Iron-based shape memory alloy-fiber fabric reinforced cement-based composite self-prestressed composite reinforcement system

Abstract

This invention discloses a self-prestressed composite reinforcement system for iron-based shape memory alloy-fiber fabric reinforced cement-based composites, comprising a reinforced concrete beam, an FRCM reinforcement layer, an Fe-SMA alloy U-shaped plate, an activation end, a data acquisition end, and a control end. The FRCM reinforcement layer is disposed on the outer surface of the reinforced concrete beam. The Fe-SMA alloy U-shaped plate is arranged along the outer periphery of the FRCM reinforcement layer and fixed to the reinforced concrete beam. The activation end is connected to the Fe-SMA alloy U-shaped plate and is used to electrically heat the Fe-SMA alloy U-shaped plate. The data acquisition end is connected to the Fe-SMA alloy U-shaped plate and is used to collect the temperature information and deformation of the Fe-SMA alloy U-shaped plate. The control end is communicatively connected to the activation end and the data acquisition end and is used to control the activation end to repeatedly electrically heat the Fe-SMA alloy U-shaped plate and control the temperature of the Fe-SMA alloy U-shaped plate to be 160~200℃.

Description

Technical Field

[0001] This invention relates to the field of civil engineering structure reinforcement and intelligent structural maintenance technology, specifically to a self-prestressed composite reinforcement system of iron-based shape memory alloy-fiber fabric reinforced cement-based composite. Background Technology

[0002] For bridge structures, fatigue damage accumulates under the influence of reciprocating traffic, requiring timely reinforcement and repair. Currently, fiber-reinforced polymers (FRPs), widely used in the reinforcement field, have advantages such as being lightweight and high-strength. However, they typically use organic polymers (such as epoxy resin) as the impregnation matrix, which results in insufficient high-temperature resistance and UV aging resistance. Furthermore, epoxy resins have a certain degree of toxicity, poor compatibility with concrete components, and are difficult to apply to low-temperature, humid, or irregular concrete surfaces.

[0003] To overcome the problem of interfacial delamination in traditional FRP reinforcement, previous research has proposed placing shape memory alloy (SMA) prestressed members on the outside of the outer composite material. These SMA members are activated by electricity to generate circumferential compressive force, providing additional constraint to the outer composite material and improving its stress stability. However, this technology uses resin-based FRP as the reinforcement target and relies primarily on one-time activation to apply prestress, lacking effective measures to address the prestress attenuation problem during long-term service. Furthermore, resin-based materials are sensitive to temperature changes and are prone to performance degradation under repeated heating conditions, thus limiting the long-term application of this technology in engineering.

[0004] Fabric-reinforced cementitious matrix (FRCM) uses inorganic mortar as a matrix and possesses excellent fire resistance, permeability, and compatibility with concrete. It boasts advantages such as variable fiber geometry, good material compatibility, minimal temperature influence, good permeability, non-flammability, non-toxicity during construction, and wide applicability, making it a research hotspot in the reinforcement field. However, without epoxy resin, the dry fiber bundles within FRCM are difficult to fully impregnate with the mortar, leading to fiber pull-out and slippage. Structures reinforced with FRCM exhibit multiple fiber-mortar and mortar-concrete interfaces, making them prone to various failure modes such as interface delamination and fiber pull-out, thus limiting the full realization of its reinforcement effect.

[0005] Therefore, how to introduce active restraint components suitable for long-term engineering service conditions into the FRCM reinforcement system, and how to achieve maintainability and stability of the reinforced structure during its service life while ensuring structural and material safety, are problems that existing technologies urgently need to solve. Summary of the Invention

[0006] To address the common problems in existing bridge structure reinforcement technologies, such as weak interfacial bonding, low fiber utilization, difficulty in maintaining prestress over a long period, lack of self-adjusting capability during service life, and difficulty in balancing structural durability and intelligent maintenance in traditional reinforcement methods, this invention proposes a self-prestressed composite reinforcement system of iron-based shape memory alloy-fiber fabric reinforced cement-based composite.

