High slump loss resistant polycarboxylic acid water reducer and preparation method thereof

Abstract

The invention discloses a high-slump-loss-resistant polycarboxylic acid water reducer and a preparation method thereof, and belongs to the technical field of high-efficiency water reducers. The high-slump-loss-resistant polycarboxylic acid water reducer comprises a component A and a component B. The component A is an aqueous solution of a polycarboxylic acid water reducer, and the component B is an aqueous solution of a polycarboxylic acid water reducer. The polycarboxylate superplasticizer is formed by copolymerizing a polyether macromonomer, a carboxylic acid monomer, a chain transfer agent and a slump retaining functional monomer, wherein the molar ratio of the polyether macromonomer to the carboxylic acid monomer to the chain transfer agent to the slump retaining functional monomer is 1: (2.5-3.5): (0.1-0.25): (0.05-0.15); the slump retaining functional monomer comprises methacryloyloxyethyl iminodiacetic acid and imidazole acetic acid polyether terminal hydroxyl ester; and the component B is a zinc salt aqueous solution. According to the water reducing agent provided by the invention, through a double-component synergistic effect mechanism, the slump retaining time of concrete is remarkably prolonged while excellent water reducing performance is ensured, and the requirements of harsh working conditions such as long-distance transportation and high-temperature construction are met.

Description

Technical Field

[0001] This invention relates to the field of high-efficiency water-reducing agent technology, specifically to a high slump-retention polycarboxylate water-reducing agent and its preparation method. Background Technology

[0002] Chemical admixtures are an indispensable component of modern concrete, and their importance is widely recognized. In most industrialized countries, concrete produced using chemical admixtures accounts for more than 80% of total concrete production. Chemical admixtures are diverse, encompassing water-reducing agents, retarders, accelerators, stabilizers, defoamers, foaming agents, and shrinkage inhibitors. The application of these admixtures greatly improves the workability of concrete, increases the mechanical strength and durability of structural members, and enables them to better adapt to complex and changing environmental conditions and engineering requirements.

[0003] Among them, polycarboxylate superplasticizers (PCE) have shown particularly outstanding performance. Continuous innovation in PCE technology is driving the continuous improvement of concrete performance. The flexible molecular design and structural control characteristics of PCE not only provide strong support for the research and development of application systems such as ultra-high performance concrete, self-leveling concrete, and self-compacting concrete, but also allow for the customization of various functional additives such as retarder, slump retainer, viscosity reducer, and air entrainer according to application requirements. At the same time, PCE technology is of great significance in promoting the low-carbon development of the building materials industry.

[0004] However, with the continuous development of concrete engineering technology, the performance requirements for polycarboxylate superplasticizers are becoming increasingly stringent. In practical engineering applications, concrete often faces harsh conditions such as long-distance transportation, high-temperature construction, and long pouring times, which places higher demands on the slump retention performance of superplasticizers. Although traditional polycarboxylate superplasticizers have excellent water-reducing properties, their slump retention performance often fails to meet the above requirements. Excessive slump loss in concrete can lead to construction difficulties, increased pumping resistance, and decreased concrete uniformity, seriously affecting project quality and construction efficiency.

[0005] In the prior art, the main methods to improve the slump retention performance of polycarboxylate superplasticizers include: (1) increasing the dosage of superplasticizer, but this will lead to increased costs and problems such as concrete bleeding; (2) compounding retarders, but improper dosage of retarders will affect the early strength development of concrete; (3) designing polycarboxylate molecular structures with slow-release function, but the selection and ratio optimization of functional monomers in the prior art still need to be improved.

[0006] Therefore, developing a polycarboxylate superplasticizer that combines excellent water-reducing performance and high slump retention is of great significance for meeting the high-performance requirements of modern concrete engineering. Summary of the Invention

[0007] To overcome the shortcomings of the existing technology, the present invention provides a high slump retention polycarboxylate superplasticizer and its preparation method. The superplasticizer, through a two-component synergistic mechanism, significantly extends the slump retention time of concrete while ensuring excellent water reduction performance, thus meeting the needs of harsh working conditions such as long-distance transportation and high-temperature construction.

