Air-entraining viscosity-reducing polycarboxylate superplasticizer and preparation method thereof

Abstract

The invention discloses an air-entraining type viscosity-reducing polycarboxylic acid water reducer and a preparation method thereof, the polycarboxylic acid water reducer is prepared by taking unsaturated polyether macromonomer, unsaturated acid monomer, vinyl polyacetylene monomer and functional monomer as main raw materials through free radical polymerization reaction under the action of an oxidizing agent, a reducing agent and a chain transfer agent. The unsaturated acid monomer is introduced, so that water reducer molecules can be well adsorbed on the surfaces of particles, the electrostatic repulsion effect is exerted, and the particles are further dispersed; the vinyl polyacetylene monomer and the functional monomer are subjected to gradient hydrolysis in alkaline cement paste, carboxyl is gradually released, and the re-adsorption-dispersion effect of water reducing agent molecules on cement particles within a long time is ensured, so that the slump loss is effectively reduced, and the concrete workability is improved. And the process is simple, the raw materials are cheap, large-batch production and manufacturing are facilitated, and the batch concrete matching and selecting requirements are met.

Description

Technical Field

[0001] The invention belongs to the technical field of polycarboxylic acid water reducers, and particularly relates to an air-entraining viscosity-reducing polycarboxylic acid water reducer and a preparation method thereof. Background Art

[0002] In modern construction projects, concrete is an important building material, and the optimization and improvement of its performance are directly related to the quality, durability and economy of the project. Especially in the field of water conservancy projects, hydraulic concrete has been in service for a long time in a humid and changeable environment, and the requirements for its durability are more stringent. In order to further improve the performance of polycarboxylate water reducer and meet the demand for higher durability of concrete in water conservancy projects, air-entraining viscosity-reducing polycarboxylate water reducer came into being. This new type of water reducer not only inherits the original excellent performance of polycarboxylate water reducer, but also introduces air-entraining mechanism and viscosity-reducing function through specific molecular design.

[0003] The introduction of air entrainment mechanism can effectively improve the durability of concrete, such as resistance to freeze-thaw cycles, seawater and impact and abrasion. Introducing an appropriate amount of small bubbles inside the concrete can buffer the damage to the concrete caused by external stress and improve the toughness and durability of the concrete. At the same time, these small bubbles can also serve as channels for water evaporation, reduce the water pressure inside the concrete, and prevent the concrete from cracking.

[0004] The realization of viscosity reduction function helps to reduce the plastic viscosity of concrete and improve the fluidity and pumpability of concrete. This is of great significance for improving the workability of concrete, reducing construction difficulty and improving construction efficiency. Especially in the preparation process of high-grade concrete, the application of viscosity-reducing polycarboxylic acid water-reducing agent is indispensable.

[0005] Polycarboxylate water reducer has become a new means to reduce the viscosity of high-strength concrete due to its strong designability of molecular structure. The invention patent with authorization announcement number: CN106883355B discloses a low air entrainment and viscosity reduction type polycarboxylate water reducer and its preparation method, which is prepared by free radical polymerization of alkyl phosphate triester mixture, isopentanol polyoxyethylene ether, and unsaturated carboxylic acid under the action of initiator and chain transfer agent. The present invention introduces an alkyl phosphate triester monomer containing two double bonds on the main chain, so that the obtained polycarboxylate water reducer molecule presents a heterocyclic multi-branched structure, increases the thickness of the polycarboxylate water reducer adsorption layer, and can significantly reduce the plastic viscosity of concrete. At the same time, by introducing a phosphate triester structure into the molecular structure of the polycarboxylate water reducer, the defoaming performance of the obtained polycarboxylate water reducer can be effectively improved and its air entrainment can be reduced. The corresponding existing product is the viscosity reduction and collapse protection type polycarboxylate water reducer sold on the market by China Construction Commercial Concrete Co., Ltd.

[0006] The invention patent with publication number CN104371081A discloses a method for preparing a fast-dispersing and viscosity-reducing polycarboxylic acid cement dispersant. The method uses an unsaturated macromolecular monomer containing a tertiary amino group as a reducing agent that can participate in polymerization to obtain a hyperbranched polycarboxylic acid cement dispersant. The obtained polycarboxylic acid cement dispersant has the advantages of high water reduction rate, fast dispersion speed, and reduced concrete viscosity. The corresponding existing product is the air-entraining polycarboxylic acid water-reducing agent sold on the market by Jiangsu Subote New Materials Co., Ltd.

