Water reducing agent for high-alkali cement and preparation method of water reducing agent

Abstract

The invention 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 of the water reducing agent. Ethylene glycol monovinyl polyglycol ether is adopted as a macromonomer, and a functional monomer and an alcohol amine modified monomer are prepared to improve the structure of the water reducing agent; a redox system is adopted for polymerization reaction at normal temperature, the prepared water reducing agent is good in adaptability to high-alkali cement and high in water reducing and collapse preventing capacity, the strength of concrete is not affected, and the preparation process is low in energy consumption, efficient and rapid.

Description

Technical Field

[0001] The present invention relates to the technical field of cement-based building material admixtures, in particular to a water reducer for high-alkali cement and a preparation method thereof. Background Art

[0002] With the rapid development of the construction industry, water reducers have become an indispensable component of concrete and represent the strongest development trend among concrete admixtures. While maintaining the initial concrete state and cement content, adding a water reducer to concrete mixing can reduce water demand and improve concrete performance. As a new generation of water reducers, polycarboxylate water reducers offer advantages such as low dosage, excellent slump retention, improved concrete performance, highly designable molecular structures, significant potential for high-performance development, simple production processes, and environmental friendliness. These exceptional properties have distinguished polycarboxylate water reducers from other water reducers, making them one of the most popular concrete admixtures.

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

[0004] A major disadvantage of polycarboxylate superplasticizers is their sensitivity to raw materials. Changes in cement types and uneven sand and gravel quality can easily lead to poor adaptability of polycarboxylate superplasticizers, resulting in fluctuations in the construction performance of mortar and concrete. Cement alkali content is a key indicator. In early research on building materials, excessive alkali content in concrete could cause an alkali-aggregate reaction, leading to expansion and cracking, reduced durability, and a threat to the safety of concrete components. However, in recent years, with the continuous development of building materials technology, new technical updates have been made to cement alkali content indicators. Previously, it was generally believed that the alkali content of ordinary cement was generally between 0.6% and 0.8%. The latest national standard GB175-2023, "General Portland Cement," has adjusted the alkali content requirement from a mandatory indicator to a negotiated requirement for supply and demand, requiring only that the alkali content of low-alkali cement must not exceed 0.6%. With the application of large-scale industrial solid waste in cement clinker production, the fluctuation of alkali content in cement for ordinary engineering has increased accordingly. For cement with high alkali content, it will also cause sensitivity of water reducers and affect the performance of cement-based slurry. However, there are few water reducers with good adaptability to high-alkali cement developed in the existing technology. Summary of the Invention

[0005] In order to solve the problems existing in the prior art, the present invention provides a water reducer for high-alkali cement. Ethylene glycol monovinyl polyethylene glycol ether is used as a macromonomer, and functional monomers and alcoholamine-modified monomers are prepared to improve the structure of the water reducer. A polymerization reaction is carried out using a redox system at room temperature. The prepared water reducer has good adaptability to high-alkali cement and can be used for high-alkali cement with an alkali content higher than 1.0%. It has strong water-reducing and slump-preventing capabilities, does not affect the strength of concrete, and has a low energy consumption, high efficiency, and rapid preparation process.

[0006] Specifically, the method for preparing a high-alkali cement water reducer of the present invention comprises the following steps: 1) Weigh 12-16 parts of water, 15-20 parts of small monomer, 2-5 parts of functional monomer, 8-12 parts of alcoholamine modified monomer, and 0.5-1 part of chain transfer agent by weight, stir evenly to obtain material A. 2) Weigh 35-45 parts of water, 12-18 parts of small monomer, 1-5 parts of functional monomer, 3-7 parts of alcoholamine modified monomer, and 0.3-0.5 parts of reducing agent by weight, stir evenly to obtain material B. 3) Weigh 320-380 parts of ethylene glycol monovinyl polyethylene glycol ether and 250-300 parts of water by weight, add them to a reactor and mix evenly, then add 5-10 parts of small monomer, 4-6 parts of functional monomer, 1-3 parts of ferrous sulfate, and 1-3 parts of oxidant, stir evenly, add material A and material B dropwise, continue to keep warm and stir after the addition is complete, and adjust the pH value to 5-7 to obtain the product.

