Cement-based piezoelectric composite material with high force-electric response performance and preparation method thereof

Abstract

The application relates to the technical field of cement-based piezoelectric composite materials, and discloses a cement-based piezoelectric composite material with high force-electric response performance and a preparation method thereof, which is composed of a modified cement matrix and surface-modified PZT piezoelectric ceramic particles, and the raw material components and contents include Portland cement, surface-modified PZT piezoelectric ceramic particles, conductive nano-modifying agent, active interface modifier, water reducing agent, deionized water and carbonization inhibitor; the application is synergistically combined with the surface-modified PZT piezoelectric ceramic particles, the conductive nano-modified cement matrix, the composite carbonization inhibitor and the segmented polarization process, is optimized in multiple dimensions from the particle interface, the matrix structure, the forming process and the polarization system, and the mechanical properties and the piezoelectric stability of the cement-based piezoelectric composite material are significantly improved. The PZT piezoelectric ceramic particles are subjected to surface modification treatment of alkali coarse activation and composite coating crosslinking, the alkali solution can remove the inert oxide layer on the particle surface layer, and the surface activity is improved.

Description

Technical Field

[0001] This invention relates to the field of cement-based piezoelectric composite materials technology, and in particular to a cement-based piezoelectric composite material with high mechanical-electric response performance and its preparation method. Background Technology

[0002] Cement-based piezoelectric composites combine the structural load-bearing capacity of cement-based materials with the force-to-electricity conversion function of piezoelectric ceramics. They can directly convert mechanical energy such as structural stress, vibration, and impact into electrical signals, showing broad application prospects in engineering fields such as structural health monitoring, intelligent sensing, and energy harvesting. Currently, most cement-based piezoelectric composites are prepared by doping unmodified PZT piezoelectric particles with ordinary silicate cement as the matrix, which presents some problems in actual preparation and service.

[0003] Ordinary PZT piezoelectric ceramic particles have an inert oxide layer on their surface, resulting in weak interfacial bonding and poor compatibility with the cement matrix. During mixing and molding, they are prone to agglomeration and sedimentation, making it difficult to form a uniform and stable composite system. This leads to increased internal defects and lower force-to-electricity conversion efficiency. Furthermore, the cement matrix is ​​susceptible to carbonization during hydration and long-term service, continuously eroding internal pores and interfaces. This disrupts the weak conductive pathways within the material, increasing piezoelectric signal transmission loss and reducing stability, resulting in a significant decrease in sensing accuracy after prolonged use.

[0004] In existing technologies, cement matrices are typically not specifically treated for conductivity and interface, resulting in a lack of effective charge transport channels between piezoelectric particles and the matrix, leading to insufficient force-electric response sensitivity. Furthermore, PZT particles lack additional treatment, resulting in low domain orientation and poor response efficiency during polarization. Therefore, this invention provides a cement-based piezoelectric composite material with high force-electric response performance. Summary of the Invention

[0005] To address the problems in the prior art, the present invention provides a cement-based piezoelectric composite material with high mechanical-electric response performance.

[0006] The technical solution adopted by this invention to solve its technical problem is: a cement-based piezoelectric composite material with high mechanical-electric response performance, which is composed of a modified cement matrix and surface-modified PZT piezoelectric ceramic particles. By mass, the raw material components and contents include: 40-60 parts of silicate cement, 30-50 parts of surface-modified PZT piezoelectric ceramic particles, 1-5 parts of conductive nano-modifier, 0.5-2 parts of active interface modifier, 0.3-1 part of water-reducing agent, 15-25 parts of deionized water, and 0.8-2.5 parts of carbonation inhibitor; The modified cement matrix is ​​made of silicate cement, conductive nano-modifier, active interface modifier, water-reducing agent, deionized water, and carbonation inhibitor. The carbonization inhibitor is a composite system of nano-calcium hydroxide and fly ash, used to inhibit the carbonization of the cement matrix and protect the conductive network.

[0007] As a further technical solution, the preparation method of the surface-modified PZT piezoelectric ceramic particles includes the following steps: S1 coarse activation treatment: PZT piezoelectric ceramic particles are immersed in NaOH alkaline solution at a temperature of 80-100℃ and a concentration of 1-3mol / L for 1-2 hours at a material-to-liquid ratio of 1:10 to remove the inert oxide layer on the surface of PZT particles. S2 Composite Coating Crosslinking and Charge Regulation Modification: Prepare a coating solution by adding 3-8 wt% silane coupling agent KH550, 2-5 wt% nano-titanium dioxide with a particle size of 20-50 nm, 0.5-1.5 wt% crosslinking agent glutaraldehyde, and 0.1-0.3 wt% amino-modified graphene quantum dots with a particle size of 5-10 nm to an ethanol aqueous solution with a volume ratio of 1:1. Disperse the coating solution in an ultrasonic environment of 20-40 kHz for 30 min. Then add PZT particles that have undergone coarse activation treatment to the coating solution at a material-to-liquid ratio of 1:8-10. Stir and react at a constant temperature of 60-70℃ for 1-3 h, and then filter. S3 Drying and Curing Treatment: Place the PZT particles treated in step S2 in a vacuum drying oven at 80-100℃ and dry them under vacuum for 1 hour. Then, heat treat them in a constant temperature oven at 120-150℃ for 30 minutes and cool them to room temperature.

[0008] As a further technical solution, the amino grafting rate of the amino-modified graphene quantum dots is 15-20%.

[0009] As a further technical solution, the conductive nanomodifier is a mixture of carbon nanotubes and nano titanium dioxide, with a mass ratio of 1:2-4, wherein the particle size of the nano titanium dioxide is 20-50 nm; the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent with a solid content of 40-50%.

[0010] As a further technical solution, the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 10-20 nm and an aspect ratio of 500-1000; the active interface modifier is an epoxy emulsion with a solid content of 30-50% and a viscosity of 100-200 mPa·s at 25°C.

[0011] As a further technical solution, the mass ratio of nano-calcium hydroxide to fly ash in the carbonization inhibitor is 1:3-5, the particle size of nano-calcium hydroxide is 30-50nm, and the fly ash is grade I fly ash.

