Hybrid FRP Composite Reinforcing Bar

Abstract

The present invention relates to a hybrid FRP composite reinforcing bar for concrete structures. The composite reinforcing bar according to the present invention comprises a central core in which a plurality of continuous carbon fibers are arranged in the longitudinal direction, a reinforcing layer in which basalt fibers are wound or laminated at different orientation angles surrounding the outer circumference of the central core, a resin matrix that integrates the carbon fibers and the basalt fibers, and a surface irregularity structure including spiral ribs or longitudinal protrusions to improve adhesion to concrete. The carbon fibers improve axial tensile strength and elastic modulus, and the basalt fibers improve transverse restraint, impact resistance, chemical resistance, and protection performance of the central core. Furthermore, the required structural performance and economic efficiency can be secured by adjusting the arrangement ratio of carbon fibers and basalt fibers and the winding angle of the basalt fibers. The composite reinforcing bar of the present invention can be manufactured by a process of forming a central core by impregnating carbon fibers with resin and pultrusion, filament winding basalt fibers around the outer circumference, forming a surface irregularity structure, and then curing and cutting. Accordingly, it offers superior lightness, corrosion resistance, and durability compared to conventional metal reinforcing bars, and can improve tensile performance, crack inhibition, and concrete adhesion performance compared to general single-fiber FRP reinforcing bars.

Description

Technology Field

[0001] The present invention relates to a structural reinforcing bar using fiber reinforced polymer (FRP), and more specifically, to a hybrid FRP composite reinforcing bar having a multilayer structure in which basalt fiber and carbon fiber are compositely arranged, and a method for manufacturing the same.

[0002] More specifically, the invention relates to a hybrid FRP composite reinforcing bar and a method for manufacturing the same, which can simultaneously secure high tensile strength, excellent corrosion resistance, excellent fatigue performance, high concrete adhesion, and long-term durability as a composite reinforcing bar to replace reinforcing bars applied to concrete structures. Background Technology

[0004] Reinforced concrete structures are used in various fields, including buildings, bridges, tunnels, ports, and marine structures.

[0005] However, ordinary rebar is easily corroded by chlorides, seawater, de-icing agents, etc., which causes concrete cracking, peeling of the coating, and a decrease in the durability of the structure.

[0006] To address these issues, FRP reinforcing bars are being widely researched recently. FRP reinforcing bars are generally manufactured using glass fiber reinforced polymer (GFRP), carbon fiber reinforced polymer (CFRP), aramid fiber reinforced polymer (AFRP), and basalt fiber reinforced polymer (BFRP). Among these, basalt fiber is produced by melting natural basalt, making it highly eco-friendly. It also possesses advantages such as high heat resistance, excellent chemical resistance, excellent alkali resistance, and a relatively low cost. On the other hand, while carbon fiber has very high elastic modulus and tensile strength, it is expensive to manufacture and highly brittle.

[0007] Therefore, although hybrid FRPs combining two or more types of fibers are currently being researched, most existing technologies remain at the level of simply mixing fibers or laminating them in the same direction, and there is a lack of technology capable of simultaneously improving adhesion to concrete, enhancing fatigue performance, suppressing cracking, and ensuring economic feasibility. Prior art literature

[0009] (Patent Document 0001) KR 10-2554753 B1 (Registration Date July 07, 2023)(Patent Document 0002) KR 10-0709292 B1 (Registration Date April 12, 2007) The problem to be solved

[0010] The objective of the present invention is to provide a hybrid FRP composite reinforcing bar that simultaneously improves economic efficiency and structural performance by optimally arranging basalt fibers and carbon fibers according to their respective roles.

[0011] In addition, it improves corrosion resistance and fatigue performance while enhancing adhesion to concrete.

[0012] In addition, it improves productivity through a manufacturing process that combines pultrusion and filament winding. means of solving the problem

[0014] To achieve the above objective, the hybrid FRP composite reinforcing bar of the present invention comprises the following composition.

[0015] The core secures high tensile strength and elastic modulus by arranging multiple continuous carbon fiber bundles axially.

[0016] The intermediate reinforcement layer improves shear resistance and fatigue performance by winding basalt fibers in a spiral or cross-oriented manner.

[0017] The outer layer forms a protective layer using basalt fibers and thermosetting resin to improve alkali resistance and corrosion resistance.

[0018] The surface rib layer forms a spiral rib or protrusion structure to increase adhesion strength with concrete. Epoxy resin, vinyl ester resin, or polyurethane-based resin may be used as the resin.

