Feasibility of a wave propagation-based active crack detection technique for nondestructive evaluations(NDE)of concrete structures with surface bonded and embedded piezoelectric-ceramic(PZT)patches was studied.At first,the wave propagation mechanisms in concrete were analyzed.Then,an active sensing system with integrated actuators/sensors was constructed.One PZT patch was used as an actuator to generate high frequency waves,and the other PZT patches were used as sensors to detect the propagating wave.Scattered wave signals from the damage can be obtained by subtracting the baseline signal of the intact structure from the recorded signal of the damaged structure.In the experimental study,progressive cracked damage inflicted artificially on the plain concrete beam is assessed by using both lateral and thickness modes of the PZT patches.The results indicate that with the increasing number and severity of cracks,the magnitude of the sensor output decreases for the surface bonded PZT patches,and increases for the embedded PZT patches. Feasibility of a wave propagation-based active crack detection technique for nondestructive evaluations (NDE) of concrete structures with surface bonded and embedded piezoelectric-ceramic (PZT) patches was studied. At first, the wave propagation mechanisms in concrete were. active sensing system with integrated actuators / sensors was constructed. One PZT patch was used as an actuator to generate high frequency waves, and the other PZT patches were used as sensors to detect the propagating wave. subtracting the baseline signal of the intact structure from the recorded signal of the damaged structure. In the experimental study, progressive cracked damage inflicted artificially on the plain concrete beam is assessed by using both both lateral and thickness modes of the PZT patches. with the increasing number and severity of cracks, the magnitude of the sensor output decreases for the surface bonded PZT patche s, and increases for the embedded PZT patches.