Low-sensitivity early-strength polycarboxylate superplasticizer and preparation method thereof

Abstract

The invention discloses a low-sensitivity early-strength polycarboxylate superplasticizer and a preparation method thereof, and belongs to the technical field of concrete admixtures. The water reducing agent is prepared from ethylene glycol monovinyl polyoxyethylene ether, maleoyl chitosan oligosaccharide, 3-[[2-(methacryloyloxy) ethyl] dimethylammonium] propionate, unsaturated carboxylic acid and other raw materials through low-temperature copolymerization in a redox system. Maleoyl chitosan oligosaccharide and a specific cationic monomer are introduced to generate a synergistic effect: the cationic monomer preferentially anchors clay, and a chitosan oligosaccharide derivative provides a rigid skeleton and dynamic dispersion compensation, so that excellent mud resistance, low sensitivity and early strength are jointly realized. The product has strong adaptability to cement, can significantly improve the early strength and workability retention ability of mud-containing aggregate concrete, and is suitable for high-performance concrete engineering under complex raw material conditions.

Description

Technical Field

[0001] This invention belongs to the technical field of cement concrete admixture materials, specifically relating to a low-sensitivity, early-strength polycarboxylate superplasticizer and its preparation method. Background Technology

[0002] Polycarboxylate superplasticizers, as third-generation high-performance superplasticizers, play a crucial role in modern concrete technology and construction engineering. However, with the increasing diversification of concrete raw material sources and greater quality fluctuations, traditional polycarboxylate superplasticizers have revealed several systemic technical bottlenecks in practical applications.

[0003] First, the inadequacy of these products' adaptability to different cement compositions is particularly evident. Factors such as the tricalcium aluminate content in the cement, and differences in gypsum morphology and dissolution rate, significantly impact their dispersion effect, even causing a sharp drop in fluidity and excessively rapid loss over time, demonstrating a high sensitivity to the cement's chemical environment. Second, the presence of clay minerals in the aggregate poses another serious challenge. Expansive clays, especially montmorillonite, not only adsorb large amounts of water-reducing agent molecules, leading to a reduction in effective content, but also disrupt the rheological state of the paste through interlayer water absorption and ion exchange. This manifests primarily as decreased initial fluidity and poor slump retention in concrete, and in severe cases, even affects the later-stage strength development and durability of concrete. Meanwhile, most early-strength polycarboxylate superplasticizers currently on the market rely on introducing strongly polar functional groups (such as sulfonic acid groups and amide groups) to accelerate the hydration process. However, this structural design often sacrifices the optimal adsorption conformation of molecules on the cement particle surface, making it difficult to achieve efficient synergy between early-strength function and dispersion performance. Most products rely on conventional monomers such as acrylic acid for preparation. To achieve early strength, complex compounding is often required, which not only increases the difficulty of quality control but may also cause new compatibility problems due to competitive adsorption between components. In addition, existing polycarboxylate superplasticizers mainly focus on improving a single performance, making it difficult to achieve synergistic optimization of low sensitivity and early strength.

[0004] For example, existing patent CN202311533484.1 discloses an environmentally friendly energy-saving water-reducing agent and its preparation process. Specifically, it includes the following steps: Step 1: Quaternizing chitosan to obtain quaternized chitosan; then grafting it with hyperbranched monomers to obtain modified chitosan; Step 2: Grafting the modified chitosan with acid anhydrides, then grafting it with unsaturated monomers to obtain a polycarboxylate water-reducing agent. While this method improves the dispersion performance of the water-reducing agent, the modified chitosan introduces chloride ion risks, and its technical route focuses on "slow release and delayed hydration," failing to solve the technical challenges of "low sensitivity and early strength."

[0005] Existing patent CN202411007546.X discloses a low-temperature early-strength water-reducing agent and its preparation method. This invention involves first subjecting monomers obtained from amidation and esterification reactions to a Michael addition reaction to obtain polyester macromonomers, then reacting them with polyether macromonomers, carboxylic acid small monomers, and sulfonic acid small monomers via free radical polymerization. Following this, functional modifications are achieved through Hofmann degradation and amidation reactions, and finally, a Thiol-ene reaction is conducted with thiolized trehalose to synthesize the low-temperature early-strength water-reducing agent. This technical route is complex, with multiple reaction steps leading to high production costs and poor batch stability. Furthermore, the introduction of thiolized trehalose poses a potential biodegradation risk, which is detrimental to long-term storage and engineering applications. In addition, its reliance on sulfonic acid monomers to enhance early-strength performance easily exacerbates sensitivity to mud-containing aggregates, making it difficult to achieve a balance between low sensitivity and early strength. Moreover, its implementation relies on multiple polymeric raw materials such as polyether macromonomers and amidated chitosan; the strong spatial structure between these materials easily induces cross-linking side reactions, leading to gelation problems in the product and affecting its application stability.

[0006] Therefore, developing a water-reducing agent that can simultaneously and synergistically address the high sensitivity to cement / clay and also possess excellent early strength is a long-standing but unresolved technical challenge in this field. Summary of the Invention

[0007] This invention addresses the technical bottleneck of existing water-reducing agents that struggle to simultaneously achieve low sensitivity and early strength performance. Through molecular structure design and optimized preparation processes, it provides a low-sensitivity, early-strength polycarboxylate superplasticizer. This superplasticizer not only exhibits excellent adaptability to variations in cement type and clay content, effectively reducing sensitivity, but also significantly promotes early strength development in concrete while maintaining excellent dispersion and slump retention. The technical solution employed in this invention involves introducing maleylated chitosan oligosaccharide segments and a specific cationic functional monomer, 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate, into the polycarboxylate superplasticizer molecular structure. This synergistically regulates the molecular adsorption properties, charge density, and interaction with cement hydration products, ensuring the uniformity of the product's molecular structure and the stability of its performance, thereby obtaining a low-sensitivity, early-strength polycarboxylate superplasticizer with superior overall performance.

