A self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe and its manufacturing process

Abstract

This invention relates to the field of composite pipe technology, and discloses a self-healing carbon fiber prestressed steel cylinder concrete (FRP) composite pipe and its manufacturing process. The composite pipe comprises, from the inside out, a photocured FRP inner anti-corrosion layer, a spiral welded steel cylinder, a self-healing concrete core, a three-dimensional CFRP prestressed layer, a potential equalization layer, and an FRP sand-filled outer protective layer. The manufacturing process includes the preparation of the spiral welded steel cylinder and socket, anchor installation, vertical casting and curing of the self-healing concrete core, fabrication of the three-dimensional CFRP prestressed layer, coating of the potential equalization layer, fabrication of the FRP sand-filled outer protective layer, and fabrication of the photocured FRP inner anti-corrosion layer. This invention uses a cement-based penetrating crystallizing material and Bacillus-calcium lactate microcapsules to form a composite self-healing system, achieving chemical-biological synergistic repair of cracks; the simultaneous laying of circumferential and longitudinal carbon fibers to form a three-dimensional prestressed structure significantly improves axial load-bearing capacity; and the graphene-ceramic filler potential equalization layer effectively inhibits galvanic corrosion.

Description

Technical Field

[0001] This invention relates to the field of composite pipe technology, specifically to a self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe and its manufacturing process. Background Technology

[0002] Prestressed concrete cylinder pipe (PCCP) is a widely used pressure pipeline in long-distance water conveyance projects both domestically and internationally. Its traditional structure consists of a steel cylinder, a concrete core, prestressed steel wires, and a mortar protective layer. Prestressed steel wires apply circumferential prestress to the steel cylinder or concrete core to counteract the circumferential tensile stress generated by internal pressure, thereby achieving high-pressure transmission. However, traditional PCCP has the following significant drawbacks:

[0003] Poor corrosion resistance: Prestressed steel wires are susceptible to corrosion from soil acidity, sewage, chloride ions and other factors, leading to rust and expansion, damaging the concrete protective layer, and ultimately causing prestressing failure and pipe bursts (industry statistics show that corrosion-induced PCCP failures account for more than 40%).

[0004] Poor tensile strength of concrete core pipe or mortar protective layer: Due to inherent defects in the properties of concrete and mortar, microscopic, shrinkage, and cracking phenomena may occur in the pipeline during production and service, which is the main cause of prestressed steel wire failure.

[0005] Excessive weight: The density of the steel wire is approximately 7.8 g / cm³. 3 It accounts for 20%-30% of the total weight of the pipeline, resulting in high transportation costs (a single DN2200mm PCCP weighs over 15 tons) and high installation difficulty (requiring large hoisting equipment).

[0006] In recent years, carbon fiber reinforced polymer (CFRP) composites have gained popularity due to their low density (1.6-2.0 g / cm³). 3 With its advantages of high strength (tensile strength ≥3000MPa, 5-10 times that of steel) and corrosion resistance (resistant to acids and alkalis, and resistant to chloride ion penetration), CFRP is increasingly being used in bridge cables, pipeline reinforcement, and other fields. However, the following problems remain unresolved in the application of CFRP in PCCP:

[0007] The interfacial bond strength between CFRP and the core is insufficient, making it prone to debonding.

[0008] The tensioning process of CFRP prestressed tendons (such as tension force control and anchorage design) differs greatly from that of traditional steel wire, and there is a lack of systematic adaptation solutions.

[0009] The collaborative stress mechanism between the ring-shaped CFRP ribs and the core is unclear, which can easily lead to local stress concentration.

[0010] Therefore, it is necessary to develop a new type of PCCP based on CFRP prestressed tendons to solve the problems of corrosion, concrete cracking and self-weight of traditional PCCPs. Summary of the Invention

[0011] The purpose of this invention is to provide a self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe and its manufacturing process to solve the problems mentioned in the background art.

[0012] To achieve the above objectives, on the one hand, the present invention provides a self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe, wherein the composite pipe comprises, from the inside out: a light-cured FRP inner anti-corrosion layer, a spiral welded steel cylinder, a self-healing concrete core, a three-dimensional CFRP prestressed layer, a potential equalization layer, and an FRP sand-filled outer protective layer, and the two ends of the composite pipe are respectively connected to a socket anti-corrosion steel ring and a spigot anti-corrosion steel ring by anchors;

[0013] The self-healing concrete core is composed of self-healing concrete, which contains a composite self-healing system composed of cement-based penetrating crystallizing material and microbial repair agent. The amount of cement-based penetrating crystallizing material is based on the total mass of cementitious materials in the self-healing concrete.

[0014] The three-dimensional CFRP prestressed layer is composed of circumferentially wound carbon fibers and longitudinally laid carbon fibers simultaneously impregnated with resin under tension.

[0015] The potential equalization layer is composed of conductive materials and ceramic fillers dispersed in a resin matrix.

[0016] Preferably, the microbial remediation agent is Bacillus-calcium lactate microcapsules, with a dosage of 0.8 × 10⁻⁶. 8 Up to 1.2×10 8 The self-healing concrete contains cfu / kg of cementitious material, and the dosage of the cementitious material is 1.0%-2.0% of the mass of the cementitious material.

[0017] Preferably, the core of the Bacillus-calcium lactate microcapsule is a mixture of Bacillus spores and calcium lactate powder, and the capsule wall is a sodium alginate-chitosan composite membrane.

