Preparation method of anti-freezing high-dispersion water reducing agent

Abstract

The invention relates to the technical field of concrete admixtures, and particularly discloses a preparation method of an anti-freezing high-dispersion water reducing agent, which comprises the following steps: S1, preparing a base material: adding an allyl polyoxyethylene ether macromonomer and deionized water into a reaction container to form a macromonomer aqueous solution; then adding a sulfonic acid small monomer and a first part of initiator into the macromonomer aqueous solution; s2, preparation of a material A: dissolving acrylic acid, acrylamide, a hydroxyl-containing acrylate monomer or a hydroxyl-containing methacrylate monomer, a polyethylene glycol acrylate monomer or a polyethylene glycol methacrylate monomer and urea in deionized water to prepare the material A; s3, preparation of a material B: dissolving a chain transfer agent, a reducing agent and a second part of initiator in deionized water to prepare the material B; s4, dropwise adding and polymerizing: dropwise adding the material A and the material B into the reaction container at the same time; and S5, post-processing. The scheme is used for solving the problem that high dispersibility and anti-freezing property of concrete in a low-temperature environment cannot be effectively considered in the prior art.

Description

Technical Field

[0001] This invention relates to the field of concrete admixture technology, specifically to a method for preparing an antifreeze highly dispersible water-reducing agent. Background Technology

[0002] Polycarboxylate superplasticizers, as third-generation high-performance superplasticizers, have become an indispensable key material in modern concrete engineering due to their advantages such as low dosage, high water reduction rate, and environmental friendliness. However, in cold regions or during winter construction, low temperatures can severely weaken the dispersibility of superplasticizers, exacerbate slump loss in concrete, and delay cement hydration, leading to slow early strength development and even frost damage. Therefore, developing polycarboxylate superplasticizers with excellent low-temperature dispersibility, antifreeze properties, and early strength is a key technical requirement for ensuring the quality and progress of concrete construction in low-temperature environments.

[0003] Currently, the technical approaches to improving the freeze-thaw durability of concrete can be mainly divided into two categories: one is to directly add inorganic salt antifreeze components (such as calcium nitrate, sodium nitrite, etc.), but this can easily lead to accelerated slump loss in concrete, and excessive addition may cause risks such as salt precipitation and steel corrosion; the other is to introduce air-entraining agents, which buffer the stress generated by freeze-thaw cycles by forming a large number of uniform, closed microbubbles in the concrete. The latter approach is often achieved by using air-entraining agents in combination with water-reducing agents.

[0004] In existing technologies, researchers have modified air-entraining agents in various ways to obtain better antifreeze performance, especially for harsh saline-freezing environments (such as coastal areas). For example, Chinese invention patent CN118878244A discloses a method for preparing an antifreeze highly dispersed water-reducing agent. This method first involves arginine grafting and methylation of natural air-entraining triterpenoid saponins to obtain a modified amino acid-grafted triterpenoid saponin. This modified saponin is then mixed with commercially available polycarboxylate-based water-reducing agent powder (such as PC-1009), sodium carboxymethyl cellulose, etc., in an ethanol-water solution. Finally, the mixture is dried and pulverized to obtain a solid composite water-reducing agent. The core of this technical solution lies in enhancing the air-entraining efficiency and stability of triterpenoid saponins through chemical modification, and then introducing them into the concrete system through physical compounding. The aim is to improve the concrete's resistance to freeze-thaw cycles and chloride ion penetration in corrosive media such as high concentrations of sodium chloride, sodium sulfate, or seawater.

[0005] However, the aforementioned technical route based on "air-entraining agent modification + physical compounding" has the following limitations: First, its preparation process is complex, involving multiple chemical reactions (Mannich reaction, methylation) and subsequent dialysis purification, mixing, drying, and pulverization processes, resulting in high energy consumption and a long production cycle. Second, the final product is a solid powder, which needs to be dissolved again before use, increasing the inconvenience of the construction process. More importantly, this technology mainly focuses on solving the durability problem of concrete in harsh salt-freezing environments during long-term use, and its performance advantage is reflected in the retention rate of dynamic modulus of elasticity after hundreds of freeze-thaw cycles. However, this solution does not give sufficient attention to or effectively address the more urgent combined needs of maintaining the workability (i.e., high dispersibility), preventing frost damage, and rapidly developing early strength of fresh concrete in conventional low-temperature construction in winter. While the introduction of air-entraining agents improves frost resistance, it often weakens the early strength of concrete to a certain extent, and its contribution to improving the dispersibility and slump retention capacity of water-reducing agents at low temperatures is limited.

