Concrete external curing agent for extreme high-temperature environment, preparation method and application

Abstract

The invention discloses a concrete external curing agent for an extreme high-temperature environment as well as a preparation method and application thereof, and belongs to the technical field of chemical additives of building materials. When the concrete external curing agent used in the extreme high-temperature environment is prepared, (3-mercaptopropyl) trimethoxysilane modified cellulose nanocrystals, a nonionic polyurethane associated thickener, styrene, butyl acrylate, methyl methacrylate, a hydrophilic functional monomer, a crosslinking functional monomer and a reactive emulsifier are added; the concrete external curing agent for the extreme high-temperature environment, prepared by the preparation method disclosed by the invention, has excellent construction performance in the high-temperature environment, and has good high-temperature-resistant curing performance in an application stage.

Description

Technical Field

[0001] This invention belongs to the field of chemical additives for building materials, and particularly relates to concrete external curing agents for use in extreme high-temperature environments, their preparation methods, and applications. Background Technology

[0002] Concrete curing is a crucial step in ensuring its mechanical properties and long-term durability. For conventional environments, various mature external curing technologies have been developed, such as film mulching and water spraying, and spraying curing agents. Among these, concrete external curing agents based on film-forming and water-retention mechanisms have been widely used in bridges, roads, and building construction due to their advantages such as convenient construction and water-saving efficiency.

[0003] However, as my country's infrastructure construction extends deeper into the geologically complex western regions, tunnel projects often face extreme construction environments characterized by high rock temperatures, high air temperatures, strong heat radiation, and low humidity, posing a severe challenge to existing concrete curing technologies. According to publicly available measured data from tunnel projects (such as a deep-buried tunnel on the Sichuan-Tibet Railway and a high-temperature tunnel in Xinjiang), the temperature of the surrounding rock at the tunnel face can be maintained above 80℃ for extended periods, while the air temperature inside the tunnel exceeds 50℃, and the relative humidity is less than 30%, creating typical "high-temperature dry heat" and cave-like effects.

[0004] To adapt to spraying operations on reverse-sloping structures such as tunnel arches and sidewalls, curing agents need to have low initial viscosity to ensure sprayability. However, extreme high temperatures cause the film layer of conventional curing agents to soften rapidly and the viscosity to drop sharply, resulting in ineffective adhesion on vertical or inclined substrates and severe sagging and dripping. This not only leads to significant material waste but also prevents the formation of a complete and continuous sealed curing film on the concrete surface. High-temperature environments significantly enhance moisture evaporation kinetics, while the barrier properties of conventional curing agents are greatly reduced under heat. Simultaneously, intense heat radiation may directly damage the integrity of the organic polymer film, causing it to lose its water-retention function, allowing moisture to rapidly dissipate from the concrete surface and failing to provide the necessary conditions for continuous cement hydration.

[0005] Most commercially available concrete curing agents are designed for normal or mild climates, and their formulations cannot meet the heat resistance limits and rheological properties required for extreme conditions. While some studies have attempted to improve workability by increasing solids content or adding common thickeners, these approaches often come at the cost of either sacrificing spray atomization or failing to maintain long-lasting anti-sagging and water-retention properties under dynamic high temperatures. Therefore, developing a high-performance concrete external curing agent specifically designed for extreme high-temperature environments, capable of easy spraying during construction, strong adhesion to complex facades without dripping during application, and effectively locking in moisture to inhibit evaporation, has become an urgent market demand in specialized fields such as tunnel engineering. Summary of the Invention

[0006] To solve the above-mentioned technical problems, this invention proposes a concrete external curing agent for extreme high temperature environments, its preparation method, and its application. The concrete external curing agent provided by this invention is a concrete external curing agent that has excellent thixotropic properties, anti-sagging properties, and water retention properties during the construction and application stages in high temperature environments.

[0007] To achieve the above objectives, the present invention provides an external curing agent for concrete used in extreme high-temperature environments, comprising the following components by weight: 10-30 parts of silane-modified cellulose nanocrystal dispersion, 15.8 parts of initiator solution, 100-120 parts of pre-emulsion, 0.2 parts of photoinitiator, 1-1.5 parts of nonionic polyurethane associative thickener (HEUR thickener), and 0.2 parts of defoamer; The raw materials for the silane-modified cellulose nanocrystal dispersion, based on parts by mass, consist of 2 parts cellulose nanocrystals, 98 parts water, and 1.0-2.0 parts (3-mercaptopropyl)trimethoxysilane. The initiator solution is composed of 0.5 parts by weight of a water-soluble thermal decomposition initiator and 0.3 parts by weight of a buffer. The pre-emulsion is composed of 25 parts water, 2.5 parts composite emulsifier and 100 parts monomer mixture by weight. The composite emulsifier is composed of 1.1 parts reactive emulsifier, 0.9 parts anionic emulsifier and 0.5 parts nonionic emulsifier, based on parts by weight. The monomer mixture is composed of 50-55 parts styrene, 38-43 parts butyl acrylate, 4 parts methyl methacrylate, 1.5 parts hydrophilic functional monomers and 1.0-1.5 parts crosslinking functional monomers by mass.

[0008] Furthermore, the preparation method of the silane-modified cellulose nanocrystal dispersion is as follows: cellulose nanocrystals (CNCs) are added to water and dispersed evenly to prepare a cellulose nanocrystal dispersion. The pH is adjusted to 4.5 with dilute hydrochloric acid, and (3-mercaptopropyl)trimethoxysilane is added. The reaction is carried out under heating conditions to obtain the silane-modified cellulose nanocrystal dispersion.

