Viscosity-reducing polycarboxylate water reducer and preparation method thereof

Abstract

The application relates to the technical field of concrete admixture application, in particular to a viscosity-reducing polycarboxylate water reducing agent and a preparation method thereof. The water reducing agent is composed of modified viscosity-reducing polycarboxylate mother liquor, silane-modified white silica ash, compounded suspension stabilizer, functional auxiliary agent and water. The modified mother liquor is prepared by using iso-pentenyl polyethylene glycol ether, double viscosity-reducing monomers and acrylic monomers as raw materials, and by using a composite initiation system to realize stage temperature control polymerization. The silane-modified white silica ash is prepared by surface modification of white silica ash with a purity of more than 98% by using gamma-aminopropyl triethoxysilane. The compounded suspension stabilizer is a compound of fumed silica and hydroxypropyl methyl cellulose. The viscosity of the water reducing agent is reduced by chemical-physical synergy, the viscosity-reducing index is less than or equal to 0.79, the concrete emptying time is less than or equal to 28s, the concrete is not layered after 60 days, the water reducing agent has the properties of anti-freezing and anti-chloride ion erosion, is suitable for complex engineering scenes of C60 and above high-strength concrete, the preparation process is simple and environment-friendly, and the industrial application value is remarkable.

Description

Technical Field

[0001] This invention belongs to the field of concrete admixture application technology, and in particular relates to a viscosity-reducing polycarboxylate superplasticizer and its preparation method. Background Technology

[0002] Concrete, as the most widely used basic material in the field of engineering construction, has always focused on improving its performance by enhancing strength, optimizing construction adaptability, and expanding environmental compatibility. High-strength concrete, with a strength grade of C60 or higher, is widely used in bridges, pipe piles, core components of high-rise buildings, and marine engineering projects—scenarios with stringent structural load-bearing requirements—due to its excellent mechanical properties and durability. To achieve high strength, high-strength concrete requires a mix design with high cementitious material content and a low water-cement ratio. It often incorporates mineral admixtures with large specific surface areas and irregular particle morphologies. However, this leads to reduced particle spacing and increased frictional resistance in the fresh concrete paste, resulting in poor fluidity of the excess paste. Ultimately, this causes problems such as high paste viscosity, pumping difficulties, and poor workability, severely hindering the widespread application of high-strength concrete.

[0003] Currently, the main methods for reducing the viscosity of high-strength concrete are increasing the dosage of water-reducing agents and optimizing the particle size distribution using high-quality ultrafine powders. Increasing the dosage of water-reducing agents to lower concrete viscosity has several drawbacks. First, it increases costs. Second, it can cause excessive retardation, extending the demolding period. Third, fresh concrete is prone to segregation and bleeding, making construction more difficult. While there is considerable research on optimizing the particle size distribution of high-quality ultrafine powders to reduce concrete viscosity, it has limitations. The fluidity of fresh concrete mainly relies on the strong adsorption and dispersion effects of high-efficiency water-reducing agents. The inconvenience of producing and using ultrafine powders as viscosity reducers also limits their application. Summary of the Invention

[0004] To address the problems of high production cost, long production cycle, and difficulty in balancing viscosity reduction effect with system stability in existing technologies, this invention provides a viscosity-reducing polycarboxylate superplasticizer and its preparation method. The technical solution adopted by this invention to solve the above problems is as follows: a viscosity-reducing polycarboxylate superplasticizer and its preparation method, the preparation method steps are as follows: add the prescribed amount of water to an industrial-grade compound mixing tank, start the variable frequency stirring device, control the speed at 300-400 r / min, add silane-modified white silica fume via a screw conveyor, start a high-speed disperser to assist dispersion for 15-20 min, then accurately deliver the modified viscosity-reducing mother liquor and functional additives through a metering pump, continue stirring for 20-25 min, finally add a compound suspension stabilizer, start circulating stirring for 30-35 min, filter through a 200-mesh filter to remove mechanical impurities, and obtain a uniformly suspended viscosity-reducing polycarboxylate superplasticizer; The viscosity-reducing polycarboxylate superplasticizer is formulated from the following raw materials in the indicated mass fractions: 15%–25% modified viscosity-reducing mother liquor, 12%–25% silane-modified silica fume, 1.5%–3.5% compounded suspension stabilizer, 2%–5% functional additives, and the remainder being water. The modified viscosity-reducing mother liquor is prepared by staged temperature-controlled polymerization of the following raw materials in parts by weight: 25-35 parts of isopentenyl polyethylene glycol ether, 8-15 parts of the first viscosity-reducing monomer, 3-8 parts of the second viscosity-reducing monomer, and 3-6 parts of acrylic acid or its derivatives. The first viscosity-reducing monomer is dimethylaminoethyl methacrylate, and the second viscosity-reducing monomer is dimethylaminopropyl acrylate. The silane-modified white silica fume is prepared by modifying the surface of white silica fume with γ-aminopropyltriethoxysilane using white silica fume with a purity of 98% or higher as a base material. The amount of γ-aminopropyltriethoxysilane used is 1% to 3% of the mass of white silica fume. The compound suspension stabilizer is a mixture of fumed silica and hydroxypropyl methylcellulose in a mass ratio of 7:3 to 4:1, and the functional additive is ethylene glycol monomethyl ether.

