Composite functional cement additive and preparation method thereof

Abstract

The invention provides a composite functional cement additive and a preparation method thereof, and belongs to the technical field of cement. The additive comprises the following components: polycarboxylic acid modified condensation, triisopropanolamine, triethanolamine and sodium gluconate. The polycarboxylic acid modified condensation compound is formed by copolymerizing methyl allyl polyoxyethylene ether, acrylic acid and 2-hydroxyethyl methacrylate phosphate which are used as comonomers. Through molecular design and component compounding, multiple synergistic effects are generated. And the unique structure can effectively delay the aggregation of cement particles and greatly improve the workability of the slurry. All functional components are integrally designed, so that the compatibility problem is avoided, and the performance stability is ensured. Meanwhile, by refining pores and optimizing a microstructure, the anti-permeability and durability of the concrete are remarkably enhanced, and the comprehensive performance is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of cement technology, and in particular relates to a composite functional cement additive and its preparation method. Background Technology

[0002] Cement, as the most important building binder, directly determines the workability, mechanical strength, and long-term durability of concrete and mortar. To optimize the various properties of cement-based materials, chemical admixtures have become an indispensable component of modern concrete technology. Historically, the application of admixtures has evolved from single-function to multi-functional composites.

[0003] Early admixtures were mostly single-function chemicals, such as: ordinary water-reducing agents (e.g., lignin sulfonates) used only to reduce water consumption and improve fluidity; retarders (e.g., sugars, phosphates) used only to delay cement hydration and prolong setting time; or early-strength agents (e.g., sodium sulfate, triethanolamine) used only to accelerate early strength development. These single-function admixtures often had limitations in solving specific problems or caused new ones. For example, using a high-efficiency water-reducing agent alone could lead to excessively rapid slump loss in concrete, affecting construction; while using a retarder alone in high-temperature environments could adversely affect the early and later strength of concrete.

[0004] As construction projects evolve towards complex environments such as high-rise buildings, large-span structures, deep-sea applications, and frigid conditions, diverse and high-standard requirements are being placed on concrete performance. Against this backdrop, a "simple compounding" method has emerged, which physically mixes two or more single admixture components with different functions. This method solves some problems to a certain extent; for example, mixing water-reducing agents and retarders to prepare pumping agents for use in large-volume concrete or high-temperature season construction. However, this simple physical compounding has inherent drawbacks: First, the compatibility of different types of admixture molecules in the cement-water system may be poor, leading to competitive adsorption or mutual interference, causing the function of one or more components to fail or be significantly weakened, i.e., producing an "antagonistic effect"; second, the optimal dosage range of each component may be mutually restrictive, making it difficult to find a globally optimal ratio, resulting in large performance fluctuations; third, to achieve the desired effect, it is often necessary to increase the total dosage, leading to increased costs and potentially introducing harmful ions (such as excessive chloride ions or alkali content).

[0005] The composite functional cement additives described in this field refer to homogeneous and stable products that are compounded in specific proportions and processes by combining two or more chemical substances with dominant functions and positive synergistic effects, based on the cement hydration mechanism and concrete performance requirements, through scientific component design. The core objective is to achieve "functional compounding" and "performance synergy," that is, to simultaneously impart two or more significantly improved properties to cement-based materials through a single addition, with the synergistic effect of these properties being superior to the simple summation of the individual functional components, while minimizing or eliminating the side effects of the components.

[0006] Based on market demand and technological development, composite functional cement additives are mainly designed and combined around the following core functions, forming corresponding classifications: (1) Workability Adjustment and Maintenance Type: The core of this type of composite additive is to solve the problems of concrete fluidity, pumpability, and loss over time. A typical example is a retarding high-performance water-reducing agent (or pumping agent). It combines a high-efficiency water-reducing component (such as polycarboxylate) and a retarding and slump-maintaining component. The water-reducing component provides initial high fluidity, while the retarding component effectively slows down fluidity loss by inhibiting the initial hydration of cement, especially the hydration of tricalcium aluminate (C3A), ensuring that the concrete maintains good workability during long-distance transportation or complex structure pouring. When used for large-volume concrete, the retarding component also helps to reduce the hydration heat peak.

