Concrete interface repairing material as well as construction method and application thereof

Abstract

The invention belongs to the technical field of concrete reinforcing and repairing, and particularly relates to a concrete interface repairing material and a construction method and application thereof. The concrete interface repairing material comprises an interface processing layer, a first stress buffer layer, a graphene fiber grid layer, a second stress buffer layer and a concrete repairing layer, the component of the interface treatment layer comprises graphene; the first stress buffer layer and / or the second stress buffer layer comprises the following components: epoxy resin, a curing agent, a flexibilizer and graphene nanosheets; the graphene fiber grid layer comprises a fiber grid and a graphene coating deposited on the surface of the fiber grid. The concrete interface repairing material disclosed by the invention is beneficial to solving or improving at least one of the problems of poor interface bonding effect, stress concentration and poor long-term durability in the concrete reinforcing process in the prior art.

Description

Technical Field

[0001] This invention belongs to the field of concrete reinforcement and repair technology, specifically relating to a concrete interface repair material and its construction method and application. Background Technology

[0002] As my country's infrastructure construction enters a stock era, a large number of concrete structures are experiencing problems such as insufficient load-bearing capacity, crack expansion, and protective layer peeling due to factors such as extended service life, increased load, and environmental erosion. Statistics show that my country currently has over 1 million bridges, of which approximately 40% have entered their maintenance and repair period; the existing building area exceeds 60 billion square meters, and a large number of buildings require seismic reinforcement and performance upgrades. There is an urgent need for high-performance, easy-to-construct, and monitorable new reinforcement materials and technologies for the reinforcement and repair of load-bearing structures such as bridges, buildings, tunnels, and hydraulic structures.

[0003] Currently, concrete structure strengthening technologies mainly include steel plate bonding, fiber-reinforced polymer (FRP) bonding, external steel cladding, and cross-section enlargement. Among these, fiber-reinforced fabric bonding is widely used due to its high strength, corrosion resistance, and ease of construction. In recent years, fiber mesh reinforced cementitious composite (TRC / TRM) has gradually emerged as a new strengthening technology, offering better air permeability, high-temperature resistance, and compatibility with the matrix compared to traditional FRP. However, existing fiber reinforcement technologies still face the following key challenges: 1. Insufficient interfacial adhesion: The interfaces between new and old concrete, and between fibers and the matrix, are weak points in reinforced structures. Due to differences in the properties of new and old concrete materials, improper interface treatment, and the presence of microcracks, the interfacial bond strength is typically only 50-70% of the strength of the concrete itself. Under load, the interface is highly susceptible to delamination failure, leading to reinforcement failure. This degradation is particularly pronounced under long-term conditions such as fatigue loading and temperature cycling. Traditional reinforcement techniques primarily rely on structural adhesives or cement mortar for bonding, but the interfacial bonding between these materials and fibers and concrete is mainly based on physical adsorption and mechanical interlocking, lacking effective chemical bonding. Furthermore, the interfacial microstructure is discontinuous and contains numerous defects.

[0004] 2. Stress concentration caused by a sudden change in stiffness: The elastic modulus of fiber-reinforced materials (such as carbon fiber cloth) typically reaches 200-300 GPa, while the elastic modulus of concrete is only 30-40 GPa, a difference of nearly 10 times. This abrupt change in stiffness can cause severe stress concentration at the interface, accelerating the initiation and propagation of interfacial cracks. Current technologies lack effective stress transition and buffering mechanisms, making it difficult to achieve coordinated stress distribution between the old and new materials.

[0005] 3. Long-term durability issues are prominent: Fiber-based materials, especially glass fiber and basalt fiber, are prone to performance degradation under alkaline environments, chloride ion corrosion, and freeze-thaw cycles. While traditional epoxy resin matrices possess good bonding properties, their aging resistance is limited, and they degrade under ultraviolet radiation and humid conditions. Due to the lack of effective protective measures, the long-term durability of reinforced structures is difficult to guarantee, typically requiring reinforcement after 5-10 years.

[0006] In recent years, graphene, as a novel two-dimensional nanomaterial, has gained attention due to its excellent mechanical properties (tensile strength of approximately 130 GPa and Young's modulus of approximately 1 TPa) and electrical conductivity (conductivity up to 10⁻⁶). 6 S / m), specific surface area (theoretical value 2630m²) 2 Graphene has garnered significant attention due to its chemical stability and compressive strength. Studies on its application in cement-based composites have shown that adding small amounts of graphene can significantly improve the compressive strength, flexural strength, and durability of concrete. The sheet-like structure of graphene can fill the microscopic pores of the cement matrix, blocking the penetration of corrosive media; its abundant surface functional groups can form chemical bonds with cement hydration products; and its excellent electrical conductivity can be used to construct strain-sensing networks. However, existing research mainly focuses on the direct incorporation of graphene into concrete, with limited research on its use in modifying fiber-reinforced materials and improving interfacial bonding performance, particularly its systematic application in concrete reinforcement interfaces, which is almost entirely lacking.

[0007] In summary, existing concrete structure reinforcement technologies have significant shortcomings in terms of interfacial bonding, stress transfer, and long-term durability.

[0008] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0009] The purpose of this invention is to provide a concrete interface repair material, its construction method, and its application, so as to help solve or improve at least one of the problems of poor interface bonding, stress concentration, and poor long-term durability that easily occur in the process of concrete reinforcement in the prior art.

[0010] To achieve the above objectives, the present invention provides the following technical solution: a concrete interface repair material, comprising: an interface treatment layer, a first stress buffer layer, a graphene fiber mesh layer, a second stress buffer layer, and a concrete repair layer; the interface treatment layer comprises graphene; the first stress buffer layer and / or the second stress buffer layer comprises epoxy resin, a curing agent, a toughening agent, and graphene nanosheets; the graphene fiber mesh layer comprises a fiber mesh and a graphene coating deposited on the surface of the fiber mesh.

[0011] Preferably, the graphene fiber mesh layer is prepared by a method comprising the following steps: A1, using the fiber mesh as the anode and the stainless steel plate as the cathode, immersing it in an electrophoretic solution, applying voltage for electrophoretic deposition, and depositing a graphene oxide functional layer on the surface of the fiber mesh; A2, removing the fiber mesh obtained in step A1 from the electrophoretic solution, drying it, and then immersing it in an ascorbic acid solution for a reduction reaction to obtain a reduced graphene oxide transition layer; A3, immersing the fiber mesh obtained in step A2 in a silane coupling agent solution for surface modification treatment, drying and curing it after modification to obtain the modified graphene layer.

[0012] Preferably, in step A1, the electrophoretic solution is a mixed solution of graphene oxide, carbon nanotubes, a dispersant, and a solvent; the pH of the electrophoretic solution is adjusted to 7-9 with ammonia; the concentration of graphene oxide in the electrophoretic solution is 2wt%-4wt%, and the concentration of carbon nanotubes is 0.5wt%-1wt%; the dispersant is a polycarboxylic acid-based dispersant; and the solvent is anhydrous ethanol and / or N,N-dimethylformamide.

[0013] Preferably, in step A1, the electrophoretic deposition voltage is 30-50V, the time is 5-15min, and the temperature is 25±2℃; in step A2, the concentration of the ascorbic acid solution is 8-12g / L, the reduction reaction time is 1-3h, followed by heat treatment at 100-140℃ for 20-40min; in step A3, the silane coupling agent solution is a 2wt%-3wt% ethanol solution, and the soaking time is 20-40min; the silane coupling agent is at least one of KH-560, KH-550, and KH-570.

[0014] Preferably, the components of the first stress buffer layer and / or the second stress buffer layer, by mass parts, include: 100 parts epoxy resin, 0.5-1.5 parts graphene nanosheets, 30-40 parts curing agent, and 5-10 parts toughening agent.

[0015] Preferably, the epoxy resin is at least one selected from E-51, E-44, and E-20 epoxy resins; the graphene nanosheets have a particle size of 1-10 μm, a thickness of 5-50 nm, and a specific surface area of ​​50-500 m². 2 / g; the curing agent is at least one of polyamide curing agent, fatty amine curing agent and aromatic amine curing agent; the toughening agent is at least one of rubber particles, polyurethane and carboxyl-terminated nitrile rubber.

[0016] Preferably, the thickness of the first stress buffer layer is 1-3 mm; the thickness of the second stress buffer layer is 1-2 mm; and the fiber mesh is at least one of carbon fiber mesh, basalt fiber mesh, glass fiber mesh, and hybrid fiber mesh.

[0017] The present invention also provides a construction method for a concrete interface repair material, which adopts the following technical solution: A construction method for a concrete interface repair material includes the following steps: (1) Base treatment: pre-treat the old concrete and apply an interface agent containing graphene after pre-treatment. After the surface is dry, an interface treatment layer is obtained; (2) Apply the first buffer layer; (3) Lay a graphene fiber mesh layer; (4) Apply the second buffer layer; (5) Pour the concrete repair layer.

[0018] The present invention also provides an application of a concrete interface repair material, which adopts the following technical solution: the application of the concrete interface repair material as described above in bridge reinforcement, building structure reinforcement, tunnel lining repair or hydraulic structure protection.

[0019] Beneficial effects: The first and second stress buffer layers in the concrete interface reinforcement material of this invention help solve the stress concentration problem caused by the abrupt change in stiffness between the fiber mesh and concrete. The elastic modulus of the first and / or second stress buffer layers can be controlled by adjusting the graphene content, which helps to achieve a gradient transition from high-modulus fibers to low-modulus concrete. At the same time, the layered structure of graphene nanosheets can fill the micropores of the first and second stress buffer layers, reduce defects and stress concentration points, improve the integrity of the interface and stress transfer efficiency, and enable the new and old concrete to truly achieve synergistic stress distribution.

[0020] The concrete interface reinforcement material of this invention can significantly improve the durability of the reinforcement layer through the shielding and isolation effects of graphene. The sheet structure of graphene can form a physical barrier at the interface, blocking the penetration of corrosive media such as chloride ions and sulfate ions; the excellent chemical stability of graphene ensures that it does not degrade under alkaline environments and corrosive media, maintaining a long-term protective effect and ensuring the long-term service performance of the reinforced structure in harsh environments.

[0021] The concrete interface strengthening material of this invention exhibits excellent performance, with an interfacial bond strength of 3.5-4.5 MPa, 120% higher than that of untreated interfaces, meeting the requirements of GB 50367-2013 "Code for Design of Strengthening Concrete Structures"; a shear strength of 6.0-8.0 MPa, 140% higher than traditional strengthening methods; and a fatigue life of 10 years. 6 Secondary fracture; interfacial fracture energy reaches 180-250 J / m 2 It improves by 260%, demonstrating excellent toughness and energy dissipation capabilities.

[0022] The construction method of this invention is mature and reliable, requires no large equipment, can be operated at room temperature, and is highly adaptable. It can be used for reinforcement and repair of various projects such as bridges, building structures, tunnels, and hydraulic structures, providing an innovative technical solution for the long service life of concrete structures. 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: Figure 1 This is a SEM image of the graphene fiber mesh layer in Example 1. Detailed Implementation

[0024] 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.

[0025] 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.