[0007] A self-prestressed composite reinforcement system of iron-based shape memory alloy-fiber fabric reinforced cement-based composite includes a reinforced concrete beam, an FRCM reinforcement layer, an Fe-SMA alloy U-shaped plate, an activation end, a data acquisition end, and a control end. The FRCM reinforcement layer is provided on the outer surface of the reinforced concrete beam; The Fe-SMA alloy U-shaped plate is arranged along the outer periphery of the FRCM reinforcement layer and fixed to the reinforced concrete beam; The activation end is connected to the Fe-SMA alloy U-shaped plate and is used to electrically heat the Fe-SMA alloy U-shaped plate; The acquisition end is connected to the Fe-SMA alloy U-shaped plate and is used to acquire the temperature information and deformation amount of the Fe-SMA alloy U-shaped plate; The control terminal is communicatively connected to the activation terminal and the acquisition terminal, and is used to control the activation terminal to repeatedly energize and heat the Fe-SMA alloy U-shaped plate, and to control the temperature of the Fe-SMA alloy U-shaped plate to be 160~200℃.

[0008] Optionally, the FRCM reinforcement layer includes a fiber fabric and an inorganic mortar covering the surface of the fiber fabric.

[0009] Optionally, the fiber fabric includes at least one of carbon fiber, basalt fiber, glass fiber, aramid fiber, and p-phenylenediazole fiber.

[0010] Optionally, the inorganic mortar includes at least one of cement-based mortar, lime-based mortar, and phosphate-based mortar.

[0011] Optionally, the two ends of the Fe-SMA alloy U-shaped plate are fixed to the reinforced concrete beam by at least one of the following methods: bolt connection, anchor bolt connection, clamp connection, sleeve connection, and pre-embedded connection.

[0012] Optionally, the bottom of the Fe-SMA alloy U-shaped plate is bonded to the FRCM reinforcement layer, the top opening of the U-shaped plate is higher than the upper surface of the reinforced concrete beam, and the top two ends of the top opening of the U-shaped plate are connected together by bolts.

[0013] Optionally, the activation end includes an electrode disposed on the surface of the Fe-SMA alloy U-shaped plate and a power supply device connected to the electrode.

[0014] Optionally, the acquisition end includes a thermocouple and a strain gauge disposed on the surface of the Fe-SMA alloy U-shaped plate.

[0015] Optionally, when the deformation measured by the acquisition terminal exceeds a preset strain threshold, the control terminal automatically activates the power supply to supplement the prestress.

[0016] Optionally, the preset strain threshold is 0.5%-1%; Preferably, when considering cyclic loading, the preset strain threshold is 0.2% to 0.7%.

[0017] A method for self-prestressed composite reinforcement of iron-based shape memory alloy-fiber fabric reinforced cement-based composites, employing the aforementioned system, includes the following steps: Step 1) Pour an FRCM reinforcement layer on the surface of the reinforced concrete beam. First, pour the bottom layer of mortar, lay the fiber fabric, then pour the top layer of mortar and cure it. Step 2) Fit the Fe-SMA alloy U-shaped plate around the outer perimeter of the FRCM reinforcement layer; Step 3) Connect the acquisition end to the surface of the Fe-SMA alloy U-shaped plate, fix the electrode on the Fe-SMA surface and connect the activation end; Step 4) The control end controls the activation end to perform the first power-on heating activation of Fe-SMA, generating circumferential prestress inside Fe-SMA, while controlling the activation temperature to not exceed 200℃. Step 5) During the service life of the structure, continuously monitor the strain change of Fe-SMA. When the strain increment reaches the preset strain threshold, automatically trigger the activation end, reheat and activate it to replenish the prestress loss.

[0018] The technical solution of this invention has the following beneficial effects: (1) This invention applies circumferential prestress to the FRCM reinforcement layer using an Fe-SMA alloy U-shaped plate, placing the fiber fabric and inorganic mortar in a constrained state. This enhances the interfacial bonding performance between the fiber fabric and the inorganic mortar, reduces the risk of the fiber fabric slipping or being pulled out of the organic mortar during stress, thereby increasing the fiber fabric's participation in the reinforcement system and improving reinforcement efficiency and utilization efficiency. This invention introduces an intelligent control system consisting of a data acquisition end, a control end, and an activation end to monitor and control the temperature and deformation state of the Fe-SMA alloy U-shaped plate. When the prestress decays, a reactivation process can be triggered to supplement the reinforcement prestress, thus enabling the reinforcement system to adjust according to its own state changes during structural service, achieving intelligent repair and long-term stable reinforcement of the bridge structure.

