By: Len LaFond
Before you start drilling, cutting, or sawing into concrete, it’s important to make sure that there’s nothing embedded in there that could cause harm to workers or damage the infrastructure.
But how do you determine which approach to take? Should you have the concrete slab scanned using Ground Penetrating Radar? Or would X-Ray be better?
Let’s break down the pros and cons of each so you can make an informed decision for your next construction job.
Ground Penetrating Radar (GPR)
- With scanning, technicians only need access to one side of the slab, so the overall process takes less time – usually it can be completed in an hour and a half.
- When you simply need to find a clear area in the slab to drill, scanning is a quick and easy way to determine that.
- GPR does not pose a hazard to people or objects.
- GPR is lower cost than X-Ray.
- Scanned images can be more difficult to evaluate, so the interpretations tend to be subjective.
- Areas with strong electromagnetic signals can interfere with the wave forms created by the scan, resulting in objects being missed and/or inaccurate data sets.
- If the concrete slab contains a complex assortment of objects, it can be harder sort out what each image represents.
- When you need to see exactly is in the concrete, X-ray provides a very accurate image. This is important to customers who need definitive information as to whether the object is rebar or conduit.
- The interpretation isn’t subjective.
- Accurately knowing what is in the concrete can provide long-term cost savings in terms of preventing damage to the building or surrounding structure and protecting worker safety.
- The X-ray process uses cobalt-60, a highly radioactive isotope, which means that radiation hazards are introduced to the site.
- Technicians must undergo special training and certification to control the radiation hazard.
- Special procedures must be followed to ensure everyone’s safety, including: erecting radiation warning signs and barriers; policing the 150-foot radius area during exposure to ensure no one enters without proper authorization; conducting work during off-business hours (usually at night) to limit exposure; wearing special monitoring devices; etc.
- X-ray has a concrete slab thickness limitation of 20 inches.
- Both sides of the slab or wall must be accessible in order to X-ray.
- X-ray is a slower process than scanning – takes five to six hours from start to finish.
- Because X-ray takes longer and more precautions must be introduced, it’s more expensive than scanning.
These images will give you an idea for the visual differences between scanning and X-ray:
Ground Penetrating Radar:
The vertical and horizontal lines shown in the black/white/gray plan map are some kind of reinforcing components (possibly rebar or wire mesh). The white diagonal line is likely to be a utility of some sort.
The vertical white lines and horizontal red lines in the red/white/blue image represent reinforcing components at different depths in the slab.
The wider red line in the upper part of the image with the bulbous area to the left is likely a reinforcing component with an electrical component that runs beside it. The bulbous area is possibly a utility box or electrical box.
The red diagonal line is most likely a conduit (electrical pipe) – something other than a reinforcing component.
This image shows the exposure device that takes the X-ray and an actual image of what the X-ray device took (two panels and the connection between the two panels).
If a hole needed to be drilled between the two panels, the X-ray image makes it possible to steer the driller away from the connecting points.
This X-ray image would also be able to show the customer the condition of the connection – whether there is any corrosion or modularity of the epoxy around the pins.
Both GPR and X-ray can provide valuable information prior to cutting, sawing, or drilling. The decision about which option to use will depend on the parameters of the project and how definitive the image needs to be.
Be sure to work with a provider that has the capabilities to provide both services and has the expertise and experience to offer objective assessments and recommendations for which service to use for the job.