An iron-carbon coated long-period fiber grating sensor for steel bar corrosion monitoring

Abstract

The present invention provides an iron-carbon coated long-period fiber grating sensor for monitoring steel corrosion, which belongs to the technical field of structural health monitoring. The iron-carbon coated long-period fiber grating sensor for monitoring steel corrosion includes a long-period grating, a core, a cladding, a buffer coating, a conductive film and an iron-carbon film. Based on the high sensitivity of the long-period fiber grating to the refractive index of the external environment and the iron-carbon film having the same main component as carbon steel, the device realizes non-destructive, online real-time and quantitative monitoring of the corrosion status of steel bars in concrete structures, accurately determines the durability of concrete structures, and thus ensures the safety of major and important structures. The present invention has a simple structure, reasonable design, strong applicability, high sensitivity, strong reliability, and has broad application prospects and promotion markets.

Description

Technical Field

[0001] The invention relates to an iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion in concrete structures, belonging to the technical field of structural health monitoring, and in particular to an iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion. Background Art

[0002] Concrete structures are widely used in civil engineering construction because they give full play to the high tensile strength of steel bars and the high compressive strength of concrete. They are the most widely used civil engineering materials in the world today. However, for concrete structures in marine environments such as seaport projects, docks, coastal highway bridges, cross-sea bridges, and other coastal construction projects, steel corrosion is one of the important factors for the durability failure of concrete structures. Therefore, it is necessary to effectively monitor the steel corrosion status of the structure and grasp the actual damage degree of the structure in real time, providing an important basis for structural durability assessment, remaining life prediction, and reinforcement and maintenance.

[0003] At present, the methods for monitoring steel corrosion can be roughly divided into two categories: electrochemical methods and non-electrochemical methods. Among them, electrochemical methods include half-cell potential method, linear polarization method, AC impedance method, electrochemical noise method, etc., and non-electrochemical methods include surface inspection method, weight loss method, ultrasonic method, eddy current method, acoustic emission method, etc. However, most of the above monitoring methods have problems such as inconvenient operation, complex monitoring process, long monitoring execution time, and low monitoring accuracy.

[0004] In recent years, due to the advantages of optical fiber, such as being small and light, resistant to electromagnetic interference, and capable of networking, some sensors based on optical fiber sensing technology have also been used for monitoring steel corrosion. Compared with ordinary optical fiber sensing technology, long-period fiber gratings are highly sensitive to the refractive index of the external environment and are better suited for monitoring steel corrosion inside concrete.

[0005] Therefore, for the monitoring of steel bar corrosion conditions, it is very necessary to provide a long-period fiber grating sensor that is anti-interference, highly sensitive to the steel bar corrosion state, accurate and reliable based on the high sensitivity of long-period fiber grating to the refractive index of the external environment, thereby providing an important basis for the durability life prediction of concrete structures. Summary of the invention

[0006] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide an iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion, the purpose of which is to achieve non-destructive, online real-time, quantitative monitoring of the corrosion condition of steel bars in concrete structures, accurately determine the durability of concrete structures, and thus ensure the safety of major important engineering structures.

[0007] The technical solution of the present invention:

[0008] An iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion, comprising a long-period grating 1, a fiber core 2, a cladding 3, a buffer coating 4, a conductive film 5 and an iron-carbon film 6;

[0009] The fiber core 2, cladding 3, buffer coating layer 4, conductive film 5 and iron-carbon film 6 are all cylindrical media;

[0010] The long period grating 1 is written into the middle local position of the fiber core 2;

[0011] The outer side of the core 2 is a cladding 3 , the outer sides of both ends of the cladding 3 are buffer coating layers 4 , the outer side of the middle part of the cladding is a conductive film 5 , and the outer side of the conductive film 5 is an iron-carbon film 6 .

[0012] The long period grating 1 is a one-dimensional grating with a one-dimensional periodic structure, and its period and total length are adjusted according to the size of the detection object.

[0013] The refractive index of the core 2 is greater than the refractive index of the cladding 3 .

[0014] The conductive film 5 is formed by depositing a conductive material, and the conductive material is graphene, silver or gold.

[0015] The thickness of the conductive film 5 and the iron-carbon film 6 is adjusted according to the sensor sensitivity requirements.

[0016] Working principle of the present invention:

[0017] Long-period fiber grating is a distributed structure with periodic modulation of the core refractive index. This modulation couples the incident light guided in the core fundamental mode with the cladding mode propagating in the same direction, thereby generating a series of attenuation bands in the transmission spectrum due to absorption and scattering. The resonant wavelength of the attenuation band is λ res depends on the grating period and the refractive indices of the core, cladding and surrounding medium and is given by:

[0018]

[0019] Where n core (λ) is the effective refractive index of the core fundamental mode at wavelength λ, is the effective refractive index of the i-th order cladding mode, Λ is the grating period; is the core refractive index n 1 , cladding refractive index n 2 and the refractive index of the surrounding medium n 3 function.