[0019] The manufacturing method involves forming a core using a pultrusion process, winding basalt fibers around the outer surface through a filament winding process, and finally curing the material. Effects of the invention

[0021] According to the present invention, the following effects can be obtained.

[0022] Higher tensile strength than conventional BFRP can be secured through the carbon fiber core layer.

[0023] Manufacturing costs can be reduced compared to CFRP by minimizing the use of expensive carbon fiber and predominantly utilizing basalt fiber. Since it does not corrode like rebar, long-term durability is enhanced in marine structures, ports, bridges, tunnels, and the like.

[0024] The spiral orientation structure of basalt fibers effectively distributes repetitive loads, reducing crack formation.

[0025] The double rib structure and spiral outer layer improve adhesion strength with concrete, thereby increasing pull-out resistance. The outer layer inhibits the penetration of alkali and moisture, reducing the deterioration of fibers and resin.

[0026] It can be applied to shapes similar to existing rebar, offering excellent on-site applicability, and allows for construction without the need for separate special equipment. Brief explanation of the drawing

[0028] FIG. 1 is an overall perspective view of a composite reinforcing bar according to the present invention. Figure 2 is a cross-sectional view showing the cross-sectional structure of a composite reinforcing bar. Figure 3 is an enlarged cross-sectional view showing the laminated structure of a core carbon fiber layer and a basalt fiber reinforcement layer. Figure 4 is a schematic diagram showing the helical orientation structure of basalt fibers. FIG. 5 is a perspective view showing the surface rib shape of a composite reinforcing bar. Figure 6 is a process diagram showing a manufacturing process using pultrusion and filament winding. FIG. 7 is a schematic diagram showing the state in which the composite reinforcing bar of the present invention is embedded inside concrete. FIG. 8 is a conceptual diagram comparing the bond performance and tensile behavior of conventional reinforcing bars and the composite reinforcing bars of the present invention. Specific details for implementing the invention

[0029] Referring to FIGS. 1 and 2, the composite reinforcing bar (100) comprises a carbon fiber core (110), a basalt fiber layer (120), a resin layer (130), and an outer layer (140) having a spiral rib and / or protrusion structure (150).

[0030] The carbon fiber core (110) is positioned at the center of the entire cross-section and is oriented continuously in the axial direction. The carbon fibers in the carbon fiber core can be 12K or 24K Carbon Tow. The diameter is arranged to form a central core of about 2 to 8 mm.

[0031] The volume ratio of carbon fiber is preferably in the range of 10 to 40% of the total volume of the composite reinforcement. If this range is exceeded, economic efficiency decreases or it becomes difficult to secure sufficient stiffness.

[0032] The basalt fiber layer (120) is laminated to wrap around the outer surface of the center. The basalt fibers of the basalt fiber layer are laminated in multiple layers on the outer surface of the carbon fiber.

[0033] Shear strength and fatigue strength are increased by spiral winding. The orientation angle can be any one of ±30°, ±45°, or ±60°.

[0034] Since the ±30° winding layer arranges fibers nearly parallel to the axial direction, it offers high load transfer efficiency, resulting in increased axial tensile strength, increased elastic modulus, and reduced long-term deflection. Consequently, it can effectively share the axial load with the carbon fiber core.

[0035] The ±45° coil layer is the standard orientation most commonly used in composites, and it can enhance effects such as shear stress distribution, increased torsional resistance, extended fatigue life under repeated loading, and suppression of delamination.

[0036] Although the ±60° coil layer has slightly reduced axial performance, it has a greater lateral reinforcement effect, which increases the restraining force against concrete expansion pressure. This allows for the absorption of external shocks, suppression of crack propagation, protection of the carbon fiber core, and improved adhesion stability with concrete.

[0037] The basalt fiber layer may consist of a coil layer having a single orientation angle, but it may also be formed of multiple coil layers having different orientation angles.

[0038] As described above, the ±30° coil layer improves axial tensile strength and elastic modulus, the ±45° coil layer improves shear stress distribution and fatigue resistance, and the ±60° coil layer improves transverse restraint, impact resistance, and crack suppression effects. Therefore, by stacking coil layers with different orientation angles in this way, the overall structural performance of the composite reinforcement against axial load, shear load, and cyclic load can be improved.

[0039] Therefore, a plurality of coiled layers are formed of two or more basalt fiber layers having different orientation angles, and may be stacked including at least two of ±30°, ±45°, and ±60° orientation angles.

[0040] When the total volume of the reinforcing fibers is set to 100, the volume ratio of the carbon fiber layer to the basalt fiber layer can be set to a range of 15:85 to 45:55.

