Reduction type polycarboxylate superplasticizer and preparation method thereof

Abstract

The invention relates to the technical field of concrete admixture application, in particular to a reduction type polycarboxylic acid water reducing agent and a preparation method thereof.The water reducing agent is formed by compounding modified reduction type polycarboxylic acid mother liquor, a micro-expansion component, a water retention component and water, the modified mother liquor is prepared from isopentenyl polyglycol ether, a triblock reduction monomer and acrylic acid or a derivative thereof, and the micro-expansion component and the water retention component are added into the triblock reduction monomer; the triblock shrinkage-reducing monomer is prepared through ultrasonic-microwave synergistic polymerization and gradient pH regulation and control, the triblock shrinkage-reducing monomer is of a hydrophobic alkyl-siloxane-ester group structure, and the micro-expansion component and the water-retaining component achieve the triple effects of shrinkage inhibition, shrinkage compensation and water loss delay through the synergistic effect of the micro-expansion component and the water-retaining component. According to the invention, the shrinkage reduction rate is high, the strength is stable, the preparation time of the product is greatly shortened by ultrasonic-microwave synergistic polymerization and gradient pH preparation, the product is not layered within 60 days, the product is suitable for various concrete working conditions, and the industrial application is convenient.

Description

Technical Field

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

[0002] Concrete, as the most widely used engineering material globally, is extensively used in various engineering fields such as construction, bridges, and tunnels due to its advantages of high strength, high durability, and low cost. However, shrinkage deformation during the hydration and hardening process of concrete is the core cause of its cracking; more than 80% of non-load-bearing cracks in concrete engineering are caused by shrinkage deformation. These cracks compromise the integrity and density of concrete, accelerate the penetration of corrosive media such as moisture and chloride ions, significantly reduce structural durability, and even affect the safe service life of the project.

[0003] To address the problem of shrinkage cracking in concrete, shrinkage-reducing polycarboxylate superplasticizers, as functional concrete admixtures, have become a research hotspot in the industry. Polycarboxylate superplasticizers achieve efficient water reduction through the steric hindrance effect of their comb-like molecular structure. Simultaneously, shrinkage-reducing functional groups can be introduced through molecular design, achieving both water reduction and shrinkage reduction performance at low dosages. They have gradually replaced traditional naphthalene-based and lignin sulfonate superplasticizers. In existing technologies, researchers mainly develop shrinkage-reducing polycarboxylate superplasticizers through two pathways: one is to modify the side chain structure of polycarboxylate molecules to optimize steric hindrance and water retention capacity; the other is to introduce shrinkage-reducing monomers containing ester groups, ether groups, etc., during the polymerization process, utilizing group hydrolysis or interfacial interactions to reduce the capillary negative pressure inside the concrete, thereby inhibiting shrinkage.

[0004] Although existing shrinkage-reducing polycarboxylate superplasticizers have achieved certain application results, they still have significant technical defects in actual engineering: the shrinkage-reducing monomers have single functions and poor synergistic effects. Most existing shrinkage-reducing monomers are single ester or ether structures, which can only achieve shrinkage through a single mechanism of action and lack multifunctional synergistic design; the preparation process is inefficient and the performance is unstable: existing shrinkage-reducing polycarboxylate mother liquors mostly adopt traditional water bath heating polymerization processes, resulting in uneven mixing and dispersion of monomers, leading to low grafting rate of shrinkage-reducing groups. In addition, the pH value is fixed during the polymerization process, which easily leads to excessive hydrolysis of ester groups or incomplete reaction, causing fluctuations in the shrinkage-reducing performance of the same batch of products. Summary of the Invention

[0005] To address the problems of limited functionality, poor synergistic effect, low preparation efficiency, and poor performance stability of existing shrinkage-reducing monomers, this invention provides a shrinkage-reducing polycarboxylate superplasticizer and its preparation method. The technical solution adopted by this invention to solve the above problems is: a shrinkage-reducing polycarboxylate superplasticizer and its preparation method, wherein the shrinkage-reducing polycarboxylate superplasticizer is compounded from the following raw materials in the indicated mass fractions: 8%–12% modified shrinkage-reducing polycarboxylate mother liquor, 1%–3% micro-expansion component, 1%–2% water-retaining component, and the balance being water;

[0006] The modified shrinkage-reducing polycarboxylic acid mother liquor is prepared by ultrasonic-microwave synergistic polymerization. The raw materials, by mass, include: 25-40 parts of isopentenyl polyethylene glycol ether, 8-15 parts of triblock shrinkage-reducing monomer, 3-6 parts of acrylic acid or its derivative, 0.9-1.3 parts of initiator, 0.1-0.3 parts of reducing agent, 0.003-0.006 parts of catalyst, and 0.7-1.1 parts of chain transfer agent.

[0007] The triblock shrinkage monomer has a hydrophobic alkyl-siloxane-ester triblock structure and is prepared by a three-step reaction of polyethylene glycol monomethyl ether or a mixture thereof with oxidized konjac glucomannan, hydrophobic alkyl grafting, and siloxane modification.

[0008] The polymerization process employs gradient pH control: pH = 3-4 in the initial stage of the reaction, pH = 5-6 in the middle stage of the reaction, and pH = 7-8 in the later stage of the reaction.

[0009] The aforementioned shrinkage-reducing polycarboxylate superplasticizer, wherein the shrinkage-reducing polycarboxylate superplasticizer mother liquor is prepared by polymerizing the following raw materials in parts by weight: 20-50 parts of isopentenyl polyethylene glycol ether, 5-10 parts of shrinkage-reducing monomer, and 2-5 parts of acrylic acid or its derivatives. The isopentenyl polyethylene glycol ether serves as the main side chain of the comb-shaped molecule, and this dosage range ensures sufficient steric hindrance effect, ensuring that the water reduction rate of the superplasticizer is ≥25%. The shrinkage-reducing monomer serves as the core shrinkage-reducing functional component, and this dosage ensures that the triblock hydrophobic-siloxane-ester group fully exerts its water retention, surface tension reduction, and interface strengthening effects, resulting in a 28-day shrinkage ratio ≤72%.

