3-1-2 type cement-based piezoelectric composite material and preparation method thereof

Abstract

A 3-1-2 cement-based piezoelectric composite material comprises a piezoelectric ceramic rod, a cement matrix and a piezoelectric ceramic substrate, the structural connectivity is defined as 3-1-2, and three phases are the cement matrix, are continuous in all directions as continuous phases and are used for realizing acoustic impedance matching with concrete; the first phase is piezoelectric ceramic rods which are continuously distributed in a cement matrix in a rod-shaped or columnar discrete manner along the thickness direction; the two phases are piezoelectric ceramic substrates, and in the thickness direction, the piezoelectric ceramic rod array is connected with one piezoelectric ceramic substrate in series to form a stable framework structure with transverse and longitudinal supports. The invention further provides a preparation method of the 3-1-2 type cement-based piezoelectric composite material. The acoustic matching advantage and the structural stability advantage of the material are fused.

Description

Technical Field

[0001] This invention falls under the technical categories of structural intelligent sensing, multiphase piezoelectric functional materials, and nondestructive testing in civil engineering. Specifically, it relates to a 3-1-2 type cement-based piezoelectric composite material for monitoring the health of concrete structures, possessing acoustic impedance matching, excellent electromechanical coupling performance, and high mechanical stability, as well as an efficient preparation process for achieving structural integration of this material. Background Technology

[0002] Currently, combining piezoelectric ceramics with polymers is the mainstream method for fabricating acoustic transducers. Traditional type 1-3 piezoelectric composite materials (piezoelectric ceramic rod arrays embedded in a polymer matrix) reduce the acoustic impedance to some extent, but a significant difference remains between them and concrete (acoustic impedance approximately 8-12 MRayl), leading to sound wave reflection and energy loss at the interface, affecting detection sensitivity. Furthermore, the relatively limited mechanical strength, thermal stability, and chemical compatibility with concrete of the polymer matrix restrict the reliability and lifespan of sensors in long-term, array-embedded applications within concrete. However, the aforementioned existing technologies still have the following limitations: Insufficient integration of structure and performance: This scheme is essentially a three-phase asymmetric composite of "cement matrix-organic polymer-ceramic skeleton". While the introduction of organic polymer enhances some mechanical properties, its long-term weather resistance (such as aging and creep) and interfacial stability with the cement matrix under temperature and humidity changes still face challenges, potentially affecting the long-term service performance of the sensor within concrete. Furthermore, the presence of the polymer phase introduces uncertainty into the overall acoustic properties of the material, hindering the achievement of optimal acoustic matching with concrete.

[0003] The design lacks mechanical support and decoupling: While this approach focuses on improving performance through a porous framework and filler phase, it fails to fundamentally address the mechanical stability issues of composite materials in the transverse and longitudinal directions. This is particularly problematic under long-term cyclic loading or impact, where uneven internal stress distribution can lead to performance degradation. Furthermore, the lack of a dedicated structural design to address vibration crosstalk (i.e., decoupling between components) during multi-sensor unit (array) operation limits its application in scenarios requiring high spatial resolution detection.

[0004] Complexity and uniformity of the preparation process: The preparation of porous ceramic frameworks relying on sodium alginate ionogel method requires high process control, and it is difficult to ensure the uniformity and repeatability of the framework structure. At the same time, the multi-step composite process of "cement casting-polymer filling" is cumbersome and it is difficult to ensure perfect bonding and performance consistency of the three-phase interface.

[0005] Therefore, the civil engineering field urgently needs a novel piezoelectric composite material and its preparation method. This material must not only achieve better matching with concrete in terms of acoustic impedance, but also possess a higher degree of structural integration, excellent mechanical stability and long-term durability. Furthermore, it should be able to effectively suppress crosstalk between components through structural design, thereby truly meeting the stringent requirements of long-term, high-precision, arrayed acoustic emission non-destructive testing within concrete structures. This invention presents an innovative solution in this context.

[0006] There is currently no publicly reported or practical technology that can systematically and integratedly design and prepare the three phases of cement-based continuous phase, piezoelectric ceramic rod array, and piezoelectric ceramic substrate that provides transverse and longitudinal mechanical support and decoupling in the form of a 3-1-2 type composite structure, and specifically use it for long-term high-precision acoustic emission non-destructive testing inside concrete structures. Summary of the Invention

[0007] In order to overcome the dual defects of sensor acoustic impedance mismatch and poor structural mechanical stability in the prior art, the present invention provides a 3-1-2 type cement-based piezoelectric composite material and its preparation method that integrates the advantages of material acoustic matching and structural stability.

