Slow-release polycarboxylate superplasticizer adaptive to sulfate-resistant cement and preparation method of slow-release polycarboxylate superplasticizer

Abstract

The invention relates to the technical field of water reducing agents, in particular to a slow-release polycarboxylic acid water reducing agent adaptive to sulfate-resistant cement and a preparation method of the slow-release polycarboxylic acid water reducing agent. The invention relates to an unsaturated polyoxyethylene ether grafted cyclosiloxane-tetramethyl tetravinyl cyclotetrasiloxane-acrylic acid-methacrylic acid-acrylamide-2-acrylamide-2-methylpropanesulfonic acid, an initiator, a reducing agent, a chain transfer agent, a pH regulator and deionized water. In component design, carboxyl, sulfo and amido polar groups on a main chain can be tightly adsorbed with cement particles, and a water reducing effect is achieved through electrostatic repulsion and a steric hindrance effect; from the perspective of the preparation process, the use of the chain transfer agent avoids overlarge molecular weight or cross-linking of a polymer, so that the water reducer can resist the interference of gypsum and fly ash in a sulfate-resistant cement system, not only has a water reducing effect, but also can maintain the flowability and plasticity of concrete for a long time, thereby improving the durability and construction quality of concrete engineering.

Description

Technical Field

[0001] The present invention relates to the technical field of water-reducing agents, and specifically, to a slow-release polycarboxylate water-reducing agent adapted to sulfate-resistant cement and a preparation method thereof. Background Art

[0002] At present, in the field of construction engineering, especially in arid regions with high soil sulfate content, concrete projects face serious sulfate corrosion problems. In various scenarios such as water conservancy projects, railway projects, highway projects, construction projects, and docks and breakwaters exposed to seawater, concrete structures are suffering from varying degrees of sulfate erosion, which greatly affects the durability and service life of concrete projects.

[0003] To ensure the durability of concrete projects, sulfate-resistant Portland cement (referred to as sulfate-resistant cement) is often used in engineering. Although the raw materials used in sulfate-resistant cement are basically the same as those of Portland cement, there are great differences in the requirements for the clinker mineral composition. It is necessary to limit the content of tricalcium aluminate (C3A) and tricalcium silicate (C3S) in the clinker to improve the ability of the cement to resist sulfate corrosion.

[0004] In the field of concrete admixtures, water-reducing agents are the most widely used and have the widest application range. As the third-generation high-performance concrete admixture, polycarboxylate-based water-reducing agents (PCE) have been increasing in production year by year due to their excellent water-reducing and dispersing properties, as well as energy-saving and environmental protection characteristics. However, general polycarboxylate high-performance water-reducing agents have poor performance retention for sulfate-resistant cement, or basically no use effect. This is because components such as gypsum and fly ash added to sulfate-resistant cement have a negative impact on general high-performance polycarboxylate water-reducing agents, resulting in poor general adaptability. The typical phenomenon is that the initial state of the concrete is good, but the change over time is fast. For example, the fluidity of the cement paste at 30 min can drop from the initial 200 mm to an unmeasurable level, indirectly making it difficult to guarantee the quality performance of the concrete.

[0005] For slow-release polycarboxylate water-reducing agents, there are currently some related technologies. For example, Chinese Patent Publication No. CN119661788A discloses a slow-release polycarboxylate water-reducing agent and a preparation method thereof, which can achieve the slow release of water-reducing performance. However, since this technology is not targeted at sulfate-resistant cement, there are some deficiencies: on the one hand, in the sulfate-resistant cement environment, its molecular structure cannot effectively resist the interference of gypsum and fly ash, resulting in a rapid attenuation of the water-reducing agent performance; on the other hand, the slow-release effect of this water-reducing agent is poor in sulfate-resistant cement, and in concrete projects using sulfate-resistant cement, it affects the slow-release performance of the water-reducing agent during long-term construction, not only reducing the fluidity and plasticity of the concrete, but also affecting the strength development and durability of the concrete.

[0006] In view of this, there is an urgent need for a slow-release polycarboxylate water reducer adapted to sulfate-resistant cement and its preparation method. Summary of the Invention

[0007] The purpose of the present invention is to provide a slow-release polycarboxylate water reducer adapted to sulfate-resistant cement and its preparation method to solve the problems raised in the above-mentioned background technology.

[0008] To achieve the above purpose, on the one hand, the present invention provides a slow-release polycarboxylate water reducer adapted to sulfate-resistant cement, comprising the following raw materials:

[0009] The dosage of unsaturated polyoxyethylene ether grafted cyclic siloxane (by weight) is 26 parts - 34 parts; the dosage of tetramethyltetravinylcyclotetrasiloxane is 12 parts - 18 parts; the dosage of acrylic acid is 18 parts - 22 parts; the dosage of methacrylic acid is 6 parts - 9 parts; the dosage of acrylamide is 4 parts - 8 parts; the dosage of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) is 4 parts - 7 parts; the dosage of the initiator is 0.6 parts - 1 part, and the initiator is ammonium persulfate; the dosage of the reducing agent is 0.2 parts - 0.6 parts, and the reducing agent is sodium bisulfite; the dosage of the chain transfer agent is 0.1 parts - 0.4 parts, and the chain transfer agent is mercaptoethanol; the pH regulator is sodium hydroxide solution; the dosage of deionized water is 120 parts - 160 parts;

[0010] The peroxy bond (-O-O-) in the ammonium persulfate molecule is unstable and will break down in the reaction system to generate sulfate radicals (SO4 - ); at the same time, sodium bisulfite undergoes an oxidation-reduction reaction with the oxidizing substance generated by the decomposition of ammonium persulfate to generate free radicals;

