A water reducing agent gel, its preparation method and use

Abstract

The present application relates to a kind of water-reducing agent gel and its preparation method and application, including the following steps: acrylic ester monomer, crosslinking agent, initiator, catalyst and water are mixed uniformly, pre-reaction is carried out under protective atmosphere, first water-reducing agent and emulsifier are added, continue to react, after reaction is completed, polymer gel is prepared by post-treatment;Polymer gel is placed into second water-reducing agent buffer solution, is dispersed by stirring, is treated by soaking and is filtered, and water-reducing agent gel is obtained.The present application adds first water-reducing agent to participate in polymerization reaction in the process of preparing polymer gel, water gel structure is introduced into water gel, so that water gel network structure becomes more compact, mechanical property is greatly improved, network structure is kept intact when being extruded, colliding;Water-reducing agent gel has pH response effect, so that second water-reducing agent can be slowly released in concrete, and avoid later slump loss too fast.

Description

Technical Field

[0001] This invention relates to the field of admixtures for building materials, specifically to a water-reducing agent gel, its preparation method, and its application. Background Technology

[0002] Concrete admixtures are substances added to concrete before or during mixing to improve its performance. With the rapid development of the concrete industry, the water-reducing agent industry has also entered a period of vigorous growth. Currently, the proportion of manufactured sand and environmentally friendly renewable manufactured sand being used continues to rise, posing a significant challenge to the development of concrete admixtures.

[0003] In the application of manufactured sand concrete, the loss of slump over time (the loss of slump within a certain period of time) is amplified by factors such as fineness modulus, mud and powder content, and particle morphology. This loss is particularly pronounced in hot summer weather, causing significant difficulties in construction and posing serious risks to the quality of concrete structures. Taking effective measures to address the uncontrollable problem of concrete slump loss can greatly promote the healthy and orderly development of the ready-mixed concrete industry.

[0004] Polymer hydrogels are polymers with a three-dimensional network synthesized from hydrophilic, water-soluble monomers. They can absorb water and swell in aqueous solutions, exhibiting excellent water retention capacity. Smart hydrogels undergo physical or chemical changes in response to external alterations such as pH, temperature, light, and magnetic fields. These unique properties make this technology widely applicable in fields such as medical engineering, bioengineering, and sensor engineering. It also holds great promise for the preparation of admixtures. However, ordinary hydrogels have poor mechanical properties. During concrete mixing, the network structure is disrupted due to the compression and collision of sand and gravel, leading to the rapid release of admixtures and failing to achieve a long-term, slow release effect. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a water-reducing agent gel, its preparation method and application, thereby solving the technical problem that the poor slow-release effect of water-reducing agents in the prior art leads to a large loss of concrete fluidity over time.

[0006] To achieve the above-mentioned technical objectives, the technical solution provided by this invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a water-reducing agent gel, comprising the following steps: S1, mixing an acrylate monomer, a crosslinking agent, an initiator, a catalyst and water uniformly, 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 after post-treatment after the reaction is completed; S2, placing the polymer gel in a second water-reducing agent buffer solution, dispersing by stirring, soaking and filtering to obtain the water-reducing agent gel.

[0008] Secondly, the present invention provides a water-reducing agent gel prepared by the above preparation method.

[0009] Thirdly, the present invention provides an application of the above-mentioned water-reducing agent gel as a concrete water-reducing agent.

[0010] Compared with the prior art, the beneficial effects of the present invention include:

[0011] This invention incorporates a first water-reducing agent into the polymerization reaction during the preparation of the polymer gel. By introducing the water-reducing agent structure into the hydrogel, the hydrogel network structure becomes denser, significantly improving its mechanical properties and maintaining its integrity under compression and impact. A second water-reducing agent buffer solution is then prepared using a second water-reducing agent and sodium gluconate. The resulting water-reducing agent gel, after absorbing the buffer solution, is used as a concrete admixture. The pH-responsive effect of the polymer gel effectively controls the release rate of the water-reducing agent, allowing it to be slowly released into the concrete. This ensures the concrete retains its flowability for a longer period and prevents excessive slump loss later on. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0013] To address the shortcomings of existing manufactured sand concrete applications, such as significant loss of concrete fluidity over time and poor slow-release effect of conventional water-reducing agents, which fail to achieve a long-term slow release effect, this invention provides a water-reducing agent gel, its preparation method, and its application. This invention introduces the water-reducing agent structure into the hydrogel, making the hydrogel network structure more compact and significantly improving its mechanical properties. The network structure remains intact under compression and impact, and the release rate of the water-reducing agent is effectively controlled through the pH response effect of the polymer gel.

