An epoxy resin-graphene composite underwater repair material and a preparation method and application thereof

Abstract

The application belongs to the technical field of hydraulic engineering materials, and particularly relates to an epoxy resin-graphene composite underwater repairing material and a preparation method and application thereof. Components of the epoxy resin-graphene composite underwater repairing material of the application include a composite prepolymer, a curing agent, a thixotropic agent and a preservative. Components of the composite prepolymer include a graphene dispersion liquid, an epoxy resin, a waterproof modifier and a toughening agent. The epoxy resin-graphene composite underwater repairing material of the application has excellent underwater construction performance and long-term durability, can be normally cured in water or a humid environment, is helpful to realize high-strength bonding, and has good anti-permeation effect.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy engineering materials technology, specifically relating to an epoxy resin-graphene composite underwater repair material, its preparation method, and its application. Background Technology

[0002] Concrete structures in hydraulic engineering projects are exposed to complex aquatic environments for extended periods, facing multiple challenges including osmotic pressure, chemical corrosion, and freeze-thaw cycles, making them prone to cracking, leakage, and corrosion. Traditional underwater repair materials mainly include underwater concrete, polymer mortar, and epoxy resin, but these have the following problems:

[0003] First, traditional epoxy resin materials are difficult to cure in underwater environments, resulting in low bond strength and making it difficult to form effective bonds under humid or underwater conditions. Second, existing repair materials lack sufficient impermeability and durability, and are prone to performance degradation under long-term water exposure. Third, traditional materials lack sufficient toughening properties, making them prone to cracking under structural deformation and temperature changes.

[0004] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0005] The purpose of this invention is to provide an epoxy resin-graphene composite underwater repair material, its preparation method, and its application, so as to help solve or improve the problem of poor underwater repair effect of traditional epoxy resin materials.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an epoxy resin-graphene composite underwater repair material, wherein the components of the epoxy resin-graphene composite underwater repair material include: a composite prepolymer, a curing agent, a thixotropic agent, and a preservative; the components of the composite prepolymer include a graphene dispersion, an epoxy resin, a waterproof modifier, and a toughening agent.

[0007] Preferably, the mass ratio of the graphene dispersion to the epoxy resin is 1:(8-15); the mass ratio of the composite prepolymer to the curing agent is 10:(2-4).

[0008] Preferably, the epoxy resin is a mixture of bisphenol A type epoxy resin and polyether modified epoxy resin; the mass ratio of the bisphenol A type epoxy resin and the polyether modified epoxy resin is (3-7):1, and the epoxy value is 0.45-0.65 equivalents / 100g.

[0009] Preferably, the waterproof modifier is an organosilane-modified polyurethane prepolymer containing isocyanate groups and siloxane structures, with a molecular weight of 2000-8000; the mass ratio of the waterproof modifier to the epoxy resin is (0.5-2):(8-15).

[0010] Preferably, the organosilane-modified polyurethane prepolymer is prepared by a method comprising the following steps: A1, reacting polyether polyol and isocyanate monomer at a molar ratio of 1:(2-2.5) under nitrogen protection at 70-90°C for 2-4 hours to obtain a polyurethane prepolymer with terminal isocyanate groups; A2, adding a silane coupling agent containing amino or epoxy groups to the above prepolymer, wherein the molar ratio of the silane coupling agent to the isocyanate groups in the prepolymer is (0.1-0.3):1, and reacting at 50-70°C for 1-3 hours to allow the active groups in the silane coupling agent to react with some of the isocyanate groups, thereby grafting the siloxane structure onto the polyurethane backbone; A3, cooling to room temperature to obtain the organosilane-modified polyurethane prepolymer containing isocyanate groups and a siloxane structure.

[0011] Preferably, the toughening agent is at least one of polyetheramine, amino-terminated nitrile rubber, and flexible aliphatic diamine; the mass ratio of the toughening agent to the epoxy resin is (0.2-1):(8-15); the preservative is at least one of zinc phosphate, molybdate, and zinc powder; and the mass ratio of the preservative to the curing agent is (0.05-0.3):(2-4).

[0012] Preferably, the curing agent is a modified polyamine curing agent; the modified polyamine curing agent has an amine value of 200-450 mg KOH / g and a viscosity of 500-3000 mM. It contains hydrophilic polyethylene glycol segments and hydrophobic aliphatic or alicyclic amino groups as active groups.

[0013] Preferably, the modified polyamine curing agent is prepared by a method comprising the following steps: B1, using an aliphatic polyether amine or an alicyclic amine as a base curing agent, wherein the amine value of the base curing agent is 300-600 mg KOH / g, and heating to 60-80°C under nitrogen protection; B2, adding polyethylene glycol glycidyl ether or polyethylene glycol diglycidyl ether dropwise to the base curing agent as a hydrophilic modifier, wherein the number average molecular weight of the polyethylene glycol segments of the hydrophilic modifier is 40. 0-2000, epoxy value 0.3-0.8 equivalents / 100g, mass ratio of hydrophilic modifier to base curing agent is (0.2-0.5):1; during the dripping process, control the hourly dripping amount to not exceed 30% of the total amount; after the dripping is completed, react at 70-90℃ for 3-6h until the amine value drops to 65%-80% of the initial value; B3, cool to below 50℃, add defoamer and leveling agent, mix thoroughly to obtain modified polyamine curing agent.

[0014] Preferably, the thixotropic agent is modified bentonite or organosilicon thixotropic agent, and the mass ratio of the thixotropic agent to the curing agent is (0.1-0.5):(2-4).

[0015] Preferably, the modified bentonite is prepared by a method comprising the following steps: C1, preparing an organic modifier solution by dissolving a quaternary ammonium cationic surfactant in deionized water to prepare an aqueous solution with a mass concentration of 10%-20%; C2, dispersing dry bentonite powder in hot water at a solid-liquid mass ratio of 1:(5-10) in 60-80°C, stirring for 30-60 minutes to allow it to fully swell and disperse, forming a uniform bentonite suspension; C3, adding the organic modifier solution dropwise under continuous stirring, wherein the organic modifier... The dosage is calculated as 100%-150% of the cation exchange capacity of bentonite, that is, 100-150 mmol of quaternary ammonium salt is added for every 100 mmol of cation exchange capacity. The dropping time is controlled at 1-2 hours. After the dropping is completed, the reaction is continued to be stirred at 70-90℃ for 2-4 hours. C4. After the reaction is completed, the mixture is allowed to stand and separate into layers. The supernatant is discarded, and the precipitate is washed with hot water 3-5 times. C5. The washed modified bentonite is dried, ground, and passed through a 200-mesh sieve at 80-120℃ to obtain the modified bentonite.

[0016] The present invention also provides a method for preparing the epoxy resin-graphene composite underwater repair material as described above, which adopts the following technical solution: The method for preparing the epoxy resin-graphene composite underwater repair material as described above includes the following steps: S1, mixing the graphene dispersion with epoxy resin, waterproof modifier and toughening agent to obtain a composite prepolymer; S2, mixing the composite prepolymer with curing agent, thixotropic agent and preservative.

[0017] Preferably, the method further includes step S3: after step S2, pre-curing is carried out at 25-35°C and 65%-85% relative humidity for 2-6 hours.

[0018] The present invention also provides an application of the epoxy resin-graphene composite underwater repair material as described above, which adopts the following technical solution: the application of the epoxy resin-graphene composite underwater repair material as described above in underwater crack repair, seepage prevention reinforcement and corrosion protection of concrete structures in hydraulic engineering.

[0019] Beneficial effects:

[0020] The epoxy resin-graphene composite underwater repair material of the present invention has excellent underwater construction performance and long-term durability. It can cure normally underwater or in humid environments, which helps to achieve high-strength bonding and has good anti-seepage effect.

[0021] The epoxy resin-graphene composite underwater repair material of this invention is highly environmentally friendly, has a simple process flow, low equipment requirements, low raw material costs, is easy to scale up production, and offers significant economic benefits. Furthermore, this epoxy resin-graphene composite underwater repair material exhibits outstanding application performance and good construction properties, making it suitable for various underwater construction methods and applicable to the repair of hydraulic and marine engineering structures.

[0022] The epoxy resin-graphene composite underwater repair material of the present invention has excellent underwater curing performance. It can cure normally in the underwater environment with an initial setting time of 2-4 hours, an underwater bonding strength of more than 15 MPa, a compressive strength of more than 80 MPa, and an impermeability grade of P12, which meets the technical requirements of water conservancy projects. Attached Figure Description

[0023] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. Wherein:

[0024] Figure 1 This is a schematic diagram of the overall chemical structure of an epoxy resin-graphene composite underwater repair material according to an embodiment of the present invention.

[0025] Figure 2 This is a schematic diagram of the layered functional structure of an epoxy resin-graphene composite underwater repair material according to an embodiment of the present invention; wherein, R represents the polyurethane main chain structure. Detailed Implementation

[0026] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0027] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0028] This invention addresses the problem of poor underwater repair performance of traditional epoxy resin materials by providing an epoxy resin-graphene composite underwater repair material.

[0029] The epoxy resin-graphene composite underwater repair material of this invention comprises: a composite prepolymer, a curing agent, a thixotropic agent, and a preservative; the composite prepolymer comprises graphene dispersion, epoxy resin, a waterproof modifier, and a toughening agent.

