The two most important questions to answer during a subsurface concrete inspection prior to drilling or cutting are: 1. What is it? and 2. Where is it? Is ground-penetrating radar (GPR) the right choice, or is X-ray imaging the way to go? The answer may be surprising.
GPR equipment cannot identify what something is, only that something is present. It is up to the GPR practitioner to identify whether an object is rebar or post-tension cable - a very important distinction. For this reason, GPR is considered to be subjective using interpreted data, experience and visual clues available to the GPR practitioner. GPR signal cannot penetrate through metal objects, but the equipment can approximate depth from the surface, provided the object isn't obscured by a more shallow object.
On the other hand, X-ray produces images that often clearly show the telltale ridges of rebar or the strands of post-tension cables, clearly identifying what the object is. It's well known that X-ray does not provide depth information, even relative depth can be difficult to ascertain from images. It is for these reasons that we often recommend using both methodologies in conjunction with one another for optimal results. Capture an image using X-ray to clearly identify what the object is, then use GPR to accurately map the object's position and depth to the concrete surface.
The GPR data collection process and the process of capturing an X-ray image are dissimilar. Although the combination of GPR and X-ray will ultimately yield the best results, project budget, timeline and worksite details may dictate using one method over the other. GPR data is collected in real time by rolling the GPR antenna across one side of the concrete surface. The GPR practitioner analyzes the data and marks their findings on the concrete. The GPR practitioner can work alone, the process is relatively quick and there is little interference to other work activity in the area. Capturing images using X-ray is quite different. Due to safety regulations, a team of two qualified individuals is required, as defined by state legislation. Additionally, the X-ray crew must have access to both sides of the concrete to capture an image. They must also define and restrict access to the work zone during exposures, which may prevent others from working nearby.
Safety, schedule and cost are three key components to any project. Using GPR will give results quickly, but the data is subject to analysis and interpretation. Using X-ray will help remove the uncertainty of what is in the concrete, but comes with more regulation and requirements. The combination of both will provide the best results to safely drill or cut into the concrete, avoiding incident or injury. Keep your project safe and on schedule by allowing Penhall Technologies to use GPR and X-ray on the concrete prior to cutting and/or drilling.
For more information, visit www.penhall.com or call (800) PENHALL [736-4255].
