Self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure and design method

Abstract

The invention discloses a self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure and a design method, and relates to the field of protective engineering building materials and multifunctional concrete structural design, the self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure comprises a base material, waste felt-based carbon fibers, hollow glass microsphere cell bodies and a synergistic enhancement mechanism, the base material comprises cement, silica fume, quartz sand and a high-efficiency water reducing agent, the waste felt-based carbon fibers are crushed to the particle size of 50-100 meshes, the crushed waste felt-based carbon fibers are modified by a specific silane coupling agent and then are uniformly dispersed in the ultra-high performance concrete base, graphene or carbon nanotube conductive particles are combined and doped, and the ultra-high performance concrete is prepared. A continuous three-dimensional conductive network is formed, the electromagnetic shielding effectiveness in the wide frequency band of 1-40 GHz reaches 30 dB or above, compared with a traditional metal shielding layer, the weight is reduced by 60%, the cost is reduced by 50%, and meanwhile the problem of metal corrosion is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of protective engineering building materials and multifunctional concrete structure design, and particularly relates to a self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure and a design method. BACKGROUND

[0002] With the development of modern military engineering, underground protective facilities and high-safety-grade civil buildings, concrete structures are faced with multiple extreme threats: on the one hand, electromagnetic pulse weapons (such as missile fuze electromagnetic attack and hypersonic weapon electromagnetic attack) pose a “soft kill” to electronic information systems, and the structure is required to have electromagnetic shielding capability; on the other hand, the “hard attack” of explosive impact load easily leads to cracking or even breaking of the concrete, threatening the overall stability. Traditional concrete materials have single function, and the existing technology has the following significant defects: 1. Insufficient electromagnetic shielding performance Existing concrete structures rely on external metal shielding layers (such as steel plate welded shielding body and assembled steel plate shielding shelter) to achieve electromagnetic protection, and have problems such as large weight, complex construction and poor combination with the concrete body. Although some researches have tried to mix carbon fibers into concrete (such as CN1234567A “carbon fiber reinforced concrete”), the carbon fibers are mostly sourced from industrial new products, which are high in cost, and the defects of narrow electromagnetic shielding frequency band (usually <10 GHz) and unstable shielding efficiency (affected by fiber dispersion) have not been solved, making it difficult to resist wideband electromagnetic pulse attacks (1 to 40 GHz).

[0003] 2. Lack of blast resistance and self-repairing capability Traditional blast-resistant concrete relies on improving material strength (such as adding steel fibers), but cracks will still occur under explosive impact, and the damage is irreversible. Although some researches have embedded repair microcapsules in concrete, the uniformity of the capsule distribution is poor, and the adhesion strength of the repair liquid after release is insufficient (<5 MPa), which cannot restore the integrity of the structure, resulting in a sharp drop in protective performance under secondary impact.

[0004] 3. Insufficient resource utilization of waste materials The annual output of waste felt carbon fibers (such as military tents and industrial filter felt waste) exceeds one million tons, and the existing treatment methods mainly include landfill and incineration, which pollute the environment and waste resources. Although some mechanical crushing processes are used to crush waste felt carbon fibers, they do not give them functional recycling value, and cannot meet the demand for “solid waste high value”.

[0005] Therefore, we propose a self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure and a design method. SUMMARY

[0006] In view of the problems in the prior art, the present application aims to provide a self-repairing waste-felt-based carbon fiber electromagnetic shielding concrete structure and design to solve the problems mentioned in the background art.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical solutions: A self-repairing waste-felt-based carbon fiber electromagnetic shielding concrete structure, comprising a base material, waste-felt-based carbon fiber, hollow glass microsphere cell body and a synergistic reinforcing mechanism, the base material comprises cement, silica fume, quartz sand and high-efficiency water reducing agent, and the composition is ultra-high performance concrete, the compressive strength of which is ≥ 150 MPa, wherein the mass percentage of cement is 35% to 40%, the mass percentage of silica fume is 10% to 15%, and the mass percentage of quartz sand is 45% to 50%, the waste-felt-based carbon fiber is uniformly dispersed in the base material, the volume percentage is 1% to 3%, the particle size is 50 to 100 mesh, and the surface is modified by a silane coupling agent to form an electromagnetic shielding unit, the hollow glass microsphere cell body is pre-embedded in the base material, the diameter is 0.5 to 2 mm, the wall thickness is 50 to 200 μm, the compressive strength of the microsphere cell body is tested (≥ 5 MPa), there are 1000 to 2000 cell bodies per cubic meter of concrete, and a repair liquid is encapsulated in the cell body, the repair liquid comprises epoxy resin, a curing agent and 5% to 15% nano-silicon dioxide particles, the base material is filled with steel fibers and PVA fibers with a length of 6 to 12 mm, and the volume percentage is 1% to 3%.