[0005] The aforementioned viscosity-reducing polycarboxylate superplasticizer utilizes a composite initiation system for the polymerization of the modified viscosity-reducing mother liquor. This system comprises an initiator and a composite reducing agent. The initiator is a mixture of hydrogen peroxide and potassium persulfate in a mass ratio of 1:1 to 2:1. The composite reducing agent is a mixture of L-ascorbic acid and sodium bisulfite in a mass ratio of 2:1. Both initiators are free radical initiators. Hydrogen peroxide has a lower decomposition temperature, while potassium persulfate has a higher decomposition temperature. Their combined use forms a wide-temperature-range initiation system, broadening the reaction temperature adaptability range. To avoid the problem of reactions being too fast or too slow due to a single initiator, the optimized 1:1 to 2:1 ratio ensures the continuous and stable generation of free radicals, resulting in more uniform monomer polymerization. The composite reducing agent L-ascorbic acid and sodium bisulfite form a synergistic reducing system, which can efficiently react with the initiator in a redox reaction. By reducing the activation energy, it accelerates the generation of free radicals and regulates the reaction rate. The reducing properties of L-ascorbic acid are milder, which can avoid over-reduction caused by excessive sodium bisulfite. The 2:1 ratio can balance the reduction efficiency and reaction controllability, and reduce impurities in the polymerization process.

[0006] The above-mentioned viscosity-reducing polycarboxylate superplasticizer, wherein the modified viscosity-reducing mother liquor is prepared by the following steps: (1) In an industrial-grade polymerization reactor, isopentenyl polyethylene glycol ether, the first viscosity-reducing monomer, and the second viscosity-reducing monomer are dissolved in deionized water to prepare a bottom solution with a mass concentration of 55% to 60%. The bottom solution is heated to 35 to 40°C and kept at that temperature by a jacketed temperature control system. At the same time, solution A and solution B are prepared in a mixing tank. Solution A is acrylic acid or its derivative dissolved in water, and solution B is a composite reducing agent, ferrous sulfate, and sodium hypophosphite dissolved in water. (2) Add the composite initiation system to the polymerization reactor, let it stand for 5 minutes, and then add liquid A and liquid B simultaneously through a metering and dropping device. Liquid A is added within 2 hours and liquid B is added within 2.5 hours. When the addition reaches 1 hour, the temperature of the reaction system is raised to 48-52°C by jacket temperature control. (3) After the addition of liquid A and liquid B is completed, the temperature of the reaction system is lowered to 38-42℃, and the reaction is continued for 1 hour. Finally, water is added to adjust the solid content of the system to 42%-45% to obtain the modified viscosity-reducing mother liquor. The catalyst is ferrous sulfate, and the chain transfer agent is selected from sodium hypophosphite or isopentenyl mercaptopropionic acid.

[0007] In the above-mentioned viscosity-reducing polycarboxylate superplasticizer, the amount of ferrous sulfate in step (1) of the preparation of the modified viscosity-reducing mother liquor is 0.003% to 0.005% of the mass of isopentenyl polyethylene glycol ether, and the amount of sodium hypophosphite is 0.5% to 1% of the mass of isopentenyl polyethylene glycol ether. Ferrous sulfate acts as a catalyst in the polymerization reaction, accelerating the generation of free radicals by promoting electron transfer between the initiator and the reducing agent. It is a key auxiliary agent for the initiation and continuation of the reaction. Sodium hypophosphite controls the growth length of the polycarboxylate molecular chain by transferring the active center of free radicals. It is a core auxiliary agent for adjusting the molecular weight of the mother liquor.

[0008] The above-mentioned viscosity-reducing polycarboxylate superplasticizer, wherein the isopentenyl polyethylene glycol ether has the following general formula: The general formula is n=30~60, preferably n=40~50.

[0009] The preparation steps of the silane-modified silica fume in the above-mentioned viscosity-reducing polycarboxylate superplasticizer are as follows: (1) In the modified reaction vessel, γ-aminopropyltriethoxysilane is weighed at 1% to 3% of the mass of white silica fume and mixed with an ethanol aqueous solution to prepare a modifier solution, wherein the volume ratio of ethanol to water in the ethanol aqueous solution is 1:3. (2) Hydrophobic alkyl grafting: Add white silica fume with a purity of 98% or higher to the modifier solution through a quantitative feeder, and stir and react for 1.5 to 2 hours at 60 to 70°C and a stirring speed of 200 to 250 r / min; (3) The mixture after the reaction is dried at 80°C by a belt dryer, pulverized to a particle size of 1-3 μm by an air jet mill, passed through a 200-mesh sieve, and stored in a sealed silo for later use.

[0010] The aforementioned viscosity-reducing polycarboxylate superplasticizer uses acrylic acid or its derivatives as one or a mixture of two of acrylic acid and methacrylic acid. Acrylic acid has high reactivity, with a polymerization reactivity ratio of ≈1.1, allowing it to rapidly copolymerize with viscosity-reducing monomers and ensuring a uniform distribution of hydrophilic carboxyl groups in the molecular chain. Methacrylic acid, due to the presence of methyl side chains, has slightly lower reactivity, with a polymerization reactivity ratio of ≈0.8, but it can adjust the extensibility of the molecular chain through steric hindrance, avoiding excessive entanglement. When used alone or in combination, both can form a stable alternating copolymer structure with the two viscosity-reducing monomers, achieving a monomer conversion rate of over 95%. This effectively avoids block polymerization or monomer residue caused by differences in reactivity, ensuring a uniform molecular structure in the mother liquor with a molecular weight distribution PDI of 1.8–2.2, laying the foundation for efficient viscosity reduction.

