Polycarboxylate water reducer for concrete, preparation method and application thereof

Abstract

The application relates to the technical field of concrete, and particularly discloses a polycarboxylic acid water reducing agent for concrete, a preparation method and application. The polycarboxylic acid water reducing agent is mainly made of the following raw materials in parts by weight: isopentenyl alcohol polyoxyethylene ether 100 parts, hydroxyethyl acrylate 16-20 parts, acrylic acid 9-11 parts, 2-methacryloyloxyethyl choline phosphate 6-8 parts, methacryloyl ethyl sulfobetaine 6-8 parts, diacetone acrylamide 3-5 parts, acrylamide 3-5 parts, an initiator 0.6-1 part, a pro-initiator 0.4-0.6 part, a chain transfer agent 2-3 parts, calcium sulfate whiskers 4-6 parts and water 270-335 parts. The polycarboxylic acid water reducing agent is applied to concrete, so that the concrete has the advantages of high slump and extension degree retention time, low bleeding, high compressive strength, and the like, effectively improves the situation that the slump loss of the concrete is too fast due to long-time transportation or high-temperature transportation, and meets the market demand.

Description

Technical Field

[0001] This application relates to the field of concrete technology, and more specifically, to a polycarboxylate superplasticizer for concrete, its preparation method, and its application. Background Technology

[0002] Water-reducing agents are concrete admixtures that reduce the amount of water used in mixing and are an indispensable raw material in concrete preparation. Common water-reducing agents include polycarboxylate superplasticizers, aminosulfonate superplasticizers, naphthalene-based superplasticizers, and melamine-based superplasticizers. Polycarboxylate superplasticizers can adsorb onto the surface of cement particles and exert a dispersing effect. They are characterized by low dosage, environmental friendliness, and high degree of molecular structural freedom, and have gained market recognition and are widely used in the construction of subways, bridges, water conservancy projects, tunnels, nuclear power plants, and other engineering projects.

[0003] In engineering construction, concrete requires pre-mixing, transportation, and pumping for pouring. Since slump loss is unavoidable during transportation, concrete needs to maintain a good slump after transport to meet the requirements of pumping. Under conditions of long-term or high-temperature transportation, excessively rapid slump loss severely affects the workability of the concrete, leading to construction difficulties and quality issues. Currently, some researchers add retarders such as sodium gluconate and sugar to concrete. While these can slow down the setting process, they also tend to cause bleeding. Other researchers have modified water-reducing agents, obtaining retarded carboxylic acid water-reducing agents. These agents mainly introduce acid anhydrides, hydroxyalkyl esters, and amides into their molecular structure, which can improve the problem of rapid slump loss. However, the slump retention time is generally only 2 hours, and further improvements are needed to meet higher requirements. Summary of the Invention

[0004] In order to increase the slump retention time of concrete and improve the situation where the slump of concrete is lost too quickly due to long-term or high-temperature transportation, this application provides a polycarboxylate superplasticizer for concrete, its preparation method and application.

[0005] In a first aspect, this application provides a polycarboxylate superplasticizer for concrete, employing the following technical solution:

[0006] A polycarboxylate superplasticizer for concrete is mainly composed of the following raw materials in parts by weight: 100 parts isopentenyl alcohol polyoxyethylene ether, 16-20 parts hydroxyethyl acrylate, 9-11 parts acrylic acid, 6-8 parts 2-methacryloyloxyethyl phosphocholine, 6-8 parts methacryloylethyl sulfobetaine, 3-5 parts diacetone acrylamide, 3-5 parts acrylamide, 0.6-1 part initiator, 0.4-0.6 parts accelerator, 2-3 parts chain transfer agent, 4-6 parts calcium sulfate whiskers, and 270-335 parts water.

[0007] The polycarboxylate superplasticizer of this application, when applied to concrete, exhibits advantages such as a slump loss rate of <7% over 6 hours, a spread loss rate of <8% over 6 hours, a bleeding rate of <1%, and a compressive strength of >43 MPa over 28 days. This allows the concrete to demonstrate the advantages of high slump and spread retention time, low bleeding, and high compressive strength, effectively improving the situation where concrete suffers excessive slump loss due to long-term or high-temperature transportation, and meeting market demands.

