Composite material low-magnetism concrete slab with zero-magnetism space structure and construction method

Abstract

The invention relates to the technical field of civil engineering, in particular to a composite material low-magnetism concrete slab with a zero-magnetism space structure and a construction method, and provides a composite material low-magnetism concrete slab for civil engineering and a construction method. Comprising low-magnetism concrete, carbon fiber stress ribs, end anchoring structures, composite material stirrup ribs, low-magnetism concrete cushion blocks, plastic ribbons, wood formworks and formwork low-magnetism steel nails, and the low-magnetism concrete is made of a low-magnetism base material; the wood template is used for supporting and shaping the structure; the formwork low-magnetic steel nails are low-magnetic steel nails; according to the scheme, through effective combination of the composite material and the low-magnetism concrete, the problems that in a traditional zero-magnetism space structure, low-magnetism steel bars are adopted in a low-magnetism concrete structure, the low-magnetism steel bars are prone to magnetism reversion, and magnetism is difficult to control are well solved by means of non-magnetism, high strength and high durability of the composite material; the system construction method from material production, transportation, storage to construction is formed, non-magnetization packaging of the structure is completed, and the method is an ideal zero-magnetic space structure construction method.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering, and in particular to a construction technology of a composite material low-magnetic concrete slab with a zero-magnetic space structure used in civil engineering. Background Art

[0002] The composite low-magnetic concrete slab of the zero-magnetic space structure is a new type of low-magnetic concrete structure, which is composed of low-magnetic concrete, carbon fiber stress-bearing bars, end anchoring structure, composite stirrup bars, low-magnetic concrete pads, and plastic cable ties. The composite material has the characteristics of non-magnetic, lightweight, high strength and corrosion resistance. It can control the magnetism of the structure from the source and achieve long-term non-magnetic properties, solving the problem of easy anti-magnetism and difficult control of magnetism in traditional low-magnetic reinforced concrete structures, and breaking the monopoly of low-magnetic steel bars in the field of zero-magnetic space structure construction. Compared with low-magnetic steel bars, the cost is reduced by about 10%. The end anchoring structure can solve the problem of carbon fiber reinforcement anchorage failure in carbon fiber reinforced concrete structures under fire. Through engineering applications, a complete set of non-magnetic construction technology of raw material production-transportation-storage-construction has been formed to achieve non-magnetic packaging of the structure.

[0003] For example, the invention patent with publication number CN119663981A discloses a non-magnetic concrete frame structure with additional aluminum ribs and FRP bars and non-magnetic concrete. The disclosed structure uses FRP bars and low-magnetic concrete to achieve low structural magnetization. Additional aluminum ribs are used at the ends of the FRP bars to reduce the anchoring length of the FRP bars, and a low-magnetic concrete mix ratio is proposed to ensure the low magnetism of the concrete.

[0004] However, the additional aluminum rib FRP bar non-magnetic concrete frame structure and the aluminum additional ribs in the non-magnetic concrete are difficult to effectively bond with the FRP bars. Since the FRP bars have weak shear resistance, the FRP bars are easily damaged when the additional ribs are pressed using the crimping technology, resulting in the FRP bar concrete structure being unable to be used normally. In addition, there is no mention of magnetic control measures for the FRP bar concrete structure from material production-transportation-storage-construction, which can easily cause magnetic contamination of the material and thus fail to meet the magnetic requirements. Summary of the Invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a composite low-magnetic concrete slab and a construction method for a zero-magnetic space structure; the scheme of the present invention can achieve effective bonding between the composite sleeve at the end of the carbon fiber reinforcement and the carbon fiber reinforcement, and the industrialized production of the composite sleeve can improve the anchoring efficiency of the composite sleeve and the carbon fiber reinforcement, and can ensure that the carbon fiber reinforcement and concrete of the structure are reliably anchored under fire, forming a complete set of non-magnetic construction process of raw material production-transportation-storage-construction, preventing magnetic contamination of materials and structures during the construction process, and realizing non-magnetic packaging of the structure.

