Concrete composite pipe and processing method thereof

Abstract

The invention relates to the field of civil engineering materials and pipeline structures, in particular to a concrete composite pipe and a machining method thereof. The problems that a composite pipeline is limited in bearing capacity, prone to cracking and poor in durability are solved. The composite pipe sequentially comprises a self-sensing concrete lining layer, a negative Poisson's ratio restraint layer, a fiber reinforced composite layer and an intelligent protective outer layer from inside to outside. The self-sensing concrete lining layer is made of conductive fiber reinforced polymer concrete, and strain self-sensing and damage self-monitoring are achieved. The negative Poisson's ratio restraint layer is of a double-arrow-shaped steel metamaterial structure, and the bearing capacity and ductility of the pipeline are improved; the fiber reinforced composite layer adopts a hybrid fiber grid to provide additional circumferential constraint and prevent corrosion; the intelligent protection outer layer is made of a shape memory polymer composite material, and self-repairing can be achieved. The adhesive is sprayed on the surface of the restraint layer, the fiber reinforced composite layer is wound and laid, the shape memory polymer outer layer is coated through lateral extrusion, and the composite pipe is obtained through staged curing.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of civil engineering materials and pipeline structures, and particularly relates to a concrete composite pipe and a processing method thereof. BACKGROUND

[0002] Concrete pipes are widely used in water supply and drainage and municipal engineering due to low material and cost. However, the traditional reinforced concrete pipes have many problems in the use process: Firstly, the tensile capacity of concrete is low, and cracks are easily generated on the pipe wall under external load. The occurrence of cracks not only weakens the structural bearing capacity, but also provides a channel for water and corrosive media to enter, leading to internal steel corrosion and seriously affecting durability. In order to control cracking, the traditional method is to arrange a ring-shaped steel cage in the pipe wall to improve the tensile strength, but the steel only bears the tensile force after the concrete cracks, at which time the pipe stiffness has been significantly reduced. In addition, even if the crack width is controlled within 0.01 inch according to the specification, it may still be detrimental to long-term durability.

[0003] Secondly, the bearing capacity of reinforced concrete pipes is limited, and brittle failure is easily caused under uneven foundation or overload. In order to improve the bearing capacity and toughness of the pipe, the industry has developed various reinforced pipes, such as prestressed concrete pipes, fiber reinforced concrete pipes, etc. However, ordinary fiber reinforced concrete pipes only rely on the addition of steel fibers or synthetic fibers in the concrete to suppress cracks, and the bearing capacity is limited; prestressed or steel sleeve constraint can significantly improve the strength and ductility of the pipe, but there are problems of high manufacturing cost or complex post-maintenance. In addition, ordinary pipes lack structural health monitoring and self-repairing capabilities, and often need to be replaced after leakage or damage, which is high in maintenance cost and affects use.

[0004] In summary, the existing technology urgently needs a new type of concrete pipe that has significantly improved bearing capacity, crack resistance, durability and intelligent functions. SUMMARY

[0005] The purpose of the present application is to provide a concrete composite pipe and a processing method thereof, in order to overcome the defects of insufficient bearing capacity and durability, easy cracking and lack of intelligent functions of the existing reinforced concrete pipe. The concrete composite pipe of the present application realizes high bearing capacity and high ductility through innovative material combination and structural design, and has intelligent characteristics such as strain self-sensing and crack self-repairing, thereby significantly improving the performance and service life of the pipe.

[0006] The specific technical scheme is as follows: A concrete composite pipe and a processing method thereof, comprising the following steps: S1: the geopolymer slurry and carbon nanotube dispersion liquid are mixed and stirred to obtain concrete, 1.5% to 2.5% of the volume of the concrete is added to the chopped copper-coated steel fiber, the carbon nanotube is uniformly distributed and coated on the surface of the aggregate and the fiber in the high-speed stirrer, the self-sensing concrete material is obtained, the mixed concrete material is quickly poured into a circular ring-shaped steel mold, a centrifugal forming machine is started, and a three-stage variable speed process centrifugation is carried out, and a ring-shaped wet concrete inner lining blank is obtained after centrifugation; then, step curing is carried out, and a composite pipe containing a self-sensing concrete inner lining is prepared; Further, the geopolymer slurry, the composition and the amount are as follows: 1 part of siliceous and aluminous cementing material as a reference, 0.4 to 0.6 parts of alkaline activator solution, 1.0 to 1.5 parts of quartz sand, and 0.3 to 0.45 parts of water; the siliceous and aluminous cementing material is prepared by mixing I-grade fly ash and granulated blast furnace slag at a mass ratio of 1:1, and the alkaline activator solution is prepared by mixing 10 mol / L NaOH solution and water glass at a mass ratio of 1:1.