[0008] 2-Methacryloxyethyl phosphorocholine contains double bonds, ester groups, trimethylamine cationic groups, and phosphate anionic groups. Methacryloxyethyl sulfobetaine contains double bonds, ester groups, dimethylamine cationic groups, and sulfate anionic groups. By simultaneously adding 2-methacryloxyethyl phosphorocholine and methacryloxyethyl sulfobetaine to the raw materials, the double bonds facilitate polymerization with the monomers. Ester groups, trimethylamine cationic groups, phosphate anionic groups, dimethylamine cationic groups, and sulfate anionic groups are introduced into the side chains. Through their synergistic effects, the hydrophilic groups of the polycarboxylate superplasticizer are improved, increasing slump and spread retention time. Furthermore, the bonding strength between the raw materials is increased, thereby enhancing the compressive strength of concrete.

[0009] Diacetone acrylamide contains double bonds, ketone carbonyl groups, and peptide bonds. Acrylamide contains double bonds and amide groups. Simultaneous addition of diacetone acrylamide and acrylamide to the raw materials utilizes the double bonds to induce polymerization with the monomers, introducing ketone carbonyl groups, peptide bonds, and amide groups into the side chains. This not only improves the hydrophilic groups of the polycarboxylate superplasticizer, increasing slump and spread retention time, but also allows for molecular interactions between the ketone carbonyl groups and peptide bonds, and cross-linking between the ketone carbonyl groups and amide groups. During concrete setting, this increases the degree of cross-linking of the side chains and the bonding strength between the raw materials. Adding calcium sulfate whiskers to the raw materials further enhances the bonding strength between the three-dimensional network structures of the concrete, further improving the effectiveness of the polycarboxylate superplasticizer, increasing the compressive strength of the concrete, and meeting higher market demands.

[0010] Optionally, the initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, and hydrogen peroxide. Preferably, the initiator is ammonium persulfate.

[0011] Ammonium persulfate, sodium persulfate, potassium persulfate, and hydrogen peroxide are soluble in water and can decompose to release free radicals, which can initiate copolymerization of monomers.

[0012] Optionally, the initiator is one or more of ascorbic acid, potassium sulfite, and ferrous sulfate. Preferably, the initiator is ascorbic acid.

[0013] Ascorbic acid, potassium sulfite, and ferrous sulfate all have reducing properties. When combined with an initiator, they can form a redox system, promote the generation of free radicals by the initiator, and enhance the free radical copolymerization reaction.

[0014] Optionally, the chain transfer agent is one or both of mercaptoacetic acid and mercaptopropionic acid. Preferably, the chain transfer agent is mercaptoacetic acid.

[0015] Both mercaptoacetic acid and mercaptopropionic acid can effectively reduce the occurrence of explosive polymerization during monomer copolymerization and increase the stability of polycarboxylate superplasticizer preparation.

[0016] Optionally, the calcium sulfate whiskers have an average length of 40-80 μm and an average diameter of 1-4 μm.

[0017] By adopting the above technical solution, the length and diameter of calcium sulfate whiskers are within this range, which can make them have excellent dispersibility, enhance the uniformity of raw material mixing, improve the effect of calcium sulfate whiskers, and enhance the compressive strength of concrete.

[0018] Secondly, this application provides a method for preparing the above-mentioned polycarboxylate superplasticizer for concrete, using the following technical solution:

[0019] A method for preparing the above-mentioned polycarboxylate superplasticizer for concrete includes the following steps:

[0020] Add the initiator to the first portion of water and mix to obtain premix A, which is then set aside.

[0021] Add the initiator and chain transfer agent to the second portion of water and mix to obtain premix solution B, which is then set aside.

[0022] Add hydroxyethyl acrylate and acrylic acid to the third part of water and mix to obtain premix C, which is then set aside.

[0023] Add 2-methacryloyloxyethyl phosphoric acid choline, methacryloylethyl sulfobetaine, diacetone acrylamide, and acrylamide to the fourth part of water and mix to obtain premix solution D, which is ready for use.

