A pH-responsive intelligent release polycarboxylic acid water reducing agent, a preparation method and application thereof

Abstract

The application discloses a pH response type intelligent release polycarboxylic water reducing agent and a preparation method and application thereof, and belongs to the field of water reducing agents, and solves the problem of early strength reduction of concrete caused by the retarding component of traditional water reducing agents.The preparation method comprises the following steps: dissolving isoamylene polyoxyethylene ether in water to prepare a base solution; dissolving a chain transfer agent and a reducing agent in water to prepare A liquid; dissolving an unsaturated carboxylic acid monomer, hydroxyethyl methacrylate and an unsaturated carboxylic acid ester containing a tertiary amine group in water to prepare B liquid; adding an initiator into the base solution, and then adding the A liquid and the B liquid into the base solution drop by drop at normal temperature, and continuing to react for at least 1 h after the dropping is completed, so that the pH response type intelligent release polycarboxylic water reducing agent is obtained.The pH response type intelligent release polycarboxylic water reducing agent can respond to the pore liquid pH and ion change in the cement hydration process, realizes intelligent on-demand release of the slurry dispersion performance, slows down the slump loss of the slurry, and improves the field construction and workability.

Description

Technical Field

[0001] This invention belongs to the field of water-reducing agents, specifically relating to a pH-responsive smart-release polycarboxylate water-reducing agent, its preparation method, and its application. Background Technology

[0002] Polycarboxylate superplasticizers (PCEs) have become an indispensable key component of modern high-performance concrete due to their advantages such as high water reduction rate, low dosage, and strong designability of molecular structure. Traditional PCEs typically adsorb rapidly onto the surface of cement particles in the early stages of mixing, dispersing them through electrostatic repulsion and steric hindrance. However, this rapid adsorption and dispersion leads to a faster slump loss in fresh concrete, which is not conducive to long-distance transportation and on-site construction. Moreover, the excessive dispersing force on cement in the early hydration stage may hinder the orderly development of the system's early microstructure.

[0003] Currently, methods to mitigate slump loss mainly include adding slow-release water-reducing agents or retarding components such as sodium gluconate and citric acid. However, these methods suffer from insufficient control precision, impact on early strength, or inconvenience in construction. Smart-responsive water-reducing agents offer a novel approach to address these issues, and developing a pH-responsive smart-release polycarboxylate water-reducing agent with a well-defined structure, sensitive response, and easy preparation is of great significance. Summary of the Invention

[0004] The purpose of this invention is to provide a pH-responsive smart-release polycarboxylate superplasticizer to solve the problem of early strength reduction in concrete caused by the retarding components of traditional superplasticizers.

[0005] Another objective of this invention is to provide a method for preparing a pH-responsive smart-release polycarboxylate superplasticizer.

[0006] A third objective of this invention is to provide an application of a pH-responsive smart-release polycarboxylate superplasticizer.

[0007] The technical solution of this invention is: (one) A pH-responsive smart-release polycarboxylate superplasticizer has the following general molecular formula: In the formula, R is -N(CH3)2, -N(CH2CH3)2, or -N(CH2CH2OH)2, and a, b, c, d, and e represent the degree of polymerization of each monomer in the polymer. Based on the feed ratio, a∶b∶c∶d∶e = 1~3∶1~10∶1~3∶1~2∶1~4. (two) A method for preparing a pH-responsive smart-release polycarboxylate superplasticizer includes the following steps: A. Dissolve isopentenyl alcohol polyoxyethylene ether in water to prepare a base solution; B. Dissolve the chain transfer agent and reducing agent in water to prepare solution A; C. Dissolve unsaturated carboxylic acid monomers, hydroxyethyl methacrylate, and unsaturated carboxylic acid esters containing tertiary amine groups in water to prepare solution B; D. After adding the initiator to the base liquid, add solution A and solution B dropwise to the base liquid at room temperature. The dropwise addition time of solution A is controlled at 3.5 hours and the dropwise addition time of solution B is controlled at 2.5 hours. After the dropwise addition is completed, continue the reaction for at least 1 hour to obtain the pH-responsive smart release polycarboxylate superplasticizer.

