Retarding type polycarboxylic acid water reducing agent as well as preparation method and application thereof

Abstract

The invention provides a retarding type polycarboxylate superplasticizer as well as a preparation method and application thereof, and belongs to the technical field of building material concrete admixtures. The retarding type polycarboxylic acid water reducing agent is prepared from the following raw materials in parts by weight: 300 to 400 parts of polyether macromonomer, 60 to 150 parts of unsaturated carboxylic acid micromonomer, 30 to 60 parts of unsaturated sulfonic acid monomer, 15 to 30 parts of alkylphenol polyoxyethylene ether phosphate, 1.5 to 12 parts of chain transfer agent, 2 to 15 parts of initiator, 15 to 50 parts of caustic soda liquid and 200 to 600 parts of solvent. The polycarboxylic acid water reducing agent product with the retarding characteristic is synthesized through an RAFT method, the binding force between phosphate radicals and calcium ions in a cement pore liquid of the preparation raw material alkylphenol polyoxyethylene ether phosphate is high, hydration of C3A and formation of ettringite are delayed, the retarding effect of the water reducing agent is enhanced, and the polycarboxylic acid water reducing agent has the anion characteristic and the nonionic characteristic and can be used as a water reducing agent. And the workability of the concrete is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of building material concrete admixtures, and in particular to a slow-setting polycarboxylate water reducer, a preparation method thereof and an application thereof. Background Art

[0002] Polycarboxylate superplasticizers are typically produced through free radical polymerization. Conventional free radical polymerization systems are prone to high concentrations of free radicals, which can easily lead to radical fusion and termination, making effective polymerization difficult to control and potentially resulting in the formation of complex aggregate structures. Furthermore, the resulting polycarboxylate superplasticizers exhibit a wide molecular weight distribution, with molecular weights and the resulting molecular structures randomly arranged, resulting in a disordered structure. Crosslinking and branching can also occur during the polymerization reaction, impacting the final molecular properties. Therefore, the use of a "living" or controllable free radical polymerization method to assemble a relatively uniform condensed phase and obtain structurally controllable polycarboxylate superplasticizer polymers has become a research hotspot.

[0003] Reversible addition-fragmentation chain transfer (RAFT) polymerization, a "living" / controlled radical polymerization method, utilizes a reversible chain transfer process to control the radical polymerization process. It uses thiocarbonyl compounds as chain transfer agents and exhibits a high chain transfer constant. The polymerization reaction conditions are relatively mild and the monomers are widely applicable. It can be used to prepare polycarboxylate superplasticizers with specific structures and properties, such as linear block, grafted, star, and dendritic structures. Through RAFT polymerization, retarding functional groups are grafted onto the polycarboxylate superplasticizer. Traditionally, the retarding component of polycarboxylate superplasticizers is introduced through physical mixing, rather than chemical bonding, which can lead to poor compatibility and precipitation. In invention patent CN105153375A, the polycarboxylate superplasticizer synthesized by the RAFT method has a narrow molecular weight distribution, but the product's functionality is limited, requiring further functionalization through subsequent compounding.

[0004] Invention patent CN119638319A utilizes a conventional water reducer compounded with a retarding component to produce a retarding water reducer, resulting in poor product stability and unstable retarding effects. Invention patent CN110818906A utilizes the ATRP method to synthesize a functionalized water reducer, but this synthesis method carries the potential risk of catalyst residues affecting concrete performance.

[0005] Therefore, it is of great significance to develop a slow-setting polycarboxylate water-reducing agent product with good effect and strong material environmental adaptability. Summary of the Invention

[0006] In view of the technical problems existing in the background technology, the present invention provides a retarding polycarboxylate water reducer and a preparation method and application thereof, aiming to solve the technical problems of poor retarding performance and workability of existing polycarboxylate water reducers.

[0007] In a first aspect, the present invention provides a slow-setting polycarboxylate water-reducing agent, the raw materials for its preparation comprising, by weight, 300-400 parts of a polyether macromonomer, 60-150 parts of an unsaturated carboxylic acid small monomer, 30-60 parts of an unsaturated sulfonic acid monomer, 15-30 parts of an alkylphenol polyoxyethylene ether phosphate, 1.5-12 parts of a chain transfer agent, 2-15 parts of an initiator, 15-50 parts of liquid alkali, and 200-600 parts of a solvent.

