Distributed photoelectric composite concrete cracking monitoring sensor

Abstract

The invention belongs to the field of structural health monitoring, and discloses a distributed photoelectric composite concrete cracking monitoring sensor which sequentially comprises an optical fiber sensing element, an optical fiber inner packaging layer, a coaxial cable sensing element and a sensor outer packaging layer from inside to outside. Firstly, a test section of an optical fiber sensing element is embedded into an optical fiber inner packaging layer; then, the coaxial cable sensing element and the coaxial cable sensing element are packaged in a sensor outer packaging layer made of fiber reinforced plastics in parallel; and the optical fiber sensing element with the optical fiber inner packaging layer, the coaxial cable sensing element and the sensor outer packaging layer are fixedly combined into a whole. The distributed photoelectric composite concrete cracking monitoring sensor is low in manufacturing cost, large in coverage and good in durability, and has small-strain high-precision measurement and low-precision local large deformation measurement capabilities.

Description

Technical Field

[0001] This invention belongs to the field of structural health monitoring and relates to a distributed photoelectric composite concrete crack monitoring sensor. Background Technology

[0002] Concrete, due to its high compressive strength, ease of construction, and low cost, is widely used in many fields such as road and bridge construction, housing, and hydraulic engineering, and is one of the most widely used materials in modern construction. In recent years, the global annual production of cement concrete has exceeded 4 billion tons, and asphalt concrete has reached nearly 2 billion tons. Concrete, when subjected to overload or long-term operation under changing conditions, is prone to damage accumulation, resistance decay, and cracking. Concrete cracking impairs the structure's impermeability, weakens its resistance to sulfate and chloride erosion, accelerates structural aging, and affects the normal use and safe operation of the structure. Furthermore, as concrete cracks expand and new cracks form, structural damage intensifies and can even lead to sudden accidents. Given the prevalence of cracked concrete structures during normal service, real-time monitoring of the crack development process is essential for timely detection of early structural damage, implementation of appropriate reinforcement measures, and understanding of the evolution of concrete cracking damage.

[0003] Traditional methods for monitoring concrete cracking, such as non-destructive testing using wave propagation, resistance strain gauges, piezoelectric ceramic sensors, and fiber optic grating sensors, generally have certain problems and limitations. For example, ultrasonic and acoustic emission technologies can retrieve instantaneous information about crack location or width, but they are easily affected by ambient noise and rely on inspection cycles, making it difficult to detect crack damage in a timely manner. Furthermore, their placement is limited, hindering large-area, real-time, and continuous monitoring of crack propagation. While piezoelectric ceramic sensors can identify structural damage, their brittleness makes them unsuitable for static strain measurement, and they require complex encapsulation protection before installation. Resistance strain gauges offer high accuracy and their surface placement does not affect the concrete structure's stress, but they have weak electromagnetic interference resistance, a small measurement range, and poor durability, failing to meet the needs of large-scale, long-term monitoring. Fiber optic grating sensors have been widely used in various engineering fields in recent years due to their high measurement accuracy, small size, corrosion resistance, high temperature resistance, and electromagnetic interference resistance. However, as point sensors similar to resistance strain gauges, they can only monitor strain and displacement at a localized location, making it difficult to capture large-area and random concrete cracks.

[0004] Optoelectronic composite sensing technology, which integrates the complementary advantages and disadvantages of distributed fiber optic sensing (DOFS) and coaxial cable strain sensing (CC-FPI), can achieve both high-precision testing at small strain stages and relatively low-precision testing throughout the entire process, covering a large coverage area. Applying it to concrete crack monitoring can not only identify concrete cracking damage but also obtain information on the entire evolution of crack development. However, DOFS, which achieves monitoring ranges of tens or hundreds of meters or even larger, uses a single optical fiber as both the sensing unit and the transmission medium. When deforming together with the concrete, a large strain at a single point can cause the fiber to break, leading to the failure of distributed sensing and signal transmission along the entire fiber. This problem is one of the main reasons restricting the large-scale engineering application of DOFS technology. Summary of the Invention

[0005] The purpose of this invention is to provide a distributed photoelectric composite concrete crack monitoring sensor with good durability and strong engineering applicability.