[0007] The present invention uses ethylene glycol monovinyl polyethylene glycol ether, which is a new type of polyether macromolecular polymerization monomer. It is derived from a green and environmentally friendly synthesis process, has high double bond activity, and its reaction activity is much greater than that of general macromolecular polymerization monomers, making it easier for polymerization reactions to occur. On this basis, functional monomers are added to adjust the dispersion of long side chains on high-alkali cement particles, and combined with the modification effect of alcohol amine modified monomers, small monomers are used to adjust the structure of the water reducer, thereby improving the adaptability of high-alkali cement slurry, reducing fluidity loss, and significantly improving the performance of concrete, thereby enhancing its workability and durability.

[0008] In the preparation process of the present invention, since different monomers have different polymerization reaction activities and polymerization reaction rates, in order to improve the conversion rate of low-activity monomers and avoid homopolymerization of high-activity monomers, ethylene glycol monovinyl polyethylene glycol ether, part of the functional monomers and small monomers are first added, and the other part of the functional monomers, small monomers and alcoholamine-modified monomers are added dropwise for polymerization reaction.

[0009] Preferably, the functional monomer preparation process is as follows: weigh 70-90 parts of acrylamide and 460-520 parts of water by weight, mix them evenly, then add 8-12 parts of hydroxyethyl acrylate, 1-3 parts of chain transfer agent, 7-9 parts of oxidant, and 80-90 parts of small monomer by weight, stir evenly, add 10-20 parts of small monomer and 1-3 parts of reducing agent dropwise by weight respectively, keep warm and stir, and cool to obtain the product.

[0010] The present invention introduces a functional monomer, designated as 301 functional monomer, and grafts an ester monomer onto a polyether monomer, so that the synthesized polycarboxylate water-reducing agent can have multiple functional properties. Moreover, after the pre-reaction of each component of the functional monomer, there is still a strong polymerization activity. Since the raw material hydroxyethyl acrylate can increase the fluidity and water-reducing property of concrete, and form an interaction during the concrete hardening process, thereby improving the strength and durability of concrete. In addition, under a high-alkali cement environment, the hydrolysis characteristics of the ester monomer in an alkaline environment will gradually hydrolyze in an alkaline environment as the cement hydration proceeds, and the concrete pore solution becomes strongly alkaline. The carboxyl groups formed by the polymer molecules during the hydrolysis reaction will continuously adsorb and disperse the cement particles, thereby more fully ensuring that the high-alkali cement can maintain fluidity for a long time in concrete. In addition, the long-chain ester monomer also has a certain hydrophobicity. By introducing a hydrophobic substance into the polycarboxylate water-reducing agent structure, its performance during the cement hydration process can be improved, thereby extending the slump retention time of the concrete.

[0011] Preferably, the small monomer is at least one of acrylic acid and methacrylic acid.

[0012] Preferably, the chain transfer agent is at least one of thioglycolic acid and mercaptopropionic acid.

[0013] Preferably, the reducing agent is vitamin C, and the oxidizing agent is hydrogen peroxide.

[0014] Preferably, in step 3), the dropwise addition time of material A is 20-30 min, the dropwise addition time of material B is 50-60 min, and the insulation temperature is 20-40°C.

[0015] Preferably, the preparation process of the alcoholamine modified monomer is as follows: 8-12 parts of maleic anhydride, 8-10 parts of diethanol monoisopropanolamine, 30-50 parts of water, and 0.05-0.2 parts of a catalyst are weighed by weight, the temperature is raised for reaction, 15-20 parts of ethylene glycol monovinyl polyethylene glycol ether is added by weight, and the reaction is continued with stirring to obtain the product.

[0016] The addition of an alcoholamine-modified monomer, diethanol monoisopropanolamine, significantly reduces the viscosity and surface tension of concrete, thereby improving its fluidity and pumpability. The alcoholamine coats high-alkali cement particles, slowing hydration and increasing durability and setting time. The alcoholamine's emulsifying effect also mitigates the effects of water reducers on the sensitivity of high-alkali cement. Therefore, the introduction of an alcoholamine-modified monomer enables the use of polycarboxylate water-reducers in concrete engineering to combine emulsification, anti-agglomeration, and enhanced contact between cement particles and water, providing an effective means for improving the compatibility of water-reducers with high-alkali cement and optimizing the cement hydration process. Furthermore, diethanol monoisopropanolamine can promote both early and late strength development in cement concrete. The introduction of amino groups (NH₂) enhances the lubricating effect of the polycarboxylate mother liquor on concrete, improving cement slurry fluidity, reducing over-hydration, and extending the working life of concrete. This characteristic of high-alkali cement can significantly improve the adaptability of cement in different regions and reduce the risks of high-alkali cement in concrete production and use. This is especially important in the production and construction of commercial concrete. It can ensure that the concrete maintains sufficient fluidity during long-distance transportation and pumping to meet the requirements of on-site construction.

