A kind of water reducing agent for concrete and preparation method thereof

Abstract

The present invention belongs to the technical field of concrete admixtures, and specifically relates to a water reducing agent for concrete and a preparation method thereof. The preparation method comprises the following steps: adding montmorillonite to a stearyl trimethyl ammonium chloride solution, adding zinc chloride, adjusting the pH, stirring the reaction, calcining the obtained product, obtaining pretreated montmorillonite, adding the montmorillonite, aluminum nitrate and magnesium nitrate to water, adding sodium hydroxide and sodium carbonate, stirring the reaction to obtain a first modified montmorillonite, adding the montmorillonite to water and dispersing it uniformly, adding a surfactant, adjusting the pH, stirring the reaction to obtain a second modified montmorillonite, adding the montmorillonite and allyl polyoxyethylene ether to concentrated sulfuric acid, stirring the reaction, adding the product, sodium methacrylic acid, methacrylic acid, and hydroquinone to water to obtain a solution A, taking an initiator and adding it to water to obtain a solution B, respectively dropping the solution A and the solution B into water, and then keeping warm, adjusting the pH, collecting the product, and adding nano-hydroxyapatite to the product to obtain the product.

Description

Technical Field

[0001] The invention belongs to the technical field of concrete admixtures, and particularly relates to a water reducing agent for concrete and a preparation method thereof. Background Art

[0002] Water reducer is a concrete admixture that can significantly reduce the amount of mixing water while maintaining the slump of concrete. It has a dispersing effect on cement particles after being added to the concrete mixture, which can improve its workability, reduce the unit water consumption, improve the fluidity of the concrete mixture, or reduce the unit cement consumption and save cement. Most of them belong to anionic surfactants, and are usually divided into: lignin sulfonate water reducers, naphthalene water reducers, melamine water reducers, aminosulfonate water reducers, fatty acid water reducers, and polycarboxylate water reducers according to their chemical composition. Among them, polycarboxylate water reducers are recognized as the future development direction of concrete admixtures due to their low dosage, high dispersibility, high water reduction rate, and excellent durability.

[0003] Chinese patent CN116535579A, a polycarboxylic acid water reducer for concrete and its preparation process, discloses a method for preparing a polycarboxylic acid water reducer. Chinese patent CN112661915A, a water reducer for recycled concrete and its preparation method, discloses a method for preparing a water reducer for recycled concrete. However, the water-reducing performance of the water reducer prepared by the above method and the increase of concrete strength in a short time still have a lot of room for improvement. Based on this, it is necessary to improve the preparation process of the water reducer to further improve the water-reducing performance of the water reducer and broaden its application in the field of concrete technology. Summary of the invention

[0004] In order to overcome the deficiencies of the prior art, the primary purpose of the present invention is to provide a method for preparing a water reducing agent for concrete, which is simple to operate and easy to put into actual production.

[0005] Another object of the present invention is to provide a water reducing agent for concrete, which has high water reducing performance.

[0006] The purpose of the present invention is achieved through the following technical solutions:

[0007] A method for preparing a water reducing agent for concrete comprises the following steps:

[0008] (1) adding montmorillonite to an aqueous solution of stearyltrimethylammonium chloride, then adding zinc chloride, adjusting the pH of the solution to neutral, stirring and reacting, purifying the reaction solution to obtain a product, and calcining the product to obtain pretreated montmorillonite;

[0009] (2) adding the montmorillonite pretreated in step (1), aluminum nitrate and magnesium nitrate into water, and then adding sodium hydroxide and sodium carbonate, stirring and reacting to obtain a first modified montmorillonite;

[0010] (3) adding the first modified montmorillonite prepared in step (2) into water and dispersing the mixture uniformly, adding a surfactant, adjusting the pH value of the solution, stirring the mixture at room temperature, and collecting the product to obtain a second modified montmorillonite;

[0011] (4) adding the second modified montmorillonite and allyl polyoxyethylene ether prepared in step (3) into concentrated sulfuric acid, stirring for reaction, and collecting the product;

[0012] (5) adding the product of step (4), sodium methacrylic acid, methacrylic acid, and hydroquinone into water to obtain a solution A, adding an initiator into water to obtain a solution B, respectively dropping the solution A and the solution B into water under heating conditions, and then carrying out a heat-insulating reaction after the dropping is completed. After the reaction is completed, an alkali solution is added to adjust the pH value of the solution, and the product is collected after spray drying;

[0013] (6) Add nano-hydroxyapatite to the product of step (5) to obtain a water reducing agent for concrete.

