Composite admixture for inhibiting invalid adsorption of calcined clay to water reducing agent as well as use method and application of composite admixture

Abstract

The invention relates to the technical field of cement additives, in particular to a composite additive for inhibiting invalid adsorption of calcined clay to a water reducing agent as well as a use method and application of the composite additive. The composite additive is composed of a component A and a component B, the component A is a dicationic sacrificial agent which is prepared by reacting poly (N, N-dimethylallylamine) with tetrakis hydroxymethyl phosphonium sulfate in an aqueous solution at 60-80 DEG C; and the component B is a polycarboxylic acid type water reducing agent which is prepared from an unsaturated polyether macromonomer, an unsaturated carboxylic acid monomer and a phosphate group-containing unsaturated monomer through an aqueous solution free radical copolymerization reaction. Through the synergistic effect of the component A dicationic sacrificial agent and the component B specific structure water reducing agent, invalid adsorption of calcined clay to the water reducing agent is powerfully blocked, the use amount of the water reducing agent can be reduced, the initial fluidity and slump retention capacity of concrete are remarkably improved, the preparation process is mature, raw materials are easy to obtain, and the preparation method is suitable for large-scale industrial production and has wide application prospects. The method can be widely applied to green concrete.

Description

Technical Field

[0001] This application relates to the field of cement additives technology, and in particular to a composite admixture that inhibits the ineffective adsorption of water-reducing agents by calcined clay, as well as its usage and application. Background Technology

[0002] Driven by the "dual carbon" strategy, calcined clay is increasingly used as an auxiliary cementitious material in concrete, which can reduce cement usage and carbon emissions. However, the layered silicate minerals (such as montmorillonite) remaining in calcined clay have extremely strong adsorption properties, which can cause strong ineffective adsorption of polycarboxylate superplasticizer (PCE) molecules. This prevents the superplasticizer from fully exerting its dispersing effect, seriously deteriorating the workability of concrete. To ensure the construction performance of concrete, it is necessary to significantly increase the amount of superplasticizer, resulting in a surge in costs.

[0003] The existing solutions to this problem mainly fall into three categories: One approach is simply to increase the amount of PCE used, but this method is not only costly but also has limited effectiveness. Secondly, common small molecule sacrificial agents (such as sodium sulfate and triethanolamine) are compounded, but these sacrificial agents do not last long and are difficult to meet the continuous adsorption requirements of calcined clay. Third, new types of PCE can be synthesized (such as by adjusting the side chain density or by modifying with quaternary ammonium salts). However, the synthesis process of quaternary ammonium salt modified PCE is complex and its stability is poor in the high alkalinity environment of cement systems. The scheme of adjusting the side chain density is essentially a passive defense and is not effective in the face of strongly adsorbent calcined clay.

[0004] Therefore, developing solutions that can strongly block adsorption sites without significantly increasing costs and are easy to industrialize has become an urgent need for the industry.

[0005] Furthermore, while existing solutions have reported the use of cationic polymers (such as poly(N,N-dimethylallylamine)) or quaternary ammonium salts to modify PCE to address clay adsorption, these solutions have significant limitations: 1) the effect of small-molecule cationic sacrificial agents is not long-lasting; 2) when poly(N,N-dimethylallylamine) is used alone, its adsorption strength and coverage efficiency for clay are still insufficient to completely protect the PCE; 3) the synthesis of quaternary ammonium salt-modified PCE is complex and may be unstable in highly alkaline environments. In particular, for calcined clay added as a major cementing component, its total adsorption amount and persistence are far higher than that of clay occasionally mixed in the aggregate, leading to a rapid decline in the effectiveness of existing anti-mud technology.

[0006] Therefore, developing a novel admixture scheme with strong adsorption, long-lasting effect, and good compatibility with cement systems to inhibit the ineffective adsorption of water-reducing agents by calcined clay is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] This application addresses the aforementioned technical challenges by providing a composite admixture solution based on a "dual synergistic mechanism".

[0008] This application provides a composite admixture that inhibits the ineffective adsorption of water-reducing agents by calcined clay: The composite admixture includes component A and component B; wherein, component A is a dicationic sacrificial agent, which is prepared by reacting poly(N,N-dimethylallylamine) with tetramethylolphosphine sulfate in an aqueous solution at 60-80°C; component B is a polycarboxylate superplasticizer, which is prepared by free radical copolymerization of a monomer mixture in an aqueous solution; wherein, the monomer mixture includes unsaturated polyether macromonomers, unsaturated carboxylate monomers, and unsaturated monomers containing phosphate groups.