[0024] Heat the fifth portion of water to 40-60℃, add isopentenyl alcohol polyoxyethylene ether and calcium sulfate whiskers and mix, then add premix A and mix. Then add premix B, premix C and premix D dropwise simultaneously. After the addition is complete, keep warm and stir for 2-4 hours, cool down, add alkali to adjust the pH to 6-7, and obtain polycarboxylic acid copolymer mixture.

[0025] The initiator is pre-prepared into premix A, the initiator and chain transfer agent are pre-prepared into premix B, hydroxyethyl acrylate and acrylic acid are pre-prepared into premix C, and 2-methacryloyloxyethyl phosphoric acid choline, methacryloylethyl sulfobetaine, diacetone acrylamide, and acrylamide are pre-prepared into premix D. This facilitates the dissolution of the raw materials and improves the uniformity of the mixture. Simultaneously, premixes B, C, and D are continuously added dropwise to facilitate the copolymerization reaction of the raw materials. The preparation method of this application facilitates the preparation and control of polycarboxylate superplasticizers and enhances the stability of the polycarboxylate superplasticizer preparation.

[0026] Optionally, the weight ratio of the first part water, the second part water, the third part water, the fourth part water, and the fifth part water is 7:(25-35):(55-65):(45-55):(140-160).

[0027] The total amount of water is fixed, and then the distribution of the first, second, third, fourth and fifth portions of water is limited to facilitate the preparation of premixed solution A, premixed solution B, premixed solution C and premixed solution D.

[0028] Optionally, the dropping time of premixed solution B is 3.5-4.5 h; the dropping time of premixed solution C is 2.5-3.5 h; and the dropping time of premixed solution D is 0.5-1.5 h.

[0029] By adopting the above technical solution, the dropping time of premixed liquid B, premixed liquid C, and premixed liquid D is limited, and the dropping time of premixed liquid B is the longest, which can continuously provide initiators and chain transfer agents, facilitating the copolymerization reaction of raw materials.

[0030] Optionally, the alkali is one or more selected from sodium hydroxide solution, sodium carbonate solution, and triethanolamine solution. Preferably, the alkali is sodium hydroxide solution with a mass concentration of 5-15%.

[0031] Sodium hydroxide solution, sodium carbonate solution, and triethanolamine solution can all adjust the pH value. Furthermore, compared to using sodium carbonate solution or triethanolamine solution as the alkali, choosing sodium hydroxide solution as the alkali not only facilitates the preparation of the alkali, but also reduces the amount of alkali used due to sodium hydroxide being a strong alkali.

[0032] Thirdly, this application provides an application of the aforementioned polycarboxylate superplasticizer for concrete, employing the following technical solution:

[0033] An application of the above-mentioned polycarboxylate superplasticizer for concrete, wherein the polycarboxylate superplasticizer is incorporated into the concrete, and the amount of polycarboxylate superplasticizer added is 0.1-3 wt% of the cementitious material.

[0034] By adopting the above technical solution, polycarboxylate superplasticizer can be applied to the preparation of concrete, and when the amount of polycarboxylate superplasticizer added is 0.1-3wt% of the cementitious material, the polycarboxylate superplasticizer can have a good effect.

[0035] In summary, this application has the following beneficial effects: The polycarboxylate superplasticizer for concrete of this application adds 2-methacryloyloxyethyl phosphocholine and methacryloylethyl sulfobetaine to the raw materials, introducing ester groups, trimethylamine cationic groups, phosphate anionic groups, dimethylamine cationic groups, and sulfate anionic groups into the side chains. Adding diacetone acrylamide and acrylamide to the raw materials introduces ketone carbonyl groups, peptide bonds, and amide groups into the side chains. Through their mutual cooperation, the hydrophilic groups of the polycarboxylate superplasticizer are improved, enhancing its performance. When applied to concrete, it exhibits a 6-hour slump loss rate of <7%, a 6-hour spread loss rate of <8%, a concrete bleeding rate of <1%, and a 28-day compressive strength of >43 MPa, giving the concrete the advantages of high slump and spread retention time, low bleeding, and high compressive strength, meeting market demands. Detailed Implementation

[0036] To make this application easier to understand, the following detailed description will be provided with reference to embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of application of this application. Unless otherwise specified, the raw materials or components used in this application can be obtained commercially or by conventional methods.