[0006] In order to achieve the above-mentioned purpose, the present invention provides a composite material low-magnetic concrete board for zero-magnetic space structure and a construction method, comprising low-magnetic concrete, carbon fiber stress reinforcement, end anchoring structure, composite material stirrup reinforcement, low-magnetic concrete pad, plastic cable tie, wooden formwork, and low-magnetic steel nails for supporting formwork, characterized in that the low-magnetic concrete is a concrete material, the carbon fiber stress reinforcement is arranged in the low-magnetic concrete and cooperates with the concrete to bear force; the end anchoring structure is arranged at the support of the carbon fiber reinforcement; the composite material stirrup reinforcement is arranged on the bottom reinforcement to support the upper reinforcement mesh; the low-magnetic concrete pad supports the distance between the reinforcement and the formwork to ensure the thickness of the reinforcement protective layer; the plastic cable tie is used to fix the carbon fiber reinforcement mesh and the stirrup reinforcement; the wooden formwork is used for structural support and shaping; and the low-magnetic steel nails for supporting the formwork are used to fix the formwork.

[0007] Furthermore, the low-magnetic concrete comprises cement, machine-made sand, crushed stone, and water-reducing agent, wherein the cement is white Portland cement or Type II Portland cement, and the residual magnetic intensity of the cement paste test block is not greater than 4.0nT; the machine-made sand and crushed stone are limestone or quartz stone, and the residual magnetic intensity is not greater than 2.5nT; the water-reducing agent is a small molecular chain polycarboxylic acid water-reducing agent, the water reduction rate is greater than 25%, and the residual magnetic intensity is not greater than 2.5nT; the concrete includes two strength grades, C30 and C40, and three residual magnetic intensity grades, 2.5nT, 5nT, and 10nT.

[0008] Furthermore, the carbon fiber stress-bearing reinforcement is a carbon fiber threaded reinforcement, the thread pitch is preferably 10 to 15 mm, and the thread depth is preferably ≥ 0.15 mm; the end is provided with a thread connected to the anchoring structure, and the thread depth is preferably 15 mm to 20 mm.

[0009] Furthermore, the end anchoring structure is arranged on the composite material stress-bearing reinforcement at the support. The anchoring structure adopts a composite material sleeve with a thickness of 2 mm and a length of 50 mm to 100 mm. Threads are set on both the inside and the outside. The thread depth is preferably 15 mm to 20 mm. The inner thread is connected to the carbon fiber reinforcement, and the outer thread is used to enhance its bonding strength with the concrete.

[0010] Furthermore, the composite material stirrup bar is made of glass fiber threaded bar and is prefabricated in a factory into a "J" shape.

[0011] Furthermore, the low magnetic concrete pad is made of low magnetic mortar and is processed into a "concave" shape in a mold. The radius of the "concave" shape matches the diameter of the carbon fiber rib and is preferably 2 mm larger than the diameter of the carbon fiber.

[0012] Furthermore, the plastic cable tie is used to tie the stress reinforcement and stirrup reinforcement instead of the steel wire.

[0013] Furthermore, the wooden template should be made of pine wood, which is not easily affected by moisture and deformed.

[0014] Furthermore, the formwork low-magnetic steel nails should preferably be made of low-magnetic steel, with a residual magnetic strength requirement of ≤5nT, and the surface should be coated with an anti-corrosion coating.

[0015] In order to achieve the above-mentioned object, the present invention provides a composite material low-magnetic concrete slab for a zero-magnetic space structure in civil engineering and a construction method thereof, which is characterized by comprising the following steps:

[0016] S1. Carbon fiber rebar preparation: Using a pultrusion and winding process, the pultrusion equipment is sprayed with an epoxy resin coating to prevent magnetic contamination. Multiple strands of resin-impregnated carbon fiber filaments are twisted into a threaded shape. The ends are then pressed into a die to create threads that match the anchor sleeve.

[0017] S2. Composite Sleeve Preparation: Using a pultrusion and winding process, a composite sleeve is formed in a die with internal and external threads. The internal threads match the threads at the ends of the carbon fiber ribs.

[0018] S3. Composite stirrup reinforcement preparation: Using resin transfer molding, fiber filaments are threaded into a closed mold and injected with epoxy resin. High pressure (0.5-1.0 MPa) is applied to the fiber preform, and after curing, a "J"-shaped stirrup reinforcement is formed.

[0019] S4. Transportation and Storage of Composite Materials: Carbon fiber reinforcements, composite sleeves, and composite stirrups must be packed and shipped in sealed plastic bags. During transportation, wooden blocks must be placed underneath to reduce friction with the truck. Loading and unloading must be performed using a shoulder pole beam and nylon bags. Upon arrival at the site, random inspections must be conducted on the composite materials, and they must meet the requirements before they can enter the site. For storage, separate low-magnetic storage areas must be designated, and mixing with steel components is strictly prohibited. Insulating rubber mats (thickness ≥ 5mm) or wooden pallets must be laid on the ground for easy access.

