JPH0532441A - Cement additive - Google Patents

Abstract

PURPOSE:To improve the flowability, water-reducing effect and strength of concrete by adding a specific copolymer and the copolymer of N-substituted-alpha,beta- unsaturated monocarboxylic acid amide derivative (NMCA) with vinyl acetate, etc. CONSTITUTION:(A) NMCA of the formula [R1 is H, lower alkyl; R2 is 1-4C linear or branched alkylene; X is H, alkali (ine earth) metal, (organic) ammonium] is copolymerized with (B) an unsaturated carboxylic acid (salt) in an A/B molar ratio of 95/5 to 5/95 to produce (C) a copolymer having a weight- average mol. wt. of 750-300000. The component A is copolymerized with (D) an unsaturated carboxylic acid ester or vinyl acetate in an A/D molar ratio of 95/5 to 40/60 in the presence of a persulfate salt, etc., by a redox polymerization method to produce (E) a copolymer having a weight-average mol.wt. of 10000-300000. The components C and E are mixed with each other in a C/E weight ratio of 50/50 to 95/5 to provide the objective cement additive.

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 properties as a dispersant, a water reducing agent, a fluidizing agent and the like.

[0002]

In recent years, cement compounds such as cement paste, mortar and concrete have been used in large amounts in the fields of civil engineering, construction, secondary concrete products and the like. Admixtures called dispersants, water-reducing agents, superplasticizers, etc. are added to these cement compounds for the purpose of improving slump and workability.

Conventionally, as such admixtures, those mainly containing lignin sulfonate and those mainly containing β-naphthalene sulfonate formalin condensate have been known, but both have advantages and disadvantages. There was no admixture that showed good performance in terms of dispersion fluidity and hardening characteristics of cement.

Japanese Patent Publication No. 2-16260 discloses an N-substituted-α, β-unsaturated monocarboxylic acid amide N-substituted with a sulfonic acid group-containing residue and an α, β-unsaturated monocarboxylic acid. It is described that the salt of the above copolymer is used as an admixture for cement. In addition, Japanese Patent Publication 1-55210
The publication proposes to use a homopolymer of 2-acrylamido-2-methylpropane sulfonate or a copolymer of this monomer and 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-acrylamido-2-methylpropane sulfonate, unsaturated monocarboxylic acid salt, unsaturated carboxylic acid ester and / or acrylonitrile, styrene, vinyl acetate is used as a dispersant for cement. Has been done. In addition, JP-A-62-21695
No. 0 discloses a copolymer of 2-acrylamido-2-methylpropane sulfonate, an unsaturated carboxylic acid salt, and an adduct of unsaturated carboxylic acid with ethylene oxide and / or propylene oxide. Is proposed to be used as.

However, although all of these admixtures or dispersants improve slump loss, they require a large amount of addition in order to obtain initial fluidity (slump), and the amount of water added. Needed to be increased.
Therefore, the hardening characteristics of the cement were deteriorated, and the strength was remarkably reduced.

[0007]

DISCLOSURE OF THE INVENTION The present invention has excellent initial fluidity, prevents the fluidity from deteriorating, and has a water-reducing effect even with a small amount of addition. It is intended to provide a cement admixture having almost no entrainment 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 acid amide derivative represented by Chemical formula 2,

[Chemical 2] (In the formula, R _{1 is} hydrogen or a lower alkyl group R ₂ : a linear or branched alkylene group having 1 to 4 carbon atoms X: hydrogen, alkali metal, alkaline earth metal, ammonium, organic ammonium)

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

(B): (A) N- shown by the above chemical formula 2
A substituted-α, β-unsaturated monocarboxylic acid amide derivative,

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

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Specific examples of the N-substituted-α, β-unsaturated monocarboxylic acid amide derivative of the above-mentioned monomer component (A) include 2-acrylamido-2-methylpropanesulfonic acid and 2-acrylamidoethanesulfone. Acid, 2-
Methacrylamidoethanesulfonic acid, 3-methacrylamidopropanesulfonic acid or salts thereof can be mentioned.

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), an organic ammonium salt such as an alkali metal salt, an alkaline earth metal salt, an ammonium salt, an amine salt or an alkanolamine salt is used.

The (a) copolymer of the present invention comprises the above (A),
The copolymerization ratio of the copolymerization component (B) is (A) / molar ratio.
(B) = It is necessary to be in the range of 95/5 to 5/95, preferably 55/45 to 85/15, and 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 characteristics of the cured product deteriorate.