[0011] Acrylic acid, methacrylic acid, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) undergo a polymerization reaction under the action of free radicals to form a main chain structure. Polar groups such as carboxyl groups, sulfonic acid groups, and amide groups are distributed on the main chain, which can adsorb on the surface of cement particles and disperse the cement particles through electrostatic repulsion and steric hindrance effects, thereby achieving the water reduction effect;

[0012] Both the unsaturated polyoxyethylene ether-grafted cyclosiloxane and tetramethyltetravinylcyclotetrasiloxane contain carbon-carbon double bonds. During the polymerization reaction, their double bonds will undergo an addition reaction with the main-chain radicals, thereby being incorporated into the main chain or side chain of the polymer. Among them: the unsaturated polyoxyethylene ether-grafted cyclosiloxane and tetramethyltetravinylcyclotetrasiloxane participate in the polymerization reaction and are incorporated into the main chain or side chain of the polymer; the polyoxyethylene ether segment in the unsaturated polyoxyethylene ether-grafted cyclosiloxane provides a steric hindrance effect, which helps to disperse cement particles. At the same time, the cyclosiloxane structure enhances the corrosion resistance and stability of the water reducer; tetramethyltetravinylcyclotetrasiloxane further adjusts the molecular structure of the polymer, enhances its adsorption and dispersion performance on cement particles, and helps to achieve the slow-release performance of the water reducer, enabling it to play a role more durably in the sulfate-resistant cement system.

[0013] Mercaptoethanol reacts with free radicals during the polymerization process to control the molecular weight and molecular structure of the polymer, prevent the polymer from having too large a molecular weight or undergoing crosslinking, and enable the water reducer to have a degree of polymerization and performance that reach an equilibrium state.

[0014] In the present invention, ammonium persulfate decomposes to generate sulfate radicals, and sodium bisulfite undergoes an oxidation-reduction reaction with it to also generate free radicals. These free radicals initiate the polymerization of acrylic acid, methacrylic acid, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) to form a main chain with polar groups such as carboxyl, sulfonic acid, and amide groups. The main chain adsorbs on the surface of cement particles and, through electrostatic repulsion and steric hindrance effects, realizes the water-reducing effect of dispersing cement particles; at the same time, the unsaturated polyoxyethylene ether-grafted cyclosiloxane and tetramethyltetravinylcyclotetrasiloxane participate in the polymerization and are incorporated into the main chain or side chain. The former's polyoxyethylene ether segment provides steric hindrance to help disperse cement particles, and the cyclosiloxane structure enhances corrosion resistance and stability. The latter adjusts the molecular structure, enhances the adsorption and dispersion performance on cement particles, and realizes the slow-release effect; mercaptoethanol reacts with free radicals to control the molecular weight and structure of the polymer, prevent the molecular weight from being too large or undergoing crosslinking, and balance the degree of polymerization and performance of the water reducer.

[0015] Here, the peroxy bond in the ammonium persulfate molecule is unstable and will homolytically cleave to generate sulfate radicals in the reaction system; sodium bisulfite undergoes an oxidation-reduction reaction with the oxidizing substance generated by the decomposition of ammonium persulfate to further generate free radicals, thereby initiating the subsequent polymerization reaction. The reaction formula is as follows:

[0016] Decomposition of ammonium persulfate: (Homolytic cleavage to generate sulfate radicals);

[0017] Reaction of sodium bisulfite with sulfate radicals: (Oxidation-reduction reaction to generate new free radicals);

[0018] Acrylic acid, methacrylic acid, acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) are under the action of free radicals (such as ). Under the action of free radicals, the carbon-carbon double bonds (C=C) in the monomer molecules of acrylic acid, methacrylic acid, acrylamide, and AMPS are opened, and a free radical polymerization reaction occurs. The free radical first adds to the monomer to form a monomer free radical, and then the monomer free radical continuously adds to other monomer molecules, causing the molecular chain to gradually grow and form a polymer main chain with a degree of polymerization; the main chain structure with polar groups such as carboxyl (-COOH), sulfonic acid group (-SO3H), and amide group (-CONH2) distributed on the main chain can adsorb metal ions (such as calcium ion Ca 2+ ) on the surface of cement particles, and disperse the cement particles through electrostatic repulsion and steric hindrance effects to achieve the water reduction effect. The reaction formula is as follows:

[0019] Chain initiation: R · +CH2=CH-COOH→R-CH2-CH · -COOH (R · represents a free radical);

[0020] Chain growth: R-CH2-CH-COOH + nCH2=CH-COOH→R-(CH2-CH-COOH) n -CH2-CH.-COOH;

[0021] Chain termination (taking coupling termination as an example):

[0022] 2R-(CH2-CH-COOH) n -CH2-CH·-COOH→R-(CH2-CH-COOH) 2n+2 -R;

[0023] The unsaturated polyoxyethylene ether-grafted cyclosiloxane and tetramethyltetravinylcyclotetrasiloxane molecules contain carbon-carbon double bonds (C=C). During the polymerization reaction, their double bonds can undergo an addition reaction with the main chain free radicals, thereby being incorporated into the main chain or side chain of the polymer; the polyoxyethylene ether chain segment in the unsaturated polyoxyethylene ether-grafted cyclosiloxane can provide a steric hindrance effect, further hindering the aggregation of cement particles and contributing to the dispersion of cement particles; the cyclosiloxane structure enhances the corrosion resistance and stability of the water reducer; the tetramethyltetravinylcyclotetrasiloxane adjusts the molecular structure of the polymer, enhances the adsorption and dispersion performance of cement particles, and at the same time helps to achieve the slow release performance of the water reducer, enabling it to play a role more persistently in the sulfate-resistant cement system. The reaction formula is as follows:

[0024] R-(CH2-CH-COOH) n -CH2-CH-COOH + CH2=CH-[Si4C6H14 ] → R-(CH2-CH-COOH) n -CH2-CH-CH2-CH-

[0025] [Si4C6H 14 ];

[0026] The hydrogen atom on the thiol group (-SH) in the mercaptoethanol molecule is highly active. During the polymerization reaction, the chain free radical captures the hydrogen atom from the mercaptoethanol molecule, terminating the chain free radical and generating a new free radical (such as S · -CH2-CH2-OH); the new free radicals can initiate new monomer polymerization reactions, which can control the molecular weight and molecular structure of the polymer, prevent the polymer molecular weight from being too large or cross-linking, and make the polymerization degree and performance of the water reducer reach a balanced state. The reaction formula is as follows:

[0027] R-(CH2-CH-COOH) n -CH2-CH-COOH+HS-CH2-CH2-OH→R-(CH2-CH-COOH) n -CH2-CH2-COOH+S . -C

[0028] H2-CH2-OH.

[0029] On the other hand, according to Figure 1 As shown, the present invention provides a method for preparing a slow-release polycarboxylate water-reducing agent adapted for sulfate-resistant cement, comprising the following steps:

[0030] S1, pre-mixing operation: unsaturated polyoxyethylene ether grafted cyclosiloxane and tetramethyltetravinylcyclotetrasiloxane are added to a reaction kettle equipped with a stirring device and a thermometer, and then 60-80 parts of deionized water are added to the reaction kettle, and the stirrer is turned on, and stirred at a speed of 200r / min-300r / min for 20min-30min to fully blend the two to form a uniform mixed system;

[0031] S2. Preparation of monomer solution and initiator system: Add acrylic acid, methacrylic acid, acrylamide and 2-acrylamide-2-methylpropanesulfonic acid (AMPS) into a container, add 30-50 parts of deionized water, stir evenly, and prepare a monomer mixed solution; prepare two separate containers, put the initiator and the reducing agent into them respectively, dissolve each in 10-20 parts of deionized water, and prepare the required initiator solution and reducing agent solution;

[0032] S3. Low-temperature polymerization reaction: Turn on the refrigeration device of the reaction kettle and lower the temperature inside the reaction kettle to 10 - 20 °C; while the stirring device is continuously stirring, use a constant-pressure dropping funnel to dropwise add the monomer mixed solution, initiator solution, and reducing agent solution respectively, and the dropping process takes 2h - 3h; after the dropping is completed, keep the temperature inside the reaction kettle at 10 - 20 °C and continue the reaction for 3h - 4h to fully polymerize the monomers.

[0033] S4. Chain transfer reaction: After the polymerization reaction is completed, add a chain transfer agent to the reaction kettle, and the stirring device continues to stir for 1h - 2h to control the molecular weight and molecular structure of the polymer through the chain transfer reaction, avoiding excessive molecular weight or crosslinking.

[0034] S5. pH adjustment: Use a pH regulator to adjust the pH value of the reaction solution to 6 - 7 to make the solution neutral or weakly alkaline, so as to improve the stability of the water reducer.

[0035] S6. Product treatment: After adjusting the pH value, the stirring device continues to stir for 30min - 40min to make the solution mix evenly; discharge the prepared slow-release polycarboxylate water reducer suitable for sulfate-resistant cement from the reaction kettle and filter it to remove the existing impurities.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] 1. In the slow-release polycarboxylate water reducer suitable for sulfate-resistant cement and its preparation method, in terms of raw materials, the unsaturated polyoxyethylene ether-grafted cyclosiloxane and tetramethyltetravinylcyclotetrasiloxane participate in the polymerization. The former's polyoxyethylene ether chain segment provides steric hindrance, which is beneficial to the dispersion of cement particles, and the cyclosiloxane structure enhances corrosion resistance and stability; the latter adjusts the molecular structure, improves the adsorption and dispersion performance of cement particles, and increases the slow-release effect; from the preparation process, the low-temperature polymerization reaction can increase the controllability and stability of the reaction. The use of a chain transfer agent avoids excessive molecular weight or crosslinking of the polymer, making the performance of the water reducer reach a balance. In the sulfate-resistant cement system, this water reducer can effectively resist the interference of gypsum and fly ash, not only having good water-reducing effects in the initial stage but also maintaining the fluidity and plasticity of concrete for a long time, thereby improving the durability and construction quality of concrete projects.

[0038] 2. In the slow-release polycarboxylate water reducer suitable for sulfate-resistant cement and its preparation method, in terms of composition design, the polar groups such as carboxyl, sulfonic acid, and amide groups on the main chain can tightly adsorb to cement particles, achieving an efficient water-reducing effect through electrostatic repulsion and steric hindrance effects. At the same time, the siloxane structure can increase the corrosion resistance and stability of the water reducer, effectively resist sulfate erosion, thereby increasing the long-term stable working performance of concrete in a sulfate erosion environment, reducing quality problems caused by corrosion, and lowering the engineering maintenance cost and safety risks. Brief Description of the Drawings

[0039] Figure 1 This is a flowchart of the preparation method of the slow-release polycarboxylate water reducer adapted to the sulfate-resistant cement of the present invention. Detailed Embodiments

[0040] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of the present invention.

