A fiber fabric reinforced cementitious composite prestressed reinforcement system and method

Abstract

The application discloses a kind of fiber fabric reinforced cement-based composite material prestressed reinforcement system, including concrete structure, fiber fabric reinforced cement-based composite material layer, iron-based shape memory alloy material, monitoring control unit;The fiber fabric reinforced cement-based composite material layer includes fiber grid and inorganic cement matrix;The iron-based shape memory alloy material is arranged along the two ends of fiber grid extension direction in the fiber fabric reinforced cement-based composite material layer, one end is fixed with the fiber grid, the other end is fixed with the concrete structure;The monitoring control unit is connected with the fiber fabric reinforced cement-based composite material layer and iron-based shape memory alloy material.The application is arranged along the fiber direction by iron-based shape memory alloy material after pre-stretching, and pre-tightening force along the fiber direction is applied to fiber grid after being activated by heating, to prevent fiber bending in fiber layer, bending.

Description

Technical Field

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

[0002] Fabric-reinforced cementitious matrix (FRCM) uses inorganic cement mortar instead of organic resin as the matrix, offering advantages such as good physicochemical compatibility with concrete, excellent fire resistance, good permeability, minimal temperature influence, and non-toxic and harmless construction. However, due to the difficulty in fully impregnating the dry fiber bundles in FRCM with the cement mortar, the fibers are prone to pull-out and slippage from the mortar, resulting in low fiber utilization and limiting its full reinforcement effect.

[0003] To address the aforementioned issues, existing technologies have proposed methods for applying prestress to FRCM fibers. Typically, tensioning equipment is used to tension the fibers before pouring mortar. After the mortar solidifies, the tension is released to enhance the synergistic effect between the fibers and the mortar. However, tensioning equipment is bulky, and prestressing using it is complex, making it unsuitable for on-site operations. Furthermore, once the prestress is applied, it cannot be adjusted based on prestress loss during service.

[0004] Existing technologies also disclose methods for applying prestress to carbon fiber reinforced polymer (CFRP) composites using shape memory alloy (SMA) materials. However, such methods typically involve only one heat activation during the construction phase, followed by fixing of the connection devices, making it impossible to reactivate and replenish prestress based on prestress loss during the structure's service life. Furthermore, since CFRP uses an organic resin matrix, repeated heat activation and thermal cycling will cause the resin matrix to soften, age, and even debond from the concrete interface, resulting in prestress transfer failure.

[0005] Therefore, there is an urgent need for a fiber-reinforced cement-based composite prestressing system and method that can apply prestress to the fibers inside the FRCM without relying on heavy tensioning equipment, and can monitor the prestress status and reactivate and replenish it during the service life of the structure to meet the needs of the structure's life cycle maintenance. Summary of the Invention

[0006] To address the complexity of prestressing construction using tensioning equipment in existing fiber-reinforced cement-based composite (FRCM) reinforcement technologies, this invention provides a prestressed reinforcement system and method for fiber-reinforced cement-based composites.

[0007] A fiber-reinforced cement-based composite prestressed reinforcement system includes a concrete structure, a fiber-reinforced cement-based composite layer, an iron-based shape memory alloy material, and a monitoring and control unit. The fiber-reinforced cement-based composite material layer comprises a fiber mesh and an inorganic cement matrix; The iron-based shape memory alloy material is arranged at both ends along the extension direction of the fiber mesh in the fiber-reinforced cement-based composite material layer, with one end fixed to the fiber mesh and the other end fixed to the concrete structure. The monitoring and control unit is connected to the fiber-reinforced cement-based composite material layer and the iron-based shape memory alloy material.

[0008] Optionally, the fiber mesh includes at least one of carbon fiber, basalt fiber, glass fiber, and aramid fiber.

[0009] Optionally, the inorganic cement matrix includes at least one of cement mortar, phosphate cement mortar, and geopolymer mortar.

[0010] Optionally, the iron-based shape memory alloy material is in a pre-stretched state.

[0011] Optionally, the iron-based shape memory alloy material is fixed to the concrete structure by at least one of the following methods: bolt connection, anchor bolt connection, clamp connection, sleeve connection, pre-embedded connection, and adhesive fixation.

