Slow-release polycarboxylate superplasticizer and preparation method thereof

Abstract

The invention relates to a slow-release polycarboxylic acid water reducing agent, which is prepared from the following raw materials in parts by weight: 90 to 260 parts of citronellyl ester-terminated polyether monomer; 20 to 32 parts of unsaturated ester monomer; 8-15 parts of an unsaturated acid monomer; 4-8 parts of a quaternary ammonium salt compound; 4-8 parts of an unsaturated amide monomer; 1.5 to 3.0 parts of an oxidizing agent; 0.2 to 0.4 part of a reducing agent; 0.8 to 1.5 parts of a chain transfer agent; and water; wherein the citronellyl ester terminated polyether monomer is prepared from the following raw materials: unsaturated ester, ethylene glycol monovinyl polyethylene glycol, a catalyst and a polymerization inhibitor. By introducing the citronellyl ester terminated polyether monomer, the branched chain density is reduced, the molecular chain is smoother, the fluidity of concrete can be maintained, the slump loss is delayed, and the introduction of the citronellyl ester terminated polyether monomer not only enhances the steric hindrance effect and slump loss resistance of the polycarboxylate superplasticizer, but also enhances the slump loss resistance of the polycarboxylate superplasticizer. And the concrete can keep good flowability for a long time.

Description

Technical Field

[0001] The invention relates to the technical field of concrete admixtures, in particular to a slow-release polycarboxylate water-reducing agent and a preparation method thereof. Background Art

[0002] Concrete is the largest and most widely used building material in the world. It is widely used in various types of buildings, bridges, tunnels and infrastructure construction. In recent years, with the continuous improvement of the scale and technical requirements of engineering construction, higher standards have been put forward for the performance of concrete. Concrete not only needs to have good durability, but also needs to meet performance requirements such as high fluidity, high strength, light weight and high crack resistance. At the same time, it should have the characteristics of low energy consumption, low cost and suitable for rapid construction. In addition, since concrete mixing plants are usually located in suburban areas outside the city, the workability and stability of concrete during transportation and construction has also become an important consideration.

[0003] The application of admixtures is an important way to improve concrete performance and promote the development of concrete technology. As one of the most important admixtures, concrete water reducers have significant effects in optimizing concrete performance, reducing water consumption, increasing strength and improving durability. Among them, polycarboxylic acid high-efficiency water reducers have become the most mainstream water reducer technology with their advantages of small dosage, high water reduction rate, strong slump retention ability, improved air content and reduced shrinkage.

[0004] However, in practical applications, the problem of too fast concrete slump loss is still a major technical difficulty in engineering construction. Concrete slump loss not only affects long-distance transportation, pumping and pouring, but may also lead to reduced construction efficiency and quality problems such as shrinkage cracking and reduced strength. To address this problem, the following methods are currently used:

[0005] Increasing water consumption: Slump loss can be delayed by increasing the water-cement ratio, but this will significantly increase the air content of concrete, reduce its impermeability, and have an adverse effect on strength and durability.

[0006] Increasing the dosage of water reducing agent: Although it can improve the slump loss to a certain extent, it is easy to cause problems such as early bleeding and segregation of concrete, which will further destroy workability and increase the difficulty of production quality control.

[0007] Adding retarders: retarders can delay the setting time and reduce the slump loss, but their effect is easily affected by temperature, which may cause fluctuations in construction quality. In addition, the difference in compatibility between retarders and cement may affect the later strength performance of concrete.

[0008] Therefore, the existing technology still has certain limitations and it is difficult to simultaneously meet the requirements for maintaining the fluidity of concrete and the construction quality requirements. In view of the above problems, by designing and modifying the molecular structure of polycarboxylate water-reducing agent, it is expected to develop a new type of polycarboxylate water-reducing agent with a slow-release function, thereby effectively improving the slump retention ability of concrete, improving the workability and crack resistance of concrete, and meeting the needs of high-performance concrete under long-distance transportation and complex construction conditions. The research and development of this technology is of great significance to promoting technological progress in the field of concrete admixtures and the sustainable development of the construction industry. Summary of the invention

[0009] Based on this, it is necessary to provide a new type of polycarboxylic acid water-reducing agent with a slow-release function, so as to effectively improve the slump retention ability of concrete, improve the workability and crack resistance of concrete, and meet the needs of high-performance concrete under long-distance transportation and complex construction conditions.

