Preparation method of modified polycarboxylate superplasticizer for concrete

Abstract

The invention relates to the technical field of water reducing agents, and discloses a preparation method of a modified polycarboxylic acid water reducing agent for concrete, which comprises the following steps: taking isobutenol polyoxyethylene ether, acrylic acid, mercaptopropionic acid, vitamin C, phytate nano silicon dioxide and the like as raw materials; a dialkenyl structure contained in phytic acid nano silicon dioxide reacts with a base material to obtain a modified polycarboxylic acid water reducing agent, and the polycarboxylic acid water reducing agent prepared from nano silicon dioxide and phytic acid is applied to concrete, so that the mechanical property and the retarding effect of the concrete can be improved, and the service life of the concrete is prolonged. And the method has a wide application prospect in large-volume and high-pump-stroke concrete construction.

Description

Technical Field

[0001] This invention relates to the field of water-reducing agent technology, specifically to a method for preparing a modified polycarboxylate water-reducing agent for concrete. Background Art

[0002] Cement is the key binding material in concrete. Polycarboxylate superplasticizers, with their high water reduction rate and improved workability, have become an indispensable component in concrete mix design. However, in large-scale engineering construction, the widespread use of large-volume, high-pump-lift concrete construction places higher demands on the fluidity, dispersibility, and retarding properties of high-efficiency superplasticizers. Poor retarding properties can lead to through-cracks. Phytic acid, also known as inositol hexaphosphate or cyclohexanehexaphosphate, has a strong chelating ability and can chelate with ions such as calcium, iron, magnesium, and zinc.

[0003] For example, the patent with authorization announcement number CN113248171B discloses a method for preparing a high-performance polycarboxylate superplasticizer. This invention adds nano-silica to the polycarboxylate superplasticizer, which can improve the water-reducing effect of the superplasticizer. However, it does not mean that applying the polycarboxylate superplasticizer to concrete can improve the mechanical properties and retarding effect of large-volume, high-pump-stroke concrete. Summary of the Invention

[0004] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides a method for preparing a modified polycarboxylate superplasticizer for concrete. When the prepared modified polycarboxylate superplasticizer is applied to concrete, it not only possesses the flow properties of traditional polycarboxylate superplasticizers but also enhances the mechanical properties and retarding effect of concrete.

[0005] (II) Technical Solution A method for preparing a modified polycarboxylate superplasticizer for concrete, the method comprising the following steps: At room temperature, isobutylene alcohol polyoxyethylene ether is added to deionized water and stirred to disperse. Then, acrylic acid, mercaptopropionic acid, vitamin C, and phytic acid nano silica are added and stirred to mix evenly. Hydrogen peroxide and ammonium persulfate are added and stirred to react for 2-4 hours. Water is added until the solid content is 40%, and stirring is continued until evenly mixed. The product is then discharged to obtain the modified polycarboxylate superplasticizer for concrete.

[0006] This invention utilizes the carboxyl and phosphate groups in a modified polycarboxylate superplasticizer for concrete, which can chelate with calcium ions through electrostatic attraction and rapidly adsorb onto the surface of positively charged cement particles. The hydrophilic polyether long side chains fully extend in the aqueous phase surrounding the cement particles, forming a thick hydration film. When two cement particles approach each other, these extended long side chains physically overlap. Compressing these highly hydrophilic and solvated long chains requires work and generates a strong steric repulsion force. This steric hindrance effectively prevents cement particles from re-aggregating within a short distance. Even after the electrostatic repulsion weakens due to increased ion concentration in the system (such as increased ion dissolution during hydration), the steric hindrance can still maintain a good dispersion state of the cement particles for a long time and stably. Adding it to concrete can effectively increase its flow and dispersion effect.

[0007] Preferably, the ratio of isobutylene polyoxyethylene ether, acrylic acid, vitamin C, and phytic acid-modified nano silica is 100g:(15-20)g:(0.2-0.4)g:(10-15)g.

