A solid shrinkage type polycarboxylic acid water reducing agent, a preparation method and application thereof

Abstract

The application belongs to the technical field of concrete admixtures, and discloses a solid shrinkage-reducing polycarboxylic water reducing agent and a preparation method and application thereof. The method adopts a solvent-free bulk polymerization process, melts and heats polyether macromonomer, adds an initiator, and dropwise adds acrylic acid, ester monomer M-TB and a chain transfer agent for melt copolymerization. After the reaction is completed, the product is cooled to obtain a solid product, and no spray drying post-treatment is needed, so that energy consumption is low, no solvent is discharged, and the product is convenient to transport. The ester monomer M-TB is introduced to make the water reducing agent molecules have a shrinkage-reducing group, which can effectively reduce the pore solution surface tension, inhibit water evaporation, and significantly reduce the drying shrinkage of cement mortar. The shrinkage-reducing polycarboxylic water reducing agent prepared by the method has a 28d drying shrinkage reduction rate of 29.3% when the mixing amount is 0.1%, has no negative effect on the compressive strength, realizes the synergistic optimization of water reducing, shrinkage reducing and strength increasing, has a lower mixing amount compared with a commercially available shrinkage-reducing agent, has no compatibility problem, and is suitable for industrial production.

Description

Technical Field

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

[0002] Polycarboxylate superplasticizers, as third-generation high-performance superplasticizers, have become an indispensable core component of modern high-performance concrete due to their outstanding advantages such as high water reduction rate, good slump retention, strong molecular structure designability, and environmental friendliness. They are widely used in major engineering projects such as high-speed railways, cross-sea bridges, and super high-rise buildings. Compared with traditional naphthalene-based and melamine-based superplasticizers, polycarboxylate superplasticizers have superior water reduction and shrinkage resistance. Although polycarboxylate superplasticizers have good shrinkage resistance, they still cannot completely suppress shrinkage cracking in concrete. Shrinkage cracking in concrete is one of the main factors affecting its structural durability and service life. Statistics show that non-load-bearing cracks caused by shrinkage deformation account for as much as 80% of concrete cracks, especially drying shrinkage and autogenous shrinkage, which have become common quality problems in modern concrete engineering and are key issues that urgently need to be addressed in the field of concrete admixtures.

[0003] To suppress concrete shrinkage, engineering projects often employ measures such as adding expansive agents, fibers, or shrinkage-reducing agents. Expansive agents generate hydration products like ettringite, causing volume expansion to compensate for concrete shrinkage. However, they suffer from drawbacks including high water demand, strict curing conditions, high dosage (typically 6%–15% of cementitious materials), and adverse effects on concrete fluidity and strength. While fiber incorporation can constrain concrete deformation and inhibit crack propagation, fibers are randomly distributed within the concrete, are expensive, and may affect the workability of fresh concrete. Shrinkage-reducing agents are surfactants that reduce capillary pressure by lowering the surface tension of the capillary solution, making them an effective means of suppressing concrete shrinkage. However, traditional shrinkage-reducing agents also have significant drawbacks: firstly, they require high dosages (usually 1%–3% of cementitious materials), resulting in high costs; secondly, they have compatibility issues when compounded with polycarboxylate superplasticizers, easily leading to segregation or performance degradation; and thirdly, they have a certain air-entraining effect, negatively impacting concrete strength.

[0004] Polycarboxylate dispersants are highly designable in molecular structure and have environmentally friendly preparation processes. Shrink-reducing functional groups can be assembled onto the macromolecules according to actual needs, allowing for the development of polycarboxylate superplasticizers with shrinkage-reducing properties. Currently, the mainstream polymerization methods for polycarboxylate dispersants include solution polymerization and bulk polymerization, with aqueous solution polymerization being the dominant method. To improve transportation convenience and reduce long-distance transportation costs, spray drying is often performed after aqueous solution polymerization to obtain solid polycarboxylate superplasticizers. However, the polymer is prone to degradation at high temperatures, and this method adds approximately 150-200 kWh of energy consumption per ton of product. Therefore, it suffers from high energy consumption, large equipment investment, and poor product performance. Summary of the Invention

[0005] In order to overcome the shortcomings and deficiencies of the existing technology, the primary objective of this invention is to provide a solid shrinkage-reducing polycarboxylate superplasticizer, which is prepared based on bulk polymerization and has excellent water-reducing and dispersing properties, shrinkage reduction properties and mechanical reinforcement effects.