[0010] To achieve the above object, the present invention provides a technical solution:

[0011] A sustained-release polycarboxylate water-reducing agent, wherein the raw materials for preparing the sustained-release polycarboxylate water-reducing agent include, by weight:

[0012] 90-260 parts of citronellyl end-capped polyether monomer;

[0013] 20-32 parts of unsaturated ester monomer;

[0014] 8-15 parts of unsaturated acid monomer;

[0015] 4 to 8 parts of quaternary ammonium salt compound;

[0016] 4 to 8 parts of unsaturated amide monomer;

[0017] 1.5-3.0 parts of oxidant;

[0018] 0.2-0.4 parts of reducing agent;

[0019] 0.8 to 1.5 parts of a chain transfer agent; and water;

[0021] The raw materials for preparing the citronellal end-capped polyether monomer include unsaturated ester, ethylene glycol monovinyl polyethylene glycol, a catalyst and an inhibitor.

[0022] Specifically, the reducing agent includes at least one of ascorbic acid, sodium formaldehyde sulfoxylate, sodium sulfite, bleaching powder, sodium bisulfite and sodium hypophosphite, wherein the sodium hypophosphite can also serve as a chain transfer agent;

[0023] The oxidant comprises at least one of hydrogen peroxide, sodium peroxide, potassium peroxide, magnesium peroxide, sodium persulfate, ammonium persulfate, sodium dichromate, potassium dichromate and potassium permanganate;

[0024] The chain transfer agent includes at least one of thioglycolic acid, sodium hypophosphite, trisodium phosphate, mercaptopropionic acid, mercaptoethanol and thioglycolic acid;

[0025] The unsaturated acid monomer includes at least one of acrylic acid, methacrylic acid, fumaric acid, maleic anhydride and itaconic acid;

[0026] The unsaturated ester monomer includes at least one of hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate and vinyl acetate.

[0027] Preferably, the structural formula of the citronellal end-capped polyether monomer is as follows:

[0028]

[0029] Wherein, R1 is CH3-, H-, CH3CH2CH2- or CH3CH2-;

[0030] R2 is CH3-, H-, CH3CH2CH2- or CH3CH2-;

[0031] R3 is CH3-, H-, CH3CH2CH2- or CH3CH2-.

[0032] Preferably, the unsaturated ester comprises at least one of citronellyl acetate, citronellyl formate, citronellyl butyrate and citronellyl propionate, and its general structural formula is: R-COOC6H 11 CH(OH)CH2CH2CH3, wherein R is CH3, H, CH3CH2CH2, CH3CH2.

[0033] Preferably, the catalyst comprises at least one of concentrated sulfuric acid, heteropoly acid, stannous oxide and dibutyltin oxide.

[0034] Preferably, the polymerization inhibitor includes at least one of p-hydroxyanisole, hydroquinone, p-tert-butylcatechol and phenothiazine.

[0035] Preferably, the weight ratio of the ethylene glycol monovinyl polyethylene glycol, the unsaturated ester, the catalyst and the inhibitor is (160-180): (100-140): (3-6): (0.4-0.8).

[0036] Preferably, the structural formula of the quaternary ammonium salt compound is as follows:

[0037] Preferably, the raw materials for preparing the sustained-release polycarboxylate water-reducing agent further include: 0.01 to 0.02 parts of ferrous sulfate, in parts by weight.

[0039] The present invention also provides a method for preparing a sustained-release polycarboxylate water-reducing agent, the method comprising the steps of:

[0040] The citronellal end-capped polyether monomer, the unsaturated amide monomer, the oxidant and water are stirred evenly to completely dissolve them to obtain a base solution;

[0041] Add liquid A and liquid B dropwise to the base liquid, and after the addition is completed, continue to keep warm and react for 1h to 2h to obtain the slow-release polycarboxylate water-reducing agent;

[0042] Wherein, the liquid A is an aqueous solution of an unsaturated acid monomer, an unsaturated ester monomer and a quaternary ammonium salt compound;

[0043] Liquid B is an aqueous solution of a reducing agent and a chain transfer agent.

