Concrete Reinforcement Mapping (Rebar)

900MHz radar antenna in use over a motorway slip road.

900MHz radar antenna in use over a motorway slip road.

Why map reinforced concrete?

Most structural concrete used in modern construction is reinforced with a mesh of bars. When remedial work is to be carried out on these structures it is important to know where the rebars are located within the concrete slab. Examples may include:

  • Planning the locations of exploratory boreholes
  • Strength assessment where no records are available
  • Piling for new foundations
  • Or simply, was it installed? 

 

The Techniques

Due to the hard, opaque nature of concrete intrusive investigations is not a viable option. Hand held metal detectors can be used to establish the presence of re-inforcing bars but the most suitable method to accurately map them is Ground Penetrating Radar (GPR). GPR operates by emitting pulses of electromagnetic energy which are then reflected back from boundaries between materials with differing electrical properties.

The Output

The strength of responses, along with the time taken from emission to reception, are analysed to give cross sectional information which can be clearly marked out on site. This data can be displayed in plan format (Time-slice) and with high quality referencing the position of the re-inforcing bars can be accurately transferred to a CAD drawing for display.  

Radargram of a cross section through a concrete slab. The peaks at 4cm depth represents the position of the rebar. The reinforcement is positioned at 0.2m horizontal separation.

Radargram of a cross section through a concrete slab. The peaks at 4cm depth represents the position of the rebar. The reinforcement is positioned at 0.2m horizontal separation.

3D plan of abstracted radar data.

3D plan of abstracted radar data.

Timeslice plot of radar data collected at 0.2m intervals.

Timeslice plot of radar data collected at 0.2m intervals.