[0041] Preferably, the volume ratio of carbon fibers to basalt fibers is 20:80 to 40:60, and more preferably 25:75 to 35:65.

[0042] In one embodiment, the carbon fiber core (110) may be formed to occupy 15% to 30% of the total cross-sectional area of ​​the composite reinforcing bar, and the basalt fiber layer (120) may be formed to occupy 35% to 55% of the total cross-sectional area of ​​the composite reinforcing bar. In this case, a resin layer (130), an outer layer (140), a rib layer (150), and longitudinal protrusions (160) may be disposed in the remaining cross-sectional area.

[0043] If the carbon fiber content is less than 15% of the total fiber volume, the improvement effect on the axial elastic modulus and tensile strength may not be sufficient.

[0044] On the other hand, if the carbon fiber content exceeds 45% of the total fiber volume, the manufacturing cost increases and the thickness of the outer basalt fiber reinforcement layer (120) decreases, which may limit the improvement effect of impact resistance, lateral restraint and concrete adhesion.

[0045] If the content of basalt fibers is less than 55% of the total fiber volume, the thickness of the outer reinforcing layer protecting the carbon fiber center core (110) and the lateral reinforcing effect may not be sufficient. On the other hand, if the content of basalt fibers exceeds 85% of the total fiber volume, the axial stiffness and high strength characteristics provided by the carbon fibers may be relatively reduced.

[0046] The resin of the resin layer (130) may be epoxy, vinyl ester, or polyurethane resin. In the case of epoxy, bisphenol A-based epoxy is preferred. An anhydride-based or amine-based curing agent may be used.

[0047] The outer layer (140) forms a protective layer using epoxy resin on the outer side of the basalt fiber. The thickness of the protective layer is 0.2 to 1.5 mm. The outer layer inhibits the penetration of alkali, chloride, and moisture. The outer layer (140) may further be provided with a spiral rib or protrusion structure (150) formed on the outer surface of the reinforcing layer to improve adhesion with concrete.

[0048] The spiral rib or protrusion structure (150) can form continuous spiral ribs (150) on the outer surface. The height of the rib is 0.5 to 2.5 mm. The pitch is 5 to 20 mm. If necessary, a double rib structure can be applied by forming longitudinal protrusions (160) together. The spiral rib or protrusion structure (150) can be formed together, and the adhesion strength with concrete is greatly improved.

[0049] Referring to Fig. 6, the composite reinforcing bar is manufactured in the order of ① carbon fiber supply → ② resin impregnation → ③ pultrusion → ④ basalt fiber winding → ⑤ rib formation → ⑥ heat curing → ⑦ cutting → ⑧ inspection.

[0050] Specifically, it can be manufactured by including the steps of: arranging carbon fiber bundles axially; forming a core by pultrusion while impregnating the carbon fibers with a thermosetting resin; winding basalt fibers in a spiral or cross orientation on the outer surface of the core; impregnating the wound basalt fibers with resin and forming a rib structure on the outer surface; and manufacturing a composite reinforcing bar by curing and cutting.

[0051] Referring to Fig. 7, composite reinforcement can be applied to concrete structures such as bridges, ports, tunnels, nuclear power plants, and offshore plants. It can be arranged in the same way as reinforcing bars.

[0052] Composite reinforcing bars with a diameter of 16 mm were manufactured and performance tests were conducted. As a result, in the tensile test, the tensile strength was approximately 1,700–2,000 MPa and the elastic modulus was 90–130 GPa. After 1,000 hours of salt water immersion, the decrease in strength was found to be 5% or less.

[0053] Referring to Figure 8, the results of the adhesion test showed that the Pull-out Test results exhibited an adhesion strength approximately 20–35% higher than that of general BFRP.

[0054] Even in the fatigue test, no significant delamination occurred after 1 million repeated loads.

[0056] As another embodiment, the following embodiment may be proposed.

[0057] [Example 1]

[0058] A composite reinforcing bar with a diameter of 16 mm may be manufactured, and the following composition ratio may be applied based on the total volume of the composite reinforcing bar.

[0059] Carbon fiber core (110): 22% of the total volume of the composite reinforcement,

[0060] Basalt fiber layer (120): 48% of the total volume of the composite reinforcement

[0061] Resin layer (130): 25% of the total volume of the composite reinforcement

[0062] Skin layer (140) and rib layer (150): 5% of the total volume of the composite reinforcement

[0063] In this case, the ratio of carbon fibers to basalt fibers in the total fiber volume was set to approximately 31:69. The carbon fibers were arranged substantially parallel to the longitudinal direction of the composite reinforcing bar, and the basalt fibers were wound around the outer circumference of the carbon fiber center core in an alternating orientation of +45° and -45°.

