Rebar scanning and location survey
GPR rebar scanning shows where the reinforcement sits inside concrete, how it is spaced and how deep it is, without coring or breaking out.
What the survey finds
When you need a rebar survey
A rebar survey is usually commissioned before work that could hit the reinforcement, or when nobody is sure how a structure was built. Typical reasons are:
- drilling, coring or anchoring into slabs, walls, columns or beams
- checking the as-built reinforcement against design drawings
- structural assessments where the original drawings are missing
- planning openings or alterations in existing concrete
- supporting a condition assessment where cover depth matters
You may also see this service called a rebar scan, a GPR rebar survey or concrete scanning.
What the survey finds
GPR picks up steel reinforcement and also bars made of fibre reinforced polymer (FRP), which a metal detector or cover meter cannot see. We record where the bars are, the spacing in each direction, how many layers there are and the depth of cover to the first layer.
The same scan also shows other items cast into the concrete, such as conduits, ducts and post-tension cables. Where you also need slab thickness or services beneath the slab, a concrete floor slab survey covers it.
How it is done
We scan the concrete in a grid with a high-frequency GPR antenna. It works from one side of the element, so access to the back face is not needed. Findings can be marked on the surface as we go, so your contractor can drill straight away. For larger areas or a permanent record, the data is processed in the office and drawn up in CAD.
Examples of our work
- A one-tonne stone lion. A restaurant under construction planned to install a large stone sculpture, but the contractor wasn't confident in the old floor drawings. Our survey confirmed two layers of reinforcement: bars at 10 cm spacing about 13 cm below the surface, and a second layer about 20 cm down. The client could then confirm the floor would carry the load.
- Steel beams and hollow pots. Before new staircases were built, we located a steel beam and the reinforcement in one floor, with depths to each layer drawn in CAD. In a second area, careful processing showed two bars between the hollow pots of the floor, which set the construction method for the new stair.
Limits you should know about
GPR resolves individual bars well, but very dense or closely spaced reinforcement can hide a second layer or anything beneath it. Bar diameter can only be estimated from GPR. If you need a confirmed diameter, a small break-out at one location gives the answer, and the GPR results then extend it across the area. We will tell you at the quoting stage if the element is likely to limit the results.
Why use GPR rather than coring
- It causes no damage to the concrete.
- It covers large areas quickly, rather than giving information at a few holes.
- It reduces the risk of cutting reinforcement when you drill.
- It is usually cheaper than an intrusive investigation.
Our senior surveyors have over 20 years' experience of GPR concrete scanning, and we carry out rebar surveys as a subcontractor for other surveying firms as well as for contractors and engineers directly.
Questions we're asked
Can GPR find plastic or fibre reinforcement?
Yes. GPR responds to the change in material, so it detects FRP bars as well as steel. A cover meter only detects metal.
How deep can a rebar survey see?
With high-frequency antennas we can normally see reinforcement up to about 300 to 500 mm into concrete. The useful depth depends on the concrete and on how dense the top layer of bars is.
Can you measure the diameter of the bars?
GPR gives an estimate only. Where diameter matters for a structural check, we recommend exposing one bar to confirm it.