[0012] As a further technical solution, the method for preparing the modified cement matrix includes the following steps: a. Conductive agent dispersion treatment: Carbon nanotubes and nano-titanium dioxide are mixed evenly according to the mass ratio, and 1-3wt% sodium dodecylbenzenesulfonate dispersant is added. The mixture is added to deionized water and ultrasonically dispersed in an ultrasonic environment of 20-40kHz for 40-60min. At the same time, the pH value of the dispersion system is adjusted to 6.5-7.5 with dilute hydrochloric acid with a concentration of 0.1mol / L to form a uniform and stable conductive nano-dispersion. b. Modification of the matrix for synergistic crack resistance and carbonation inhibition: First, mix silicate cement with an active interface modifier, a water-reducing agent, and a carbonation inhibitor and stir for 2 minutes. Then, slowly add the conductive nano-dispersion and continue stirring at a low speed of 100-200 r / min for 3 minutes. Finally, add 0.3-1 wt% of the crack-resistant component polypropylene fiber, and stir at a high speed of 500-800 r / min for 5 minutes to obtain the modified cement paste, which is the modified cement matrix. The polypropylene fibers have a length of 5-10 mm and a diameter of 20-30 μm.

[0013] A method for preparing cement-based piezoelectric composite materials with high mechanical-electrical response properties includes the following steps: (1) Raw material preparation and pretreatment: Prepare each raw material according to the mass fractions mentioned above, and prepare surface-modified PZT piezoelectric ceramic particles and modified cement matrix respectively; (2) Composite stirring: The surface-modified PZT piezoelectric ceramic particles are slowly added to the modified cement slurry and stirred at a low speed of 100-200 r / min for 5-8 min. During the stirring process, the stirring is stopped for 10 s every 2 min. At the same time, ultrasonic dispersion at 20-40 kHz is used for 1 min to avoid PZT particle agglomeration. (3) Gradient pressure molding: The mixture that has been stirred evenly in step (2) is filled into a steel mold. First, a pre-pressure of 5MPa is applied for 1 minute, and then the pressure is gradually increased to 60-80MPa at a rate of 5MPa / min. The pressure is maintained for 3-5 minutes. During the pressure holding process, ultrasonic 20-40kHz is used to assist in exhaust. (4) Curing: After molding, the sample is demolded and placed in a standard curing box with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 days. Then, it is placed in a constant temperature drying oven at 60℃ for 24 hours to remove the free water inside the sample. (5) Segmented polarization treatment: Silver-plated electrodes were prepared on the upper and lower surfaces of the cured sample by vacuum evaporation. The sample was then placed in a silicone oil bath for segmented polarization. The polarization process was as follows: First, the temperature was raised to 80℃ at a rate of 2℃ / min at room temperature, and polarized for 30min at an electric field strength of 1kV / mm at 80℃. Then, the temperature was raised to 120℃ at a rate of 1℃ / min, and polarized for 60min at an electric field strength of 2kV / mm at 120℃. Finally, the temperature was slowly lowered to room temperature at a rate of 2-3℃ / min, and polarization was continued for 30min while keeping the electric field strength constant before depressurization. The fluctuation range of the electric field strength during the polarization process did not exceed ±5%.

[0014] As a further technical solution, the low-speed stirring rate in step (2) is 100-200 r / min, and the high-speed stirring rate when preparing modified cement paste in step (4) is 500-800 r / min. The stirring process is carried out by mechanical stirring.

[0015] As a further technical solution, the thickness of the silver-plated electrode in step (5) is 5-10 μm, and the vacuum degree during vacuum evaporation is 1×10⁻⁶. -3 -5×10 -3 Pa, the vapor deposition temperature is 150-200℃, and after vapor deposition, it is allowed to cool naturally to room temperature for later use.

[0016] The beneficial effects of this invention are: This invention significantly improves the mechanical-electric response performance and service stability of cement-based piezoelectric composite materials by combining surface-modified PZT piezoelectric ceramic particles and conductive nano-modified cement matrix, optimizing and enhancing aspects such as particle interface and matrix structure.

[0017] PZT piezoelectric ceramic particles undergo surface modification treatment including alkaline coarse activation and composite coating crosslinking. The alkaline solution removes the inert oxide layer on the particle surface, enhancing surface activity. A silane coupling agent, nano-titanium dioxide, amino-modified graphene quantum dots, and a crosslinking agent together form a uniform coating layer. This dense and conductive composite layer modification improves the interfacial bonding strength and dispersibility between the particles and the cement matrix, reduces agglomeration and interfacial defects, thereby lowering charge transport resistance and increasing force-to-electricity conversion efficiency. The amino-modified graphene quantum dots can regulate the charge distribution on the particle surface, improving the domain orientation efficiency during polarization, enabling the composite material to output electrical signals faster and more stably under stress.

[0018] A conductive nanomodifier, a composite of carbon nanotubes and nano-titanium dioxide, is introduced into the cement matrix. These two components, in a specific ratio, form a continuous, interconnected three-dimensional conductive network. This network can rapidly conduct the charge generated by the piezoelectric response, thereby reducing internal impedance and improving signal transmission efficiency, solving the problems of poor conductivity and lag in traditional cement matrices. An active interface modifier strengthens the interfacial bonding between the matrix and piezoelectric particles, reducing interfacial debonding and microcrack formation, and improving the mechanical properties of the composite material. A carbonization inhibitor, a composite of nano-calcium hydroxide and primary fly ash, can rapidly consume carbon dioxide in the environment and fill matrix pores. Because it effectively inhibits carbonization of the cement matrix, it protects the internal conductive network from damage, thereby improving the stability and durability of the material during long-term service and extending its service life.