[0007] (2) Early-strength and high-strength type: This type of composite additive aims to rapidly improve early strength, shorten the demolding and curing cycle, or formulate high-strength concrete. A typical example is the early-strength high-efficiency water-reducing agent. It combines high-efficiency water-reducing components and early-strength catalytic components. The water-reducing components lay the foundation for high strength by significantly reducing the water-cement ratio; while the early-strength components (such as sulfates and organic amines) can accelerate the hydration of tricalcium silicate (C3S), promote the early formation of large amounts of ettringite, or act as a catalyst, enabling concrete to obtain high early strength within a few hours.

[0008] (3) Durability Enhancement Type: This type of composite additive focuses on improving the long-term durability of concrete, including impermeability, freeze-thaw resistance, and erosion resistance. Common types include air-entraining water-reducing agents and waterproof and compacting composite agents. Air-entraining water-reducing agents combine highly efficient water-reducing components and air-entraining components (such as rosin thermal polymers and saponins), introducing a large number of uniform and stable microbubbles, which can not only significantly improve the freeze-thaw cycle resistance of concrete, but also improve its workability. Waterproof and compacting agents may combine multiple components such as water-reducing, expansive, and hydrophobic agents, which together improve the compactness and impermeability of concrete by reducing pores, blocking capillary channels, or generating moderate expansion compressive stress.

[0009] (4) Special functional type: designed to meet special construction environments or performance requirements. For example, antifreeze composite pumping agents combine water-reducing, air-entraining, early-strength, and antifreeze components to ensure that concrete can maintain the fluidity required for construction in negative temperature environments, prevent early freezing of internal free water, and promote strength development at low temperatures. There are also composite agents suitable for precast components, which may simultaneously contain multiple functions such as high-efficiency water reduction, early strength, and retarding (for surface conditioning).

[0010] The core technology of composite functional additives lies in the synergistic effect between their components, which is mainly based on the following principles: (1) Synergistic effect of adsorption and dispersion: Surfactant molecules with different structures exhibit different adsorption behaviors on the surface of cement particles. For example, the combined use of water-reducing agent molecules with different adsorption groups and side chain lengths can achieve more comprehensive and robust adsorption and encapsulation of cement particles, generating stronger steric hindrance and electrostatic repulsion, thereby resulting in better and more durable dispersion. This is the basis of high-performance water-reducing agent composite technology.

[0011] (2) Timing control of hydration process: Cement hydration is a complex process that occurs in stages. Composite additives can precisely intervene in key stages. For example, in "retarded high-efficiency water-reducing agent", the retarding component preferentially adsorbs on the surface of C3A, which has the highest activity, inhibiting its rapid hydration and consumption of water-reducing agent molecules. This "protects" the water-reducing agent molecules to adsorb more on the surface of C3S, which has the dominant strength, allowing it to fully exert its dispersing effect. This timing control avoids the ineffective consumption of components and achieves functional complementarity.

[0012] (3) Optimization of pore structure and interface structure: Different components work together to optimize the cement paste structure at the microscopic level. Water-reducing agents lower the water-cement ratio and reduce the number of macropores; air-entraining agents introduce closed microbubbles that can block the connection of harmful channels; and an appropriate amount of expanding agents generates an expanding phase that can refine pores and compensate for shrinkage. These effects combined can significantly improve the density of concrete and the structure of the aggregate-paste interface transition zone, thereby synergistically improving mechanical properties and durability.

[0013] (4) Eutectic and antifreeze mechanism: In antifreeze composites, some organic antifreeze components can lower the freezing point of water, while early strength components promote the rapid formation of a strength skeleton in cement at low temperatures. The two work together to prevent frost damage. At the same time, the buffer space provided by the air-entraining agent can accommodate the volume expansion caused by water freezing. The three together constitute a complete low-temperature protection mechanism for concrete.

