A wet-mixed mortar long-acting water-retaining agent and a preparation method thereof

Abstract

The application provides a wet-mixed mortar long-acting water-retaining agent and a preparation method thereof. The wet-mixed mortar long-acting water-retaining agent is prepared by free radical copolymerization of four monomers A, B, C and D. The monomer A is an acrylic compound, the monomer B is an acrylamide compound, the monomer C is a hydroxyalkyl acrylate compound, and the monomer D is vinyl acetate. The molar ratio of the monomers A, B, C and D is 1.0:(1.0-3.0):(0.5-3.0):(8.0-20.0). The weight average molecular weight of the wet-mixed mortar long-acting water-retaining agent is 1x10 5 -3x10 5 The wet-mixed mortar long-acting water-retaining agent has good workability, does not cause segregation and bleeding, has small consistency loss, long working efficiency, good water retention, and the water retention rate can reach more than 93% after 30 hours.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of building materials, in particular to a long-acting water-retaining agent for wet-mixed mortar and a preparation method thereof. BACKGROUND

[0002] Wet-mixed mortar, also known as premixed mortar, is a finished mortar product prepared by reasonably mixing cement, fine aggregate, admixture and water and manufactured in a factory, transported to a construction site by a mixing tank truck, stored in a special container and kept workable for a certain period of time. Wet-mixed mortar has the advantages of saving resources, protecting the environment and stable quality. Wet-mixed mortar often needs to have high workability, especially good water retention, viscosity, long setting performance and excellent workability, and the key to fundamentally improving and enhancing the performance of mortar is to use high-performance wet-mixed mortar admixture. Wet-mixed mortar admixture is generally composed of water-reducing and strengthening components (containing air entraining agent), thickening and water-retaining components and setting retarding components, but the performance of current mortar admixtures is uneven, and the development of mortar admixtures lags far behind that of concrete water-reducing agents. Therefore, the research on mortar admixtures will become a focus of attention in the development of the mortar industry.

[0003] Water retention performance of wet-mixed mortar is one of the most important indicators, and only wet-mixed mortar with excellent water retention performance can ensure its workability and facilitate smooth construction. At present, the thickening and water-retaining components in wet-mixed mortar are mainly cellulose ethers, and the commonly used cellulose ethers are carboxymethyl cellulose ether (CMC) and hydroxypropyl cellulose ether (HPMC). The CMC molecular structure contains carboxyl groups, and the HPMC molecular structure contains hydroxyl groups or hydroxypropyl groups. The former dissolves faster in water, but the former easily chelates with multivalent metal ions to produce precipitates, which cannot meet the long-term water retention purpose of wet-mixed mortar. The latter does not form precipitates by chelating with multivalent metal ions, but has a big problem of solubility in water, which causes the wet-mixed mortar admixture compound product to precipitate. In recent years, water-soluble polymers such as anionic polyacrylamide are also often used as water-retaining agents. Anionic polyacrylamide has high solubility in water, and the long-chain molecules and negative groups have strong ability to change free water into bound water, but it does not have long-term water retention effect.

[0004] Patent ZL201910459034.X discloses "a water-retaining type wet-mixed mortar plasticizer and its preparation method". The polyether monomer, cumenyl polyoxyethylene ether, 2-amino-3-p-hydroxyphenyl propionic acid ester and catalyst are mixed, then the initiator solution is added, after reaction, the mixed solution A composed of acrylic acid and 3-hydroxyphenyl phosphoric acid dihydro lauric alcohol ester is added, and the solution B composed of initiator and chain transfer agent is added, after reaction, the pH is adjusted to 7-8, and the wet-mixed mortar plasticizer with a molecular weight of 60000-100000 is obtained. The wet-mixed mortar plasticizer disclosed in the application has a small molecular weight, and only the 2h consistency loss and the initial water retention rate of the mortar are tested in the application examples, and the long-term consistency loss and water retention rate are not mentioned.

