Rebar mapping and concrete imaging surveys

Rebar for structural reinforced concrete element

Ground Penetrating Radar (GPR) provides excellent rebar mapping, reinforcing steel location, concrete imaging and information about the concrete sub-surface to depths of 400mm. The high resolution data is far superior to that offered by most other techniques.

Advantages of GPR concrete imaging

GPR detects changes in the sub-surface, therefore it is not limited to detection of reinforcement or metallic objects. It can be used to provide immediate results on site, or the data can be saved electronically and analysed off-site to provide detailed results such as high resolution rebar mapping.

Using a high frequency antenna, high resolution is possible to depths up to 400mm. Lower antenna frequencies provide greater penetration depth, albeit at a lower resolution.

  • Detect metallic and non-metallic objects and features
  • Map rebar distribution
  • Can resolve two layers of reinforcement
  • Detect voids
  • Identify changes in construction
  • Determine slab thickness
  • Requires access to one side only

The results from our GPR Concrete Imaging can be used to confirm as-built drawings, determine reinforcement detail when do drawings are available and to carry out structural assessments. Suitable for locating rebar and tendons before you cut, core or drill.

Locating deep reinforcing steel

Location of deep reinforcing steel (rebar) in reinforced concrete can be difficult. Cover meters and the Hilti Ferroscan are typically limited to approximately 100mm. GPR offers major advantages for locating deep reinforcing steel:

  • High resolution scans to detect rebar up to 400mm deep
  • Lower antenna frequencies to detect deeper rebar
  • Locate deep rebar, orientation and depth of cover
  • Rebar can be located in real time
  • GPR scan data can be saved for off-site analysis including AutoCAD plotting

Ground penetrating radar can be used with different antenna frequencies to provide a range of penetration depths and resolutions.  A higher frequency antenna (typically in the range 2.6GHz to 1.5GHz) provides high resolution and depth penetration up to 400mm. Lower frequencies provide greater depth penetration, but at a lower resolution and may not be able to resolve individual bars.

Site Survey

Site surveys are undertaken by our trained and experienced GPR surveyors. Depending on survey requirements and access, scanning is undertaken either on a regular orthogonal grid or using standalone scans as required. Typically the collected site data is analysed off-site, meaning that the site data collection is quick and efficient.

Two reinforcement layers mapped by GPR

High resolution rebar mapping using GPR

A GSSI SIR3000/4000 GPR control unit is generally used with a high frequency antenna (typically in the range 2.6 GHz to 1.5 GHz). The 2.0 GHz Palm antenna is very compact and particularly useful for scanning small areas where access is restricted.

2.0 GHz GSSI Palm antenna allows scanning to within 45mm of an obstruction

The 2.0 GHz GSSI Palm antenna is very compact and allows scanning to within 45mm of an obstruction


Rebar mapping, reinforcing steel location and concrete imaging results can be plotted in CAD, presented on annotated radargrams (cross-section view), depth slices (plan view - see example below) or on sketches.

Radargram showing cross section reinforcement detail in floor slab

Radargram image showing section view through slab/beam. Dashed pink line indicates screed/concrete interface, top rebar highlighted by red dots, bottom rebar highlighted by green dots, underside of slab indicated by yellow line and down-stand beam by dashed yellow line.