[0014] Although composite functional additives have become an industry trend, existing technologies still face many challenges: First, the stability of composite systems is difficult to guarantee, especially for liquid products, which may experience stratification, crystallization, or performance degradation during long-term storage; second, the adaptability to raw materials (especially cement from different origins and processes) still needs to be improved, and the "compatibility" problem has not been completely solved; third, the continuous introduction of new components to achieve multifunctionality may lead to complex formulations, increased costs, and potential long-term durability risks such as excessive chloride ion and alkali content; finally, many existing composite products are still based on empirical physical compounding, with insufficient understanding of the molecular-level interaction mechanisms between components and their competitive and synergistic behavior in complex cementitious systems, and a lack of precise molecular design and control methods. Summary of the Invention

[0015] The purpose of this invention is to provide a composite functional cement additive, comprising the following components by weight: Polycarboxylate modified condensate 50-60 Triisopropanolamine 25-35 Triethanolamine 0.5-1.5 Sodium gluconate 0.3-0.8; The polycarboxylic acid modified condensate is copolymerized from methyl allyl polyoxyethylene ether, acrylic acid, and 2-hydroxyethyl methacrylate phosphate as comonomers.

[0016] Preferably, in the polycarboxylic acid modified condensate, the mass ratio of methyl allyl polyoxyethylene ether, acrylic acid, and 2-hydroxyethyl methacrylate phosphate is 80:12-15:8-10.

[0017] Preferably, during the copolymerization of the polycarboxylic acid modified condensate, a chain transfer agent is added, and the amount of chain transfer agent added is 0.2-0.4% of the total mass of the comonomer.

[0018] Preferably, the preparation of the polycarboxylic acid modified condensate includes the following steps: S1: Mix methyl allyl polyoxyethylene ether, acrylic acid, 2-hydroxyethyl methacrylate phosphate and water to obtain a homogeneous monomer mixture; S2: Mix the initiator and chain transfer agent with water to obtain an initiator solution; S3: Place the monomer mixture in a water bath heating environment and introduce the initiator solution into the system dropwise; after the dropwise addition is complete, maintain heating for at least 2 hours; then raise the water bath temperature by at least 5°C and maintain it for at least 0.5 hours; The entire process is carried out with stirring; a crude polycarboxylic acid copolymer solution is obtained. S4: Cool the crude polycarboxylic acid copolymer solution and add an alkaline solution dropwise while stirring; adjust the pH of the system to 6.0-7.0.

[0019] In step S2, the amount of initiator is at least 1.2% of the total mass of the polymerizing monomers; the amount of chain transfer agent added is 0.2-0.4% of the total mass of the comonomers.

[0020] The water bath heating temperature in step S3 is 60.5±0.5℃; the cooling in step S4 is to reduce the temperature of the crude polycarboxylic acid copolymer solution to ≤40℃.

[0021] Preferably, the composite functional cement additive further includes the following components: Defoamer 0.02-0.05 Trisodium citrate 0.05-0.10.

[0022] The defoamer is an organosilicon defoamer.

[0023] The composite functional cement additive of the present invention originates from the precise synergistic mechanism of its components: 1. Polycarboxylate-modified condensates are the foundation for the high performance of the entire system. Their molecular design follows a "main chain-long side chain-functional group" architecture: Methyl allyl polyoxyethylene ether: As a macromonomer, it provides long polyoxyethylene ether (PEO) side chains. These hydrophilic long side chains fully extend in aqueous solution and, after adsorption onto the surface of cement particles, generate a strong steric hindrance effect, which is the core source of ultra-high water reduction rate.

[0024] Acrylic acid forms the main chain or short side chain of the polymer, providing a high density of carboxyl groups (-COO). - The carboxyl groups ionize in the alkaline environment of cement paste, giving the polymer backbone a negative charge, which helps disperse cement particles through electrostatic repulsion. Simultaneously, the carboxyl groups can react with calcium ions (Ca²⁺). + This plays a role and is one of the main anchoring points for polymer adsorption on the surface of cement particles.

[0025] 2-Hydroxyethyl methacrylate phosphate is the key functional monomer. The introduced phosphate group (-PO4H2) affects calcium ions (Ca²⁺). + Phosphate groups possess a chelating ability far stronger than carboxyl groups, forming a more robust and durable adsorption on the surface of cement particles. This strong adsorption exhibits a "slow-release" characteristic, continuously providing dispersing force, which is the main reason for the significant improvement in slump retention. Simultaneously, phosphate groups can also participate in the hydration process, refining hydration products and further increasing structural density.

[0026] The three components are copolymerized via free radicals to form a copolymer with a "comb-like" structure. The molecular weight is precisely controlled within an ideal range by a chain transfer agent (mercaptopropionic acid), ensuring its good solubility in water and optimal adsorption conformation on the surface of cement particles.

