1. Impact-echo method
In an IE test, a stress pulse is generated at the surface of the
element. The pulse spreads to the test object and is reflected
by cracks, flaws or interfaces, and boundaries. The surface
response caused by the arrival of reflected waves is monitored
using a high precision receiving transducer (Malhotra
and Carino, 2004).9
When stress waves travel within the concrete element,
a part of emitted acoustic waves by the stress pulse on the
surface is reflected over the boundary layers where the different
material stiffness changes. The data received by the
transducer is analyzed in the frequency domain to measure
the wave speed and the thickness. The test is widely
used to evaluate the location and extent of delamination in
concrete decks. This procedure has been standardized as
the ASTM C1383, “Standard Test Method for Measuring the
P-Wave Speed and the Thickness of Concrete Plates Using
the Impact-Echo Method.”10 The application of the IE method
for detection of delamination in concrete decks with asphalt
overlays is somewhat limited to low temperatures. Another
major complication in the test occurs when engineers want
to identify the boundaries of the delaminated area. In this
case, a very dense test grid is required which would make the
test more labour-intensive and time-consuming.
2. Corrosion inspection and monitoring
Corrosion inspection in concrete bridge decks is mainly
done through Half-Cell Corrosion Potential Survey (ASTM
C 876).11 Half-cell tests provide valuable information about
the likelihood of corrosion activity in concrete bridge decks.
The test is relatively rapid and enables scanning a large area
in a relatively short period. A major challenge in performing
a half-cell potential test is preparing the test points in the
decks with asphalt overlay or decks with waterproofing. Also,
the test results might not be conclusive in the case of epoxy
coated rebar.
3. Ground penetrating radar
GPR is a very useful technique for non-destructive evaluation
of concrete. GPR uses pulsed electromagnetic radiation
to scan concrete. It can be used to locate rebar, voids and
delamination in the depth of concrete decks. When it comes
to testing bridge decks, GPR has a great advantage as it can
detect defects from the asphalt overlay. Sneed et al. reported
that “GPR can be used to evaluate the condition of a concrete
bridge deck with or without an asphalt or concrete overlay.”
GPR consists of a transmitter antenna, a receiver antenna
and a signal processing unit. GPR emits electromagnetic
pulses (radar pulses) with specific central frequency to scan
FEATURE
Impact
Flaw/Defect
T
PHOTOS: FPRIMEC
Impact-echo testing for evaluating Half-cell corrosion potential mapping (corrosion survey)
delamination in concrete bridge decks
Schematic view of
impact-echo test for
evaluating the location
of sub-surface defects
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