[0007] Further, the carbon nanotube dispersion liquid is prepared by mixing multi-walled carbon nanotubes and polycarboxylate dispersant at a mass ratio of 1:1, using an ultrasonic disperser for 30 minutes, and the amount is 0.4% to 0.8% of the mass of the gel material.

[0008] Further, the three-stage variable speed process centrifugation is as follows: low-speed centrifugation: centrifugal acceleration 0.7 to 0.9g, rotation 1.5 to 2.5 minutes; medium-speed centrifugation: centrifugal acceleration 1.8 to 2.2g, rotation 1 to 2 minutes; high-speed centrifugation: centrifugal acceleration 7 to 9g, rotation 2 to 4 minutes.

[0009] Further, the step curing is as follows: room temperature standing: the steel mold is placed at room temperature for 1 hour to complete the initial setting, steam curing: the steel mold is moved into a steam curing pool, the temperature is gradually increased from room temperature to 75 to 85℃, and maintained for 3 to 4 hours, demolding and wet curing: the sample is taken out and demolded, and placed in a curing room with a relative humidity of more than 95% for wet curing for 7 days.

[0010] S2: a double-arrow unit periodic array pattern is drawn by computer-aided drawing, the unit geometric parameters are: a node angle of 45°, a unit length of 60mm, and a waist width of 20mm; a double-arrow grid pattern is cut on a stainless steel plate by using a precision laser cutting machine, a plane grid plate is obtained, the grid plate is placed in a special mold for welding, and a composite pipe containing a negative Poisson's ratio constraint layer is prepared; Further, welding, the specific operation is to apply pressure through a hydraulic machine, make the arrow part protrude 1.5-2.5 mm along the thickness direction, the web part is bent, and a plurality of grid plates are bent into arc shapes along the circumferential direction, arranged closely to the outer surface of the concrete lining layer, and laser welding is used to connect the arc-shaped grid plates end to end into a cylindrical steel shell, the welding seam is 20 mm long and arranged staggered with an interval of 100 mm, and welding is carried out.

[0011] S3: the outer surface of the composite pipe containing the negative Poisson's ratio constraint layer prepared in step S2 is sprayed with modified epoxy resin adhesive, the adhesive is surface-dried, and fiber winding is carried out; after completing 2 mm thick layers, the pipe body is transferred into a 60 DEG C environment and kept for 2 hours, after complete winding, the pipe body is placed in an 80 DEG C environment and kept for 8 hours, and a composite pipe containing a fiber-reinforced composite layer is prepared; Further, the continuous fiber bundle impregnated with epoxy resin includes carbon fiber, glass fiber and basalt fiber.

[0012] Further, the specific sequence is as follows: the first layer is a mixed bundle of carbon fiber and basalt fiber wound in the ±45° direction along the pipe axis, the second layer is a glass fiber bundle wound in the 0° direction along the pipe axis, and subsequent layers are wound in the ±45° / 0° sequence alternately until the designed thickness of 8 mm is reached.

[0013] S4: the shape memory resin and the chopped carbon fiber are heated and melted in a double screw extruder, and a continuous tape is extruded, and the chopped carbon fiber accounts for 3%-8% of the total mass of the shape memory resin and the chopped carbon fiber; while the pipe body is slowly rotating, the molten polymer tape is spirally wound and pasted on the surface of the fiber composite layer from one end, and the adjacent tapes are wound with the edges overlapping about half of the tape width, and then heating and curing are carried out: the infrared heater is started to carry out stage heating, and a concrete composite pipe is prepared.

[0014] Further, the stage heating has the following specific parameters: the first stage is to heat to 65-75 DEG C and keep for 0.5-1.5 hours; the second stage is to heat to 110 DEG C-130 DEG C and keep for 2-4 hours; and the third stage is to naturally cool to room temperature.

[0015] Compared with the prior art, the present application has the following beneficial effects: (1) The conductive network embedded in the self-sensing concrete lining layer is very sensitive to strain and damage, and can monitor the stress and health condition of the pipe in real time by measuring the resistance change, so that the lining layer has a sensing function and can realize the structural health monitoring of the whole pipe without additional equipment.

[0016] (2) The negative Poisson's ratio constraint layer actively compresses the concrete in the lateral direction, so that the concrete in the pipe wall is not easy to crack under high pressure, and the fiber-reinforced composite layer provides additional hoop strength, and the superposition of the two can improve the axial pressure and internal pressure bearing capacity of the pipe.