[0027] 2. The early-strength function is achieved by a complex system composed of triisopropanolamine and triethanolamine, and their mechanisms of action are complementary: Triisopropanolamine primarily catalyzes the hydration of tricalcium silicate (C3S) and tetracalcium aluminoferrite (C4AF). It alters the crystallization habit of the hydration product, calcium hydroxide (CH), transforming it from a coarse, plate-like structure into fine, granular particles that are uniformly distributed within the cement paste. This optimizes the interfacial transition zone structure, significantly enhancing early strength and contributing positively to later strength growth.

[0028] Triethanolamine significantly promotes the hydration of tricalcium aluminate (C3A), accelerating the early formation of ettringite and rapidly building an early strength framework. When combined in a specific ratio (approximately 25-35: 0.5-1.5), it achieves comprehensive and balanced catalysis of the main cement minerals, avoiding the hydration imbalances or weak later-stage strength growth problems that may be caused by using a single ethanolamine.

[0029] 3. Principles of adjustment and stabilization of auxiliary components Sodium gluconate, as a retarding and slump-preserving component, has a carboxyl group that can competitively react with Ca²⁺. + This combination temporarily delays the formation and growth of hydration product crystal nuclei, allowing time for the adsorption and dispersion of polycarboxylic acid molecules, and together with the phosphate ester groups, ensures the maintenance of workability.

[0030] Trisodium citrate, as a stabilizer and retarder, can effectively complex free metal ions in the system, preventing premature failure or flocculation of polycarboxylic acid molecules due to fluctuations in ion concentration, and enhancing the storage stability of the product and its compatibility with different batches of cement.

[0031] Organosilicon defoamers, with their extremely low surface tension, can quickly destroy and suppress large air bubbles introduced by surfactants such as polyether side chains, ensuring that the air content of concrete is composed of small, closed microbubbles, thereby maintaining good workability while avoiding strength loss.

[0032] Compared with the prior art, the composite functional cement additive provided by the present invention has the following significant beneficial effects: The composite functional cement additive provided by this invention achieves the following technical effects in the performance regulation of cement-based materials through the synergistic effect of its components: (1) Synergistic enhancement of mechanical property development rate and final strength: The approximately 30% water reduction rate provided by the polycarboxylate-modified condensate fundamentally improves the density and potential strength of cement paste by reducing the water-cement ratio. At the same time, the composite early strength invention composed of triisopropanolamine and triethanolamine can effectively catalyze the hydration reaction of tricalcium silicate (C3S) and tetracalcium aluminoferrite (C4AF) and optimize the crystal morphology of the hydration product calcium hydroxide. The synergistic effect of the two increases the 3-day compressive strength of concrete and stabilizes the later strength development.

[0033] (2) Significantly improves the workability retention of cement paste: Traditional early-strength water-reducing agents often lead to increased fluidity loss over time due to accelerated hydration. In this invention, the phosphate groups on the polycarboxylic acid backbone have strong chelating and dynamic adsorption properties for calcium ions, and the combination with sodium gluconate inhibits the initial hydration of cement, thus delaying the aggregation of cement particles.

[0034] (3) Achieving multifunctional integration and ensuring compatibility: This invention integrates efficient dispersion, early strength, slump retention, compaction enhancement, and stability regulation functions into a single product. The components complement each other: the chain transfer agent precisely controls the polymer molecular weight to match the early strength invention; a trace amount of defoamer eliminates harmful large bubbles without affecting the necessary gas content; trisodium citrate chelates free ions to improve the stability of the invention. This invention avoids compatibility issues that may arise from on-site multi-component compounding, ensuring the reliability and reproducibility of performance.

[0035] (4) Optimizing the microstructure to enhance durability: The high water-reducing effect and the pore-refining effect of phosphate groups work together to promote the formation of a denser microstructure in the cement paste, reducing the total porosity and the proportion of harmful macropores (diameter > 50 nm). This structure effectively hinders the migration of moisture and corrosive ions, thereby enabling the concrete to exhibit higher impermeability, chloride ion penetration resistance, and freeze-thaw cycle resistance. The addition of trisodium citrate further helps to stabilize the paste volume and reduce the risk of early cracking.