[0008] Preferably, the unsaturated polyether macromonomer includes at least one of ethylene glycol monovinyl polyethylene glycol ether, 4-hydroxybutyl vinyl polyethylene glycol ether, isopentanol polyoxyethylene ether, and vinyl polyoxyethylene ether; and the weight average molecular weight of the unsaturated polyether macromonomer is 2000-6000.

[0009] Preferably, the unsaturated carboxylic acid small monomer includes at least one of methacrylic acid, fumaric acid, acrylic acid, and maleic anhydride.

[0010] Preferably, the unsaturated sulfonic acid monomer includes at least one of 2-acrylamido-2-methylpropanesulfonic acid and methacrylamidopropyl-N,N-dimethylpropanesulfonic acid.

[0011] Preferably, the initiator includes at least one of BPO (dibenzoyl peroxide), AIBN (azobisisobutyronitrile), and ammonium persulfate.

[0012] Preferably, the chain transfer agent includes at least one of bis(carboxymethyl)trithiocarbonate and dibenzyltrithiocarbonate.

[0013] Preferably, the solvent includes ethanol and water.

[0014] In a second aspect, the present invention provides a method for preparing a slow-setting polycarboxylate water-reducing agent, comprising the following steps: The polyether macromonomer, unsaturated carboxylic acid small monomer, unsaturated sulfonic acid monomer, alkylphenol polyoxyethylene ether phosphate, chain transfer agent and initiator are dissolved in a solvent, stirred evenly, and heated under nitrogen protection to carry out polymerization reaction. After the reaction is completed, it is cooled to room temperature and the pH is adjusted to 6-7 to obtain a slow-setting polycarboxylate water reducer.

[0015] Preferably, the reaction temperature of the polymerization reaction is 70° C. to 120° C., and the reaction time is 4 to 10 hours.

[0016] In a third aspect, the present invention provides a use of a slow-setting polycarboxylate water-reducing agent in preparing concrete.

[0017] Preferably, the solid content of the retarding polycarboxylate water-reducing agent in the concrete is 0.2 wt% to 0.4 wt%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The present invention synthesizes a polycarboxylate water-reducing agent product with slow-setting properties by the RAFT method. The raw material alkylphenol polyoxyethylene ether phosphate has a strong binding force with calcium ions in the cement pore fluid, which delays C3A hydration and ettringite formation, enhances the slow-setting effect of the water-reducing agent, and has both anionic and nonionic properties, so that the workability of concrete is improved. The slow-setting polycarboxylate water-reducing agent provided by the present invention has obvious slow-setting effect, low dosage and simple preparation method. Not only can it effectively extend the concrete curing time, it is suitable for long-distance transportation, and can also be used in large-volume concrete and complex structure casting scenes. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 The concrete is in the state of being discharged from the machine after adding the polycarboxylate water-reducing agent described in Example 3 of the present invention; Figure 2 This is the state of concrete leaving the machine after adding the polycarboxylate water-reducing agent described in Comparative Example 5 of the present invention. DETAILED DESCRIPTION

[0020] The following embodiments of the technical solution of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only examples and are not intended to limit the scope of protection of the present invention.

[0021] In order to solve the technical problems of poor retarding performance and workability of existing polycarboxylate water-reducers, the present invention provides a retarding polycarboxylate water-reducer, a preparation method thereof, and an application thereof. The polycarboxylate water-reducer is prepared by a RAFT method using unsaturated polyether macromonomers, unsaturated carboxylic acid micromonomers, unsaturated sulfonic acid monomers, and alkylphenol polyoxyethylene ether phosphate as raw materials. The phosphate groups in the resulting polycarboxylate water-reducer molecules have a strong complexing ability for calcium ions and are preferentially adsorbed on the surface of cement particles. The long polyether side chains provide steric hindrance, enhancing dispersibility. The water-reducer is adsorbed on the surface of unhydrated cement particles, increasing the thickness of the adsorption layer, preventing free water from approaching, inhibiting cement hydration, and exerting a retarding effect. The alkylphenol polyoxyethylene ether phosphate has surfactant properties, good foaming and foam stability, and improves the workability of concrete. The sulfonic acid groups form stable hydrogen bonds with water molecules, enhancing product stability.

