
If the amount is less than 3 mol, the viscosity of the aqueous solution becomes high, handling becomes difficult, and the slump holding force is deteriorated.

The reducing agent such as sulfite is used in an amount of 0.01 to 10 mol, preferably 0.01 to 0.1 mol, per 1 mol of persulfate.
It is desirable to use them together in a proportion of 09 mol. This amount is 1
When the amount is more than 0 mol, the salt concentration of the obtained copolymer becomes high, and the durability of the cement is deteriorated. On the other hand, if the amount is less than 0.01 mol, the polymerization rate is reduced, and the initial fluidity and slump holding power are significantly deteriorated.

The polymerization temperature is preferably from 15 to 70 ° C. If the polymerization temperature exceeds 70 ° C., thermal decomposition of persulfate occurs, and the polymerization rate decreases, leading to deterioration in initial fluidity and slump holding power. Also, when the polymerization temperature is lower than 15 ° C., the polymerization rate is reduced, and the same phenomenon occurs.

The time required for the polymerization is usually about 20 minutes to 4 hours, but is appropriately selected depending on the ratio of the monomers, the concentration of the aqueous solution and the like. The pH of the polymerization reaction is preferably 2 or more.

In addition, as long as the effects of the present invention are not impaired,
With respect to the monomer components (A) and (B) of the copolymer (a) and the monomer components (A) and (C) of the copolymer (b), other copolymer components such as styrene and acrylonitrile are further added. , Methacrylonitrile, acrylamide, methacrylamide, acrylate, methacrylate, vinyl acetate and the like may be copolymerized.

In the cement admixture of the present invention, (a),
(B) The copolymer was prepared by (a) / (b) = 50 / 50-95.
/ 5 weight ratio, preferably 70/30 to 90/10 weight ratio. If the weight ratio exceeds 95/5, the slump holding power is degraded, and setting delay may be caused. Conversely, if it is less than 50/50, the initial fluidity is poor.

When the combination of the molecular weights of (a) / (b) copolymers is a low molecular weight / high molecular weight combination of less than 40,000, the initial fluidity is good, but the slump holding effect is slightly inferior. It has high air entrainment and slightly deteriorates in terms of cement strength. Also, polymer / polymer of less than 70000 /
In the case of a combination of low molecules, there is almost no air entrainment,
The initial fluidity is slightly inferior, and the slump holding effect slightly deteriorates after 30 minutes.

In the present invention, (a),
(B) In both copolymers, the monomer components (A) constituting each copolymer may be the same or different.

The blend of the copolymers (a) and (b) of the present invention is desirably added to the cement blend in an amount of 0.01 to 2.0% by weight based on the amount of cement. The admixture of the present invention can be used in the form of an aqueous solution or powder, and the addition time can be any time from kneading to molding of the cement product. If necessary, a concrete admixture material such as a known AE agent, an AE water reducer, a high-performance AE water reducer, a hardening accelerator, a setting retarder, a rust inhibitor, a separation reducer, a swelling agent, and a polymer admixture may be used. They can be used together.

[0033]

According to the present invention, the copolymer (a) obtained by copolymerizing the following monomer components (A) and (B) and the copolymer (b) obtained by copolymerizing the monomer components (A) and (C) are obtained. ) By using a copolymer in combination as a cement admixture, a copolymer of the two components (A) and (B), a copolymer of the two components (A) and (C), As compared with the three-component copolymers (B) and (C), excellent fluidity can be obtained, and the fluidity can be prevented from lowering with time, and hardly shows air entrainment to cement. Therefore, a high water reducing effect is obtained, and the fluidity is good even in a system with a small amount of added water, and the hardening properties of the cement, and a high-strength hardened cement can be obtained without adversely affecting the properties after hardening. it can.

(A) N-substituted-α, β-unsaturated monocarboxylic amide derivatives. (B) an unsaturated carboxylic acid or a salt thereof. (C) unsaturated carboxylic acid esters or vinyl acetate.

[0035]

【Example】

Production Example 1 A reactor equipped with a reflux condenser, a dropping funnel, and a gas introduction tube and having a stirrer having a content of 300 ml and containing 0.29 mol (67
g) aqueous solution of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS.Na) and 0.1
3 mol (14 g) of sodium methacrylate (MA · N
a) An aqueous solution was added, the atmosphere was replaced with nitrogen, and the temperature was raised while flowing nitrogen. When the temperature reached 50 ° C., 0.019 mol (2.38 g) of potassium bisulfite dissolved in a small amount of water and 0.02 mol of ammonium persulfate dissolved in a small amount of water (4.
75 g) was added, and polymerization was carried out for 1 hour while maintaining the polymerization temperature at 50 ° C. At this time, the AMPS for all the reaction systems was used.
-The concentration of Na and MA-Na was 30 wt%.

