Water reducing agent for high-alkali cement and method for preparing the same

Abstract

The application relates to the technical field of cement-based building material admixtures, in particular to a water reducing agent for high-alkali cement and a preparation method thereof. The water reducing agent is prepared by adopting ethylene glycol monovinyl polyethylene glycol ether as a macromonomer, and a functional monomer and an alcohol amine modified monomer are prepared to improve the structure of the water reducing agent, and a redox system is used for polymerization reaction at normal temperature. The prepared water reducing agent is good in adaptability to high-alkali cement, high in water reducing and slump retaining capacity, does not affect the strength of concrete, and is low in energy consumption and efficient and fast in preparation process.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of cement-based building material admixtures, in particular to a water reducing agent for high-alkali cement and a preparation method thereof. BACKGROUND

[0002] With the rapid development of the construction industry, water reducing agents have become an indispensable component in concrete and are the strongest development trend of concrete admixtures. Under the condition that the initial state of the concrete and the cement content remain unchanged, the water demand can be reduced and the workability of the concrete can be improved by mixing the water reducing agent when the concrete is mixed. As a new generation of water reducing agent, polycarboxylate superplasticizer has the advantages of low dosage, good slump retention performance, good concrete workability, strong designability of molecular structure, great potential for high performance, simple production process and green environmental protection. Polycarboxylate superplasticizer has become one of the most popular concrete admixtures due to its excellent functional characteristics.

[0003] Polycarboxylate superplasticizers are usually obtained by solution radical polymerization, for example, by radical polymerization of monomers and derivatives containing unsaturated double bonds, to generate a comb-shaped polycarboxylic copolymer with a main chain and multiple side chains. The main chain of the copolymer is connected with hydrophilic functional groups such as carboxyl, hydroxyl, sulfonic acid group and amino group, and the side chain is grafted with polyoxyethylene / propylene with different polymerization degrees.

[0004] One of the major disadvantages of polycarboxylate superplasticizers is that they are sensitive to raw materials. Changes in cement varieties and uneven quality of sand and gravel can easily cause poor adaptability of polycarboxylate superplasticizers, resulting in fluctuations in the workability of mortar and concrete. The alkali content of cement is an important indicator. In the early research of building materials, high alkali content in concrete can cause alkali-aggregate reaction, leading to expansion and cracking of concrete, reducing the durability of concrete and threatening the safety of concrete components. However, with the continuous development of building material technology in recent years, the alkali content index of cement has been updated with new technology. It was previously believed that the alkali content of ordinary cement was generally 0.6-0.8%. The latest national standard GB175-2023 "General Portland Cement" has adjusted the requirement for alkali content from a mandatory index to a supply and demand negotiation item, only requiring that the alkali content of low-alkali cement should not exceed 0.6%. With the application of bulk industrial solid waste in cement clinker production, the fluctuation of alkali content of ordinary engineering cement has increased accordingly. For high-alkali cement, it will also cause sensitivity of water reducing agents and affect the performance of cement-based slurries. However, there are few water reducing agents in the prior art that have good adaptability to high-alkali cement. SUMMARY

[0005] In order to solve the problems in the prior art, the application provides a water reducing agent for high-alkali cement, which is prepared by using ethylene glycol monovinyl polyethylene glycol ether as a large monomer, modifying the structure of the water reducing agent by preparing functional monomers and alcohol amine modified monomers, and performing polymerization reaction at normal temperature by using an oxidation-reduction system, so that the prepared water reducing agent has good adaptability to high-alkali cement, can be applied to high-alkali cement with alkali content higher than 1.0%, has strong water reducing and slump retaining capacity, does not affect the strength of concrete, and has low energy consumption and high efficiency and rapidness in the preparation process.