[0008] Preferably, the amount of hydrogen peroxide used is 0.5-0.8% of the mass of isobutylene polyoxyethylene ether; the amount of mercaptopropionic acid used is 0.3-0.6% of the mass of isobutylene polyoxyethylene ether; and the amount of ammonium persulfate used is 1.5-2% of the mass of isobutylene polyoxyethylene ether.

[0009] Preferably, the method for preparing the phytic acid-modified nano-silica includes the following steps: (1) γ-glycidyl etheroxypropyltrimethoxysilane was added to ethanol solvent, acetic acid was added to adjust the pH to 3-4, magnetic stirring was performed, nano-silica was added, magnetic stirring was performed for 10-12 h, after stirring was completed, centrifuged, washed with deionized water, and dried to obtain silanized nano-silica. Undispersed nano-silica not only fails to effectively exert its nucleation effect, but may also weaken concrete performance, reduce its durability, and affect its overall performance due to material aggregation. Dispersed nano-silica, when added to concrete, can adsorb ions in the cement pore solution through its high surface area, accelerating their aggregation and saturation on the surface of nanoparticles, thereby precipitating hydration products. At the same time, the reduced ion concentration in the pore solution will stimulate the cement to release additional ions to achieve ion balance in the pore solution. This can effectively increase the compressive and flexural strength of cement-based materials, reduce porosity, and improve the density of concrete.

[0010] (2) Add 4-penten-1-amine and 2-(2-propen-1-yl) to an 80% ethanol aqueous solution, mix well, then add phytic acid, stir and react at room temperature for 5-8 hours. After the reaction is completed, centrifuge, wash with deionized water, and dry to obtain alkenylated phytic acid. In this reaction, the phosphate group contained in phytic acid reacts with the amino group to obtain alkenylated phytic acid, that is, an alkenyl structure is introduced into it. When it is copolymerized with acrylic acid, the density of molecular chain crosslinking can be increased to form a network structure. On the one hand, phytic acid has a strong chelating ability for calcium ions, which can capture calcium ions released in the early hydration in cement pores, reduce their concentration in the liquid phase, reduce the formation of hydration products, delay the hydration process, optimize the pore distribution of mortar, and reduce porosity. On the other hand, it can also adsorb with carboxylic acid and other groups on the surface of cement particles to form a dense adsorption film, block water molecules from contacting, further inhibit the hydration process, and improve the water-reducing effect and dispersion effect of the water-reducing agent.

[0011] (3) Add silanized nano silica to ethanol solvent, then add alkenylated phytic acid to it, control the temperature at 70-80℃, stir for 3-5 hours, centrifuge, wash with deionized water, and dry to obtain phytic acid nano silica, which improves the density of concrete.

[0012] More preferably, in step (1), the ratio of γ-glycidyl etheroxypropyltrimethoxysilane to nano silica is (0.8-1) mL:1 g.

[0013] More preferably, in step (2), the ratio of 4-penten-1-amine, 2-(2-propen-1-yl), and phytic acid is (0.15-0.3) g: 1 g.

[0014] More preferably, in step (3), the mass ratio of silanized nano-silica to phytic acid is 1g:(0.03-0.05)g.

[0015] (iii) Beneficial technical effects This invention uses uniformly dispersed nano-silica, utilizing the nucleation effect of nano-silica to induce a decrease in the ion concentration in the pore solution, thereby forming more hydration products. This stimulates cement dissolution and releases more ions to balance the particle concentration in the pore solution (i.e., nano-silica promotes the cement hydration process through nucleation). During this process, the newly formed hydration products are far from the surface of cement particles, and the deposition of newly formed hydration products on the surface of cement particles is minimized, accelerating cement dissolution. This makes the microstructure of cement-based materials more compact, effectively improving the internal void distribution and porosity of concrete mortar, promoting the development of macroscopic mechanical properties, maximizing the utilization of highly active minerals in cement, and improving the overall performance of concrete.

