n colder environments, concrete floors may contain in-floor heating tubes. A closed system will circulate hot water through these tubes, which will warm the concrete, and subsequently the air above it, either for comfort or to prevent ice formation (on driveways). (Image above shows radiant tubing layout before concrete is poured).
When coring in these areas, it’s important to scan the area with GPR, to ensure these tubes are not damaged during coring. This article provides 5 tips to help you locate and differentiate heating tubes from other embedded objects:
1. Fill ‘em up – Most modern tubes are 1/2” diameter, constructed using PEX, or cross-linked polyethylene, material. From GPR theory, we know that small, air-filled, non-metallic conduits are hard to locate, due to the weak reflection they produce. We can greatly increase our chances of seeing these tubes by ensuring they are filled with liquid (or turning the system on), thereby increasing the reflectivity of the tubes to the GPR signal.
2. Look for the curvature – in-floor heating tubes are laid out in such a way that there are lots of curves and bends, especially near the walls. When doing a scan, if you can see the curvature, you know these are in-floor heating tubes. Figure 1 shows these tubes, laid over rebar.
Sometimes during placement of the heating tubes in the concrete, some sections, most often near the curved ends, will “float up” in the wet concrete. These sections appear in shallower depth slices before the rest of the tubes are visible in the deeper depth slices.
3. Collect a high-resolution grid – closely spaced lines will spatially sample the subsurface more, allowing you to see the curvature better. In Conquest, this is referred to as a high-resolution grid. The depth slice in Figure 1 (lines collected 2 inches apart) shows the curvature better than the depth slice in Figure 2 (lines collected 4 inches apart). Note the circles in the image below, highlighting these differences. Collecting a high-resolution grid will help you to differentiate the heating tubes from the rebar.
4. Compare depth on the line scans – heating tubes can be placed above or below the rebar, or even sometimes placed between rebar and wire mesh. Looking at a line scan will reveal this depth difference. For example, in Figure 3 , the depth slices determined the curved heating tubes were above the rebar; the hyperbolas indicated by the yellow arrows are the heating tubes. The other hyperbolas in between them are the rebar.
5. Collect large grids – if time and space permit, it’s always better to collect larger size grids. The larger coverage area will provide the big picture and allow you to see how things are laid out. Objects that overlap in some places may deviate in others, and this will be more noticeable in a larger grid.
Ensure you use the tips above to safely and accurately locate tubes prior to cutting or coring.
Data courtesy of Craig Campbell, G3Tech.
