| Impact-Echo
is a nondestructive test method specifically developed for concrete and
masonry structures. The method has achieved unparalled success with flaw
detection in concrete and masonry structures. WDP has been an industry
leader in the application of impact-echo in the evaluation of concrete
and masonry structures and in the development of new applications for the
method.
The impact-echo
method uses transient stress waves generated in the concrete or masonry
by an elastic, low-energy impact on the surface of the member. As the stress
waves propagate through the material being tested, they are reflected by
air interfaces within the member and the external boundaries of the member.
Examples of air interfaces are: delaminations, voids/honeycombing, and
cracks.
Wave arrivals
at the surface of the concrete or masonry are recorded by a displacement
transducer placed near the impact point. The record of displacement versus
time is transformed into the frequency domain for ease of signal analysis.
The presence and nature of any internal flaws or external interfaces can
be determined from analysis of the time-domain waveform and frequency spectrum.
Impact-echo
is often confused with ultrasonic methods such as pulse-velocity and pulse-echo.
Unlike ultrasonic methods, impact-echo utilizes lower frequency sound (2
to 20 kHz, typically). The use of lower frequencies allows impact-echo
to overcome the high signal attenuation and noise frequently encountered
with ultrasonic methods.
|
|
Typical
applications of Impact-Echo Testing include:
-
Slab thickness
measurements (ASTM C-964)
-
Detecting delaminations,
cracks and voids
-
Evaluating unconsolidated
concrete
-
Locating voids
in grouted tendon ducts
-
Locating subgrade
voids beneath foundation slabs
-
Evaluating mine
shafts and tunnel liners
-
Finding voids
in grouted masonry
-
Evaluating distributed
damage in concrete (ASR, DEF)
|