[0009] As a further improvement of the present invention, the raw materials used are in the following weight proportions: 310-350 parts of isopentenyl alcohol polyoxyethylene ether, 36-45 parts of unsaturated carboxylic acid monomer, 3-7 parts of hydroxyethyl methacrylate, 7-12 parts of unsaturated carboxylic acid ester containing tertiary amine group, 2.2-2.5 parts of initiator, 2.5-3 parts of chain transfer agent, 0.8-1 parts of reducing agent, and 295-335 parts of water.

[0010] As a further improvement of the present invention, the unsaturated carboxylic acid monomers are acrylic acid and maleic anhydride.

[0011] As a further improvement of the present invention, the monomer of the unsaturated carboxylic acid ester containing the tertiary amine group is one or more of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and 2-(N,N-di(2-hydroxyethyl)amino)ethyl methacrylate.

[0012] As a further improvement of the present invention, the initiator is hydrogen peroxide.

[0013] As a further improvement of the present invention, the reducing agent is ascorbic acid.

[0014] As a further improvement of the present invention, the chain transfer agent is 3-mercaptopropionic acid. (three) Application of a pH-responsive smart-release polycarboxylate superplasticizer in ultra-high performance concrete.

[0016] Furthermore, the pH-responsive smart-release polycarboxylate superplasticizer has a solid dosage of 0.6% to 1.0% of the total mass of the cementitious material.

[0017] The pH-responsive intelligent release polycarboxylate superplasticizer of the present invention can be mixed and compounded with at least one concrete admixture known in the prior art, including defoamers, early strength agents, slump retainers, air-entraining agents, and expanding agents.

[0018] In the initial stage of mixing silicate cement with water, clinker minerals rapidly dissolve free alkali, and the pH value of the pore liquid quickly reaches about 13.0. The alkalinity of the system is at a relatively low level throughout the hydration process, and trace amounts of hydrogen ions remain in the liquid phase. The water-reducing agent of this invention carries pH-sensitive tertiary amine functional groups on its side chains, which undergo slight protonation under this environment, giving the polymer molecules a weak positive charge. Relying on the attraction between positive and negative electrostatics, the polymer can quickly adsorb onto the surface of negatively charged cement mineral particles, giving the slurry excellent initial dispersion properties. As cement hydration continues, tricalcium silicate continues to hydrate to generate calcium hydroxide, and the concentration of hydroxide ions in the pore liquid continuously accumulates, the pH value of the system gradually increases, and the concentration of calcium ions in the liquid phase increases simultaneously. The high concentration of hydroxide ions completely inhibits the protonation of the tertiary amine groups, and the side-chain tertiary amine transforms into an electrically neutral structure. The polymer molecules retain only the negative charge generated by the ionization of the main chain carboxyl groups. At this point, the electrostatic repulsion between the polymer and the equally negatively charged cement particles is greatly enhanced. The water-reducing agent molecules that were previously adsorbed on the particle surface gradually desorb and are released into the pore fluid, continuously replenishing the dispersed components, slowing down the slump loss of the paste, and maintaining the workability of the concrete for a longer period of time. At the same time, the molecule can gently regulate the cement hydration rate, avoiding the early strength reduction problem caused by traditional retarding components, and achieving the long-term maintenance of concrete workability and the synergistic development of mechanical strength.

[0019] Compared with the prior art, the present invention has the following advantages: This invention relates to a pH-responsive intelligent release polycarboxylate superplasticizer that responds to changes in pH and ion concentration in the pore liquid during cement hydration, enabling intelligent, on-demand release of the slurry's dispersion performance. This reduces slump loss and improves workability during on-site construction. The mechanism involves the gradual ionization of carboxyl groups in the acrylic and maleic anhydride segments of the copolymer backbone as the pH of the pore liquid increases, increasing the amount of negative charge. The tertiary amine groups R at the ends of the unsaturated carboxylic acid ester segments containing tertiary amine groups undergo reversible protonation with pH changes, achieving dynamic charge transformation. These two types of functional groups synergistically regulate the adsorption rate of the polymer on the surface of cement particles and hydration products. Simultaneously, the long polyether side chains of the isopentenyl alcohol polyoxyethylene ether segments construct a solvation layer, providing stable steric hindrance and weakening the flocculation interference caused by calcium ions in the pore liquid. This allows the dispersion ability to be gradually released in accordance with the cement hydration process, achieving on-demand control of dispersion performance.