[0037] Example

[0038] Table 1. Content of each raw material in polycarboxylate superplasticizer (unit: kg)

[0039]

[0040]

[0041] Example 1

[0042] A polycarboxylate superplasticizer for concrete, the raw material ratio of which is shown in Table 1.

[0043] The isopentenyl alcohol polyoxyethylene ether is TPEG-2400, selected from Hubei Kewode Chemical Co., Ltd.; the initiator is ammonium persulfate; the accelerator is ascorbic acid; the chain transfer agent is mercaptoacetic acid; and the average length of the calcium sulfate whiskers is 50 μm and the average diameter is 3 μm.

[0044] A method for preparing a polycarboxylate superplasticizer for concrete includes the following steps:

[0045] Divide the water into five parts: the first part, the second part, the third part, the fourth part, and the fifth part, with a weight ratio of 7:30:62:48:153.

[0046] Add the initiator to the first batch of water and stir for 10 minutes to obtain premix A, which is then ready for use.

[0047] Add the initiator and chain transfer agent to the second portion of water, stir for 10 minutes to obtain premix B, and set aside.

[0048] Add hydroxyethyl acrylate and acrylic acid to the third portion of water, stir for 20 minutes to obtain premix C, and set aside.

[0049] Add 2-methacryloyloxyethyl phosphoric acid choline, methacryloylethyl sulfobetaine, diacetone acrylamide, and acrylamide to the fourth portion of water, stir for 20 minutes, and obtain premixed solution D for later use.

[0050] The fifth portion of water was heated to 50°C, and isopentenyl alcohol polyoxyethylene ether and calcium sulfate whiskers were added. The mixture was stirred for 30 minutes. Then, premixed solution A was added, and the mixture was stirred for 5 minutes. Subsequently, premixed solutions B, C, and D were added dropwise simultaneously, with premixed solution B added over 4 hours, premixed solution C over 3 hours, and premixed solution D over 1 hour. After the addition was complete, the mixture was kept at this temperature and stirred for 3 hours. The temperature was then cooled to 25°C, and a 10% sodium hydroxide solution was added to adjust the pH to 6.5, thus obtaining the polycarboxylic acid copolymer mixture.

[0051] Example 2

[0052] A polycarboxylate superplasticizer for concrete differs from Example 1 in that the raw material ratio of the polycarboxylate superplasticizer is different, and its raw material ratio is shown in Table 1.

[0053] Example 3

[0054] A polycarboxylate superplasticizer for concrete differs from Example 1 in that the raw material ratio of the polycarboxylate superplasticizer is different, and its raw material ratio is shown in Table 1.

[0055] Comparative Example

[0056] Comparative Example 1

[0057] A polycarboxylate superplasticizer for concrete differs from Example 1 in that an equal amount of isopentenyl polyoxyethylene ether replaces 2-methacryloyloxyethyl phosphate choline and methacryloylethyl sulfobetaine in the raw materials of the polycarboxylate superplasticizer.

[0058] Comparative Example 2

[0059] A polycarboxylate superplasticizer for concrete differs from Example 1 in that an equal amount of 2-methacryloyloxyethyl phosphocholine is used instead of methacryloylethyl sulfobetaine in the raw materials of the polycarboxylate superplasticizer.

[0060] Comparative Example 3

[0061] A polycarboxylate superplasticizer for concrete differs from Example 1 in that an equal amount of methacryloylethyl sulfobetaine is used instead of 2-methacryloyloxyethyl phosphocholine in the raw materials of the polycarboxylate superplasticizer.

[0062] Comparative Example 4

[0063] A polycarboxylate superplasticizer for concrete differs from Example 1 in that an equal amount of isopentenyl alcohol polyoxyethylene ether replaces diacetone acrylamide and acrylamide in the raw materials of the polycarboxylate superplasticizer.

[0064] Comparative Example 5

[0065] A polycarboxylate superplasticizer for concrete differs from Example 1 in that an equal amount of diacetone acrylamide is used instead of acrylamide in the raw materials of the polycarboxylate superplasticizer.

[0066] Comparative Example 6

[0067] A polycarboxylate superplasticizer for concrete differs from Example 1 in that an equal amount of acrylamide is used instead of diacetone acrylamide in the raw materials of the polycarboxylate superplasticizer.

