A kind of collapse-retaining polycarboxylate water-reducing agent and preparation method thereof

Abstract

The present application discloses a slump-retaining polycarboxylate water reducer and a preparation method thereof, and relates to the technical field of concrete admixtures. Wherein, the slump-retaining polycarboxylate water reducer includes 15-20 parts by weight of unsaturated polyether monomer, 4.2-5.8 parts by weight of maleic anhydride-modified hydroxycellulose derivative, 3.8-4.5 parts by weight of functional monomer, 35-40 parts by weight of unsaturated carboxylic acid, 0.5-1 parts by weight of chain transfer agent, 0.5-1 parts by weight of oxidant, 0.25-0.5 parts by weight of reducing agent and 500 parts by weight of water; wherein, the maleic anhydride-modified hydroxycellulose derivative is obtained by reacting maleic anhydride with a hydroxycellulose derivative, and the functional monomer is obtained by reacting N-hydroxymethyl acrylamide and an aqueous solution of phosphorus pentoxide under the action of a catalyst. The slump-retaining polycarboxylate water reducer of the present application can be applied to the slump-retaining of concrete mixtures with large mud content in sand and gravel aggregates.

Description

Technical Field

[0001] The present application relates to the field of concrete admixtures, and in particular to a collapse-preserving polycarboxylate water-reducing agent and a preparation method thereof. Background Art

[0002] With the continuous expansion of infrastructure, the amount of concrete used has increased year by year. Among them, the slump and slump loss of concrete are important indicators for testing the working performance of concrete. At present, there is often a problem of long distance between the production enterprises of ready-mixed concrete and the construction sites. In addition, since high-quality sand and gravel aggregates have gradually become scarce due to large-scale development, and low-quality sand and gravel aggregates contain a lot of mud (mud content greater than 1.5%), it is easy to cause the slump loss of concrete to be too fast, which greatly reduces the working performance of ready-mixed concrete.

[0003] In order to improve the above problems, the related technology usually introduces groups with hydrolysis slow-release adsorption effect such as acrylate and acrylamide into polycarboxylic acid water-reducing agents. However, these polycarboxylic acid water-reducing agents have poor slump retention performance for concrete mixtures with high mud content in sand and gravel aggregates. Summary of the invention

[0004] In order to improve the problem in the related art that the polycarboxylate water reducer has poor slump-retaining performance for concrete mixtures with large mud content of sand and gravel aggregates, the present application provides a slump-retaining polycarboxylate water reducer and a preparation method thereof.

[0005] A collapse-retaining polycarboxylic acid water-reducing agent comprises 15-20 parts by weight of an unsaturated polyether monomer, 4.2-5.8 parts by weight of a maleic anhydride-modified hydroxycellulose derivative, 3.8-4.5 parts by weight of a functional monomer, 35-40 parts by weight of an unsaturated carboxylic acid, 0.5-1 parts by weight of a chain transfer agent, 0.5-1 parts by weight of an oxidant, 0.25-0.5 parts by weight of a reducing agent and 500 parts by weight of water; wherein the maleic anhydride-modified hydroxycellulose derivative is obtained by reacting maleic anhydride with a hydroxycellulose derivative, and the functional monomer is obtained by reacting N-hydroxymethyl acrylamide with an aqueous solution of phosphorus pentoxide under the action of a catalyst.

[0006] In the present application, the collapse-preserving polycarboxylate water-reducing agent is obtained by copolymerization of unsaturated polyether monomer, maleic anhydride-modified hydroxycellulose derivative, functional monomer and unsaturated carboxylic acid, wherein the collapse-preserving polycarboxylate water-reducing agent contains long side chains, has a large steric hindrance effect, and has good dispersibility, and can be stably adsorbed on the surface of cement particles, helping the cement particles to disperse, reducing the attraction between cement particles, and helping to form a slurry with good fluidity. In addition, the maleic anhydride-modified hydroxycellulose derivative and the functional monomer can synergistically improve the anti-mud performance and water-reducing performance of the collapse-preserving polycarboxylate water-reducing agent, and at the same time, can also release carboxyl groups in the later stage to ensure the fluidity of the later slurry, and can be suitable for the collapse-preserving of concrete mixtures with large mud content in sand and gravel aggregates.