[0022] In a first aspect, an embodiment of the present invention provides a slow-setting polycarboxylate water-reducing agent, the raw materials for its preparation comprising, by weight: 300-400 parts of a polyether macromonomer, 60-150 parts of an unsaturated carboxylic acid small monomer, 30-60 parts of an unsaturated sulfonic acid monomer, 15-30 parts of an alkylphenol polyoxyethylene ether phosphate, 1.5-12 parts of a chain transfer agent, 2-15 parts of an initiator, 15-50 parts of liquid alkali, and 200-600 parts of a solvent.

[0023] In the technical solution of the embodiment of the present invention, the phosphate group of the slow-setting polycarboxylate water-reducing agent carries two negative charges and has a stronger ability to complex calcium ions. Therefore, in the cement system, the phosphate group will be adsorbed on the surface of the cement particles faster, more preferentially, and more frequently, while the long polyether side chain in the water-reducing agent provides steric hindrance, thereby enhancing dispersibility. In addition, the phosphate group adsorbed on the surface of the cement particles will produce electrostatic repulsion with the adjacent negative charges, which can make the main chain more rigid, facilitate the initial adsorption of the molecule, and improve the initial dispersibility. The polycarboxylate water-reducing agent containing phosphate groups is adsorbed on the surface of unhydrated cement particles, and the thickness of the adsorption layer increases. At the same time, the presence of the adsorption layer prevents the approach of free water molecules, inhibits cement hydration, delays the exothermic peak, and plays a slow-setting role. The surfactant properties of alkylphenol polyoxyethylene ether phosphate esters reflect good foaming and foam stability in the product, thereby improving the workability of concrete. In addition, the sulfonic acid group can form hydrogen bonds with water molecules. The presence of two S=O bonds enhances the ability of S to attract electrons from water molecules, making it easier to form stable hydrogen bonds with water molecules. In the negative ion -SO3 - The two π bonds and two oxygen atoms share a negative charge, making -SO3 - Stable and insensitive to external cationic attacks, the product has better stability. At the same time, the unsaturated sulfonic acid monomers have large side groups, which enhance the rigidity of the macromolecular chain and improve the overall performance of the product.

[0024] Furthermore, in some embodiments, the unsaturated polyether macromonomer includes at least one of ethylene glycol monovinyl polyethylene glycol ether, 4-hydroxybutyl vinyl polyethylene glycol ether, isopentanol polyoxyethylene ether, and vinyl polyoxyethylene ether; and the weight average molecular weight of the unsaturated polyether macromonomer is 2000~6000.

[0025] Furthermore, in some embodiments, the unsaturated carboxylic acid small monomer includes at least one of methacrylic acid, fumaric acid, acrylic acid, and maleic anhydride.

[0026] Furthermore, in some embodiments, the unsaturated sulfonic acid monomer includes at least one of 2-acrylamido-2-methylpropanesulfonic acid and methacrylamidopropyl-N,N-dimethylpropanesulfonic acid.

[0027] Furthermore, in some embodiments, the initiator includes at least one of BPO (dibenzoyl peroxide), AIBN (azobisisobutyronitrile), and ammonium persulfate.

[0028] Furthermore, in some embodiments, the chain transfer agent includes at least one of bis(carboxymethyl)trithiocarbonate and dibenzyltrithiocarbonate.

[0029] Further, in some embodiments, the solvent includes ethanol and water.

[0030] In a second aspect, an embodiment of the present invention provides a method for preparing a slow-setting polycarboxylate water-reducing agent, comprising the following steps: The polyether macromonomer, unsaturated carboxylic acid small monomer, unsaturated sulfonic acid monomer, alkylphenol polyoxyethylene ether phosphate, chain transfer agent and initiator are dissolved in a solvent, stirred evenly, and heated under nitrogen protection to carry out polymerization reaction. After the reaction is completed, it is cooled to room temperature and the pH is adjusted to 6-7 to obtain a slow-setting polycarboxylate water reducer.