[0026] This invention addresses the problem that existing technologies often suffer from at least one of the following issues during concrete reinforcement: poor interfacial bonding, stress concentration, and poor long-term durability. It provides a concrete interface repair material.

[0027] The concrete interface repair material of this invention includes: an interface treatment layer, a first stress buffer layer, a graphene fiber mesh layer, a second stress buffer layer, and a concrete repair layer; the interface treatment layer comprises graphene; the first stress buffer layer and / or the second stress buffer layer comprises epoxy resin, curing agent, toughening agent, and graphene nanosheets; the graphene fiber mesh layer comprises a fiber mesh and a graphene coating deposited on the surface of the fiber mesh.

[0028] The inventors discovered in their research that graphene, as a two-dimensional nanomaterial, possesses excellent mechanical properties (tensile strength of approximately 130 GPa) and electrical conductivity (conductivity up to 10). 6 S / m) and ultra-large specific surface area (theoretical value 2630m²) 2While a single coating can achieve both chemical bonding with fibers and electrical conductivity, it is difficult to simultaneously meet the requirements. Furthermore, in traditional reinforced structures, the stiffness difference between fibers and concrete is nearly tenfold, easily leading to stress concentration at the interface. If graphene coatings can be made multifunctional through gradient functionalization design, combined with nano-anchoring structures and stress buffer layer designs, it could help solve or improve the aforementioned problems in current concrete structure reinforcement technologies.

[0029] The first and second stress buffer layers in the concrete interface reinforcement material of this invention help solve the stress concentration problem caused by the abrupt change in stiffness between the fiber mesh and concrete, and realize the gradient transition from high-modulus fiber to low-modulus concrete. At the same time, the layered structure of graphene nanosheets can fill the micropores of the first and second stress buffer layers, reduce defects and stress concentration points, improve the integrity of the interface and stress transfer efficiency, and enable the new and old concrete to truly achieve synergistic stress distribution.

[0030] In a preferred embodiment of the concrete interface repair material of the present invention, the graphene fiber mesh layer is prepared by a method comprising the following steps: A1, using the fiber mesh as the anode and the stainless steel plate as the cathode, immersing it in an electrophoretic solution, applying voltage for electrophoretic deposition, and depositing a graphene oxide functional layer on the surface of the fiber mesh; A2, removing the fiber mesh obtained in step A1 from the electrophoretic solution, drying it, and then immersing it in an ascorbic acid solution for a reduction reaction to obtain a reduced graphene oxide transition layer; A3, immersing the fiber mesh obtained in step A2 in a silane coupling agent solution for surface modification treatment, and drying and curing it after modification to obtain the modified graphene layer. The purpose of step A3 is to form a modified graphene layer. The reaction mechanism includes: the methoxy group of the silane coupling agent is hydrolyzed in solution to generate silanol groups (Si-OH); the silanol groups undergo a condensation reaction with the carboxyl and hydroxyl groups remaining on the graphene surface to form Si-OC bonds; some silanol groups undergo self-condensation to form a polysiloxane network; and the epoxy groups are retained in the outermost layer to provide active sites for the reaction with the epoxy resin matrix in the second stress buffer layer.

[0031] In the concrete interface reinforcement material of the present invention, the graphene fiber mesh helps to achieve synergistic reinforcement of the fiber-coating-matrix multiphase interface. Specifically: in step A1, a graphene oxide functionalized layer is deposited on the surface of the fiber mesh, where the carboxyl and hydroxyl functional groups help to form chemical bonds with the fiber surface, significantly improving the adhesion of the graphene coating to the fiber mesh; after step A2, some of the graphene oxide can be converted into reduced graphene oxide, which helps to give the graphene coating certain electrical conductivity; after step A3, at least some of the reduced graphene oxide can be converted into modified graphene grafted with silane coupling agent. The grafted silane coupling agent helps to achieve a continuous interface transition between the graphene fiber mesh layer and the stress buffer layer. Combined with the bonding between the stress buffer layer and the concrete matrix, multi-level interface synergistic reinforcement from the fiber mesh to the concrete matrix is ​​finally achieved, avoiding the problem that a single coating cannot adequately match the multiphase interfaces.

[0032] In a preferred embodiment of the concrete interface repair material of the present invention, in step A1, the electrophoretic solution is a mixed solution of graphene oxide, carbon nanotubes, a dispersant, and a solvent; the concentration of graphene oxide in the electrophoretic solution is 2wt%-4wt% (e.g., 2wt%, 2.5wt%, 3wt%, 3.5wt%, or 4wt%), and the concentration of carbon nanotubes is 0.5wt%-1wt% (e.g., 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1wt%); the dispersant is a polycarboxylic acid-based dispersant; and the solvent is anhydrous ethanol and / or N,N-dimethylformamide. The presence of carbon nanotubes in the electrophoretic solution allows for directional growth of the carbon nanotubes during electrophoresis to form nano-needle-like anchoring structures, which helps to enhance the mechanical interlocking effect of the interface. Furthermore, in practical applications, the carbon nanotubes in the graphene mesh layer can be vertically inserted into the epoxy resin matrix of the stress buffer layer to form "nail"-shaped mechanical anchoring points. This expands the interfacial bonding between the fiber mesh layer and the stress buffer layer from simple physical adsorption and chemical bonding to a triple enhancement mechanism of "chemical bonding + mechanical anchoring + van der Waals forces," significantly improving the interface's shear resistance and peel resistance.

[0033] The concentration of graphene oxide directly affects the coating thickness and uniformity. If the graphene oxide concentration is too high, the following consequences occur: the electrophoretic solution viscosity is too high, affecting the migration speed of charged particles; the deposition rate is too fast, resulting in uneven coating thickness; it easily accumulates on the fiber mesh surface, causing defects; and agglomeration and precipitation easily occur during electrophoresis, affecting coating quality. If the graphene oxide concentration is too low, the following consequences occur: the deposition rate is too slow, resulting in low production efficiency; it is difficult to form a coating of sufficient thickness to meet performance requirements; the coating coverage is insufficient, leaving exposed areas; and multiple depositions increase process complexity and cost. Anhydrous ethanol is a polar protic solvent with good miscibility with water, which is beneficial to the stability of the electrophoretic deposition process; DMF is a polar aprotic solvent with even stronger solubility for graphene.

[0034] Preferably, the solvent is a mixed solution of anhydrous ethanol and DMF, with a mass ratio of anhydrous ethanol to DMF of 3:1 to 1:1 (e.g., 3:1, 2:1, 1.5:1, or 1:1). The use of anhydrous ethanol and DMF in combination allows for a balance between dispersion and process stability.

[0035] Preferably, the dispersant is a polycarboxylate superplasticizer and / or sodium polyacrylate; the molecular weight of the dispersant is 2000-10000 (e.g., 2000, 4000, 6000, 8000, or 10000). The dispersant prevents the aggregation of graphene sheets and carbon nanotubes through electrostatic repulsion and steric hindrance, ensuring uniform dispersion in the solvent. If too much dispersant is used, an excessively thick adsorption layer will form on the fiber surface, affecting the adhesion of the graphene coating; if too little dispersant is used, the dispersion effect will be insufficient, easily leading to aggregation.

[0036] The selection of carbon nanotube concentration in the electrophoresis solution is mainly based on the following considerations: As the core material of the nanoneedle anchoring structure, carbon nanotubes need to form an appropriately dense directional distribution on the surface of the fiber mesh; when the carbon nanotube concentration is 0.5 g / L, its mass ratio with graphene oxide is approximately 1:4-1:6. This ratio ensures sufficient anchor point density without affecting the continuity of the graphene sheets due to excessive concentration; excessively high carbon nanotube concentration increases the viscosity of the electrophoresis solution, affecting deposition uniformity; excessively low carbon nanotube concentration cannot form an effective nanoneedle structure. The directional growth mechanism of carbon nanotubes is as follows: During electrophoretic deposition, negatively charged carbon nanotubes migrate along the direction of electric field lines under the action of electric field force; when they reach the surface of the fiber mesh, which serves as the anode, due to electrostatic attraction, the carbon nanotubes tend to align perpendicular to the fiber mesh surface; the subsequent deposition of graphene oxide sheets fixes the carbon nanotubes in this orientation; during multilayer deposition, carbon nanotubes continue to grow directionally, forming a "needle" structure. Specifically, the deposition density and orientation of carbon nanotubes can be controlled by adjusting the electrophoresis voltage and deposition time.

[0037] Preferably, the electrophoretic solution is obtained by mixing graphene oxide, carbon nanotubes, a dispersant, and a solvent, ultrasonically dispersing the mixture for 30-60 min (e.g., 30 min, 40 min, 50 min, or 60 min), and then adjusting the pH to 7-9 (e.g., 7, 7.5, 8, 8.5, or 9) with ammonia. Adjusting the pH of the electrophoretic solution to 7-9 allows the graphene oxide to become negatively charged within this pH range, facilitating electrophoretic deposition on the anode surface. If the pH is too low, it reduces the surface charge density of the graphene oxide, affecting deposition efficiency; if the pH is too high, although it can increase the deposition rate, it leads to a loose coating structure and decreased adhesion. An appropriate pH value also contributes to the stable dispersion of carbon nanotubes in the electrophoretic solution.

[0038] More preferably, the ultrasonic power is 300-600W (e.g., 300W, 400W, 500W or 600W) and the frequency is 40kHz.

[0039] In a preferred embodiment of the concrete interface repair material of the present invention, in step A1, the voltage for electrophoretic deposition is 30-50V (e.g., 30V, 35V, 40V, 45V, or 50V), the time is 5-15min (e.g., 5min, 8min, 10min, 12min, or 15min), and the temperature is 25±2℃ (e.g., 23℃, 24℃, 25℃, 26℃, or 27℃). The choice of voltage has a decisive influence on the coating quality. If the voltage is too high, the electrophoretic rate will be too fast, resulting in excessive kinetic energy from charged particles impacting the fiber mesh surface, easily causing coating damage; electrolysis of water may occur, generating hydrogen and oxygen bubbles, destroying the coating's density; rapid deposition will lead to high internal stress in the coating, making it prone to cracking after drying; energy consumption will increase, and equipment requirements will be higher. If the voltage is too low, the electric field force will be insufficient, resulting in slow migration of charged particles and a low deposition rate; the coating thickness will be difficult to achieve the design requirements; carbon nanotubes will have difficulty obtaining sufficient directional driving force and cannot grow perpendicular to the fiber surface; the production cycle will be long, and the economic efficiency will be poor. The electrophoresis time needs to be set to balance coating thickness and uniformity. If the time is too long, the following will occur: the coating will be too thick, increasing internal stress and decreasing adhesion; the deposition rate will decrease in the later stages, but energy consumption will continue to increase; it may also lead to increased surface roughness of the coating; in addition, prolonged electric field action may cause local overheating. If the electrophoresis time is too short, the following will occur: the coating thickness will be insufficient, failing to form a complete three-layer gradient structure; the directional growth of carbon nanotubes will be insufficient, resulting in poor anchoring effect; the coating coverage will be low, with numerous defects; and the continuity of the conductive network will be poor. Temperature control is also crucial to the stability of electrophoretic deposition. 25±2℃ is the most suitable operating temperature because: at this temperature, the solvent viscosity is moderate, which is conducive to the migration of charged particles; it avoids concentration changes caused by solvent evaporation at high temperatures; it does not reduce ionic conductivity due to low temperatures; and room temperature conditions are convenient for industrial production.