[0010] The above-mentioned shrinkage-reducing polycarboxylate superplasticizer and its preparation method, wherein the isopentenyl polyethylene glycol ether has the following general formula:

[0011]

[0012] The general formula is n=30~60, preferably n=40~50.

[0013] The above-mentioned shrinkage-reducing polycarboxylate superplasticizer and its preparation method, wherein the preparation of the mother liquor includes the following steps:

[0014] (1) Ultrasonic pretreatment: The triblock shrinkage monomer is mixed with the acrylic acid or its derivative and ultrasonically treated for 10 to 20 minutes under the conditions of power 200 to 300W and frequency 30 to 40kHz to obtain a pre-dispersed monomer solution;

[0015] (2) Preparation of the base solution: Dissolve the isopentenyl polyethylene glycol ether and the pre-dispersed monomer solution in water to prepare a base solution with a mass concentration of 50% to 60%;

[0016] (3) Preparation of solution A and solution B: Mix the remaining amount of acrylic acid or its derivative with water to obtain solution A, and mix the reducing agent, catalyst, chain transfer agent with water to obtain solution B;

[0017] (4) Microwave polymerization: Add initiator to the bottom liquid, transfer to microwave reactor, and simultaneously add solution A and solution B at a power of 300-500W and a temperature of 55-65℃. Solution A is added in 2 hours and solution B is added in 2.5 hours. Gradient pH control is adopted in the polymerization process: pH=3-4 in the initial stage of reaction 0-1h, pH=5-6 in the middle stage of reaction 1-2h, and pH=7-8 in the later stage of reaction 2-2.5h.

[0018] (5) Post-treatment: After the addition is completed, continue the reaction for 1 hour, add water to adjust the mass concentration to 40%, and the modified shrinkage polycarboxylic acid mother liquor is obtained.

[0019] The initiator is selected from hydrogen peroxide or ammonium persulfate, the reducing agent is selected from L-ascorbic acid or sodium bisulfite, the catalyst is ferrous sulfate, and the chain transfer agent is selected from sodium hypophosphite or mercaptopropionic acid.

[0020] The above-mentioned shrinkage-reducing polycarboxylate superplasticizer and its preparation method, wherein the preparation steps of the triblock shrinkage-reducing monomer are as follows:

[0021] (1) Esterification reaction: Polyethylene glycol monomethyl ether with a molecular weight of 500 is reacted with maleic anhydride at a molar ratio of 1:1.1 to 1:1.3 at 80 to 90°C for 5 to 6 hours to obtain an ester intermediate;

[0022] (2) Hydrophobic alkyl grafting: 1-bromohexane is added to the ester intermediate, wherein the molar ratio of 1-bromohexane to the ester intermediate is 0.3 to 0.5:1, and the reaction is carried out at 70 to 80 °C for 3 to 4 hours to introduce C6 hydrophobic alkyl groups;

[0023] (3) Siloxane modification: γ-methacryloxypropyltrimethoxysilane is added, wherein the molar ratio of γ-methacryloxypropyltrimethoxysilane to ester intermediate is 0.2 to 0.4:1, and the reaction is carried out at 85 to 95 °C for 2 to 3 h to obtain a triblock condensed monomer.

[0024] In the above-mentioned shrinkage-reducing polycarboxylate superplasticizer and its preparation method, in step (1) of the preparation step of the triblock shrinkage-reducing monomer, the polyethylene glycol monomethyl ether can be replaced with a mixture of polyethylene glycol monomethyl ether: oxidized konjac glucomannan = 7:3 to 8:2. The degree of substitution of the oxidized konjac glucomannan is 0.3 to 0.5. The ratio of 7:3 to 8:2 ensures that the shrinkage performance does not decrease after the bio-based substitution. At the same time, the bio-based content reaches 20% to 30%, achieving a significant environmental improvement. The degree of substitution of 0.3 to 0.5 ensures the reactivity and hydrophilicity of the oxidized konjac glucomannan. The reactivity can effectively esterify with maleic anhydride, and the hydrophilicity avoids the decrease in dispersibility caused by excessive hydrophobicity.

[0025] The aforementioned shrinkage-reducing polycarboxylate superplasticizer and its preparation method, wherein the micro-expansion component is a mixture of triethanolamine and aluminum sulfate in a mass ratio of 1:1, and the water-retaining component is maltodextrin:hydroxypropyl methylcellulose:xanthan gum = 8:1:1. Triethanolamine can accelerate cement hydration and promote the reaction of aluminum sulfate with hydration products to form ettringite. The 1:1 ratio can ensure that the ettringite formation rate matches the concrete shrinkage rate. In the early 1-7 days, it provides moderate expansion, at which time the expansion rate is 0.02%-0.03%, compensating for plastic shrinkage and early drying shrinkage. In the later 28 days, the expansion tends to stabilize, at which time the expansion rate is ≤0.05%, avoiding strength reduction or cracking caused by excessive expansion. Maltodextrin forms hydrogen bonds with water molecules through polycarboxyl groups, delaying water evaporation and solving early drying shrinkage. Hydroxypropyl methylcellulose increases the viscosity of the paste, reduces water migration, and forms a synergistic effect of water retention and thickening with maltodextrin. Xanthan gum, as a structural stabilizer, forms a three-dimensional network structure, locks in moisture, and prolongs the water retention time.

[0026] The preparation method of the aforementioned shrinkage-reducing polycarboxylate superplasticizer is as follows: Deionized water of the prescribed amount is added to an industrial-grade compounding kettle equipped with a vacuum feeding device. A low-speed homogenizing stirring system is started, and the rotation speed is stably controlled at 200–250 r / min. Micro-expansion components and water-retaining components, pretreated by pulverizing to below 120 mesh and vacuum drying to a moisture content ≤5%, are added through a closed solid feeding station equipped with a dust recovery device. A homogenizing emulsifier is started to assist dissolution for 15–20 min. The viscosity fluctuation is confirmed to be ≤5% using an online viscosity-shrinkage rate monitoring instrument, indicating that the solid components are completely dissolved. Subsequently, the modified shrinkage-reducing polycarboxylate mother liquor is precisely delivered through a dual-metering pump parallel conveying system. A low-temperature constant-temperature circulation system is started to control the temperature of the compounding system at 18–25℃. Stirring is continued for 30–40 min until the system is homogeneous. After removing trace amounts of insoluble impurities through a 5μm precision membrane filter, the mixture is transferred to a finished product storage tank equipped with a pressure balancing device through a nitrogen-sealed pipeline conveying system, resulting in a homogeneous and stable shrinkage-reducing polycarboxylate superplasticizer.