[0020] S5. Preparation of low-magnetic concrete: Low-magnetic concrete is produced at an on-site mixing station. A sieving machine is used to screen incoming aggregates to remove those with a residual magnetic strength greater than 2.5nT before mixing and pouring.

[0021] S6. Preparation of low magnetic concrete pads: Select low magnetic mortar, pour the mortar into a plastic mold, and form low magnetic concrete pads after curing;

[0022] S7. Formwork: Pine wood is preferred, and low-magnetic steel nails are used for connection. Rubber hammers are used during construction, and iron hammers are strictly prohibited.

[0023] S8. Carbon fiber reinforcement frame binding: First, arrange the bottom layer of carbon fiber reinforcement using plastic tie wraps. Solid ties are used at the edges of the slab, and jump ties are used in the middle of the slab. After the bottom layer of reinforcement mesh is tied, place low-magnetic concrete pads at the bottom of the reinforcement. These low-magnetic concrete pads are arranged in a 1mx1m grid in a plum blossom pattern, with adjacent pads staggered and arranged in a jump pattern. Arrange "J"-shaped composite stirrup bars, with the first row ≤800mm from the edge. Arrange them in a rectangular or plum blossom pattern, with a spacing of ≤1.0m between double-layer meshes. Tie them perpendicular to the bottom layer of carbon fiber reinforcement, avoiding direct contact with the formwork or padding. Tie the top layer of carbon fiber reinforcement using the same binding principles as the bottom layer of carbon fiber reinforcement to form the carbon fiber reinforcement frame.

[0024] S9. Concrete pouring: The vibrator should use a non-metallic shell (such as a nylon rod head) to avoid magnetic contamination of the concrete caused by the steel pipe wall. The transport tank truck should be reversed for ≥20 seconds before unloading to prevent iron filings from settling. The free fall height during pouring should be ≤1m. If the height is too high, a nylon chute should be used for buffering. The depth of the vibrator inserted into the lower layer should be ≥8cm, and the distance between vibration points should be ≤30cm.

[0025] Compared with the prior art, the composite material low-magnetic concrete slab and construction method for the zero-magnetic space structure for civil engineering provided by the present invention have the following beneficial effects:

[0026] 1. The present invention designs a composite anchoring sleeve and arranges the sleeve on the carbon fiber reinforcement at the support. The composite anchoring sleeve is connected to the carbon fiber reinforcement through an internal thread. The connection node is reliable and the thread length can be adjusted to meet different anchoring strength requirements. This structure remains at room temperature or has a small temperature rise under fire, providing the carbon fiber reinforcement with effective end anchoring strength with concrete under fire.

[0027] 2. The present invention proposes a complete set of non-magnetic construction processes for raw material production, transportation, storage and construction, thereby effectively preventing magnetic contamination of materials and structures during the entire construction process and realizing non-magnetic packaging of the structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0029] Figure 1 Schematic diagram of a composite material low magnetic concrete slab with a zero magnetic space structure according to the present invention;

[0030] Figure 2 Schematic diagram of composite anchor sleeve;

[0031] Figure 3 Flowchart of the construction method of composite material low magnetic concrete slab in the present invention.

[0032] In the figure: 1. Low-magnetic concrete; 2. Carbon fiber reinforcement; 3. Composite material sleeve; 4. Composite material stirrup reinforcement; 5. Low-magnetic concrete pad. DETAILED DESCRIPTION

[0033] In order to make the technical means, creative features, objectives and effects achieved by the present invention easier to understand, the present invention is further described below with reference to specific illustrations.

[0034] See also Figure 1 and Figure 2 , which shows an example of the composition of a composite material low-magnetic concrete slab for a zero-magnetic space structure in civil engineering provided by the present invention.

[0035] Based on the diagram, the composite low-magnetic concrete slab of the zero-magnetic space structure used in civil engineering is mainly composed of low-magnetic concrete, CFRP threaded bars, end anchoring structures, composite stirrup bars, low-magnetic concrete pads, and plastic cable ties.

[0036] The present invention further provides a corresponding preparation scheme for the composite material low-magnetic concrete slab with a zero-magnetic space structure used in civil engineering.

[0037] See also Figure 3 The method for constructing a composite material low-magnetic concrete slab for a zero-magnetic space structure in civil engineering provided by the present invention comprises the following steps:

[0038] S1. CFRP bar preparation: Stranded carbon fiber tows are impregnated with resin, extruded and wound at a certain tension using a pultrusion machine to form a threaded surface. The ends are pressed into threads that match the anchor sleeve using a pressing die.