[0068] Comparative Example 7

[0069] A polycarboxylate superplasticizer for concrete differs from Example 1 in that an equal amount of water is used to replace calcium sulfate whiskers in the raw materials of the polycarboxylate superplasticizer.

[0070] Performance testing

[0071] The polycarboxylate superplasticizers obtained in Examples 1-3 and Comparative Examples 1-7 were respectively incorporated into concrete, and the concrete was subjected to the following performance tests. The test results are shown in Table 2.

[0072] The concrete is made from the following raw materials: 282 kg of cement, 83 kg of fly ash, 730 kg of sand, 1130 kg of aggregate, 150 kg of water, and 3 kg of polycarboxylate superplasticizer. The cement is Huaxin Cement P.O42.5; the fly ash is Grade I fly ash; the sand is river sand with a fineness modulus of 2.7; and the aggregate has a continuous gradation of 5-30 mm.

[0073] Furthermore, in accordance with GB / T50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures", the slump, spread, bleeding rate and setting time of the concrete were tested.

[0074] According to GB / T50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Concrete", the 28-day compressive strength of concrete was tested.

[0075] Table 2 Detection Results

[0076]

[0077]

[0078] As shown in Table 2, when the polycarboxylate superplasticizer of this application is applied to concrete, the slump of the concrete after 6 hours is 220-230 mm, and the spread after 6 hours is 525-540 mm. At this point, the slump loss rate after 6 hours is 4.2-6.4%, and the spread loss rate after 6 hours is 6.9-7.9%, demonstrating high slump and spread retention. Furthermore, the bleeding rate of the concrete is 0.7-0.8%, exhibiting the advantage of low bleeding. Simultaneously, the setting time of the concrete is 255-265 min, and the compressive strength after 28 days is 43.8-45.1 MPa, demonstrating excellent setting time and high strength. This effectively improves the situation where the slump of concrete is too rapidly lost due to long-term or high-temperature transportation, meeting market demands.

[0079] Comparative Examples 1-3 were compared with Example 1, with Comparative Example 1 as the basis. Compared to Comparative Example 1, Comparative Example 2 added 2-methacryloyloxyethyl phosphorocholine to the raw materials of the polycarboxylate superplasticizer; Comparative Example 3 added methacryloylethyl sulfobetaine to the raw materials of the polycarboxylate superplasticizer compared to Comparative Example 1; and Example 1 added both 2-methacryloyloxyethyl phosphorocholine and methacryloylethyl sulfobetaine to the raw materials of the polycarboxylate superplasticizer compared to Comparative Example 1. It can be seen that the simultaneous addition of 2-methacryloyloxyethyl phosphorocholine and methacryloylethyl sulfobetaine to the raw materials, through their synergistic effect, can significantly increase slump and spread, and also increase setting time and compressive strength.

[0080] Comparative Examples 4-6 were compared with Example 1, with Comparative Example 4 as the basis. Compared to Comparative Example 4, Comparative Example 5 added diacetone acrylamide to the raw materials of the polycarboxylate superplasticizer; Comparative Example 6 added acrylamide to the raw materials of the polycarboxylate superplasticizer compared to Comparative Example 4; and Example 1 added both diacetone acrylamide and acrylamide to the raw materials of the polycarboxylate superplasticizer compared to Comparative Example 4. This demonstrates that the simultaneous addition of diacetone acrylamide and acrylamide to the raw materials, and the synergistic effect between them, results in superior overall performance of the concrete. This is mainly because diacetone acrylamide contains ketone carbonyl groups and peptide bonds, while acrylamide contains amide groups. The ketone carbonyl groups and peptide bonds have molecular forces, and the ketone carbonyl groups and amide groups can crosslink, increasing the degree of crosslinking of the side chains of the polycarboxylate superplasticizer, improving the dispersion uniformity of the polycarboxylate superplasticizer, and enhancing its performance.

[0081] Comparing Comparative Example 7 and Example 1, Example 1, compared to Comparative Example 7, added calcium sulfate whiskers to the raw materials of the polycarboxylate superplasticizer. It can be seen that adding calcium sulfate whiskers to the raw materials has virtually no effect on the slump, spread, bleeding rate, and setting time of the concrete, but it significantly improves the compressive strength of the concrete. That is, adding calcium sulfate whiskers is beneficial to improving the performance of concrete and can meet higher requirements.