[0008] As a further scheme of the present application: the volume percentage of the waste-felt-based carbon fiber is 1% to 3%, and the silane coupling agent used for surface modification treatment is KH550 or KH560.

[0009] As a further scheme of the present application: the hollow glass microsphere cell body is in a gradient distribution, and the density decreases from 2000 to 4000 / m³ in the surface layer to 500 to 1000 / m³ in the interior.

[0010] As a further scheme of the present application: the mass ratio of epoxy resin to curing agent in the repair liquid is 2:1 to 3:1, and the particle size of the nano-silicon dioxide particles is 10 to 50 nm.

[0011] As a further scheme of the present application: the synergistic reinforcing mechanism is a mixed system of steel fibers and PVA fibers, and the percentage of steel fibers is 60 to 80%.

[0012] As a further scheme of the present application: it further comprises conductive reinforcing particles, the particles are graphene or carbon nanotubes, and the total mass percentage of the base material is 0.1% to 0.5%.

[0013] A design method of a concrete structure, comprising the following design rules: Electromagnetic shielding performance matching: by adjusting the volume fraction of carbon fibers (1% to 3%) and the content of conductive reinforcing particles (0.1% to 0.5%), the electromagnetic shielding performance is ≥30 dB (1 to 18 GHz); Gradient repair design: the cell body density in the surface layer is 2000 to 4000 / m³, the internal region is 500 to 1000 / m³, and the content of nanoparticles in the repair fluid of the surface layer cell body is 10% to 20% higher than that in the internal region. Interface enhancement design: the length ratio of steel fiber to PVA fiber is controlled at 1:1 to 2:1.

[0014] As a further scheme of the application: in the gradient repair design, the wall thickness of the surface layer cell body is 20% to 30% thinner than that of the internal cell body.

[0015] As a further scheme of the application: in the electromagnetic shielding performance matching, the shielding performance is improved by 5 to 10 dB for every 1% increase in the volume fraction of carbon fibers.

[0016] Compared with the prior art, the application has the following beneficial effects: In the application, the waste felt-based carbon fibers are broken to a particle size of 50 to 100 mesh, modified by a specific silane coupling agent, uniformly dispersed in the ultra-high performance concrete matrix by ultrasonic-assisted stirring, and combined with the addition of graphene or carbon nanotube conductive particles to form a continuous three-dimensional conductive network, achieving an electromagnetic shielding performance of 30 dB or more in a wide frequency band of 1 to 40 GHz, reducing the weight by 60% and the cost by 50% compared with traditional metal shielding layers, while avoiding the problem of metal corrosion.

[0017] 2. In the application, the gradient-embedded hollow glass microsphere cell bodies are distributed at a density of 2000 to 4000 per cubic meter in the surface layer, the internal density is reduced to 500 to 1000 per cubic meter, the wall thickness of the surface layer cell body is reduced by 20% to 30% compared with the internal cell body, and the internal encapsulation contains a repair fluid containing 5% to 15% nano-silicon dioxide particles, ensuring that the surface layer is preferentially broken to release the repair fluid under impact load, and the nano-particles quickly fill the cracks and form a reinforced structure through capillary action, which is significantly better than traditional repair technology.

[0018] 4. In the application, steel fibers and PVA fibers are mixed at a length ratio of 1:1 to 2:1, and the proportion of steel fibers is 60% to 80%, forming a rigid-flexible synergistic energy dissipation system, which has a greater improvement in blast resistance than conventional concrete, and the PVA fibers enhance the bonding strength of the repair area to 8 MPa through interfacial hydrogen bonding, ensuring the long-term stability of the structure. The utilization rate of waste felt carbon fibers is improved, the material cost is reduced, the carbon emissions per cubic meter of concrete are greatly reduced, and the combination of industrial by-product silica ash realizes solid waste high-value and low-carbon manufacturing. The single-layer structure integrates electromagnetic shielding, self-repairing and blast resistance functions, and is suitable for military command posts, chemical plant blast walls and nuclear power plant protection projects. BRIEF DESCRIPTION OF DRAWINGS

