Ground-penetrating radar (GPR) scanning is the step that separates professional concrete cutting from dangerous guesswork. Every serious UAE cutting contractor scans before they cut. This guide explains how GPR works, what it reliably finds, where its limits are, and when you should insist on it.
How GPR works on concrete
A GPR antenna emits pulses of electromagnetic energy into the concrete. Different materials reflect energy at different rates — a steel rebar bar reflects much more strongly than the surrounding concrete; an air void reflects differently again; a plastic duct reflects differently from steel.
The antenna moves across the surface while continuously transmitting and recording. The result is a colour-coded profile showing the depth and position of reflectors within the concrete.
A trained GPR operator reads this profile and marks the locations of:
- Rebar (top and bottom mat, chairs)
- Post-tension cables (both sheaths and anchorages)
- Embedded conduits and ducts
- Voids or honeycombing
- Variations in slab depth
The scan is done from the surface. No drilling, no core extraction, no damage to the slab.
What GPR reliably finds in UAE construction
Post-tension cables
Post-tension slabs and beams are the primary GPR application in UAE. PT cables are high-strength steel wire bundles inside a plastic sheath, typically 15–25mm diameter, running in predictable patterns from anchorage to anchorage.
GPR reliably identifies PT cables in most UAE slab types because:
- Steel reflects strongly against concrete background
- The cables are at predictable depths (80–120mm below top surface in typical slabs)
- Their paths are geometrically regular (straight runs or gentle curves)
Nicking a PT cable is a structural emergency. GPR is mandatory on any PT slab before drilling or sawing.
Rebar mats
Top and bottom reinforcing mats are easily identified. GPR can distinguish mat spacing, bar diameter (approximately), cover depth, and whether double layers are present.
This is valuable for blade selection — heavy rebar requires different diamond specifications and affects pricing.
Embedded conduits and pipes
Electrical conduits, copper pipes and plastic drainage sleeves inside slabs show as voids or strong reflectors depending on their material and fill state. An air-filled plastic conduit looks different from a water-filled copper pipe, but both are distinguishable from the surrounding concrete.
Voids and honeycombing
Poor concrete vibration, particularly in columns and walls, creates voids that GPR can identify. This is useful before installing chemical anchors — a void in the bond zone makes an anchor unreliable.
What GPR does not reliably find
Being honest about limitations is important. GPR is not X-ray vision.
Thin plastic sheets: A 2mm damp-proof membrane or slip sheet may not produce a clear reflection.
Congested reinforcement zones: Where top mat, bottom mat, stirrups and PT cables are all present, the reflections overlap and individual elements can be hard to distinguish. This typically occurs in transfer beams and PT beams with shear links.
Chloride contamination: GPR can detect voids but cannot directly measure chloride concentration or carbonation depth. For corrosion assessment, cores and chemical analysis are needed.
Deep scanning limitations: Standard GPR in concrete loses resolution below about 300mm. Most UAE slabs are 200–300mm, so PT cables in the bottom third of a deep transfer slab may not be detected reliably from the top surface. In these cases, scanning from both sides is necessary.
Stacked elements: If a slab sits on a beam that sits on a column, the sheer number of reflectors from the beam cage can mask what's in the slab immediately above.
How a GPR scan works on site
- Surface preparation: The area to be scanned must be accessible. Tiles, carpet or screed don't prevent scanning, but thick bituminous coatings can attenuate the signal.
- Grid marking: The operator marks the scan grid on the floor with chalk lines. Standard grid is 100–200mm centres for detailed bore location work; 500mm centres for general condition surveys.
- Scanning: The antenna is pushed across the surface following the grid. Modern antennas are self-calibrating and record GPS-correlated position in real time.
- Analysis: The operator reviews the data profile and marks bore-safe zones directly on the slab surface — typically a 100–200mm clear zone around each located feature.
- Report: A scan report showing detected features, bore locations, and any areas of uncertainty. This is handed to the drill or saw crew as their working document.
Time on site: 30–60 minutes for a standard floor plate (1,000–2,000 sqm). Longer for congested transfer structures.
When you must scan before cutting
Always scan before:
- Any drilling or sawing on a post-tension slab (identified by PT anchorages, blister plates at slab edges, or confirmed in structural drawings)
- Any penetration through a slab where current as-built drawings are unavailable
- Any anchor installation in a beam or column
- Any work on a slab built before 2000 where contractor documentation is incomplete
Scan strongly recommended (even with drawings):
- Any slab where drawings show PT but the exact cable locations aren't dimensioned
- Older UAE slabs where contractors may have varied from drawing positions
- Any element that shows cracking or distress (could indicate previous damage)
- Any work within 500mm of a beam line
The false economy of skipping GPR
A GPR scan costs AED 600–1,500. A PT cable repair after it's been nicked costs AED 15,000–80,000+ and involves stopping all work on the affected bay, structural assessment, PT specialist repair, and retesting.
We have been called to projects where a previous contractor drilled without scanning, nicked a cable, and then disappeared. The project owner paid twice: once for the cutting, and again for the repair and structural sign-off.
Scan first. It's the only responsible way to work on UAE construction.