[0018] Preferably, in the three-dimensional CFRP prestressed layer, the circumferentially wound carbon fibers are large-tow carbon fibers, and the longitudinally laid carbon fibers are small-tow carbon fibers; the circumferential winding tension is 45-55% of the tensile strength of the carbon fibers, and the longitudinal laying tension is 40-50% of the tensile strength of the carbon fibers.

[0019] Preferably, the conductive material of the potential equalization layer is graphene, the ceramic filler is a mixture of Al2O3 and TiO2, the resin matrix is ​​epoxy resin, the thickness of the potential equalization layer is 150-250μm, and the volume resistivity is 1-10Ω·cm.

[0020] Preferably, the photocurable FRP inner anti-corrosion layer is made of vinyl ester photocurable prepreg, and the Barcol hardness after curing is ≥50.

[0021] Preferably, the FRP sand-filled outer protective layer has a functionally graded structure, comprising, from the outside to the inside:

[0022] Weather-resistant layer: composed of weather-resistant resin and ultraviolet absorber;

[0023] Structural layer: made of alkali-free glass fiber and structural resin through circumferential winding, with a fiber volume content of 65%-75%;

[0024] Interface layer: composed of a flexible resin with an elastic modulus lower than that of the structural layer resin.

[0025] On the other hand, this invention discloses a manufacturing process for a self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe, comprising the following steps:

[0026] S1: Fabricate a spiral welded steel cylinder and weld a socket anti-corrosion steel ring and a spigot anti-corrosion steel ring to its two ends respectively. Weld anchors to the outer walls of the socket anti-corrosion steel ring and the spigot anti-corrosion steel ring respectively.

[0027] S2: Vertically pour the self-healing concrete to form a self-healing concrete core, and then steam cure it.

[0028] S3: Fix the ends of the carbon fiber prestressing tendons to the anchorage, use a vertical winding machine to simultaneously wind the circumferential carbon fibers and lay the longitudinal carbon fibers, and impregnate them with epoxy resin under tension. After curing, a three-dimensional CFRP prestressed layer is formed.

[0029] S4: Apply a potential equalization layer by spraying or scraping outside the three-dimensional CFRP prestressed layer;

[0030] S5: The FRP sand-filled outer protective layer is fabricated outside the potential equalization layer using a winding method;

[0031] S6: The light-cured FRP inner anti-corrosion layer is formed on the inner wall of the self-healing concrete core.

[0032] Preferably, in step S2, the steam curing process is as follows: after standing still for 1-2 hours, the temperature is raised to 60℃±5℃ and kept at a constant temperature for 8-12 hours.

[0033] Preferably, in step S4, the slurry of the potential equalization layer is prepared by the following method: mixing graphene conductive slurry, nano Al2O3 powder, nano TiO2 powder with epoxy resin and its curing agent, and stirring evenly using a high-speed shear disperser.

[0034] The beneficial effects of this invention are as follows:

[0035] 1. Superior Intelligent Self-Healing and High Impermeability: Cement-based penetrating crystalline material (CCCW) generates insoluble crystals under water permeation, rapidly sealing micron-level capillaries and microcracks; while Bacillus-calcium lactate microcapsules rupture when crack development leads to a drop in local pH, releasing the bacteria to metabolize calcium lactate and generate calcium carbonate precipitate, actively repairing wider macro-cracks. These two components constitute a synergistic system of "chemical instant sealing - biological long-term repair," significantly improving the density and durability of concrete.

[0036] 2. Excellent omnidirectional mechanical properties and structural safety: The innovative three-dimensional CFRP prestressed layer provides circumferential prestress to resist internal pressure through circumferentially wound fibers, while providing axial prestress to resist bending stress through longitudinally laid fibers. This spatial force system structure makes the pipeline a highly integral pressure-bearing cylinder, greatly improving its stress performance and effectively preventing longitudinal cracking caused by uneven foundation settlement.

[0037] 3. Fundamental Enhancement of Durability and Active Corrosion Protection: First, the use of carbon fiber composite materials completely replaces the easily corroded prestressed steel wire, eliminating the source of corrosion at its material origin. Second, the unique potential equalization layer establishes a continuous equipotential body outside the pipeline, eliminating the corrosion current generated between the CFRP (cathode) and the metal component (anode) due to the potential difference, fundamentally inhibiting galvanic corrosion and providing active and durable protection for the pipeline.

[0038] 4. Synergistic and Comprehensive Benefits: The composite pipe of this invention is not a simple material replacement and superposition, but rather an integrated design of materials, structure, and function, enabling complementary and synergistic effects among its components. For example, the self-healing system ensures the integrity of the concrete, thereby protecting the internal steel cylinder; the three-dimensional CFRP layer provides strength while its lightweight properties reduce its own weight; and the potential equalization layer ensures the long-term electrochemical compatibility of all metal components with CFRP. This systematic solution generates a synergistic effect of "1+1>2," achieving a leapfrog improvement in the overall performance of the pipeline.

[0039] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0040] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings:

[0041] Figure 1 This diagram shows a longitudinal cross-sectional view of the self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe provided by the present invention.

[0042] Figure 2 This diagram shows an enlarged cross-sectional view of the self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe provided by the present invention.

[0043] Figure 3 A detailed diagram of the socket structure of the self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe provided by the present invention is shown.

[0044] Figure 4 A schematic diagram of the structure of the anchor provided by the present invention is shown;

[0045] Figure 5 A top view of the anchor provided by the present invention is shown;

[0046] Figure 6 A rendering of the self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe provided by the present invention is shown.

[0047] Figure 7 The diagram shows the layer structure of the self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe provided by the present invention.