[0007] However, although the products obtained by the above two solutions have the effect of air entrainment, the chain strength of the air-stabilizing structure in the polycarboxylic acid water-reducing agent does not play a general role after being actually mixed with concrete, resulting in poor water reduction, collapse prevention and air entrainment effects, thereby resulting in poor durability of the concrete. Summary of the invention

[0008] The object of the present invention is to provide an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent and a preparation method thereof, so as to solve the problems existing in the prior art.

[0009] To achieve the above object, the present invention provides the following technical solution: an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent, the general structural formula of which is shown in Formula 1:

[0010]

[0011] In formula 1, R1 is selected from H or CH3; R2 is selected from at least one unsaturated carboxylic acid monomer; X is selected from CH2O, C2H4O or OC4H6O; wherein a, b, c, d, and n are positive integers selected from 1 to 50.

[0012] A method for preparing an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent comprises the following steps:

[0013] Step 1: Mix unsaturated acid monomers, vinyl polyacetylene monomers dissolved in tetrahydrofuran, functional monomers and chain transfer agents, and add water to obtain a mixed solution A; mix a reducing agent and water to obtain a mixed solution B;

[0014] Step 2: dissolving the unsaturated polyether macromonomer in water at room temperature, adding an oxidant after it is completely dissolved, and then dropping the mixed solution A and the mixed solution B respectively, stirring for reaction and then keeping warm, finally cooling to room temperature and diluting with water to a solid content of 50%, to obtain an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] The air-entrained viscosity-reducing polycarboxylate water-reducing agent in the present invention can provide a steric hindrance effect after being combined with concrete, ensuring the dispersion effect of the water-reducing agent molecules on the particles; ensuring the re-adsorption-dispersion effect of the water-reducing agent molecules on the cement particles for a long time, thereby effectively reducing collapse and improving the workability of concrete. While increasing the air content of concrete, the polycarboxylate water-reducing agent has a certain viscosity-reducing effect due to the increase in air content.

[0017] The preparation method of the air-entraining viscosity-reducing polycarboxylic acid water-reducing agent of the present invention has a simple process and cheap raw materials, is conducive to mass production and manufacturing, and meets the needs of batch concrete matching. DETAILED DESCRIPTION

[0018] The technical solutions in the embodiments of the present invention will be described clearly and completely below.

[0019] An air-entraining type viscosity-reducing polycarboxylic acid water-reducing agent, the general structural formula of which is shown in Formula 1:

[0020]

[0021] In formula 1, R1 is selected from H or CH3; R2 is selected from at least one unsaturated carboxylic acid monomer; X is selected from CH2O, C2H4O or OC4H6O; wherein a, b, c, d, and n are positive integers selected from 1 to 50.

[0022] The invention comprises the following components in parts by weight: 380 parts of unsaturated polyether macromonomer, 5-20 parts of unsaturated acid monomer, 8-15 parts of vinyl polyacetylene monomer and 1-10 parts of functional monomer.

[0023] It is made of unsaturated polyether macromonomers, unsaturated acid monomers, vinyl polyacetylene monomers, and functional monomers as main raw materials, and is produced through free radical polymerization under the action of oxidants, reductants, and chain transfer agents.

[0024] The unsaturated polyether macromonomer is at least one of isopentanol polyoxyethylene ether, 4-hydroxybutyl vinyl polyoxyethylene ether and isoethylene glycol monovinyl polyoxyethylene ether with a molecular weight in the range of 2400 to 3000;

[0025] At least one of unsaturated acid monomers selected from acrylic acid, methacrylic acid, maleic anhydride, sodium methacrylic acid sulfonate and itaconic acid;

[0026] The vinyl polyacetylene monomer is 4-polyphenylethynyl biphenyl acrylate with a molecular weight of 2400, which is prepared by living polymerization of phenylethynyl and 4-ethynyl biphenyl acrylate. The general structural formula of 4-ethynyl biphenyl acrylate is shown in Formula 2, and the general structural formula of 4-polyphenylethynyl biphenyl acrylate is shown in Formula 3;

[0027]

[0028] The functional monomer is at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, ethyl acrylate and 2-methyl methacrylate.

