Mistras Group
Infrasense Performs GPR Testing on Concrete Parking Structure
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Infrasense, Inc., one of the leading subsurface detection firms in the nation,
recently completed ground penetrating radar (GPR) testing of select areas of a
five-level parking structure in Rochester, New York. Corrosion of the post-
tensioned steel within the concrete slabs, especially near expansion joints, was a
primary focus of the subsurface investigation. Using a walking-based survey with
a 1.6 GHz GPR antenna to provide higher resolution data, the designated survey
areas were scanned in less than two days, with 100% coverage achieved in all
accessible areas and minimal disruption to garage parking services. The results
of this investigation will be used for future rehabilitation planning. In 2009,
Infrasense performed similar nondestructive evaluation services for a different
parking garage in Rochester.

Nondestructive evaluation (NDE) uses a number of techniques to determine
material or structural properties without causing damage to the structure being
evaluated. Because these techniques can be applied to a wide range of structures
without any adverse effects, they have become a powerful decision-making tool
in the assessment of as-built conditions, and in the inspection and maintenance
of infrastructure. The type of structure and the condition to be detected dictates
what NDE techniques will be most useful in a condition assessment.

Ground penetrating radar (GPR) is an NDE technique that operates by
transmitting short pulses of electromagnetic energy into the concrete, using a
boxed antenna attached to a survey vehicle or rolled along the slab. These pulses
are reflected back to the antenna providing a record of the properties and
thicknesses of the layers within the slab. GPR can detect the depth and spacing
of reinforcing steel, and the thickness of concrete slabs. It is able to detect
subsurface deterioration of a slab through changes in the radar signal through
the concrete. These results make GPR a useful tool in planning preventative
maintenance and avoiding severe and costly structural issues down the road.

In addition to GPR surveys, impact echo testing is an NDE technique used to
determine slab thickness, to identify areas of delamination and substandard
concrete. An elastic wave is generated by an impact source, and the clarity and
frequency of the wave reflection indicates the slab thickness and condition.
Impact echo tests may be used in conjunction with ground-penetrating radar to
detect areas of the slab that have already begun to deteriorate and measure the
extent of the deterioration. In the past, Infrasense has used impact echo testing
on similar parking garage surveys.

Nondestructive evaluation techniques allow us rapidly and economically assess
the condition of parking structures. This information then enables owners to
better allocate their maintenance funds to ensure the areas of significant damage
are repaired, and eliminates the costs and risks of performing unnecessary
maintenance.

About Infrasense, Inc.

Since 1987, Infrasense, Inc. has applied state-of-the-art technologies to address
the most difficult challenges in subsurface scanning. Infrasense’s engineers are
able to nondestructively extract critical information from a diverse range of
structures. In addition to providing ongoing subsurface evaluation services to
clients across the country, the firm has also conducted numerous research
programs to advance the field of subsurface detection and non-destructive
evaluation.
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