[0008] To achieve the above-mentioned technical objectives, the technical solution adopted by the present invention is as follows: A low-sensitivity, early-strength polycarboxylate superplasticizer comprises the following raw materials: base material, oxidant, mixed solution A, mixed solution B, mixed solution C, and neutralizing solution. The amounts of each raw material by weight are as follows: The base material includes ethylene glycol monovinyl polyoxyethylene ether (EPEG). The mixture comprises: 380-395 parts of maleylated chitosan oligosaccharide aqueous solution, 95-119 parts of maleylated chitosan oligosaccharide aqueous solution, and 333-345 parts of pure water; 2-6 parts of oxidant; the mixture A comprises 11-13.5 parts of 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate and 22-28 parts of pure water; the mixture B comprises 28.8-41.5 parts of unsaturated carboxylic acid and 20-38 parts of pure water; the mixture C comprises 0.3-0.5 parts of reducing agent, 1.9-3.9 parts of chain transfer agent, and 22-38 parts of pure water; and the neutralizing solution is 18-27 parts of 30% sodium hydroxide aqueous solution.

[0009] Furthermore, the degree of polymerization of the ethylene glycol monovinyl polyoxyethylene ether is 44-80.

[0010] Furthermore, the preparation method of the maleylated chitosan oligosaccharide aqueous solution is as follows: 10 parts by weight of fully dried chitosan oligosaccharide are dissolved in 100-150 parts of anhydrous dimethyl sulfoxide (DMSO). Under nitrogen protection, 20-30 parts by weight of a 40% maleic anhydride DMSO solution are slowly added dropwise to the chitosan oligosaccharide solution over 0.5-1 hour. After the addition is complete, the mixture is continuously stirred and reacted at 50±5℃ for 8-10 hours. After the reaction, the product is cooled to room temperature, filtered, purified, and then diluted with pure water to prepare a 10% aqueous solution of the maleylated chitosan oligosaccharide product.

[0011] Furthermore, the degree of polymerization of the chitosan oligosaccharide is ≤10.

[0012] This invention utilizes natural biomass chitosan oligosaccharide as a raw material and develops a functional monomer through chemical modification. The specific process involves: under an inert gas atmosphere, the amino groups on the chitosan oligosaccharide chain undergo a ring-opening amidation reaction with maleic anhydride, thereby simultaneously grafting unsaturated double bonds and carboxyl groups onto its rigid backbone to obtain maleylated chitosan oligosaccharide. In the copolymerization stage, this functional monomer copolymerizes with EPEG-type polyether macromonomers under the action of an initiation system, introducing the rigid structure of the chitosan oligosaccharide into the polycarboxylic acid molecule backbone in the form of side chains through its unsaturated double bonds. This design brings two benefits: firstly, the newly added suspended carboxyl groups effectively enhance the controllable adjustment ability of cement paste dispersibility; secondly, the residual amide groups can utilize their coordination effect to capture calcium ions released in the early stages of cement hydration, forming a stable complex structure, thereby promoting the early strength development of concrete; simultaneously, relying on its inherent rigid backbone and positive charge characteristics, it can also play a nucleation guiding and catalytic role in early hydration, promoting the formation of early-strength phases such as ettringite, thereby significantly improving the early compressive strength of hardened concrete.

[0013] Furthermore, the oxidant is hydrogen peroxide and / or ammonium persulfate.

[0014] Furthermore, the unsaturated carboxylic acid is acrylic acid and / or methacrylic acid.

[0015] Furthermore, the reducing agent is one or more of sodium formaldehyde sulfoxylate, L-ascorbic acid, or sodium dioctyl succinate E51.

[0016] Furthermore, the chain transfer agent is one or more of mercaptoacetic acid, mercaptopropionic acid, or 2-mercaptoethanol.

[0017] A method for preparing a low-sensitivity, early-strength polycarboxylate superplasticizer includes the following steps: (1) Preparation of mixed droplet solution: After adding the measured amount of pure water from mixed solution A to a container, nitrogen gas is introduced for protection, and then 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate is added and mixed evenly to obtain mixed solution A; the unsaturated carboxylic acid in mixed solution B is mixed evenly with pure water to obtain mixed solution B; the reducing agent is dissolved in pure water, and then the measured amount of chain transfer agent is added to obtain mixed solution C; (2) Polymerization reaction process: First, the pure water, maleyl chitosan oligosaccharide aqueous solution and ethylene glycol monovinyl polyoxyethylene ether (EPEG) measured in the base material are stirred and dissolved in the reaction vessel. Then, the system is cooled to 5-10℃ and an oxidant is added and stirred for 3-5 minutes. Next, mixed solution A, mixed solution B and mixed solution C are added dropwise simultaneously within 1-2 hours. The process temperature is controlled to be ≤15℃. During the entire reaction process, the pH value of the system is maintained in the range of 6-8 by gradually adding neutralizing solution. After the dropwise addition is completed, the system is kept at the same temperature for 1-2 hours to obtain the target product.

