The rebar scanner is a device passed over the concrete surface that, with an electromagnetic field, locates the steel bars: their position, their spacing, how deep they are (the cover) and an approximate diameter. It is used to check an existing slab or column without drilling it. In March 2025, at Bodegas Centurión, it was used to check the two slabs that cover the grease tanks.
How it was done
The covers measure 2.8 and 2.9 by 4.0 m, are 27 cm thick and have five openings each. Five scans were made on each cover: three in the short direction and two in the long one. Each scan gives a profile with the position and depth of every bar detected.
What it found
- No. 3 (3/8") bars in both slabs.
- Cover of 80 to 100 mm, above the NSR-10 minimums (C.7.7.1): 40 mm for No. 5 bars and smaller in concrete exposed to the weather and 75 mm in concrete permanently in contact with the ground.
- Very irregular spacing: 9 to 47 cm between bars.
What the device cannot tell
The scanner sees the steel layer closest to the scanned face. With 10 cm of cover in a 27 cm slab, the report concluded there may be two layers of reinforcement or a single one in the middle, and that this is only confirmed by scanning the underside. Also, with small bars and large covers the device may miss some bars, which partly explains the irregular spacing.
Why spacing matters
The NSR-10 requires a minimum shrinkage and temperature reinforcement in slabs: a ratio of 0.0018 with 420 MPa bars, with spacing no greater than 5 times the thickness or 450 mm (C.7.12.2). In a 27 cm slab that is 486 mm² per meter; with No. 3 bars, of 71 mm² each, bars at about 15 cm in total would be needed. This is an illustrative DDES calculation, not a result of the report. If there were a single layer with bars at 47 cm, that ratio would not be met. That is why the report recommended inspecting the underside and, if a single layer is confirmed, checking the capacity of the covers for their design loads.
When to ask for a rebar scan
- Before drilling or anchoring into an existing slab or column.
- When there are no structural drawings or they do not match what was built.
- In assessments of existing buildings and in strengthening work.
- To verify covers in aggressive environments, such as near the sea.
See how we work in assessment of existing structures and the full project at Bodegas Centurión.
Sources: rebar scanner test report on the grease tank covers, Bodegas Centurión, March 20, 2025; NSR-10, C.7.7.1 and C.7.12.2.
Frequently asked questions
What does a rebar scanner detect?
The position, spacing and depth (cover) of the steel bars closest to the scanned face, and an approximate diameter. It does not reliably see deeper layers.
How much minimum reinforcement does a slab need under the NSR-10?
For shrinkage and temperature, a ratio of 0.0018 with 420 MPa bars, spaced at most 5 times the thickness or 450 mm (C.7.12.2).