[0006] Specifically, the preparation method of the water reducing agent for high-alkali cement comprises the following steps:

[0007] 1) 12-16 parts of water, 15-20 parts of small monomers, 2-5 parts of functional monomers, 8-12 parts of alcohol amine modified monomers and 0.5-1 part of a chain transfer agent are weighed according to weight parts, and are uniformly stirred to obtain A material,

[0008] 2) 35-45 parts of water, 12-18 parts of small monomers, 1-5 parts of functional monomers, 3-7 parts of alcohol amine modified monomers and 0.3-0.5 part of a reducing agent are weighed according to weight parts, and are uniformly stirred to obtain B material,

[0009] 3) 320-380 parts of ethylene glycol monovinyl polyethylene glycol ether and 250-300 parts of water are weighed according to weight parts, are uniformly mixed in a reaction kettle, 5-10 parts of small monomers, 4-6 parts of functional monomers, 1-3 parts of ferrous sulfate and 1-3 parts of an oxidizing agent are added and uniformly stirred, A material and B material are added dropwise, after the dropwise addition is completed, the stirring is continued, and the pH value is adjusted to 5-7, and the water reducing agent is obtained.

[0010] The ethylene glycol monovinyl polyethylene glycol ether used in the application is a novel polyether macromolecular polymerization monomer, is obtained from a green and environmentally-friendly synthesis process, has high double bond activity, has much higher reaction activity than general macromolecular polymerization monomers, is more prone to polymerization, the dispersion of long side chains on high-alkali content cement particles is adjusted by adding functional monomers, the modification effect of the alcohol amine modified monomers is combined, the structure of the water reducing agent is adjusted by using small monomers, the adaptability of high-alkali cement slurry can be improved, the loss of fluidity can be reduced, the performance of concrete can be significantly improved, and the workability and durability are improved.

[0011] In the preparation process, the polymerization reaction activity and the polymerization reaction rate of different monomers are different, in order to improve the conversion rate of low-activity monomers and avoid homopolymerization of high-activity monomers, the ethylene glycol monovinyl polyethylene glycol ether, part of the functional monomers and the small monomers are firstly added, and the other part of the functional monomers, the small monomers and the alcohol amine modified monomers are added dropwise to perform polymerization reaction.

[0012] Preferably, the functional monomer preparation process is: 70-90 parts by weight of acrylamide, 460-520 parts by weight of water are weighed and uniformly mixed, then 8-12 parts by weight of hydroxyethyl acrylate, 1-3 parts by weight of chain transfer agent, 7-9 parts by weight of oxidizing agent, 80-90 parts by weight of small monomer are added, stirred uniformly, 10-20 parts by weight of small monomer and 1-3 parts by weight of reducing agent are added dropwise respectively, and then the mixture is incubated and stirred, and cooled to obtain the product.

[0013] The functional monomer introduced in the application is denoted as 301 functional monomer, and the ester monomer is grafted onto the polyether monomer, so that the synthesized polycarboxylic acid water reducer can have multiple functional properties, and the components of the functional monomer still have strong polymerization activity after pre-reaction. Since the raw material hydroxyethyl acrylate can increase the fluidity and water reducing property of concrete, and form interaction during the hardening process of concrete, the strength and durability of concrete are improved. In addition, in the high-alkali cement environment, the hydrolysis characteristics of the ester monomer in the alkaline environment will gradually hydrolyze the ester monomer in the alkaline environment as the cement hydration proceeds, and the carboxyl groups formed in the hydrolysis reaction process of the polymer molecules will continuously adsorb and disperse the cement particles, so that the fluidity of the high-alkali cement in the concrete can be maintained for a longer period of time. In addition, the long-chain ester monomer also has certain hydrophobicity, and by introducing hydrophobic substances into the structure of the polycarboxylic acid water reducer, the performance of the polycarboxylic acid water reducer in the cement hydration process can be improved, thereby prolonging the slump retention time of the concrete.

[0014] Preferably, the small monomer is at least one of acrylic acid and methacrylic acid.

[0015] Preferably, the chain transfer agent is at least one of mercaptoacetic acid and mercaptopropionic acid.

[0016] Preferably, the reducing agent is vitamin C, and the oxidizing agent is hydrogen peroxide.

[0017] Preferably, in step 3), the A material is added dropwise for 20-30 min, the B material is added dropwise for 50-60 min, and the incubation temperature is 20-40℃.