[0006] The technical solution of the present invention:

[0007] A distributed photoelectric composite concrete crack monitoring sensor comprises, from the innermost layer to the outermost layer, an optical fiber sensing element 1, an inner optical fiber encapsulation layer 2, a coaxial cable sensing element 3, and an outer sensor encapsulation layer 4. First, the test section of the optical fiber sensing element 1 is embedded in the inner optical fiber encapsulation layer 2. Then, it is encapsulated parallel to the coaxial cable sensing element 3 within the outer sensor encapsulation layer 4, which is composed of fiber-reinforced plastic (FRP). The optical fiber sensing element 1, the coaxial cable sensing element 2, and the outer sensor encapsulation layer 4 are integrally bonded. An RF connector 5 is connected to the end of the coaxial cable sensing element 3. The optical fiber sensing element 1, located outside the outer sensor encapsulation layer 4, is encased in an armored protective sleeve 6 and connected to a jumper wire 7. The optical fiber sensing element 1 measures the strain information of the deployed section and locates the damage, while the coaxial cable sensing element 3 is used for monitoring the crack evolution under subsequent high-strain conditions.

[0008] The inner encapsulation layer 2 of the optical fiber is composed of a flexible insulating layer, reinforcing fiber filaments, and adhesive.

[0009] The flexible isolation layer is made of impermeable synthetic plastics, high-performance polymer films (polyphenylene sulfide, polytetrafluoroethylene or polypropylene film) or polyurethane, etc.

[0010] The reinforcing fiber is glass-reinforced fiber plastic, carbon fiber-reinforced plastic, basalt fiber-reinforced plastic, or aramid fiber-reinforced plastic;

[0011] The adhesive used should be selected based on the actual flexible isolation layer material and reinforcing fiber material used, and can be a modified resin pressure-sensitive adhesive or a polyurethane adhesive; the adhesive of the inner encapsulation layer 2 of the optical fiber can ensure that it is bonded and fastened under small strain (less than 5000με-10000με) and bonded and disconnected under large strain (greater than 5000με-10000με).

[0012] The number of reflection points of the coaxial cable sensing element 3 is determined by the required length of the structure, and the spacing between the reflection points is within the theoretical range of 20mm to 1200mm. The manufacturing method is any one of the necking method, drilling method and cavity method.

[0013] The outer encapsulation layer 4 of the fiber-reinforced plastic sensor is made of glass-reinforced fiber plastic, carbon fiber-reinforced plastic, basalt fiber-reinforced plastic, or aramid fiber-reinforced plastic.

[0014] The beneficial effects of this invention are as follows: The distributed photoelectric composite concrete crack monitoring sensor of this invention, through special encapsulation and protection of the fiber optic sensing element in the photoelectric composite sensor, ensures effective and high-precision monitoring in the early stages of local damage, while maintaining the signal transmission capability of the fiber optic cable even under conditions of large local damage. This effectively solves the problem of global signal transmission and strain measurement failure caused by single-point failure of the distributed fiber optic sensor. Combined with the external overall FRP encapsulation, it can adapt to extreme service environment conditions, and the manufacturing process is simple, making it highly applicable in engineering. This distributed photoelectric composite concrete crack monitoring sensor is low in cost, has a large coverage area, good durability, and combines the capabilities of high-precision measurement of small strains with relatively low-precision measurement of large local deformations. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the main components of a distributed photoelectric composite concrete crack monitoring sensor.

[0016] Figure 2 This is a schematic diagram of the cross-section of a distributed photoelectric composite concrete crack monitoring sensor.

[0017] Figure 3 This is a schematic diagram of the inner encapsulation layer structure of an optical fiber.

[0018] In the diagram: 1. Fiber optic sensing element; 2. Inner fiber optic encapsulation layer; 3. Coaxial cable sensing element; 4. Outer sensor encapsulation layer; 5. RF connector; 6. Armored protective sleeve; and 7. Jumper wire. Detailed Implementation

[0019] The specific embodiments of the present invention will now be described in detail with reference to the technical solutions and accompanying drawings.