[0014] The invention adds stearyl trimethyl ammonium chloride to montmorillonite to weaken the binding force between montmorillonite layers and increase its specific surface area. Zinc ions enter the montmorillonite layers through ion exchange and form zinc oxide after calcination, further expanding the montmorillonite layers to obtain a network-like montmorillonite. Then, aluminum oxide and magnesium oxide are inserted into the network-like montmorillonite to improve its strength and stability to obtain a first modified montmorillonite. The first modified montmorillonite is surface-modified to obtain a second modified montmorillonite, which is added to concentrated sulfuric acid with allyl polyoxyethylene ether to connect the modified montmorillonite with the allyl polyoxyethylene ether, and then free radical copolymerization is carried out with other monomers, and finally nano hydroxyapatite is added to obtain a water reducer.

[0015] Furthermore, in step (1), the mass ratio of zinc chloride, stearyltrimethylammonium chloride and montmorillonite is 1:(0.1-0.5):(10-15).

[0016] Furthermore, in step (1), the stirring reaction temperature is 75-80°C, and the stirring reaction time is 1-3h; the calcination temperature is 450-500°C, and the calcination time is 4-6h.

[0017] Furthermore, in step (2), the mass ratio of the pretreated montmorillonite, aluminum nitrate, magnesium nitrate, sodium hydroxide and sodium carbonate is 1: (0.8-1.2): (1.3-1.5): (0.5-0.75): (1.5-2); the stirring reaction temperature is 100-110° C., and the stirring reaction time is 3-5 h.

[0018] Furthermore, in step (3), the mass ratio of the first modified montmorillonite to the surfactant is 1:(1.5-2); the surfactant is sodium dodecylbenzene sulfonate; the pH of the solution is adjusted to 2-3; and the stirring time is 3-5 hours.

[0019] Furthermore, in step (4), the mass ratio of the second modified montmorillonite, allyl polyoxyethylene ether and concentrated sulfuric acid is 1: (1.5-3): (0.1-0.5); the relative molecular mass of the allyl polyoxyethylene ether is 1200-2500; the stirring reaction temperature is 50-65°C, and the stirring reaction time is 50-60min.

[0020] Furthermore, in step (5), the mass ratio of the product of step (4), sodium methacrylic acid, methacrylic acid, hydroquinone, and initiator is 1: (2.5-4): (8-12): (0.3-0.6): (0.08-0.15); the initiator is ammonium persulfate.

[0021] Furthermore, in step (5), the heating temperature is 70-80° C.; the insulation time is 2-4 hours; and the pH of the solution is adjusted to neutral.

[0022] Furthermore, based on the total mass of the water reducing agent, the amount of the nano-hydroxyapatite added in step (6) is 0.2-0.3% of the total mass of the water reducing agent.

[0023] A water reducing agent for concrete is prepared by adopting the preparation method of the water reducing agent for concrete.

[0024] Compared with the prior art, the present invention has the following technical effects:

[0025] 1. The present invention first prepares modified montmorillonite by organic modification, ion exchange, and insertion of inorganic oxides, then reacts the modified montmorillonite with allyl polyoxyethylene ether to connect the modified montmorillonite with allyl polyoxyethylene ether, then performs free radical copolymerization with other monomers, and finally adds nano hydroxyapatite to obtain a water reducer. The present invention adds modified montmorillonite and nano hydroxyapatite to the traditional polycarboxylic acid water reducer, and the combined action of the two not only improves the water reducing performance of the water reducer, but also effectively improves the strength of concrete.

[0026] 2. The test results of the present invention show that the water reducing rate of the water reducing agent is more than 33.6%, and the water bleeding rate is 12.5-14.1%. After the water reducing agent is added to the concrete mixture, the 28d compressive strength of the concrete can reach 66.2-68.5MPa. DETAILED DESCRIPTION

[0027] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or replacements can also be made, all of which should be deemed to belong to the protection scope of the present invention. The specific conditions not indicated in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used, unless otherwise specified, are conventional products obtained through commercial channels.