[0030] The composite prepolymer exhibits excellent underwater adaptability, and the graphene dispersion achieves good interfacial bonding with the epoxy resin matrix, laying the foundation for the high performance of the epoxy resin-graphene composite underwater repair material of this invention. Furthermore, the graphene dispersion, as the core functional component of this invention, plays the following important roles in the composite underwater repair material: the synergistic effect of the graphene dispersion and the siloxane structure of the waterproofing modifier forms a three-dimensional barrier network during underwater curing, effectively blocking the penetration of water molecules and chloride ions, and improving the anti-seepage effect. Simultaneously, graphene, as a nano-reinforcing phase, helps to significantly improve the mechanical properties of the cured material, compensating for the strength reduction caused by underwater curing, and through its high specific surface area and oxygen-containing functional groups, forms multi-point anchoring at the wet interface, improving underwater bonding strength.

[0031] In this invention, the thixotropic agent can be organically modified bentonite or a hydrophobic organosilicon thixotropic agent. Its long alkyl chains and siloxane structure endow it with excellent hydrophobic properties, and the resulting hydrogen-bonded, physically entangled three-dimensional network is not easily destroyed in the underwater environment, maintaining high yield stress and thixotropic index. This network reversibly dissociates under shear force, causing a rapid decrease in material viscosity, facilitating construction. After shearing stops, the network quickly rebuilds, achieving rapid underwater positioning and preventing sagging. The thixotropic agent, curing agent (preferably a hydrophilic-hydrophobic amphiphilic curing agent), and waterproofing modifier (organosilane-modified polyurethane prepolymer) in the composite prepolymer work synergistically to ensure the material maintains excellent construction performance and morphological stability in the underwater environment.

[0032] The epoxy resin-graphene composite underwater repair material of the present invention has excellent underwater construction performance and long-term durability. It can be cured normally underwater or in humid environments to achieve high-strength bonding and long-term protection.

[0033] In a preferred embodiment of the epoxy resin-graphene composite underwater repair material of the present invention, the mass ratio of graphene dispersion to epoxy resin is 1:(8-15) (e.g., 1:8, 1:10, 1:12, 1:14, or 1:15); the mass ratio of composite prepolymer to curing agent is 10:(2-4) (e.g., 10:2, 10:2.5, 10:3, 10:3.5, or 10:4). If the mass ratio of graphene dispersion to epoxy resin is too small, an effective synergistic seepage-proof network cannot be formed, leading to a decrease in underwater bonding strength and reduced seepage resistance. If the mass ratio of graphene dispersion to epoxy resin is too large, excessive aqueous medium will interfere with the underwater curing reaction and prolong the curing time, causing graphene to agglomerate and form stress concentration points, resulting in a decrease in material strength. Simultaneously, excessively high viscosity of the composite prepolymer will affect fluidity and crack penetration capacity.

[0034] In a preferred embodiment of the epoxy resin-graphene composite underwater repair material of the present invention, the epoxy resin is a mixture of bisphenol A type epoxy resin and polyether modified epoxy resin; the mass ratio of bisphenol A type epoxy resin to polyether modified epoxy resin is (3-7):1 (e.g., 3:1, 4:1, 5:1, 6:1 or 7:1), and the epoxy value of the epoxy resin (the mixture of bisphenol A type epoxy resin and polyether modified epoxy resin) is 0.45-0.65 equivalents / 100g (e.g., 0.45 equivalents / 100g, 0.5 equivalents / 100g, 0.55 equivalents / 100g, 0.6 equivalents / 100g or 0.65 equivalents / 100g). Here, the epoxy value refers to the epoxy value of the mixed system measured after mixing the bisphenol A type epoxy resin and polyether modified epoxy resin according to the above mass ratio. The epoxy value reflects the concentration of epoxy groups in the epoxy resin and is a key parameter determining the curing reactivity and properties of the cured product. Controlling the epoxy value of the mixed epoxy resin system within the range of 0.45-0.65 equivalents / 100g is based on the following technical considerations: Too low an epoxy value leads to insufficient crosslinking density, resulting in decreased bond strength; too high an epoxy value degrades the toughness of the cured product, increases shrinkage, and generates internal stress and microcracks during underwater curing, affecting interfacial adhesion.

[0035] Furthermore, this invention employs a combination of bisphenol A type epoxy resin and polyether-modified epoxy resin because: bisphenol A type epoxy resin provides a high-strength skeleton and corrosion resistance, but its hydrophobicity is poor, making underwater interfacial bonding susceptible to water erosion; the polyether segments of the polyether-modified epoxy resin are hydrophilic, capable of wetting the surface of damp substrates and removing interfacial water films, while its flexible segments help improve toughness, and its low viscosity facilitates underwater penetration and filling. The combination of these two materials achieves synergy, balancing strength and interfacial adaptability in the underwater curing system, improving underwater bond strength, and simultaneously possessing good application flowability and long-term durability.

[0036] In a preferred embodiment of the epoxy resin-graphene composite underwater repair material of the present invention, the waterproofing modifier is an organosilane-modified polyurethane prepolymer containing isocyanate groups and a siloxane structure, with a molecular weight of 2000-8000; the mass ratio of the waterproofing modifier to the epoxy resin is (0.5-2):(8-15) (e.g., 0.5:8, 0.5:12, 0.5:15, 2:8, 2:10, 2:15, 1:8, 1:15, or 1:9). The use of organosilane-modified polyurethane prepolymer as the waterproofing modifier allows the isocyanate groups in the prepolymer to react with the hydroxyl and amino groups in the epoxy resin curing system, chemically bonding the waterproofing modifier to the cross-linked network, thus avoiding the problem of easy migration and loss of physically added waterproofing agents. Furthermore, the isocyanate groups it contains can react with water to form urea bonds and release CO2, actively driving away interfacial moisture, achieving in-situ underwater curing and forming a strong bond with the damp substrate. This is a key characteristic that distinguishes it from traditional epoxy resin repair materials. By repelling water films on the substrate surface and forming effective bonds with damp concrete surfaces, it helps improve underwater adhesion strength. Simultaneously, the flexibility of the polyurethane segments reduces curing shrinkage microcracks, and its siloxane structure and graphene sheets can form a synergistic barrier effect, filling the micropores of the cured network, improving impermeability, and achieving excellent underwater sealing performance.

[0037] In a preferred embodiment of the epoxy resin-graphene composite underwater repair material of the present invention, the organosilane-modified polyurethane prepolymer is prepared by a method comprising the following steps: A1, mixing polyether polyol and isocyanate monomer in a molar ratio of 1:(2-2.5) (e.g., 1:2, 1:2.1, 1:2.2, 1:2.3, 1:2.4, 1:2.5) under nitrogen protection at 70-90°C (e.g., 70°C, 80°C, or 90°C). The polyurethane prepolymer with terminal isocyanate groups is obtained after 2-4 hours (e.g., 2h, 3h, or 4h); wherein the polyether polyol is at least one selected from polytetrahydrofuran glycol, polypropylene glycol, and polyethylene glycol, with a number average molecular weight of 1000-4000, and the isocyanate monomer is at least one selected from toluene diisocyanate, diphenylmethane diisocyanate, and isophorone diisocyanate; A2, a silane coupling agent containing amino or epoxy groups is added to the above prepolymer, the silane... The silane coupling agent is at least one selected from 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, and N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane, wherein the molar ratio of the silane coupling agent to the isocyanate groups in the prepolymer is (0.1-0.3):1 (e.g., 0.1:1, 0.2:1, or 0.3:1), and the reaction is carried out at 50-70°C (e.g., 50°C, 60°C, or 70°C) for 1-3 hours. (1h, 2h, or 3h) to allow the active groups in the silane coupling agent to react with some of the isocyanate groups, grafting the siloxane structure onto the polyurethane backbone; A3, cooling to room temperature to obtain an organosilane-modified polyurethane prepolymer containing isocyanate groups and a siloxane structure (preferably, the molecular weight of the organosilane-modified polyurethane prepolymer is 2000-8000, the isocyanate group content is 3wt%-8wt%, and the silicon content is 1wt%-4wt%). During the preparation process, moisture content must be strictly controlled; the moisture content of the reaction system should be below 100ppm to avoid the reaction of isocyanate groups with water, which would lead to a decrease in the prepolymer's performance.

[0038] In step A2, the proportion of silane coupling agent significantly affects the performance of the organosilane-modified polyurethane prepolymer of this invention. The amount of silane coupling agent should be sufficient to allow the prepolymer to retain enough isocyanate groups (3wt%-8wt%) for reaction with hydroxyl or amine groups in the epoxy resin system, while also introducing an appropriate amount of siloxane structure to impart waterproofing properties. If the proportion of silane coupling agent is too high, it will consume too many isocyanate groups, reducing the reactivity and compatibility of the prepolymer with the epoxy system. Furthermore, controlling the molecular weight of the organosilane-modified polyurethane prepolymer within the range of 2000-8000 helps balance the flowability and film-forming properties of the waterproofing modifier. If the molecular weight of the organosilane-modified polyurethane prepolymer is too low, it will lead to increased volatility and poor waterproofing effect. If the molecular weight of the organosilane-modified polyurethane prepolymer is too high, it will result in excessive viscosity, affecting its dispersion uniformity in the epoxy resin system.

[0039] In a preferred embodiment of the epoxy resin-graphene composite underwater repair material of the present invention, the toughening agent is at least one of polyetheramine, amino-terminated nitrile rubber and flexible aliphatic diamine; the mass ratio of the toughening agent to the epoxy resin is (0.2-1):(8-15) (e.g., 0.2:8, 0.2:12, 0.2:15, 0.6:8, 0.6:10, 0.6:15, 1:8, 1:15 or 1:9).

[0040] In a preferred embodiment of the epoxy resin-graphene composite underwater repair material of the present invention, the curing agent is a modified polyamine curing agent, comprising hydrophilic segments and hydrophobic curing active groups. The modified polyamine curing agent used in this invention is a self-made product, prepared through a specific chemical modification process to achieve a reasonable configuration of hydrophilic segments and hydrophobic curing active groups, ensuring the excellent performance of the curing agent in an underwater environment.

