CN100381387C - A kind of amphoteric carboxylic acid comb-shaped graft copolymer concrete superplasticizer - Google Patents

Abstract

The present invention relates to a kind of concrete superplasticizer of amphoteric carboxylic acid comb-shaped graft copolymer, prepared by the following steps: 1) water-based radical copolymerization reaction: monomer a represented by general formula 1 by 8%～40%, 55-85% of monomer b represented by general formula 2, 2-20% of cationic monomer c and 0-15% of non-ionic monomer d represented by general formula (7), undergo free radical copolymerization in aqueous medium ; 2) Cross-linking reaction: After the polymerization reaction is completed, directly add the cross-linking agent represented by the general formula (8) to carry out the cross-linking reaction. This invention proposes for the first time that zwitterionic polymers can increase the saturation content of concrete superplasticizers, and introduces the concept of zwitterions into the molecular structure design of concrete admixtures, and synthesizes amphoteric carboxylic acid grafts with high water reducing rate Copolymer concrete superplasticizer completely eliminates the environmental pollution caused by the traditional concrete superplasticizer production process, and also exhibits outstanding dispersion performance and slump retention ability at a very low dosage.

Description

A kind of amphoteric carboxylic acid comb-shaped graft copolymer concrete superplasticizer

technical field

The invention relates to a high water-reducing superplasticizer for cement, concrete and mortar, specifically an amphoteric carboxylic acid comb-shaped graft copolymerized concrete superplasticizer, which belongs to the concrete admixture technology in building materials field.

Background technique

Cement concrete is the most widely used building material in the world, but it has disadvantages such as heavy weight, low strength and brittleness. With the rapid development of the construction industry, new requirements have been put forward for various aspects of concrete, such as improving the strength of concrete and improving the slump loss of concrete during transportation. Adding admixtures, especially high-efficiency water reducers, to concrete is an effective, simple and economical method to reduce the water-binder ratio, increase concrete strength, and improve various properties of concrete. Currently used mainly include modified lignin water reducer, naphthalene sulfonate formaldehyde condensate high-efficiency water reducer, melamine sulfonate formaldehyde condensate and new carboxylic acid graft copolymer superplasticizer.

The slump of traditional polycondensation-type water reducers such as naphthalene sulfonate formaldehyde condensate high-efficiency water reducer and melamine sulfonate formaldehyde condensate varies greatly over time, and the production process pollutes the environment, which is not conducive to sustainable development. Moreover, due to the restriction of the molecular structure itself and the mechanism of action, the collapse problem cannot be fundamentally solved, and the performance cannot be greatly improved, and it is impossible to meet the development needs of low water-binder ratio, high strength, and ultra-high strength concrete.

Researchers have turned their attention to carboxylic acid graft polymers, which are known as the third-generation new polymer superplasticizers. The new carboxylic acid graft polymers have: ① low dosage (0.2-0.5 %) to exert high dispersion performance; ②good slump retention, basically no loss in slump of fresh concrete within 90 minutes; ③large degree of freedom in molecular structure, many controllable parameters in admixture manufacturing technology, high performance The potential is great; ④ no strong irritant formaldehyde is used in the synthesis, and it does not cause any pollution to the environment, so it is widely used as a concrete superplasticizer, and has become a worldwide research hotspot.

CN1058474 has reported a kind of new dispersive composition that is used for the excellent slump loss characteristic of cement, and this composition is by alkenyl ether, dialkenyl ether and maleic anhydride as monomer, with Dihelium diisobutyronitrile is polymerized in toluene solvent as an initiator. The product has good slump retention ability, but the dispersion performance is not very satisfactory, and the production process is not conducive to environmental protection.

EP0924174 synthesized different polymers with two side chains of different lengths. Polymers with long side chains have good dispersion due to large steric hindrance, but poor slump retention. Chain copolymers have good slump retention performance, but poor dispersion. When two different copolymers are blended in different proportions, the composite has both a certain dispersion and a certain slump retention ability, but its dispersion and slump retention ability are far from enough.

EP1138697 and US570317 reported that expensive primary amino-terminated monomethyl polyether was used as raw material, and active primary amino groups and carboxyl groups were used for grafting reaction, but the product price was relatively expensive, which was not conducive to vigorous promotion.