[0009] Its core design philosophy is: 1. First-level synergy: Innovatively employing a dual-cationic synergistic sacrificial agent (component A) prepared by reacting poly(N,N-dimethylallylamine) with tetramethylolphosphine sulfate. Poly(N,N-dimethylallylamine) provides a long-chain cationic backbone and high charge density, while THPS acts as a crosslinking agent and phosphoric acid source. The reaction product not only possesses stronger positive charge, but the quaternary ammonium salt groups and phosphate groups on its molecular chain can generate a dual-cationic synergistic adsorption effect, binding more firmly and densely to the negatively charged sites on the calcined clay surface. The resulting organic protective film is more stable and can more persistently shield the adsorption sites between clay layers and on the surface.

[0010] 2. Second Synergistic Effect: An anti-adsorption PCE (component B) with a gradient distribution of phosphate groups was designed. Through a synthesis process of "concentrated dropwise addition" of phosphorus-containing monomers in the early stages, the front end of the polymer molecular chain (i.e., the first polymerized segment) is enriched with a high density of phosphate groups. Phosphate groups have a stronger chelating ability for calcium ions on the surface of cement particles than carboxyl groups. During use, because component A has pre-"blocked" most of the clay adsorption sites, component B molecules can more quickly and firmly adsorb onto the surface of cement particles using the high-density phosphate groups at the front end of its chain segments as an "anchor," while its rear polyether side chains can rapidly extend to exert steric hindrance. This structure of "strong anchoring at the front end and rapid extension at the rear end" adapts to the competitive adsorption environment in the presence of sacrificial agents.

[0011] 3. System Synergy: The "A first, B later" approach is key to achieving the aforementioned dual synergy. Component A, added beforehand, has ample time to occupy the clay surface. Component B, added subsequently, exhibits high selectivity and a fast adsorption rate on the cement surface amidst competition for adsorption at limited clay sites not covered by A and on the cement particle surface. This efficiently "guides" the water-reducing agent to its intended location, maximizing the utilization of the water-reducing agent dosage.

[0012] In some embodiments, the composite admixture consists of component A and component B; component A is a dicationic sacrificial agent, which is prepared by reacting poly(N,N-dimethylallylamine) with tetramethylolphosphine sulfate in an aqueous solution at 60-80°C and then cooling; wherein the dry basis mass ratio of poly(N,N-dimethylallylamine) to tetramethylolphosphine sulfate is 1:0.20 to 1:0.35.

[0013] In some embodiments, the preparation process of component A includes the following steps: Base material preparation: Poly(N,N-dimethylallylamine) is mixed with deionized water, heated to 40–50°C and stirred to dissolve, and the pH of the system is adjusted to 7.5–8.5; Dropping solution preparation: Tetramethylolphosphine sulfate is mixed with deionized water; Reaction: The dropping solution is added dropwise to the base material over a period of 1.5–2 hours, and after the addition is complete, the mixture is reacted at 60–80°C for 1.5–2 hours to obtain the final product.

[0014] In some embodiments, component B is prepared by aqueous free radical copolymerization of unsaturated polyether macromonomers, unsaturated carboxylic acid monomers, and unsaturated monomers containing phosphate groups at a reaction temperature of 15–40°C under the action of an initiator, a reducing agent, and a chain transfer agent.

[0015] In some embodiments, component B is a polycarboxylate superplasticizer, whose polymer molecules contain structural units derived from unsaturated polyether macromonomers, unsaturated carboxylic acid monomers, and phosphate-containing unsaturated monomers.

[0016] In some embodiments, the unsaturated polyether macromonomer is a combination of at least two of isopentenyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, and ethylene glycol monovinyl polyethylene glycol ether, with a molecular weight of 1200 to 6000; the unsaturated carboxylic acid monomer is at least one of acrylic acid, methacrylic acid, methyl methacrylate, and dimethylaminoethyl methacrylate; and the phosphate-containing unsaturated monomer is one or more of methacryloyloxyethyl phosphate and vinylphosphonic acid.

[0017] In some embodiments, the phosphate-containing unsaturated monomer accounts for 15% to 35% of the total mass of the unsaturated carboxylic acid and the phosphate-containing unsaturated monomer.