The weight average molecular weight of the copolymer thus obtained was 120,000 as measured by gel permeation chromatography (GPC). This was used for the copolymer (a) of Examples 3, 9 to 11 and Comparative Example 1 described later.

Preparation Example 2 Based on the reactor of Preparation Example 1, 0.32 mol (72 g)
Of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS.Na) and 0.08 mol (8 g) of methyl methacrylate (MMA) were added to replace with nitrogen, and the temperature was raised while flowing nitrogen. At the time when the temperature reached 50 ° C., potassium bisulfite 0.0
048 mol (0.59 g) and 0.005 mol (1.12 g) of ammonium persulfate dissolved in a small amount of water were added, and polymerization was carried out for 30 minutes while maintaining the polymerization temperature at 50 ° C.
At this time, the concentration of AMPS · Na and methyl methacrylate relative to the whole reaction system was 30 wt%.

The weight average molecular weight of the thus obtained copolymer was 110,000 as measured by gel permeation chromatography (GPC). This was used for the copolymer (b) of Examples 3, 9 to 11 and Comparative Example 2 described later.

Hereinafter, the addition amounts of potassium bisulfite and ammonium persulfate are appropriately changed, and others are different in the molecular weights used in Examples 5 to 7 (a) and
(B) A copolymer was produced.

The copolymers used in Examples 12 to 17 were produced by changing the types or ratios of the copolymerized monomers. However, in the production of the copolymer (a) used in Example 17, potassium bisulfite was used instead of potassium bisulfite.
In the production example of the copolymer (b) of No. 2, potassium pyrosulfite was used.

Examples 1 to 5 and Comparative Examples 1 to 5 Copolymer (a) of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS.Na) / sodium methacrylate (MA.Na) having different molar ratios Polymer and sodium 2-acrylamido-2-methylpropanesulfonate (AMPS.Na) having different copolymerization molar ratio
A blend containing the (b) copolymer of / methyl methacrylate (MMA) was used as a hydraulic cement admixture, and its performance was evaluated.

The mixture was weighed by mixing the composition A shown in Table 1 so that the kneading amount became 50 liters, and the total amount and a predetermined amount of the cement admixture (0.3 wt% as a pure component with respect to the cement) were 10%.
The mixture was put into a 0 liter Eirich mixer and kneaded for 90 seconds.

Remove the mixture from the mixer and immediately
Slump is measured in accordance with IS A 1101 and air volume is measured in accordance with JIS A 1128,
This measured value was taken as the value immediately after.

Further, after exactly the same kneading was performed in another mixer, the setting time was determined according to Annex 1 of JIS A6204.
The measurement was carried out according to the method described in (1). After the measurement, the mixture is
Transfer to a 0-liter tilting mixer, and operate at low speed (2 rpm
m), and after a lapse of a predetermined time, the slump and the amount of air with time were measured by the same test. Further, the compressive strength after 7 days and 28 days after curing was measured according to JIS A 1108.

The following results are shown separately in Tables 2 and 3 below. Further, without adding a cement admixture, an attempt was made to mix a base concrete having a slump value of 18.0 cm immediately after kneading, and the blended composition was shown as composition B in Table 1 with reference to the blended composition. In addition, when it mix | blends with the composition A of Table 1 without adding a cement admixture, there is no initial fluidity and it cannot mix substantially.

From these results, it can be seen that the admixture of the present invention provides excellent initial fluidity even with a small amount of addition and a high water reduction, and also has a good slump holding effect. In addition, it hardly exhibits air entrainment and does not adversely affect the properties of the cement after curing.

[0047]

[Table 1] Note) Cement: ordinary Portland cement (specific gravity 3.1
6) Sand: Kisarazuyama sand (specific gravity 2.59) Coarse aggregate: Kuzuu crushed stone (specific gravity 2.71)

Examples 6 to 8 2-acrylamides having different molecular weights obtained in Production Examples
2-methylpropanesulfonic acid ・ Na (AMPS ・ N
a) / (meth) acrylic acid · Na (MA · Na) copolymer (molar ratio: 69/31) and 2-acrylamido-2-methylpropanesulfonic acid · Na (A) having different molecular weights
The performance as a hydraulic cement admixture was evaluated in the same manner for a compound obtained by combining the copolymer (MPS.Na) / methyl methacrylate (MMA) with the (b) copolymer (molar ratio: 80/20). The results are shown separately in Tables 4 and 5.