[0018] Preferably, the alcohol amine modified monomer preparation process is: 8-12 parts by weight of maleic anhydride, 8-10 parts by weight of diethanol mono-isopropanol amine, 30-50 parts by weight of water, and 0.05-0.2 parts by weight of catalyst are weighed and mixed, and then the mixture is heated and reacted, 15-20 parts by weight of ethylene glycol monovinyl polyethylene glycol ether is added, and the mixture is continuously stirred and reacted to obtain the product.

[0019] The alcohol amine modified monomer is added, the viscosity and surface tension of the concrete can be obviously reduced by introducing diethanol monoisopropanolamine, so that the fluidity and pumpability of the concrete are improved, the alcohol amine can coat high-alkali cement particles, delay the hydration speed, improve the durability and setting time, and the emulsifying effect of the alcohol amine can also resist the influence of the water reducing agent on the sensitivity of the high-alkali cement. Therefore, the introduction of the alcohol amine modified monomer enables the polycarboxylic acid water reducing agent to have the mechanisms of emulsification, anti-agglomeration and promotion of the full contact of the cement particles and water in the application of the polycarboxylic acid water reducing agent in the concrete engineering, and provides an effective means for improving the adaptability of the water reducing agent to the high-alkali cement and optimizing the cement hydration process. Moreover, the diethanol monoisopropanolamine can also promote the early and late strength development of the cement concrete, the introduction of the amino group (NH2) can enhance the lubricating effect of the polycarboxylic acid mother liquor on the concrete, improve the fluidity of the cement paste, reduce the situation that the cement hydration is too fast, and prolong the working time of the concrete. The characteristics of the high-alkali cement can obviously improve the adaptability of the cement in different regions and reduce the risk of the high-alkali cement in the concrete production and use, which is particularly important in the production and construction of ready-mixed concrete, and can ensure that the concrete maintains sufficient fluidity in the long-distance transportation and pumping process and meets the requirements of the site construction.

[0020] Preferably, the catalyst is p-toluenesulfonic acid.

[0021] Preferably, the temperature rising reaction is temperature rising to 100-115 DEG C for 2.5-4 hours.

[0022] The application also belongs to a typical polycarboxylic acid type water reducing agent, which has other characteristics of the polycarboxylic acid water reducing agent except for the good adaptability to the high-alkali cement, for example, the carboxylic acid groups on the main chain are negatively charged and adsorbed on the surface of the cement particles after hydrolysis, the long side chain with hydrophilicity plays a dispersion role through steric hindrance, the hydrogen peroxide-ferrous sulfate-Vc redox system is used in the synthesis process, and the polymerization can be carried out at room temperature.

[0023] The dispersibility of the polycarboxylic acid type water reducing agent mainly depends on the good steric hindrance effect of the polyether macromonomer, the long side chain produces a physical steric hindrance effect between the cement particles, which can effectively hinder the flocculation of the cement particles. However, if the content of the polyether macromonomer is too high, the content of the carboxyl group is correspondingly too low, which will affect the adsorption capacity of the copolymer and reduce the hydrophilic performance of the polymer. Therefore, the technology slightly reduces the amount of the polyether macromonomer, increases the amount of the alcohol amine modified monomer and the functional monomer, optimizes the molecular structure of the polycarboxylic acid, changes the polymerization of the polycarboxylic acid from the original binary or ternary copolymerization to multi-copolymerization, and improves the adaptability of the water reducing agent to the high-alkali cement.

[0024] The application also relates to a water reducing agent for high-alkali cement, which is prepared by the above preparation method.

[0025] The application also relates to application of the water-reducing agent to preparation of building material products by using high-alkali cement.

