A powder polycarboxylate water reducer specially used for machine-made aggregate and its preparation method

Abstract

The present invention discloses a powdered polycarboxylic acid water reducer specially used for machine-made aggregates and a preparation method thereof. The present invention introduces boric acid groups and catechol groups into traditional polycarboxylic acid molecular chains. By adjusting the pH value to form borate bonds, the polycarboxylic acid molecules can be cross-linked, which can effectively reduce the solubility of the product, increase the melting point of the product, reduce the drying temperature, improve the drying efficiency, avoid the damage to the performance of the powdered polycarboxylic acid by conventional high-temperature drying methods, and ensure the storage stability of the powdered polycarboxylic acid product. Since the borate bonds can quickly undergo reversible coordination exchange in the cement paste and dissociate, the powdered polycarboxylic acid can quickly become a linear structure in the cement paste and thus dissolve quickly, exerting a water-reducing effect. In addition, the catechol monomer contained in the molecular chain can make the molecular chain have stronger adsorption and bonding ability, making the cement paste more easily adsorbed on the surface of the machine-made aggregate with lower surface energy, thereby effectively improving the workability, workability, mechanical and durability of the machine-made aggregate concrete.

Description

Technical Field

[0001] The invention belongs to the field of polymer materials, and in particular relates to a powdered polycarboxylate water reducer specially used for machine-made aggregates and a preparation method thereof. The product can be used for the construction of machine-made aggregate concrete. Background Art

[0002] With the unprecedented growth of the domestic economy and construction industry, the scale of infrastructure and related construction is growing exponentially. High-performance concrete, one of the most important engineering materials, is also undergoing continuous development and advancement. One of its key characteristics is the incorporation of chemical admixtures as a key component. Water reducers, by modifying the rheological properties of concrete, can reduce the water-cement ratio while improving concrete construction performance. They have become an essential component of high-performance concrete. Third-generation polycarboxylate water reducers, due to their advantages such as low dosage, high water reduction rate, excellent slump retention, low shrinkage, and high modification potential, have been widely used in the preparation of high-performance concrete. They have replaced traditional lignin sulfonate and naphthalene-based water reducers and become the mainstay of the current water reducer market. Due to their ease of modification and significant impact on concrete performance, various new types of polycarboxylate water reducers have become an important means of regulating the properties of high-performance concrete.

[0003] Due to my country's massive demand for concrete materials, natural sand and gravel resources are insufficient to meet demand. Furthermore, to protect the ecological environment and ensure river navigation and bridge safety, the extraction of natural sand and gravel is becoming increasingly restricted, leading to higher prices. In current concrete production, manufactured sand and gravel aggregates, produced through mechanical crushing and screening of parent rock, have gradually become the primary source of construction aggregate. It is anticipated that high-performance concrete using manufactured aggregates will be a major trend in the future development of concrete. There are certain differences in the properties of manufactured aggregates compared to natural aggregates. Due to regional variations in parent rock, production equipment, and processes, the strength, particle size distribution, and stone dust content of manufactured aggregates can also fluctuate significantly. For manufactured aggregates made from parent rock, such as basalt or iron ore tailings, low surface energy often forms during the preparation process, making it difficult for cement paste to adhere to these surfaces. This often results in concrete paste deficiency, exposed stone, and unstable air content. These factors significantly impact the cohesiveness, workability, and compatibility of the mix, and may even compromise the mechanical and durability properties of concrete structures. Therefore, specialized performance adjustments are necessary to meet specific application requirements.

[0004] Mussels are marine organisms that can adhere firmly to surfaces such as ship hulls and reefs. Research has found that this extremely strong underwater adhesion ability originates from the secreted mussel foot protein, which exhibits extremely strong adhesion to various substrate surfaces. The catechol groups in the DOPA structure play a crucial role in its strong underwater adhesion properties. Therefore, introducing catechol-containing monomers, mainly dopamine, into polymers to produce mussel-inspired molecules is one of the most effective means to develop highly adhesive functional materials. Currently, relevant researchers have also studied high-adhesion polycarboxylate water-reducers, such as those disclosed in patents CN109627394A, CN108359064A, and CN112661914A. However, the polycarboxylate water-reducers prepared by these patents have certain limitations. In addition, some technologies introduce catechol groups that have a certain inhibitory effect on free radical polymerization, resulting in reduced polymerization efficiency and less than ideal product performance.