[0041] Embodiment 1: The embodiment of the present invention provides a preparation method of a slow-release polycarboxylate water reducer adapted to sulfate-resistant cement, which is used in the coastal breakwater concrete project and includes the following steps:

[0042] Pre-mixing operation: Add 34 parts of unsaturated polyoxyethylene ether grafted cyclic siloxane and 18 parts of tetramethyltetravinylcyclotetrasiloxane into a reaction kettle equipped with a stirring device and a thermometer, and then add 80 parts of deionized water into the reaction kettle; turn on the stirrer and stir at a speed of 300 r / min for 30 min to form a uniform mixed system;

[0043] Preparation of monomer solution and initiator system: Put 22 parts of acrylic acid, 9 parts of methacrylic acid, 8 parts of acrylamide and 7 parts of 2-acrylamido-2-methylpropanesulfonic acid into a clean container, and then add 50 parts of deionized water and stir evenly to make a monomer mixed solution; prepare two separate clean containers, put 1 part of ammonium persulfate and 0.6 part of sodium bisulfite into them respectively, and dissolve them in 20 parts of deionized water respectively to prepare the required initiator solution and reducing agent solution;

[0044] Low-temperature polymerization reaction: Turn on the refrigeration device of the reaction kettle and lower the temperature in the reaction kettle to 20 °C; under continuous stirring of the stirring device, use a constant-pressure dropping funnel to slowly drop the monomer mixed solution, initiator solution and reducing agent solution respectively, control the dropping speed, and complete the dropping process within 3 h; after the dropping is completed, keep the temperature in the reaction kettle at 20 °C and continue to react for 4 h to fully polymerize the monomers;

[0045] Chain transfer reaction: After the polymerization reaction is completed, add 0.4 part of mercaptoethanol as a chain transfer agent into the reaction kettle, and the stirring device continues to stir for 2 h.

[0046] pH adjustment: Use sodium hydroxide solution as a pH regulator to adjust the pH value of the reaction solution to 7 to make the solution neutral;

[0047] Product treatment: After adjusting the pH value, the stirring device continues to stir for 36 minutes, and then the prepared slow-release polycarboxylate superplasticizer for sulfate-resistant cement is discharged from the reaction kettle, filtered to remove existing impurities.

[0048] Comparative Example 1: The present invention provides a preparation method of a slow-release polycarboxylate superplasticizer for sulfate-resistant cement, which is used in coastal breakwater concrete projects and includes the following steps:

[0049] Premixing operation: Add 20 parts of unsaturated polyoxyethylene ether-grafted cyclic siloxane and 8 parts of tetramethyltetravinylcyclotetrasiloxane to a reaction kettle equipped with a stirring device and a thermometer, and then add 40 parts of deionized water to the reaction kettle; turn on the stirrer and stir at a speed of 150 r / min for 15 minutes to form a mixed system;

[0050] Preparation of monomer solution and initiation system: Put 10 parts of acrylic acid, 3 parts of methacrylic acid, 3 parts of acrylamide, and 3 parts of 2-acrylamido-2-methylpropanesulfonic acid into a clean container, and then add 20 parts of deionized water, stir evenly to make a monomer mixed solution; prepare two separate clean containers, put 0.3 parts of ammonium persulfate and 0.1 part of sodium bisulfite into them respectively, and dissolve them in 5 parts of deionized water to prepare the required initiator solution and reducing agent solution;

[0051] Low-temperature polymerization reaction: Turn on the refrigeration device of the reaction kettle and lower the temperature in the reaction kettle to 25 °C; under continuous stirring of the stirring device, use a constant pressure dropping funnel to slowly drop the monomer mixed solution, initiator solution, and reducing agent solution respectively, control the dropping speed so that the dropping process is completed within 4 hours; after the dropping is completed, keep the temperature in the reaction kettle at 25 °C and continue to react for 2 hours to polymerize the monomers;

[0052] Chain transfer reaction: After the polymerization reaction is completed, add 0.05 part of mercaptoethanol as a chain transfer agent to the reaction kettle, and the stirring device continues to stir for 0.5 hour;

[0053] pH adjustment: Use sodium hydroxide solution as a pH regulator to adjust the pH value of the reaction solution to 8 to make the solution alkaline;

[0054] Product treatment: The same as in Example 1.

[0055] Comparative Example 2: The present invention provides a preparation method of a slow-release polycarboxylate superplasticizer for sulfate-resistant cement, which is used in coastal breakwater concrete projects and includes the following steps:

[0056] Premixing operation: The same as in Example 1, but the stirrer stirs at a speed of 400 r / min for 40 minutes;

[0057] Preparation of monomer solution and initiation system: Add 30 parts of acrylic acid, 12 parts of methacrylic acid, 10 parts of acrylamide, and 10 parts of 2-acrylamido-2-methylpropanesulfonic acid into a clean container, then add 60 parts of deionized water and stir evenly to prepare a monomer mixed solution; Prepare two separate clean containers, put 1.5 parts of ammonium persulfate and 0.8 part of sodium bisulfite into them respectively, and dissolve each in 25 parts of deionized water to prepare the required initiator solution and reducing agent solution;

[0058] Low-temperature polymerization reaction: Turn on the refrigeration device of the reaction kettle and lower the temperature in the reaction kettle to 5°C; Under continuous stirring of the stirring device, use a constant-pressure dropping funnel to slowly drop the monomer mixed solution, initiator solution, and reducing agent solution respectively, control the dropping rate, and complete the dropping process within 1.5 h; After the dropping is completed, keep the temperature in the reaction kettle at 5°C and continue the reaction for 5 h to polymerize the monomers;

[0059] Chain transfer reaction: After the polymerization reaction is completed, add 0.6 part of mercaptoethanol as a chain transfer agent to the reaction kettle, and the stirring device continues to stir for 3 h;

[0060] pH adjustment: Use sodium hydroxide solution as a pH regulator to adjust the pH value of the reaction solution to 5 to make the solution acidic;

[0061] Product treatment: The same as in Example 1.