[0011] The aforementioned viscosity-reducing polycarboxylate superplasticizer employs a multi-stage filtration process in its compounding mixing tank. First, large particles are removed through a 200-mesh filter, followed by a 300-mesh precision filter to remove fine impurities. The solid content of the filtered product is controlled at 42%–45%, with a fluctuation range of ≤±0.5%. The viscosity at 25°C is 500–800 mPa·s, ensuring smooth pumping during construction. This staged filtration removes both large and fine particles, improving the compatibility of the superplasticizer with cement and mineral admixtures. It prevents water seepage and segregation in the concrete slurry, ensuring uniform mechanical properties of the high-strength concrete. The 25°C temperature and 500–800 mPa·s viscosity maintain a certain degree of fluidity in the high-strength concrete while ensuring uniform mixing of the superplasticizer and slurry, guaranteeing smooth pumping during construction.

[0012] The aforementioned viscosity-reducing polycarboxylate superplasticizer, wherein the functional additive ethylene glycol monomethyl ether can be compounded with propylene glycol butyl ether at a mass ratio of 3:1 to 2:1, with the dosage of the functional additive remaining at 2% to 5%, enables concrete to withstand 300 freeze-thaw cycles at -20℃ with a strength loss of ≤4.8%. Simultaneously, it improves the compatibility of the superplasticizer with mineral admixtures in high-strength concrete, preventing slurry bleeding. Ethylene glycol monomethyl ether exerts a basic antifreeze effect by lowering the freezing point of concrete, while propylene glycol butyl ether possesses both antifreeze properties and interfacial activity, improving the compatibility of the additive with cement paste and reducing the structural damage caused by ice crystallization within the paste at low temperatures. The two work synergistically to enhance the antifreeze effect and improve the strength stability after freeze-thaw cycles, covering more low-temperature construction scenarios and improving the product's regional adaptability.

[0013] As described above, the beneficial effects of the viscosity-reducing polycarboxylate superplasticizer and its preparation method provided by this invention are as follows: This invention utilizes a chemical-physical synergistic viscosity-reducing design through the compounding of two viscosity-reducing monomers, namely dimethylaminoethyl methacrylate + dimethylaminopropyl acrylate + silane-modified silica fume. This design ensures that the superplasticizer molecules are uniformly adsorbed on the cement surface and have a well-developed structure. The silane modification of the silica fume improves its compatibility by more than 30%, resulting in a more durable ball-bead effect. Ultimately, the viscosity-reducing index is reduced to below 0.76, a decrease of 8%–10% compared to traditional products. The concrete collapse and drainage time is shortened to less than 26 seconds, completely solving the problem of difficult pumping of high-strength concrete. Unlike existing superplasticizers with only a single viscosity-reducing function, this invention adds a functional additive, ethylene glycol monomethyl ether, which further enhances the viscosity reduction of concrete. With a freezing point dropping to -15℃ to -10℃, it can withstand 300 freeze-thaw cycles with a strength loss of only 5.2%, making it suitable for construction in extremely cold regions. The synergistic effect of silane-modified white silica fume and mother liquor can also enhance the concrete's resistance to chloride ion erosion, extending its application to corrosive environments such as marine engineering. The overall preparation process requires no complex equipment; it can be completed simply through step-by-step stirring and temperature-controlled dripping, making it easy to operate and scale up production. The raw materials used are high-purity white silica fume, conventional polyether monomers, and environmentally friendly additives, with no harmful byproducts generated, meeting green production requirements. The product dosage is only 1% to 2% of the mass of concrete cementitious materials, reducing project costs by 15% to 20% compared to traditional high-dosage water-reducing agents, while avoiding problems such as delayed setting and extended demolding cycles, thus improving construction efficiency. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart of the overall preparation process for viscosity-reducing polycarboxylate superplasticizers. Figure 2 Flowchart for the preparation of silane-modified white silica fume; Figure 3 This is a flowchart of the preparation process for modified viscosity-reducing mother liquor. Detailed Implementation

[0016] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the invention.

[0017] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. When a component is said to be "set on" another component, it can be directly set on the other component or there may be an intervening component.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0019] A viscosity-reducing polycarboxylate superplasticizer and its preparation method are disclosed. The preparation method comprises the following steps: adding the prescribed amount of water to an industrial-grade compound mixing tank, starting a variable frequency stirring device with the speed controlled at 300-400 r / min, adding silane-modified silica fume via a screw conveyor, and starting a high-speed disperser for assisted dispersion for 15-20 min. Subsequently, the modified viscosity-reducing mother liquor and functional additives are precisely delivered through a metering pump and stirred continuously for 20-25 min. Finally, a compound suspension stabilizer is added, and the circulating stirring is started for 30-35 min. The mixture is then filtered through a 200-mesh filter to remove mechanical impurities, resulting in a uniformly suspended viscosity-reducing polycarboxylate superplasticizer. The viscosity-reducing polycarboxylate superplasticizer is formulated from the following raw materials in the indicated mass fractions: 15%–25% modified viscosity-reducing mother liquor, 12%–25% silane-modified silica fume, 1.5%–3.5% compounded suspension stabilizer, 2%–5% functional additives, and the remainder is water. The modified viscosity-reducing mother liquor is prepared by staged temperature-controlled polymerization of the following raw materials in parts by weight: 25-35 parts of isopentenyl polyethylene glycol ether, 8-15 parts of the first viscosity-reducing monomer, 3-8 parts of the second viscosity-reducing monomer, and 3-6 parts of acrylic acid or its derivatives. The first viscosity-reducing monomer is dimethylaminoethyl methacrylate, and the second viscosity-reducing monomer is dimethylaminopropyl acrylate. Silane-modified white silica fume is prepared by modifying the surface of white silica fume with a purity of over 98% using γ-aminopropyltriethoxysilane. The amount of γ-aminopropyltriethoxysilane used is 1% to 3% of the mass of white silica fume. The compound suspension stabilizer is a mixture of fumed silica and hydroxypropyl methylcellulose in a mass ratio of 7:3 to 4:1, and the functional additive is ethylene glycol monomethyl ether.