[0005] Furthermore, the vast majority of current polycarboxylic acid admixture products are supplied and used in solution form, resulting in significant additional costs for packaging, transportation, and warehousing. Furthermore, since most polycarboxylic acid admixtures incorporate sustained-release groups to enhance their sustained-release and collapse-preserving properties, their stability in water is difficult to guarantee, leading to hydrolysis and reduced product effectiveness. This is particularly true for polycarboxylic acid molecules containing catechol. The catechol groups are easily oxidized by air in aqueous solutions to form quinones, rendering them ineffective and making them difficult to store in solution for long periods. Therefore, developing powdered polycarboxylic acid admixtures is crucial for reducing overall costs and extending shelf life, and is currently a research hotspot. Currently, the main technologies for preparing polycarboxylic acid water reducers are spray drying, bulk polymerization, or the addition of drying adsorbents, such as patents CN110643001B and CN113429526A. However, these technologies all have disadvantages such as significant performance differences compared to liquids, slow remelting, and easy agglomeration. This is due to the molecular chain structure of the polycarboxylic acid itself. Therefore, designing polycarboxylic acid molecules that are easy to dry and pulverize based on their molecular structure is an important research method.

[0006] In summary, the effect of the machine-made sand water-reducing agent prepared by the existing technology is not obvious, and is often accompanied by problems such as difficulty in use and unstable effect, and lacks corresponding powderization technology. Therefore, it is of great significance to the entire industry to develop a powdered machine-made sand water-reducing agent with high adaptability to machine-made aggregates based on molecular design. Summary of the Invention

[0007] The purpose of the present invention is to solve the above problems and provide a powder polycarboxylate water-reducing agent specially used for machine-made aggregate and a preparation method thereof.

[0008] The powdered polycarboxylate water-reducing agent for machine-made aggregates is obtained by copolymerizing a polyether macromonomer, an unsaturated carboxylic acid, an unsaturated carboxylic acid ester, an unsaturated boric acid monomer, and an unsaturated catechol monomer, adjusting the pH value of the product, and then vacuum drying and crushing the product. The molar ratio of the polyether macromonomer:unsaturated carboxylic acid:unsaturated carboxylic acid ester:unsaturated boric acid monomer:unsaturated catechol monomer is 1:(1-5):(0.5-6):(0.05-0.5):(0.05-0.5); and the molar ratio of the unsaturated boric acid monomer to the unsaturated catechol monomer is 1:(0.9-1.1).

[0009] The polyether macromonomer is at least one of isobutylene alcohol polyethylene glycol ether, isopentenol polyethylene glycol ether, allyl polyethylene glycol ether, and ethylene glycol monovinyl ether polyoxyethylene ether with a molecular weight of 1600 to 4000; the unsaturated carboxylic acid is at least one of acrylic acid, methacrylic acid, fumaric acid, and itaconic acid; and the unsaturated carboxylic acid ester is at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and hydroxypropyl methacrylate.

[0010] The unsaturated boronic acid monomer is at least one of 3-acrylamidophenylboronic acid, 4-vinylphenylboronic acid, 4-acrylatephenylboronic acid, 4-methacrylatephenylboronic acid and 4-acryloyloxymethylphenylboronic acid; the unsaturated catechol monomer is at least one of dopaminemethacrylamide, dopamineacrylamide, dopamethacrylamide, dopaacrylamide and 4-vinylcatechol.

[0011] The preparation method of the powdered polycarboxylate water-reducing agent for machine-made aggregate comprises the following steps:

[0012] (1) Macromolecular polymerization: Add polyether macromonomer and water into the reaction vessel and stir to dissolve until a uniform clear solution is obtained. Under stirring conditions, the polymerization monomer solution containing unsaturated boric acid monomer, unsaturated catechol monomer, unsaturated carboxylic acid and unsaturated carboxylic acid ester and the initiator and chain transfer agent solution are added dropwise into the reaction bottle respectively. The reaction temperature is 18-70°C, and the addition time is 1.5-3h and 2-3.5h respectively. The polymerization monomer solution must be added earlier than the initiator and chain transfer agent solution. After the addition is completed, keep warm for 1-3.5h to obtain the polymerization product solution.

