Fabrication And Properties Of 1-3 Orthotropic Cement Based Piezoelectric Composite

Cement based piezoelectric composites, which have effectively overcomed the compatibility problem between traditional smart intelligent materials and concrete material in civil engineering structures, have draw people's attention in the civil engineering field. It is a promising new type of multifunctional material. But the cement based piezoelectric composite has the characteristic of isotropy. It has the equal sensitivity for stress waves from different directions and can not distinguish the direction of the plane stress waves. Thus, it has some difficult to positioning the crack of the concrete structures accurately.1-3 orthotropic cement based piezoelectric composites were fabricated by the cut-filling and arrange-filling technique, using PZT-51 ceramic as functional material and cement as passive matrix. Piezoceramic rods are poled in the axis x direction. A formation of interdigitated electrode was constructed using DAD-91E conductive adhesive internal composite. The internal electric field distribution and coupled vibration modal of the traditional cement based piezoelectric composites were changed. With keeping the benefits of cement based piezoelectric composites, the disadvantage of isotropic were solved. This material offer the orthogonal anisotropic piezoelectricity because of the difference between the piezoelectric strain coefficient d₃₃ and d₃₁. It can effectively distinguish the stress waves from the different directions on the same surface. The influence of piezoelectric ceramic volume fraction, aspect ratio of piezoelectric ceramic rods, electrode width and different cement matrix on performance of the composites were analyzed. Its application in acoustic emission (AE) sensor was studied.The internal structure, composite principle and distribution of internal electric field of the 1-3 orthotropic piezoelectric composite were analyzed. The design process of the composite was presented. The factors of orthotropic cement based piezoelectric composite, which provides a theoretical basis for the experiment, were analyzed. The piezoelectric arrays internal the composites were analyzed by experiment and finite element simulation, which provide theoretical basis for the fabrication of different bandwidth composite. The piezoelectric constant d₃₃ of 1-3 orthotropic cement based piezoelectric composite is much higher than monolithic piezoelectric ceramic and the general 1-3 cement based piezoelectric composite. While the horizontal effect coefficient is much smaller. It indicates that the sensing capabilities of 1-3 orthotropic cement based piezoelectric composite is greatly improved, furthermore, it offer orthotropic properties of piezoelectricity and has different receiving sensitivity for the stress waves from the orthogonal directions.The various affecting factors of the composite were researched and the results were listed as follow. The volume fraction of piezoelectric ceramic is the important factors on sensing properties of the composite. With increasing of piezoelectric ceramic volume fraction, piezoelectric constants of the composites increases gradually. Length-width ratio of piezoelectric ceramic rods is an important factor on orthotropic properties of the composite. With the length-width ratio increases, the horizontal effect coefficient decreases evidently and the piezoelectric constant d₃₃ increases. The performance of the composites has little changed with the variation of thickness. The base-frame reduces the orthotropic properties of the composites. The horizontal effect coefficient decreases along with the thickening of base-frame. When the electrode spacing is determined, with the increase of the width of branch electrode, piezoelectric constant d₃₃ decreases, while horizontal effect coefficient increases. The influence of the different cement matrix on properties of the composite was researched. The results show that composites which belite-barium calcium sulphoaluminate cement was used as matrix, offer the best piezoelectric properties at early hydration stage. Piezoelectric constant d₃₃ of the composite increases along with the incease of water-cement ratio. Cement matrix and water-cement ratio have little effect on the horizontal effect coefficient.The application of orthotropic cement based piezoelectric composite in acoustic emission (AE) sensor was studied. Compared to the monolithic piezoelectric ceramic and general 1-3 type cement based piezoelectric composite, this material shows significantly different receiving sensitivity for the acoustic emission signals from different directions. This phenomenon verifies the orthotropic properties of this composite. Using the orthotropic cement-based piezoelectric sensor, attenuation of the acoustic emission signal internal concrete material was studied. With the increase of piezoelectric constant of composite, the utmost detection distance of the sensor increases. The size of sensor is an important factor of sensitivity. Therefore, in practice, the design of aspect ratios of piezoelectric ceramic rods should be based on the actual situation.