Fiber Bragg grating sensor for in-situ real-time monitoring of concrete rust cracking strain field around steel bars and rust cracking prediction

Abstract

A fiber grating sensor for real-time monitoring of concrete rust cracking strain field and rust cracking prediction in situ includes a support system, a fiber fixing system, a radial strain measurement sensor, a circumferential strain measurement sensor, a signal demodulation system and a data acquisition system. The fiber fixing system is arranged on the support system, the radial strain measurement sensor and the circumferential strain measurement sensor are inserted into the fiber fixing system, the radial strain measurement sensor and the circumferential strain measurement sensor are respectively connected to the signal demodulation system, and the signal demodulation system is connected to the data acquisition system. The present invention provides a fiber grating sensor with simple operation, short test cycle, low cost, and capable of real-time monitoring of radial and circumferential rust cracking strain field changes of concrete around steel bars in situ, improving the accuracy and authenticity of the results, which is of vital importance for in-depth research on the problem of reduced concrete durability caused by steel bar corrosion, and provides a basic guarantee for future concrete structure durability design.

Description

Technical Field

[0001] The invention belongs to the field of concrete strain field monitoring, and relates to a fiber grating sensor for in-situ real-time monitoring of concrete rust cracking strain field around steel bars and rust cracking prediction. Background Art

[0002] As one of the most important building materials in the world today, concrete is widely used due to its advantages in material, cost, production process, etc. It is not only used in various civil engineering projects, but also a very important material in shipbuilding, machinery industry, marine development and other projects. For concrete structures in marine environment and deicing salt environment, steel corrosion is the main factor affecting the durability of concrete structures. A large number of concrete structures have caused serious economic losses due to the deterioration of durability, and have also exerted tremendous pressure and adverse effects on the world's energy supply, environmental pollution and sustainable development.

[0003] The degradation of concrete structure performance caused by steel bar corrosion is due to the production of corrosive substances. The density of corrosion products is lower than that of steel bars. They accumulate on the surface of steel bars and expand in volume, generating rust expansion pressure between steel bars and concrete, which leads to cracking and peeling of concrete outside the steel bars. In fact, concrete not only bears expansion force in the radial direction, but also tensile stress in the circumferential direction. Therefore, the problem of concrete cracking caused by steel bar corrosion should be studied from the perspective of various anisotropic damages of concrete under multi-axial stress state. In-situ real-time monitoring of the changes in the radial and circumferential rust cracking strain field of concrete around steel bars is helpful to statistically analyze various aspects of steel bar corrosion data, and provide a basis for predicting the degree and time of rust cracking of reinforced concrete under different environments in the future.

[0004] The Chinese patent authorization announcement number is CN104567709A, the authorization announcement date is January 14, 2015, and the name is "A W-shaped fiber grating sensor patch"; the Chinese patent authorization announcement number is CN205561776U, the authorization announcement date is September 7, 2016, and the name is "A fiber grating patch strain sensor"; the Chinese patent authorization announcement number is CN107218900A, the authorization announcement date is September 29, 2017, and the name is "A PCCP strain testing method based on fiber grating strain sensing technology". All three invention applications use patch-type fiber grating sensors to obtain the data to be tested. Although the patch-type sensor can monitor radial strain in real time, it can only be arranged in a single straight line direction and cannot obtain the strain along the circumferential direction of the steel bar. It cannot truly reflect the circumferential strain field of the surrounding concrete when the steel bar rusts and expands, and cannot obtain accurate and reliable data to predict the degree and time of rust cracking of reinforced concrete under different conditions. Summary of the invention