[0013] (2) Drying and pulverizing process: add an appropriate amount of alkali to the polymer product solution to adjust the pH value to 9-10, then let it stand at room temperature for 24 hours in a tray. Put the solution after standing in a vacuum dryer to dry. After drying, the solid is crushed to obtain a powdered polycarboxylic acid water reducer for machine-made sand.

[0014] In step (1), the initiator system is at least one of potassium persulfate, ammonium persulfate, azobisisopropylaminobenzoic acid hydrochloride, azobisisobutylaminobenzoic acid dihydrochloride, hydrogen peroxide-ascorbic acid initiation system, hydrogen peroxide-diaobaikai initiation system and ammonium persulfate-sodium sulfite initiation system, and the amount used is 0.3-3% of the amount of the monomer used. The chain transfer agent is at least one of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, mercaptopropanol, sodium hypophosphite, trisodium phosphate, and CTA1420, and the amount used is 0.2-2% of the amount of the monomer used.

[0015] In step (2), at least one of sodium hydroxide, potassium hydroxide, triethylamine, triethanolamine or an aqueous solution thereof is used; the vacuum degree of vacuum drying is 80-120 Pa, the drying temperature is 50-85° C., and the drying time is 2-5 h.

[0016] The positive effects of the powder polycarboxylate water-reducing agent specially used for machine-made aggregate and the preparation method thereof are:

[0017] (1) Compared with the existing polycarboxylic acid water-reducing agent, the polycarboxylic acid water-reducing agent for machine-made sand prepared in the present invention introduces a monomer with a catechol group into the polymer side chain, which makes the molecular chain have a strong adsorption and bonding ability, so that the cement paste can be easily adsorbed on the surface of the machine-made aggregate with low surface energy, effectively improving the workability, workability and mechanical and durability of the machine-made aggregate concrete.

[0018] (2) The present invention introduces phenylboronic acid groups that can produce reversible covalent interactions with catechol groups. By controlling the reversible transformation of the borate ester formed by the phenylboronic acid groups and the catechol groups, the polycarboxylic acid macromolecular chains have different chain structures under different pH values ​​and solution environments, thereby playing a role in intelligently regulating the polycarboxylic acid molecules. During the polymerization and storage processes, the catechol groups mainly exist in the form of borate esters. On the one hand, this reduces the inhibitory effect of the catechol groups during the polymerization process and increases the polymerization rate. On the other hand, it reduces the oxidation reaction of the catechol groups during storage, ensuring the storage stability of the product.

[0019] (3) By controlling the pH value, the borate ester bond formed between the phenylboronic acid group and the catechol group can cross-link the polycarboxylic acid molecules, which helps to reduce the solubility of the product and increase the melting point of the product. This allows the product drying process to be carried out efficiently at a lower temperature, effectively avoiding the damage to the product performance caused by the high temperature of the conventional drying method, while ensuring the storage stability of the product powder. At the same time, because the borate ester bond can quickly undergo reversible coordination exchange in the metal ion solution and dissociate, the dried product can quickly transform into a linear structure in the cement paste, thereby quickly dissolving and exerting a water-reducing effect. DETAILED DESCRIPTION

[0020] The present invention will be described in further detail below with reference to specific embodiments.

[0021] Example 1: A powder polycarboxylate water-reducing agent specially used for machine-made aggregates, the preparation process of which is as follows:

[0022] 85 g of isobutylene alcohol polyethylene glycol ether with a molecular weight of 2400 and 4.8 g of 3-acrylamidophenylboronic acid were added to a reaction vessel containing 75 g of water and stirred to dissolve, and a polymerization monomer solution (containing 12 g of acrylic acid, 6 g of hydroxyethyl acrylate, 6 g of dopamine methacrylamide, and 30 g of water) and an initiator solvent (containing 1 g of potassium persulfate, 2 g of mercaptopropionic acid, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction temperature was 65° C., and the dropping time was 2 h and 2.5 h, respectively. After the dropwise addition was completed, the temperature was kept for 2 h to obtain a polycarboxylic acid solution.

[0023] Add an appropriate amount of 35% by mass sodium hydroxide aqueous solution to the polymerization product solution to adjust the pH value to 9-10, then let it stand at room temperature in a tray for 24 hours. Place the solution after standing in a vacuum dryer and dry it at a vacuum degree of 90 Pa and a drying temperature of 55°C. After drying, the solid obtained is crushed to obtain a powdered polycarboxylate water-reducing agent specifically for machine-made aggregates.