[0041] Preferably, the modified polyamine curing agent is prepared by a method comprising the following steps: B1. Using an aliphatic polyether amine (a compound with a primary amino group at the end of the polyether backbone) or an alicyclic amine (an amine compound with an amino group attached to an alicyclic structure; for example, isophorone diamine, dicyclohexylmethane diamine, etc.) as a base curing agent, wherein the amine value of the base curing agent is 300-600 mg KOH / g (e.g., 600 mg KOH / g, 600 mg KOH / g, 600 mg KOH / g or 600 mg KOH / g). H / g), heated to 60-80℃ (e.g., 60℃, 70℃ or 80℃) under nitrogen protection; wherein, the aliphatic polyether amine is selected from polyether diamine or polyether triamine, with a number average molecular weight of 200-2000; the alicyclic amine is selected from at least one of isophorone diamine, dicyclohexylmethane diamine and m-phenylenediamine; B2, polyethylene glycol glycidyl ether or polyethylene glycol diglycidyl ether is added dropwise to the base curing agent as a hydrophilic modifier, wherein the number average molecular weight of the polyethylene glycol segment of the hydrophilic modifier is 400-2 The epoxy value is 0.3-0.8 equivalents / 100g, and the mass ratio of hydrophilic modifier to base curing agent is (0.2-0.5):1 (e.g., 0.2:1, 0.3:1, 0.4:1, or 0.5:1). The dripping rate should be controlled during the dripping process, with the hourly dripping amount not exceeding 30% of the total amount to avoid localized overheating. After dripping, the reaction should be carried out at 70-90℃ (e.g., 70℃, 80℃, or 90℃) for 3-6 hours (e.g., 3h, 4h, 5h, or 6h). The process involves a ring-opening addition reaction between the epoxy groups in the hydrophilic modifier and some of the primary amine groups in the base curing agent, grafting polyethylene glycol segments onto the base curing agent molecule to form a hydroxyl-containing secondary amine structure. During the reaction, the amine value needs to be measured periodically. The reaction is stopped when the amine value drops to 65%-80% of the initial value to ensure that the curing agent retains sufficient active amines for the curing reaction of the epoxy resin. B3. After cooling to below 50°C, an appropriate amount of defoamer and leveling agent are added and thoroughly mixed to obtain the modified polyamine curing agent. Preferably, the modified polyamine curing agent is a light yellow to amber transparent or semi-transparent liquid with an amine value of 200-450 mgKOH / g (e.g., 200 mgKOH / g, 300 mgKOH / g, 400 mgKOH / g, or 450 mgKOH / g) and a viscosity of 500-3000 mg / g. (For example, 500m) 1000m 2000m or 3000m It contains hydrophilic polyethylene glycol segments and hydrophobic aliphatic or alicyclic amino groups as active groups.

[0042] The core of this preparation method lies in precisely controlling the amount of hydrophilic modifier and the degree of reaction to achieve molecular structure regulation. The reaction is controlled within the range of 65%-80% of the initial amine value, introducing sufficient hydrophilic polyethylene glycol segments (molecular weight 400-2000) to improve underwater curing performance while retaining sufficient active amino groups for epoxy crosslinking. This modification strategy creatively solves the technical bottlenecks faced by traditional hydrophobic polyamine curing agents in underwater environments, such as poor wetting and low curing efficiency due to water molecule competition. The modified curing agent effectively penetrates the water film on the substrate surface through hydrophilic segments to establish direct contact. Simultaneously, the polyethylene glycol segments preferentially combine with water molecules to form a hydration layer, protecting the active amino groups from water molecule attack, significantly reducing side reactions, and improving curing efficiency and crosslinking density. This unconventional technical route, which promotes drainage through hydrophilicity and adapts to the aquatic environment for underwater curing, helps to improve underwater curing speed and bond strength, reduce internal bubbles and porosity of the cured product, and shorten the initial setting time. The effect of this modified polyamine curing agent is significantly better than that of conventional curing agents.

[0043] In a preferred embodiment of the epoxy resin-graphene composite underwater repair material of the present invention, the thixotropic agent is modified bentonite or organosilicon thixotropic agent, and the mass ratio of the thixotropic agent to the curing agent is (0.1-0.5):(2-4) (e.g., 0.1:2, 0.1:3, 0.1:4, 0.3:2, 0.3:3, 0.3:4, 0.5:2, 0.5:3 or 0.5:4); the preservative is at least one of zinc phosphate, molybdate and zinc powder, and the mass ratio of the preservative to the curing agent is (0.05-0.3):(2-4) (e.g., 0.05:2, 0.05:3, 0.05:4, 0.15:2, 0.15:3, 0.15:4, 0.3:2, 0.3:3 or 0.3:4). Among them, the modified bentonite is a self-made product, prepared through an organic modification process to ensure its dispersibility and thixotropic effect in the epoxy resin system; the organosilicon thixotropic agent can be a commercially available product, such as a thixotropic agent product made by surface treatment of fumed silica with organosilicon.

[0044] Preferably, the modified bentonite is prepared by a method comprising the following steps: C1. Drying sodium-based bentonite at 80-100℃ (e.g., 80℃, 90℃, or 100℃) for 2-4 hours (e.g., 2 hours, 3 hours, or 4 hours) to reduce its moisture content to below 5%, and grinding it through a 200-mesh sieve to obtain dried bentonite powder; wherein the cation exchange capacity of the sodium-based bentonite should be not less than 80 mmol / 100g, and the swelling capacity should be not less than 15 mL / 2g; C2. Preparing an organic modifier solution by dissolving a quaternary ammonium salt cationic surfactant in deionized water to prepare an aqueous solution with a mass concentration of 10%-20%; wherein the quaternary ammonium salt cationic surfactant... The surfactant is at least one of hexadecyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dioctadecyldimethylammonium chloride, and benzylhexadecyldimethylammonium chloride; C3, dry bentonite powder is dispersed in hot water at 60-80°C (e.g., 60°C, 70°C, or 80°C) at a solid-liquid mass ratio of 1:(5-10) (e.g., 1:5, 1:6, 1:7, 1:8, 1:9, or 1:10), and stirred for 30-60 min (e.g., 30 min, 40 min, 50 min, or 60 min) to allow it to fully swell and disperse, forming a uniform bentonite suspension; C4, the above-mentioned organic modifier is slowly added dropwise under continuous stirring. The amount of organic modifier added to the solution is calculated based on 100%-150% of the cation exchange capacity of bentonite, i.e., 100-150 mmol of quaternary ammonium salt is added per 100 mmol of cation exchange capacity. The dropping time is controlled at 1-2 hours (e.g., 1 hour, 1.3 hours, 1.6 hours, or 2 hours). After the dropping is completed, the reaction is continued at 70-90°C (e.g., 70°C, 80°C, or 90°C) with stirring for 2-4 hours (e.g., 2 hours, 3 hours, or 4 hours). This allows the cations in the quaternary ammonium salt to enter the bentonite interlayer through ion exchange, displacing inorganic sodium ions. Simultaneously, the long-chain alkyl groups of the quaternary ammonium salt enter the bentonite layers, expanding the interlayer spacing and altering the... The surface of the bentonite changes from hydrophilic to hydrophobic; C5. After the reaction, allow it to stand and separate into layers, discard the upper clear liquid, and wash the precipitate with hot water 3-5 times. After each wash, centrifuge or filter to remove the wash water until the chloride ion content in the wash water is less than 50 ppm; C6. Dry the washed modified bentonite at 80-120℃ (e.g., 80℃, 90℃, 100℃, 110℃ or 120℃) for 6-12 hours (e.g., 6h, 7h, 8h, 9h, 10h, 11h or 12h). Turn it over every 2 hours during the drying process to ensure uniform drying; C7. After drying, grind it and pass it through a 200-mesh sieve to obtain the modified bentonite product. The modified bentonite is a light gray to light yellow powder with an organic content of 25wt%-40wt%. The interlayer spacing is increased from 1.2-1.5nm before modification to 1.8-3.5nm. It exhibits good dispersibility and thixotropy in polar solvents and epoxy resins.

[0045] This invention modifies bentonite by increasing the interlayer spacing from 1.2-1.5 nm to 1.8-3.5 nm through quaternary ammonium salt ion exchange (addition amount of 100%-150% of cation exchange capacity), transforming the surface from hydrophilic to hydrophobic. This innovatively solves the technical bottleneck of natural bentonite agglomerating into defect sources in epoxy resin systems due to its strong hydrophilicity, and swelling and damaging material integrity in underwater environments due to water absorption. The modified bentonite exhibits good compatibility with epoxy resin. The increased interlayer spacing facilitates the peeling of layers to form a nanoscale three-dimensional network structure, providing excellent thixotropic properties (thixotropic index 3.5-5.5), preventing sagging during standing and reducing viscosity during construction. The hydrophobic surface prevents material damage due to water absorption and swelling in underwater repair applications, while the layered barrier structure extends the water molecule penetration path, improving impermeability. Compared to the phase separation and high porosity (8%-12%) of natural bentonite, modified bentonite has better anti-sagging properties, which helps to reduce the porosity of the solidified material, improve the impermeability, and reduce the water absorption rate.

[0046] Selection guidelines for organosilicon thixotropic agents: When using organosilicon thixotropic agents, hydrophobic thixotropic agents prepared by the gas phase method and surface-treated with organosilicones such as dimethyldichlorosilane, hexamethyldisilazane, or polydimethylsiloxane are preferred, with a specific surface area of ​​150-300 m². 2 / g, particle size 5-20nm, hydrophobicity greater than 50%; commercially available products such as Degussa's Aerosil R972 and R974 or Cabot's Cab-O-Sil TS-720 can meet the requirements. Organosilicon thixotropic agents form a three-dimensional network structure in epoxy resin systems through hydrogen bonding and physical entanglement, endowing the material with excellent thixotropic and anti-sagging properties.