[0006] Another objective of this invention is to provide a method for preparing the above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer, which is solvent-free, simple in process, low in energy consumption, and can directly obtain solid products.

[0007] Another object of the present invention is to provide the application of the above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer in concrete or mortar.

[0008] The objective of this invention is achieved through the following technical solution: A solid shrinkage-reducing polycarboxylate superplasticizer is prepared by melt bulk polymerization of the following raw materials in parts by mass: 60-80 parts polyether macromonomer, 5-10 parts acrylic acid, 3-10 parts esterified monomer M-TB, 0.5-2 parts initiator, and 0.3-0.6 parts chain transfer agent.

[0009] The polyether macromonomer is methyl allyl polyoxyethylene ether or isopentenyl polyoxyethylene ether, with a molecular weight of 100-10000.

[0010] The esterified monomer M-TB has the following structural formula (1): (1).

[0011] The esterified monomer M-TB is maleic acid mono(triethylene glycol monobutyl ether) ester obtained by esterification reaction of maleic anhydride and triethylene glycol monobutyl ether. Specifically, it is prepared according to the following steps: maleic anhydride and triethylene glycol monobutyl ether are mixed in a molar ratio of 1:(1-2), p-toluenesulfonic acid catalyst is added, and the mixture is reacted at 100-140℃ for 3-6 hours to obtain the esterified monomer M-TB.

[0012] The initiator is benzoyl peroxide, azobisisobutyronitrile, azobisisovalerate, or tert-butyl peroxide, and the chain transfer agent is at least one of ethylene glycol dimercaptoacetate, trimethylolpropane tris(2-mercaptoacetate), and pentaerythritol tetramercaptoacetate.

[0013] The preparation method of the above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer includes the following steps: (1) Add the polyether macromonomer to the reactor, heat it to 70-90℃ to melt it completely, add the initiator, and obtain molten polyether macromonomer; (2) Mix acrylic acid, esterified monomer M-TB and chain transfer agent evenly to obtain a mixed monomer solution. Then, under stirring conditions, add the mixed monomer solution dropwise to the molten polyether macromonomer obtained in step (1). The dropwise addition time is controlled at 0.5-3 hours. After the dropwise addition is completed, keep the reaction at 75-90℃ for 1-2 hours. (3) After the reaction is complete, the material is discharged after cooling to 40-60℃ and cooled to room temperature to obtain solid shrinkage-reducing polycarboxylate superplasticizer.

[0014] The dropping time in step (2) is set according to the half-life of the initiator at the reaction temperature to ensure the dynamic balance between the concentration of free radicals and the concentration of monomers during the reaction.

[0015] The above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer is used in concrete or mortar.

[0016] Compared with commercially available shrinkage reducers and expansion agents, the solid shrinkage-reducing polycarboxylate superplasticizer has a lower dosage when achieving a similar shrinkage rate, does not have compatibility issues with compounding, and has no negative effect on strength; specifically, at a dosage of 0.1%, the 28-day drying shrinkage rate is reduced by 29.3%.