Examples 9 to 11 (a) of AMPS · Na / MA · Na obtained in Production Examples
Copolymer (molar ratio 69/31, weight average molecular weight 120,
(B) copolymer of AMPS.Na/MMA (molar ratio 80/20, weight average molecular weight 110,000)
, And the performance as a hydraulic cement admixture was similarly evaluated for the blends having different blend ratios. The results are shown separately in Tables 6 and 7.

Examples 12 to 17 The copolymer (a) obtained by displacing the component (B) copolymer obtained in the Production Examples and the copolymer (b) obtained by displacing the component (C) copolymerized monomer were used. About the compound with a polymer, the performance as a hydraulic cement admixture was evaluated similarly. The results are shown separately in Tables 8 and 9.

[0051]

[Table 2]Table 2: Compounding ratio of (a) / (b) copolymer = 80/20 (weight ratio)  Cement admixture * ¹ (a) copolymer (b) copolymer AMPS ・ Na / MA ・ Na weight average AMPS ・ Na / MMA weight average(Molar ratio) Molecular weight (Molar ratio) Molecular weight Actual 1 95/5 750 50/50 300,000 Application 2 85/15 30,000 70/30 290,000 Example 3 69/31 120,000 80/20 110,000 4 55/45 230,000 90/10 50,0005 5/95 300,000 95/5 10,000  1 69/31 120,000--Ratio 2--70/30 110,000 Comparison 3 AMPS, Na / MA, Na / MMA (molar ratio) = 30/50/20 101,000 Example 4 97/3 500 98 / 25,0005 3/97 400,000 30/70 350,000  * 1) The additive amount of cement admixture is 0.1% as pure content.
3% (vs. cement). Note) For Examples 1 to 3 and Comparative Example 4, the AE agent was used.
With 0.01% Vinsol (Yamaso Chemical Co., Ltd.)
Added. Comparative Example 3 has a ternary composition comprising three monomer components.
Only the polymer was added.

[0052]

[Table 3] Table 3: (a) / (b) blending ratio of copolymer = 80/20 (weight ratio) Evaluation Result Slump change with time Change with air change with time Compressive strength (cm) (%) (Kgf / cm ²⁾ after 30 min 60 min 90 min after 30 min 60 min 90 min 7 days 28 days 1 18.0 17.0 15.5 14.0 4.8 4.5 4.9 5.1 700 880 real 2 18.5 16.5 15.5 14.5 4.5 4.7 4.8 4.9 740 920 facilities 3 19.0 20.0 20.0 20.0 4.5 4.4 4.2 4.7 750 950 Example 4 19.0 20.0 17.0 15.0 4.4 3.6 3.4 4.2 730 930 5 20.0 20.5 18.0 14.0 4.2 3.4 3.2 3.6 720 910 1 21.0 22.0 8.0-1.0 1.1 1.0---Ratio 2 18.0 18.5 17.5 16.0 14.0 12.0 16.0 17.0 650 800 Comparison 3 20.0 19.5 17.5 9.0 5.1 4.5 4.6 4.8 690 850 Example 4 16.5 14.5 7.0 − 3.4 3.2 3.1 − − − 5 18.0 19.0 18.5 17.5 12.0 11.0 14.0 19.0 620 790

[0053]

[Table 4] Note) The additive amount of cement admixture is 0.3
wt%. In Examples 6 and 7, Vinsol (manufactured by Yamamune Chemical Co., Ltd.) 0.01% was added as an AE agent.

[0054]

[Table 5]Table 5: Compounding ratio of (a) / (b) copolymer = 80/20 (weight ratio) Evaluation results  Slump time change Air amount change with time Compressive strength(cm) (%) (Kgf / cm ² )  Immediately after Half an hour 60 minutes 90 minutes Immediately after Half an hour 60 minutes 90 minutes 7th 28th day Actual 6 18.0 16.6 15.4 14.0 4.6 4.8 4.9 5.0 710 920 Application 7 18.4 20.0 20.0 20.0 4.4 4.3 4.1 4.7 740 950Example 8 17.2 19.0 16.0 14.0 4.6 3.8 3.4 5.0 730 940

[0055]

[Table 6] Note) The additive amount of cement admixture is 0.3
wt% (based on cement). In Examples 9 to 10, Vinsol (Yamasune Chemical Co., Ltd.) was used as an AE agent.
0.01%.