[0018] In some embodiments, the preparation process of component B includes the following steps: Base material preparation: Mix unsaturated polyether macromonomers with deionized water; Preparation of the first drop: Mix the unsaturated monomer containing phosphate groups with deionized water; Preparation of the second drop: Mix the unsaturated carboxylic acid monomer with deionized water; Preparation of the third drop: Dissolve the initiator, reducing agent, and chain transfer agent in deionized water; Copolymerization reaction: The first, second and third drops of the solution are added simultaneously at 15-40℃. After the addition is complete, the mixture is kept at this temperature for 0.5-1 hour to mature. After cooling, the pH is adjusted to 5-7.0 to obtain the final product. In this process, more than 80% of the total amount of the unsaturated monomer containing phosphate groups is added during the first third of the total dropping time; the total dropping time is 1.5 to 3 hours.

[0019] In some embodiments, the mass ratio of the unsaturated polyether macromonomer to the unsaturated carboxylic acid monomer is 200:(10-20). This application also provides a method for using a composite admixture to inhibit the ineffective adsorption of water-reducing agents by calcined clay: during concrete mixing, component A of the composite admixture described above is pre-mixed with mixing water and cementitious materials for 30-60 seconds, and then component B is added and mixing continues until homogeneous; wherein the solid dosage of component A is 0.05%-0.2% of the total mass of cementitious materials, and the solid dosage of component B is 0.1%-0.25% of the total mass of cementitious materials.

[0020] This application also provides the application of the composite admixture as described in any of the preceding claims in green concrete.

[0021] Compared with the prior art, this application has the following advantages: This application utilizes the synergistic effect of component A (dual-cationic sacrificial agent) and component B (specifically structured water-reducing agent) to strongly block the ineffective adsorption of water-reducing agent by calcined clay, thereby reducing the amount of water-reducing agent required and significantly improving the initial fluidity and slump retention of concrete. In addition, the preparation process of the composite admixture components of this application is mature and the raw materials are readily available, making it suitable for large-scale industrial production and applicable to green concrete. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be described clearly and completely below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0023] This application also provides the following embodiments and comparative examples: 1. Preparation of raw material components Preparation of sacrificial agent (component A), sample A: In a four-necked flask equipped with a condenser, stirrer, and thermometer, add 100g of poly(N,N-dimethylallylamine) (solid, Mw approximately 10,000) and 150g of deionized water, and stir to dilute. Heat to 40–50°C and stir to dissolve. Add an appropriate amount of 10% sodium hydroxide aqueous solution to adjust the pH of the system to approximately 8. Slowly add a solution prepared from 45 parts by weight of tetramethylphosphoric acid sulfate (PTHS, 75% aqueous solution) and 100 parts by weight of water over 2 hours. During the addition, replenish the sodium hydroxide aqueous solution to ensure the pH of the reaction solution is maintained at approximately 8. After the addition is complete, continue the reaction at 60°C for another 2 hours. After the reaction is complete, cool to room temperature; this is the sacrificial agent component A.

[0024] Preparation of sacrificial agent (component A), sample A-1: In a four-necked flask equipped with a condenser, stirrer, and thermometer, add 100g of poly(N,N-dimethylallylamine) (solid, Mw approximately 10,000) and 150g of deionized water, and stir to dilute. Heat to 40–50°C and stir to dissolve. Add an appropriate amount of 10% sodium hydroxide aqueous solution to adjust the pH of the system to approximately 8. Slowly add a solution prepared from 35 parts by weight of tetramethylphosphoric acid sulfate (PTHS, 75% aqueous solution) and 100 parts by weight of water over 1.5 hours. During the addition, replenish the sodium hydroxide aqueous solution to ensure the pH of the reaction solution is maintained at approximately 8. After the addition is complete, continue the reaction at 65°C for 1.5 hours. After the reaction is complete, cool to room temperature; this is the sacrificial agent component A.

[0025] Preparation of polycarboxylate superplasticizer (component B): The molecular weight is 1200 to 6000, and the combination of at least two of isopentenyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, and ethylene glycol monovinyl polyethylene glycol ether.

[0026] Sample B: (1) Preparation of base material: In a four-necked flask equipped with a stirrer, condenser, constant pressure dropping funnel and thermometer, add 120g of isopentenyl polyoxyethylene ether (molecular weight of 2400), 80g of methyl allyl polyoxyethylene ether (molecular weight of 6000) and 100g of deionized water, stir to dissolve, and then add 1.5g of hydrogen peroxide.

