A tunnel shield segment special anti-cracking composite fiber and a preparation method thereof

Abstract

The application discloses a kind of tunnel shield segment special anti-crack composite fiber and preparation method thereof, the fiber is core sheath structure, basalt fiber is used as core material, surface is covered with conductive polymer interface layer, carbon nanotube reinforcing layer and slow-release microcapsule layer in proper order.The anti-crack synthetic fiber of the application uses basalt fiber as core material, surface is modified with the polymer coating containing carbon nanotube through plasma grafting technology, then self-repairing factor is loaded through biomimetic microcapsule technology, and multi-layer composite structure is formed.The application solves the technical problems of insufficient fiber and concrete matrix interface adhesion, poor dispersibility and limited single fiber function in the prior art, achieves the unexpected technical effects of more than 40% improvement of anti-crack performance, more than P12 improvement of impermeability grade, and crack self-repairing function.In addition, the application first applies plasma surface modification technology used in aerospace field and microcapsule technology used in biomedical field to synthetic fiber preparation, and breaks the field technical barriers.

Description

Technical Field

[0001] This invention relates to the field of tunnel engineering construction materials technology, and in particular to a special crack-resistant synthetic fiber for tunnel shield segments and its preparation method. Background Technology

[0002] As the main supporting component of a tunnel structure, tunnel shield segments have much higher requirements for crack resistance and durability than similar materials in ordinary scenarios, and must be adapted to the harsh underground service environment and long-term load-bearing requirements. Therefore, their crack resistance and durability are directly related to the safety and service life of the tunnel project. Traditional tunnel segments mostly use reinforced concrete structures, but the inherent brittleness of concrete easily leads to cracks in the segments during manufacturing, transportation, installation, and use, affecting the tunnel's waterproof performance and operational safety.

[0003] Currently, the main approach to improving the crack resistance of tunnel segments is to add fiber materials. However, existing technologies still have the following unresolved problems:

[0004] 1. Poor fiber dispersion: Fibers tend to clump together in concrete and are unevenly distributed, resulting in localized weak strength;

[0005] 2. Insufficient interfacial bonding strength: The interfacial bonding strength between the fiber and the concrete matrix is ​​low, making it difficult to fully utilize the reinforcing effect of the fiber;

[0006] 3. Insufficient impermeability: There is an interfacial transition zone between the fiber and the concrete matrix, which easily forms a seepage channel;

[0007] 4. Poor material compatibility: When multiple fibers are mixed, they are difficult to work together due to differences in their physicochemical properties;

[0008] 5. Limited functionality: Existing fibers mainly provide physical reinforcement and lack active protection functions. Summary of the Invention

[0009] To address the problem that existing technologies, even with the addition of fiber materials, still cannot meet the requirements for crack resistance and durability, this invention provides a special crack-resistant synthetic fiber for tunnel shield segments and its preparation method.

[0010] The technical solution of the present invention is as follows:

[0011] A special anti-crack synthetic fiber for tunnel shield segments is characterized by a core-sheath structure, with basalt fiber as the core material and a conductive polymer interface layer, a carbon nanotube reinforcement layer and a slow-release microcapsule layer sequentially coated on the surface.

[0012] Preferably, the basalt fiber has a diameter of 18-22 μm and an aspect ratio of 60-80, and its surface is treated with low-temperature oxygen plasma to form a nanoscale rough structure.

[0013] Preferably, the conductive polymer interface layer is a composite of polyaniline and epoxy resin, wherein the mass ratio of polyaniline to epoxy resin is 1:2-4, and the thickness is 0.5-1.2 μm.

[0014] Preferably, the carbon nanotube reinforcing layer is a hybrid system of multi-walled carbon nanotubes modified with silane coupling agent and polyvinyl alcohol, wherein the content of multi-walled carbon nanotubes is 3%-8% of the polymer mass.

[0015] Preferably, the sustained-release microcapsule layer comprises a urea-formaldehyde resin shell and a core material, wherein the core material is a mixture of water-based epoxy resin and a curing agent, and has a thickness of 0.2-0.5 μm.

[0016] The method for preparing the aforementioned crack-resistant synthetic fiber for tunnel shield segments is characterized by comprising the following steps:

[0017] (1) Basalt fibers are subjected to low-temperature oxygen plasma treatment with a power of 800-1200W and a treatment time of 5-10 minutes to produce nanoscale roughness and active groups on the fiber surface.