[0009] Furthermore, the CNCs are carboxylated cellulose nanofibers. The thermal decomposition initiation temperature of CNCs is very high (typically exceeding 200°C, even reaching 300°C), far higher than the heat distortion temperature of styrene-acrylic emulsion polymers. When CNCs are uniformly dispersed in the polymer matrix, they form a nano-network structure. This structure effectively hinders heat transfer and diffusion, delaying the thermal degradation process of the entire material at high temperatures, thus protecting the polymer matrix like a barrier. In addition, CNCs possess extremely high modulus (stiffness) and strength. At high temperatures, styrene-acrylic polymers soften and their strength decreases, but the rigid network formed by CNCs maintains structural integrity. It provides solid mechanical support for the softened polymer, effectively inhibiting deformation, creep, and shrinkage of the coating at high temperatures, maintaining the coating's hardness, adhesion, and other mechanical properties. CNCs can form tortuous paths in the film, greatly hindering the permeation of oxygen and water vapor. High-temperature aging is often accompanied by oxidative degradation and hydrolytic degradation. CNCs slow down the oxidation rate by blocking oxygen and reduce the occurrence of hydrolysis reactions by blocking water vapor. This is key to delaying aging. The abundant hydroxyl groups on the surface of CNCs can form strong hydrogen bonds and other interactions with polymer molecular chains, effectively "anchoring" the polymer molecular chains. This effect restricts the mobility of polymer chains at high temperatures, thereby increasing the glass transition temperature (Tg) of the material to some extent, allowing the coating to maintain good performance at higher temperatures.

[0010] The (3-mercaptopropyl)trimethoxysilane of this invention can effectively improve the surface properties of CNCs. CNCs themselves are highly hydrophilic due to their abundant hydroxyl groups, resulting in poor compatibility with hydrophobic matrices and a tendency to aggregate. The methoxysilane (-Si(OCH3)3) at one end of the MPTS molecule hydrolyzes under acidic conditions to generate silanol (-Si(OH)3), which then undergoes dehydration condensation with the hydroxyl groups on the CNCs surface, forming a strong Si-OC covalent bond. This anchors the MPTS to the CNCs surface, successfully grafting its terminal thiol group (-SH). This modification not only imparts hydrophobicity to the CNCs through the long-chain alkyl group of MPTS, improving their dispersibility in hydrophobic matrices and avoiding stress defects caused by filler aggregation, but also transforms the CNCs from an inert filler into a reactive nano-crosslinking agent. The grafted thiol group can form CSC covalent bonds with the polymer chain through efficient click chemistry, achieving strong interfacial bonding, effectively transferring stress, and constructing a highly crosslinked network structure. This structure features high bond energy and good thermal stability, which restricts the movement of polymer chains at high temperatures, preventing the coating from softening and becoming sticky, and ensuring the coating remains stable even at 80℃. Simultaneously, the strong interfacial bonding and the reinforcing effect of the CNCs network endow the coating with high initial strength and modulus in the early stages of drying, effectively resisting gravity and achieving anti-sagging properties during construction on facades or arched roofs. Furthermore, the excellent hydrolysis resistance of CS covalent bonds and the dense cross-linked network significantly inhibit the penetration of water vapor and alkaline substances (such as Ca(OH)2), protecting not only the concrete substrate but also enhancing the coating's own durability and long-term weather resistance. In the synthesis of CNCs-modified and subsequent curing agent emulsions, MPTS's irreplaceable role stems from the highly efficient mercapto-alkene click chemistry mediated by its terminal mercapto groups. Compared to conventional silane coupling agents (such as methacryloxysilane (KH-570)), although KH-570 can participate in free radical copolymerization, its reaction mode is closer to that of ordinary monomers, mainly forming linear linkages rather than effective cross-linking networks, and its ester bonds have poor stability under alkaline conditions. Aminosilanes (such as KH-550) mainly rely on hydrogen bonds or ionic bonds in polymers, and these forces are easily destroyed in the strongly alkaline and high-humidity environment of concrete, leading to interfacial failure. Epoxysilanes (such as KH-560) require specific conditions to undergo a slow and incomplete condensation reaction with the functional groups on the polymer chain. MPTS, on the other hand, can directly and efficiently form stable CSC covalent crosslinks with the carbon-carbon double bonds on the polymer chain under mild UV conditions, thereby transforming cellulose nanocrystals from physical fillers into nano-crosslinking points firmly anchored in the polymer network.This unique mechanism not only achieves interfacial strength far exceeding that of physical adsorption and ordinary chemical bonds, but also simultaneously and synergistically endows the composite material with excellent high-temperature resistance (no softening or flowing at 80°C), excellent alkali / water resistance, long-term resistance to concrete corrosive media, and strong in-situ reinforcement and anti-sagging properties for vertical plastering. Its reaction pathway is specific and has excellent compatibility with emulsion polymerization processes, avoiding side reactions and storage instability problems that may be caused by other functional groups.

[0011] Furthermore, the HEUR thickener, ACRYSOL RM-12W, adsorbs onto emulsion particles and CNCs in concrete exterior curing agents used in extreme high-temperature environments through its hydrophobic ends, forming a dynamic three-dimensional network structure. This characteristic brings key advantages to concrete exterior curing agents used in extreme high-temperature environments: before application and during storage, the network provides high static viscosity, effectively preventing solid particle sedimentation, ensuring product storage stability and easy remixing; during application on vertical surfaces and arched ceilings, the high viscosity provides excellent anti-sagging properties, ensuring uniform curing film thickness without sag; and under the shear force of spraying or rolling, the network is temporarily disrupted, leading to a decrease in viscosity, making application easier and smoother. More importantly, during film formation, the network optimizes leveling, slows down moisture evaporation, and promotes the formation of a denser and more complete sealing film, thereby improving the moisturizing and curing effect. Moreover, the HEUR molecules ultimately reversibly embed into the polymer phase, avoiding the leaving of hydrophilic channels within the film, contributing positively to the final water resistance and durability of concrete exterior curing agents used in extreme high-temperature environments.