[0044] Preferably, the method for preparing the quaternary ammonium salt compound monomer comprises the steps of:

[0045] dissolving dopamine in an acidic solution to obtain a dopamine solution;

[0046] dissolving an aldehyde compound in an alcohol solution to obtain an aldehyde compound solution;

[0047] Adding an aldehyde compound solution to the dopamine solution, stirring for 18 to 24 hours, and adjusting the pH value to neutral to obtain compound A;

[0048] In a water bath at 55°C to 65°C, the compound A is dissolved in an alcohol solution, a base is added, and after reacting for 3h to 5h, a 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is added dropwise, and the reaction is continued for 4h to 5h to obtain a quaternary ammonium salt compound.

[0049] Preferably, the preparation process of the citronella-terminated polyether monomer is as follows:

[0050] The unsaturated ester and ethylene glycol monovinyl polyethylene glycol are placed in a reactor, and then a catalyst and a polymerization inhibitor are added, and the reaction is carried out at a constant temperature of 100 to 120° C. for 8 to 12 hours. When the reaction is completed, a citronellal end-capped polyether monomer is obtained.

[0051] Beneficial effects of the present invention:

[0052] 1. The raw materials required for the preparation of the present invention are common and easily available, the cost is low, the preparation process is simple, and it is green and environmentally friendly;

[0053] 2. The present invention reduces the branch density by introducing citronella ester-terminated polyether monomers, making the molecular chain more flexible, which helps to maintain the fluidity of concrete and delay the slump loss. In addition, the introduction of citronella ester-terminated polyether monomers not only enhances the steric hindrance effect and slump retention ability of the polycarboxylate water reducer, but also enables the concrete to maintain good fluidity for a long time.

[0054] 3. In the preparation method of the present invention, citronellal end-capped polyether monomer, unsaturated ester monomer, unsaturated carboxylic acid monomer, unsaturated amide monomer, quaternary ammonium salt compound, oxidant, reducing agent and water are copolymerized to introduce carboxylate, ester and amide groups into the polymer molecular structure.

[0055] The citronellyl ester-terminated polyether macromonomer in the side chain of the water reducer is connected to the main chain of the water reducer through oxygen, which reduces the spatial resistance of the side chain swing of the polyether macromonomer in the side chain of the water reducer, makes the polyether macromonomer in the side chain of the water reducer more free, improves the wrapping and entanglement of the polyether macromonomer in the side chain of the water reducer, and thus has a strong adsorption capacity; at the same time, the ester group is continuously hydrolyzed during the cement hydration process, continues to react with the cement hydration product, inhibits the growth of Ca(OH)2 and AFt crystal nuclei, slows down the hydration rate, and prolongs the cement hydration induction period, thereby improving the dispersion retention. The amide group protects the carboxyl group to a certain extent, reduces the initial adsorption rate of the carboxyl group in the water reducer on cement particles, and gradually hydrolyzes in an alkaline environment, and then releases the carboxyl group, which continues to slowly adsorb the cement particles, thereby showing good dispersibility and fluidity.

[0056] 4. The polycarboxylate water-reducing agent prepared by the method of the present invention has the advantages of low dosage, high water reduction rate, good workability, and can significantly improve the sustained release of concrete and has a wide adaptability to the mud content of sand and gravel. DETAILED DESCRIPTION

[0057] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0058] In the examples, the test methods used are conventional methods unless otherwise specified, and the materials, reagents, etc. used are all commercially available unless otherwise specified.

[0059] 1. Preparation of citronellyl ester-terminated polyether monomer A

[0060] 1. Citronellyl terminated polyether monomer A1:

[0061] 100 g of citronellyl acetate and 160 g of ethylene glycol monovinyl polyethylene glycol were placed in a reactor, and then 3 g of concentrated sulfuric acid and 0.3 g of hydroquinone were added. The mixture was reacted at a constant temperature of 115° C. for 8 h under a nitrogen atmosphere. After the reaction, the temperature was lowered to 50° C. to obtain citronellyl end-capped polyether monomer A1.