[0062] Comparative Example 3: The preparation method of a water reducer adapted to sulfate-resistant cement in the prior art is used in the coastal breakwater concrete project, including the following steps:

[0063] Premixing operation: Add a certain amount of ordinary polyether monomer and a small amount of silane coupling agent into the reaction kettle, add an appropriate amount of deionized water, and stir and mix;

[0064] Preparation of monomer solution and initiation system: Mix monomers such as acrylic acid and methacrylic acid, and add a certain amount of deionized water to prepare a monomer solution; Use a single initiator and dissolve it in a small amount of deionized water to prepare an initiator solution;

[0065] Polymerization reaction: Directly add the monomer solution and the initiator solution into the reaction kettle and carry out the reaction at room temperature. The reaction time is short to polymerize the monomers;

[0066] Subsequent treatment: After the polymerization reaction is completed, no chain transfer agent is added for the chain transfer reaction; Use other alkaline solutions to adjust the pH value to slightly alkaline, and obtain the water reducer product after simple filtration.

[0067] Example 2: The present invention provides a preparation method of a slow-release polycarboxylate water reducer adapted to sulfate-resistant cement, which is used in the highway bridge construction scenario in arid areas with high soil sulfate content, including the following steps:

[0068] Pre - mixing operation: Add 26 parts of unsaturated polyoxyethylene ether - grafted cyclic siloxane and 12 parts of tetramethyltetravinylcyclotetrasiloxane into a reaction kettle equipped with a stirring device and a thermometer, and then add 60 parts of deionized water into the reaction kettle; Turn on the stirrer and stir at a speed of 200 r / min for 20 min to form a uniform mixed system;

[0069] Preparation of monomer solution and initiation system: Add 18 parts of acrylic acid, 6 parts of methacrylic acid, 4 parts of acrylamide, and 4 parts of 2 - acrylamido - 2 - methylpropanesulfonic acid (AMPS) into a container, and then add 30 parts of deionized water and stir evenly to prepare a monomer mixed solution; Prepare two separate containers, put 0.6 parts of ammonium persulfate and 0.2 parts of sodium bisulfite into them respectively, and dissolve them in 10 parts of deionized water each to prepare an initiator solution and a reducing agent solution;

[0070] Low - temperature polymerization reaction: Turn on the refrigeration device of the reaction kettle and lower the temperature in the reaction kettle to 10°C; While the stirring device is continuously stirring, use a constant - pressure dropping funnel to drop the monomer mixed solution, the initiator solution, and the reducing agent solution respectively, and control the dropping rate to complete the dropping process within 2 h; After the dropping is completed, keep the temperature in the reaction kettle at 10°C and continue the reaction for 3 h to fully polymerize the monomers;

[0071] Chain - transfer reaction: After the polymerization reaction is completed, add 0.1 part of mercaptoethanol as a chain - transfer agent into the reaction kettle, and the stirring device continues to stir for 1 h;

[0072] pH adjustment: Use sodium hydroxide solution to adjust the pH value of the reaction solution to 6 to make the solution weakly alkaline;

[0073] Product treatment: After adjusting the pH value, the stirring device continues to stir for 30 min; Discharge the prepared slow - release polycarboxylate superplasticizer suitable for sulfate - resistant cement from the reaction kettle and filter it to remove the existing impurities.

[0074] Comparative Example 4: The present invention provides a preparation method of a slow - release polycarboxylate superplasticizer suitable for sulfate - resistant cement, which is used in the construction scenario of highway bridges in arid areas with high soil sulfate content, and includes the following steps:

[0075] Pre - mixing operation: Add 15 parts of unsaturated polyoxyethylene ether - grafted cyclic siloxane and 8 parts of tetramethyltetravinylcyclotetrasiloxane into a reaction kettle equipped with a stirring device and a thermometer, and then add 40 parts of deionized water into the reaction kettle; Turn on the stirrer and stir at a speed of 180 r / min for 18 min to form a mixed system;

[0076] Preparation of monomer solution and initiation system: Add 10 parts of acrylic acid, 4 parts of methacrylic acid, 2 parts of acrylamide, and 2 parts of 2-acrylamido-2-methylpropanesulfonic acid into a container, then add 20 parts of deionized water, stir evenly to make a monomer mixed solution; Prepare two separate containers, put 0.4 parts of ammonium persulfate and 0.15 parts of sodium bisulfite into them respectively, and dissolve each in 8 parts of deionized water to prepare an initiator solution and a reducing agent solution;

[0077] Low-temperature polymerization reaction: Turn on the refrigeration device of the reaction kettle, and lower the temperature inside the reaction kettle to 15 °C; Use a constant-pressure dropping funnel to drop the monomer mixed solution, initiator solution, and reducing agent solution respectively, control the dropping rate, and complete the dropping process within 2.5 h; After the dropping is completed, keep the temperature inside the reaction kettle at 15 °C and continue the reaction for 2.5 h to fully polymerize the monomers;

[0078] Chain transfer reaction: After the polymerization reaction is completed, add 0.08 parts of mercaptoethanol as a chain transfer agent to the reaction kettle, and the stirring device continues to stir for 0.8 h;

[0079] pH adjustment: Use sodium hydroxide solution to adjust the pH value of the reaction solution to 6.5 to make the solution weakly alkaline;

[0080] Product treatment: The same as in Example 2.