[0006] Therefore, there is an urgent need in this field for a new technical approach that can synthesize a multifunctional integrated polycarboxylate superplasticizer that possesses low-temperature high dispersibility properties and can effectively promote early strength of concrete at low temperatures and reduce freezing point through more direct and efficient molecular design. This would simplify the process, facilitate use, and better meet the construction performance requirements in low-temperature environments. Summary of the Invention

[0007] The present invention aims to provide a method for preparing an antifreeze high-dispersibility water-reducing agent, so as to solve the problem that the existing technology cannot effectively balance the high dispersibility and antifreeze properties of concrete under low-temperature conditions.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing an antifreeze highly dispersible water-reducing agent includes the following steps: S1. Preparation of base material: Add 3750 to 3850 parts by mass of allyl polyoxyethylene ether macromonomer and 2950 to 3050 parts by mass of deionized water to the reaction vessel to form a macromonomer aqueous solution; control the solution temperature at 26℃-30℃, and then add 18-22 parts by mass of sulfonic acid small monomer and 13-17 parts by mass of the first part of the initiator to the macromonomer aqueous solution; S2, Preparation of Material A: Dissolve 310-330 parts of acrylic acid, 8-12 parts of acrylamide, 75-85 parts of hydroxyl-containing acrylate monomers or hydroxyl-containing methacrylate monomers, 95-105 parts of polyethylene glycol acrylate monomers or polyethylene glycol methacrylate monomers, and 45-55 parts of urea in 480-520 parts of deionized water, mix evenly, and obtain Material A; S3, B material preparation: Dissolve 11-13 parts of chain transfer agent, 4-6 parts of reducing agent and 13-17 parts of second part initiator in 430-470 parts of deionized water, mix evenly to obtain material B; S4. Droplet polymerization: Add component A and component B dropwise into the substrate in the reaction vessel simultaneously to carry out the polymerization reaction. Control the reaction temperature at 42℃-48℃ during the droplet process. The total droplet time for component A is 100-150 minutes, and the total droplet time for component B is 120-180 minutes. S5. Post-treatment: After the addition is complete, keep warm and mature for 60-90 minutes. Then add 55-65 parts of calcium nitrate to the reaction system, stir and mix evenly. Finally, adjust the pH value to 6 to 8 with liquid alkali, and add deionized water to make the solid content of the final product 38%-42%, thus obtaining the antifreeze high dispersion polycarboxylate superplasticizer.

[0009] The principles and advantages of this scheme are: 1. Integrated Synthesis and Functional Integration: This scheme directly bonds the macromonomer allyl polyoxyethylene ether with various functional small monomers, including sulfonic acid groups, carboxyl groups, amide groups, hydroxyl groups, long polyether side chains, and urea, to construct a polycarboxylic acid polymer backbone with a specific molecular structure. This structure itself endows the water-reducing agent with excellent cement particle dispersibility (high dispersibility). Based on this, calcium nitrate is added as a highly efficient and low-cost early-strength antifreeze component, forming a stable functional composite system with the polymer solution.

[0010] 2. Molecular design and low-temperature performance assurance: Sulfonic acid monomers (such as sodium methallyl sulfonate): provide strong electrostatic repulsion, ensuring rapid and efficient initial dispersion ability even at low temperatures.

[0011] 3. Hydroxyl-containing monomers (such as hydroxyethyl acrylate) and long-chain polyether monomers (such as MPEGAA): The introduced hydroxyl groups and long ether chains can effectively lower the freezing point of the solution, enhance the hydrophilicity and solubility of the polymer at low temperatures, and help maintain fluidity.

[0012] 4. Urea: As a reaction component, it not only participates in regulating the polymerization process, but also has the function of lowering the freezing point and maintaining dispersion.

[0013] 5. The addition of calcium nitrate accelerates the hydration reaction of cement at low temperatures, improving early strength; nitrate ions lower the freezing point of the system. Adding it after the polymerization reaction is complete avoids interference with the polymerization process, ensuring the integrity and dispersion performance of the main polymer structure.

[0014] Preferably, as an improvement, step S4 employs a segmented dripping method, including: First stage: Add 40%-60% of the total amount of material A and 40%-60% of the total amount of material B dropwise, and control the reaction temperature at 42℃-45℃; Second stage: Add the remaining A and B materials dropwise, and control the reaction temperature at 45℃-48℃.

[0015] Beneficial effects: By adding the polymer at controlled temperature in stages, the polymerization rate and molecular chain growth process can be controlled more precisely, avoiding explosive polymerization or uneven reaction, thereby obtaining polymer products with more concentrated molecular weight distribution and more controllable structure, and improving their low-temperature dispersion performance and stability.

