The Facts About GPR

GPR, or Ground Penetrating Radar, is a convenient and effective way to see what is going on underneath a concrete slab. In the past, if someone wanted to inspect underneath a concrete slab, they would have to either drill holes in it or break up the slab. Imaging technology has progressed over the years to provide a clearer look, without damaging the concrete.

A benefit of the improved technology is that it is now easier to see what is underneath the concrete. This information will help prevent damage to utilities and equipment and harm to employees and other people. Damaging pipes, cables, wires, and other structural objects can cost you money and time, in addition to being dangerous. By imaging conduits, structural supports, and reinforcements ahead of time, you minimize the chances of damage occurring.

Early Tech Used X-rays

GPR to view under concreteOne of the first methods of imaging beneath the concrete was through the use of X-ray machines. Unfortunately, there were a lot of drawbacks to using X-rays. There needed to be a film on the opposite side of the area being scanned, which could be difficult, if not impossible. Additionally, people would need to be evacuated due to radiation concerns. Depending on the type of structure, the number of people, the location, and other variables, this could be a very involved process. 

If these issues were overcome, you would still have to wait while the images were processed off-site, then interpreted. This could take days to complete. While the images were good for seeing materials like rebar, it was not a simple process.

GPR is the Tech of Today

Although X-rays and other methods are still used today, GPR is the best method available. Solving some of the issues that occur with these older methods, GPR is becoming increasingly popular. GPR systems don’t require film, doesn’t emit dangerous radiation, and the data can be accessed immediately. There are options that GPR can use that aren’t available to other types of tech. Different frequencies can be used to identify different depths and along with 3D imaging, GPR can also display visuals in 2D and 1D. This can be useful in viewing congested areas.

GPR 101

So how does GPR work, exactly? The basics of a Ground Penetrating Radar system is the utilization of an antenna that produces an electromagnetic radio wave. This radio wave travels through concrete, soil, and other materials until the wave “hits” something, creating a discontinuity in the wave. When the wave encounters a disruption, some of the wave is reflected off the object and travels back to the antenna. 

When the radio wave energy returns to the GPR unit, the two-way travel time and the amplitude is recorded. The travel time will determine the depth of the object and the amplitude shows how different the object was compared to the surrounding material. More energy is reflected the more there is a difference between the two materials. A trained GPR engineer can analyze this data and determine if the object is rebar, PVC, cable, or something else.

To scan a concrete surface, the GPR unit is placed on the surface and pushed along the concrete. This will produce a 2D image of what lies beneath. When several images are collected, they can be used to create a “depth map” or “time slice”. These collected images can show embedded objects at varying depths. The machines take the detailed scans, but it takes a highly-trained technician to interpret the data.

Concrete Construction and GPR

The accuracy of the GPR scans and the skills of the technician lends itself to concrete construction issues. By being able to precisely locate things like rebar, conduits, tension cables, and other objects, the contractor can avoid accidents while cutting or drilling into the concrete. The technician will be able to let the contractor not only know that there is something in the concrete but where it is and what it is made of.

Another use of GPR in relation to concrete is to determine the thickness of the slab. The radio wave that is emitted by the unit not only can detect objects, but it can determine when the concrete ends and the soil begins. Contractors can use this data to assess the deterioration of the concrete and the structural capacity of the slab. Older methods might have only covered one section of the concrete, but the GPR can cover large areas.

GPR is extremely useful when it comes to identifying cracks and voids beneath the concrete surface. It is vital that these problem areas are identified and repaired. A skilled GPR technician will be able to analyze the data and identify these defects.

Find a Skilled GPR Operator

Just about anyone can buy a GPR unit, but it takes skill and expertise to effectively use the machine. The tasks that the GPR unit can do range from the fairly basic job of locating and marking obstacles to void and crack detection. Make sure that the GPR technician you hire can complete the job you need. An operator with basic knowledge can determine the difference between steel and concrete, but you will want to hire someone with more training and experience if you need to complete more complicated tasks.

If you have any questions regarding GPR, please feel free to contact the experts at and Pro Foundation Technology. We will be happy to answer any questions you may have and help you effectively use GPR on your next project.


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