GPR (Ground Penetrating Radar) is the ideal technology for locating, imaging and mapping rebar within concrete structures.
GPR lends itself to different survey approaches from small scale (confirmation of build consistent with the design) or just to get an idea what is present. To localised areas (high resolution scanning in specific locations), to wide areas (scanning of entire bridges or structures to confirm rebar distribution and some structural features). Every survey is different and it requires experience to adopt the best approach for each job.
With our wide range of GPR equipment, with differing centre frequencies and performance characteristics, KB GPR Surveys is well positioned to choose the most appropriate tool for every job.
How a GPR rebar detection and mapping survey in concrete is performed
We will attend site and perform the survey using our advanced GPR equipment. KB GPR Surveys has a wide variety of GPR of several different frequencies and manufacturers and this allows us to choose the most appropriate tool for any job. This will usually involve marking the surface in paint, crayon or chalk to indicate accurately referenced scan positions and then passing our equipment across the surface in a series of sequential scans until the area has been thoroughly covered in two directions.
On-site rebar location or pre-drill surveys
In the case of an on-site rebar detection or pre-drill survey, we will perform a data interpretation on-site and mark the locations of the individual rebar on the surface. This allows us to make use of information visible on-site but restricts us in that we can only view one GPR scan at a time and cannot perform a quality control. On-site rebar location surveys are usually performed immediately prior to drilling so that damage to rebar can be minimised or avoided.
Rebar mapping and imaging
For rebar mapping and imaging, (on the majority of occasions) we collect the GPR data on site and then post-process the data in the office using our advanced GPR post-processing and imaging software. In this case we will import all of the data collected on site and accurately reference it together to form a 3D image, we then able to visualise it in different ways and see the location and distribution of rebar’s beneath the surface. This allows us to base our decisions on more information, in addition, all of our post-processed surveys are subject to an internal quality control before the results are issued.
In this case our typical deliverable with be a short report and/or CAD drawings which clearly detail the requested information.
Why use GPR for rebar detection and mapping in concrete
GPR is a completely non-invasive and non-destructive technology (NDT), which does not require any intrusive investigation methods to work successfully. It is particularly ideal for investigating concrete structures to locate, image and map rebar because concrete is homogeneous and there is a strong dielectric contrast between the concrete and the rebar.
GPR is completely non-destructive and non-invasive technology (NDT) and can reliably detect rebar to a depth of approximately 50cm.
However, GPR does have some limitations: it is not able to penetrate through a closely spaced mesh of reinforcing metal fibres, or very closely spaced (a few cm’s) rebar mesh. GPR also has poor lateral resolution, it is therefor not possible to recover the diameter of rebar or to detect subtle changes in its condition. For these types of information it is recommended that the GPR survey is carried out to provide coverage across the site and then invasive surveys are commissioned at specific locations.
Although GPR cannot completely remove the need for invasive surveys, it will dramatically reduce the requirement and adds significant value by complete the larger picture.