[0005] Patent CN202010454186.3 discloses "a wet-mixed mortar additive and its preparation method". The wet-mixed mortar additive is composed of water reducing agent 1-5%, water retaining agent 0.1-1.0%, plastic retention time regulator 5-15%, air entraining agent 1-4%, viscosity regulator 0.1-0.3%, and the balance is water. The water retaining agent in the application is made by mixing hydroxypropyl methylcellulose, hydroxypropyl starch ether and redispersible latex powder, which can be completely dispersed at 60-70℃, and when mixed with other additives, stratification phenomenon is easy to occur. SUMMARY

[0006] In order to solve the problems of low solubility of the commonly used water retaining component (cellulose ether or water-soluble polymer) in the existing wet-mixed mortar additive, poor compatibility with other additive components, and insufficient long-term water retention performance, the application provides a wet-mixed mortar long-term water retaining agent, which has high solubility, good compatibility with other additive components, and the prepared wet-mixed mortar has good workability, small consistency loss, and long working efficiency, and the application also provides a preparation method of the long-term water retaining agent.

[0007] A wet-mixed mortar long-term water retaining agent, which is prepared by free radical copolymerization of four monomers A, B, C and D,

[0008] The monomer A is an acrylic compound, and the structural formula of the acrylic compound is: Wherein M1 is H, monovalent alkali metal ion or ammonium ion; R1 is H or CH3; the carboxylic acid group in acrylic compound provides adsorption group and electric repulsion in polymer, so that the cement particle diameter increases, the resistance of polymer molecular chain movement increases, not only makes the polymer can effectively and stably fix the free water molecule, but also can prevent the entanglement between polymer molecules, thereby increasing the solubility of polymer itself and the compatibility with other additives, at the same time, the ability of negative group to change free water into bound water is enhanced, the water retention of polymer is improved. The content of monomer A is too low, the electrostatic repulsion is weak, which cannot prevent the entanglement of polymer molecular chain, affects the solubility of itself and the compatibility with other additives when compounding, and affects the water retention of polymer. The content of monomer A is too high, which enhances the adsorption rate of polymer on cement particles, and the adsorption rate is too fast, which leads to the quick " failure" of water retention of polymer.

[0009] The monomer B is acrylamide compound, and the structural formula of the acrylamide compound is as follows: Wherein R2 is H or CH3; R3 and R4 are independently C n H 2n+1 or (CH2) p OC q H 2q+1 , n is an integer of 0-4, p is an integer of 1-3, and q is an integer of 0-4; wherein, R3 and R4 cannot be (CH2) p OC q H 2q+1 at the same time; when R3 is (CH2) p OC q H 2q+1 , R4 is H; when R4 is (CH2) p OC q H 2q+1 , R3 is H; the hydrogen bond association ability between amide molecules in acrylamide compound is strong, which can strongly lock free water and enhance the water retention of polymer; if the number of carbon atoms of alkyl / hydroxyalkyl represented by R3 and R4 in the structural formula of acrylamide compound is too large, the hydrogen bond association between amide molecules will be reduced, thereby reducing the water retention of polymer and affecting the solubility of polymer. At the same time, the polymerization activity of acrylamide compound is high, which can make the polymer have a certain molecular weight, which is also the key to the excellent water retention of polymer. In addition, the amide monomer can also release adsorption groups in the strong alkaline environment of cement, but the speed is slower than that of hydroxyalkyl acrylate compound, so it can have a synergistic effect with hydroxyalkyl acrylate compound, and further ensure the long-acting water retention of polymer. The content of monomer B is too high, which enhances the entanglement between polymer molecular chains, thereby affecting the consistency of mortar; the content of monomer B is too low, which cannot guarantee the molecular weight of polymer, thereby affecting the water retention of polymer.

[0010] The monomer C is a hydroxyalkyl acrylate compound, and the structural formula of the hydroxyalkyl acrylate compound is:

[0011] wherein R5 is H or CH3; R6 represents C m H 2m OH, m is an integer of 2-4, and a too large value of m will affect the hydrolysis ability and hydrolysis rate of the monomer C. The hydroxyalkyl acrylate compound can gradually release the adsorption groups of carboxylic acid in the strong alkaline environment of cement, so that a persistent and stable adsorption between the polymer and the cement particles is formed, and thus the free water molecules can be continuously and stably fixed by the polymer molecules. If the content of the monomer C is too high, the initial water retention performance of the polymer is insufficient; and if the content of the monomer C is too low, the water retention performance in the later period cannot be guaranteed.