[0007] In some specific embodiments, the unsaturated polyether monomer is at least one of ethylene glycol monovinyl polyoxyethylene ether, isopentenyl polyoxyethylene ether, and methyl allyl polyoxyethylene ether.

[0008] Preferably, in the ethylene glycol monovinyl polyoxyethylene ether, isopentenyl polyoxyethylene ether and methyl allyl polyoxyethylene ether, the degree of polymerization of the polyoxyethylene ether chain segment is in the range of 30-40.

[0009] In the present application, in ethylene glycol monovinyl polyoxyethylene ether, isopentenyl polyoxyethylene ether and methyl allyl polyoxyethylene ether, the degree of polymerization of the polyoxyethylene ether chain segment is preferably in the range of 30-40, which is beneficial to further improve the slump-retaining performance of the slump-retaining polycarboxylic acid water-reducing agent for concrete mixtures with high mud content of sand and gravel aggregates. At the same time, it can also improve the strength of concrete specimens with high mud content of sand and gravel aggregates.

[0010] Further preferably, the unsaturated polyether monomer is a composition of ethylene glycol monovinyl polyoxyethylene ether and isopentenyl polyoxyethylene ether or methyl allyl polyoxyethylene ether, and the weight ratio of ethylene glycol monovinyl polyoxyethylene ether to isopentenyl polyoxyethylene ether or methyl allyl polyoxyethylene ether is 1:(1-1.5).

[0011] In the present application, the unsaturated polyether monomer preferably includes linear ethylene glycol monovinyl polyoxyethylene ether and branched isopentenyl polyoxyethylene ether or methyl allyl polyoxyethylene ether, which is beneficial to further improve the dispersibility of the slump-retaining polycarboxylic acid water-reducing agent, and is beneficial to further improve the slump-retaining performance of the slump-retaining polycarboxylic acid water-reducing agent on concrete mixtures with a large mud content of sand and gravel aggregates, and can improve the strength of concrete specimens with a large mud content of sand and gravel aggregates, and further improve the water reduction rate of the slump-retaining polycarboxylic acid water-reducing agent on concrete with a large mud content of sand and gravel aggregates, and reduce the influence of water consumption on the slump of concrete mixtures with a large mud content of sand and gravel aggregates.

[0012] In some specific embodiments, the preparation method of the maleic anhydride modified hydroxy cellulose derivative is as follows: 4.5-5.5 parts by weight of the hydroxy cellulose derivative is added to 100 parts by weight of the solvent, the temperature is raised to 50-55° C., and the mixture is stirred until uniformly dissolved to obtain a hydroxy cellulose derivative solution;

[0013] 1-1.5 parts by weight of a 5% sodium acetate aqueous solution and 25-30 parts by weight of a 10% maleic anhydride aqueous solution are added dropwise to 50-55 parts by weight of a hydroxycellulose derivative solution. After the addition is completed, the temperature is raised to 80-90° C. to react for 2-3 hours, and then the solvent is removed by vacuum, and then dried to obtain a maleic anhydride-modified hydroxycellulose derivative.

[0014] In the present application, a hydroxy cellulose derivative reacts with maleic anhydride under the action of an aqueous sodium acetate solution to generate a maleic anhydride-modified hydroxy cellulose derivative. The maleic anhydride-modified hydroxy cellulose derivative is a substance with an ester group and an unsaturated double bond, which can be copolymerized with other monomers to increase the steric hindrance of the collapse-retaining polycarboxylic acid water-reducing agent. At the same time, it can also synergistically improve the anti-mud performance and collapse-retaining property of the collapse-retaining polycarboxylic acid water-reducing agent with the functional monomer.

[0015] Preferably, the solvent is water.

[0016] In some specific embodiments, the hydroxycellulose derivative is at least one of hydroxypropyl cellulose, hydroxymethyl cellulose and hydroxypropyl methyl cellulose.

[0017] In some specific embodiments, the preparation method of the functional monomer is as follows:

[0018] 4-5 parts by weight of N-hydroxymethyl acrylamide are added to 20-30 parts by weight of dimethylformamide, stirred evenly, heated to 135-140° C., 300-400 parts by weight of a 0.2% phosphorus pentoxide aqueous solution and 0.1-0.2 parts by weight of a catalyst are added dropwise, and after the addition is completed, the reaction is carried out for 4-6 hours, water is removed during the reaction, and finally dimethylformamide is removed by reduced pressure distillation to obtain a functional monomer.