[0029] The oxidant is at least one of ammonium persulfate, hydrogen peroxide and potassium persulfate, and the amount of the oxidant is 0.2-0.4% of the total mass of each reaction monomer;

[0030] The reducing agent is at least one of L-ascorbic acid, isoascorbic acid, ferrous sulfate, sodium methylthiosulfate, sodium sulfite, and sodium bisulfite, and the amount of the reducing agent is 0.05-0.2% of the total mass of each reaction monomer;

[0031] The chain transfer agent is at least one of mercaptoacetic acid, mercaptopropionic acid and mercaptoethanol, and the amount of the chain transfer agent is 0.2-0.4% of the total mass of each reaction monomer.

[0032] The reaction equation of polycarboxylate water reducer is shown in equation 4:

[0033]

[0034] When R1 is CH3, X is CH2O or C2H4O; when R1 is H, X is OC4H6O; wherein a, b, c, d, and n are positive integers ranging from 1 to 50.

[0035] A method for preparing an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent comprises the following steps:

[0036] Step 1: Mix unsaturated acid monomers, vinyl polyacetylene monomers dissolved in tetrahydrofuran, functional monomers and chain transfer agents, and add water to obtain a mixed solution A; mix a reducing agent and water to obtain a mixed solution B;

[0037] Step 2: dissolving the unsaturated polyether macromonomer in water at room temperature, adding an oxidant thereto after it is completely dissolved, and then dropping the mixed solution A and the mixed solution B respectively, stirring for reaction and then keeping warm, and finally cooling to room temperature and diluting with water to a solid content of 50% to obtain an air-entraining type viscosity-reducing polycarboxylic acid water-reducing agent; in step 2, the dropping time of the mixed solution A is 1-3h, and the dropping time of the mixed solution B is 1.5-3.5h; the insulation reaction temperature is 35°C, and the insulation time is 0.5h-1h.

[0038] In combination with the above, the following embodiments and comparative examples are given below:

[0039] Example 1

[0040] An air-entraining viscosity-reducing polycarboxylic acid water-reducing agent, the preparation method of which is as follows:

[0041] (1) In a glass reactor equipped with a thermometer and a stirrer, 380 parts of isoethylene glycol monovinyl polyoxyethylene ether with a molecular weight of 2400 and 360 parts of deionized water were added in sequence and stirred until fully dissolved to obtain a reactant base solution;

[0042] (2) 15 parts of acrylic acid, 10 parts of 4-polyphenylethynyl biphenyl acrylate, 3 parts of hydroxyethyl acrylate, 2 parts of hydroxypropyl acrylate, 1 part of mercaptoethanol and 30 parts of deionized water were mixed to prepare a mixed solution A; 0.6 parts of L-ascorbic acid and 40 parts of deionized water were mixed to prepare a mixed solution B;

[0043] (3) While stirring, add 1.5 parts of hydrogen peroxide to the reactant base liquid, first add mixed solution B dropwise, then add mixed solution A dropwise 2 minutes later, add mixed solution A dropwise for 60 minutes, and add mixed solution B dropwise for 90 minutes; after the addition is complete, keep warm for 60 minutes, add water to dilute to a solid content of 50%, and thus obtain an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent.

[0044] Example 2

[0045] An air-entraining viscosity-reducing polycarboxylic acid water-reducing agent, the preparation method of which is as follows: (1) in a glass reactor equipped with a thermometer and a stirrer, 380 parts of isoethylene glycol monovinyl polyoxyethylene ether with a molecular weight of 2400 and 360 parts of deionized water are added in sequence, and stirred until fully dissolved to obtain a reactant base liquid;

[0046] (2) 12 parts of acrylic acid, 8 parts of 4-polyphenylethynyl biphenyl acrylate, 4 parts of hydroxypropyl acrylate, 1.5 parts of thioglycolic acid and 30 parts of deionized water were mixed to prepare a mixed solution A; 0.6 parts of isoascorbic acid and 40 parts of deionized water were mixed to prepare a mixed solution B;

[0047] (3) While stirring, add 1.3 parts of hydrogen peroxide to the reactant base liquid, first add mixed solution B dropwise, then add mixed solution A dropwise 2 minutes later, add mixed solution A dropwise for 60 minutes, and add mixed solution B dropwise for 90 minutes; after the addition is complete, keep warm for 60 minutes, add water to dilute to a solid content of 50%, and obtain an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent.