[0017] The present invention has the following advantages and beneficial effects compared with the prior art: (1) The present invention adopts a bulk polymerization method, using molten polyether macromonomer as the reaction medium. No additional solvent is required. After the reaction, a solid product with a solid content of nearly 100% is obtained directly. This avoids the high energy consumption process of spray drying after aqueous solution polymerization. The process is simple, environmentally friendly, and low in cost. The product is also easy to transport and store for a long time. (2) By introducing the self-made maleic anhydride functional monomer M-TB, the present invention successfully grafts the triethylene glycol monobutyl ether shrinkage-reducing group onto the polycarboxylic acid molecular backbone; compared with the traditional polycarboxylic acid water-reducing agent compound shrinkage-reducing agent, the solid shrinkage-reducing polycarboxylic acid water-reducing agent system of the present invention not only retains the high water-reducing performance, but also has a lower additive dosage under the same shrinkage-reducing effect, and there is no compatibility problem of compounding; (3) Mechanical properties studies show that the introduction of an appropriate amount of shrinkage monomer can improve the mechanical properties of cement mortar; compared with traditional polycarboxylate superplasticizer compound expansion agent, it can significantly reduce the amount of admixture, and the superplasticizer of the present invention has no negative impact on the strength of concrete. Attached Figure Description

[0018] Figure 1 The NMR spectrum of the esterified monomer M-TB is shown. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Preferably, the esterified monomer M-TB in the following examples is prepared by the following method: maleic anhydride and triethylene glycol monobutyl ether are mixed in a molar ratio of 1:1.2, p-toluenesulfonic acid catalyst is added, and the mixture is reacted at 120°C for 4 hours to obtain the esterified monomer M-TB.

[0021] Figure 1 The NMR spectrum of the obtained esterified monomer M-TB shows a broad singlet at δ 11.19 ppm, attributed to the proton signal of the carboxyl group (-COOH), confirming the formation of a free carboxyl group after ring opening of maleic anhydride. A multiplet at δ 6.32 ppm indicates that the double bond was not destroyed during the reaction. A triplet at δ 4.33 ppm is attributed to the methylene group (-COO-CH) attached to the ester bond. 2- This is direct evidence of successful ester bond formation. NMR results confirm the successful synthesis of the target maleic anhydride functional monomer via esterification. The obtained esterified monomer M-TB has the structural formula shown in equation (1): (1).

[0022] The mass ratios of polyether macromonomer, acrylic acid, and esterified monomer M-TB, as well as the dropping time in step (2) in the following examples are shown in Table 1.

[0023] Example 1: A solid shrinkage-reducing polycarboxylate superplasticizer is prepared by melt bulk polymerization of the following raw materials in parts by mass: 70 parts methyl allyl polyoxyethylene ether, 7.4 parts acrylic acid, 3.3 parts esterified monomer M-TB, 1.4 parts initiator benzoyl peroxide, and 0.4 parts chain transfer agent ethylene glycol dithiocarboxylate.

[0024] The preparation method of the above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer specifically includes the following steps: (1) Add methyl allyl polyoxyethylene ether to the reactor, heat it to 75°C to melt it completely, and then add the initiator benzoyl peroxide to obtain molten polyether macromonomer; (2) Mix acrylic acid, esterified monomer M-TB and chain transfer agent ethylene glycol dithiocarbamate evenly to obtain a mixed monomer solution. Under stirring conditions, add the mixed monomer solution dropwise at a constant rate to the molten polyether macromonomer obtained in step (1) for a time of 2 hours. (3) After the addition is complete, continue to keep the reaction at 75°C for 1 hour; (4) After the reaction is complete, the material is discharged after cooling to 50°C and cooled to room temperature to obtain solid shrinkage-reducing polycarboxylate superplasticizer.

[0025] Example 2: A solid shrinkage-reducing polycarboxylate superplasticizer is prepared by melt bulk polymerization of the following raw materials in parts by mass: 70 parts ethylene glycol monovinyl polyethylene glycol ether, 6.3 parts acrylic acid, 6.6 parts esterified monomer M-TB, 1.4 parts initiator azobisisobutyronitrile, and 0.4 parts chain transfer agent trimethylolpropane dimercaptoacetic acid.