[0017] (3) The shape memory polymer of the intelligent protection outer layer can automatically close the fine cracks of the pipe wall under thermal excitation, and cooperates with internal self-healing to improve the overall water tightness of the pipeline.

[0018] (4) The multi-layer structure of the composite pipe is tightly protected inside and outside: the fiber composite layer and the shape memory outer layer jointly prevent water and corrosion, so that the core steel structure and the steel fiber are not directly exposed to the erosion environment, and excellent durability is shown. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The preparation process flow chart of the concrete composite pipe is shown in the figure.

[0020] Figure 2 The schematic diagram of the concrete composite pipe is shown in the figure.

[0021] Figure 3 The schematic diagram of the double-arrow hole grid plate is shown in the figure.

[0022] Figure 4 The comparison chart of the compression strength and permeability coefficient test results of examples 1-3 and comparative examples 1-5 is shown in the figure.

[0023] Figure 5 The comparison chart of the strength recovery rate test results of examples 1-3 and comparative examples 1-5 is shown in the figure. DETAILED DESCRIPTION

[0024] The following examples further explain and illustrate the technical solutions of the present application. It is particularly pointed out that each specific embodiment is a specific embodiment and explanation of the technical solution, and should not be regarded as a limitation on the protection scope of the present application. Those skilled in the art still have the right to modify the technical solutions of these examples, to replace some or all of the technical features with equivalent replacements, and these modifications or replacements do not change the essence of the corresponding technical solutions, and do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions described in the present application. As shown in the figure, it is a preparation process flow chart of a concrete composite pipe, and the preparation steps are as follows: Figure 1 The preparation process flow chart of the concrete composite pipe is shown in the figure. The composite pipe of the present application is composed of a self-sensing concrete lining layer, a negative Poisson ratio constraint layer, a fiber reinforced composite layer and an intelligent protection outer layer from inside to outside, as shown in the figure. Figure 2As shown; wherein the self-sensing concrete inner lining layer is mixed with conductive fibers, geopolymer slurry and carbon nanotube dispersion to achieve strain self-sensing and damage self-monitoring; the negative Poisson's ratio restraint layer is welded with a double-arrow-shaped steel metamaterial structure to improve the carrying capacity and ductility of the pipeline; the fiber-reinforced composite layer uses hybrid fiber mesh to provide additional hoop restraint and protection against corrosion; the intelligent protective outer layer uses shape memory polymer composite materials, which can achieve self-repairing; the surface of the restraint layer is sprayed with adhesive, and the continuous fiber bundle impregnated with epoxy resin is laid in a specific order, and the shape memory polymer outer layer is coated through lateral extrusion. The specific preparation steps are as follows: (1) Preparation of self-sensing concrete inner lining layer Prepare the raw materials according to the mix proportion of geopolymer concrete, including: silico-aluminate cementitious material, alkaline activator solution, quartz sand, water, and steel fiber, etc. For the conductive component, take multi-walled carbon nanotubes and add a surface activator to deionized water, and use ultrasonic dispersion for more than 30 minutes to prepare a stable carbon nanotube dispersion. Mix the dispersion with the pre-prepared geopolymer slurry and add short-cut copper-plated steel fibers, and stir well under high-speed stirring to make the carbon nanotubes uniformly distributed and coated on the surface of the aggregate and fibers, thereby obtaining a well-stirred self-sensing concrete mixture. Then, pour the prepared concrete mixture into the inner lining steel mold quickly. Start the centrifugal forming machine to form the concrete mixture with a three-stage variable speed centrifugal process: initially rotate at low speed to make the concrete slurry evenly cover the steel mold wall and basically form; then increase the speed to medium speed to promote the aggregate to migrate to the outer layer under the action of centrifugal force and the slurry to further compact; finally, accelerate to high speed to fully remove excess water and bubbles in the slurry and make the concrete structure dense. After centrifugal forming, a ring-shaped wet concrete inner lining blank is obtained. The centrifugally formed concrete inner lining needs to be subjected to step-by-step curing: first, place the steel mold at room temperature and keep the concrete undisturbed to complete the initial setting; then move the steel mold into the steam curing pool and gradually increase the temperature to make the geopolymer reaction proceed fully and the early strength grow rapidly; then take out the sample and remove the mold, and place it in a curing room for continued wet curing to ensure the development of late strength and dimensional stability, and the self-sensing concrete inner lining layer is formed with a through conductive network in the material.

