Concrete water reducer and preparation method thereof

Abstract

The invention provides a concrete water reducing agent and a preparation method thereof, and belongs to the technical field of water reducing agents. Adding the modified chitin, 1-vinyl-3-butylimidazolium trifluoromethanesulfonate, a silane coupling agent with double bonds, methacrylic acid, trans-butenedioic acid and an initiator into dimethylformamide, heating and stirring for reaction, removing methylbenzene under reduced pressure, and performing alkali washing and alcohol washing to obtain the concrete water reducing agent. The modified chitin is prepared by modifying chitin modified by sodium sulfonate and acrylic acid with tannic acid. Modified chitin, 1-vinyl-3-butylimidazolium trifluoromethanesulfonate, a silane coupling agent with double bonds, methacrylic acid and trans-butenedioic acid are copolymerized to prepare the polycarboxylate superplasticizer, molecules of the polycarboxylate superplasticizer are of a comb-shaped structure, a main chain of the polycarboxylate superplasticizer is provided with a plurality of active groups with high polarity, and a side chain of the polycarboxylate superplasticizer is provided with hydrophilic active groups. The water-reducing agent has the characteristics of low doping amount, high water-reducing rate, high reinforcing effect, high plasticity retaining property and volume stability, and has wide application prospects.

Description

Technical Field

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

[0002] In recent years, concrete has played an important role in my country's engineering construction. Since water reducers can effectively improve the performance of concrete and have good economic benefits, they are widely used in many countries. The application of high-efficiency water reducers in engineering has received more and more attention and has become an indispensable material in concrete.

[0003] Water reducers have gone through the development process from lignin sulfonate, naphthalene sulfonate condensate (naphthalene-based water reducer), aliphatic and polycarboxylic acid series. Lignosulfonate is the most commonly used common water reducer, but it is easy to cause slow setting during the mixing process of the water reducer, and often introduces a large amount of air, which affects the performance of concrete; the sodium sulfate content of naphthalene-based water reducers is inevitably high during the mixing process, which leads to an increase in the alkali content in the admixture, a decrease in the durability of concrete, and alkali-aggregate reaction in many projects, which greatly shortens the service life. In addition, aromatic sulfonates are potentially toxic to humans and organisms. The raw material ratio of formaldehyde, acetone and other monomers used in the production of aliphatic water reducers is difficult to control, resulting in poor performance of the water reducer and compatibility issues with the cement matrix.

[0004] The existing polycarboxylate water reducer has high cost and different polymerization degrees in the synthesis process, which leads to different performances. In addition, the contradiction between supply and demand of sand and gravel in my country is prominent, and natural sand is gradually replaced by machine-made sand. However, machine-made sand is much different from natural sand in particle shape, gradation, surface texture and 0.075mm stone powder particles, which leads to failure of water reducer or decrease of water reduction efficiency, thus having a significant impact on concrete performance. In addition, SO4 contained in cement 2- Ions have a great influence on the effect of use. A large amount of SO4 2- Ions will directly affect the amount of polycarboxylate water-reducing agent molecules adsorbed on cement particles, which greatly weakens the water-reducing effect of the water-reducing agent, thus causing the problem of water seepage. Research and engineering practice have shown that after the water-reducing agent is added to cement, it is usually possible to encounter problems such as poor compatibility between the water-reducing agent and cement, sensitivity to the mud content of sand and gravel aggregates, and unstable workability of fresh concrete.

[0005] Chinese patent application CN108101407A discloses a polycarboxylic acid composite water reducer and a preparation method thereof. The polycarboxylic acid composite water reducer comprises the following components in parts by weight: 50-60 parts of polycarboxylic acid water reducer, 30-40 parts of aliphatic water reducer, 15-20 parts of propanesulfonic acid, 10-15 parts of air entraining agent, 10-15 parts of triethanolamine, and 3-5 parts of chlorinated hydrocarbons. In addition to water-reducing performance, the polycarboxylic acid composite water reducer also has antifreeze performance, but its compatibility with cement has not been studied, and the chlorinated hydrocarbons with strong volatility added in the invention are toxic and will cause environmental pollution.

