An unsaturated phosphate ester and polycarboxylate superplasticizer containing catechol groups and its preparation method thereof.

Abstract

This invention belongs to the field of concrete technology, and specifically relates to an unsaturated phosphate ester containing catechol groups and a polycarboxylate superplasticizer and its preparation method. The unsaturated phosphate ester containing catechol groups has the following structural formula: wherein R1 is hydrogen or methyl, and R2 is methyl or ethyl, in order to solve the problems of sensitivity of concrete under different ambient temperatures, different aggregate mud content, and different admixture dosages, rapid loss and large hysteresis return, as well as bleeding.

Description

Technical Field

[0001] This invention belongs to the field of concrete technology, and specifically relates to an unsaturated phosphate ester and polycarboxylate superplasticizer containing catechol groups and its preparation method. Background Technology

[0002] With the rapid development of China's economy, the construction industry has also experienced unprecedented growth. Concrete, as the most widely used and consumed building material in modern times, has seen continuous advancements in its preparation technology. Concrete admixtures, especially water-reducing agents, are key raw materials for the development of high-performance concrete. They can achieve good fluidity, improve workability, and increase strength in concrete at relatively low dosages, and are widely used in major projects such as highways, bridges, tunnels, and dams. Polycarboxylate superplasticizers are the third generation of high-performance water-reducing agents, developed after ordinary water-reducing agents represented by lignin sulfonates and high-efficiency water-reducing agents represented by naphthalene-based and aminosulfonate-based agents. They have advantages such as high water reduction rate, low dosage, and diverse structure and function, which can reduce costs. However, they also have the drawback of high sensitivity to concrete materials, easily leading to problems such as excessively rapid concrete loss, segregation, and bleeding, increasing the difficulty of concrete production control.

[0003] Currently, manufactured sand aggregate has gradually replaced natural sand as the main source of construction sand. However, due to the rapid application of manufactured sand, insufficient understanding of it, and inadequate production processes and management, the performance of manufactured sand differs significantly from that of natural sand (rough particle surface, many sharp edges, poor gradation, etc.). Furthermore, the source of the parent rock is unstable, resulting in large fluctuations in stone powder content and inconsistent quality. This often leads to problems such as poor coating properties, poor fluidity, significant losses, and easy segregation and bleeding in concrete mixtures, easily causing potential quality hazards in engineering projects. Summary of the Invention

[0004] The embodiments of the present invention provide an unsaturated phosphate ester and polycarboxylate superplasticizer containing catechol groups and a method for preparing the same, in order to solve the problems of sensitivity, rapid loss and large hysteresis return, and bleeding of concrete under different ambient temperatures, different aggregate mud content, and different admixture dosages.

[0005] To achieve the above objectives, the embodiments of the present invention adopt the following technical solutions:

[0006] This application provides an unsaturated phosphate ester containing a catechol group, the structural formula of which is as follows:

[0007]

[0008] Wherein, R1 is hydrogen or methyl, and R2 is methyl or ethyl.

[0009] This application also provides a method for preparing an unsaturated phosphate ester containing a catechol group, comprising the following steps:

[0010] An unsaturated phosphate ester containing catechol groups was prepared by mixing 2-aminoethyl (meth)acrylate hydrochloride with protocatechuic aldehyde and dimethyl (ethyl) phosphite and reacting them under the action of an alkaline catalyst.

[0011] In some embodiments, the molar ratio of 2-aminoethyl (meth)acrylate hydrochloride, protocatechuic aldehyde, dimethyl (ethyl) phosphite to the alkaline catalyst is (1.00-1.05):1:1:1.16.

[0012] In some embodiments, the alkaline catalyst comprises at least one of trimethylamine, triethylamine, and 4-dimethylaminopyridine.

[0013] In some embodiments, the reaction temperature is 60-80°C and the reaction time is 4-5 hours.

[0014] This application also provides a polycarboxylate superplasticizer, comprising the following components:

[0015] Polyether macromonomer, unsaturated acid, unsaturated phosphate ester containing catechol group as described above, unsaturated ester, chain transfer agent, oxidizing agent, reducing agent and alkaline solution.