[0024] Example 2: A powder polycarboxylate water-reducing agent specially used for machine-made aggregates, the preparation process of which is as follows:

[0025] 80 g of prenol polyethylene glycol ether with a molecular weight of 2000, 2.7 g of 4-vinylphenylboronic acid and 1.5 g of hydrogen peroxide solution were added to a reaction vessel containing 70 g of water and stirred to dissolve. Then, a polymerization monomer solution (containing 10 g of methacrylic acid, 8 g of hydroxypropyl acrylate, 3.75 g of dopamethacrylamide, and 30 g of water) and an initiator solvent (containing 0.4 g of ascorbic acid, 1.8 g of CTA1420, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction starting temperature was 22° C. The dropwise addition time was 2.5 h and 3 h, respectively. After the dropwise addition was completed, the temperature was kept for 1.5 h to obtain a polycarboxylic acid solution.

[0026] Add an appropriate amount of 35% by mass potassium hydroxide aqueous solution to the polymerization product solution to adjust the pH value to 9-10, then let it stand at room temperature in a tray for 24 hours. Place the solution after standing in a vacuum dryer and dry it at a vacuum degree of 100 Pa and a drying temperature of 60°C. After drying, the solid obtained is crushed to obtain a powdered polycarboxylate water-reducing agent specifically for machine-made aggregates.

[0027] Example 3: A powder polycarboxylate water-reducing agent specially used for machine-made aggregates, the preparation process of which is as follows:

[0028] 80 g of allyl polyethylene glycol ether with a molecular weight of 2000 and 8 g of 4-acrylated phenylboronic acid were added to a reaction vessel containing 75 g of water and stirred to dissolve. A polymerization monomer solution (containing 7.5 g of acrylic acid, 7.5 g of fumaric acid, 4 g of hydroxyethyl methacrylate, 10 g of dopamethacrylamide, and 30 g of water) and an initiator solvent (containing 1.2 g of ammonium persulfate, 1.5 g of mercaptoethanol, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction temperature was 68° C., and the dropwise addition time was 1.5 h and 2 h, respectively. After the dropwise addition was completed, the temperature was kept for 2 h to obtain a polycarboxylic acid solution.

[0029] Add an appropriate amount of triethanolamine to the polymerization product solution to adjust the pH value to 9-10, then let it stand at room temperature for 24 hours in a tray. Place the solution after standing in a vacuum dryer and dry it at a vacuum degree of 100 Pa and a drying temperature of 65°C. After drying, the solid obtained is crushed to obtain a powdered polycarboxylic acid water reducer specifically for machine-made aggregates.

[0030] Example 4: A powder polycarboxylate water-reducing agent specially used for machine-made aggregates, the preparation process of which is as follows:

[0031] 90 g of ethylene glycol monovinyl ether polyoxyethylene ether with a molecular weight of 3000, 8 g of 4-methacrylate phenylboronic acid and 1.25 g of hydrogen peroxide solution were added to a reaction vessel containing 80 g of water and stirred to dissolve, and a polymerization monomer solution (containing 7 g of acrylic acid, 7 g of itaconic acid, 2 g of hydroxyethyl acrylate, 3 g of hydroxypropyl methacrylate, 10 g of dopaacrylamide, and 30 g of water) and an initiator solvent (containing 0.5 g of bleaching powder, 2.8 g of sodium hypophosphite, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction starting temperature was 20° C., the dropping time was 1 h and 1.5 h, respectively, and the temperature was kept for 1.5 h after the dropwise addition was completed to obtain a polycarboxylic acid solution.

[0032] Add an appropriate amount of triethylamine to the polymerization product solution to adjust the pH value to 9-10, then let it stand at room temperature for 24 hours in a tray. Place the solution after standing in a vacuum dryer and dry it at a vacuum degree of 90 Pa and a drying temperature of 50°C. After drying, the solid is crushed to obtain a powdered polycarboxylic acid water-reducing agent specifically for machine-made aggregates.