[0020] The polymerization of the modified viscosity-reducing mother liquor employs a composite initiation system, which consists of an initiator and a composite reducing agent. The initiator is a mixture of hydrogen peroxide and potassium persulfate in a mass ratio of 1:1 to 2:1. The composite reducing agent is a mixture of L-ascorbic acid and sodium bisulfite in a mass ratio of 2:1. Both initiators are free radical initiators. Hydrogen peroxide has a lower decomposition temperature, while potassium persulfate has a higher decomposition temperature. Their combined use forms a wide-temperature-range initiation system, broadening the reaction temperature adaptability range and avoiding the limitations of using a single initiator. To address the issue of reactions being too fast or too slow, the optimized 1:1 to 2:1 ratio ensures the continuous and stable generation of free radicals, resulting in more uniform monomer polymerization. The composite reducing agent L-ascorbic acid and sodium bisulfite form a synergistic reducing system, which can efficiently react with the initiator in a redox reaction. By lowering the activation energy, it accelerates the generation of free radicals while regulating the reaction rate. The reducing properties of L-ascorbic acid are milder, avoiding over-reduction caused by excessive sodium bisulfite. The 2:1 ratio balances reduction efficiency and reaction controllability, reducing impurities during the polymerization process.

[0021] The preparation of modified viscosity-reducing mother liquor includes the following steps: (1) In an industrial-grade polymerization reactor, isopentenyl polyethylene glycol ether, the first viscosity-reducing monomer and the second viscosity-reducing monomer are dissolved in deionized water to prepare a bottom liquid with a mass concentration of 55% to 60%. The bottom liquid is heated to 35 to 40°C and kept at that temperature by a jacketed temperature control system. At the same time, solution A and solution B are prepared in a mixing tank. Solution A is acrylic acid or its derivative dissolved in water, and solution B is a composite reducing agent, ferrous sulfate and sodium hypophosphite dissolved in water. (2) Add the composite initiation system to the polymerization reactor, let it stand for 5 minutes, and then add liquid A and liquid B simultaneously through a metering and dropping device. Liquid A is to be added within 2 hours and liquid B is to be added within 2.5 hours. When the addition reaches 1 hour, the temperature of the reaction system is raised to 48-52℃ by jacket temperature control. (3) After the addition of liquid A and liquid B is completed, the temperature of the reaction system is lowered to 38-42℃, and the reaction is continued for 1 hour. Finally, water is added to adjust the solid content of the system to 42%-45% to obtain the modified viscosity-reducing mother liquor. The catalyst is ferrous sulfate, and the chain transfer agent is selected from sodium hypophosphite or isopentenyl mercaptopropionic acid.

[0022] In the preparation steps of the modified viscosity-reducing mother liquor, the amount of ferrous sulfate in step (1) is 0.003% to 0.005% of the mass of isopentenyl polyethylene glycol ether, and the amount of sodium hypophosphite is 0.5% to 1% of the mass of isopentenyl polyethylene glycol ether. Ferrous sulfate acts as a catalyst in the polymerization reaction, accelerating the generation of free radicals by promoting electron transfer between the initiator and the reducing agent. It is a key auxiliary agent for the start-up and continuation of the reaction. Sodium hypophosphite controls the growth length of polycarboxylic acid molecular chains by transferring the active center of free radicals. It is a core auxiliary agent for adjusting the molecular weight of the mother liquor.

[0023] The general formula for isopentenyl polyethylene glycol ether is shown below: The general formula is n=30~60, and the preferred formula is n=40~50.

[0024] The preparation steps of silane-modified white silica fume are as follows: (1) In the modified reaction vessel, γ-aminopropyltriethoxysilane is weighed at 1% to 3% of the mass of white silica fume and mixed with an ethanol aqueous solution to prepare a modifier solution. The volume ratio of ethanol to water in the ethanol aqueous solution is 1:3. (2) Hydrophobic alkyl grafting: Add white silica fume with a purity of 98% or higher to the modifier solution through a quantitative feeder, and stir and react for 1.5 to 2 hours at 60 to 70°C and a stirring speed of 200 to 250 r / min; (3) The mixture after the reaction is dried at 80°C by a belt dryer, pulverized to a particle size of 1-3 μm by an air jet mill, passed through a 200-mesh sieve, and stored in a sealed silo for later use.

[0025] Acrylic acid or its derivatives are one or a mixture of two of acrylic acid and methacrylic acid. Acrylic acid has high reactivity, with a polymerization reactivity ratio of ≈1.1, and can rapidly copolymerize with viscosity-reducing monomers, ensuring a uniform distribution of hydrophilic carboxyl groups in the molecular chain. Methacrylic acid, due to the presence of methyl side chains, has slightly lower reactivity, with a polymerization reactivity ratio of ≈0.8, but can adjust the extensibility of the molecular chain through steric hindrance, avoiding excessive entanglement. When used alone or in combination, both can form a stable alternating copolymer structure with the two viscosity-reducing monomers, with a monomer conversion rate of over 95%, effectively avoiding block polymerization or monomer residues caused by differences in reactivity, ensuring a uniform molecular structure in the mother liquor, with a molecular weight distribution PDI of 1.8–2.2, laying the foundation for efficient viscosity reduction.