[0016] The molar ratio of the polyether macromonomer, unsaturated acid, unsaturated phosphate ester containing catechol group, unsaturated ester, chain transfer agent, oxidant, reducing agent and alkaline solution is 1: (1.5-2.5): (0.2~0.5): (3.0~4.0): (0.1~0.6): (0.1~0.3): (0.02~0.04): (0.3~0.5).

[0017] In some embodiments, the molecular weight of the polyether macromonomer is 2000-3000, and the polyether macromonomer includes at least one of isobutylene polyoxyethylene ether, isopentenyl polyoxyethylene ether, vinyl polyethylene glycol ether, and ethyleneoxybutyl polyethylene glycol ether.

[0018] In some embodiments, the unsaturated acid includes at least one selected from acrylic acid, methacrylic acid, maleic anhydride, itaconic acid, and fumaric acid.

[0019] The unsaturated ester includes at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

[0020] In some embodiments, the chain transfer agent includes at least one of mercaptoethanol, mercaptoacetic acid, mercaptopropionic acid, and sodium hypophosphite.

[0021] The oxidant includes at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate.

[0022] The reducing agent includes at least one of sodium formaldehyde sulfoxylate and L-ascorbic acid.

[0023] The alkali includes at least one of sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine.

[0024] This application also provides a method for preparing a polycarboxylate superplasticizer, comprising the following steps:

[0025] The polyether macromonomer is reacted with an oxidant, an unsaturated acid, an unsaturated ester, an unsaturated phosphate ester containing a catechol group, a chain transfer agent, and a reducing agent at a temperature of 10~40℃ and kept at this temperature for 0.5~3h. After the temperature is maintained, an alkali is added to obtain the polycarboxylate superplasticizer.

[0026] The positive effects of this invention are:

[0027] 1. The unsaturated phosphate ester containing catechol groups provided by the present invention introduces catechol groups into the molecular structure of the unsaturated ester. When used in the synthesis of polycarboxylate superplasticizers, it can improve the adsorption capacity of cement paste on the surface of low surface energy manufactured sand, effectively improve the dispersion ability of superplasticizers in concrete and the workability of concrete.

[0028] 2. The unsaturated phosphate ester containing catechol groups provided by this invention introduces phosphate ester groups into the molecular structure. When used in the synthesis of polycarboxylate superplasticizers, it can change the molecular structure of the side chains of polycarboxylate superplasticizer molecules, causing the polycarboxylate superplasticizer molecules to generate a large number of phosphate ions and small molecule alcohols when hydrolyzed in cement paste. This can greatly delay the cement hydration process, thereby solving the shortcomings of traditional polycarboxylate superplasticizers such as sensitivity to concrete materials and poor workability. It achieves the dual functions of low sensitivity and high slump retention of polycarboxylate superplasticizers.

[0029] 3. The polycarboxylate superplasticizer of the present invention introduces unsaturated ester monomers into its molecular structure, which can slowly release a large number of carboxylate ions that play a water-reducing role under alkaline conditions, further improving the slump retention effect of the polycarboxylate superplasticizer.

[0030] 4. The preparation process of the unsaturated phosphate ester containing catechol groups in this invention is simple, easy to operate, and pollution-free.

[0031] 5. The polycarboxylate superplasticizer involved in this invention has excellent performance, with advantages such as strong slump retention, good adaptability to cement, insensitivity to the mud and powder content in concrete materials, and improved workability of concrete. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below. Obviously, the described embodiments are merely some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other implementation methods obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0033] Example 1

[0034] Preparation of unsaturated phosphate esters containing catechol groups: 100 mL of anhydrous ethanol was added to a clean reaction vessel, followed by 12.2 g of 2-aminoethyl acrylate hydrochloride, 13.8 g of protocatechuic aldehyde, and 11.7 g of triethylamine. The mixture was stirred until fully dissolved. Then, 11.0 g of dimethyl phosphite was added dropwise to the solution. The temperature was maintained at 60 °C for 4 hours. The white precipitate was removed by filtration, yielding a light yellow liquid. The ethanol was removed by rotary evaporation, yielding a light yellow solid. The solid powder was dried under vacuum, yielding a light yellow powder, which is the unsaturated phosphate ester containing catechol groups (denoted as BQP-1), and its structural formula is as follows:

[0035]

[0036] A polycarboxylate superplasticizer was prepared by polymerization of an unsaturated phosphate ester (BQP-1) containing catechol groups. The preparation process is as follows:

[0037] 337g of vinyl polyethylene glycol ether (VPEG) with a molecular weight of 3000 and 342g of water were added to a reaction vessel and stirred to dissolve. Simultaneously, components A and B were prepared for dropwise addition. Component A consisted of 17g acrylic acid, 40g hydroxyethyl acrylate, 8g unsaturated phosphate ester containing catechol groups (BQP-1), and 20g water, mixed thoroughly. Component B consisted of 1.8g mercaptopropionic acid, 0.5g L-ascorbic acid, and 60g water, mixed thoroughly. The initial temperature inside the reaction vessel was controlled at 15℃. 3.0g of 27.5% hydrogen peroxide solution was added to the reaction solvent at once. After stirring for 5 minutes, components A and B were added dropwise. Component A was added over 50 minutes, and component B over 60 minutes. After the addition of component B was complete, the mixture was kept at this temperature for 60 minutes. Water was added to adjust the polymer concentration, and alkali was added to adjust the pH to 5-6, yielding a low-sensitivity, high-slump-retention polycarboxylate superplasticizer PCE-1 with a solid content of 40%.

[0038] Example 2

[0039] Preparation of unsaturated phosphate esters containing catechol groups: 100 mL of anhydrous ethanol was added to a clean reaction vessel, followed by 12.2 g of 2-aminoethyl acrylate hydrochloride, 13.8 g of protocatechuic aldehyde, and 11.7 g of triethylamine. The mixture was stirred until fully dissolved. Then, 13.8 g of diethyl phosphite was added dropwise to the solution. The temperature was maintained at 60 °C for 4 hours. The white precipitate was removed by filtration, yielding a light yellow liquid. The ethanol was removed by rotary evaporation, yielding a light yellow solid. The solid powder was dried under vacuum, which is the unsaturated phosphate ester containing catechol groups (denoted as BQP-2), and its structural formula is as follows:

[0040]

[0041] A polycarboxylate superplasticizer was prepared by polymerization of an unsaturated phosphate ester (BQP-2) containing catechol groups. The preparation process is as follows:

[0042] 337g of vinyl polyethylene glycol ether (VPEG) with a molecular weight of 3000 and 342g of water were added to a reaction vessel and stirred to dissolve. Simultaneously, components A and B were prepared for dropwise addition. Component A consisted of 17g acrylic acid, 40g hydroxyethyl acrylate, 8.7g catechol-based unsaturated phosphate ester (BQP-2), and 20g water, mixed thoroughly. Component B consisted of 1.8g mercaptopropionic acid, 0.5g L-ascorbic acid, and 60g water, mixed thoroughly. The initial temperature inside the reaction vessel was controlled at 15℃. 3.0g of 27.5% hydrogen peroxide solution was added to the reaction solvent at once. After stirring for 5 minutes, components A and B were added dropwise. Component A was added over 50 minutes, and component B over 60 minutes. After the addition of component B was complete, the mixture was kept at this temperature for 60 minutes. Water was added to adjust the polymer concentration, and alkali was added to adjust the pH to 5-6, yielding a low-sensitivity, high-slump-retention polycarboxylate superplasticizer PCE-2 with a solid content of 40%.

[0043] Example 3

[0044] Preparation of unsaturated phosphate esters containing catechol groups: 100 mL of anhydrous ethanol was added to a clean reaction vessel, followed by 13.7 g of 2-aminoethyl methacrylate hydrochloride, 13.8 g of protocatechuic aldehyde, and 11.7 g of triethylamine. The mixture was stirred until fully dissolved. Then, 11 g of dimethyl phosphite was added dropwise to the solution. The temperature was maintained at 60 °C for 4 hours. The white precipitate was removed by filtration, yielding a light yellow liquid. The ethanol was removed by rotary evaporation, yielding a light yellow solid. The solid powder was dried under vacuum, which is the unsaturated phosphate ester containing catechol groups (denoted as BQP-3), and its structural formula is as follows:

[0045]

[0046] A polycarboxylate superplasticizer was prepared by polymerizing an unsaturated phosphate ester (BQP-3) containing catechol groups. The preparation process is as follows:

[0047] 337g of vinyl polyethylene glycol ether (VPEG) with a molecular weight of 3000 and 342g of water were added to a reaction vessel and stirred to dissolve. Simultaneously, components A and B were prepared for dropwise addition. Component A consisted of 17g acrylic acid, 40g hydroxyethyl acrylate, 8.4g catechol-based unsaturated phosphate ester (BQP-3), and 20g water, mixed thoroughly. Component B consisted of 1.8g mercaptopropionic acid, 0.5g L-ascorbic acid, and 60g water, mixed thoroughly. The initial temperature inside the reaction vessel was controlled at 15℃. 3.0g of 27.5% hydrogen peroxide solution was added to the reaction solvent at once. After stirring for 5 minutes, components A and B were added dropwise. Component A was added over 50 minutes, and component B over 60 minutes. After the addition of component B was complete, the mixture was kept at this temperature for 60 minutes. Water was added to adjust the polymer concentration, and then alkali was added to adjust the pH to 5-6, yielding a low-sensitivity, high-slump-retention polycarboxylate superplasticizer PCE-3 with a solid content of 40%.

[0048] Example 4

[0049] Preparation of unsaturated phosphate esters containing catechol groups: 100 mL of anhydrous ethanol was added to a clean reaction vessel, followed by 13.7 g of 2-aminoethyl methacrylate hydrochloride, 13.8 g of protocatechuic aldehyde, and 11.7 g of triethylamine. The mixture was stirred until fully dissolved. Then, 13.8 g of diethyl phosphite was added dropwise to the solution. The temperature was maintained at 60 °C for 4 hours. The white precipitate was removed by filtration, yielding a light yellow liquid. The ethanol was removed by rotary evaporation, yielding a light yellow solid. The solid powder was dried under vacuum, which is the unsaturated phosphate ester containing catechol groups (denoted as BQP-4), and its structural formula is as follows:

[0050]

[0051] A polycarboxylate superplasticizer was prepared by polymerizing an unsaturated phosphate ester (BQP-4) with a catechol group. The preparation process is as follows:

[0052] 337g of vinyl polyethylene glycol ether (VPEG) with a molecular weight of 3000 and 342g of water were added to a reaction vessel and stirred to dissolve. Simultaneously, components A and B were prepared for dropwise addition. Component A consisted of 17g acrylic acid, 40g hydroxyethyl acrylate, 9g catechol-based unsaturated phosphate ester (BQP-4), and 20g water, mixed thoroughly. Component B consisted of 1.8g mercaptopropionic acid, 0.5g L-ascorbic acid, and 60g water, mixed thoroughly. The initial temperature inside the reaction vessel was controlled at 15℃. 3.0g of 27.5% hydrogen peroxide solution was added to the reaction solvent at once. After stirring for 5 minutes, components A and B were added dropwise. Component A was added over 50 minutes, and component B over 60 minutes. After the addition of component B was complete, the mixture was kept at this temperature for 60 minutes. Water was added to adjust the polymer concentration, and alkali was added to adjust the pH to 5-6, yielding a low-sensitivity, high-slump-retention polycarboxylate superplasticizer PCE-4 with a solid content of 40%.

[0053] Comparative Example 1: Conventional slump-retaining polycarboxylate superplasticizer

[0054] 337g of vinyl polyethylene glycol ether (VPEG) with a molecular weight of 3000 and 342g of water were added to a reaction vessel and stirred to dissolve. Simultaneously, components A and B were prepared for dropwise addition. Component A consisted of 17g acrylic acid, 42.7g hydroxyethyl acrylate, and 20g water, mixed thoroughly. Component B consisted of 1.8g mercaptopropionic acid, 0.5g L-ascorbic acid, and 60g water, mixed thoroughly. The initial temperature inside the reaction vessel was controlled at 15℃. 3.0g of 27.5% hydrogen peroxide solution was added to the reaction solvent at once. After stirring for 5 minutes, components A and B were added dropwise. Component A was added over 50 minutes, and component B over 60 minutes. After the addition of component B was complete, the mixture was kept at this temperature for 60 minutes. Water was added to adjust the polymer concentration, and then alkali was added to adjust the pH to 5-6, yielding polycarboxylate superplasticizer D1 with a solid content of 40%.