[0048] Explanation of reference numerals in the attached figures:

[0049] 1. Light-cured FRP inner anti-corrosion layer, 2. Spiral welded steel cylinder, 3. Self-healing concrete core, 4. Three-dimensional CFRP prestressed layer, 5. Potential equalization layer, 6. FRP sand-filled outer protective layer, 7. Anchor, 71. Upper anchor block, 72. Lower anchor block, 73. Bolt, 74. Anchor bending bar, 8. Socket anti-corrosion steel ring, 9. Spiral anti-corrosion steel ring. Detailed Implementation

[0050] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0051] It should be noted that all reagents and raw materials used in this invention are commercially available, and the reagents are of analytical grade.

[0052] The polycarboxylate superplasticizer is sourced from Jiangsu Subote New Material Co., Ltd., and its model number is PCA®-9.

[0053] The low-viscosity, room-temperature curing epoxy resin is sourced from Guangdong Hengda New Materials Technology Co., Ltd., and its model number is K-9423B.

[0054] The flexible epoxy resin is sourced from Forsmann Technology (Beijing) Co., Ltd., and its model number is EPICLON EXA-4850-150.

[0055] The isophthalic unsaturated polyester resin is sourced from Nanjing Boyuan Resin Technology Co., Ltd., and its model number is P6409.

[0056] The vinyl ester light-curing prepreg was prepared by the method disclosed in Example 1 of the specification of a visible light-curing vinyl ester resin composite material prepreg and its preparation and use method disclosed in Chinese Patent CN201610068220.7.

[0057] The neopentyl phthalate gel coat resin is sourced from Qingdao Jiachuang New Materials Co., Ltd., and its model number is GE1000S.

[0058] Sodium alginate is sourced from Hubei Hengjie Chemical Co., Ltd., with CAS number 9005-38-3.

[0059] Chitosan is sourced from Hunan Greenvine Biotechnology Co., Ltd., with CAS number 9012-76-4.

[0060] Reference Figure 1-7 This invention discloses a self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe. The composite pipe includes, from the inside out: a light-cured FRP inner anti-corrosion layer 1, a spiral welded steel cylinder 2, a self-healing concrete core 3, a three-dimensional CFRP prestressed layer 4, a potential equalization layer 5, and an FRP sand-filled outer protective layer 6. The two ends of the composite pipe are respectively connected to a socket anti-corrosion steel ring 8 and a spigot anti-corrosion steel ring 9 through anchors 7.

[0061] The self-healing concrete core 3 is composed of self-healing concrete, which contains a composite self-healing system composed of cement-based penetrating crystallizing material and microbial repair agent. The amount of cement-based penetrating crystallizing material is based on the total mass of cementitious materials in the self-healing concrete.

[0062] The three-dimensional CFRP prestressed layer 4 is composed of circumferentially wound carbon fibers and longitudinally laid carbon fibers simultaneously impregnated with resin under tension.

[0063] The potential equalization layer 5 is composed of conductive materials and ceramic fillers dispersed in a resin matrix.

[0064] The self-healing concrete core 3 of this invention achieves "rapid sealing + long-term repair" through the synergy of chemical crystallization (CCCW) and biomineralization (microorganisms). CCCW rapidly generates crystals upon contact with water, blocking microcracks; microorganisms are activated deep within the cracks (when the alkaline environment is disrupted), metabolizing to produce calcium carbonate and repairing wider cracks. The three-dimensional CFRP prestressed layer 4 resists the circumferential tensile stress generated by internal pressure through circumferential fibers and resists the axial bending stress of the pipe (such as that caused by foundation settlement) through longitudinal fibers, forming a complete spatial force system that fundamentally solves the mechanical defects of traditional pipes' axial fragility. The potential equalization layer 5 establishes an equipotential body outside the pipe using conductive materials (graphene), making the potential difference between components of different materials such as CFRP, steel cylinder, and socket approach zero, thereby suppressing galvanic corrosion current driven by potential difference and actively protecting metal components.

[0065] Preferably, the microbial remediation agent is Bacillus-calcium lactate microcapsules, with a dosage of 0.8 × 10⁻⁶. 8 Up to 1.2×10 8 CFU / kg self-healing concrete, with cement-based penetrating crystallizing material admixture at 1.0%-2.0% of the cementitious material mass. 1.0%-2.0% CCCW ensures sufficient active material to trigger the crystallization reaction; 0.8×10 8 Up to 1.2×10 8 The microcapsule dosage of CFU / kg in self-healing concrete ensures that there are sufficient repair units in the concrete, so that enough bacteria can be activated and participate in the repair when cracks appear.

[0066] Furthermore, the self-healing concrete core 3 also incorporates 0.5%-1.5% nano-silica by weight of the total cementitious material. Nano-SiO2 possesses an extremely high specific surface area and pozzolanic activity, enabling it to rapidly react with cement hydration products Ca(OH)2 to generate more CSH gel, refining the pore structure of the concrete and reducing permeability. Its enormous specific surface area provides abundant nucleation sites for the crystallization of CCCW and the deposition of bacterial metabolites, accelerating and enhancing the formation and filling effect of the self-healing product.

[0067] Preferably, the core of the Bacillus-calcium lactate microcapsule is a mixture of Bacillus spores and calcium lactate powder, and the capsule wall is a sodium alginate-chitosan composite membrane.

