Test method for simulating bonding durability of FRP (Fiber Reinforce Plastic) bar in actual service environment of marine concrete structure
By pre-setting crack channels in FRP bar-concrete bonded specimens, the propagation of concrete cracks in a marine environment is simulated, solving the problem of inaccurate simulation of FRP bar corrosion environment in existing technologies. This achieves accuracy and controllability in durability testing and is suitable for durability research on marine concrete structures.
Patent Information
- Application Number
- CN202610263059.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-05
- Publication Date
- 2026-04-24
AI Technical Summary
Existing technologies lack experimental methods to simulate the real corrosion environment of FRP bars inside concrete structures in marine environments, resulting in inaccurate studies on the durability of the bond interface between FRP bars and concrete.
Crack channels were pre-set in the FRP bar-concrete bond specimens. The propagation of concrete cracks in the specimens was simulated in a marine environment by holding the specimens. An accelerated corrosion device was used to simulate the alkali-salt coupled corrosion environment, so as to accurately simulate the corrosion process of the FRP bar.
It enables a realistic simulation of the corrosion state of the FRP bar-concrete bond interface in a marine environment, improving the accuracy and controllability of durability tests, and is applicable to durability studies of various types of marine concrete structures.
Smart Images
Figure CN121917438A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of marine engineering structure durability research technology, specifically to a test method for FRP reinforcement bond durability under simulated actual service environment of marine concrete structures. Background Technology
[0002] The construction of marine infrastructure such as cross-sea bridges, ports, and undersea tunnels is accelerating. However, under the long-term effects of the harsh marine environment, the commonly used reinforced concrete structures face serious corrosion damage, which has become a prominent challenge restricting the long-term safe operation and sustainable development of marine engineering. Studies have shown that many completed seaports and terminals exhibit significant corrosion within ten years of operation, with annual economic losses due to corrosion reaching 3% to 4% of my country's GDP. Therefore, improving the durability of marine engineering structures has become a key task in promoting the high-quality development of the marine economy. Fiber-reinforced polymer (FRP), a composite material made of fibers and resin, has advantages over steel, such as corrosion resistance, fatigue resistance, and a high strength-to-weight ratio. Therefore, replacing steel bars in marine engineering concrete structures with FRP bars can significantly solve the problem of structural damage and economic losses caused by severe steel corrosion, improve the durability of marine engineering structures, and reduce life-cycle costs.
[0003] However, even cost-effective glass fiber reinforced polymer (GFRP) and basalt fiber reinforced polymer (BFRP) reinforcements can corrode their resin and fibers in long-term alkaline and saline environments, leading to deterioration of the mechanical properties of FRP-reinforced concrete components. Current durability studies focus only on single corrosive environments, i.e., purely alkaline or saline environments. However, for concrete structures in marine engineering, cracks are small in the early stages of service, and salt ions from seawater diffuse slowly inward, placing the FRP reinforcement primarily in the strongly alkaline environment of the concrete. As service time increases, under the influence of long-term loads, concrete cracks will continue to develop. When the cracks reach the reinforcement surface, corrosive salt ions from the external seawater accumulate through the crack channels at the interface between the FRP reinforcement and the concrete, forming an alkaline-salt coupled corrosion environment. Notably, in an alkaline environment, the resin on the outside of the FRP reinforcement hydrolyzes, further exacerbating the corrosion of the internal fibers by salt ions. Therefore, compared to a single corrosion mode, the evolution of an alkaline environment followed by an alkaline-salt coupled corrosion environment within marine-serviced concrete components leads to more severe deterioration of the mechanical properties of the FRP reinforcement.
[0004] Currently, research on the long-term mechanical properties of the bond interface between FRP bars and concrete lacks consideration of the evolution of the internal reinforcement in concrete structures under actual marine service conditions. Corrosion is crucial for the long-term mechanical property evolution of FRP bars and their bond interface. Therefore, this invention proposes a load-bearing bond durability test method that can accurately simulate the development of concrete cracks, thereby realizing the true corrosion state and evolution process of FRP bars inside concrete structures under actual marine conditions. This provides new ideas and technologies for the development of durability testing research on FRP-reinforced concrete structures. Summary of the Invention
[0005] To address the problem that traditional accelerated corrosion tests often yield unreliable results due to significant differences between the corrosion state at the FRP reinforcement-concrete bond interface and the actual corrosion environment in marine structures, this invention proposes a test method that simulates the evolution of the real corrosion environment of FRP reinforcements in concrete components under marine service conditions.