[0016] Preferably, as an improvement, in step S1, the sulfonic acid monomer is sodium methylpropene sulfonate; and the first initiator is ammonium persulfate.

[0017] Beneficial effects: The sulfonic acid groups provided by sodium methacrylate sulfonate have a strong dispersing effect at low temperatures; ammonium persulfate has a mild initiation and is well matched with the process temperature. The synergy of the two ensures a stable start-up and efficient progress of the polymerization reaction.

[0018] Preferably, as an improvement, in step S2, the hydroxyl-containing acrylate monomer or the hydroxyl-containing methacrylate monomer is hydroxyethyl acrylate; the polyethylene glycol acrylate monomer or the polyethylene glycol methacrylate monomer has a polyethylene glycol segment molecular weight of 400.

[0019] Beneficial effects: Hydroxyethyl acrylate enhances hydrophilicity and water retention, while the 400 molecular weight polyether monomer provides suitable steric hindrance. The combination of these two factors enhances the adsorption, dispersion, and slump retention capabilities of the water-reducing agent at low temperatures.

[0020] Preferably, as an improvement, in step S3, the chain transfer agent is mercaptopropionic acid; the reducing agent is vitamin C; and the second initiator is ammonium persulfate.

[0021] Beneficial effects: Mercaptopropionic acid effectively regulates molecular weight; the redox system composed of vitamin C and ammonium persulfate has high initiation efficiency at low temperatures, avoiding damage to functional structures caused by high temperatures.

[0022] Preferably, as an improvement, in step S4, the polymerization reaction is carried out under stirring at a speed of 55-65 r / min.

[0023] Preferably, as an improvement, the heat preservation and maturation time in step S5 is 60-90 minutes.

[0024] The antifreeze-resistant, highly dispersed polycarboxylate superplasticizer prepared in this invention improves the performance of concrete under low-temperature conditions. By controlling the copolymerization of a specific structured allyl polyoxyethylene ether macromonomer with various functional small monomers containing sulfonic acid groups, carboxyl groups, amide groups, hydroxyl groups, and long polyether chains, a polymer backbone with both strong electrostatic repulsion and excellent steric mechanics is constructed, endowing the superplasticizer with superior cement particle dispersion ability. Furthermore, calcium nitrate is introduced in the later stages of synthesis for functionalization modification. This component effectively lowers the freezing point of the liquid phase in the concrete system to prevent frost damage and accelerates the low-temperature hydration process of cement.

[0025] Based on the above mechanism, this invention solves a long-standing problem in low-temperature construction. Concrete using this water-reducing agent not only maintains excellent fresh-mixed workability at -5℃, but also promotes early strength development. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a method for preparing an antifreeze-type highly dispersed polycarboxylate superplasticizer according to an embodiment of the present invention. Detailed Implementation

[0027] The following detailed description illustrates the specific implementation method: Example 1 A method for preparing an antifreeze type highly dispersed polycarboxylate superplasticizer, the specific steps of which are as follows: S1. Preparation of base material: Add 3800 kg of allyl polyoxyethylene ether and 3000 kg of deionized water to a 10T reactor, start stirring to completely dissolve them, and control the solution temperature at 28℃. Then add 20 kg of sodium methyl propylene sulfonate and 15 kg of ammonium persulfate to the aqueous solution of the macromonomer, and stir to dissolve evenly.

[0028] S2, Preparation of Material A: In the preparation vessel for Material A, add 500 kg of deionized water, start stirring, and then add 320 kg of acrylic acid, 10 kg of acrylamide, 80 kg of hydroxyethyl acrylate, 100 kg of polyethylene glycol monomethyl ether methacrylate and 50 kg of urea in sequence. Stir until completely dissolved to obtain Material A.

[0029] S3, Preparation of B Material: In the B material preparation vessel, add 450 kg of deionized water, start stirring, and then add 12 kg of mercaptopropionic acid, 5 kg of vitamin C and 15 kg of ammonium persulfate in sequence, stirring until completely dissolved to obtain B material.

[0030] S4. Droplet Polymerization: Materials A and B are simultaneously and uniformly added dropwise to the bottom of the reactor using metering pumps. The total droplet addition time for material A is 120 minutes, and for material B, it is 150 minutes. Segmented temperature control is used during the droplet addition process. First stage: Add 50% of the total amount of material A and material B dropwise, and control the reaction temperature at 44℃.

[0031] Second stage: Add the remaining A and B materials dropwise, and slowly raise the reaction temperature to 46℃.

[0032] The stirring speed was maintained at 60 r / min throughout the entire dropping process.