[0008] The technical solution adopted by this invention to solve its technical problem is: A 3-1-2 type cement-based piezoelectric composite material includes piezoelectric ceramic rods (PZT), a cement matrix, and a piezoelectric ceramic substrate. The structural connectivity is defined as 3-1-2, wherein the 3rd phase is the cement matrix, which is a continuous phase (3-0) that is continuous in all directions to achieve acoustic impedance matching with concrete; the 1st phase is the piezoelectric ceramic rod, which is continuous along the thickness direction (3 direction) and is distributed in a rod-shaped or columnar manner in the cement matrix; the 2nd phase is the piezoelectric ceramic substrate, in which an array of piezoelectric ceramic rods is connected in series with a piezoelectric ceramic substrate in the thickness direction to form a stable skeleton structure with lateral and longitudinal support.

[0009] Furthermore, the volume fraction V of the piezoelectric ceramic rod f Satisfying 0.2≤V f ≤0.4.

[0010] A method for preparing a 3-1-2 type cement-based piezoelectric composite material includes the following steps: Step 1, Fabrication of piezoelectric ceramic rod array (cutting-filling), the process is as follows: 1.1 Prepare a pre-polarized or to-be-polarized PZT ceramic substrate; 1.2 Using an ultrasonic vibration drilling machine or a high-precision cutting machine, perform precise array cutting along the thickness direction on the PZT substrate to form regularly arranged PZT rod-shaped units; A high-performance cement-based slurry is prepared and uniformly and fully filled into the array gaps between PZT rod units. The slurry is then vibrated to compact it and cured for the first time under a set temperature and humidity to form a PZT / cement composite upper layer structure with acoustic impedance matching characteristics. Step 2, Piezoelectric ceramic substrate preparation: Prepare a piezoelectric ceramic substrate that matches the size of the PZT rod array. This substrate serves as the mechanical support layer and decoupling layer for the transducer array. Step 3. Structural Assembly and Connection: The lower electrode surface of the cured PZT is firmly connected in series with the upper surface of the piezoelectric ceramic substrate using conductive adhesive or welding process to form a complete 3-1-2 type composite structure. Step 4, Secondary Polarization and Encapsulation: Apply a high-voltage DC electric field to the assembled composite material for secondary polarization to ensure the piezoelectric response performance of the overall structure.

[0011] Furthermore, in step 2, the cement-based slurry contains silica fume or nano-silica to improve the density and mechanical strength of the cement matrix.

[0012] In step S3, the series connection is achieved using conductive epoxy resin adhesive or welding process.

[0013] In step 4, the sides and back of the composite material are treated with waterproofing, vibration damping, or sound reflection backing.

[0014] The beneficial effects of this invention are mainly reflected in: 1. Balancing acoustic matching and high sensitivity: This is the first time cement-based materials have been used as the filling phase in this type of structure. The cement matrix phase achieves high compatibility between the equivalent acoustic impedance and concrete (approximately 3–15 MRayl), ensuring low-loss transmission of acoustic signals in the concrete and greatly improving the signal-to-noise ratio and sensitivity of acoustic emission detection; 2. Strong structural stability and impact resistance: The introduced piezoelectric ceramic substrate and cement matrix together form a robust ceramic-cement composite skeleton. This gives the sensor excellent lateral and longitudinal mechanical support, making it less susceptible to external mechanical impacts or changes in ambient temperature, resulting in stable and reliable performance. 3. Good component decoupling effect: The connection between the piezoelectric ceramic substrate and the upper composite structure, as well as the layered structure of the material itself, helps to reduce vibration crosstalk between components and improve the consistency and accuracy of array operation. 4. Wide range of applications: The composite material structure is robust and highly compatible with concrete, making it particularly suitable for embedded, long-term, and array-based health monitoring applications of concrete structures, with broad market prospects. Attached Figure Description

[0015] Figure 1This is a schematic diagram of the structure of the cement-based piezoelectric composite material of the present invention, type 3-1-2.

[0016] Figure 2 This is a schematic diagram of cutting / drilling a PZT substrate.

[0017] Figure 3 This is a schematic diagram of sound wave transmission when a composite material is connected to a concrete matrix. Detailed Implementation

[0018] The present invention will now be further described with reference to the accompanying drawings.