[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a test method for the bond durability of FRP bars under simulated marine concrete structure service environment. In the casting of the bonded specimen between the FRP bar and concrete, a concrete crack channel is pre-set. A load is applied to the bonded specimen, and the load-bearing bonded specimen is placed in a seawater accelerated corrosion device. Based on theoretical calculations, the opening time of the crack channel is determined to simulate the moment when concrete cracks in the service component extend to the reinforcing bar. This realizes the transformation of the alkaline corrosion environment at the FRP bar-concrete bond interface into an alkali-salt coupled corrosion environment, thereby simulating the actual corrosion environment evolution process caused by the expansion of concrete cracks in marine engineering structures in service.
[0007] The bonding specimen includes a cubic wooden mold 1 with holes at both ends; a widened wooden block 2 is attached to one side of the cubic wooden mold 1, and a fixing bracket 3 is provided on the widened wooden block 2; the fixing bracket 3 fixes the end joint of the U-shaped tube 4 used to simulate crack channels; the bent end of the U-shaped tube 4 has a hole, and the end joint of the U-shaped tube 4 is sealed with a rubber sleeve 6. Two PVC pipes 8 pass through the openings at both ends of the cubic wooden mold 1; FRP reinforcement 7 passes through the two PVC pipes 7, with structural adhesive filling the space between them; concrete 9 is poured into the cubic wooden mold 1; the FRP reinforcement 7 located between the two PVC pipes 7 inside the cubic wooden mold 1 directly contacts the concrete 9, forming a bonding test area; a perforated U-shaped pipe 4 is embedded in the cubic concrete 9; a threaded steel pipe 10 is fitted onto the loading end of the FRP reinforcement 7, and the threaded steel pipe 10 extends into the load-bearing bracket; The load-bearing support includes three reaction steel plates and four screw rods. The screws pass through the four corners of multiple reaction steel plates in sequence to form a load-bearing bracket; the threaded steel pipe 10 at the loading end of the FRP reinforcement 7 passes through the central holes of three reaction steel plates in sequence; after passing through the second reaction steel plate 12, the threaded steel pipe 10 is screwed into the fixing nut 19; after passing through the third reaction steel plate 13, the threaded steel pipe 10 is screwed into the load sensor 20 and the force-applying nut 18; rotating the force-applying nut 18 applies tensile force to the FRP reinforcement 7 of the bonded specimen through the reaction steel plates; The accelerated corrosion device includes a water tank 21 filled with seawater, with an external insulation board 22 attached to the outside; a specimen support 23 is provided at the bottom of the water tank 21, on which the bonded specimen is placed; the rubber sleeve 6 is removed from the end of the U-shaped tube 4, one end is a water inlet and the other end is a water outlet, and a water suction device is connected to the water outlet end to complete the flow of seawater inside the concrete specimen, realizing the simulation of seawater seepage in the concrete crack channel; a heating rod 26 and a temperature sensor 27 are installed on the water tank support, both of which are connected to a temperature control switch 28; a glass plate 29 is placed on the top of the water tank 21.