[0031] In the technical solution of the embodiment of the present invention, the RAFT method is a controllable / active free radical polymerization method that can accurately control the growth of the polymer chain. By adjusting the amount of chain transfer agent and the reaction conditions, the molecular weight of the polymer can be accurately controlled, the molecular weight distribution can be narrower, and the performance consistency of the product can be improved. Among them, the polyether macromonomer provides long polyether side chains, which copolymerize with unsaturated carboxylic acid small monomers, unsaturated sulfonic acid monomers, etc. during the polymerization process. The long polyether side chains provide steric hindrance to prevent cement particles from aggregating; the unsaturated carboxylic acid small monomers and unsaturated sulfonic acid monomers introduce hydrophilic groups such as carboxyl and sulfonic groups, which further disperse the cement particles through electrostatic repulsion. Alkylphenol polyoxyethylene ether phosphate introduces phosphate groups to enhance the complexing ability for calcium ions and improve the retarding effect.

[0032] Furthermore, in some embodiments, the polymerization reaction temperature is 70° C. to 120° C., and the reaction time is 4 to 10 hours.

[0033] In the technical solution of the embodiment of the present invention, the mild reaction conditions reduce equipment investment costs and production risks, and are suitable for large-scale industrial production. In addition, the mild reaction conditions also help reduce the occurrence of side reactions and improve the purity and quality of the product.

[0034] In a third aspect, an embodiment of the present invention provides a use of a slow-setting polycarboxylate water-reducing agent in preparing concrete.

[0035] Furthermore, in some embodiments, the solid content of the retarding polycarboxylate water-reducing agent in the concrete is 0.2 wt % to 0.4 wt %.

[0036] Some specific examples are listed below. It should be noted that the examples described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention. Where specific techniques or conditions are not specified in the examples, the techniques or conditions described in the literature in this field or the product specifications were used. Where the manufacturers of the reagents or instruments used are not specified, they are all conventional products that can be purchased commercially.

[0037] 1. Preparation method Example 1 A method for preparing a slow-setting polycarboxylate water-reducing agent comprises the following steps: S1. Add 350 parts of isopentanol polyoxyethylene ether macromonomer, 70 parts of acrylic acid, 40 parts of 2-acrylamido-2-methylpropanesulfonic acid, 17 parts of alkylphenol polyoxyethylene ether phosphate, 3.2 parts of bis(carboxymethyl)trithiocarbonate, and 5.7 parts of BPO to a three-necked flask, dissolve the above reagents in a mixed solution of 400 parts of anhydrous ethanol and water in a ratio of 1:1, and start stirring. S2. Nitrogen was introduced into the reaction vessel for 30 minutes, and the vessel was sealed with a balloon filled with nitrogen. The vessel was placed in a constant temperature oil bath at 110°C for polymerization for 5 hours. The balloon was untied, air was introduced, and the vessel was cooled to room temperature. Finally, 35 parts of liquid alkali with a mass fraction of 30% was added to adjust the pH value to 6-7 to obtain a slow-setting polycarboxylate water reducer prepared by the RAFT method.

[0038] Example 2 A method for preparing a slow-setting polycarboxylic acid-based water-reducing agent comprises the following steps: S1. Add 380 parts of ethylene glycol monovinyl polyethylene glycol ether macromonomer, 85 parts of maleic anhydride, 32 parts of methacrylamidopropyl-N,N-dimethylpropanesulfonic acid, 20 parts of alkylphenol polyoxyethylene ether phosphate, 5.7 parts of dibenzyl trithiocarbonate, and 7.6 parts of AIBN to a three-necked flask, dissolve the above reagents in a mixed solution of 450 parts of anhydrous ethanol and water in a ratio of 1:1, and start stirring. S2. Nitrogen was introduced into the reaction vessel for 30 minutes, and the vessel was sealed with a balloon filled with nitrogen. The vessel was placed in a constant temperature oil bath at 90°C for polymerization for 7 hours. The balloon was untied, air was introduced, and the vessel was cooled to room temperature. Finally, 40 parts by mass of 30% liquid caustic soda was added to adjust the pH value to 6-7 to obtain a retarded polycarboxylate water reducer prepared by the RAFT method.