In addition, in order to solve the slump loss of concrete, US5362324 and US5661206 have reported the synthesis of ester crosslinked bodies, which have good slump properties due to chain scission and molecular weight reduction under the alkaline medium of cement. High retention capacity, but the dispersion is not very good, not suitable for the preparation of low water-binder ratio, ultra-high strength concrete.

With the development of concrete technology towards low water-binder ratio, high strength, ultra-high strength, high flow, and high durability, it is necessary to further develop high-efficiency superplasticizers with better water-reducing rate and slump retention performance. Many scholars have made a lot of research and experimentation.

US2002/0193547A1 describes the preparation method of polycarboxylate superplasticizer, which adopts the adduct of polyethyleneimine and ethylene oxide with a certain molecular weight to carry out graft reaction with glycidyl methacrylate at low temperature Prepare a macromonomer with reactive polymerization activity, and then carry out a copolymerization reaction with methacrylic acid and methoxypolyethylene glycol methacrylate monoester in an aqueous solution medium to obtain the target product, which has good dispersion and dispersion retention properties .

US6680348B1 also describes a method for preparing a water-soluble amphoteric carboxylic acid superplasticizer, using excessive diethylenetriamine or polyethylenepolyamine and adipic acid for condensation reaction to prepare a polycondensate with active amine groups, Afterwards, carry out grafting reaction with equimolar methacrylic acid to prepare a macromonomer containing amine groups, and then use the remaining amine groups on the macromonomer to carry out ring-opening polymerization with ethylene oxide in a high-pressure reactor to prepare a compound that can participate in The cationic macromonomer component of the polymerization reaction is finally subjected to a copolymerization reaction with sodium methacrylic acid and methoxy polyethylene glycol methacrylic acid monoester in an aqueous solution reaction medium to obtain the target product. The product has good dispersibility and dispersion retention performance.

However, the preparation process of such copolymers described in US2002/0193547A1 and US6680348B1 patents is complex, the operation is difficult to control, and the amount of admixtures is relatively high when preparing high-strength concrete.

Therefore, there are many problems about polycarboxylate superplasticizers at present. The synthesis process of these products is unsatisfactory, unclean and uneconomical, and its application performance is not completely satisfactory. Although some products have good Good dispersibility, but the ability to maintain dispersibility is not good. Some products have a certain ability to maintain slump, but the dispersibility is not good. Moreover, the current polycarboxylate admixture product has a low saturation point, and the water reducing rate is difficult to reach more than 35%. Even if the dosage is increased, the water reducing performance is difficult to further improve, which cannot meet the needs of the development of low water-binder ratio, high strength and high performance concrete .

Contents of the invention

The purpose of the present invention is to develop amphoteric carboxylic acid comb-shaped graft copolymers that do not have the disadvantages described in the background technology, are relatively simple in production technology and have good application performance and can be used as concrete superplasticizers.

The researchers of the present invention have found through a large number of experimental studies that comb copolymers with short grafted side chains have low dispersibility due to weak steric hindrance effects, but good dispersion retention, while comb-shaped copolymers with longer grafted side chains The chain copolymer is beneficial to the early fluidity due to the strong steric hindrance effect, but the fluidity retention ability is poor. Therefore, in order to improve its dispersion performance, a large number of long polyether side chains must be introduced into the main chain to provide steric hindrance, thereby providing its good dispersion performance.

The researchers of the present invention have found through a large number of experimental studies that the cement system is a high-salt, high-pH system, and the molecular conformation of the traditional carboxylic acid graft copolymer is greatly affected by the salt concentration, especially Ca ²⁺ . If the conformation is in the cement If the system is more compact, the adsorption will be slower, and the steric resistance provided will be lower, which is not conducive to the dispersion of concrete. The main chain of the carboxylic acid graft copolymer is designed as a zwitterionic polymer, which reduces its sensitivity to inorganic salt ions, maintains its stretched conformation, and can also provide electrostatic repulsion, thereby improving its dispersion performance.

The researchers of the present invention also found that when the main chain of the carboxylic acid graft copolymer is designed as an amphoteric polymer, its saturation content as a concrete superplasticizer can be greatly increased, and the water-binder ratio of concrete can be greatly reduced.

