GPR GPR Applications & Site Assessment

Question 1

When scanning a concrete slab to locate post-tension cables, the GPR operator should primarily be concerned with:

Accepted Answer

Accurately mapping cable positions to avoid saw-cutting or coring through them

Answer

The dielectric constant of the formwork

Answer

Measuring the exact diameter of the cables

Answer

Determining the concrete mix design

Question 2

What GPR antenna frequency range is most appropriate for scanning reinforced concrete slabs up to 18 inches thick?

Accepted Answer

900 MHz–2.6 GHz

Answer

10–50 MHz

Answer

100–250 MHz

Answer

5–10 GHz

Question 3

During a utility detection survey, a GPR operator identifies a hyperbolic reflection that is accompanied by strong ringing and a polarity consistent with a high dielectric contrast. This most likely indicates:

Accepted Answer

A metallic pipe or conduit

Answer

A PVC pipe filled with air

Answer

A clay-filled void

Answer

A tree root

Question 4

The American Concrete Institute (ACI) and ASNT guidelines recommend that GPR concrete scanning be performed by:

Accepted Answer

Personnel certified to an appropriate GPR qualification level

Answer

Any licensed engineer without special GPR training

Answer

The structural engineer of record only

Answer

A building inspector

Question 5

Which condition would most significantly reduce GPR effectiveness when scanning for utilities in urban soil?

Accepted Answer

High clay content with elevated moisture

Answer

Dry sandy soil

Answer

Limestone bedrock

Answer

Asphalt surface layer

Question 6

When performing a GPR scan over an area suspected of containing a void beneath a concrete pavement, the void would most likely appear as:

Accepted Answer

A strong, flat reflector with a polarity reversal at the void-air interface

Answer

A hyperbolic diffraction with ringing

Answer

A continuous low-amplitude band

Answer

A gradual decrease in signal brightness