[0019] In the present application, N-hydroxymethyl acrylamide reacts with an aqueous solution of phosphorus pentoxide under the action of a catalyst to generate a functional monomer, which also contains an ester group and an unsaturated double bond, and can be copolymerized with other monomers to increase the steric hindrance of the collapse-retaining polycarboxylic acid water-reducing agent. At the same time, it can also synergistically improve the anti-mud performance and collapse-retaining property of the collapse-retaining polycarboxylic acid water-reducing agent with a maleic anhydride-modified hydroxycellulose derivative.

[0020] Wherein, the catalyst is preferably 4-dimethylaminopyridine.

[0021] In some specific embodiments, the unsaturated carboxylic acid is at least one of acrylic acid and methacrylic acid.

[0022] In some specific embodiments, the chain transfer agent is at least one of thioglycolic acid, mercaptoethanol, and mercaptopropionic acid.

[0023] In some specific embodiments, the oxidant is at least one of ammonium persulfate, sodium persulfate, and potassium persulfate.

[0024] In some specific embodiments, the reducing agent is at least one of sodium sulfite and sodium bisulfite.

[0025] In the second aspect, the present application provides a method for preparing a collapse-retaining polycarboxylate water-reducing agent using the following technical solution: A method for preparing a collapse-retaining polycarboxylate water-reducing agent, comprising the following steps:

[0026] Add maleic anhydride modified hydroxy cellulose derivative and functional monomer into water with a total weight of 30-40% of the water formula, stir evenly, and obtain liquid A;

[0027] Add unsaturated polyether monomer and unsaturated carboxylic acid to water with a total weight of 20-25% of the total water formula, stir evenly, and obtain liquid B; add oxidant to water with a total weight of 10-15% of the total water formula, and obtain liquid C;

[0028] Add the reducing agent to water in an amount of 10-15% of the total weight of the water formula to obtain liquid D;

[0029] Add the chain transfer agent to the remaining amount of water to obtain liquid E;

[0030] Add liquid B, liquid C, liquid D and liquid E to liquid A at the same time, keep the temperature at 60-70°C and react for 1.5-2.5 hours to obtain a collapse-retaining polycarboxylic acid water-reducing agent.

[0031] In the present application, the above method is used to prepare the collapse-retaining polycarboxylic acid water-reducing agent, which is beneficial to improving the stability of the product. At the same time, the process is simple and has low requirements on equipment, which is conducive to promotion.

[0032] In summary, this application at least includes the following beneficial technical effects:

[0033] (1) In the present application, the collapse-preserving polycarboxylic acid water-reducing agent is obtained by copolymerization of unsaturated polyether monomers, maleic anhydride-modified hydroxycellulose derivatives, functional monomers and unsaturated carboxylic acids, wherein the collapse-preserving polycarboxylic acid water-reducing agent contains long side chains, has a large steric hindrance effect, and has good dispersibility. It can be stably adsorbed on the surface of cement particles, helps to disperse cement particles, reduces the attraction between cement particles, and helps to form a slurry with good fluidity. In addition, the maleic anhydride-modified hydroxycellulose derivatives and the functional monomers can synergistically improve the anti-mud performance and water-reducing performance of the collapse-preserving polycarboxylic acid water-reducing agent. At the same time, the carboxyl group can be released in the later stage to ensure the fluidity of the slurry in the later stage, and it can be suitable for the collapse-preserving slurry with a large mud content in sand and gravel aggregates.

[0034] (2) In the present application, the polymerization degree of the polyoxyethylene ether chain segment in ethylene glycol monovinyl polyoxyethylene ether, isopentenyl polyoxyethylene ether and methyl allyl polyoxyethylene ether is preferably in the range of 30-40, which is beneficial to further improve the slump-retaining performance of the slump-retaining polycarboxylic acid water-reducing agent for concrete mixtures with high mud content of sand and gravel aggregates. At the same time, it can also improve the strength of concrete specimens with high mud content of sand and gravel aggregates.