[0020] Therefore, the resonant wavelength λ res As the refractive index n of the medium around the grating 3 changes with the changes.

[0021] The iron-carbon film electroplated on the outside of the long-period grating is used to simulate the composition of low-carbon steel widely used in reinforced concrete structures. When the iron-carbon film is corroded, the refractive index of the medium around the grating changes from n 3 becomes n′ 3 , resulting in a change in the transmission spectrum, the resonant wavelength in the transmission spectrum changes from λ res becomes λ′ res .

[0022] The change in the resonant wavelength is Right now

[0023]

[0024] The percentage of mass loss of iron-carbon film caused by corrosion and the change of resonance wavelength The relationship can be expressed as follows:

[0025]

[0026] Where β is the mass loss percentage of the iron-carbon film and the change in the resonant wavelength The linear relationship coefficient is determined by experimental fitting.

[0027] Therefore, the iron-carbon coated long-period fiber grating sensor is arranged around the steel bars in the concrete structure, and the change in the resonant wavelength of the iron-carbon coated long-period fiber grating sensor is measured. According to the relationship (3), the mass loss percentage η of the iron-carbon film can be obtained, and the quantitative monitoring of the corrosion state of the iron-carbon film can be realized. Since the iron-carbon film has the same composition as the steel bars in the concrete structure, the quantitative monitoring of the corrosion state of the steel bars under test can also be realized.

[0028] Beneficial effects of the present invention:

[0029] (1) The present invention realizes quantitative monitoring of the degree of steel bar corrosion by monitoring the change in the resonant wavelength of the long-period fiber grating transmission spectrum.

[0030] (2) The present invention has high sensitivity, because the high sensitivity to the refractive index of the external environment makes it highly sensitive to the corrosion state of the steel bars.

[0031] (3) The present invention is easy to deploy and can realize online real-time monitoring of the corrosion status of steel bars.

[0032] (4) The present invention has extremely high resolution, which can reach nanometer or sub-nanometer level.

[0033] (5) The present invention can realize non-destructive monitoring and can non-destructively monitor the steel corrosion condition of the concrete structure, thereby implementing better management and maintenance of the engineering structure.

[0034] (6) The present invention has fast monitoring speed and high accuracy, and provides a theoretical basis and experimental data support for the durability life prediction of engineering structures.

[0035] (7) The present invention has good environmental adaptability and long service life.

[0036] (8) The present invention has a simple structure, reasonable design, strong applicability, and broad application prospects and promotion market. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The schematic diagram of the structure of the iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion of the present invention;

[0038] Figure 2 It is a cross-sectional view taken along line AA of the iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion according to the present invention;

[0039] Figure 3 It is a BB cross-sectional view of the iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion of the present invention;

[0040] Figure 4 A schematic diagram of the arrangement of the iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion of the present invention applied to monitoring steel bars in actual concrete structures;

[0041] Figure 5 Schematic diagram of the sensing mechanism of the iron-carbon coated long-period fiber grating sensor, (a) before the iron-carbon film is corroded, (b) after the iron-carbon film is corroded.

[0042] In the figure: 1 long period grating; 2 fiber core; 3 cladding; 4 buffer coating layer; 5 conductive film; 6 iron carbon film. DETAILED DESCRIPTION

[0043] In order to make the purpose, features and advantages of the present invention more obvious and easy to understand, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described below are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0044] like Figures 1 to 3 As shown, an embodiment of an iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion provided by the present invention comprises a long-period grating 1, a core 2, a cladding 3, a buffer coating layer 4, a conductive film 5, and an iron-carbon film 6;

[0045] The fiber core 2, cladding 3, buffer coating layer 4, conductive film 5, and iron-carbon film 6 are all cylindrical media;

[0046] The long period grating 1 is written into the middle local position of the fiber core 2;

[0047] The outer side of the core 2 is a cladding 3, the outer sides of both ends of the cladding 3 are buffer coating layers 4, the outer side of the middle part of the cladding 3 is a conductive film 5, and the outer side of the conductive film 5 is an iron-carbon film 6; the conductive film 5 is a silver film;

[0048] The period of the long period grating 1 is 386.9 μm and the total length is 40 mm;

[0049] The diameter of the fiber core 2 is 8.2 μm, the diameter of the cladding 3 is 125 μm, and the diameter of the buffer coating layer 4 is 245 μm;

[0050] The refractive index of the core 2 is 1.469, and the refractive index of the cladding 3 is 1.463;

[0051] The thickness of the silver film is 800 nm, the thickness of the iron-carbon film 6 is 20 μm, and the lengths of the silver film and the iron-carbon film 6 are both 10 cm;

[0052] In an embodiment of the present invention, a method for preparing an iron-carbon coated long-period fiber grating sensor for monitoring steel corrosion includes the iron-carbon coated long-period fiber grating sensor for monitoring steel corrosion described in any one of the above, comprising the following steps:

[0053] Step S1: Take a section doped with GeO 2 A single-mode optical fiber (Corning SMF-28e optical fiber) was used, and a fiber stripper was used to strip off a 10 cm long buffer coating layer in the middle of the optical fiber.