[0039] Example 3 A method for preparing a slow-setting polycarboxylic acid-based water-reducing agent comprises the following steps: S1. Add 300 parts of isopentanol polyoxyethylene ether macromonomer, 100 parts of methacrylic acid, 53 parts of 2-acrylamido-2-methylpropanesulfonic acid, 25 parts of alkylphenol polyoxyethylene ether phosphate, 7.6 parts of bis(carboxymethyl)trithiocarbonate, and 8.3 parts of BPO to a three-necked flask, dissolve the above reagents in a mixed solution of 400 parts of anhydrous ethanol and water in a ratio of 1:1, and start stirring. S2. Nitrogen was introduced into the reaction vessel for 30 minutes and sealed with a balloon filled with nitrogen. The vessel was placed in a constant temperature oil bath at 80°C for polymerization for 7 hours. The balloon was untied, air was introduced and the vessel was cooled to room temperature. Finally, 45 parts of liquid alkali with a mass fraction of 30% was added to adjust the pH value to 6-7 to obtain a slow-setting polycarboxylate water reducer prepared by the RAFT method.

[0040] Example 4 A method for preparing a slow-setting polycarboxylic acid-based water-reducing agent comprises the following steps: S1. Add 320 parts of ethylene glycol monovinyl polyethylene glycol ether macromonomer, 120 parts of fumaric acid, 40 parts of 2-acrylamido-2-methylpropanesulfonic acid, 25 parts of alkylphenol polyoxyethylene ether phosphate, 9.6 parts of bis(carboxymethyl)trithiocarbonate, and 12.7 parts of ammonium persulfate to a three-necked flask, dissolve the above reagents in a mixed solution of 500 parts of anhydrous ethanol and water in a ratio of 1:1, and start stirring. S2. Nitrogen was introduced into the reaction vessel for 30 minutes, and the vessel was sealed with a balloon filled with nitrogen. The vessel was placed in a constant temperature oil bath at 100°C for polymerization reaction for 8 hours. The balloon was untied, air was introduced and the vessel was cooled to room temperature. Finally, 30 parts by mass of liquid caustic soda was added to adjust the pH value to 6-7 to obtain a retarding polycarboxylate water reducer prepared by the RAFT method.

[0041] Example 5 A method for preparing a slow-setting polycarboxylic acid-based water-reducing agent comprises the following steps: S1. Add 330 parts of vinyl polyoxyethylene ether macromonomer, 90 parts of acrylic acid, 30 parts of 2-acrylamido-2-methylpropanesulfonic acid, 15 parts of alkylphenol polyoxyethylene ether phosphate, 2.0 parts of bis(carboxymethyl)trithiocarbonate, and 3.9 parts of BPO to a three-necked flask, dissolve the above reagents in a mixed solution of 400 parts of anhydrous ethanol and water in a ratio of 1:1, and start stirring. S2. Nitrogen was introduced into the reaction vessel for 30 minutes, and the vessel was sealed with a balloon filled with nitrogen. The vessel was placed in a constant temperature oil bath at 70°C for polymerization for 4.5 hours. The balloon was untied, air was introduced, and the vessel was cooled to room temperature. Finally, 35 parts of liquid alkali with a mass fraction of 30% was added to adjust the pH value to 6-7 to obtain a slow-setting polycarboxylate water reducer prepared by the RAFT method.