[0033] Example 5: A powder polycarboxylate water-reducing agent specially used for machine-made aggregates, the preparation process of which is as follows:

[0034] 80 g of prenol polyethylene glycol ether with a molecular weight of 2400 and 8.1 g of 4-acryloyloxymethylphenylboronic acid were added to a reaction vessel containing 70 g of water and stirred to dissolve. A polymerization monomer solution (containing 13 g of acrylic acid, 6 g of hydroxybutyl acrylate, 5.4 g of 4-vinylcatechol, and 30 g of water) and an initiator solvent (containing 1 g of azobisisobutylamidine dihydrochloride, 1.6 g of mercaptopropionic acid, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction temperature was 60° C., and the dropwise addition time was 2 h and 2.5 h, respectively. After the dropwise addition was completed, the temperature was kept for 2.5 h to obtain a polycarboxylic acid solution.

[0035] Add an appropriate amount of 35% by mass sodium hydroxide aqueous solution to the polymerization product solution to adjust the pH value to 9-10, then let it stand at room temperature in a tray for 24 hours. Place the solution after standing in a vacuum dryer and dry it at a vacuum degree of 90 Pa and a drying temperature of 60°C. After drying, the solid is crushed to obtain a powdered polycarboxylic acid water-reducing agent specifically for machine-made aggregates.

[0036] Example 6: A powder polycarboxylate water-reducing agent specially used for machine-made aggregates, the preparation process of which is as follows:

[0037] 65 g of isopentanol polyethylene glycol ether with a molecular weight of 2400, 25 g of isobutylene glycol ether with a molecular weight of 1800, and 3.6 g of 4-vinylphenylboronic acid were added to a reaction vessel containing 80 g of water and stirred for dissolution. A polymerization monomer solution (containing 8.5 g of methacrylic acid, 7 g of itaconic acid, 2.5 g of hydroxypropyl acrylate, 3.5 g of hydroxybutyl methacrylate, 6 g of dopamethacrylamide, and 30 g of water) and an initiator solvent (containing 1 g of azodiisopropylamidazole hydrochloride, 1.2 g of mercaptopropanol, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction temperature was 62° C., and the dropping time was 1.5 h and 2 h, respectively. After the dropwise addition was completed, the mixture was kept warm for 3 h to obtain a polycarboxylic acid solution.

[0038] Add an appropriate amount of 35% by mass potassium hydroxide aqueous solution to the polymerization product solution to adjust the pH value to 9-10, then let it stand at room temperature in a tray for 24 hours. Place the solution after standing in a vacuum dryer and dry it at a vacuum degree of 100 Pa and a drying temperature of 55°C. After drying, the solid obtained is crushed to obtain a powdered polycarboxylate water-reducing agent specifically for machine-made aggregates.

[0039] Example 7: A powder polycarboxylate water-reducing agent specially used for machine-made aggregates, the preparation process of which is as follows:

[0040] 85 g of isobutylene alcohol polyethylene glycol ether with a molecular weight of 2400 and 8.1 g of 3-acrylamidophenylboronic acid were added to a reaction vessel containing 100 g of water and stirred to dissolve. A polymerization monomer solution (containing 12 g of acrylic acid, 6 g of hydroxyethyl acrylate, 9 g of dopamine acrylamide, and 30 g of water) and an initiator solvent (containing 1 g of potassium persulfate, 2 g of mercaptopropionic acid, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction temperature was 65° C., and the dropwise addition time was 2 h and 2.5 h, respectively. After the dropwise addition was completed, the mixture was kept warm for 2 h to obtain a polycarboxylic acid solution.

[0041] Add an appropriate amount of 35% by mass sodium hydroxide aqueous solution to the polymerization product solution to adjust the pH value to 9-10, then let it stand at room temperature in a tray for 24 hours. Place the solution after standing in a vacuum dryer and dry it at a vacuum degree of 90 Pa and a drying temperature of 60°C. After drying, the solid is crushed to obtain a powdered polycarboxylic acid water-reducing agent specifically for machine-made aggregates.

[0042] Comparative Example 1: Conventional polycarboxylate water reducer

[0043] 85g of 2400-molecular-weight isobutylene alcohol polyglycol ether was added to a reaction vessel containing 80g of water and stirred to dissolve. A monomer solution (containing 12g of acrylic acid, 6g of hydroxyethyl acrylate, and 30g of water) and an initiator solvent (containing 1g of potassium persulfate, 2g of mercaptopropionic acid, and 20g of water) were then added dropwise to the reaction vessel for reaction at 65°C for 2h and 2.5h, respectively. After the addition was complete, the mixture was incubated for 2h to obtain a copolymer product. A 35% by mass aqueous sodium hydroxide solution was then added to neutralize the mixture to a pH of approximately 6 to obtain a conventional polycarboxylate superplasticizer.