[0026] The water-reducing agent has the following technical advantages:

[0027] 1. The water-reducing agent has good adaptability to high-alkali cement and can be used for high-alkali cement with alkali content higher than 1%,

[0028] 2. The water-reducing agent has high water-reducing rate, good slump retention effect and does not reduce the mechanical properties of cement-based materials,

[0029] 3. The water-reducing agent can be synthesized at room temperature and has high preparation efficiency. DETAILED DESCRIPTION

[0030] To characterize the technical effects of the application, the water-reducing agent is prepared and its performance is tested. Specifically, a certain brand of cement is used, the alkali content of which is 1.1% after detection, the cement paste test in GB / T8077-2012 "Test Method for Homogeneity of Concrete Admixtures" is referred to for flow degree test, in each test, the cement dosage is 300g, the cement slurry water is 87g, and the water-reducing agent dosage is 3g; the concrete slump and spread test is carried out according to GB / T 50080-2016 "Standard Test Methods for Performance of Ordinary Concrete Mixture", and the compressive strength test is carried out according to GB / T50081-2002 "Standard Test Methods for Mechanical Properties of Ordinary Concrete", the sand used is machine-made sand with a fineness modulus of 2.6, and the water-reducing agent dosage is 1.5% of the mass of the cementitious material.

[0031] During the test, the functional monomer preparation process is as follows: 80 parts of acrylamide and 500 parts of water are weighed and uniformly mixed, then 10 parts of hydroxyethyl acrylate, 2 parts of mercaptoacetic acid, 8 parts of hydrogen peroxide and 85 parts of acrylic acid are added and uniformly stirred, 15 parts of acrylic acid and 2 parts of vitamin C are added dropwise, and then the mixture is kept stirring and cooled to obtain the functional monomer; the alcohol amine modified monomer preparation process is as follows: 10 parts of maleic anhydride, 9 parts of diethanol mono-isopropyl amine, 40 parts of water and 0.1 parts of catalyst are weighed, heated to 110℃ and reacted for 3h, then 18 parts of ethylene glycol monovinyl polyethylene glycol ether is added and the mixture is continuously stirred and reacted to obtain the alcohol amine modified monomer.

[0032] Example 1

[0033] The water-reducing agent is prepared by the following steps:

[0034] 1) 15 parts of water, 16 parts of acrylic acid, 5 parts of functional monomer, 9 parts of alcohol amine modified monomer and 0.6 parts of mercaptoacetic acid are weighed and uniformly stirred to obtain A material,

[0035] 2) 40 parts of water, 15 parts of acrylic acid, 3 parts of functional monomer, 6 parts of alcohol amine modified monomer, 0.4 parts of vitamin C were weighed according to parts by weight, stirred uniformly to obtain B material,

[0036] 3) 360 parts of ethylene glycol monovinyl polyethylene glycol ether, 270 parts of water were weighed according to parts by weight, mixed uniformly in a reaction kettle, then 8 parts of acrylic acid, 5 parts of functional monomer, 2 parts of ferrous sulfate, 2 parts of hydrogen peroxide were added, stirred uniformly, A material and B material were added dropwise, after the dropwise addition was completed, 30℃ incubation stirring was continued, the pH value was adjusted to 6.5, and it was obtained.

[0037] After detection, the initial fluidity of cement paste was 265 mm, the 1h fluidity was 265 mm, the 2h fluidity was 250 mm, the initial slump / extension of concrete was 245 mm / 610 mm, the 1h slump / extension was 235 mm / 595 mm, the 7d compressive strength was 36.6 MPa, and the 28d compressive strength was 39.2 MPa.

[0038] Example 2

[0039] The preparation method comprises the following steps:

[0040] 1) 15 parts of water, 15 parts of acrylic acid, 4 parts of functional monomer, 11 parts of alcohol amine modified monomer, and 0.5 parts of mercaptoacetic acid were weighed according to parts by weight, stirred uniformly to obtain A material,

[0041] 2) 40 parts of water, 14 parts of acrylic acid, 5 parts of functional monomer, 5 parts of alcohol amine modified monomer, and 0.4 parts of vitamin C were weighed according to parts by weight, stirred uniformly to obtain B material,

[0042] 3) 370 parts of ethylene glycol monovinyl polyethylene glycol ether, 270 parts of water were weighed according to parts by weight, mixed uniformly in a reaction kettle, then 5 parts of acrylic acid, 4 parts of functional monomer, 2 parts of ferrous sulfate, and 2.5 parts of hydrogen peroxide were added, stirred uniformly, A material and B material were added dropwise, after the dropwise addition was completed, 30℃ incubation stirring was continued, the pH value was adjusted to 6.5, and it was obtained.