[0006] Chinese patent application CN107117853A discloses a high-efficiency composite water reducer for concrete and its application. The composite water reducer is prepared from 10-40 parts of polycarboxylic acid mother liquor, 4-15 parts of air entraining agent, 15-30 parts of hydrophilic colloid, 0.1-1 parts of retarder, 0.8-2 parts of sodium sulfate, 1-5 parts of wood calcium, 5-20 parts of cellulose water-retaining material and 30-70 parts of water as raw materials. The composite water reducer has the properties of slow release, collapse retention, early strength and high strength, water retention, etc., greatly reduces the unit water consumption of concrete. The composite water reducer is applied in concrete preparation to improve the compactness of concrete, greatly reduce the amount of cement, reduce shrinkage, and improve the stability of concrete. It has the characteristics of low dosage and significant effect when used in concrete, is environmentally friendly, and has good economic and social benefits. The invention does not solve the compatibility problem of composite water reducer and cement. Summary of the invention

[0007] The purpose of the present invention is to provide a concrete water reducing agent and a preparation method thereof. The preparation method is simple, the raw material source is wide, the cost is low, the molecule is in a comb-shaped structure, the main chain has a plurality of active groups with strong polarity, the side chain has a hydrophilic active group, the concrete water reducing agent has the characteristics of low dosage, high water reducing rate, high reinforcing effect, high plasticity retention and volume stability, and has broad application prospects.

[0008] The technical solution of the present invention is achieved in this way:

[0009] The invention provides a method for preparing a concrete water reducing agent. The method comprises the following steps: adding modified chitosan, 1-vinyl-3-butylimidazole trifluoromethanesulfonate, a silane coupling agent with double bonds, methacrylic acid, trans-butenedioic acid and an initiator into dimethylformamide, heating and stirring for reaction, removing toluene under reduced pressure, and washing with alkali and alcohol to obtain the concrete water reducing agent. The modified chitosan is prepared by modifying chitosan with sodium sulfonate and acrylic acid and then with tannic acid.

[0010] As a further improvement of the present invention, the mass ratio of the modified chitin, 1-vinyl-3-butylimidazole trifluoromethanesulfonate, silane coupling agent with double bonds, methacrylic acid, trans-butenedioic acid and initiator is 7-10:3-4:2-3:3-5:2-4:0.01-0.02.

[0011] As a further improvement of the present invention, the temperature of the heating and stirring reaction is 55-65° C. and the time is 3-5 h.

[0012] As a further improvement of the present invention, the preparation method of the modified chitosan is as follows:

[0013] S1. Adding chitosan to an alkali solution, heating and stirring, filtering, washing, and drying to obtain pretreated chitosan;

[0014] S2. The pretreated chitin was added to dimethyl sulfoxide, sodium 3-chloro-2-hydroxypropane sulfonate was added, the reaction was heated with stirring, filtered, washed, and dried to obtain an intermediate product;

[0015] S3. The intermediate product and methacrylic acid are added to toluene, p-toluenesulfonic acid and hydroquinone are added, the reaction is heated to reflux, the solvent is removed under reduced pressure, washed, dried, and recrystallized to obtain an intermediate product 2;

[0016] S4. Add the intermediate product 2 into water, add tannic acid and a catalyst, heat and stir to react, filter, wash, and dry to obtain modified chitosan.

[0017] As a further improvement of the present invention, the alkali solution in step S1 is a 10-15wt% NaOH or KOH solution, and the temperature of the heating and stirring treatment is 40-50°C and the time is 1-2h.

[0018] As a further improvement of the present invention, in step S2, the mass ratio of the pretreated chitin to sodium 3-chloro-2-hydroxypropane sulfonate is 10:3-5, the temperature of the heating and stirring reaction is 60-70° C., and the time is 4-6 hours.