[0039] S2. Composite Sleeve Preparation: Using a pultrusion and winding process, a composite sleeve is formed in a die with internal and external threads. The internal threads match the threads at the ends of the carbon fiber ribs.

[0040] S3. Composite stirrup reinforcement preparation: Using resin transfer molding, fiber filaments are threaded into a closed mold, and epoxy resin is injected. High pressure (0.8 MPa) is applied to the fiber preform, and after curing, a "J"-shaped stirrup reinforcement is formed.

[0041] S4. Transportation and Storage of Composite Materials: Carbon fiber reinforcements, composite sleeves, and composite stirrups are packaged and shipped in sealed plastic bags. During transportation, wooden blocks are placed underneath to reduce friction with the truck. Loading and unloading is performed using a shoulder pole beam and nylon bags. Upon arrival at the site, random inspections are conducted on the composite materials, and only those meeting the requirements can be admitted. For storage, separate low-magnetic storage areas are designated, and mixing with steel components is strictly prohibited. Wooden pallets are laid on the ground for easy access.

[0042] S5. Preparation of low-magnetic concrete: Low-magnetic concrete is produced at an on-site mixing station. A sieving machine is used to screen incoming aggregates to remove those with a residual magnetic strength greater than 2.5nT before mixing and pouring.

[0043] S6. Preparation of low magnetic concrete pads: Select low magnetic mortar, pour the mortar into a plastic mold, and form low magnetic concrete pads after curing;

[0044] S7. Formwork: Use pine wood, connect with low-magnetic steel nails, and use a rubber hammer during construction;

[0045] S8. Carbon fiber reinforcement frame binding: First, arrange the bottom layer of carbon fiber reinforcement using plastic tie wraps. Solid ties are used at the edges of the slab, and jump ties are used in the middle. After the bottom layer of reinforcement mesh is tied, place low-magnetic concrete pads at the bottom of the reinforcement. These low-magnetic concrete pads are arranged in a 1mx1m grid in a plum blossom pattern, with adjacent pads staggered and arranged in a jump pattern. Arrange "J"-shaped composite stirrup bars, starting 500mm from the edge. Arrange them in a rectangular or plum blossom pattern, with double-layer meshes spaced 1.0m apart. Tie them perpendicularly to the bottom layer of carbon fiber reinforcement, preventing direct contact with the formwork or padding. Tie the top layer of carbon fiber reinforcement using the same binding principles as the bottom layer of carbon fiber reinforcement to form the carbon fiber reinforcement frame.

[0046] S9. Concrete pouring: Use a non-metallic shell (such as a nylon rod head) for the vibrator to avoid magnetic contamination of the concrete caused by the steel pipe wall. The transport tank truck should be reversed for 20 seconds before unloading to prevent iron filings from settling. The free fall height during pouring should be ≤1m. The vibrator should be inserted into the lower layer to a depth of 16cm, with a vibration point spacing of 30cm. Try to avoid touching the carbon fiber reinforcement during vibration.

[0047] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are intended to illustrate the present invention only and are not intended to limit the scope of the invention. The experimental methods in the following examples where specific conditions are not specified are generally measured in accordance with national standards. If there are no corresponding national standards, then the methods are carried out in accordance with general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0048] Unless otherwise defined or indicated, all professional and scientific terms used herein have the same meaning as those familiar to those skilled in the art. In addition, any methods and materials similar or equivalent to those described herein can be applied to the methods of the present invention.

[0049] Example 1

[0050] In this example, a composite low-magnetic concrete slab made of zero-magnetic space structure for civil engineering was prepared by the following steps. The slab was 200 mm thick, with 8 mm diameter carbon fiber reinforcements arranged in two layers in both directions with a spacing of 100 mm and a protective layer thickness of 15 mm:

[0051] S1: Preparation of CFRP reinforcement: 48K large-tow carbon fiber filaments are used to produce 8mm diameter CFRP threaded reinforcement through pultrusion and winding process. The thread pitch is 15mm and the thread depth is 0.17mm. The end is provided with a thread connecting with the anchor structure. The thread depth is preferably 15mm and the thread length is 100mm.

