ACOUSTIC
EMISSION & NDT SCIENTIFIC PUBLICATIONS
Damage Level Evaluation
and Characterization by Acoustic Emission and
Acousto-Ultrasonics in Concrete Under Compressive Loads
15th World Conference
on Non-Destructive Testing, Rome, Italy, 15-21 October,
2000
Apostolos
Tsimogiannis, Barbara Georgali. Dr. Athanasios
Anastasopoulos
The level of damage sustained by
concrete structures is an area with increasing interest. At present
monitoring damage in concrete is performed mainly by microscopic
analysis which is a destructive method and requires a significant
time interval to produce results and by simple compressive strength
tests which also requires sample removal. Localized inspection by
Non Destructive Testing (NDT) methods encounters a number of
difficulties in concrete structures due to the nature of the
material and can thus be applied only in a limited number of cases
and usually when macro-cracking or other form of damage exists.
Acoustic Emission (AE) has been used successfully in monitoring
damage accumulation, crack growth etc. in large concrete structures
when loads can be applied (bridges, piers etc.). Location of damage
is possible along with other parameters (crack growth, orientation
etc.). In structures where load application is difficult (e.g.
buildings) the method is not used. To monitor damage on buildings
Acousto-Ultrasonic (AU) is suggested as a technique. AU has been
used to quantify macro-cracking in concrete structures. In the
present work mortar cement specimens are being monitored by AE and
AU during compressive tests to failure. AE is used to confirm
microscopic damage in the specimens under loading. The state of the
concrete is simultaneously monitored by AU and an attempt to
correlate damage level as given by AU with AE measurements is made.
The attempt is to characterize damage at early stages and produce an
indication of approaching failure of the material. An attempt is
also made to correlate AU/AE parameters to the mechanisms producing
the microscopic damage in the specimens at early stages using
microscopy findings for various times in the specimens’ lives. The
results show clear indications that AU can detect sustained damage
at the microscopic level in concrete and can give early indications
of oncoming failure. In addition AU provides a means to monitor and
characterize events at the microscopic level of concrete in real-time.