[0019] This invention employs a gradient pressure molding and segmented polarization process. Gradient pressure combined with ultrasonic assistance can expel internal pores in the mixture, improving density and uniformity. Segmented polarization uses a step-by-step heating-holding-cooling process, which allows for gradual and sufficient domain orientation under different temperature fields, avoiding local breakdown and residual internal stress, thereby significantly improving the piezoelectric response coefficient and signal stability. The components and process steps work synergistically: surface modification improves particle compatibility, the conductive network enhances charge transport, carbonization inhibitors extend service life, and gradient molding and segmented polarization improve structural and polarization uniformity. Ultimately, this results in a cement-based piezoelectric composite material that simultaneously possesses high mechanical-electric response sensitivity, excellent mechanical strength, good carbonization resistance, and long-term cycling stability. Attached Figure Description

[0020] Figure 1 This is a comparison chart of the piezoelectric coefficient retention rates of an example and a comparative example of a cement-based piezoelectric composite material with high mechanical-electric response performance. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] This invention provides a cement-based piezoelectric composite material with high mechanical-electrical response performance, composed of a modified cement matrix and surface-modified PZT piezoelectric ceramic particles. By weight, the raw material components and contents include 40-60 parts silicate cement, 30-50 parts surface-modified PZT piezoelectric ceramic particles, 1-5 parts conductive nano-modifier, 0.5-2 parts active interface modifier, 0.3-1 part water-reducing agent, 15-25 parts deionized water, and 0.8-2.5 parts carbonation inhibitor. The carbonation inhibitor is a composite system of nano-calcium hydroxide and fly ash, used to inhibit the carbonation of the cement matrix and protect the conductive network.

[0023] Preparation of surface-modified PZT piezoelectric ceramic particles: The present invention first modifies the surface of PZT piezoelectric ceramic particles. The modification process includes coarse activation treatment, composite coating crosslinking and charge regulation modification, and drying and curing treatment.

[0024] Rough activation treatment: PZT piezoelectric ceramic particles are immersed in NaOH alkaline solution at a temperature of 80-100℃ and a concentration of 1-3mol / L for 1-2 hours at a material-to-liquid ratio of 1:10 to remove the inert oxide layer on the surface of PZT particles.

[0025] Composite Coating, Crosslinking, and Charge-Controlled Modification: A coating solution was prepared by adding 3-8 wt% silane coupling agent KH550, 2-5 wt% nano-titanium dioxide with a particle size of 20-50 nm, 0.5-1.5 wt% crosslinking agent glutaraldehyde, and 0.1-0.3 wt% amino-modified graphene quantum dots with a particle size of 5-10 nm to a 1:1 volume ratio of ethanol to aqueous solution. The coating solution was dispersed in an ultrasonic environment at 20-40 kHz for 30 min. Then, PZT particles that had undergone coarse activation treatment were added to the coating solution at a material-to-liquid ratio of 1:8-10. The mixture was stirred and reacted at a constant temperature of 60-70℃ for 1-3 h, followed by filtration. The preferred amino grafting rate of the amino-modified graphene quantum dots was 15-20%.

[0026] Drying and curing treatment: The PZT particles after composite coating, crosslinking and charge regulation modification treatment were placed in a vacuum drying oven at 80-100℃ and dried for 1 hour. Then, they were heat-treated in a constant temperature furnace at 120-150℃ for 30 minutes and cooled to room temperature to obtain surface-modified PZT piezoelectric ceramic particles.

[0027] Preparation of modified cement matrix: The conductive nanomodifier is a mixture of carbon nanotubes and nano-titanium dioxide in a mass ratio of 1:2-4, with the nano-titanium dioxide having a particle size of 20-50 nm. The carbon nanotubes are preferably multi-walled carbon nanotubes with a diameter of 10-20 nm and an aspect ratio of 500-1000. The water-reducing agent is preferably a polycarboxylate-based high-efficiency water-reducing agent with a solid content of 40-50%. The active interface modifier is an epoxy-based emulsion with a solid content of 30-50% and a viscosity of 100-200 mPa·s at 25°C.

[0028] The mass ratio of nano-calcium hydroxide to fly ash in the carbonization inhibitor is 1:3-5, the particle size of nano-calcium hydroxide is 30-50nm, and the fly ash is grade I fly ash.

[0029] The preparation of modified cement matrix includes conductive agent dispersion treatment, matrix synergistic crack resistance and carbonation inhibition modification.

[0030] Conductive agent dispersion treatment: Carbon nanotubes and nano-titanium dioxide are mixed evenly at a mass ratio, and 1-3wt% sodium dodecylbenzenesulfonate dispersant is added. The mixture is then added to deionized water and ultrasonically dispersed in a 20-40kHz ultrasonic environment for 40-60 minutes. At the same time, the pH value of the dispersion system is adjusted to 6.5-7.5 with 0.1mol / L dilute hydrochloric acid to form a uniform and stable conductive nano-dispersion.

[0031] Synergistic crack resistance and carbonation inhibition modification of the matrix: First, silicate cement is mixed with an active interface modifier, a water-reducing agent, and a carbonation inhibitor, and stirred for 2 minutes. Then, a conductive nano-dispersion is slowly added, and the mixture is stirred at a low speed of 100-200 r / min for 3 minutes. Finally, 0.3-1 wt% of crack-resistant polypropylene fiber (by weight of silicate cement) is added, and the mixture is stirred at a high speed of 500-800 r / min for 5 minutes to obtain a modified cement paste, which is the modified cement matrix. The polypropylene fiber has a length of 5-10 mm and a diameter of 20-30 μm.

[0032] Preparation method of cement-based piezoelectric composite materials: Raw material preparation and pretreatment: Prepare each raw material according to the mass fraction, and prepare surface-modified PZT piezoelectric ceramic particles and modified cement matrix respectively.

[0033] Composite mixing: Slowly add the surface-modified PZT piezoelectric ceramic particles into the modified cement slurry, and stir at a low speed of 100-200 r / min for 5-8 min. During the stirring process, stop stirring for 10 s every 2 min, and at the same time use 20-40 kHz ultrasonic dispersion for 1 min to avoid PZT particle agglomeration.

[0034] Gradient pressure molding: The mixed material that has been thoroughly stirred is filled into a steel mold. First, a pre-pressure of 5MPa is applied for 1 minute, and then the pressure is gradually increased to 60-80MPa at a rate of 5MPa / min. This pressure is maintained for 3-5 minutes. During the pressure holding process, ultrasonic assisted degassing is used at 20-40kHz.