[0027] (2) Preparation of the first drop: Mix 8g of methacryloyloxyethyl phosphate (PMEA) with 20g of deionized water.

[0028] (3) Preparation of the second drop: Mix 12g of acrylic acid (AA) and 3g of methacrylic acid with 30g of deionized water.

[0029] (4) Preparation of the third drop: Dissolve 0.3g of vitamin C (VC) and 0.8g of mercaptopropionic acid in 40g of deionized water.

[0030] (5) Polymerization reaction: When the reactor temperature reaches 25-40℃, the first, second, and third drops of liquid are added simultaneously. The first drop is added in a concentrated manner in the early stage (80% of the first drop is added within the first third of the total adding time), and the total adding time for the first drop is 3 hours. The second and third drops are added at a uniform rate within 3 hours.

[0031] After the addition is complete, keep it warm and mature for 1 hour. Then adjust the pH to 5-7.0 with a 30% sodium hydroxide aqueous solution to obtain the polycarboxylate superplasticizer.

[0032] Sample B-1: (1) Preparation of base material: In a four-necked flask equipped with a stirrer, condenser, constant pressure dropping funnel and thermometer, add 100g of ethylene glycol monovinyl polyethylene glycol ether (molecular weight of 5000) and 100g of ethylene glycol monovinyl polyethylene glycol ether (molecular weight of 1200) and 80g of deionized water, stir to dissolve, and then add 1.2g of hydrogen peroxide.

[0033] (2) Preparation of the first drop: Mix 8g of methacryloyloxyethyl phosphate (PMEA) with 30g of deionized water; (3) Preparation of the second drop: Mix 16g of acrylic acid (AA) and 2g of methyl methacrylate with 30g of deionized water; (4) Preparation of the third drop: Dissolve 0.4g of vitamin C (VC) and 0.9g of mercaptopropionic acid in 40g of deionized water.

[0034] (5) Polymerization reaction: When the temperature of the reactor is 15-25℃, the first drop, the second drop and the third drop are added simultaneously. The first drop is added in a concentrated manner in the early stage (80% of the first drop is added in the first third of the total adding time), and the total adding time of the first drop is 1.5h; the second drop and the third drop are added at a uniform rate within 1.5 hours.

[0035] After the addition is complete, keep warm and mature for 0.5 hours. Then adjust the pH to 5-7.0 with a 30% sodium hydroxide aqueous solution to obtain the final product.

[0036] Sample B-2: The only difference between sample B-2 and sample B-1 is the amount of unsaturated carboxylic acid monomer and phosphate-containing unsaturated monomer used. Specifically, sample B-2 contains 15g of unsaturated carboxylic acid monomer (12g acrylic acid + 3g methacrylic acid) and 3g of methacryloyloxyethyl phosphate. The other preparation processes and steps are the same as those for sample B-1, and the first drop is also added in a concentrated manner in the early stage.

[0037] Sample B-3: The preparation process and steps are the same as those of sample B, with the only difference being that the first drop was added at a constant rate (all monomers were added at a constant rate within 3 hours).

[0038] Sample B-4: The preparation process and steps are the same as those of sample B-1. The only difference from sample B is that the polyether macromonomer used is 200g of ethylene glycol monovinyl polyethylene glycol ether (molecular weight 3000).

[0039] 2. Preparation of composite admixtures in the examples and comparative examples: Example 1 During the concrete mixing process, sample A is first premixed with mixing water and cementitious materials for 60 seconds, and then sample B is added and mixed evenly to obtain the concrete mixture.

[0040] Among them, the solid content of sample A is 0.10% of the total mass of cementitious material, and the solid content of sample B is 0.20% of the total mass of cementitious material.

[0041] Example 2 During the concrete mixing process, sample A is first premixed with mixing water and cementitious materials for 60 seconds, and then sample B-1 is added and mixed evenly to obtain the concrete mixture.

[0042] Among them, the solid content of sample A is 0.10% of the total mass of cementitious material, and the solid content of sample B-1 is 0.20% of the total mass of cementitious material.

[0043] Example 3 During the concrete mixing process, sample A is first premixed with mixing water and cementitious materials for 30 seconds, and then sample B-2 is added and mixed evenly to obtain the concrete mixture.

