Water reducing agent gel as well as preparation method and application thereof

Abstract

The preparation method comprises the following steps: uniformly mixing an acrylate monomer, a cross-linking agent, an initiator, a catalyst and water, carrying out a pre-reaction under a protective atmosphere, adding a first water reducing agent and an emulsifier, continuing the reaction, and carrying out post-treatment after the reaction is completed to prepare a polymer gel; and putting the polymer gel into a second water reducing agent buffer solution, stirring, dispersing, soaking and filtering to obtain the water reducing agent gel. The first water reducing agent is added in the process of preparing the polymer gel to participate in the polymerization reaction, and the structure of the water reducing agent is introduced into the hydrogel, so that the network structure of the hydrogel becomes more compact, the mechanical property is greatly improved, and the network structure is kept intact when the hydrogel is extruded and collided; the water reducing agent gel has a pH response effect, so that the second water reducing agent can be slowly released in the concrete, and the situation that the slump loss is too fast in the later period is avoided.

Description

Technical Field

[0001] The invention relates to the field of admixtures for building materials, and in particular to a water reducing agent gel and a preparation method and application thereof. Background Art

[0002] Concrete admixtures refer to substances added to concrete before or during mixing to improve the performance of concrete. With the rapid development of the concrete industry, the water reducing agent industry has also entered a period of vigorous development. At present, the proportion of machine-made sand and environmentally friendly renewable machine-made sand continues to rise, which brings a great challenge to the development of concrete admixtures.

[0003] In the application of machine-made sand concrete engineering, the loss of concrete fluidity (the loss of slump in a certain period of time) increases due to the influence of fineness modulus, mud and powder content, and particle morphology. In particular, in hot summer weather, the loss of concrete fluidity over time is greater, which makes actual construction difficult, which brings serious hidden dangers to the quality of concrete structures. Taking effective measures to solve the problem of uncontrollable concrete slump loss can greatly promote the healthy and orderly development of the commercial concrete industry.

[0004] Polymer hydrogel is a polymer with a three-dimensional network synthesized from hydrophilic water-soluble monomers. It can absorb water and swell in aqueous solution and has good water retention capacity. Smart hydrogels will undergo physical or chemical changes when external factors such as pH, temperature, light, and magnetic field change. These unique functions make this technology widely used in many fields such as medical engineering, bioengineering, and sensor engineering. This technology has great application prospects in the preparation of admixtures. However, ordinary hydrogels have poor mechanical properties. During the concrete mixing process, the network structure is destroyed due to the extrusion and collision of sand and gravel, and the admixture is released quickly, which cannot achieve the effect of long-term slow release. Summary of the invention

[0005] The purpose of the present invention is to overcome the above technical deficiencies, provide a water reducing agent gel and a preparation method and application thereof, and solve the technical problem in the prior art that the water reducing agent has a poor sustained release effect and causes a large loss of concrete fluidity over time.

[0006] In order to achieve the above technical purpose, the technical solution provided by the present invention is: In a first aspect, the present invention provides a method for preparing a water reducer gel, comprising the following steps: S1, uniformly mixing an acrylate monomer, a crosslinking agent, an initiator, a catalyst and water, conducting a pre-reaction under a protective atmosphere, and then adding a first water reducer and an emulsifier to continue the reaction, and obtaining a polymer gel through post-treatment after the reaction is completed; S2, placing the polymer gel into a second water reducer buffer solution, stirring, dispersing, soaking and filtering to obtain a water reducer gel.

[0007] In a second aspect, the present invention provides a water reducing agent gel prepared by the above preparation method.

[0008] In a third aspect, the present invention provides a use of the water-reducing agent gel as a concrete water-reducing agent.