[0068] Preferably, in the three-dimensional CFRP prestressed layer 4, the circumferentially wound carbon fibers are large-tow carbon fibers, and the longitudinally laid carbon fibers are small-tow carbon fibers; the circumferential winding tension is 45-55% of the carbon fiber tensile strength, and the longitudinal laying tension is 40-50% of the carbon fiber tensile strength. Specifically, the circumferentially wound carbon fibers are T800 grade large-tow carbon fibers with a tow strength ≥48K, and the longitudinally laid carbon fibers are T700 grade small-tow carbon fibers with a tow strength of 12K. The volume ratio of circumferentially wound to longitudinally laid carbon fibers is (3-5):1. The use of large tows (≥48K) in the circumferential direction ensures efficiency and cost, while the use of small tows (12K) in the longitudinal direction ensures laying flexibility. The T700 grade ensures high strength and lightweight. The circumferential tension (45-55%) is key to balancing the application of effective prestress and avoiding pressure loss on the concrete during tensioning. The longitudinal tension is slightly lower (40-50%) because concrete's axial compressive and shear strength is generally weaker than its circumferential strength. Lower tension can prevent excessive longitudinal compressive stress from causing internal damage or interfacial delamination of the concrete.

[0069] Preferably, the conductive material of the potential equalization layer 5 is graphene, the ceramic filler is a mixture of Al2O3 and TiO2, the resin matrix is ​​epoxy resin, the thickness of the potential equalization layer 5 is 150-250 μm, and the volume resistivity is 1-10 Ω·cm. Graphene forms a three-dimensional conductive network, ensuring the efficiency and continuity of potential equalization. The Al2O3 / TiO2 ceramic filler improves the coating's hardness, wear resistance, and corrosion resistance, protecting the fragile graphene conductive network from damage during construction and service, ensuring the protection lifespan. The 150-250 μm thickness ensures the continuity and mechanical integrity of the coating; the 1-10 Ω·cm volume resistivity is crucial, as materials within this range have sufficient conductivity to equalize the potential without being too low in resistance, thus avoiding the formation of large corrosion current loops and achieving the ideal state of "equalization without conducting current".

[0070] Preferably, the light-cured FRP inner anti-corrosion layer 1 is made of vinyl ester light-cured prepreg, and its reinforcing fibers are corrosion-resistant E-CR glass fiber or basalt fiber, with a Barcol hardness ≥50 after curing. The light-cured FRP inner anti-corrosion layer 1 adopts a composite system of vinyl ester light-cured prepreg and special fibers, and the resin is rapidly cross-linked and cured by ultraviolet light, forming a dense anti-corrosion barrier within tens of seconds. Its mechanism of action is that the photoinitiator generates free radicals when excited, triggering a chain polymerization reaction of the double bonds of vinyl ester resin. At the same time, the E-CR glass fiber or basalt fiber forms a strong interface with the resin, which not only ensures the wear resistance requirement of Barcol hardness ≥50, but also achieves perfect adhesion with the concrete matrix, forming a continuous and stable anti-corrosion lining.

[0071] In this embodiment, the spiral welded steel cylinder 2 is integrally welded from Q235 steel strip with a thickness of 1.2-2.0mm using a spiral welding machine. Its core function is to form a continuous and uniform anti-seepage sealing layer. Precisely controlled process parameters during welding ensure that the weld is defect-free. The resulting continuous metal shell serves as both the primary pressure barrier for the pipeline and, through optimized material usage, achieves a lightweight design, providing a stable and reliable substrate for subsequent functional layers.

[0072] The steel rings of both the socket anti-corrosion steel ring 8 and the spigot anti-corrosion steel ring 9 undergo hot-dip galvanizing for corrosion protection, with a zinc-dip layer thickness of not less than 80μm. Hot-dip galvanizing forms a zinc-iron alloy layer with a thickness ≥80μm. This alloy layer provides both physical barrier protection and cathodic protection via metallurgical bonding. Its protective mechanism lies in the fact that zinc has a lower electrode potential than the base steel; when the coating is damaged, it preferentially corrodes, thus protecting the substrate and ensuring that the weakest end area of ​​the pipeline maintains complete sealing and structural stability during long-term service.

[0073] In this embodiment, the anchor 7 is a carbon fiber reinforced anchor, specifically including an upper anchor block 71, a lower anchor block 72, a bolt 73, and an anchoring bend rib 74. Anchoring bend ribs 74 are welded to both sides of the bottom of the lower anchor block 72. The side of the anchoring bend rib 74 away from the anchor block 72 is welded to the outer wall of the socket anti-corrosion steel ring 8 or the spigot anti-corrosion steel ring 9. The lower anchor block 72 adjusts the spatial position of the anchor 7 through the anchoring bend rib 74, ensuring that the bottom of the groove on the upper surface is flush with the outer surface of the self-healing concrete core 3. During installation, the lower anchor block 71 is first welded and fixed to the outer wall of the socket anti-corrosion steel ring 8 or the spigot anti-corrosion steel ring 9 by the flexible anchor bending ribs 74 on both sides. The anchor bending ribs 74 are precisely bent and adjusted so that the groove on the upper surface of the lower anchor block 71 is flush with the outer surface of the self-healing concrete core 3. Then, the carbon fiber prestressed tendon is straightly embedded into the groove of the lower anchor block 71, covering the upper anchor block 72, and high-strength bolts 73 are used to pass through the bolt holes of the upper and lower blocks. Finally, the nuts 73 are tightened to the specified torque in a diagonal sequence using a torque wrench, thereby forming a reliable anchoring system that achieves smooth prestress transmission.

[0074] Preferably, the FRP sand-filled outer protective layer 6 has a functionally graded structure, comprising, from the outside to the inside:

[0075] Weather-resistant layer: composed of weather-resistant resin and ultraviolet absorber;

[0076] Structural layer: made of alkali-free glass fiber and structural resin through circumferential winding, with a fiber volume content of 65%-75%;

[0077] Interface layer: composed of a flexible resin with an elastic modulus lower than that of the structural layer resin.