[0027] The aforementioned shrinkage-reducing polycarboxylate superplasticizer is stored under the following conditions: 15–30°C, nitrogen sealing pressure 0.02–0.05 MPa. It exhibits no stratification or sedimentation within 12 months of storage, and its viscosity at 25°C is 300–500 mg / L. The product exhibits a 7-day shrinkage rate of ≤72% and a 28-day shrinkage rate of ≤65% for concrete. The compounding process utilizes a PLC distributed control system to synchronously monitor mixing speed, system temperature, pH value, and viscosity, ensuring that the shrinkage rate fluctuation range between different batches is ≤±3%. It is suitable for engineering scenarios with stringent shrinkage control requirements, such as large-volume concrete and prestressed concrete. A mild storage temperature of 15–30℃ prevents degradation of shrinkage-reducing monomers due to high temperatures, while a nitrogen sealing pressure of 0.02–0.05 MPa isolates the product from air, preventing oxidation and deterioration of the water-retaining components. These two factors work synergistically to ensure the product remains stratified and sediment-free for 12 months of storage, far exceeding the 6-month storage period of conventional water-reducing agents, thus reducing inventory pressure for engineering projects. The viscosity at 25℃ is 300–500 mg / L. The limitations ensure that the product's fluidity remains stable during storage, preventing uncontrolled dosage during application due to sudden viscosity changes. The PLC system synchronously monitors stirring speed, temperature, pH value, and viscosity, precisely controlling key parameters affecting shrinkage rate from the compounding stage, which is the core guarantee for achieving consistent batch performance.

[0028] As described above, the beneficial effects of the shrinkage-reducing polycarboxylate superplasticizer and its preparation method provided by this invention are as follows: Relying on the multifunctional synergistic effect of the hydrophobic alkyl-siloxane-ester triblock shrinkage-reducing monomers, combined with a micro-expansion component of triethanolamine and aluminum sulfate in a 1:1 ratio, and a water-retaining component of maltodextrin-hydroxypropyl methylcellulose-xanthan gum in an 8:1:1 ratio, a triple synergistic effect of inhibiting shrinkage, compensating for shrinkage, and delaying water loss is achieved. This effectively inhibits cracks caused by plastic shrinkage, drying shrinkage, and autogenous shrinkage in concrete, significantly improving the durability of engineering structures. Simultaneously, the efficient grafting of the shrinkage-reducing monomers and polycarboxylate molecules ensures a synergistic unity between the shrinkage-reducing effect and the water-reducing function, without sacrificing the flowability and workability of the concrete; ultrasonic- Microwave-assisted polymerization and gradient pH control processes increase the grafting rate of shrinkage-reducing monomers to over 94% and reduce the molecular weight distribution coefficient of the product to around 1.7. The 28-day shrinkage rate of the same batch of products fluctuates by ±2%, and the water reduction rate fluctuates by ±1%, solving the problem of large performance fluctuations in products produced by existing processes. On the other hand, the compounding sequence of water-micro-expansion component-water-retaining component-mother liquor and the 10% mass concentration control ensure that the product does not separate or precipitate after 60 days of storage. The construction dosage is only 0.8% to 1.2% of the mass of cementitious materials, which is compatible with the dosage of conventional water-reducing agents. No adjustment of the construction process is required, and it can be widely adapted to different engineering scenarios such as low water-cement ratio concrete and ordinary working condition concrete. It has high convenience for industrial production and on-site application. Attached Figure Description

[0029] 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.

[0030] Figure 1 This is a flowchart illustrating the overall preparation process of shrinkage-reducing polycarboxylate superplasticizers.

[0031] Figure 2 This is a flowchart of the preparation process of shrinkage-reduced polycarboxylate mother liquor;

[0032] Figure 3 This is a flowchart of the preparation process of triblock condensed monomers. Detailed Implementation

[0033] 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.

[0034] 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.

[0035] 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.

[0036] A shrinkage-reducing polycarboxylate superplasticizer and its preparation method are disclosed. The shrinkage-reducing polycarboxylate superplasticizer is compounded from the following raw materials in the indicated mass fractions: 8%–12% modified shrinkage-reducing polycarboxylate mother liquor, 1%–3% micro-expansion component, 1%–2% water-retaining component, and the balance being water.

[0037] Modified shrinkage-reducing polycarboxylate mother liquor was prepared by ultrasonic-microwave synergistic polymerization. The raw materials, by weight, included: 25-40 parts of isopentenyl polyethylene glycol ether, 8-15 parts of triblock shrinkage-reducing monomer, 3-6 parts of acrylic acid or its derivative, 0.9-1.3 parts of initiator, 0.1-0.3 parts of reducing agent, 0.003-0.006 parts of catalyst, and 0.7-1.1 parts of chain transfer agent.

[0038] The triblock condensation monomer has a hydrophobic alkyl-siloxane-ester triblock structure and is prepared by a three-step reaction of polyethylene glycol monomethyl ether or a mixture thereof with oxidized konjac glucomannan, hydrophobic alkyl grafting, and siloxane modification.

[0039] The polymerization process employs gradient pH control: pH = 3-4 in the initial stage of the reaction, pH = 5-6 in the middle stage of the reaction, and pH = 7-8 in the later stage of the reaction.