[0040] Preferably, in step A1, during the electrophoretic deposition process, the electrode spacing is 50-100 mm (e.g., 50 mm, 60 mm, 70 mm, 80 mm, 90 mm or 100 mm).

[0041] Preferably, the carbon nanotubes have a length of 50-200 nm (e.g., 50 nm, 80 nm, 100 nm, 150 nm, or 200 nm) and a diameter of 10-50 nm (e.g., 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm). The distribution density of the carbon nanotubes in the graphene oxide functional layer is 10. 8- 10 10 root / cm 2(For example, 1×10) 8 5×10 8 1×10 9 5×10 9 Or 1×10 10 root / cm 2 If the length of the carbon nanotubes is too short, then: during subsequent repairs of new concrete, the carbon nanotubes will not penetrate deep enough into the stress buffer layer, resulting in weak mechanical anchoring; it will also cause insufficient embedding with the graphene oxide coating, making them prone to detachment; furthermore, excessively short carbon nanotubes cannot cross the interface transition zone, limiting the anchoring effect. If the length of the carbon nanotubes is too long, then: during electrophoretic deposition, they are difficult to maintain a vertical orientation, easily bending or collapsing; excessively long carbon nanotubes are also prone to entanglement, affecting dispersion; excessively long carbon nanotubes will also significantly increase the surface roughness of the coating, affecting its bonding with the second stress buffer layer; finally, excessively long carbon nanotubes will result in higher costs and poor economic efficiency. The diameter of the carbon nanotubes also affects the anchoring strength and electrical properties. If the diameter of the carbon nanotubes is too small, then: the mechanical strength of the carbon nanotubes is insufficient, making them prone to breakage under stress, with limited mechanical contribution; excessively small diameters will also make it difficult to control their dispersion and orientation. If the diameter of carbon nanotubes is too large, then: although the strength of a single carbon nanotube is high, the number of nanotubes decreases for the same mass, resulting in a lower anchoring point density; the surface area to volume ratio of carbon nanotubes decreases, reducing the contact area with the substrate; furthermore, excessively large diameter carbon nanotubes cause rapid sedimentation in the electrophoretic solution, leading to poor dispersion stability. The distribution density of carbon nanotubes is mainly determined by the concentration of carbon nanotubes in the electrophoretic solution and the process parameters (voltage, time) of electrophoretic deposition, which together determine the overall effectiveness of the anchoring structure (the distribution state of carbon nanotubes in the coating after electrophoretic deposition can be verified by SEM characterization).

[0042] In a preferred embodiment of the concrete interface repair material of the present invention, in step A2, the concentration of the ascorbic acid solution is 8-12 g / L (e.g., 8 g / L, 9 g / L, 10 g / L, 11 g / L or 12 g / L), the reduction reaction temperature is 60-80°C (e.g., 60°C, 65°C, 70°C, 75°C or 80°C), the reduction reaction time is 1-3 h (e.g., 1 h, 2 h or 3 h), followed by heat treatment at 100-140°C (e.g., 100°C, 110°C, 120°C, 130°C or 140°C) for 20-40 min (e.g., 20 min, 25 min, 30 min, 35 min or 40 min). Ascorbic acid, as a green reducing agent, works by utilizing the strong reducing properties of its enediol structure. This enediol structure in the ascorbic acid molecule can reduce the oxygen-containing functional groups in graphene oxide (GO), restoring the conjugated π-electron structure of graphene. The reduced graphene (rGO) exhibits significantly improved conductivity, decreasing from 10⁻⁶ of GO. -2 -10-4 The S / m is increased to 100-1000 S / m for rGO; some carboxyl and hydroxyl groups are retained to ensure continuity with the outer layer modification. If the ascorbic acid concentration is too high, the reduction reaction will be too vigorous, potentially leading to complete reduction of the graphene sheets and loss of necessary functional groups; excessive reduction will increase the hydrophobicity of the graphene sheets, affecting subsequent silanization reactions; and it will increase raw material costs, resulting in poor economic efficiency. If the ascorbic acid concentration is too low, the reduction reaction will be insufficient, the conductivity will not meet requirements, and too many oxygen-containing functional groups will remain in the coating, affecting structural stability; in addition, a lower concentration will require a longer reaction time, reducing production efficiency. The selection of the reduction reaction temperature is based on kinetic and thermodynamic considerations; if the reduction reaction temperature is too high, the reaction rate will be too fast, making it difficult to control the degree of reduction; at higher reaction temperatures, ascorbic acid may undergo side reactions or decomposition; furthermore, the fiber mesh may also be thermally deformed at higher reaction temperatures, affecting dimensional stability. If the reduction reaction temperature is too low, on the one hand, the activation energy will be insufficient, resulting in low reduction efficiency; on the other hand, the reaction time will need to be significantly extended, leading to a long production cycle; and it may also result in difficulty achieving the designed conductivity target. The heat treatment step helps to further remove residual moisture and solvents from the coating; it also helps to promote π-π stacking between graphene sheets, increasing the coating density; furthermore, it can further reduce some incompletely reduced graphene oxide; finally, the heat treatment step helps to enhance the interfacial bonding strength between the coating and the fiber mesh.

[0043] In a preferred embodiment of the concrete interface repair material of the present invention, in step A3, the silane coupling agent solution is a 2%-3% (e.g., 2%, 2.3%, 2.6%, or 3%) ethanol solution, and the soaking time is 20-40 min (e.g., 20 min, 25 min, 30 min, 35 min, or 40 min); the silane coupling agent is at least one of KH-560, KH-550, and KH-570. However, if the concentration of the silane coupling agent is too high, excessive silane will form multilayer adsorption on the fiber mesh surface, resulting in an excessively thick coating and a loose structure; this will further lead to high shrinkage stress during curing, making cracks more likely; in addition, excessive self-condensation between silanes will also consume the active groups originally used for reaction with the matrix, increasing raw material costs and VOC emissions. If the concentration of silane coupling agent is too low, the following will occur: insufficient silanization, low outer layer coverage, resulting in insufficient reaction sites with the epoxy resin matrix in the stress buffer layer during subsequent applications, and reduced interfacial bonding strength; in addition, it will also reduce the alkali resistance and durability of the coating; moreover, if the concentration of silane coupling agent is too low, multiple immersion treatments are required, increasing the complexity of the process.

[0044] KH-560 (γ-glycidoxypropyltrimethoxysilane) plays the following key roles in this invention: the epoxy group can undergo ring-opening reactions with the carboxyl and hydroxyl groups on the graphene surface to achieve covalent bonding; it acts as a bridging molecule to connect the graphene coating and the stress buffer layer; it maintains chemical stability in an alkaline environment to ensure long-term durability; KH-550 (γ-aminopropyltriethoxysilane) and KH-570 (γ-methacryloyloxypropyltrimethoxysilane) can act as auxiliary coupling agents, providing amino and double bond functional groups respectively, to further enhance interfacial reactivity.

[0045] Preferably, in step A3, the drying temperature is 60-80℃ (e.g., 60℃, 65℃, 70℃, 75℃, or 80℃), and the drying time is 20-40 min (e.g., 20 min, 25 min, 30 min, 35 min, or 40 min); the curing temperature is 80-120℃ (e.g., 80℃, 90℃, 100℃, 110℃, or 120℃), and the curing time is 1-3 h (e.g., 1 h, 1.5 h, 2 h, 2.5 h, or 3 h). The selection of the drying temperature helps to remove the solvent and avoid coating cracking caused by excessively rapid drying; furthermore, this temperature helps to promote the hydrolysis and initial condensation reaction of the silane. The curing step in this invention mainly serves the following purposes: to complete the condensation reaction between the silane coupling agent and graphene, to form a stable polysiloxane network structure, to ensure that the activity of the epoxy groups (glycidyl ether groups in the molecular structure of silane coupling agent KH-560) is retained, and to improve the heat resistance and chemical stability of the coating.

[0046] In a preferred embodiment of the concrete interface repair material of the present invention, the components of the first stress buffer layer and / or the second stress buffer layer, by mass parts, include: 100 parts of epoxy resin, 0.5-1.5 parts of graphene nanosheets (e.g., 0.5 parts, 0.8 parts, 1.0 parts, 1.2 parts or 1.5 parts), 30-40 parts of curing agent (e.g., 30 parts, 33 parts, 36 parts or 40 parts), and 5-10 parts of toughening agent (e.g., 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts).

[0047] Preferably, the epoxy resin is at least one of E-51 type epoxy resin, E-44 type epoxy resin, and E-20 type epoxy resin. Specifically, the E-51 type epoxy resin has an epoxy value of 0.48-0.54 eq / 100g and a viscosity of 8000-15000 mM. The E-44 epoxy resin (epoxy value 0.41-0.47eq / 100g) has a moderate molecular weight and viscosity, making it easy to mix and disperse with graphene nanosheets. After curing, it exhibits good mechanical properties and chemical resistance. The E-20 epoxy resin (epoxy value 0.22-0.25eq / 100g) has a slightly higher molecular weight and better toughness of the cured product, but it has a higher viscosity.

[0048] More preferably, the epoxy resin is a mixture of E-51 type epoxy resin and E-44 type epoxy resin, with a mass ratio of E-51 type epoxy resin to E-44 type epoxy resin of 7:3-5:5 (e.g., 7:3, 6:4 or 5:5). This mixture balances processing performance and mechanical properties; if the proportion of E-51 type epoxy resin is too high, the cured product will be brittle; if the proportion of E-44 type epoxy resin is too high, the system viscosity will be too high, making it difficult to uniformly mix the graphene nanosheets.

[0049] Preferably, the graphene nanosheets have a particle size of 1-10 μm (e.g., 1 μm, 3 μm, 5 μm, 7 μm or 10 μm), a thickness of 5-50 nm (e.g., 5 nm, 15 nm, 30 nm, 40 nm or 50 nm), and a specific surface area of ​​50-500 m². 2 / g (e.g., 50m² / g, 150m² / g, 300m² / g, 400m² / g, or 500m² / g). The mechanism of action of graphene nanosheets in the first and / or second stress buffer layers includes: the sheet structure of graphene nanosheets can deflect and bridge microcracks, improving fracture toughness; the large specific surface area of ​​graphene nanosheets provides extensive contact with epoxy resin molecules, enhancing interfacial bonding; the slip effect between graphene sheets can dissipate energy, improving impact resistance; the conductivity of graphene sheets can endow the first and / or second stress buffer layers with strain sensing function; in addition, the sheet structure of graphene can block the penetration of moisture and corrosive media, improving durability. The selection of graphene nanosheet particle size needs to balance the reinforcing effect and dispersibility. If the particle size of graphene nanosheets is too small, then: although the dispersibility is good, the reinforcing effect is limited; the contact area between sheets is small, making it difficult to form an effective conductive network; and the bridging effect on cracks is weak. If the particle size of graphene nanosheets is too large, then: they are difficult to disperse uniformly in epoxy resin and are prone to agglomeration; excessively large particle sizes will cause their sedimentation rate to be fast, affecting the stability of the system; large-sized sheets may introduce defects, which will reduce mechanical properties. If the thickness of graphene nanosheets is too thin, then: although the conductivity and mechanical properties are optimal, the preparation is difficult and costly; in addition, ultrathin sheets are prone to curling, and their orientation in the matrix is ​​difficult to control; too small a thickness will also result in relatively poor chemical stability. If the thickness of graphene nanosheets is too thick (>50nm, equivalent to more than 100 layers), then: their thickness is close to that of graphite microflakes, losing the unique properties of graphene; conductivity and mechanical properties will also decrease significantly, and the dispersibility in the matrix will become poor. Theoretically, the specific surface area of ​​a single layer of graphene can reach 2630m². 2 / g, but the specific surface area of ​​graphene nanosheets used in engineering applications is typically 50-500m² due to the large number of layers. 2 / g. If the specific surface area of ​​graphene nanosheets is too small, it indicates severe agglomeration or too many layers, and the performance is close to that of ordinary graphite powder.