[0018] Beneficial effects: (1) This invention aims to simultaneously overcome the challenges of low sensitivity and early strength by synergistically combining a functional monomer with a specific structure (maleicyl chitosan oligosaccharide) with a specific cationic monomer (3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate). First, regarding resistance to mud sensitivity, the amide bond and carboxyl group in the maleicyl chitosan oligosaccharide molecule can effectively adsorb onto the surface of cement particles, adjust the thickness of the hydration diffusion layer, and significantly improve the slurry's tolerance to changes in the external environment, thus achieving low sensitivity. The cationic monomer 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate (providing strong electrostatic anchoring) first binds to the negatively charged clay to form protective sites, reducing the adsorption and consumption of the main dispersion segments (EPEG and carboxyl groups) by the clay. At the same time, the rigid skeleton and amide group of maleicyl chitosan oligosaccharide further stabilize this effect, and the carboxyl groups released by its slow hydrolysis can dynamically replenish the consumed dispersion groups. The synergy of the two enhances the dispersion stability and adaptability of the system in complex environments.

[0019] (2) Secondly, regarding early strength and dispersibility, the amide group and rigid structure of maleic acylated chitosan oligosaccharide can selectively promote the formation of early strength minerals through coordination and nucleation effects without excessively interfering with the dispersion of cement particles; while the cationic monomer provides electrostatic anchoring and can also form a hydrogen bond network with cement hydration products through its ester group, further enhancing the early strength development rate. Under the synergistic effect of the two, not only is the dispersion failure problem caused by clay adsorption of traditional water-reducing agents effectively avoided, but the setting and hardening process of cement-based materials is also significantly accelerated, achieving early strength while maintaining high fluidity, making it suitable for concrete engineering applications in complex sand and gravel environments.

[0020] (3) In summary, regarding anti-mud properties, the cationic monomer preferentially and reversibly occupies the active sites of clay through electrostatic interactions, while the rigid side chains of maleylated chitosan oligosaccharides enhance the adsorption stability of the molecules on complex interfaces. The amide groups continuously replenish carboxyl groups after hydrolysis, forming a dynamic anti-mud protection-dispersion compensation dual mechanism. Cement paste test data shows that the decrease in fluidity (approximately 10-20 mm) in the example with 0.5% montmorillonite content was far less than that of commercially available sample 1 (approximately 50 mm) and sample 2 (approximately 70 mm). Regarding the synergistic effect of early strength and dispersion, the amide groups and rigid framework provided by the chitosan oligosaccharide derivatives can precisely promote the formation of the early strength phase without disrupting the overall dispersion system; the introduction of the cationic monomer unexpectedly optimized the adsorption layer structure of the copolymer on the surface of mud-containing cement particles, making the dispersion effect more durable. Concrete performance tests show that, under conditions containing mud (Formula 2), the 1-day compressive strength of the example concrete remained above 15 MPa, and the 7-day strength was almost unaffected by the mud content. In contrast, all comparative examples and commercially available samples showed a significant decrease in strength after the presence of mud. The stepwise performance degradation of Comparative Examples 1-3 clearly demonstrates that the synergistic effect of this invention disappears when any key component is missing. This high-level balance of 'mud resistance-early strength-dispersion' triple performance achieved through specific molecular structure design represents a significant technological advancement and provides a reliable guarantee for the application of high-performance concrete in complex environments. Detailed Implementation

[0021] The technical solution of the present invention will be further described below with reference to specific embodiments, but it is not limited thereto.

[0022] Example 1 A low-sensitivity, early-strength polycarboxylate superplasticizer comprises the following raw materials: a base material, an oxidant, a mixed solution A, a mixed solution B, a mixed solution C, and a neutralizing solution. The amounts of each raw material by weight are as follows: the base material comprises 395 parts of ethylene glycol monovinyl polyoxyethylene ether (EPEG), 118.5 parts of maleicylated chitosan oligosaccharide aqueous solution, and 344 parts of pure water; the oxidant comprises 3.9 parts; the mixed solution A comprises 11 parts of 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate and 22 parts of pure water; the mixed solution B comprises 28.8 parts of unsaturated carboxylic acid and 30 parts of pure water; the mixed solution C comprises 0.36 parts of reducing agent, 2.44 parts of chain transfer agent, and 26 parts of pure water; the neutralizing solution is 18 parts of a 30% sodium hydroxide aqueous solution.

[0023] The degree of polymerization of the ethylene glycol monovinyl polyoxyethylene ether is 67.

[0024] The preparation method of the maleylated chitosan oligosaccharide aqueous solution is as follows: 10 parts by weight of fully dried chitosan oligosaccharide are dissolved in 100 parts by weight of anhydrous dimethyl sulfoxide (DMSO). Under nitrogen protection, 20 parts by weight of a 40% maleic anhydride DMSO solution are slowly added dropwise to the chitosan oligosaccharide solution over 0.5 hours. After the addition is complete, the mixture is continuously stirred and reacted at 50±5℃ for 8 hours. After the reaction, the product is cooled to room temperature, filtered, purified, and then diluted with pure water to prepare a 10% aqueous solution of the maleylated chitosan oligosaccharide product.

[0025] The degree of polymerization of the chitosan oligosaccharide is ≤10.

[0026] The oxidant is hydrogen peroxide.

[0027] The unsaturated carboxylic acid is acrylic acid.

[0028] The reducing agent is sodium dioctyl succinate sulfonate E51.

[0029] The chain transfer agent is 2-mercaptoethanol.

[0030] A method for preparing a low-sensitivity, early-strength polycarboxylate superplasticizer includes the following steps: (1) Preparation of mixed droplet solution: After adding the measured amount of pure water from mixed solution A to a container, nitrogen gas is introduced for protection, and then 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate is added and mixed evenly to obtain mixed solution A; the unsaturated carboxylic acid in mixed solution B is mixed evenly with pure water to obtain mixed solution B; the reducing agent is dissolved in pure water, and then the measured amount of chain transfer agent is added to obtain mixed solution C; (2) Polymerization reaction process: First, the pure water, maleic oxychitosan oligosaccharide aqueous solution and ethylene glycol monovinyl polyoxyethylene ether (EPEG) measured in the base material are stirred and dissolved in the reaction vessel. Then, the system is cooled to 5-10℃ and an oxidant is added and stirred for 3 minutes. Next, mixed solution A, mixed solution B and mixed solution C are added dropwise simultaneously within 1 hour, and the process temperature is controlled to be ≤15℃. During the entire reaction process, the pH value of the system is maintained in the range of 6-8 by gradually adding neutralizing solution. After the dropwise addition is completed, the system is kept at the same temperature for 1 hour to obtain the target product.