[0016] Furthermore, this invention utilizes the carboxyl and phosphate groups contained in the modified polycarboxylate superplasticizer to generate chelated calcium ions and utilizes the nucleation effect of nano-silica to adsorb calcium ions, thereby reducing the formation of hydration products. Moreover, since the polycarboxylate superplasticizer contains a large number of network structures, it can further block the nucleation sites of hydration products, delay the formation of hydration products, improve the retarding effect, and thus improve the overall performance of concrete. Detailed Implementation

[0017] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] Example 1

[0019] (1) Add 20 mL of γ-glycidoxypropyltrimethoxysilane to ethanol solvent, add acetic acid to adjust the pH to 3, stir magnetically, then add 20 g of nano silica, stir magnetically for 12 h, after stirring, centrifuge, wash with deionized water, and dry to obtain silanized nano silica. In this reaction, the silanized hydroxyl groups generated after the hydrolysis of γ-glycidoxypropyltrimethoxysilane are dehydrated and condensed with the hydroxyl groups on the surface of nano silica to obtain silanized nano silica.

[0020] (2) Add 0.2g of 4-penten-1-amine, 2-(2-propen-1-yl) to an 80% ethanol aqueous solution, mix well, then add 1g of phytic acid, stir and react for 7h at room temperature, centrifuge, wash with deionized water, and dry to obtain alkenylated phytic acid.

[0021] (3) Add 15g of silanized nano silica to ethanol solvent, then add 0.45g of alkenylated phytic acid, control the temperature at 75℃, stir for 5h, centrifuge, wash with deionized water, and dry to obtain phytic acid nano silica. Utilize the epoxy groups contained in silanized nano silica and the phosphate groups contained in alkenylated phytic acid to carry out a ring-opening reaction, introducing phytic acid onto the surface of nano silica, thus obtaining phytic acid nano silica.

[0022] (4) At room temperature, add 100g of isobutylene polyoxyethylene ether to deionized water, stir and disperse, then add 15g of acrylic acid, 0.3g of mercaptopropionic acid, 0.4g of vitamin C and 10g of phytic acid nano silica, stir and mix evenly, then add 0.5g of hydrogen peroxide and 1.5g of ammonium persulfate, stir and react for 3h, add water until the solid content is 40%, continue to stir evenly, discharge the material, and obtain the modified polycarboxylate superplasticizer for concrete.

[0023] Example 2

[0024] (1) Add 18 mL of γ-glycidoxypropyltrimethoxysilane to ethanol solvent, add acetic acid to adjust the pH to 4, stir magnetically, add 20 g of nano silica, stir magnetically for 10 h, centrifuge, wash with deionized water, and dry to obtain silanized nano silica.

[0025] (2) Add 0.15g of 4-penten-1-amine, 2-(2-propen-1-yl) to an 80% ethanol aqueous solution, mix well, then add 1g of phytic acid, stir and react for 5h at room temperature, centrifuge, wash with deionized water, and dry to obtain alkenylated phytic acid.

[0026] (3) Add 15g of silanized nano silica to ethanol solvent, then add 0.6g of alkenylated phytic acid, control the temperature at 80℃, stir for 3h, centrifuge, wash with deionized water, and dry to obtain phytic acid-modified nano silica.

[0027] (4) At room temperature, add 100g of isobutylene polyoxyethylene ether to deionized water, stir and disperse, then add 17g of acrylic acid, 0.4g of mercaptopropionic acid, 0.3g of vitamin C and 12g of phytic acid nano silica, stir and mix evenly, then add 0.6g of hydrogen peroxide and 1.6g of ammonium persulfate, stir and react for 4h, add water until the solid content is 40%, continue to stir evenly, discharge the material, and obtain the modified polycarboxylate superplasticizer for concrete.

[0028] Example 3

[0029] (1) Add 16 mL of γ-glycidoxypropyltrimethoxysilane to ethanol solvent, add acetic acid to adjust the pH to 4, stir magnetically, add 20 g of nano silica, stir magnetically for 11 h, centrifuge, wash with deionized water, and dry to obtain silanized nano silica.