[0055] Comparative Example 2: Conventional phosphate ester slump-retaining polycarboxylate superplasticizer

[0056] 337g of vinyl polyethylene glycol ether (VPEG) with a molecular weight of 3000 and 342g of water were added to a reaction vessel and stirred to dissolve. Simultaneously, components A and B were prepared for dropwise addition. Component A consisted of 17g acrylic acid, 40g hydroxyethyl acrylate, 5.3g commercially available 2-hydroxyethyl methacrylate phosphate, and 20g water, mixed thoroughly. Component B consisted of 1.8g mercaptopropionic acid, 0.5g L-ascorbic acid, and 60g water, mixed thoroughly. The initial temperature inside the reaction vessel was controlled at 15℃. 3.0g of 27.5% hydrogen peroxide solution was added to the reaction solvent at once. After stirring for 5 minutes, components A and B were added dropwise. Component A was added over 50 minutes, and component B over 60 minutes. After the addition of component B was complete, the mixture was kept at this temperature for 60 minutes. Water was added to adjust the polymer concentration, and then alkali was added to adjust the pH to 5-6, yielding polycarboxylate superplasticizer D2 with a solid content of 40%.

[0057] The low-sensitivity, high-slump-retention polycarboxylate superplasticizers (PCE-1, PCE-2, PCE-3, and PCE-4) synthesized in Examples 1-4 were subjected to the following performance tests compared with the high-slump-retention polycarboxylate superplasticizers (D1 and D2) synthesized in Comparative Examples 1-2. Specifically, the paste preparation tests were compared between the products of this invention and the comparative high-slump-retention polycarboxylate superplasticizers.

[0058] The test was conducted according to GB / T8022-2012 "Test Method for Homogeneity of Concrete Admixtures". The cement used was Esheng P.O42.5R cement, with a cement dosage of 500g and a water dosage of 145g. Specific experimental data are shown in Table 1.

[0059] Table 1

[0060]

[0061] As can be seen from the data in Table 1, under the same paste ratio and dosage, Examples 1-4 have a longer sustained-release effect and less loss in the later stage compared with Comparative Examples 1-2. This indicates that the high slump-retention polycarboxylate superplasticizer of the present invention has better slump-retention performance.

[0062] The product of this invention is compared with the concrete of a comparative high-slump-resistance polycarboxylate superplasticizer.

[0063] The concrete mix design was carried out according to GB 8076-2008 "Concrete Admixtures". The cement used was Esheng P.O42.5R cement, grade II fly ash, manufactured sand from Guanghan (fineness modulus 3.0, mud content 5%), and ordinary crushed stone gradation (5~31.5, mud content 1%). The admixture dosage was 1.8% of the binder weight (admixture solution with a solid content of 10%, water-reducing mother liquor to slump-retaining mother liquor ratio of 6.5:3.5). The concrete mix proportion was: water 165kg, cement 280kg, fly ash 70kg, manufactured sand 900kg, and crushed stone 1000kg. Specific experimental data are shown in Table 2.

[0064] Table 2

[0065]

[0066] As can be seen from the data in Table 2, when the concrete mixtures of Examples 1-4 of the present invention are used in manufactured sand concrete, the concrete mixtures exhibit better state, better slump retention, and superior 28-day compressive strength compared to Comparative Examples 1-2. This is because, by introducing the unsaturated phosphate ester containing catechol groups as described in the present invention, the catechol groups are introduced into the side chains of the polycarboxylate superplasticizer polymer. This effectively enhances the adhesion of the polycarboxylate superplasticizer molecules to the low surface energy surface of manufactured sand, thereby reducing bleeding and slurry seepage, and thus improving the workability and homogeneity of the concrete mixture. Simultaneously, the hydrolysis of the polycarboxylate superplasticizer molecules in the cement paste continuously releases a large amount of phosphate ions and small molecule alcohols, which can significantly delay the cement hydration process, thus playing a role in slump retention. The synergistic effect of the catechol groups and phosphate ester groups jointly improves the workability and homogeneity of the concrete mixture, thereby enhancing the durability and compressive strength of the concrete.