The researchers found that the amphoteric carboxylic acid comb-shaped graft copolymers can be copolymerized by directly introducing cationic monomers and adopting an aqueous solution copolymerization method. The synthesized copolymers exhibit excellent dispersion properties and high saturation content.

The researchers found that increasing the proportion of long side chains in the copolymer will inevitably lead to a decrease in its slump retention ability. The researchers found that by introducing polymers or monomers that can undergo cross-linking reactions, the carboxylic acid polymers are partially Cross-linking reaction, the partially cross-linked carboxylic acid copolymer is hydrolyzed in the alkaline environment of the cement slurry, and gradually converted into a low-molecular polymer with a dispersing function, so as to achieve the purpose of improving the slump retention performance, and at the same time through Adjusting the relative ratio of anions and cations can also change the adsorption state of the graft copolymer on cement particles, which is also beneficial to improve its slump retention performance.

Find according to above-mentioned research, the amphoteric carboxylic acid class comb copolymer concrete superplasticizer of the present invention is prepared by the following steps:

1) Water-based radical copolymerization reaction: 8% to 40% of monomer a, 55 to 85% of monomer b, 2 to 20% of cationic monomer c, 0-15% of nonionic monomer d, in an aqueous medium Free radical copolymerization occurs in ; where,

Monomer a is represented by general formula (1):

In the formula, R is a hydrogen atom or a methyl group, and M is a hydrogen atom, an alkali metal ion, an alkaline earth metal ion, an ammonium ion or an organic amine group;

Monomer b is represented by general formula (2):

In the formula, R is a hydrogen atom or a methyl group, _R1 is an alkyl group with 1 to 22 carbon atoms, AO is an oxyalkylene group with 2 to 4 carbon atoms or a mixture of two or more such oxyalkylene groups, If AO is a mixture of two or more such oxyalkylene groups, these groups can be added in a block or random form, and n is the average addition mole number of oxyalkylene groups, which is 10 to 150;

Cationic monomer c adopts the material represented by general formula (4), or general formula (5) or chemical formula (6):

Wherein: R is a hydrogen atom or a methyl group;

R ₂ , R ₃ , R ₁ : H or C ₁ ~ C ₁₀ alkyl, R5: H or C ₁ ~ C ₄ alkyl;

R ₆ , R ₇ : C ₁ ~ C ₁ alkyl or hydroxyethyl or hydroxypropyl;

A: F, Cl, Br, I, or BF ₁ ;

X: O or NH; p, q: positive integers from 0 to 3

The nonionic monomer d is represented by the general formula (7):

Among them: R is a hydrogen atom or a methyl group, R ₈ : C ₁ ~ C ₄ alkyl or hydroxyethyl or hydroxypropyl

2) crosslinking reaction: after the polymerization reaction finishes, directly add the crosslinking agent shown in general formula (8), carry out crosslinking reaction,

The compound represented by the general formula (2) of the present invention consists of a monoalkyl polyether represented by the general formula (3) and an unsaturated carboxylic acid represented by the general formula (1) in a small amount of solvent medium, an acid catalyst and a little polymerization inhibitor The esterification reaction takes place under certain conditions.

R ₁ O(AO)nH (3)

Within the scope of the present invention, monomer a (general formula 1) mainly includes acrylic acid, methacrylic acid and their corresponding acrylates or methacrylates. These monomers can be used alone or in the form of two or more components. Use in mixtures.

Monomer b (formula 2) is suitable polyether monoacrylate or polyether monomethacrylate, the branched polyether macromolecule (formula 3) is an alkylene oxide having a weight average molecular weight of about 200 to 8000 For polymers, suitable alkylene oxides include ethylene oxide, propylene oxide, butylene oxide, and the like, and mixtures thereof. They can be linear or branched polymers, homopolymers or copolymers, random or block copolymers, diblock or multiblock copolymers. Preferred monomers b are polyethylene glycol alkyl ether acrylates, polyethylene glycol alkyl ether methacrylates, alkyl ether acrylates of block or random copolymers of ethylene oxide and propylene oxide or Alkyl ether methacrylate, under the condition of a small amount of solvent medium, acid catalyst and a little polymerization inhibitor by monoalkyl polyether shown in general formula (3) and unsaturated carboxylic acid shown in general formula (1) Generated by esterification reaction. n is the average added mole number of oxyalkylene groups, and is 10-150, preferably 12-130, and more preferably 15-60.