[0008] A test method for the bond durability of FRP bars under simulated marine concrete structure service environment includes the following steps: Step 1: Make a mold: Cut a wooden template according to the size of the specimen, and use a pneumatic nail gun to fix the wooden templates together to form a cube mold 1; make holes at the center of the two opposite sides of the cube mold 1, nail wooden blocks into the top of the cube mold 1 along the four sides, and rivet a fixing bracket 3 for simulating crack channels in the middle of the wooden blocks so that the fixing bracket 3 spans the top of the cube wooden mold 1. Step 2: Install FRP reinforcement: Insert both ends of the bonding section of FRP reinforcement 7 into PVC pipe 8 respectively. Use structural adhesive to fill the gap between FRP reinforcement 7 and PVC pipe 8. After the structural adhesive has cured, insert FRP reinforcement 7 into the cube wooden mold 1 with holes at both ends and fix it in the center of the cube mold 1. Step 3: Set up crack channels: Bend the straight round steel pipe into a U-shape, make multiple holes at the bent end of the U-shaped pipe 4, and put rubber sleeves 6 on the joints at both ends of the U-shaped pipe 4; install the completed U-shaped pipe 4 on the fixing frame of the cube wooden mold 1, and adjust the length of the U-shaped pipe 4 into the cube mold 1 so that it is located on the upper surface of the FRP reinforcement 7. Step 4: Make bonding specimens: Pour concrete 9 into the completed cube mold. After the concrete has set, remove all wooden molds and cure them to form FRP reinforcement 7 with cracked channels bonded to concrete specimens. Step 5: Applying load to the FRP reinforcement: Install a load-bearing bracket on the upper end of the bonded specimen. The load-bearing bracket consists of three reaction steel plates and four screws. The position of the reaction steel plates is fixed by the screws at the four corners of the reaction steel plates. The loading end of the FRP reinforcement 7 is fitted into the threaded steel pipe 10. Structural adhesive is injected between the FRP reinforcement 7 and the threaded steel pipe 10 for connection. The threaded steel pipe 10 passes through the center of the three reaction steel plates. After passing through the third reaction steel plate 13, the steel pipe is fitted into the load sensor 20. A force-applying nut 18 is fitted above the load sensor 20. Then, by rotating the force-applying nut 18, the reaction steel plates are squeezed to apply tension to the FRP reinforcement 7. When the load sensor reaches the predetermined value, tighten the fixing nut 19 on the second reaction steel plate 12 to maintain the specimen under load. Remove the third reaction steel plate 13 and the load sensor 20 and force-applying nut 18 on it. Step 6, Corrosion Test Apparatus: Insulation boards are installed around the water tank 21, and a specimen support 23 is installed at the bottom. The load-bearing bonded specimen with sealed rubber sleeves at both ends of the U-shaped tube 4 is placed on the specimen support 23. Natural seawater is poured into the water tank 21 so that the seawater submerges the upper surface of the bonded specimen. The required immersion temperature is provided by a heating rod 26, and a constant temperature of the seawater in the water tank is achieved by a temperature sensor 27 and a temperature control switch. A glass cover 29 is used on the upper part of the water tank 21 to prevent seawater evaporation. Step 7, Corrosion Environment Evolution Simulation: The bonded specimen sealed with rubber sleeves at both ends of the U-tube 4 is immersed in seawater. At this stage, the FRP reinforcement inside the bonded specimen is only in the strongly alkaline corrosion environment of concrete. According to the actual time for concrete cracks to extend to the FRP reinforcement in marine service components, the rubber sleeves 6 at both ends of the U-tube are opened to form a concrete crack channel. A water suction device 24 is connected to one end of the U-tube 4 to pump air, so that seawater flows throughout the entire U-tube 4, simulating the real change cycle of seawater seeping through the concrete cracks in the marine structure to the interface between the FRP reinforcement and the concrete. The salt ions in the seawater and the alkaline ions in the concrete mix with each other, forming the evolution of the alkaline-salt coupled corrosion environment of the FRP reinforcement 7. Step 8, Specimen treatment: After soaking for the preset time, remove the bonded specimen from the corrosion test device and let it dry. Remove the holding device fixed to the loading end of the FRP bar of the bonded specimen, put the threaded steel pipe 10 into the loading end of the FRP bar and polish it, and then perform a pull-out test.
[0009] The calculation process for the time it takes for concrete cracks in marine-grade service components to propagate to FRP reinforcement is as follows: (I) Calculation of concrete crack propagation rate; (1) Converted to expansion speed: (2) in, L The length of the concrete crack extension;F The frequency of load cycles borne by the component; X This represents the number of load cycles. DS I Indicates the stress intensity factor amplitude. DS I = S I,max - S I,min Stress intensity factor under maximum load S I,max and stress intensity factor under minimum load S I,min According to bending moment M Substitute the size into equation (3) for calculation; n This represents the crack propagation coefficient of concrete. B This represents the concrete crack correction factor related to concrete strength. (3) in, b and h These are the cross-sectional length and height, respectively; (II) Prediction of the time it takes for concrete cracks to propagate to the reinforcement; Given the initial concrete crack length L 0 and target concrete crack length L target Integrating formula (1), the stress intensity factor amplitude is calculated. DS I With crack length L The linear variation, after integration, yields the following expression for the relationship between the length of concrete cracks in service components and the number of load cycles: (4) in, H These are coefficients related to load and cross-section; Ultimately, the time required for concrete cracks to propagate to the reinforcement. T for: (5) The time it takes for cracks to propagate to the reinforcement location in concrete members actually in marine service is determined by formulas (1) to (5). T According to the design service life of marine engineering structures C It can determine the proportion of time during which the corrosion environment of the internal FRP reinforcement of a concrete structure serving in a marine environment changes from alkaline to alkali-salt coupled corrosion environment throughout the entire service life of the component. T / CBased on the above time ratio calculation, according to the duration of the accelerated corrosion test, it is possible to determine the moment when the rubber sleeves at both ends of the U-tube are opened during the accelerated corrosion test to form an alkaline-salt coupled corrosion environment, thereby accurately simulating the transformation from alkaline to alkaline-salt coupled corrosion environment inside the concrete structure actually in service in a marine environment.