[0020] The pH-responsive intelligent release polycarboxylate superplasticizer of this invention has a limited degree of carboxyl ionization in the initial stage of concrete mixing. Therefore, the initial adsorption strength of the superplasticizer is moderate, which will not cause excessive dispersion of cement particles in the early stage. This is conducive to the early orderly hydration of cement particles, which can refine the early capillary pores, optimize the distribution of hydration products, and improve the early microstructure of concrete. Compared with traditional small molecule retarder components, it has no obvious side effect of inhibiting early hydration, thus playing a role in improving the early strength of concrete.

[0021] This invention relates to a pH-responsive intelligent release polycarboxylate superplasticizer. On the one hand, it can replace the R group at the end of the unsaturated carboxylic acid ester chain containing tertiary amine groups (optionally -N(CH3)2, -N(CH2CH3)2, or -N(CH2CH2OH)2, to regulate the pH threshold of tertiary amine protonation). On the other hand, it can adjust the molar ratio of each comonomer, flexibly adjusting its pH response threshold from both the side chain and main chain dimensions. It can adapt to the hydration pH evolution characteristics corresponding to different cement types, mineral admixture systems, and temperature and humidity construction conditions, thus meeting diverse engineering requirements.

[0022] In this invention, the terminal hydroxyl groups of the hydroxyethyl methacrylate chain segment can enhance the anchoring effect between the polymer and the hydration product through hydrogen bonding, reduce the desorption failure of the water-reducing agent in a high-ion environment, and improve rheological stability. In addition, the synthesis route of multi-monomer copolymerization follows the mature aqueous solution free radical polymerization process, which has moderate preparation difficulty and is convenient for industrial-scale production. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to specific embodiments.

[0024] In the following examples, the molecular weight of isopentenyl alcohol polyoxyethylene ether is 2400. All reagents used in this invention are commercially available.

[0025] Example 1 A method for preparing a pH-responsive smart-release polycarboxylate superplasticizer includes the following steps: A. Add 310g of isopentenyl alcohol polyoxyethylene ether and 180g of water to a four-necked flask, stir to dissolve, and prepare the base solution. B. Dissolve 2.5g of 3-mercaptopropionic acid and 1.0g of ascorbic acid in 90g of water to prepare solution A; C. Dissolve 30g acrylic acid, 6g maleic anhydride, 7g hydroxyethyl methacrylate, and 12g dimethylaminoethyl methacrylate in 25g of water to prepare solution B. D. Add 2.5g of hydrogen peroxide to the base liquid and stir for 5 minutes. Then, at room temperature, use a peristaltic pump to add solution A and solution B dropwise to the base liquid. The dropwise addition time of solution A is 3 hours, and the dropwise addition rate of solution B is 2.5 hours. After the dropwise addition is completed, continue the reaction for 1 hour to obtain the pH-responsive smart release polycarboxylate superplasticizer.

[0026] The structural formula of the pH-responsive smart-release polycarboxylate superplasticizer is as follows: Example 2 A method for preparing a pH-responsive smart-release polycarboxylate superplasticizer includes the following steps: A. Add 330g of isopentenyl alcohol polyoxyethylene ether and 200g of water to a four-necked flask, stir to dissolve, and prepare the base solution; B. Dissolve 3g of 3-mercaptopropionic acid and 0.8g of ascorbic acid in 90g of water to prepare solution A; C. Dissolve 32g acrylic acid, 8g maleic anhydride, 6g hydroxyethyl methacrylate, and 9g dimethylaminoethyl methacrylate in 25g of water to prepare solution B. D. Add 2.2g of hydrogen peroxide to the base liquid and stir for 5 minutes. Then, at room temperature, use a peristaltic pump to add solution A and solution B dropwise to the base liquid. The dropwise addition time of solution A is 3 hours, and the dropwise addition rate of solution B is 2.5 hours. After the dropwise addition is completed, continue the reaction for 1 hour to obtain the pH-responsive smart release polycarboxylate superplasticizer.