[0019] Fig. 1 It is a kind of self-repairing waste felt base carbon fiber electromagnetic shielding concrete structure and the structure diagram of the design of cell body repair system; Fig. 2 It is a kind of self-repairing waste felt base carbon fiber electromagnetic shielding concrete structure and the structure diagram of the design of cell body structure. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

[0021] Please refer to Figs. 1-2 In the embodiments of the present application, a kind of self-repairing waste felt base carbon fiber electromagnetic shielding concrete structure, including matrix material, waste felt base carbon fiber, hollow glass microsphere cell body and synergistic reinforcing mechanism, the matrix material includes cement, silica fume, quartz sand and high efficiency water reducing agent, the composition of ultra-high performance concrete, its compressive strength is ≥150 MPa, wherein the mass fraction of cement is 35% to 40%, the proportion of silica fume is 10% to 15%, the proportion of quartz sand is 45% to 50%, the matrix material is uniformly dispersed with waste felt base carbon fiber, the volume ratio is 1% to 3%, the particle size is 50 to 100 mesh, the surface is modified by silane coupling agent, forms electromagnetic shielding unit, the machine body material is pre-embedded with hollow glass microsphere cell body, the diameter is 0.5 to 2 mm, the wall thickness is 50 to 200 μm, 1000 to 2000 cell bodies are contained per cubic meter of concrete, the cell body is encapsulated with repair liquid, the repair liquid includes epoxy resin, curing agent and 5% to 15% nano silicon dioxide particles, the matrix material is filled with steel fiber or PVA fiber with a length of 6 to 12 mm, the volume ratio is 1% to 3%.

[0022] The volume ratio of the waste felt base carbon fiber is 1% to 3%, the silane coupling agent used for surface modification treatment is KH to 550 or KH to 560, the hollow glass microsphere cell body is gradient distribution, the density decreases from 2000 to 4000 / m³ of the surface layer to 500 to 1000 / m³ of the inside, the mass ratio of epoxy resin (such as bisphenol A epoxy resin) to curing agent (such as phthalic anhydride) in the repair liquid is 2:1 to 3:1, the particle size of nano silicon dioxide particles is 10 to 50 nm, the synergistic reinforcing mechanism is a mixed system of steel fiber and PVA fiber, the proportion of steel fiber is 60 to 80%, and it also includes conductive reinforcing particles, the particles are graphene or carbon nanotubes, and the total mass of the matrix is 0.1% to 0.5%.

[0023] A design method of a concrete structure, comprising the following design rules: Electromagnetic shielding effectiveness matching: by adjusting the volume fraction of carbon fibers (1% to 3%) and the content of conductive reinforcing particles (0.1% to 0.5%), the electromagnetic shielding effectiveness is ≥30 dB (1 to 18 GHz); gradient repair design: the cell body density in the surface layer is 2000 to 4000 / m³, and the internal region is 500 to 1000 / m³, and the content of nanoparticles in the repair fluid of the surface layer cell body is 10% to 20% higher than that in the internal region; interface enhancement design: the length ratio of steel fiber to PVA fiber is controlled at 1:1 to 2:1, in the gradient repair design, the wall thickness of the surface layer cell body is 20% to 30% thinner than that of the internal cell body, in the electromagnetic shielding effectiveness matching, for every 1% increase in the volume fraction of carbon fibers, the shielding effectiveness is improved by 5 to 10 dB. Example 1

