In 1939, a suspension bridge at Portsmouth, Ohio, experienced stress-corrosion cracking of the main-cable wires at anchorage points located at each end of the bridge. Watchmen were placed in the anchor chambers where the fractures had been detected. Subsequently, they reported hearing the sounds of further wire breakage on quiet nights. When this was reported, a decision was made to recable the bridge (1). That was one of the earliest documented instances of the use of the acoustic emission phenomena in a structural application.

Also, in the late 1930's, L. Obert and W. I. Duval at the U. S. Bureau of Mines were performing sonic tests on rock mines. They were surprised to find that stressed rock pillars emitted micro-level sounds (2). Those noises were later termed "rock-talk."

Unlike the early acoustic emission structural monitoring at Portsmouth, the "rock-talk" phenomena has been the subject of continuous ongoing geotechnical research since the late 1930's.

Over the years, much progress has been made in civil engineering applications using acoustic-emission (AE) testing. However, most of those applications are still in developmental stages. Also, some of the past research is contradictory. Therefore, the potential AE user should perform preliminary tests to ascertain the viability of the intended AE procedure. Both laboratory and field tests should be performed under controlled conditions to ensure the applicability and usefulness of that test method before it is employed in service. While this approach is expensive, subsequent cost savings from AE in-service testing, compared to other nondestructive methods, usually justifies those expenditures.

The following three sections discuss the primary applications of acoustic emission in civil engineering. Those are 1) geotechnical, 2) structures, and 3) special component testing. Due to the vast scope of AE research, these reviews are certainly not complete. There are several state-of-the-art AE reviews that provide reference to specific applications (3, 4).

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Prepared as a contribution to NONDESTRUCTIVE TESTING HANDBOOK, The American Society for Nondestructive Testing.