[0044] Among them, the solid content of sample A is 0.10% of the total mass of cementitious material, and the solid content of sample B-2 is 0.20% of the total mass of cementitious material.

[0045] Comparative Example 1 (Difference from Example 2: Sample A was replaced with an equal mass of commercially available polyquaternium sacrificial agent) During the concrete mixing process, the commercially available polyquaternary ammonium salt sacrificial agent is first premixed with the mixing water and cementitious materials for 30 seconds, and then sample B-1 is added and the mixture is stirred evenly to obtain the concrete mixture.

[0046] Among them, the solid dosage of commercially available polyquaternary ammonium sacrificial agent is 0.10% of the total mass of cementitious material, and the solid dosage of sample B-1 is 0.20% of the total mass of cementitious material.

[0047] Comparative Example 2 (Difference from Example 2: Only sample B-2 was incorporated) The difference from Example 2 is that sample A is not added during the concrete mixing process; instead, sample B-2 is added and mixed evenly with mixing water and cementitious materials to obtain a concrete mixture.

[0048] Among them, the solid content of sample B-2 is 0.3% of the total mass of cementitious material.

[0049] Comparative Example 3 (Difference from Example 3: Sample B-2 was replaced with an equal mass of commercially available phosphate-modified anti-mud PCE) The difference from Example 3 is that, in the concrete mixing process, Sample A is first premixed with mixing water and cementitious materials for 60 seconds, and then commercially available phosphate-modified anti-mud PCE is added and stirred evenly to obtain the concrete mixture.

[0050] Among them, the solid content of sample A is 0.10% of the total mass of cementitious materials, and the solid content of phosphate modified anti-mud PCE is 0.20% of the total mass of cementitious materials.

[0051] Comparative Example 4 (Difference from Example 2: Samples A and B-1 were replaced with an equal mass of phosphate-modified anti-mud PCE) The difference from Example 2 is that, during the concrete mixing process, the phosphate-modified anti-mud PCE is premixed with the mixing water and cementitious materials for 60 seconds, and then mixed evenly to obtain the concrete mixture.

[0052] The phosphate-modified anti-mud PCE content is 0.3% of the total mass of the cementitious material.

[0053] Comparative Example 5 (Difference from Example 3: Sample B-2 was replaced with sample B-3 of equal mass) The difference from Example 3 is that, in the concrete mixing process, sample A is first premixed with mixing water and cementitious materials for 60 seconds, and then sample B-3 is added and stirred evenly to obtain concrete mixture.

[0054] Among them, the solid content of sample A is 0.10% of the total mass of cementitious material, and the solid content of sample B-3 is 0.20% of the total mass of cementitious material.

[0055] Comparative Example 6 (Difference from Example 3: Sample B-2 was replaced with sample B-4 of equal mass) The difference from Example 3 is that, during the concrete mixing process, Sample A is first pre-mixed with mixing water and cementitious materials for 60 seconds, and then Sample B-4 is added and stirred evenly to obtain the concrete mixture.

[0056] Among them, the solid content of sample A is 0.10% of the total mass of cementitious material, and the solid content of sample B-4 is 0.20% of the total mass of cementitious material.

[0057] Comparative Example 7 (commercially available polyquaternium sacrificial agent + commercially available ordinary PCE) The difference from Example 2 is that, in the concrete mixing process, the commercially available polyquaternary ammonium salt sacrificial agent is first premixed with the mixing water and cementitious materials for 60 seconds, and then commercially available ordinary PCE is added and stirred evenly to obtain the concrete mixture.

[0058] The solid dosage of commercially available polyquaternary ammonium sacrificial agent is 0.10% of the total mass of cementitious materials, and the solid dosage of commercially available ordinary PCE is 0.20% of the total mass of cementitious materials.

[0059] The additive addition details for the examples and comparative examples are summarized in Table 1 below: Table 1

[0060] Performance application tests of the products in the examples and comparative examples: I. Product Application Performance Testing in Examples and Comparative Examples Raw material specifications: Cement: P·O42.5; Calcined clay: Metakaolin (calcined at 800℃); Aggregate: Manufactured sand (fineness modulus 2.8), 5-20mm continuously graded crushed stone.