[0014] In a first aspect, the present invention provides a method for preparing a water-reducing agent gel, comprising the following steps:

[0015] S1, acrylate monomers, crosslinking agent, initiator, catalyst and water are mixed evenly and pre-reacted under a protective atmosphere. Then, the first water-reducing agent and emulsifier are added and the reaction continues. After the reaction is completed, the polymer gel is obtained by post-treatment.

[0016] S2, the polymer gel is placed in the second water-reducing agent buffer solution, and after stirring, dispersing, soaking and filtering, the water-reducing agent gel is obtained.

[0017] Preferably, in step S1, the first water-reducing agent is a first polycarboxylate water-reducing agent.

[0018] More preferably, the preparation steps of the first polycarboxylate superplasticizer include:

[0019] Unsaturated polyoxyethylene ether monomers are mixed with water to prepare a base material with a mass concentration of 55-65%. A chain transfer agent is added simultaneously under stirring. After stirring evenly, an oxidant is added. After the oxidant is added for 5-10 minutes, an olefin-based functional monomer solution and a reducing agent solution are added dropwise to react and obtain a polycarboxylate superplasticizer.

[0020] 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.

[0021] More preferably, the chain transfer agent is one or more of sodium hypophosphite, mercaptoacetic acid, and mercaptopropionic acid; the mass ratio of unsaturated polyoxyethylene ether monomer to chain transfer agent is (180-190):(2-6).

[0022] More preferably, the oxidant is one or more of hydrogen peroxide solution and ammonium persulfate, and the mass fraction of the hydrogen peroxide solution is 25-30%; the mass ratio of unsaturated polyoxyethylene ether monomer to oxidant is (180-190):(1-3).

[0023] 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).

[0024] More preferably, the reducing agent is one or more of vitamin C and sodium formaldehyde sulfoxylate; the mass fraction of the reducing agent solution is 0.5-1.5%; and the mass ratio of unsaturated polyoxyethylene ether monomer to reducing agent is (180-190):(0.5-1.5). Among these, sodium formaldehyde sulfoxylate is preferably E51.

[0025] More preferably, the olefin-based functional monomer solution is added at a time of 55–65 min, the reducing agent solution is added at a time of 75–85 min, and after the addition is complete, the reaction is allowed to proceed for 25–35 min to obtain the polycarboxylate superplasticizer.

[0026] Preferably, in step S1, the acrylate monomer is one or more of dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate.

[0027] Preferably, in step S1, the crosslinking agent is one or more of acrylamide, methacrylamide, and dimethylallylamine.

[0028] Preferably, in step S1, the initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, hydrogen peroxide, etc.

[0029] Preferably, in step S1, the catalyst is one or more of cuprous chloride, cuprous bromide, and ferrous sulfate.

[0030] Preferably, in step S1, the emulsifier is one or more of Span 60, Span 80, Span 85, and Tween 80.

[0031] Preferably, in step S1, the mass ratio of acrylate monomers, crosslinking agent, initiator, catalyst, and 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 crosslinking agent to water is (0.5–5.0):100; and the amount of emulsifier is 25–35% of the total mass of the above components.

[0032] When using emulsifiers in this invention, by adjusting the proportion of different components in the emulsifier, the reaction solution is encapsulated and uniformly dispersed by the hydrophobic emulsifier under ultrasonic dispersion and mechanical stirring conditions, which can avoid local large-scale gel aggregation and thus prevent the gel size from being too large.

[0033] Preferably, in step S1, the pre-reaction is carried out at 20–40°C for 0.5–2 hours; the continued reaction is carried out at 40–60°C for 4–6 hours.

[0034] Preferably, in step S1, nitrogen protection and ultrasonic dispersion are used in both the pre-reaction and continued reaction processes.

[0035] Preferably, in step S1, the post-processing includes settling, filtering, washing, and drying.

[0036] Preferably, in step S2, the second water-reducing agent buffer solution is prepared by dissolving the second polycarboxylate water-reducing agent and sodium gluconate in water and controlling the pH value to be 5-11. The solid content of the second water-reducing agent buffer solution is 12-18%. The second polycarboxylate water-reducing agent is the same as the first polycarboxylate water-reducing agent. In this invention, better results can be obtained by using the second polycarboxylate water-reducing agent and sodium gluconate in combination.

[0037] Preferably, in step S2, the soaking time is 3 to 5 hours.

[0038] Secondly, the present invention provides a water-reducing agent gel prepared by the above preparation method.

[0039] Thirdly, the present invention provides an application of the above-mentioned water-reducing agent gel as a concrete water-reducing agent.