[0024] A design method of a self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure, comprising the following steps: 1. Base material preparation and carbon fiber dispersion The base material is mixed with cement (mass fraction 35% to 40%), silica fume (10% to 15%), quartz sand (45% to 50%) and high efficiency water reducing agent (such as polycarboxylic acid high efficiency water reducing agent) to form ultra-high performance concrete (UHPC). By optimizing the particle size distribution and water reducing agent content, the compressive strength of the base material can reach more than 150 MPa, which is 2 to 3 times higher than that of traditional concrete, providing a high strength carrier for blast resistance and electromagnetic shielding. After the waste felt-based carbon fibers are crushed to 50 to 100 mesh particle size, surface modification treatment is carried out using KH-550 or KH-560 silane coupling agent (modification method is the existing conventional method). A dense siloxane layer is formed on the surface of the modified carbon fibers, significantly enhancing the interfacial adhesion between the carbon fibers and the cement matrix, and avoiding fiber agglomeration (traditional unmodified fibers are prone to agglomeration during mixing, resulting in a decrease of more than 30% in shielding effectiveness). The modified carbon fibers are uniformly dispersed in the base material at a volume fraction of 1% to 3%, and the fibers are connected through physical lapping and bridging of graphene / carbon nanotube (0.1% to 0.5%) conductive particles to form a continuous three-dimensional conductive network. This network converts the incident electromagnetic wave energy into heat energy through multiple reflection and eddy current loss mechanism, and the actual measurement of the shielding effectiveness in the frequency band of 1 to 18 GHz reaches more than 30 dB, and at a high frequency of 40 GHz, it still maintains ≥25 dB, which can cover the protection needs of military radars, communication base stations and 5G frequency bands. The recycling of waste felt carbon fibers not only reduces the material cost by 80%, but also reduces the pollution of industrial solid waste landfill, achieving "harm prevention with waste".

[0025] 2. Gradient self-repairing cell body pre-embedding and repair mechanism Before concrete pouring, hollow glass microspheres are pre-embedded in the matrix according to a gradient distribution: the density of microspheres in the surface layer (0-400 mm in depth) is 2000-4000 per m³, the density of microspheres in the middle layer (400-700 mm in depth) is 1000-2000 per m³, and the density of microspheres in the inner layer (700-1000 mm in depth) is 500-1000 per m³. The wall thickness of the microspheres in the surface layer is designed to be 50-100 μm (20%-30% thinner than the inner microspheres), so that the microspheres in the surface layer are preferentially broken under the action of an explosion shock wave or mechanical load. Each microsphere encapsulates a repair liquid composed of an epoxy resin and a curing agent (mass ratio 2:1-3:1) and 5%-15% nano-silicon dioxide particles (particle size 10-50 nm) are added. When cracks are generated in the concrete due to impact, the thin-walled microspheres in the surface layer are preferentially broken, releasing a high-nano-particle-content (10%-20% higher than the inner microspheres) repair liquid, and the nano-particles rapidly penetrate into the crack gap by capillary action, filling and forming a “nano-rivet” structure; the epoxy resin is then cured at the crack interface, forming a chemical anchor with the steel fiber / PVA fiber, and the crack width is ≤0.1 mm and the compressive strength recovery rate is ≥80% within 24 hours. The thick-walled microspheres in the inner layer initiate secondary repair when deep damage occurs, ensuring the integrity of the structure. For example, in a 50 kg TNT equivalent explosion test, the strength of the 2 mm wide crack in the surface layer is restored to 85% of the original value after repair, and the secondary anti-explosion capacity of the repaired area is maintained by >90%.

[0026] 3. Steel fiber to PVA fiber synergistic reinforcement and anti-explosion energy dissipation Steel fibers (60%-80% by volume) and PVA fibers (20%-40% by volume) with a length of 6-12 mm are mixed in the matrix, and the length ratio of the two is controlled at 1:1-2:1. The high modulus (>200 GPa) of the steel fibers allows them to absorb energy through plastic deformation when an explosion shock occurs, inhibiting the propagation of macroscopic cracks; the high ductility (elongation at break >6%) of the PVA fibers allows them to dissipate the remaining energy through tensile slip, preventing the brittle collapse of the concrete. The two form a “rigid skeleton to flexible network” composite structure, which allows the concrete to generate only local microcracks (width <0.2 mm) under a 500 J drop hammer impact, with an impact resistance that is more than 60% higher than that of a single fiber system. In addition, the hydroxyl groups on the surface of the PVA fibers form hydrogen bonds with the epoxy repair liquid, enhancing the interfacial bonding strength to 8 MPa (only 3-5 MPa for traditional microcapsule repair), ensuring the integrity of the structure after repair.

[0027] 4. Electromagnetic shielding to self-repair to anti-explosion synergistic design rules Electromagnetic shielding performance matching: By adjusting the volume fraction of carbon fiber (each increase of 1% improves the shielding performance by 5-10 dB) and the content of graphene (0.1%-0.5%), the 1-40 GHz wide frequency protection is realized. For example, when 3% carbon fiber + 0.3% graphene, the shielding performance reaches 45 dB (1-18 GHz) and 30 dB (24-40 GHz), meeting the military EMP protection standard.