[0078] The functionally graded FRP sand-filled outer sheath 6 achieves multiple protective effects through a three-layer gradient structure design. The weather-resistant layer utilizes weather-resistant resin and UV absorbers to form stable chemical bonds, effectively resisting environmental aging. The structural layer, by precisely controlling the fiber volume content to 65%-75%, forms a highly efficient composite system where fibers bear the load and resin transmits force. The interface layer uses flexible resin as a stress buffer, leveraging its high strain characteristics to absorb interfacial shear stress and prevent interlayer delamination. This gradient design gives the outer sheath excellent weather resistance, high strength, and interfacial stability, providing long-term reliable physical protection for pipelines.

[0079] Example 1

[0080] Example 1 (DN1000mm pipe)

[0081] 1. Preparation of spiral welded steel cylinder 2 and socket

[0082] Material: 1.5mm thick, 1250mm wide Q235B hot-rolled steel strip.

[0083] Method: The steel strip is formed by a spiral pipe rolling machine, and a continuous weld is formed using double-sided submerged arc welding. After welding, the weld is subjected to 100% X-ray inspection. The socket anti-corrosion steel ring 8 and the spigot anti-corrosion steel ring 9 are rolled and welded from Q235 steel plates. After sandblasting to remove rust, they undergo hot-dip galvanizing treatment in a 460℃ zinc bath, with a zinc-dip galvanized layer thickness of 80μm, thus obtaining the spiral welded steel cylinder 2. The spiral welded steel cylinder 2 is then assembled with the socket anti-corrosion steel ring 8 and the spigot anti-corrosion steel ring 9 using CO2 gas shielded welding.

[0084] 2. Anchor installation 6

[0085] Method: Twelve sets of anchoring bending ribs 74 are evenly welded circumferentially to the outer walls of the socket anti-corrosion steel ring 8 and the spigot anti-corrosion steel ring 9. The bending ribs 74 are anchored using special clamps, and the spatial position of the lower anchor block 72 is precisely adjusted. A level is used for calibration to ensure that after installation, the bottom of the groove on the upper surface is flush with the designed outer surface of the self-healing concrete core 3 to be cast in the future, with the tolerance controlled within ±1mm.

[0086] 3. Vertical casting and curing of self-healing concrete pipe cores

[0087] Preparation of Bacillus-Calcium Lactate Microcapsules

[0088] Solution preparation:

[0089] Bacterial suspension: Bacillus spore powder and calcium lactate powder were mixed at a ratio of 1:3 (mass ratio), and an appropriate amount of trehalose (the concentration of trehalose in the final suspension was 5% (w / v, g / mL)) was added as a preservative. The suspension was then resuspended in sterile physiological saline to prepare a high-concentration Bacillus-calcium lactate mixed suspension (the McFarland turbidity of Bacillus was 2.0 McF, and the concentration of calcium lactate was 170 g / L). The suspension was then placed on ice for later use.

[0090] 3% (w / v, g / mL) sodium alginate solution: Slowly add 3g of sodium alginate to deionized water to a total volume of 100mL, stir magnetically until completely dissolved, autoclave (115℃, 15min), and then cool to room temperature.

[0091] 1.5% (w / v, g / mL) chitosan solution: Dissolve 1.5 g of chitosan in a 1% (v / v) acetic acid solution to a total volume of 100 mL, stir magnetically overnight until completely dissolved, and adjust the pH to 5.8 with NaOH.

[0092] 100mM calcium chloride solution.

[0093] Enzyme cross-linking solution: Dissolve transglutaminase (TG enzyme) in phosphate buffer at pH 6.5 to prepare an enzyme solution with a concentration of 20 U / mL.

[0094] Preparation steps

[0095] Preparation of mixed adhesive solution:

[0096] A 3% (w / v, g / mL) sodium alginate solution, a 2% (w / v, g / mL) sodium caseinate solution, and a 2% (w / v, g / mL) gelatin solution were mixed in a volume ratio of 7:2:1 and stirred evenly in a 40°C water bath to obtain a mixed adhesive solution. Subsequently, a Bacillus-calcium lactate mixed suspension (the volume ratio of the suspension to the mixed adhesive solution was 1:9) was added while stirring and mixed thoroughly to form a homogeneous core material-wall material mixture.

[0097] Microcapsule initial forming (drip method):

[0098] Using a sterile syringe or dropper, the core-wall material mixture is added dropwise at a constant rate to a 100mM calcium chloride solution under magnetic stirring. Upon contact with the calcium chloride solution, the sodium alginate on the surface of the droplet undergoes ionic cross-linking with calcium ions to form preliminary gel microspheres. These microspheres are then allowed to solidify in the solution for 25 minutes to stabilize the gel structure.

[0099] Chitosan coating:

[0100] The pre-formed microcapsules were filtered out, rinsed with sterile deionized water, and then transferred to a 1.5% (w / v, g / mL) chitosan solution. The solution was gently stirred for 15 min. The microcapsules were filtered out again and rinsed with deionized water.

[0101] Enhanced enzyme cross-linking:

[0102] The chitosan-coated microcapsules were immersed in a 20 U / mL TG enzyme solution and reacted with gentle shaking at 40°C for 2 hours.

[0103] Post-processing and storage:

[0104] Washing: After the reaction is complete, filter out the microcapsules and wash them thoroughly with sterile physiological saline to remove residual enzymes and reagents;

[0105] Curing: The microcapsules were placed again in a fresh 50mM calcium chloride solution and cured at 4°C for 4 hours to further stabilize the structure;

[0106] Storage: After filtering out the microcapsules and draining off the water, suspend them in sterile physiological saline containing 10% glycerol and store at 4°C in the dark.