[0019] As a further improvement of the present invention, in step S3, the mass ratio of the intermediate product, methacrylic acid, p-toluenesulfonic acid and hydroquinone is 10:2-4:0.2-0.3:0.3-0.5, and the heating reflux reaction time is 4-6 hours.

[0020] As a further improvement of the present invention, the mass ratio of the intermediate product 2, tannic acid and catalyst in step S4 is 10:3-4:0.2-0.5, the catalyst is a Tris-HCl solution with a pH of 8.5-9.5, the temperature of the heating and stirring reaction is 40-50°C, and the time is 2-4h.

[0021] As a further improvement of the present invention, the silane coupling agent with a double bond is selected from at least one of KH570, vinyltriethoxysilane, and vinyltrimethylsilane; the initiator is selected from at least one of azobisisobutyronitrile, azobisisovaleronitrile, sodium persulfate, potassium persulfate, and ammonium persulfate.

[0022] The present invention further protects a concrete water reducing agent prepared by the above preparation method.

[0023] The present invention has the following beneficial effects:

[0024] The polymerizable monomer of the present invention contains silane with double bonds. On the one hand, silane is applied to recycled aggregate concrete as a hydrophobic agent to improve the durability of the concrete. At the same time, an organic silane group is introduced into the molecular structure of the polycarboxylic acid-based high-efficiency water-reducing agent. The chemical properties of the organic silane are utilized to provide the polycarboxylic acid-based water-reducing agent with a strong interaction ability for chemical bonding with cement particles, thereby improving its performance in high-strength concrete.

[0025] In addition, the polymerizable monomer of the present invention also includes 1-vinyl-3-butyl imidazole trifluoromethanesulfonate, which is adsorbed on the surface of cement particles by introducing an imidazole group with a rigid structure and hydrophilicity, and associates with water molecules in the form of hydrogen bonds to form a stable water film on the surface of cement particles, thereby preventing direct contact between cement particles, avoiding the problems of poor adaptability to cement, sensitivity to the mud content of sand and gravel aggregates, and unstable workability of fresh concrete, and increasing the sliding ability of cement particles, playing a lubricating role, improving the fluidity of cement paste, increasing the workability and slump retention of concrete mixtures, improving the strength and durability of concrete, and reducing the fission, shrinkage and thermal deformation caused by the hydration of cement.

[0026] The present invention also prepares and adds modified chitin, which releases more hydroxyl groups on the surface after alkali treatment, and introduces sulfonate groups after coupling modification with sodium 3-chloro-2-hydroxypropane sulfonate, which greatly reduces the SO4 contained in cement. 2- The effect of ions on water reducers improves the tax reduction effect and avoids the problem of water seepage. The intermediate product then undergoes an esterification reaction with methacrylic acid to form double bonds, making it easy to copolymerize. Finally, it is modified with tannic acid to greatly increase the carboxyl content of the product. The carboxyl group is adsorbed on the surface of cement particles and associates with water molecules in the form of hydrogen bonds to form a stable water film on the surface of cement particles, preventing direct contact between cement particles, increasing the sliding ability of cement particles, playing a lubricating role, improving the fluidity of cement slurry, and further improving the water reduction effect. At the same time, carboxyl groups are introduced on the surface of chitin to produce electrostatic repulsion dispersion, weak dissociation and hydrophilic effects, thereby achieving the performance of slump retention and water reduction. Using chitin as a raw material has low cost and high efficiency in water reduction.