[0008] The technical solution for achieving the objective of this invention is as follows: A high slump-retention polycarboxylate superplasticizer includes component A and component B. Component A is an aqueous solution of the polycarboxylate superplasticizer, which is copolymerized from polyether macromonomers, carboxylic acid monomers, chain transfer agents, and slump-retention functional monomers. The molar ratio of the polyether macromonomers, carboxylic acid monomers, chain transfer agents, and slump-retention functional monomers is 1:(2.5~3.5):(0.1~0.25):(0.05~0.15). The slump-retention functional monomers include methacryloyloxyethyliminodiacetic acid and imidazole acetic acid polyether-terminated hydroxyl esters. Component B is an aqueous solution of zinc salt.

[0009] In one specific embodiment, the polyether macromonomer is selected from one or more of methyl allyl polyoxyethylene ether, allyl polyoxyethylene ether, or ethylene glycol monovinyl polyethylene glycol ether; the carboxylic acid monomer is selected from one or more of acrylic acid, methacrylic acid, maleic acid, or fumaric acid; the chain transfer agent is selected from one or more of mercaptoacetic acid, mercaptopropionic acid, or sodium hypophosphite; and the molar ratio of the methacryloyloxyethyliminodiacetic acid and the imidazole acetic acid polyether terminal hydroxyl ester is 1:(0.5~2).

[0010] In one specific embodiment, the molecular weight of the polyether macromonomer is 700-2400.

[0011] In one specific embodiment, the zinc salt in the zinc salt aqueous solution is selected from either zinc nitrate or zinc acetate; preferably, the zinc salt in the zinc salt aqueous solution is zinc acetate; and the zinc ion concentration in the zinc salt aqueous solution is 1-5 wt%.

[0012] In one specific embodiment, Zn in component A and component B 2+ The molar ratio of the slump-preserving functional monomer to the slump-preserving monomer is 1:(2~4).

[0013] In one specific embodiment, the methacryloyloxyethyliminodiacetic acid is the product of a nucleophilic ring-opening addition reaction between iminodiacetic acid and glycidyl methacrylate under alkaline conditions at 40-80°C; the molar ratio of iminodiacetic acid to glycidyl methacrylate is 1:(0.8-1.5).

[0014] In one specific embodiment, the imidazole acetic acid polyether-terminated hydroxyl ester is the product of esterification reaction between imidazole acetic acid and polyether macromonomer in the presence of a coupling agent and a catalyst; the preparation method is as follows: imidazole acetic acid and polyether macromonomer are reacted in an organic solvent in the presence of a coupling agent and a catalyst at a temperature range of 0~60°C for 4~24 hours to obtain the imidazole acetic acid polyether-terminated hydroxyl ester; the polyether macromonomer is selected from methyl allyl polyoxyethylene ether or allyl polyoxyethylene ether, with a molecular weight range of 700~2400; the molar ratio of imidazole acetic acid to polyether macromonomer is 1:(1~1.2).

[0015] This invention also protects a method for preparing the high slump-retention polycarboxylate superplasticizer, comprising the following steps: Component A: Under inert gas protection, polyether macromonomers, chain transfer agents, and water are mixed and heated to 40°C~80°C to obtain a base material; carboxylic acid monomers, slump-preserving functional monomers, and water are mixed to obtain solution A; initiator and water are mixed to obtain solution B; under stirring, solution A and solution B are added dropwise to the base material respectively, with a dropwise addition time of 2~5 hours. After the dropwise addition is completed, the reaction is kept at the temperature for 1~3 hours to obtain component A, which is then sealed and stored. Component B: Dissolve the zinc salt in water to prepare a zinc salt aqueous solution with a zinc ion concentration of 1~5wt%, and store it in a sealed container; When using, mix component A and component B on site and then add them to the concrete.

[0016] In one specific embodiment, the dripping time of liquid A is 2.5 to 4 hours, the dripping time of liquid B is 3 to 5 hours, and liquid B is dripped 0.5 to 1 hour later than liquid A.