[0019] (2) The circumferential prestress applied by the Fe-SMA alloy U-shaped plate forms a continuous constraint on the FRCM reinforcement layer, which helps to improve the interface stress state between the FRCM reinforcement layer and the reinforced concrete beam to be reinforced, reduce the possibility of interface peeling failure, and thus improve the overall stability and effectiveness of the reinforcement system.

[0020] (3) The present invention uses FRCM material. The FRCM material uses inorganic mortar (cement-based material) as the matrix material. The fiber fabric and the inorganic mortar are not fully impregnated. The Fe-SMAU type plate can solve the peeling problem between FRCM and the structure to be reinforced, and can also improve the bonding performance between the fiber fabric and the inorganic mortar, thereby improving the utilization rate of the fiber fabric inside the inorganic mortar.

[0021] (4) In this invention, FRCM material is used instead of traditional FRP material. In FRCM material, inorganic mortar (cement-based material) is used as matrix material. Cement-based material is not very sensitive to temperature and is suitable for multiple electrical activation to compensate for the loss of prestress. However, the matrix material inside FRP material softens and ages after multiple cycles of heating. After the matrix material softens and ages, the reinforcement effect is significantly reduced.

[0022] (5) The present invention uses Fe-SMAU type plate as an activatable circumferential prestressed member, which has the characteristics of good low cycle fatigue life, low material cost, simple manufacturing process and can be mass-produced under normal pressure, making it suitable for batch application in engineering, especially in the field of bridge reinforcement.

[0023] (6) Fe-SMA has high elastic stiffness (elastic modulus between approximately 150-200 GPa, close to that of steel), and its maximum elongation can reach over 40%, exhibiting high strength and high toughness. Thus, under the same cross-section and arrangement conditions, it can provide effective circumferential restraint and prestress transfer capabilities. Its stiffness advantage can directly serve the mechanism of "fiber bundle compaction - interface slip suppression - delayed pull-out / peeling" in the FRCM system, improving fiber utilization and reinforcement efficiency.

[0024] (7) Fe-SMA can achieve rapid resistance heating activation in the range of 100–160°C, generating a prestress of about 300MPa. The activation temperature window is low, which reduces the thermal impact and energy consumption and is conducive to segmented or local reactivation. In this invention, for the FRCM system, low temperature activation is more conducive to avoiding unnecessary thermal damage to mortar or concrete and disturbance of the water content state. Attached Figure Description

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram illustrating the effect of the intelligent self-healing composite reinforcement system in Embodiments 1-3 of the present invention.

[0027] Figure 2 The deformation evolution curve of Fe-SMA under cyclic loading; Figure 3 The activation temperature-stress curve for Fe-SMA. Detailed Implementation

[0028] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0029] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, are also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0030] The terms “comprising,” “including,” “having,” “containing,” etc., used in this document are all open-ended, meaning they include but are not limited to. The terms “first” and “second” used in this document are for descriptive purposes only, and features specified as “first” or “second” may explicitly or implicitly include at least one of those features.

[0031] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. Unless otherwise specified, the technical means used in the following embodiments are conventional means well known to those skilled in the art; the experimental methods used are all conventional methods; and the equipment, apparatus, materials, reagents, etc., used are all commercially available.

[0032] In a first aspect, the present invention provides a self-prestressed composite reinforcement system for iron-based shape memory alloy-fiber fabric reinforced cement-based composites, comprising a reinforced concrete beam, an FRCM reinforcement layer, an Fe-SMA alloy U-shaped plate, an activation end, a data acquisition end, and a control end; the FRCM reinforcement layer is disposed on the outer surface of the reinforced concrete beam; the Fe-SMA alloy U-shaped plate is arranged along the outer periphery of the FRCM reinforcement layer and fixed to the reinforced concrete beam; the activation end is connected to the Fe-SMA alloy U-shaped plate and is used to electrically heat the Fe-SMA alloy U-shaped plate; the data acquisition end is used to collect temperature information and deformation of the Fe-SMA alloy U-shaped plate; the control end is communicatively connected to the activation end and the data acquisition end and is used to control the activation end to repeatedly electrically heat the Fe-SMA alloy U-shaped plate and control the temperature of the Fe-SMA alloy U-shaped plate to be 160~200℃.