[0062] 2. Citronellyl terminated polyether monomer A2:

[0063] 100 g of citronellyl butyrate and 160 g of ethylene glycol monovinyl polyethylene glycol were placed in a reactor, and then 3 g of stannous oxide and 0.3 g of phenothiazine were added. The mixture was reacted at a constant temperature of 115° C. for 8 h under a nitrogen atmosphere. After the reaction, the temperature was lowered to 50° C. to obtain citronellyl butyrate-terminated polyether monomer A2.

[0064] 2. Preparation of Quaternary Ammonium Salt Compound B

[0065] 1. Preparation of quaternary ammonium salt compound B1:

[0066] 1.6 g of dopamine was dissolved in 80 mL of acetic acid, and then 1.2 g of salicylaldehyde was dissolved in 100 mL of anhydrous methanol and added to the dopamine solution, and stirred for 18 hours. The pH value was adjusted to 7 using sodium hydroxide solution, and then washed with an appropriate washing solvent and vacuum dried to obtain compound A.

[0067] 1.6 g of compound A was dissolved in 100 mL of isopropanol, 10 mL of 40% sodium hydroxide was added, and the mixture was reacted in a water bath at 55° C. for 4 h. Subsequently, 30 mL of 3-chloro-2-hydroxypropyltrimethylammonium chloride aqueous solution (40 wt.%) was slowly added dropwise under the same water bath conditions, the temperature was controlled at 60° C., and the reaction was continued for 4-5 hours. Finally, the obtained product was washed with an alcohol solution and dried under vacuum to obtain a quaternary ammonium salt compound B1.

[0068] 2. Preparation of quaternary ammonium salt compound B2:

[0069] 1.6 g of dopamine was dissolved in 80 mL of acetic acid, and then 2.0 g of 4-bromo-2-hydroxybenzaldehyde was dissolved in 100 mL of anhydrous methanol and added to the dopamine solution, and stirred for 24 hours. The pH value was adjusted to neutral using a sodium hydroxide solution, and then washed with an appropriate washing solvent and vacuum dried to obtain compound A.

[0070] 1.6 g of compound A was dissolved in 100 mL of isopropanol, 10 mL of 40% sodium hydroxide was added, and the mixture was reacted in a water bath at 55° C. for 4 h. Subsequently, 30 mL of an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (wt. 40%) was slowly added dropwise under the same water bath conditions, the temperature was controlled at 60° C., and the reaction was continued for 4-5 hours. Finally, the resulting product was washed with an alcohol solution and dried under vacuum to obtain a quaternary ammonium salt compound B2.

[0071] 3. Preparation of quaternary ammonium salt compound B3:

[0072] 1.6 g of dopamine was dissolved in 80 mL of acetic acid, and then 1.5 g of o-vanillin was dissolved in 100 mL of anhydrous methanol and added to the dopamine solution, and stirred for 20 hours. The pH value was adjusted to neutral using a sodium hydroxide solution, and then washed with an appropriate washing solvent and vacuum dried to obtain compound A.

[0073] Next, 1.6 g of compound A was dissolved in 100 mL of isopropanol, 10 mL of 40% sodium hydroxide was added, and the mixture was reacted in a water bath at 55° C. for 4 h. Subsequently, 30 mL of an aqueous solution of 3-chloro-2-hydroxypropyltrimethylammonium chloride (wt. 40%) was slowly added dropwise under the same water bath conditions, the temperature was controlled at 60° C., and the reaction was continued for 4-5 hours. Finally, the resulting product was washed with an alcohol solution and dried under vacuum to obtain a quaternary ammonium salt compound B3.

[0074] 3. Preparation of sustained-release polycarboxylate water reducer

[0075] Example 1

[0076] 180 g of citronellyl end-capped polyether monomer A1 and 300 g of water were placed in a four-necked flask, stirred and dissolved, and then 0.01 g of ferrous sulfate, 4 g of acrylamide and 1.5 g of hydrogen peroxide were added, and the reaction temperature was adjusted to 35° C. to obtain a base solution.

[0077] Liquid A and liquid B are added dropwise to the bottom liquid in the four-necked flask at the same time. After the addition is completed, the mixture is kept warm for 1 hour, and then liquid alkali is added for neutralization to obtain a slow-release polycarboxylate water-reducing agent.