[0018] (2) The fiber treated in step (1) is immersed in a polyaniline and epoxy resin composite emulsion for the first coating to form a conductive polymer interface layer. The solid content of the emulsion is 20-30%, and the immersion time is 3-7 minutes.

[0019] (3) The carbon nanotube reinforcement layer is adsorbed onto the fibers obtained in step (2) by electrostatic self-assembly technology to form a carbon nanotube reinforcement layer;

[0020] (4) The fibers obtained in step (3) are microencapsulated using a fluidized bed process to form a sustained-release microcapsule layer;

[0021] (5) The final product is obtained after UV curing and hot air drying.

[0022] A concrete shield tunnel segment containing the aforementioned crack-resistant synthetic fiber is characterized in that each cubic meter of concrete contains 1.5-2.5 kg of crack-resistant synthetic fiber, 25-40 kg of steel fiber, 320-450 kg of cement, 140-170 kg of water, 1000-1250 kg of coarse aggregate, 550-750 kg of fine aggregate, 60-90 kg of mineral powder and fly ash, and 0.5%-2% of water-reducing agent and 2%-5% of rust inhibitor by weight of cementitious materials.

[0023] The technical effects of this invention are as follows:

[0024] The crack-resistant synthetic fiber of this invention uses basalt fiber as the core material, and the surface is modified with a polymer coating containing carbon nanotubes through plasma grafting technology. Furthermore, self-healing factors are loaded using biomimetic microcapsule technology to form a multi-layered composite structure. Compared with traditional fibers, this invention solves the technical problems of insufficient bonding strength between fibers and the concrete matrix, poor dispersibility, and limited function of a single fiber in existing technologies. It achieves technical effects such as a crack resistance improvement of over 40%, an impermeability grade increase to P12 or higher, and the ability to self-heal cracks.

[0025] Specifically, compared with existing technologies, it has the following outstanding technological innovations:

[0026] 1. Material System Innovation: The application of plasma surface modification technology and microencapsulation technology to synthetic fiber preparation breaks through the technological barriers in this field. Traditional fiber modification often employs simple surface etching or coating techniques, resulting in limited functionality. This invention, however, utilizes a multi-layered structural design to enable fibers to simultaneously possess multiple functions, including reinforcement, toughening, conductivity, and self-healing.

[0027] 2. Innovative Structural Design: Employing a multi-layered core-sheath structure, this invention differs from traditional single-phase fibers. Through biomimetic design, mimicking the structure of plant roots, it creates graded roughness on the fiber surface, significantly improving the interfacial bond strength between the fiber and concrete.

[0028] 3. Innovative Dispersion Mechanism: By imparting conductivity to the fibers, an external electric field is used to achieve the directional distribution of the fibers in concrete, completely solving the technical problems of easy fiber clumping and uneven distribution.

[0029] Based on this, the crack-resistant synthetic fiber provided by the present invention has the following outstanding technical effects:

[0030] 1. Synergistic Enhancement Effect: When the fiber and steel fiber composite of this invention are used in concrete shield tunnel segments, they exhibit a significant synergistic effect. Tests show that, with the same total fiber content, the crack resistance of the fiber-steel fiber composite system of this invention is more than 40% higher than that of a single steel fiber system and more than 25% higher than that of a conventional synthetic fiber-steel fiber composite system. This effect far exceeds the expectations of those skilled in the art.

[0031] 2. Self-healing function: The microcapsules in the fiber can automatically release repair substances when cracks occur, achieving self-healing. Tests have shown that for cracks no wider than 0.3mm, the self-healing efficiency can reach over 85%, a function that traditional fibers do not possess at all.

[0032] 3. Interface enhancement effect: Through multi-layer interface design, the interfacial bonding strength between fiber and concrete is 3-5 times higher than that of ordinary synthetic fibers, effectively solving the problem of fiber pull-out and giving full play to the fiber reinforcement effect.

[0033] 4. Significantly improved impermeability: The fiber of this invention can improve the impermeability grade of concrete shield tunnel segments to above P12, which is significantly improved compared with ordinary fiber concrete (P8-P10). This is mainly due to the good dispersibility and self-healing function of the fiber, which blocks the seepage channels. Detailed Implementation

[0034] To better understand the present invention, specific descriptions are provided below through embodiments. It should be noted that the following embodiments are for further illustration only and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention still fall within the scope of protection of the present invention.

[0035] In addition, unless otherwise stated, all raw materials used are commercially available.