[0082] It should be noted that the embodiments described above are only for explaining this application and do not constitute any limitation on this application. This application has been described with reference to typical embodiments, but it should be understood that the terms used therein are descriptive and explanatory terms, not limiting terms. Modifications can be made to this application within the scope of the claims, and revisions can be made to the invention without departing from the scope and spirit of this application. Although the application described herein relates to specific methods, materials, and embodiments, it does not mean that this application is limited to the specific examples disclosed herein; on the contrary, this application can be extended to all other methods and applications with the same function.

Claims

1. A polycarboxylate superplasticizer for concrete, characterized in that: It is mainly made from the following raw materials in parts by weight: 100 parts isopentenyl alcohol polyoxyethylene ether, 16-20 parts hydroxyethyl acrylate, 9-11 parts acrylic acid, 6-8 parts 2-methacryloyloxyethyl phosphoric acid choline, 6-8 parts methacryloylethyl sulfobetaine, 3-5 parts diacetone acrylamide, 3-5 parts acrylamide, 0.6-1 part initiator, 0.4-0.6 parts accelerator, 2-3 parts chain transfer agent, 4-6 parts calcium sulfate whiskers, and 270-335 parts water.

2. The polycarboxylate superplasticizer for concrete according to claim 1, characterized in that: The initiator is one or more of ammonium persulfate, sodium persulfate, potassium persulfate, and hydrogen peroxide.

3. The polycarboxylate superplasticizer for concrete according to claim 1, characterized in that: The initiator is one or more of ascorbic acid, potassium sulfite, and ferrous sulfate.

4. The polycarboxylate superplasticizer for concrete according to claim 1, characterized in that: The chain transfer agent is one or both of mercaptoacetic acid and mercaptopropionic acid.

5. A polycarboxylate superplasticizer for concrete according to claim 1, characterized in that: The average length of the calcium sulfate whiskers is 40-80 μm and the average diameter is 1-4 μm.

6. A method for preparing a polycarboxylate superplasticizer for concrete as described in any one of claims 1-5, characterized in that: Includes the following steps: Add the initiator to the first portion of water and mix to obtain premix A, which is then set aside. Add the initiator and chain transfer agent to the second portion of water and mix to obtain premix solution B, which is then set aside. Add hydroxyethyl acrylate and acrylic acid to the third part of water and mix to obtain premix C, which is then set aside. Add 2-methacryloyloxyethyl phosphoric acid choline, methacryloylethyl sulfobetaine, diacetone acrylamide, and acrylamide to the fourth part of water and mix to obtain premix solution D, which is ready for use. Heat the fifth portion of water to 40-60℃, add isopentenyl alcohol polyoxyethylene ether and calcium sulfate whiskers and mix, then add premix A and mix. Then add premix B, premix C and premix D dropwise simultaneously. After the addition is complete, keep warm and stir for 2-4 hours, cool down, add alkali to adjust the pH to 6-7, and obtain polycarboxylic acid copolymer mixture.

7. The method for preparing a polycarboxylate superplasticizer for concrete according to claim 6, characterized in that: The weight ratio of the first part water, the second part water, the third part water, the fourth part water, and the fifth part water is 7:(25-35):(55-65):(45-55):(140-160).

8. The method for preparing a polycarboxylate superplasticizer for concrete according to claim 6, characterized in that: The dropping time for premixed solution B is 3.5-4.5 h; the dropping time for premixed solution C is 2.5-3.5 h; and the dropping time for premixed solution D is 0.5-1.5 h.

9. The method for preparing a polycarboxylate superplasticizer for concrete according to claim 6, characterized in that: The alkali is one or more of sodium hydroxide solution, sodium carbonate solution, and triethanolamine solution.

10. An application of a polycarboxylate superplasticizer for concrete as described in any one of claims 1-5, characterized in that: Polycarboxylate superplasticizer is added to concrete, and the amount of polycarboxylate superplasticizer added is 0.1-3 wt% of the cementitious material.

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