[0012] Optionally, the monitoring and control unit includes: The acquisition end is connected to the surface of the fiber-reinforced cement-based composite material layer and the iron-based shape memory alloy material; The activation end is electrically connected to the iron-based shape memory alloy material; The control terminal is connected to the acquisition terminal and the activation terminal.

[0013] Optionally, the acquisition end includes a strain gauge disposed on the surface of the fiber-reinforced cementitious composite material layer and a thermocouple connected to an iron-based shape memory alloy material.

[0014] Optionally, the activation terminal is used to apply an excitation current with a current density of 5-9 A / mm² to the iron-based shape memory alloy material to heat the iron-based shape memory alloy material, and the heating temperature is 160-200℃.

[0015] This invention also proposes a method for prestressed reinforcement of fiber-reinforced cementitious composite materials, using the above-mentioned system, comprising the following steps: Step 1) The iron-based shape memory alloy material is pre-stretched by heating to produce pre-deformation. One end of the pre-stretched iron-based shape memory alloy material is fixed to the fiber mesh, and the other end is fixed to the surface of the concrete structure. Step 2) Activate the iron-based shape memory alloy material by heating; Step 3) Cast inorganic cement matrix material onto the surface of the fiber mesh to form a fiber fabric reinforced cement matrix composite material layer; Step 4) Attach strain gauges to the surface of the fiber-reinforced cement-based composite material layer; attach electrodes and thermocouples to the surface of the iron-based shape memory alloy material; connect the strain gauges and thermocouples to the acquisition end, electrically connect the electrodes to the activation end, and connect the acquisition end and the activation end through the control end; Step 5) The acquisition end acquires the strain data of the strain gauge. When the strain data meets the preset conditions, the iron-based shape memory alloy material is heated and activated again.

[0016] Preferably, the strain data satisfies the preset condition according to Calculate the prestress retention rate when Then, the iron-based shape memory alloy material is heated and activated again; wherein... The prestress threshold, =0.7-0.9; where The strain values ​​obtained by monitoring strain gauges at the acquisition end. This represents the initial strain value of the strain gauge.

[0017] The technical solution of this invention has the following advantages: This invention arranges pre-stretched iron-based shape memory alloy material along the fiber direction, fixing one end to a fiber mesh and the other end to a concrete structure. After heating and activation, a pre-tightening force is applied along the fiber direction to the fiber mesh, preventing fiber bending and twisting within the fiber layer, inhibiting interfacial slippage between the fiber and the inorganic cement matrix, and improving fiber utilization. Simultaneously, by applying prestress to the fiber mesh, further prestress is applied to the reinforced structure itself, increasing the cracking load of the reinforced component.

[0018] This invention uses a monitoring and control unit to continuously collect strain data of the fiber mesh during the service life of the structure. When preset conditions are met, it automatically triggers reheating activation, realizing real-time monitoring and replenishment of prestress and meeting the maintenance needs of the structure throughout its entire life cycle.

[0019] This invention employs fiber-reinforced cementitious composite material (FRCM). In FRCM, the fibers and inorganic cement cannot be fully impregnated, resulting in some natural bending within the fibers. Under external tensile stress, this can easily lead to interfacial slippage damage between the fibers and the mortar. Pre-tensioning with Fe-SMA straightens the fibers, eliminating natural bending and allowing for more thorough contact between the fibers and the mortar, thus improving the utilization rate of the fibers within the FRCM mortar. Furthermore, after prestressing, the natural stress recovery process causes micro-expansion of the fibers due to the Poisson effect, further enhancing the bond between the internal fibers and the mortar, thereby strengthening the reinforcement effect. Attached Figure Description

[0020] 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.

[0021] Figure 1 This is a schematic diagram illustrating the effect of the fiber fabric reinforced cement-based composite prestressed reinforcement system in Embodiment 1 of the present invention. Detailed Implementation

[0022] 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.

[0023] 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.

[0024] 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 have been described herein, any methods and materials similar to or equivalent to those described herein may be used in the implementation or testing of this invention.