[0033] S5. Post-treatment: After the addition of material B is complete, keep the mixture at 46℃ for 60 minutes. Then, add 60 kg of calcium nitrate to the reactor and stir for 30 minutes to ensure uniform mixing. Finally, add liquid alkali to adjust the pH of the reaction solution to 7.0, and add deionized water to adjust the solid content of the final product to 40%, thus obtaining the antifreeze high-dispersion polycarboxylate superplasticizer.

[0034] Example 2 A method for preparing an antifreeze type highly dispersed polycarboxylate superplasticizer, the specific steps of which are as follows: S1. Preparation of base material: Add 3750 kg of allyl polyoxyethylene ether and 3050 kg of deionized water to a 10T reactor, start stirring to completely dissolve them, and control the solution temperature at 26℃. Then add 22 kg of sodium methyl propylene sulfonate and 13 kg of ammonium persulfate to the aqueous solution of the macromonomer, and stir to dissolve evenly.

[0035] S2, Preparation of Material A: In the preparation vessel for Material A, add 520 kg of deionized water, start stirring, and then add 310 kg of acrylic acid, 12 kg of acrylamide, 75 kg of hydroxyethyl acrylate, 105 kg of polyethylene glycol monomethyl ether acrylate and 45 kg of urea in sequence. Stir until completely dissolved to obtain Material A.

[0036] S3, Preparation of B Material: In the B material preparation vessel, add 470 kg of deionized water, start stirring, and then add 11 kg of mercaptopropionic acid, 6 kg of vitamin C and 13 kg of ammonium persulfate in sequence. Stir until completely dissolved to obtain B material.

[0037] S4. Droplet Polymerization: Materials A and B are simultaneously and uniformly added dropwise to the bottom of the reactor using metering pumps. The total droplet addition time for material A is 110 minutes, and for material B, it is 140 minutes. Segmented temperature control is used during the droplet addition process. First stage: Add 40% of the total amount of material A and material B dropwise, and control the reaction temperature at 42℃.

[0038] Second stage: Add the remaining A and B materials dropwise, and slowly raise the reaction temperature to 45℃.

[0039] The stirring speed was maintained at 65 r / min throughout the entire dropping process.

[0040] S5. Post-treatment: After the addition of material B is complete, maintain the temperature at 45℃ for 75 minutes. Then, add 55 kg of calcium nitrate to the reactor and stir for 30 minutes to ensure uniform mixing. Finally, add liquid alkali to adjust the pH of the reaction solution to 6.5, and add deionized water to adjust the solid content of the final product to 38%, thus obtaining the antifreeze high-dispersion polycarboxylate superplasticizer.

[0041] Example 3 A method for preparing an antifreeze type highly dispersed polycarboxylate superplasticizer, the specific steps of which are as follows: S1. Preparation of base material: Add 3850 kg of allyl polyoxyethylene ether and 2950 kg of deionized water to a 10T reactor, start stirring to completely dissolve them, and control the solution temperature at 30℃. Then add 18 kg of sodium methyl methacrylate and 17 kg of ammonium persulfate to the aqueous solution of the macromonomer, and stir to dissolve evenly.

[0042] S2, Preparation of Material A: In the preparation vessel for Material A, add 480 kg of deionized water, start stirring, and then add 330 kg of acrylic acid, 8 kg of acrylamide, 85 kg of hydroxyethyl acrylate, 95 kg of polyethylene glycol monomethyl ether methacrylate and 55 kg of urea in sequence. Stir until completely dissolved to obtain Material A.

[0043] S3, Preparation of B Material: In the B material preparation vessel, add 430 kg of deionized water, start stirring, and then add 13 kg of mercaptopropionic acid, 4 kg of vitamin C and 17 kg of ammonium persulfate in sequence. Stir until completely dissolved to obtain B material.

[0044] S4. Droplet Polymerization: Materials A and B are simultaneously and uniformly added dropwise to the bottom of the reactor using metering pumps. The total droplet addition time for material A is 130 minutes, and the total droplet addition time for material B is 160 minutes. Segmented temperature control is used during the droplet addition process. First stage: Add 60% of the total amount of material A and material B dropwise, and control the reaction temperature at 43℃.

[0045] Second stage: Add the remaining A and B materials dropwise, and slowly raise the reaction temperature to 48℃.

[0046] The stirring speed was maintained at 55 r / min throughout the entire dropping process.

[0047] S5. Post-treatment: After the addition of material B is complete, maintain the temperature at 48℃ for 90 minutes. Then, add 65 kg of calcium nitrate to the reactor and stir for 30 minutes to ensure uniform mixing. Finally, add liquid alkali to adjust the pH of the reaction solution to 7.5, and add deionized water to adjust the solid content of the final product to 42%, thus obtaining the antifreeze high-dispersion polycarboxylate superplasticizer.