[0012] The monomer D is vinyl acetate; the vinyl acetate can gradually release a large amount of hydroxyl groups in the strong alkaline environment of cement, and the hydroxyl groups can form hydrogen bonds with the free water molecules to fix the free water molecules, which is a powerful guarantee for the long-acting water retention of the polymer. If the content of the monomer D is too low, the content of the hydroxyl groups is insufficient, which affects the water retention performance of the polymer; and if the content of the monomer D is too high, the water solubility of the polymer is affected.

[0013] The molar ratio of the monomer A, the monomer B, the monomer C and the monomer D is 1.0:1.0-3.0:0.5-3.0:8.0-20.0.

[0014] The weight average molecular weight of the wet-mixed mortar long-acting water retention agent is 1×10 5 -3×10 5 .

[0015] The preparation method of the wet-mixed mortar long-acting water retention agent specifically comprises the following steps:

[0016] (1) In a reactor, the monomer A, the monomer B, the monomer C, the monomer D and a certain amount of deionized water are added, and the solution is neutralized to pH=7-8 by NaOH.

[0017] (2) After the deoxygenation operation, the temperature is raised to 45-55°C under stirring.

[0018] (3) The initiator is prepared into a solution a with a mass concentration of 0.5%-1.0%, and the chain transfer agent is prepared into a solution b with a mass concentration of 0.5%-1.0%; the solution a and the solution b are respectively dropped into the reactor within 2-3h, and after the dropping is completed, the reaction is started, and until the reaction is completed, the wet-mixed mortar long-acting water retention agent with a solid content of 5%-10% and a weight average molecular weight of 1×10 5 -3×10 5 is obtained.

[0019] The reactor in step (1) is a reactor equipped with a thermometer, a stirrer, and a dropping funnel.

[0020] The deoxygenation operation in step (2) is achieved by continuously purging nitrogen into the reactor.

[0021] The initiator in step (3) is a water-soluble azo initiator or a persulfate initiator; the water-soluble azo initiator is at least one selected from azobisdiisobutylamidine hydrochloride, azobisdiisobutylimidazole hydrochloride, azobis cyanovaleric acid, and azobisdiisopropylimidazole; and the persulfate initiator is at least one selected from sodium persulfate, potassium persulfate, and ammonium persulfate.

[0022] The amount of the initiator is 1.0% to 3.0% of the total mass of monomers A, B, C, and D. Too much initiator will generate more free radicals, accelerate the reaction rate, and reduce the molecular weight of the product; too little initiator will generate fewer free radicals, slow down the reaction, and even stop the polymerization.

[0023] The chain transfer agent in step (3) is at least one selected from dodecanethiol, hexadecanethiol, mercaptoethanol, mercaptoacetic acid, 2-mercaptopropionic acid, and 3-mercaptopropionic acid.

[0024] The amount of the chain transfer agent is 0.5% to 2.0% of the total number of moles of monomers A, B, C, and D. Too much or too little chain transfer agent will make the molecular weight of the product too small or too large, resulting in the loss of the proper function of the product.

[0025] The dropping time of the initiator and chain transfer agent solution in step (3) is 2 to 3 hours, and the solvent of the initiator and chain transfer agent solution is water. The concentration of the initiator and chain transfer agent aqueous solution is not required to be high, as long as it can be dropped within a given time. A higher concentration means slower dropping, and a lower concentration means faster dropping. Too high a concentration means less solution volume, and the dropping speed is difficult to control. Therefore, the initiator and chain transfer agent are both prepared into a solution with a mass concentration of 0.5% to 1.0%.

[0026] The reaction temperature in step (3) is 70°C to 80°C, and the reaction time is 3 to 4 hours. The reaction temperature is determined by the decomposition temperature of the aforementioned initiator. Too high or too low a temperature will change the half-life of the initiator, affect the polymerization rate and the relative molecular weight of the polymerization product, and thus change the comprehensive performance of the polymerization product.