[0035] Curing: After molding, the sample is demolded and placed in a standard curing chamber with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 days. Then, it is placed in a constant temperature drying oven at 60℃ for 24 hours to remove free water from the sample.

[0036] Segmented polarization treatment: Silver-plated electrodes were prepared on the upper and lower surfaces of the cured sample using vacuum evaporation. The thickness of the silver-plated electrodes was 5-10 μm, and the vacuum degree during vacuum evaporation was 1×10⁻⁶. -3 -5×10 -3 The vapor deposition temperature is 150-200℃, and the sample is allowed to cool naturally to room temperature after deposition. The sample is then placed in a silicone oil bath for segmented polarization. The polarization process is as follows: first, the temperature is increased to 80℃ at a rate of 2℃ / min, and polarized for 30 min at 80℃ and an electric field strength of 1kV / mm; then, the temperature is increased to 120℃ at a rate of 1℃ / min, and polarized for 60 min at 120℃ and an electric field strength of 2kV / mm; finally, the temperature is slowly reduced to room temperature at a rate of 2-3℃ / min, and polarization continues for 30 min while maintaining a constant electric field strength before depressurization. The fluctuation range of the electric field strength during polarization should not exceed ±5%.

[0037] This invention significantly improves the mechanical-electric response performance of cement-based piezoelectric composite materials by modifying the surface of PZT piezoelectric ceramic particles and the conductivity and carbonization resistance of the cement matrix, combined with gradient pressure molding and segmented polarization processes. At the same time, it inhibits the carbonization of the cement matrix, improves the structural stability and service life of the material, and solves the problems of low mechanical-electric conversion efficiency, easy carbonization failure, and easy particle agglomeration of traditional cement-based piezoelectric composite materials.

[0038] Example 1: 1. Preparation of surface-modified PZT piezoelectric ceramic particles: S1 coarse activation treatment: PZT piezoelectric ceramic particles are immersed in NaOH alkaline solution with a concentration of 1mol / L at a material-to-liquid ratio of 1:10 for 1 hour to remove the inert oxide layer on the surface of PZT particles.

[0039] S2 Composite Coating Crosslinking and Charge-Controlled Modification: A coating solution was prepared by adding 3 wt% silane coupling agent KH550, 2 wt% nano-titanium dioxide with a particle size of 20 nm, 0.5 wt% crosslinking agent glutaraldehyde, and 0.1 wt% amino-modified graphene quantum dots with a particle size of 5 nm to a 1:1 volume ratio of ethanol-water solution. The amino grafting rate of the amino-modified graphene quantum dots was 15%. The coating solution was dispersed in a 20 kHz ultrasonic environment for 30 min. Then, PZT particles that had undergone coarse activation treatment were added to the coating solution at a material-to-liquid ratio of 1:8. The mixture was stirred and reacted at a constant temperature of 60 °C for 1 h, followed by filtration.

[0040] S3 Drying and Curing Treatment: The PZT particles treated in step S2 are placed in an 80℃ vacuum drying oven for 1 hour, followed by heat treatment in a 120℃ constant temperature oven for 30 minutes, and then cooled to room temperature.

[0041] 2. Preparation of modified cement matrix: Raw material composition (by weight): 40 parts silicate cement, 1 part conductive nano-modifier, 0.5 parts active interface modifier, 0.3 parts water-reducing agent, 15 parts deionized water, and 0.8 parts carbonization inhibitor. Conductive nano-modifier: Carbon nanotubes to nano-titanium dioxide in a 1:2 mass ratio, with nano-titanium dioxide particle size of 20 nm; the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 10 nm and an aspect ratio of 500. Water-reducing agent: Polycarboxylate-based high-efficiency water-reducing agent with a solid content of 40%. Active interface modifier: Epoxy-based emulsion with a solid content of 30% and a viscosity of 100 mPa·s at 25℃. Carbonization inhibitor: Nano-calcium hydroxide to fly ash in a 1:3 mass ratio, with nano-calcium hydroxide particle size of 30 nm; the fly ash is grade I fly ash.

[0042] a. Conductive agent dispersion treatment: Carbon nanotubes and nano-titanium dioxide are mixed evenly, 1 wt% sodium dodecylbenzenesulfonate dispersant is added, deionized water is added, and the mixture is ultrasonically dispersed in a 20 kHz ultrasonic environment for 40 min. The pH value is adjusted to 6.5 with 0.1 mol / L dilute hydrochloric acid to form a conductive nano-dispersion.

[0043] b. Modification of matrix for synergistic crack resistance and carbonation inhibition: Silicate cement is mixed with active interface modifier, water-reducing agent and carbonation inhibitor for 2 min. Conductive nano-dispersion is slowly added and stirred at a low speed of 100 r / min for 3 min. Polypropylene fiber with a length of 5 mm and a diameter of 20 μm is added at 0.3 wt% of the mass of silicate cement. The mixture is stirred at a high speed of 500 r / min for 5 min to obtain modified cement paste.

[0044] 3. Preparation of cement-based piezoelectric composite materials: (1) Raw material preparation and pretreatment: Prepare raw materials according to the above proportions, and prepare surface-modified PZT piezoelectric ceramic particles and modified cement matrix.

[0045] (2) Composite stirring: The surface-modified PZT piezoelectric ceramic particles are slowly added to the modified cement slurry and stirred at a low speed of 100r / min for 5min. Stirring is stopped for 10s after a 2min interval and then dispersed by ultrasonic waves at 20kHz for 1min.

[0046] (3) Gradient pressure molding: The mixture is filled into a steel mold, a pre-pressure of 5MPa is applied for 1min, the pressure is increased to 60MPa at a rate of 5MPa / min, and the pressure is held for 3min. During the pressure holding, 20kHz ultrasonic waves are used to assist in venting.