[0005] In order to overcome the shortcomings of the existing fiber grating sensors, such as cumbersome operation, long test cycle, high cost, and inability to monitor the radial and circumferential rust crack strain field changes of concrete around steel bars in real time, the present invention provides a fiber grating sensor with simple operation, short test cycle, low cost, and the ability to monitor the radial and circumferential rust crack strain field changes of concrete around steel bars in real time, thereby improving the accuracy and authenticity of the results, which is of vital importance for in-depth research on the problem of reduced concrete durability caused by steel bar corrosion, and provides a basic guarantee for the future durability design of concrete structures.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A fiber grating sensor for in-situ real-time monitoring of concrete rust cracking strain field around steel bars and rust cracking prediction comprises a support system, an optical fiber fixing system, a radial strain measurement sensor, a circumferential strain measurement sensor, a signal demodulation system and a data acquisition system. The optical fiber fixing system is arranged on the support system, the radial strain measurement sensor and the circumferential strain measurement sensor are inserted into the optical fiber fixing system, the radial strain measurement sensor and the circumferential strain measurement sensor are respectively connected to the signal demodulation system, and the signal demodulation system is connected to the data acquisition system.

[0008] Furthermore, the support system includes an adaptive frame system, a tie system, a fixed ring and fixed nodes. The fixed nodes are arranged one-to-one at equal intervals on the fixed ring and the adaptive frame system. The fixed nodes are arranged at the junction of the tie system and the optical fiber fixing system. The fixed ring is connected to the tie system, and the tie system is connected to the adaptive frame system.

[0009] Furthermore, the optical fiber fixing system includes a radial fixing system and an annular fixing system. The optical fiber fixing system is a hollow tubular structure. The radial fixing system includes a horizontal transverse fixing structure and a vertical vertical fixing structure. The annular fixing system includes a set number of circular fixing structures with overlapping circle centers and diameters that are related multiples. A small hole is opened on the top of each circular fixing structure. The radial strain measurement sensor and the annular strain measurement sensor pass through the small hole into the circular fixing structure, go around the circular fixing structure once, and then fill the small hole with high viscosity glue for packaging. The radial fixing system is stacked on the annular fixing system, and then the radial fixing system is bonded at the stacking position with high viscosity glue.

[0010] Furthermore, the surface of the radial fixing system uses thread processing technology, and the support system and the optical fiber fixing system are fused and formed at one time.

[0011] The adaptive frame system is a stable polygonal structure. The tie-tying system uses a plurality of tie-tying fixing structures. The shapes and sizes of the fixing rings and the fixing nodes are variable. The fixing nodes arranged one-to-one at equal intervals on the fixing rings and the adaptive frame system are used to fix the radial fixing system. The fixing nodes arranged at the connection between the tie-tying system and the optical fiber fixing system are used to connect and fix the circumferential fixing system.

[0012] In the present invention, the rust cracking condition of concrete around the steel bars is measured by annular and radial biaxial measurement, and the biaxial rust cracking strain field of concrete is monitored in real time. Moreover, the rust cracking degree and rust cracking time of concrete under different conditions can be predicted according to the obtained rust cracking strain data. The device inserts the radial strain measurement sensor and the annular strain measurement sensor into the optical fiber fixing system and seals them with high-viscosity glue, thereby ensuring that the strain measurement sensor does not deform or displace in the optical fiber fixing system, thereby affecting the measurement accuracy of the rust cracking strain at the measured position. The device arranges a number of fixed nodes at the connection between the tie system and the optical fiber fixing system, which are used to connect and fix the annular fixing system, thereby preventing the annular fixing system from being deformed or displaced. The fixing system rotates or moves during concrete pouring; this device uses thread processing technology on the surface of the radial fixing system, superimposes the radial fixing system on the annular fixing system, and fixes the radial fixing system with high-viscosity glue, and arranges fixed nodes one by one at equal intervals on the fixing ring and the adaptive frame system to straighten and fix the radial fixing system, ensuring that the radial fixing system will not move in any direction with the concrete pouring, affecting the monitoring of the radial rust crack strain field of the concrete; this device integrates the optical fiber fixing system and the support system into a single shape, ensuring that the optical fiber fixing system and the support system are located in the same plane, ensuring that the support system is on the optical fiber The device has a supporting and stabilizing effect on the fixing system; the device clamps the fixing ring on the steel bar to ensure that the device is perpendicular to the steel bar and is clamped in the concrete formwork, ensuring that the optical fiber fixing system is in close contact with the concrete interface, effectively avoiding the problem of displacement of the optical fiber Bragg grating sensor during concrete pouring, and improving the accuracy of in-situ monitoring and the accuracy of the results; the device can change the grating pitch of the radial strain measurement sensor and the annular strain measurement sensor, especially making reference marks at certain intervals on the sensor, causing a signal change in the reflected wavelength, and the demodulation device can deduce the strain condition of the reference mark position by detecting the change in wavelength, so as to realize the detection of concrete rust crack strain. Real-time monitoring of variable fields has good controllability and high accuracy; if multiple gratings are written into the same optical fiber to form a sensor array, and the multiple written gratings are insensitive to strain, multiple physical quantities (temperature, stress, concentration, etc.) can be measured simultaneously; the adaptive frame system used in the present device can be a quadrilateral, or a more stable hexagonal or other polygonal structure, which can better fit and fix the optical fiber annular fixed structure; the tie system used in the present device can use one or more tie fixing structures between the horizontal transverse fixed structure and the vertical vertical structure; the shape and size of the fixed ring and fixed node used in the present device can be adjusted according to actual conditions.