Further, the copolymer (a) of the present invention is required to have a weight average molecular weight in the range of 750 to 300,000, preferably 40,000 to 300,000, more preferably 90,000 to 230,000.
When the weight average molecular weight exceeds 300,000, the viscosity of the aqueous solution becomes high, making it difficult to handle, and the initial fluidity is significantly deteriorated. On the contrary, when the molecular weight is less than 750, the slump holding power deteriorates.

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

The (b) copolymer of the present invention comprises the above (A),
The copolymerization ratio of the copolymerization component of (C) is a molar ratio of (A) /
(C) = 95 / 5-40 / 60, preferably 80/20
It is necessary to be in the range of 50/50. When the copolymerization ratio exceeds 95/5, the holding power of the slump is significantly deteriorated, while when it is less than 40/60, the amount of air increases and the cement strength is poor.

The weight average molecular weight of the copolymer (b) of the present invention is required to be 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, making it difficult to handle, and the slump holding power is significantly deteriorated. On the other hand, when the molecular weight is less than 10,000, the amount of air increases and the slump holding power also deteriorates.

The (a) and (b) copolymers of the present invention are
For example, it can be synthesized by radical polymerization, but using a redox initiator in which a persulfate is combined with a reducing agent selected from sulfite, bisulfite and pyrosulfite as a radical initiator, aqueous solution polymerization or suspension is used. The above-mentioned (A) and (B) monomer components by polymerization, or
Those obtained by copolymerizing the monomer components (A) and (C) are preferable. As a result, the desired effect of the present invention is 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 in which ammonium persulfate and potassium bisulfite are combined is preferable.

(A) In the copolymerization reaction of the copolymer,
The components (A) and (B) may be added to the reaction system at the same time, 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) to the reaction system at the same time.

The persulfate concentration is preferably 0.003 to 0.2 mol, and preferably 0.007 to 0.1 mol, per 1 mol of the vinyl monomer. The persulfate concentration is 0.
If it exceeds 2 moles, the weight average molecular weight of the obtained copolymer is lowered and the slump holding power is also deteriorated. Conversely, 0.00
When the amount is less than 3 mol, the viscosity of the aqueous solution becomes high, which makes the handling difficult and also causes deterioration of the slump holding power.

The reducing agent such as sulfite is 0.01 to 10 mol, preferably 0.01 to 0.
It is desirable to use them together in a ratio of 09 mol. This amount is 1
When it 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, when the amount is less than 0.01 mol, the polymerization rate is lowered, and the initial fluidity and the slump holding power are significantly deteriorated.

The polymerization temperature is preferably 15 to 70 ° C. If the polymerization temperature exceeds 70 ° C., thermal decomposition of the persulfate will occur, the polymerization rate will decrease, and the initial fluidity and slump retention will deteriorate. Moreover, even if the polymerization temperature is lower than 15 ° C., the polymerization rate is lowered and the same phenomenon occurs.

The time required for the polymerization is usually about 20 minutes to 4 hours, but it 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.

Further, within a range not impairing the effects of the present invention,
In addition 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, acrylic acid ester, methacrylic acid ester, vinyl acetate and the like may be copolymerized.

In the cement admixture of the present invention, (a),
The (b) copolymer is (a) / (b) = 50/50 to 95
/ 5 weight ratio, preferably 70/30 to 90/10 weight ratio. If the weight ratio exceeds 95/5, the slump holding power may be deteriorated and the setting may be delayed. On the contrary, when it is less than 50/50, the initial fluidity is poor.

When the molecular weight combination of the (a) / (b) copolymer is a low molecular weight / high molecular weight combination of less than 40,000, the initial fluidity is good, but the slump retention effect is rather inferior. It has high air entrainment and is slightly deteriorated in terms of cement strength. Polymer / polymer less than 70,000 /
In the case of a combination of small molecules, there is almost no air entrainment,
The initial fluidity is slightly inferior, and the slump holding effect deteriorates slightly after 30 minutes.

In the present invention, (a), which is used in combination,
(B) In both copolymers, the monomer component (A) constituting each copolymer may be the same or different.