[0012] Furthermore, the crosslinking functional monomer is hydroxyethyl methacrylate.

[0013] Furthermore, the hydrophilic functional monomer is acrylic acid.

[0014] This invention uses styrene, butyl acrylate, methyl methacrylate, a hydrophilic functional monomer, and a crosslinking functional monomer as monomers to prepare a polymer. Styrene, butyl acrylate, and methyl methacrylate form the polymer chain backbone. Styrene provides rigidity, high Tg, heat resistance, and water resistance, serving as the backbone for maintaining the strength of the coating at 80°C. Butyl acrylate provides flexibility, film-forming properties, and adhesion to concrete substrates. Methyl methacrylate helps provide hardness, weather resistance, and gloss, further adjusting Tg and heat resistance. The crosslinking functional monomer is specifically hydroxyethyl methacrylate, whose molecular structure contains hydroxyl groups, providing sites for possible later crosslinking (such as with silane hydrolysates), further improving water resistance and hardness. The hydrophilic functional monomer is specifically acrylic acid, whose molecular structure contains hydrophilic carboxyl groups, primarily improving the stability of the emulsion polymerization process and the final product through electrostatic repulsion (-COO⁻).

[0015] Further, the reactive emulsifier is 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate (DNS-86); the anionic emulsifier is nonylphenol polyoxyethylene (4) ether ammonium sulfate (CO-436); and the nonionic emulsifier is dodecylphenol polyoxyethylene ether (OP-10). This invention uses the reactive emulsifier DNS-86, the anionic emulsifier CO-436, and the nonionic emulsifier OP-10 as a composite emulsifier. DNS-86 can chemically bond to the polymer chain, irreversibly stabilizing the emulsion particles and greatly improving the water resistance of the final coating. CO-436 provides electrostatic repulsion, synergistically working with the reactive emulsifier to ensure stable polymerization. OP-10 provides steric stability, is insensitive to pH and electrolytes, and enhances the chemical stability of the emulsion.

[0016] Furthermore, the water-soluble thermal decomposition initiator is ammonium persulfate (APS), which decomposes at 80°C to generate free radicals and initiate the polymerization reaction; the buffer is sodium bicarbonate, used to maintain the pH stability of the system and prevent the initiator efficiency from decreasing and the emulsion from breaking down due to the pH drop caused by acrylic acid; the photoinitiator is benzoyl methyl ether (DMPA), which decomposes under ultraviolet (UV) light to generate free radicals, effectively stimulating the thiol-alkene click chemical reaction between the thiol groups on the cellulose nanocrystals and the carbon-carbon double bonds in the polymer, thereby constructing a stable covalent crosslinking network; the defoamer is selected from mineral oil defoamers.

[0017] For example, the mineral oil defoamer is BASF Foamaster MO 21900 (WBA), which suppresses bubbles generated during production and application to avoid coating defects.

[0018] The present invention also provides a method for preparing the above-mentioned concrete external curing agent for extreme high temperature environments, comprising the following steps: Weigh each raw material according to its mass fraction; Reactive emulsifiers, anionic emulsifiers, nonionic emulsifiers and water are mixed and stirred to dissolve. Styrene, butyl acrylate, methyl methacrylate, hydrophilic functional monomers and crosslinking functional monomers are added and stirred evenly to form a pre-emulsion. A water-soluble thermal decomposition and buffer agent is added to water to form an initiator solution; One-third volume of initiator solution was added to the silane-modified cellulose nanocrystal dispersion. After the reaction, the pre-emulsion and the remaining two-thirds volume of initiator solution were added. The reaction was carried out under heating conditions. After the reaction was completed, the temperature was lowered to room temperature, a photoinitiator was added, and the curing reaction was carried out under ultraviolet conditions. After the curing reaction was completed, the pH was adjusted to 8 to obtain an in-situ polymerized emulsion. A diluted nonionic polyurethane associative thickener solution was added to the in-situ polymerized emulsion, stirred until homogeneous, and then an antifoaming agent was added. The mixture was then filtered to obtain the concrete external curing agent for extreme high-temperature environments.

[0019] The present invention also provides an application of the above-mentioned concrete external curing agent for extreme high temperature environments in the preparation of concrete for use in extreme high temperature environments.

[0020] Compared with the prior art, the present invention has the following advantages and technical effects: This invention incorporates (3-mercaptopropyl)trimethoxysilane-modified cellulose nanocrystals, nonionic polyurethane associative thickener, styrene, butyl acrylate, methyl methacrylate, hydrophilic functional monomers, crosslinking functional monomers, reactive emulsifiers, anionic emulsifiers, and nonionic emulsifiers when preparing a concrete external curing agent for extreme high-temperature environments. The concrete external curing agent prepared by this invention exhibits excellent workability under high-temperature conditions and good high-temperature curing performance during application. Detailed Implementation

[0021] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0022] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0023] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0024] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0025] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0026] An embodiment of the present invention provides an external curing agent for concrete in extreme high-temperature environments, comprising the following components by weight: 10-30 parts of silane-modified cellulose nanocrystal dispersion, 15.8 parts of initiator solution, 100-120 parts of pre-emulsion, 0.2 parts of photoinitiator, 1-1.5 parts of nonionic polyurethane associative thickener, and 0.2 parts of defoamer; The raw materials for the silane-modified cellulose nanocrystal dispersion, based on parts by mass, consist of 2 parts cellulose nanocrystals, 98 parts water, and 1.0-2.0 parts (3-mercaptopropyl)trimethoxysilane. The initiator solution is composed of 0.5 parts by weight of a water-soluble thermal decomposition initiator and 0.3 parts by weight of a buffer. The pre-emulsion is composed of 25 parts water, 2.5 parts composite emulsifier and 100 parts monomer mixture by weight. The composite emulsifier is composed of 1.1 parts reactive emulsifier, 0.9 parts anionic emulsifier and 0.5 parts nonionic emulsifier, based on parts by weight. The monomer mixture is composed of 50-55 parts styrene, 38-43 parts butyl acrylate, 4 parts methyl methacrylate, 1.5 parts hydrophilic functional monomers and 1.0-1.5 parts crosslinking functional monomers by mass.