[0033] In one alternative embodiment, the FRCM reinforcement layer comprises a fibrous fabric and an inorganic mortar covering the surface of the fibrous fabric layer.

[0034] In one optional embodiment, the fiber fabric includes at least one of carbon fiber, basalt fiber, glass fiber, aramid fiber, and p-phenylenediazole fiber. In one optional embodiment, the inorganic mortar includes at least one of cement-based mortar, lime-based mortar, and phosphate-based mortar.

[0035] In one optional embodiment, the two ends of the Fe-SMA alloy U-shaped plate are fixed to the reinforced concrete beam by at least one of bolt connection, anchor bolt connection, clamp connection, sleeve connection, and pre-embedded connection.

[0036] In one optional embodiment, the activation end includes an electrode disposed on the surface of the Fe-SMA alloy U-shaped plate and a power supply device connected to the electrode.

[0037] In one alternative implementation, the acquisition terminal includes a thermocouple, and the acquisition terminal transmits temperature information to the control terminal.

[0038] In one optional implementation, when the deformation measured by the acquisition terminal exceeds a preset threshold, the control terminal automatically activates the power supply to supplement the prestress.

[0039] In one optional implementation, the preset strain threshold is 0.05%-0.2%.

[0040] Secondly, this invention also discloses a method for self-prestressed composite reinforcement of iron-based shape memory alloy-fiber fabric reinforced cement-based composites, employing the above-mentioned system and including the following steps: (1) The FRCM reinforcement layer is poured in layers on the surface of the structure to be reinforced. First, the bottom layer of mortar is poured, the fiber fabric is laid, and then the top layer of mortar is poured and cured. (2) Fit the Fe-SMA alloy U-shaped plate around the outer perimeter of the FRCM reinforcement layer; (3) Connect the acquisition end to the surface of the Fe-SMA alloy U-shaped plate, fix the electrode on the Fe-SMA surface and connect the activation end; (4) The control end controls the activation end to perform the first power-on heating activation of Fe-SMA, generating circumferential prestress inside Fe-SMA, while controlling the activation temperature not to exceed 200℃. (5) During the service life of the structure, the strain change of Fe-SMA is continuously monitored. When the strain increment reaches the preset threshold, the reheating activation is automatically triggered to replenish the prestress loss.

[0041] The Fe-SMA alloy of this invention has the chemical composition Fe-17Mn-5Si-10Cr-5Ni (wt%), and is a typical Fe-Mn-Si shape memory alloy with excellent fatigue resistance. It was purchased from Zhong Sheng Xu Long Machinery Co., Ltd., and its shape recovery stress can be activated by electric heating. The experimental alloy was smelted using industrial pure iron (mainly impurities C, Al, etc.), nickel, electrolytic manganese, silicon, electrolytic chromium, and ferrovanadium, mixed according to the designed ratio, and smelted in a medium-frequency vacuum induction furnace at a vacuum degree of 10⁻² Torr. After the raw materials melted, they were held at a temperature of 30 min to homogenize the composition, and then cast into 25 kg ingots in a metal mold. To eliminate the inhomogeneity of the ingot composition, the ingot was homogenized by annealing at 1200℃ for 24 h to remove the surface oxide scale, cut off the cap, and rolled into a 4 mm thick plate blank at 900℃-1200℃. Finally, it was machined into samples of the required size.

[0042] The FRCM of this invention is prepared by self-casting using purchased carbon fiber and high-strength mortar. The mortar is purchased from Wuxi Maizida Building Materials Co., Ltd., and the standard is GB / T50448-2015, with a standard strength of over 60MPa after curing. The carbon fiber is purchased from Shanghai Saikeou Building Technology Co., Ltd., and the standard is GB / T 3354-2014, with a specification of 12K and an ultimate tensile strength of 3400MPa.