[0027] The structural formula of the pH-responsive smart-release polycarboxylate superplasticizer is as follows: Example 3 A method for preparing a pH-responsive smart-release polycarboxylate superplasticizer includes the following steps: A. Add 350g of isopentenyl alcohol polyoxyethylene ether and 220g of water to a four-necked flask, stir to dissolve, and prepare the base solution; B. Dissolve 2.8g of 3-mercaptopropionic acid and 0.9g of ascorbic acid in 90g of water to prepare solution A; C. Dissolve 37g acrylic acid, 8g maleic anhydride, 3g hydroxyethyl methacrylate, and 7g dimethylaminoethyl methacrylate in 25g of water to prepare solution B. D. Add 2.3g of hydrogen peroxide to the base liquid and stir for 5 minutes. Then, at room temperature, use a peristaltic pump to add solution A and solution B dropwise to the base liquid. The dropwise addition time of solution A is 3 hours, and the dropwise addition rate of solution B is 2.5 hours. After the dropwise addition is completed, continue the reaction for 1 hour to obtain the pH-responsive smart release polycarboxylate superplasticizer.

[0028] The structural formula of the pH-responsive smart-release polycarboxylate superplasticizer is as follows: Example 4 A method for preparing a pH-responsive smart-release polycarboxylate superplasticizer includes the following steps: A. Add 330g of isopentenyl alcohol polyoxyethylene ether and 200g of water to a four-necked flask, stir to dissolve, and prepare the base solution; B. Dissolve 3g of 3-mercaptopropionic acid and 0.8g of ascorbic acid in 90g of water to prepare solution A; C. Dissolve 32g acrylic acid, 6g maleic anhydride, 7g hydroxyethyl methacrylate, and 10g diethylaminoethyl methacrylate in 25g of water to prepare solution B. D. Add 2.2g of hydrogen peroxide to the base liquid and stir for 5 minutes. Then, at room temperature, use a peristaltic pump to add solution A and solution B dropwise to the base liquid. The dropwise addition time of solution A is 3 hours, and the dropwise addition rate of solution B is 2.5 hours. After the dropwise addition is completed, continue the reaction for 1 hour to obtain the pH-responsive smart release polycarboxylate superplasticizer.

[0029] The structural formula of the prepared water-reducing agent is as follows: Example 5 A method for preparing a pH-responsive smart-release polycarboxylate superplasticizer includes the following steps: A. Add 330g of isopentenyl alcohol polyoxyethylene ether and 200g of water to a four-necked flask, stir to dissolve, and prepare the base solution; B. Dissolve 3g of 3-mercaptopropionic acid and 0.8g of ascorbic acid in 90g of water to prepare solution A; C. Prepare solution B by mixing 32g acrylic acid, 10g maleic anhydride, 4g hydroxyethyl methacrylate, 9g 2-(N,N-di(2-hydroxyethyl)amino)ethyl methacrylate, and 25g water. D. Add 2.2g of hydrogen peroxide to the base liquid and stir for 5 minutes. Then, at room temperature, use a peristaltic pump to add solution A and solution B dropwise to the base liquid. The dropwise addition time of solution A is 3 hours, and the dropwise addition rate of solution B is 2.5 hours. After the dropwise addition is completed, continue the reaction for 1 hour to obtain the pH-responsive smart release polycarboxylate superplasticizer.

[0030] The structural formula of the pH-responsive smart-release polycarboxylate superplasticizer is as follows: Comparative Example 1 A water-reducing agent synthesized without the addition of an unsaturated carboxylic acid ester containing a tertiary amine group was used as a comparative example. The preparation steps are as follows: A. Add 330g of isopentenyl alcohol polyoxyethylene ether and 200g of water to a four-necked flask, stir to dissolve, and prepare the base solution; B. Dissolve 3g of 3-mercaptopropionic acid and 0.8g of ascorbic acid in 90g of water to prepare solution A; C. Dissolve 37g acrylic acid, 8g maleic anhydride, and 3g hydroxyethyl methacrylate in 25g water to prepare solution B. D. Add 2.2g of hydrogen peroxide to the base liquid, stir for 5 minutes, and then add solution A and solution B dropwise to the base liquid at room temperature using a peristaltic pump. The dropwise addition time of solution A is 3 hours, and the dropwise addition rate of solution B is 2.5 hours. After the dropwise addition is completed, continue the reaction for 1 hour to obtain a common polycarboxylate superplasticizer.

