Fabrication And Properties Of Cement-based Piezoelectric Composites

Cement-based piezoelectric composites can overcome the deficiency which the traditional piezoelectric materials have bad compatibility with civil engineering's main structural material—concrete. It not only has sensing function, but also actuating property, which is very suitable for application in civil engineering fields. Therefore, research and development of the cement-based piezoelectric composite play an extremely important role in advancing all kinds of civil engineering structure to be intelligent.0-3 cement-based piezoelectric composites and 1-3 cement-based piezoelectric composites were fabricated by compressing technique and cut-filling process, respectively. The piezoelectric properties and dielectric properties of two kinds of composites were studied in detail, and its applications were investigated.The dependences of piezoelectric properties of composites on poling conditions were studied. The results show that for the 0-3 sulphoaluminate cement-based piezoelectric composites, the optimum poling field E, poling time t and poling temperature Tare 4.0kV/mm, 30min and 80℃¹00℃, respectively.The influence of piezoelectric ceramic content, particle size and cement matrix on the 0-3 cement-based piezoelectric composites was researched in detail. The results show that with increasing the PLN content, piezoelectric strain factor d₃₃, piezoelectric voltage factor g33, dielectric constant ε_r and dielectric loss tgδ, electromechanical coupling coefficient K_p and K_t, remanent polarization P_r and coercive field E_c increase, but mechanical quality Q_m fluctuate between 19 and 50. Only when PLN content is larger than 70%, can the cement-based piezoelectric composites show good piezoelectric properties. With increasing the PLN particle size, the d₃₃, g33, K_p, K_t, P_r and E_c all increase. When PLN particle size is larger than 100 urn, the value of d₃₃ and g33 is nearly independent of the PLN particle size. The piezoelectric properties of the composites made from sulphoaluminate cement are superior than that of the piezoelectric composites made from Portland cement, which is just contrary to the dielectric properties. This is attributed to that the sulphoaluminate cement has better early and late mechanical properties and better combination with ceramic particles than Portland cement. Under the samecondition, for the former, K? and Kt increase with increasing PLN ceramic content, but for the latter, Kp and Kt decrease and fluctuate sharply. With increase of the frequency, the polarization mechanism of two different matrix composites is nearly the same, that is, at the low frequency, the interface polarization is dominant. At the high frequency, it shows good dielectric-frequency stability.From relation between dielectric constant and frequency, temperature, it is obtained that the dielectric constant of 0-3 cement-based piezoelectric composites decreases sharply with the frequency increasing, which is mainly due to various polarization in the cement matrix and interface polarization in the composite. At high frequency, the dielectric constant and dielectric loss change slightly, which means that the cement-based piezoelectric composites have good high frequency stability. In the temperature range between -40°Cand 150°C, the 0-3 cement-based piezoelectric composites shows excellent dielectric- temperature stability.Influences of cement hydration ages and humidity on the piezoelectric properties and dielectric properties of the 0-3 cement-based piezoelectric composites were studied. The results indicate that the piezoelectric properties of the cement based piezoelectric composites are very different from that of the piezoelectric ceramics and polymer/ceramic piezoelectric composites. For the latter, the piezoelectric properties decrease with the prolonging of time, while that of the cement based piezoelectric composite are improved with increasing the cement hydration age. When the cement hydration age exceeds a certain value, J33 tended to be a constant. The value of t/33 increases slightly with increase of the environmental humidity below 60%, while sharply increases with increase of humidity above 60%. The effect of environmental humidity on dielectric constant of the composite is mainly ascribed to change of water absorbed. Increasing of water absorbed improve ionic mobility and polarizability in interface zone, which leads to the remarkable increase of composites dielectric constant. The contribution of water to the polarization is mainly at low frequency, and conductive loss is dominant in dielectric loss.With increasing volume fraction of PMN, the c/33, Kp, Kt, ex, Pr and Ec value of 1-3 cement-based piezoelectric composites increase, but g33 value reduces. Compared with g33 value of PMN, the #33 value of the composite is much bigger, which greatly improve sensing property of the composites. At lower and higherfrequencies, the dielectric constant and dissipation factor change steadily, which exhibit good dielectric-frequency stability. The temperature has little effect on the dielectric constant in the temperature range between -30 °C and 150°C, which shows that 1-3 cement-based piezoelectric composite has good dielectric -temperature stability.The laws that the properties of the 1 -3 cement-based piezoelectric composite vary with ratio of width to thickness(w/t) of PMN ceramic rod were investigated. The results show that the J33, Kp, Ku Qm, er, tgS and acoustic impedance Z value of 1-3 cement-based piezoelectric composites decrease with increasing w/t of PMN ceramic rod, but the ï¿¡33 value is nearly independent of w/t of PMN ceramic rod. When the volume fraction of PMN is 22.72%, the acoustic impedance Z value similar to that of the concrete can be obtained by adjusting w/t of PMN ceramic rod, which can effectively solve the mismatch problem of intelligent materials and concrete structure.According to the feature of cement-based piezoelectric composites, a date acquisition system suitable for the composites was designed, and the research of its application was carried out. The results show that 0-3 and 1-3 cement-based piezoelectric composites have good mechano-electric effect, that is, the voltage is produced in two kinds composites under compressive stress, which increases or decreases as the load increases or decrease. This indicates that cement-based piezoelectric composites are suitable for health monitoring of structures in the civil engineering.