[0048] The above embodiments of the present invention improve the performance of concrete under low-temperature conditions. When applied to concrete, it exhibits strong dispersion ability for cement particles, high initial slump with minimal slump loss over time, effectively ensuring the workability of concrete under low-temperature conditions. Especially in low-temperature construction, the water-reducing agent of the present invention significantly overcomes the problems of decreased dispersion efficiency, accelerated slump loss, and slow early strength development caused by conventional polycarboxylate water-reducing agents at low temperatures, enabling concrete to maintain excellent fluidity and workability even at -5°C.

[0049] Meanwhile, by introducing functional components such as calcium nitrate, this invention not only provides highly efficient dispersion but also endows concrete with excellent antifreeze and early-strength properties. This water-reducing agent not only lowers the freezing point of the pore solution within the concrete, preventing early frost damage, but also accelerates the hydration process of cement at low temperatures, promoting rapid early strength formation. It achieves a synergistic balance of "high dispersion, antifreeze, and early-strength" performance in low-temperature environments, providing reliable technical support for the smooth construction and quality assurance of concrete projects during cold seasons.

[0050] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for preparing an antifreeze-type highly dispersible water-reducing agent, characterized in that, Includes the following steps: S1. Preparation of base material: Add 3750 to 3850 parts by mass of allyl polyoxyethylene ether macromonomer and 2950 to 3050 parts by mass of deionized water to the reaction vessel to form a macromonomer aqueous solution; control the solution temperature at 26℃-30℃, and then add 18-22 parts by mass of sulfonic acid small monomer and 13-17 parts by mass of the first part of the initiator to the macromonomer aqueous solution; S2, Preparation of Material A: Dissolve 310-330 parts of acrylic acid, 8-12 parts of acrylamide, 75-85 parts of hydroxyl-containing acrylate monomers or hydroxyl-containing methacrylate monomers, 95-105 parts of polyethylene glycol acrylate monomers or polyethylene glycol methacrylate monomers, and 45-55 parts of urea in 480-520 parts of deionized water, mix evenly, and obtain Material A; S3, B material preparation: Dissolve 11-13 parts of chain transfer agent, 4-6 parts of reducing agent and 13-17 parts of second part initiator in 430-470 parts of deionized water, mix evenly to obtain material B; S4. Droplet polymerization: Add component A and component B dropwise into the substrate in the reaction vessel simultaneously to carry out the polymerization reaction. Control the reaction temperature at 42℃-48℃ during the droplet process. The total droplet time for component A is 100-150 minutes, and the total droplet time for component B is 120-180 minutes. S5. Post-treatment: After the addition is complete, keep warm and mature, then add 55-65 parts of calcium nitrate to the reaction system, stir and mix evenly, finally adjust the pH value to 6 to 8 with liquid alkali, and add deionized water to make the solid content of the final product 38%-42%, thus obtaining the antifreeze high dispersion polycarboxylate superplasticizer.

2. The preparation method of the antifreeze highly dispersible water-reducing agent according to claim 1, characterized in that: Step S4 employs a segmented dripping method, including: First stage: Add 40%-60% of the total amount of material A and 40%-60% of the total amount of material B dropwise, and control the reaction temperature at 42℃-45℃; Second stage: Add the remaining A and B materials dropwise, and control the reaction temperature at 45℃-48℃.

3. The preparation method of the antifreeze highly dispersible water-reducing agent according to claim 1, characterized in that: In step S1, the sulfonic acid monomer is sodium methylpropene sulfonate; the first initiator is ammonium persulfate.

4. The preparation method of the antifreeze highly dispersible water-reducing agent according to claim 3, characterized in that: In step S2, the hydroxyl-containing acrylate monomer or the hydroxyl-containing methacrylate monomer is hydroxyethyl acrylate; the polyethylene glycol acrylate monomer or the polyethylene glycol methacrylate monomer has a polyethylene glycol segment molecular weight of 400.

5. The preparation method of the antifreeze type highly dispersible water-reducing agent according to claim 1, characterized in that: In step S3, the chain transfer agent is mercaptopropionic acid; the reducing agent is vitamin C; and the second initiator is ammonium persulfate.

6. The method for preparing the antifreeze-type highly dispersible water-reducing agent according to claim 1, characterized in that: In step S4, the polymerization reaction is carried out under stirring at a speed of 55-65 r / min.

7. The preparation method of the antifreeze highly dispersible water-reducing agent according to claim 6, characterized in that: The cooking time in step S5 is 60-90 minutes.

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