[0028] 1. Embodiment

[0029] Example 1

[0030] Example 1 provides a method for preparing a water reducing agent for concrete, and the specific preparation process is as follows:

[0031] (1) According to the mass ratio of zinc chloride, stearyl trimethyl ammonium chloride and montmorillonite of 1:0.3:12, montmorillonite was added to an aqueous solution of stearyl trimethyl ammonium chloride, and zinc chloride was then added. After stirring evenly, the pH of the solution was adjusted to neutral, and the reaction was stirred at 78°C for 2 hours. After the reaction was completed, the reaction solution was filtered, washed, and dried to obtain a product; the product was calcined at 470°C for 5 hours to obtain pretreated montmorillonite.

[0032] (2) The montmorillonite pretreated in step (1), aluminum nitrate and magnesium nitrate are added to water, and then sodium hydroxide and sodium carbonate are added, and the mixture is stirred and reacted at 105° C. for 4 hours. After the reaction is completed, the reaction solution is filtered, washed and dried to obtain a first modified montmorillonite.

[0033] (3) According to the mass ratio of the first modified montmorillonite to sodium dodecylbenzene sulfonate of 1:1.8, the first modified montmorillonite of step (2) is added into water and dispersed evenly, and then sodium dodecylbenzene sulfonate is added, and the pH value of the solution is adjusted to 2.5. The solution is stirred at room temperature for 4 hours, and allowed to stand for precipitation. The solid phase product is collected, washed, and vacuum dried to obtain a second modified montmorillonite.

[0034] (4) The second modified montmorillonite and allyl polyoxyethylene ether (relative molecular weight: 2000) prepared in step (3) were added to concentrated sulfuric acid in a mass ratio of 1:2:0.3, and the mixture was stirred at 55° C. for 52 minutes to collect the product.

[0035] (5) The product of step (4), sodium methacrylic acid, methacrylic acid, hydroquinone and ammonium persulfate are added to water in a mass ratio of 1:3:9:0.5:0.10 to obtain a solution A; ammonium persulfate is added to water to obtain a solution B; at 75°C, solution A and solution B are respectively added dropwise to water in a mass ratio of solution A, solution B and water of 2:1:2; after the addition is completed, the mixture is kept warm for reaction for 3 hours, the temperature is lowered to 40°C, sodium hydroxide solution is added to adjust the pH of the solution to neutral, and the solution is spray dried to collect the product.

[0036] (6) Add nano-hydroxyapatite to the product of step (5) in an amount of 0.25% of the total mass of the water reducer to obtain a water reducer for concrete.

[0037] Example 1 also provides a water reducing agent for concrete, which is prepared by the above preparation method.

[0038] Example 2

[0039] Example 2 provides a method for preparing a water reducing agent for concrete, and the specific preparation process is as follows:

[0040] (1) According to the mass ratio of zinc chloride, stearyl trimethyl ammonium chloride and montmorillonite of 1:0.5:15, montmorillonite was added to an aqueous solution of stearyl trimethyl ammonium chloride, and zinc chloride was then added. After stirring evenly, the pH of the solution was adjusted to neutral, and the reaction was stirred at 75°C for 3 hours. After the reaction was completed, the reaction solution was filtered, washed, and dried to obtain a product; the product was calcined at 500°C for 4 hours to obtain pretreated montmorillonite.

[0041] (2) The montmorillonite pretreated in step (1), aluminum nitrate and magnesium nitrate are added to water according to the mass ratio of the pretreated montmorillonite, aluminum nitrate, magnesium nitrate, sodium hydroxide and sodium carbonate of 1:1.2:1.5:0.75:2, and then sodium hydroxide and sodium carbonate are added. The mixture is stirred and reacted at 100° C. for 5 hours. After the reaction is completed, the reaction solution is filtered, washed and dried to obtain a first modified montmorillonite.

[0042] (3) According to the mass ratio of the first modified montmorillonite to sodium dodecylbenzene sulfonate of 1:2, the first modified montmorillonite of step (2) is added into water and dispersed evenly, and then sodium dodecylbenzene sulfonate is added, and the pH value of the solution is adjusted to 3. The mixture is stirred at room temperature for 3 h, and allowed to stand for precipitation. The solid phase product is collected, washed, and vacuum dried to obtain a second modified montmorillonite.

[0043] (4) The second modified montmorillonite and allyl polyoxyethylene ether (relative molecular weight: 1200) prepared in step (3) were added to concentrated sulfuric acid in a mass ratio of 1:3:0.5, and the mixture was stirred at 50° C. for 60 min to collect the product.