[0020] like Figure 1 and Figure 2As shown, this distributed photoelectric composite concrete crack monitoring sensor includes an optical fiber sensing element 1, an inner optical fiber encapsulation layer 2, a coaxial cable sensing element 3, an outer sensor encapsulation layer 4, an RF connector 5, an armored protective sleeve 6, and a jumper wire 7. During fabrication, the optical fiber sensing element 1 is first embedded into the inner optical fiber encapsulation layer 2. Specifically, adhesive is evenly applied to the surface of the optical fiber sensing element 1 and reinforcing fiber filaments are wound around it. It is then fixed inside a non-adhesive flexible isolation layer and compacted to form a distributed optical fiber strain testing section. The reinforcing fiber filaments are used to improve strain transfer efficiency under small strains and to increase the overall tensile strength of the encapsulation structure. They are arranged at fixed intervals in both horizontal and vertical directions. The geometric dimensions of the flexible isolation layer are determined by the interface interaction mechanism and the interface contact area required to ensure strain transfer efficiency. The thickness of the encapsulated optical fiber sensing section is approximately 0.3 mm. Slight differences may occur depending on the selection of different constituent materials; to prevent excessively low strain transfer efficiency, the thickness should not be too large. The encapsulated fiber optic sensing element 1 and coaxial cable sensing element 3 are encapsulated in parallel within a sensor outer encapsulation layer 4 composed of FRP of a certain thickness (determined by the stiffness of the substrate material and the magnitude of the external load during structural forming, and at least 0.5 mm beyond the outer diameter of the coaxial cable sensing element). After forming, the fiber optic sensing element 1 with the attached inner fiber optic encapsulation layer 2, the coaxial cable sensing element 3, and the sensor outer encapsulation layer 4 are solidified into one unit. The distributed photoelectric composite concrete cracking monitoring sensor is connected to a distributed fiber optic sensing demodulator via an optical switch to demodulate the optical signal representing the strain information of the measured substrate sensed by the single-mode fiber, measure the strain information of the sensor deployment section, and locate local damage. At the same time, the coaxial cable sensing element is connected to a vector network analyzer via a connector to demodulate the time-frequency domain signal transmitted by the coaxial cable, thereby realizing effective monitoring of strain evolution in the later stage of damage.

Claims

1. A distributed photoelectric composite concrete crack monitoring sensor, characterized in that, The distributed photoelectric composite concrete crack monitoring sensor consists of an optical fiber sensing element (1), an inner optical fiber encapsulation layer (2), a coaxial cable sensing element (3), and an outer sensor encapsulation layer (4) from the inner layer to the outer layer. First, the test section of the optical fiber sensing element (1) is embedded in the inner optical fiber encapsulation layer (2). Then, it is encapsulated in parallel with the coaxial cable sensing element (3) in the outer sensor encapsulation layer (4) made of fiber-reinforced plastic. The optical fiber sensing element (1) with the inner optical fiber encapsulation layer (2) and the coaxial cable sensing element (2) are fixed together with the outer sensor encapsulation layer (4). The end of the coaxial cable sensing element (3) is connected to the radio frequency connector (5). The optical fiber sensing element (1) located outside the outer sensor encapsulation layer (4) is wrapped with an armored protective sleeve (6) and connected to a jumper (7). The optical fiber sensing element (1) measures the strain information of the deployment section and performs damage location. The coaxial cable sensing element (3) is used for crack evolution monitoring under large strain conditions in the later stage.

2. The distributed photoelectric composite concrete crack monitoring sensor according to claim 1, characterized in that, The inner encapsulation layer (2) of the optical fiber is mainly composed of a flexible isolation layer, reinforcing fiber filaments and adhesive.

3. The distributed photoelectric composite concrete crack monitoring sensor according to claim 2, characterized in that, The flexible isolation layer is made of impermeable synthetic plastic, high-performance polymer film, or polyurethane.

4. The distributed photoelectric composite concrete crack monitoring sensor according to claim 2, characterized in that, The reinforcing fiber is glass-reinforced fiber plastic, carbon fiber-reinforced plastic, basalt fiber-reinforced plastic, or aramid fiber-reinforced plastic.

5. The distributed photoelectric composite concrete crack monitoring sensor according to claim 2, characterized in that, The adhesive used should be selected based on the flexible release layer material and reinforcing fiber material actually used, and can be a modified resin pressure-sensitive adhesive or a polyurethane adhesive.

6. The distributed photoelectric composite concrete crack monitoring sensor according to claim 1, characterized in that, The number of reflection points of the coaxial cable sensing element (3) is determined by the required length of the structure. The spacing between the reflection points is within the theoretical range of 20mm to 1200mm. The manufacturing method is any one of the necking method, drilling method and cavity method.

7. The distributed photoelectric composite concrete crack monitoring sensor according to claim 1, characterized in that, The outer encapsulation layer (4) of the fiber-reinforced plastic sensor is made of glass-reinforced fiber plastic, carbon fiber-reinforced plastic, basalt fiber-reinforced plastic or aramid fiber-reinforced plastic.

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