When it comes to discovering what is inside concrete prior to drilling or cutting, construction workers generally have two options from which to choose: X-ray or Ground-Penetrating Radar (GPR).
Understanding the differences between the two — especially their benefits and drawbacks — is crucial for determining which method is best for a specific job.
The Differences between X-ray and GPR
- Concrete X-ray or radiography uses a radioactive source to produce an image on a film. The process requires access to both sides of a slab, for the imaging film on one side and for the emitting source on the other.
- Ground-Penetrating Radar (GPR) uses electromagnetic energy to penetrate concrete and return reflected signals that reveal the subsurface layout of a structure. Unlike its X-ray counterpart, GPR is extremely safe, emitting about 1/100th the radiation level as a cell phone.
Pros and Cons
Overall, Ground-Penetrating Radar is generally the more efficient, cost-effective and safer non-destructive testing choice. And with recent advancements in radar technology, GPR is incredibly accurate, yielding images in real-time. However, there are circumstances in which X-ray may be recommended for the most accurate picture.
|SAFETY||Extremely safe. Radiation emitted is equivalent to high-frequency radio waves (10MHz to 1GHz).||Radiation risk. Safety equipment and clearance are required, and the process often requires the evacuation of a jobsite while the image is captured.|
|COST & EFFICIENCY||Mobile and affordable. With today’s technology, GPR technicians can provide real-time results in-person.||Cumbersome and costly. While X-ray technology is also improving, it is still much more time-consuming to set-up, and costly to develop the film, which is frequently done off-site.|
|COVERAGE AREA||Nearly unlimited. The amount of imaging that can be done in one session is primarily determined by the difficulty of the slab and the experience of the technician. Once the equipment is set-up, however, GPR technicians are still very mobile and can scan various locations onsite.||Limited area. Data collection is dependent on the size of the film swath. Imaging is generally done in 14″ x 17″ increments; large areas require repeatedly setting up the equipment in each area that needs to be X-rayed.|
|ACCESS||Flexible. For the vast majority of imaging needs, GPR technicians only require access to one side of the structure or slab. For extremely thick concrete, however, it may be helpful to scan from multiple sides to ensure accuracy.||Two sides needed. Because of how the X-ray works, the technicians must have clear access to both the front and back sides of the concrete. This can become problematic in tight areas, and impossible for utility or slab-on-grade scanning.|
|VISUALS||High Resolution. The strength and precision of today’s GPR equipment is sufficient for many imaging needs. However, the radar signal may become scattered in wet or extremely congested decks, resulting in limited visibility.||Higher Resolution. To-date, x-ray yields the highest resolution image for non-destructive testing methods. It is most useful for imaging extremely congested decks that are difficult to distinguish with GPR.|
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