[0027] This invention provides a concrete external curing agent suitable for extreme high-temperature environments. It has excellent construction performance in high-temperature environments and good high-temperature curing performance during application.

[0028] In a preferred embodiment of the present invention, the preparation method of silane-modified cellulose nanocrystal dispersion is as follows: cellulose nanocrystals (CNCs) are added to water and dispersed evenly to obtain a cellulose nanocrystal dispersion. The pH is adjusted to 4.5 with dilute hydrochloric acid, and (3-mercaptopropyl)trimethoxysilane is added. The reaction is carried out under heating conditions to obtain silane-modified cellulose nanocrystal dispersion.

[0029] In a preferred embodiment of the present invention, the cellulose nanocrystals are carboxylated cellulose nanowhiskers.

[0030] In a preferred embodiment of the present invention, the concentration of the cellulose nanocrystal dispersion is 2 wt%.

[0031] In a preferred embodiment of the present invention, the concentration of dilute hydrochloric acid is 2.4 mol / L.

[0032] In a preferred embodiment of the present invention, when adding (3-mercaptopropyl)trimethoxysilane, the stirring speed is 1000 rpm, and the (3-mercaptopropyl)trimethoxysilane is added dropwise over a time of 30 minutes; after adding (3-mercaptopropyl)trimethoxysilane, the reaction is carried out at 60°C for 3 hours.

[0033] In a preferred embodiment of the present invention, the crosslinking functional monomer is hydroxyethyl methacrylate.

[0034] In a preferred embodiment of the present invention, the hydrophilic functional monomer is acrylic acid.

[0035] In a preferred embodiment of the present invention, the reactive emulsifier is DNS-86; the anionic emulsifier is CO-436; and the nonionic emulsifier is OP-10.

[0036] In a preferred embodiment of the present invention, the water-soluble thermal decomposition initiator is ammonium persulfate (APS); the buffer is sodium bicarbonate; the photoinitiator is benzoyl methyl ether; and the defoamer is selected from mineral oil defoamers.

[0037] In a preferred embodiment of the present invention, the mineral oil defoamer is BASF Foamaster MO 2190.

[0038] Embodiments of the present invention also provide a method for preparing the above-mentioned concrete external curing agent for extreme high-temperature environments, comprising the following steps: Weigh each raw material according to its mass fraction; Reactive emulsifiers, anionic emulsifiers, nonionic emulsifiers and water are mixed and stirred to dissolve. Styrene, butyl acrylate, methyl methacrylate, hydrophilic functional monomers and crosslinking functional monomers are added and stirred evenly to form a pre-emulsion. A water-soluble thermal decomposition and buffer agent is added to water to form an initiator solution; One-third volume of initiator solution was added to the silane-modified cellulose nanocrystal dispersion. After the reaction, pre-emulsion and the remaining two-thirds volume of initiator solution were added. The reaction was carried out under heating conditions. After the reaction was completed, the temperature was lowered to room temperature, a photoinitiator was added, and the curing reaction was carried out under ultraviolet (UV) conditions. After the curing reaction was completed, the pH was adjusted to 8 to obtain an in-situ polymerized emulsion. A diluted nonionic polyurethane associative thickener solution was added to the in-situ polymerized emulsion, stirred until homogeneous, and then an antifoaming agent was added. The mixture was then filtered to obtain an external curing agent for concrete used in extreme high-temperature environments.

[0039] In a preferred embodiment of the present invention, after adding styrene, butyl acrylate, methyl methacrylate, hydrophilic functional monomers and crosslinking functional monomers, the mixture is sheared at a high speed of 3000 rpm for 15 minutes to ensure uniform mixing.

[0040] In a preferred embodiment of the present invention, the pre-emulsion is dripped over 3-3.5 hours; the initiator solution is dripped over 3.5-4 hours.

[0041] In a preferred embodiment of the present invention, when the curing reaction is carried out under UV conditions, the wavelength of the UV lamp is 365 nm and the light intensity is 100 mW / cm². 2 Irradiate for 10-15 minutes.

[0042] In a preferred embodiment of the present invention, the pH adjuster for adjusting the pH to 8 is ammonia.

[0043] In a preferred embodiment of the invention, filtration is performed using a 120-mesh filter.

[0044] Embodiments of the present invention also provide an application of the above-mentioned concrete external curing agent for extreme high temperature environments in the preparation of concrete for use in extreme high temperature environments.

[0045] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0046] Unless otherwise specified, the parts in this invention refer to parts by mass.

[0047] It should be noted that the raw materials and reagents used in the embodiments and comparative examples of this invention were all purchased. As an example, the cellulose nanocrystals were purchased from Guilin Qihong Technology Co., Ltd., and were carboxylated cellulose nanowhiskers, brand CNF-C, with a diameter of 4-20 nm, a length of 1-3 μm, and surface groups of -COOH and -OH; the HEUR thickener was purchased from Dow Chemical, model ACRYSOL RM-12W; the defoamer was a mineral oil defoamer, specifically BASF Foamaster MO 2190 (WBA).

[0048] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0049] The technical solution of the present invention will be further illustrated by the following embodiments.

