Acoustic emission testing

Steel reinforced concrete specimens of loaded and unloaded
configuration were placed in contact with seawater in a state of
accelerated corrosion. They were simultaneously monitored for acoustic
emission and the results were analyzed in an evaluation of the use of
acoustic emission as a nondestructive monitor of corrosion induced
cracking. It was shown that, in a laboratory environment, counts and
amplitude information are sensitive indicators of the levels of
cracking within the concrete specimen; and thereby the degree of
corrosion damage may be inferred. Analytical models applicable to the
representation of acoustic emission amplitude distribution are
discussed also.

The acoustic emission investigations reported herein are divided into two experimental sets. In the first, the concrete specimens were stressed internally, and the resulting acoustic emissions were monitored. In the second, specimens were subjected to fracture mechanics tests and simultaneously studied for AE signals. For both sets, two kinds of concrete were studied--regular concrete and concrete containing fly ash. The specimens were stressed internally by subjecting them to an accelerated state of corrosion in a marine environment. The corroded specimens were then tested for impact and flexural strengths to study the effect of fly ash replacement on rebar corrosion in a marine environment, and to ascertain any correlation between the monitored AE signals and residual strength. Furthermore, an attempt was made to predict the remaining life of the specimens. For the externally stressed specimens, AE was used to determine the load at initiation of unstable crack propagation terms of ultimate load. These tests have immediate and relevant applications to field problems.

The acoustic emission (AE) testing reported herein was
conducted on a large size prestressed concrete slab placed
in contact with sea water in a state of electrically induced
accelerated corrosion. AE signals were monitored and
successfully analyzed in an attempt to evaluate the severity
of the deformation process in the concrete as a result of
the corrosion induced cracking. Several features of the AE
data which were sensitive to the process were plotted to
show the different levels of the cracking due to the
corrosion. These were amplitude, counts and energy
distributions, and event distribution with time. A location
test was employed to find the source of the activities. The
results of the amplitude distributions were found to have
similar characteristics to those obtained from the
reinforced concrete AE experiments performed at Florida
Atlantic University (1,2). These tests can be easily
applied to a field location for an early detection of the
deformation process in the concrete structures.

Measured values of attenuation with distance, amplitude distribution,
and propagation velocity of acoustic emissions associated with
embedded metcil corrosion induced cracking in a concrete slab are
presented. An extensive review of acoustic emission signal processing
techniques and theoretical background material is also included.
The study points out how attenuation and propagation velocity of the
acoustic emission signal affects various signal processing techniques
and verifies an amplitude distribution spreading rrodel. The need
for further defirlition of attentuation values caused by fluid loading
of the concrete surface is also discussed.

In this investigation acoustic emission techniques were employed to
detect deterioration of reinforced concrete. As a result of various
laboratory tests, acoustic emission activity was found to be due to
development of cracking only. Acoustic emission techniques were able
to locate cracks in a specimen by linear location. Various acoustic
emission parameters such as amplitude, signal shape and frequency
were also analyzed and discussed. It was concluded that acoustic
emission techniques provided a feasible method for detection of deterioration
and cracking of steel reinforced structures in laboratory
studies as well as in a field environment.