[0026] The preparation method of the above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer specifically includes the following steps: (1) Add ethylene glycol monovinyl polyethylene glycol ether to a reaction vessel, heat it to 75°C to melt it completely, and then add the initiator azobisisobutyronitrile to obtain molten polyether macromonomer; (2) Mix acrylic acid, esterified monomer M-TB and chain transfer agent dithiocarboxylic acid trimethylolpropane ester evenly to obtain a mixed monomer solution. Under stirring conditions, add the mixed monomer solution dropwise at a uniform rate to the molten polyether macromonomer obtained in step (1) and control the dropwise addition time to 2 hours. (3) After the addition is complete, continue to keep the reaction at 75°C for 1 hour; (4) After the reaction is complete, the material is discharged after cooling to 50°C and cooled to room temperature to obtain solid shrinkage-reducing polycarboxylate superplasticizer.

[0027] Example 3: A solid shrinkage-reducing polycarboxylate superplasticizer is prepared by melt bulk polymerization of the following raw materials in parts by mass: 70 parts isopentenyl alcohol polyoxyethylene ether, 5.3 parts acrylic acid, 9.9 parts esterified monomer M-TB, 1.4 parts initiator azobisisobutyronitrile, and 0.4 parts chain transfer agent ethylene glycol dithiocarboxylate.

[0028] The preparation method of the above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer specifically includes the following steps: (1) Add isopentenyl alcohol polyoxyethylene ether to the reactor, heat it to 75°C to melt it completely, and then add the initiator azobisisobutyronitrile to obtain molten polyether macromonomer; (2) Mix acrylic acid, esterified monomer M-TB and chain transfer agent ethylene glycol dithiocarbamate evenly to obtain a mixed monomer solution. Under stirring conditions, add the mixed monomer solution dropwise at a constant rate to the molten polyether macromonomer obtained in step (1) for a time of 2 hours. (3) After the addition is complete, continue to keep the reaction at 75°C for 1 hour; (4) After the reaction is complete, the material is discharged after cooling to 50°C and cooled to room temperature to obtain solid shrinkage-reducing polycarboxylate superplasticizer.

[0029] Example 4: A solid shrinkage-reducing polycarboxylate superplasticizer is prepared by melt bulk polymerization of the following raw materials in parts by mass: 70 parts methyl allyl polyoxyethylene ether, 7.4 parts acrylic acid, 3.3 parts esterified monomer M-TB, 1.4 parts initiator azobisisobutyronitrile, and 0.4 parts chain transfer agent ethylene glycol dithiocarboxylate.

[0030] The preparation method of the above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer specifically includes the following steps: (1) Add methyl allyl polyoxyethylene ether to the reactor, heat it to 75°C to melt it completely, and then add the initiator azobisisobutyronitrile to obtain molten polyether macromonomer; (2) Mix acrylic acid, esterified monomer M-TB and chain transfer agent ethylene glycol dithiocarbamate evenly to obtain a mixed monomer solution. Under stirring conditions, add the mixed monomer solution dropwise at a uniform rate to the molten polyether macromonomer obtained in step (1). The dropwise addition time is controlled at 2.5 hours. (3) After the addition is complete, continue to keep the reaction at 75°C for 1 hour; (4) After the reaction is complete, the material is discharged after cooling to 50°C and cooled to room temperature to obtain solid shrinkage-reducing polycarboxylate superplasticizer.

[0031] Example 5: A solid shrinkage-reducing polycarboxylate superplasticizer is prepared by melt bulk polymerization of the following raw materials in parts by mass: 70 parts methyl allyl polyoxyethylene ether, 7.4 parts acrylic acid, 1.6 parts esterified monomer M-TB, 1.4 parts initiator azobisisobutyronitrile, and 0.4 parts chain transfer agent ethylene glycol dimercaptoacetate.

