Concrete Scanning Before You Core, Cut, or Drill
A core barrel through a post-tension tendon is a structural repair, not a patch. Scanning is the ten minutes that prevents it.
What It Is
Concrete scanning is ground penetrating radar run at a higher frequency against a structure instead of soil. A handheld or cart-mounted antenna is passed over the surface on a grid and the reflections are read live, so the rebar mat, embedded conduit, radiant tubing, and post-tension tendons get marked directly on the concrete before anything cuts into it.
Higher frequency buys resolution — the ability to separate closely spaced bars — at the cost of penetration depth. For structural elements that is the correct trade.
Why It Replaced Concrete X-Ray
X-ray requires access to both faces of the element, a radiation exclusion zone that clears the floor above and below, licensed personnel, and a wait while film is processed. Radar needs one face, no exclusion zone, and gives an answer in real time with marks on the slab.
X-ray still has niche uses where its image quality matters, but for clearing a penetration on an occupied or active site, scanning is the practical method.
Post-Tension Tendons Are the Reason
A post-tension tendon is a high-strength steel cable tensioned after the concrete cured. Cutting one releases stored energy violently, and the consequence is not a repair to the penetration — it is a repair to the structure, usually with an engineer involved and the area shut down.
Tendons drape through a slab rather than running at constant depth, which is exactly why a scan has to be done at the actual penetration location rather than inferred from a drawing.
What a Scan Can and Cannot Resolve
Can: the rebar mat and its cover, embedded conduit, radiant heat tubing, tendon locations, voids and delamination, and slab thickness where the far face is reachable by the signal.
Cannot, reliably: distinguish a tendon from a conduit or a bar with total certainty in every case — congestion, closely spaced targets, and heavy top reinforcement all degrade the record. A good technician tells you which targets are confidently identified and which are ambiguous, and will move a penetration a few inches rather than call a coin flip.
How to Prepare for a Scan
- Have the proposed penetration locations marked, or at least the constraint the location has to satisfy — a scan is much more useful when it can tell you where you can cut
- Clear the surface. Anything on the slab is ground the antenna cannot cover
- Bring the structural drawings if they exist, even if they are unreliable — they tell the technician what to expect
- Know whether the element is post-tensioned. If nobody knows, treat it as though it is until the scan says otherwise
- Allow the scan to move your penetration. That flexibility is what makes it useful
Frequently asked questions
Is concrete scanning the same as utility locating?
Same instrument family, different target and different frequency. Utility locating looks for pipe and cable in soil; concrete scanning looks for steel and conduit inside a structural element. Many locating companies do both, and the catalog treats concrete scanning as a distinct method precisely because the physics, the frequencies, and the failure modes differ.
How thick a slab can be scanned?
It depends on the element and the reinforcement rather than on a single number. A dense top mat of rebar reflects much of the signal and shadows what is beneath it, so a heavily reinforced deck reads shallower than a lightly reinforced one of the same thickness. Ask the technician what they expect to see on your structure before scheduling.
Can you scan a wall or a ceiling?
Yes. Radar needs contact with the surface, not gravity, so vertical and overhead scanning are routine — walls, columns, beams, and the underside of decks. Access and reach are the practical constraints, so say up front if the work is at height or in a confined space.
What if the scan says the location is not clear?
Then the location moves, which is the point of scanning before rather than after. A technician who marks the targets will normally also help identify the nearest clear window that satisfies your constraint. If the penetration genuinely cannot move, that becomes an engineering conversation rather than a drilling one.
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