[0017] In one specific embodiment, the heat preservation reaction temperature is 50℃~70℃, and the heat preservation time is 1.5~4 hours; after the reaction is completed, the pH is adjusted to 6.0~7.0 with an alkaline substance, and then diluted with deionized water to a solid content of 40%~50%.

[0018] In one specific embodiment, the number average molecular weight of the polycarboxylate superplasticizer in component A is 8000~20000.

[0019] In the technical solution of this invention, the carboxyl group in the carboxylic acid monomer can also react with Zn. 2+ The formation of monodentate coordination results in a retarding effect. However, the coordination constant of monodentate coordination is relatively low, while the polydentate chelation of diacetic acid in methacryloyloxyethyliminodiacetic acid can form a five- or six-membered chelate ring. The chelation effect significantly increases the apparent stability constant, therefore Zn... 2+ It preferentially coordinates with diacetic acid in methacryloyloxyethyliminodiacetic acid.

[0020] This invention also protects the application of the high slump retention polycarboxylate superplasticizer in harsh working conditions such as marine cement, marine engineering concrete, high-temperature pumped concrete, and mud-containing aggregate concrete, which require long-distance transportation and high-temperature construction.

[0021] Beneficial effects

[0022] This invention provides a high slump-retention polycarboxylate superplasticizer and its preparation method, which achieves high slump-retention effect through a synergistic sustained-release mechanism of dual slump-retention functional monomers. Specifically, the polycarboxylate superplasticizer molecule in component A incorporates specific slump-retention functional monomers (methacryloyloxyethyliminodiacetic acid and imidazole acetic acid polyether terminal hydroxyl esters) to construct two independent sustained-release channels on the molecular side chain, forming a time-synergistic slump-retention system with zinc ions in component B.

[0023] Specifically, methacryloyloxyethylimino contains an iminodiacetic acid group, making it a polydentate ligand capable of reacting with Zn. 2+ A stable chelate complex is formed. When component A and component B are mixed in-situ, Zn... 2+ It preferentially coordinates with diacetic acid groups to form a dynamic cross-linked network on the surface of cement particles, initially reducing excessive adsorption of water-reducing agent molecules onto cement and avoiding bleeding problems caused by excessive initial slump. As cement hydration progresses, the pH rapidly increases (>12), and Zn... 2+ The coordination bond with the diacetic acid group is due to Zn 2+ The carboxyl groups are destroyed as they are converted into zinc hydroxide / calcium zincate precipitate, and the carboxyl groups are gradually released. At the same time, the precipitate forms a physical adsorption layer on the surface of cement hydration products, which slows down the growth of hydration crystals. The released carboxyl groups are then adsorbed on the surface of newly formed hydrated calcium silicate (CSH), maintaining the dispersion of the slurry through electrostatic repulsion, thus achieving slump retention in the middle and later stages.

[0024] The ester bonds in the hydroxyl-terminated side chain of imidazole acetate polyether ester undergo alkaline hydrolysis in the strongly alkaline environment of cement (pH>12), gradually releasing free carboxylate ions. This chemical slow-release process forms a time gradient with the coordination-precipitation slow-release of methacryloyloxyethylimino monomer: the ester bond hydrolysis rate is relatively slow (half-life approximately 1-2 hours), mainly releasing carboxyl groups during the transport waiting period (1-3 hours), continuously providing electrostatic adsorption sites to compensate for the consumption of water-reducing agent due to hydration progress. Simultaneously, the imidazole ring in the side chain is physically adsorbed onto the surface of cement particles and hydration products through hydrogen bonding (imidazole NH and silanol groups Si-OH on the cement surface) and hydrophobic interactions, forming a weak adsorption shielding layer. This physical adsorption is independent of electrostatic interactions. In clay-containing systems, the imidazole ring can preferentially occupy adsorption sites on the surface of clay minerals through competitive adsorption, preventing the polycarboxylate backbone from being consumed by layered silicate intercalation, reducing the ineffective loss of water-reducing agent in clay-containing concrete, and indirectly improving slump retention performance.