[0081] Comparative Example 5: The present invention provides a preparation method of a slow-release polycarboxylate water reducer adapted to sulfate-resistant cement for use in highway bridge construction scenarios in arid areas with high soil sulfate content, including the following steps:

[0082] Premixing operation: The same as in Example 2, but without adding unsaturated polyoxyethylene ether-grafted cyclic siloxane;

[0083] Preparation of monomer solution and initiation system: Add 25 parts of acrylic acid, 8 parts of methacrylic acid, 6 parts of acrylamide, and 6 parts of 2-acrylamido-2-methylpropanesulfonic acid into a container, then add 40 parts of deionized water, stir evenly to make a monomer mixed solution; Put 0.9 parts of ammonium persulfate and 0.5 parts of sodium bisulfite into another container and dissolve them in 15 parts of deionized water to prepare an initiator solution and a reducing agent solution;

[0084] Low-temperature polymerization reaction: Turn on the refrigeration device of the reaction kettle, and lower the temperature inside the reaction kettle to 8 °C; While the stirring device is continuously stirring, use a constant-pressure dropping funnel to drop the monomer mixed solution, initiator solution, and reducing agent solution respectively, control the dropping rate, and complete the dropping process within 1.8 h; After the dropping is completed, keep the temperature inside the reaction kettle at 8 °C and continue the reaction for 3.5 h to fully polymerize the monomers;

[0085] Chain transfer reaction: After the polymerization reaction is completed, 0.3 parts of mercaptoethanol is added to the reaction kettle as a chain transfer agent, and the stirring device continues to stir for 1.5 h;

[0086] pH adjustment: The pH value of the reaction solution is adjusted to 7.5 with sodium hydroxide solution to make the solution alkaline;

[0087] Product treatment: The same as in Example 2.

[0088] Comparative Example 6: The preparation method of a water reducing agent adapted to sulfate resistant cement in the prior art is adopted for the highway bridge construction scenario in arid areas with high soil sulfate content, including the following steps:

[0089] Premixing operation: Ordinary polyether and a small amount of modifier are added to the reaction kettle, and a certain amount of deionized water is added and stirred and mixed;

[0090] Preparation of monomer solution and initiation system: Select some common monomers and mix them, and add deionized water to make a monomer solution; Use a conventional initiator and dissolve it in an appropriate amount of deionized water to make an initiator solution;

[0091] Polymerization reaction: The monomer solution and the initiator solution are added to the reaction kettle and reacted at a certain temperature. The reaction time is determined according to experience to polymerize the monomers;

[0092] Subsequent treatment: After the reaction is completed, no chain transfer reaction is carried out; Use other alkaline substances to adjust the pH value to an appropriate range, and obtain the water reducing agent product through simple filtration.

[0093] Test Example 1: The slow-release polycarboxylate water reducing agent provided in Example 1 is compared with Comparative Example 1, Comparative Example 2 and Comparative Example 3

[0094] Test conditions: In the simulated environment of coastal breakwater concrete engineering, simulate the erosion of seawater on concrete; Use sulfate resistant cement, the water-cement ratio is fixed at 0.4, and the dosage of water reducing agent is 1.5% of the cement quality; The environmental temperature is controlled at 20±2°C to simulate the average temperature environment of this area, and the humidity is maintained at 60±5% to simulate the humidity conditions of coastal areas; In the concrete mix ratio, the cement dosage is 400 kg / m 3 , the sand ratio is 35%, the maximum particle size of the coarse aggregate is 20 mm, and at the same time, the sulfate concentration of seawater is simulated to be 3000 mg / L to ensure the consistency and comparability of the test.

[0095] The test method is as follows:

[0096] Cement paste fluidity test: The test was carried out in accordance with the "Test Method for Measuring the Fluidity of Cement Paste" (GB / T8077-2012); Weigh 300 g of sulfate-resistant cement, add the water reducer solution and water calculated according to the dosage of the water reducer, and stir evenly using the specified stirring method. Then quickly pour it into the truncated cone mold. Lift the mold steadily, measure the maximum diameter of the cement paste flowing on the glass plate and the diameter in the direction perpendicular to it, and take the average value as the cement paste fluidity, with the unit of mm;

[0097] Concrete slump test: The test was carried out in accordance with the "Standard Test Method for Properties of Fresh Concrete" (GB / T50080-2016); Put the fresh concrete mixture into the slump cone in three layers according to the standard method, and insert the tamper 25 times for each layer. The insertion should be carried out from the outside to the center along the spiral direction. When tamping the bottom layer, the tamper should penetrate the entire depth. When tamping the second and top layers, the tamper should penetrate this layer and insert into the next layer by 20 - 30 mm. After tamping the top layer, scrape off the excess concrete and level it with a trowel; Lift the slump cone vertically and measure the height of the fresh concrete mixture falling, which is the slump, with the unit of mm.

[0098] Concrete time-dependent loss test: At 0 min, 30 min, and 60 min after the fresh concrete mixture is stirred, test its slump according to the above concrete slump test method, and calculate the slump loss values at different time points. The slump loss value = slump at 0 min - slump at a certain time point.