[0048] Example 3

[0049] An air-entraining viscosity-reducing polycarboxylic acid water-reducing agent, the preparation method of which is as follows:

[0050] (1) In a glass reactor equipped with a thermometer and a stirrer, 380 parts of isopentanol polyoxyethylene ether with a molecular weight of 2400 and 360 parts of deionized water were added in sequence and stirred until fully dissolved to obtain a reactant base solution;

[0051] (2) 8 parts of acrylic acid, 2 parts of sodium methallyl sulfonate, 4 parts of 4-polyphenylethynyl biphenyl acrylate, 2 parts of hydroxypropyl acrylate, 1.2 parts of mercaptopropionic acid, 0.2 parts of mercaptoethanol and 60 parts of deionized water were mixed to prepare a mixed solution A; 0.1 parts of ferrous sulfate, 0.5 parts of isoascorbic acid and 40 parts of deionized water were mixed to prepare a mixed solution B;

[0052] (3) While stirring, add 1.5 parts of hydrogen peroxide to the reactant base liquid, first add the mixed solution B dropwise, then add the mixed solution A dropwise after 2 minutes, add the mixed solution A dropwise for 90 minutes, and add the mixed solution B dropwise for 120 minutes; after the addition is complete, keep warm for 90 minutes, add water to dilute to a solid content of 50%, and obtain an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent.

[0053] Example 4

[0054] An air-entraining viscosity-reducing polycarboxylic acid water-reducing agent, the preparation method of which is as follows:

[0055] (1) In a glass reactor equipped with a thermometer and a stirrer, 380 parts of 4-hydroxybutyl vinyl polyoxyethylene ether with a molecular weight of 3000 and 360 parts of deionized water were added in sequence, and stirred until fully dissolved to obtain a reactant base solution;

[0056] (2) 8 parts of acrylic acid, 4 parts of maleic anhydride, 4 parts of itaconic acid, 4 parts of 4-polyphenylethynyl biphenyl acrylate, 4 parts of ethyl acrylate, 1 part of mercaptoethanol, 0.5 parts of mercaptopropionic acid and 30 parts of deionized water were mixed to prepare a mixed solution A; 0.4 parts of L-ascorbic acid, 0.2 parts of ferrous sulfate and 40 parts of deionized water were mixed to prepare a mixed solution B;

[0057] (3) Under stirring, 1.2 parts of ammonium persulfate were added to the reactant base liquid, and the mixed solution B was first added dropwise, and then the mixed solution A was added dropwise 2 minutes later. The mixed solution A was added dropwise for 60 minutes, and the mixed solution B was added dropwise for 80 minutes. After the addition was completed, the mixture was kept warm for 60 minutes, and water was added to dilute it to a solid content of 50%, thereby obtaining an air-entraining type viscosity-reducing polycarboxylic acid water-reducing agent.

[0058] Comparative Example 1

[0059] An air-entraining viscosity-reducing polycarboxylic acid water-reducing agent is prepared based on Example 2, without adding ene-acetylene monomers and functional monomers during the preparation process, and other conditions remain unchanged. The preparation method is as follows:

[0060] (1) In a glass reactor equipped with a thermometer and a stirrer, 380 parts of isoethylene glycol monovinyl polyoxyethylene ether with a molecular weight of 2400 and 360 parts of deionized water were added in sequence and stirred until fully dissolved to obtain a reactant base solution;

[0061] (2) 24 parts of acrylic acid, 1.5 parts of thioglycolic acid and 30 parts of deionized water were mixed to prepare a mixed solution A; 0.6 parts of isoascorbic acid and 40 parts of deionized water were mixed to prepare a mixed solution B;

[0062] (3) While stirring, add 1.3 parts of hydrogen peroxide to the reactant base liquid, first add mixed solution B dropwise, then add mixed solution A dropwise 2 minutes later, add mixed solution A dropwise for 60 minutes, and add mixed solution B dropwise for 90 minutes; after the addition is complete, keep warm for 60 minutes, add water to dilute to a solid content of 50%, and obtain an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent.