[0047] (4) Curing: After demolding, the sample is cured in a curing box at 20±2℃ and relative humidity ≥95% for 28 days, and then dried in a constant temperature drying oven at 60℃ for 24 hours. (5) Segmented polarization treatment: Silver-plated electrodes are vacuum-deposited on the upper and lower surfaces of the sample, with an electrode thickness of 5μm and a vacuum degree of 1×10 -3 Pa, vapor deposition temperature 150℃, cooled for later use. The sample was placed in a silicone oil bath, heated from room temperature to 80℃ at 2℃ / min, polarized at 80℃ and 1kV / mm for 30min; heated to 120℃ at 1℃ / min, polarized at 120℃ and 2kV / mm for 60min; cooled to room temperature at 2℃ / min, maintained electric field polarization for 30min, and then depressurized, with electric field fluctuation ≤±5%.

[0048] Example 2: 1. Preparation of surface-modified PZT piezoelectric ceramic particles: S1 coarse activation treatment: PZT piezoelectric ceramic particles are immersed in NaOH alkaline solution at 100℃ and 3mol / L concentration for 2 hours at a material-to-liquid ratio of 1:10 to remove the inert oxide layer on the surface of PZT particles.

[0049] S2 Composite Coating Crosslinking and Charge-Controlled Modification: A coating solution was prepared by adding 8 wt% silane coupling agent KH550, 5 wt% nano-titanium dioxide with a particle size of 50 nm, 1.5 wt% crosslinking agent glutaraldehyde, and 0.3 wt% amino-modified graphene quantum dots with a particle size of 10 nm to a 1:1 volume ratio of ethanol-water solution. The amino grafting rate of the amino-modified graphene quantum dots was 20%. The coating solution was dispersed in a 40 kHz ultrasonic environment for 30 min. Then, PZT particles that had undergone coarse activation treatment were added to the coating solution at a 1:10 material-to-liquid ratio. The mixture was stirred and reacted at a constant temperature of 70 °C for 3 h, followed by filtration.

[0050] S3 Drying and Curing Treatment: The PZT particles treated in step S2 are placed in a vacuum drying oven at 100℃ and dried under vacuum for 1 hour. Then, they are heat-treated in a constant temperature oven at 150℃ for 30 minutes and cooled to room temperature.

[0051] 2. Preparation of modified cement matrix: Raw material composition (by weight): 60 parts silicate cement, 5 parts conductive nano-modifier, 2 parts active interface modifier, 1 part water-reducing agent, 25 parts deionized water, and 2.5 parts carbonization inhibitor. Conductive nano-modifier: Carbon nanotubes to nano-titanium dioxide in a 1:4 mass ratio, with nano-titanium dioxide particle size of 50 nm; the carbon nanotubes are multi-walled carbon nanotubes with a diameter of 20 nm and an aspect ratio of 1000. Water-reducing agent: Polycarboxylate-based high-efficiency water-reducing agent with a solid content of 50%. Active interface modifier: Epoxy-based emulsion with a solid content of 50% and a viscosity of 200 mPa·s at 25℃. Carbonization inhibitor: Nano-calcium hydroxide to fly ash in a 1:5 mass ratio, with nano-calcium hydroxide particle size of 50 nm; the fly ash is grade I fly ash.

[0052] a. Conductive agent dispersion treatment: Carbon nanotubes and nano-titanium dioxide are mixed evenly, 3wt% sodium dodecylbenzenesulfonate dispersant is added, deionized water is added, and the mixture is ultrasonically dispersed in a 40kHz ultrasonic environment for 60min. The pH value is adjusted to 7.5 with 0.1mol / L dilute hydrochloric acid to form a conductive nano-dispersion.

[0053] b. Modification of matrix for synergistic crack resistance and carbonation inhibition: Silicate cement is mixed with active interface modifier, water-reducing agent and carbonation inhibitor for 2 min. Conductive nano-dispersion is slowly added and stirred at a low speed of 200 r / min for 3 min. Polypropylene fiber with a length of 10 mm and a diameter of 30 μm is added at a high speed of 800 r / min for 5 min to obtain modified cement paste.

[0054] 3. Preparation of cement-based piezoelectric composite materials: (1) Raw material preparation and pretreatment: Prepare raw materials according to the above proportions, and prepare surface-modified PZT piezoelectric ceramic particles and modified cement matrix.

[0055] (2) Composite stirring: The surface-modified PZT piezoelectric ceramic particles are slowly added to the modified cement slurry and stirred at a low speed of 200r / min for 8min. Stirring is stopped for 10s after a 2min interval and then dispersed by ultrasonic waves at 40kHz for 1min.

[0056] (3) Gradient pressure molding: The mixture is filled into a steel mold, and a pre-pressure of 5MPa is applied for 1min. The pressure is increased to 80MPa at a rate of 5MPa / min and held for 5min. During the holding period, 40kHz ultrasonic waves are used to assist in venting.

[0057] (4) Curing: After demolding, place in a curing box at 20±2℃ and relative humidity ≥95% for 28 days, and then place in a constant temperature drying box at 60℃ for 24 hours.

[0058] (5) Segmented polarization treatment: Silver-plated electrodes are vacuum-deposited on the upper and lower surfaces of the sample, with an electrode thickness of 10 μm and a vacuum degree of 5 × 10⁻⁶. -3Pa, vapor deposition temperature 200℃, cooled for later use. The sample was placed in a silicone oil bath, heated from room temperature to 80℃ at 2℃ / min, polarized at 80℃ and 1kV / mm for 30min; heated to 120℃ at 1℃ / min, polarized at 120℃ and 2kV / mm for 60min; cooled to room temperature at 3℃ / min, maintained electric field polarization for 30min, and then depressurized, with electric field fluctuation ≤±5%.

[0059] Example 3: 1. Preparation of surface-modified PZT piezoelectric ceramic particles: S1 coarse activation treatment: PZT piezoelectric ceramic particles are immersed in NaOH alkaline solution at 90℃ and concentration of 2mol / L for 1.5h at a material-to-liquid ratio of 1:10 to remove the inert oxide layer on the surface of PZT particles.

