What Is GPR Scanning and How Does It Work?

Ground penetrating radar scanner on concrete slab

Ground Penetrating Radar (GPR) scanning is a non-destructive method for imaging what's inside concrete or underground without breaking the surface. If you're drilling, coring, cutting, or excavating, GPR tells you what's in the way before your equipment moves.

How GPR Works

A GPR antenna emits a short pulse of radar energy into the material being scanned — concrete, soil, asphalt, or rock. When that pulse hits something with different electromagnetic properties (a rebar bar, a conduit, a void, a tendon sheath), part of the energy reflects back to the antenna. The scanner records the time it takes for each reflection to return, which indicates the depth of the object. Software then displays these reflections as a cross-section image called a radargram.

A skilled technician reads the radargram in real time. Different objects produce different signal patterns. Rebar in a grid arrangement produces a series of parabolic (hyperbolic) reflections. Conduit running parallel to the scan direction shows as a continuous layer. Post-tension tendons, which run in banded parallel paths, show up as evenly spaced reflections in two perpendicular directions. Voids produce strong reflections because air has very different properties from concrete or soil.

What GPR Can Detect

Rebar — grid spacing, depth of top and bottom mat, and bar direction
Post-tension tendons — path direction, approximate spacing, and banded zones
Electrical conduit and plumbing — metallic and larger non-metallic lines embedded in or below concrete
Voids and delamination — air gaps within or beneath a slab or pavement structure
Slab thickness — the scan shows the bottom of the slab as a strong reflection
Underground utilities — electric, water, gas, telecom, and sewer lines in soil

What GPR Cannot Always Detect

GPR is a powerful tool, but it has real limitations that are important to understand:

Non-metallic conduit without tracer wire — PVC pipe in soil may not reflect clearly if there is little contrast with surrounding material
Very deep utilities — signal penetration decreases with depth. In wet soil or heavily reinforced concrete, the signal weakens faster
Objects behind dense reinforcement — a heavily congested top mat can mask reflections from objects below it
Fiberglass rebar — does not reflect radar the same way as steel
PT tendon condition — GPR shows tendon location and path, not whether the tendon is under tension or has failed

A good GPR technician communicates these limitations clearly so the contractor can make informed decisions.

GPR vs. Concrete X-Ray

GPR is non-ionizing radiation — the same frequency range as radar and Wi-Fi. It is safe to use in occupied buildings, requires no area evacuation, and needs no radiation permits. Concrete X-ray uses ionizing radiation (similar to medical X-ray), which requires area clearance and permits. GPR is faster to set up, can cover large areas, and is the practical default for most construction applications. X-ray is occasionally used when a photographic-quality image of a specific small area is required and the space can be cleared.

When GPR Scanning Makes Sense on a Job

Call for a GPR scan when any of these apply:

You're coring into a slab and you don't know what's inside
You suspect the slab may be post-tensioned
You're anchoring into a wall or structural member
You're trenching through a site with incomplete utility records
You're excavating on private property where 811 marks don't apply
You're doing renovation work on a building with no current drawings

The scan takes less time than a patch repair. It costs less than a utility strike. And it protects your crew, your schedule, and your liability.

Schedule a GPR Scan in Florida

Tell us your project scope, slab type, and target date. We'll confirm scheduling quickly.

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