[0025] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0026] In a first aspect, the present invention discloses a fiber fabric reinforced cement-based composite material prestressed reinforcement system, comprising a concrete structure, a fiber fabric reinforced cement-based composite material layer, an iron-based shape memory alloy material, and a monitoring and control unit; The fiber-reinforced cement-based composite material layer comprises a fiber mesh and an inorganic cement matrix; The iron-based shape memory alloy material is arranged at both ends along the extension direction of the fiber mesh in the fiber-reinforced cement-based composite material layer, with one end fixed to the fiber mesh and the other end fixed to the concrete structure. The monitoring and control unit is connected to the fiber-reinforced cement-based composite material layer and the iron-based shape memory alloy material.

[0027] In one alternative embodiment, the fiber mesh comprises at least one of carbon fiber, basalt fiber, glass fiber, and aramid fiber.

[0028] In one alternative embodiment, the inorganic cement matrix includes at least one of cement mortar, phosphate cement mortar, and geopolymer mortar.

[0029] In one alternative embodiment, the iron-based shape memory alloy material is in a pre-stretched state.

[0030] In one optional embodiment, the iron-based shape memory alloy material is fixed to the concrete structure by at least one of bolt connection, anchor bolt connection, clamp connection, sleeve connection, pre-embedded connection, and adhesive fixation.

[0031] In one optional implementation, the monitoring and control unit includes: The acquisition end is disposed on the surface of the fiber-reinforced cement-based composite material layer; The activation end is electrically connected to the iron-based shape memory alloy material; The control terminal is connected to the acquisition terminal and the activation terminal.

[0032] In one alternative implementation, the acquisition end includes a strain gauge, and the acquisition end transmits strain data to the control end.

[0033] In one optional embodiment, the activation terminal applies an excitation current with a current density of 5-9 A / mm² to the iron-based shape memory alloy material, and controls the heating temperature to be 160-200℃.

[0034] Secondly, the present invention also discloses a method for prestressing reinforcement of fiber-reinforced cement-based composite materials, using the above-mentioned system, comprising the following steps: (1) The iron-based shape memory alloy material is pre-stretched to produce pre-deformation. One end of the pre-stretched iron-based shape memory alloy material is fixed to the fiber mesh, and the other end is fixed to the surface of the concrete structure. (2) The iron-based shape memory alloy material is activated by heating; (3) Inorganic cement matrix material is cast onto the surface of the fiber mesh to form a fiber fabric reinforced cement matrix composite material layer; (4) Collect the strain data of the fiber mesh. When the strain data meets the preset conditions, heat the iron-based shape memory alloy material again to activate it.

[0035] In one optional implementation, the strain data satisfies a preset condition according to... Calculate the prestress retention rate when Then, the iron-based shape memory alloy material is heated and activated again; wherein... The prestress threshold, =0.7-0.9; where The strain values ​​obtained by monitoring strain gauges at the acquisition end. This represents the initial strain value of the strain gauge.

[0036] 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.

[0037] 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.

[0038] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0039] Example 1 like Figure 1 As shown, this embodiment provides a fiber fabric reinforced cement-based composite prestressed reinforcement system and method.

[0040] (1) System Construction In this embodiment, the concrete structure 1 to be reinforced is a reinforced concrete T-beam with a span of 10m and multiple vertical cracks at the bottom of the beam.

[0041] A fiber-reinforced cementitious composite layer 2 is applied to the tension surface of the bottom beam of the concrete structure 1 to be reinforced. The fiber-reinforced cementitious composite layer 2 comprises a fiber mesh 21 and an inorganic cement matrix 22 enclosing the fiber mesh 21. The fiber mesh 21 is a carbon fiber mesh with a mesh size of 10mm × 10mm, and the fiber bundles are 12K carbon fiber bundles. The inorganic cement matrix 22 is ordinary silicate cement mortar with a water-cement ratio of 0.4, incorporating polypropylene fibers to improve crack resistance.

[0042] Iron-based shape memory alloy material (Fe-SMA material 3) is arranged at both ends along the fiber direction of the fiber-reinforced cement-based composite layer 2. Fe-SMA material 3 is a MnSiCrNiFe alloy material with a thickness of 2 mm, a width of 50 mm, and a length determined according to the beam width. Fe-SMA material 3 is in a pre-stretched state with a pre-stretch strain of 2%. One end of Fe-SMA material 3 is bonded and fixed to the end of the fiber mesh 21 with high-strength, high-temperature resistant epoxy resin adhesive, and the other end is bonded and fixed to the bottom of the beam of the concrete structure 1 to be reinforced with high-strength, high-temperature resistant epoxy resin adhesive.