[0060] S2 Composite Coating Crosslinking and Charge-Controlled Modification: A coating solution was prepared by adding 5 wt% silane coupling agent KH550, 3.5 wt% nano-titanium dioxide with a particle size of 35 nm, 1 wt% crosslinking agent glutaraldehyde, and 0.2 wt% amino-modified graphene quantum dots with a particle size of 7.5 nm to a 1:1 volume ratio of ethanol-water solution. The amino grafting rate of the amino-modified graphene quantum dots was 17.5%. The coating solution was dispersed in a 30 kHz ultrasonic environment for 30 min. Then, PZT particles that had undergone coarse activation treatment were added to the coating solution at a material-to-liquid ratio of 1:9. The mixture was stirred and reacted at a constant temperature of 65℃ for 2 h, followed by filtration.

[0061] S3 Drying and Curing Treatment: The PZT particles treated in step S2 were placed in a vacuum drying oven at 90℃ and dried for 1 hour. Then, they were heat-treated in a constant temperature oven at 135℃ for 30 minutes and cooled to room temperature.

[0062] 2. Preparation of modified cement matrix: Raw material composition (by weight): 50 parts silicate cement, 3 parts conductive nano-modifier, 1.25 parts active interface modifier, 0.65 parts water-reducing agent, 20 parts deionized water, and 1.65 parts carbonization inhibitor. Conductive nano-modifier: Carbon nanotubes to nano-titanium dioxide in a 1:3 mass ratio; nano-titanium dioxide particle size 35 nm; carbon nanotubes are multi-walled carbon nanotubes with a diameter of 15 nm and an aspect ratio of 750. Water-reducing agent: Polycarboxylate-based high-efficiency water-reducing agent with a solid content of 45%. Active interface modifier: Epoxy-based emulsion with a solid content of 40% and a viscosity of 150 mPa·s at 25℃. Carbonization inhibitor: Nano-calcium hydroxide to fly ash in a 1:4 mass ratio; nano-calcium hydroxide particle size 40 nm; fly ash is grade I fly ash.

[0063] a. Conductive agent dispersion treatment: Carbon nanotubes and nano-titanium dioxide are mixed evenly, 2wt% sodium dodecylbenzenesulfonate dispersant is added, deionized water is added, and the mixture is ultrasonically dispersed in a 30kHz ultrasonic environment for 50min. The pH value is adjusted to 7.0 with 0.1mol / L dilute hydrochloric acid to form a conductive nano-dispersion.

[0064] b. Modification of matrix for synergistic crack resistance and carbonation inhibition: Silicate cement is mixed with active interface modifier, water-reducing agent and carbonation inhibitor for 2 min. Conductive nano-dispersion is slowly added and stirred at a low speed of 150 r / min for 3 min. Polypropylene fiber with a length of 7.5 mm and a diameter of 25 μm is added at 0.65 wt% of the mass of silicate cement. The mixture is stirred at a high speed of 650 r / min for 5 min to obtain modified cement paste.

[0065] 3. Preparation of cement-based piezoelectric composite materials: (1) Raw material preparation and pretreatment: Prepare raw materials according to the above proportions, and prepare surface-modified PZT piezoelectric ceramic particles and modified cement matrix.

[0066] (2) Composite stirring: The surface-modified PZT piezoelectric ceramic particles were slowly added to the modified cement slurry and stirred at a low speed of 150r / min for 6.5min. The stirring was stopped for 10s after a 2min interval and dispersed by ultrasonic waves at 30kHz for 1min.

[0067] (3) Gradient pressure molding: The mixture is filled into a steel mold, and a pre-pressure of 5MPa is applied for 1min. The pressure is increased to 75MPa at a rate of 5MPa / min and held for 4min. During the holding period, 30kHz ultrasonic waves are used to assist in venting.

[0068] (4) Curing: After demolding, place in a curing box at 20±2℃ and relative humidity ≥95% for 28 days, and then place in a constant temperature drying box at 60℃ for 24 hours.

[0069] (5) Segmented polarization treatment: Silver-plated electrodes are vacuum-deposited on the upper and lower surfaces of the sample, with an electrode thickness of 7.5 μm and a vacuum degree of 3 × 10⁻⁶. -3 Pa, vapor deposition temperature 175℃, cooled for later use. The sample was placed in a silicone oil bath, heated from room temperature to 80℃ at 2℃ / min, polarized at 80℃ and 1kV / mm for 30min; heated to 120℃ at 1℃ / min, polarized at 120℃ and 2kV / mm for 60min; cooled to room temperature at 2.5℃ / min, maintained electric field polarization for 30min, and then depressurized, with electric field fluctuation ≤±5%.

[0070] Comparative Example 1: Compared with Example 3, no carbonization inhibitor was added, but the other raw materials, process parameters, and preparation steps were exactly the same.

[0071] Comparative Example 2: Compared with Example 3, the PZT piezoelectric ceramic particles were not surface modified, and unmodified PZT particles were used directly. The other raw materials, process parameters, and preparation steps were exactly the same.

[0072] Comparative Example 3: Compared with Example 3, no conductive nanomodifier was added, but the other raw materials, process parameters, and preparation steps were exactly the same.

[0073] Comparative Example 4: Compared to Example 3, a conventional single-stage polarization process was used, replacing the segmented polarization treatment. All other raw materials, process parameters, and preparation steps remained identical. The conventional polarization process involved direct polarization at room temperature and an electric field strength of 2 kV / mm for 90 minutes, followed by natural cooling and depressurization.

[0074] test: Experiment 1: Piezoelectric strain constant d 33 test Experimental objective: To test the piezoelectric strain constant d of Examples 1-3 and Comparative Examples 1-4. 33 The effects of carbonization inhibitors, PZT surface modification, conductive nano-modifiers, and segmented polarization on the mechanoelectric conversion performance of the material were verified.

[0075] Experimental principle: A quasi-static piezoelectric coefficient measuring instrument is used to test the piezoelectric response of the sample under quasi-static alternating load, and the piezoelectric strain constant d is directly obtained. 33 A higher value indicates better power-to-electricity conversion performance.

[0076] Experimental apparatus: Quasi-static d 33 Measuring instruments, pressure testing machines, and electronic balances.