[0050] Example 1 A method for preparing an external curing agent for concrete used in extreme high-temperature environments, comprising the following steps: S1. Preparation of silane-modified cellulose nanocrystal dispersion: 2 parts (by mass, the same below) of cellulose nanocrystals were added to 98 parts of deionized water and dispersed at 5000 rpm for 30 minutes to prepare a 2 wt% cellulose nanocrystal dispersion. The pH was adjusted to 4.5 with dilute hydrochloric acid (concentration 2.4 mol / L, the same below). 1.5 parts of (3-mercaptopropyl)trimethoxysilane (MPTS) were added dropwise while stirring at 1000 rpm. The addition time was controlled at 30 minutes. After the addition was completed, the mixture was reacted at 60℃ for 3 hours to obtain the silane-modified cellulose nanocrystal dispersion, denoted as mCNCs aqueous dispersion. S2. Preparation of pre-emulsion: In a pre-emulsion tank, add 25 parts of deionized water and 2.5 parts of composite emulsifier (the composite emulsifier consists of reactive emulsifier DNS-86, anionic emulsifier CO-436, and nonionic emulsifier OP-10, wherein the reactive emulsifier DNS-86 is 1.1 parts, the anionic emulsifier CO-436 is 0.9 parts, and the nonionic emulsifier OP-10 is 0.5 parts), stir to dissolve, and then add 100 parts of monomer mixture (the monomer mixture consists of styrene, butyl acrylate, methyl methacrylate, acrylic acid, and hydroxyethyl methacrylate, wherein styrene is 55 parts, butyl acrylate is 38.5 parts, methyl methacrylate is 4 parts, acrylic acid is 1.5 parts, and hydroxyethyl methacrylate is 1.0 part), and shear at a high speed of 3000 rpm for 15 minutes to form a stable and uniform pre-emulsion; S3. In-situ emulsion polymerization: Dissolve 0.5 parts ammonium persulfate (APS) and 0.3 parts sodium bicarbonate in 15 parts deionized water to prepare an initiator solution; add 20 parts of the mCNCs aqueous dispersion prepared in step S1 to a four-necked flask, purge with nitrogen for 30 minutes to remove oxygen, heat to 80±2℃, add 1 / 3 volume of the initiator solution, react for 20 minutes, and simultaneously add 110 parts of the pre-emulsion prepared in step S2 and the remaining 2 / 3 volume of the initiator solution through two dropping funnels. The pre-emulsion is added over 3.5 hours, and the initiator solution is added over 4 hours; after the addition is complete, keep at 80℃ for 1 hour to allow the monomers to react fully. After the reaction is complete, cool the reaction system to room temperature, add 0.2 parts benzoyl methyl ether, and then place the system under a UV lamp (wavelength 365nm, light intensity 100 mW / cm²). 2The emulsion was irradiated and stirred at 200 rpm for 15 minutes. Ammonia was added to adjust the pH of the emulsion to 8, resulting in an in-situ polymerized emulsion. (The above UV curing conditions are a small-scale laboratory example. In industrial production, those skilled in the art can make reasonable adjustments to the light source wavelength, light intensity, irradiation time, stirring speed, and reactor configuration according to equipment capabilities and material characteristics to ensure that the material is fully irradiated by ultraviolet light and completes the mercapto-olefin click chemical reaction. Such adjustments are considered to be part of the conventional process scale-up capability.) S4. Post-treatment and optimization: Pre-dilute 1.0 part of HEUR thickener with 50 parts of deionized water. Add the diluted HEUR solution to the emulsion obtained in step S3 under low-speed stirring (200 rpm) and continue stirring for 20 minutes to make it uniform. Then add 0.2 parts of defoamer and stir at low speed (200 rpm) for 10 minutes. Filter the material through a 120-mesh filter to obtain a concrete external curing agent for extreme high-temperature environments.

[0051] Example 2 A method for preparing an external curing agent for concrete used in extreme high-temperature environments, comprising the following steps: S1. Preparation of silane-modified cellulose nanocrystal dispersion: 2 parts of cellulose nanocrystals were added to 98 parts of deionized water and dispersed at 5000 rpm for 30 minutes to prepare a 2wt% cellulose nanocrystal dispersion. The pH was adjusted to 4.5 with dilute hydrochloric acid, and 1.0 part of MPTS was added dropwise under stirring at 1000 rpm for 30 minutes. After the addition was completed, the mixture was reacted at 60℃ for 3 hours to obtain the silane-modified cellulose nanocrystal dispersion, denoted as mCNCs aqueous dispersion. S2. Preparation of pre-emulsion: In a pre-emulsion tank, add 25 parts of deionized water and 2.5 parts of composite emulsifier (the composite emulsifier consists of reactive emulsifier DNS-86, anionic emulsifier CO-436, and nonionic emulsifier OP-10, wherein the reactive emulsifier DNS-86 is 1.1 parts, the anionic emulsifier CO-436 is 0.9 parts, and the nonionic emulsifier OP-10 is 0.5 parts), stir to dissolve, and then add 100 parts of monomer mixture (the monomer mixture consists of styrene, butyl acrylate, methyl methacrylate, acrylic acid, and hydroxyethyl methacrylate, wherein styrene is 50.5 parts, butyl acrylate is 43 parts, methyl methacrylate is 4 parts, acrylic acid is 1.5 parts, and hydroxyethyl methacrylate is 1.0 part), and shear at a high speed of 3000 rpm for 15 minutes to form a stable and uniform pre-emulsion; S3. In-situ emulsion polymerization: Dissolve 0.5 parts APS and 0.3 parts sodium bicarbonate in 15 parts deionized water to prepare an initiator solution; add 10 parts of the mCNCs aqueous dispersion prepared in step S1 to a four-necked flask, purge with nitrogen for 30 minutes to remove oxygen, heat to 80±2℃, add 1 / 3 volume of the initiator solution, react for 20 minutes, and simultaneously add 100 parts of the pre-emulsion prepared in step S2 and the remaining 2 / 3 volume of the initiator solution through two dropping funnels. The pre-emulsion is added over 3 hours, and the initiator solution is added over 3.5 hours; after the addition is complete, keep at 80℃ for 1 hour to allow the monomers to react fully. After the reaction is complete, cool the reaction system to room temperature, add 0.2 parts benzoyl methyl ether, and then place the system under a UV lamp (wavelength 365nm, light intensity 100 mW / cm²). 2 Irradiate and stir at 200 rpm for 15 minutes, add ammonia water, adjust the pH of the emulsion to 8, and obtain the emulsion of in-situ polymerization; S4. Post-treatment and optimization: Pre-dilute 1.5 parts of HEUR thickener with 50 parts of deionized water. Add the diluted HEUR solution to the emulsion obtained in step S3 under low-speed stirring (200 rpm) and continue stirring for 20 minutes to make it uniform. Add 0.2 parts of defoamer and stir at low speed (200 rpm) for 10 minutes. Filter the material through a 120-mesh filter to obtain a concrete external curing agent for extreme high-temperature environments.