[0025] (2) Processing and installation of negative Poisson's ratio restraint layer By utilizing the special deformation characteristics of negative Poisson's ratio structure, components that contract radially under pressure can be designed to constrain the concrete, thereby improving its strength and ductility.

[0026] According to the designed pipe size, 2205 duplex stainless steel plate is selected to manufacture the confinement layer. Double-arrow type unit periodic array pattern is drawn by computer aided drawing, and the unit geometric parameters are as follows: the angle between nodes is 45°, the unit length is 60 mm, and the waist width is 20 mm; the grid pattern is cut on the steel plate by using a precision laser cutting machine, to obtain a planar double-arrow hole grid plate, as shown in the accompanying drawings. Figure 3 The plate is then placed in a special mold, and pressure is applied by a hydraulic machine. A plurality of processed grid plates are bent into an arc shape in the circumferential direction and arranged closely to the outer surface of the concrete lining layer. A plurality of arc-shaped grid plates are connected end to end by laser welding to form a complete cylindrical steel shell, which is wrapped around the concrete lining layer to form a confinement layer. In the welding process, the length of each weld is controlled, and the distance is staggered to avoid excessive heat affected by continuous welding. After welding, it is checked to ensure that the steel shell is closely attached to the lining concrete without obvious gaps. The obtained negative Poisson's ratio confinement layer steel shell has the characteristics of simultaneous shrinkage and extrusion under axial compression after the above processing. When a simple axial loading test is performed, it is observed that after the axial pressure is applied, the diameter of the steel shell tends to decrease, rather than expanding radially like a normal ring. This confirms its negative Poisson's ratio behavior, which can provide effective active confinement to the internal concrete.

[0027] (3) Winding forming of fiber reinforced composite layer After the installation of the metal confinement layer on the outer surface of the concrete pipe base, the fiber reinforced composite layer is continued to be made. A layer of modified epoxy resin adhesive is sprayed on the outer surface of the steel shell, with the purpose of increasing the adhesion of the subsequent fiber composite material to the metal surface and playing a role in isolating rust. After the adhesive is surface dried, the multi-axis numerical control fiber winding machine is started, and the continuous fiber bundle pre-impregnated with epoxy resin is gradually wound on the outer surface of the pipe according to the set tension. The fiber laying adopts a multi-layer and multi-angle cross method: first, a layer of carbon fiber and basalt fiber hybrid bundle is wound in the ±45° direction along the pipe axis to improve the shear connection in the hoop and axial directions; then a layer of glass fiber bundle is wound in the 0° direction along the pipe axis to mainly bear the hoop tensile force; and then the ±45° / 0° sequence is continued to be alternately laid until the designed composite layer thickness is reached. During the entire winding process, the fiber bundle tension and yarn spacing are controlled to ensure that the fibers are tightly attached and uniformly distributed. After each 2mm thick layer is completed, the pipe body is transferred to a warming environment for a certain period of time to promote partial curing of the resin to prevent slippage of the inner layer of fibers when multiple layers are stacked. After the entire fiber winding is completed, the pipe body is cured to fully cure and cross-link the resin, and after cooling, a thin but firm fiber reinforced composite layer is obtained. This layer is integrated with the metal confinement layer and the concrete inner layer through adhesive and resin penetration, firmly attached and not peeled off; the fiber reinforced composite layer not only bears the hoop tensile force, but also further enhances the pipe wall's resistance to internal pressure and external load, and also serves as a barrier to prevent water and corrosive media from entering the inner layer, thereby improving the overall structure's impermeability and corrosion resistance.

[0028] (4) Coating of the intelligent protective outer layer Shape memory polymers are endowed with a specific shape when initially formed, and can recover the original shape remembered when subjected to a certain stimulus. By utilizing this property, the outer layer material of the present application remains in a solidified state during normal use of the pipe, and when micro-cracks or local deformation of the pipe wall occur, the outer layer material can be shrunk by heating it above its glass transition temperature to trigger its shape recovery function, thereby automatically healing and sealing the cracks; Specifically, a shape memory polymer composite material outer layer is coated on the outer surface of the cured fiber reinforced composite layer. A thermally induced shape memory resin is used as a matrix, and short carbon fibers are added to improve thermal conductivity and strength. The composite material pellets are heated and melted in a twin-screw extruder, and a continuous tape is extruded. While the pipe body is slowly rotating, the molten polymer tape is spirally wound and adhered to the surface of the fiber composite layer from one end. The outer layer is evenly covered on the entire pipe body by extruding and winding. The edges of adjacent tapes overlap by half the width to ensure that there are no gaps. After winding is completed, the infrared heater is started to heat the entire pipe body in stages: first, heat to 65-75℃ and keep for 0.5-1.5 hours to make the shape memory polymer fully softened and penetrate into the surface of the lower layer of fiber composite material; then heat to 110-130℃ and keep for 2-4 hours to complete the crosslinking and shape setting of the shape memory polymer; finally, naturally cool to room temperature. During the cooling process, the shape memory polymer shrinks a certain volume, further tightly binds to the surface of the pipe body, and forms a very thin but very strong protective outer shell. At this point, the concrete composite pipe has completed the entire layer structure.