[0013] The beneficial effects of the present invention are mainly manifested in: by detecting the changes in the central wavelength of the fiber grating sensor, real-time monitoring of the radial and circumferential rust cracking strain field changes of the concrete around the steel bars is achieved, laying a foundation for future predictions of the rust cracking degree and rust cracking time of reinforced concrete under different conditions. The present invention has the advantages of simple structure, high sensitivity, anti-electromagnetic interference, easy installation, and corrosion resistance, and has good promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a schematic diagram of the structural principle of the utility model.

[0015] Figure 2 The utility model is a schematic diagram of the structural principle of the support system involved.

[0016] Figure 3 It is a front view of the optical fiber fixing system involved in the utility model.

[0017] Figure 4 It is a left view of the optical fiber fixing system involved in the utility model.

[0018] Figure 5 This is a top view of the optical fiber fixing system involved in the utility model.

[0019] Figure 6 It is a schematic diagram of the hollow tubular structure of the optical fiber fixing structure involved in the utility model.

[0020] Figure 7 This is a schematic diagram of the structural principle of a fiber grating sensor for in-situ real-time monitoring of the rust crack strain field of concrete around steel bars and rust crack prediction provided in Example 1 of the utility model.

[0021] Figure 8 This is a schematic diagram of the structural principle of a fiber grating sensor for in-situ real-time monitoring of the rust crack strain field of concrete around steel bars and rust crack prediction provided in Example 2 of the utility model.

[0022] Fig. 9 This is a schematic diagram of the structural principle of a fiber grating sensor for in-situ real-time monitoring of the rust crack strain field of concrete around steel bars and rust crack prediction provided in Example 3 of the utility model.

[0023] Fig.10 This is a table of test parameters and test results for rust cracking of concrete around steel bars obtained from the test of Example 3 of the utility model.

[0024] In the figure: 1—support system; 2—optical fiber fixing system; 3—radial strain measurement sensor; 4—circumferential strain measurement sensor; 5—signal demodulation system; 6—data acquisition system; 7—concrete formwork; 11—adaptive frame system; 12—tension system; 13—fixed ring; 14—node fixing point; 21—radial fixing system; 22—circumferential fixing system; 221—circumferential fixing structure; 211—horizontal transverse fixing structure; 212—vertical fixing structure. DETAILED DESCRIPTION

[0025] The present invention will be further described below in conjunction with the accompanying drawings.

[0026] Reference Figures 1 to 10 A fiber grating sensor for in-situ real-time monitoring of concrete rust cracking strain field around steel bars and rust cracking prediction, comprising a support system 1, an optical fiber fixing system 2, a radial strain measurement sensor 3, an annular strain measurement sensor 4, a signal demodulation system 5, and a data acquisition system 6. The optical fiber fixing system 2 is arranged on the support system 1, the radial strain measurement sensor 3 and the annular strain measurement sensor 4 are inserted into the optical fiber fixing system 2, the radial strain measurement sensor 3 and the annular strain measurement sensor 4 are respectively connected to the signal demodulation system 5, and the signal demodulation system 5 is connected to the data acquisition system 6.

