GPR Concrete Scanning Common Misconceptions

August 1, 2017

Penhall analyst conducting concrete scanning
Concrete Scanning Using Ground Penetrating Radar (GPR)

Ground Penetrating Radar (GPR) is a very effective scanning method to ensure safety when coring or cutting into concrete. However, there are still a lot of misconceptions about what GPR can and cannot do. This list will help you understand GPR before you hire a concrete scanning service for your project.

I can scan myself if I buy the equipment

While setting up and using the GPR equipment is easy, interpreting the data is complicated. A major misconception is that GPR shows a clear image of what is in the concrete. Actually, the screen reflects a black and white image resembling TV static. When the antenna picks up on an object, it reflects as a hyperbola on the screen. GPR analysts go through extensive training to be able to interpret the data, and to know how to differentiate between objects on the screen.

GPR can be successful under any surface condition

Moisture in concrete plays a huge role in the success of concrete scanning. Moisture raises conductivity, meaning the equipment’s signal bounces right back, making it difficult to get good data readings. Concrete that is less than three months old has a higher moisture content than concrete that has had more time to cure so it’s best to wait before scanning. Other difficult surfaces can include insulation, marble, granite floors, among others.

underground wire locating
Analyst performing underground wire locating

GPR can scan at any depth

The GPR equipment in concrete scanning applications is only able to scan up to 20 inches. If we have access to both sides of the slab, then the analyst would be able to scan thicker concrete.

The GPR equipment can differentiate between objects

As mentioned before, the screen of the equipment shows data in a very general state. Different objects, such as post tension cable or rebar, aren’t displayed in a distinctive way, nor do they show a difference in the hyperbola. Thanks to the expertise of the analyst, he/she can distinguish between the different lines and patterns to read the data.

GPR is 100% precise

While GPR is considered to be one of the most effective forms of non-destructive testing, it is not perfect. GPR is as accurate as one-fourth of an inch from the center of the target and less than half-inch in depth under ideal circumstances (for example, well-aged concrete). Some of the variables in the concrete that affect accuracy can be: wire mesh, pan decking, and multiple layers of rebar.

We hope that this list gave you a better understanding of GPR concrete scanning. By deciding to scan the concrete at your jobsite, you are reducing safety and financial costs for your construction project.


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