[0026] The finished product filtration in the compound mixing tank adopts a multi-stage filtration process. First, large particles are removed through a 200-mesh filter, and then fine impurities are filtered through a 300-mesh precision filter. The solid content of the filtered product is controlled at 42% to 45%, with a fluctuation range of ≤ ±0.5%. The viscosity at 25℃ is 500 to 800 mPa·s, ensuring smooth pumping during construction. The staged filtration can remove large and fine particles, improve the compatibility of water-reducing agents with cement and mineral admixtures, and prevent water seepage and segregation in the concrete paste. This ensures the uniform mechanical properties of high-strength concrete. The 25℃ temperature and viscosity of 500 to 800 mPa·s maintain a certain degree of fluidity of high-strength concrete while ensuring uniform mixing of the water-reducing agent and the paste, thus guaranteeing smooth pumping during construction.

[0027] The functional additive ethylene glycol monomethyl ether can be compounded with propylene glycol butyl ether at a mass ratio of 3:1 to 2:1. After compounding, the dosage of the functional additive remains 2% to 5%. This allows concrete to withstand 300 freeze-thaw cycles at -20℃ with a strength loss of ≤4.8%. It also improves the compatibility of water-reducing agents with mineral admixtures in high-strength concrete, preventing slurry bleeding. Ethylene glycol monomethyl ether exerts its basic antifreeze effect by lowering the freezing point of concrete, while propylene glycol butyl ether combines antifreeze properties with interfacial activity, improving the compatibility of the additive with cement paste and reducing the damage to the structure caused by ice crystallization inside the paste at low temperatures. The two work synergistically to enhance the antifreeze effect and improve the strength stability after freeze-thaw cycles, covering more low-temperature construction scenarios and improving the regional adaptability of the product.

[0028] Example 1 Add 345g of deionized water to an industrial-grade compound mixing tank, start the variable frequency stirring device, and stabilize the speed at 350r / min. Add 200g of pretreated silane-modified white silica fume via a screw conveyor. Turn on a 18kW high-speed disperser to assist dispersion for 18min to ensure no obvious agglomeration. Then, add 200g of modified viscosity-reducing mother liquor (isoprene-based polyethylene glycol ether n=45, containing 12 parts of the first viscosity-reducing monomer dimethylaminoethyl methacrylate and 5 parts of the second viscosity-reducing monomer dimethylaminopropyl acrylate, with a solid content of 43%) via a metering pump. The mixture was stirred for 22 minutes, and then 25 g of compound suspension stabilizer (18 g of hydrophilic fumed silica + 7 g of hydroxypropyl methylcellulose, mass ratio 5:2) was added. The mixture was stirred for another 32 minutes using a circulating stirring mode. After multi-stage filtration (first removing large particles with a 200-mesh filter, then filtering fine impurities with a 300-mesh precision filter), the viscosity at 25℃ was measured to be 650 mPa·s and the solid content was 43.2% (fluctuation ±0.3%), resulting in a uniformly suspended viscosity-reducing polycarboxylate superplasticizer.

[0029] Example 2 Add 345g of deionized water to an industrial-grade compound mixing tank, start the variable frequency stirring device (350r / min), add 200g of silane-modified white silica fume (same as in Example 1) through a screw conveyor, disperse for 18min using a high-speed disperser (18kW), add 200g of modified viscosity-reducing mother liquor (containing 8 parts of the first viscosity-reducing monomer, 3 parts of the second viscosity-reducing monomer, isopentenyl polyethylene glycol ether n=45, solid content 43%) and 30g of ethylene glycol monomethyl ether by a metering pump, stir for 22min, add 25g of compound suspension stabilizer (same as in Example 1), circulate and stir for 32min, after multi-stage filtration, the viscosity at 25℃ is 680mPa·s and the solid content is 43.0%, thus obtaining a viscosity-reducing polycarboxylate superplasticizer.

[0030] Example 3 Add 345g of deionized water to an industrial-grade compound mixing tank, start the variable frequency stirring device (350r / min), add 200g of silane-modified white silica fume (same as in Example 1) through a screw conveyor, disperse for 18min using a high-speed disperser (18kW), add 200g of modified viscosity-reducing mother liquor (containing 15 parts of the first viscosity-reducing monomer, 8 parts of the second viscosity-reducing monomer, isopentenyl polyethylene glycol ether n=45, solid content 43%) and 30g of ethylene glycol monomethyl ether by a metering pump, stir for 22min, add 25g of compound suspension stabilizer (same as in Example 1), circulate and stir for 32min, after multi-stage filtration, the viscosity at 25℃ is measured to be 620mPa·s and the solid content is 43.5%, thus obtaining a viscosity-reducing polycarboxylate superplasticizer.

[0031] Example 4 Add 345g of deionized water to an industrial-grade compound mixing tank, start the variable frequency stirring device (350r / min), add 200g of silane-modified white silica fume (98% purity, modified with 1% γ-aminopropyltriethoxysilane, particle size 1-3μm) through a screw conveyor, disperse for 18min using a high-speed disperser (18kW), add 200g of modified viscosity-reducing mother liquor (same as in Example 1) and 30g of ethylene glycol monomethyl ether by a metering pump, stir for 22min, add 25g of compound suspension stabilizer (same as in Example 1), circulate and stir for 32min, after multi-stage filtration, the viscosity at 25℃ is 720mPa·s and the solid content is 42.8%, thus obtaining a viscosity-reducing polycarboxylate superplasticizer.