[0010] The advantages of this invention compared to the prior art are: (1) The durability test method of the present invention can accurately simulate the evolution process of the real corrosion environment of the FRP reinforcement inside the concrete structure in actual service in the ocean, and effectively solves the problem that the existing single accelerated corrosion mode test cannot reasonably reflect the real deterioration law of the FRP reinforcement inside the concrete structure in service in marine engineering and its bonding interface.
[0011] (2) Compared with existing cracking techniques, the simulated concrete crack technique in this durability test method is controllable and easy to implement, and the specimens and devices are less difficult to manufacture. By using the theory of concrete crack propagation time prediction, it is possible to accurately simulate the transition time from alkaline to alkali-salt coupled corrosion environment inside concrete components actually in service in marine environments. In terms of controlling the time when concrete cracks lead to FRP bars, this technique can be realistic, accurate and controllable, which helps the bond durability test of load-bearing FRP bars to more realistically reflect the stress and corrosion environment evolution cycle of FRP bars inside concrete structures actually in service in marine environments.
[0012] (3) The test method of the present invention can simulate the degree of concrete cracking and the resulting seawater corrosion salt ion intrusion effect of components under different load levels and service stages by changing the diameter of the U-tube, the number of openings in the U-tube, and the load-bearing level of the FRP reinforcement. It can comprehensively simulate the real corrosion state of the internal reinforcement of concrete structures actually in service in marine environments. Therefore, this method can be extended to the durability study of various types of concrete structures in service in marine environments, and has strong applicability. Attached Figure Description
[0013] Figure 1 This is a schematic diagram of the cube mold of the present invention; Figure 2 This is a schematic diagram of the load-bearing bonded specimen with cracked channels according to the present invention; Figure 3 This is a schematic diagram of the accelerated corrosion testing system of the present invention; Figure 4 This is a schematic diagram of seawater seeping through the crack channel according to the present invention; Figure 5 for Figure 4 A side view diagram; Figure 6 For bonded specimens subjected to central pull-out loading after corrosion.
[0014] In the diagram: 1-Cube wooden mold; 2-Wide wooden block; 3-Fixed bracket; 4-U-shaped tube; 5-Hole; 6-Rubber sleeve; 7-FRP reinforcement; 8-PVC pipe; 9-Concrete; 10-Threaded steel pipe; 11-First reaction steel plate; 12-Second reaction steel plate; 13-Third reaction steel plate; 14-First screw; 15-Second screw; 16-Third screw; 17-Fourth screw; 18-Force nut; 19-Fixing nut; 20-Load sensor; 21-Water tank; 22-Insulation board; 23-Specimen bracket; 24-Water absorber; 25-Salt ion; 26-Heating rod; 27-Temperature sensor; 28-Temperature control switch; 29-Glass cover. Detailed Implementation
[0015] The present invention will now be specifically described with reference to the accompanying drawings and an embodiment.