Typical ions that can be cited as cationic monomer c are methacryloyloxyethyltrimethylammonium chloride, methacryloyloxyethyldimethylbenzylammonium chloride, methacryloyloxypropyl Trimethylammonium Chloride, Methacryloyloxypropyldimethylbenzylammonium Chloride, Acryloyloxyethyltrimethylammonium Chloride, Acryloyloxyethyldimethylbenzylammonium Chloride, Propylene Amidopropyltrimethylammonium Chloride, Acrylamidopropyldimethylbenzylammonium Chloride, Methacrylamidopropyltrimethylammonium Chloride, Methacrylamidopropyldimethylbenzyl ammonium chloride, dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylamide, N,N-dimethylaminomethacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, dimethylaminoethylacrylamide, dimethyldiallylammonium chloride.

Can be used as non-ionic monomer d mainly acrylate or methacrylate monomers, typical examples include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate ester, butyl methacrylate, hydroxyalkyl acrylate and hydroxyalkyl methacrylate, preferably methyl acrylate, methyl methacrylate, hydroxyalkyl acrylate and hydroxyalkyl methacrylate, more Preferred are methyl acrylate, hydroxypropyl acrylate, hydroxyethyl acrylate, and hydroxyethyl methacrylate. These components can be used alone or in combination.

Typical examples of the crosslinking agent f that can participate in the crosslinking reaction include diglycidyl phthalate, diglycidyl adipate, various molecular weight polyethylene glycol diglycidyl esters, various molecular weight Polypropylene glycol diglycidyl ester, and polyethylene glycol-polypropylene glycol diglycidyl ester.

Within the scope of the present invention, monomer a (general formula 1) is necessary, monomer a accounts for 8-40% of the total amount of monomers, and the content of monomer a is too low, and the synthetic superplasticizer cannot be fully adsorbed to cement Particles, so they cannot play a dispersive role. If the content is too high, the copolymer will absorb too quickly, and the fluidity of the fresh concrete or mortar mixed with the copolymer will also lose quickly.

Monomer b such as the long-chain polyether monoacrylate or polyether monomethacrylate shown in general formula (2) is copolymerized into the main chain, and its long branch mainly provides steric hindrance, thereby improving the comb shape. The dispersibility and dispersion retention ability of graft copolymer to cement. Monomer b accounts for 55-85% of the total amount of monomers. If the content of monomer c is too low, the dispersion of the synthesized copolymer will be weak. If the content is too high, the slump loss of the produced copolymer will be large.

Cationic monomer c is represented by general formula (3) and monomer c accounts for 2 to 20% of the total amount of monomers, preferably 4 to 15%. The content of monomer c is too low to act as an amphoteric polymer. The synthesized The saturated content of the copolymer is not high, if the monomer c content is too high, the synthesized copolymer will not only produce precipitation but also have poor dispersion and dispersion retention.

Monomer d is optional, but generally it is about 0-15% of the total amount of monomers.

Free radical copolymerization itself is relatively unimportant, and the water-soluble initiator that is suitable for the inventive method is conventional free radical water-soluble initiator and mixture thereof, comprises water-soluble ammonium persulfate, potassium persulfate, sodium persulfate and hydrogen peroxide etc. The total initiator added to the reaction mixture should account for about 0.1-15.0% of the total amount of monomers added, preferably about 0.2-12% (by weight), and the actual added amount has a lot to do with the type of initiator used.

It is advisable to control the concentration of comonomer in 15-40%, and the reaction time is probably controlled in 5-10 hours. The monomer mixture and the initiator solution are added separately and simultaneously to control the uniformity of the distribution of the copolymer chain segments and the stability of the polymerization reaction itself. should. The polymerization temperature itself is preferably carried out at 60-100°C, which is mainly related to the decomposition temperature of the initiator used.

After the copolymerization reaction is over, at this temperature, a certain amount of cross-linking agent is directly added. The structure of the cross-linking agent is shown in general formula (8). When the molecular weight is fixed before cross-linking, the greater the amount of cross-linking agent, The greater the viscosity, the worse the dispersibility. If the amount of cross-linking agent is too large, the cross-linking density between the two polymer molecules will be too high. The copolymer will become a water-insoluble gel and will no longer have dispersibility. Therefore, the amount of cross-linking agent must be controlled in an appropriate amount, at most one cross-linking point is reached between every two molecules, so that the cross-linking does not affect the initial fluidity of the polymer, and at the same time it can improve its flow retention performance. It is more appropriate to control the dosage of the cross-linking agent in the range of 0.5-3% of the total weight of the polymerized monomers, and the cross-linking reaction is finished after 1h-3h of stirring reaction.