[0027] The polycarboxylic acid water reducer prepared by copolymerizing modified chitin, 1-vinyl-3-butylimidazole trifluoromethanesulfonate, a silane coupling agent with a double bond, methacrylic acid and trans-butenedioic acid has a simple preparation method, a wide source of raw materials and low cost. The molecule presents a comb-shaped structure, has a plurality of active groups with strong polarity on the main chain, and a hydrophilic active group on the side chain. The polycarboxylic acid water reducer has the characteristics of low dosage, high water reduction rate, high reinforcement effect, high plasticity and volume stability, and has broad application prospects. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0029] Preparation Example 1 Preparation of modified chitin

[0030] The following steps are involved:

[0031] S1. 1 g of chitosan was added to 50 mL of a 10 wt% NaOH solution, heated to 40 ° C, stirred for 1 h, filtered, washed, and dried to obtain pretreated chitosan;

[0032] S2. 1 g of pretreated chitin was added to 100 mL of dimethyl sulfoxide, 0.3 g of sodium 3-chloro-2-hydroxypropane sulfonate was added, the mixture was heated to 60 ° C, the pH of the mixed solution was adjusted to 7.5 with a 30% mass fraction of NaOH aqueous solution, the reaction was stirred for 4 h, filtered, washed, and dried to obtain an intermediate product;

[0033] S3. 1 g of the intermediate product and 0.2 g of methacrylic acid were added to 100 mL of toluene, 0.02 g of p-toluenesulfonic acid and 0.03 g of hydroquinone were added, and the mixture was heated under reflux for 4 h. The solvent was removed under reduced pressure, washed, dried, and recrystallized to obtain an intermediate product 2;

[0034] S4. 1 g of intermediate product 2 was added to 100 mL of water, 0.3 g of tannic acid and 0.02 g of catalyst were added, heated to 40 ° C, stirred for 2 h, filtered, washed, and dried to obtain modified chitin;

[0035] The catalyst is a Tris-HCl solution with a pH of 8.5.

[0036] Preparation Example 2 Preparation of modified chitin

[0037] The following steps are involved:

[0038] S1. 1 g of chitosan was added to 50 mL of a 15 wt% KOH solution, heated to 50 ° C, stirred for 2 h, filtered, washed, and dried to obtain pretreated chitosan;

[0039] S2. 1 g of pretreated chitin was added to 100 mL of dimethyl sulfoxide, 0.5 g of sodium 3-chloro-2-hydroxypropane sulfonate was added, the mixture was heated to 70 ° C, the pH of the mixed solution was adjusted to 8.5 with a 40% mass fraction of NaOH aqueous solution, the reaction was stirred for 6 h, filtered, washed, and dried to obtain an intermediate product;

[0040] S3. 1 g of the intermediate product and 0.4 g of methacrylic acid were added to 100 mL of toluene, 0.03 g of p-toluenesulfonic acid and 0.05 g of hydroquinone were added, and the reaction was heated under reflux for 6 h. The solvent was removed under reduced pressure, washed, dried, and recrystallized to obtain an intermediate product 2;

[0041] S4. Add 1 g of intermediate product 2 to 100 mL of water, add 0.4 g of tannic acid and 0.05 g of catalyst, heat to 50 ° C, stir and react for 4 h, filter, wash, and dry to obtain modified chitin;

[0042] The catalyst is a Tris-HCl solution with a pH of 9.5.

[0043] Preparation Example 3 Preparation of modified chitosan

[0044] The following steps are involved:

[0045] S1. 1 g of chitosan was added to 50 mL of 12 wt% NaOH solution, heated to 45 ° C, stirred for 1.5 h, filtered, washed, and dried to obtain pretreated chitosan;

[0046] S2. 1 g of pretreated chitin was added to 100 mL of dimethyl sulfoxide, 0.4 g of sodium 3-chloro-2-hydroxypropane sulfonate was added, the mixture was heated to 65 ° C, the pH of the mixed solution was adjusted to 8 with a 35% mass fraction of NaOH aqueous solution, the reaction was stirred for 5 h, filtered, washed, and dried to obtain an intermediate product;

[0047] S3. 1 g of the intermediate product and 0.3 g of methacrylic acid were added to 100 mL of toluene, 0.025 g of p-toluenesulfonic acid and 0.04 g of hydroquinone were added, and the mixture was heated under reflux for 5 h. The solvent was removed under reduced pressure, washed, dried, and recrystallized to obtain an intermediate product 2;

[0048] S4. 1 g of intermediate product 2 was added to 100 mL of water, 0.35 g of tannic acid and 0.03 g of catalyst were added, heated to 45 ° C, stirred for 3 h, filtered, washed, and dried to obtain modified chitin;

[0049] The catalyst is a Tris-HCl solution with a pH of 9.