[0027] The support system 1 includes an adaptive frame system 11, a tie system 12, a fixed ring 13 and a fixed node 14. The adaptive frame system 11 can use a stable polygonal structure such as a quadrilateral or hexagon. The tie system 12 can use a plurality of tie fixing structures. The shapes and sizes of the fixed ring 13 and the fixed node 14 are variable. A plurality of fixed nodes 14 are arranged one-to-one at equal intervals on the fixed ring 13 and the adaptive frame system 11 for fixing the radial fixing system 21. A plurality of fixed nodes 14 are arranged at the junction of the tie system 12 and the optical fiber fixing system 2 for connecting and fixing the annular fixing system 22. The fixed ring 13 is connected to the tie system 12, and the tie system 12 is connected to the adaptive frame system 11. The support system 1 is formed by one-time melt casting of high-strength alloy material.

[0028] The optical fiber fixing system 2 includes a radial fixing system 21 and an annular fixing system 22. The optical fiber fixing system 2 is a hollow tubular structure. The radial fixing system 21 includes a horizontal transverse fixing structure 211 and a vertical vertical fixing structure 212. The surface of the radial fixing system 21 uses thread processing technology. The annular fixing system 22 includes a plurality of circular fixing structures 221 with overlapping centers and diameters that are related multiples. A small hole is opened on the top of each of the circular fixing structures 221. The radial strain measurement sensor 3 and the annular strain measurement sensor 4 penetrate into the circular fixing structure 221 from the small hole, go around the circular fixing structure 221 once, and then fill the small hole with high viscosity glue for packaging. The radial fixing system 21 is stacked on the annular fixing system 22, and then the radial fixing system 21 is bonded at the stacking position with high viscosity glue. The optical fiber fixing system 2 is molded by a high-hardness fiber-reinforced composite material in one step.

[0029] The support system 1 and the optical fiber fixing system 2 are formed by melting and molding at one time.

[0030] Embodiment 2 The test method of a fiber Bragg grating sensor for real-time in-situ monitoring of the concrete rust cracking strain field around steel bars and rust cracking prediction described in the utility model comprises the following steps:

[0031] Step 1: Preparation of the device: According to the shape and size of the required cast specimen, the type, diameter and position of the required steel bars embedded in the specimen, determine the shape and size of the support system 1, the shape and diameter of the fixed ring 13 in the support system 1, the ring spacing of the ring fixing structure 211, and the number of required ring fixing structures 211; respectively determine the length, grating pitch, measurement step and accuracy of the fiber Bragg grating in the radial strain measurement sensor 3 and the annular strain measurement sensor 4 inserted in each ring fixing structure 211, and produce a fiber Bragg grating sensor device suitable for in-situ real-time monitoring of the real-time rust cracking strain field of concrete around steel bars and rust cracking prediction.

[0032] Step 2: Preparation before casting the specimen: a number of fiber grating sensors are fixed on the steel bars at intervals using the fixed rings 13 in the support system 1 to ensure that the sensors will not shift during the casting of the concrete specimen, and the number of fiber grating sensors required is totaled; when placed, the outer edge of the support system 1 frame is close to the inner wall of the concrete mold 7 to ensure that the entire plane of the fiber grating sensor is placed perpendicular to the steel bars; the radial strain measurement sensor 3 and the fiber grating of the annular strain measurement sensor 4 in each circular fixed structure 211 are connected to a number of wires respectively, and the wires are carefully and orderly placed on the outside of the concrete mold 7 to prevent them from being mixed into the concrete mold 7 and being damaged.

[0033] Step 3: Prepare concrete specimens: determine the properties and mix ratio of the concrete raw materials, and after vibration, pour and compact it in the concrete mold 7. During the operation, pay attention to adjust the sensor plane to always be perpendicular to the steel bars; after the concrete is formed, remove the mold and place the specimen under standard conditions for 28 days of curing; take out the cured concrete, connect each fiber grating sensor to a signal demodulation system 5 with several wires, and the number of signal demodulation systems 5 required is totaled; connect the signal demodulation system 5 with the data acquisition system 6 with wires.