[0025] Furthermore, the polyether macromonomer provides steric hindrance, while the carboxylic acid monomer provides basic electrostatic repulsion; the two work synergistically to ensure basic water-reducing effect. The chain transfer agent controls the molecular weight distribution (PDI < 2.0), preventing abnormal increases in system viscosity after the participation of metal ions. The introduction of slump-retaining monomers does not affect the main chain conformation, but through the aforementioned multiple synergistic mechanisms of coordination-precipitation-hydrolysis-adsorption, it significantly extends the workability retention time of concrete.

[0026] The high slump retention polycarboxylate superplasticizer of the present invention has the advantages of excellent slump retention performance (2h loss rate <10%), high water reduction rate (>25%), strong adaptability to mud content, simple preparation process, and controllable cost. It meets the needs of harsh working conditions such as long-distance transportation and high-temperature construction, and is easy to industrialize. Attached Figure Description

[0027] Figure 1 Infrared spectrum of imidazole acetic acid polyether terminal hydroxyl esterified product; Figure 2 The infrared spectrum of the high slump-resistance polycarboxylate superplasticizer in Example 2 is shown. Detailed Implementation

[0028] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0029] Unless otherwise specified, the experimental methods used in the embodiments are conventional methods, and the materials and reagents used are commercially available unless otherwise specified.

[0030] The raw materials used in the examples and comparative examples are described below: Polyether macromonomer 1: Methyl allyl polyoxyethylene ether, molecular weight 2000, Guangdong Wengjiang Chemical Reagent Co., Ltd.; Polyether macromonomer 2: methyl allyl polyoxyethylene ether, molecular weight 2400, Guangdong Wengjiang Chemical Reagent Co., Ltd.; Carboxylic acid monomer 1: methacrylic acid, purity 99%, with 100ppm MEHQ added as a polymerization inhibitor, Nantong Runfeng Petrochemical Co., Ltd. Carboxylic acid monomer 2: Acrylic acid, 99% purity, with 100ppm MEHQ added as a polymerization inhibitor, Nantong Runfeng Petrochemical Co., Ltd. Chain transfer agent 1: mercaptoacetic acid, 95% purity, Shanghai Aladdin Biochemical Technology Co., Ltd.; Chain transfer agent 2: Sodium hypophosphite, purity over 98%, Shanghai Maclean Biochemical Technology Co., Ltd. Slump-retaining functional monomer 1: Methacryloxyethyliminodiacetic acid, prepared in-house, preparation method as follows: In a three-necked round-bottom flask equipped with a thermometer, electric stirrer, and nitrogen inlet, add 133 g (1 mol) iminodiacetic acid, 80 g (2 mol) sodium hydroxide, and 2 L of deionized water. Heat to 50 °C and stir to dissolve the iminodiacetic acid in the water. Then, slowly add 142 g (1 mol) glycidyl methacrylate (containing 100 ppm MEHQ stabilizer) dropwise over 2-3 hours until the addition is complete. After the addition is finished, maintain the temperature at 50 °C and continue stirring for 2 hours. A clear, homogeneous solution is obtained after the reaction. Cool the reaction solution to room temperature and adjust the pH to 2.0-2.5 with 1 M hydrochloric acid to convert the product to a free acid form. Transfer the acidified solution to a separatory funnel and extract three times with 500 mL of ethyl acetate. Combine the organic phases. Wash the organic phase twice with 300 mL of saturated sodium chloride solution to remove residual water and inorganic salts. Add 50 g of anhydrous sodium sulfate and dry for 4 hours. Filter to remove the desiccant. The solvent in the filtrate was removed by rotary evaporation under reduced pressure at 40℃ and -0.09 MPa to obtain the crude product. The crude product was recrystallized with a mixed solvent of isopropanol / n-hexane (1:2, v / v), cooled to 0-5℃ for 2 hours to crystallize, filtered, and dried under vacuum at 35℃ to constant weight to obtain methacryloyloxyethyliminodiacetic acid with a yield of 75%.