[0031] Example 2 A low-sensitivity, early-strength polycarboxylate superplasticizer comprises the following raw materials: a base material, an oxidant, a mixed solution A, a mixed solution B, a mixed solution C, and a neutralizing solution. The amounts of each raw material by weight are as follows: the base material comprises 394 parts of ethylene glycol monovinyl polyoxyethylene ether (EPEG), 119 parts of maleic oxychitosan aqueous solution, and 342 parts of pure water; 6 parts of oxidant; the mixed solution A comprises 12.5 parts of 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate and 25 parts of pure water; the mixed solution B comprises 34.1 parts of unsaturated carboxylic acid and 20 parts of pure water; the mixed solution C comprises 0.5 parts of reducing agent, 3.9 parts of chain transfer agent, and 22 parts of pure water; and the neutralizing solution is 21 parts of a 30% sodium hydroxide aqueous solution.

[0032] The degree of polymerization of the ethylene glycol monovinyl polyoxyethylene ether is 78.

[0033] The preparation method of the maleylated chitosan oligosaccharide aqueous solution is as follows: 10 parts by weight of fully dried chitosan oligosaccharide are dissolved in 120 parts by weight of anhydrous dimethyl sulfoxide (DMSO). Under nitrogen protection, 25 parts by weight of a 40% maleic anhydride DMSO solution are slowly added dropwise to the chitosan oligosaccharide solution over 1 hour. After the addition is complete, the mixture is stirred continuously at 50±5℃ for 8 hours. After the reaction, the product is cooled to room temperature, filtered, purified, and then diluted with pure water to prepare a 10% aqueous solution of the maleylated chitosan oligosaccharide product.

[0034] The degree of polymerization of the chitosan oligosaccharide is ≤10.

[0035] The oxidant is ammonium persulfate.

[0036] The unsaturated carboxylic acid is methacrylic acid.

[0037] The reducing agent is L-ascorbic acid.

[0038] The chain transfer agent is 2-mercaptoethanol.

[0039] A method for preparing a low-sensitivity, early-strength polycarboxylate superplasticizer includes the following steps: (1) Preparation of mixed droplet solution: After adding the measured amount of pure water from mixed solution A to a container, nitrogen gas is introduced for protection, and then 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate is added and mixed evenly to obtain mixed solution A; the unsaturated carboxylic acid in mixed solution B is mixed evenly with pure water to obtain mixed solution B; the reducing agent is dissolved in pure water, and then the measured amount of chain transfer agent is added to obtain mixed solution C; (2) Polymerization reaction process: First, the pure water, maleic oxychitosan oligosaccharide aqueous solution and ethylene glycol monovinyl polyoxyethylene ether (EPEG) measured in the base material are stirred and dissolved in the reaction vessel. Then, the system is cooled to 5-10℃ and an oxidant is added and stirred for 3 minutes. Next, mixed solution A, mixed solution B and mixed solution C are added dropwise simultaneously within 1 hour, and the process temperature is controlled to be ≤15℃. During the entire reaction process, the pH value of the system is maintained in the range of 6-8 by gradually adding neutralizing solution. After the dropwise addition is completed, the system is kept at the same temperature for 2 hours to obtain the target product.

[0040] Example 3 A low-sensitivity, early-strength polycarboxylate superplasticizer comprises the following raw materials: a base material, an oxidant, a mixed solution A, a mixed solution B, a mixed solution C, and a neutralizing solution. The amounts of each raw material by weight are as follows: the base material comprises 380 parts of ethylene glycol monovinyl polyoxyethylene ether (EPEG), 95 parts of maleic oxychitosan aqueous solution, and 333 parts of pure water; the oxidant comprises 3.8 parts; the mixed solution A comprises 13.5 parts of 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate and 28 parts of pure water; the mixed solution B comprises 41.5 parts of unsaturated carboxylic acid and 38 parts of pure water; the mixed solution C comprises 0.3 parts of reducing agent, 1.9 parts of chain transfer agent, and 38 parts of pure water; and the neutralizing solution comprises 27 parts of a 30% sodium hydroxide aqueous solution.

[0041] The degree of polymerization of the ethylene glycol monovinyl polyoxyethylene ether is 67.

[0042] The preparation method of the maleylated chitosan oligosaccharide aqueous solution is as follows: 10 parts by weight of fully dried chitosan oligosaccharide are dissolved in 150 parts by weight of anhydrous dimethyl sulfoxide (DMSO). Under nitrogen protection, 30 parts by weight of a 40% maleic anhydride DMSO solution are slowly added dropwise to the chitosan oligosaccharide solution over 1 hour. After the addition is complete, the mixture is stirred continuously at 50±5℃ for 10 hours. After the reaction, the product is cooled to room temperature, filtered, purified, and then diluted with pure water to prepare a 10% aqueous solution of the maleylated chitosan oligosaccharide product.

[0043] The degree of polymerization of the chitosan oligosaccharide is ≤10.

[0044] The oxidant is ammonium persulfate.

[0045] The unsaturated carboxylic acid is acrylic acid.

[0046] The reducing agent is sodium dioctyl succinate sulfonate E51.