[0078] Liquid A is a solution prepared from 10 g of acrylic acid, 24 g of hydroxyethyl acrylate, 4 g of quaternary ammonium salt compound B1 and 10 g of water, and the dropwise addition time of liquid A is 70 min;

[0079] Solution B is a solution prepared from 0.2 g of ascorbic acid, 0.10 g of mercaptoethanol and 42 g of water, and the dropwise addition time of solution B is 60 min.

[0080] Example 2

[0081] 180 g of citronella ester-terminated polyether monomer A2 and 300 g of water were placed in a four-necked flask, stirred and dissolved, and then 0.01 g of ferrous sulfate, 4 g of acrylamide and 1.5 g of hydrogen peroxide were added, and the reaction temperature was adjusted to 20° C. to obtain a base solution.

[0082] Liquid A and liquid B are added dropwise to the bottom liquid in the four-necked flask at the same time. After the addition is completed, the mixture is kept warm for 2 hours, and then liquid alkali is added for neutralization to obtain a slow-release polycarboxylate water-reducing agent.

[0083] Liquid A is a solution prepared from 10 g of methacrylic acid, 24 g of hydroxypropyl acrylate, 4 g of quaternary ammonium salt compound B2 and 10 g of water, and the dropwise addition time of liquid A is 50 min;

[0084] Liquid B is a solution prepared from 0.2 g of bleaching powder, 1.5 g of sodium hypophosphite and 42 g of water, and the addition time of liquid B is 80 min.

[0085] Example 3

[0086] 90 g of citronellyl ester-terminated polyether monomer A1, 90 g of ethylene glycol monovinyl polyethylene glycol ether and 300 g of water were placed in a four-necked flask, stirred and dissolved, and then 0.01 g of ferrous sulfate, 4 g of acrylamide and 1.5 g of hydrogen peroxide were added, and the reaction temperature was adjusted to 30° C. to obtain a base solution.

[0087] Liquid A and liquid B are added dropwise to the bottom liquid in the four-necked flask at the same time. After the addition is completed, the mixture is kept warm for 1.5 hours, and then liquid alkali is added for neutralization to obtain a slow-release polycarboxylate water-reducing agent.

[0088] Liquid A is a solution prepared from 10 g of acrylic acid, 24 g of hydroxyethyl acrylate, 4 g of quaternary ammonium salt compound B3 and 10 g of water. The dropwise addition time of liquid A is 60 min.

[0089] Liquid B is a solution prepared from 0.2 g of sodium formaldehyde sulfoxylate, 0.10 g of thioglycolic acid and 42 g of water, and the dropwise addition time of liquid B is 70 min.

[0090] Comparative Example 1

[0091] The difference from Example 1 is that the citronellal end-capped polyether monomer A1 is replaced with an equal amount of ethylene glycol monovinyl polyethylene glycol ether.

[0092] Comparative Example 2

[0093] The difference from Example 1 is that no quaternary ammonium salt compound is added, and the amount of water is adjusted so that the solid content of the prepared slow-release polycarboxylate water-reducing agent is the same as that in Example 1.

[0094] Comparative Example 3

[0095] Commercially available slow-release water reducer Point-THS.

[0096] The polycarboxylate water-reducing agent samples synthesized in Examples 1-3 and Comparative Examples 1-3 and commercially available polycarboxylate water-reducing agents were tested for initial slump and expansion of concrete and slump and expansion over time of the polycarboxylate water-reducing agent samples synthesized in Examples 1-3 and Comparative Examples 1-2 and commercially available polycarboxylate water-reducing agents according to GB8076-2008 "Concrete Admixtures" and GB 8077-2023 "Test Method for Homogeneity of Concrete Admixtures". The concrete mix ratios are shown in Table 1, and the results are shown in Table 2.

[0097] Table 1 Concrete mix ratio

[0098]

[0099] Table 2 Concrete performance test results

[0100]

[0101]

[0102] As can be seen from the results in Table 2, the experimental results of Examples 1 to 3 and Comparative Examples 1 to 3 show that in the concrete experiment, when the initial expansion degree of the polycarboxylate water-reducing agent prepared by the present invention is equivalent, the dosage of the water-reducing agent used in the embodiment is much lower than that in the comparative example, which can explain that the application performance (slow-release performance) of the concrete of the embodiment is much better than that of the reference sample and the comparative sample. Where the citronella ester-terminated polyether monomer is not added, the sustained-release ability of the concrete is poor; where the quaternary ammonium salt compound is not added, the sustained-release ability is poor when the dosage is high. The polycarboxylate water-reducing agent prepared by the present invention has good sustained-release performance, can improve the workability of concrete, and has a significant improvement in mechanical properties, has no adverse effects, is widely applicable, and is fast to prepare and efficient.