[0016] The diagram shows the following: The mold for making the bonded specimen is a cubic wooden mold 1 with holes at both ends. A widened wooden block 2 is attached to one side of the cubic wooden mold. A fixing bracket 3 is provided on the widened wooden block 2. The fixing bracket 3 fixes a U-shaped tube 4 used to simulate crack channels. The bent end of the U-shaped tube 4 has a hole 5. Both ends of the U-shaped tube 4 are sealed with rubber sleeves 6. Two PVC pipes 8 pass through openings at both ends of the cubic wooden mold 1, and FRP reinforcement 7 passes through the two PVC pipes 7. Concrete 9 is poured into the cubic wooden mold 1, and the FRP reinforcement 7 between the two PVC pipes 7 is in direct contact with the concrete 9, forming a bonding test area. A perforated U-shaped pipe 4 is embedded in the cubic concrete 9, and a threaded steel pipe 10 is fitted onto the loading end of the FRP reinforcement 7, extending into the load-bearing bracket. The first screw 14, the second screw 15, the third screw 16, and the fourth screw 17 pass through the four corners of the three reaction steel plates, forming the load-bearing bracket. The threaded steel pipe 10 at the loading end of the FRP reinforcement 7 passes sequentially through the center of the first reaction steel plate 11, the second reaction steel plate 12, and the third reaction steel plate 13. A hole is formed; a threaded steel pipe 10 is screwed into a fixing nut 19 after passing through the second reaction steel plate 12; a load sensor 20 and a force-applying nut 18 are screwed into the threaded steel pipe 10 when passing through the third reaction steel plate 13; the force-applying nut 18 is rotated to apply tension to the FRP reinforcement 7 of the bonded specimen through the reaction steel plate; the accelerated corrosion device includes a water tank 21 filled with seawater, an external insulation board 22, a specimen support 23 at the bottom of the water tank, on which the bonded specimen is placed; rubber sleeves 6 are removed at both ends of a U-shaped tube 4, one end is a water inlet and the other end is a water outlet, a water suction device 24 is connected to the water outlet end to complete the flow of seawater inside the concrete specimen, realize the simulation of seawater seepage in the concrete crack channel, and transport corrosion salt ions 25. A heating rod 26 and a temperature sensor 27 are installed on the water tank support, both of which are connected to a temperature control switch 28, and a glass plate 29 is placed on the top of the water tank.
[0017] Specific Implementation: A 150 mm × 150 mm × 150 mm cube wooden mold 1 is made by cutting a wooden template. Holes 2 with a diameter of 16 mm are drilled at the center of each of the two opposite faces of the cube wooden mold. A widened wooden block 2 with a width of 20 mm is nailed into the upper part of the mold. A fixing bracket 3 for simulating crack channels is riveted to the middle of the widened wooden block. An 800 mm long and 12 mm diameter FRP (fiberglass reinforced plastic) rib 7 is used, with a 60 mm long bonded section. 50 mm long PVC pipes 8 are inserted into both ends of the bonded section. The outer diameter of the PVC pipe 8 is 16 mm and the inner diameter is 13 mm. The FRP rib 7 is inserted into the center of the cube wooden mold 1 with holes at both ends. A 4 mm diameter round steel pipe is bent into a U-shaped tube 4. Multiple holes 5 with a diameter of 2 mm are made at the bent end of the U-shaped tube 4. Rubber sleeves 6 are fitted onto both ends of the U-shaped tube 4. Install the completed U-shaped tube 4 onto the fixing frame 3 of the cubic wooden mold, and adjust the length of the U-shaped tube 4 extending into the cubic mold so that it is located on the upper surface of the FRP reinforcement 7. Pour concrete 9 into the completed cubic mold 1, wait 24 hours for the concrete to set, remove all wooden molds, and place the specimen in the curing room for curing.
[0018] After curing, a load-bearing bracket is installed on the upper end of the bonded specimen. The bracket consists of three 200 mm side-length reaction steel plates and four 500 mm long screws. The position of the reaction steel plates is fixed by the screws at the four corners of the steel plates. A 300 mm long and 30 mm diameter threaded steel pipe 10 is inserted into the loading end of the FRP reinforcement 7. Structural adhesive is injected between the FRP reinforcement 7 and the threaded steel pipe 10 for connection. The threaded steel pipe 10 passes through the center of the three steel plates. After passing through the third reaction steel plate 13, the threaded steel pipe is fitted with a load sensor 20. A force-applying nut 18 is fitted above the load sensor 20. Then, by rotating the force-applying nut 18, the reaction steel plates are compressed to apply tension to the FRP reinforcement 7. When the load sensor 20 reaches the predetermined value, the fixing nut 19 on the second reaction steel plate 12 is tightened to maintain the specimen under load. The third reaction steel plate 13 and the reaction force application devices, including the load sensor 20 and the force-applying nut 18, are then removed.