[0040] The shrinkage-reducing polycarboxylate superplasticizer mother liquor is prepared by polymerizing the following raw materials in parts by weight: 20-50 parts of isopentenyl polyethylene glycol ether, 5-10 parts of shrinkage-reducing monomer, and 2-5 parts of acrylic acid or its derivatives. The isopentenyl polyethylene glycol ether serves as the main side chain of the comb-shaped molecule. This dosage range ensures sufficient steric hindrance effect, ensuring that the water reduction rate of the superplasticizer is ≥25%. The shrinkage-reducing monomer serves as the core shrinkage-reducing functional component. This dosage ensures that the triblock hydrophobic-siloxane-ester group can fully exert its water retention, surface tension reduction, and interface strengthening effects, resulting in a 28-day shrinkage ratio ≤72%.

[0041] The general formula for isopentenyl polyethylene glycol ether is shown below:

[0042]

[0043] The general formula is n=30~60, and preferably n=40~50.

[0044] The preparation of the mother liquor includes the following steps:

[0045] (1) Ultrasonic pretreatment: The triblock shrinkage monomer is mixed with acrylic acid or its derivatives and ultrasonically treated for 10 to 20 minutes at a power of 200 to 300 W and a frequency of 30 to 40 kHz to obtain a pre-dispersed monomer solution.

[0046] (2) Preparation of the base solution: Dissolve isopentenyl polyethylene glycol ether and pre-dispersed monomer solution in water to prepare a base solution with a mass concentration of 50% to 60%;

[0047] (3) Preparation of solution A and solution B: Mix the remaining amount of acrylic acid or its derivative with water to obtain solution A, and mix the reducing agent, catalyst, chain transfer agent with water to obtain solution B;

[0048] (4) Microwave polymerization: Add initiator to the bottom liquid, transfer to microwave reactor, and simultaneously add solution A and solution B at a power of 300-500W and a temperature of 55-65℃. Solution A is added in 2 hours and solution B is added in 2.5 hours. Gradient pH control is used in the polymerization process: pH = 3-4 in the initial stage of reaction 0-1h, pH = 5-6 in the middle stage of reaction 1-2h, and pH = 7-8 in the later stage of reaction 2-2.5h.

[0049] (5) Post-treatment: After the addition is completed, continue the reaction for 1 hour, add water to adjust the mass concentration to 40%, and the modified shrinkage polycarboxylic acid mother liquor is obtained.

[0050] The initiator is selected from hydrogen peroxide or ammonium persulfate, the reducing agent is selected from L-ascorbic acid or sodium bisulfite, the catalyst is ferrous sulfate, and the chain transfer agent is selected from sodium hypophosphite or mercaptopropionic acid.

[0051] The preparation steps of the triblock shrinkage monomer are as follows:

[0052] (1) Esterification reaction: Polyethylene glycol monomethyl ether with a molecular weight of 500 is reacted with maleic anhydride at a molar ratio of 1:1.1 to 1:1.3 at 80 to 90°C for 5 to 6 hours to obtain an ester intermediate;

[0053] (2) Hydrophobic alkyl grafting: 1-bromohexane is added to the ester intermediate, with a molar ratio of 1-bromohexane to ester intermediate of 0.3 to 0.5:1. The reaction is carried out at 70 to 80 °C for 3 to 4 hours to introduce C6 hydrophobic alkyl groups.

[0054] (3) Siloxane modification: γ-methacryloxypropyltrimethoxysilane is added, and the molar ratio of γ-methacryloxypropyltrimethoxysilane to ester intermediate is 0.2-0.4:1. The reaction is carried out at 85-95℃ for 2-3 hours to obtain a triblock condensed monomer.

[0055] Please refer to Figure 1 and Figure 3 The protective film 1 is made of PET film or PP film with a thickness of 0.05-0.2mm, a temperature resistance of not less than 150℃, a surface tension of ≥38mN / m, and a peel strength of ≥5N / cm between the protective film 1 and the adjacent carbon fiber layer 2 and UD carbon fiber prepreg layer 4. PET film has excellent scratch resistance, chemical corrosion resistance and dimensional stability, while PP film has better flexibility, lower cost and excellent low temperature resistance, making it suitable for vehicles in cold regions. The 0.05-0.2mm range design can ensure that the film has sufficient tear resistance to effectively resist daily scratches. The temperature resistance of the protective film 1 of not less than 150℃ meets the requirements of the hot pressing process in production and the working conditions during vehicle operation. The surface tension of ≥38mN / m ensures good wetting and adhesion between adjacent layers, avoiding air bubbles or gaps between layers. The peel strength of ≥5N / cm can ensure a lasting bond between layers and resist vibration under working conditions.

[0056] In step (1) of the preparation of the triblock shrinkage monomer, polyethylene glycol monomethyl ether can be replaced with a mixture of polyethylene glycol monomethyl ether and oxidized konjac glucomannan = 7:3 to 8:2. The degree of substitution of oxidized konjac glucomannan is 0.3 to 0.5. The ratio of 7:3 to 8:2 ensures that the shrinkage performance does not decrease after the bio-based substitution. At the same time, the bio-based content reaches 20% to 30%, achieving a significant environmental improvement. The degree of substitution of 0.3 to 0.5 ensures the reactivity and hydrophilicity of oxidized konjac glucomannan. The reactivity can effectively esterify with maleic anhydride, and the hydrophilicity avoids the decrease in dispersibility caused by excessive hydrophobicity.

[0057] The micro-expansion component is a mixture of triethanolamine and aluminum sulfate in a 1:1 mass ratio. The water-retaining component is maltodextrin, hydroxypropyl methylcellulose, and xanthan gum in a ratio of 8:1:1. Triethanolamine accelerates cement hydration and promotes the reaction of aluminum sulfate with hydration products to form ettringite. The 1:1 ratio ensures that the ettringite formation rate matches the concrete shrinkage rate. It provides moderate expansion in the early 1-7 days, with an expansion rate of 0.02%-0.03%, compensating for plastic shrinkage and early drying shrinkage. After 28 days, the expansion tends to stabilize, with an expansion rate ≤0.05%, avoiding strength reduction or cracking caused by excessive expansion. Maltodextrin forms hydrogen bonds with water molecules through polycarboxyl groups, delaying water evaporation and solving early drying shrinkage. Hydroxypropyl methylcellulose increases the viscosity of the paste, reduces water migration, and forms a synergistic effect of water retention and thickening with maltodextrin. Xanthan gum acts as a structural stabilizer, forming a three-dimensional network structure to lock in moisture and prolong the water retention time.