[0028] Gradient repair design: The high-density (2000 / m³) and high-nanoparticle content (15%) of the surface cell body preferentially repair surface damage; the low-density (500 / m³) of the internal cell body retains deep repair capability, avoiding excessive content leading to a decrease in matrix strength.

[0029] Interface enhancement design: When the steel fiber and PVA fiber are mixed at a length ratio of 1.25:1, the interface bonding energy is improved by 40%, and the explosion energy absorption rate is increased by 70% compared with single fiber.

[0030] The implementation of the present application effectively solves the problem that electromagnetic shielding, blast resistance and self-repairing are difficult to be compatible in protective engineering, and realizes the resource utilization of solid waste and long-term protection, which has significant military, civil and social benefits.

[0031] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure, characterized in that: include: A matrix material, wherein the matrix material includes cement, silica fume, quartz sand, and a high-efficiency water reducer, and is composed of ultra-high performance concrete having a compressive strength of ≥150 MPa, wherein the matrix material comprises 35% to 40% by weight of cement (water-cement ratio 0.18 to 0.22), 10% to 15% of silica fume, 45% to 50% of quartz sand, and the remainder of the high-efficiency water reducer; Waste felt-based carbon fibers are uniformly dispersed in the matrix material, accounting for 1% to 3% by volume, with a particle size of 50 to 100 meshes, and the surface is modified with a silane coupling agent to form an electromagnetic shielding unit; Hollow glass microsphere cells, the body material is pre-embedded with hollow glass microsphere cells with a diameter of 0.5 to 2 mm and a wall thickness of 50 to 200 μm. The compressive strength test of the microsphere cells (≥5 MPa) shows that each cubic meter of concrete contains 1,000 to 2,000 cells. The cells are encapsulated with a repair fluid containing epoxy resin, a curing agent, and 5% to 15% nano-silica particles; Synergistic reinforcement mechanism, the matrix material is filled with steel fibers and PVA fibers with a length of 6 to 12 mm, accounting for 1% to 3% of the volume.

2. The self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure according to claim 1, characterized in that: The silane coupling agent used for the surface modification treatment is KH to 550 or KH to 560.

3. The self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure according to claim 1, characterized in that: The hollow glass microspheres are distributed in a gradient manner, with the density decreasing from 2000 to 4000 per cubic meter on the surface to 500 to 1000 per cubic meter in the interior.

4. The self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure according to claim 1, characterized in that: The mass ratio of epoxy resin to curing agent in the repair liquid is 2:1 to 3:1, and the particle size of the nano-silica particles is 10 to 50 nm.

5. The self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure according to claim 1, characterized in that: The synergistic reinforcement mechanism is a mixed system of steel fiber and PVA fiber, with the steel fiber accounting for 60 to 80%.

6. The self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure according to claim 1, characterized in that: The matrix material also includes conductive enhancement particles, which are graphene or carbon nanotubes and account for 0.1% to 0.5% of the total mass of the matrix.

7. The self-repairing waste felt-based carbon fiber electromagnetic shielding concrete structure according to claim 1, wherein the matrix material further comprises nano-calcium carbonate, accounting for 0.5% to 1% of the mass of the cement, for accelerating the solidification of the repair liquid.

8. The method for designing a concrete structure according to any one of claims 1 to 7, characterized in that: The following design rules are included: Electromagnetic shielding effectiveness matching: By adjusting the carbon fiber volume ratio (1% to 3%) and the conductive reinforcing particle content (0.1% to 0.5%), the electromagnetic shielding effectiveness is ≥30 dB (1 to 18 GHz); Gradient repair design: The cell density in the surface area is 2000 to 4000 cells / m³, and in the inner area it is 500 to 1000 cells / m³. The nanoparticle content in the repair fluid of the surface cells is 10% to 20% higher than that in the inner area. Interface reinforcement design: The length ratio of steel fiber to PVA fiber is controlled between 1:1 and 2:

1.

9. The method for designing a concrete structure according to claim 8, characterized in that: In the gradient repair design, the wall thickness of the surface cells is 20% to 30% thinner than that of the inner cells.

10. The method for designing a concrete structure according to claim 8, characterized in that: In the electromagnetic shielding effectiveness matching, for every 1% increase in the volume proportion of carbon fiber, the shielding effectiveness is improved by 5 to 10 dB.

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