[0031] Slump-resistant monomer 2: Imidazole acetate polyether terminal hydroxyl ester: self-made, preparation method as follows: In a three-necked flask equipped with a mechanical stirrer, thermometer, and nitrogen inlet, under nitrogen protection, 0.1 mol of imidazole acetic acid and 0.105 mol of methyl allyl polyoxyethylene ether (molecular weight 2000) were added, followed by 200 mL of anhydrous dichloromethane. The mixture was stirred for 30 min until the polyether was completely dissolved and the imidazole acetic acid was partially suspended. Then, 0.01 mol of 4-dimethylaminopyridine (DMAP) was added and stirred for 10 min to ensure uniform dispersion. The temperature was lowered to 0–5°C (ice-salt bath), and 0.12 mol of dicyclohexylcarbodiimide (DCC) was slowly added in batches, controlling the addition rate to keep the temperature below 10°C to prevent localized overheating. After the addition was complete, the mixture was allowed to return to room temperature and stirred continuously for 12 hours.

[0032] After the reaction, the generated dicyclohexylurea white precipitate was removed by filtration. The filtrate was washed twice with 500 mL of saturated sodium bicarbonate solution (to remove unreacted imidazole acetic acid), then once with 200 mL of 0.1 M citric acid solution (to convert residual DCC into a water-soluble urea derivative for removal), and finally once with 300 mL of saturated sodium chloride solution. The organic phase was dried for 4 hours with 100 g of anhydrous sodium sulfate and filtered. The solution was concentrated under reduced pressure at 40°C and -0.09 MPa to remove dichloromethane, yielding the crude product. The crude product was dissolved in 200 mL of toluene and heated to 60°C to dissolve. The solution was filtered while hot to remove trace amounts of insoluble matter, and recrystallized at 0–5°C for 2 hours. The resulting white solid powder was obtained by filtration. The powder was dried under vacuum at 35°C to constant weight, with a yield of 84.2%. The infrared spectrum of the imidazole acetic acid polyether terminal hydroxyl ester (measured using a PE Pargon 1000 Fourier transform infrared spectrometer after KBr pelleting) is as follows: Figure 1 As shown.

[0033] Unless otherwise specified, all components and raw materials used in the embodiments and comparative examples of this invention are commercially available, and the same type of components and raw materials are used in each parallel experiment.

[0034] Example 1

[0035] A high slump-retention polycarboxylate superplasticizer is prepared as follows: Component A: In a reaction vessel, add 2400g (1mol) of methyl allyl polyoxyethylene ether (molecular weight 2400), 13.5g (0.14mol) of mercaptoacetic acid and 1500g of deionized water, stir and heat to 60℃, and purge with nitrogen for 30 minutes.

[0036] Preparation of solution A: Mix and dissolve 258g (3mol) of methacrylic acid, 8.25g (0.03mol) of methacryloyloxyethyliminodiacetic acid, 126.48g (0.06mol) of imidazole acetic acid polyether terminal hydroxyl ester (molecular weight calculated as 2108) and 500g of deionized water.

[0037] Preparation of solution B: Dissolve 6.84g (0.03mol) of ammonium persulfate in 100g of deionized water.

[0038] While stirring, start adding liquid A and liquid B. Control the addition of liquid A to be completed at a uniform rate within 3 hours; control the addition of liquid B to be completed within 3.5 hours (i.e., 0.5 hours later than the addition of liquid A).

[0039] After the addition is complete, continue the reaction at 60°C for 2 hours.

[0040] After the reaction was completed, the mixture was cooled to room temperature and the pH was adjusted to 6.0 with 32wt% sodium hydroxide solution to obtain a pale yellow transparent liquid. Deionized water was added to dilute the liquid to a solid content of 45%.

[0041] The molecular weight of the obtained water-reducing agent was determined by gel permeation chromatography (GPC, Waters 2414, differential detector, column: Shodex OHpak SB-806M, mobile phase: 0.1M NaNO3 solution, flow rate: 1.0 mL / min, column temperature: 40℃, calibrated with polyethylene glycol standard). The results showed that the number-average molecular weight (Mn) was 18,500 g / mol, the weight-average molecular weight (Mw) was 32,000 g / mol, and the PDI was 1.73.

[0042] Component B: Dissolve zinc acetate in water to prepare a zinc salt aqueous solution with a zinc ion concentration of 3wt%.

[0043] When using, mix component A and component B according to Zn 2+ After being mixed on-site with methacryloyloxyethyliminodiacetic acid at a molar ratio of 1:2.5, it is then added to the concrete.

