Concrete Scanning

What Concrete Scanning is

Concrete scanning is ground penetrating radar applied to a structure: a slab on grade, an elevated deck, a wall, a beam, or a column. A technician runs a small high-frequency antenna over the exact footprint of a planned penetration and images the steel and services embedded in the concrete, then marks clear zones on the surface where a core barrel, saw blade, or anchor bit can pass without hitting anything. The targets are reinforcing bar and welded wire mesh, post-tension tendons, electrical and communications conduit, radiant heat tubing, drain and plumbing lines cast into or under the slab, and voids or delaminations in the concrete itself. The instrument is the same family of equipment used for soil GPR, but the antenna frequency, the scan pattern, the interpretation, and the consequences of getting it wrong are all different, which is why it is quoted and scheduled as its own job. The reason the service exists at all is post-tension: a stressed tendon carries tens of thousands of pounds of force, and cutting one releases that energy violently, injures people, and turns a routine floor opening into an engineered structural repair.

How it works

A handheld or small cart-mounted antenna, typically in the 1.6 to 2.7 GHz range for concrete work, sends short pulses into the slab and records the reflections. Steel returns almost all of the energy that reaches it, so rebar and tendons image strongly, while air voids, plastic conduit, and delaminations show up as weaker contrasts in the dielectric properties of the material. Each target crossed at right angles appears in the scan as a downward-opening hyperbola, and because a bar running parallel to the direction of travel produces no hyperbola at all, the technician scans in a grid with a second set of passes at ninety degrees to the first. Depth comes from the two-way travel time converted using an assumed signal velocity in that concrete, which the operator calibrates by fitting hyperbola shape or by referencing a target of known depth, so moisture content in the slab directly affects the number. What the customer receives is marked on the concrete itself: target lines in marker or crayon, an outlined clear zone for the penetration, usually a buffer of a couple of inches on either side of each mark to account for positional uncertainty, and photographs of the marked area for the file.

When to choose Concrete Scanning

Scan before every penetration of a structural element where the reinforcement layout is not known with certainty, and always before any penetration of a post-tensioned slab, no matter what the drawings show. It is the practical choice over radiography on most jobs because it needs access to one face only, requires no exclusion zone or site evacuation, and produces an answer in minutes rather than after film processing, so the trades around it keep working. It suits core drilling for plumbing and conduit risers, saw-cut openings for stairs and elevators, anchor and dowel drilling into decks, and any retrofit into an existing building where the as-builts are missing or were never followed. Book it immediately ahead of the cut rather than days in advance, because the deliverable is a set of marks on a working floor: they get walked on, washed off, covered by stored material, and they only apply to the layout that was scanned, so a penetration that moves six inches after the scan is an unscanned penetration. Where the cut goes all the way through a slab on grade and into the soil beneath, pair it with private utility locating for the sub-slab and site utilities, since the reinforcement above will limit what the scan can see below the slab. On a post-tensioned deck, remember that the plan position of a tendon is only half the answer: tendons drape through the span, so the same tendon sits at a different depth over a support than it does at midspan, and drilled embedment depth has to respect that.