[0032] Example 5 Add 345g of deionized water to an industrial-grade compound mixing tank, start the variable frequency stirring device (350r / min), add 200g of silane-modified white silica fume (98% purity, modified with 3% γ-aminopropyltriethoxysilane, particle size 1-3μm) through a screw conveyor, disperse for 18min using a high-speed disperser (18kW), add 200g of modified viscosity-reducing mother liquor (same as in Example 1) and 30g of ethylene glycol monomethyl ether by a metering pump, stir for 22min, add 25g of compound suspension stabilizer (same as in Example 1), circulate and stir for 32min, after multi-stage filtration, the viscosity at 25℃ is 580mPa·s and the solid content is 43.3%, thus obtaining a viscosity-reducing polycarboxylate superplasticizer.

[0033] Example 6 Add 345g of deionized water to an industrial-grade compound mixing tank, start the variable frequency stirring device (350r / min), add 200g of silane-modified white silica fume (same as in Example 1) through a screw conveyor, disperse for 18min using a high-speed disperser (18kW), add 200g of modified viscosity-reducing mother liquor (same as in Example 1) and functional additives (22.5g of ethylene glycol monomethyl ether + 7.5g of propylene glycol butyl ether, mass ratio 3:1) by a metering pump, stir for 22min, add 25g of compound suspension stabilizer (same as in Example 1), circulate and stir for 32min, after multi-stage filtration, the viscosity at 25℃ is 630mPa·s and the solid content is 43.1%, thus obtaining a viscosity-reducing polycarboxylate superplasticizer.

[0034] Comparison Group 1 (Commercially Available Products) Add 480g of deionized water to an industrial-grade compound mixing tank, start the variable frequency stirring device (300r / min), add 200g of a commercially available brand of viscosity-reducing polycarboxylate superplasticizer through a metering pump, stir for 30min until completely dissolved, and obtain a comparison sample after filtration through a 150-mesh filter (without multi-stage filtration, the viscosity fluctuates greatly at 25℃, approximately 450~900mPa·s).

[0035] Control group 2 (unmodified white silica fume) Add 345g of deionized water to an industrial-grade compound mixing tank, start the variable frequency stirring device (350r / min), add 200g of unmodified white silica fume (98% purity, untreated with silane, particle size 1-3μm) through a screw conveyor, disperse for 18min using a high-speed disperser (18kW) (a small amount of agglomeration still exists), add 200g of modified viscosity-reducing mother liquor (same as in Example 1) and 30g of ethylene glycol monomethyl ether using a metering pump, stir for 22min, add 25g of compound suspension stabilizer (same as in Example 1), circulate and stir for 32min, after multi-stage filtration, the filtration efficiency is reduced by 30% due to the agglomerated particles clogging the filter screen, resulting in a suspension containing fine agglomerates (viscosity 950mPa·s at 25℃).

[0036] Comparison Group 3 (Single viscosity-reducing monomer) Add 345g of deionized water to an industrial-grade compound mixing tank, start the variable frequency stirring device (350r / min), add 200g of silane-modified white silica fume (same as in Example 1) through a screw conveyor, disperse for 18min using a high-speed disperser (18kW), add 200g of modified viscosity-reducing mother liquor (containing only 17 parts of the first viscosity-reducing monomer, no second viscosity-reducing monomer, isopentenyl polyethylene glycol ether n=45) and 30g of ethylene glycol monomethyl ether by a metering pump, stir for 22min, add 25g of compound suspension stabilizer (same as in Example 1), circulate and stir for 32min, after multi-stage filtration, the viscosity at 25℃ is measured to be 850mPa·s and the solid content is 42.5%, thus obtaining the comparison sample.

[0037] Control group 4 (without functional adjuvants) 375g of deionized water was added to an industrial-grade compound mixing tank. A variable frequency stirrer (350 r / min) was started, and 200g of silane-modified white silica fume (same as in Example 1) was added via a screw conveyor. The mixture was dispersed for 18 min using a high-speed disperser (18kW). 200g of modified viscosity-reducing mother liquor (same as in Example 1) was added via a metering pump, and the mixture was stirred for 22 min. Then, 25g of compound suspension stabilizer (same as in Example 1) was added, and the mixture was circulated and stirred for 32 min. After multi-stage filtration, the viscosity at 25℃ was measured to be 780 mPa·s, and the solid content was 42.7%. A control sample was obtained (no freeze-thaw resistance; significant strength loss occurred after 50 freeze-thaw cycles at -10℃). The viscosity-reducing polycarboxylate superplasticizers prepared in Examples 1-6 and Comparative Groups 1-4 were tested on 10 samples by adding 2% of the viscosity-reducing polycarboxylate superplasticizer according to the test methods in JC / T2361-2016 "Mortar and Concrete Viscosity Reducers". The collapse time, viscosity reduction index, and compressive strength ratio were determined according to JC / T2361-2016 "Mortar and Concrete Viscosity Reducers", where the viscosity reduction index was set to ≤0.79, the collapse time was set to ≤28s, the frost resistance loss was set to ≤8% according to the frost resistance requirements for severely cold regions in GB / T50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete", and the 60-day stability was determined according to GB / T8077-2012 "Concrete..." The test method for homogeneity of soil admixtures requires no stratification or sedimentation during storage. The slurry bleeding level is based on the industry-standard grading (0 = no bleeding, 1 = trace bleeding ≤5mL, 2 = small amount of bleeding 5-10mL, 3 and above = obvious bleeding). The construction compatibility standard is set at ≤1. The test environment is room temperature 25℃±2℃, and the concrete mix ratio is C60 high-strength concrete (water-cement ratio 0.32). The appearance of the water-reducing agent is observed after 28 days. The test results are shown in Table 1.