[0047] In a preferred embodiment of the epoxy resin-graphene composite underwater repair material of the present invention, the graphene dispersion is prepared by a method comprising the following steps: (1) pre-impregnation treatment, in which expandable graphite is impregnated in a mixed solution of hydrosilicone oil and tetraethyl orthosilicate for 0.5-4 h (e.g., 0.5 h, 1 h, 2 h, 3 h or 4 h); (2) microwave expansion, in which the pre-impregnated expandable graphite is heated for 5-60 s (e.g., 5 s, 10 s, 20 s, 30 s, 40 s, 50 s or 60 s) under microwave power of 800-1200 W (e.g., 800 W, 900 W, 1000 W, 1100 W or 1200 W) to obtain expanded graphite; (3) preparation of a stripping solution, in which 0.1-5 parts (e.g., 0.1 parts, 1 part, 2 parts, 3 parts, 4 parts or 5 parts) of an alkaline catalyst calcium hydroxide and silane are coupled. Mix 1-10 parts of agent (e.g., 1 part, 3 parts, 5 parts, 7 parts, 9 parts or 10 parts), 10-50 parts of ethanol (e.g., 10 parts, 20 parts, 30 parts, 40 parts or 50 parts) and 50-200 parts of water (e.g., 50 parts, 100 parts, 150 parts or 200 parts) by weight to obtain a stripping solution; (4) Stripping and dispersion: add expanded graphite to the stripping solution and disperse it for 30-120 min (e.g., 30 min, 60 min, 90 min or 120 min) at a speed of 5000-20000 rpm (e.g., 5000 rpm, 10000 rpm, 15000 rpm or 20000 rpm) using a high-speed shear emulsifier. Use hydrogen gas generated by hydrogen-containing silicone oil for chemical stripping. At the same time, silane coupling agent and calcium ions form a polysilsesquioxane structure to stabilize graphene and obtain a graphene dispersion.

[0048] While graphene possesses excellent mechanical and barrier properties, its dispersion stability and interfacial bonding in polymer matrices have always been challenging issues for its application. This invention addresses the specific requirements of underwater-curing epoxy resin systems by developing a graphene dispersion preparation technology, enabling the effective application of graphene in underwater repair materials.

[0049] The graphene dispersion prepared by the method of this invention exhibits excellent dispersion stability. The polysilsesquioxane structure formed by the silane coupling agent and calcium ions effectively stabilizes the graphene, and the dispersion remains stable in an aqueous medium for a long period of time, showing no significant precipitation after standing for 6 months.

[0050] Preferably, the hydrogen-containing silicone oil is a polymethylhydrosiloxane containing Si-H bonds or a copolymer of polymethylhydrosiloxane and polydimethylsiloxane, with a molecular weight of 1000-10000; the weight ratio of tetraethyl orthosilicate to the hydrogen-containing silicone oil is 1:0.5-1:3 (e.g., 1:0.5, 1:1, 1:2 or 1:3).

[0051] Preferably, the silane coupling agent is an amino-containing silane coupling agent, including at least one of 3-aminopropyltriethoxysilane, N-(β-aminoethyl)-γ-aminopropyltrimethoxysilane and N-phenyl-3-aminopropyltrimethoxysilane.

[0052] Preferably, in step (4), the weight ratio of expanded graphite to the stripping solution is 1:10 to 1:100 (e.g., 1:10, 1:30, 1:50, 1:70, 1:90 or 1:100).

[0053] Preferably, step (4) is followed by a centrifugation step, in which the graphite agglomerates are removed by centrifugation at a speed of 2000-8000 rpm (e.g., 2000 rpm, 4000 rpm, 6000 rpm or 8000 rpm) for 30-90 min (e.g., 30 min, 50 min, 70 min or 90 min) under nitrogen or argon protection.

[0054] Preferably, the graphene dispersion contains 0.5-2.0 mg / mL of graphene (e.g., 0.5 mg / mL, 1.0 mg / mL, 1.5 mg / mL or 2.0 mg / mL) and has 2-8 layers.

[0055] This invention also proposes a method for preparing an epoxy resin-graphene composite underwater repair material. The method for preparing the epoxy resin-graphene composite underwater repair material in this embodiment includes the following steps: S1, mixing graphene dispersion with epoxy resin, waterproof modifier and toughening agent to obtain composite prepolymer; S2, mixing composite prepolymer with curing agent, thixotropic agent and preservative.

[0056] In a preferred embodiment of the preparation method of the epoxy resin-graphene composite underwater repair material of the present invention, step S3 is further included: after step (2), pre-curing for 2-6 hours (e.g., 2 hours, 3 hours, 4 hours, 5 hours or 6 hours) under the conditions of 25-35°C (e.g., 25°C, 27°C, 30°C, 32°C or 35°C) and relative humidity of 65%-85% (e.g., 65%, 70%, 75%, 80% or 85%).

[0057] The present invention also proposes the application of the epoxy resin-graphene composite underwater repair material as described above: the application of the epoxy resin-graphene composite underwater repair material as described above in underwater crack repair, seepage prevention reinforcement and corrosion protection of concrete structures in hydraulic engineering.

[0058] The epoxy resin-graphene composite underwater repair material of the present invention, its preparation method, and its application are described in detail below through specific embodiments.

[0059] The sources of the main raw materials used in the following examples are as follows: Expandable graphite: Qingdao Tianshengda Graphite Co., Ltd., model KP300, flake graphite, 80 mesh, expandable ratio 300 times, fixed carbon content ≥99%; Hydrogen-containing silicone oil: Jiangxi Lanxing Xinghuo Organosilicon Co., Ltd., model DH-3000; Polymethylhydrosiloxane, number average molecular weight 3000, hydrogen content 1.5%-1.6%; Tetraethyl orthosilicate: Nanjing Shuguang Chemical Group Co., Ltd., industrial grade, purity ≥99%; Calcium hydroxide: Tianjin Kemio Chemical Reagent Co., Ltd., analytical grade; 3-aminopropyltriethoxysilane: Nanjing Shuguang Silicon Industry Co., Ltd., model KH-550, purity ≥98%; Bisphenol A type epoxy resin: Jiangsu Sanmu Group Co., Ltd., model E-51, epoxy value 0.51 equivalents / 100g, viscosity 11000-14000m (25℃); Polyether-modified epoxy resin: Wuxi Resin Factory Co., Ltd., model FEP-02, epoxy value 0.35 equivalents / 100g, viscosity 800-1500m (25℃); Organosilane-modified polyurethane prepolymer: prepared according to the method described in this specification, wherein the polyether polyol is polytetrahydrofuran diol PTMG2000 produced by Shandong Yinuowei Polyurethane Co., Ltd., with a number average molecular weight of 2000; the isocyanate monomer is toluene diisocyanate TDI-80 produced by Wanhua Chemical Group Co., Ltd.; polyether amine toughening agent: Huntsman Performance Products (China) Co., Ltd., model D-2000, polyether diamine, with a number average molecular weight of 2000 and an amine value of 530-560 mg KOH / g; amino-terminated nitrile butadiene rubber: Goodyear Tire & Rubber Company, model HYCAR ATBN. 1300X16, number average molecular weight 3500, amine value 0.45-0.48mmol / g; Flexible aliphatic diamine: BASF, Germany, polyetheramine D-230, number average molecular weight 230; Modified polyamine curing agent: prepared according to the method described in this specification, wherein the base curing agent is Huntsman's polyetheramine D-400 (number average molecular weight 400, amine value 1200-1250mg). KOH / g) and isophorone diamine (purity ≥99.5%) from Baling Petrochemical Company were mixed at a mass ratio of 1:1; polyethylene glycol glycidyl ether was PEG-600 glycidyl ether produced by Jiangsu Haian Petrochemical Plant, with a polyethylene glycol segment molecular weight of 600 and an epoxy value of 0.55 equivalents / 100g; modified bentonite: prepared according to the method described in this specification, using sodium bentonite (cation exchange capacity 90mmol / 100g, expansion capacity 18mL / 2g) produced by Zhejiang Huatai New Material Co., Ltd. and cetyltrimethylammonium chloride (chemically pure, content ≥98%) produced by Shanghai Chenguang Fine Chemical Co., Ltd.; organosilicon thixotropic agent: Evonik Industries AG, model Aerosil R974, hydrophobic fumed silica, specific surface area Particle size 12nm, hydrophobicity greater than 90%; Zinc phosphate: Tianjin Guangfu Fine Chemical Research Institute, industrial grade, zinc content ≥50%; Molybdate preservative: Shanghai Shiyi Chemical Technology Co., Ltd., sodium molybdate, industrial grade. Content ≥99.5%; Zinc powder: Shanghai Yuejiang Titanium Dioxide Chemical Products Co., Ltd., model 300 mesh, zinc content ≥99%, average particle size 5μm.

[0060] Example 1

[0061] The epoxy resin-graphene composite underwater repair material of this embodiment was prepared by a method including the following steps:

[0062] S1. Epoxy Resin Composite: Take 500mL of graphene dispersion and mix it with 4000g of bisphenol A type epoxy resin, 1000g of polyether modified epoxy resin, 600g of organosilane modified polyurethane prepolymer and 300g of polyether amine toughening agent (weight ratio 1:10:1.2:0.6). Vacuum degassing for 30min yields the composite prepolymer.

[0063] S2. Preparation of underwater curing system: Mix 5900g of composite prepolymer with 1800g of modified polyamine curing agent, 180g of modified bentonite thixotropic agent and 120g of zinc phosphate preservative (weight ratio 10:3:0.3:0.2), and stir rapidly for 5min to obtain the epoxy resin-graphene composite underwater repair material of this embodiment.