[0035] (3) In the present application, the unsaturated polyether monomer preferably includes linear ethylene glycol monovinyl polyoxyethylene ether and branched isopentenyl polyoxyethylene ether or methyl allyl polyoxyethylene ether, which is beneficial to further improve the dispersibility of the slump-retaining polycarboxylic acid water-reducing agent, and is beneficial to further improve the slump-retaining performance of the slump-retaining polycarboxylic acid water-reducing agent on concrete mixtures with a large mud content of sand and gravel aggregates, and can improve the strength of concrete specimens with a large mud content of sand and gravel aggregates, and further improve the water reduction rate of the slump-retaining polycarboxylic acid water-reducing agent on concrete with a large mud content of sand and gravel aggregates, and reduce the influence of water consumption on the slump of concrete mixtures with a large mud content of sand and gravel aggregates. DETAILED DESCRIPTION

[0036] The following is a further description of this application in conjunction with specific experiments:

[0037] Preparation Example

[0038] [Preparation Example 1-1]

[0039] A maleic anhydride modified hydroxycellulose derivative, the preparation method is as follows:

[0040] Add 4.5 g of hydroxypropyl methylcellulose (purchased from Foshan Sanzhong Environmental Protection Technology Co., Ltd., model SZ034-01) to 100 g of water, raise the temperature to 50°C, and stir until it is uniformly dissolved to obtain a hydroxypropyl methylcellulose solution;

[0041] To 50 g of hydroxypropyl methylcellulose solution, add 1 g of 5% sodium acetate aqueous solution and 25 g of 10% maleic anhydride aqueous solution. After the addition is complete, heat to 80°C and react for 2 hours. Then, vacuum remove water and dry to obtain a maleic anhydride-modified hydroxycellulose derivative.

[0042] [Preparation Example 1-2]

[0043] A maleic anhydride modified hydroxycellulose derivative, the preparation method is as follows:

[0044] Add 5.5 g of hydroxyethyl methylcellulose (purchased from Guangdong Hongyou Biotechnology Co., Ltd.) to 100 g of water, raise the temperature to 55°C, and stir until it is uniformly dissolved to obtain a hydroxyethyl methylcellulose solution;

[0045] To 55 g of hydroxyethyl methylcellulose solution, add dropwise 1.5 g of 5% sodium acetate aqueous solution and 30 g of 10% maleic anhydride aqueous solution. After the addition is complete, heat to 90°C and react for 3 h. Then, vacuum remove water and dry to obtain a maleic anhydride-modified hydroxycellulose derivative.

[0046] [Preparation Example 2-1]

[0047] A functional monomer, the preparation method is as follows:

[0048] Add 4 g of N-hydroxymethylacrylamide to 20 g of dimethylformamide, stir evenly, heat to 135°C, drop 300 g of 0.2% phosphorus pentoxide aqueous solution and 0.1 g of 4-dimethylaminopyridine, and react for 4 hours after the addition is complete. Remove water during the reaction, and finally remove dimethylformamide by reduced pressure distillation to obtain a functional monomer.

[0049] [Preparation Example 2-2]

[0050] A functional monomer, the preparation method is as follows:

[0051] Add 5 g of N-hydroxymethylacrylamide to 30 g of dimethylformamide, stir evenly, heat to 140°C, drop 400 g of 0.2% phosphorus pentoxide aqueous solution and 0.2 g of 4-dimethylaminopyridine, and react for 6 hours after the addition is complete. Remove water during the reaction, and finally remove dimethylformamide by reduced pressure distillation to obtain a functional monomer.

[0052] Example

[0053] [Example 1]

[0054] A collapse-retaining polycarboxylate water-reducing agent is prepared from the following raw materials:

[0055] Unsaturated polyether monomer: 15 g; in this embodiment, the unsaturated polyether monomer is ethylene glycol monovinyl polyoxyethylene ether, and the degree of polymerization of the polyoxyethylene ether chain segment is 30;

[0056] Maleic anhydride-modified hydroxycellulose derivative: 4.2 g; in this example, the maleic anhydride-modified hydroxycellulose derivative is the maleic anhydride-modified hydroxycellulose derivative prepared in [Preparation Example 1-1];

[0057] Functional monomer: 3.8 g; in this embodiment, the functional monomer is the functional monomer prepared in [Preparation Example 2-1];

[0058] Unsaturated carboxylic acid: 35 g; in this embodiment, the unsaturated carboxylic acid is acrylic acid;

[0059] Chain transfer agent: 0.5 g; in this embodiment, the chain transfer agent is thioglycolic acid;

[0060] Oxidant: 0.5 g; in this embodiment, the oxidant is sodium persulfate;

[0061] Reducing agent: 0.25 g; in this embodiment, the reducing agent is sodium bisulfite;

[0062] Water: 500g.