[0027] Compared with the prior art, the present application has the following advantages:

[0028] 1. The wet-mixed mortar long-acting water-retaining agent of the present application has good homogeneity and will not appear uneven phenomena such as precipitation and separation when compounded with other additives (such as water-reducing agents, retarders, air-entraining agents, etc.).

[0029] 2. The long-acting water-retaining agent for wet-mixed mortar is rich in hydroxyl, carboxyl, amido and other groups capable of forming hydrogen bonds with water molecules, so that the free water in the mortar system is fixed to play a water-retaining role.

[0030] 3. The long-acting water-retaining agent for wet-mixed mortar contains ester groups, amido groups and other groups capable of hydrolyzing in the strong alkaline environment of cement, continuously releasing hydroxyl groups and carboxyl groups to play a long-acting water-retaining role.

[0031] 4. The long-acting water-retaining agent for wet-mixed mortar mainly plays a long-acting water-retaining role through hydrogen bonding between the polymer and water molecules and the interaction between the polymer and cement particles, so that the polymer chain movement is increased in resistance, the water molecules are fixed, and the long-acting water-retaining role is played. It has no negative effect on the initial consistency of the mortar.

[0032] 5. The long-acting water-retaining agent for wet-mixed mortar applied to wet-mixed mortar has good workability, does not appear segregation and bleeding, has small consistency loss, long working efficiency, good water retention of mortar, and the water retention rate can reach more than 93% after 30 hours. DETAILED DESCRIPTION

[0033] The technical solutions of the present application will be described clearly and completely below in combination with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0034] In the embodiments of the present application, the weight average molecular weight Mw of the polymer is determined by Wyatt technology corporation gel permeation chromatograph (miniDAWN Tristar laser light scattering detector).

[0035] The raw materials used in the synthesis examples and their codes are as follows in Table 1:

[0036] Table 1 Raw materials used in the synthesis examples and their codes

[0037]

[0038]

[0039]

[0040] Synthesis Example 1

[0041] In a glass reactor equipped with a thermometer, a stirrer, a dropping funnel, a nitrogen inlet tube, 7.2 g of A-1, 21.3 g of B-1, 23.2 g of C-1, 129 g of D and 1499 g of deionized water were added, and the solution was neutralized to pH = 7-8 with 4 g of NaOH. The stirring was started, the reactor was purged with nitrogen while stirring, and the temperature was raised to 50°C. 3.6 g of initiator I-1 and 2.5 g of chain transfer agent K-1 were separately prepared into a solution a with a mass concentration of 1.0% and a solution b with a mass concentration of 0.5%. The solution a and the solution b were dropped into the reactor in 2-3 h, after the dropping was completed, the temperature was raised to 70-80°C, and the reaction was continued at this temperature for 3-4 h to obtain a wet-mixed mortar long-term water-retaining agent solution with a solid content of 7.5% and a weight average molecular weight of 1.98 x 10 5

[0042] Synthetic Examples 2-10 of the Invention

[0043] Synthetic Examples 2-10 of the Invention were prepared according to the procedure of Synthetic Example 1, and were fed according to the proportions described in Table 2, Table 3.

[0044] Table 2 Proportions for preparing synthetic examples

[0045] Examples Monomer A Monomer D Monomer C Monomer D A:B:C:D (molar ratio) 1 A-1 B-1 C-1 D 1:3:2:15 2 A-1 B-2 C-2 D 1:2:2:15 3 A-1 B-3 C-3 D 1:2:3:8 4 A-2 B-4 C-1 D 1:3:0.5:20 5 A-1 B-5 C-1 D 1:3:2:15 6 A-1 B-6 C-1 D 1:1:2:8 7 A-1 B-7 C-1 D 1:3:2:15 8 A-1 B-1 C-1 D 1:1:2:15 9 A-1 B-1 C-1 D 1:3:0.5:15 10 A-1 B-1 C-1 D 1:3:2:8

[0046] Table 2 (continued)

[0047]

[0048] Table 3 Amounts of monomers used in preparing synthetic examples, molecular weight and solid content of products

[0049]

[0050]

[0051] Application Examples

[0052] The application will be further described below in connection with application examples. In the application, Comparative Example 1 is hydroxypropyl methylcellulose ether; Comparative Example 2 is a polymer with a solid content of 7.5% and a molecular weight of 2.02 x 10 5 5 5 ​​​Comparative Example 5 is a polymer with a solid content of 7.5% and a molecular weight of 2.03 x 10 5 .