[0044] The solution after standing is placed in a vacuum dryer for drying at a vacuum degree of 100 Pa and a drying temperature of 60° C. The solid obtained after drying is crushed to obtain a powdered polycarboxylate water reducer.

[0045] Comparative Example 2: Conventional polycarboxylate water reducer

[0046] 80 g of prenol polyethylene glycol ether with a molecular weight of 2000, 9 g of 4-vinylphenylboronic acid and 1.5 g of hydrogen peroxide solution were added to a reaction vessel containing 70 g of water and stirred to dissolve. Then, a polymerization monomer solution (containing 10 g of methacrylic acid, 8 g of hydroxypropyl acrylate, 12 g of dopamethacrylamide, and 30 g of water) and an initiator solvent (containing 0.4 g of ascorbic acid, 1.8 g of CTA1420, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction starting temperature was 22° C., and the dropwise addition times were 2.5 h and 3 h, respectively, to obtain a polycarboxylic acid solution.

[0047] An appropriate amount of 35% by mass potassium hydroxide aqueous solution was added to the polymerization product solution to adjust the pH value to 9-10, and then the solution was allowed to stand at room temperature for 24 hours in a tray. The solution after standing was placed in a vacuum dryer for drying at a vacuum degree of 100 Pa and a drying temperature of 60°C. The solid obtained after drying was crushed to obtain a powdered polycarboxylate water reducer.

[0048] Comparative Example 3: Polycarboxylate water reducer

[0049] 80 g of prenol polyethylene glycol ether with a molecular weight of 2000, 0.9 g of 4-vinylphenylboronic acid and 1.5 g of hydrogen peroxide solution were added to a reaction vessel containing 70 g of water and stirred to dissolve. Then, a polymerization monomer solution (containing 10 g of methacrylic acid, 8 g of hydroxypropyl acrylate, 1.2 g of dopamethacrylamide, and 30 g of water) and an initiator solvent (containing 0.4 g of ascorbic acid, 1.8 g of CTA1420, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction starting temperature was 22° C. The dropwise addition time was 2.5 h and 3 h, respectively. After the dropwise addition was completed, the temperature was kept for 1.5 h to obtain a polycarboxylic acid solution.

[0050] An appropriate amount of 35% by mass potassium hydroxide aqueous solution was added to the polymerization product solution to adjust the pH value to 9-10, and then the solution was allowed to stand at room temperature for 24 hours in a tray. The solution after standing was placed in a vacuum dryer for drying at a vacuum degree of 100 Pa and a drying temperature of 60°C. The solid obtained after drying was crushed to obtain a powdered polycarboxylate water reducer.

[0051] Comparative Example 4: Polycarboxylate water reducer

[0052] 80 g of prenol polyethylene glycol ether with a molecular weight of 2400 and 2.7 g of 4-acryloyloxymethylphenylboronic acid were added to a reaction vessel containing 70 g of water and stirred to dissolve. A polymerization monomer solution (containing 13 g of acrylic acid, 6 g of hydroxybutyl acrylate, 5.4 g of 4-vinylcatechol, and 30 g of water) and an initiator solvent (containing 1 g of azobisisobutyramidine dihydrochloride, 1.6 g of mercaptopropionic acid, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction temperature was 60° C., and the dropwise addition time was 2 h and 2.5 h, respectively. After the dropwise addition was completed, the temperature was maintained for 2.5 h to obtain a polycarboxylic acid solution.

[0053] Add an appropriate amount of 35% by mass sodium hydroxide aqueous solution to the polymerization product solution to adjust the pH value to 9-10, and then let it stand at room temperature in a tray for 24 hours. Place the solution after standing in a vacuum dryer and dry it at a vacuum degree of 90 Pa and a drying temperature of 60°C. After drying, the solid is crushed to obtain a powdered polycarboxylate water reducer.