[0009] Compared with the prior art, the beneficial effects of the present invention include: The invention adds a first water reducer to participate in the polymerization reaction during the preparation of the polymer gel, introduces the water reducer structure into the hydrogel, makes the hydrogel network structure more compact, greatly improves the mechanical properties, and keeps the network structure intact when subjected to extrusion and collision; then, a second water reducer buffer solution is prepared by using a second water reducer and sodium gluconate, and the water reducer gel obtained after the polymer gel absorbs the second water reducer buffer solution is used as a concrete admixture, and the pH response effect of the polymer gel is used to effectively control the release speed of the water reducer, so that the second water reducer can be slowly released in the concrete, thereby ensuring that the concrete has a long-term flow property and avoiding excessive slump loss in the later stage. DETAILED DESCRIPTION

[0010] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0011] In view of the defects that the fluidity of concrete loses greatly over time in existing machine-made sand concrete engineering applications, the conventional water reducer has a poor sustained-release effect and cannot achieve the effect of long-term slow release, the present invention provides a water reducer gel and a preparation method and application thereof. The present invention introduces a water reducer structure into the hydrogel so that the network structure of the hydrogel becomes denser and the mechanical properties are greatly improved. The network structure remains intact when squeezed or collided, and the release rate of the water reducer is effectively controlled through the pH response effect of the polymer gel.

[0012] In a first aspect, the present invention provides a method for preparing a water reducing agent gel, comprising the following steps: S1, uniformly mixing an acrylic ester monomer, a crosslinking agent, an initiator, a catalyst and water, performing a pre-reaction under a protective atmosphere, then adding a first water reducing agent and an emulsifier, continuing the reaction, and obtaining a polymer gel through post-treatment after the reaction is completed; S2, placing the polymer gel in a second water reducing agent buffer solution, stirring, dispersing, soaking and filtering to obtain a water reducing agent gel.

[0013] Preferably, in step S1, the first water reducer is a first polycarboxylate water reducer.

[0014] Further preferably, the preparation steps of the first polycarboxylate water-reducing agent include: Unsaturated polyoxyethylene ether monomer and water are prepared into a base material with a mass concentration of 55-65%, and a chain transfer agent is added under stirring. After stirring evenly, an oxidant is added; after the oxidant is added for 5-10 minutes, an olefin functional monomer solution and a reducing agent solution are added dropwise to react to obtain a polycarboxylic acid water reducer.

[0015] More preferably, the unsaturated polyoxyethylene ether monomer is one or more of methyl allyl alcohol polyoxyethylene ether, 4-hydroxybutyl vinyl ether, and ethylene glycol monovinyl polyethylene glycol ether.

[0016] More preferably, the chain transfer agent is one or more of sodium hypophosphite, thioglycolic acid, and mercaptopropionic acid; and the mass ratio of the unsaturated polyoxyethylene ether monomer to the chain transfer agent is (180-190):(2-6).

[0017] More preferably, the oxidant is one or more of a hydrogen peroxide solution and ammonium persulfate, the mass fraction of the hydrogen peroxide solution is 25-30%; the mass ratio of the unsaturated polyoxyethylene ether monomer to the oxidant is (180-190): (1-3).

[0018] More preferably, the olefin-based functional monomer is one or more of acrylic acid, acrylic anhydride, maleic acid, and maleic anhydride; the mass concentration of the olefin-based functional monomer solution is 15-20%; and the mass ratio of the unsaturated polyoxyethylene ether monomer to the olefin-based functional monomer is (180-190): (15-20).

[0019] More preferably, the reducing agent is one or more of vitamin C and diacid; the mass fraction of the reducing agent solution is 0.5-1.5%; the mass ratio of the unsaturated polyoxyethylene ether monomer to the reducing agent is (180-190): (0.5-1.5). Among them, diacid is preferably E51.

[0020] More preferably, the olefin functional monomer solution is added dropwise for 55 to 65 minutes, and the reducing agent solution is added dropwise for 75 to 85 minutes. After the addition is completed, the polycarboxylate water-reducing agent is obtained by reacting for 25 to 35 minutes.

[0021] Preferably, in step S1, the acrylic acid ester monomer is one or more of dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate.

[0022] Preferably, in step S1, the cross-linking agent is one or more of acrylamide, methacrylamide, and dimethylallylamine.

[0023] Preferably, in step S1, the initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, etc.

[0024] Preferably, in step S1, the catalyst is one or more of cuprous chloride, cuprous bromide, and ferrous sulfate.

[0025] Preferably, in step S1, the emulsifier is one or more of Span 60, Span 80, Span 85, and Tween 80.