[0043] The acquisition device of this invention is a dynamic acquisition instrument manufactured by Donghua Testing Co., Ltd., and is from Donghua Acquisition Instrument.

[0044] The activation end of this invention is a resistance activation device manufactured by Re-Ferg, which can generate a 535A current for resistance heating after being powered on.

[0045] The control terminal of this invention can be any one or a combination of a microcontroller, a PLC, an embedded controller, and an industrial computer.

[0046] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0047] Example 1 This embodiment provides a specific implementation of an intelligent self-healing composite reinforcement system for bridge structures. Taking a reinforced concrete bridge as the object to be reinforced, such as… Figure 1 As shown, it includes a reinforced concrete beam 1, an FRCM reinforcement layer 2, an Fe-SMA alloy U-shaped plate 3, an activation end 91, a data acquisition end 93, and a control end 92. The FRCM reinforcement layer 2 is disposed on the outer surface of the reinforced concrete beam 1; the Fe-SMA alloy U-shaped plate 3 is arranged along the outer periphery of the FRCM reinforcement layer 2 and fixed to the reinforced concrete beam. Figure 1 As shown, the bottom of the Fe-SMA alloy U-shaped plate is bonded to the FRCM reinforcement layer, and the opening at the top of the U-shaped plate is higher than the upper surface of the reinforced concrete beam. The two ends of the top opening of the U-shaped plate are connected together by screws 5 and nuts 4. The activation end 91 is connected to the Fe-SMA alloy U-shaped plate through electrode 6 and is used to electrically heat the Fe-SMA alloy U-shaped plate. The acquisition end 93 is connected to the Fe-SMA alloy U-shaped plate 3 through thermocouple 8 and strain gauge 7 and is used to acquire the temperature information and deformation of the Fe-SMA alloy U-shaped plate, respectively. The control end 92 is communicatively connected to the activation end 91 and the acquisition end 93 and is used to control the activation end to repeatedly electrically heat the Fe-SMA alloy U-shaped plate and control the temperature of the Fe-SMA alloy U-shaped plate to be 160~200℃.

[0048] The method of using this system for intelligent self-healing composite reinforcement is as follows: First, a fiber-reinforced cement-based composite (FRCM) reinforcement layer is constructed on the outer surface of the reinforced concrete bridge beam in layers. Specifically, a layer of cement-based mortar is first poured on the surface of the beam as the bottom layer mortar. Before the bottom layer mortar is completely set, carbon fiber fabric is laid on it. Then, an upper layer of cement-based mortar is poured on the surface of the carbon fiber fabric and cured to make the FRCM reinforcement layer form as a whole.

[0049] After the FRCM reinforcement layer has cured, the iron-based shape memory alloy (Fe-SMA) plate is bent into an Fe-SMA alloy U-shaped plate and arranged along the outer perimeter of the FRCM reinforcement layer. Both ends are fixed to the reinforced concrete beam with bolts. Electrodes 6 are placed on the surface of the Fe-SMA alloy U-shaped plate and connected to the activation end. Strain gauges 7 are also attached to the surface of the Fe-SMA alloy U-shaped plate to collect deformation information, and thermocouples 8 are placed on the surface of the Fe-SMA alloy U-shaped plate to collect temperature information. The activation end is controlled by the control terminal to perform the first power-on heating activation of the Fe-SMA U-shaped plate, generating circumferential prestress. During the activation process, the temperature information collected by the acquisition terminal is used to control the heating process, keeping the temperature of the Fe-SMA U-shaped plate within a preset safe range. After heating and activation, the strain reaches 0.12%.

[0050] After the reinforced concrete bridge structure enters service, the acquisition unit continuously collects deformation and temperature information of the Fe-SMA alloy U-shaped plate and transmits the data to the control unit. When the Fe-SMA alloy U-shaped plate experiences stress relaxation under sustained or cyclic loading, resulting in a strain increment of 0.1%, the control unit triggers the activation unit to re-energize and re-heat the Fe-SMA alloy U-shaped plate to replenish prestress. During the re-activation process, the control unit controls the heating process based on the acquired temperature information, maintaining the temperature of the Fe-SMA alloy U-shaped plate at 180℃. After re-heating and activation, the strain is measured to reach 0.15%.