[0040] Main mechanism of action and advantages of this invention:

[0041] (1) In the process of preparing polymer gel, the present invention adds a first water-reducing agent to participate in the polymerization reaction. By introducing the water-reducing agent structure into the hydrogel, the hydrogel network structure becomes denser and the mechanical properties are greatly improved. The network structure remains intact when subjected to compression and collision. Then, a second water-reducing agent buffer solution is prepared by using a second water-reducing agent. The water-reducing agent gel obtained after the polymer gel absorbs the second water-reducing agent buffer solution is used as a concrete admixture. The second water-reducing agent can be slowly released in the concrete to ensure that the concrete has long-term flow properties.

[0042] (2) The polymer gel of the present invention contains tertiary amine groups, exhibiting a pH-responsive effect. Under acidic conditions, the tertiary amine groups bind to H+. + Protonation occurs, transforming the polymer into positively charged amino cations. This repulsion causes the polymer chains to extend, gradually increasing the size of the gel network and the swelling ratio, allowing the second water-reducing agent to penetrate the gel. Under alkaline conditions, the amino cations deprotonate to form tertiary amine groups, reducing the repulsion force, causing the gel network to shrink, decreasing the swelling ratio, and releasing the second water-reducing agent. The size of the water-reducing agent gel and the release rate of the second water-reducing agent can be controlled by adjusting the pH of the buffer solution.

[0043] (3) The water-reducing agent gel prepared in this invention has good pH adaptability and good stability under acidic and weakly alkaline conditions. When added to concrete, it will not immediately release the second water-reducing agent. As the pH value of the cement hydration cement paste gradually increases, the second water-reducing agent will be released from the polymer gel when the pH value exceeds a certain range. The addition of the water-reducing agent gel will not affect the initial workability of the concrete due to the immediate release of the water-reducing agent, thereby ensuring that the concrete has good workability.

[0044] (4) The present invention uses emulsifiers to adjust the size of the synthesized gel, avoiding localized large-scale gel aggregation. The production process is simple, the polymer gel is biodegradable, and it is green and environmentally friendly.

[0045] The present invention will be further described below with reference to specific embodiments.

[0046] Example 1

[0047] (1) Add 110 mL of water, 183 g of ethylene glycol monovinyl polyethylene glycol ether, and 4 g of sodium hypophosphite to a four-necked flask equipped with a stirrer and thermometer, keeping the temperature at 10 °C. After stirring evenly, add 2 g of 27% hydrogen peroxide solution at once, and stir evenly for 5 min. Then, simultaneously and slowly pump water A (19% by mass) containing 15 g of acrylic acid and 3 g of acrylic anhydride, and water B (0.8% by mass) containing 1 g of sodium formaldehyde sulfoxylate (E51) into the four-necked flask using a peristaltic pump. Add solution A for 60 min and solution B for 80 min, keeping the reaction temperature at 25-35 °C. After the addition is complete, keep the temperature at 25-35 °C for 30 min to obtain the unsaturated polycarboxylate superplasticizer.

[0048] (2) Weigh 75g of acrylamide aqueous solution (2% by mass) and add it to the reactor. Measure 16.08g of dimethylaminoethyl methacrylate and mix it in, then perform ultrasonic dispersion. After dispersing for 20 min under nitrogen protection, add 0.14g of ammonium persulfate, and continue to purge with nitrogen for 15 min to remove oxygen. Add 50mg of cuprous chloride. Under nitrogen protection, react in a constant temperature water bath at 35℃ for 1 h. Then add 25g of the polycarboxylate superplasticizer prepared in step (1), and simultaneously add 14.3g of Span 80 and Tween 80 mixed in a 5:1 ratio as an emulsifier and disperse for 10 min. Then react at 50℃ under nitrogen protection for 5 h, and continue ultrasonic dispersion during the reaction. After the reaction is complete, let it stand for 2 h, then filter to obtain the sample. Soak, wash, filter, and vacuum dry thoroughly with ethanol. Repeat three times to obtain polymer gel.

[0049] (3) Place the polymer gel in the second water-reducing agent buffer solution and stir to disperse. Soak for 4 hours. 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. The water-reducing agent gel is obtained by filtration.

[0050] Comparative Example 1

[0051] The only difference from Example 1 is that polycarboxylate superplasticizer is not added in step (2), while the other steps and conditions are the same as in Example 1.

[0052] Comparative Example 2

[0053] The only difference from Example 1 is that no emulsifier is added in step (2), while the other steps and conditions are the same as in Example 1.

[0054] Performance testing

[0055] 1. The water-reducing agent gels prepared in Examples 1, 1, and 2 were soaked in water or sodium hydroxide solutions with different pH values. The particle sizes are shown in Table 1 below.