[0043] (2) Construction steps 1. Roughen and clean the bottom of the beam, then apply a bonding agent; 2. Pre-stretch the Fe-SMA sheet to 2% strain; 3. Bond one end of the pre-stretched Fe-SMA sheet 3 to the fiber mesh 21, and the other end to the concrete at the bottom of the beam; 4. Initial activation: The control terminal 43 controls the activation terminal 42 to apply a current density of 7 A / mm² through the electrode 5, and monitors the temperature through the thermocouple 6. After heating to 160°C, the power is cut off and the device is allowed to cool naturally to establish the initial prestress. 5. Pouring: First, pour the bottom layer mortar (5mm thick) on the surface of the fiber mesh 21, then lay the fiber mesh, and then pour the top layer mortar (5mm thick), and cure for 28 days; 6. Service life monitoring reactivation: The acquisition end 41 collects strain data, and the control end 43 calculates the prestress retention rate Rε(t)=εf(t) / εf,0. When Rε(t)=0.8, the reheating activation is automatically triggered (current density 7 A / mm², target temperature 180℃).

[0044] The experimental results are as follows: (1) Initial activation effect: The initial pre-strain εf,0 = 1250 micro-strain was measured on the surface strain gauge 7 of the FRCM layer; the mid-span cracking load increased from 18.5kN before reinforcement to 26.8kN (an increase of 45%).

[0045] (2) Cyclic load test: After applying 200,000 cycles of load (3-25kN, simulating vehicle fatigue), the current strain εf=875 microstrain was measured, and the prestress retention rate Rε=0.70.

[0046] (3) Reactivation effect: Reactivation is triggered when Rε≤0.8. After reactivation, the strain recovers to εf=1180 microstrain, the prestress retention rate recovers to Rε=0.94, and the cracking load recovers to 25.9kN (recovery rate 96.6%).

[0047] Example 2 like Figure 1 As shown, this embodiment provides a fiber fabric reinforced cement-based composite prestressed reinforcement system and method.

[0048] The difference between this embodiment and Embodiment 1 is that: the fiber mesh is a basalt fiber mesh; the inorganic cement matrix is ​​phosphate cement mortar; and the iron-based shape memory alloy material is fixed to the concrete structure at both ends by bolt connection.

[0049] A current density of 9 A / mm² was applied, and the temperature was heated to 160°C before power was cut off and the system cooled. Reactivation was triggered when the prestress threshold reached 0.9.

[0050] The experimental results are as follows: (1) Initial activation effect: The initial pre-strain εf,0 = 1120 microstrain was measured by strain gauges on the surface of the FRCM layer; the mid-span cracking load increased from 18.5kN before reinforcement to 25.1kN (an increase of 35.7%).

[0051] (2) Cyclic load test: After applying 200,000 cycles of load (3-25kN, simulating vehicle fatigue), the current strain εf=940 microstrain was measured, and the prestress retention rate Rε=0.87.

[0052] (3) Reactivation effect: Reactivation is triggered when Rε≤0.9. After reactivation, the strain recovers to εf=1040 microstrain, and the prestress retention rate recovers to Rε=0.96.

[0053] Example 3 The difference between this embodiment and Embodiment 1 is that the inorganic cement matrix is ​​phosphate cement mortar; A current density of 5 A / mm² is applied, and the temperature is heated to 200°C before being cooled down. Reactivation is triggered when the prestress threshold is 0.7.

[0054] The experimental results are as follows: (1) Initial activation effect: The initial pre-strain εf,0 = 1030 microstrain was measured by strain gauges on the surface of the FRCM layer; the mid-span cracking load increased from 18.5kN before reinforcement to 28.2kN (an increase of 52.4%).

[0055] (2) Cyclic load test: After applying 200,000 cycles of load (3-25kN, simulating vehicle fatigue), the current strain εf=805 microstrain was measured, and the prestress retention rate Rε=0.70.