[0017] Preferably, the catalyst is p-toluenesulfonic acid.

[0018] Preferably, the temperature-raising reaction is carried out by heating the temperature to 100-115° C. for 2.5-4 hours.

[0019] The present invention is also a typical polycarboxylate water reducer. In addition to having good adaptability to high-alkali cement, it still has other characteristics of polycarboxylate water reducers. For example, the carboxylic acid groups on its main chain are negatively charged and adsorbed on the surface of cement particles after hydrolysis, and the long hydrophilic side chains exert a dispersing effect through steric hindrance. The synthesis process adopts a hydrogen peroxide-ferrous sulfate-Vc redox system, and polymerization can be carried out at room temperature.

[0020] The dispersibility of polycarboxylic acid-based water-reducing agents relies primarily on the excellent steric hindrance of polyether macromonomers. Their long side chains create physical steric hindrance between cement particles, effectively hindering their flocculation. However, if the polyether macromonomer content is too high, and the corresponding carboxyl content is too low, this will affect the copolymer's adsorption capacity and reduce its hydrophilic properties. Therefore, this technology uses a slightly reduced dosage of polyether macromonomer and an increased dosage of alcoholamine-modified monomers and functional monomers to optimize the polycarboxylic acid molecular structure, transforming the polymerization of the polycarboxylic acid from a binary or ternary copolymer to a multi-component copolymer, thereby improving the water-reducing agent's adaptability to high-alkali cement.

[0021] The present invention also relates to a water reducing agent for high alkali cement, which is specifically prepared by the above preparation method.

[0022] The present invention also relates to the use of the water reducer in the preparation of building materials using high-alkali cement. Preferably, the water reducer is added in an amount of 0.5-2% by weight of the cementitious material.

[0023] The water reducer of the present invention has the following technical advantages: 1. It has good adaptability to high alkali cement and can be used for high alkali cement with alkali content higher than 1%. 2. The water-reducing agent of the present invention has a high water-reducing rate and good collapse-preventing effect, and does not reduce the mechanical properties of cement-based materials. 3. The water reducer of the present invention can be synthesized at room temperature and has high preparation efficiency. DETAILED DESCRIPTION

[0024] In order to characterize the technical effect of the present invention, a water reducer was prepared and its performance was tested. Specifically, a certain brand of cement was used, and the alkali content was found to be 1.1%. The fluidity test was carried out with reference to the cement paste test in GB / T8077-2012 "Test method for homogeneity of concrete admixtures". In each group of tests, the cement dosage was 300 g, the water used for cement slurry was 87 g, and the water reducer dosage was 3 g; the concrete slump and expansion tests were carried out with reference to GB / T 50080-2016 "Standard test method for performance of ordinary concrete mixtures", and the compressive strength test was carried out with reference to GB / T50081-2002 "Standard test method for mechanical properties of ordinary concrete". The sand used was machine-made sand with a fineness modulus of 2.6, and the water reducer dosage was 1.5% of the mass of the cementitious material.

[0025] During the experiment, the preparation process of the functional monomer is as follows: 80 parts of acrylamide and 500 parts of water are weighed by weight, mixed evenly, and then 10 parts of hydroxyethyl acrylate, 2 parts of thioglycolic acid, 8 parts of hydrogen peroxide, and 85 parts of acrylic acid are added by weight, stirred evenly, 15 parts of acrylic acid and 2 parts of vitamin C are added dropwise by weight respectively, kept warm and stirred, and cooled to obtain the product; the preparation process of the alcoholamine modified monomer is as follows: 10 parts of maleic anhydride, 9 parts of diethanol monoisopropanolamine, 40 parts of water, and 0.1 parts of catalyst are weighed by weight, the temperature is raised to 110°C and the reaction is carried out for 3 hours, 18 parts of ethylene glycol monovinyl polyethylene glycol ether are added by weight, and the stirring reaction is continued to obtain the product.

[0026] Example 1 The preparation method of the water reducing agent comprises the following steps: 1) Weigh 15 parts of water, 16 parts of acrylic acid, 5 parts of functional monomer, 9 parts of alcoholamine modified monomer, and 0.6 parts of thioglycolic acid by weight, stir evenly to obtain material A. 2) Weigh 40 parts of water, 15 parts of acrylic acid, 3 parts of functional monomer, 6 parts of alcoholamine modified monomer, and 0.4 parts of vitamin C by weight, stir evenly to obtain material B. 3) Weigh 360 parts of ethylene glycol monovinyl polyethylene glycol ether and 270 parts of water by weight, add them to a reactor and mix evenly, then add 8 parts of acrylic acid, 5 parts of functional monomer, 2 parts of ferrous sulfate, and 2 parts of hydrogen peroxide, stir evenly, add material A and material B dropwise, continue stirring at 30°C after the addition is complete, and adjust the pH value to 6.5 to obtain the product.