[0047] The chain transfer agent is mercaptopropionic acid.

[0048] A method for preparing a low-sensitivity, early-strength polycarboxylate superplasticizer includes the following steps: (1) Preparation of mixed droplet solution: After adding the measured amount of pure water from mixed solution A to a container, nitrogen gas is introduced for protection, and then 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate is added and mixed evenly to obtain mixed solution A; the unsaturated carboxylic acid in mixed solution B is mixed evenly with pure water to obtain mixed solution B; the reducing agent is dissolved in pure water, and then the measured amount of chain transfer agent is added to obtain mixed solution C; (2) Polymerization reaction process: First, the pure water, maleic oxychitosan oligosaccharide aqueous solution and ethylene glycol monovinyl polyoxyethylene ether (EPEG) measured in the base material are stirred and dissolved in the reaction vessel. Then, the system is cooled to 5-10℃ and an oxidant is added and stirred for 5 min. Next, mixed solution A, mixed solution B and mixed solution C are added dropwise simultaneously within 2 h, and the process temperature is controlled to be ≤15℃. During the entire reaction process, the pH value of the system is maintained in the range of 6-8 by gradually adding neutralizing solution. After the dropwise addition is completed, the system is kept at the same temperature for 2 h to obtain the target product.

[0049] Example 4 A low-sensitivity, early-strength polycarboxylate superplasticizer comprises the following raw materials: a base material, an oxidant, a mixed solution A, a mixed solution B, a mixed solution C, and a neutralizing solution. The amounts of each raw material by weight are as follows: the base material comprises 395 parts of ethylene glycol monovinyl polyoxyethylene ether (EPEG), 107 parts of maleic oxychitosan aqueous solution, and 345 parts of pure water; 2 parts of oxidant; the mixed solution A comprises 12.3 parts of 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate and 24 parts of pure water; the mixed solution B comprises 36.6 parts of unsaturated carboxylic acid and 25 parts of pure water; the mixed solution C comprises 0.3 parts of reducing agent, 2.8 parts of chain transfer agent, and 26 parts of pure water; and the neutralizing solution is 24 parts of a 30% sodium hydroxide aqueous solution.

[0050] The degree of polymerization of the ethylene glycol monovinyl polyoxyethylene ether is 67.

[0051] The preparation method of the maleylated chitosan oligosaccharide aqueous solution is as follows: 10 parts by weight of fully dried chitosan oligosaccharide are dissolved in 100 parts of anhydrous dimethyl sulfoxide (DMSO). Under nitrogen protection, 30 parts by weight of a 40% maleic anhydride DMSO solution are slowly added dropwise to the chitosan oligosaccharide solution over 1 hour. After the addition is complete, the mixture is stirred continuously at 50±5℃ for 10 hours. After the reaction, the product is cooled to room temperature, filtered, purified, and then diluted with pure water to prepare a 10% aqueous solution of the maleylated chitosan oligosaccharide product.

[0052] The degree of polymerization of the chitosan oligosaccharide is ≤10.

[0053] The oxidant is hydrogen peroxide.

[0054] The unsaturated carboxylic acid is methacrylic acid.

[0055] The reducing agent is sodium formaldehyde sulfoxylate.

[0056] The chain transfer agent is mercaptoacetic acid.

[0057] A method for preparing a low-sensitivity, early-strength polycarboxylate superplasticizer includes the following steps: (1) Preparation of mixed droplet solution: After adding the measured amount of pure water from mixed solution A to a container, nitrogen gas is introduced for protection, and then 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate is added and mixed evenly to obtain mixed solution A; the unsaturated carboxylic acid in mixed solution B is mixed evenly with pure water to obtain mixed solution B; the reducing agent is dissolved in pure water, and then the measured amount of chain transfer agent is added to obtain mixed solution C; (2) Polymerization reaction process: First, the pure water, maleic oxychitosan oligosaccharide aqueous solution and ethylene glycol monovinyl polyoxyethylene ether (EPEG) measured in the base material are stirred and dissolved in the reaction vessel. Then, the system is cooled to 5-10℃ and an oxidant is added and stirred for 5 min. Next, mixed solution A, mixed solution B and mixed solution C are added dropwise simultaneously within 2 h, and the process temperature is controlled to be ≤15℃. During the entire reaction process, the pH value of the system is maintained in the range of 6-8 by gradually adding neutralizing solution. After the dropwise addition is completed, the system is kept at the same temperature for 2 h to obtain the target product.

[0058] Comparative Example 1 Compared to Example 1, this comparative example replaces the maleylated chitosan oligosaccharide aqueous solution with an equal amount of unmodified chitosan oligosaccharide aqueous solution, while keeping the remaining raw material ratios and preparation process conditions unchanged from Example 1. That is: A polycarboxylate superplasticizer comprises the following raw materials: a base material, an oxidizing agent, a mixed solution A, a mixed solution B, a mixed solution C, and a neutralizing solution. The amounts of each raw material by weight are as follows: the base material comprises 395 parts of ethylene glycol monovinyl polyoxyethylene ether (EPEG), 118.5 parts of chitosan oligosaccharide aqueous solution, and 344 parts of pure water; the oxidizing agent comprises 3.9 parts; the mixed solution A comprises 11 parts of 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate and 22 parts of pure water; the mixed solution B comprises 28.8 parts of unsaturated carboxylic acid and 30 parts of pure water; the mixed solution C comprises 0.36 parts of reducing agent, 2.44 parts of chain transfer agent, and 26 parts of pure water; and the neutralizing solution comprises 18 parts of a 30% sodium hydroxide aqueous solution.

[0059] The degree of polymerization of the ethylene glycol monovinyl polyoxyethylene ether is 67.