[0043] The initial fluidity of cement paste was 275 mm, the 1h fluidity was 265 mm, the 2h fluidity was 260 mm, the initial slump / extension of concrete was 255 mm / 620 mm, the 1h slump / extension was 255 mm / 610 mm, the 7d compressive strength was 37.3 MPa, and the 28d compressive strength was 40.1 MPa.

[0044] Comparative Example 1

[0045] The preparation method comprises the following steps:

[0046] 1) 15 parts of water, 15 parts of acrylic acid, 4 parts of functional monomer, 11 parts of alcohol amine modified monomer, and 0.5 parts of mercaptoacetic acid were weighed according to parts by weight, stirred uniformly to obtain A material,

[0047] 2) 40 parts of water, 14 parts of acrylic acid, 5 parts of functional monomer, 5 parts of alcohol amine modified monomer, 0.4 parts of vitamin C were weighed by weight parts, stirred uniformly to obtain B material,

[0048] 3) 370 parts of MPEG, 270 parts of water were weighed by weight parts, mixed uniformly in a reaction kettle, then 5 parts of acrylic acid, 4 parts of functional monomer, 2 parts of ferrous sulfate, 2.5 parts of hydrogen peroxide were added, stirred uniformly, A material and B material were added dropwise, after the dropwise addition was completed, 30°C incubation stirring was continued, the pH value was adjusted to 6.5, and then it was obtained.

[0049] The initial fluidity of cement paste was 240 mm, the 1 h fluidity was 230 mm, the 2 h fluidity was 210 mm, the initial slump / extension of concrete was 220 mm / 560 mm, the 1 h slump / extension was 200 mm / 460 mm, the 7 d compressive strength was 35.1 MPa, and the 28 d compressive strength was 36.7 MPa.

[0050] Comparative Example 2

[0051] The preparation method of the water reducing agent comprises the following steps:

[0052] 1) 15 parts of water, 15 parts of acrylic acid, 4 parts of acrylamide, 11 parts of alcohol amine modified monomer, and 0.5 parts of mercaptoacetic acid were weighed by weight parts, stirred uniformly to obtain A material,

[0053] 2) 40 parts of water, 14 parts of acrylic acid, 5 parts of hydroxyethyl acrylate, 5 parts of alcohol amine modified monomer, and 0.4 parts of vitamin C were weighed by weight parts, stirred uniformly to obtain B material,

[0054] 3) 370 parts of ethylene glycol monovinyl polyethylene glycol ether and 270 parts of water were weighed by weight parts, mixed uniformly in a reaction kettle, then 5 parts of acrylic acid, 4 parts of hydroxyethyl acrylate, 2 parts of ferrous sulfate, and 2.5 parts of hydrogen peroxide were added, stirred uniformly, A material and B material were added dropwise, after the dropwise addition was completed, 30°C incubation stirring was continued, the pH value was adjusted to 6.5, and then it was obtained.

[0055] The initial fluidity of cement paste was 240 mm, the 1 h fluidity was 230 mm, the 2 h fluidity was 210 mm, the initial slump / extension of concrete was 220 mm / 560 mm, the 1 h slump / extension was 200 mm / 460 mm, the 7 d compressive strength was 35.1 MPa, and the 28 d compressive strength was 36.7 MPa.

[0056] Comparative Example 3

[0057] The preparation method of the water reducing agent comprises the following steps:

[0058] 1) 15 parts of water, 15 parts of acrylic acid, 4 parts of functional monomer, 11 parts of maleic anhydride, and 0.5 parts of mercaptoacetic acid were weighed by weight parts, stirred uniformly to obtain A material,

[0059] 2) 40 parts of water, 14 parts of acrylic acid, 5 parts of functional monomer, 5 parts of maleic anhydride, 0.4 parts of vitamin C were weighed by weight parts, and stirred uniformly to obtain B material,

[0060] 3) 370 parts of ethylene glycol monovinyl polyethylene glycol ether, 270 parts of water were weighed by weight parts, mixed uniformly in a reaction kettle, and then 5 parts of acrylic acid, 4 parts of functional monomer, 2 parts of ferrous sulfate, 2.5 parts of hydrogen peroxide were added, stirred uniformly, and then A material and B material were added dropwise. After the dropwise addition was completed, 30℃ was continued to be stirred, the pH value was adjusted to 6.5, and then it was obtained.

