Two nondestructive testing (NDT) methods that have been developed over the past decade, and are finding increasing applications in various aspects of civil engineering. These methods, 'Impact Echo' (IE) and 'Acoustic Emission' (AE) are based on acoustic waves of different frequency domains. The IE technique involves sounding a structure and assessing its properties from the frequency of the internal reflections [1]. The AE method is passive, and involves monitoring the microseismic waves that are generated from cracks and other structural anomalies [2]. While IE involves frequencies in the order of 10-50 kHz, AE involves the frequency range of 100 kHz - 1 MHz. Consequently the instrumentation and the wave propagation phenomena are radically different in the two techniques. These methods are being increasingly applied to assess pavements, bridge decks and superstructures, as well as a host of other structural components. The author has been involved in a number of research projects on the subject and is a member of a number of national committees which relate to these technological developments. The paper will cover current research issues, as well as provide a description of successful applications in the United States. The objective of the presentation is to familiarize the audience with various aspects of acoustic technology, and to explore the future of these developments. REFERENCES
- A. K. Maji, S. Paul and M. L. Wang, "Improved Impact-Echo Technique by Signal Processing", J. Research in Nondestructive Evaluation, ASNT, V 2, No. 1, 1990
- A. K. Maji and R. Sahu, "Acoustic Emissions from Reinforced Concrete", Experimental Mechanics J., V 34, No. 4, December, 1994 pp. 379-388
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