GEOPHYSICAL
ENGINEERING

Concrete Reinforcement Mapping (Rebar)

Concrete reinforcement (rebar) is located in both ground slabs and within the walls of many buildings. 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.

SUMO uses high frequency Ground Penetrating (GPR) to locate these individual rebars, along with a cover meter which can estimate the diameter of the individual bars.

Above: Section View of GPR data showing rebar at 100mm depth.

Above: GSSI 2Ghz Palm Antenna.

Data is either recorded and/or interpreted on site, depending on your requirement, budget and timescales, to produce 3 survey outputs…

Mark out survey
Mark out survey with basic reporting
Post processed Survey with full reporting

Output 1: Mark Out Survey

A basic mark out survey is where a GPR survey is interpreted on site and the location of the rebar is marked in situ. A cover metre may also be used to estimate the depth to the rebar, which is also noted on site. Whether on walls, floors or columns, this method is ideal if intrusive work is planned shortly after the survey, meaning that the contractor knows exactly where to avoid when drilling. There is no permanent record made and so this is only appropriate for the construction phase and not planning stages. This is the cheapest and quickest survey output available.

Output 2: Mark out survey with basic reporting

This option is employed where intrusive work is scheduled soon after the survey, but the site is too complex to warrant a simple mark out survey. It also gives you a permanent record of what was surveyed at that time.

In the example below, a GPR survey was conducted over 6 columns on the fifth floor of a hospital in order to investigate reinforcing and understand the load bearing of the columns before constructing an additional floor above. The location of the surveyed columns was marked on site, then recorded on a digital plan, along with the position of the rebar within those columns.

Output 3: Post processed survey with full reporting

A full desk-based analysis of the data and production of a full report is useful at the design and planning phase and/or if the site is more complex.

In the example below, two layers of rebar have been located (inner mesh and outer mesh). The data is displayed both as radargram (section views of the data) and as a digital plan interpretation. The results indicate that the outer mesh has a cover depth range of 15 - 20mm and the internal, inner mesh cover depth is typically between 50 -70mm. Cover meter readings indicate that the both horizontal and vertical rebars of the outer mesh appear to have an indicative diameter of 7mm.