[0099] Concrete compressive strength test: In accordance with the "Standard Test Method for Mechanical Properties of Ordinary Concrete" (GB / T50081-2019), make concrete cube specimens with dimensions of 150 mm×150 mm×150 mm, with 3 specimens in each group; Cure them under the curing conditions (temperature 20±2 °C, relative humidity above 95%) until the age (3 d, 7 d, 28 d), and test their compressive strength, with the unit of MPa; When testing the compressive strength, place the specimen on the lower platen of the testing machine. The bearing surface of the specimen should be perpendicular to the top surface during molding. Start the testing machine. When the upper platen approaches the specimen, adjust the ball seat to make the contact balanced, and apply the load continuously and evenly. The loading speed is: when the concrete strength grade < C30, take 0.3 - 0.5 MPa per second; when the concrete strength grade ≥ C30 and < C60, take 0.5 - 0.8 MPa per second; when the concrete strength grade ≥ C60, take 0.8 - 1.0 MPa per second. When the specimen is approaching failure and starts to deform rapidly, stop adjusting the throttle of the testing machine until the specimen fails, and then record the failure load; The compressive strength calculation formula is: where f cu is the compressive strength of the concrete cube specimen (MPa), F is the failure load of the specimen (N), and A is the bearing area of the specimen (mm 2 ).

[0100] Table 1 shows the detection indexes of the slow-release polycarboxylate water reducer used in the concrete project of coastal breakwaters.

[0101] Example 1 Comparative Example 1 Comparative Example 2 Comparative Example 3 Cement paste fluidity (mm) 240 180 200 160 Initial slump (mm) 220 160 180 140 Slump loss after 30 min (mm) 30 80 60 100 Slump loss after 60 min (mm) 50 120 100 150 3-day compressive strength (MPa) 20 12 15 10 7-day compressive strength (MPa) 35 22 28 18 28-day compressive strength (MPa) 50 30 38 25 Compressive strength loss rate after 28-day immersion (%) 10 30 20 40

[0102] As shown in Table 1, the slow-release polycarboxylate water reducer adapted to sulfate-resistant cement in Example 1 has good performance in the simulated environment of coastal breakwater concrete projects. Its cement paste fluidity reaches 240 mm, the initial slump is 220 mm, and the slump losses at 30 min and 60 min are only 30 mm and 50 mm respectively, indicating that the water reducer has good initial dispersion performance and good slow-release performance, and can maintain the fluidity and plasticity of concrete for a long time. At the same time, its compressive strengths at 3 d, 7 d, and 28 d are 20 MPa, 35 MPa, and 50 MPa respectively, which are significantly higher than those of the comparative examples, indicating that the water reducer can effectively promote the development of concrete strength. In addition, the compressive strength loss rate after 28-day immersion is only 10%, showing that the water reducer has obvious effects in resisting sulfate erosion and can enhance the durability of concrete structures.

[0103] Test Example 2: Compare the slow-release polycarboxylate water reducer provided in Example 2 with Comparative Example 4, Comparative Example 5, and Comparative Example 6.

[0104] Test conditions: In the simulated environment of highway bridge construction in arid areas with high soil sulfate content, simulate the erosion of high sulfate in the soil of this area on concrete; use sulfate-resistant cement, the water-cement ratio is set to 0.38, and the water reducer dosage is 1.2% of the cement mass; the environmental temperature is maintained at 25 ± 2 °C to simulate the actual temperature of this area, and the humidity is 30 ± 5%, which conforms to the humidity characteristics of arid areas; in the concrete mix ratio, the cement dosage is 420 kg / m 3 , the sand ratio is 38%, the maximum particle size of the coarse aggregate is 25 mm, and at the same time, simulate the sulfate concentration in the soil is 5000 mg / kg.

[0105] The test method is as follows:

[0106] Cement paste fluidity test: The same as Test Example 1;

[0107] Concrete slump test: The same as Test Example 1;

[0108] Concrete time-dependent loss test: The same as Test Example 1;

[0109] Concrete compressive strength test: The same as Test Example 1.

[0110] Test for the sulfate erosion resistance performance of concrete: The dry-wet cycling method is adopted. The concrete specimens cured for 28 days are immersed in a sodium sulfate solution with a mass fraction of 10% for 16 hours, and then dried in an oven at (80±5)°C for 8 hours for one cycle. After 20 dry-wet cycles, observe the appearance change of the specimens and test their compressive strength loss rate. The compressive strength loss rate = (compressive strength before cycling - compressive strength after cycling) / compressive strength before cycling × 100%.

[0111] Table 2 shows the detection indexes of the slow-release polycarboxylate water reducer used in the construction scenario of highway bridges in arid areas with high soil sulfate content

[0112]

[0113]

[0114] As shown in Table 2, in the simulated environment of highway bridge construction in arid areas with high soil sulfate content, the water reducer of Example 2 also performs excellently; the fluidity of cement paste is 230 mm, the initial slump is 210 mm, and the slump losses at 30 min and 60 min are 25 mm and 40 mm respectively, indicating that it can also maintain good water-reducing and slow-release properties in this environment; in terms of compressive strength, the compressive strengths at 3 d, 7 d, and 28 d are 18 MPa, 32 MPa, and 48 MPa respectively, which are better than those of the comparative examples, helping to improve the early and late strengths of the concrete structure; the compressive strength loss rate after 20 dry-wet cycles is only 8%, showing that this water reducer can effectively improve the erosion resistance of concrete in the high-sulfate soil environment and enable the long-term stability of the concrete structure.

[0115] In summary, the slow-release polycarboxylate water reducer adapted to sulfate-resistant cement of the present invention can effectively resist the interference of gypsum and fly ash in different engineering environments through raw material selection and preparation process. It not only has a good initial water-reducing effect, but also has good slow-release performance, can maintain the working performance of concrete for a long time, improve the strength and sulfate erosion resistance of concrete, and thus enhance the durability and construction quality of concrete projects.