[0056] Table 1 Comparison of gel particle size of water-reducing agents

[0057]

[0058] Compared with Comparative Example 2, the particle size of the water-reducing agent 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-reducing agent gel obtained in Comparative Example 1 without adding polycarboxylate water-reducing agent is smaller than that in Example 1.

[0059] 2. C30 concrete mix design verification was conducted. The blank group used commercially available Subote polycarboxylate admixture (15% solid content). In the comparative examples and examples, in addition to using commercially available Subote polycarboxylate admixture, the water-reducing agent gel prepared in Comparative Examples 1-2 and Example 1 was also added to the concrete by the same mass for mixing. By adjusting the amount of commercially available admixture and the water-reducing agent gel prepared in Comparative Examples 1-2 and Example 1, the initial concrete slump was controlled to be 220±10mm and the concrete spread to be 600±20mm. The specific mix design parameters are shown in Table 2 below.

[0060] Table 2 Concrete mix proportion parameters (kg)

[0061]

[0062] The slump and spread of each group were measured at the initial, 2h, 4h and 6h, and the test results are shown in Table 3 below.

[0063] Table 3 Concrete slump and spread

[0064]

[0065] As shown in Table 3, the water-reducing agent gel obtained by this invention can effectively prolong the slump retention time of concrete mixtures. In Comparative Example 1, no polycarboxylate superplasticizer (first superplasticizer) was added during the preparation of the polymer gel, resulting in a slightly inferior performance in concrete. Example 1, by introducing the polycarboxylate superplasticizer (first superplasticizer) structure into the hydrogel, made the hydrogel network structure denser, significantly improving its mechanical properties. During concrete mixing, the network structure remained well-maintained under pressure and impact, thereby regulating the rate at which the second superplasticizer was slowly released from the polymer gel, thus ensuring good workability of the concrete for a period of time.

[0066] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a water-reducing agent gel, characterized in that, Includes the following steps: S1, acrylate monomers, crosslinking agent, initiator, catalyst and water are mixed evenly and pre-reacted under a protective atmosphere. Then, the first water-reducing agent and emulsifier are added and the reaction continues. After the reaction is completed, the polymer gel is obtained by post-treatment. The first water-reducing agent is the first polycarboxylate water-reducing agent and participates in the polymerization reaction. The preparation steps of the first polycarboxylate superplasticizer include: Unsaturated polyoxyethylene ether monomers are mixed with water to prepare a base material with a mass concentration of 55-65%. A chain transfer agent is added simultaneously under stirring. After stirring evenly, an oxidant is added. After the oxidant is added for 5-10 minutes, an olefin-based functional monomer solution and a reducing agent solution are added dropwise. The reaction yields a polycarboxylate superplasticizer. S2, the polymer gel is placed in the second water-reducing agent buffer solution, and after stirring, dispersing, soaking and filtering, the water-reducing agent gel is obtained.

2. The method for preparing the water-reducing agent gel according to claim 1, 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, mercaptoacetic acid, and mercaptopropionic acid; The oxidant is one or more of hydrogen peroxide solution and ammonium persulfate; The olefin-based 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 sodium formaldehyde sulfoxylate. The mass ratio of the unsaturated polyoxyethylene ether monomer, chain transfer agent, oxidant, olefin-based functional monomer, and reducing agent is (180-190):(2-6):(1-3):(15-20):(0.5-1.5). The olefin-based functional monomer solution is added over a period of 55–65 min, and the reducing agent solution is added over a period of 75–85 min. After the addition is complete, the reaction is allowed to proceed for 25–35 min to obtain the polycarboxylate superplasticizer.

3. The method for preparing the water-reducing agent gel according to claim 1, characterized in that, In step S1, the acrylate monomer is one or more of dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, and diethylaminoethyl methacrylate. The crosslinking agent is one or more selected from 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.

4. The method for preparing the water-reducing agent gel according to claim 1, characterized in that, In step S1, the mass ratio of the acrylate monomer, crosslinking agent, initiator, catalyst, and 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 crosslinking agent to water is (0.5–5.0):100; The amount of the emulsifier is 25-35% of the total mass of the acrylate monomers, crosslinking agent, initiator, catalyst and first water-reducing agent.

5. The method for preparing the water-reducing agent gel according to claim 1, characterized in that, In step S1, the pre-reaction is carried out at 20–40°C for 0.5–2 hours; the continued reaction is carried out at 40–60°C for 4–6 hours. Both the pre-reaction and the continued reaction processes employ nitrogen protection and ultrasonic dispersion.

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

7. The water-reducing agent gel prepared by the preparation method according to any one of claims 1-6.

8. The application of the water-reducing agent gel as described in claim 7 as a concrete water-reducing agent.

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