[0052] S2: Preparation of composite sleeve: Glass fiber yarn is used, and a pultrusion winding molding process is adopted to press it into a 50mm long sleeve with inner and outer threads in a pressing mold. The outer thread depth is 15mm, the inner thread depth is 15mm, and the length is 50mm. The anchoring effect of the composite sleeve is determined by concrete pull-out specimens. Five composite sleeve carbon fiber reinforced concrete pull-out specimens are made respectively. The pull-out performance is shown in the following table. Assuming that the fire resistance limit of the structure is 1h, according to the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials" (GB50608-2020), the carbon fiber reinforcement at the bottom of the plate rises by 442°C when the fire resistance limit is 1h, and the composite sleeve anchoring sleeve at the support rises by 5°C (still at room temperature). By consulting the literature, the strength of the carbon fiber reinforcement at this temperature is 373MPa. To be conservative, the anchoring strength of the composite sleeve is taken as the minimum value of 583MPa>373MPa. Therefore, the composite anchoring sleeve can ensure reliable anchoring of the carbon fiber reinforcement under fire.

[0053]

[0054] S3: Composite stirrup preparation: Using resin transfer molding, fiber filaments are inserted into a closed mold and injected with epoxy resin. High pressure (0.8 MPa) is then applied to the fiber preform to form a "J"-shaped stirrup after curing. The stirrup has a height of 154 mm and a support section length of 200 mm.

[0055] S4: Transportation and storage of composite materials: Carbon fiber reinforcement, composite sleeves, and composite stirrup reinforcements shall be marked separately and packed in sealed plastic bags for shipment. During transportation, wooden blocks shall be placed underneath to reduce friction with the truck. Loading and unloading shall be carried out using shoulder pole beams + nylon bags. Composite materials shall be randomly inspected upon arrival at the site, with no less than 5 pieces tested per batch. The inspection requirements are that the residual magnetic intensity shall be less than 1nT, the tensile strength shall be ≥1800MPa, and the elastic modulus shall be ≥170GPa. Only after meeting the requirements can they be brought into the site. During storage, independent low-magnetic storage areas shall be designated. Mixing with steel components is strictly prohibited. Wooden pallets shall be laid on the ground for easy access.

[0056] S5: Preparation of low magnetic concrete: Low magnetic concrete is produced at the on-site mixing station. A screening machine is used to screen the incoming aggregates to remove aggregates with a residual magnetic intensity greater than 2.5nT before mixing and pouring.

[0057] S6. Preparation of low-magnetic concrete pads: Low-magnetic mortar was selected and poured into a plastic mold. After curing, a concave-shaped low-magnetic concrete pad was formed. The radius of the concave shape was 12 mm.

[0058] S7. Formwork: Use pine wood, connect with low-magnetic steel nails, use a rubber hammer during construction, and the formwork height is 210mm;

[0059] S8. Carbon fiber reinforcement frame binding: Arrange carbon fiber reinforcement in two layers, bidirectionally, with spacing of 100mm. First, lay the bottom layer of carbon fiber reinforcement and secure with plastic tie wraps. Solid ties are used at the edges of the slab and jump ties are used in the middle. After the bottom layer of reinforcement mesh is secured, place low-magnetic concrete pads at the bottom of the reinforcement. These low-magnetic concrete pads are arranged in a 1mx1m grid in a plum blossom pattern, with adjacent pads staggered and arranged in a jump pattern. Lay out "J"-shaped composite stirrup bars, with the first row starting 500mm from the edge. Arrange them in a rectangular or plum blossom pattern, with a spacing of 1.0m between the two layers of mesh. Tie them perpendicularly to the lower layer of carbon fiber reinforcement, avoiding direct contact with the formwork or padding. Tie the top layer of carbon fiber reinforcement using the same binding principles as the bottom layer, forming a carbon fiber reinforcement frame. If steel components are interspersed within the construction structure, cover them with plastic film to prevent magnetic contamination from scratches.

[0060] S9. Concrete pouring: Use a nylon rod head for the vibrator, reverse it for 20 seconds before unloading the transport tanker, and the free fall height during pouring should be ≤1m. The vibrator should be inserted into the lower layer to a depth of 16cm, and the vibration point spacing should be 30cm. Try to avoid touching the carbon fiber reinforcement during vibration.