[0116] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions in the specification are only preferred examples of the present invention and do not limit the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A slow-release polycarboxylate water reducer adapted to sulfate-resistant cement, characterized in that It includes the following raw materials: Unsaturated polyoxyethylene ether grafted cyclic siloxane, tetramethyltetravinylcyclotetrasiloxane, acrylic acid, methacrylic acid, acrylamide, 2-acrylamido-2-methylpropanesulfonic acid, initiator, reducing agent, chain transfer agent, pH regulator and deionized water; The peroxy bond in the initiator molecule is unstable and will break down in the reaction system to generate sulfate radicals; at the same time, the reducing agent undergoes an oxidation-reduction reaction with the oxidizing substance generated by the decomposition of the initiator to generate radicals; The acrylic acid, methacrylic acid, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid undergo a polymerization reaction under the action of radicals to form a main chain structure, and polar groups such as carboxyl groups, sulfonic acid groups and amide groups are distributed on the main chain, which can adsorb on the surface of cement particles and disperse the cement particles through electrostatic repulsion and steric hindrance effects; Both the unsaturated polyoxyethylene ether grafted cyclic siloxane and tetramethyltetravinylcyclotetrasiloxane molecules contain carbon-carbon double bonds. During the polymerization reaction process, their double bonds will undergo an addition reaction with the main chain radicals, thereby being incorporated into the main chain or side chain of the polymer.

2. The slow-release polycarboxylate water reducer adapted to sulfate-resistant cement according to claim 1, wherein The dosage of the unsaturated polyoxyethylene ether grafted cyclic siloxane is 26 parts - 34 parts; the dosage of the tetramethyltetravinylcyclotetrasiloxane is 12 parts - 18 parts; the dosage of the acrylic acid is 18 parts - 22 parts; the dosage of the methacrylic acid is 6 parts - 9 parts; the dosage of acrylamide is 4 parts - 8 parts; the dosage of the 2-acrylamido-2-methylpropanesulfonic acid is 4 parts - 7 parts; the dosage of the initiator is 0.6 parts - 1 part; the dosage of the reducing agent is 0.2 parts - 0.6 parts; the dosage of the chain transfer agent is 0.1 parts - 0.4 parts; the dosage of the deionized water is 120 parts - 160 parts.

3. The sustained-release polycarboxylate water reducer adapted to sulfate-resistant cement according to claim 1, wherein The initiator uses ammonium persulfate; the reducing agent uses sodium bisulfite; the chain transfer agent uses mercaptoethanol; the pH regulator uses sodium hydroxide solution.

4. A preparation method of a slow-release polycarboxylate water reducer for adapting sulfate-resistant cement according to any one of claims 1-3, characterized in that, It includes the following steps: S1. Premixing operation: Add the unsaturated polyoxyethylene ether grafted cyclic siloxane and tetramethyltetravinylcyclotetrasiloxane into a reaction kettle equipped with a stirring device and a thermometer, and then add 60 - 80 parts of deionized water into the reaction kettle. Start the stirrer to stir to form a uniform mixed system; S2. Preparation of monomer solution and initiation system: Add acrylic acid, methacrylic acid, acrylamide and 2-acrylamido-2-methylpropanesulfonic acid (AMPS) into a container, and then add 30 - 50 parts of deionized water and stir evenly to prepare a monomer mixed solution; then prepare two independent containers, put the initiator and the reducing agent into them respectively, and dissolve them in 10 - 20 parts of deionized water respectively to prepare the required initiator solution and reducing agent solution; S3. Low-temperature polymerization reaction: Turn on the refrigeration device of the reaction kettle to cool down the temperature. Under continuous stirring of the stirring device, use a constant pressure dropping funnel to dropwise add the monomer mixed solution, the initiator solution and the reducing agent solution respectively; after the dropping is completed, keep the temperature in the reaction kettle and continue to react for 3h - 4h to fully polymerize the monomers; S4. Chain transfer reaction: After the polymerization reaction is completed, add the chain transfer agent into the reaction kettle and continue to stir with the stirring device; S5, pH adjustment: Use a pH regulator to adjust the pH value of the reaction solution; S6, product treatment: After adjusting the pH value, the stirring device continues to stir to make the solution mix evenly; Release the prepared slow-release polycarboxylate superplasticizer for sulfate-resistant cement from the reaction kettle and filter it.

5. The preparation method of the slow-release polycarboxylate water reducer adapted to sulfate-resistant cement according to claim 4, characterized in that, In the above S1, the stirrer stirs at a speed of 200 r / min - 300 r / min for 20 min - 30 min.

6. The preparation method of the slow-release polycarboxylate water reducer adapted to sulfate-resistant cement according to claim 4, characterized in that, In the above S3, the refrigeration device of the reaction kettle cools the temperature to 10 - 20 °C.

7. The preparation method of the slow-release polycarboxylate water reducer adapted to sulfate-resistant cement according to claim 4, characterized in that, In the above S3, the dropping process of the monomer mixed solution, initiator solution and reducing agent solution takes 2 h - 3 h.

8. The preparation method of the slow-release polycarboxylate water reducer adapted to sulfate-resistant cement according to claim 4, characterized in that, In the above S4, the stirring device continues to stir for 1 h - 2 h.

9. The preparation method of the slow-release polycarboxylate water reducer adapted to sulfate-resistant cement according to claim 4, characterized in that, In the above S5, the pH value is adjusted to 6 - 7 to make the solution neutral or weakly alkaline.

10. The preparation method of the slow-release polycarboxylate water reducer adapted to sulfate-resistant cement according to claim 4, characterized in that, In the above S6, the stirring device continues to stir for 30 min - 40 min.

Images