[0044] (5) According to the mass ratio of the product of step (4), sodium methacrylic acid, methacrylic acid, hydroquinone and ammonium persulfate of 1:4:12:0.6:0.15, the product of step (4), sodium methacrylic acid, methacrylic acid and hydroquinone are added to water to obtain solution A, and ammonium persulfate is added to water to obtain solution B; at 70°C, according to the mass ratio of solution A, solution B and water of 2:1:2, solution A and solution B are respectively added dropwise to water, after the addition is completed, the reaction is kept warm for 4 hours, the temperature is lowered to 40°C, sodium hydroxide solution is added to adjust the pH of the solution to neutral, and then the solution is spray dried to collect the product.

[0045] (6) Add nano-hydroxyapatite to the product of step (5) in an amount of 0.2% of the total mass of the water reducer to obtain a water reducer for concrete.

[0046] Example 2 also provides a water reducing agent for concrete, which is prepared using the above preparation method.

[0047] Example 3

[0048] Example 3 provides a method for preparing a water reducing agent for concrete, and the specific preparation process is as follows:

[0049] (1) According to the mass ratio of zinc chloride, stearyl trimethyl ammonium chloride and montmorillonite of 1:0.1:10, montmorillonite was added to an aqueous solution of stearyl trimethyl ammonium chloride, and zinc chloride was then added. After stirring evenly, the pH of the solution was adjusted to neutral, and the reaction was stirred at 80°C for 1 hour. After the reaction was completed, the reaction solution was filtered, washed, and dried to obtain a product; the product was calcined at 450°C for 6 hours to obtain pretreated montmorillonite.

[0050] (2) The montmorillonite pretreated in step (1), aluminum nitrate and magnesium nitrate are added to water according to the mass ratio of the pretreated montmorillonite, aluminum nitrate, magnesium nitrate, sodium hydroxide and sodium carbonate of 1:0.8:1.3:0.5:1.5, and then sodium hydroxide and sodium carbonate are added. The mixture is stirred and reacted at 110° C. for 3 h. After the reaction is completed, the reaction solution is filtered, washed and dried to obtain a first modified montmorillonite.

[0051] (3) According to the mass ratio of the first modified montmorillonite to sodium dodecylbenzene sulfonate of 1:1.5, the first modified montmorillonite of step (2) is added into water and dispersed evenly, and then sodium dodecylbenzene sulfonate is added, and the pH value of the solution is adjusted to 2. The solution is stirred at room temperature for 5 hours, and allowed to stand for precipitation. The solid phase product is collected, washed, and vacuum dried to obtain a second modified montmorillonite.

[0052] (4) The second modified montmorillonite and allyl polyoxyethylene ether (relative molecular weight: 2500) prepared in step (3) were added to concentrated sulfuric acid in a mass ratio of 1:1.5:0.1, and the mixture was stirred at 65°C for 50 minutes to collect the product.

[0053] (5) The product of step (4), sodium methacrylic acid, methacrylic acid, hydroquinone and ammonium persulfate are added to water in a mass ratio of 1:2.5:8:0.3:0.08 to obtain a solution A, and ammonium persulfate is added to water to obtain a solution B; at 80°C, solution A and solution B are added dropwise to water in a mass ratio of solution A: solution B: water of 2:1:2, and after the addition is completed, the mixture is kept warm for reaction for 2 hours, cooled to 40°C, sodium hydroxide solution is added to adjust the pH of the solution to neutral, and the solution is spray dried to collect the product.

[0054] (6) Add nano-hydroxyapatite to the product of step (5) in an amount of 0.3% of the total mass of the water reducer to obtain a water reducer for concrete.

[0055] Example 3 also provides a water reducing agent for concrete, which is prepared using the above preparation method.

[0056] 2. Comparative Example

[0057] Comparative Example 1 provides a method for preparing a water reducing agent, which is different from Example 1 in that:

[0058] Omit steps (1)-(4);

[0059] In step (5), allyl polyoxyethylene ether is used instead of the product obtained in step (4) of Example 1 to prepare the subsequent water reducing agent; the rest is the same as in Example 1.