[0064] [Example 2]

[0065] A composite reinforcing bar with a diameter of 16 mm can be manufactured, and the following composition ratio can be applied to bridges or long-span structures requiring high axial tensile strength and elastic modulus.

[0066] Carbon fiber core (110): 28% of the total volume of the composite reinforcement

[0067] Basalt fiber layer (120): 42% of the total volume of the composite reinforcement

[0068] Resin layer (130): 25% of the total volume of the composite reinforcement

[0069] Skin layer (140) and rib layer (150): 5% of the total volume of the composite reinforcement

[0070] In this case, the ratio of carbon fiber to basalt fiber in the total fiber volume was set to 40:60. By increasing the ratio of carbon fiber, higher axial elastic modulus and tensile strength than in Example 1 can be secured.

[0071] [Example 3]

[0072] The following composition ratios may be applied to marine structures, port facilities, or concrete structures exposed to repeated impact and corrosive environments.

[0073] Carbon fiber core layer (110): 18% of the total volume of the composite reinforcement

[0074] Basalt fiber layer (120): 52% of the total volume of the composite reinforcement

[0075] Resin matrix (130): 25% of the total volume of the composite reinforcement

[0076] Skin layer (140) and rib layer (150): 5% of the total volume of the composite reinforcement

[0077] In this case, the ratio of carbon fiber to basalt fiber in the total fiber volume was set to approximately 26:74. By increasing the proportion of the basalt fiber reinforcement layer, impact resistance, chemical resistance, lateral restraint, and the protective performance of the carbon fiber core against the external environment can be improved.

[0078] [Example 4]

[0079] Composite reinforcing bars for general concrete structures designed to ensure a balance of economic efficiency and structural performance can be manufactured with the following composition ratios.

[0080] Carbon fiber core layer (110): 20% to 25% of the total volume of the composite reinforcement

[0081] Basalt fiber layer (120): 45% to 50% of the total volume of the composite reinforcement

[0082] Resin layer (130): 20% to 30% of the total volume of the composite reinforcing bar

[0083] Outer skin layer (140) and rib layer (150): 3% to 8% of the total volume of the composite reinforcement

[0084] In this composition range, the axial tensile load is mainly borne by the carbon fiber central core, and the propagation of transverse cracks, interfacial delamination, and external impact can be suppressed by the basalt fiber reinforcement layer.

[0085] However, the above fiber arrangement ratio may be changed depending on the diameter of the composite reinforcing bar, required tensile strength, required elastic modulus, shape of the surface rib, type of resin, type of concrete structure to which it is applied, and usage environment, and the scope of the present invention is not limited to the above figures. Explanation of the symbols

[0087] 100 : Composite reinforcement 110 : Carbon fiber center 120: Basalt fiber layer 130: Resin layer 140 : Outer layer 150 : Rib layer 160 : Protrusion 170 : Concrete

Claims

Claim 1 A fiber reinforced polymer (FRP) composite reinforcing bar used in concrete structures comprises: a carbon fiber core (110) containing carbon fiber bundles arranged continuously in the axial direction; a basalt fiber layer (120) formed to surround the outer circumference of the core and having basalt fibers stacked in a spiral or cross orientation; and a resin layer (130) impregnated to integrate the carbon fibers and basalt fibers. A hybrid FRP composite reinforcing bar comprising: an outer layer (140) having a spiral rib and / or protrusion structure (150) formed on the outer surface of the reinforcing bar to improve adhesion with concrete; wherein the carbon fiber center (110) occupies 10 to 40% of the total fiber volume of the composite reinforcing bar, and the basalt fiber layer (120) is formed as a plurality of coiled layers, each coiled layer is formed to have an orientation angle of ±30° to ±60° with respect to the axial direction, wherein the orientation angle includes at least two of ±30°, ±45°, and ±60°, and the outer layer (160) forms a composite rib structure including spiral ribs and longitudinal protrusions formed between the spiral ribs to improve mechanical bonding strength with concrete. Claim 2 A method for manufacturing a composite reinforcing bar according to claim 1, comprising: a step of arranging carbon fiber bundles in an axial direction; a step of forming a core by pultrusion while impregnating the carbon fibers with a thermosetting resin; a step of winding basalt fibers in a spiral or cross orientation on the outer surface of the core; a step of impregnating the wound basalt fibers with resin and forming a rib structure on the outer surface; and a step of manufacturing a composite reinforcing bar by curing and cutting; characterized in that it comprises a hybrid FRP composite reinforcing bar.

Images