[0061] Calcined clay was used, and its effects on concrete, as specified in GB8076-2008 "Concrete Admixtures," were tested according to the methods outlined in the examples and comparative proportions. The concrete mix proportion was: cement 280 kg / m³. 3 120 kg of calcined clay and 750 kg / m³ of sand 3 Stone 1050kg / m 3 160kg / m³ of water 3 The results are shown in Table 2.

[0062] Table 2. Concrete performance test results

[0063] In Table 2, the "-" indicates that the loss is too great and there is no expansion.

[0064] The test results show that: Compared to the embodiments, the comparative examples have the following shortcomings: Comparative Example 1: Commercially available polyquaternary ammonium salt sacrificial agent was used, but its adsorption strength and persistence were insufficient, with a spread of only 420 mm in 1 hour; Comparative Example 2: Without using a sacrificial agent, simply increasing the amount of water-reducing agent to 0.30% still could not effectively improve initial dispersibility and dispersion retention; Comparative Example 3: Using the sacrificial agent of this invention and commercially available quaternary ammonium salt modified anti-sludge, the spread of the anti-sludge decreased significantly after 1 hour; Comparative Example 4: Using only phosphate-modified anti-mud PCE, the anti-mud effect is generally poor. Comparative Example 5: When component B-3 was added using a uniform dropwise process, the phosphate groups failed to form an effective gradient protective layer, thus failing to effectively improve the initial dispersibility and dispersion retention. Comparative Example 6: Using sample B-4 (single polyether structure), although it was compounded with component A, the distribution of phosphate groups did not match the adsorption kinetics, and the expansion rate after 1 hour was still low.

[0065] Comparative Example 7: Using commercially available polyquaternium sacrificial agent and commercially available ordinary PCE, the dispersibility was average and the dispersion retention was poor.

[0066] Second, performance testing (adaptability testing) of the products from the examples and comparative examples applied to different types of calcined clay: The test was conducted according to the method for determining the fluidity of cement paste in GB / T8077-2023 "Test Method for Homogeneity of Concrete Admixtures", with a water-cement ratio of 0.29.

[0067] The fixed amount of cement is 240g, the amount of clay is 60g, and the amount of water is 87g. The amount of sacrificial agent and water-reducing agent refers to the dry basis mass of the total amount of cement and clay. The sacrificial agent is added by mixing it with cement and clay for 30 seconds first, and then adding water and water-reducing agent.

[0068] The results are shown in Table 3.

[0069] Table 3

[0070] The specific characteristics of different clay types are shown in Table 4 below: Table 4

[0071] In summary, the combination in Example 2 exhibits the best performance and adaptability across different types of calcined clay.

[0072] This application should include at least the following design concept, mechanism of action, and beneficial effects: Significant synergistic inhibition effect: Component A, through the synergistic effect of two cations, strongly and persistently occupies the adsorption sites of calcined clay; Component B utilizes the phosphate groups with a gradient distribution on its molecular chain to achieve "self-preferential adsorption". The two work synergistically from different pathways, completely solving the problem of ineffective adsorption of water-reducing agents by calcined clay. Compared with existing technologies, the anti-adsorption effect is more stable and longer-lasting. Significantly reduces the amount of water-reducing agent used: The composite admixture of this application can give full play to the dispersing effect of the water-reducing agent, and reduce the amount of PCE used while ensuring the workability of concrete, thus significantly reducing the production cost of concrete. Improved concrete workability: It not only gives concrete excellent initial fluidity, but also effectively improves slump retention, avoiding the problem of excessive slump loss during construction and ensuring smooth construction. Mature technology and easy to industrialize: Both components of the composite additive are prepared using a mature aqueous phase synthesis process. The raw materials are readily available and the cost is controllable. The reaction conditions are mild and no special equipment is required, enabling stable and large-scale production. Good compatibility: It has good compatibility with cement systems and will not have a negative impact on the setting, hardening and mechanical properties of concrete, making it widely applicable.

[0073] Finally, it should be noted that: The abbreviation for tetrahydroxymethylphosphine sulfate is THPS.

[0074] The specific parameters or some commonly used reagents or raw materials in the above embodiments are specific embodiments or preferred embodiments under the concept of this application, and are not intended to limit them; those skilled in the art can make adaptive adjustments within the concept and protection scope of this application.