[0061] In this example, a low-magnetic concrete structure is formed by combining composite materials and low-magnetic concrete. The structure has a double-layer, bidirectional arrangement of 8mm diameter carbon fiber reinforcements and a protective layer thickness of 15mm. By utilizing the non-magnetic, high-strength and high-durability properties of composite materials, it can better solve the problem that low-magnetic reinforcements in low-magnetic concrete structures using low-magnetic reinforcements in traditional zero-magnetic space structures are prone to anti-magnetism and difficult to control magnetism. The structural magnetism problem is solved from the root of the material, and a systematic construction method is proposed, which forms from material production, transportation, storage to construction, and completes the non-magnetic packaging of the structure.

[0062] Example 2

[0063] In this example, a composite low-magnetic concrete slab of zero-magnetic space structure for civil engineering was prepared by the following steps. The slab was 200 mm thick, with 10 mm diameter carbon fiber reinforcements arranged in two layers in both directions with a spacing of 150 mm and a protective layer thickness of 15 mm:

[0064] S1: Preparation of CFRP reinforcement: 48K large-tow carbon fiber filaments are used to produce 8mm diameter CFRP threaded reinforcement through pultrusion and winding process. The thread pitch is 15mm and the thread depth is 0.3mm. The end is provided with a thread connecting with the anchor structure. The thread depth is preferably 20mm and the thread length is 100mm.

[0065] S2: Preparation of composite sleeve: Glass fiber yarn is used, and a pultrusion winding molding process is adopted to press it into a 50mm long sleeve with inner and outer threads in a pressing mold. The outer thread depth is 15mm, the inner thread depth is 20mm, and the length is 50mm. The anchoring effect of the composite sleeve is determined by concrete pull-out specimens. Five composite sleeve carbon fiber reinforced concrete pull-out specimens are made respectively. The pull-out performance is shown in the following table. Assuming that the fire resistance limit of the structure is 1h, according to the "Technical Standard for Engineering Application of Fiber Reinforced Composite Materials" (GB50608-2020), the carbon fiber reinforcement at the bottom of the plate rises by 403℃ when the fire resistance limit is 1h. The composite sleeve anchoring sleeve at the support (beam size 400mmx600mm, composite sleeve placed in the center of the beam) rises by 5℃ (still at room temperature). According to the literature, the strength of the carbon fiber reinforcement at this temperature is 389MPa. To be conservative, the anchoring strength of the composite sleeve is taken as the minimum value of 628MPa>389MPa. Therefore, the composite anchoring sleeve can ensure reliable anchoring of the carbon fiber reinforcement under fire.

[0066]

[0067] S3: Preparation of composite stirrups: Using resin transfer molding, fiber filaments are inserted into a closed mold and injected with epoxy resin. High pressure (0.8 MPa) is then applied to the fiber preform to form a "J"-shaped stirrup after curing. The stirrup has a height of 150 mm and a support section length of 200 mm.

[0068] S4: Transportation and storage of composite materials: Carbon fiber reinforcement, composite sleeves, and composite stirrup reinforcements shall be marked separately and packed in sealed plastic bags for shipment. During transportation, wooden blocks shall be placed underneath to reduce friction with the truck. Loading and unloading shall be carried out using shoulder pole beams + nylon bags. Composite materials shall be randomly inspected upon arrival at the site, with no less than 5 pieces tested per batch. The inspection requirements are that the residual magnetic intensity shall be less than 1nT, the tensile strength shall be ≥1800MPa, and the elastic modulus shall be ≥170GPa. Only after meeting the requirements can they be brought into the site. During storage, independent low-magnetic storage areas shall be designated. Mixing with steel components is strictly prohibited. Wooden pallets shall be laid on the ground for easy access.

[0069] S5: Preparation of low magnetic concrete: Low magnetic concrete is produced at the on-site mixing station. A screening machine is used to screen the incoming aggregates to remove aggregates with a residual magnetic intensity greater than 2.5nT before mixing and pouring.

[0070] S6. Preparation of low-magnetic concrete pads: Low-magnetic mortar was selected and poured into a plastic mold. After curing, a concave-shaped low-magnetic concrete pad was formed. The radius of the concave shape was 12 mm.