[0050] Preferably, the curing agent is at least one of polyamide curing agents, aliphatic amine curing agents, and aromatic amine curing agents.

[0051] Preferably, by weight percentage, the curing agent comprises 60wt%-80wt% (e.g., 60wt%, 70wt%, or 80wt%) of polyamide curing agent, 10wt%-25wt% (e.g., 10wt%, 15wt%, 20wt%, or 25wt%) of aliphatic amine curing agent, and 10wt%-15wt% (e.g., 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, or 10wt%) of aromatic amine curing agent. This curing agent can balance curing speed, mechanical properties, toughness, and durability.

[0052] Preferably, the toughening agent is at least one of rubber particles, polyurethane, and carboxyl-terminated nitrile butadiene rubber (CTBN). The toughening mechanism includes: the rubber phase forming a "second phase" in the matrix, undergoing cavitation under stress, and absorbing energy; crack propagation encountering the flexible rubber phase undergoes deflection and bridging, increasing fracture toughness; the interface between the rubber phase and the epoxy matrix can undergo shear yielding, dissipating energy; and improving the material's impact resistance and fatigue resistance. Specifically, rubber particles (particle size 10-50 μm) have a significant toughening effect, but excessive addition will significantly reduce the elastic modulus and strength; polyurethane toughening agents can chemically react with epoxy resins, exhibiting good compatibility, but are more expensive; CTBN is the most widely used liquid toughening agent for epoxy resins, and its terminal carboxyl groups can react with epoxy groups to form chemical bonds, resulting in good toughening effect without significantly reducing heat resistance.

[0053] Preferably, the components of the first stress buffer layer and / or the second stress buffer layer further include 0.2 parts of defoamer. The defoamer can be an organosilicon defoamer (e.g., polydimethylsiloxane) or a mineral oil defoamer. Its function is to: reduce the surface tension of the system and promote the escape of bubbles; prevent bubbles introduced during stirring and application from remaining in the buffer layer; and improve the density and interfacial adhesion strength of the first stress buffer layer and / or the second stress buffer layer. If too much defoamer is used, it may affect the curing reaction or cause precipitation on the surface; if it is not added or the amount is too small, the bubbles will be difficult to completely eliminate, becoming stress concentration points.

[0054] In a preferred embodiment of the concrete interface repair material of the present invention, the thickness of the first stress buffer layer is 1-3 mm (e.g., 1 mm, 1.5 mm, 2 mm, 2.5 mm, or 3 mm). If the thickness of the first stress buffer layer is too small, then: the stress buffering effect is insufficient, the stiffness gradient transition is inadequate; it is difficult to fill the microscopic unevenness and defects on the old concrete surface; the tolerance for unevenness of the interface treatment layer is low; and the ability to resist local stress concentration is weak. If the thickness of the first stress buffer layer is too large, then: the shrinkage stress during curing increases, which may cause internal cracks; the heat release during curing is large, the temperature peak is high, which may cause thermal damage; the excessively thick soft layer may reduce the overall stiffness and affect the load-bearing capacity; and the curing time is prolonged, affecting construction efficiency.

[0055] Preferably, the elastic modulus of the first stress buffer layer is 5-15 GPa; the elastic modulus of the first stress buffer layer can be adjusted by the amount of graphene nanosheets added. If the elastic modulus of the first stress buffer layer is too low (<5 GPa), then: the stress transfer efficiency is low, and the reinforcing effect of the graphene fiber mesh cannot be effectively utilized; the first stress buffer layer deforms too much under load, affecting structural performance and causing large long-term creep. If the elastic modulus of the first stress buffer layer is too high, then: the stiffness difference between it and concrete (30-40 GPa) and graphene fiber mesh (200-300 GPa) is still large, and the buffering effect is limited; in addition, the toughness decreases, the impact resistance is reduced, and the stress concentration problem cannot be fundamentally solved.

[0056] In a preferred embodiment of the concrete interface repair material of the present invention, the thickness of the second stress buffer layer is 1-2 mm (e.g., 1 mm, 1.3 mm, 1.6 mm, or 2 mm). The main functions of the second stress buffer layer are: to protect the graphene fiber mesh layer from direct impact and abrasion by the freshly poured concrete; to fill the voids in the graphene fiber mesh, forming a continuous stress transfer interface; to provide stress transition between the graphene fiber mesh and the new concrete; and to seal the conductive network of the graphene coating, preventing short circuits between the graphene fiber mesh and reinforcing steel or other components. Preferably, the second stress buffer layer completely encapsulates the graphene fiber mesh layer.

[0057] Preferably, the amount of graphene nanosheets in the second stress buffer layer is 0.5-1.0 parts. The amount of graphene nanosheets in the first and / or second stress buffer layers will affect the elastic modulus of the first and / or second stress buffer layers; the amount of graphene nanosheets in the second stress buffer layer is 0.5-1.0 parts, which helps to improve flexibility and the encapsulation of graphene fiber mesh.

[0058] In a preferred embodiment of the concrete interface repair material of the present invention, the fiber mesh is at least one of carbon fiber mesh, basalt fiber mesh, glass fiber mesh, and hybrid fiber mesh; the mesh spacing is 30-80mm, and the tensile strength is ≥2000MPa; the fiber mesh is laid in single or double layers, and when double-layered, a staggered overlap method is used, with an overlap length ≥150mm. The choice of mesh spacing affects the reinforcement effect; if the mesh spacing is too small, the mesh is too dense, making it difficult for the second stress buffer layer material to fully penetrate; it also places high demands on construction operations; performance improvement is limited, and the cost-effectiveness is low. If the mesh spacing is too large, the fiber coverage is low, the reinforcement effect decreases; the load distribution is uneven, easily leading to stress concentration; and the crack control effect is poor. The commonly used mesh spacing is 50mm×50mm, which achieves a good balance between performance and economy. For important structures or parts under complex stress, 40mm×40mm or 30mm×50mm (different primary and secondary directions) can be used. A tensile strength of ≥2000MPa is based on the following considerations: meeting the basic strength requirements for structural reinforcement; ensuring that the fiber fails before the concrete under ultimate load, achieving ductile failure; and guaranteeing a safety reserve under long-term loads. Using high-strength fibers (such as carbon fiber, with a tensile strength of 3000-4000MPa) can further improve the reinforcement effect.

[0059] Fiber mesh can be laid in single or double layers; single-layer laying is suitable for: light to moderate reinforcement needs; situations where the structural bearing capacity is large and the reinforcement thickness is limited; double-layer laying is suitable for: heavy reinforcement or severe structural damage; seismic reinforcement; situations where a high increase in bearing capacity is required.

[0060] When laying double layers, a staggered overlap method is used, meaning the second layer of mesh is staggered from the first by half a mesh spacing (e.g., 25mm). The advantages of staggered overlap are: avoiding fiber bundle overlap between the two mesh layers, preventing sudden changes in local stiffness; improving fiber coverage and load distribution uniformity; reducing stress concentration and improving reinforcement effectiveness. An overlap length of ≥150mm is based on ensuring reliable stress transfer in the overlap area, meeting relevant specifications, and preventing premature failure at the overlap. In actual construction, the overlap length at edges and areas with complex stress distribution should be appropriately increased to 200-300mm.

[0061] Preferably, the graphene fiber mesh is fixed to the old concrete base layer by anchors. For example, the anchors can be chemical anchors (the diameter, anchoring depth, and spacing of the anchors can be determined according to the actual engineering needs; for example, the diameter of the chemical anchors can be 10-16mm, the anchoring depth can be ≥80mm; the spacing of the anchors at the edge of the reinforced structure is 200mm, and the spacing in the middle of the reinforced structure is 300mm).

[0062] In a preferred embodiment of the concrete interface reinforcement structure of the present invention, a health monitoring system is further included; the health monitoring system uses a continuous conductive network formed by a graphene coating as a distributed strain sensor to monitor the interface stress distribution and crack propagation by measuring the resistance change of the conductive network.

[0063] The working principle of the health monitoring system is as follows: the graphene coating forms a continuous conductive network on the surface of the fiber mesh; when the interface is strained, the spacing between the graphene sheets in the conductive network changes, resulting in a change in the tunneling resistance; crack propagation will cut off part of the conductive path, and the resistance will increase significantly; by monitoring the resistance changes in different areas, the stress distribution and damage state of the interface can be calculated.

[0064] The present invention also proposes a construction method for concrete interface repair materials. The construction method for concrete interface repair materials in the present invention includes the following steps: (1) Base layer pretreatment: grinding the old concrete until a solid base layer is exposed, repairing the cracks, sprinkling water to moisten until saturated and dry; applying an interface agent containing graphene and waiting for the surface to dry; (2) applying the first buffer layer; (3) laying the graphene fiber mesh layer; (4) applying the second buffer layer; (5) pouring the concrete repair layer.

[0065] This invention also proposes the application of concrete interface repair materials, specifically their application in bridge reinforcement, building structure reinforcement, tunnel lining repair, or hydraulic structure protection.

[0066] The concrete interface repair material and its construction method of the present invention will be described in detail below through specific embodiments.