The blend of the copolymers (a) and (b) of the present invention is preferably 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 a powder, and the addition time can be any time between the kneading and molding of the cement product. In addition, if necessary, known admixtures of concrete such as AE agents, AE water reducing agents, high-performance AE water reducing agents, hardening accelerators, setting retarders, rust preventives, separation reducing agents, expanding agents, polymer admixtures, etc. It can also be used together.

[0033]

According to the present invention, the copolymer (a) in which the following monomer components (A) and (B) are copolymerized and the monomer components (A) and (C) are copolymerized (b). ) By using the copolymer in combination as a cement admixture, a copolymer of both components (A) and (B) or a copolymer of both components (A) and (C), and further (A), Compared with the three-component copolymers (B) and (C), excellent fluidity is obtained, deterioration of the fluidity over time is prevented, and air entrainment to cement is hardly exhibited. Therefore, a high water reducing effect can be obtained, and even in a system with a small amount of water added, the fluidity is good, and it is possible to obtain a cement hardened product having high strength without adversely affecting the hardening characteristics of cement and the characteristics after hardening. it can.

(A) N-substituted-α, β-unsaturated monocarboxylic acid amide derivative. (B) Unsaturated carboxylic acid or a salt thereof. (C) Unsaturated carboxylic acid ester or vinyl acetate.

[0035]

【Example】

Production Example 1 In a reactor equipped with a reflux condenser, a dropping funnel and a gas introduction tube and having an inner volume of 300 ml and equipped with a stirrer, 0.29 mol (67
g) Sodium 2-acrylamido-2-methylpropanesulfonate (AMPS.Na) in water and 0.1
3 mol (14 g) of sodium methacrylate (MA ・ N
a) An aqueous solution was added to replace the atmosphere 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, AMPS for all reaction systems
-The concentration of Na and MA-Na was 30 wt%.

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

Production Example 2 Based on the reactor of Production Example 1, 0.32 mol (72 g)
Of sodium 2-acrylamido-2-methylpropanesulfonate (AMPS.Na) aqueous solution and 0.08 mol (8 g) of methyl methacrylate (MMA) were added to replace nitrogen, and the temperature was raised while flowing nitrogen. At 50 ° C, potassium bisulfite dissolved in a small amount of water 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 concentrations of AMPS · Na and methyl methacrylate were 30 wt% with respect to the total reaction system.

The weight average molecular weight of the thus obtained copolymer was 110000 as measured by gel permeation chromatography (GPC). This was used as the (b) copolymer of Examples 3 and 9 to 11 and Comparative Example 2 described later.

Hereinafter, the addition amounts of potassium bisulfite and ammonium persulfate were changed as appropriate, and the others were based on the above-mentioned production method, and the molecular weights used in Examples 5 to 7 were different (a),
(B) A copolymer was produced.

Further, the copolymers used in Examples 12 to 17 were produced by changing the kinds or ratios of the copolymerized monomers. However, in the production of the (a) copolymer used in Example 17, potassium bisulfite was used in place of potassium bisulfite in Example 1
In the production example of the copolymer (b) of 2 above, potassium pyrosulfite was used.

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

The composition A of Table 1 below was weighed so that the kneading amount was 50 liters, and the total amount and a predetermined amount of cement admixture (0.3 wt% of cement as pure content) were adjusted to 10
The mixture was put into a 0 liter Erich mixer and kneaded for 90 seconds.

Remove the mixture from the mixer and immediately remove J
The slump is measured according to IS A 1101, and the air amount is measured according to JIS A 1128.
This measured value was taken as the value immediately after.

After the same kneading was carried out in another mixer, the setting time was set to Annex 1 of JIS A6204.
It was measured by the method described in. After measurement, mix 10
Transferred to a 0 liter tilting mixer, low speed (2 rp
After stirring for a predetermined time, the slump and the air amount over time were measured by the same test. Furthermore, 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. Furthermore, without adding a cement admixture, an attempt was made to mix base concrete so that the slump value immediately after kneading would be 18.0 cm, and this mix composition is shown as composition B in Table 1. If the composition A of Table 1 is used without adding the cement admixture, there is no initial fluidity and substantially no kneading is possible.