[0036] This invention achieves multiple synergistic effects through molecular design and component compounding. The polycarboxylate-modified condensate provides efficient dispersion and steric hindrance, combined with the strong adsorption and slow-release properties of the phosphate ester groups, significantly accelerating early strength development and enhancing final strength in conjunction with the composite early-strength component. Its unique structure effectively delays cement particle aggregation, greatly improving the workability retention of the paste. The integrated design of each functional component avoids compatibility issues and ensures performance stability. Simultaneously, this additive significantly enhances the impermeability and durability of concrete by refining pores and optimizing the microstructure, resulting in a significant improvement in overall performance. Detailed Implementation

[0037] To better understand the present invention, the present invention will be further described below with reference to specific serial numbers. The terminology used in the serial numbers is for describing specific embodiments and does not constitute a limitation on the scope of protection of the present invention.

[0038] In the specific implementation methods, unless otherwise specified, the experimental methods used are all conventional methods, and the materials and reagents used are all commercially available unless otherwise specified.

[0039] Unless otherwise specified, percentages (%) in the specific implementation method are assumed to be volume percentages.

[0040] Example 1: Preparation of polycarboxylic acid modified condensate Includes the following steps: S1: Raw material preparation and pretreatment Methyl allyl polyoxyethylene ether: molecular weight approximately 2400, industrial grade; Acrylic acid: chemically pure.

[0041] 2-Hydroxyethyl methacrylate phosphate: Industrial grade.

[0042] Initiator: Ammonium persulfate, chemically pure.

[0043] Chain transfer agent: mercaptopropionic acid, chemically pure.

[0044] Neutralizing agent: 30% sodium hydroxide solution.

[0045] Solvent: Deionized water.

[0046] The mass ratio of methyl allyl polyoxyethylene ether, acrylic acid, and 2-hydroxyethyl methacrylate phosphate is 80:12:8.

[0047] The amount of chain transfer agent added is 0.2% of the total mass of the comonomer.

[0048] The amount of initiator added is 1.2% of the total mass of the comonomer.

[0049] S2: In a container equipped with a stirrer, a constant-pressure dropping funnel, a thermometer, and a reflux condenser, add methyl allyl polyoxyethylene ether and acrylic acid. Slowly add 2-hydroxyethyl methacrylate phosphate. Add an appropriate amount of deionized water, start stirring, and stir at room temperature for 30 minutes until the system becomes a homogeneous milky white liquid; thus obtaining the monomer mixture.

[0050] S3: In a separate container, add ammonium persulfate and mercaptopropionic acid dissolved in deionized water and stir until completely clear; thus obtaining the initiator solution; S4: Place the container of the monomer mixture in a constant temperature water bath at 60°C.

[0051] After the system temperature stabilizes at 60°C, begin adding the initiator solution dropwise. The total dropwise addition time should be controlled to be completed within 2.5-3.0 hours.

[0052] After the addition is complete, continue to heat and mature at 60°C for 1.5 hours to ensure complete monomer conversion.

[0053] After curing, the reaction system was heated to 65°C and the reaction continued for 0.5 hours to decompose the residual initiator. Stirring was maintained throughout the process; a crude polycarboxylate copolymer solution was obtained. S5: Allow the crude polycarboxylic acid copolymer solution to cool naturally to below 40°C.

[0054] While stirring continuously, slowly add 30% sodium hydroxide solution to adjust the pH of the system to 6.0-7.0.

[0055] After neutralization, continue stirring for 30 minutes to obtain a viscous liquid, which is the polycarboxylic acid modified condensate.

[0056] Example 2 Preparation of polycarboxylic acid modified condensate The difference from Example 1 is that in step S1: The mass ratio of methyl allyl polyoxyethylene ether, acrylic acid, and 2-hydroxyethyl methacrylate phosphate is 80:15:10.

[0057] The amount of chain transfer agent added is 0.4% of the total mass of the comonomer.

[0058] The amount of initiator added is 1.2% of the total mass of the comonomer.

[0059] Example 3 Preparation of polycarboxylic acid condensates The difference from Example 1 is that in step S1: The comonomer does not contain 2-hydroxyethyl methacrylate phosphate; the mass ratio of methyl allyl polyoxyethylene ether to acrylic acid is 80:12.

[0060] Example 4 (1) Preparation of composite functional cement additives: Weigh each component according to the mass parts in Table 1 below, and then mix and stir evenly to obtain the corresponding composite functional cement additives.