[0019] A water tank 21, measuring 2000 mm × 1000 mm × 1000 mm, is surrounded by insulation boards 22. A specimen support 23 is installed at the bottom. The specimen, supported by a U-shaped tube 4 with sealed rubber sleeves 6 at both ends, is placed on the support 23. Natural seawater is filled into the tank, submerging the upper surface of the specimen. A heating rod 26 heats the seawater to provide the required immersion temperature of 40°C. A temperature sensor 27 monitors the seawater temperature. When the temperature drops below 40°C, a temperature control switch 28 activates the heating rod 27 to continue heating the seawater, thus maintaining a constant temperature within the tank. A glass cover 29 is used on the top of the tank to prevent seawater evaporation.
[0020] Next, we calculate the crack initiation time leading to the FRP bar, which also determines the corrosion duration of the FRP bar in alkaline corrosion environment and alkali-salt coupled corrosion environment, respectively.
[0021] This paper focuses on FRP-reinforced concrete flexural members under cyclic loading in marine engineering, calculating the propagation of concrete cracks to the FRP reinforcement. Based on literature review and actual engineering data, the fundamental parameters of FRP-reinforced concrete flexural members under marine service conditions are shown in the table below: Table 1 Basic Parameter Table
[0022] Calculate the magnitude of the bending moment under load: (1) Calculate the number of load cycles required for a concrete crack to propagate to the reinforcement: (2) (3) Calculate the time required for concrete cracks to propagate to the reinforcement: (4) Extended time converted to years: (5) Based on the above calculations, it is clear that in a marine environment, after 12 years of service, concrete cracks in this concrete structure will extend to the reinforcement, causing the corrosion environment of the reinforcement to change from alkaline to an alkali-salt coupled corrosion environment. Given that the design service life of concrete structures in a marine environment is 70 years, and based on the ratio of the actual time for concrete cracks to extend to the reinforcement to the structure's service life, it can be deduced that for specimens with an accelerated corrosion test cycle of 12 months, the bonded specimens sealed with rubber sleeves at both ends of the U-shaped tube need to be immersed in seawater for 2 months. During this stage, the FRP reinforcement 7 inside the specimen is in a strongly alkaline corrosive environment of the concrete.
[0023] After two months of alkaline corrosion, the rubber sleeves 6 at both ends of the U-shaped tube were opened to open the concrete crack channels. A water suction device 24 was connected to one end of the U-shaped tube to extract air, allowing seawater to flow throughout the entire U-shaped tube. This simulated seawater seeping through the concrete cracks to the interface between the FRP reinforcement and the concrete. The salt ions 25 in the seawater mixed with the alkaline ions in the concrete, forming an alkaline-salt coupled corrosion environment at the bonding interface between the FRP reinforcement 7 and the concrete 9. This alkaline-salt coupled corrosion state was maintained for another 10 months of durability immersion test, thus achieving an accurate simulation of the evolution of the internal environment of concrete structures from alkaline to alkaline-salt coupled corrosion under marine service conditions.
[0024] After the immersion time is reached, the bonded specimen is removed from the corrosion test device and placed indoors to air dry naturally. The holding device fixed to the loading end of the FRP bar 7 of the bonded specimen is removed, and the threaded steel pipe 10 is inserted into the loading end of the FRP bar and polished. Then the pull-out test can be performed.
Claims
1. A test method for the bond durability of FRP bars under simulated actual service conditions of marine concrete structures, characterized in that, In the casting of FRP reinforcement-concrete bond specimens, concrete crack channels are pre-set. The bond specimens are subjected to a holding load and placed in a seawater accelerated corrosion device. The opening time of the crack channels is determined according to theoretical calculations to simulate the moment when concrete cracks in service components extend to the reinforcement. This realizes the transformation of the alkaline corrosion environment at the FRP reinforcement-concrete bond interface into an alkali-salt coupled corrosion environment, thereby simulating the actual corrosion environment evolution process caused by the extension of concrete cracks in marine engineering structures in service in the ocean.