[0029] Example 1 Table 1 Raw material information table A concrete composite pipe and its processing method, the specific steps are as follows: S1: Mix and stir the geopolymer slurry and carbon nanotube dispersion to obtain concrete, add 2.0% of short copper-coated steel fiber by volume of concrete, stir in a high-speed mixer to make the carbon nanotubes uniformly distributed and coated on the surface of the aggregate and fiber, obtain self-aware concrete material, quickly pour the prepared concrete material into a circular steel mold with a thickness of 10 mm and an inner diameter of 600 mm, start the centrifugal forming machine, and perform three-stage variable speed process centrifugation: low-speed centrifugation: centrifugal acceleration 0.8g, rotation 2 minutes; medium-speed centrifugation: centrifugal acceleration 2.0g, rotation 1.5 minutes; high-speed centrifugation: centrifugal acceleration 8g, rotation 3 minutes; after centrifugation, a ring-shaped wet concrete inner lining blank is obtained; then perform step-by-step curing, first place the steel mold at room temperature for 1 hour to complete initial setting, steam curing: move the steel mold into a steam curing pool, gradually increase the temperature from room temperature to 80℃, and keep for 3.5 hours, demolding and wet curing: remove the sample from the mold and place it in a curing room with a relative humidity of more than 95% for wet curing for 7 days, to prepare a composite pipe containing a self-aware concrete inner lining; The geopolymer slurry consists of 1 part of siliceous and aluminous cementing material as a reference, 0.5 parts of alkaline activator solution, 1.3 parts of quartz sand, and 0.4 parts of water. The siliceous and aluminous cementing material is prepared by mixing I-grade fly ash and granulated blast furnace slag at a mass ratio of 1:1, and the alkaline activator solution is prepared by mixing 10 mol / L NaOH solution and water glass at a mass ratio of 1:1.

[0030] Carbon nanotube dispersion liquid, mixed by multi-walled carbon nanotubes and polycarboxylate dispersant at a mass ratio of 1:1, treated by ultrasonic disperser for 30 minutes, and the amount is 0.6% of the mass of the gel material.

[0031] S2: draw a double-arrow type unit periodic array pattern by computer aided drawing, the unit geometric parameters are: the included angle between nodes is 45°, the unit length is 60 mm, and the waist width is 20 mm; then cut a double-arrow grid pattern on a 2205 duplex stainless steel plate with a thickness of 3 mm by using a precision laser cutting machine to obtain a plane grid plate, place the grid plate in a special mold for welding, apply pressure by a hydraulic machine to make the arrow part protrude in the thickness direction by 2 mm and the web part bend, bend a plurality of grid plates into an arc shape along the circumferential direction, arrange the arc-shaped grid plates closely to the outer surface of the concrete lining layer, use laser welding to connect the arc-shaped grid plates end to end into a cylindrical steel shell, the welds are arranged in a staggered manner with a length of 20 mm and an interval of 100 mm, and welding is performed to prepare a composite pipe containing a negative Poisson's ratio constraint layer; S3: spray modified epoxy resin adhesive on the outer surface of the composite pipe containing the negative Poisson's ratio constraint layer prepared in step S2, with a thickness of 1 mm, wait for the adhesive to dry, and perform fiber winding: start a multi-axis numerical control fiber winding machine, and wind the fiber bundle impregnated with epoxy resin on the outer surface of the pipe according to a specific order; the first layer: wind one layer of carbon fiber and basalt fiber hybrid bundle in the ±45° direction along the pipe axis, the second layer: wind one layer of glass fiber bundle in the 0° direction along the pipe axis, and the subsequent layers are alternately laid in the ±45° / 0° order until the designed thickness of 8 mm is reached; after completing each 2 mm thick layer, the pipe body is transferred into a 60°C environment for 2 hours to promote partial curing of the resin and prevent fiber slippage, and after the entire winding is completed, the pipe body is placed in an 80°C environment for post-curing for 8 hours to fully cure and crosslink the resin, thereby preparing a composite pipe containing a fiber reinforced composite layer; The continuous fiber bundle impregnated with epoxy resin comprises carbon fiber, glass fiber and basalt fiber.