[0050] Comparative Preparation Example 1

[0051] Compared with Preparation Example 3, the difference is that step S4 is not performed.

[0052] The following steps are involved:

[0053] S1. 1 g of chitosan was added to 50 mL of 12 wt% NaOH solution, heated to 45 ° C, stirred for 1.5 h, filtered, washed, and dried to obtain pretreated chitosan;

[0054] S2. 1 g of pretreated chitin was added to 100 mL of dimethyl sulfoxide, 0.4 g of sodium 3-chloro-2-hydroxypropane sulfonate was added, the mixture was heated to 65 ° C, the pH of the mixed solution was adjusted to 8 with a 35% mass fraction of NaOH aqueous solution, the reaction was stirred for 5 h, filtered, washed, and dried to obtain an intermediate product;

[0055] S3. Add 1 g of the intermediate product and 0.3 g of methacrylic acid into 100 mL of toluene, add 0.025 g of p-toluenesulfonic acid and 0.04 g of hydroquinone, heat and reflux for 5 h, remove the solvent under reduced pressure, wash, dry, and recrystallize to obtain modified chitin.

[0056] Comparative Preparation Example 2

[0057] Compared with Preparation Example 3, the difference is that step S2 is not performed.

[0058] The following steps are involved:

[0059] S1. 1 g of chitosan was added to 50 mL of 12 wt% NaOH solution, heated to 45 ° C, stirred for 1.5 h, filtered, washed, and dried to obtain pretreated chitosan;

[0060] S2. 1 g of pretreated chitin and 0.3 g of methacrylic acid were added to 100 mL of toluene, 0.025 g of p-toluenesulfonic acid and 0.04 g of hydroquinone were added, and the mixture was heated under reflux for 5 h. The solvent was removed under reduced pressure, washed, dried, and recrystallized to obtain an intermediate product 2.

[0061] S3. 1 g of intermediate product 2 was added to 100 mL of water, 0.35 g of tannic acid and 0.03 g of catalyst were added, heated to 45 ° C, stirred for 3 h, filtered, washed, and dried to obtain modified chitin;

[0062] The catalyst is a Tris-HCl solution with a pH of 9.

[0063] Example 1

[0064] A method for preparing a concrete water reducing agent comprises the following steps: adding 7g of modified chitosan prepared in Preparation Example 1, 3g of 1-vinyl-3-butylimidazole trifluoromethanesulfonate, 2g of vinyltrimethylsilane, methacrylic acid, 2g of trans-butenedioic acid and 0.01g of sodium persulfate into dimethylformamide, heating to 55°C under nitrogen protection, stirring for reaction for 3h, removing toluene under reduced pressure, washing with 20wt% NaOH solution and ethanol, and preparing the concrete water reducing agent.

[0065] Take a small amount of the prepared concrete water reducer, grind it with KBr and press it into a tablet. Use Fourier transform infrared spectrometer to analyze its functional group structure. -1 It is the characteristic absorption peak of -OH; 2937cm -1 and 2822cm -1 The stretching vibration absorption peak of CH bond in methyl and methylene is at 1720cm -1 The absorption peak at 1475cm indicates the presence of carboxyl -COOH and -COO-, and the peak at this location is relatively large, indicating the strength of the -COOH functional group in the product; -1 1237cm is the bending vibration absorption peak of CH bond in methyl and methylene; -1 and 1135cm -1 The stretching vibration absorption peak of CN bond is at 950-1080cm -1 The peak is the COC stretching vibration peak; 952cm -1 , 622cm -1 and 525cm -1 The peak is the stretching vibration peak of sulfonate group.