[0071] S7. Formwork: Use pine wood, connect with low-magnetic steel nails, use a rubber hammer during construction, and the formwork height is 210mm;

[0072] S8. Carbon fiber reinforcement frame binding: Arrange carbon fiber reinforcement in two layers, bidirectionally, with spacing of 150mm. First, lay the bottom layer of carbon fiber reinforcement and secure with plastic tie wraps. Solid ties are used at the edges of the slab, and jump ties are used in the middle of the slab. After the bottom layer of reinforcement mesh is secured, place low-magnetic concrete pads at the bottom of the reinforcement. These low-magnetic concrete pads are arranged in a 1mx1m grid in a plum blossom pattern, with adjacent pads staggered and arranged in a jump pattern. Arrange "J"-shaped composite stirrup bars, with the first row starting 500mm from the edge. Arrange them in a rectangular or plum blossom pattern, with a spacing of 1.0m between the two layers of mesh. Tie them perpendicularly to the lower layer of carbon fiber reinforcement, avoiding direct contact with the formwork or padding. Tie the top layer of carbon fiber reinforcement using the same binding principles as the bottom layer, forming a carbon fiber reinforcement frame. If steel components are interspersed within the construction structure, cover them with plastic film to prevent magnetic contamination from scratches.

[0073] S9. Concrete pouring: Use a nylon rod head for the vibrator, reverse it for 20 seconds before unloading the transport tanker, and the free fall height during pouring should be ≤1m. The vibrator should be inserted into the lower layer to a depth of 16cm, and the vibration point spacing should be 30cm. Try to avoid touching the carbon fiber reinforcement during vibration.

[0074] In this example, a low-magnetic concrete structure is formed by combining composite materials and low-magnetic concrete. The structure has a double-layer, bidirectional arrangement of 10mm diameter carbon fiber reinforcements and a protective layer thickness of 15mm. By utilizing the non-magnetic, high-strength and high-durability properties of composite materials, it can better solve the problem that low-magnetic reinforcements in low-magnetic concrete structures using low-magnetic reinforcements in traditional zero-magnetic space structures are prone to anti-magnetism and difficult to control magnetism. The structural magnetism problem is solved from the root of the material, and a systematic construction method is proposed, which forms from material production, transportation, storage to construction, and completes the non-magnetic packaging of the structure.

[0075] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the foregoing embodiments. The foregoing embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention. Such changes and modifications are intended to fall within the scope of the present invention. The scope of protection claimed in the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite material low-magnetic concrete slab with a zero-magnetic space structure for civil engineering and a construction method thereof, wherein the composite material low-magnetic concrete slab comprises low-magnetic concrete, carbon fiber stress reinforcement, end anchoring structure, composite material stirrup reinforcement, low-magnetic concrete pad, plastic cable tie, wooden formwork, and low-magnetic steel nails for supporting formwork, characterized in that: The low-magnetic concrete is a concrete material, and the carbon fiber stress-bearing reinforcement is arranged in the low-magnetic concrete to cooperate with the concrete in bearing force; the end anchoring structure is arranged on the carbon fiber reinforcement at the support; the composite material stirrup reinforcement is arranged on the bottom reinforcement to support the upper reinforcement mesh; the low-magnetic concrete pad supports the distance between the reinforcement and the formwork to ensure the thickness of the reinforcement protective layer; the plastic cable tie is used to fix the carbon fiber reinforcement mesh and the stirrup reinforcement; the wooden formwork is used for structural support and shaping; the low-magnetic steel nails for supporting the formwork are used to fix the formwork.

2. The low magnetic concrete according to claim 1, characterized in that The ingredients include cement, machine-made sand, crushed stone, and water-reducing agent, among which the cement is white Portland cement or Type II Portland cement, and the residual magnetic intensity of the cement paste test block is not more than 4.0nT; the machine-made sand and crushed stone are limestone or quartz stone, and the residual magnetic intensity is not more than 2.5nT; the water-reducing agent is a small molecular chain polycarboxylic acid water-reducing agent, with a water reduction rate greater than 25% and a residual magnetic intensity not more than 2.5nT; the concrete includes two strength grades, C30 and C40, and three residual magnetic intensity grades, 2.5nT, 5nT, and 10nT.

3. The carbon fiber reinforcement according to claim 1, characterized in that: The carbon fiber reinforcement should be in the form of threaded reinforcement, the thread pitch should be 10-15mm, and the thread depth should be ≥0.15mm to provide reliable bonding between the carbon fiber reinforcement and the concrete; the end should be provided with a thread connecting with the anchoring structure, and the thread depth should be 15mm-20mm to ensure reliable anchoring of the carbon fiber reinforcement and concrete in the structure under fire.

4. The end anchoring structure according to claim 1, characterized in that: The composite material stress-bearing reinforcement is set at the support, and the anchoring structure adopts a composite material sleeve with a thickness of 2mm and a length of 50mm to 100mm. Threads are set on both the inside and outside, and the thread depth is preferably 15mm to 20mm. The inner thread is connected to the carbon fiber reinforcement, and the outer thread is used to enhance its bonding strength with the concrete.

