If you manage, renovate, or assess existing concrete structures, you’ve likely run into this scenario: you need to understand what reinforcement is inside the slab or wall in front of you, but the original drawings are missing, incomplete, or simply wrong. 

Ground-penetrating radar (GPR) scanning has become the standard answer to this problem. It’s fast, non-destructive, and can be done without shutting down operations. But not all questions about your concrete are equally easy to answer with GPR, and understanding the difference could save your project from unnecessary cost and risk.

What GPR concrete scanning for sure will tell you

First, let’s dig into some technical stuff, for better context. GPR works by sending electromagnetic pulses into a concrete surface and recording how they reflect back from objects inside — primarily reinforcement bars (rebar). Two things come out of this very cleanly:

Rebar location and layout

Where are the bars? How are they spaced? Are they running in one direction or two? This is the most straightforward output of any concrete scan, and modern systems can generate accurate 3D maps of the reinforcement layout across large areas in a matter of hours — something that would have required breaking open the structure entirely just a decade ago. That said, existing systems typically deliver centimetre-level accuracy at best, and only when the concrete’s properties are known in advance. Birdsview’s system does this automatically, delivering millimetre precision as a one-click process.

Concrete cover depth

How deep below the surface is the reinforcement? Cover depth is critical for assessing corrosion risk, planning safe drilling and coring, and evaluating structural capacity against current codes. GPR measures this reliably across the scanned area — giving engineers a complete picture rather than a bunch of spot measurements.

For many decisions , such as: “Is it safe to cut here?”; “Is the cover sufficient?” — these two data points are all you need.

The question most systems still can’t answer: rebar diameter

Spoiler: we can, but we will talk about it a bit later in this post.

Here’s where it gets more complicated. Rebar diameter is arguably one of the most structurally significant pieces of information you can have about an existing concrete element. It directly determines the cross-sectional area of steel, which is central to any load-bearing capacity calculation. And yet, for most of GPR’s history, it has been the one measurement that scanning couldn’t reliably provide.

We have to clarify that detecting rebar position (where the bars are and roughly how deep) is something conventional GPR can do. But millimetre-accurate cover depth is an entirely different challenge, and not something that existing on the market systems can reliably deliver. Getting there requires interpreting much subtler signal characteristics: the precise shape of the reflection, the amplitude envelope, the way the signal degrades with depth — all influenced by concrete mix, moisture content, and rebar spacing. Rebar diameter is still hard, and it can’t be solved without first solving another thing – accurate cover depth. Traditional GPR interpretation, even by experienced operators, typically produces only a rough estimate on both counts, or no estimate at all.

The traditional industry-standard workaround has been physical verification: drilling a core sample to expose and measure the rebar directly. But this is destructive, time-consuming, and only gives you point measurements in a structure that may span hundreds of square metres. Some scanning solutions do claim to solve the diameter problem, but only under a restricted set of conditions — specific rebar spacing, no crossing reinforcement, and a precisely known cover depth.

That being said, our solution is the only one in the world that works without these “prerequisites”. Our solution does it with dry or wet concrete, tightly spaced rebars, and without needing prior assumptions. Sorry for making it sound a bit like a sales pitch, but the truth is that…it is true.

What changes when you can measure diameter non-destructively

Consider a concrete slab that was built in two phases, with different reinforcement specifications. Without diameter data, a structural engineer assessing the element that has to be changed, has to either drill multiple cores across the entire area, or apply conservative assumptions that may significantly overestimate the required reinforcement. No doubt that in most cases it will push the project toward costly upgrades that may not actually be necessary.

And this is what we do.

In one recent project, our system predicted rebar diameters of 6.2mm and 6.8mm across two measurement points. The ground truth, verified against known specifications, was 7mm. That level of accuracy — 1 to 3mm across a full scan — changes what you can actually decide without drilling.

In a bridge mapping project with two structures built in different stages, the ability to map not just rebar position but diameter across the full structure confirmed reinforcement placement that conflicted with the available drawings — allowing the engineering team to verify their conclusions without a single core.

In another project, a team needed to remove concrete across 250 square metres to install new heavy equipment foundations — without hitting reinforcement. A full scan, including diameter data, showed them exactly where it was safe to cut.

The big question: how are we able to do that? Explaining from the technical side

The signal analysis behind our diameter estimation is built on Full Waveform Inversion (FWI) — a technique with deep roots in the seismic sector, where Norway has long been among the global leaders. Norway’s oil and gas industry developed world-class expertise in advanced FWI algorithms to map what lies deep beneath the seabed.

Where conventional GPR reads only the first reflection from an object, FWI analyses the entire waveform: its shape, amplitude, and how it changes with depth. In oil and gas, this allowed geophysicists to distinguish between rock, sediment, and hydrocarbons from surface measurements alone. Applied to concrete, the same principle allows us to extract physical properties from the signal — including the diameter of the rebar producing it.

The result is that information which previously required physical verification can now be read directly from the scan — in real time in the field.

How this knowledge will be useful for different experts

For building owners and asset managers, reliable non-destructive rebar data means faster, more confident decision-making on retrofit and renovation, without the cost and disruption of extensive coring programmes.

For structural engineers, it means the assessment model you build is grounded in measured data rather than assumed section properties, which directly affects the quality of the advice you can give your client.

For contractors planning cutting, coring or demolition, it means knowing exactly what’s in front of you before the first drill bit touches the concrete.

What’s coming next

Using our new, updated scanner Birdsview Concrete, we were able to get 1 to 3mm accuracy on rebar diameter estimation. To our knowledge, achieving this using GPR is something the industry has not previously delivered in a commercially deployable system. Beside that, you get the data almost immediately: the analysis runs automatically on the cloud — no software installation, no manual post-processing, no specialist required. You scan, and see the results real-time, in the field.

To come to this point, we’ve spent the past year building the hardware and software infrastructure to make this possible and accessible to everyone, even those who don’t have “technical” knowledge.