[0038] Table 1 - Test Results

[0039] Comparing Example 1 (dual viscosity-reducing monomers 12:5), Example 2 (8:3), and Example 3 (15:8), it can be seen that within the range of 8:3 to 15:8, the higher the ratio (15:8), the shorter the collapse time, the lower the viscosity reduction index, and the better the viscosity reduction effect. Moreover, the 28-day strength ratio is ≥106% under medium to high ratios (12:5 to 15:8), proving that a balance between viscosity reduction efficiency and strength stability can be achieved in this range. Among them, the 12:5 ratio has better overall performance in terms of strength development (108%) and viscosity reduction index (0.76).

[0040] Compared with Examples 1 (2% silane modifier), 4 (1%), and 5 (3%), it can be seen that when the amount of silane modifier is 2% to 3%, the collapse time is shortened and the viscosity reduction index is reduced, resulting in a better viscosity reduction effect. 1% is the critical effective amount (only satisfying the viscosity reduction index ≤ 0.79), and when the amount is ≥ 2%, the 28-day strength ratio is ≥ 108%, proving that sufficient modifier can ensure the dispersibility of white silica fume and promote strength development. The 3% amount shows the best performance in terms of viscosity reduction (0.74) and strength (109%).

[0041] Compared with control group 1, Example 1 had a collapse emptying time of 26.2s, a viscosity reduction index of 0.76, a 28-day compressive strength ratio of 108%, and a freeze-thaw loss of 5.1% at -20℃. Control group 1 (commercially available) had corresponding values ​​of 33.8s, 0.92, 103%, and 12.5%. It can be seen that the dual viscosity-reducing monomer and silane-modified white silica fume system of the present invention has a viscosity reduction index that is 17.4% lower than that of commercially available products, a collapse time that is 22.5% shorter, a 28-day strength ratio that is 4.9% higher, and a freeze-thaw loss that is 60% lower. It fully demonstrates the generational advantages in viscosity reduction efficiency, strength stability, and freeze resistance.

[0042] Compared with control group 2 (unmodified white silica fume), Example 1 showed a collapse emptying time of 26.2s, a viscosity reduction index of 0.76, a 28-day compressive strength ratio of 108%, and no stratification at 60 days. Control group 2 (unmodified white silica fume) showed the same values: 38.6s, 1.05, 101%, and bottom sedimentation. It is evident that the unmodified white silica fume's agglomeration caused a 38.2% spike in the viscosity reduction index, a 47.3% increase in collapse time, a 6.5% lower 28-day strength ratio, and poor system stability. This demonstrates that silane modification is the core innovation for solving the problems of poor compatibility and insufficient stability of viscosity reducers, and is a key support for the viscosity reduction effect and long-term performance of this invention.

[0043] Compared with control group 3 (single viscosity-reducing monomer), Example 1 had a collapse emptying time of 26.2s, a viscosity reduction index of 0.76, and a 28-day compressive strength ratio of 108%, while control group 3 (single viscosity-reducing monomer) had 31.5s, 0.89, and 104% respectively. It can be seen that the single viscosity-reducing monomer, due to its simple molecular structure and function, has a higher viscosity reduction index of 17.1%, a longer collapse time of 20.2%, and a lower 28-day strength ratio of 3.7%. This proves that the synergistic effect of amine adsorption and ester polarity regulation of the dual viscosity-reducing monomers can simultaneously optimize viscosity reduction efficiency and strength development, which is the core design of this invention that distinguishes it from traditional solutions.

[0044] Compared with control group 4 (without functional additives), Example 1 showed a strength loss of 5.1% and a slurry bleeding grade of 0 after 300 freeze-thaw cycles at -20℃, while control group 4 (without functional additives) showed a strength loss of 28.6% and a grade of 2. It can be seen that the antifreeze performance was completely lost without functional additives (the loss exceeded the standard by 20.6%), and grade 2 bleeding occurred. This proves that functional additives are not only the key to antifreeze performance, but their interfacial activity can also optimize slurry compatibility and avoid the adverse effects of bleeding on construction and strength. They are the core adaptable components for engineering in cold environments.

[0045] This invention, through a core design that optimizes the proportion of dual viscosity-reducing monomers, combines silane-modified white silica fume with functional additives, achieves comprehensive performance with a 28-day compressive strength ratio ≥105%, a -20℃ freeze-thaw loss ≤5.4%, no stratification at 60 days, and a water bleeding grade of 0, while maintaining a collapse and emptying time ≤28s and a viscosity-reducing index ≤0.79. The dual viscosity-reducing monomers, modified white silica fume, and functional additives create a synergistic effect, comprehensively surpassing comparative solutions lacking these core features, fully validating the innovation and engineering practicality of the technical solution. The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A viscosity-reducing polycarboxylate superplasticizer, characterized in that: It is formulated from the following raw materials in the indicated mass fractions: 15%–25% modified viscosity-reducing mother liquor, 12%–25% silane-modified white silica fume, 1.5%–3.5% compounded suspension stabilizer, 2%–5% functional additives, and the balance being water; The modified viscosity-reducing mother liquor is prepared by staged temperature-controlled polymerization of the following raw materials in parts by weight: 25-35 parts of isopentenyl polyethylene glycol ether, 8-15 parts of the first viscosity-reducing monomer, 3-8 parts of the second viscosity-reducing monomer, and 3-6 parts of acrylic acid or its derivatives. The first viscosity-reducing monomer is dimethylaminoethyl methacrylate, the second viscosity-reducing monomer is dimethylaminopropyl acrylate, and the acrylic acid or its derivatives are one or a mixture of two of acrylic acid and methacrylic acid. The silane-modified white silica fume is prepared by modifying the surface of white silica fume with γ-aminopropyltriethoxysilane using white silica fume with a purity of 98% or higher as a base material. The amount of γ-aminopropyltriethoxysilane used is 1% to 3% of the mass of white silica fume. The compound suspension stabilizer is a mixture of fumed silica and hydroxypropyl methylcellulose in a mass ratio of 7:3 to 4:

1. The functional additive is ethylene glycol monomethyl ether, or a compound of ethylene glycol monomethyl ether and propylene glycol butyl ether in a mass ratio of 3:1 to 2:

1. The amount of functional additive after compounding is still 2% to 5%.

2. The viscosity-reducing polycarboxylate superplasticizer according to claim 1, characterized in that: The polymerization of the modified viscosity-reducing mother liquor adopts a composite initiation system, which consists of an initiator and a composite reducing agent. The initiator is a mixture of hydrogen peroxide and potassium persulfate in a mass ratio of 1:1 to 2:1, and the composite reducing agent is a mixture of L-ascorbic acid and sodium bisulfite in a mass ratio of 2:

1.

3. The viscosity-reducing polycarboxylate superplasticizer according to claim 2, characterized in that: The preparation of the modified viscosity-reducing mother liquor includes the following steps: (1) In an industrial-grade polymerization reactor, isopentenyl polyethylene glycol ether, the first viscosity-reducing monomer, and the second viscosity-reducing monomer are dissolved in deionized water to prepare a bottom solution with a mass concentration of 55% to 60%. The bottom solution is heated to 35 to 40°C and kept at that temperature by a jacketed temperature control system. At the same time, solution A and solution B are prepared in a mixing tank. Solution A is acrylic acid or its derivative dissolved in water, and solution B is a composite reducing agent, ferrous sulfate, and sodium hypophosphite dissolved in water. Ferrous sulfate is a catalyst, and sodium hypophosphite is a chain transfer agent. (2) Add the composite initiation system described in claim 2 to the polymerization reactor, let it stand for 5 minutes, and then add liquid A and liquid B simultaneously through a metering and dropping device. Liquid A is added within 2 hours and liquid B is added within 2.5 hours. When the addition reaches 1 hour, the temperature of the reaction system is raised to 48-52°C by jacket temperature control. (3) After the addition of liquid A and liquid B, the temperature of the reaction system is lowered to 38-42℃, and the reaction is continued for 1 hour. Finally, water is added to adjust the solid content of the system to 42%-45% to obtain the modified viscosity-reducing mother liquor.

4. The viscosity-reducing polycarboxylate superplasticizer according to claim 3, characterized in that: In the preparation steps of the modified viscosity-reducing mother liquor, the amount of ferrous sulfate in step (1) is 0.003% to 0.005% of the mass of isopentenyl polyethylene glycol ether, and the amount of sodium hypophosphite is 0.5% to 1% of the mass of isopentenyl polyethylene glycol ether.

5. The viscosity-reducing polycarboxylate superplasticizer according to claim 1, characterized in that: The general formula for polyethylene glycol ethers is shown below: The general formula is n=30~60.

6. The viscosity-reducing polycarboxylate superplasticizer according to claim 1, characterized in that: The preparation steps of the silane-modified white silica fume are as follows: (1) In the modified reaction vessel, γ-aminopropyltriethoxysilane is weighed at 1% to 3% of the mass of white silica fume and mixed with an ethanol aqueous solution to prepare a modifier solution, wherein the volume ratio of ethanol to water in the ethanol aqueous solution is 1:

3. (2) Hydrophobic alkyl grafting: Add white silica fume with a purity of 98% or higher to the modifier solution through a quantitative feeder, and stir and react for 1.5 to 2 hours at 60 to 70°C and a stirring speed of 200 to 250 r / min; (3) The mixture after the reaction is dried at 80°C by a belt dryer, pulverized to a particle size of 1-3 μm by an air jet mill, passed through a 200-mesh sieve, and stored in a sealed silo for later use.

7. A method for preparing the viscosity-reducing polycarboxylate superplasticizer as described in claim 1, characterized in that: The steps are as follows: Add the prescribed amount of water to an industrial-grade compound mixing tank, start the variable frequency stirring device, control the speed at 300-400 r / min, add silane-modified white silica fume via a screw conveyor, turn on the high-speed disperser to assist dispersion for 15-20 min, then accurately deliver the modified viscosity-reducing mother liquor and functional additives through a metering pump, and continue stirring for 20-25 min, finally add the compound suspension stabilizer, turn on the circulation stirring for 30-35 min, filter through a 200-mesh filter to remove mechanical impurities, and obtain a uniformly suspended viscosity-reducing polycarboxylate superplasticizer.

8. The method for preparing a viscosity-reducing polycarboxylate superplasticizer according to claim 7, characterized in that: The compounding mixing tank, polymerization reactor, and modification reactor are all equipped with cleaning devices for easy cleaning after batch production. The finished product filtration of the compounding mixing tank adopts a multi-stage filtration process, first removing large particulate impurities through a 200-mesh filter, and then filtering fine impurities through a 300-mesh precision filter. The solid content of the filtered product is controlled at 42% to 45%, with a fluctuation range of ≤ ±0.5%, and the viscosity at 25°C is 500 to 800 mPa·s, ensuring smooth pumping during construction.

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