[0063] A method for preparing a collapse-retaining polycarboxylate water-reducing agent comprises the following steps:

[0064] Add maleic anhydride modified hydroxy cellulose derivative and functional monomer into water with a total weight of 35% of the water formula, stir evenly, and obtain liquid A;

[0065] Add unsaturated polyether monomer and unsaturated carboxylic acid to water with a total weight of 25% of the water formula, stir evenly, and obtain liquid B;

[0066] Add the oxidant to water in an amount of 10% by weight of the total weight of the water formula to obtain liquid C;

[0067] Add the reducing agent to water in an amount of 10% by weight of the total water formula to obtain liquid D;

[0068] Add the chain transfer agent to the remaining amount of water to obtain liquid E;

[0069] Add liquid B, liquid C, liquid D and liquid E to liquid A at the same time, keep the temperature at 65°C and react for 2 hours to obtain a collapse-retaining polycarboxylic acid water-reducing agent.

[0070] [Example 2]

[0071] A collapse-preserving polycarboxylic acid water-reducing agent, which differs from [Example 1] in that the components and proportions are different. In this example, the collapse-preserving polycarboxylic acid water-reducing agent is prepared from the following raw materials:

[0072] Unsaturated polyether monomer: 20 g; in this embodiment, the unsaturated polyether monomer is methyl allyl polyoxyethylene ether, and the degree of polymerization of the polyoxyethylene ether chain segment is 40;

[0073] Maleic anhydride-modified hydroxycellulose derivative: 5.8 g; in this embodiment, the maleic anhydride-modified hydroxycellulose derivative is the maleic anhydride-modified hydroxycellulose derivative prepared in [Preparation Example 1-2];

[0074] Functional monomer: 4.5 g; in this embodiment, the functional monomer is the functional monomer prepared in [Preparation Example 2-2];

[0075] Unsaturated carboxylic acid: 40 g; in this embodiment, the unsaturated carboxylic acid is methacrylic acid;

[0076] Chain transfer agent: 1 g; in this embodiment, the chain transfer agent is mercaptoethanol;

[0077] Oxidant: 1g; in this embodiment, the oxidant is ammonium persulfate;

[0078] Reducing agent: 0.5 g; in this embodiment, the reducing agent is sodium sulfite;

[0079] Water: 500g.

[0080] [Example 3]

[0081] A collapse-retaining polycarboxylic acid water-reducing agent, which differs from [Example 1] in that: the unsaturated polyether monomer adopts methyl allyl polyoxyethylene ether, and the degree of polymerization of the polyoxyethylene ether chain segment is 30.

[0082] [Example 4]

[0083] A collapse-retaining polycarboxylic acid water-reducing agent, which differs from [Example 1] in that: the unsaturated polyether monomer adopts a composition of ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether, the weight ratio of ethylene glycol monovinyl polyoxyethylene ether to methyl allyl polyoxyethylene ether is 1:1, and the polymerization degree of the polyoxyethylene ether chain segment in ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether is 30.

[0084] [Example 5]

[0085] A collapse-retaining polycarboxylic acid water-reducing agent, which differs from [Example 1] in that: the unsaturated polyether monomer adopts a composition of ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether, the weight ratio of ethylene glycol monovinyl polyoxyethylene ether to methyl allyl polyoxyethylene ether is 3:1, and the polymerization degree of the polyoxyethylene ether chain segment in ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether is 30.

[0086] [Example 6]

[0087] A collapse-retaining polycarboxylic acid water-reducing agent, which differs from [Example 1] in that: the unsaturated polyether monomer adopts a composition of ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether, the weight ratio of ethylene glycol monovinyl polyoxyethylene ether to methyl allyl polyoxyethylene ether is 1:3, and the polymerization degree of the polyoxyethylene ether chain segment in ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether is 30.