[0067] The main raw materials used in the following examples were sourced from: Graphene oxide: Suzhou Carbon-Feng Graphene Technology Co., Ltd., sheet diameter 2-5μm, thickness 1-5nm, oxygen content 30-40wt%; Carbon nanotubes: Shenzhen Nanoport Co., Ltd., multi-walled carbon nanotubes, outer diameter 10-30nm, length 10-30μm, purity >95%; Graphene nanosheets: Ningbo Moxi Technology Co., Ltd., sheet diameter 3-8μm, thickness 10-30nm, specific surface area 150-350m². 2 / g; Silane coupling agent KH-560: Nanjing Nengde New Material Technology Co., Ltd., purity ≥97%; Silane coupling agent KH-550: Nanjing Nengde New Material Technology Co., Ltd., purity ≥98%; Polycarboxylate dispersant: Jiangsu Bote New Material Co., Ltd., solid content 40%, molecular weight 5000; Anhydrous ethanol: Sinopharm Chemical Reagent Co., Ltd., analytical grade, purity ≥99.7%; N,N-Dimethylformamide (DMF): Sinopharm Chemical Reagent Co., Ltd., analytical grade, purity ≥99.5%; Ascorbic acid: Aladdin Reagent Co., Ltd., purity ≥99%; Ammonia water: Sinopharm Chemical Reagent Co., Ltd., mass fraction 25-28%; Epoxy resin E-51: Nanya Plastics Industry Co., Ltd., epoxy value 0.48-0.54eq / 100g, viscosity 11000-14000m / 25℃; Epoxy resin E-44: Lanxing Chemical New Materials Co., Ltd., epoxy value 0.41-0.47 eq / 100g; Polyamide curing agent 651: Anqing Petrochemical Polyamide Co., Ltd., amine value 260-310mgKOH / g, viscosity 5000-10000m / 25℃; Carboxyl-terminated nitrile butadiene rubber (CTBN): Chang Chun Petrochemical Co., Ltd., Taiwan, molecular weight 3000-4000, carboxyl content 1.8-2.2%; Organosilicon defoamer: Dow Corning, DC65 defoamer; Carbon fiber mesh: Zhejiang Jinggong Carbon Fiber Co., Ltd., 12K carbon fiber braiding, mesh spacing 50mm×50mm, tensile strength ≥3500MPa; Basalt fiber mesh: Sichuan Aerospace Tuoxin Basalt Industry Co., Ltd., mesh spacing 50mm×50mm, tensile strength ≥2200MPa; Chemical anchors: Hilti (China) Trading Co., Ltd., HIT-RE 500 injection-type anchoring adhesive + M12 screw, anchoring depth 100mm; Conductive copper wire: Shenzhen Jinhuanyu Wire & Cable Co., Ltd., multi-strand tin-plated copper wire, diameter 0.75mm 2 Interface agent: Nippon Paint (China) Co., Ltd., concrete interface treatment agent.

[0068] Example 1 The concrete interface repair material of this embodiment includes an interface treatment layer, a first stress buffer layer, a graphene fiber mesh layer, a second stress buffer layer, and a concrete repair layer. The interface treatment layer consists of an interface agent and graphene nanosheets, with the graphene nanosheets having a doping amount of 0.5 wt%; the thickness of the interface treatment layer is 0.2 mm. First stress buffer layer: By weight, it consists of 100 parts of epoxy resin E-51, 0.5 parts of graphene nanosheets, 30 parts of polyamide curing agent 651, 5 parts of carboxyl-terminated nitrile rubber, and 0.2 parts of silicone defoamer; the thickness of the first stress buffer layer is 1 mm; the first stress buffer layer is prepared by a method including the following steps: I. Epoxy resin E-51 (epoxy value 0.50 eq / 100g, viscosity...) 100 parts were heated to 50°C, causing its viscosity to decrease to approximately [value missing]. II. Weigh out 0.5 parts of graphene nanosheets according to the specified proportion (sheet diameter 3-5μm, thickness 10-20nm, specific surface area 180m²). 2 Add the graphene nanosheets to the heated epoxy resin (at 800 rpm) and stir for 20 minutes using a mechanical stirrer, while simultaneously using an ultrasonic probe (200W) to assist dispersion for 10 minutes to ensure uniform dispersion; III. Add 30 parts of polyamide curing agent 651 (amine value 280 mg KOH / g, viscosity... IV. Add 5 parts of carboxyl-terminated nitrile rubber (carboxyl content 2.0%, molecular weight 3500), and stir for 20 minutes until completely dissolved; V. Add 0.2 parts of silicone defoamer, and stir for 5 minutes; VI. Defoam under vacuum for 15 minutes at a vacuum degree of -0.09 MPa to obtain a uniform first stress buffer layer material. The viscosity of this material at 25℃ is approximately 8000 m... The applicable period is about 4 hours, and the elastic modulus after curing is 5.2 GPa (obtained after testing).

[0069] Graphene fiber mesh layer: A carbon fiber mesh with a 50mm × 50mm mesh spacing is used, and a graphene coating is deposited on the fiber surface; specifically, the graphene fiber mesh layer (SEM image of the graphene fiber mesh layer in this embodiment is shown below) Figure 1 (As shown) It is prepared by a method including the following steps: A1. Preparation of electrophoresis solution: Mix graphene oxide (2-3 μm in diameter), carbon nanotubes (10-20 nm in outer diameter and 10-20 μm in length), polycarboxylate dispersant (3000 molecular weight, 40% solid content) and mixed solvent in a certain proportion. Disperse the mixture using an ultrasonic probe (300 W power, 40 kHz frequency) for 30 minutes. Adjust the pH to 7.0 with 28% ammonia water to obtain a pale yellow semi-transparent electrophoresis solution (the concentrations of each raw material in the electrophoresis solution are: 2 wt% graphene oxide, 0.5 wt% carbon nanotubes, and 0.3% polycarboxylate dispersant; the solvent is a mixture of anhydrous ethanol and DMF (mass ratio 2:1)). A2. Electrophoretic deposition: A carbon fiber mesh (12K carbon fiber, mesh spacing 50mm×50mm, tensile strength 3500MPa) is used as the anode, and a stainless steel plate (304 stainless steel, thickness 2mm) is used as the cathode. The electrode spacing is 60mm. The mesh is immersed in the electrophoretic solution, and a voltage of 30V is applied for electrophoretic deposition. The temperature is controlled at 25±2℃ and the time is 5 minutes to obtain a fiber mesh with a graphene oxide functional layer deposited on the surface, which is then ready for use. A3. Drying and Reduction: The fiber mesh obtained in step A2 is slowly removed from the electrophoresis solution, and the surface droplets are dried by blowing with a hair dryer at a low temperature. Then, it is placed in an 80℃ oven to dry for 2 hours. Subsequently, it is immersed in ascorbic acid solution (concentration 8g / L, solvent is deionized water) and reduced in a 60℃ water bath for 1 hour, with stirring every 15 minutes. After removal, it is rinsed 3 times with deionized water and heat-treated in a 120℃ oven for 30 minutes to obtain a fiber mesh with a reduced graphene oxide transition layer, which is ready for use. A4. Surface modification: Immerse the fiber mesh obtained in step A3 into a silane coupling agent solution (KH-560 concentration 2wt%, solvent is anhydrous ethanol) at room temperature for 30 min, gently shaking the container every 10 min to promote wetting; after removal, pre-dry in a 60℃ oven for 30 min, and then cure at 100℃ for 2 h to obtain a modified graphene layer.

[0070] Second stress buffer layer: The composition of the second stress buffer layer is the same as that of the first buffer layer; the thickness of the second stress buffer layer is 1 mm. Concrete repair layer: C30 concrete is used for repair; the thickness of the concrete repair layer is 40mm.

[0071] The construction method in this embodiment includes the following steps: (1) Base treatment: Use an angle grinder equipped with diamond grinding discs to grind the old concrete surface to remove loose layers, oil stains and laitance. Grind to a depth of 2-3mm to achieve a surface roughness Ra of 6-8μm, exposing solid aggregate; blow away dust with a blower; for fine cracks with a width <0.2mm, use epoxy resin (two-component, viscosity) Low-pressure grouting repair; for cracks 0.2-1.0mm wide, manually chisel out a V-shaped groove (5-8mm wide, 8-12mm deep), fill with epoxy mortar; moisten with water until saturated and dry (no visible water on the surface but saturated inside); apply graphene-modified interface agent (obtained by adding 0.5wt% graphene nanosheets to the concrete interface treatment agent), with a coating amount of approximately 0.3kg / m². 2 After the surface has dried (approximately 2-3 hours), proceed with subsequent construction. (2) Apply the first stress buffer layer: Pour the material of the first stress buffer layer onto the treated old concrete surface, apply it evenly with a 6mm notched scraper, and control the thickness to 1mm; use a plastic roller to remove air bubbles and ensure that the surface is flat and free of holes. (3) Laying the graphene fiber mesh: Before the first stress buffer layer initially sets (the material surface is still sticky, within about 1.5-2 hours), lay the graphene fiber mesh longitudinally, and use a plastic roller to roll it from the middle to both sides to remove air bubbles, so that the mesh is fully embedded in the buffer layer; the transverse mesh is then laid, with an overlap length of 150mm, and additional buffer layer material is applied to the overlap to ensure adhesion; chemical anchors (Hilti HIT-RE 500+M12 screws) are installed every 500mm, with a drilling diameter of 14mm and a depth of 100mm, and the anchor spacing at the edge is 200mm and the spacing in the middle is 300mm; a 300mm long conductive copper wire (0.75mm in diameter) is pre-welded to the head of the anchor. 2 (Multi-strand tin-plated copper wire); (4) Electrical connection: A monitoring unit is set up every 2m×2m. The conductive copper wires of the four anchor bolts are collected and welded to the input end of the data acquisition device. The conductive copper wires are arranged along the direction of the grid fiber and temporarily fixed with tape to prevent them from falling off. The connection points are sealed with heat shrink tubing and epoxy resin for waterproofing. (5) Apply the second stress buffer layer: Immediately after the graphene fiber mesh is laid, apply the second stress buffer layer material (the same composition as the first stress buffer layer) with a thickness of 1 mm, completely covering the mesh, and smooth it with a scraper to ensure that the mesh is not exposed; (6) Pouring new concrete: Before the second stress buffer layer sets (within about 2 hours), pour a new C30 concrete repair layer with a thickness of 40mm; use a plate vibrator to fully vibrate to ensure compaction and avoid honeycombing; after initial setting (about 6-8 hours), start water curing, no less than 3 times a day, and the curing period is no less than 14 days.

[0072] Example 2 The difference between the concrete interface repair material in this embodiment and that in Embodiment 1 is: 1) First stress buffer layer: by weight, it consists of 100 parts of epoxy resin E-51, 1.0 part of graphene nanosheets, 35 parts of polyamide curing agent 651, 7 parts of carboxyl-terminated butadiene nitrile rubber, and 0.2 parts of silicone defoamer; the thickness of the first stress buffer layer is 2 mm. 2) Graphene fiber mesh layer: The concentrations of each raw material in the electrophoresis solution in step A1 are: 3 wt% graphene oxide, 0.75 wt% carbon nanotubes, and 0.4% polycarboxylic acid dispersant; the solvent is a mixture of anhydrous ethanol and DMF (mass ratio 2:1); 3) The electrophoretic deposition parameters in step A2 are: voltage 40V, time 10min, temperature 25±2℃; 4) In step A3, the concentration of ascorbic acid solution is 10 g / L, the temperature of the reduction reaction is 70℃, and the time of the reduction reaction is 2 h; 5) The thickness of the second stress buffer layer is 1.5 mm (the composition of the second stress buffer layer is the same as that of the first stress buffer layer). Tests showed that the elastic modulus of the first and second stress buffer layers after curing was 9.5 GPa.

[0073] The construction method of the concrete interface repair material in this embodiment is the same as that in Embodiment 1.