[0036] Example 1

[0037] This embodiment describes a special anti-crack synthetic fiber for tunnel shield segments. The synthetic fiber has a core-sheath structure, with basalt fiber as the core material and a conductive polymer interface layer, a carbon nanotube reinforcement layer, and a slow-release microcapsule layer sequentially coated on the surface.

[0038] The specific formula and preparation method are as follows:

[0039] (1) Basalt fiber pretreatment: Basalt fibers with a diameter of 20 μm and a length of 12 mm, with an aspect ratio of 60-80, were selected and placed in a low-temperature plasma treatment device. Oxygen was used as the treatment gas, and the fiber was treated for 8 minutes at a power of 1000W to form a nanoscale rough structure on the fiber surface and introduce active groups. This can significantly improve the mechanical interlocking force between the fiber and the polymer.

[0040] (2) Construction of the conductive polymer interface layer: Pretreated basalt fibers were immersed in a polyaniline / epoxy resin composite emulsion with a polyaniline to epoxy resin mass ratio of 1:3 and an emulsion solid content of 25%. The immersion time was 5 minutes. The coating thickness was then controlled using a mold with a 100 μm pore size. Preliminary curing was performed at 80°C for 10 minutes to form a conductive polymer interface layer with a thickness of approximately 0.8 μm. The introduction of polyaniline endowed the fibers with certain electrical conductivity, enabling them to be directionally distributed in concrete under the influence of an electric field, thus solving the problem of uneven fiber dispersion.

[0041] (3) Construction of carbon nanotube reinforcement layer: Multi-walled carbon nanotubes (length 10-20μm, outer diameter 8-15nm) are surface modified with aminosilane coupling agent to graft active groups that can react with polyvinyl alcohol and concrete hydration products onto their surface, thus becoming "molecular bridges" connecting inorganic nanomaterials and organic polymers.

[0042] The modified carbon nanotubes were mixed with a polyvinyl alcohol solution, with the carbon nanotube content being 5% of the polymer mass. Through strong hydrogen bonds and possible covalent bonding, the long PVA chains entangled and encapsulated the carbon nanotubes, forming a stable three-dimensional hybrid network that transferred the nanoscale enhancement effect to the macroscopic level. The mixture was then dispersed in deionized water to prepare a 0.5 mg / mL dispersion.

[0043] The fibers obtained in step (2) were subjected to electrostatic self-assembly at a voltage of 15 kV and a flow rate of 2 mL / min to adsorb a modified three-dimensional hybrid network of carbon nanotubes. Subsequently, they were heat-treated at 120 °C for 20 minutes to form a carbon nanotube reinforcement layer. The carbon nanotubes formed nanoscale protrusions on the fiber surface, further increasing the mechanical interlocking force between the fiber and concrete. Simultaneously, their high specific surface area and strong van der Waals forces significantly improved the interfacial bonding performance.

[0044] (4) Microcapsule coating: Urea-formaldehyde resin microcapsules were prepared by in-situ polymerization, with the core material being a mixture of water-based epoxy resin and latent curing agent (mass ratio 5:1). The fibers obtained in step (3) were placed in a fluidized bed, and the fibers were kept in a fluidized state with an air flow rate of 8 m / s. The microcapsule suspension was atomized and sprayed into the fiber through a nozzle at an inlet temperature of 60°C and an outlet temperature of 40°C, so that the microcapsules were uniformly attached to the fiber surface, forming a slow-release microcapsule layer with a thickness of 0.3 μm. When microcracks occur in the concrete, the stress concentration at the crack tip will cause the microcapsules to rupture, releasing the repair material and automatically filling the crack, thus achieving a self-healing function.

[0045] (5) Post-treatment: After initial curing by ultraviolet radiation (wavelength 365nm, intensity 800mJ / cm²), it is dried in hot air at 80℃ for 30 minutes to obtain the final crack-resistant synthetic fiber product.

[0046] Example 2

[0047] The difference between this embodiment and Embodiment 1 is that:

[0048] In step (1), the basalt fiber has a diameter of 18 μm and a length of 15 mm, the plasma treatment power is 1200 W, and the treatment time is 5 minutes.

[0049] In step (2), the mass ratio of polyaniline to epoxy resin is 1:2, the solid content of the emulsion is 30%, and the thickness of the conductive polymer interface layer is about 1.0 μm.

[0050] In step (3), the concentration of the carbon nanotube dispersion is 0.8 mg / mL and the electrostatic self-assembly voltage is 18 kV.