[0026] Preferably, in step S1, the mass ratio of the acrylate monomer, the crosslinking agent, the initiator, the catalyst and the first water reducer is (12.5-19.0): (1.2-2.5): (0.12-0.25): (0.03-0.08): (18.75-25); the mass ratio of the crosslinking agent and water is (0.5-5.0): 100; and the amount of the emulsifier used is 25-35% of the total mass of the above components.

[0027] When the present invention uses an emulsifier, by adjusting the ratio of different components in the emulsifier, the reaction solution is wrapped and evenly dispersed by the hydrophobic emulsifier under ultrasonic dispersion and mechanical stirring conditions, thereby avoiding local large gel aggregation and causing the gel size to be too large.

[0028] Preferably, in step S1, the preliminary reaction is carried out at 20-40°C for 0.5-2h; and the continued reaction is carried out at 40-60°C for 4-6h.

[0029] Preferably, in step S1, nitrogen protection and ultrasonic dispersion are used during both the pre-reaction and the continued reaction.

[0030] Preferably, in step S1, the post-treatment includes standing, filtering, washing and drying.

[0031] Preferably, in step S2, the second water reducer buffer solution is prepared by dissolving the second polycarboxylate water reducer and sodium gluconate in water and controlling the pH value to be 5 to 11, and the solid content of the second water reducer buffer solution is 12 to 18%; the second polycarboxylate water reducer is the same as the first polycarboxylate water reducer. In the present invention, better effects can be obtained by using the second polycarboxylate water reducer and sodium gluconate in combination.

[0032] Preferably, in step S2, the soaking treatment time is 3 to 5 hours.

[0033] In a second aspect, the present invention provides a water reducing agent gel prepared by the above preparation method.

[0034] In a third aspect, the present invention provides a use of the water-reducing agent gel as a concrete water-reducing agent.

[0035] The main mechanism of action and advantages of the present invention: (1) In the process of preparing the polymer gel, the first water reducer is added to participate in the polymerization reaction. By introducing the water reducer structure into the hydrogel, the network structure of the hydrogel becomes denser, the mechanical properties are greatly improved, and the network structure remains intact when subjected to extrusion and collision. Then, the second water reducer is used to prepare the second water reducer buffer solution, and the water reducer gel obtained after the polymer gel absorbs the second water reducer buffer solution is used as a concrete admixture. The second water reducer can be slowly released in the concrete to ensure that the concrete has long-term flow properties. (2) The polymer gel of the present invention contains tertiary amine groups, which have a pH response effect. Under acidic conditions, the tertiary amine groups bind to H + Protonation occurs, and it is converted into amino cations with positive charge, which produces mutual repulsion, stretching the polymer chain, gradually increasing the gel network structure, increasing the swelling ratio, and the second water reducer enters the gel; under alkaline conditions, the amino cations are deprotonated to form tertiary amine groups, the repulsion is reduced, the gel network structure shrinks, the swelling ratio decreases, the second water reducer is released, and the size of the water reducer gel decreases. The size of the water reducer gel and the release rate of the second water reducer can be controlled by adjusting the pH value of the second water reducer buffer solution; (3) The water-reducing agent gel prepared by the present invention has good pH adaptability and good stability under acidic and weakly alkaline conditions. When added to concrete, the second water-reducing agent will not be released immediately. As the pH value of the cement hydration slurry gradually increases, when the pH value exceeds a certain range, the second water-reducing agent is released from the polymer gel. The addition of the water-reducing agent gel will not affect the initial working performance of the concrete due to the immediate release of the water-reducing agent, thereby ensuring that the concrete has good working performance; (4) The present invention uses an emulsifier to adjust the size of the synthesized gel to avoid local large-scale gel aggregation. The production process is simple, the polymer gel is degradable, and it is green and environmentally friendly.

[0036] The present invention will be further described below with reference to specific embodiments.

[0037] Example 1 (1) Add 110 mL of water, 183 g of ethylene glycol monovinyl polyglycol ether, and 4 g of sodium hypophosphite to a four-necked flask equipped with a stirrer and a thermometer, and control the temperature at 10°C. After stirring evenly, add 2 g of a 27% by mass hydrogen peroxide solution at one time. After stirring evenly for 5 minutes, slowly pump solution A (mass fraction 19%) containing 15 g of acrylic acid and 3 g of acrylic anhydride and solution B (mass fraction 0.8%) containing 1 g of bleach (E51) into the above four-necked flask through a peristaltic pump to react. Solution A is added for 60 minutes, and solution B is added for 80 minutes. The reaction temperature is controlled at 25-35°C. After the addition is completed, keep the temperature at 25-35°C for 30 minutes to obtain an unsaturated polycarboxylic acid water reducer.