[0027] After testing, the initial fluidity of cement paste is 265mm, the fluidity in 1h is 265mm, the fluidity in 2h is 250mm, the initial slump / extension of concrete is 245mm / 610mm, the slump / extension in 1h is 235mm / 595mm, the compressive strength at 7d is 36.6MPa, and the compressive strength at 28d is 39.2MPa.

[0028] Example 2 The preparation method of the water reducing agent comprises the following steps: 1) Weigh 15 parts of water, 15 parts of acrylic acid, 4 parts of functional monomer, 11 parts of alcoholamine modified monomer, and 0.5 parts of thioglycolic acid by weight, stir evenly to obtain material A. 2) Weigh 40 parts of water, 14 parts of acrylic acid, 5 parts of functional monomer, 5 parts of alcoholamine modified monomer, and 0.4 parts of vitamin C by weight, stir evenly to obtain material B. 3) Weigh 370 parts of ethylene glycol monovinyl polyethylene glycol ether and 270 parts of water by weight, add them to a reactor and mix evenly, then add 5 parts of acrylic acid, 4 parts of functional monomer, 2 parts of ferrous sulfate, and 2.5 parts of hydrogen peroxide, stir evenly, add material A and material B dropwise, continue stirring at 30°C after the addition is complete, and adjust the pH value to 6.5 to obtain the product.

[0029] The initial fluidity of cement paste is 275mm, the fluidity in 1h is 265mm, the fluidity in 2h is 260mm, the initial slump / extension of concrete is 255mm / 620mm, the slump / extension in 1h is 255mm / 610mm, the compressive strength at 7d is 37.3MPa, and the compressive strength at 28d is 40.1MPa.

[0030] Comparative Example 1 The preparation method of the water reducing agent comprises the following steps: 1) Weigh 15 parts of water, 15 parts of acrylic acid, 4 parts of functional monomer, 11 parts of alcoholamine modified monomer, and 0.5 parts of thioglycolic acid by weight, stir evenly to obtain material A. 2) Weigh 40 parts of water, 14 parts of acrylic acid, 5 parts of functional monomer, 5 parts of alcoholamine modified monomer, and 0.4 parts of vitamin C by weight, stir evenly to obtain material B. 3) Weigh 370 parts of MPEG and 270 parts of water by weight, add them to a reactor and mix evenly. Then add 5 parts of acrylic acid, 4 parts of functional monomer, 2 parts of ferrous sulfate, and 2.5 parts of hydrogen peroxide, stir evenly, and add material A and material B dropwise. After the addition is complete, continue stirring at 30°C and adjust the pH to 6.5.

[0031] The initial fluidity of cement paste is 240mm, the fluidity in 1h is 230mm, the fluidity in 2h is 210mm, the initial slump / extension of concrete is 220mm / 560mm, the slump / extension in 1h is 200mm / 460mm, the compressive strength at 7d is 35.1MPa, and the compressive strength at 28d is 36.7MPa.

[0032] Comparative Example 2 The preparation method of the water reducing agent comprises the following steps: 1) Weigh 15 parts of water, 15 parts of acrylic acid, 4 parts of acrylamide, 11 parts of alcoholamine modified monomer, and 0.5 parts of thioglycolic acid by weight, stir evenly to obtain material A. 2) Weigh 40 parts of water, 14 parts of acrylic acid, 5 parts of hydroxyethyl acrylate, 5 parts of alcoholamine modified monomer, and 0.4 parts of vitamin C by weight, stir evenly to obtain material B. 3) Weigh 370 parts of ethylene glycol monovinyl polyethylene glycol ether and 270 parts of water by weight, add them to a reactor and mix evenly. Then add 5 parts of acrylic acid, 4 parts of hydroxyethyl acrylate, 2 parts of ferrous sulfate, and 2.5 parts of hydrogen peroxide, stir evenly, and add material A and material B dropwise. After the addition is complete, continue stirring at 30°C and adjust the pH value to 6.5 to obtain the product.

[0033] The initial fluidity of cement paste is 195mm, no fluidity after 1 hour, the initial slump / extension of concrete is 200mm / 520mm, no fluidity after 1 hour, the compressive strength at 7 days is 33.4MPa, and the compressive strength at 28 days is 35.0MPa.