[0053] The mortar mix ratio in the present application is shown in Table 4, and the performance test results of each example and comparative example are shown in Table 5. The setting adjusting component in Table 4 is a 20% sucrose solution, and the air entraining component is sodium dodecyl sulfate. The consistency of the wet-mixed mortar with the admixture described in the present application is determined according to the method described in JGJ / T 70-2009 "Standard Test Methods for Basic Properties of Building Mortar" 4, the apparent density is determined and calculated according to the method described in JGJ / T 70-2009 "Standard Test Methods for Basic Properties of Building Mortar" 5, and the water retention rate is determined and calculated according to the method described in JGJ / T 70-2009 "Standard Test Methods for Basic Properties of Building Mortar" 7. In each example, the dosage of the admixture and the water amount are adjusted to keep the initial consistency of the mortar at 95±5 mm, and the initial apparent density of the mortar at 1750±50 kg / m 3 .

[0054] Table 4 Wet-mixed mortar mix ratio

[0055]

[0056] Table 5 Performance test of each example and comparative example

[0057]

[0058]

[0059] The data in Table 5 show that: (1) the wet-mixed mortar containing the coagulation-adjusting component, the air-entraining component and the water-retaining component (Examples 1-10) has a 6h apparent density loss rate of <3.5%, a 24h apparent density loss rate of <6.5%, a 32h apparent density loss rate of <10.5%, a small consistency loss, an initial consistency of 95±5mm, a 6h consistency of 95±5mm, a 24h consistency of 90±5mm, a 32h consistency of 87±5mm, a good long-acting water-retaining property with an initial water-retention rate of >95% and a 32h water-retention rate of >93%, and thus effectively ensuring the workability of the wet-mixed mortar; (2) Comparative Example 1 is a hydroxypropyl cellulose ether which has poor solubility and precipitates after standing for a period of time after being compounded with other additives, has a 32h apparent density loss rate of >13%, a consistency of only 40mm, and a water-retention rate of only 83.2%, which are all inferior to those of the examples; (3) Comparative Example 2, compared with the examples, does not contain monomer D (vinyl acetate) and has a significantly reduced content of hydroxyl groups in the polymer, which affects the various properties of the mortar, has a 32h apparent density loss rate of 14%, a consistency of only 42mm, and initial, 6h, 24h and 32h water-retention rates of 92.7%, 87.7%, 83.5% and 80.1% respectively, which are all inferior to those of the examples; (4) Comparative Example 3, compared with the examples, does not contain monomer C ((methyl)acrylic acid hydroxyl ester) and has a reduced action duration of the polymer, which affects the long-acting water-retaining property of the mortar, has an initial water-retention rate of 94.6% and a 32h water-retention rate of 90.6%, which are both inferior to those of the examples; (5) Comparative Example 4, compared with the examples, does not contain monomer B ((methyl)acrylamide or its derivative) and affects the molecular weight and action duration of the polymer, thereby affecting the various properties of the mortar, has a 32h apparent density loss rate of 13%, a consistency of only 47mm, an initial water-retention rate of 93.3% and a 32h water-retention rate of 81.5%, which are all inferior to those of the examples; (6) Comparative Example 5, compared with the examples, does not contain monomer A ((methyl)acrylic acid) and mainly affects the compatibility of the polymer with other additives after compounding, and the reduction of negative electric groups reduces the ability of free water to become bound water, thereby affecting the various properties of the mortar, which are all inferior to those of the examples.