[0061] The initial fluidity of cement paste is 200mm, 1h has no fluidity, the initial slump / extension of concrete is 190mm / 400mm, 1h has no fluidity, the 7d compressive strength is 30.3MPa, and the 28d compressive strength is 34.5MPa.

[0062] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for preparing a water reducing agent for a high-alkali cement, characterized by, It comprises the following steps: 1) 12-16 parts by weight of water, 15-20 parts by weight of small monomers, 2-5 parts by weight of functional monomers, 8-12 parts by weight of alcohol amine modified monomers, 0.5-1 parts by weight of chain transfer agent are weighed and stirred uniformly to obtain A material, 2) 35-45 parts by weight of water, 12-18 parts by weight of small monomers, 1-5 parts by weight of functional monomers, 3-7 parts by weight of alcohol amine modified monomers, 0.3-0.5 parts by weight of reducing agent are weighed and stirred uniformly to obtain B material, 3) 320-380 parts by weight of ethylene glycol monovinyl polyethylene glycol ether and 250-300 parts by weight of water are weighed and mixed uniformly in a reaction kettle, then 5-10 parts by weight of small monomers, 4-6 parts by weight of functional monomers, 1-3 parts by weight of ferrous sulfate and 1-3 parts by weight of oxidizing agent are added and stirred uniformly, A material and B material are added dropwise, after the dropwise addition is completed, the pH value is adjusted to 5-7, and the product is obtained; The preparation process of the functional monomer is that 70-90 parts by weight of acrylamide and 460-520 parts by weight of water are mixed uniformly, then 8-12 parts by weight of hydroxyethyl acrylate, 1-3 parts by weight of chain transfer agent, 7-9 parts by weight of oxidizing agent and 80-90 parts by weight of small monomers are added, stirred uniformly, 10-20 parts by weight of small monomers and 1-3 parts by weight of reducing agent are added dropwise respectively, and the product is obtained after heat preservation and cooling. The small monomer is at least one of acrylic acid and methacrylic acid. The preparation process of the alcohol amine modified monomer is that 8-12 parts by weight of maleic anhydride, 8-10 parts by weight of diethanol monoisopropanolamine, 30-50 parts by weight of water and 0.05-0.2 parts by weight of catalyst are weighed and reacted after being heated, then 15-20 parts by weight of ethylene glycol monovinyl polyethylene glycol ether is added and the reaction is continued.

2. The method of claim 1, wherein the high-alkali cement is prepared by adding the water-reducing agent to the cement. The chain transfer agent is at least one of mercaptoacetic acid and mercaptopropionic acid. ​ 3. The method for preparing a superplasticizer for a high-alkali cement according to any one of claims 1 to 2, characterized by, The reducing agent is vitamin C and the oxidizing agent is hydrogen peroxide.

4. The method of claim 1, wherein the superplasticizer for high-alkali cement is prepared by adding 0.1 to 0.3 parts by weight of the dispersant to 100 parts by weight of the cement. In step 3), the dropwise addition time of A material is 20-30 min, the dropwise addition time of B material is 50-60 min, and the heat preservation temperature is 20-40℃.

5. The method of claim 4, wherein the superplasticizer for high-alkali cement is prepared by adding 0.1 to 0.3 parts by weight of the dispersant to 100 parts by weight of the cement. The catalyst is p-toluenesulfonic acid.

6. The method of claim 5, wherein the superplasticizer for high-alkali cement is prepared by adding 0.1 to 0.3 parts by weight of the dispersant to 100 parts by weight of the cement. The heating reaction is heating to 100-115℃ for 2.5-4h.

7. A water reducing agent for high-alkali cement, characterized by Prepared by the preparation method of any one of claims 1-6. Prepared by the preparation method of any one of claims 1-6.