[0044] Example 2

[0045] In a reaction vessel, add 2000g (1mol) of methyl allyl polyoxyethylene ether (molecular weight 2000), 22g (0.25mol) of sodium hypophosphite and 1200g of deionized water, stir and heat to 55℃, and purge with nitrogen to remove oxygen for 30min.

[0046] Preparation of solution A: 230.6g (3.2mol) acrylic acid, 27.5g (0.1mol) methacryloyloxyethyliminodiacetic acid, 105.4g (0.05mol) imidazole acetic acid polyether terminal hydroxyl ester (molecular weight calculated as 2108), and 500g deionized water.

[0047] Preparation of solution B: 5.7g (0.025mol) of ammonium persulfate and 2.5g (0.024mol) of sodium bisulfite are dissolved in 150g of deionized water.

[0048] The temperature is raised to 65°C, and liquid A (to be dripped in 3 hours) and liquid B (to be dripped in 3.5 hours) are dripped simultaneously.

[0049] After the addition is complete, maintain the temperature at 65°C for 2.5 hours.

[0050] Cool to 40℃, adjust pH to 6.5 with 32wt% sodium hydroxide solution, and dilute with deionized water to a water-reducing agent solution with a solid content of 45%.

[0051] The water-reducing agent was determined by gel permeation chromatography (GPC) to have a number-average molecular weight (Mn) of 9300 g / mol, a weight-average molecular weight (Mw) of 16500 g / mol, and a molecular weight distribution index (PDI) of 1.77. The infrared spectrum of the water-reducing agent (measured using a PE Pargon 1000 Fourier transform infrared spectrometer, after drying and KBr pelleting) is as follows: Figure 2 As shown.

[0052] Component B: Dissolve zinc nitrate in water to prepare a zinc salt aqueous solution with a zinc ion concentration of 3wt%.

[0053] When using, mix component A and component B according to Zn 2+ After being mixed on-site with methacryloyloxyethyliminodiacetic acid at a molar ratio of 1:4, it is then added to the concrete.

[0054] Example 3

[0055] In a reaction vessel, add 2000g (1mol) of methyl allyl polyoxyethylene ether (molecular weight 2000), 18.4g (0.2mol) of mercaptoacetic acid and 1200g of deionized water, stir and heat to 55℃, and purge with nitrogen to remove oxygen for 30min.

[0056] Preparation of solution A: 215.3g (2.5mol) methacrylic acid, 13.75g (0.05mol) methacryloyloxyethyliminodiacetic acid, 105.4g (0.05mol) imidazole acetic acid polyether terminal hydroxyl ester, and 250g deionized water.

[0057] Preparation of solution B: 5.7g (0.025mol) of ammonium persulfate and 2.5g (0.024mol) of sodium bisulfite are dissolved in 150g of deionized water.

[0058] The temperature is raised to 65°C, and liquid A (to be dripped in 3 hours) and liquid B (to be dripped in 3.5 hours) are dripped simultaneously.

[0059] After the addition is complete, maintain the temperature at 65°C for 2.5 hours.

[0060] Cool to 40℃, adjust pH to 6.5 with 32wt% sodium hydroxide solution, and dilute with deionized water to a water-reducing agent solution with a solid content of 45%.

[0061] The water-reducing agent was determined by gel permeation chromatography (GPC) to have a number-average molecular weight (Mn) of 15,600 g / mol, a weight-average molecular weight (Mw) of 28,500 g / mol, and a molecular weight distribution index (PDI) of 1.82.

[0062] Component B: Dissolve zinc acetate in water to prepare a zinc salt aqueous solution with a zinc ion concentration of 3wt%.

[0063] When using, mix component A and component B according to Zn 2+ After being mixed on-site with methacryloyloxyethyliminodiacetic acid at a molar ratio of 1:2, it is then added to the concrete.

[0064] Comparative Example 1 Compared with Example 3, the difference is that no slump-preserving monomer is added, and it is copolymerized only from polyether macromonomers, acrylic acid and sodium hypophosphite.