[0056] (3) Reactivation effect: Reactivation is triggered when Rε≤0.7. After reactivation, the strain recovers to εf=1070 microstrain, and the prestress retention rate recovers to Rε=0.93.

[0057] Based on the above experiments, this invention, by arranging pre-stretched iron-based shape memory alloy material along the fiber direction, fixing one end to the fiber mesh and the other end to the concrete structure, and applying a pre-tightening force along the fiber direction to the fiber mesh after heating activation, prevents the fibers within the fiber layer from bending or twisting, inhibits interfacial slippage between the fibers and the inorganic cement matrix, and improves fiber utilization. Simultaneously, by applying prestress to the fiber mesh, further prestress is applied to the reinforced structure itself, increasing the cracking load of the reinforced component.

[0058] 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 fiber-reinforced cement-based composite prestressed reinforcement system, characterized in that, This includes concrete structures, fiber-reinforced cementitious composite layers, iron-based shape memory alloy materials, and monitoring and control units; The fiber-reinforced cement-based composite material layer comprises a fiber mesh and an inorganic cement matrix; The iron-based shape memory alloy material is arranged at both ends along the extension direction of the fiber mesh in the fiber-reinforced cement-based composite material layer, with one end fixed to the fiber mesh and the other end fixed to the concrete structure. The monitoring and control unit is connected to the fiber-reinforced cement-based composite material layer and the iron-based shape memory alloy material.

2. The system according to claim 1, characterized in that, The fiber mesh includes at least one of carbon fiber, basalt fiber, glass fiber, and aramid fiber.

3. The system according to claim 1, characterized in that, The inorganic cement matrix includes at least one of cement mortar, phosphate cement mortar, and geopolymer mortar.

4. The system according to claim 1, characterized in that, The iron-based shape memory alloy material is in a pre-stretched state.

5. The system according to claim 1, characterized in that, The iron-based shape memory alloy material is fixed to the concrete structure by at least one of the following methods: bolt connection, anchor bolt connection, clamp connection, sleeve connection, pre-embedded connection, and adhesive fixation.

6. The system according to claim 1, characterized in that, The monitoring and control unit includes: The acquisition end is connected to the surface of the fiber-reinforced cement-based composite material layer and the iron-based shape memory alloy material; The activation end is electrically connected to the iron-based shape memory alloy material; The control terminal is connected to the acquisition terminal and the activation terminal.

7. The system according to claim 6, characterized in that, The acquisition end includes a strain gauge disposed on the surface of the fiber-reinforced cementitious composite material layer and a thermocouple connected to an iron-based shape memory alloy material.

8. The system according to claim 6, characterized in that, The activation terminal is used to apply an excitation current with a current density of 5-9 A / mm² to the iron-based shape memory alloy material to heat the iron-based shape memory alloy material, and the heating temperature is 160-200℃.

9. A method for prestressing reinforcement of fiber-reinforced cementitious composite materials, employing the system described in claim 1, characterized in that, Includes the following steps: Step 1) The iron-based shape memory alloy material is pre-stretched by heating to produce pre-deformation. One end of the pre-stretched iron-based shape memory alloy material is fixed to the fiber mesh, and the other end is fixed to the surface of the concrete structure. Step 2) Activate the iron-based shape memory alloy material by heating; Step 3) Cast inorganic cement matrix material onto the surface of the fiber mesh to form a fiber fabric reinforced cement matrix composite material layer; Step 4) Attach strain gauges to the surface of the fiber-reinforced cementitious composite layer; Electrodes and thermocouples are attached to the surface of an iron-based shape memory alloy material; the strain gauges and thermocouples are connected to the acquisition end, the electrodes are electrically connected to the activation end, and the acquisition end and the activation end are connected through a control end; Step 5) The acquisition end acquires the strain data of the strain gauge. When the strain data meets the preset conditions, the iron-based shape memory alloy material is heated and activated again.

10. The method according to claim 9, characterized in that, The strain data meets the preset condition as follows: Calculate the prestress retention rate when Then, the iron-based shape memory alloy material is heated and activated again; wherein... The prestress threshold, =0.7-0.9; in The strain values ​​obtained by monitoring strain gauges at the acquisition end. This represents the initial strain value of the strain gauge.

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