After the cross-linking reaction, the carboxylic acid or acid anhydride can be converted into a salt form by reacting with a base. The finished product is named SSP, and its pH value is best adjusted to 7.0-8.5. If the pH value is too low or too high, the polymer The storage stability is not good.

In the present invention, the weight-average molecular weight of the comb-shaped graft copolymer SSP used as a concrete superplasticizer is not particularly limited, generally at 5,000-500,000, but considering its slump retention performance and dispersion performance, it is preferably 10,000-100,000, If the molecular weight is too small, not only the water-reducing performance will decrease, but also the slump-retaining ability will drop significantly. If the molecular weight is too large, not only the water-reducing performance will decrease, but also the slump-holding ability will also decrease significantly.

When used, the conventional dosage of the concrete superplasticizer of the present invention is 0.2-0.5% of the total adhesive material. If a higher water-reducing rate is required, the dosage can be increased, even up to 1.0% of the total adhesive material. Of course, if the added amount is less than 0.20%, the slump retention capacity of fresh concrete is not satisfactory.

Of course, the concrete superplasticizer of the present invention can also be combined with at least one selected from known sulfamic acid-based water-reducers in the prior art, lignin-based common water-reducers and existing polycarboxylic acid-based superplasticizers. agent mixed.

In addition, in addition to the known concrete water reducers mentioned above, air-entraining agents, expansion agents, retarders, early strength agents, tackifiers, shrinkage reducers and defoamers can also be added therefrom.

Compared with prior art, advantage of the present invention is obvious:

①The present invention adopts an environment-friendly aqueous solution copolymerization method, does not use toxic substance formaldehyde, does not use highly corrosive fuming sulfuric acid and concentrated sulfuric acid, and the reaction process can achieve zero emissions, without generating any waste gas, waste water, and waste residue, realizing Clean production of concrete water reducer; completely eliminate the pollution of the environment caused by the traditional production process of concrete water reducer;

②The present invention proposes for the first time that zwitterionic polymers can increase the saturation content of concrete superplasticizers, and introduces the concept of zwitterions into the molecular structure design of concrete admixtures, and synthesizes amphoteric carboxylic acid grafts with high water reducing rate. Branch copolymer concrete superplasticizer;

③Compared with conventional water reducers, the concrete superplasticizer prepared in the present invention also exhibits outstanding dispersion performance and slump retention ability at very low dosage, and with the increase of dosage, water reducing The rate will continue to increase, its saturation point is very high, and the product enhancement effect is good. When the admixture is tested according to the JC473-2001 "Concrete Pumping Agent" standard, when the amount of cement is 0.3%, the water reduction rate can reach 38%, and the water reduction rate can reach 45% when the amount is increased. No matter in the early stage or in the middle and late stage, the strength growth is relatively stable, and the low cement dosage of 390kg realizes the preparation of C80 strength grade concrete;

4. The concrete superplasticizer prepared in the present invention has good adaptability to cement and admixtures, has good slump retention ability, and the slump of freshly mixed concrete does not lose substantially within 90 minutes, if the addition is less than 0.20% , then its fresh concrete slump retention capacity is unsatisfactory;

⑤ The concrete superplasticizer prepared in the present invention has extremely high water-reducing performance, and the water-reducing rate can reach up to 45%, which is more suitable for preparing high-strength, ultra-high-strength concrete, self-compacting high-strength concrete and active powder concrete.

6. The concrete superplasticizer prepared in the present invention can not only be used in the dispersing of various cements, but also can greatly increase the amount of mineral admixtures (slag, fly ash and silica fume, etc.) in concrete (up to 70%), which is conducive to environmental protection and sustainable development, and can also be used in the dispersion of hydraulic materials other than cement, such as gypsum, coal powder, ceramics and other powder materials.

