Rebar Location and Mapping Surveys

GPR (Ground Penetrating Radar) is ideal for all kinds of rebar survey including reinforcing steel location, rebar mapping and concrete imaging.

Rebar mapping surveys can determine rebar distribution (spacing and depth of the different rebar layers), rebar cover thickness, overall concrete slab thickness, and detect any other features within concrete including post tension cables, conduits, ducts, and voids. If rebar locations are required in real time, a GPR survey can be used to locate the reinforcing steel and mark the positions directly on site. Concrete imaging is used to produce highly detailed images at specific locations.


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What is rebar?

Rebar, or reinforcement steel, is a steel bar or mesh of steel wires. Rebar is used in concrete construction to strengthen the concrete when it is under tension. Concrete is strong in compression but weak in tension, so by adding rebar, it improves the tensile strength of the concrete.

How does rebar strenghten concrete?

Rebar is a steel bar or mesh of steel wires. Rebar is used as a tension device to strengthen concrete when it is under tension. It does this by adding tension-resisting forces to the concrete and gives it good tensile strength as the steel bars absorb tensile loading.

Why use GPR for rebar surveys?

GPR is a completely non-invasive and non-destructive technology (NDT) that can reliably detect reinforcing steel bars and other features in concrete up to a depth 50cm (or greater, depending on the centre frequency of the GPR used for the survey and the spacing between the bars). GPR is ideal for concrete imaging and rebar mapping surveys because concrete is a homogeneous material and there is a strong dielectric contrast between the concrete and the metal rebar.

GPR can detect multiple layers of reinforcement and due to its small size it can be used to detect reinforcing bars to within 10cm of an obstruction. Under most circumstances, it is only necessary to access a slab from one side.

Rebar survey deliverables

Typical deliverables from a rebar mapping survey will be a CAD drawing and/or report which clearly details the requested information. In the case of rebar location with on-site mark out, the deliverable will be the marks left on site.

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Limitations of GPR for concrete imaging and rebar mapping surveys

GPR does have some limitations: it is not able to penetrate through a closely spaced mesh, resin reinforced with metal fibres, or very closely spaced reinforcing bars. GPR also has limited lateral resolution and it is not possible to measure the diameter of rebars or to detect subtle changes in their condition. For this type of information it is recommended that a GPR survey is carried out to provide coverage across the site and then invasive surveys can be commissioned at specific locations to expose rebar and allow measurement that way.

Rebar mapping surveys

Rebar mapping surveys

Our surveyor will attend site and mark the surface in paint, crayon or chalk to indicate accurately referenced scan locations. We will then make passes of the GPR across the surface in a series of sequential scans to collect and save GPR data until the area has been thoroughly scanned in an orthogonal grid. This data is recorded for post processing and interpretation at our office.

At our office, the data is imported into our advanced GPR imaging software and the scans are processed and referenced into a 3D image showing the locations of all the rebar and structural features within the concrete. This image is used to produce a map of the location and distribution of rebars and other features in CAD.

On-site rebar location surveys

On-site rebar location surveys

If survey results are required directly on site, the survey will be performed in a similar way However, we perform interpretation of the GPR data in real time and mark the locations of the individual rebars directly on the surface. On-site rebar location surveys are often requested for rebar avoidance during drilling or to target coring activities.

GPR vs. induction-based technology (cover meters) for detecting reinforcing bars

KB GPR Surveys recommend the use of GPR for rebar location surveys. Although GPR requires more expertise to use, it offers improved performance and functionality with respect to induction-based technology (such as Ferroscan). See our blog for further information and comparative equipment tests.

If you require a rebar survey, contact KB GPR Surveys for a quotation at info@kbgprsurveys.co.uk

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