[0103] It should be noted that the specific parameters or some reagents in the above embodiments are specific embodiments or preferred embodiments of the present invention, rather than limiting the present invention; those skilled in the art can make adaptive adjustments within the scope of the present invention.

Claims

1. A sustained-release polycarboxylate water-reducing agent, characterized in that: The raw materials for preparing the sustained-release polycarboxylate water-reducing agent include, by weight: water; The raw materials for preparing the citronellal end-capped polyether monomer include unsaturated ester, ethylene glycol monovinyl polyethylene glycol, a catalyst and an inhibitor.

2. The sustained-release polycarboxylate water-reducing agent according to claim 1, characterized in that: The structural formula of the citronellyl end-capped polyether monomer is as follows: Wherein, R1 is CH3-, H-, CH3CH2CH2- or CH3CH2-; R2 is CH3-, H-, CH3CH2CH2- or CH3CH2-; R3 is CH3-, H-, CH3CH2CH2- or CH3CH2-.

3. The sustained-release polycarboxylate water-reducing agent according to claim 1, characterized in that: The unsaturated ester includes at least one of citronellyl acetate, citronellyl formate, citronellyl butyrate and citronellyl propionate.

4. The sustained-release polycarboxylate water-reducing agent according to claim 1, characterized in that: The catalyst includes at least one of concentrated sulfuric acid, heteropoly acid, stannous oxide and dibutyltin oxide.

5. The sustained-release polycarboxylate water-reducing agent according to claim 1, characterized in that: The polymerization inhibitor includes at least one of p-hydroxyanisole, hydroquinone, p-tert-butylcatechol and phenothiazine.

6. The sustained-release polycarboxylate water-reducing agent according to claim 1, characterized in that: The weight ratio of the ethylene glycol monovinyl polyethylene glycol, the unsaturated ester, the catalyst and the inhibitor is (160-180): (100-140): (3-6): (0.4-0.8).

7. The sustained-release polycarboxylate water-reducing agent according to claim 1, characterized in that: The structural formula of the quaternary ammonium salt compound is as follows: One of them.

8. The sustained-release polycarboxylate water-reducing agent according to claim 1, characterized in that: In parts by weight, the raw materials for preparing the sustained-release polycarboxylate water-reducing agent also include: 0.01-0.02 parts of ferrous sulfate.

9. A method for preparing a sustained-release polycarboxylate water-reducing agent according to any one of claims 1 to 8, characterized in that: The preparation method comprises the steps of: The citronellyl end-capped polyether monomer, the unsaturated amide monomer, the oxidant and water are stirred evenly to completely dissolve them to obtain a base solution; Add liquid A and liquid B dropwise to the base liquid, and after the addition is completed, continue to keep warm and react for 1h to 2h to obtain the slow-release polycarboxylate water-reducing agent; Wherein, the liquid A is an aqueous solution of an unsaturated acid monomer, an unsaturated ester monomer and a quaternary ammonium salt compound; Liquid B is an aqueous solution of a reducing agent and a chain transfer agent.

10. The method for preparing the sustained-release polycarboxylate water-reducing agent according to claim 9, characterized in that: The preparation method of the quaternary ammonium salt compound monomer comprises the steps of: dissolving dopamine in an acidic solution to obtain a dopamine solution; dissolving an aldehyde compound in an alcohol solution to obtain an aldehyde compound solution; Adding an aldehyde compound solution to the dopamine solution, stirring for 18 h to 24 h, and adjusting the pH value to neutral to obtain compound A; In a water bath at 55°C to 65°C, the compound A is dissolved in an alcohol solution, a base is added, and after reacting for 3h to 5h, a 3-chloro-2-hydroxypropyltrimethylammonium chloride solution is added dropwise, and the reaction is continued for 4h to 5h to obtain a quaternary ammonium salt compound.

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