[0034] Comparative Example 3 The preparation method of the water reducing agent comprises the following steps: 1) Weigh 15 parts of water, 15 parts of acrylic acid, 4 parts of functional monomer, 11 parts of maleic anhydride, and 0.5 parts of thioglycolic acid by weight, stir evenly to obtain material A. 2) Weigh 40 parts of water, 14 parts of acrylic acid, 5 parts of functional monomer, 5 parts of maleic anhydride, and 0.4 parts of vitamin C by weight, stir evenly to obtain material B. 3) Weigh 370 parts of ethylene glycol monovinyl polyethylene glycol ether and 270 parts of water by weight, add them to a reactor and mix evenly, then add 5 parts of acrylic acid, 4 parts of functional monomer, 2 parts of ferrous sulfate, and 2.5 parts of hydrogen peroxide, stir evenly, add material A and material B dropwise, continue stirring at 30°C after the addition is complete, and adjust the pH value to 6.5 to obtain the product.

[0035] The initial fluidity of cement paste is 200mm, no fluidity after 1 hour, the initial slump / expansion of concrete is 190mm / 400mm, no fluidity after 1 hour, the compressive strength at 7 days is 30.3MPa, and the compressive strength at 28 days is 34.5MPa.

[0036] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a water reducer for high alkali cement, characterized in that: The steps include: 1) Weigh 12-16 parts of water, 15-20 parts of small monomer, 2-5 parts of functional monomer, 8-12 parts of alcoholamine modified monomer, and 0.5-1 part of chain transfer agent by weight, stir evenly to obtain material A. 2) Weigh 35-45 parts of water, 12-18 parts of small monomer, 1-5 parts of functional monomer, 3-7 parts of alcoholamine modified monomer, and 0.3-0.5 parts of reducing agent by weight, stir evenly to obtain material B. 3) Weigh 320-380 parts of ethylene glycol monovinyl polyethylene glycol ether and 250-300 parts of water by weight, add them to a reactor and mix evenly, then add 5-10 parts of small monomer, 4-6 parts of functional monomer, 1-3 parts of ferrous sulfate, and 1-3 parts of oxidant, stir evenly, add material A and material B dropwise, continue to keep warm and stir after the addition is complete, and adjust the pH value to 5-7 to obtain the product.

2. The method for preparing a high alkali cement water reducer according to claim 1, wherein: The functional monomer preparation process comprises the following steps: weighing 70-90 parts of acrylamide and 460-520 parts of water by weight, mixing them uniformly, then adding 8-12 parts of hydroxyethyl acrylate, 1-3 parts of chain transfer agent, 7-9 parts of oxidant, and 80-90 parts of small monomer by weight, stirring them uniformly, and then dropwise adding 10-20 parts of small monomer and 1-3 parts of reducing agent by weight, stirring while keeping warm, and cooling to obtain the functional monomer.

3. The method for preparing a high alkali cement water reducer according to any one of claims 1 to 2, characterized in that: The small monomer is at least one of acrylic acid and methacrylic acid.

4. The method for preparing a high alkali cement water reducer according to any one of claims 1 to 2, characterized in that: The chain transfer agent is at least one of mercaptoacetic acid and mercaptopropionic acid.

5. The method for preparing a high alkali cement water reducer according to any one of claims 1 to 2, characterized in that: The reducing agent is vitamin C, and the oxidizing agent is hydrogen peroxide.

6. The method for preparing a high alkali cement water reducer according to claim 1, wherein: In step 3), the dropwise addition time of material A is 20-30 min, the dropwise addition time of material B is 50-60 min, and the insulation temperature is 20-40°C.

7. The method for preparing a high alkali cement water reducer according to claim 1, wherein: The preparation process of the alcoholamine modified monomer comprises the following steps: weighing 8-12 parts of maleic anhydride, 8-10 parts of diethanol monoisopropanolamine, 30-50 parts of water, and 0.05-0.2 parts of a catalyst by weight, heating the mixture for reaction, adding 15-20 parts of ethylene glycol monovinyl polyethylene glycol ether by weight, and continuing to stir the mixture for reaction to obtain the alcoholamine modified monomer.

8. The method for preparing a high alkali cement water reducer according to claim 7, wherein: The catalyst is p-toluenesulfonic acid.

9. The method for preparing a high alkali cement water reducer according to claim 7, wherein: The temperature-raising reaction is carried out by heating the temperature to 100-115° C. and reacting for 2.5-4 hours.

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