[0107] Formula (per m) 3 ):

[0108] Cementitious materials: 500 kg (P.O42.5 cement: 380 kg, Grade I fly ash: 80 kg, silica fume: 40 kg);

[0109] Self-healing components:

[0110] Cement-based penetrating crystalline material (CCCW): 7.5 kg (1.5% of cementitious materials);

[0111] Bacillus-calcium lactate microcapsules: 5.0 kg (guaranteeing an effective viable count of 1×10⁻⁶) 8 (cfu / kg self-healing concrete);

[0112] Nano-silica: 5.0 kg (1.0% of cementitious material);

[0113] Aggregates: Medium sand (fineness modulus 2.6): 650 kg; Crushed stone (5-25 mm continuous gradation): 1150 kg;

[0114] Water: 160kg (water-to-binder ratio 0.32);

[0115] Polycarboxylate superplasticizer: 12.5kg (40% solids content);

[0116] Preparation method:

[0117] Add the aggregate, all the cementitious materials, CCCW, nano silica, and microcapsules into a vertical shaft planetary mixer and dry mix for 2 minutes until the color is uniform.

[0118] Dissolve the polycarboxylate-based high-performance water-reducing agent in water, add it to a mixer, and wet mix for 3 minutes to form a concrete mixture with good fluidity.

[0119] The concrete mixture is poured into a pre-assembled vertical mold containing a spiral welded steel cylinder 2, and compaction is ensured by combining an attached vibrator with an immersion vibrator.

[0120] Curing: After pouring, allow the mold to stand still for 1.5 hours, then introduce steam and heat it to 65℃ at a rate of 15℃ / h, maintaining this temperature for 10 hours. Stop the steam supply and allow the mold to cool naturally until the temperature difference with the environment is 15℃ before demolding. After demolding, spray water for curing for 7 days.

[0121] 4. Fabrication of the three-dimensional CFRP prestressed layer

[0122] Material:

[0123] Circular fiber: T800SC-48K carbon fiber yarn, tensile strength 2400MPa;

[0124] Longitudinal fiber: T700SC-12K carbon fiber prepreg yarn, resin content 35%;

[0125] Resin system: Low viscosity room temperature curing epoxy resin (epoxy value 0.51, viscosity 850 mPa·s).

[0126] Preparation method:

[0127] The cured core structure is hoisted onto a vertical CNC winding machine;

[0128] Anchoring and tensioning: Insert the starting end of the circumferential carbon fiber yarn into the groove of the lower anchoring block 72 at one end, press the upper anchoring block 71 on, and tighten the bolt 73 to the specified torque (e.g., 50 N·m) with a torque wrench to anchor.

[0129] Synchronous winding: Start the winding machine, set the circumferential winding tension to 1200MPa (50% of tensile strength), the longitudinal laying tension to 1080MPa (45% of tensile strength), and the circumferential winding pitch to 20mm. The machine performs circumferential winding and longitudinal laying simultaneously, ensuring the fibers are fully impregnated as they pass through the resin impregnation tank;

[0130] After wrapping to the other end, anchor in the same way. Cure at ambient temperature for 24 hours.

[0131] 5. Potential equalization layer 5 coating

[0132] formula:

[0133] Epoxy resin (E-51): 100 parts (by weight, the same below);

[0134] Conductive material: Graphene conductive paste (5% solid content): 40 parts (equivalent to 2 parts dry graphene);

[0135] Ceramic filler, by weight: nano Al2O3 powder (average particle size 30nm): 15 parts, nano TiO2 powder (average particle size 50nm): 10 parts;

[0136] Curing agent (polyamide 650): 35 parts;

[0137] Preparation method: First, graphene conductive slurry and epoxy resin are mixed evenly using a high-speed shear disperser (3000 rpm, 30 min). Then, ceramic filler and curing agent are added, and the mixture is stirred at low speed until no agglomeration occurs. Using an airless spraying device, the mixed slurry is evenly sprayed onto the surface of the three-dimensional CFRP prestressed layer 4. The wet film thickness is controlled, and after curing at room temperature for 24 h, a dense coating with a dry film thickness of 200 μm and a volume resistivity of 5 Ω·cm is formed.

[0138] 6. Fabrication of FRP Sand-Filled Outer Sheath 6

[0139] Gradient structures and methods:

[0140] Interface layer: Apply a layer of flexible epoxy resin (elastic modulus 1.5 GPa).

[0141] Mortar cushion layer: A vertical roller shot blasting machine is used to mix quartz sand (average mesh size 65 mesh) and isophthalic unsaturated polyester resin at a ratio of 4:1 (mass ratio) and spray it to form a cushion layer of about 4mm thickness.

[0142] Structural layer: alkali-free glass fiber roving (2400 tex) impregnated with corrosion-resistant vinyl ester resin, wound in a circumferential manner, controlling the fiber volume content to 70%, and wound 2 layers to the designed thickness;

[0143] Weather-resistant layer: Finally, a layer of isophenylene neopentyl glycol gel coat resin with added ultraviolet absorber (UV-531, added at 0.3% of the weight of isophenylene neopentyl glycol gel coat resin) is applied.