[0051] Example 3

[0052] The difference between this embodiment and Embodiment 1 is that:

[0053] In step (1), the basalt fiber has a diameter of 22 μm and a length of 10 mm, the plasma treatment power is 800 W, and the treatment time is 10 minutes.

[0054] In step (2), the mass ratio of polyaniline to epoxy resin is 1:4, the solid content of the emulsion is 20%, and the thickness of the conductive polymer interface layer is about 0.6 μm.

[0055] In step (3), the concentration of the carbon nanotube dispersion is 0.3 mg / mL, and the electrostatic self-assembly voltage is 12 kV.

[0056] Example 4

[0057] This embodiment describes the fabrication of concrete shield tunnel segments. The crack-resistant synthetic fibers prepared in the above embodiments are used to fabricate concrete shield tunnel segments. The specific steps are as follows:

[0058] 1. Ingredients: Weigh the following raw materials per cubic meter of concrete:

[0059] Cement: 380kg

[0060] Water: 160kg

[0061] Coarse aggregate: 1150kg (maximum particle size 25mm, continuous gradation)

[0062] Fine aggregate: 650kg (fineness modulus 2.6-2.8)

[0063] Mineral powder and fly ash: 75 kg (mass ratio 1:1)

[0064] Steel fiber: 35kg (length-to-diameter ratio 50-60)

[0065] Crack-resistant synthetic fiber: 2.0kg

[0066] Water-reducing agent: 1.2% of the mass of cementitious material (based on solid content).

[0067] Rust inhibitor: 3% of the mass of cementitious material

[0068] 2. Mixing: Use a forced mixer and add materials in the following order:

[0069] First, add coarse aggregate, fine aggregate, cement, mineral powder, and fly ash and dry mix for 30 seconds;

[0070] Add water-reducing agent, rust inhibitor and 80% water, and stir for 60 seconds;

[0071] Add steel fibers and crack-resistant synthetic fibers, and stir for 30 seconds;

[0072] Add the remaining water and continue stirring for 90 seconds. The total stirring time should be no less than 3 minutes.

[0073] 3. Pouring and Vibration: The mixed fiber-reinforced concrete is poured into the steel formwork of the pipe segment coated with release agent, and the reinforcing cage is installed at the same time. The concrete is then compacted by a combination of attached vibrating table and immersion vibrator.

[0074] 4. Curing: After pouring, let stand for 2 hours, then steam cure, with a heating rate not exceeding 15℃ / h, a maximum temperature of 55℃, and maintain the temperature for 4 hours. Then allow it to cool naturally until the temperature difference with the environment is less than 20℃ before demolding. After demolding, place it in a water tank for curing for no less than 7 days, or use spray curing for no less than 14 days.

[0075] Performance testing:

[0076] To verify the technical effectiveness of the present invention, the following performance comparison test was designed.

[0077] Test segments 1-3

[0078] The crack-resistant synthetic fibers prepared using Examples 1-3 were used to prepare concrete specimens according to the segment preparation method in Example 4, resulting in test segments 1-3. Specifically, test segment 1 had a fiber content of 2.0 kg / m³ and a steel fiber content of 35 kg / m³, test segment 2 had a fiber content of 1.5 kg / m³ and a steel fiber content of 40 kg / m³, and test segment 3 had a fiber content of 2.5 kg / m³ and a steel fiber content of 30 kg / m³.

[0079] Comparative Example 1

[0080] Ordinary polypropylene fiber was used, with a fiber content of 2.0 kg / m³, and steel fiber content of 35 kg / m³. Other conditions were the same as those for the test segments.

[0081] Comparative Example 2

[0082] No synthetic fibers were added, only steel fibers were added at a dosage of 35 kg / m³, and other conditions were the same as those for the test tube segments.

[0083] Comparative Example 3

[0084] It uses 50kg / m³ steel fiber and 1.5kg / m³ ordinary synthetic fiber.

[0085] Comparative Example 4

[0086] The method involves adding 0.8 kg of polyaniline fiber and 18 kg of basalt fiber per cubic meter of concrete to replace the fibers and some steel fibers of the present invention. The remaining raw material ratios and preparation processes are consistent with those in Example 1.

[0087] The test samples obtained from the above embodiments (still referred to as Embodiments 1-3) and the comparative examples were subjected to performance tests, and the results are shown in Table 1.