[0030] (2) Add 0.2g of 4-penten-1-amine, 2-(2-propen-1-yl) to an 80% ethanol aqueous solution, mix well, then add 1g of phytic acid, stir and react for 6h at room temperature, centrifuge, wash with deionized water, and dry to obtain alkenylated phytic acid.

[0031] (3) Add 15g of silanized nano silica to ethanol solvent, then add 0.75g of alkenylated phytic acid, control the temperature at 70℃, stir for 4h, centrifuge, wash with deionized water, and dry to obtain phytic acid-modified nano silica.

[0032] (4) At room temperature, add 100g of isobutylene polyoxyethylene ether to deionized water, stir and disperse, then add 18g of acrylic acid, 0.5g of mercaptopropionic acid, 0.2g of vitamin C and 14g of phytic acid nano silica, stir and mix evenly, then add 0.8g of hydrogen peroxide and 1.8g of ammonium persulfate, stir and react for 2h, add water until the solid content is 40%, continue to stir evenly, discharge the material, and obtain the modified polycarboxylate superplasticizer for concrete.

[0033] Example 4

[0034] (1) Add 18 mL of γ-glycidoxypropyltrimethoxysilane to ethanol solvent, add acetic acid to adjust the pH to 4, stir magnetically, add 20 g of nano silica, stir magnetically for 11 h, centrifuge, wash with deionized water, and dry to obtain silanized nano silica.

[0035] (2) Add 0.3g of 4-penten-1-amine, 2-(2-propen-1-yl) to an 80% ethanol aqueous solution, mix well, then add 1g of phytic acid, stir and react for 8h at room temperature, centrifuge, wash with deionized water, and dry to obtain alkenylated phytic acid.

[0036] (3) Add 15g of silanized nano silica to ethanol solvent, then add 0.5g of alkenylated phytic acid, control the temperature at 70℃, stir for 5h, centrifuge, wash with deionized water, and dry to obtain phytic acid-modified nano silica.

[0037] (4) At room temperature, add 100g of isobutylene polyoxyethylene ether to deionized water, stir and disperse, then add 20g of acrylic acid, 0.6g of mercaptopropionic acid, 0.4g of vitamin C and 15g of phytic acid nano silica, stir and mix evenly, then add 0.6g of hydrogen peroxide and 2g of ammonium persulfate, stir and react for 4h, add water until the solid content is 40%, continue to stir evenly, discharge the material, and obtain the modified polycarboxylate superplasticizer for concrete.

[0038] Comparative Example 1 The difference between this comparative example and Example 1 is that nano-silica is used instead of phytic acid nano-silica in step (4).

[0039] Comparative Example 2 The difference between this comparative example and Example 1 is that: in step (4), alkenylated phytic acid is used instead of phyticated nano-silica.

[0040] According to GB / T8077-2023, the fluidity was tested, the water-cement ratio was 0.29, the water-reducing agent dosage was 0.5%, and the cement was P.O42.5 grade Portland cement.

[0041] According to GB / T50081-2019, the flexural strength was tested after 28 days.

[0042] Table 1:

[0043] The higher the fluidity, the better the dispersibility. As shown in the table, the water-reducing agent prepared by this invention has excellent dispersibility when applied to concrete. This excellent dispersibility is based on the compatibility of carboxyl groups and phosphate groups contained in the modified polycarboxylate water-reducing agent prepared by this invention. Undispersed nano-silica agglomerates in concrete, which is not conducive to the dispersion of concrete. Therefore, it has the worst fluidity and the worst dispersibility.

[0044] The modified polycarboxylate superplasticizer prepared in this invention, when applied to concrete, not only fills the micropores of the concrete with uniformly dispersed nano-silica, improving the distribution of the micropore structure and thus forming a dense microstructure, thereby enhancing the mechanical properties of the concrete and inhibiting hydration to improve the slow-release effect, but also, the polycarboxylate superplasticizer with a cross-linked network structure can form a network structure in the concrete, forming bridge connections between hydration products, which is beneficial for dispersing stress loads and further improving the mechanical properties of the concrete.