[0064] The graphene dispersion was prepared using a method comprising the following steps:

[0065] (1) Pre-impregnation treatment: Take 20g of expandable graphite (flake graphite, 80 mesh, expansion ratio 300 times) and add it to a mixed solution of 12g of hydrosilicone oil (polymethylhydrosiloxane, molecular weight 3000) and 8g of tetraethyl orthosilicate. Impregnate at room temperature for 2 hours, stirring once every 30 minutes to ensure that the mixed solution fully penetrates into the graphite layers. The weight ratio of tetraethyl orthosilicate to hydrosilicone oil is 1:1.5.

[0066] (2) Microwave expansion: The pre-impregnated expandable graphite is placed in a microwave oven and heated at 1000W for 30 seconds to obtain expanded graphite with a volume expansion of about 200 times.

[0067] (3) Preparation of stripping solution: Prepare stripping solution by weight: 2 parts calcium hydroxide, 6 parts 3-aminopropyltriethoxysilane, 30 parts ethanol, and 120 parts deionized water. Stir and mix thoroughly.

[0068] (4) Exfoliation and dispersion: 10g of expanded graphite obtained in step (2) was added to 1000mL of exfoliation solution (weight ratio 1:100), and dispersed for 90min using a high-speed shear emulsifier at 15000rpm. During this process, the hydrogen-containing silicone oil decomposes under the catalysis of calcium hydroxide to generate hydrogen gas, which is then inserted between the graphite layers to achieve chemical exfoliation; at the same time, 3-aminopropyltriethoxysilane forms a polysilsesquioxane network structure with calcium ions, stabilizing the exfoliated graphene sheets.

[0069] (5) Separation and purification: The dispersion was centrifuged at 5000 rpm for 60 min to remove the unexfoliated graphite agglomerates and obtain a stable graphene dispersion with a concentration of 1.2 mg / mL (transmission electron microscopy showed that the graphene dispersion in this example was mainly distributed in 3-6 layers, the ID / IG ratio of Raman spectroscopy was 0.26, and the graphene dispersion showed no obvious precipitation after standing at room temperature for 6 months).

[0070] Organosilane-modified polyurethane prepolymers were prepared by the following steps: A1. Polyether polyol and isocyanate monomer were reacted at 80°C for 3 hours under nitrogen protection in a molar ratio of 1:2.2 to obtain isocyanate-terminated polyurethane prepolymers; wherein the polyether polyol was polytetrahydrofuran diol with a number average molecular weight of 2000, and the isocyanate monomer was toluene diisocyanate; A2. 3-aminopropyltriethoxysilane (silane coupling agent) was added to the above prepolymers, with a molar ratio of silane coupling agent to isocyanate groups in the prepolymers of 0.2:1, and the mixture was reacted at 60°C for 2 hours to allow the active groups in the silane coupling agent to react with some of the isocyanate groups, grafting the siloxane structure onto the polyurethane backbone; A3. The mixture was cooled to room temperature to obtain organosilane-modified polyurethane prepolymers containing isocyanate groups and siloxane structures, with a molecular weight of 5000, an isocyanate group content of 5.5 wt%, and a silicon content of 2.5 wt%. Moisture content must be strictly controlled during the preparation process. The moisture content of the reaction system should be less than 100 ppm to avoid the reaction of isocyanate groups with water, which would lead to a decrease in the performance of the prepolymer.

[0071] The modified polyamine curing agent is prepared by the following steps: B1. Polyether diamine (number average molecular weight 400, amine value 1225 mg KOH / g) and isophorone diamine (purity ≥ 99.5%) are mixed at a mass ratio of 1:1 as a base curing agent and heated to 70°C under nitrogen protection; B2. Polyethylene glycol glycidyl ether is added dropwise to the base curing agent as a hydrophilic modifier. The number average molecular weight of the polyethylene glycol segment of the hydrophilic modifier is 600, the epoxy value is 0.55 equivalents / 100g, and the mass ratio of the hydrophilic modifier to the base curing agent is 0.35:1. The dropping rate should be controlled during the dropping process, and the amount added per hour should not exceed 25% of the total amount to avoid local overheating of the reaction; after the dropping is completed, it is heated to 80°C. Under certain conditions, the reaction is allowed to proceed for 4.5 hours, allowing the epoxy groups in the hydrophilic modifier to undergo a ring-opening addition reaction with some of the primary amine groups in the base curing agent. This grafts polyethylene glycol segments onto the base curing agent molecule, forming a hydroxyl-containing secondary amine structure. During the reaction, the amine value needs to be measured periodically. The reaction is stopped when the amine value drops to 72% of the initial value to ensure that the curing agent retains sufficient active amines for the curing reaction of the epoxy resin. B3. After cooling to 45℃, add an appropriate amount of defoamer (0.2 wt% of the total mass of the system after the reaction of the base curing agent and the hydrophilic modifier) ​​and leveling agent (0.3 wt% of the total mass of the system after the reaction of the base curing agent and the hydrophilic modifier). After thorough mixing, the modified polyamine curing agent is obtained. This modified polyamine curing agent is a light yellow to amber transparent or semi-transparent liquid with an amine value of 320 mg KOH / g and a viscosity of 1200 mM. It contains hydrophilic polyethylene glycol segments and hydrophobic aliphatic amino groups for curing active groups.

[0072] Modified bentonite was prepared by the following steps: C1. Sodium-based bentonite (cation exchange capacity 90 mmol / 100 g, swelling capacity 18 mL / 2 g) was dried at 90 °C for 3 h to reduce its moisture content to 4%, and then ground through a 200-mesh sieve to obtain dried bentonite powder; C2. An organic modifier solution was prepared by dissolving hexadecyltrimethylammonium chloride (content ≥98%) in deionized water to prepare a 15% aqueous solution; C3. The dried bentonite powder was dispersed in hot water at 70 °C at a solid-liquid mass ratio of 1:7 and stirred for 45 min to allow it to fully swell and disperse, forming a uniform bentonite suspension; C4. The above organic modifier solution was slowly added dropwise under continuous stirring. The amount of organic modifier added was calculated based on 120% of the cation exchange capacity of the bentonite, i.e., per 100 mmol / L. C5. Add 120 mmol of quaternary ammonium salt to the cation exchange capacity, with the addition time controlled at 1.5 h. After the addition is complete, continue stirring the reaction at 80 °C for 3 h, so that the cations in the quaternary ammonium salt enter the bentonite interlayer through ion exchange, replacing the inorganic sodium ions. At the same time, the long-chain alkyl groups of the quaternary ammonium salt enter the bentonite interlayer, expanding the interlayer spacing and changing the bentonite surface from hydrophilic to hydrophobic. C6. After the reaction is complete, allow it to stand and separate into layers. Discard the supernatant and wash the precipitate with hot water 4 times. After each wash, centrifuge or filter to remove the wash water until the chloride ion content in the wash water is less than 30 ppm. C7. Dry the washed modified bentonite at 100 °C for 8 h. Turn it over every 2 h during the drying process to ensure uniform drying. C8. After drying, grind it and pass it through a 200-mesh sieve to obtain the modified bentonite product. The modified bentonite is a light gray to light yellow powder with an organic content of 32 wt%. The interlayer spacing is increased from 1.3 nm before modification to 2.4 nm. It exhibits good dispersibility and thixotropy in polar solvents and epoxy resins.

[0073] The overall chemical structure diagram of the epoxy resin-graphene composite underwater repair material in this embodiment is shown below. Figure 1 As shown; Figure 1 The overall chemical structure of the epoxy resin-graphene composite underwater repair material was demonstrated, showing the complete molecular structure formed by connecting various functional components through chemical bonds, with graphene sheets as the core; from Figure 1 The chemical bonding relationships between the components and the overall network structure can be observed. Specifically, the surface of the graphene sheets is functionalized with silane coupling agents, which hydrolyze and condense to form a polysilsesquioxane network. This network is... Bonded graphene sheets The polysilsesquioxane network structure is stabilized through coordination. The amino groups of the silane coupling agent on the graphene surface react with the isocyanate groups in the organosilane-modified polyurethane prepolymer to form urea bonds. Simultaneously, the isocyanate groups of the prepolymer react with the hydroxyl groups generated during epoxy resin curing to form urethane bonds, chemically bonding the waterproofing modifier into the system. The epoxy resin reacts with the modified polyamine curing agent to form a cross-linked network backbone. The siloxane segments of the organosilane-modified polyurethane prepolymer provide hydrophobicity, while the polyether segments provide flexibility. The entire system forms a three-dimensional network structure through chemical bonding and coordination, achieving a synergistic effect among the components.