[0032] The preparation method of the above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer specifically includes the following steps: (1) Add methyl allyl polyoxyethylene ether to the reactor, heat it to 75°C to melt it completely, and then add the initiator azobisisobutyronitrile to obtain molten polyether macromonomer; (2) Mix acrylic acid, esterified monomer M-TB and chain transfer agent ethylene glycol dithiocarbamate evenly to obtain a mixed monomer solution. Under stirring conditions, add the mixed monomer solution dropwise at a uniform rate to the molten polyether macromonomer obtained in step (1). The dropwise addition time is controlled at 1.5 hours. (3) After the addition is complete, continue to keep the reaction at 75°C for 1 hour; (4) After the reaction is complete, the material is discharged after cooling to 50°C and cooled to room temperature to obtain solid shrinkage-reducing polycarboxylate superplasticizer.

[0033] Comparative Example 1: A solid shrinkage-reducing polycarboxylate superplasticizer is prepared by melt bulk polymerization of the following raw materials in parts by mass: 70 parts methyl allyl polyoxyethylene ether, 8.4 parts acrylic acid, 1.4 parts azobisisobutyronitrile (AIB) initiator, and 0.4 parts ethylene glycol dithiocarboxylate (DMCA) chain transfer agent.

[0034] The preparation method of the above-mentioned solid shrinkage-reducing polycarboxylate superplasticizer specifically includes the following steps: (1) Add methyl allyl polyoxyethylene ether to the reactor, heat it to 75°C to melt it completely, and then add the initiator azobisisobutyronitrile to obtain molten polyether macromonomer; (2) Mix acrylic acid and chain transfer agent ethylene glycol dithiocarbamate evenly to obtain a mixed monomer solution. Under stirring conditions, add the mixed monomer solution dropwise at a constant rate to the molten polyether macromonomer obtained in step (1). The dropwise addition time is controlled within 2 hours. (3) After the addition is complete, continue to keep the reaction at 75°C for 1 hour; (4) After the reaction is complete, the material is discharged after cooling to 50°C and cooled to room temperature to obtain solid shrinkage-reducing polycarboxylate superplasticizer.

[0035] Comparative Example 2 is a commercially available reduced-size polycarboxylate superplasticizer, which is a colorless to slightly yellow transparent liquid with an effective component of ≥20.0%.

[0036] The above Examples 1-5 and Comparative Examples 1-2 were used for performance testing. The tests were conducted according to the following standards, and the test results are shown in Table 2.

[0037] (1) Drying shrinkage rate: The test was conducted in accordance with JC / T 603-2004 "Test Method for Drying Shrinkage of Cement Mortar". The mortar mix ratio was cement:standard sand = 1:2, and the water-reducing agent dosage was 0.1%. 25mm×25mm×280mm specimens were formed and cured at a temperature of 20±3℃ and a relative humidity of 50±4%. The length change was measured after 28 days and the drying shrinkage rate was calculated.

[0038] (2) Cement mortar strength: The test was conducted in accordance with GB / T 17671-1999 "Test Method for Cement Mortar Strength (ISO Method)". The mortar mix ratio was cement:standard sand = 1:3, the water-cement ratio was 0.30, the shrinkage reducer dosage was 1%, and the water-reducing agent dosage was 0.1%. 40mm×40mm×160mm specimens were formed and cured to a standard age of 28 days. The flexural and compressive strengths were then tested.

[0039] Table 1 shows the mass ratios and addition times of each raw material in Examples 1-5 and Comparative Example 1.

[0040] Table 2 compares the basic performance parameters of the water-reducing agents in Examples 1-5 and Comparative Examples 1-2.

[0041] As can be seen from the test results in Table 2, compared with the comparative example, the 28-day drying shrinkage rates of Examples 1-5 all decreased to varying degrees. Among them, Example 4 had the lowest 28-day drying shrinkage rate at 0.140%, which was 29.3% lower than that of Comparative Example 1 without M-TB. This indicates that the present invention effectively inhibits the drying shrinkage of cement mortar by introducing the shrinkage-reducing monomer M-TB. The 28-day flexural and compressive strengths of Examples 1-5 were all higher than those of the comparative example, with Example 4 having the highest flexural and compressive strengths, reaching 6.42 MPa and 62.9 MPa, respectively. This indicates that the shrinkage-reducing polycarboxylate superplasticizer prepared by the present invention, with a dosage of only 0.1%, not only has a good shrinkage-reducing effect but also improves flexural and compressive strength to varying degrees. Compared with Comparative Example 2, the solid shrinkage-reducing polycarboxylate superplasticizer can achieve a similar shrinkage-reducing effect with a lower dosage, does not have compatibility issues with compounding, and has no negative effect on strength.