[0060] The oligosaccharide aqueous solution is prepared by adding fully dried chitosan oligosaccharide to pure water to prepare an aqueous solution with a mass concentration of 10%.

[0061] The degree of polymerization of the chitosan oligosaccharide is ≤10.

[0062] The oxidant is hydrogen peroxide.

[0063] The unsaturated carboxylic acid is acrylic acid.

[0064] The reducing agent is sodium dioctyl succinate sulfonate E51.

[0065] The chain transfer agent is 2-mercaptoethanol.

[0066] A method for preparing a polycarboxylate superplasticizer includes the following steps: (1) Preparation of mixed droplet solution: After adding the measured amount of pure water from mixed solution A to a container, nitrogen gas is introduced for protection, and then 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate is added and mixed evenly to obtain mixed solution A; the unsaturated carboxylic acid in mixed solution B is mixed evenly with pure water to obtain mixed solution B; the reducing agent is dissolved in pure water, and then the measured amount of chain transfer agent is added to obtain mixed solution C; (2) Polymerization reaction process: First, the pure water and chitosan oligosaccharide aqueous solution measured in the base material are stirred and dissolved in the reaction vessel. Then, the system is cooled to 5-10℃ and an oxidant is added and stirred for 3 minutes. Next, mixed solution A, mixed solution B and mixed solution C are added dropwise simultaneously within 1 hour, and the process temperature is controlled to be ≤15℃. During the entire reaction process, the pH value of the system is maintained in the range of 6-8 by gradually adding neutralizing solution. After the dropwise addition is completed, the system is kept warm and matured at the same temperature for 1 hour to obtain the target product.

[0067] Comparative Example 2 In this comparative example, except for the omission of 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate, the remaining raw material ratios and preparation process conditions remained unchanged from Example 1. That is: A polycarboxylate superplasticizer comprises the following raw materials: a base material, an oxidizing agent, a mixed solution A, a mixed solution B, a mixed solution C, and a neutralizing solution. The amounts of each raw material by weight are as follows: the base material comprises 395 parts of ethylene glycol monovinyl polyoxyethylene ether (EPEG), 118.5 parts of maleicylated chitosan oligosaccharide aqueous solution, and 344 parts of pure water; the oxidizing agent comprises 3.9 parts; the mixed solution A comprises 33 parts of pure water; the mixed solution B comprises 28.8 parts of unsaturated carboxylic acid and 30 parts of pure water; the mixed solution C comprises 0.36 parts of reducing agent, 2.44 parts of chain transfer agent, and 26 parts of pure water; and the neutralizing solution comprises 18 parts of a 30% sodium hydroxide aqueous solution.

[0068] The degree of polymerization of the ethylene glycol monovinyl polyoxyethylene ether is 67.

[0069] The preparation method of the maleylated chitosan oligosaccharide aqueous solution is as follows: 10 parts by weight of fully dried chitosan oligosaccharide are dissolved in 100 parts by weight of anhydrous dimethyl sulfoxide (DMSO). Under nitrogen protection, 20 parts by weight of a 40% maleic anhydride DMSO solution are slowly added dropwise to the chitosan oligosaccharide solution over 0.5 hours. After the addition is complete, the mixture is continuously stirred and reacted at 50±5℃ for 8 hours. After the reaction, the product is cooled to room temperature, filtered, purified, and then diluted with pure water to prepare a 10% aqueous solution of the maleylated chitosan oligosaccharide product.

[0070] The degree of polymerization of the chitosan oligosaccharide is ≤10.

[0071] The oxidant is hydrogen peroxide.

[0072] The unsaturated carboxylic acid is acrylic acid.

[0073] The reducing agent is sodium dioctyl succinate sulfonate E51.

[0074] The chain transfer agent is 2-mercaptoethanol.

[0075] A method for preparing a polycarboxylate superplasticizer includes the following steps: (1) Preparation of mixed droplet solution: Mix the unsaturated carboxylic acid in mixed solution B with pure water to obtain mixed solution B; dissolve the reducing agent in pure water, and then add a measured amount of chain transfer agent to obtain mixed solution C; (2) Polymerization reaction process: First, the pure water, maleic oxychitosan oligosaccharide aqueous solution and ethylene glycol monovinyl polyoxyethylene ether (EPEG) measured in the base material are stirred and dissolved in the reaction vessel. Then, the system is cooled to 5-10℃ and an oxidant is added and stirred for 3 minutes. Next, mixed solution A, mixed solution B and mixed solution C are added dropwise simultaneously within 1 hour, and the process temperature is controlled to be ≤15℃. During the entire reaction process, the pH value of the system is maintained in the range of 6-8 by gradually adding neutralizing solution. After the dropwise addition is completed, the system is kept at the same temperature for 1 hour to obtain the target product.

[0076] Comparative Example 3 In this comparative example, except that the maleylated chitosan oligosaccharide aqueous solution was replaced with an equal amount of unmodified chitosan oligosaccharide aqueous solution and 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate was not used, the remaining components and preparation steps were the same as in Example 1. That is: A polycarboxylate superplasticizer comprises the following raw materials: a base material, an oxidizing agent, a mixed solution A, a mixed solution B, a mixed solution C, and a neutralizing solution. The amounts of each raw material by weight are as follows: the base material comprises 395 parts of ethylene glycol monovinyl polyoxyethylene ether (EPEG), 118.5 parts of chitosan oligosaccharide aqueous solution, and 344 parts of pure water; the oxidizing agent comprises 3.9 parts; the mixed solution A comprises 33 parts of pure water; the mixed solution B comprises 28.8 parts of unsaturated carboxylic acid and 30 parts of pure water; the mixed solution C comprises 0.36 parts of reducing agent, 2.44 parts of chain transfer agent, and 26 parts of pure water; and the neutralizing solution comprises 18 parts of a 30% sodium hydroxide aqueous solution.