[0054] Comparative Example 5: Polycarboxylate water reducer

[0055] 80 g of prenol polyethylene glycol ether with a molecular weight of 2400 and 20 g of 4-acryloyloxymethylphenylboronic acid were added to a reaction vessel containing 70 g of water and stirred to dissolve. A polymerization monomer solution (containing 13 g of acrylic acid, 6 g of hydroxybutyl acrylate, 5.4 g of 4-vinylcatechol, and 30 g of water) and an initiator solvent (containing 1 g of azobisisobutylamidine dihydrochloride, 1.6 g of mercaptopropionic acid, and 20 g of water) were dropwise added to the reaction vessel for reaction. The reaction temperature was 60° C., and the dropwise addition time was 2 h and 2.5 h, respectively. After the dropwise addition was completed, the temperature was maintained for 2.5 h to obtain a polycarboxylic acid solution.

[0056] Add an appropriate amount of 35% by mass sodium hydroxide aqueous solution to the polymerization product solution to adjust the pH value to 9-10, and then let it stand at room temperature in a tray for 24 hours. Place the solution after standing in a vacuum dryer and dry it at a vacuum degree of 90 Pa and a drying temperature of 60°C. After drying, the solid is crushed to obtain a powdered polycarboxylate water reducer.

[0057] Effect description:

[0058] Mortar tests were conducted using the polycarboxylate superplasticizer powder for machine-made aggregates according to GB / T 17671, "Test Methods for Cement Mortar Strength," using standard cement and basalt machine-made sand. The mortar fluidity was adjusted to 190 ± 10 mm. The mortar was then tested for consistency and delamination, as well as for compressive strength after 7 days of molding. The test results are shown in Table 2.

[0059] Table 1 Mortar test results

[0060]

[0061] From the data in the table, it can be seen that Examples 1 to 7 of the present invention are better than Comparative Examples 1 to 5 in terms of consistency, delamination and 7d compressive strength, which shows that the Examples of the present invention can effectively reduce viscosity, improve slurry adhesion and reduce mortar segregation.

[0062] The present invention's powdered polycarboxylate superplasticizer for machine-made aggregates was used in C30 concrete using machine-made sand, using iron tailings sand as the example and comparative example. Concrete tests were conducted in accordance with GB / T50080-2002, "Standard for Testing Methods for Ordinary Concrete Mixture Properties," and GB / T50081-2019, "Standard for Testing Methods for Physical and Mechanical Properties of Concrete." The mixture state was recorded, and the pressure-water bleeding rate ratio and 28-day compressive strength were tested. The C30 concrete mix proportions are shown in Table 3. The concrete test results are shown in Table 4.

[0063] Table 2 C30 concrete mix proportion

[0064] cement fly ash Machine-made sand gravel water admixtures 300 80 820 1086 165 0.38

[0065] Table 3 Concrete test results

[0066]

[0067] As can be seen from the data in Table 4, the water reduction rates of Examples 1 to 7 when used in machine-made sand concrete are significantly improved compared to those of Comparative Examples 1 to 5. This is because the dynamic borate bonds formed by the introduced boric acid and catechol groups form micro-crosslinks, which shorten the high-temperature drying time of the polycarboxylate water-reducer during the drying process. This reduces the group decomposition and chain transfer of the polycarboxylic acid molecular chains caused by high temperatures during the drying process, thereby keeping the powdered polycarboxylic acid molecular chains more intact and achieving better results. In addition, the dynamic borate bonds dissociate in the cement paste due to the coordination substitution between the boric acid groups and the metal ions, causing the polycarboxylic acid molecules to gradually restore their linear form and redissolve, releasing free catechol groups to provide better adhesion, resulting in a better overall mixture state, significantly superior pressure water bleeding rate ratio, and 28d compressive strength.

[0068] In Comparative Example 1, due to the lack of introduction of the corresponding groups, a large amount of denaturation occurred during the drying process, resulting in significantly poorer performance of the powder water-reducing agent. In Comparative Example 2, due to the excessive introduction of groups, excessive cross-linking occurred during the polymerization process, significantly reducing the degree of polymerization and thus the effectiveness. In Comparative Example 3, due to the insufficient introduction of groups, the micro-crosslinking effect was not significant. In Comparative Example 4, due to the low boric acid content, a large number of catechol groups were not protected, resulting in oxidation during drying and use, which significantly reduced the effectiveness. In Comparative Example 5, due to the excessive boric acid content, the cross-linking ratio was insufficient, and the free boric acid hindered the dissociation of the micro-crosslinks, resulting in a significant decline in overall effectiveness.