[0144] 7. Fabrication of the UV-cured FRP inner anti-corrosion layer 1

[0145] method:

[0146] Inner wall treatment: Sandblasting is used to treat the inner wall of the spiral welded steel cylinder 2 to thoroughly remove oxide scale, oil stains and rust, achieving the Sa2.5 level rust removal standard, exposing the metal color, and forming a clean, dry, active surface with a certain degree of roughness;

[0147] Application and Curing: The vinyl ester UV-curable prepreg is applied to the inner wall of the spiral welded steel cylinder 2, and air bubbles are removed with a pressure roller. Then, a UV-LED curing light source (wavelength 365nm, intensity 1200mW / cm²) is applied. 2 Suspended in the center of the pipe, it is pulled through the pipe at a uniform speed of 0.5m / min, so that the prepreg is completely cured within 60s, forming a smooth inner lining with a thickness of 2mm and a Barcol hardness of 55.

[0148] Example 2

[0149] The specific components and preparation methods are largely the same as in Example 1, with the following differences:

[0150] Self-healing concrete: CCCW admixture 1.0%, microcapsule admixture 0.8×10 8 CFU / kg self-healing concrete, with nano-SiO2 content of 0.5%;

[0151] Three-dimensional CFRP prestressed layer 4: circumferential tensile stress 45%, longitudinal tensile stress 40%;

[0152] Potential equalization layer 5: 150 μm thick.

[0153] Example 3

[0154] The specific components and preparation methods are largely the same as in Example 1, with the following differences:

[0155] Self-healing concrete: CCCW admixture 2.0%, microcapsule admixture 1.2×10⁻⁶ 8 CFU / kg self-healing concrete, with a nano-SiO2 content of 1.5%;

[0156] Three-dimensional CFRP prestressed layer 4: circumferential tensile stress 55%, longitudinal tensile stress 50%;

[0157] Potential equalization layer 5: 250 μm thick.

[0158] Comparative Example 1

[0159] Compared to Example 1, the self-healing concrete uses only 2.0% cement-based penetrating crystalline material (CCCW) and does not contain any Bacillus-calcium lactate microcapsules or nano silica.

[0160] Comparative Example 2

[0161] Compared with Example 1, the three-dimensional CFRP prestressed layer is replaced with traditional prestressed steel wire, and the special carbon fiber anchor is replaced with a traditional steel wire anchor, thus eliminating the potential equalization layer.

[0162] Comparative Example 3

[0163] Compared to Example 1, the carbon fiber prestressed layer is only wound in the circumferential direction, completely eliminating the laying of longitudinal fibers.

[0164] Comparative Example 4

[0165] Compared to Example 1, the coating step of the potential equalization layer is completely omitted, allowing the three-dimensional CFRP layer to directly contact the FRP outer sheath.

[0166] The composite tubes prepared in Examples 1-3 and Comparative Examples 1-4 were subjected to corresponding performance tests. The test standards and methods are as follows, and the test results are recorded in Table 1.

[0167] 1. Water Permeability Test: Refer to DB1310 / T296—2023 "Test Method for Water Permeability of Ordinary Concrete". During testing, a hydrostatic pressure tester is used to apply hydrostatic pressure to the specimen in stages (e.g., increasing by 0.1 MPa at each stage and holding the pressure for 30 minutes), while observing the surface. When water seepage appears on the specimen surface, record the pressure value at that moment.

[0168] 2. Crack self-healing efficiency: First, microcracks are artificially created on the material; then, they are allowed to self-heal under specified conditions (such as time, temperature, and humidity); finally, the changes in crack length or width before and after healing are measured using a high-resolution microscope (such as a laser confocal microscope). Crack self-healing efficiency is quantified by calculating the percentage of healed area or the crack size reduction rate. The core formula is: (initial crack size - healed crack size) / initial crack size × 100%.

[0169] 3. Axial Bending Capacity: According to GB / T 228.1-2021 "Metallic Materials - Tensile Testing". During testing, a universal testing machine is used to apply an axial bending load to a specimen of specified dimensions. The testing machine applies the load at a constant rate until the specimen fails or the deformation reaches a predetermined value. Load and displacement data are recorded during the process. The maximum load that the specimen can withstand before failure is its axial bending capacity.

[0170] 4. Corrosion rate of steel rings: The commonly used laboratory method is the neutral salt spray test (NSS). This involves placing the steel ring sample in a dedicated salt spray chamber and continuously spraying it with a 5% sodium chloride solution at 35°C for several hours to hundreds of hours to accelerate corrosion. Before and after corrosion, the mass change of the sample is accurately measured (weight loss method), and the corrosion depth per unit time is calculated using the formula: corrosion rate = (mass loss) / (material density × surface area × time).

[0171] Table 1 Performance Test Results

[0172]

[0173] Comparative Example 1 (chemical self-healing only): Its crack self-healing efficiency (66%) was significantly lower than that of Example 1 (92%), proving that the single chemical self-healing system has limited ability to repair macroscopic cracks larger than 0.2 mm; while the microbial repair agent can effectively fill macroscopic cracks through biomineralization. The two work together to form a complete crack repair system. The absence of either mechanism will lead to a significant decrease in self-healing performance.

[0174] Comparative Example 2 (Traditional steel wire prestressed concrete): This comparative group showed comprehensive deterioration in key indicators such as seepage pressure (1.2 MPa), self-healing efficiency (<10%), and steel ring corrosion rate (12.6%). This proves that traditional prestressed steel wire will rust and expand in a corrosive environment, leading to concrete cracking. Furthermore, ordinary concrete lacks self-healing ability, which essentially reveals the necessity of material system innovation to improve pipeline durability.

[0175] Comparative Example 3 (circumferential prestress only): Its axial bending capacity (204 kN) was reduced by about 28% compared with Example 1 (285 kN), and longitudinal cracking occurred in the bending test. This clearly verifies the key role of longitudinal carbon fiber in resisting bending stress by providing axial prestress. The lack of longitudinal reinforcement will lead to severe stress concentration and failure of the pipe under asymmetric load.