[0067] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope described in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. An unsaturated phosphate ester containing a catechol group, characterized in that, Its structural formula is as follows: ； Wherein, R1 is hydrogen or methyl, and R2 is methyl or ethyl.

2. A method for preparing an unsaturated phosphate ester containing a catechol group as described in claim 1, characterized in that, Includes the following steps: 2-Aminoethyl acrylate hydrochloride was mixed with protocatechuic aldehyde and dimethyl phosphite, and reacted under the action of an alkaline catalyst to prepare an unsaturated phosphate ester containing catechol groups. Alternatively, 2-aminoethyl methacrylate hydrochloride can be mixed with protocatechuic aldehyde and diethyl phosphite, and reacted under the action of an alkaline catalyst to prepare an unsaturated phosphate ester containing catechol groups.

3. The preparation method according to claim 2, characterized in that, The molar ratio of 2-aminoethyl acrylate hydrochloride, protocatechuic aldehyde, dimethyl phosphite, and alkaline catalyst is 1.00-1.05:1:1:1.

16. The molar ratio of 2-aminoethyl methacrylate hydrochloride, protocatechuic aldehyde, diethyl phosphite, and alkaline catalyst is 1.00-1.05:1:1:1.

16.

4. The preparation method according to claim 3, characterized in that, The alkaline catalyst includes at least one of trimethylamine, triethylamine, and 4-dimethylaminopyridine.

5. The preparation method according to claim 2, characterized in that, The reaction temperature is 60-80℃, and the reaction time is 4-5 hours.

6. A polycarboxylate superplasticizer, characterized in that, It includes the following components: Polyether macromonomer, unsaturated acid, unsaturated phosphate ester containing catechol group as described in claim 1, unsaturated ester, chain transfer agent, oxidizing agent, reducing agent and base; The molar ratio of the polyether macromonomer, unsaturated acid, unsaturated phosphate ester containing catechol group, unsaturated ester, chain transfer agent, oxidant, reducing agent and alkaline solution is 1: (1.5-2.5): (0.2~0.5): (3.0~4.0): (0.1~0.6): (0.1~0.3): (0.02~0.04): (0.3~0.5).

7. The polycarboxylate superplasticizer according to claim 6, characterized in that, The polyether macromonomer has a molecular weight of 2000-3000, and the polyether macromonomer includes at least one of isobutylene alcohol polyoxyethylene ether, isopentenyl alcohol polyoxyethylene ether, vinyl polyethylene glycol ether, and ethyleneoxybutyl polyethylene glycol ether.

8. The polycarboxylate superplasticizer according to claim 6, characterized in that, The unsaturated acid includes at least one of acrylic acid, methacrylic acid, itaconic acid, and fumaric acid; The unsaturated ester includes at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and hydroxypropyl methacrylate.

9. The polycarboxylate superplasticizer according to claim 6, characterized in that, The chain transfer agent includes at least one of mercaptoethanol, mercaptoacetic acid, mercaptopropionic acid, and sodium hypophosphite; The oxidant includes at least one of hydrogen peroxide, ammonium persulfate, sodium persulfate, and potassium persulfate; The reducing agent includes at least one of sodium formaldehyde sulfoxylate and L-ascorbic acid; The alkali includes at least one of sodium hydroxide, potassium hydroxide, triethylamine, and triethanolamine.

10. A method for preparing a polycarboxylate superplasticizer as described in any one of claims 6-9, characterized in that, Includes the following steps: The polyether macromonomer is reacted with an oxidant, an unsaturated acid, an unsaturated ester, an unsaturated phosphate ester containing a catechol group, a chain transfer agent, and a reducing agent at a temperature of 10~40℃ and kept at this temperature for 0.5~3h. After the temperature is maintained, an alkali is added to obtain the polycarboxylate superplasticizer.

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