[0069] From the above experimental results, it can be seen that the performance of the powder polycarboxylate water-reducing agent of the present invention is significantly improved compared with the conventional powder polycarboxylate water-reducing agent, and it can effectively improve the adhesion ability of the concrete paste using machine-made aggregates, thereby improving the workability of the mixture, preventing water and slurry bleeding, and improving the homogeneity of the overall concrete mixture. In addition, the coordination effect and hydrogen bonding effect of the catechol functional group jointly play a role in improving the strength of the concrete.

[0070] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A powder polycarboxylate water reducer for machine-made sand, characterized in that The powder polycarboxylate water reducer is obtained by copolymerizing a polyether macromonomer, an unsaturated carboxylic acid, an unsaturated carboxylic acid ester, an unsaturated boric acid monomer and an unsaturated catechol monomer, adjusting the pH value and then vacuum drying and crushing the product. The molar ratio of the polyether macromonomer: unsaturated carboxylic acid: unsaturated carboxylic acid ester: unsaturated boric acid monomer: unsaturated catechol monomer is 1:(1-5):(0.5-6):(0.05-0.5):(0.05-0.5); the molar ratio of the unsaturated boric acid monomer to the unsaturated catechol monomer is 1:(0.9-1.1); and the unsaturated boric acid monomer is at least one of 3-acrylamidophenylboric acid, 4-vinylphenylboric acid, 4-acrylatephenylboric acid, 4-methacrylatephenylboric acid and 4-acryloyloxymethylphenylboric acid.

2. A powder polycarboxylate water reducer for machine-made sand according to claim 1, characterized in that The polyether macromonomer is at least one of isobutylene alcohol polyethylene glycol ether, isopentenol polyethylene glycol ether, allyl polyethylene glycol ether, and ethylene glycol monovinyl ether polyoxyethylene ether with a molecular weight of 1600 to 4000; the unsaturated carboxylic acid is at least one of acrylic acid, methacrylic acid, fumaric acid, and itaconic acid; and the unsaturated carboxylic acid ester is at least one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxybutyl acrylate, and hydroxypropyl methacrylate.

3. The powder polycarboxylate water reducer for machine-made sand according to claim 1, characterized in that The unsaturated catechol monomer is at least one of dopamine methacrylamide, dopamine acrylamide and 4-vinyl catechol.

4. The method for preparing a powder polycarboxylate water reducer for machine-made sand according to claim 1, characterized in that The following steps are involved: (1) Macromolecular polymerization: Add a polyether macromonomer and water into a reaction vessel and stir to dissolve until a uniform clear solution is obtained. Under stirring, a polymerization monomer solution containing an unsaturated boric acid monomer, an unsaturated catechol monomer, an unsaturated carboxylic acid and an unsaturated carboxylic acid ester, and an initiator and a chain transfer agent solution are respectively added dropwise into the reaction flask. The reaction temperature is 18-70°C, and the addition time is 1.5-3 hours and 2-3.5 hours, respectively. The polymerization monomer solution must be added earlier than the initiator and chain transfer agent solution. After the addition is completed, the temperature is kept for 1-3.5 hours to obtain a polymerization product solution. (2) Drying and pulverizing process: add appropriate amount of alkali to the polymerization product solution to adjust the pH value to 9-10, then let it stand at room temperature for 24 hours in a tray. Put the solution after standing in a vacuum dryer to dry. After drying, the solid is crushed to obtain a powder polycarboxylic acid water reducer for machine-made sand.

5. The preparation method according to claim 4, characterized in that: In step (1), the initiator system is at least one of potassium persulfate, ammonium persulfate, azobisisopropylamidazole hydrochloride, azobisisobutylamidine dihydrochloride, hydrogen peroxide-ascorbic acid initiation system, hydrogen peroxide-dilution initiation system and ammonium persulfate-sodium sulfite initiation system; and the chain transfer agent is at least one of mercaptoethanol, thioglycolic acid, mercaptopropionic acid, mercaptopropanol, sodium hypophosphite, trisodium phosphate and CTA1420.

6. The preparation method according to claim 4, wherein: In step (2), at least one of sodium hydroxide, potassium hydroxide, triethylamine, triethanolamine or an aqueous solution thereof is used; the vacuum degree of vacuum drying is 80-120 Pa, the drying temperature is 50-85° C., and the drying time is 2-5 h.

7. Use of the powdered polycarboxylate water-reducing agent for machine-made sand according to claim 1 as a water-reducing agent or a conditioner for machine-made sand concrete.

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