[0051] Example 2 This embodiment, based on Embodiment 1, provides an implementation method under different material combinations. The fiber fabric in the FRCM reinforcement layer is made of glass fiber fabric, and the inorganic mortar is made of cement-based mortar. During construction, a layered pouring method is also adopted, with the bottom layer of mortar, glass fiber fabric, and top layer of mortar sequentially laid on the outer surface of the reinforced concrete beam, followed by curing.

[0052] After the FRCM reinforcement layer is formed, the Fe-SMA alloy plate is bent into a U-shape and fitted onto the outer perimeter of the FRCM reinforcement layer. Both ends are fixed to the reinforced concrete beam using anchors. The Fe-SMAU plate is activated by electrical heating via an activation end. A data acquisition end collects the temperature and deformation information of the Fe-SMAU plate and transmits this information to a control end. The control end adjusts the activation process based on the collected temperature information and determines whether the Fe-SMAU plate needs to be re-energized based on the deformation information, thereby adjusting the reinforcement prestress. After heating and activation, the strain is measured to reach 0.10%.

[0053] After the bridge structure enters service, the acquisition unit continuously collects deformation and temperature information of the Fe-SMA alloy U-shaped plate and transmits the data to the control unit. When the Fe-SMA alloy U-shaped plate experiences stress relaxation under sustained or cyclic loading, resulting in a strain increment of 0.2%, the control unit triggers the activation unit to re-energize and re-heat the Fe-SMA alloy U-shaped plate to replenish prestress. During the re-activation process, the control unit controls the heating process based on the acquired temperature information, maintaining the temperature of the Fe-SMA alloy U-shaped plate at 190℃. After re-heating and activation, the strain is measured to reach 0.14%.

[0054] Example 3 This embodiment provides a specific implementation method for an intelligent self-healing composite reinforcement system for bridge structures. Taking a reinforced concrete bridge as the object to be reinforced, a fiber-reinforced cementitious composite (FRCM) reinforcement layer is first constructed on the outer surface of the beam in layers. Specifically, a layer of lime-based mortar is first coated on the surface of the beam as the bottom layer mortar. Before the bottom layer mortar is completely set, carbon fiber fabric is laid. Then, an upper layer of lime-based mortar is poured on the surface of the carbon fiber fabric and cured to allow the FRCM reinforcement layer to be formed as a whole.

[0055] After the FRCM reinforcement layer has cured, a Fe-SMA alloy plate is bent into a U-shape and arranged along the outer perimeter of the FRCM reinforcement layer, with both ends fixed to the reinforced concrete beam using clamps. Electrodes are placed on the surface of the Fe-SMA alloy U-shaped plate and connected to the activation end. Strain gauges are also attached to the surface of the Fe-SMA alloy U-shaped plate to collect deformation information, and thermocouples are placed in the reinforcement system to collect temperature information. The activation end is controlled by a control terminal to perform the first power-on heating activation of the Fe-SMA plate, inducing circumferential prestress. During the activation process, the heating process is controlled by the collected temperature information to keep the temperature of the Fe-SMA plate within a preset safe range. After heating and activation, the strain is measured to reach 0.11%.

[0056] After the bridge structure enters service, the acquisition unit continuously collects deformation and temperature information of the Fe-SMA alloy U-shaped plate and transmits the data to the control unit. When the Fe-SMA alloy U-shaped plate experiences stress relaxation under sustained or cyclic loading, resulting in a strain increment of 0.05%, the control unit triggers the activation unit to re-energize and re-heat the Fe-SMA alloy U-shaped plate to replenish the prestress. During the re-activation process, the control unit controls the heating process based on the acquired temperature information, maintaining the temperature of the Fe-SMA alloy U-shaped plate at 200℃. After re-heating and activation, the detected strain reaches 0.16%.