[0074] The schematic diagram of the layered functional structure of the epoxy resin-graphene composite underwater repair material in this embodiment is shown below. Figure 2 As shown, the material is divided into five layers from the inside out, each layer demonstrating its main chemical composition and function, emphasizing the hierarchical nature of the material and the synergistic mechanism of each layer. Specifically: the first layer is a graphene functionalized layer, where the six-membered ring network structure of graphene provides basic mechanical reinforcement, and the functional groups such as hydroxyl, carboxyl, and amino groups on the surface provide reaction sites for subsequent functionalization modifications, while also endowing the graphene sheets with a certain degree of dispersion stability; the second layer is a silane coupling agent functionalized layer, formed by the condensation reaction of silanol groups with hydroxyl or carboxyl groups on the graphene surface after the hydrolysis of 3-aminopropyltriethoxysilane. Covalent bonds are used to attach the silane coupling agent to the graphene surface, with the amino terminus extending outwards to provide reactive groups for the next functionalization layer, thus achieving organic modification of the graphene surface; the third layer is a polysilsesquioxane-calcium complex stabilizing layer, through which multiple silane coupling agent molecules... The first layer consists of a polysilsesquioxane network structure formed by the condensation of bonds. Calcium ions (derived from calcium hydroxide during the preparation of the graphene dispersion) coordinate with oxygen atoms and amino groups in the siloxane network to form stable complexes. This layer stabilizes the graphene dispersion, prevents agglomeration, and enhances interfacial bonding. The fourth layer is an epoxy resin crosslinking network layer, containing a mixed matrix of bisphenol A type epoxy resin and polyether-modified epoxy resin. The epoxy groups react with the amino groups in the modified polyamine curing agent to form a highly crosslinked three-dimensional network structure. The polyether segments provide flexibility, while the bisphenol A segments provide rigidity and strength. This layer is the main structural layer of the material and determines its basic mechanical properties. The fifth layer is an organosilane-modified polyurethane toughening and waterproof layer. The isocyanate groups in the organosilane-modified polyurethane prepolymer are chemically bonded to the system in two ways: one is by reacting with the amino groups of the silane coupling agent to form urea bonds ( Secondly, it reacts with the hydroxyl groups generated during the epoxy resin curing process to form urethane bonds. The polyether segments provide excellent flexibility and impact resistance, while the siloxane structure spontaneously migrates to the material surface and pore interfaces to form a hydrophobic layer. This layer plays a crucial role in toughening, waterproofing, and enhancing underwater adaptability. These five layers are tightly bonded together chemically to form a cohesive whole. The synergistic function of each layer contributes to the material's excellent underwater curing performance, high-strength adhesion, and long-term durability. Graphene and its functionalized layers provide mechanical reinforcement and barrier protection, the epoxy resin crosslinked network layer provides a strong framework, and the organosilane-modified polyurethane toughening layer completes the structure.

[0075] Example 2

[0076] The only difference between this embodiment and Example 1 is that the preparation method of the graphene dispersion is different. Specifically, in the preparation process of the graphene dispersion in this embodiment: the immersion time in step (1) is 0.5h; in step (2), the microwave power is 800W and the heating time is 5s; in the exfoliation solution, the amount of alkaline catalyst is 0.1 parts, the amount of silane coupling agent is 1 part, the amount of ethanol is 10 parts, and the amount of water is 50 parts; in step (4), the shearing speed is 5000rpm and the dispersion time is 30min; in step (5), the centrifugation is 2000rpm for 30min.

[0077] In this embodiment, the graphene dispersion concentration is 0.6 mg / mL, the number of graphene layers is mainly distributed in 2-5 layers, and the ID / IG ratio is 0.29.

[0078] In this embodiment, the mass ratio of graphene dispersion, epoxy resin, organosilane modified polyurethane prepolymer and polyetheramine toughening agent is 1:8:0.5:0.2; the mass ratio of composite prepolymer, modified polyamine curing agent, modified bentonite thixotropic agent and zinc phosphate preservative is 10:2:0.1:0.05; the rest are consistent with Example 1.

[0079] Example 3

[0080] The only difference between this embodiment and Example 1 is that the preparation method of the graphene dispersion is different. Specifically, in the preparation process of the graphene dispersion in this embodiment: the immersion time in step (1) is 4h; in step (2), the microwave power is 1200W and the heating time is 60s; in the exfoliation solution, the amount of alkaline catalyst is 5 parts, the amount of silane coupling agent is 10 parts, the amount of ethanol is 50 parts, and the amount of water is 200 parts; in step (4), the shearing speed is 20000rpm and the dispersion time is 120min; in step (5), the centrifugation is 8000rpm for 90min.

[0081] In this embodiment, the graphene dispersion concentration is 1.8 mg / mL, the number of graphene layers is mainly distributed in 2-4 layers, and the ID / IG ratio is 0.22.

[0082] In this embodiment, the mass ratio of graphene dispersion, epoxy resin, organosilane modified polyurethane prepolymer and polyetheramine toughening agent is 1:15:2:1; the mass ratio of composite prepolymer, modified polyamine curing agent, modified bentonite thixotropic agent and zinc phosphate preservative is 10:4:0.5:0.3; the rest are consistent with Example 1.

[0083] Example 4

[0084] The epoxy resin-graphene composite underwater repair material of this embodiment was prepared by a method including the following steps:

[0085] S1. Epoxy Resin Composite: Take 500 mL of graphene dispersion and mix it with 3500 g of bisphenol A type epoxy resin, 1000 g of polyether modified epoxy resin, 1000 g of organosilane modified polyurethane prepolymer (same as in Example 1) and 500 g of amino-terminated butadiene nitrile rubber toughening agent. Stir and mix at 500 r / min for 30 min, and then degas under vacuum for 30 min to obtain the composite prepolymer.

[0086] S2. Preparation of underwater curing system: 6000g of composite prepolymer, 2400g of modified polyamine curing agent (same as in Example 1), 240g of organosilicon thixotropic agent, and 180g of molybdate preservative are mixed and stirred rapidly for 5 minutes to obtain the epoxy resin-graphene composite underwater repair material of this example.

[0087] In this embodiment, the mass ratio of graphene dispersion, epoxy resin, organosilane-modified polyurethane prepolymer, and toughening agent is 1:9:2:1; the mass ratio of composite prepolymer, modified polyamine curing agent, thixotropic agent, and preservative is 10:4:0.4:0.3. The mass ratio of bisphenol A epoxy resin to polyether-modified epoxy resin is 3.5:1. The graphene dispersion was prepared according to the method of Example 1, with a concentration of 1.2 mg / mL; all other parameters remained consistent with Example 1.

[0088] Example 5

[0089] The difference between this embodiment and Example 1 is that the toughening agent is a flexible aliphatic diamine; the thixotropic agent is a mixture of modified bentonite (the same as in Example 1) and organosilicon thixotropic agent in a mass ratio of 1:1.

[0090] Specifically, 500 mL of graphene dispersion was mixed with 4800 g of bisphenol A type epoxy resin, 800 g of polyether modified epoxy resin, 750 g of organosilane modified polyurethane prepolymer (same as in Example 1), and 300 g of flexible aliphatic diamine. The mixture was then vacuum degassed for 30 min to obtain a composite prepolymer. 6650 g of the composite prepolymer was then mixed with 2100 g of modified polyamine curing agent (same as in Example 1), 210 g of a mixed thixotropic agent of modified bentonite and organosilicon, and 140 g of zinc phosphate preservative. The mixture was rapidly stirred for 5 min to obtain the epoxy resin-graphene composite underwater repair material of this example.

[0091] In this embodiment, the mass ratio of graphene dispersion, epoxy resin, organosilane-modified polyurethane prepolymer, and flexible aliphatic diamine toughening agent is 1:11.2:1.5:0.6; the mass ratio of composite prepolymer, modified polyamine curing agent, thixotropic agent compound, and zinc phosphate preservative is 10:3.2:0.32:0.21. The mass ratio of bisphenol A epoxy resin to polyether-modified epoxy resin is 6:1. The graphene dispersion is prepared according to the method of Example 1; all other aspects are consistent with Example 1.

[0092] Example 6

[0093] The preparation method of the epoxy resin-graphene composite underwater repair material in this embodiment includes the following steps: S1, take 500mL of graphene dispersion and mix it with 4600g of bisphenol A type epoxy resin, 900g of polyether modified epoxy resin, 800g of organosilane modified polyurethane prepolymer, and 400g of polyetheramine toughening agent, and vacuum degas for 30min to obtain a composite prepolymer. S2, mix 6700g of composite prepolymer with 2000g of modified polyamine curing agent, 200g of modified bentonite thixotropic agent, and 100g of zinc phosphate preservative, and stir rapidly for 5min to obtain the epoxy resin-graphene composite underwater repair material of this embodiment.

[0094] In this embodiment, the mass ratio of graphene dispersion, epoxy resin, organosilane-modified polyurethane prepolymer, and polyetheramine toughening agent is 1:11:1.6:0.8; the mass ratio of composite prepolymer, modified polyamine curing agent, modified bentonite thixotropic agent, and zinc phosphate preservative is 10:3:0.3:0.15. The mass ratio of bisphenol A epoxy resin to polyether-modified epoxy resin is 5:1. The graphene dispersion is prepared according to the method of Example 1; all other aspects are consistent with Example 1.

[0095] Example 7

[0096] The preparation method of the epoxy resin-graphene composite underwater repair material in this embodiment includes the following steps: S1, Take 500 ml of graphene dispersion and mix it with 4000 g of bisphenol A type epoxy resin, 1000 g of polyether modified epoxy resin, 600 g of organosilane modified polyurethane prepolymer, and 300 g of polyether amine and amino-terminated nitrile rubber mixed toughening agent (mass ratio 1:1), and vacuum degas for 30 min to obtain the composite prepolymer. S2, Mix 5900 g of the composite prepolymer with 1500 g of modified polyamine curing agent, 150 g of modified bentonite thixotropic agent, and 90 g of zinc powder corrosion inhibitor, and stir rapidly for 5 min to obtain the epoxy resin-graphene composite underwater repair material of this embodiment.

[0097] In this embodiment, the mass ratio of graphene dispersion, epoxy resin, organosilane-modified polyurethane prepolymer, and mixed toughening agent is 1:10:1.2:0.6; the mass ratio of composite prepolymer, modified polyamine curing agent, modified bentonite thixotropic agent, and zinc powder preservative is 10:2.5:0.25:0.15. The mass ratio of bisphenol A epoxy resin to polyether-modified epoxy resin is 4:1. The graphene dispersion is prepared according to the method of Example 1; all other aspects are consistent with Example 1.