2. The test method for FRP reinforcement bond durability under simulated actual service environment of marine concrete structures according to claim 1, characterized in that, The bonding specimen includes a cubic wooden mold (1) with holes at both ends; a widened wooden block (2) is attached to one side of the cubic wooden mold (1), and a fixing bracket (3) is provided on the widened wooden block (2); the fixing bracket (3) fixes the end joint of the U-shaped tube (4) used to simulate crack channels; the bent end of the U-shaped tube (4) has a hole, and the end joint of the U-shaped tube (4) is sealed with a rubber sleeve (6). Two PVC pipes (8) pass through the openings at both ends of the cubic wooden mold (1); FRP reinforcement (7) passes through the two PVC pipes (7), and structural adhesive is filled between them; concrete (9) is poured into the cubic wooden mold (1); the FRP reinforcement (7) between the two PVC pipes (7) located in the cubic wooden mold (1) directly contacts the concrete (9) to form a bonding test area; a perforated U-shaped pipe (4) is embedded in the cubic concrete (9); the loading end of the FRP reinforcement (7) is fitted with a threaded steel pipe (10), and the threaded steel pipe (10) extends into the load-bearing bracket; The load-bearing support includes three reaction steel plates and four screw rods. The screws pass through the four corners of multiple reaction steel plates in sequence to form a load-bearing bracket; the threaded steel pipe (10) at the loading end of the FRP reinforcement (7) passes through the central holes of the three reaction steel plates in sequence; after passing through the second reaction steel plate (12), the threaded steel pipe (10) is screwed into the fixing nut (19); after passing through the third reaction steel plate (13), the threaded steel pipe (10) is screwed into the load sensor (20) and the force-applying nut (18); rotating the force-applying nut (18) applies tension to the FRP reinforcement (7) of the bonded specimen through the reaction steel plates; The accelerated corrosion device includes a water tank (21) filled with seawater, with an external insulation board (22); a specimen support (23) is provided at the bottom of the water tank (21), and a bonded specimen is placed on the specimen support (23). The rubber sleeve (6) is removed from the end joint of the U-shaped tube (4), one end is a water inlet and the other end is a water outlet. A water suction device is connected to one end of the water outlet to complete the flow of seawater inside the concrete specimen and realize the simulation of seawater seepage in the concrete crack channel; a heating rod (26) and a temperature sensor (27) are installed on the water tank support, and both are connected to a temperature control switch (28). A glass plate (29) is covered on the top of the water tank (21).
3. The test method for FRP reinforcement bond durability under simulated actual service environment of marine concrete structures according to claim 1 or 2, characterized in that, Includes the following steps: Step 1: Make a mold: Cut a wooden template according to the size of the specimen, and use a pneumatic nail gun to fix the wooden templates together to form a cube mold (1); make holes at the center of the two opposite sides of the cube mold (1), nail wooden blocks into the upper part of the cube mold (1) along the four sides, and rivet a fixing bracket (3) for simulating crack channels in the middle of the wooden blocks so that the fixing bracket (3) spans the upper part of the cube wooden mold (1); Step 2, Install FRP reinforcement: Insert the two ends of the bonding section of FRP reinforcement (7) into PVC pipe (8) respectively. Use structural adhesive to fill the gap between FRP reinforcement (7) and PVC pipe (8). After the structural adhesive has cured, insert FRP reinforcement (7) into the cube wooden mold (1) with holes at both ends and fix it in the center of the cube mold (1). Step 3: Set up crack channels: Bend the straight round steel pipe into a U-shape, make multiple holes at the bent end of the U-shaped pipe (4), and put rubber sleeves (6) on the joints at both ends of the U-shaped pipe (4); install the completed U-shaped pipe (4) on the fixing frame of the cubic wooden mold (1), and adjust the length of the U-shaped pipe (4) into the cubic mold (1) so that it is located on the upper surface of the FRP reinforcement (7); Step 4: Make bonding specimens: Pour concrete (9) into the completed cube mold. After the concrete has set, remove all wooden molds and cure them to form FRP bars (7) with cracked channels bonded to concrete specimens. Step 5, Applying load to FRP reinforcement: Install a load-bearing bracket on the upper end of the bonded specimen. The load-bearing bracket consists of three reaction steel plates and four screws. The position of the reaction steel plates is fixed by the screws at the four corners of the reaction steel plates. The loading end of the FRP reinforcement (7) is fitted into the threaded steel pipe (10). Structural adhesive is injected between the FRP reinforcement (7) and the threaded steel pipe (10) for connection. The threaded steel pipe (10) passes through the center of the three reaction steel plates. After passing through the third reaction steel