From these results, it is understood that the admixture of the present invention provides excellent initial fluidity even when the amount added is small and the water reduction rate is high, and the slump retention effect is good. Further, it shows almost no air entrainment and does not adversely affect the cement characteristics 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) / methacrylic acid / Na (MA / Na) (a) 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 blend in which (B) copolymer of MPS.Na) / methyl methacrylate (MMA) (molar ratio 80/20) was combined. The results are shown separately in Table 4 and Table 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,
000) and a (b) copolymer of AMPS / Na / MMA (molar ratio 80/20, weight average molecular weight 110,000).
The performance as a hydraulic cement admixture was evaluated in the same manner with respect to the blends containing and having different blending ratios. The results are shown separately in Table 6 and Table 7.

Examples 12 to 17 Copolymers (a) obtained by displacing the comonomers of the component (B) obtained in the production examples and copolymers (b) obtained by displacing the copolymerization monomers of the component (C). The performance as a hydraulic cement admixture was similarly evaluated for the blend with the polymer. The results are shown separately in Table 8 and Table 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 98/2 5,0005 3/97 400,000 30/70 350,000   * 1) The amount of cement admixture added is 0.
3% (against cement). Note) For Examples 1 to 3 and Comparative Example 4, the AE agent
Vinsol (manufactured by Yamasou Chemical Co., Ltd.) 0.01%
Added Comparative Example 3 is a ternary compound composed of three monomer components.
Only polymer was added.

[0052]

[Table 3] Table 3: Compounding ratio of (a) / (b) copolymer = 80/20 (weight ratio) Evaluation Result Slump time change Air amount change with time Compressive strength (cm) (%) (Kgf / cm ² ) Immediately 30 minutes 60 minutes 90 minutes Immediately 30 minutes 60 minutes 90 minutes 7 days 28 days 1 18.0 17.0 15.5 14.0 4.8 4.5 4.9 5.1 700 880 Actual 2 18.5 16.5 15.5 14.5 4.5 4.7 4.8 4.9 740 920 Application 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 amount of cement admixture added is 0.3
wt%. For Examples 6 to 7, 0.01% of Vinsol (manufactured by Yamasou Chemical Co., Ltd.) was added as an AE agent.

[0054]

[Table 5]Table 5: Compounding ratio of (a) / (b) copolymer = 80/20 (weight ratio)         Evaluation results          Slump change over time Air amount change over time Compressive strength         (cm)  (%)  (Kgf / cm ² )         Right after Half an hour 60 minutes 90 minutes  Right 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 amount of cement admixture added is 0.3
wt% (relative to cement). For Examples 9 to 10, Vinsol (Yamaso Chemical Co., Ltd.) was used as an AE agent.
Manufactured) 0.01% was added.

[0056]

[Table 7]         Evaluation results          Slump change over time Air amount change over time Compressive strength         (cm)  (%)  (Kgf / cm ² )         Right after Half an hour 60 minutes 90 minutes  Right 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 Application 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)          Composition AMPS ・ Na / (B) Weight average Composition AMPS ・ Na / Weight average a / b         Minute (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) The amount of cement admixture added is 0.3w as pure content
t% (relative to cement). In addition, in Examples 12 to 17
As for AE, Vinsol (Yamaso Chemical Co., Ltd.)
Manufactured) 0.01% was added.

[0058]

[Table 9]         Evaluation results          Slump change over time Air amount change over time Compressive strength         (cm)  (%)  (Kgf / cm ² )         Right after Half an hour 60 minutes 90 minutes  Right 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 Application 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

Claims (4)

[Claims] 1. (a): (A) An N-substituted-α, β-unsaturated monocarboxylic acid amide derivative represented by Chemical formula 1, and (In the formula, R _{1 is} hydrogen or a lower alkyl group R _{2 is} a linear or branched alkylene group having 1 to 4 carbon atoms X is hydrogen, alkali metal, alkaline earth metal, ammonium, organic ammonium) (B) Unsaturated A copolymer with a carboxylic acid or a salt thereof, wherein the copolymerization ratio is (A) / (B) = 95/5 in molar ratio.
To 5/95 and a weight average molecular weight of 75
0 to 300000 copolymers, and (b): (A) N-substituted-α, β represented by the above chemical 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) = 95/5 to 40/60, and a cement admixture containing a copolymer having a weight average molecular weight of 10,000 to 300,000. 2. The cement admixture according to claim 1, wherein (B) in the component (a) is methacrylic acid or a salt thereof. 3. The component (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. The copolymer of the above components (a) and (b) is produced by redox polymerization using persulfate and at least one of sulfite, bisulfite and pyrosulfite as a polymerization initiator. The cement admixture according to claim 1, 2 or 3, which has been added.