[0063] Comparative Example 2

[0064] An air-entraining viscosity-reducing polycarboxylic acid water-reducing agent is prepared based on Example 2. During the preparation process, no functional monomer is added and other conditions are kept unchanged. The preparation method is as follows:

[0065] (1) In a glass reactor equipped with a thermometer and a stirrer, 380 parts of isoethylene glycol monovinyl polyoxyethylene ether with a molecular weight of 2400 and 360 parts of deionized water were added in sequence and stirred until fully dissolved to obtain a reactant base solution;

[0066] (2) 20 parts of acrylic acid, 4 parts of hydroxypropyl acrylate, 1.5 parts of thioglycolic acid and 30 parts of deionized water were mixed to prepare a mixed solution A; 0.6 parts of isoascorbic acid and 40 parts of deionized water were mixed to prepare a mixed solution B;

[0067] (3) While stirring, add 1.3 parts of hydrogen peroxide to the reactant base liquid, first add mixed solution B dropwise, then add mixed solution A dropwise 2 minutes later, add mixed solution A dropwise for 60 minutes, and add mixed solution B dropwise for 90 minutes; after the addition is complete, keep warm for 60 minutes, add water to dilute to a solid content of 50%, and obtain an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent.

[0068] Comparative Example 3

[0069] An air-entraining viscosity-reducing polycarboxylic acid water-reducing agent is prepared based on Example 2, without adding olefin monomers during the preparation process, and maintaining other conditions unchanged. The preparation method is as follows:

[0070] (1) In a glass reactor equipped with a thermometer and a stirrer, 380 parts of isoethylene glycol monovinyl polyoxyethylene ether with a molecular weight of 2400 and 360 parts of deionized water were added in sequence and stirred until fully dissolved to obtain a reactant base solution;

[0071] (2) 16 parts of acrylic acid, 8 parts of 4-polyphenylethynyl biphenyl acrylate, 1.5 parts of thioglycolic acid and 30 parts of deionized water were mixed to prepare a mixed solution A; 0.6 parts of isoascorbic acid and 40 parts of deionized water were mixed to prepare a mixed solution B;

[0072] (3) While stirring, add 1.3 parts of hydrogen peroxide to the reactant base liquid, first add mixed solution B dropwise, then add mixed solution A dropwise 2 minutes later, add mixed solution A dropwise for 60 minutes, and add mixed solution B dropwise for 90 minutes; after the addition is complete, keep warm for 60 minutes, add water to dilute to a solid content of 50%, and obtain an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent.

[0073] Comparative Example 4

[0074] Air-entraining polycarboxylic acid water-reducing agent sold on the market by Jiangsu Subote New Materials Co., Ltd.

[0075] Comparative Example 5

[0076] The viscosity-reducing and collapse-preserving polycarboxylic acid water-reducing agent sold on the market by China Construction Ready-Mixed Concrete Co., Ltd.

[0077] Test example

[0078] (1) Esheng cement P·O 42.5 was used to compare cement paste with the water-reducing agent in Examples 1-4 and Comparative Examples 1-5. The water-binder ratio was 0.29. The time change of cement paste fluidity within 0 to 3 hours was tested. The test results are shown in Table 1.

[0079] Table 1: Test table of pure slurry fluidity at room temperature

[0080]

[0081] It can be seen from the data in Table 1 that, when 4-polyphenylethynyl biphenyl acrylate and hydroxypropyl acrylate are used simultaneously in Example 2 and Comparative Example 2, better early release and late slump retention effects are achieved, indicating that 4-polyphenylethynyl biphenyl acrylate has certain water reduction and slump retention effects. At the same time, it can be seen from the data in the table that the overall performance of the cement paste fluidity of Examples 1-4 is better than that of Comparative Examples 1-5 in 0-2h, and the release rules are basically the same, indicating that the air-entraining type viscosity-reducing polycarboxylic acid water-reducing agent synthesized by 4-polyphenylethynyl biphenyl acrylate used in Examples 1-4 of the present invention has a good water reduction rate and early slump retention ability.