[0060] Comparative Example 2

[0061] Comparative Example 2 provides a method for preparing a water reducing agent, which is different from Example 1 in that:

[0062] Omit steps (1)-(2);

[0063] In step (3), montmorillonite is used instead of the first modified montmorillonite to prepare the subsequent water reducing agent; the rest is the same as in Example 1.

[0064] Comparative Example 3

[0065] Comparative Example 3 provides a method for preparing a water reducing agent, which is different from Example 1 in that:

[0066] Step (2) is omitted, and the rest is the same as in Example 1.

[0067] Comparative Example 4

[0068] Comparative Example 4 provides a method for preparing a water reducing agent, which is different from Example 1 in that:

[0069] Step (6) is omitted, and the rest is the same as in Example 1.

[0070] Performance testing

[0071] The test concrete mix ratio is: 360kg cement, 521kg sand, 1184kg gravel, of which the cement is 42.5R Portland cement.

[0072] (1) Water reduction performance test

[0073] The water reducing agents obtained in Examples 1-3 and Comparative Examples 1-4 were added in an amount equal to 0.5 wt% of the amount of cement, and the water reducing rate of the water reducing agents was tested according to the method in GB / 8076-2008 "Concrete Admixtures". The results are shown in Table 1.

[0074] (2) Water seepage performance test

[0075] The water reducing agents obtained in Examples 1-3 and Comparative Examples 1-4 were added in an amount equal to 0.5 wt% of the amount of cement, and the water bleeding rate of the concrete mixture was detected according to the method in GB / 8076-2008 "Concrete Admixtures". The smaller the water bleeding rate, the stronger the anti-water bleeding performance of the concrete. The results are shown in Table 1.

[0076] (3) Retarding performance test

[0077] The water reducing agents obtained in Examples 1-3 and Comparative Examples 1-4 were added in an amount of 0.5 wt% of the amount of cement. The initial setting time and final setting time of the concrete were tested according to the method in GB / 8076-2008 "Concrete Admixtures", and the setting time difference was calculated. The setting time difference was used to characterize the retarding properties of the concrete mixture. The larger the setting time difference, the stronger the coagulation properties of the concrete mixture. The results are shown in Table 1.

[0078] Table 1 Performance results of water reducing agents of Examples 1-3, Comparative Examples 1-4 and corresponding concrete

[0079]

[0080] It can be seen from Table 1 that the water reducing agent obtained in Examples 1-3 has a relatively high water reducing rate, reaching more than 33.6%. When the water reducing agent obtained in Examples 1-3 is used in concrete, the concrete has excellent anti-bleeding and slow setting properties.

[0081] Compared with Examples 1-3, Comparative Example 1 uses allyl polyoxyethylene ether as a raw material to polymerize with other monomers to prepare a traditional polycarboxylate water reducer, and the water reducer of Comparative Example 2 uses montmorillonite instead of the first modified montmorillonite for subsequent preparation during the preparation process; the water reducer of Comparative Example 3 uses pretreated montmorillonite instead of the first modified montmorillonite for subsequent preparation during the preparation process; the water reducer of Comparative Example 4 does not use nano hydroxyapatite during the preparation process. The water reducing performance of the water reducers prepared by the above four methods is lower than that of Examples 1-3, among which the water reducing rate of the water reducer prepared by the preparation method of Comparative Example 1 is the lowest, only 15.2%.

[0082] Compared with Examples 1-3, when the water reducing agents obtained in Comparative Examples 1-4 are used in concrete, the water resistance and retarding properties of the concrete are reduced to varying degrees, among which the water resistance and retarding properties of Comparative Example 1 are the worst.

[0083] (4) Strength performance test

[0084] The water reducing agent obtained in Examples 1-3 and Comparative Examples 1-4 was added in an amount of 0.5 wt% of the amount of cement, and the strength of the concrete was tested according to GB / T50081-2019 "Test Methods for Physical and Mechanical Properties of Concrete", characterized by compressive strength. The results are shown in Table 2.

[0085] Table 2 Compressive strength results of concrete obtained by adding water reducing agent of Examples 1-3 and Comparative Examples 1-4

[0086]

[0087] It can be seen from Table 2 that when the water reducing agent obtained in Examples 1-3 is used in concrete, the concrete has a higher compressive strength.