[0074] Example 3 The difference between the concrete interface repair material in this embodiment and that in Embodiment 1 is: 1) First stress buffer layer: by weight, it consists of 60 parts of epoxy resin E-51, 40 parts of epoxy resin E-41, 1.5 parts of graphene nanosheets, 40 parts of curing agent (the mass ratio of polyamide curing agent 651 to aromatic amine curing agent is 7:3; the aromatic amine curing agent is diaminodiphenylmethane), 10 parts of carboxyl-terminated butadiene-acrylonitrile rubber, and 0.2 parts of silicone defoamer; the thickness of the first stress buffer layer is 3 mm. 2) Graphene fiber mesh layer: The concentrations of each raw material in the electrophoresis solution in step A1 are: 4 wt% graphene oxide, 1 wt% carbon nanotubes, and 0.5% polycarboxylic acid dispersant; the solvent is a mixture of anhydrous ethanol and DMF (mass ratio 2:1); 3) The electrophoretic deposition parameters in step A2 are: voltage 50V, time 15min, temperature 25±2℃, and electrode spacing 80mm; 4) In step A3, the concentration of ascorbic acid solution is 12 g / L, the temperature of the reduction reaction is 80℃, and the time of the reduction reaction is 3 h; 5) In step A4, the silane coupling agent solution is a mixed solution of KH-560 and KH-550 (concentration 3wt%, solvent is anhydrous ethanol), the soaking time is 30 min, and the drying temperature is 80℃; 6) The graphene fiber mesh adopts a double-layer carbon fiber mesh, with the second layer laid 25mm off from the first layer and an overlap length of 200mm. 7) The thickness of the second stress buffer layer (with the same composition as the first stress buffer layer) is 2 mm.

[0075] Tests showed that the elastic modulus of both the first and second stress buffer layers after curing was 14.2 GPa.

[0076] The construction method of the concrete interface repair material in this embodiment is the same as that in Embodiment 1, but the anchor bolt spacing is adjusted to 150mm at the edge and 250mm in the middle.

[0077] Example 4 The difference between the concrete interface repair material in this embodiment and that in Embodiment 1 is: 1) First stress buffer layer: by weight, it consists of 100 parts of epoxy resin E-51, 0.8 parts of graphene nanosheets, 32 parts of curing agent (polyamide curing agent 651), 6 parts of carboxyl-terminated butadiene-acrylonitrile rubber, and 0.2 parts of silicone defoamer; the thickness of the first stress buffer layer is 1.5 mm. 2) Graphene fiber mesh layer: The concentrations of each raw material in the electrophoresis solution in step A1 are: 2.5 wt% graphene oxide, 0.6 wt% carbon nanotubes, and 0.35% polycarboxylic acid dispersant; the solvent is a mixture of anhydrous ethanol and DMF (mass ratio 2:1); 3) The electrophoretic deposition parameters in step A2 are: voltage 35V, time 8min, temperature 25±2℃, and electrode spacing 80mm; 4) Basalt fiber mesh (grid spacing 50mm×50mm, tensile strength 2200MPa) is used instead of carbon fiber mesh; 5) The thickness of the second stress buffer layer (with the same composition as the first stress buffer layer) is 2 mm.

[0078] 6) Tests showed that the elastic modulus of both the first and second stress buffer layers after curing was 7.8 GPa.

[0079] The construction method of the concrete interface repair material in this embodiment is the same as that in Embodiment 1.

[0080] Example 5 The difference between the concrete interface repair material in this embodiment and that in Embodiment 2 is: 1) First stress buffer layer (the composition of the second stress buffer layer is the same as that of the first stress buffer layer): by weight, it consists of 100 parts of epoxy resin E-51, 1.2 parts of graphene nanosheets, 36 parts of curing agent (the mass ratio of polyamide curing agent 651 to aromatic amine curing agent is 8:2; the aromatic amine curing agent is diaminodiphenylmethane), 8 parts of polyurethane toughening agent, and 0.2 parts of silicone defoamer; graphene nanosheet parameters: sheet diameter 5-8μm, thickness 30-40nm, specific surface area 280m². 2 / g; 2) Anchor bolt diameter 14mm, anchoring depth 110mm; 3) The spacing of the graphene fiber mesh is 30mm × 30mm; 4) The elastic modulus of the first and second stress buffer layers after curing was tested to be 11.5 GPa.

[0081] The construction method of the concrete interface repair material in this embodiment is the same as that in Embodiment 2.

[0082] Example 6 The difference between the concrete interface repair material in this embodiment and that in Embodiment 1 is: 1) First stress buffer layer (the composition of the second stress buffer layer is the same as that of the first stress buffer layer): by weight, it consists of 100 parts epoxy resin (the mass ratio of epoxy resin E-51 type to E-20 type is 8:2), 0.6 parts graphene nanosheets, 31 parts curing agent (polyamide curing agent type 651), 5.5 parts rubber particles (particle size 20-40μm), and 0.2 parts silicone defoamer; 2) A hybrid fiber mesh (12K carbon fiber in the warp and glass fiber in the weft) with a mesh spacing of 50mm × 50mm was used; anhydrous ethanol was used as the solvent in the preparation of the graphene fiber mesh; electrophoretic deposition was carried out under pH 8.0 conditions; 3) The elastic modulus of the first and second stress buffer layers after curing was tested to be 6.5 GPa.

[0083] The construction method of the concrete interface repair material in this embodiment is the same as that in Embodiment 1.

[0084] Example 7 The difference between the concrete interface repair material in this embodiment and that in Embodiment 3 is: 1) First stress buffer layer (the composition of the second stress buffer layer is the same as that of the first stress buffer layer): by weight, it consists of 100 parts of epoxy resin E-51, 1.3 parts of graphene nanosheets, 38 parts of curing agent (polyamide curing agent 651), 9 parts of carboxyl-terminated nitrile rubber, and 0.2 parts of silicone defoamer; the thickness of the first stress buffer layer is 2.5 mm; graphene nanosheet parameters: sheet diameter 8-10 μm, thickness 40-50 nm, specific surface area 420 m² / g. 2 / g; 2) The graphene fiber mesh uses basalt fiber mesh with a mesh spacing of 80mm×80mm; 3) The thickness of the second stress buffer layer is 1.8 mm; 4) Tests showed that the elastic modulus of both the first and second stress buffer layers after curing was 12.8 GPa.

[0085] The construction method of the concrete interface repair material in this embodiment is the same as that in Embodiment 3.

[0086] Example 8 The difference between this embodiment and Embodiment 2 is as follows: 1) Carbon nanotube parameters: outer diameter 40-50nm, length 20-30μm; 2) After electrophoretic deposition, the carbon nanotubes are oriented perpendicular to the surface of the fiber mesh, and their effective anchoring length exposed outside the graphene coating is 120-150 nm. 3) The reduction reaction was carried out using hydrazine hydrate solution (5% concentration, 80℃ reduction reaction temperature, 1h reaction time) instead of ascorbic acid; 4) The silane coupling agent used in step A4 is KH-570 (γ-methacryloyloxypropyltrimethoxysilane); 5) The graphene nanosheets in the first buffer layer have a diameter of 1-3 μm, a thickness of 5-15 nm, and a specific surface area of ​​450 m². 2 / g.

[0087] The remaining components and construction methods are the same as in Example 2.

[0088] Example 9 This example demonstrates the application of base slab reinforcement for a municipal bridge (built 20 years ago, concrete strength C30, with cracks appearing at the bottom of some beams): (1) Scope of reinforcement: the bottom slab at the mid-span of the bridge, with an area of ​​120m²; (2) The technical solution of Example 3 is adopted, with double-layer carbon fiber mesh laid in a staggered manner; (3) Special treatment: Due to the large number of cracks at the bottom of the beam (width 0.1-1.5mm), first use epoxy resin to fill and repair cracks with a width <0.5mm, and then fill and repair cracks with a width of 0.5-1.5mm by chiseling grooves; for concrete spalling areas (depth 5-15mm), use polymer mortar to repair and level them. (4) Construction environment control: Mobile scaffolding and dust covers are used to ensure the cleanliness of the construction surface; the ambient temperature is 15-25℃ and the relative humidity is 60-75%; (5) Quality inspection: 28 days after the reinforcement was completed, a pull-out test was conducted (one test point was set for every 20m², for a total of 6 points) to test the interfacial bond strength. The results were 3.8-4.3MPa, with an average of 4.05MPa, which met the specification requirements (≥2.5MPa). One year after the reinforcement was completed, no cracks, peeling or other defects were found during the visual inspection, and the reinforcement effect was good.

[0089] Comparative Example 1 The difference between this comparative example and Example 2 is that the amount of graphene nanosheets used in the first stress buffer layer is 2.5 parts; the remaining composition and construction method are the same as in Example 2.

[0090] Comparative Example 2 The difference between this comparative example and Example 1 is that no graphene nanosheets are added to the first stress buffer layer; the remaining composition and construction method are the same as in Example 1.

[0091] Comparative Example 3 The difference between this comparative example and Example 1 is that the amount of graphene oxide in the electrophoresis solution is 5 wt%; the remaining composition and construction method are the same as in Example 1.

[0092] Comparative Example 4 The difference between this comparative example and Example 1 is that the amount of carbon nanotubes used in the electrophoresis solution is 1.5 wt%; the remaining composition and construction method are the same as in Example 1.

[0093] Comparative Example 5 The difference between this comparative example and Example 1 is that no graphene coating was deposited on the surface of the fiber mesh, and an untreated carbon fiber mesh was used directly; the rest of the composition and construction method are the same as in Example 1.

[0094] Comparative Example 6 The difference between this comparative example and Example 1 is that: no first stress buffer layer and second stress buffer layer are set, the graphene-coated fiber mesh is directly pasted on the interface treatment layer, and then new concrete is poured; the rest of the composition and construction method are the same as in Example 1.

[0095] Comparative Example 7 The difference between this comparative example and Example 1 is that no carbon nanotubes are added to the electrophoresis solution (because the electrophoresis solution does not contain carbon nanotubes, the graphene coating on the surface of the fiber mesh does not have a nano-needle anchoring structure); the rest of the composition and construction method are the same as in Example 1.

[0096] Comparative Example 8 The difference between this comparative example and Example 1 is that step A3 is omitted in the preparation of the graphene fiber mesh, and silanization is performed directly; the coating is pure graphene oxide and has no conductivity; the remaining composition and construction method are the same as in Example 1.

[0097] Comparative Example 9 The difference between this comparative example and Example 2 is that the thickness of the first stress buffer layer is 0.5 mm and the thickness of the second buffer layer is 0.5 mm; the remaining composition and construction method are the same as in Example 2.

[0098] Comparative Example 10 The difference between this comparative example and Example 3 is that the thickness of the first stress buffer layer is 5mm; the remaining composition and construction method are the same as in Example 3.

[0099] Comparative Example 11 The difference between this comparative example and Example 1 is that a traditional epoxy resin adhesive (two-component, without graphene nanosheets) is used to replace the first and second stress buffer layers; specifically, its composition is: 100 parts of epoxy resin E-51, 30 parts of polyamide curing agent 650, and 50 parts of quartz sand (particle size 0.1-0.3mm); the remaining composition and construction method are the same as in Example 1.