[0082] (2) The air-entraining viscosity-reducing polycarboxylate water-reducing agents prepared in Examples 1-4 and Comparative Examples 1-5 and the comparative samples were applied to C60 concrete using the same admixture formula. The mix proportion of C60 concrete is shown in Table 2. The time-dependent fluidity and collapse time of the concrete were compared (the viscosity of the concrete was tested by the inverted slump cone test. The shorter the time it takes for the concrete to flow out of the inverted slump cone, the smaller the viscosity of the concrete). Among them, the cement was Esheng Cement P·O 42.5, the fineness modulus of the machine-made sand was 2.6; the crushed stone was a continuously graded crushed stone with a particle size of 5-20 mm, the mineral powder was S95 grade mineral powder, and the polycarboxylate water-reducing agent was added in an amount of 2.1wt%. The test methods refer to GB / T50080-2016 "Standard Test Methods for Properties of Ordinary Concrete Mixtures", GB / T50080-2016 "Standard Specification for Air Content of Concrete" and GB / T50081-2002 "Standard Test Methods for Mechanical Properties of Ordinary Concrete". The test results are shown in Tables 3 and 4.

[0083] Table 2C60 concrete mix ratio (kg / m 3 )

[0084] Label cement Fly ash Mineral powder Machine-made sand 5-20 stones water C60 420 60 60 800 910 150

[0085] Table 3 C60 concrete test table at room temperature

[0086]

[0087] Table 4 Record of collapse time of C60 concrete at room temperature

[0088]

[0089] Combining Table 3 and Table 4, it can be seen that the air-entraining viscosity-reducing polycarboxylic acid water-reducing agent synthesized in Examples 1-4 can significantly improve the initial and slump-retaining performance of concrete, while increasing the air content of concrete, and reducing the collapse time and viscosity of concrete. Among them, Example 2 uses 2400 molecular weight isoethylene glycol monovinyl polyoxyethylene ether to more effectively reduce the viscosity of concrete and increase the air content of concrete. Comparative Example 1 has a significant loss of concrete in 1-2h due to the lack of a combination of unsaturated esters and vinyl polyacetylene monomers in the water-reducing agent molecular structure, resulting in a poor state of concrete and a large slump loss, which in turn shows unfavorable factors such as high viscosity after loss and poor air content; while Comparative Example 2, in which vinyl polyacetylene monomers are not introduced but unsaturated ester monomers are introduced, has a slightly better loss of concrete, and a slightly better air content and viscosity after loss, but its initial collapse time is significantly increased, indicating that the introduction of 4-polyphenylethynyl biphenyl acrylate effectively reduces the initial viscosity of concrete. At the same time, the viscosity reduction and air entrainment effects of Examples 1-4 are better than those of Comparative Examples 4-5 using commercially available viscosity-reducing water-reducing agents, and the slump-retaining and air-stabilizing performances are significantly improved compared with Comparative Examples 3 and Comparative Examples 4-5 of the commercially available conventional slump-retaining polycarboxylic acid water-reducing agents, indicating that the air-entraining viscosity-reducing polycarboxylic acid water-reducing agents synthesized in Examples 1-4 have certain air-entraining and air-stabilizing effects due to their unique molecular structure, thereby exerting good water-reducing, slump-retaining, air-entraining and continuous viscosity-reducing effects.

[0090] Based on this, in the present invention, an unsaturated polyether macromonomer with a molecular weight in the range of 2400 to 3000 is introduced as a hydrophobic long side chain to provide a steric hindrance effect and ensure the dispersing effect of the water reducer molecules on the particles; the introduction of unsaturated acid monomers can achieve better adsorption of the water reducer molecules on the surface of the particles, exert electrostatic repulsion, and further disperse the particles; vinyl polyacetylene monomers and functional monomers are gradually hydrolyzed in alkaline cement paste to gradually release carboxyl groups, thereby ensuring the re-adsorption-dispersion effect of the water reducer molecules on the cement particles for a long time, thereby effectively reducing collapse and improving the workability of concrete.

[0091] In the present invention, the introduction of vinyl polyacetylene monomers and hydrophobic long chains effectively improves the amphiphilicity of the polycarboxylate water-reducing agent, so that the polycarboxylate water-reducing agent plays a certain emulsifying role and has an air entraining effect, thereby increasing the air content of the concrete. At the same time, due to the increase in the air content, the polycarboxylate water-reducing agent has a certain viscosity reduction effect.