5. The composite stirrup according to claim 1, characterized in that: Glass fiber threaded bars are selected and prefabricated in the factory into a "J" shape.

6. The low magnetic concrete spacer according to claim 1, characterized in that: The material is low-magnetic mortar, which is processed into a "concave" shape in the mold. The radius of the "concave" shape matches the diameter of the carbon fiber rib and should be 2mm larger than the diameter of the carbon fiber.

7. The plastic cable tie according to claim 1, characterized in that: Plastic cable ties are used instead of steel wire to tie the stress reinforcement and stirrup reinforcement.

8. The wooden formwork according to claim 1, characterized in that: The material should be pine wood, which is not easily affected by moisture and deformed.

9. The formwork low-magnetic steel nail according to claim 1, characterized in that: Low magnetic steel should be used, the residual magnetic strength should be ≤5nT, and the surface should be coated with anti-corrosion coating. A composite material low magnetic concrete slab for a zero magnetic space structure in civil engineering and a construction method thereof, characterized in that: The following steps are involved: S1. Carbon fiber rebar preparation: Using a pultrusion and winding process, the pultrusion equipment is sprayed with an epoxy resin coating to prevent magnetic contamination. Multiple strands of resin-impregnated carbon fiber filaments are twisted into a threaded shape. The ends are then pressed into a die to create threads that match the anchor sleeve. S2. Composite Sleeve Preparation: Using a pultrusion and winding process, a composite sleeve is formed in a die with internal and external threads. The internal threads match the threads at the ends of the carbon fiber ribs. S3. Composite stirrup reinforcement preparation: Using resin transfer molding, fiber filaments are threaded into a closed mold and injected with epoxy resin. High pressure (0.5-1.0 MPa) is applied to the fiber preform, and after curing, a "J"-shaped stirrup reinforcement is formed. S4. Transportation and Storage of Composite Materials: Carbon fiber reinforcements, composite sleeves, and composite stirrups must be packed and shipped in sealed plastic bags. During transportation, wooden blocks must be placed underneath to reduce friction with the truck. Loading and unloading must be performed using a shoulder pole beam and nylon bags. Upon arrival at the site, random inspections must be conducted on the composite materials, and they must meet the requirements before they can enter the site. For storage, separate low-magnetic storage areas must be designated, and mixing with steel components is strictly prohibited. Insulating rubber mats (thickness ≥ 5mm) or wooden pallets must be laid on the ground for easy access. S5. Preparation of low-magnetic concrete: Low-magnetic concrete is produced at an on-site mixing station. A sieving machine is used to screen incoming aggregates to remove those with a residual magnetic strength greater than 2.5nT before mixing and pouring. S6. Preparation of low magnetic concrete pads: Select low magnetic mortar, pour the mortar into a plastic mold, and form low magnetic concrete pads after curing; S7. Formwork: Pine wood is preferred, and low-magnetic steel bars are used for connection. Rubber hammers are used during construction, and iron hammers are strictly prohibited. S8. Carbon fiber reinforcement frame binding: First, arrange the bottom layer of carbon fiber reinforcement using plastic tie wraps. Solid ties are used at the edges of the slab, and jump ties are used in the middle. After the bottom layer of reinforcement mesh is tied, place low-magnetic concrete pads at the bottom of the reinforcement. These low-magnetic concrete pads are arranged in a 1mx1m grid in a plum blossom pattern, with adjacent pads staggered and arranged in a jump pattern. Arrange "J"-shaped composite stirrup bars, with the first row ≤800mm from the edge. Arrange them in a rectangular or plum blossom pattern, with a spacing of ≤1.0m between double-layer meshes. Tie them perpendicular to the bottom layer of carbon fiber reinforcement, avoiding direct contact with the formwork or padding. Tie the top layer of carbon fiber reinforcement using the same binding principles as the bottom layer of carbon fiber reinforcement to form the carbon fiber reinforcement frame. S9. Concrete pouring: The vibrator should use a non-metallic shell (such as a nylon rod head) to avoid magnetic contamination of the concrete caused by the steel pipe wall. The transport tank truck should be reversed for ≥20 seconds before unloading to prevent iron filings from settling. The free fall height during pouring should be ≤1m. If the height is too high, a nylon chute should be used for buffering. The depth of the vibrator inserted into the lower layer should be ≥8cm, and the distance between vibration points should be ≤30cm.

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