[0032] S4: melt epoxy-based shape memory resin and chopped carbon fiber in a twin-screw extruder, and the chopped carbon fiber accounts for 5% of the total mass of the shape memory resin and the chopped carbon fiber; extrude a continuous strip with a thickness of 3 mm and a width of 50 mm, while slowly rotating the pipe body, spiral the molten polymer strip from one end and paste it on the surface of the fiber composite layer, and ensure that the strip uniformly covers the entire pipe body, and then heat and cure: start the infrared heater for staged heating, the first stage: heat to 70°C and keep for 1 hour; the second stage: heat to 120°C and keep for 3 hours; the third stage: naturally cool to room temperature; thereby preparing the concrete composite pipe of the present application.

[0033] Example 2 Reference to the preparation method of Example 1, but different in that: In step S1, the amount of short copper-plated steel fiber accounts for 1.5% of the volume of concrete; The composition and amount of the geopolymer slurry are: 1 part of siliceous and aluminous cementing material as a reference, 0.6 parts of alkaline activator solution, 1.5 parts of quartz sand, and 0.45 parts of water; Low-speed centrifugation: centrifugal acceleration 0.7g, rotation 2.5 minutes; medium-speed centrifugation: centrifugal acceleration 1.8g, rotation 2 minutes; high-speed centrifugation: centrifugal acceleration 7g, rotation 4 minutes; In steam curing, the temperature gradually increases from room temperature to 75℃, and is maintained for 4 hours; In step S2, the arrowhead part is raised by 1.5mm in the thickness direction; In step S3, the thickness of the modified epoxy resin adhesive is 0.8mm; In step S4, the amount of short carbon fiber accounts for 3% of the total mass of epoxy-based shape memory resin and short carbon fiber; Stage heating, first stage: heating to 65℃, maintaining for 1.5 hours; second stage: heating to 110℃, maintaining for 4 hours.

[0034] Example 3 Reference to the preparation method of Example 1, but different in that: In step S1, the amount of short copper-plated steel fiber accounts for 2.5% of the volume of concrete; The composition and amount of the geopolymer slurry are: 1 part of siliceous and aluminous cementing material as a reference, 0.4 parts of alkaline activator solution, 1.0 parts of quartz sand, and 0.3 parts of water; Low-speed centrifugation: centrifugal acceleration 0.9g, rotation 1.5 minutes; medium-speed centrifugation: centrifugal acceleration 2.2g, rotation 1 minute; high-speed centrifugation: centrifugal acceleration 9g, rotation 2 minutes; In steam curing, the temperature gradually increases from room temperature to 85℃, and is maintained for 3 hours; In step S2, the arrowhead part is raised by 2.5mm in the thickness direction; In step S3, the thickness of the modified epoxy resin adhesive is 1.2mm; In step S4, the amount of short carbon fiber accounts for 3%-8% of the total mass of epoxy-based shape memory resin and short carbon fiber; Stage heating, first stage: heating to 75℃, maintaining for 0.5 hours; second stage: heating to 130℃, maintaining for 2 hours.

[0035] Comparative Example 1 Reference to the preparation method of Example 1, but using ordinary oligomer concrete inner lining layer, without adding carbon nanotube dispersion liquid and copper-plated steel fiber. The remaining steps are the same.

[0036] Comparative Example 2 Reference to the preparation method of Example 1, but omit the negative Poisson's ratio constraint layer, using ordinary steel pipe as the constraint layer, without active lateral compression ability, directly bent into an arc and welded into a cylindrical steel shell, coated in the self-aware concrete lining layer outside. The remaining steps are the same.

[0037] Comparative Example 3 Reference to the preparation method of Example 1, but not winding the fiber reinforced composite layer only single fiber winding, only using glass fiber winding, winding thickness reaches the same design thickness as Example 1. The remaining steps are the same.

[0038] Comparative Example 4 Reference to the preparation method of Example 1, but omitting the intelligent protective outer layer composed of shape memory polymer, using a stable performance ordinary epoxy resin coating as the outermost protective layer. The remaining steps are the same.