[0066] Example 2

[0067] A method for preparing a concrete water reducing agent comprises the following steps: adding 10 g of the modified chitin prepared in Preparation Example 2, 4 g of 1-vinyl-3-butylimidazole trifluoromethanesulfonate, 3 g of vinyltriethoxysilane, methacrylic acid, 4 g of trans-butenedioic acid and 0.02 g of potassium persulfate into dimethylformamide, heating to 65° C. under nitrogen protection, stirring for reaction for 5 h, removing toluene under reduced pressure, washing with 20 wt % NaOH solution and ethanol, and preparing the concrete water reducing agent.

[0068] Example 3

[0069] A method for preparing a concrete water reducing agent comprises the following steps: adding 8g of the modified chitin prepared in Preparation Example 3, 3.5g of 1-vinyl-3-butylimidazole trifluoromethanesulfonate, 2.5g of silane coupling agent KH570, methacrylic acid, 3g of trans-butenedioic acid and 0.015g of ammonium persulfate into dimethylformamide, heating to 60°C under nitrogen protection, stirring for reaction for 4h, removing toluene under reduced pressure, washing with 20wt% NaOH solution and ethanol, and preparing the concrete water reducing agent.

[0070] Comparative Example 1

[0071] Compared with Example 3, the difference is that the modified chitosan is prepared by Comparative Preparation Example 1.

[0072] Comparative Example 2

[0073] Compared with Example 3, the difference is that the modified chitosan is prepared by Comparative Preparation Example 2.

[0074] Comparative Example 3

[0075] Compared with Example 3, the difference is that no modified chitosan is added.

[0076] The details are as follows:

[0077] A preparation method of a concrete water reducing agent comprises the following steps: adding 3.5 g of 1-vinyl-3-butylimidazole trifluoromethanesulfonate, 2.5 g of a silane coupling agent KH570, methacrylic acid, 3 g of trans-butenedioic acid and 0.015 g of ammonium persulfate into dimethylformamide, heating to 60 DEG C under nitrogen protection, stirring for reaction for 4 hours, removing toluene under reduced pressure, washing with a 20wt% NaOH solution and ethanol, and obtaining the concrete water reducing agent.

[0078] Comparative Example 4

[0079] Compared with Example 3, the difference is that 1-vinyl-3-butylimidazole trifluoromethanesulfonate is not added.

[0080] The details are as follows:

[0081] A method for preparing a concrete water reducing agent comprises the following steps: adding 8g of the modified chitin prepared in Preparation Example 3, 2.5g of a silane coupling agent KH570, methacrylic acid, 3g of trans-butenedioic acid and 0.015g of ammonium persulfate into dimethylformamide, heating to 60°C under nitrogen protection, stirring for reaction for 4h, removing toluene under reduced pressure, washing with a 20wt% NaOH solution and washing with ethanol to prepare the concrete water reducing agent.

[0082] Comparative Example 5

[0083] Compared with Example 3, the difference is that the silane coupling agent KH570 is not added.

[0084] The details are as follows:

[0085] A method for preparing a concrete water reducing agent comprises the following steps: adding 8g of the modified chitin prepared in Preparation Example 3, 3.5g of 1-vinyl-3-butylimidazole trifluoromethanesulfonate, methacrylic acid, 3g of trans-butenedioic acid and 0.015g of ammonium persulfate into dimethylformamide, heating to 60°C under nitrogen protection, stirring for reaction for 4h, removing toluene under reduced pressure, washing with 20wt% NaOH solution and ethanol, and preparing the concrete water reducing agent.

[0086] Test Example 1

[0087] Under the conditions of laboratory temperature of 35°C and relative humidity of 69%, the concrete water reducing agent prepared in Examples 1-3 or Comparative Examples 1-5 and similar products available on the market were added in an amount of 0.5wt%. Concrete mix ratio: cement (Fujian "Minfu" brand P·O42.5R cement) 240kg; sand (granite machine-made sand produced by a certain building materials company in Xiamen) 775kg; water 165kg; crushed stone (5-25cm continuous graded crushed stone) 986kg; fly ash (Zhangzhou Houshi secondary fly ash) 80kg; slag powder (S95 grade slag powder of Sangang Power Plant) 80kg.