[0088] [Example 7]

[0089] A collapse-retaining polycarboxylic acid water-reducing agent, which differs from [Example 4] in that the polymerization degree of the polyoxyethylene ether chain segments in ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether are both 10.

[0090] [Example 8]

[0091] A collapse-retaining polycarboxylic acid water-reducing agent, which differs from [Example 4] in that the polymerization degree of the polyoxyethylene ether chain segment in ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether is 50.

[0092] Comparative Example

[0093] [Comparative Example 1]

[0094] A polycarboxylic acid water-reducing agent, which differs from [Example 1] in that: the maleic anhydride-modified hydroxycellulose derivative is replaced by an equal amount of a functional monomer prepared in [Preparation Example 2-1].

[0095] [Comparative Example 2]

[0096] A polycarboxylic acid water-reducing agent, which differs from [Example 1] in that: the functional monomer is replaced by an equal amount of a maleic anhydride-modified hydroxycellulose derivative obtained in [Preparation Example 1-1].

[0097] [Comparative Example 3]

[0098] A polycarboxylic acid water-reducing agent, which differs from [Example 1] in that the functional monomer is replaced by an equal amount of N-hydroxymethyl acrylamide.

[0099] [Comparative Example 4]

[0100] A polycarboxylic acid water-reducing agent, which differs from [Example 1] in that: the functional monomer is replaced by a combination of N-hydroxymethyl acrylamide and acrylic acid phosphate, and the weight ratio of N-hydroxymethyl acrylamide to acrylic acid phosphate is 1:1.

[0101] Performance testing

[0102] The mix ratio of the benchmark concrete C60 is shown in Table 1. The cement used is Huaxin Cement PO42.5, the fly ash used is first-grade fly ash, the fineness modulus of the sand used is 2.6-2.9, and the mud content is about 2.15%; the gravel used is a second-grade mix, of which 5mm-10mm (mud content is about 1.8%) accounts for about 40%, and 10mm-20mm (mud content is about 1.6%) accounts for about 60%.

[0103] Table 1

[0104]

[0105]

[0106] The water-cement ratio in mix 1 is about 0.4, and the water-cement ratio in mix 2 is about 0.37.

[0107] Test 1, slump: The slump-retaining polycarboxylate water-reducing agent in each embodiment and comparative example was added to the above-mentioned reference concrete C60 at 0.5% (solid) of cement dosage to prepare concrete mixtures 1-12 respectively, and then the slump of each concrete mixture and the reference concrete mixture at 0min and 120min was tested with reference to Section 4 of GB / T50080-2016 "Standard for Performance Test Methods of Ordinary Concrete Mixtures". Among them, the concrete mixture is qualified if the slump can be maintained above 180mm after 2h.

[0108] Test 2: Compressive strength: The concrete mixture in Test 1 was made into concrete specimens with a size of 200mm*200mm*200mm, and then cured at 25℃ for 28d. The compressive strength of the concrete specimens was then tested in accordance with GB / T 50081-2019.

[0109] Table 2

[0110]

[0111]

[0112] Table 3

[0113]

[0114] The difference between Comparative Example 1-2 and Example 1 is that in Comparative Example 1, the maleic anhydride-modified hydroxycellulose derivative in the polycarboxylate water-reducing agent is replaced by an equal amount of functional monomers obtained in [Preparation Example 2-1], and the functional monomers in the polycarboxylate water-reducing agent in Comparative Example 2 are replaced by an equal amount of maleic anhydride-modified hydroxycellulose derivatives obtained in [Preparation Example 1-1]. Combined with the test data in Table 2-3, it can be seen that the slump-preserving performance of the polycarboxylate water-reducing agent in Comparative Examples 1 and 2 for concrete mixtures with a large mud content of sand and gravel aggregates is reduced, and the compressive strength of the corresponding concrete specimens is also reduced. In addition, the slump-preserving performance of concrete mixtures with a large mud content of sand and gravel aggregates is greatly affected by water fluctuations. When the water-cement ratio of the concrete mixture drops from 0.4 to 0.37, the slump of the concrete mixture after 2 hours cannot meet the use requirements. It can be seen that the combination of maleic anhydride modified hydroxy cellulose derivatives and functional monomers is beneficial to improving the mud resistance of the slump-retaining polycarboxylic acid water-reducing agent, improving the slump-retaining performance of the slump-retaining polycarboxylic acid water-reducing agent on concrete mixtures with a large mud content of sand and gravel aggregates, and at the same time can increase the water reduction rate of the polycarboxylic acid water-reducing agent and reduce the influence of water consumption on the slump of concrete mixtures with a large mud content of sand and gravel aggregates.