[0100] Experimental Example The interfacial bond strength, shear strength, fatigue life, interfacial fracture energy, and chloride ion diffusion coefficient of the concrete interface-reinforced structures in the above embodiments and comparative examples were tested. Test method: 1. Interfacial bond strength test: Pull-out tests were conducted according to GB / T 50728-2011 "Technical Specification for Safety Appraisal of Strengthening Materials for Engineering Structures" and ASTM D7522 standard: (1) Prepare C30 concrete test blocks with dimensions of 150mm×150mm×100mm. After curing for 28 days, strengthen the surface according to the method of the example or comparative example. The thickness of the strengthening layer includes the interface treatment layer (0.2mm), the first stress buffer layer, the graphene fiber mesh layer, the second stress buffer layer, and the newly poured concrete layer (total thickness of about 50mm); (2) After curing the strengthening layer for 28 days, use a diamond saw to cut a circular cut with a diameter of 50mm on the surface of the strengthening layer. The cutting depth is just enough to cut the fiber mesh without damaging the old concrete; (3) Attach a steel pull-out head with a diameter of 50mm to the center of the circular cut using epoxy adhesive (cured for 24 hours); (4) Use a pull-out testing machine (accuracy ±1%FS) to test the surface of the strengthening layer. (5) Apply the load at a uniform rate until the specimen fails; record the maximum pull-out force and calculate the interfacial bond strength: , where F is the maximum pull-out force (N) and D is the diameter of the pull-out circle (50mm); (6) Observe and record the failure mode: interface failure (debonding of the interface between the reinforcement layer and the old concrete), concrete failure (the old concrete is pulled apart) or mixed failure; (7) Make 6 specimens for each group, remove the highest and lowest values ​​and take the average value.

[0101] 2. Shear strength test: Double shear tests were conducted according to Appendix C of GB 50367-2013 "Code for Design of Strengthening Concrete Structures": (1) Prepare L-shaped concrete specimens (vertical plate 150mm×150mm×50mm, bottom plate 150mm×200mm×50mm, C30 concrete), and leave a 10mm wide gap at the connection between the vertical plate and the bottom plate; (2) Reinforce the gap according to the method of the example or comparative example to form a reinforced interface; (3) After curing for 28 days, place the specimen in a double shear clamp and apply shear load to the vertical plate through a universal testing machine at a loading rate of 1mm / min; (4) Record the maximum load at shear failure and calculate the shear strength: τ=F / A, where F is the maximum shear force (N) and A is the shear area (150mm×10mm×2); (5) Make 5 specimens for each group and take the average value.

[0102] 3. Fatigue life test: Fatigue tests were conducted according to GB / T 50152-2012 "Standard for Test Methods of Concrete Structures": (1) Prepare specimens identical to those used for interfacial bond strength testing; (2) Perform cyclic pull-out tests using a hydraulic servo fatigue testing machine with a loading frequency of 5 Hz, a stress ratio R = 0.1 (minimum stress / maximum stress), and the maximum stress being 70% of the static bond strength; (3) Record the number of cycles N at which the specimen fails, which is defined as the fatigue life; (4) Test 3 specimens in each group and take the average value.

[0103] 4. Interfacial fracture energy test: According to RILEM TC The 50-FMC standard uses the three-point bending beam method for testing: (1) Prepare a composite beam specimen with dimensions of 400mm×100mm×100mm. The lower part is old concrete (C30, length 400mm) and the upper part is a reinforcement layer (prepared according to the example or comparative method, length 300mm, thickness including buffer layer and fiber mesh about 5mm, without pouring new concrete); (2) Pre-cast an initial crack (depth 20mm, width 2mm) in the middle of the interface and cure for 28 days; (3) Use a three-point bending loading device with a span of 300mm and a loading rate of 0.05mm / min, and record the load-displacement curve and crack propagation process at the same time (using digital image correlation technology DIC monitoring); (4) Calculate the fracture energy according to the load-displacement curve integral: Gf=∫F·dδ / A, where F is the load (N), δ is the displacement (mm), and A is the initial crack area (100mm×2mm); (5) Test 4 specimens in each group and take the average value.

[0104] 5. Chloride ion diffusion coefficient test: The electromigration method was adopted in accordance with NT BUILD 492 and ASTM C1556 standards: (1) A cylindrical specimen with a diameter of 100 mm and a thickness of 50 mm (including old concrete, reinforced interface and part of new concrete) was drilled from the reinforced specimen; (2) The sides of the specimen were sealed with epoxy resin, exposing only two end faces; (3) The specimen was installed in a diffusion cell with 0.5 mol / L NaCl solution on one side (cathode side) and 0.3 mol / L NaOH solution on the other side (anode side); (4) A DC voltage of 30 V was applied and energized for 24 hours; (5) After the test, the specimen was split open and 0.1 mol / L AgNO3 solution was sprayed on the cross-section. The white precipitate front is the chloride ion penetration depth; (6) The penetration depth at 5 locations was measured and the average value xd was taken; (7) The chloride ion diffusion coefficient was calculated according to the Nernst-Planck equation: D=(RT) / (zFE)×[xd-α√(xd)] / t; Where: D is the chloride ion diffusion coefficient (m² / s); R is the gas constant 8.314 J / (mol·K); T is the absolute temperature (K); z is the chloride ion valence (1); F is the Faraday constant 96485 C / mol; E is the electric field strength (V / m); xd is the chloride ion penetration depth (m); t is the energizing time (s); α is the experimental constant (calibrated by standard sample, α=0.0239 in this experiment); (8) Three samples are tested in each group, and the average value is taken.

[0105] 6. Long-term durability testing: (1) Freeze-thaw resistance: According to GB / T 50082-2009 standard, the reinforced specimen (150mm×150mm×150mm) was subjected to a rapid freezing and thawing cycle test. The freeze-thaw medium was 3% NaCl solution, the temperature range was -17±2℃ to 8±2℃, and each cycle was 4 hours. The mass loss and relative dynamic elastic modulus were measured every 25 cycles. The test was carried out for 300 cycles or until the relative dynamic elastic modulus dropped to 60%. The number of cycles and mass loss when the relative dynamic elastic modulus reached 60% were recorded. (2) Carbonization performance: According to GB / T According to the 50082-2009 standard, the reinforced specimen (100mm×100mm×400mm) was placed in a carbonization box with a temperature of 20±2℃, relative humidity of 70±5%, and CO2 concentration of 20±3%. At 28 days, 56 days, and 90 days, the specimen was split open and 1% phenolphthalein ethanol solution was sprayed on the cross-section to measure the carbonization depth (colorless area). (3) Interface bond strength retention rate: Pull-out tests were performed on the specimens after freeze-thaw cycles and after carbonization, and the strength retention rate was calculated as: strength after treatment / initial strength × 100%.

[0106] The test results are shown in Tables 1 and 2 below: Table 1 Performance test results of the embodiment

[0107] Table 2 Comparative Performance Test Results

[0108] Table 3. Long-term durability test results of Examples 1-3

[0109] "Unreinforced concrete" refers to the original C30 concrete test block that has not undergone any reinforcement treatment, serving as a blank control group.

[0110] It can be seen from the above table 1-3: (1) Performance analysis of Examples 1-9: The graphene-reinforced fiber mesh concrete interface strengthening structures in Examples 1-9 exhibit excellent comprehensive performance. The interfacial bond strength reached 3.6-4.5 MPa, an increase of 80%-125% compared to the interfacial bond strength of unreinforced concrete (1.5-2.0 MPa). All specimens failed due to concrete failure rather than interfacial failure, indicating that the interfacial bond strength exceeded the strength of the concrete itself, truly achieving synergistic work between the old and new concrete. The shear strength reached 6.2-8.0 MPa, an increase of 148%-171% compared to the unreinforced interface (2.5-3.5 MPa), significantly improving the shear resistance of the interface.

[0111] The fatigue life reaches 850,000-1,350,000 cycles, which is 6-14 times that of traditional FRP strengthening (80,000-150,000 cycles). This is attributed to the effective dispersion of stress concentration and slowing down fatigue crack propagation by the gradient graphene coating and stress buffer layer. The interfacial fracture energy reaches 185-248 J / m. 2 Compared to unreinforced interfaces (50-80 J / m) 2 The 232%-310% increase indicates that the material has excellent toughness and energy dissipation ability, which is attributed to the crack bridging and deflection effect of graphene nanosheets and the role of toughening agents.

[0112] The chloride ion diffusion coefficient is 1.0-1.8×10⁻⁶. -12 m 2 / s, compared to unreinforced concrete (3.5-4.5×10 -12 m 2 The chloride ion permeation channel is blocked by 60%-75% of the chloride ion permeation channel, and the layered structure of graphene forms an effective physical barrier, significantly improving durability.

[0113] Examples 1-3 employed a gradient design in terms of graphene nanosheet doping, buffer layer thickness, and graphene coating thickness, resulting in an increasing trend in various performance indicators. Overall, optimizing the proportions and structural parameters within the scope of the claims can further improve the comprehensive performance of the reinforced structure. Example 3, using a double-layer mesh and optimized formulation, achieved optimal performance: interfacial bonding strength of 4.5 MPa, fatigue life of 1.35 million cycles, and chloride ion diffusion coefficient of only 1.0 × 10⁻⁶. -12 m 2 / s.

[0114] Example 4 uses a basalt fiber mesh, whose performance is slightly lower than that of the carbon fiber mesh (Examples 1-3). However, even with adjustments to other parameters, its performance is still significantly better than the comparative examples, indicating that the technical solution of this invention is applicable to different types of fiber meshes. Examples 5 and 7 use different mesh spacings (30mm and 80mm), respectively. Combined with their respective formula adjustments, both achieved good reinforcement effects, indicating that the mesh spacing within the range of 30-80mm can be flexibly selected according to actual engineering needs.

[0115] Example 10 was applied in actual bridge reinforcement, achieving a pull-out strength of 4.05 MPa after 28 days and maintaining its appearance intact after one year, demonstrating the engineering applicability of the invention. Although Example 10 used the same concrete interface repair material as Example 1 for reinforcement, the experimental results differed from those of Example 1 due to differences in on-site construction conditions, environmental temperature and humidity, and substrate condition compared to the laboratory (this difference falls within the normal range of differences between laboratory and on-site construction conditions).

[0116] Long-term durability tests (Table 4) show that after 300 freeze-thaw cycles, Examples 1-3 maintained a relative dynamic modulus of elasticity of 87%-91%, with a mass loss of only 1.5%-2.1%, and a bond strength retention rate of 86%-90%, far superior to unreinforced concrete (relative dynamic modulus of elasticity 55%, mass loss 7.2%). The carbonization depth after 90 days was only 2.8-4.2 mm, a reduction of 66%-78% compared to unreinforced concrete (12.5 mm), and the bond strength retention rate after carbonization reached 92%-96%. These data fully demonstrate that graphene-reinforced structures possess excellent freeze-thaw resistance, carbonization resistance, and long-term bond performance, meeting the durability requirements under harsh environments.

[0117] (2) Analysis of the problems in Examples 1-11: The interfacial bond strength of Comparative Example 1 decreased to 2.8 MPa, a 32% decrease compared to Example 2. This was because the excessive amount of graphene nanosheets led to an excessively high viscosity of the buffer layer (measured viscosity at 25°C reached...). The graphene exhibits poor workability, making it difficult to fully impregnate the fiber mesh and resulting in numerous air bubbles and pore defects. Furthermore, the excessive aggregation of graphene sheets disrupts the continuity of the epoxy matrix, thus reducing mechanical properties. The fatigue life is only 450,000 cycles because the aggregated graphene becomes the initiation source of fatigue cracks. The failure mode is interfacial failure, indicating interfacial bonding failure.