[0045] Refer to GB / T1346-2024 to test the setting time.

[0046] Table 2:

[0047] As shown in the table, the modified polycarboxylate superplasticizer prepared by this invention has a good retarding effect and is well applied in the construction of large-volume, high-pump-head concrete. This is because the modified polycarboxylate superplasticizer prepared by this invention contains nano-silica, as well as carboxyl and phosphate groups, which can chelate with calcium ions, delay the cement hydration process, and prolong the initial and final setting times. Therefore, the modified polycarboxylate superplasticizer prepared by this invention has broad application prospects in the construction of large-volume, high-pump-head concrete.

[0048] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a modified polycarboxylate superplasticizer for concrete, characterized in that, The preparation method includes the following steps: At room temperature, isobutylene alcohol polyoxyethylene ether is added to deionized water and stirred to disperse. Then, acrylic acid, mercaptopropionic acid, vitamin C, and phytic acid nano silica are added and stirred to mix evenly. Hydrogen peroxide and ammonium persulfate are added and stirred to react for 2-4 hours. Water is added until the solid content is 40%, and stirring is continued until evenly mixed. The product is then discharged to obtain the modified polycarboxylate superplasticizer for concrete.

2. The preparation method of the modified polycarboxylate superplasticizer for concrete according to claim 1, characterized in that, The ratio of isobutylene alcohol polyoxyethylene ether, acrylic acid, vitamin C, and phytic acid nano silica is 100g:(15-20)g:(0.2-0.4)g:(10-15)g.

3. The preparation method of the modified polycarboxylate superplasticizer for concrete according to claim 1, characterized in that, The amount of hydrogen peroxide used is 0.5-0.8% of the mass of isobutylene polyoxyethylene ether; the amount of mercaptopropionic acid used is 0.3-0.6% of the mass of isobutylene polyoxyethylene ether; and the amount of ammonium persulfate used is 1.5-2% of the mass of isobutylene polyoxyethylene ether.

4. The preparation method of the modified polycarboxylate superplasticizer for concrete according to claim 1, characterized in that, The preparation method of the phytic acid-modified nano-silica includes the following steps: (1) γ-glycidyl etheroxypropyltrimethoxysilane was added to ethanol solvent, acetic acid was added to adjust the pH to 3-4, magnetic stirring was performed, nano-silica was added, magnetic stirring was performed for 10-12 h, after stirring was completed, centrifuged, washed with deionized water, and dried to obtain silanized nano-silica. (2) Add 4-penten-1-amine, 2-(2-propen-1-yl) to an 80% ethanol aqueous solution, mix well, then add phytic acid, stir and react at room temperature for 5-8 hours. After the reaction is completed, centrifuge, wash with deionized water, and dry to obtain alkenylated phytic acid. (3) Add silanized nano-silica to ethanol solvent, then add alkenylated phytic acid to it, control the temperature at 70-80℃, stir the reaction for 3-5 hours, centrifuge, wash with deionized water, and dry to obtain phytic acid-modified nano-silica.

5. The method for preparing the modified polycarboxylate superplasticizer for concrete according to claim 4, characterized in that, In (1), the ratio of γ-glycidyl etheroxypropyltrimethoxysilane to nano silica is (0.8-1) mL:1 g.

6. The method for preparing the modified polycarboxylate superplasticizer for concrete according to claim 4, characterized in that, In (2), the ratio of 4-penten-1-amine, 2-(2-propen-1-yl), and phytic acid is (0.15-0.3) g: 1 g.

7. The method for preparing the modified polycarboxylate superplasticizer for concrete according to claim 4, characterized in that, In (3), the mass ratio of silanized nano-silica to phytic acid is 1g:(0.03-0.05)g.

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