[0176] Comparative Example 4 (without potential equalization layer): Although its mechanical properties are comparable to those of Example 1, the corrosion rate of the steel ring (8.7%) increased by 17 times. This directly confirms that in the coexistence system of carbon fiber (cathode) and metal component (anode), the potential equalization layer is the core value of eliminating potential difference and suppressing galvanic corrosion current by establishing an equipotential body, which is the key guarantee for the long-term durability of the composite system.

[0177] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention. Furthermore, it should be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0178] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe, characterized in that, The composite pipe comprises, from the inside out: a light-cured FRP inner anti-corrosion layer, a spiral welded steel cylinder, a self-healing concrete core, a three-dimensional CFRP prestressed layer, a potential equalization layer, and an FRP sand-filled outer protective layer. The two ends of the composite pipe are respectively connected to a socket anti-corrosion steel ring and a spigot anti-corrosion steel ring by anchors. The photocurable FRP inner anti-corrosion layer is made of vinyl ester photocurable prepreg, and the Barcol hardness after curing is ≥50. The method for manufacturing the photocurable FRP internal anti-corrosion layer: Inner wall treatment: The inner wall of the spiral welded steel cylinder is surface treated by sandblasting to achieve the Sa2.5 level rust removal standard; Application and Curing: The vinyl ester UV-curable prepreg is applied to the inner wall of the spiral welded steel cylinder. A UV-LED curing light source is suspended at the center of the pipe, with a wavelength of 365nm and an intensity of 1200mW / cm². 2 It is pulled through the pipe at a constant speed of 0.5 m / min, so that the prepreg is completely cured within 60 seconds; The self-healing concrete core is composed of self-healing concrete, which contains a composite self-healing system composed of cement-based penetrating crystallizing material and microbial repair agent. The amount of cement-based penetrating crystallizing material is based on the total mass of cementitious material in the self-healing concrete. The self-healing concrete core also contains 0.5%-1.5% nano-silica, which accounts for 0.5%-1.5% of the total mass of cementitious material. The three-dimensional CFRP prestressed layer is composed of circumferentially wound carbon fibers and longitudinally laid carbon fibers simultaneously impregnated with resin under tension. The circumferentially wound carbon fibers are large-tow carbon fibers, and the circumferential winding tension is 45-55% of the tensile strength of the carbon fibers. The longitudinally laid carbon fibers are small-tow carbon fibers, and the longitudinal laying tension is 40-50% of the tensile strength of the carbon fibers. The potential equalization layer is composed of conductive material and ceramic filler dispersed in a resin matrix. The conductive material is graphene, the ceramic filler is a mixture of Al2O3 and TiO2, the resin matrix is ​​epoxy resin, the thickness of the potential equalization layer is 150-250 μm, and the volume resistivity of the potential equalization layer is 1-10 Ω·cm.

2. The self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe according to claim 1, characterized in that, The microbial remediation agent is Bacillus-calcium lactate microcapsules, with a dosage of 0.8 × 10⁻⁶. 8 Up to 1.2×10 8 The self-healing concrete contains cfu / kg of cementitious material, and the dosage of the cementitious material is 1.0%-2.0% of the mass of the cementitious material.

3. The self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe according to claim 2, characterized in that, The core of the Bacillus-calcium lactate microcapsule is a mixture of Bacillus spores and calcium lactate powder, and the capsule wall is a sodium alginate-chitosan composite membrane.

4. The self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe according to claim 1, characterized in that, The FRP sand-filled outer protective layer has a functionally graded structure, comprising, from the outside to the inside: Weather-resistant layer: composed of weather-resistant resin and ultraviolet absorber; Structural layer: made of alkali-free glass fiber and structural resin through circumferential winding, with a fiber volume content of 65%-75%; Interface layer: composed of a flexible resin with an elastic modulus lower than that of the structural layer resin.

5. A manufacturing process for a self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Fabricate a spiral welded steel cylinder and weld a socket anti-corrosion steel ring and a spigot anti-corrosion steel ring to its two ends respectively. Weld anchors to the outer walls of the socket anti-corrosion steel ring and the spigot anti-corrosion steel ring respectively. S2: Vertically pour the self-healing concrete to form a self-healing concrete core, and then steam cure it. S3: Fix the ends of the carbon fiber prestressing tendons to the anchorage, use a vertical winding machine to simultaneously wind the circumferential carbon fibers and lay the longitudinal carbon fibers, and impregnate them with epoxy resin under tension. After curing, a three-dimensional CFRP prestressed layer is formed. S4: Apply a potential equalization layer by spraying or scraping outside the three-dimensional CFRP prestressed layer; S5: The FRP sand-filled outer protective layer is fabricated outside the potential equalization layer using a winding method; S6: The light-cured FRP inner anti-corrosion layer is formed on the inner wall of the self-healing concrete core.

6. The manufacturing process of the self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe according to claim 5, characterized in that, In step S2, the steam curing process is as follows: after standing still for 1-2 hours, the temperature is raised to 60℃±5℃ and kept at a constant temperature for 8-12 hours.

7. The manufacturing process of the self-healing carbon fiber prestressed steel cylinder concrete FRP composite pipe according to claim 5, characterized in that, In step S4, the slurry of the potential equalization layer is prepared by the following method: graphene conductive slurry, nano Al2O3 powder, nano TiO2 powder are mixed with epoxy resin and its curing agent, and stirred evenly using a high-speed shear disperser.

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