[0039] Comparative Example 5 Prepare a traditional concrete composite pipe, mix cement, sand, gravel and water in a mass ratio of 1:1.5:3:0.5 to form a concrete mixture, pour into a steel mold with an inner diameter of 600 mm, and use a centrifugal molding machine to perform three-stage variable speed centrifugation according to Example 1. After centrifugation, a wet concrete pipe blank is obtained, and then standard curing is performed to obtain a traditional concrete pipe.

[0040] The comprehensive performance of the concrete composite pipes prepared in Examples 1-3 and Comparative Examples 1-5 was compared, Load capacity test: according to the standard ASTM C39 / C39M-24 "Standard Test Method for Compressive Strength of Cylindrical Concrete Specimens", the compressive strength test method was used for testing; Durability test: according to GB / T 50082-2024 "Standard Test Method for Long-Term Performance and Durability of Concrete", salt spray test was performed for 1000 hours, and the permeability coefficient was calculated by measuring the mass loss rate.

[0041] Self-healing ability test: using pre-cracking method, a crack with a width of 0.20 mm is introduced on the surface of the pipe body, then heated to 70°C for 1 hour, and the crack width change is measured. The healing rate calculation formula is: (initial crack width-healed crack width) / initial crack width x 100%.

[0042] The specific test comparison results are shown in Table 2, Figure 4 , Figure 5 as shown in Table 2. Table 2 Comparison of comprehensive performance of Examples 1-3 and Comparative Examples 1-5 From the above comparison results, in Comparative Example 1, ordinary concrete lining is used, and the compressive strength is low, which shows that the addition of carbon nanotubes and copper plated steel fibers may slightly enhance the strength of the concrete matrix through fiber bridging and improving the interface transition zone, thus resulting in no self-healing ability; in Comparative Example 2, the negative Poisson's ratio constraint layer is replaced with an ordinary steel pipe as the constraint layer, which does not have the active lateral compression ability, resulting in a sharp decrease in bearing capacity and no self-healing ability; in Comparative Example 3, the fiber-reinforced composite layer is mainly composed of high-strength fibers and a resin matrix, which is tightly wrapped outside the constraint layer through a winding process. Its high specific strength and modulus greatly compensate for the deficiency of the insufficient tensile capacity of concrete, and cooperates with the constraint layer to form an optimal stress system of "internal compression and external tension", thus using only a single fiber layer results in a sharp decrease in bearing capacity and no self-healing ability, and is insufficient to form an effective barrier, resulting in a significant deterioration of durability indicators; in Comparative Example 4, the intelligent protective outer layer composed of shape memory polymers is replaced with an ordinary epoxy resin coating with stable performance as the outermost protective layer, and the bearing capacity is comparable to the examples, but the healing rate is extremely low and the durability is poor, which proves the dominant position of the outer layer in self-healing and self-corrosion resistance; in Comparative Example 5, the bearing capacity is poor, completely without self-healing ability, and the durability is the worst, which highlights the many pain points of traditional concrete materials in monitoring, bearing and durability.

Claims

1. A concrete composite pipe, characterized in that, the composite pipe is composed of a self-sensing concrete inner layer, a negative Poisson's ratio constraint layer, a fiber-reinforced composite layer and an intelligent protective outer layer from inside to outside; the self-sensing concrete inner layer is obtained by mixing conductive fibers with geopolymer slurry and carbon nanotube dispersion liquid, realizing strain self-sensing and damage self-monitoring, the geopolymer slurry is composed of siliceous and aluminous cementing material, alkaline activator solution, quartz sand and water; the negative Poisson's ratio constraint layer uses a double-arrow steel metamaterial structure to improve the pipe carrying capacity and ductility, the surface of the constraint layer is sprayed with adhesive, and the pre-impregnated epoxy resin continuous fiber bundle is laid in a specific order, and the lateral extrusion is coated with a shape memory polymer outer layer; the fiber-reinforced composite layer uses hybrid fiber mesh to provide additional hoop constraint and protection against corrosion; the intelligent protective outer layer uses shape memory polymer composite material, which can realize self-repairing. 2.The concrete composite pipe of claim 1, characterized in that, the amount of the geopolymer slurry is: siliceous and aluminous cementing material 1 part as a reference, alkaline activator solution 0.4-0.6 parts, quartz sand 1.0-1.5 parts, and water 0.3-0.45 parts; the siliceous and aluminous cementing material is prepared by mixing I-grade fly ash and granulated blast furnace slag at a mass ratio of 1:1, and the alkaline activator solution is prepared by mixing 10 mol / L NaOH solution and water glass at a mass ratio of 1:

1. 3.The concrete composite pipe of claim 1, characterized in that, the carbon nanotube dispersion liquid is prepared by mixing multi-walled carbon nanotubes and polycarboxylate dispersant at a mass ratio of 1:1, ultrasonic treatment for 30 minutes, and the amount is 0.4%-0.8% of the mass of the siliceous and aluminous cementing material. 4.The concrete composite pipe of claim 1, characterized in that, the pre-impregnated epoxy resin continuous fiber bundle includes carbon fiber, glass fiber and basalt fiber.