[0056]

[Table 7]  Evaluation results  Slump time change Air amount change with time Compressive strength(cm) (%) (Kgf / cm ² )  Immediately after Half an hour 60 minutes 90 minutes Immediately after Half an hour 60 minutes 90 minutes 7th 28th day Actual 9 20.0 19.0 17.5 15.5 4.2 3.6 3.8 4.0 740 940 Allocation 10 19.0 20.0 20.0 20.0 4.5 4.4 4.2 4.7 750 950Example 11 18.0 18.5 17.5 16.0 4.8 4.5 4.7 5.0 720 910

[0057]

[Table 8]  Cement admixture (a) copolymer (b) copolymer Mixing ratio (B) (C) Adult AMPS ・ Na / (B) Weight average Adult AMPS ・ Na / Weight average a / bMinute (Molar ratio) Molecular weight Minute (C) (molar ratio) Molecular weight wt ratio 12 AA ・ Na 30/70 46,000 MA 60/40 90,000 80/20 Actual 13 AA ・ Na 50/50 54,000 EA 60/40 95,000 80/20 Application 14 AA ・ Na 60/40 30,000 EMA 70/30 80,000 80/20 Example 15 ML ・ Na 59/41 45,000 DMM 80/20 80,000 70/30 16 ML ・ Na 59/41 45,000 DEM 80/20 87,000 70/30 17 AA ・ Na 80/20 47,000 VA 60/40 75,000 60/40 AA · Na: Sodium acrylate ML · Na: Sodium maleate MA: Methyl acrylate EA: Ethyl acrylate EMA: Ethyl methacrylate DMM: Dimethyl maleate DEM: Diethyl maleate VA: Vinyl acetate Note) Addition of cement admixture The amount is 0.3w as pure content
t% (vs. cement). In Examples 12 to 17,
As an AE agent, Vinsol (Yamasune Chemical Co., Ltd.)
0.01%.

[0058]

[Table 9]  Evaluation results  Slump time change Air amount change with time Compressive strength(cm) (%) (Kgf / cm ² )  Immediately after Half an hour 60 minutes 90 minutes Immediately after Half an hour 60 minutes 90 minutes 7th 28th day 12 18.0 17.5 16.0 14.0 4.0 3.8 3.9 4.1 710 920 Actual 13 18.0 17.8 16.5 15.0 4.2 3.9 4.0 4.2 730 930 Allocation 14 18.5 19.0 18.0 16.0 4.5 4.3 4.7 4.9 720 940 Example 15 18.0 17.0 15.0 14.0 3.9 3.5 3.6 3.6 710 930 16 18.0 17.5 16.5 15.0 4.0 3.6 3.6 3.7 720 93017 20.0 19.0 17.5 15.0 3.8 3.4
3.5 3.5 690 900

Continuation of the front page (56) References JP-A-5-17191 (JP, A) JP-A-4-55355 (JP, A) JP-A-4-12039 (JP, A) JP-A-3-228856 (JP) JP-A-62-216950 (JP, A) JP-A-4-89900 (JP, A) JP-A-60-171256 (JP, A) JP-A-61-209944 (JP, A) JP-A-3-257047 (JP, A) JP-A-3-257046 (JP, A) JP-A-3-228855 (JP, A) JP-B 2-5701 (JP, B2) JP-B 1-55210 (JP, A) B2) (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 24/26

Claims (4)

(57) [Claims] (A): (A) an N-substituted-α, β-unsaturated monocarboxylic acid amide derivative represented by the formula (1): (Wherein, R ₁ : hydrogen or a lower alkyl group R ₂ : a linear or branched alkylene group having 1 to 4 carbon atoms X: hydrogen, an alkali metal, an alkaline earth metal, ammonium, or an organic ammonium) (B) unsaturated A copolymer with a carboxylic acid or a salt thereof, wherein the copolymerization ratio is (A) / (B) = 95/5 in a molar ratio.
５5/95 and a weight average molecular weight of 75
(B): (A) N-substituted-α, β represented by the above formula (1)
A copolymer of an unsaturated monocarboxylic acid amide derivative and (C) an unsaturated carboxylic acid ester or vinyl acetate, wherein the copolymerization ratio is (A) /
(C) = A cement admixture characterized by containing a copolymer having a weight average molecular weight of 10,000 to 300,000 in a range of 95/5 to 40/60. 2. The cement admixture according to claim 1, wherein (B) in the component (a) is methacrylic acid or a salt thereof. 3. The method according to claim 1, wherein (C) in the component (b) is methyl methacrylate, ethyl methacrylate, methyl acrylate,
The cement admixture according to claim 1 or 2, which is ethyl acrylate, dimethyl maleate, diethyl maleate or vinyl acetate. 4. A copolymer of the components (a) and (b) produced by redox polymerization using a persulfate and at least one of a sulfite, a bisulfite and a pyrosulfite as a polymerization initiator. The cement admixture according to claim 1, 2 or 3, which has been prepared.