[0038] (2) Weigh 75g of acrylamide aqueous solution (mass fraction 2%) and add it to the reactor, weigh 16.08g of dimethylaminoethyl methacrylate and mix it therein, and perform ultrasonic dispersion. After dispersion under nitrogen protection for 20 min, add 0.14g of ammonium persulfate, continue to pass nitrogen to deoxygenate for 15 min, and add 50mg of cuprous chloride. Under nitrogen protection, place it in a constant temperature water bath at 35°C for reaction for 1h, then add 25g of the polycarboxylic acid water reducer prepared in step (1), and at the same time add 14.3g of an emulsifier mixed with Span 80 and Tween 80 in a ratio of 5:1 to disperse for 10min, and then react at 50°C for 5h under nitrogen protection, and continue ultrasonic dispersion during the reaction. After the reaction is completed, let it stand for 2h, then filter to obtain a sample, soak it fully with ethanol, wash it, filter it and vacuum dry it, repeat three times to obtain a polymer gel.

[0039] (3) placing the polymer gel in a second water-reducing agent buffer solution, stirring and dispersing, and soaking for 4 hours, wherein the second water-reducing agent is composed of the polycarboxylic acid water-reducing agent synthesized in step (1) and sodium gluconate, the solid contents of the polycarboxylic acid water-reducing agent and sodium gluconate are 14% and 1%, respectively, and the pH value is controlled at 10-11; filtering to obtain the water-reducing agent gel.

[0040] Comparative Example 1 The only difference from Example 1 is that no polycarboxylic acid water-reducing agent is added in step (2), and the other steps and conditions are the same as those in Example 1.

[0041] Comparative Example 2 The only difference from Example 1 is that no emulsifier is added in step (2), and the other steps and conditions are the same as those in Example 1.

[0042] Performance Testing 1. The water reducing agent gels prepared in Example 1, Comparative Example 1 and Comparative Example 2 were immersed in water or sodium hydroxide solutions with different pH values, and the particle sizes were shown in Table 1 below.

[0043] Table 1 Comparison of particle size of water reducing agent gel

[0044] Compared with Comparative Example 2, the particle size of the water reducer gel obtained by adding emulsifier in Comparative Example 1 and Example 1 is smaller than that in Comparative Example 2; compared with Example 1, the particle size of the water reducer gel obtained by not adding polycarboxylic acid water reducer in Comparative Example 1 is smaller than that in Example 1.

[0045] 2. C30 concrete trial mix verification was conducted, wherein the blank group was a commercially available Subote polycarboxylic acid admixture finished product (solid content 15%), and in addition to the commercially available Subote polycarboxylic acid admixture finished product, the water reducer gel prepared in Comparative Examples 1-2 and Example 1 was added to the concrete in the same mass for mixing in the comparative examples and examples. By adjusting the amount of commercially available admixture finished product and the water reducer gel prepared in Comparative Examples 1-2 and Example 1, the initial concrete slump was controlled to be 220±10mm, and the concrete expansion was 600±20mm. The specific mix ratio parameters are shown in Table 2 below.

[0046] Table 2 Concrete mix parameters (kg)

[0047] The slump and expansion of each group at initial stage, 2h, 4h and 6h were measured respectively. The test results are shown in Table 3 below.

[0048] Table 3 Concrete slump and expansion

[0049] It can be seen from the results in Table 3 that the water-reducing agent gel obtained in the present invention can effectively prolong the slump retention time of the concrete mixture. In the process of preparing the polymer gel in Comparative Example 1, no polycarboxylate water-reducing agent (first water-reducing agent) was added, and the obtained finished product had a slightly poor effect in the concrete. In Example 1, by introducing the structure of the polycarboxylate water-reducing agent (first water-reducing agent) into the hydrogel, the network structure of the hydrogel became more compact, the mechanical properties were greatly improved, and the network structure was kept good when it was squeezed and collided during the concrete mixing process, thereby adjusting the speed of the slow release of the second water-reducing agent from the polymer gel, thereby ensuring that the concrete has good working performance for a period of time.