[0052] Example 3 A method for preparing an external curing agent for concrete used in extreme high-temperature environments, comprising the following steps: S1. Preparation of silane-modified cellulose nanocrystal dispersion: 2 parts of cellulose nanocrystals were added to 98 parts of deionized water and dispersed at 5000 rpm for 30 minutes to prepare a 2wt% cellulose nanocrystal dispersion. The pH was adjusted to 4.5 with dilute hydrochloric acid, and 2.0 parts of MPTS were added dropwise under stirring at 1000 rpm for 30 minutes. After the addition was completed, the mixture was reacted at 60℃ for 3 hours to obtain the silane-modified cellulose nanocrystal dispersion, denoted as mCNCs aqueous dispersion. S2. Preparation of pre-emulsion: In a pre-emulsion tank, add 25 parts of deionized water and 2.5 parts of composite emulsifier (the composite emulsifier consists of reactive emulsifier DNS-86, anionic emulsifier CO-436, and nonionic emulsifier OP-10, wherein the reactive emulsifier DNS-86 is 1.1 parts, the anionic emulsifier CO-436 is 0.9 parts, and the nonionic emulsifier OP-10 is 0.5 parts), stir to dissolve, and then add 100 parts of monomer mixture (the monomer mixture consists of styrene, butyl acrylate, methyl methacrylate, acrylic acid, and hydroxyethyl methacrylate, wherein styrene is 52 parts, butyl acrylate is 41.5 parts, methyl methacrylate is 4 parts, acrylic acid is 1.5 parts, and hydroxyethyl methacrylate is 1.0 part), and shear at a high speed of 3000 rpm for 15 minutes to form a stable and uniform pre-emulsion; S3. In-situ emulsion polymerization: Dissolve 0.5 parts ammonium persulfate (APS) and 0.3 parts sodium bicarbonate in 15 parts deionized water to prepare an initiator solution; add 30 parts of the mCNCs aqueous dispersion prepared in step S1 to a four-necked flask, purge with nitrogen for 30 minutes to remove oxygen, heat to 80±2℃, add 1 / 3 volume of the initiator solution, react for 20 minutes, and simultaneously add 120 parts of the pre-emulsion prepared in step S2 and the remaining 2 / 3 volume of the initiator solution through two dropping funnels. The pre-emulsion is added over 3.5 hours, and the initiator solution is added over 4 hours; after the addition is complete, keep at 80℃ for 1 hour to allow the monomers to react fully. After the reaction is complete, cool the reaction system to room temperature, add 0.2 parts benzoyl methyl ether, and then place the system under a UV lamp (wavelength 365nm, light intensity 100 mW / cm²). 2 Irradiate and stir at 200 rpm for 15 minutes, add ammonia water, adjust the pH of the emulsion to 8, and obtain the emulsion of in-situ polymerization; S4. Post-treatment and optimization: Pre-dilute 1.2 parts of HEUR thickener with 50 parts of deionized water. Add the diluted HEUR solution to the emulsion obtained in step S3 under low-speed stirring (200 rpm) and continue stirring for 20 minutes to make it uniform. Add 0.2 parts of defoamer and stir at low speed (200 rpm) for 10 minutes. Filter the material through a 120-mesh filter to obtain a concrete external curing agent for extreme high-temperature environments.

[0053] Example 4 A method for preparing an external curing agent for concrete used in extreme high-temperature environments, comprising the following steps: S1. Preparation of silane-modified cellulose nanocrystal dispersion: Same as in Example 1; S2. Preparation of pre-emulsion: In a pre-emulsion tank, add 25 parts of deionized water and 2.5 parts of composite emulsifier (the composite emulsifier consists of reactive emulsifier DNS-86, anionic emulsifier CO-436, and nonionic emulsifier OP-10, wherein the reactive emulsifier DNS-86 is 1.1 parts, the anionic emulsifier CO-436 is 0.9 parts, and the nonionic emulsifier OP-10 is 0.5 parts), stir to dissolve, and then add 100 parts of monomer mixture (the monomer mixture consists of styrene, butyl acrylate, methyl methacrylate, acrylic acid, and hydroxyethyl methacrylate, wherein styrene is 53 parts, butyl acrylate is 40 parts, methyl methacrylate is 4 parts, acrylic acid is 1.5 parts, and hydroxyethyl methacrylate is 1.5 parts). Shear at high speed at 3000 rpm for 15 minutes to form a stable and uniform pre-emulsion. S3. In-situ emulsion polymerization: Dissolve 0.5 parts APS and 0.3 parts sodium bicarbonate in 15 parts deionized water to prepare an initiator solution; add 25 parts of the mCNCs aqueous dispersion prepared in step S1 to a four-necked flask, purge with nitrogen for 30 minutes to remove oxygen, heat to 80±2℃, add 1 / 3 volume of the initiator solution, react for 20 minutes, and simultaneously add 115 parts of the pre-emulsion prepared in step S2 and the remaining 2 / 3 volume of the initiator solution through two dropping funnels. The pre-emulsion is added over 3.5 hours, and the initiator solution is added over 4 hours. After the addition is complete, keep the mixture at 80℃ for 1 hour to allow the monomers to react fully. After the reaction is complete, cool the reaction system to room temperature, add 0.2 parts benzoyl methyl ether, and then place the system under a UV lamp (wavelength 365nm, light intensity 100). (mW / cm²), irradiated and stirred at 200 rpm for 15 minutes, ammonia water was added, and the pH of the emulsion was adjusted to 8 to obtain the in-situ polymerized emulsion; S4. Post-treatment and optimization: Pre-dilute 1.0 part of HEUR thickener with 50 parts of deionized water. Add the diluted HEUR solution to the emulsion obtained in step S3 under low-speed stirring (200 rpm) and continue stirring for 20 minutes to make it uniform. Add 0.2 parts of defoamer and stir at low speed (200 rpm) for 10 minutes. Filter the material through a 120-mesh filter to obtain a concrete external curing agent for extreme high-temperature environments.