[0042] Comparative Example 1 This comparative example provides a method for preparing a conventional slow-setting polycarboxylate superplasticizer: 360 parts of ethylene glycol monovinyl polyglycol ether monomer are added to a four-necked flask, 230 parts of water are added with stirring, and dissolved at 50°C. 1.9 parts of ammonium persulfate are then added and mixed thoroughly. Component A and Component B solutions are then added dropwise, with the addition of Component B complete over 3 hours and Component A complete over 3.5 hours. Component B is an aqueous solution of 8 parts hydroxyethyl acrylate, 32 parts acrylic acid, and 60 parts tap water; and Component A is an aqueous solution of 1.2 parts L-ascorbic acid, 1.3 parts mercaptoethanol, and 100 parts tap water. After the addition of Component A and Component B, the mixture is incubated at 40°C for 2 hours. After cooling to room temperature, the mixture is neutralized to a pH of 6-8 with the addition of liquid caustic soda. Water is then added until the solids content of the solution reaches 40%, thereby producing a conventional slow-setting polycarboxylate superplasticizer.

[0043] Comparative Example 2 This comparative example is the ordinary polycarboxylate water-reducing agent product M15 that Wuhan Sanyuan Special Building Materials Co., Ltd. has switched to producing.

[0044] The preparation method of the common polycarboxylate water reducer is as follows: 336 parts of isopentanol polyoxyethylene ether monomer are added to a four-necked flask, 260 parts of water are added and stirred, and after dissolving at 25°C, 3.2 parts of hydrogen peroxide are added and mixed, and component A and component B solutions are started to be added dropwise, and the component B solution is added dropwise after 3 hours, and the component A solution is added dropwise after 3.5 hours; wherein the component A solution is an aqueous solution prepared from 1.4 parts of L-ascorbic acid, 1.3 parts of mercaptopropionic acid and 100 parts of tap water; and the component B solution is an aqueous solution prepared from 38 parts of acrylic acid and 60 parts of tap water; after the component A solution and the component B solution are added dropwise, the mixture is kept warm at 40°C for 1 hour, cooled to room temperature, and then liquid alkali is added to neutralize the mixture to a pH of 6-8 to obtain the common polycarboxylate water reducer.

[0045] Comparative Example 3 A method for preparing a slow-setting polycarboxylic acid-based water-reducing agent comprises the following steps: S1. Add 300 parts of isopentanol polyoxyethylene ether macromonomer, 100 parts of methacrylic acid, 53 parts of 2-acrylamido-2-methylpropanesulfonic acid, 25 parts of alkylphenol polyoxyethylene ether phosphate, 7.6 parts of sodium hypophosphite, and 8.3 parts of BPO to a three-necked flask, dissolve the above reagents in 400 parts of anhydrous ethanol: water = 1:1 mixed solution, and start stirring; S2. Nitrogen was introduced into the reaction vessel for 30 minutes, and the vessel was sealed with a balloon filled with nitrogen. The vessel was placed in a constant temperature oil bath at 80°C for polymerization for 7 hours. The balloon was untied, air was introduced, and the vessel was cooled to room temperature. Finally, 45 parts of 30% by mass liquid caustic soda was added to adjust the pH value to 6-7.

[0046] The difference between this comparative example and Example 3 is that sodium hypophosphite is used as the chain transfer agent, which causes the reaction process to be unable to be effectively controlled and causes the phenomenon of violent polymerization and gelation.

[0047] Comparative Example 4 A method for preparing a slow-setting polycarboxylic acid-based water-reducing agent comprises the following steps: S1. Add 300 parts of isopentanol polyoxyethylene ether macromonomer, 100 parts of methacrylic acid, 53 parts of 2-acrylamido-2-methylpropanesulfonic acid, 25 parts of alkylphenol polyoxyethylene ether phosphate, 7.6 parts of bis(carboxymethyl)trithiocarbonate, and 1.0 part of BPO to a three-necked flask, dissolve the above reagents in a mixed solution of 400 parts of anhydrous ethanol and water in a ratio of 1:1, and start stirring. S2. Nitrogen was introduced into the reaction vessel for 30 minutes, and the vessel was sealed with a balloon filled with nitrogen. The vessel was placed in a constant temperature oil bath at 80°C for polymerization for 7 hours. The balloon was untied, air was introduced, and the vessel was cooled to room temperature. Finally, 45 parts of 30% by mass liquid caustic soda was added to adjust the pH value to 6-7.

[0048] The difference between this comparative example and Example 3 is that the amount of initiator BPO used is too small, resulting in the inability to initiate the polymerization reaction and the reaction not proceeding.