Detailed ways

Production Example

The following examples describe in more detail the process of preparing amphoteric carboxylic acid comb-shaped graft copolymers according to the method of the present invention, and these examples are given by way of illustration, but these examples in no way limit the scope of the present invention. "Parts" means "parts by weight" if not otherwise specified.

The monomers used in the following examples are shown in Table 1, and the crosslinking agent f used in the examples is shown in Table 2, and the synthetic amphoteric carboxylic acid class comb-shaped graft copolymer concrete superplasticizer is abbreviated as SSP.

In the examples of the present invention, the weight-average molecular weight _Mw of the polymer is measured by Wyatt technology corporation gel permeation chromatography (miniDAWN Tristar laser light scattering detector).

Monomer used in the embodiment of table 1

Cross-linking agent f used in the embodiment of table 2

Production Example 1 (Synthesis of SSP-1)

In a glass reactor equipped with a thermometer, a stirrer, a dropping funnel, a nitrogen gas inlet tube and a reflux condenser, add 150ml of deionized water, and purging the reaction vessel with nitrogen gas while stirring, and raise the temperature to 95°C, then add 24g (A1) and 164g (B1) and 12g (C-2), and 200 parts of water are mixed to make a mixed monomer aqueous solution, which is added dropwise to the reactor for 2 hours, and at the same time, 80 parts containing For the initiator solution of ammonium persulfate, the dropping time is about 5 hours. After the dropping is completed, the insulation reaction is 1 hour, and then 20 parts of hydrogen peroxide initiator solution containing 35% concentration are added to the reaction bottle, and the temperature is continued for 2 hours, and cooled to At room temperature, add 2.6g of cross-linking agent (F-1), stir for 1 hour, add alkali to neutralize to pH 7.5, solid content is 30.7% brown transparent liquid, molecular weight is 39,000 (SSP-1), the results are shown in Table 3.

Production Example 2-10 (Synthesis of SSP-2-10)

Prepare SSP-2-10 of the present invention according to the steps of Example 1, but the weight and type of specific monomers have changed, and feed intake according to the ratio described in Table 3, wherein the weight percentage of crosslinking agent (F) It is F/(A+B+C+D).

Comparative example 1

Same as Production Example 4, except that no cross-linking component was added after the polymerization was completed, and alkali was added to neutralize to pH 7.5 to obtain a brown transparent liquid with a solid content of 30.5% and a molecular weight of 13,000. The results are shown in Table 3.

Comparative example 2

Feed according to the proportioning ratio of Table 3, the same as the production procedure described in Production Example 1, except that no cationic monomer is added in the monomer proportioning, after the polymerization is completed, alkali is added to neutralize the pH value to 8.1, and the obtained solid content is 31.7%. Brown transparent liquid with a molecular weight of 55,000.

table 3

Application example

In the application examples, the cement used is Jinningyang 425R.P.II, the sand is medium sand with a fineness modulus M _x =2.6, and the stones are continuously graded crushed stones with a particle size of 5-20 mm.

In this example, the test methods of bleeding rate, air content and setting time refer to the relevant regulations of 6B8076-97 "Concrete Admixtures".

The slump and slump loss refer to the relevant regulations of JC473-2001 "Concrete Pumping Agent". The mix ratio used in the test is C:S:G=390:733:967. The tested concrete with the agent is adjusted to make the slump 20±2cm, and the slump and expansion retention value after 60min and 90min are measured, and the water reducing rate and the strength development of the specimens at different ages are measured at the same time. The change value, concrete compressive strength and compressive strength ratio refer to the relevant provisions of GB/T50081-2002 "Standards for Test Methods of Mechanical Properties of Ordinary Concrete".

Application Example 1

Evaluate the performance of the synthesized carboxylic acid graft copolymer in the production examples and comparative examples, the results are shown in Table 4, and its copolymer dosage is fixed at 0.3% of the total weight of cement.

Table 4

From the results, the synthesized amphoteric carboxylic acid graft copolymer within the scope of the present invention has good dispersibility and slump retention performance, and the fresh concrete slump and expansion degree do not lose substantially in 90 minutes, and the intensity growth rate is relatively large. With a low cement dosage of 390kg, the 28d compressive strength has basically reached more than 70Mpa, and the amphoteric carboxylic acid graft polymer of the present invention does not affect the setting time of concrete, but when the length of the grafted side chain is too long, although the dispersion performance Excellent, but its slump retention ability is poor (such as SSP-8). In addition, when the content of carboxylic acid group adsorption groups is too high, due to too fast adsorption, not only the initial dispersion performance is not good, but also its slump loss soon. It can also be seen from the comparative examples that the amphoteric carboxylic acid graft polymer without crosslinking has poor slump retention performance.