[0034] Step 4: Data acquisition: Turn on the switches of the signal demodulation system 5 and the data acquisition system 6, control the initial strain value to zero, use the power-on accelerated corrosion device or other test methods to perform corrosion operations on the steel bars, and start in-situ real-time monitoring of the radial and circumferential rust cracking strain field changes of the concrete around the steel bars, and record and collect data from the start of power-on to the concrete rust cracking damage process. Through the test, the radial and circumferential rust cracking strain data of the concrete around the steel bars of the specimen can be obtained, and finally the rust cracking degree and rust cracking time of the reinforced concrete can be obtained.

[0035] Example 3 The following takes the in-situ real-time monitoring of the circumferential rust crack strain field of concrete around the steel bars after the built-in fiber grating sensor is used as an example to specifically illustrate the working of the utility model.

[0036] The raw materials for mixing concrete in this embodiment are: cement is PI 52.5 grade Portland cement, sand is natural river sand with a fineness modulus of 2.64, coarse aggregate is crushed stone with a continuous grade of 5 to 20 mm, and water is laboratory tap water. The size of the specimen is a prism of 100 mm × 100 mm × 400 mm, and a HPB300 steel bar with a diameter of 12 mm is pre-embedded in the middle of the left side of the specimen, and the thickness of the protective layer is 20 mm.

[0037] Before pouring concrete, first press Figure 2 to Figure 6 and Fig. 9Configure the device components. According to the required casting specimen size of 100mm×100mm×400mm, a HPB300 steel bar with a diameter of 12mm is embedded in the middle of the left side of the specimen, and the protective layer thickness is 20mm. It is determined that the support system 1 is a 40mm×40mm regular quadrilateral structure, the fixed ring 13 in the support system 1 is a circular structure with a diameter of 12.1mm, and a circular ring fixed structure 211 is arranged with a distance of 10mm from the outer side of the steel bar; according to the arrangement of only one circular ring fixed structure 211, it is determined that no fixed node 14 is arranged on the fixed ring 13 and the adaptive frame system 11, and four fixed nodes 14 are arranged at the intersection of the tie system 12 and the optical fiber fixed system 2 for fixing the circular ring fixed structure 211; it is determined that the length of the optical fiber Bragg grating in the circumferential strain measurement sensor 4 inserted in the circular ring fixed structure 211 is 314.2mm, the grating pitch is 40μm, the measurement step is 0.1μm, and the accuracy is ±5με. Because the fiber Bragg grating sensor is relatively small in size relative to the entire concrete specimen, it is necessary to increase the frame based on the support system 1 to make the four sides of the sensor outer bracket close to the inner wall of the entire concrete mold 7, so the following is selected: Fig. 9 The support frame 1 is shown. Secondly, the support system 1 is integrally cast with aluminum alloy material, and the optical fiber fixing system 2 is once molded with polyester fiberglass material, and finally the support system 1 and the optical fiber fixing system 2 are once melted and molded to obtain a fiber grating sensor device suitable for in-situ real-time monitoring of the real-time rust cracking strain field and rust cracking prediction of concrete around steel bars.

[0038] When pouring concrete, first tighten the steel bar with iron wire to fix it in the middle of the left side of the concrete mold 7, and the thickness of the protective layer is 20mm. Then, the fiber Bragg grating sensor device is clamped on the steel bar with the fixed ring 13 in the support system 1 at a distance of 90mm, and the starting distance and the ending distance are both 20mm, to ensure that the sensor will not shift when the concrete specimen is poured. A total of four fiber Bragg grating sensor devices are required; when placed, the four sides of the support system 1 frame are close to the inner wall of the concrete mold 7 to ensure that the entire plane of the fiber Bragg grating sensor is placed perpendicular to the steel bar; the fiber Bragg gratings in the radial strain measurement sensor 3 and the circumferential strain measurement sensor 4 are connected to two and one wires respectively, and the three wires are carefully and orderly placed on the outside of the concrete mold 7 to prevent them from being mixed into the concrete mold 7 and being damaged. Finally, pour the concrete into the concrete mold 7 and vibrate it to make it dense. During the operation, pay attention to adjust the sensor plane to always be perpendicular to the steel bar. After the concrete is one day old, it is formed and demolded, and placed under standard conditions for 28 days of curing. Take out the cured concrete, connect each fiber grating sensor to a signal demodulation system 5 with three wires, and a total of four signal demodulation systems 5 are required; connect the four signal demodulation systems 5 to a data acquisition system 6 with wires.