[0077] Test method: The cured and polarized sample was processed to standard dimensions. Electrodes were prepared on both sides and fixed on the test platform. The piezoelectric strain constant d was measured along the thickness direction. 33 Five parallel tests were conducted, and the average value was taken.

[0078] Experimental data: Table 1

[0079] The piezoelectric strain constant d in Examples 1-3 33 All are at a relatively high level.

[0080] Comparative Example 1, without the addition of carbonation inhibitors, shows that the cement matrix is ​​prone to carbonation, leading to decreased density and interfacial bonding, and reduced mechanical-electrical transport efficiency. Therefore, d 33 Significantly reduced.

[0081] Comparative Example 2 did not involve surface modification of the PZT particles. The particles exhibited poor interfacial compatibility with the cement matrix, resulting in an inert interfacial layer and defects that hindered charge transport and resulted in poor dispersibility. 33 A significant decrease.

[0082] Comparative Example 3, without the addition of conductive nano-modifiers, suffers from difficulty in forming continuous conductive pathways within the material, hindering effective charge conduction and collection. 33 lowest.

[0083] Comparative Example 4 uses a single polarization process, resulting in insufficient polarization, low domain orientation, and poor force-to-electric conversion efficiency. 33 Significantly lower than the example.

[0084] Experiment 2: Cement matrix carbonation depth test: Experimental objective: To test the effect of carbonation inhibitors on the carbonation resistance of cementitious matrices.

[0085] Test principle: The phenolphthalein indicator method is used to test the carbonization depth of the sample. The smaller the depth, the better the carbonization resistance.

[0086] Test instruments: carbonization test chamber, phenolphthalein alcohol solution, calipers.

[0087] Test method: The sample was placed in a carbonization test chamber with a CO2 concentration of 20±3%, a temperature of 20±2℃, and a relative humidity of 70±5% for 28 days. The sample was then split open and sprayed with phenolphthalein solution. The depth of the uncolored area was measured. The test was repeated in three parallel tests and the average value was taken.

[0088] Experimental data: Table 2

[0089] Experimental analysis and summary: Examples 1-3, due to the addition of a composite carbonation inhibitor of nano-calcium hydroxide and fly ash, all exhibited carbonation depths no greater than 1.2 mm, demonstrating excellent anti-carbonation performance. Comparative Example 1, without the addition of a carbonation inhibitor, showed rapid carbonation of the cement matrix, reaching a depth of 5.8 mm, severely damaging the internal structure and conductive network. Comparative Examples 2, 3, and 4, by retaining the carbonation inhibitor, showed carbonation depths similar to the examples.

[0090] Experiment 3: Mechanical Properties and Piezoelectric Stability Tests Experimental objective: To test the compressive strength and piezoelectric stability of the specimens under cyclic loading, and to verify the structural reliability and mechanical-electrical response durability of the formulation system and preparation process.

[0091] Test principle: The 28-day compressive strength of the specimen is tested according to the standard method; cyclic fatigue load is applied to the specimen, the piezoelectric strain constant before and after the cycle is tested, and the performance retention rate is calculated to evaluate the stability.

[0092] Testing instruments: pressure testing machine, quasi-static piezoelectric coefficient measuring instrument, cyclic loading testing machine.

[0093] Test methods: The 28-day compressive strength of the specimens was tested according to the national standard method; 0–0.5 MPa cyclic load (low stress fatigue, more focused on sensor working conditions) was applied to the specimens, with a loading frequency of 1 Hz and 10,000 cycles. The piezoelectric strain constant after the cycles was tested, and the piezoelectric performance retention rate was calculated.

[0094] Experimental data: Table 3

[0095] Examples 1-3 exhibit high compressive strength, and their piezoelectric strain constant retention rates after cyclic loading are all above 92%, indicating a dense material structure, good interfacial bonding, and excellent piezoelectric phase stability, resulting in good structural reliability and endurance-electric response performance. Comparative Example 1, without the addition of a carbonization inhibitor, suffers from easy carbonization and loosening of the cement matrix, leading to decreased interfacial bonding and structural integrity, and a significant reduction in compressive strength and piezoelectric retention rate. Comparative Example 2, without surface modification of the PZT particles, shows weak interfacial bonding between the piezoelectric phase and the matrix, making it prone to interfacial debonding and damage under cyclic loading, resulting in significant piezoelectric performance degradation and a low retention rate. Comparative Example 3, without the addition of a conductive nano-modifier, struggles to form continuous conductive pathways, leading to easy charge accumulation and dissipation, the worst cyclic stability, and the lowest retention rate. Comparative Example 4, employing a single polarization process, suffers from insufficient domain orientation, making it prone to domain relaxation and orientation degradation under cyclic loading, resulting in a significantly lower piezoelectric retention rate than the examples.

[0096] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A cement-based piezoelectric composite material with high mechanical-electrical response performance, characterized in that, The composite material is made of modified cement matrix and surface-modified PZT piezoelectric ceramic particles. By mass, the composite material is made of the following raw material components: 40-60 parts silicate cement, 30-50 parts surface-modified PZT piezoelectric ceramic particles, 1-5 parts conductive nano-modifier, 0.5-2 parts active interface modifier, 0.3-1 part water-reducing agent, 15-25 parts deionized water, and 0.8-2.5 parts carbonation inhibitor. The modified cement matrix is ​​made of silicate cement, conductive nano-modifier, active interface modifier, water-reducing agent, deionized water, and carbonation inhibitor. The carbonization inhibitor is a composite system of nano-calcium hydroxide and fly ash.