[0049] Comparative Example 5 A method for preparing a slow-setting polycarboxylic acid-based water-reducing agent comprises the following steps: S1. Add 300 parts of prenol polyoxyethylene ether macromonomer, 100 parts of methacrylic acid, 53 parts of 2-acrylamido-2-methylpropanesulfonic acid, 25 parts of methacrylic acid phosphate, 7.6 parts of bis(carboxymethyl)trithiocarbonate, and 8.3 parts of BPO to a three-necked flask, dissolve the above reagents in 400 parts of anhydrous ethanol: water = 1:1 mixed solution, and start stirring; S2. Nitrogen was introduced into the reaction vessel for 30 minutes, and the vessel was sealed with a balloon filled with nitrogen. The vessel was placed in a constant temperature oil bath at 80°C for polymerization for 7 hours. The balloon was untied, air was introduced, and the vessel was cooled to room temperature. Finally, 45 parts of liquid caustic soda with a mass fraction of 30% was added to adjust the pH value to 6-7, thereby obtaining a retarded polycarboxylate water reducer prepared by the RAFT method.

[0050] This comparative example is compared with Example 3, except that alkylphenol polyoxyethylene ether phosphate is replaced by methacrylic acid phosphate.

[0051] Performance Testing The slow-setting polycarboxylate water-reducers prepared in Examples 1 to 5 of the present invention and the polycarboxylate water-reducers prepared in Comparative Examples 1, 2, and 4 were subjected to molecular structure parameter tests and comparative tests on concrete slump, expansion, and setting time.

[0052] Molecular weight (Mw) and PDI (molecular weight polydispersity index) were measured using gel permeation chromatography. Concrete testing was conducted in accordance with the relevant provisions of GB 8076-2008, "Concrete Admixtures," and GB / T 50080-2016, "Standard for Test Methods of Concrete Mixture Properties." The concrete mix ratio is shown in Table 1, and the various properties are shown in Table 2.

[0053] Table 1 C35 concrete mix ratio (kg / m 3 )

[0054] In Table 1, the cement is PO 42.5 grade ordinary Portland cement; the mineral powder is S95 grade; the fly ash is Class II fly ash; the fineness modulus of the river sand is 2.6~2.9, and the mud content is 1.15%; the crushed stone is 5~30mm continuously graded crushed stone; and the water is tap water.

[0055] Table 2 Performance test results

[0056] As shown in Table 2, under conditions where the initial slump and spread of concrete are essentially the same, the solid-to-solid ratios of Examples 1 to 5 are similar, indicating that the retarding polycarboxylate water-reducing agents prepared are highly stable. The PDI values ​​indicate that the polycarboxylate water-reducing agents prepared using the RAFT method have a narrower molecular weight distribution. The polycarboxylate water-reducing agents prepared in the examples of the present invention exhibit longer setting times than those in Comparative Examples 1 and 2, demonstrating superior retarding properties. The retarding effect is more pronounced than that of the conventional water-reducing agent in Comparative Example 2. The resulting water-reducing agents were used to prepare concrete. Compared to Comparative Examples 1 and 2, the concrete setting times of Examples 1 to 5 were prolonged and the PDI distribution was narrower. This demonstrates superior overall performance.

[0057] The slow-setting polycarboxylate water-reducing agents prepared in Example 3 of the present invention and Comparative Examples 1 and 5 were subjected to comparative tests on concrete slump, expansion, setting time, and workability.

[0058] The concrete test was carried out in accordance with the relevant provisions of GB 8076-2008 "Concrete Admixtures" and GB / T 50080-2016 "Standard for Test Methods of Concrete Mixture Performance". The concrete mix ratio is shown in Table 3, and the various properties are shown in Table 4. The concrete obtained in Example 3 is in the following state when it is discharged from the machine: Figure 1 As shown, the concrete exiting the machine obtained in Comparative Example 5 is as follows Figure 2 shown.