[0042] In summary, the solid shrinkage-reducing polycarboxylate superplasticizer prepared under the raw material ratio and process conditions in Example 4 exhibits the best overall performance. At a dosage of 0.1%, the 28-day drying shrinkage rate can be reduced by 29.3%, and the flexural and compressive strengths can be increased by 16.3% and 10.4%, respectively, achieving synergistic optimization of shrinkage reduction and reinforcement.

[0043] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A solid shrinkage-reducing polycarboxylate superplasticizer, characterized in that: The water-reducing agent is made by melt bulk polymerization of the following raw materials in parts by mass: 60-80 parts polyether macromonomer, 5-10 parts acrylic acid, 3-10 parts esterified monomer M-TB, 0.5-2 parts initiator, and 0.3-0.6 parts chain transfer agent.

2. The solid shrinkage-reducing polycarboxylate superplasticizer according to claim 1, characterized in that: The polyether macromonomer is methyl allyl polyoxyethylene ether or isopentenyl polyoxyethylene ether, with a molecular weight of 100-10000.

3. The solid shrinkage-reducing polycarboxylate superplasticizer according to claim 1, characterized in that: The esterified monomer M-TB has the following structural formula (1): （1）。 4. The solid shrinkage-reducing polycarboxylate superplasticizer according to claim 1, characterized in that: The esterified monomer M-TB is maleic acid mono(triethylene glycol monobutyl ether) ester obtained by esterification reaction of maleic anhydride and triethylene glycol monobutyl ether. Specifically, it is prepared according to the following steps: maleic anhydride and triethylene glycol monobutyl ether are mixed in a molar ratio of 1:(1-2), p-toluenesulfonic acid catalyst is added, and the mixture is reacted at 100-140℃ for 3-6 hours to obtain the esterified monomer M-TB.

5. A solid shrinkage-reducing polycarboxylate superplasticizer according to claim 1, characterized in that: The initiator is benzoyl peroxide, azobisisobutyronitrile, azobisisovalerate, or tert-butyl peroxide, and the chain transfer agent is at least one of ethylene glycol dimercaptoacetate, trimethylolpropane tris(2-mercaptoacetate), and pentaerythritol tetramercaptoacetate.

6. A method for preparing a solid shrinkage-reducing polycarboxylate superplasticizer according to any one of claims 1-5, characterized in that... The following steps are included: (1) Add the polyether macromonomer to the reactor, heat it to 70-90℃ to melt it completely, add the initiator, and obtain molten polyether macromonomer; (2) Mix acrylic acid, esterified monomer M-TB and chain transfer agent evenly to obtain a mixed monomer solution. Then, under stirring conditions, add the mixed monomer solution dropwise to the molten polyether macromonomer obtained in step (1). The dropwise addition time is controlled at 0.5-3 hours. After the dropwise addition is completed, keep the reaction at 75-90℃ for 1-2 hours. (3) After the reaction is complete, the material is discharged after cooling to 40-60℃ and cooled to room temperature to obtain solid shrinkage-reducing polycarboxylate superplasticizer.

7. The preparation method according to claim 6, characterized in that: The dropping time in step (2) is set according to the half-life of the initiator at the reaction temperature to ensure the dynamic balance between the concentration of free radicals and the concentration of monomers during the reaction.

8. The application of the solid shrinkage-reducing polycarboxylate superplasticizer according to claim 1 in concrete or mortar.

9. The application according to claim 8, characterized in that: When the dosage of the solid shrinkage-reducing polycarboxylate superplasticizer is 0.1%, the 28-day drying shrinkage rate is reduced by 29.3%.

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