[0077] The degree of polymerization of the ethylene glycol monovinyl polyoxyethylene ether is 67.

[0078] The oligosaccharide aqueous solution is prepared by adding fully dried chitosan oligosaccharide to pure water to prepare an aqueous solution with a mass concentration of 10%.

[0079] The degree of polymerization of the chitosan oligosaccharide is ≤10.

[0080] The oxidant is hydrogen peroxide.

[0081] The unsaturated carboxylic acid is acrylic acid.

[0082] The reducing agent is sodium dioctyl succinate sulfonate E51.

[0083] The chain transfer agent is 2-mercaptoethanol.

[0084] A method for preparing a polycarboxylate superplasticizer includes the following steps: (1) Preparation of mixed droplet solution: Mix the unsaturated carboxylic acid in mixed solution B with pure water to obtain mixed solution B; dissolve the reducing agent in pure water, and then add a measured amount of chain transfer agent to obtain mixed solution C; (2) Polymerization reaction process: First, the pure water and chitosan oligosaccharide aqueous solution measured in the base material are stirred and dissolved in the reaction vessel. Then, the system is cooled to 5-10℃ and an oxidant is added and stirred for 3 minutes. Next, mixed solution B and mixed solution C are added dropwise simultaneously within 1 hour, and the process temperature is controlled to be ≤15℃. During the entire reaction process, the pH value of the system is maintained in the range of 6-8 by gradually adding neutralizing solution. After the dropwise addition is completed, the system is kept warm and matured at the same temperature for 1 hour to obtain the target product.

[0085] Comparative Example 4 Commercially available polycarboxylate superplasticizer 1, high water-reducing mother liquor, model M171, is produced by Jiangsu Aolaite Company.

[0086] Comparative Example 5 Commercially available polycarboxylate superplasticizer 2, early-strength type mother liquor, model Sika® ViscoCrete® 20 HE, is manufactured by Sika Corporation.

[0087] Performance testing Referring to the "Test Method for Homogeneity of Concrete Admixtures" (GB / T 8077-2023), the products obtained in Examples 1-4 were compared with those in Comparative Examples 1-3 and commercially available samples 1-2 (Comparative Examples 4-5) to assess their impact on the performance of cement paste under different cement conditions and in the presence of trace amounts of soil. This was to verify the sensitivity of polycarboxylate superplasticizers to cement and soil. The cement used included benchmark cement, Yizhou cement, Conch cement, and Jidong cement. 0.5% montmorillonite by weight was added to different cements to simulate a trace soil environment. The polycarboxylate superplasticizer dosage used in the cement paste test was 0.12% of the cementitious material dosage. Each experimental group was repeated five times, and the results were averaged. The test data are summarized in Table 1.

[0088] Table 1. Cement paste test data As can be seen from the above data, under the same folding and solids content, compared with the comparative example and commercially available samples, the polycarboxylate superplasticizer provided by this invention has two significant advantages: First, it can effectively suppress the adverse effects of montmorillonite on the fluidity and other properties of cement paste, and has low sensitivity to clay; Second, it exhibits good adaptability to different cements, which is confirmed by the smaller fluctuation range of its cement paste test results (such as fluidity) among different cements.

[0089] Concrete performance was determined according to the following national standards: mixture performance according to GB / T 50080-2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures"; concrete strength according to GB / T 50081-2019 "Standard for Test Methods of Physical and Mechanical Properties of Ordinary Concrete". The concrete mix proportions are detailed in Table 2. To verify the performance of the prepared polycarboxylate superplasticizer on concrete strength and sensitivity, montmorillonite was added to Formula 1 to simulate an increase in the mud content of the aggregate, verifying the actual performance of the polycarboxylate superplasticizer. The superplasticizer dosage was consistently 0.35% (converted to solids). A blank control group was set up, i.e., no superplasticizer was added. Each experimental group was repeated five times, and the results were averaged. The performance is recorded in Table 3.

[0090] Table 2 Concrete Mix Design (Unit: kg / m³) 3 ) Table 3 Comparison of Concrete Application Performance Data As shown in Tables 1 and 3, in the cement paste test (Table 1), the products of this invention exhibited high and stable initial fluidity in different brands of cement. Crucially, after incorporating 0.5% montmorillonite to simulate a muddy environment, the fluidity decrease in the embodiments was generally controlled within 20 mm, and the performance degradation rate was significantly lower than that of Comparative Examples 2 and 3 and the two commercially available samples. This directly verifies the synergistic anti-mud mechanism of the cationic monomer (3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate) and maleylated chitosan oligosaccharide: the cationic monomer preferentially anchors to the clay surface to form a "protective layer," while the rigid skeleton and dynamic carboxyl release function of the chitosan oligosaccharide derivative jointly ensure the sustained performance of the main chain dispersion function. The drastic deterioration of fluidity in Comparative Example 2 (without cationic monomer) and Comparative Example 3 (without both) after the presence of mud further demonstrates the indispensability of this synergistic structure.