[0088] The test method for fluidity of cement paste refers to GB8077-2016.

[0089] The test was carried out in accordance with the relevant requirements of GB / T 50080-2016 "Standard for test methods of performance of ordinary concrete mixtures" and GB / T50081-2002 "Standard for test methods of mechanical properties of ordinary concrete".

[0090] The results are shown in Table 1.

[0091] Table 1

[0092]

[0093] It can be seen from the above table that the concrete water reducing agent prepared in Examples 1-3 of the present invention enables the concrete to have better comprehensive properties.

[0094] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a concrete water reducing agent, characterized in that: Modified chitosan, 1-vinyl-3-butylimidazole trifluoromethanesulfonate, a silane coupling agent with a double bond, methacrylic acid, trans-butenedioic acid and an initiator are added into dimethylformamide, heated and stirred for reaction, toluene is removed under reduced pressure, and alkali washing and alcohol washing are performed to obtain a concrete water reducing agent; the modified chitosan is chitosan modified with sodium sulfonate and acrylic acid and then modified with tannic acid.

2. The preparation method according to claim 1, characterized in that: The mass ratio of the modified chitin, 1-vinyl-3-butyl imidazole trifluoromethanesulfonate, the silane coupling agent with double bonds, methacrylic acid, trans-butenedioic acid and the initiator is 7-10:3-4:2-3:3-5:2-4:0.01-0.

02.

3. The preparation method according to claim 1, characterized in that: The temperature of the heating and stirring reaction is 55-65° C. and the time is 3-5 hours.

4. The preparation method according to claim 1, characterized in that: The preparation method of the modified chitosan is as follows: S1. Adding chitosan to an alkali solution, heating and stirring, filtering, washing, and drying to obtain pretreated chitosan; S2. The pretreated chitin was added to dimethyl sulfoxide, sodium 3-chloro-2-hydroxypropane sulfonate was added, the reaction was heated with stirring, filtered, washed, and dried to obtain an intermediate product; S3. The intermediate product and methacrylic acid are added to toluene, p-toluenesulfonic acid and hydroquinone are added, the reaction is heated to reflux, the solvent is removed under reduced pressure, washed, dried, and recrystallized to obtain an intermediate product 2; S4. Add the intermediate product 2 into water, add tannic acid and a catalyst, heat and stir to react, filter, wash, and dry to obtain modified chitosan.

5. The preparation method according to claim 4, characterized in that: The alkali solution in step S1 is a 10-15wt% NaOH or KOH solution, and the temperature of the heating and stirring treatment is 40-50°C and the time is 1-2h.

6. The preparation method according to claim 4, characterized in that: In step S2, the mass ratio of the pretreated chitin to sodium 3-chloro-2-hydroxypropane sulfonate is 10:3-5, the temperature of the heating and stirring reaction is 60-70° C., and the time is 4-6 hours.

7. The preparation method according to claim 4, characterized in that: In step S3, the mass ratio of the intermediate product, methacrylic acid, p-toluenesulfonic acid and hydroquinone is 10:2-4:0.2-0.3:0.3-0.5, and the heating reflux reaction time is 4-6h.

8. The preparation method according to claim 4, characterized in that: In step S4, the mass ratio of the intermediate product 2, tannic acid and catalyst is 10:3-4:0.2-0.5, the catalyst is a Tris-HCl solution with a pH of 8.5-9.5, the temperature of the heating and stirring reaction is 40-50° C., and the time is 2-4 hours.

9. The preparation method according to claim 1, characterized in that: The silane coupling agent with double bonds is selected from at least one of KH570, vinyl triethoxysilane, and vinyl trimethylsilane; the initiator is selected from at least one of azobisisobutyronitrile, azobisisovaleronitrile, sodium persulfate, potassium persulfate, and ammonium persulfate.

10. A concrete water reducing agent obtained by the preparation method according to any one of claims 1 to 9.

Images