[0059] Table 3 C50 concrete mix ratio (kg / m 3 )

[0060] In Table 3, the cement is PO 42.5 grade ordinary Portland cement; the mineral powder is S95 grade; the fly ash is Class II fly ash; the methylene blue (MB value) of manufactured sand is an overall indicator for determining the presence and content of expansive clay minerals (mud powder) in manufactured sand. The MB value of the manufactured sand in the mix ratio is 1.60 (>1.40), indicating that the manufactured sand is mainly composed of mud powder; the crushed stone is 5-30 mm continuously graded crushed stone; and the water is tap water.

[0061] Table 4 Performance test results

[0062] From the above test results, it can be seen that under the condition that the initial slump of concrete is basically the same, Example 3 has the smallest solid content and the best retarding effect. Figure 1 and Figure 2 By comparison, Example 3, using an alkylphenol polyoxyethylene ether water-reducing agent, exhibited excellent retarding effect, with improved concrete encapsulation and workability. However, the concrete in Comparative Example 5 exhibited more pronounced stone leakage, less slurry, and poor encapsulation. These tests demonstrate that the retarding-setting polycarboxylate water-reducing agent prepared by the present invention exhibits superior performance.

[0063] It should be noted that the present invention is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the technical solution of the present invention are all included in the technical scope of the present invention. In addition, without departing from the scope of the present invention, other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present invention.

Claims

1. A slow-setting polycarboxylate water-reducing agent, characterized in that: The preparation raw materials include, by weight: 300-400 parts of polyether macromonomer, 60-150 parts of unsaturated carboxylic acid small monomer, 30-60 parts of unsaturated sulfonic acid monomer, 15-30 parts of alkylphenol polyoxyethylene ether phosphate, 1.5-12 parts of chain transfer agent, 2-15 parts of initiator, 15-50 parts of liquid alkali, and 200-600 parts of solvent.

2. A slow-setting polycarboxylate water-reducing agent according to claim 1, characterized in that: The unsaturated polyether macromonomer includes at least one of ethylene glycol monovinyl polyethylene glycol ether, 4-hydroxybutyl vinyl polyethylene glycol ether, isopentanol polyoxyethylene ether, and vinyl polyoxyethylene ether; and the weight average molecular weight of the unsaturated polyether macromonomer is 2000-6000.

3. A slow-setting polycarboxylate water-reducing agent according to claim 1, characterized in that: The unsaturated carboxylic acid small monomer includes at least one of methacrylic acid, fumaric acid, acrylic acid, and maleic anhydride.

4. A slow-setting polycarboxylate water-reducing agent according to claim 1, characterized in that: The unsaturated sulfonic acid monomer includes at least one of 2-acrylamido-2-methylpropanesulfonic acid and methacrylamidopropyl-N,N-dimethylpropanesulfonic acid.

5. A slow-setting polycarboxylate water-reducing agent according to claim 1, characterized in that: The initiator includes at least one of BPO, AIBN and ammonium persulfate; the chain transfer agent includes at least one of bis(carboxymethyl) trithiocarbonate and dibenzyl trithiocarbonate.

6. A slow-setting polycarboxylate water-reducing agent according to claim 1, characterized in that: The solvents include ethanol and water.

7. The method for preparing the slow-setting polycarboxylate water-reducing agent according to any one of claims 1 to 6, wherein: The following steps are involved: The polyether macromonomer, unsaturated carboxylic acid small monomer, unsaturated sulfonic acid monomer, alkylphenol polyoxyethylene ether phosphate, chain transfer agent and initiator are dissolved in a solvent, stirred evenly, heated under nitrogen protection to carry out polymerization reaction, cooled to room temperature after the reaction, and adjusted to pH 6-7 to obtain the retarded polycarboxylate water reducer.

8. The method for preparing the slow-setting polycarboxylate water-reducing agent according to claim 7, wherein: The reaction temperature of the polymerization reaction is 70° C. to 120° C., and the reaction time is 4 to 10 hours.

9. Use of the slow-setting polycarboxylate water-reducing agent according to any one of claims 1 to 6 in preparing concrete.

10. The use according to claim 9, characterized in that The solid content of the retarding polycarboxylate water-reducing agent in the concrete is 0.2 wt % to 0.4 wt %.

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