Application Example 2

Taking the amphoteric carboxylic acid graft copolymer SSP-4 as an example to investigate the influence of different copolymer content on the performance of fresh concrete, at the same time using the anionic graft copolymer of Comparative Example 2 as a comparison, by adjusting the water consumption to make the fresh concrete Make the slump 20±2cm, the test results are shown in Table 5.

The test results show that the water reducing rate of the amphoteric carboxylic acid graft copolymer SSP-4 synthesized by direct copolymerization increases with the increase of the dosage. When the amount of cement is added to 0.2%, the water reducing rate is close to 30%. When the dosage is increased to 0.3%, the water-reducing rate of concrete reaches more than 38%, and the slump in 90 minutes is basically not lost. When the dosage is increased to 0.4%, the water-reducing ratio reaches 42.8%, and with the increase of the dosage, The strength growth is also relatively fast, the 3D compressive strength ratio is basically above 250%, and the 28D compressive strength ratio is basically above 200%. On the contrary, Comparative Example 2 is an anionic graft copolymer. When the amount of cement is added to 0.2%, the dispersion performance is basically saturated, and the water reducing rate increases little, and sometimes even decreases slightly when the amount is increased. However, when the content of amphoteric carboxylic acid graft copolymer is lower than 0.30%, the slump loss of fresh concrete is relatively large.

table 5

Application Example 3

Taking the amphoteric carboxylic acid graft copolymer SSP-4 as an example to prepare reactive powder concrete RPC (Reactive Powder Concrete), the most critical measure for preparing RPC is to reduce the water-cement ratio as much as possible, so a large amount of superplasticizer needs to be added. to improve its performance. Table 6 shows the mix ratio of RPC, in which the steel wire cut superfine fiber has a length of 13mm, a diameter of 0.175mm, a tensile strength of 1800Mpa, the amount of high-efficiency water reducing agent is the mass percentage of the cementitious material, and the fluidity of the slurry is 180mm-200mm.

Table 6

Table 7 shows the mechanical properties of RPC prepared using the amphoteric carboxylic acid graft copolymer SSP-4 as an example. From the test results, the amphoteric carboxylic acid graft copolymer synthesized by the present invention can meet the requirements for preparing RPC.

Table 7

Because the amphoteric carboxylic acid graft copolymer synthesized in the present invention can greatly reduce the water consumption of concrete and has high fluidity, good construction performance and excellent slump retention ability, the product is mainly used for preparing low water-binder ratio, High strength, high performance, high fluidity and reactive powder concrete.

Claims (9)

1. an amphoteric carboxylic acid class comb-shaped graft copolymer concrete superplasticizer is characterized in that it is prepared by the following steps: 1) Water-based radical copolymerization: 8% to 40% of monomer a, 55 to 85% of monomer b, 2 to 20% of cations represented by general formula (4), general formula (5) or chemical formula (6) Monomer c and 0-15% non-ionic monomer d undergo free radical copolymerization in an aqueous medium; wherein, Monomer a is represented by general formula (1): In the formula, R is a hydrogen atom or a methyl group, and M is a hydrogen atom, an alkali metal ion, an alkaline earth metal ion, an ammonium ion or an organic amine group; Monomer b is represented by general formula (2):

In the formula, R is a hydrogen atom or a methyl group, _R1 is an alkyl group with 1 to 22 carbon atoms, AO is an oxyalkylene group with 2 to 4 carbon atoms or a mixture of two or more such oxyalkylene groups, If AO is a mixture of two or more such oxyalkylene groups, then these groups are added in block or random form, n is the average addition mole number of oxyalkylene groups, which is 10-150; Cationic monomer c adopts the material represented by general formula (4), or general formula (5), chemical formula (6):