[0058] The preparation method is as follows: Add the prescribed amount of deionized water to an industrial-grade compounding reactor equipped with a vacuum feeding device. Start a low-speed homogenizing stirring system, stabilizing the speed at 200–250 r / min. Add the micro-expansion component and water-retaining component, pretreated by pulverizing to below 120 mesh and vacuum drying to ≤5% moisture content, through a closed solid feeding station equipped with a dust recovery device. Start a homogenizing emulsifier to assist dissolution for 15–20 min. Confirm viscosity fluctuation ≤5% using an online viscosity-shrinkage rate monitoring instrument, indicating complete dissolution of the solid components. Then, precisely deliver the modified shrinkage-reducing polycarboxylate mother liquor through a dual-metering pump parallel conveying system. Start a low-temperature constant-temperature circulation system to control the temperature of the compounding system at 18–25℃. Continue stirring for 30–40 min until the system is homogeneous. After removing trace amounts of insoluble impurities through a 5μm precision membrane filter, transfer the mixture to a finished product storage tank equipped with a pressure balancing device via a nitrogen-sealed pipeline conveying system, obtaining a homogeneous and stable shrinkage-reducing polycarboxylate superplasticizer.

[0059] The storage conditions for the finished shrinkage-reducing polycarboxylate superplasticizer are 15–30℃ and nitrogen sealing pressure of 0.02–0.05 MPa. It shows no stratification or sedimentation within 12 months of storage, and its viscosity is 300–500 mM at 25℃. The product exhibits a 7-day shrinkage rate of ≤72% and a 28-day shrinkage rate of ≤65% for concrete. The compounding process utilizes a PLC distributed control system to synchronously monitor mixing speed, system temperature, pH value, and viscosity, ensuring that the shrinkage rate fluctuation range between different batches is ≤±3%. It is suitable for engineering scenarios with stringent shrinkage control requirements, such as large-volume concrete and prestressed concrete. A mild storage temperature of 15–30℃ prevents degradation of shrinkage-reducing monomers due to high temperatures, while a nitrogen sealing pressure of 0.02–0.05 MPa isolates the product from air, preventing oxidation and deterioration of the water-retaining components. These two factors work synergistically to ensure the product remains stratified and sediment-free for 12 months of storage, far exceeding the 6-month storage period of conventional water-reducing agents, thus reducing inventory pressure for engineering projects. The viscosity at 25℃ is 300–500 mg / L. The limitations ensure that the product's fluidity remains stable during storage, preventing uncontrolled dosage during application due to sudden viscosity changes. The PLC system synchronously monitors stirring speed, temperature, pH value, and viscosity, precisely controlling key parameters affecting shrinkage rate from the compounding stage, which is the core guarantee for achieving consistent batch performance.

[0060] Example 1 (Single component of water-retaining component compound)

[0061] Add 820g of deionized water to an industrial-grade compounding reactor equipped with a vacuum feeding device. Start a low-speed homogenizing and stirring system at 200r / min. Add 20g of water-retaining component (maltodextrin: hydroxypropyl methylcellulose: xanthan gum = 8:1:1), which has been pretreated, pulverized to below 120 mesh, and vacuum-dried to ≤5% moisture content, through a closed solid feeding station. Start a homogenizing emulsifier to assist in dissolution for 20min. Confirm complete dissolution through online monitoring. Then, deliver the modified shrinkage type through a metering pump. 160g of polycarboxylate mother liquor (isoprene-based polyethylene glycol ether n=45, containing triblock shrinkage-reducing monomers, obtained by ultrasonic-microwave synergistic polymerization and gradient pH control, the temperature was controlled at 25℃ by turning on the low-temperature constant temperature circulation system, and the mixture was stirred continuously for 30min until homogeneous. After filtration through a 5μm precision membrane, it was transferred to the finished product storage tank through a nitrogen-sealed pipeline (nitrogen-sealed pressure 0.03MPa) to obtain the shrinkage-reducing polycarboxylate superplasticizer. The mixing process was monitored by a PLC system for stirring speed, pH (6.8~7.2) and temperature.

[0062] Example 2 (Single-component compound of micro-expansion component)

[0063] 820g of deionized water was added to an industrial-grade compounding reactor equipped with a vacuum feeding device. A low-speed homogenizing and stirring system with a rotation speed of 200r / min was started. 20g of pretreated micro-expansion component (triethanolamine: aluminum sulfate = 1:1) was added through a closed solid feeding station. The homogenizing emulsifier was turned on to assist dissolution for 20min. After confirming complete dissolution, 160g of modified shrinkage-reducing polycarboxylate mother liquor (same as in Example 1) was delivered through a metering pump. The temperature was controlled at 25℃, and the mixture was stirred continuously for 30min until homogeneous. After filtration through a 5μm precision membrane and nitrogen sealing storage, the shrinkage-reducing polycarboxylate water-reducing agent was obtained. The pH was monitored (6.5~7.0) by the PLC system during the compounding process.

[0064] Example 3 (Synergistic combination of micro-expansion and water-retaining components, core example)

[0065] 800g of deionized water was added to an industrial-grade compounding vessel equipped with a vacuum feeding device. A low-speed homogenizing stirring system with a speed of 220r / min was started. 20g of pretreated micro-expansion component (triethanolamine: aluminum sulfate = 1:1) and 20g of water-retaining component (maltodextrin: hydroxypropyl methylcellulose: xanthan gum = 8:1:1) were added through a closed solid feeding station. A homogenizing emulsifier (power 10kW) was turned on to assist in dissolution for 25min. After confirming complete dissolution, 160g of modified shrinkage-reducing polycarboxylate mother liquor (same as in Example 1) was delivered through a dual metering pump. The temperature was controlled at 22℃, and stirring was continued for 35min until homogeneous. After filtration through a 5μm precision membrane and nitrogen sealing storage (pressure 0.04MPa), the shrinkage-reducing polycarboxylate water-reducing agent was obtained. During the compounding process, the PLC system synchronously monitored the stirring speed, temperature, and pH (7.0~7.5).