[0019] Reference Figures 1-3 A 3-1-2 type cement-based piezoelectric composite material includes piezoelectric ceramic rods (PZT), a cement matrix, and a piezoelectric ceramic substrate. The structural connectivity is defined as 3-1-2, wherein the 3rd phase is the cement matrix, which is a continuous phase (3-0) that is continuous in all directions to achieve acoustic impedance matching with concrete; the 1st phase is the piezoelectric ceramic rod, which is continuous along the thickness direction (3 direction) and is distributed in a rod-shaped or columnar manner in the cement matrix; the 2nd phase is the piezoelectric ceramic substrate, in which an array of piezoelectric ceramic rods is connected in series with a piezoelectric ceramic substrate in the thickness direction to form a stable skeleton structure with lateral and longitudinal support.

[0020] The volume fraction V of the piezoelectric ceramic rod f Satisfying 0.2≤V f ≤0.4.

[0021] The equivalent acoustic impedance of the composite material is in the range of 3 MRayl to 15 MRayl to achieve low-loss acoustic coupling with the concrete matrix.

[0022] The composite material is used as an embedded or surface-deployed acoustic emission (AE) non-destructive testing sensor for concrete structures.

[0023] In this embodiment, the structure consists of an upper PZT cement composite structure and a lower piezoelectric ceramic substrate connected in series along the thickness direction (3 directions). The upper PZT cement composite structure has a 1-3 type connectivity mode, comprising a piezoelectric ceramic rod (1 phase) continuously connected along the thickness direction and a cement matrix (3 phases) continuously surrounding the piezoelectric ceramic rod. The piezoelectric ceramic substrate (2 phases) is a planar support layer connected to the upper structure, used to provide lateral mechanical support and component decoupling. The content and acoustic properties of the cement matrix are optimized to ensure that the equivalent acoustic impedance of the composite material is highly matched with the acoustic impedance of the concrete matrix.

[0024] A method for preparing a 3-1-2 type cement-based piezoelectric composite material includes the following steps: Step 1, Fabrication of piezoelectric ceramic rod array (cutting-filling), the process is as follows: 1.1 Prepare a pre-polarized or to-be-polarized PZT ceramic substrate; 1.2 Using an ultrasonic vibration drilling machine or a high-precision cutting machine, perform precise array cutting along the thickness direction on the PZT substrate to form regularly arranged PZT rod-shaped units; Step 2: Prepare high-performance cement-based slurry, fill the array gaps between PZT rod units evenly and fully with the slurry, vibrate to compact it, and perform the first curing at the set temperature and humidity to form a PZT / cement composite upper layer structure with acoustic impedance matching characteristics. Step 3. Substrate preparation and assembly: Prepare a piezoelectric ceramic substrate that matches the size of the PZT rod array. This substrate serves as the mechanical support layer and decoupling layer for the transducer array. The lower electrode surface of the cured PZT is firmly connected in series with the upper surface of the piezoelectric ceramic substrate using conductive adhesive or welding process to form a complete 3-1-2 type composite structure. Step 4, Secondary Polarization and Encapsulation: Apply a high-voltage DC electric field to the assembled composite material for secondary polarization to ensure the piezoelectric response performance of the overall structure.

[0025] Furthermore, in step 2, the cement-based slurry contains silica fume or nano-silica to improve the density and mechanical strength of the cement matrix.

[0026] In step S3, the series connection is achieved using conductive epoxy resin adhesive or welding process.

[0027] In step 4, the sides and back of the composite material are treated with waterproofing, vibration damping, or sound reflection backing.

[0028] In this embodiment, a standard 3-1-2 cement-based piezoelectric composite sensor is used, and the materials are prepared as follows: The piezoelectric ceramic substrate uses a pre-polarized commercial piezoelectric ceramic (PZT) substrate with dimensions of 15 mm × 15 mm × 10 mm, and employs PZT-5H type lead zirconate titanate piezoelectric ceramic. The cement-based slurry uses an ultra-high performance cementitious material (UHPC) formulation. The specific composition is: 600 parts of 52.5 grade silicate cement, 300 parts of quartz powder (particle size 0-400 mesh), and silica fume (specific surface area ≥15000 m²). 2 100 parts ( / kg) of high-efficiency polycarboxylate superplasticizer and 10 parts of water-binder ratio are mixed at a water-binder ratio of 0.22. The mixture is stirred at high speed in a mixer to form a uniform, highly fluid slurry.

[0029] The piezoelectric ceramic substrate uses PZT-5A piezoelectric ceramic with dimensions of 15 mm × 15 mm × 1 mm, and silver electrodes have been fabricated on the upper and lower surfaces.

[0030] The conductive adhesive is a conductive epoxy resin adhesive filled with silver paste.