plate (13), the steel pipe is fitted into the load sensor (20). A force-applying nut (18) is fitted above the load sensor (20). Then, by rotating the force-applying nut (18), the reaction steel plate is squeezed to apply tension to the FRP reinforcement (7). When the load sensor reaches the predetermined value, tighten the fixing nut (19) on the second reaction steel plate (12) to maintain the specimen under load. Remove the third reaction steel plate (13) and the load sensor (20) and force-applying nut (18) on it. Step 6, Corrosion test apparatus: Insulation boards are installed around the water tank (21), and a specimen support (23) is installed at the bottom. The load-bearing bonded specimen with sealed rubber sleeves at both ends of the U-shaped tube (4) is placed on the specimen support (23). Natural seawater is poured into the water tank (21) so that the seawater submerges the upper surface of the bonded specimen. The required immersion temperature is provided by a heating rod (26), and the constant temperature of the seawater in the water tank is achieved by a temperature sensor (27) and a temperature control switch. A glass cover (29) is used on the upper part of the water tank (21) to prevent the seawater from evaporating. Step 7, simulation of corrosion environment evolution: The bonded specimen sealed with rubber sleeves at both ends of the U-tube (4) is immersed in seawater. At this stage, the FRP reinforcement in the bonded specimen is only in the strong alkaline corrosion environment of concrete. According to the time when the concrete cracks of the actual marine service component expand to the FRP reinforcement, the rubber sleeves (6) at both ends of the U-tube are opened to form a concrete crack channel. A water suction device (24) is used to connect one end of the U-tube (4) to pump air, so that seawater flows through the entire U-tube (4) to simulate the real change cycle of seawater seeping through the concrete cracks in the marine structure to the interface between the FRP reinforcement and the concrete. The salt ions in the seawater and the alkaline ions in the concrete mix with each other to form the evolution of the alkaline-salt coupled corrosion environment of the FRP reinforcement (7). Step 8, loading specimen treatment: After soaking for the preset time, take out the bonded specimen from the corrosion test device and let it dry. Remove the holding device fixed to the loading end of the FRP bar of the bonded specimen, put the threaded steel pipe (10) into the loading end of the FRP bar and polish it. Then, perform a pull-out test loading.
4. The test method for FRP reinforcement bond durability under simulated actual service environment of marine concrete structures according to claim 3, characterized in that, The calculation process for the time it takes for concrete cracks in marine-grade service components to propagate to FRP reinforcement is as follows: (I) Calculation of concrete crack propagation rate; (1) Converted to expansion speed: (2) in, L The length of the concrete crack extension; F The frequency of load cycles borne by the component; X This represents the number of load cycles. DS I Indicates the stress intensity factor amplitude. DS I = S I,max - S I,min Stress intensity factor under maximum load S I,max and stress intensity factor under minimum load S I,min According to bending moment M Substitute the size into equation (3) for calculation; n This represents the crack propagation coefficient of concrete. B This represents the concrete crack correction factor related to concrete strength. (3) in, b and h These are the cross-sectional length and height, respectively; (II) Prediction of the time it takes for concrete cracks to propagate to the reinforcement; Given the initial concrete crack length L 0 and target concrete crack length L target Integrating formula (1), the stress intensity factor amplitude is calculated. DS I With crack length L The linear variation, after integration, yields the following expression for the relationship between the length of concrete cracks in service components and the number of load cycles: (4) in, H These are coefficients related to load and cross-section; Ultimately, the time required for concrete cracks to propagate to the reinforcement. T for: (5) The time it takes for cracks to propagate to the reinforcement location in concrete members actually in marine service is determined by formulas (1) to (5). T According to the design service life of marine engineering structures C It can determine the proportion of time during which the corrosion environment of the internal FRP reinforcement of a concrete structure serving in a marine environment changes from alkaline to alkali-salt coupled corrosion environment throughout the entire service life of the component. T / C Based on the above time ratio calculation, according to the duration of the accelerated corrosion test, it is possible to determine the moment when the rubber sleeves at both ends of the U-tube are opened during the accelerated corrosion test to form an alkaline-salt coupled corrosion environment, thereby accurately simulating the transformation from alkaline to alkaline-salt coupled corrosion environment inside the concrete structure actually in service in a marine environment.