[0066] Example 4 (Common mother liquor control, verifying the necessity of modified mother liquor)

[0067] 800g of deionized water was added to an industrial-grade compounding reactor equipped with a vacuum feeding device. A low-speed homogenizing and stirring system with a rotation speed of 220r / min was started. 20g of pretreated micro-expansion component and 20g of water-retaining component were added through a closed solid feeding station. The homogenizing emulsifier was turned on to assist dissolution for 25min. After confirming complete dissolution, 160g of ordinary polycarboxylate mother liquor (isoprene-based polyethylene glycol ether n=45, without triblock shrinkage monomers, prepared by conventional water bath polymerization) was delivered through a metering pump. The temperature was controlled at 22℃, and the mixture was stirred continuously for 35min until homogeneous. After filtration through a 5μm precision membrane and nitrogen sealing storage, the control water-reducing agent was obtained.

[0068] Example 5 (Bio-based triblock mother liquor, raw material innovation verification)

[0069] Add 800g of deionized water to an industrial-grade compounding reactor equipped with a vacuum feeding device, start a low-speed homogenizing stirring system at 220r / min, add 20g of pretreated micro-expansion component and 20g of water-retaining component through a closed solid feeding station, turn on a homogenizing emulsifier to assist dissolution for 25min, and confirm complete dissolution. Then, deliver 160g of bio-based triblock shrinkage-reducing mother liquor (30 parts of isopentenyl polyethylene glycol ether + 8 parts of bio-based triblock shrinkage-reducing monomer + 3 parts of acrylic acid, obtained by ultrasonic-microwave polymerization and gradient pH control, the bio-based monomer contains oxidized konjac glucomannan) through a metering pump, control the temperature at 22℃, and continue stirring for 35min until homogeneous. After filtration through a 5μm precision membrane and nitrogen sealing storage, the shrinkage-reducing polycarboxylate superplasticizer is obtained.

[0070] Example 6 (Mother liquor from ultrasonic-microwave process, verification of process innovation)

[0071] Add 800g of deionized water to an industrial-grade compounding reactor equipped with a vacuum feeding device, start a low-speed homogenizing stirring system at 220r / min, add 20g of pretreated micro-expansion component and 20g of water-retaining component through a closed solid feeding station, turn on a homogenizing emulsifier to assist dissolution for 25min, and confirm complete dissolution. Then, deliver 160g of ultrasonic-microwave shrinkage-reducing mother liquor (30 parts of isopentenyl polyethylene glycol ether + 8 parts of triblock shrinkage-reducing monomer + 3 parts of acrylic acid, obtained by ultrasonic pretreatment at 250W for 15min, polymerization at 400W microwave at 60℃, and gradient pH control) through a metering pump, control the temperature at 22℃, and continue stirring for 35min until homogeneous. After filtration through a 5μm precision membrane and nitrogen sealing storage, the shrinkage-reducing polycarboxylate superplasticizer is obtained.

[0072] Example 7 (Comparison of mother liquor from traditional water bath process, highlighting the advantages of ultrasound-microwave)

[0073] Add 800g of deionized water to an industrial-grade compounding reactor equipped with a vacuum feeding device, start a low-speed homogenizing stirring system at 220r / min, add 20g of pretreated micro-expansion component and 20g of water-retaining component through a closed solid feeding station, turn on a homogenizing emulsifier to assist dissolution for 25min, and confirm complete dissolution. Then, deliver 160g of traditional water bath process mother liquor (same as the raw material in Example 6, prepared by polymerization in a 60℃ water bath and fixed pH=5) through a metering pump, control the temperature at 22℃, and continue stirring for 35min until homogeneous. After filtration through a 5μm precision membrane and nitrogen sealing storage, the control water-reducing agent is obtained.

[0074] Examples 1-4 show four samples prepared with shrinkage-reducing polycarboxylate superplasticizers. Following the test methods in JC / T2361-2016 "Shrinkage-Reducing Agents for Mortar and Concrete" standard, 2% of the polycarboxylate superplasticizer was added to each sample for testing. The appearance of the superplasticizer was also observed after 28 days. The test results are shown in Table 1.

[0075] Table 1 - Test Results

[0076]

[0077] Table 2 - Experimental Data

[0078]

[0079] Compared to the core Example 3 (synergistic effect of micro-expansion and water-retaining components), Example 1 (containing only water-retaining components) and Example 2 (containing only micro-expansion components) highlight the significant advantages of the dual-component synergy. Example 1, containing only water-retaining components, has a 28-day shrinkage ratio of 70% and a shrinkage reduction rate of 30%. Example 2, containing only micro-expansion components, has a 28-day shrinkage ratio of 68% and a shrinkage reduction rate of 32%. However, Example 3, with dual-component synergy, reduces the 28-day shrinkage ratio to 60% and increases the shrinkage reduction rate to 40%, representing a reduction of 8%–10% and an increase of 8%–10% respectively compared to single components. This is not a simple performance additive. At the same time, Example 3 achieves a 28-day compressive strength ratio of 145%, an increase of 5%–7% compared to Example 1 (135%) and Example 2 (138%). This is because the dual-component synergy avoids the local aggregation problem that is prone to occur with single components, resulting in more uniform dispersion. It inhibits moisture loss through water-retaining components and achieves volume compensation through micro-expansion components, perfectly solving the industry pain points of limited shrinkage reduction effect and easy sacrifice of strength by single shrinkage reduction components.

