Detection of internal defects in concrete panels by Lamb waves

Abstract

It is investigated if internal defects in concrete beams can be detected by Lamb waves. To this aim, a number of concrete beams (8 in.×12 in.×40 in.) have been cast. Three types of defects—honeycomb, plexiglas inclusion and water-filled cracks—have been fabricated inside the beam during the casting process. Different Lamb modes have been generated in the beam by varying the signal frequency and transducer inclination angles. The Lamb waves propagate through the beam and then strike a receiving transducer. A function generator that sweeps the signal frequency continuously between 20 kHz to 160 kHz excites the transmitter. The received signal voltage (V) varies as a function of frequency (f). The V(f) curves are plotted over good and defective zones of the beam. These curves show good sensitivity of Lamb waves to defects. In other words, the shape and amplitude of the V(f) curve vary with the defect type. From this investigation it is concluded that different types of defects—honeycomb, inclusions and crack...