[0092] In the present invention, the unsaturated ester groups introduced into the functional monomer combined with the molecular structure can continuously play a re-adsorption-dispersion-viscosity reduction role on the surface of cement hydration products, effectively improving the collapse and gas stabilization effect of concrete, thereby continuously playing a viscosity reduction role and achieving the effect of reducing the late viscosity of concrete.

[0093] In the present invention, the 2400 molecular weight isoethylene glycol monovinyl polyoxyethylene ether used has a shorter side chain than the commonly used 3000 molecular weight, has a greater steric hindrance, can reduce the viscosity in concrete, and makes the concrete easier to pump.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention.

Claims

1. An air-entraining viscosity-reducing polycarboxylic acid water-reducing agent, the general structural formula of which is shown in Formula 1: In formula 1, R1 is selected from H or CH3; R2 is selected from at least one unsaturated carboxylic acid monomer; X is selected from CH2O, C2H4O or OC4H6O; wherein a, b, c, d, and n are positive integers selected from 1 to 50.

2. The air-entraining viscosity-reducing polycarboxylic acid water-reducing agent according to claim 1, characterized in that: It uses unsaturated polyether macromonomers, unsaturated acid monomers, vinyl polyacetylene monomers and functional monomers as main raw materials, and is produced through free radical polymerization under the action of oxidants, reductants and chain transfer agents.

3. The air-entraining viscosity-reducing polycarboxylic acid water-reducing agent according to claim 2, characterized in that: The invention comprises the following components in parts by weight: 380 parts of unsaturated polyether macromonomer, 5-20 parts of unsaturated acid monomer, 8-15 parts of vinyl polyacetylene monomer, and 1-10 parts of functional monomer; The unsaturated polyether macromonomer is at least one of isopentanol polyoxyethylene ether, 4-hydroxybutyl vinyl polyoxyethylene ether and isoethylene glycol monovinyl polyoxyethylene ether with a molecular weight in the range of 2400 to 3000; At least one of unsaturated acid monomers selected from acrylic acid, methacrylic acid, maleic anhydride, sodium methacrylic acid sulfonate and itaconic acid; The vinyl polyacetylene monomer is 4-polyphenylethynyl biphenyl acrylate with a molecular weight of 2400, which is prepared by active polymerization of phenylacetylene and 4-ethynyl biphenyl acrylate; The functional monomer is at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, ethyl acrylate and 2-methyl methacrylate.

4. The air-entraining viscosity-reducing polycarboxylic acid water-reducing agent according to claim 3, characterized in that: The oxidant is at least one of ammonium persulfate, hydrogen peroxide and potassium persulfate, and the amount of the oxidant is 0.2-0.4% of the total mass of each reaction monomer; The reducing agent is at least one of L-ascorbic acid, isoascorbic acid, ferrous sulfate, sodium methylthiosulfate, sodium sulfite, and sodium bisulfite, and the amount of the reducing agent is 0.05-0.2% of the total mass of each reaction monomer; The chain transfer agent is at least one of mercaptoacetic acid, mercaptopropionic acid and mercaptoethanol, and the amount of the chain transfer agent is 0.2-0.4% of the total mass of each reaction monomer.

5. The method for preparing an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step 1: Mix unsaturated acid monomers, vinyl polyacetylene monomers dissolved in tetrahydrofuran, functional monomers and chain transfer agents, and add water to obtain a mixed solution A; mix a reducing agent and water to obtain a mixed solution B; Step 2: dissolving the unsaturated polyether macromonomer in water at room temperature, adding an oxidant after it is completely dissolved, and then dropping the mixed solution A and the mixed solution B respectively, stirring for reaction and then keeping warm, finally cooling to room temperature and diluting with water to a solid content of 50%, to obtain an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent.

6. The method for preparing an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent according to claim 5, characterized in that: In step 2, the dropwise addition time of mixed solution A is 1-3 h, and the dropwise addition time of mixed solution B is 1.5-3.5 h.

7. The method for preparing an air-entraining viscosity-reducing polycarboxylic acid water-reducing agent according to claim 6, characterized in that: In step 2, the reaction temperature is kept at 35°C and the insulation time is 0.5h-1h.

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