[0057] Test case 1. A cyclic tensile loading test was conducted on the Fe-SMA material of this invention under uniaxial cyclic tensile loading. The upper limit of the load level was selected as 65% of the ultimate strength. The results are as follows: Figure 2 As shown, Fe-SMA still exhibits excellent fatigue resistance (fatigue life: 97952) even under high load levels. This demonstrates its good fatigue resistance under external cyclic loading, supporting its use as a reinforcement material in bridge construction.

[0058] 2. Activation Temperature-Stress Curve: The Fe-SMA specimen was heated to activate it, and the recovery stress after stress stabilization was recorded. For example... Figure 3 As shown, it can be found that Fe-SMA can generate recovery stresses ranging from 131MPa to 363MPa within the activation temperature range of 150℃ to 350℃, demonstrating the feasibility of applying prestress using Fe-SMA.

[0059] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A self-prestressed composite reinforcement system for iron-based shape memory alloy-fiber fabric reinforced cement-based composites, characterized in that, Includes reinforced concrete beams, FRCM reinforcement layer, Fe-SMA alloy U-shaped plate, activation end, acquisition end, and control end; The FRCM reinforcement layer is provided on the outer surface of the reinforced concrete beam; The Fe-SMA alloy U-shaped plate is arranged along the outer periphery of the FRCM reinforcement layer and fixed to the reinforced concrete beam; The activation end is connected to the Fe-SMA alloy U-shaped plate and is used to electrically heat the Fe-SMA alloy U-shaped plate; The acquisition end is connected to the Fe-SMA alloy U-shaped plate and is used to acquire the temperature information and deformation amount of the Fe-SMA alloy U-shaped plate; The control terminal is connected to the activation terminal and the acquisition terminal, and is used to control the activation terminal to repeatedly heat the Fe-SMA alloy U-shaped plate, and to control the temperature of the Fe-SMA alloy U-shaped plate to be 160~200℃.

2. The system according to claim 1, characterized in that, The FRCM reinforcement layer includes a fiber fabric and an inorganic mortar covering the surface of the fiber fabric.

3. The system of claim 2, wherein, The fiber fabric includes at least one of carbon fiber, basalt fiber, glass fiber, aramid fiber, and p-phenylenediazole fiber.

4. The system of claim 2, wherein, The inorganic mortar includes at least one of cement-based mortar, lime-based mortar, and phosphate-based mortar.

5. The system of claim 1, wherein, The two ends of the Fe-SMA alloy U-shaped plate are fixed to the reinforced concrete beam by at least one of the following methods: bolt connection, anchor bolt connection, clamp connection, sleeve connection, and pre-embedded connection.

6. The system of claim 1, wherein, The activation end includes an electrode disposed on the surface of the Fe-SMA alloy U-shaped plate and a power supply device connected to the electrode.

7. The system of claim 1, wherein, The acquisition end includes a thermocouple and a strain gauge disposed on the surface of the Fe-SMA alloy U-shaped plate.

8. The system of claim 1, wherein, When the deformation measured by the acquisition terminal exceeds the preset strain threshold, the control terminal automatically activates the power supply to supplement the prestress.

9. The system of claim 8, wherein, The preset strain threshold is 0.5%-1%; Preferably, when considering cyclic loading, the preset strain threshold is 0.2% to 0.7%.

10. A method for self-prestressed composite reinforcement of iron-based shape memory alloy-fiber fabric reinforced cement-based composites, employing the system as described in claim 1, characterized in that, Includes the following steps: Step 1) Pour an FRCM reinforcement layer on the surface of the reinforced concrete beam. First, pour the bottom layer of mortar, lay the fiber fabric, then pour the top layer of mortar and cure it. Step 2) Fit the Fe-SMA alloy U-shaped plate around the outer perimeter of the FRCM reinforcement layer; Step 3) Connect the acquisition end to the surface of the Fe-SMA alloy U-shaped plate, fix the electrode on the Fe-SMA surface and connect the activation end; Step 4) The control end controls the activation end to perform the first power-on heating activation of Fe-SMA, generating circumferential prestress inside Fe-SMA, while controlling the activation temperature to not exceed 200℃. Step 5) Continuously monitor the strain change of Fe-SMA. When the strain increment reaches the preset strain threshold, the activation end is automatically triggered to reheat and activate, thus replenishing the prestress loss.

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