[0088] Compared with Examples 1-3, when the water reducing agents obtained in Comparative Examples 1-4 are used in concrete, the compressive strength of the concrete is reduced to varying degrees, among which the strength performance of Comparative Example 1 is the worst. It can be seen from the above that the water reducing agent obtained by the present invention can improve the compressive strength of concrete.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. On the basis of the present invention, some modifications or replacements may be made thereto, but these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of protection claimed by the present invention.

Claims

1. A method for preparing a water reducing agent for concrete, characterized in that: The following steps are involved: (1) adding montmorillonite to an aqueous solution of stearyltrimethylammonium chloride, then adding zinc chloride, adjusting the pH of the solution to neutral, stirring and reacting, purifying the reaction solution to obtain a product, and calcining the product to obtain pretreated montmorillonite; (2) adding the montmorillonite pretreated in step (1), aluminum nitrate and magnesium nitrate into water, and then adding sodium hydroxide and sodium carbonate, stirring and reacting to obtain a first modified montmorillonite; (3) adding the first modified montmorillonite prepared in step (2) into water and dispersing the mixture uniformly, adding a surfactant, adjusting the pH value of the solution, stirring the mixture at room temperature, and collecting the product to obtain a second modified montmorillonite; (4) adding the second modified montmorillonite and allyl polyoxyethylene ether prepared in step (3) into concentrated sulfuric acid, stirring for reaction, and collecting the product; (5) adding the product of step (4), sodium methacrylic acid, methacrylic acid, and hydroquinone into water to obtain a solution A, adding an initiator into water to obtain a solution B, respectively dropping the solution A and the solution B into water under heating conditions, and then carrying out a heat-insulating reaction after the dropping is completed. After the reaction is completed, an alkali solution is added to adjust the pH value of the solution, and the product is collected after spray drying; (6) Add nano-hydroxyapatite to the product of step (5) to obtain a water reducing agent for concrete.

2. The method for preparing a water reducing agent for concrete according to claim 1, characterized in that: The mass ratio of zinc chloride, stearyl trimethyl ammonium chloride and montmorillonite in step (1) is 1: (0.1-0.5): (10-15).

3. The method for preparing a water reducing agent for concrete according to claim 1, characterized in that: In step (1), the stirring reaction temperature is 75-80°C, and the stirring reaction time is 1-3h; the calcination temperature is 450-500°C, and the calcination time is 4-6h.

4. The method for preparing a water reducing agent for concrete according to claim 1, characterized in that: The mass ratio of the pretreated montmorillonite, aluminum nitrate, magnesium nitrate, sodium hydroxide and sodium carbonate in step (2) is 1: (0.8-1.2): (1.3-1.5): (0.5-0.75): (1.5-2); the stirring reaction temperature is 100-110° C., and the stirring reaction time is 3-5 hours.

5. The method for preparing a water reducing agent for concrete according to claim 1, characterized in that: In step (3), the mass ratio of the first modified montmorillonite to the surfactant is 1:(1.5-2); the surfactant is sodium dodecylbenzene sulfonate; the pH of the solution is adjusted to 2-3; and the stirring time is 3-5 hours.

6. The method for preparing a water reducing agent for concrete according to claim 1, characterized in that: In step (4), the mass ratio of the second modified montmorillonite, allyl polyoxyethylene ether and concentrated sulfuric acid is 1: (1.5-3): (0.1-0.5); the relative molecular mass of the allyl polyoxyethylene ether is 1200-2500; the temperature of the stirring reaction is 50-65° C., and the stirring reaction time is 50-60 min.

7. The method for preparing a water reducing agent for concrete according to claim 1, characterized in that: In step (5), the mass ratio of the product of step (4), sodium methacrylic acid, methacrylic acid, hydroquinone and initiator is 1: (2.5-4): (8-12): (0.3-0.6): (0.08-0.15); the initiator is ammonium persulfate.

8. The method for preparing a water reducing agent for concrete according to claim 1, characterized in that: In step (5), the heating temperature is 70-80° C.; the insulation time is 2-4 hours; and the pH of the solution is adjusted to neutral.

9. The method for preparing a water reducing agent for concrete according to claim 1, characterized in that: Based on the total mass of the water reducing agent, the amount of the nano-hydroxyapatite added in step (6) is 0.2-0.3% of the total mass of the water reducing agent.

10. A water reducing agent for concrete, characterized in that: The concrete water reducing agent is prepared by the preparation method of any one of claims 1 to 9.

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