[0065] Comparative Example 2 The difference from Example 3 is that only component A of the polycarboxylate superplasticizer is prepared and it is not mixed with component B.

[0066] Comparative Example 3 Compared with Example 3, the difference is that the amount of methacryloyloxyethyliminodiacetic acid added is modified to 27.5g (0.1mol) and the amount of imidazole acetic acid polyether terminal hydroxyl esterification is 0g.

[0067] Comparative Example 4 Compared with Example 3, the difference is that the amount of methacryloyloxyethyliminodiacetic acid added is modified to 27.5g (0.1mol) and the amount of imidazole acetic acid polyether terminal hydroxyl esterification is 210.8g (0.1mol).

[0068] Performance testing (1) Water reduction rate: The water-reducing agents prepared in Examples 1-3 and Comparative Examples 1-4 were tested according to the water reduction rate section of cement mortar in GB / T 8077-2012 "Test Method for Homogeneity of Concrete Admixtures". The cement used for testing was P·O 42.5 ordinary Portland cement, the dosage of water-reducing agent was 0.2% of the cement mass (based on solid content), and the water-cement ratio was fixed at 0.29. (2) Slump: The water-reducing agents prepared in Examples 1-3 and Comparative Examples 1-4 were tested according to the slump test section of GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures". The cement used for testing was P·O42.5 ordinary Portland cement, the dosage of water-reducing agent was 0.2% of the cement mass (based on solid content), and the water-cement ratio was fixed at 0.29.

[0069] (3) Anti-mud performance: The fluidity of cement paste was tested according to GB / T 8077-2012 "Test Method for Homogeneity of Concrete Admixtures". P·O 42.5 ordinary Portland cement was used, and montmorillonite (250 mesh, produced in Tangshan, Hebei) was used to replace cement at 1.0% of the cement mass. The water-reducing agent was added at 0.2% of the cement mass (based on solid content), and the water-cement ratio was fixed at 0.29.

[0070] The test results are shown in the table below: Table 1 Performance test results of the examples and comparative examples

[0071] The test results above show that: Compared with the conventional polycarboxylate superplasticizer of Comparative Example 1, the slump loss rate of Examples 1-3 of this invention was controlled within 5% after 2 hours, demonstrating excellent slump retention performance. This verifies the synergistic slow-release mechanism of the slump-retaining monomer and zinc ions: methacryloyloxyethyliminodiacetic acid achieves mid-to-late-stage slump retention through a coordination-precipitation mechanism, while imidazole ester monomers replenish carboxyl groups through ester bond hydrolysis. The two work synergistically to cover the long-distance transport cycle. In the anti-mud test containing 1% montmorillonite, the 1-hour anti-mud retention rate of Examples 1-3 reached 86-90%, significantly higher than Comparative Example 1 and Comparative Example 3. This proves that the imidazole ring in the side chain of the imidazole acetic acid polyether terminal hydroxyl ester effectively inhibits the interlayer intercalation of clay minerals through hydrogen bond competitive adsorption and hydrophobic interaction, reducing the ineffective consumption of the superplasticizer by clay. Although Comparative Example 2 has good anti-mud properties due to the presence of imidazole ester, its slump loss rate after 2 hours reached 15.9%, significantly worse than the Examples. This indicates that the slow-release hydrolysis of imidazole esters alone is insufficient to support the requirements of long-distance transportation. Comparative Example 4, while still maintaining good anti-mud properties, saw its water reduction rate decrease to 26%, and its initial flowability drop to 270 mm. This is because excessive slump-retaining monomers form an over-crosslinked network under the action of zinc ions, which hinders the effective adsorption of water-reducing agent molecules on the surface of cement particles, resulting in a decrease in initial dispersibility.

[0072] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A high slump-retention polycarboxylate superplasticizer, characterized in that, The product comprises component A and component B. Component A is an aqueous solution of polycarboxylate superplasticizer, which is copolymerized from polyether macromonomers, carboxylic acid monomers, chain transfer agents, and slump-retaining functional monomers. The molar ratio of polyether macromonomers, carboxylic acid monomers, chain transfer agents, and slump-retaining functional monomers is 1:(2.5~3.5):(0.1~0.25):(0.05~0.15). The slump-retaining functional monomers include methacryloyloxyethyliminodiacetic acid and imidazole acetic acid polyether-terminated hydroxyl esters. Component B is an aqueous solution of zinc salt.