[0060] Conclusion: The long-acting water-retaining agent for wet-mixed mortar according to the present application has good workability when applied to wet-mixed mortar, does not cause segregation or bleeding, has a small consistency loss, a long working duration, and good water-retaining property, and has a water-retention rate of >93% after 30 hours.

[0061] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A long-lasting water-retaining agent for wet-mixed mortar, characterized in that: This long-lasting water-retaining agent for wet-mixed mortar is composed of four monomers, A, B, C, and D, through free radical copolymerization. The monomer A is an acrylic acid compound, and the structural formula of the acrylic acid compound is as follows: Where M1 is H, a monovalent alkali metal ion, or an ammonium ion; R1 is H or CH3; The monomer B is an acrylamide compound, and the structural formula of the acrylamide compound is as follows: Where R2 is H or CH3; R3 and R4 are independent and are C. n H 2n+1 Or (CH2) p OC q H 2q+1 n is an integer from 0 to 4, p is an integer from 1 to 3, and q is an integer from 0 to 4; among them, R3 and R4 cannot both be (CH2). p OC q H 2q+1 When R3 is (CH2) p OC q H 2q+1 R4 is H, when R4 is (CH2) p OC q H 2q+1 R3 is H; the monomer C is a hydroxyalkyl acrylate compound, and the structural formula of the hydroxyalkyl acrylate compound is: Where R5 represents H or CH3; R6 represents C. m H 2m OH, m is an integer between 2 and 4; The monomer D is vinyl acetate; The molar ratio of monomers A, B, C and D is 1.0:(1.0-3.0):(0.5-3.0):(8.0-20.0).

2. The long-lasting water-retaining agent for wet-mixed mortar according to claim 1, characterized in that: The weight-average molecular weight of the wet-mixed mortar long-lasting water-retaining agent is 1×10⁻⁶. 5 -3×10 5 .

3. The preparation method of the long-lasting water-retaining agent for wet-mixed mortar according to claim 1, characterized in that, The process includes the following steps: (1) Add monomer A, monomer B, monomer C, monomer D and deionized water to the reactor, and neutralize the solution to pH 7-8 with NaOH; (2) Start stirring and perform deoxygenation before heating to 45℃-55℃; (3) Prepare the initiator into a solution a with a mass concentration of 0.5%-1.0%, and the chain transfer agent into a solution b with a mass concentration of 0.5%-1.0%; Add solutions a and b dropwise to the reactor over 2-3 hours. After the addition is complete, start the reaction and continue until the reaction is complete to obtain a solid content of 5%-10% and a weight-average molecular weight of 1×10⁻⁶. 5 ~3×10 5 Long-lasting water-retaining agent for wet-mixed mortar.

4. The preparation method of the long-lasting water-retaining agent for wet-mixed mortar according to claim 3, characterized in that: The initiator in step (3) is a water-soluble azo initiator or a persulfate initiator; the water-soluble azo initiator is selected from at least one of azobisisobutylamidine hydrochloride, azobisisobutylimidazoline hydrochloride, azobisisovalerate, and azobisisopropylimidazoline; the persulfate initiator is selected from at least one of sodium persulfate, potassium persulfate, and ammonium persulfate.

5. The preparation method of the long-lasting water-retaining agent for wet-mixed mortar according to claim 3, characterized in that: The amount of initiator used is 1.0% to 3.0% of the total mass of monomers A, B, C, and D.

6. The preparation method of the long-lasting water-retaining agent for wet-mixed mortar according to claim 3, characterized in that: The chain transfer agent in step (3) is at least one of dodecanethiol, hexadecethiol, mercaptoethanol, mercaptoacetic acid, 2-mercaptopropionic acid, and 3-mercaptopropionic acid.

7. The preparation method of the long-lasting water-retaining agent for wet-mixed mortar according to claim 3, characterized in that: The amount of chain transfer agent used is 0.5%-2.0% of the total molar number of monomers A, B, C, and D.

8. The preparation method of the long-lasting water-retaining agent for wet-mixed mortar according to claim 3, characterized in that: The reaction temperature in step (3) is 70℃-80℃, and the reaction time is 3-4h.

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