[0080] Compared to Control Example 4 (ordinary polycarboxylate mother liquor without triblock shrinkage monomers), Core Example 3 (modified shrinkage-reducing mother liquor containing triblock shrinkage-reducing monomers) fully demonstrates the core technical value of the modified mother liquor. Example 3 exhibits a 28-day shrinkage ratio of 60% and a shrinkage reduction rate of 40%, while Example 4 boasts a 28-day shrinkage ratio as high as 78% and a shrinkage reduction rate of only 22%. The modified mother liquor reduces the shrinkage ratio by 18%, nearly doubling the shrinkage reduction effect. This directly overcomes the performance bottleneck of ordinary mother liquor with a shrinkage reduction rate ≤25%. From a long-term performance perspective, the implementation... The 60-day shrinkage rate of Example 3 remained at a low level of 55%, while the 60-day shrinkage rate of Example 4 was 76%, indicating a significant decline in long-term shrinkage reduction effect. In terms of storage stability, Example 3 achieved no stratification or sedimentation for 12 months, while Example 4 showed slight stratification after only 6 months. This indicates that the modified mother liquor containing hydrophobic alkyl-siloxane-ester triblock shrinkage-reducing monomers can not only achieve strong short-term shrinkage reduction but also ensure long-term shrinkage stability and significantly extend the product storage period. This is the core difference between this patent and ordinary polycarboxylate superplasticizers.

[0081] Compared to Control Example 7 (traditional water bath polymerization process), Example 6 (ultrasound-microwave synergistic polymerization process) highlights the advantages of quality improvement and efficiency enhancement brought about by process innovation. Example 6 uses a process of 250W ultrasonic pretreatment for 15 minutes followed by 400W microwave polymerization at 60℃, resulting in a 28-day shrinkage rate of 59% and a compressive strength of 148%. In contrast, Example 7, using the traditional water bath process, has a 28-day shrinkage rate of 68% and a compressive strength of only 125%. Process optimization reduces the shrinkage rate by 9% and increases the strength by 23 percentage points. Regarding batch stability, the batch shrinkage rate of Example 6 fluctuates by only ±2.0%, a 52% reduction compared to ±4.2% in Example 7. This is attributed to the efficient dispersion of monomers by ultrasonic pretreatment and the precise control of reaction temperature by microwave polymerization. This solves the defects of uneven monomer dispersion and large reaction temperature fluctuations in the traditional water bath process, achieving a triple improvement in shrinkage reduction, product strength, and batch stability, making it more suitable for large-scale industrial continuous production needs.

[0082] Example 5 (bio-based triblock shrinkage-reducing mother liquor containing oxidized konjac glucomannan) demonstrates the performance upgrade value of bio-based raw materials compared to the core Example 3 (conventional modified shrinkage-reducing mother liquor). Example 5 has a 28-day shrinkage ratio of 58% and a shrinkage reduction rate of 42%, and a 60-day shrinkage ratio of 52% and a shrinkage reduction rate of 48%, which is further optimized compared to Example 3 (28-day shrinkage ratio of 60% and shrinkage reduction rate of 40%, 60-day shrinkage ratio of 55% and shrinkage reduction rate of 45%). This is because the mixture of bio-based monomer polyethylene glycol monomethyl ether and oxidized konjac glucomannan has better hydrophilicity and biocompatibility, which can better integrate with the concrete system and enhance the shrinkage reduction effect. At the same time, the 28-day compressive strength ratio of Example 5 reaches 150%, which is higher than the 145% of Example 3. Moreover, the bio-based raw materials are more environmentally friendly and renewable. While improving performance, it also takes into account the needs of green development, providing a new direction for the raw material innovation of shrinkage-reducing polycarboxylate superplasticizers.

[0083] In summary, Examples 3 (two-component synergy + modified mother liquor), 5 (bio-based raw materials + two-component synergy + modified mother liquor), and 6 (ultrasound-microwave process + two-component synergy + modified mother liquor) are the core advantageous examples of this patent. They all simultaneously meet the patent objectives of 28-day shrinkage ratio ≤65%, shrinkage reduction rate ≥40%, compressive strength ratio ≥140%, no abnormalities after 12 months of storage, and batch fluctuation ≤±2.0%. Among them, Example 5 has the best overall performance, with a 60-day shrinkage reduction rate of 48%. It is the best embodiment of the superposition of multiple technical dimensions of this patent, including component synergy, raw material innovation, and process optimization. It is fully adaptable to engineering scenarios with stringent shrinkage control requirements, such as large-volume concrete and prestressed concrete. Compared with existing technologies, it has achieved a comprehensive breakthrough in shrinkage reduction effect, strength performance, long-term stability, and industrial applicability.

[0084] The above embodiments are merely illustrative examples and are not intended to limit the scope of the invention. Various variations that can be made in the art are not exhaustively listed here, and therefore all derived modifications are within the scope of protection of this invention.

Claims

1. A reduced polycarboxylate superplasticizer and a preparation method thereof, characterized in that: The reduced shrinkage polycarboxylic water reducing agent is prepared by compounding raw materials with the following mass fractions: modified reduced shrinkage polycarboxylic mother liquor 8-12%, micro-expansion component 1-3%, water retention component 1-2%, and the balance being water; ​ The modified reduced shrinkage polycarboxylic mother liquor is prepared by ultrasonic-microwave synergistic polymerization, and the raw materials include, by mass fraction: isoprenyl polyethylene glycol ether 25-40 parts, three-block reduced shrinkage monomer 8-15 parts, acrylic acid or its derivative 3-6 parts, initiator 0.9-1.3 parts, reducing agent 0.1-0.3 parts, catalyst 0.003-0.006 parts, chain transfer agent 0.7-1.1 parts, and the polymerization process adopts gradient pH control: pH=3-4 at the initial stage of reaction, pH=5-6 at the middle stage of reaction, and pH=7-8 at the late stage of reaction. The three-block reduced shrinkage monomer is a hydrophobic alkyl-siloxane-ester group three-block structure, which is prepared by esterification, hydrophobic alkyl grafting and siloxane modification of polyethylene glycol monomethyl ether or a mixture thereof and oxidized konjac glucomannan. 2.The reduced shrinkage polycarboxylate superplasticizer according to claim 1, characterized in that: The preparation of the reduced shrinkage polycarboxylic water reducing agent mother liquor includes polymerization of the following raw materials by mass fraction: isoprenyl polyethylene glycol ether 20-50 parts, reduced shrinkage monomer 5-10 parts, and acrylic acid or its derivative 2-5 parts. 3.The reduced shrinkage polycarboxylate superplasticizer according to claim 2, characterized in that: The isoprenyl polyethylene glycol ether has the following general formula: ， In the general formula, n=30-60, preferably n=40-50. 4.The reduced polycarboxylic water reducer mother liquor according to claim 2, characterized in that: The acrylic acid or its derivative is preferably acrylic acid, methacrylic acid or butyl acrylate.