[0091] In concrete performance tests (Table 3), the 1-day compressive strength of the embodiments of the present invention remained stable above 15.2 MPa under both clay-free (Formula 1) and clay-containing (Formula 2) conditions, and the 7-day strength exceeded 31.4 MPa. This indicates that its early strength effect is not only significant, but also has excellent tolerance to fluctuations in aggregate clay content. In contrast, all comparative examples and commercially available samples showed a significant decline in early and late strength after the addition of clay (Formula 2) (e.g., the 7-day strength of commercially available sample 2 dropped from 31.6 MPa to 25.8 MPa). This result confirms that the amide group and rigid skeleton of maleyl chitosan oligosaccharide, after synergistic optimization of adsorption conformation with cationic monomers, can effectively promote the formation of the early strength phase and resist the disorder of hydration process caused by clay interference, thereby achieving an organic unity of "early strength" and "clay resistance" performance. Under mud-containing conditions (Table 3, Formula 2), the initial and 0.5-hour slump / spread of the embodiments of the present invention are significantly better than those of the comparative examples and commercially available products, proving that its dispersion performance can still be effectively maintained in complex environments, meeting the requirements of modern construction for concrete workability.

[0092] In summary, this invention, through the copolymerization design of maleylated chitosan oligosaccharides with a specific structure and quaternary ammonium salt-type cationic monomers, does not simply produce an additive effect of functions, but rather achieves synergistic functional effects and performance enhancement at the molecular level. The cationic monomers precisely block clay adsorption sites, while the chitosan oligosaccharide derivatives maintain dispersion stability through steric hindrance and continuous carboxyl group release. Together, they construct an integrated anti-mud-dispersion-early strength mechanism. This design exhibits excellent adaptability and stability in various cement and mud-containing environments, providing a new approach for the development of high-performance concrete admixtures.

[0093] It should be noted that the above embodiments are merely some preferred embodiments of the present invention, and not all embodiments. Obviously, based on the above embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

Claims

1. A low-sensitivity, early-strength polycarboxylate superplasticizer, characterized in that, The mixture includes the following raw materials: a base material, an oxidizing agent, a mixed solution A, a mixed solution B, a mixed solution C, and a neutralizing solution. The amounts of each raw material are as follows by weight: The base material includes 380-395 parts of ethylene glycol monovinyl polyoxyethylene ether (EPEG), 95-119 parts of maleic oxychitosan oligosaccharide aqueous solution, and 333-345 parts of pure water; the oxidizing agent is 2-6 parts; the mixed solution A includes 11-13.5 parts of 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate and 22-28 parts of pure water; the mixed solution B includes 28.8-41.5 parts of unsaturated carboxylic acid and 20-38 parts of pure water; the mixed solution C includes 0.3-0.5 parts of reducing agent, 1.9-3.9 parts of chain transfer agent, and 22-38 parts of pure water; the neutralizing solution is 18-27 parts of a 30% sodium hydroxide aqueous solution.

2. The low-sensitivity early-strength polycarboxylate superplasticizer according to claim 1, characterized in that, The degree of polymerization of the ethylene glycol monovinyl polyoxyethylene ether (EPEG) is 44-80.

3. The low-sensitivity early-strength polycarboxylate superplasticizer according to claim 1, characterized in that, The method for preparing the maleylated chitosan oligosaccharide aqueous solution is as follows: Dissolve 10 parts by weight of fully dried chitosan oligosaccharide in 100-150 parts by weight of anhydrous dimethyl sulfoxide (DMSO) to obtain a chitosan oligosaccharide solution. Under nitrogen protection, slowly add 20-30 parts by weight of a 40% maleic anhydride DMSO solution to the chitosan oligosaccharide solution over 0.5-1 hour. After the addition is complete, continue stirring the reaction at 50±5℃ for 8-10 hours. After the reaction, cool the product to room temperature, filter and purify it, and add pure water to prepare a 10% (w / w) aqueous solution of the maleylated chitosan oligosaccharide product.

4. The low-sensitivity early-strength polycarboxylate superplasticizer according to claim 3, characterized in that, The degree of polymerization of the chitosan oligosaccharide is ≤10.

5. The low-sensitivity early-strength polycarboxylate superplasticizer according to claim 1, characterized in that, The oxidant is hydrogen peroxide and / or ammonium persulfate.

6. The low-sensitivity early-strength polycarboxylate superplasticizer according to claim 1, characterized in that, The unsaturated carboxylic acid is acrylic acid and / or methacrylic acid.

7. The low-sensitivity early-strength polycarboxylate superplasticizer according to claim 1, characterized in that, The reducing agent is one or more of sodium formaldehyde sulfoxylate, L-ascorbic acid, or sodium dioctyl succinate E51.

8. The low-sensitivity early-strength polycarboxylate superplasticizer according to claim 1, characterized in that, The chain transfer agent is one or more of mercaptoacetic acid, mercaptopropionic acid, or 2-mercaptoethanol.

9. A method for preparing the low-sensitivity early-strength polycarboxylate superplasticizer according to any one of claims 1-8, characterized in that, Includes the following steps: (1) Preparation of mixed droplet solution: After adding the measured amount of pure water from mixed solution A to a container, nitrogen gas is introduced for protection, and then 3-[[2-(methacryloyloxy)ethyl]dimethylammonium]propionate is added and mixed evenly to obtain mixed solution A; the unsaturated carboxylic acid in mixed solution B is mixed evenly with pure water to obtain mixed solution B; the reducing agent is dissolved in pure water, and then the measured amount of chain transfer agent is added to obtain mixed solution C; (2) Polymerization reaction process: First, the pure water, maleyl chitosan oligosaccharide aqueous solution and ethylene glycol monovinyl polyoxyethylene ether (EPEG) measured in the base material are stirred and dissolved in the reaction vessel. Then, the system is cooled to 5-10℃ and an oxidant is added and stirred for 3-5 minutes. Next, mixed solution A, mixed solution B and mixed solution C are added dropwise simultaneously within 1-2 hours. The process temperature is controlled to be ≤15℃. During the entire reaction process, the pH value of the system is maintained in the range of 6-8 by gradually adding neutralizing solution. After the dropwise addition is completed, the system is kept at the same temperature for 1-2 hours to obtain the target product.

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