[0098] Comparative Example 1

[0099] The only difference between this comparative example and Example 1 is that no graphene dispersion was added, and 4600g of bisphenol A type epoxy resin and 1150g of polyether modified epoxy resin were used directly (total amount 5750g, which is equivalent to the volume of 5000g of epoxy resin plus 500mL of graphene dispersion in Example 1). The remaining components and proportions are the same as in Example 1.

[0100] Specifically, 4600g of bisphenol A type epoxy resin, 1150g of polyether modified epoxy resin, 600g of organosilane modified polyurethane prepolymer (same as in Example 1), and 300g of polyetheramine toughening agent were mixed and vacuum degassed for 30 minutes to obtain a composite prepolymer. 5900g of the composite prepolymer was then mixed with 1800g of modified polyamine curing agent (same as in Example 1), 180g of modified bentonite thixotropic agent (same as in Example 1), and 120g of zinc phosphate preservative, and rapidly stirred for 5 minutes.

[0101] Comparative Example 2

[0102] The only difference between this comparative example and Example 1 is that the amount of graphene dispersion used is too large, and the mass ratio of graphene dispersion to epoxy resin is 1:6. The other components and proportions are the same as in Example 1.

[0103] Specifically, 800 mL of graphene dispersion was mixed with 3840 g of bisphenol A type epoxy resin, 960 g of polyether modified epoxy resin, 600 g of organosilane modified polyurethane prepolymer (same as in Example 1), and 300 g of polyetheramine toughening agent, and vacuum degassed for 30 min. The viscosity of the mixture was significantly high, and the flowability was poor. 5900 g of the composite prepolymer was mixed with 1800 g of modified polyamine curing agent (same as in Example 1), 180 g of modified bentonite thixotropic agent (same as in Example 1), and 120 g of zinc phosphate preservative, and stirred rapidly for 5 min.

[0104] Comparative Example 3

[0105] The only difference between this comparative example and Example 1 is that the amount of graphene dispersion used is too small, and the mass ratio of graphene dispersion to epoxy resin is 1:18. The other components and proportions are the same as in Example 1.

[0106] Specifically, 300 mL of graphene dispersion was mixed with 4320 g of bisphenol A type epoxy resin, 1080 g of polyether modified epoxy resin, 600 g of organosilane modified polyurethane prepolymer (same as in Example 1), and 300 g of polyetheramine toughening agent. The mixture was then vacuum degassed for 30 min to obtain a composite prepolymer. 5900 g of the composite prepolymer was then mixed with 1800 g of modified polyamine curing agent (same as in Example 1), 180 g of modified bentonite thixotropic agent (same as in Example 1), and 120 g of zinc phosphate preservative, and stirred rapidly for 5 min.

[0107] Comparative Example 4

[0108] The only difference between this comparative example and Example 1 is that no waterproof modifier (organosilane-modified polyurethane prepolymer) was added; the remaining components and proportions are the same as in Example 1.

[0109] Specifically, 500 mL of graphene dispersion was mixed with 4000 g of bisphenol A type epoxy resin, 1000 g of polyether modified epoxy resin, and 300 g of polyether amine toughening agent, and vacuum degassed for 30 min to obtain a composite prepolymer. 5900 g of the composite prepolymer was mixed with 1800 g of modified polyamine curing agent (same as in Example 1), 180 g of modified bentonite thixotropic agent (same as in Example 1), and 120 g of zinc phosphate preservative, and rapidly stirred for 5 min.

[0110] Comparative Example 5

[0111] The only difference between this comparative example and Example 1 is that an unmodified common polyamine curing agent (Huntsman's polyetheramine D-400) is used instead of the modified polyamine curing agent, while the remaining components and proportions are the same as in Example 1.

[0112] Comparative Example 6

[0113] The only difference between this comparative example and Example 1 is that unmodified natural sodium-based bentonite is used instead of the modified bentonite thixotropic agent, while the other components and proportions remain the same as in Example 1.

[0114] Comparative Example 7

[0115] The only difference between this comparative example and Example 1 is that a commercially available graphene oxide aqueous dispersion (concentration 2 mg / mL, Nanjing Xianfeng Nanomaterials Technology Co., Ltd.) is used instead of the graphene dispersion prepared in this invention, while the remaining components and proportions remain the same as in Example 1.

[0116] Comparative Example 8

[0117] The only difference between this comparative example and Example 1 is that the step of pre-mixing the graphene dispersion, epoxy resin, waterproof modifier and toughening agent to prepare the composite prepolymer is omitted, and all raw materials are directly mixed at once.

[0118] Specifically, 460 mL of graphene dispersion, 3680 g of bisphenol A type epoxy resin, 920 g of polyether modified epoxy resin, 552 g of organosilane modified polyurethane prepolymer (same as in Example 1), 276 g of polyetheramine toughening agent (i.e., the total mass of graphene dispersion, epoxy resin, waterproof modifier and toughening agent is 5900 g), 1800 g of modified polyamine curing agent (same as in Example 1), 180 g of modified bentonite thixotropic agent (same as in Example 1), and 120 g of zinc phosphate preservative were added to a container at once and quickly stirred and mixed for 5 min.

[0119] Performance testing

[0120] The underwater repair materials prepared in Examples 1-7 and Comparative Examples 1-8 were subjected to systematic performance tests. The test methods and results are as follows:

[0121] 1. Initial setting time test method:

[0122] The test was conducted according to the standard method of JC / T 907-2013 "Concrete Interface Treatment Agent". The mixed underwater repair material was placed into a cylindrical mold with a diameter of 50 mm and a height of 150 mm, and completely immersed in an underwater environment at 20°C. The initial setting time was determined using the penetration resistance method. Penetration resistance was tested every 30 minutes using a standard penetration needle (1 mm² tip area). Initial setting was defined as when the penetration resistance reached 3.5 MPa, and the time from preparation to initial setting was recorded. Three samples were tested in each group, and the average value was taken.

[0123] 2. Underwater bond strength test method:

[0124] The test was conducted according to GB / T 7124-2008 "Determination of Tensile Shear Strength of Adhesives". C40 concrete was used as the substrate. The surface of the concrete substrate was roughened by grinding and rinsed with water before immersion in water. The prepared underwater repair material was applied to the surface of the underwater concrete substrate, with a bonding area of ​​25mm × 25mm and a bonding layer thickness controlled at 2mm. The substrate was cured underwater for 7 days (water temperature 20℃). After curing, the samples were removed and subjected to tensile shear strength testing at a speed of 2mm per minute on a universal testing machine. The maximum load at failure was recorded, and the bond strength was calculated. Five samples were tested in each group, and the maximum and minimum values ​​were removed before taking the average value.

[0125] 3. Compressive strength test method:

[0126] Tests were conducted according to GB / T 50081-2019, "Standard for Test Methods of Physical and Mechanical Properties of Concrete". Cube specimens with a side length of 70.7 mm were prepared, and the mold was completely submerged underwater for casting. The specimens were cured underwater under standard curing conditions (water temperature 20±2℃) for 28 days. After curing, the specimens were removed, the surface moisture was wiped dry, and compressive strength tests were performed on a compression testing machine at a loading rate of 0.5 MPa per second. The maximum load at failure was recorded, and the compressive strength was calculated. Six specimens were tested in each group, and the maximum and minimum values ​​were removed before taking the average value.

[0127] 4. Test method for impermeability grade:

[0128] The permeability test was conducted according to the water penetration height method in GB / T 50082-2009 "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". A frustum-shaped specimen with an upper diameter of 175 mm, a lower diameter of 185 mm, and a height of 150 mm was used and cured underwater for 28 days. The specimen was placed in a permeability testing apparatus, the sides were sealed, and water pressure was applied from the lower surface. The water pressure started at 0.1 MPa and increased by 0.1 MPa every 8 hours, continuing until water seeped through the upper surface of the specimen or the water pressure reached 2.0 MPa. The permeability grade was determined based on whether the specimen showed signs of seepage and the water pressure at which seepage occurred. If no seepage occurred at 0.1 × N MPa but seepage occurred at 0.1 × (N+1) MPa, the permeability grade was PN. Six specimens were tested in each group, and the permeability grade was determined by the maximum water pressure when four or more specimens showed no seepage.

[0129] 5. Freeze-thaw cycle test method:

[0130] Freeze-thaw cycle tests were conducted according to GB / T 50082-2009, "Standard for Test Methods of Long-Term Performance and Durability of Ordinary Concrete". Prismatic specimens measuring 100mm × 100mm × 400mm were prepared and cured underwater for 28 days before the freeze-thaw cycle tests. Each freeze-thaw cycle consisted of: freezing the specimen at -20±2℃ for 2 hours, followed by thawing in water at +20±2℃ for 2 hours, for a total of 4 hours per cycle. After 100 consecutive freeze-thaw cycles, the underwater bond strength and compressive strength of the specimens were tested and compared with a control specimen that had not undergone freeze-thaw cycles to calculate the performance retention rate.

[0131] 6. Corrosion resistance test method:

[0132] Underwater bonded specimens and compression blocks were completely immersed in a 3.5% (w / w) artificial seawater solution (prepared according to ASTM D1141) at room temperature (20±2℃) for 90 consecutive days. The solution was changed every 7 days during the immersion period. After immersion, the specimens were removed, rinsed thoroughly with clean water, and the underwater bond strength was tested. The results were compared with an unimmersed control specimen to calculate the performance retention rate. Simultaneously, changes in the surface appearance of the specimens were observed, and the mass change rate was calculated by weighing.

[0133] 7. Long-term immersion test method:

[0134] The underwater bonding samples were placed in clean water and continuously immersed for 180 days under standard curing conditions of 20±2℃. The water was changed every 14 days during the immersion period to maintain water quality. After immersion, the samples were removed, and their underwater bond strength and compressive strength were tested. The results were compared with those of a control sample that had not been immersed for a long period, and the performance retention rate was calculated. The sample surface was inspected for peeling, flaking, cracking, or other defects.