[0054] Step S2: placing the stripped optical fiber on a moving platform (model: Newport PM500) with a resolution of 100 nm.

[0055] Step S3: Using CO 2 The laser beam emitted by the laser is focused by a cylindrical lens with a focal length of 50 mm to form a narrow line segment of light perpendicular to the fiber axis with a length of about 2 mm and a width of about 100 μm. Under computer control, the mobile platform is moved with the CO 2 The lasers move in coordination to write the long-period grating point by point at the location where the fiber is stripped of the 10cm long buffer coating;

[0056] Furthermore, CO 2The output power of the laser is about 7.8 W. During the long-period grating fabrication process, a broadband light source (BBS, Agilent 83437) and an optical spectrum analyzer (OSA, Yokogawa AQ6319) are used simultaneously to ensure that the transmission spectrum intensity loss is greater than 20 dB.

[0057] Step S4: Clean the optical fiber after writing the long period grating with 20% NaOH solution for 10 minutes to remove the contaminants attached to its surface, then clean it with distilled water for 3 minutes using an ultrasonic cleaner, and finally dry it in an oven at 100°C for 5 minutes.

[0058] Step S5: using a radio frequency magnetron sputtering system (Denton Vacuum Discovery-18) to perform sputtering deposition coating on the cleaned long period grating using a Ag target (produced by Kurt J. Lesker) with a purity of 99.99%, a diameter of 76.2 mm, and a thickness of 6.35 mm;

[0059] Further, the cleaned optical fiber is fixed on a copper frame to ensure that the optical fiber remains straight during the silver film deposition process, and the copper frame is placed on a platform rotating at a constant speed to ensure that the silver film is deposited evenly;

[0060] Furthermore, the silver target was pretreated for 30 minutes before the shutter between the silver target and the long period grating was opened; the silver film deposition was completed at a power of 100 W, and the base pressure of the deposition chamber before the system sputtering was about 10 -4 Pa, while during sputtering the deposition chamber is filled with 40 cubic centimeters of flowing high-purity argon gas, and the working pressure is about 1Pa.

[0061] Step S6: at room temperature of 21°C, immersing the long period grating region in an electroplating solution, connecting the positive electrode of the power supply to the graphite rod inserted into the solution, and connecting the negative electrode of the external power supply to the silver film using an alligator clip and a conductive rubber ring, and electroplating for about 2 hours to produce a 20 μm thick iron-carbon film;

[0062] Furthermore, an electroplating solution was prepared by dissolving FeSO 4·7H 2O (40 g / L), citric acid (1.2 g / L) and L-ascorbic acid (3.0 g / L) in distilled water, and the composition of the electroplating solution was intended to produce an iron-carbon film having the same main component as carbon steel; a conductive rubber ring was placed between the alligator clip and the silver film to protect the silver film and have a good electrical connection.

[0063] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion, characterized in that: The iron-carbon coated long-period optical fiber grating sensor for monitoring steel bar corrosion comprises a long-period optical fiber grating (1), a fiber core (2), a cladding (3), a buffer coating layer (4), a conductive film (5) and an iron-carbon film (6); The fiber core (2), cladding (3), buffer coating layer (4), conductive film (5) and iron-carbon film (6) are all cylindrical media; the refractive index of the fiber core (2) is greater than the refractive index of the cladding (3); The iron-carbon film (6) has the same composition as the steel bars in the concrete structure; The long-period grating (1) is written into a local middle position of the fiber core (2); The outer side of the fiber core (2) is a cladding (3), the outer sides of both ends of the cladding (3) are buffer coating layers (4), the outer side of the middle part of the cladding is a conductive film (5), and the outer side of the conductive film (5) is an iron-carbon film (6); the conductive film (5) is deposited by a conductive material, and the conductive material is graphene, silver or gold.

2. The iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion according to claim 1, characterized in that: The long period grating (1) is a one-dimensional grating with a one-dimensional periodic structure, and its period and total length are adjusted according to the size of the detection object.

3. The iron-carbon coated long-period fiber grating sensor for monitoring steel bar corrosion according to claim 1 or 2, characterized in that: The thickness of the conductive film (5) and the iron-carbon film (6) are adjusted according to the sensitivity requirements of the sensor.

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