[0039] Turn on the switches of the signal demodulation system 5 and the data acquisition system 6, control the initial strain value to zero, use the power-on accelerated corrosion device or other test methods to perform corrosion operations on the steel bars, start in-situ real-time monitoring of the changes in the circumferential rust crack strain field of the concrete around the steel bars, and record and collect data from the start of power-on to the concrete rust crack damage process. Through the test, the circumferential rust crack strain data of the concrete around the steel bars of the specimen can be obtained. The test parameters and test results of the concrete rust crack strain are as follows: Fig.10 As shown, it reflects the circumferential rust cracking strain change and rust cracking state of the concrete.

[0040] In specific implementation, the utility model does not impose any restrictions on the specific device component models, the size of the concrete specimen, the type and diameter of the steel bars, and any fiber grating sensor device and concrete specimen that can complete the above functions are acceptable.

[0041] The contents described in the embodiments of this specification are merely an enumeration of the implementation forms of the concept of the utility model. The protection scope of the utility model should not be regarded as limited to the specific forms described in the embodiments. The protection scope of the utility model also includes equivalent technical means that can be thought of by those skilled in the art based on the concept of the utility model.

Claims

1. A fiber Bragg grating sensor for real-time in-situ monitoring of concrete rust cracking strain field around steel bars and rust cracking prediction, characterized in that: The fiber Bragg grating sensor includes a support system, an optical fiber fixing system, a radial strain measurement sensor, an annular strain measurement sensor, a signal demodulation system and a data acquisition system. The optical fiber fixing system is arranged on the support system. The radial strain measurement sensor and the annular strain measurement sensor are inserted into the optical fiber fixing system. The radial strain measurement sensor and the annular strain measurement sensor are respectively connected to the signal demodulation system, and the signal demodulation system is connected to the data acquisition system. The support system includes an adaptive frame system, a tie system, a fixed ring and fixed nodes. The fixed nodes are arranged one by one at equal intervals on the fixed ring and the adaptive frame system. The fixed nodes are arranged at the intersection of the tie system and the optical fiber fixing system. The ring is connected to the tie system, and the tie system is connected to the adaptive frame system; the optical fiber fixing system includes a radial fixing system and annular fixing system, the optical fiber fixing system is a hollow tubular structure, the radial fixing system includes a horizontal transverse fixing structure and a vertical vertical fixing structure, the annular fixing system includes a set number of circular ring fixing structures with overlapping circle centers and diameters that are related multiples, and a small hole is opened on the top of each circular ring fixing structure, the radial strain measurement sensor and the annular strain measurement sensor penetrate into the circular ring fixing structure from the small hole, go around the circular ring fixing structure once, and then fill the small hole with high viscosity glue for packaging, the radial fixing system is stacked on the annular fixing system, and then the radial fixing system is bonded at the stacking position with high viscosity glue.

2. The fiber grating sensor for in-situ real-time monitoring of the concrete rust cracking strain field and rust cracking prediction around steel bars as claimed in claim 1, characterized in that: The surface of the radial fixing system uses thread processing technology, and the supporting system and the optical fiber fixing system are fused and formed at one time.

3. The fiber Bragg grating sensor for in-situ real-time monitoring of the concrete rust cracking strain field and rust cracking prediction around steel bars as claimed in claim 1, characterized in that: The adaptive frame system is a stable polygonal structure. The tie-tying system uses a plurality of tie-tying fixing structures. The shapes and sizes of the fixing rings and the fixing nodes are variable. The fixing nodes arranged one-to-one at equal intervals on the fixing rings and the adaptive frame system are used to fix the radial fixing system. The fixing nodes arranged at the connection between the tie-tying system and the optical fiber fixing system are used to connect and fix the circumferential fixing system.

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