[0088] Table 2 Performance test results of the examples and comparative examples

[0089]

[0090] Test results show that the crack-resistant synthetic fiber provided by this invention is significantly better than the comparative example in all performance indicators, especially in terms of crack resistance and impermeability, and has a self-healing function, which is impossible for traditional fibers.

[0091] It is evident that this invention, through multi-level structural design and cross-disciplinary technology integration, has successfully developed a special crack-resistant synthetic fiber for tunnel shield segments, solving a technical problem that has long remained unresolved by existing technologies.

[0092] 1. Superior crack resistance and reinforcement: The crack width reduction rate (42%-46%) of the present invention (Examples 1-3) is significantly higher than that of the comparative examples. This proves that the core-sheath multilayer composite structure has a synergistic effect on stress transfer and crack suppression, which is better than simple physical mixing or single fiber modification.

[0093] 2. High impermeability: The impermeability grade of this invention reaches P12 or higher, while the highest grade of the comparative examples is only P10. This is due to the unique self-healing function of this invention, which can actively block seepage paths, a key capability that none of the comparative examples possess.

[0094] 3. Functional completeness: While the comparative examples focus on improving mechanical properties through different fiber modification methods, this invention, through cross-domain technology integration, achieves for the first time a multi-integrated approach that combines reinforcement, toughening, conductive assisted dispersion, and crack self-healing, producing technical effects that cannot be achieved by single material modification.

[0095] 4. Self-healing capability: The introduction of microcapsule technology enables the segments to automatically repair themselves when microcracks occur, greatly improving durability and service life.

[0096] 5. Cross-domain technology integration: The innovative application of plasma modification technology, carbon nanotube reinforcement technology and microencapsulation technology to civil engineering materials has produced unexpected synergistic and synergistic technical effects.

[0097] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or equivalent modifications to the above-disclosed technical content. However, any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A special crack-resistant synthetic fiber for tunnel shield segments, characterized in that... It has a core-sheath structure, with basalt fiber as the core material, and the surface is sequentially coated with a conductive polymer interface layer, a carbon nanotube reinforcement layer and a sustained-release microcapsule layer.

2. The synthetic fiber according to claim 1, characterized in that... The basalt fibers have a diameter of 18-22 μm and an aspect ratio of 60-80. The surface is treated with low-temperature oxygen plasma to form a nanoscale rough structure.

3. The synthetic fiber according to claim 1, characterized in that... The conductive polymer interface layer is a composite of polyaniline and epoxy resin, wherein the mass ratio of polyaniline to epoxy resin is 1:2-4, and the thickness is 0.5-1.2 μm.

4. The synthetic fiber according to claim 1, characterized in that... The carbon nanotube reinforcement layer is a hybrid system of multi-walled carbon nanotubes modified with silane coupling agent and polyvinyl alcohol, wherein the content of multi-walled carbon nanotubes is 3%-8% of the polymer mass.

5. The synthetic fiber according to claim 1, characterized in that... The sustained-release microcapsule layer comprises a urea-formaldehyde resin shell and a core material, the core material being a mixture of water-based epoxy resin and a curing agent, with a thickness of 0.2-0.5 μm.

6. A method for preparing a special crack-resistant synthetic fiber for tunnel shield segments as described in any one of claims 1-5, characterized in that... Includes the following steps: (1) Basalt fibers are subjected to low-temperature oxygen plasma treatment with a power of 800-1200W and a treatment time of 5-10 minutes to produce nanoscale roughness and active groups on the fiber surface. (2) The fiber treated in step (1) is immersed in a polyaniline and epoxy resin composite emulsion for the first coating to form a conductive polymer interface layer. The solid content of the emulsion is 20-30%, and the immersion time is 3-7 minutes. (3) The carbon nanotube reinforcement layer is adsorbed onto the fibers obtained in step (2) using electrostatic self-assembly technology; (4) The fibers obtained in step (3) are microencapsulated using a fluidized bed process to form a sustained-release microcapsule layer; (5) The final product is obtained after UV curing and hot air drying.

7. A concrete shield tunnel segment comprising the crack-resistant synthetic fiber as described in any one of claims 1-5, characterized in that... Each cubic meter of concrete contains 1.5-2.5 kg of crack-resistant synthetic fiber, 25-40 kg of steel fiber, 320-450 kg of cement, 140-170 kg of water, 1000-1250 kg of coarse aggregate, 550-750 kg of fine aggregate, 60-90 kg of mineral powder and fly ash, and 0.5%-2% of water-reducing agent and 2%-5% of rust inhibitor by weight of cementitious materials.

Images