[0118] The interfacial bond strength of Comparative Example 2 was 3.2 MPa, only slightly lower than that of Example 1, but its shear strength and fatigue resistance were significantly reduced. More importantly, the chloride ion diffusion coefficient was as high as 2.5 × 10⁻⁶. -12 m 2The value of / s increased by 39% compared to Example 1, indicating a significant decrease in durability due to the lack of graphene shielding effect. The measured elastic modulus of the buffer layer was 3.8 GPa, which is too low to achieve an effective stress gradient transition, leading to stress concentration.

[0119] The interfacial bonding strength of Comparative Example 3 was only 3.0 MPa; the reason was that the concentration of graphene oxide in the electrophoresis solution was too high, resulting in a significant increase in viscosity (measured viscosity 12 m). Example 1 is 5m The migration speed of charged particles decreased, and the deposition rate was too fast and uneven. The surface roughness of the coating increased significantly (Ra=15μm; Ra=4μm in Example 1), and there were a large number of voids at the bonding interface with the buffer layer. Although the coating thickness reached 35μm, it was loose and porous inside, resulting in poor adhesion (measured pull-out adhesion of 1.8MPa, compared to 3.2MPa in Example 1).

[0120] The interfacial bond strength of Comparative Example 4 was 2.9 MPa, and the shear strength was 4.3 MPa. Excessive carbon nanotubes led to significant aggregation and precipitation in the electrophoretic solution, which could not be completely dispersed even after 60 minutes of ultrasonic dispersion. The carbon nanotube distribution in the deposited coating was extremely uneven, resulting in excessively high density in some areas, causing entanglement and discontinuous stress transmission; while other areas had insufficient density and inadequate anchoring. An excessively rough coating surface may result in some carbon nanotubes bending or breaking, which would actually reduce the anchoring effect.

[0121] The interfacial bond strength of Comparative Example 5 was only 2.5 MPa, the lowest among all comparative examples. The unmodified carbon fiber had a smooth surface, and its bond with the first and second stress buffer layers relied mainly on van der Waals forces and mechanical interlocking, resulting in insufficient bond strength. Its fatigue life was only 350,000 cycles; due to the lack of coating protection and reinforcement, the fiber-matrix interface was prone to fatigue delamination. The chloride ion diffusion coefficient was as high as 3.2 × 10⁻⁶. -12 m 2 / s, the microscopic interface between the fiber and the matrix becomes a preferential channel for chloride ion penetration. Upon failure, the fiber bundle is pulled out of the buffer layer as a whole, accompanied by a crisp pulling sound, a typical characteristic of adhesive failure.

[0122] Comparative Example 6 (without a stress buffer layer) showed a reduced interfacial bond strength of only 2.2 MPa and a shear strength of only 3.2 MPa, making it one of the worst-performing comparative examples. The fiber mesh (elastic modulus 230 GPa) was in direct contact with the concrete (elastic modulus 35 GPa), resulting in a nearly 7-fold difference in stiffness and severe stress concentration at the interface. In pull-out tests, interfacial cracking was observed as early as the initial loading stage (approximately 0.5 MPa), with rapid crack propagation leading to brittle failure. The fatigue life was only 280,000 cycles, with fatigue cracks rapidly initiating and propagating at the interface; the chloride ion diffusion coefficient was as high as 3.8 × 10⁻⁶. -12 m2 / s; interfacial microcracks become rapid channels for chloride ions.

[0123] The interfacial bond strength of Comparative Example 7 (without carbon nanotubes) was 3.1 MPa, slightly higher than Comparative Example 6, but still significantly lower than Example 1. Although the graphene coating was present, it lacked the "needle-like" anchoring effect of carbon nanotubes; the bonding between the coating and the fiber relied mainly on chemical bonding, with insufficient mechanical interlocking. In the shear test, the coating was observed to peel off along the fiber surface. The fatigue resistance was 520,000 cycles, better than Comparative Examples 5-6, but still far lower than Example 1.

[0124] The interfacial bond strength of Comparative Example 8 was 3.3 MPa, which is relatively high among the comparative examples because graphene oxide contains many oxygen functional groups and has a strong chemical bonding ability with epoxy resin. However, the mechanical properties of graphene oxide (tensile strength of about 20 GPa) are much lower than those of reduced graphene oxide (tensile strength of about 100 GPa), resulting in insufficient strength and toughness of the coating. Long-term stability is also poor; graphene oxide is easily further oxidized and degraded in alkaline environments (concrete pH of about 12-13).

[0125] The interfacial bond strength of Comparative Example 9 was 2.6 MPa. The buffer layer was too thin to effectively fill the microscopic irregularities and defects (typically 2-5 μm deep) on the old concrete surface, resulting in poor interfacial integrity and numerous micropores. The stress gradient transition was insufficient; the abrupt change in modulus from fiber (230 GPa) to concrete (35 GPa) was not effectively mitigated, and the measured stress concentration factor reached 3.8 (compared to 1.6 in Example 1). The coating was incomplete, with some fibers exposed, becoming channels for corrosive media intrusion. The fatigue life was only 380,000 cycles, and fatigue cracks propagated rapidly at the interface between the buffer layer and the concrete.

[0126] Comparative Example 10 (first buffer layer thickness 5mm) showed an interfacial bond strength of 3.1MPa, with a failure mode of mixed failure (partial interfacial failure + partial concrete failure). The excessively thick buffer layer generated significant shrinkage stress during curing, leading to microcracks within the buffer layer and creating a weak point. Furthermore, the significantly increased thickness of the first stress buffer layer resulted in a substantial increase in the curing exothermic temperature, which could cause thermal damage. The excessively thick soft layer (measured modulus 12.5GPa) reduced overall stiffness, causing excessive deformation under load and hindering load-bearing capacity. In addition, it significantly increased costs.

[0127] Comparative Example 11 exhibits an interfacial bond strength of 2.9 MPa, falling between that of Comparative Examples 2 and 5. While traditional epoxy mortar possesses a certain strength, it lacks the reinforcing and toughening effects of graphene, resulting in an interfacial fracture energy of only 130 J / m. 2The system lacks toughness and is prone to brittle fracture. The added quartz sand (0.1-0.3 mm particle size) increases the system's density and stiffness, but also increases stress concentration points, resulting in a fatigue resistance of only 470,000 cycles. The lack of a gradient transition design with a stress buffer layer means the problem of abrupt stiffness changes persists. The chloride ion diffusion coefficient is 2.7 × 10⁻⁶. -12 m 2 / s, durability is average.

[0128] In summary, this invention successfully solves key problems in the reinforcement of fiber-reinforced concrete structures, such as interfacial bonding, stress transfer, long-term durability, and intelligent monitoring, through the synergistic design of a gradient functionalized graphene coating (inner functionalized graphene oxide layer + middle reduced graphene oxide transition layer + outer modified graphene layer), a nano-needle anchoring structure (directionally grown carbon nanotubes), and a stress buffer layer (containing graphene nanosheets). The interfacial bonding strength of this invention can reach 3.6-4.5 MPa, which is 80%-125% higher than that of unreinforced interfaces; the fatigue life reaches 850,000-1,350,000 cycles, which is 6-14 times that of traditional reinforcement; the chloride ion diffusion coefficient is reduced by 60%-75%; and real-time monitoring with a strain resolution of 8 με is achieved. With excellent material properties and mature construction technology, this invention has broad application prospects in the reinforcement and repair of engineering structures such as bridges, buildings, and tunnels, and can achieve the integration of high-performance reinforcement and intelligent monitoring.

[0129] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A concrete interface repair material, characterized in that, include: Interface treatment layer, first stress buffer layer, graphene fiber mesh layer, second stress buffer layer and concrete repair layer; The components of the interface treatment layer include graphene; The components of the first stress buffer layer and / or the second stress buffer layer include: epoxy resin, curing agent, toughening agent and graphene nanosheets; The graphene fiber mesh layer includes a fiber mesh and a graphene coating deposited on the surface of the fiber mesh.

2. The concrete interface repair material as described in claim 1, characterized in that, The graphene fiber mesh layer is prepared by a method comprising the following steps: A1. Using a fiber mesh as the anode and a stainless steel plate as the cathode, immerse the fiber mesh in an electrophoretic solution and apply a voltage to perform electrophoretic deposition, depositing a graphene oxide functional layer on the surface of the fiber mesh. A2. The fiber mesh obtained in step A1 is removed from the electrophoresis solution, dried, and then immersed in ascorbic acid solution for reduction reaction to obtain a reduced graphene oxide transition layer. A3. Immerse the fiber mesh obtained in step A2 into a silane coupling agent solution for surface modification. After modification, dry and cure to obtain the modified graphene layer.

3. The concrete interface repair material as described in claim 2, characterized in that, In step A1, the electrophoretic solution is a mixed solution of graphene oxide, carbon nanotubes, dispersant and solvent; the pH of the electrophoretic solution is adjusted to 7-9 with ammonia. In the electrophoretic solution, the concentration of graphene oxide is 2wt%-4wt%, and the concentration of carbon nanotubes is 0.5wt%-1wt%. The dispersant is a polycarboxylic acid-based dispersant; the solvent is anhydrous ethanol and / or N,N-dimethylformamide.

4. The concrete interface repair material as described in claim 2, characterized in that, In step A1, the electrophoretic deposition voltage is 30-50V, the time is 5-15min, and the temperature is 25±2℃. In step A2, the concentration of ascorbic acid solution is 8-12 g / L, the reduction reaction time is 1-3 h, followed by heat treatment at 100-140℃ for 20-40 min; In step A3, the silane coupling agent solution is a 2wt%-3wt% ethanol solution, and the soaking time is 20-40 min; The silane coupling agent is at least one of KH-560, KH-550 and KH-570.

5. The concrete interface repair material as described in claim 1, characterized in that, The components of the first stress buffer layer and / or the second stress buffer layer, by mass parts, include: 100 parts epoxy resin, 0.5-1.5 parts graphene nanosheets, 30-40 parts curing agent, and 5-10 parts toughening agent.

6. The concrete interface repair material as described in claim 5, characterized in that, The epoxy resin is at least one of E-51 type epoxy resin, E-44 type epoxy resin and E-20 type epoxy resin; The graphene nanosheets have a particle size of 1-10 μm, a thickness of 5-50 nm, and a specific surface area of ​​50-500 m². 2 / g; The curing agent is at least one of polyamide curing agents, fatty amine curing agents, and aromatic amine curing agents; The toughening agent is at least one of rubber particles, polyurethane, and carboxyl-terminated nitrile butadiene rubber.

7. The concrete interface repair material as described in claim 1, characterized in that, The thickness of the first stress buffer layer is 1-3 mm; The thickness of the second stress buffer layer is 1-2 mm; The fiber mesh is at least one of carbon fiber mesh, basalt fiber mesh, glass fiber mesh, and hybrid fiber mesh.

8. The construction method of the concrete interface repair material according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Base treatment: The old concrete is pretreated and then an interface agent containing graphene is applied. After the surface is dry, an interface treatment layer is obtained. (2) Apply the first buffer layer; (3) Laying a graphene fiber mesh layer; (4) Apply the second buffer layer; (5) Pour concrete repair layer.

9. The application of the concrete interface repair material as described in any one of claims 1-7 in bridge reinforcement, building structure reinforcement, tunnel lining repair, or hydraulic structure protection.

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