2. The cement-based piezoelectric composite material with high mechanical-electrical response performance according to claim 1, characterized in that, The preparation method of the surface-modified PZT piezoelectric ceramic particles includes the following steps: S1 coarse activation treatment: PZT piezoelectric ceramic particles are immersed in NaOH alkaline solution at a temperature of 80-100℃ and a concentration of 1-3mol / L for 1-2 hours at a material-to-liquid ratio of 1:10 to remove the inert oxide layer on the surface of PZT particles. S2 Composite Coating Crosslinking and Charge Regulation Modification: Prepare a coating solution by adding 3-8 wt% silane coupling agent KH550, 2-5 wt% nano-titanium dioxide with a particle size of 20-50 nm, 0.5-1.5 wt% crosslinking agent glutaraldehyde, and 0.1-0.3 wt% amino-modified graphene quantum dots with a particle size of 5-10 nm to an ethanol aqueous solution with a volume ratio of 1:

1. Disperse the coating solution in an ultrasonic environment of 20-40 kHz for 30 min. Then add PZT particles that have undergone coarse activation treatment to the coating solution at a material-to-liquid ratio of 1:8-10. Stir and react at a constant temperature of 60-70℃ for 1-3 h, and then filter. S3 Drying and Curing Treatment: Place the PZT particles treated in step S2 in a vacuum drying oven at 80-100℃ and dry them under vacuum for 1 hour. Then, heat treat them in a constant temperature oven at 120-150℃ for 30 minutes and cool them to room temperature.

3. The cement-based piezoelectric composite material with high mechanical-electrical response performance according to claim 2, characterized in that, The amino grafting rate of the amino-modified graphene quantum dots is 15-20%.

4. The cement-based piezoelectric composite material with high mechanical-electrical response performance according to claim 1, characterized in that, The conductive nanomodifier is a mixture of carbon nanotubes and nano-titanium dioxide, with a mass ratio of 1:2-4, wherein the nano-titanium dioxide has a particle size of 20-50 nm; the water-reducing agent is a polycarboxylate-based high-efficiency water-reducing agent with a solid content of 40-50%.

5. The cement-based piezoelectric composite material with high mechanical-electrical response performance according to claim 4, characterized in that, The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 10-20 nm and an aspect ratio of 500-1000; the active interface modifier is an epoxy emulsion with a solid content of 30-50% and a viscosity of 100-200 mPa·s at 25°C.

6. The cement-based piezoelectric composite material with high mechanical-electrical response performance according to claim 1, characterized in that, The carbonization inhibitor has a mass ratio of nano-calcium hydroxide to fly ash of 1:3-5, the nano-calcium hydroxide has a particle size of 30-50 nm, and the fly ash is grade I fly ash.

7. The cement-based piezoelectric composite material with high mechanical-electrical response performance according to claim 1, characterized in that, The method for preparing the modified cement matrix includes the following steps: a. Conductive agent dispersion treatment: Carbon nanotubes and nano-titanium dioxide are mixed evenly according to the mass ratio, and 1-3wt% sodium dodecylbenzenesulfonate dispersant is added. The mixture is added to deionized water and ultrasonically dispersed in an ultrasonic environment of 20-40kHz for 40-60min. At the same time, the pH value of the dispersion system is adjusted to 6.5-7.5 with dilute hydrochloric acid with a concentration of 0.1mol / L to form a uniform and stable conductive nano-dispersion. b. Modification of the matrix for synergistic crack resistance and carbonation inhibition: First, mix silicate cement with an active interface modifier, a water-reducing agent, and a carbonation inhibitor and stir for 2 minutes. Then, slowly add the conductive nano-dispersion and continue stirring at a low speed of 100-200 r / min for 3 minutes. Finally, add 0.3-1 wt% of the crack-resistant component polypropylene fiber, and stir at a high speed of 500-800 r / min for 5 minutes to obtain the modified cement paste, which is the modified cement matrix. The polypropylene fibers have a length of 5-10 mm and a diameter of 20-30 μm.

8. The method for preparing the cement-based piezoelectric composite material with high mechanical-electrical response performance according to any one of claims 1-7, characterized in that, Includes the following steps: (1) Raw material preparation and pretreatment: Prepare each raw material according to the mass fractions mentioned above, and prepare surface-modified PZT piezoelectric ceramic particles and modified cement matrix respectively; (2) Composite stirring: The surface-modified PZT piezoelectric ceramic particles are slowly added to the modified cement slurry and stirred at a low speed of 100-200 r / min for 5-8 min. During the stirring process, the stirring is stopped for 10 s every 2 min and the mixture is dispersed by ultrasonic waves at 20-40 kHz for 1 min. (3) Gradient pressure molding: The mixture that has been stirred evenly in step (2) is filled into a steel mold. First, a pre-pressure of 5MPa is applied for 1 minute, and then the pressure is gradually increased to 60-80MPa at a rate of 5MPa / min. The pressure is maintained for 3-5 minutes. During the pressure holding process, ultrasonic 20-40kHz is used to assist in exhaust. (4) Curing: After molding, the sample is demolded and placed in a standard curing box with a temperature of 20±2℃ and a relative humidity of ≥95% for 28 days. Then, it is placed in a constant temperature drying oven at 60℃ for 24 hours to remove the free water inside the sample. (5) Segmented polarization treatment: Silver-plated electrodes were prepared on the upper and lower surfaces of the cured sample by vacuum evaporation. The sample was then placed in a silicone oil bath for segmented polarization. The polarization process was as follows: First, the temperature was raised to 80℃ at a rate of 2℃ / min at room temperature, and polarized for 30min at an electric field strength of 1kV / mm at 80℃. Then, the temperature was raised to 120℃ at a rate of 1℃ / min, and polarized for 60min at an electric field strength of 2kV / mm at 120℃. Finally, the temperature was slowly lowered to room temperature at a rate of 2-3℃ / min, and polarization was continued for 30min while keeping the electric field strength constant before depressurization. The fluctuation range of the electric field strength during the polarization process did not exceed ±5%.

9. The preparation method according to claim 8, characterized in that, In step (2), the low-speed stirring rate is 100-200 r / min, and in step (4), the high-speed stirring rate when preparing modified cement paste is 500-800 r / min. Mechanical stirring is used in both stirring processes.

10. The preparation method according to claim 8, characterized in that, The thickness of the silver-plated electrode in step (5) is 5-10 μm, and the vacuum degree during vacuum evaporation is 1×10⁻⁶. -3 -5×10 -3 Pa, the vapor deposition temperature is 150-200℃, and after vapor deposition, it is allowed to cool naturally to room temperature for later use.

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