5. A method of processing a concrete composite pipe according to any one of claims 1 to 4, characterized in that, The method comprises the following steps: S1: mixing and stirring the geopolymer slurry and the carbon nanotube dispersion liquid to obtain concrete, adding 1.5%-2.5% of the volume of the concrete of short copper-plated steel fibers, stirring in a high-speed mixer, quickly pouring the prepared concrete into a circular steel mold, starting a centrifugal forming machine, and performing three-stage variable-speed process centrifugation to obtain a concrete inner layer blank; then performing step-by-step curing to prepare a composite pipe containing a self-sensing concrete inner layer; S2: drawing a double-arrow unit periodic array pattern by computer-aided drawing, the unit geometric parameters are: a node angle of 45°, a unit length of 60 mm, and a waist width of 20 mm; then cutting a double-arrow grid pattern on a stainless steel plate using a precision laser cutting machine to obtain a planar grid plate, placing the grid plate in a special mold for welding to prepare a composite pipe containing a negative Poisson's ratio constraint layer. S3: Spraying a modified epoxy resin adhesive on the outer surface of the composite pipe containing the negative Poisson's ratio constraint layer prepared in step S2, waiting for the adhesive to dry, and performing fiber winding; after each 2 mm thick layer is completed, the pipe body is transferred to a 60℃ environment for 2 hours, and after the entire winding is completed, the pipe body is placed in an 80℃ environment for 8 hours of post-curing to prepare a composite pipe containing a fiber-reinforced composite layer; S4: Heating and melting the shape memory resin and chopped carbon fibers in a double screw extruder to extrude a continuous tape, with the chopped carbon fibers accounting for 3% to 8% of the total mass of the shape memory resin and chopped carbon fibers; while the pipe body is slowly rotating, the molten polymer tape is spirally wound and pasted on the surface of the fiber composite layer from one end, and the adjacent tapes are overlapped by half of the tape width during winding, and then heated and cured: start the infrared heater for stage heating to prepare a concrete composite pipe.

6. The processing method of claim 5, wherein the three-stage variable speed centrifugation in step S1 is specifically low-speed centrifugation: centrifugal acceleration of 0.7-0.9g, rotation for 1.5-2.5 minutes; medium-speed centrifugation: centrifugal acceleration of 1.8-2.2g, rotation for 1-2 minutes; high-speed centrifugation: centrifugal acceleration of 7-9g, rotation for 2-4 minutes.

7. The processing method of claim 5, wherein the step S1 ladder curing is specifically room temperature standing: placing the steel mold in room temperature for 1 hour to complete initial setting, steam curing: moving the steel mold into a steam curing pool, gradually increasing the temperature from room temperature to 75-85℃, and maintaining for 3-4 hours, demolding and wet curing: taking out the sample for demolding and placing it in a curing room with a relative humidity of more than 95% for 7 days of wet curing.

8. The processing method of claim 5, wherein the welding in step S2 is specifically performed by applying pressure through a hydraulic machine to make the arrowhead part protrude 1.5-2.5mm in the thickness direction and the web part to bend, bending multiple grid plates into an arc shape along the circumferential direction, arranging them tightly against the outer surface of the concrete inner lining layer, and using laser welding to connect the arc-shaped grid plates end to end into a cylindrical steel shell, with the welds being 20mm long and arranged 100mm apart.

9. The processing method of claim 5, wherein the fiber winding in step S3 is specifically performed in the following sequence: first layer: winding one layer of carbon fiber and basalt fiber hybrid bundles in the ±45° direction along the pipe axis, second layer: winding one layer of glass fiber bundles in the 0° direction along the pipe axis, and subsequent layers are alternately laid in the ±45° / 0° sequence to reach the designed thickness.

10. The processing method of claim 5, wherein the stage heating in step S4 is specifically performed in the following sequence: first stage: heating to 65-75℃ and maintaining for 0.5-1.5 hours; second stage: heating to 110-130℃ and maintaining for 2-4 hours; and third stage: naturally cooling to room temperature. ​ ​ ​ ​ ​

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