[0031] The preparation process in this embodiment is as follows: Step 1: Fabrication of piezoelectric ceramic rod array / cement composite upper layer structure: Cutting: Using a precision diamond wire cutter, the PZT-5H substrate was cut into a 4×4 regular array along the thickness direction (10 mm direction), resulting in 16 independent PZT ceramic rods. Each rod measures approximately 3.5 mm × 3.5 mm × 10 mm (considering cutting losses). The calculated volume fraction (Vf) of the rod is approximately 0.35, satisfying the requirement of 0.2 ≤ Vf ≤ 0.4.

[0032] Filling and Curing: The cut PZT rods, maintaining their original array arrangement, are placed into a special mold. The prepared UHPC slurry is carefully poured into the gaps between the rods, and the mold is then vibrated thoroughly on a vibrating table (frequency 80Hz, time 5 minutes) to remove air bubbles and achieve dense filling. Subsequently, the mold and the sample are placed in a standard curing room (temperature 20±1℃, relative humidity ≥95%) for 7 days to complete the first curing, forming a PZT / cement composite upper layer structure with high mechanical strength and good interfacial bonding.

[0033] Step 2: Structural Assembly: Remove the cured upper structure from the mold and gently sand its lower surface (the lower electrode surface of the original PZT substrate) with fine sandpaper to ensure the electrode surface is clean and flat. Evenly coat the upper surface of the piezoelectric ceramic substrate (PZT-5A) with a layer of conductive epoxy resin. Precisely align and attach the sanded surface of the upper structure to the substrate, apply a pressure of 0.5 MPa, and cure in an 80℃ oven for 2 hours to achieve a firm series connection between the upper and lower layers.

[0034] The embodiments described in this specification are merely examples of implementations of the inventive concept and are for illustrative purposes only. The scope of protection of this invention should not be considered limited to the specific forms described in these embodiments; rather, it extends to equivalent technical means conceived by those skilled in the art based on the inventive concept.

Claims

1. A 3-1-2 type cement-based piezoelectric composite material, characterized in that, The structure comprises piezoelectric ceramic rods, a cement matrix, and a piezoelectric ceramic substrate. The structural connectivity is defined as 3-1-2, where phase 3 is the cement matrix, which is continuous in all directions to achieve acoustic impedance matching with concrete; phase 1 is the piezoelectric ceramic rods, which are continuous along the thickness direction and are distributed discretely in the cement matrix in rod or columnar shapes; phase 2 is the piezoelectric ceramic substrate, in which an array of piezoelectric ceramic rods is connected in series with a piezoelectric ceramic substrate in the thickness direction to form a stable skeleton structure with lateral and longitudinal support.

2. The 3-1-2 type cement-based piezoelectric composite material as described in claim 1, characterized in that, The volume fraction V of the piezoelectric ceramic rod f Satisfying 0.2≤V f ≤0.

4.

3. A method for preparing the 3-1-2 type cement-based piezoelectric composite material as described in claim 1, characterized in that, The preparation method includes the following steps: Step 1: Fabrication of piezoelectric ceramic rod array, the process is as follows: 1.1 Prepare a pre-polarized or to-be-polarized PZT ceramic substrate; 1.2 Using an ultrasonic vibration drilling machine or a high-precision cutting machine, perform precise array cutting along the thickness direction on the PZT substrate to form regularly arranged PZT rod-shaped units; A high-performance cement-based slurry is prepared and uniformly and fully filled into the array gaps between PZT rod units. The slurry is then vibrated to compact it and cured for the first time under a set temperature and humidity to form a PZT / cement composite upper layer structure with acoustic impedance matching characteristics. Step 2, Piezoelectric ceramic substrate preparation: Prepare a piezoelectric ceramic substrate that matches the size of the PZT rod array. This substrate serves as the mechanical support layer and decoupling layer for the transducer array. Step 3. Structural Assembly and Connection: The lower electrode surface of the cured PZT is firmly connected in series with the upper surface of the piezoelectric ceramic substrate using conductive adhesive or welding process to form a complete 3-1-2 type composite structure. Step 4, Secondary Polarization and Encapsulation: Apply a high-voltage DC electric field to the assembled composite material for secondary polarization to ensure the piezoelectric response performance of the overall structure.

4. The preparation method according to claim 3, characterized in that, In step 2, the cement-based slurry contains silica fume or nano-silica to improve the density and mechanical strength of the cement matrix.

5. The preparation method according to claim 3, characterized in that, In step S3, the series connection is achieved using conductive epoxy resin adhesive or welding process.

6. The preparation method according to claim 3, characterized in that, In step 4, the sides and back of the composite material are treated with waterproofing, vibration damping, or sound reflection backing.

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