[0050] The specific implementation of the present invention described above does not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and modifications made based on the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a water reducing agent gel, characterized in that: The following steps are involved: S1, uniformly mixing an acrylic ester monomer, a crosslinking agent, an initiator, a catalyst and water, performing a pre-reaction under a protective atmosphere, then adding a first water reducing agent and an emulsifier, continuing the reaction, and obtaining a polymer gel through post-treatment after the reaction is completed; S2, placing the polymer gel in a second water reducing agent buffer solution, stirring, dispersing, soaking and filtering to obtain a water reducing agent gel.

2. The method for preparing the water reducing agent gel according to claim 1, characterized in that: The first water reducer is a first polycarboxylate water reducer.

3. The method for preparing the water reducing agent gel according to claim 2, characterized in that: The preparation steps of the first polycarboxylate water-reducing agent include: Unsaturated polyoxyethylene ether monomer and water are prepared into a base material with a mass concentration of 55-65%, and a chain transfer agent is added under stirring. After stirring evenly, an oxidant is added; after the oxidant is added for 5-10 minutes, an olefin functional monomer solution and a reducing agent solution are added dropwise to react to obtain a polycarboxylic acid water reducer.

4. The method for preparing the water reducing agent gel according to claim 3, characterized in that: The unsaturated polyoxyethylene ether monomer is one or more of methyl allyl alcohol polyoxyethylene ether, 4-hydroxybutyl vinyl ether, and ethylene glycol monovinyl polyethylene glycol ether; The chain transfer agent is one or more of sodium hypophosphite, thioglycolic acid, and mercaptopropionic acid; The oxidant is one or more of a hydrogen peroxide solution and ammonium persulfate; The olefin functional monomer is one or more of acrylic acid, acrylic anhydride, maleic acid, and maleic anhydride; The reducing agent is one or more of vitamin C and chlorpyrifos; The mass ratio of the unsaturated polyoxyethylene ether monomer, chain transfer agent, oxidant, olefin functional monomer and reducing agent is (180-190): (2-6): (1-3): (15-20): (0.5-1.5); The olefin functional monomer solution is added dropwise for 55 to 65 minutes, and the reducing agent solution is added dropwise for 75 to 85 minutes. After the addition is completed, the polycarboxylate water-reducing agent is obtained by reacting for 25 to 35 minutes.

5. The method for preparing the water reducing agent gel according to claim 1, characterized in that: In step S1, the acrylic acid ester monomer is one or more of dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate; The cross-linking agent is one or more of acrylamide, methacrylamide, and dimethylallylamine; The initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, and hydrogen peroxide; The catalyst is one or more of cuprous chloride, cuprous bromide, and ferrous sulfate; The emulsifier is one or more of Span 60, Span 80, Span 85 and Tween 80.

6. The method for preparing the water reducing agent gel according to claim 1, characterized in that: In step S1, the mass ratio of the acrylic acid ester monomer, the crosslinking agent, the initiator, the catalyst and the first water reducing agent is (12.5-19.0): (1.2-2.5): (0.12-0.25): (0.03-0.08): (18.75-25); The mass ratio of the cross-linking agent to water is (0.5-5.0):100; The amount of the emulsifier used is 25-35% of the total mass of the acrylic ester monomer, the crosslinking agent, the initiator, the catalyst and the first water reducing agent.

7. The method for preparing the water reducing agent gel according to claim 1, characterized in that: In step S1, the preliminary reaction is carried out at 20-40°C for 0.5-2h; the continued reaction is carried out at 40-60°C for 4-6h; During the pre-reaction and the continued reaction, nitrogen protection and ultrasonic dispersion are used.

8. The method for preparing the water reducing agent gel according to claim 1, characterized in that: In step S2, the second water reducer buffer solution is prepared by dissolving the second polycarboxylate water reducer and sodium gluconate in water and controlling the pH value to be 5 to 11, and the solid content of the second water reducer buffer solution is 12 to 18%; The soaking treatment time is 3 to 5 hours.

9. The water reducing agent gel obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the water reducing agent gel as claimed in claim 9 as a concrete water reducing agent.

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