Where: R is a hydrogen atom or a methyl group R ₂ , R ₃ , R ₄ : H or C ₁ to C ₁₀ alkyl, R5: H or C ₁ to C ₄ alkyl R ₆ , R ₇ : C ₁ -C ₄ alkyl or hydroxyethyl or hydroxypropyl A: F, Cl, Br, I or _BF4 X: O or NH p, q: positive integers from 0 to 3 The nonionic monomer d is represented by the general formula (7): Among them: R is a hydrogen atom or a methyl group, R ₈ : C ₁ ~ C ₄ alkyl or hydroxyethyl or hydroxypropyl 2) Cross-linking reaction: After the polymerization reaction is finished, directly add a cross-linking agent to carry out the cross-linking reaction, and the cross-linking agent is selected from diglycidyl phthalate, diglycidyl adipate, various molecular weight poly Ethylene glycol diglycidyl esters, various molecular weight polypropylene glycol diglycidyl esters, and polyethylene glycol-polypropylene glycol diglycidyl esters. 2. The amphoteric carboxylic acid comb graft copolymer concrete superplasticizer as claimed in claim 1, characterized in that its weight-average molecular weight is 5,000-500,000. 3. the amphoteric carboxylic acid comb-shaped graft copolymer concrete superplasticizer as claimed in claim 1 or 2, is characterized in that monomer a is selected from acrylic acid, methacrylic acid, acrylate or methacrylate, these Monomers are used alone or as a mixture of two or more components. 4. the amphoteric carboxylic acid class comb graft copolymer concrete superplasticizer as claimed in claim 1 or 2, is characterized in that monomer b is polyether monoacrylate or polyether monomethacrylate, and its branch Chain polyether macromolecules are oxyalkylene polymers with a weight average molecular weight of 200 to 8000. 5. the amphoteric carboxylic acid class comb-shaped graft copolymer concrete superplasticizer as claimed in claim 1 or 2, is characterized in that cationic monomer c is selected from methacryloyloxyethyl trimethyl ammonium chloride, Methacryloxyethyl Dimethylbenzyl Ammonium Chloride, Methacryloxypropyl Trimethylammonium Chloride, Methacryloxypropyl Dimethylbenzyl Ammonium Chloride, Acryloyloxyethyl Trimethyl ammonium chloride, acryloyloxyethyl dimethyl benzyl ammonium chloride, acrylamidopropyl trimethyl ammonium chloride, acrylamidopropyl dimethyl benzyl ammonium chloride, methyl Acrylamidopropyltrimethylammonium Chloride, Methacrylamidopropyldimethylbenzylammonium Chloride, Dimethylaminoethyl Methacrylate, Dimethylaminopropyl Methacrylamide, N,N-Dimethylamine methacrylamide, N,N-dimethylacrylamide, N,N-diethylacrylamide, dimethylamine ethylacrylamide or dimethyldiallyl chloride ammonium chloride. 6. the amphoteric carboxylic acid class comb graft copolymer concrete superplasticizer as claimed in claim 1 or 2, is characterized in that nonionic monomer d is acrylic acid ester or methacrylic acid ester monomer, comprises acrylic acid Methyl ester, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, hydroxyalkyl acrylate, and hydroxyalkyl methacrylate, either alone or in combination use. 7. the amphoteric carboxylic acid class comb graft copolymer concrete superplasticizer as claimed in claim 1 or 2, is characterized in that the water-soluble initiator adopted in step 1) is conventional persulfate or peroxide The species free radical initiator is selected from water-soluble ammonium persulfate, potassium persulfate, sodium persulfate or hydrogen peroxide, and these initiators are used alone or in combination; all initiators added to the reaction mixture account for the total amount of monomers added 0.1-15.0% of the amount. 8. the amphoteric carboxylic acid class comb-shaped graft copolymer concrete superplasticizer as claimed in claim 1 or 2, is characterized in that the copolymerization reaction monomer concentration is controlled at 15～40%, and the reaction time is controlled at 5～10 hours ; The monomer mixture and the initiator solution are added separately and simultaneously to control the uniformity of the distribution of the copolymer chain segments and the stability of the polymerization reaction itself. The copolymerization reaction is carried out at 60-100°C. 9. the amphoteric carboxylic acid class comb-shaped graft copolymer concrete superplasticizer as claimed in claim 1 or 2, is characterized in that step 2) in cross-linking agent consumption is monomer a, monomer b, monomer c and 0.5-3% of the total weight of the monomer d, stirred and reacted for 1h-3h, and the cross-linking reaction is completed.