[0031] The structural formula of the prepared ordinary polycarboxylate superplasticizer is as follows: The water-reducing agents prepared in Examples 1-5 and Comparative Example 1 were each prepared into 5 mg / mL solutions. The molecular weight of the polycarboxylate water-reducing agent was tested using a Shimadzu RID-20A differential detector (Japan). The chromatographic column used was an OHpak SB-804 HQ300 type. The mobile phase in the chromatograph was 0.1 mol / L NaNO3, the column temperature was 25℃, the flow rate was 0.8 ml / min, and the run time was 30 min. The surface tension of the water-reducing agents prepared in Examples 1-5 and Comparative Example 1 was tested using a Sigma 701 fully automatic surface tension meter (Sweden). The adsorption amount of the water-reducing agents prepared in Examples 1-5 and Comparative Example 1 on the surface of the cementitious material was tested using a Shimadzu TOC-VCPH total organic carbon analyzer (Japan). The test results are shown in Table 1.

[0032] Referring to GB 8076-2008 "Concrete Admixtures", the water reduction rate of the water-reducing agents prepared in Examples 1-5 and Comparative Example 1 was tested respectively; referring to T / CECS 10340-2023 "Ultra-high Performance Water-reducing Agents", the mortar flowability and mechanical properties of Examples 1-5 and Comparative Example 1 were tested. The test results are shown in Table 2.

[0033] As can be seen from the test results in Tables 1 and 2, compared with the sample of Comparative Example 1, the pH-responsive polycarboxylate superplasticizers prepared in Examples 1 to 5 of this invention have a higher adsorption capacity; the corresponding concrete mortar also exhibits a better slump retention capacity, while not having an adverse effect on the early mechanical strength development of concrete, thus achieving the technical effect of synergistic balance between long-term slump retention and early strength of concrete.

Claims

1. A pH-responsive smart-release polycarboxylate superplasticizer, characterized in that: The general molecular formula is as follows: In the formula, R is -N(CH3)2, -N(CH2CH3)2 or -N(CH2CH2OH)2, and a, b, c, d, and e represent the degree of polymerization of each monomer in the polymer.

2. A method for preparing the pH-responsive smart-release polycarboxylate superplasticizer according to claim 1, characterized in that, Includes the following steps: A. Dissolve isopentenyl alcohol polyoxyethylene ether in water to prepare a base solution; B. Dissolve the chain transfer agent and reducing agent in water to prepare solution A; C. Dissolve unsaturated carboxylic acid monomers, hydroxyethyl methacrylate, and unsaturated carboxylic acid esters containing tertiary amine groups in water to prepare solution B; D. After adding the initiator to the base liquid, add solution A and solution B dropwise to the base liquid at room temperature. After the addition is complete, continue the reaction for at least 1 hour to obtain the pH-responsive smart-release polycarboxylate superplasticizer.

3. The preparation method of a pH-responsive smart-release polycarboxylate superplasticizer according to claim 2, characterized in that, The raw materials used are in the following proportions by weight: 310-350 parts of isopentenyl alcohol polyoxyethylene ether, 36-45 parts of unsaturated carboxylic acid monomer, 3-7 parts of hydroxyethyl methacrylate, 7-12 parts of unsaturated carboxylic acid ester containing tertiary amine group, 2.2-2.5 parts of initiator, 2.5-3 parts of chain transfer agent, 0.8-1 parts of reducing agent, and 295-335 parts of water.

4. The preparation method of a pH-responsive smart-release polycarboxylate superplasticizer according to claim 3, characterized in that: The unsaturated carboxylic acid monomers are acrylic acid and maleic anhydride.

5. The preparation method of a pH-responsive smart-release polycarboxylate superplasticizer according to claim 3, characterized in that: The monomer of the unsaturated carboxylic acid ester containing a tertiary amine group is one or more of dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and 2-(N,N-di(2-hydroxyethyl)amino)ethyl methacrylate.

6. The preparation method of a pH-responsive smart-release polycarboxylate superplasticizer according to claim 3, characterized in that: The initiator is hydrogen peroxide.

7. The preparation method of a pH-responsive smart-release polycarboxylate superplasticizer according to claim 3, characterized in that: The reducing agent is ascorbic acid.

8. The preparation method of a pH-responsive smart-release polycarboxylate superplasticizer according to claim 3, characterized in that: The chain transfer agent is 3-mercaptopropionic acid.

9. The application of the pH-responsive smart-release polycarboxylate superplasticizer of claim 1 in ultra-high performance concrete.

10. The application of a pH-responsive smart-release polycarboxylate superplasticizer according to claim 9 in ultra-high performance concrete, characterized in that: The pH-responsive smart-release polycarboxylate superplasticizer has a solid content of 0.6% to 1.0% of the total mass of the cementitious material.

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