[0115] The difference between Comparative Example 3-4 and Example 1 is that the functional monomer in the polycarboxylic acid water-reducing agent in Comparative Example 3 is replaced by an equal amount of N-hydroxymethyl acrylamide, and the functional monomer in the polycarboxylic acid water-reducing agent in Comparative Example 4 is replaced by a combination of N-hydroxymethyl acrylamide and acrylic acid phosphate. Combined with the test data in Table 2-3, it can be seen that the slump retention performance of the polycarboxylic acid water-reducing agent in Comparative Example 3-4 for concrete mixtures with a large mud content of sand and gravel aggregates is reduced, and the compressive strength of the corresponding concrete specimens is also reduced. In addition, the slump retention performance of concrete mixtures with a large mud content of sand and gravel aggregates is greatly affected by water fluctuations. When the water-cement ratio of the concrete mixture drops from 0.4 to 0.37, the slump of the concrete mixture after 2 hours cannot meet the use requirements. It can be seen that the use of the functional monomer obtained by the reaction of N-hydroxymethyl acrylamide and an aqueous solution of phosphorus pentoxide under the action of a catalyst in the present application and the maleic anhydride modified hydroxycellulose derivative is beneficial to improving the slump retention performance of the polycarboxylic acid water-reducing agent on the concrete mixture with a large mud content of sand and gravel aggregates, and at the same time can improve the water reduction rate of the polycarboxylic acid water-reducing agent and reduce the effect of water consumption on the slump of the concrete mixture with a large mud content of sand and gravel aggregates.

[0116] The difference between Example 3-6 and Example 1 is that the unsaturated polyether monomers in the polycarboxylic acid water-reducing agent are different. Among them, the polycarboxylic acid water-reducing agent in Example 4 adopts a composition with a weight ratio of ethylene glycol monovinyl polyoxyethylene ether to methyl allyl polyoxyethylene ether in the range of 1: (1-1.5). Combined with the test data in Table 2-3, it can be seen that the polycarboxylic acid water-reducing agent in Example 4 further improves the slump retention performance of concrete mixtures with a large mud content of sand and gravel aggregates, and the compressive strength of the corresponding concrete specimens is also significantly improved. In addition, when the water-cement ratio of the concrete mixture decreases from 0.4 to 0.37, the slump and slump retention performance of the concrete mixture with a large mud content of sand and gravel aggregates are basically unaffected.

[0117] The difference between Example 7-8 and Example 4 is that the polymerization degree of the polyoxyethylene segment in ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether is different, wherein the polymerization degree of the polyoxyethylene segment in Example 7-8 is not within the preferred range of 30-40 in the present application. Combined with the test data in Table 2-3, it can be seen that the slump retention performance of the polycarboxylic acid water reducer in Examples 7 and 8 for concrete mixtures with a large mud content of sand and gravel aggregates is reduced, and the compressive strength of the corresponding concrete specimens is reduced. At the same time, when the water-cement ratio of the concrete mixture decreases from 0.4 to 0.37, the slump of the concrete mixture with a large mud content of sand and gravel aggregates also decreases. Therefore, in the present application, the polymerization degree of the polyoxyethylene segment in ethylene glycol monovinyl polyoxyethylene ether and methyl allyl polyoxyethylene ether is preferably within the range of 30-40.

[0118] This specific implementation manner is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the specific implementation manner as needed, but such modifications are protected by the patent law as long as they are within the scope of the claims of the present application.