[0054] Example 5 A method for preparing an external curing agent for concrete used in extreme high-temperature environments, comprising the following steps: S1. Preparation of silane-modified cellulose nanocrystal dispersion: Same as in Example 1; S2. Preparation of pre-emulsion: In a pre-emulsion tank, add 25 parts of deionized water and 2.5 parts of composite emulsifier (the composite emulsifier consists of reactive emulsifier DNS-86, anionic emulsifier CO-436, and nonionic emulsifier OP-10, wherein the reactive emulsifier DNS-86 is 1.1 parts, the anionic emulsifier CO-436 is 0.9 parts, and the nonionic emulsifier OP-10 is 0.5 parts), stir to dissolve, and then add 100 parts of monomer mixture (the monomer mixture consists of styrene, butyl acrylate, methyl methacrylate, acrylic acid, and hydroxyethyl methacrylate, wherein styrene is 54 parts, butyl acrylate is 39 parts, methyl methacrylate is 4 parts, acrylic acid is 1.5 parts, and hydroxyethyl methacrylate is 1.5 parts). Shear at high speed at 3000 rpm for 15 minutes to form a stable and uniform pre-emulsion. S3. In-situ emulsion polymerization: Dissolve 0.5 parts APS and 0.3 parts sodium bicarbonate in 15 parts deionized water to prepare an initiator solution; add 15 parts of the mCNCs aqueous dispersion prepared in step S1 to a four-necked flask, purge with nitrogen for 30 minutes to remove oxygen, heat to 80±2℃, add 1 / 3 volume of the initiator solution, react for 20 minutes, and simultaneously add 105 parts of the pre-emulsion prepared in step S2 and the remaining 2 / 3 volume of the initiator solution through two dropping funnels. The pre-emulsion is added over 3 hours, and the initiator solution is added over 3.5 hours; after the addition is complete, keep at 80℃ for 1 hour to allow the monomers to react fully. After the reaction is complete, cool the reaction system to room temperature, add 0.2 parts benzoyl methyl ether, and then place the system under a UV lamp (wavelength 365nm, light intensity 100). (mW / cm²), irradiated and stirred at 200 rpm for 15 minutes, ammonia water was added, and the pH of the emulsion was adjusted to 8 to obtain the in-situ polymerized emulsion; S4. Post-treatment and optimization: Pre-dilute 1.3 parts of HEUR thickener with 50 parts of deionized water. Add the diluted HEUR solution to the emulsion obtained in step S3 under low-speed stirring (200 rpm) and continue stirring for 20 minutes to make it uniform. Then add 0.2 parts of defoamer and stir at low speed (200 rpm) for 10 minutes. Filter the material through a 120-mesh filter to obtain a concrete external curing agent for extreme high-temperature environments.

[0055] Comparative Example 1 Same as Example 1, except that steps S1 and S3 are omitted and deionized water is used instead of the mCNCs aqueous dispersion.

[0056] Comparative Example 2 Steps S1, S2, and S3 are the same as in Example 1, except that the addition of HEUR thickener is omitted in step S4.

[0057] Comparative Example 3 Same as Example 1, except that S1 does not have a silane modification step and uses unmodified CNCs, and in S3, an equal mass fraction of CNCs aqueous dispersion is used instead of the mCNCs aqueous dispersion in Example 1.

[0058] Comparative Example 4 An emulsion-type concrete curing agent was prepared according to Example 6 of patent CN103073220A.

[0059] Performance testing: The performance of the concrete external curing agents prepared in the above examples and comparative examples was tested according to industry standard JC901-2002 "Cement Concrete Curing Agents". During testing, the slump of the concrete mix was 40mm ± 10mm as required by the standard. The concrete mix proportions are shown in Table 1. All concrete external curing agents were diluted to a solid content of 20% before use, with a coating amount of 200g / m². 2 The GK-3000 concrete admixture in Table 1 was purchased from Hebei Chang'an Yucai Technology Co., Ltd. The percentage of GK-3000 concrete admixture dosage is based on the mass of the binder, i.e., the dosage of GK-3000 concrete admixture is 0.38% of the total mass of cement and fly ash. To verify the water retention performance of the external curing agent under extreme high-temperature conditions, the curing temperature was increased from 38±2℃ to 80±2℃ based on the effective water retention rate test method in JC901-2002 "Cement Concrete Curing Agent". Furthermore, the test temperature for film-forming heat resistance was increased from 65±2℃ in the standard to 90±2℃, and melting and discoloration were observed after 10 minutes of constant temperature. The performance indicators of the concrete external curing agents prepared in the above examples and comparative examples are shown in Table 2.