2. The high slump-retention polycarboxylate superplasticizer as described in claim 1, characterized in that, The polyether macromonomer is selected from one or more of methyl allyl polyoxyethylene ether, allyl polyoxyethylene ether, or ethylene glycol monovinyl polyethylene glycol ether; the carboxylic acid monomer is selected from one or more of acrylic acid, methacrylic acid, maleic acid, or fumaric acid; the chain transfer agent is selected from one or more of mercaptoacetic acid, mercaptopropionic acid, or sodium hypophosphite; and the molar ratio of the methacryloyloxyethyliminodiacetic acid and the imidazole acetic acid polyether terminal hydroxyl ester is 1:(0.5~2).

3. The high slump retention polycarboxylate superplasticizer as described in claim 1, characterized in that, The molecular weight of the polyether macromonomer is 700~2400.

4. The high slump retention polycarboxylate superplasticizer as described in claim 1, characterized in that, The zinc salt in the zinc salt aqueous solution is selected from either zinc nitrate or zinc acetate, and the zinc ion concentration in the zinc salt aqueous solution is 1~5wt%.

5. The high slump-retention polycarboxylate superplasticizer as described in claim 1, characterized in that, Zn in component A and component B 2+ The molar ratio of the slump-preserving functional monomer to the slump-preserving functional monomer is 1:(2~4).

6. The high slump-retention polycarboxylate superplasticizer as described in claim 1, characterized in that, The methacryloyloxyethyliminodiacetic acid is the product of a nucleophilic ring-opening addition reaction between iminodiacetic acid and glycidyl methacrylate under alkaline conditions at 40-80°C; the molar ratio of iminodiacetic acid to glycidyl methacrylate is 1:(0.8-1.5).

7. The high slump-retention polycarboxylate superplasticizer as described in claim 1, characterized in that, The imidazole acetic acid polyether terminal hydroxyl ester is the product of the esterification reaction of imidazole acetic acid and polyether macromonomer in the presence of a coupling agent and a catalyst; the polyether macromonomer is selected from methyl allyl polyoxyethylene ether or allyl polyoxyethylene ether, with a molecular weight range of 700~2400; the molar ratio of imidazole acetic acid to polyether macromonomer is 1:(1~1.2).

8. The method for preparing the high slump-retention polycarboxylate superplasticizer according to any one of claims 1 to 7, characterized in that, Includes the following steps: Component A: Under inert gas protection, polyether macromonomers, chain transfer agents, and water are mixed and heated to 40°C~80°C to obtain a base material; carboxylic acid monomers, slump-preserving functional monomers, and water are mixed to obtain solution A; initiator and water are mixed to obtain solution B; under stirring, solution A and solution B are added dropwise to the base material over a period of 2~5 hours, and after the addition is complete, the reaction is maintained at the temperature for 1~3 hours to obtain component A, which is then sealed and stored. Component B: Dissolve the zinc salt in water to prepare a zinc salt aqueous solution with a zinc ion concentration of 1~5wt%, and store it in a sealed container; When using, mix component A and component B on site and then add them to the concrete.

9. The preparation method of the high slump-retention polycarboxylate superplasticizer as described in claim 8, characterized in that, The dripping time of solution A is 2.5 to 4 hours, the dripping time of solution B is 3 to 5 hours, and solution B is added 0.5 to 1 hour later than solution A. The initiator is ammonium persulfate or a combination of ammonium persulfate and sodium bisulfite. The heat preservation reaction temperature is 50℃~70℃, and the heat preservation time is 1.5~4 hours. After the reaction is completed, the pH is adjusted to 6.0~7.0 with an alkaline substance and diluted to a solid content of 40%~50%.

10. The application of the high slump retention polycarboxylate superplasticizer as described in any one of claims 1 to 7 in marine cement, marine engineering concrete, pumped concrete in high-temperature areas, and concrete containing mud aggregate.

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