Claims

1. A collapse-retaining polycarboxylate water-reducing agent, characterized in that: The invention comprises 15-20 parts by weight of an unsaturated polyether monomer, 4.2-5.8 parts by weight of a maleic anhydride-modified hydroxycellulose derivative, 3.8-4.5 parts by weight of a functional monomer, 35-40 parts by weight of an unsaturated carboxylic acid, 0.5-1 parts by weight of a chain transfer agent, 0.5-1 parts by weight of an oxidant, 0.25-0.5 parts by weight of a reducing agent and 500 parts by weight of water; wherein the maleic anhydride-modified hydroxycellulose derivative is obtained by reacting maleic anhydride with a hydroxycellulose derivative, and the functional monomer is obtained by reacting N-hydroxymethyl acrylamide with an aqueous solution of phosphorus pentoxide under the action of a catalyst; The unsaturated polyether monomer is a composition of ethylene glycol monovinyl polyoxyethylene ether and isopentenyl polyoxyethylene ether or methyl allyl polyoxyethylene ether, and the weight ratio of ethylene glycol monovinyl polyoxyethylene ether to isopentenyl polyoxyethylene ether or methyl allyl polyoxyethylene ether is 1: (1-1.5); In the ethylene glycol monovinyl polyoxyethylene ether, isopentenyl polyoxyethylene ether and methyl allyl polyoxyethylene ether, the degree of polymerization of the polyoxyethylene ether chain segment is in the range of 30-40.

2. A collapse-retaining polycarboxylate water-reducing agent according to claim 1, characterized in that: The preparation method of the maleic anhydride modified hydroxycellulose derivative is as follows: Adding 4.5-5.5 parts by weight of a hydroxycellulose derivative to 100 parts by weight of a solvent, heating to 50-55° C., and stirring until the hydroxycellulose derivative is uniformly dissolved to obtain a hydroxycellulose derivative solution; 1-1.5 parts by weight of a 5% sodium acetate aqueous solution and 25-30 parts by weight of a 10% maleic anhydride aqueous solution are added dropwise to 50-55 parts by weight of a hydroxycellulose derivative solution. After the addition is completed, the temperature is raised to 80-90° C. to react for 2-3 hours, and then the solvent is removed by vacuum, and then dried to obtain a maleic anhydride-modified hydroxycellulose derivative.

3. The collapse-retaining polycarboxylate water-reducing agent according to claim 1, characterized in that: The hydroxycellulose derivative is at least one of hydroxypropyl cellulose, hydroxymethyl cellulose and hydroxypropyl methyl cellulose.

4. The collapse-retaining polycarboxylate water-reducing agent according to claim 1, characterized in that: The preparation method of the functional monomer is as follows: 4-5 parts by weight of N-hydroxymethyl acrylamide are added to 20-30 parts by weight of dimethylformamide, and after being stirred evenly, the temperature is raised to 135-140° C., 300-400 parts by weight of a 0.2% phosphorus pentoxide aqueous solution and 0.1-0.2 parts by weight of a catalyst are dropwise added, and after the dropwise addition is completed, the reaction is carried out for 4-6 hours, water is removed during the reaction, and finally dimethylformamide is removed by reduced pressure distillation to obtain a functional monomer.

5. The collapse-retaining polycarboxylate water-reducing agent according to claim 1, characterized in that: The unsaturated carboxylic acid is at least one of acrylic acid and methacrylic acid.

6. The collapse-retaining polycarboxylate water-reducing agent according to claim 1, characterized in that: The chain transfer agent is at least one of thioglycolic acid, mercaptoethanol, and mercaptopropionic acid; the oxidant is at least one of ammonium persulfate, sodium persulfate, and potassium persulfate; and the reducing agent is at least one of sodium sulfite and sodium bisulfite.

7. A method for preparing a collapse-retaining polycarboxylate water-reducing agent according to any one of claims 1 to 6, characterized in that: The following steps are involved: Add maleic anhydride modified hydroxy cellulose derivative and functional monomer into water with a total weight of 30-40% of the water formula, stir evenly, and obtain liquid A; Add unsaturated polyether monomer and unsaturated carboxylic acid to water with a total weight of 20-25% of the water formula, stir evenly, and obtain liquid B; Add the oxidant to water in an amount of 10-15% of the total weight of the water formula to obtain liquid C; Add the reducing agent to water in an amount of 10-15% of the total weight of the water formula to obtain liquid D; Add the chain transfer agent to the remaining amount of water to obtain liquid E; Add liquid B, liquid C, liquid D and liquid E to liquid A at the same time, keep the temperature at 60-70°C and react for 1.5-2.5 hours to obtain a collapse-retaining polycarboxylic acid water-reducing agent.

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