[0135] 8. Accelerated aging test method:

[0136] Accelerated aging tests were conducted according to GB / T 16422.2-2014 "Laboratory Light Source Exposure Test Methods for Plastics - Part 2: Xenon Arc Lamp". Test conditions: Xenon lamp light source, irradiance of 0.51 W / m² / nm (wavelength 340 nm), black panel temperature 65±3℃, relative humidity 50±10%, continuous irradiation for 1000 h. Underwater adhesive strength and compressive strength of the material were tested before and after the aging test, and performance retention rate was calculated.

[0137] Test Results Summary

[0138] The materials prepared in Examples 1-7 and Comparative Examples 1-8 were subjected to the above system performance tests, and the results are summarized below:

[0139] Table 1 Comparison of key performance indicators of each embodiment and comparative example

[0140]

[0141] Table 2. Long-term durability performance test data for Examples 1-3

[0142]

[0143] Test results show that:

[0144] (1) The initial setting time of the epoxy resin-graphene composite underwater repair materials prepared in Examples 1 to 7 of this invention is controlled within the range of 2.5-3.5 h; the underwater bonding strength reaches 15.2-22.5 MPa, all exceeding the technical requirement of 15 MPa; the compressive strength reaches 82-105 MPa, all exceeding the technical requirement of 80 MPa; and the impermeability grade reaches P12-P18, all meeting the technical requirement of P12 and above. All performance indicators fully meet the technical requirements for underwater repair of water conservancy projects.

[0145] (2) Due to the lack of key components (graphene dispersion, waterproof modifier), the use of unmodified components (ordinary curing agent, natural bentonite), unreasonable formulation, or omission of key process steps, the performance indicators of Comparative Examples 1 to 8 were significantly lower than those of the Examples. In particular, the underwater bonding strength of Comparative Example 1 (without graphene), Comparative Example 4 (without waterproof modifier), and Comparative Example 5 (without modified curing agent) was only 7.8-10.2 MPa, less than 60% of that of Example 1, which fully demonstrates the important role of each key component of the present invention in the material performance.

[0146] (3) The results of Comparative Examples 2 and 3 show that there is an optimal range for the amount of graphene dispersion. Too much (1:6) or too little (1:18) will lead to a decrease in performance.

[0147] (4) Comparative Example 6 used unmodified bentonite, which resulted in the material not being able to cure properly. Comparative Example 7 used commercially available graphene oxide, which had inferior performance to the graphene dispersion prepared in this invention. Comparative Example 8 omitted the prepolymer preparation step, resulting in a short applicable period and uneven performance. These findings fully demonstrate the superiority of the technical solution and the necessity of the process route of this invention.

[0148] (5) The long-term durability tests of Examples 1-3 show that the bonding strength retention rate of the material reaches 90.1%-92.0% after 100 freeze-thaw cycles; the bonding strength retention rate reaches 87.5%-89.8% after immersion in artificial seawater for 90 days; after corrosion resistance tests, Examples 1-3 show no obvious changes in appearance, the mass change rate is less than 0.5%, and the impermeability grade remains unchanged; after immersion in clean water for 180 days, the bonding strength retention rate of Examples 1-3 reaches 84.9%-88.0%, the compressive strength retention rate is above 85%, and there is no peeling or flaking on the material surface; after 1000h accelerated aging tests, the retention rate of various mechanical properties of Examples 1-3 is above 81.6%, and the impermeability grade remains above P12, indicating that the material has excellent long-term durability and can meet the technical requirements of the 25-year design service life of water conservancy projects.

[0149] In summary, the epoxy resin-graphene composite underwater repair material of the present invention has excellent underwater curing performance and long-term durability, and has high practical value.

Claims

1. An epoxy resin-graphene composite underwater repair material, characterized in that, The epoxy resin-graphene composite underwater repair material comprises: composite prepolymer, curing agent, thixotropic agent, and preservative; The composite prepolymer comprises graphene dispersion, epoxy resin, waterproof modifier, and toughening agent; The mass ratio of the graphene dispersion to the epoxy resin is 1:(8-15); The waterproofing modifier is an organosilane-modified polyurethane prepolymer containing isocyanate groups and siloxane structures, with a molecular weight of 2000-8000. The curing agent is a modified polyamine curing agent; the modified polyamine curing agent has an amine value of 200-450 mgKOH / g and a viscosity of 500-3000 m. It contains hydrophilic polyethylene glycol segments and hydrophobic aliphatic or alicyclic amino groups as active groups; The thixotropic agent is modified bentonite or an organosilicon thixotropic agent; the modified bentonite is prepared by a method including the following steps: C1. Prepare an organic modifier solution by dissolving a quaternary ammonium salt cationic surfactant in deionized water to prepare an aqueous solution with a mass concentration of 10%-20%. C2. Disperse the dry bentonite powder in hot water at 60-80℃ at a solid-liquid mass ratio of 1:(5-10), and stir for 30-60 minutes to allow it to fully swell and disperse, forming a uniform bentonite suspension. C3. Add the organic modifier solution dropwise under continuous stirring. The amount of organic modifier is calculated as 100%-150% of the cation exchange capacity of bentonite, that is, 100-150 mmol of quaternary ammonium salt is added for every 100 mmol of cation exchange capacity. The dropwise addition time is controlled at 1-2 hours. After the dropwise addition is completed, continue stirring the reaction at 70-90℃ for 2-4 hours. C4. After the reaction is complete, let it stand to separate into layers, discard the supernatant, and wash the precipitate with hot water 3-5 times. C5. The washed modified bentonite is dried, ground, and passed through a 200-mesh sieve at 80-120℃ to obtain the modified bentonite.

2. The epoxy resin-graphene composite underwater repair material as described in claim 1, characterized in that, The mass ratio of the composite prepolymer to the curing agent is 10:(2-4).

3. The epoxy resin-graphene composite underwater repair material as described in claim 1, characterized in that, The epoxy resin is a mixture of bisphenol A type epoxy resin and polyether modified epoxy resin; The mass ratio of the bisphenol A type epoxy resin to the polyether modified epoxy resin is (3-7):1, and the epoxy value is 0.45-0.65 equivalents / 100g.

4. The epoxy resin-graphene composite underwater repair material as described in claim 1, characterized in that, The mass ratio of the waterproof modifier to the epoxy resin is (0.5-2):(8-15); The organosilane-modified polyurethane prepolymer was prepared by a method comprising the following steps: A1. Polyether polyol and isocyanate monomer are reacted at 70-90℃ for 2-4 hours under nitrogen protection in a molar ratio of 1:(2-2.5) to obtain polyurethane prepolymer with terminal isocyanate groups. A2. Add an amino or epoxy-containing silane coupling agent to the above prepolymer. The molar ratio of the silane coupling agent to the isocyanate groups in the prepolymer is (0.1-0.3):

1. React at 50-70℃ for 1-3 hours to allow the active groups in the silane coupling agent to react with some of the isocyanate groups, thereby grafting the siloxane structure onto the polyurethane backbone. A3. Cool to room temperature to obtain the organosilane-modified polyurethane prepolymer containing isocyanate groups and siloxane structures.

5. The epoxy resin-graphene composite underwater repair material as described in claim 1, characterized in that, The toughening agent is at least one of polyetheramine, amino-terminated butadiene nitrile rubber, and flexible aliphatic diamine; the mass ratio of the toughening agent to the epoxy resin is (0.2-1):(8-15); The preservative is at least one of zinc phosphate, molybdate and zinc powder, and the mass ratio of the preservative to the curing agent is (0.05-0.3):(2-4).

6. The epoxy resin-graphene composite underwater repair material as described in claim 1, characterized in that, The modified polyamine curing agent is prepared by a method comprising the following steps: B1. Using aliphatic polyether amine or alicyclic amine as the base curing agent, wherein the amine value of the base curing agent is 300-600 mgKOH / g, and heating to 60-80℃ under nitrogen protection; B2. Add polyethylene glycol glycidyl ether or polyethylene glycol diglycidyl ether as a hydrophilic modifier to the base curing agent. The number average molecular weight of the polyethylene glycol segments in the hydrophilic modifier is 400-2000, the epoxy value is 0.3-0.8 equivalents / 100g, and the mass ratio of the hydrophilic modifier to the base curing agent is (0.2-0.5):

1. During the addition process, control the amount added per hour to not exceed 30% of the total amount. After the addition is completed, react at 70-90℃ for 3-6 hours until the amine value drops to 65%-80% of the initial value. B3. Cool to below 50°C, add defoamer and leveling agent, mix thoroughly to obtain modified polyamine curing agent.

7. The epoxy resin-graphene composite underwater repair material as described in claim 1, characterized in that, The mass ratio of the thixotropic agent to the curing agent is (0.1-0.5):(2-4).

8. The preparation method of the epoxy resin-graphene composite underwater repair material according to any one of claims 1-7, characterized in that, Includes the following steps: S1. The graphene dispersion is mixed with epoxy resin, waterproof modifier and toughening agent to obtain composite prepolymer; S2. Mix the composite prepolymer with a curing agent, a thixotropic agent and a preservative.

9. The preparation method of the epoxy resin-graphene composite underwater repair material as described in claim 8, characterized in that, It also includes step S3: after step S2, pre-curing for 2-6 hours at 25-35℃ and 65%-85% relative humidity.

10. The application of the epoxy resin-graphene composite underwater repair material as described in any one of claims 1-7 in underwater crack repair, seepage prevention reinforcement, and corrosion protection of concrete structures in hydraulic engineering projects.

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