[0075] The above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A composite admixture for inhibiting the ineffective adsorption of water-reducing agents by calcined clay, characterized in that, Includes component A and component B; Component A is a dicationic sacrificial agent, which is prepared by reacting poly(N,N-dimethylallylamine) with tetramethylolphosphine sulfate in an aqueous solution at 60-80°C. Component B is a polycarboxylate superplasticizer, which is prepared by free radical copolymerization of a monomer mixture in aqueous solution; wherein the monomer mixture includes unsaturated polyether macromonomers, unsaturated carboxylate monomers, and unsaturated monomers containing phosphate groups.

2. The composite admixture according to claim 1, characterized in that, It consists of component A and component B; Component A is a dicationic sacrificial agent, which is prepared by reacting poly(N,N-dimethylallylamine) with tetramethylolphosphine sulfate in an aqueous solution at 60-80°C and then cooling; wherein the dry basis mass ratio of poly(N,N-dimethylallylamine) to tetramethylolphosphine sulfate is 1:0.20 to 1:0.

35. Component B is prepared by aqueous free radical copolymerization of unsaturated polyether macromonomers, unsaturated carboxylic acid monomers and unsaturated monomers containing phosphate groups at 15–40 °C under the action of initiators, reducing agents and chain transfer agents.

3. The composite admixture according to claim 1 or 2, characterized in that, The preparation process of component A includes the following steps: Base material preparation: Mix poly(N,N-dimethylallylamine) with deionized water, heat to 40-50℃ and stir to dissolve, and adjust the pH of the system to 7.5-8.5; Preparation of the dropping solution: Mix tetrahydroxymethylphosphonic acid sulfate with deionized water; Reaction: Add the liquid dropwise to the substrate over a period of 1.5 to 2 hours. After the addition is complete, react at 60 to 80°C for 1.5 to 2 hours to obtain the final product.

4. The composite admixture according to claim 1 or 2, characterized in that: Component B is a polycarboxylate superplasticizer, whose polymer molecules contain structural units derived from unsaturated polyether macromonomers, unsaturated carboxylic acid monomers, and unsaturated monomers containing phosphate groups.

5. The composite admixture according to claim 1 or 2, characterized in that, The unsaturated polyether macromonomer is at least two of the following: isopentenyl polyoxyethylene ether, methyl allyl polyoxyethylene ether, and ethylene glycol monovinyl polyethylene glycol ether, with a molecular weight of 1200 to 6000. The unsaturated carboxylic acid monomer is at least one of acrylic acid, methacrylic acid, methyl methacrylate, and dimethylaminoethyl methacrylate; The unsaturated monomer containing a phosphate group is one or more combinations of methacryloyloxyethyl phosphate and vinylphosphonic acid.

6. The composite admixture according to claim 1 or 2, characterized in that, The phosphate-containing unsaturated monomer accounts for 15% to 35% of the total mass of the unsaturated carboxylic acid and the phosphate-containing unsaturated monomer.

7. The composite admixture according to claim 1, characterized in that: The preparation process of component B includes the following steps: Base material preparation: Mix unsaturated polyether macromonomers with deionized water; Preparation of the first drop: Mix the unsaturated monomer containing phosphate groups with deionized water; Preparation of the second drop: Mix the unsaturated carboxylic acid monomer with deionized water; Preparation of the third drop: Dissolve the initiator, reducing agent, and chain transfer agent in deionized water; Copolymerization reaction: The first, second and third drops of the solution are added simultaneously at 15-40℃. After the addition is complete, the mixture is kept at this temperature for 0.5-1 hour to mature. After cooling, the pH is adjusted to 5-7.0 to obtain the final product. In this process, the unsaturated monomer containing phosphate groups completes more than 80% of its total addition within the first third of the total dropping time; the total dropping time is the total dropping time of the first drop, which is 1.5 to 3 hours.

8. The composite admixture according to claim 1 or 2, characterized in that: The mass ratio of the unsaturated polyether macromonomer to the unsaturated carboxylic acid monomer is 200:(10-20).

9. A method for using a composite admixture to inhibit the ineffective adsorption of water-reducing agents by calcined clay, characterized in that, During the concrete mixing process, component A of the composite admixture as described in any one of claims 1-8 is premixed with mixing water and cementitious materials for 30-60 seconds, and then component B is added and the mixture is stirred until homogeneous. The solid content of component A is 0.05% to 0.2% of the total mass of cementitious materials, and the solid content of component B is 0.1% to 0.25% of the total mass of cementitious materials.

10. The application of the composite admixture as described in any one of claims 1-4 in green concrete.

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