[0061] Table 1 (2) Performance testing In this experiment, the mix design of the reference concrete C30 was as follows: Cement 351.8Kg / m³, sand (2.6-2.9) 352Kg / m³, stone (5-10cm) 500.8Kg / m³, stone (10-20cm) 701.8Kg / m³, water 170, stone (5-10cm) 480.8Kg / m³, and the composite functional cement additive prepared in Table 1 2.0Kg / m³.

[0062] 1. Compressive strength test: Refer to GB / T 50081 The 2019 "Standard for Test Methods of Mechanical Properties of Ordinary Concrete" determines the compressive strength of concrete prepared with different composite functional cement additives. When preparing concrete specimens, the concrete cube compressive strength specimens were immediately covered with a waterproof film after molding and cured in the mold at 20℃ for up to 12 hours after final setting before demolding. Immediately after demolding, they were placed in a standard curing room at 20℃ and 98% relative humidity for curing. Compressive strength tests were conducted after 7 days and 28 days, and the test results are shown in Table 2.

[0063] 2. Uniformity test: Refer to GB / T 50080 The 2016 "Standard for Test Methods of Performance of Ordinary Concrete Mixtures" adopts the mortar density method, using the concrete mortar density deviation rate as the evaluation basis. The smaller the concrete mortar density deviation rate, the better the uniformity of the concrete. The test results are shown in Table 2.

[0064] Table 1 The above detailed description is a specific description of one of the feasible embodiments of the present invention. This embodiment is not intended to limit the patent scope of the present invention. All equivalent implementations or modifications that do not depart from the present invention should be included within the scope of the technical solution of the present invention.

Claims

1. A composite functional cement additive, characterized in that, The following components are included in parts by mass: Polycarboxylate modified condensate 50-60 Triisopropanolamine 25-35 Triethanolamine 0.5-1.5 Sodium gluconate 0.3-0.8; The polycarboxylic acid modified condensate is copolymerized from methyl allyl polyoxyethylene ether, acrylic acid, and 2-hydroxyethyl methacrylate phosphate as comonomers.

2. The composite functional cement additive according to claim 1, characterized in that, In the polycarboxylic acid modified condensate, the mass ratio of methyl allyl polyoxyethylene ether, acrylic acid, and 2-hydroxyethyl methacrylate phosphate is 80:12-15:8-10.

3. The composite functional cement additive according to claim 1, characterized in that, During the copolymerization of the polycarboxylic acid modified condensate, a chain transfer agent is added, and the amount of chain transfer agent added is 0.2-0.4% of the total mass of the comonomer.

4. The composite functional cement additive according to claim 1, characterized in that, The preparation of the polycarboxylic acid modified condensate includes the following steps: S1: Mix methyl allyl polyoxyethylene ether, acrylic acid, 2-hydroxyethyl methacrylate phosphate and water to obtain a homogeneous monomer mixture; S2: Mix the initiator and chain transfer agent with water to obtain an initiator solution; S3: Place the monomer mixture in a water bath heating environment and introduce the initiator solution into the system dropwise; after the dropwise addition is complete, maintain heating for at least 2 hours; then raise the water bath temperature by at least 5°C and maintain it for at least 0.5 hours; The entire process is carried out with stirring; a crude polycarboxylic acid copolymer solution is obtained. S4: Cool the crude polycarboxylic acid copolymer solution and add an alkaline solution dropwise while stirring; adjust the pH of the system to 6.0-7.

0.

5. The composite functional cement additive according to claim 4, characterized in that, In step S2, the amount of initiator is at least 1.2% of the total mass of the polymerizing monomers; the amount of chain transfer agent added is 0.2-0.4% of the total mass of the comonomers.

6. The composite functional cement additive according to claim 4, characterized in that, The water bath heating temperature in step S3 is 60.5±0.5℃; the cooling in step S4 is to reduce the temperature of the crude polycarboxylic acid copolymer solution to ≤40℃.

7. The composite functional cement additive according to claim 1, characterized in that, It also includes the following components: Defoamer 0.02-0.05 Trisodium citrate 0.05-0.

10.

8. The composite functional cement additive according to claim 7, characterized in that, The defoamer is an organosilicon defoamer.

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