[0060] Table 1 Concrete mix proportions (kg) for testing concrete external curing agents Table 2 Performance Indicators of Concrete External Curing Agents As shown in Table 2, all concrete external curing agents prepared in the examples for extreme high-temperature environments exhibit excellent overall performance. Example 3, due to its higher content of mCNCs and functional monomers, is expected to show the best performance in terms of water retention and strength enhancement, but its cost may be slightly higher. Examples 1 and 4 achieve a good balance between performance and cost. Example 2 uses the largest amount of HEUR thickener and is expected to have the best anti-sagging properties during construction, but its high-temperature water retention may be slightly lower due to slight differences in membrane structure.

[0061] Comparative Example 1 demonstrates the crucial role of mCNCs as nano-reinforcers and in forming a dense network; their absence leads to a significant decrease in the mechanical strength and durability of the water-retaining film. Comparative Example 2 demonstrates the key regulatory role of HEUR thickener in rheological properties and film-forming properties during application; its absence results in sagging during application, preventing the formation of a uniform film layer and thus affecting the water retention effect. Comparative Example 3 demonstrates the importance of silane modification for the interfacial bonding between CNCs and polymers; unmodified CNCs have poor compatibility with polymers, which may lead to interfacial defects after film formation, affecting the long-term water resistance and integrity of the film. This manifests as potentially unsatisfactory water solubility, and a reduction in water retention rate and strength ratio.

[0062] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A concrete external curing agent for use in extreme high-temperature environments, characterized in that, The product comprises the following components by weight: 10-30 parts of silane-modified cellulose nanocrystal dispersion, 15.8 parts of initiator solution, 100-120 parts of pre-emulsion, 0.2 parts of photoinitiator, 1-1.5 parts of nonionic polyurethane associative thickener, and 0.2 parts of defoamer. The raw materials for the silane-modified cellulose nanocrystal dispersion, based on parts by mass, consist of 2 parts cellulose nanocrystals, 98 parts water, and 1.0-2.0 parts (3-mercaptopropyl)trimethoxysilane. The initiator solution is composed of 0.5 parts by mass of a water-soluble thermal decomposition initiator and 0.3 parts by mass of a buffer. The water-soluble thermal decomposition initiator is ammonium persulfate and the buffer is sodium bicarbonate. The pre-emulsion is composed of 25 parts water, 2.5 parts composite emulsifier and 100 parts monomer mixture by weight. The composite emulsifier is composed of 1.1 parts reactive emulsifier, 0.9 parts anionic emulsifier and 0.5 parts nonionic emulsifier, based on parts by weight. The monomer mixture is composed of 50-55 parts styrene, 38-43 parts butyl acrylate, 4 parts methyl methacrylate, 1.5 parts hydrophilic functional monomers and 1.0-1.5 parts crosslinking functional monomers by mass.

2. The concrete external curing agent for extreme high-temperature environments according to claim 1, characterized in that, The preparation method of the silane-modified cellulose nanocrystal dispersion is as follows: cellulose nanocrystals are added to water and dispersed evenly to obtain a cellulose nanocrystal dispersion. The pH is adjusted to 4.5 with dilute hydrochloric acid, and (3-mercaptopropyl)trimethoxysilane is added. The reaction is carried out under heating conditions to obtain the silane-modified cellulose nanocrystal dispersion.

3. The concrete external curing agent for extreme high-temperature environments according to claim 2, characterized in that, The cellulose nanocrystals are carboxylated cellulose nanowhiskers.

4. The concrete external curing agent for extreme high-temperature environments according to claim 1, characterized in that, The cross-linking functional monomer is hydroxyethyl methacrylate.

5. The concrete external curing agent for extreme high-temperature environments according to claim 1, characterized in that, The hydrophilic functional monomer is acrylic acid.

6. The concrete external curing agent for extreme high-temperature environments according to claim 1, characterized in that, The reactive emulsifier is 1-allyloxy-3-(4-nonylphenol)-2-propanol polyoxyethylene (10) ether ammonium sulfate; the anionic emulsifier is nonylphenol polyoxyethylene (4) ether ammonium sulfate; and the nonionic emulsifier is dodecylphenol polyoxyethylene ether.

7. The concrete external curing agent for extreme high-temperature environments according to claim 1, characterized in that, The photoinitiator is benzoyl methyl ether; the defoamer is selected from mineral oil defoamers.

8. A method for preparing a concrete external curing agent for extreme high-temperature environments as described in any one of claims 1-7, characterized in that, Includes the following steps: Weigh each raw material according to its mass fraction; Reactive emulsifiers, anionic emulsifiers, nonionic emulsifiers and water are mixed and stirred to dissolve. Styrene, butyl acrylate, methyl methacrylate, hydrophilic functional monomers and crosslinking functional monomers are added and stirred evenly to form a pre-emulsion. A water-soluble thermal decomposition and buffer agent is added to water to form an initiator solution; One-third volume of initiator solution was added to the silane-modified cellulose nanocrystal dispersion. After the reaction, the pre-emulsion and the remaining two-thirds volume of initiator solution were added. The reaction was carried out under heating conditions. After the reaction was completed, the temperature was lowered to room temperature, a photoinitiator was added, and the curing reaction was carried out under ultraviolet conditions. After the curing reaction was completed, the pH was adjusted to 8 to obtain an in-situ polymerized emulsion. A diluted nonionic polyurethane associative thickener solution was added to the in-situ polymerized emulsion, stirred until homogeneous, and then an antifoaming agent was added. The mixture was then filtered to obtain the concrete external curing agent for extreme high-temperature environments.

9. The use of a concrete external curing agent for extreme high temperature environments as described in any one of claims 1-7 in the preparation of concrete for use in extreme high temperature environments.

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