5. The reduced shrinkage polycarboxylate water reducer according to claim 2, characterized by: The preparation of the reduced shrinkage polycarboxylic mother liquor includes the following steps: (1) ultrasonic pretreatment: mixing the three-block reduced shrinkage monomer and the acrylic acid or its derivative, and ultrasonic treatment under the conditions of power 200-300 W and frequency 30-40 kHz for 10-20 min to prepare a pre-dispersed monomer solution; (2) preparation of a base solution: dissolving the isoprenyl polyethylene glycol ether and the pre-dispersed monomer solution in water to prepare a base solution with a mass concentration of 50%-60%; (3) preparation of A solution and B solution: uniformly mixing the balance of acrylic acid or its derivative and water to prepare A solution, and uniformly mixing the reducing agent, catalyst and chain transfer agent with water to prepare B solution; (4) microwave polymerization: adding the initiator to the base solution, transferring to a microwave reactor, and synchronously dropping A solution and B solution under the conditions of power 300-500 W and temperature 55-65 ℃, wherein A solution is dropped for 2 h and B solution is dropped for 2.5 h, and the polymerization process adopts gradient pH control: pH=3-4 at 0-1 h of the initial stage of reaction, pH=5-6 at 1-2 h of the middle stage of reaction, and pH=7-8 at 2-2.5 h of the late stage of reaction; (5) post-treatment: continuing to react for 1 h after dropping is completed, and adjusting to a mass concentration of 40% by adding water to obtain the modified reduced shrinkage polycarboxylic mother liquor; The initiator is selected from hydrogen peroxide or ammonium persulfate, the reducing agent is selected from L-ascorbic acid or sodium bisulfite, the catalyst is ferrous sulfate, and the chain transfer agent is selected from sodium hypophosphite or mercaptopropionic acid. 6.The reduced shrinkage polycarboxylate superplasticizer and the preparation method thereof according to claim 1, characterized in that: The preparation steps of the three-block reduced shrinkage monomer are as follows: (1) Esterification reaction: polyethylene glycol monomethyl ether with a molecular weight of 500 is reacted with maleic anhyhydride at a molar ratio of 1:1.1-1:1.3 at 80-90°C for 5-6 hours to obtain an ester intermediate; (2) Hydrophobic alkyl grafting: 1-bromohexane is added to the ester intermediate, the molar ratio of the 1-bromohexane to the ester intermediate is 0.3-0.5:1, and the reaction is carried out at 70-80°C for 3-4 hours to introduce C6 hydrophobic alkyl groups; (3) Siloxane modification: γ-methacryloyloxypropyltrimethoxysilane is added, the molar ratio of the γ-methacryloyloxypropyltrimethoxysilane to the ester intermediate is 0.2-0.4:1, and the reaction is carried out at 85-95°C for 2-3 hours to obtain a triblock shrinkage-reducing monomer.

7. The shrinkable polycarboxylic water reducing agent and the preparation method thereof according to claim 6, characterized in that: In step (1) of the preparation steps of the triblock shrinkage-reducing monomer, the polyethylene glycol monomethyl ether can be replaced by a mixture of polyethylene glycol monomethyl ether: oxidized konjac glucomannan = 7:3-8:2, and the degree of substitution of the oxidized konjac glucomannan is 0.3-0.

5. 8.The reduced shrinkage polycarboxylate superplasticizer and the preparation method thereof according to claim 1, characterized in that: The micro-expanding component is a mixture of triethanolamine and aluminum sulfate at a mass ratio of 1:1, and the water-retaining component is maltodextrin: hydroxypropyl methyl cellulose: xanthan gum = 8:1:

1. 9.The reduced shrinkage polycarboxylate superplasticizer and the preparation method thereof according to claim 1, characterized in that: The preparation method steps are as follows: deionized water in the formula amount is added to an industrial-grade compounding kettle with a vacuum feeding device, a low-speed homogenizing stirring system is started, the stirring speed is stably controlled at 200-250 r / min, the micro-expanding component and the water-retaining component pretreated by being crushed to 120 mesh or less and vacuum dried to a moisture content of ≤5% are added through a closed solid feeding station equipped with a dust recovery device, a homogenizing emulsifier is started to assist dissolution for 15-20 min, the viscosity fluctuation is confirmed to be ≤5% through an online viscosity and shrinkage rate linkage monitor, at this time the solid components are completely dissolved, then the modified shrinkage-reducing polycarboxylic acid mother liquor is accurately delivered through a double-metering pump parallel delivery system, a low-temperature constant-temperature circulation system is started to control the temperature of the compounding system at 18-25°C, and the system is continuously stirred for 30-40 min until it is uniform, after removing trace insoluble impurities through a 5 μm precision membrane, the product is transferred to a finished product storage tank equipped with a pressure balancing device through a nitrogen-sealed pipeline delivery system, and a uniform and stable shrinkage-reducing polycarboxylic acid water reducing agent is obtained. 10.The shrinkable polycarboxylic water reducing agent and the preparation method thereof according to claim 9, characterized in that: The storage conditions of the finished shrinkage-reducing polycarboxylic acid water reducing agent are 15-30°C and a nitrogen-sealed pressure of 0.02-0.05 MPa, no stratification or precipitation occurs within 12 months of storage, the viscosity at 25°C is 300-500 mPa·s, the 7d shrinkage rate ratio of concrete is ≤72%, the 28d shrinkage rate ratio is ≤65%, a PLC distributed control system is used in the compounding process, the stirring speed, system temperature, pH value and viscosity are synchronously monitored, the shrinkage rate ratio fluctuation range of different batches of products is ensured to be ≤±3%, and the product is suitable for large-volume concrete, prestressed concrete and other engineering scenarios with strict shrinkage control requirements.

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