Post-Tension Cable Scanning
Post-tension cable scanning locates the stressed tendons inside a post-tensioned concrete slab so they can be avoided when drilling or coring. RebarScan surveys PT slabs across Oxfordshire to prevent tendon strikes, one of the most serious and expensive failures in concrete work. All scanning is carried out to UKCSS-compliant standards.
Request a PT Cable Scanning QuoteWhat post-tension cable scanning is
Post-tensioned slabs carry their loads through high-strength steel tendons that are stressed after the concrete has cured. Those tendons run in ducts that sweep up and down across the span in a draped profile, and they are held under enormous force. Cutting one is dangerous and structurally significant.
Post-tension cable scanning uses ground penetrating radar to find those tendons before any penetration is made. Because PT ducts are larger than ordinary reinforcement and follow a distinctive profile, an experienced engineer can distinguish them from the regular bar grid and trace where they run across an area.
The aim is to plan every core and fixing so it passes between the tendons, at a depth and position that keeps well clear of the stressed steel.
When it is required
It is required before any intrusive work into a slab known or suspected to be post-tensioned, coring for new services, forming openings, installing heavy fixings, or investigating the structure. PT construction is common in car parks, commercial floor plates and transfer structures built from the 1980s onward, so any penetration into a slab of that type warrants confirmation. The consequences of a strike make this one of the clearest cases for scanning under CDM risk control.
What is detected
- Post-tension tendons and their ducts
- The line and approximate drape profile of the cables
- Ordinary reinforcement running alongside the tendons
- Anchorages and zones to keep clear
- Safe positions and depths for proposed penetrations
How it works
The engineer scans the area of the proposed penetration with GPR, interpreting the profiles against the slab type and any tendon drawings to separate cables from reinforcement. The line of each tendon is marked on the surface and clear zones are identified for the planned work. Findings are agreed with the responsible engineer before drilling begins. The survey is non-destructive and needs no power or water.
Who commissions it
Post-tension cable scanning is commissioned by structural engineers responsible for PT slabs, contractors and coring specialists penetrating commercial floors and car parks, fit-out teams installing services in post-tensioned buildings, and asset owners altering existing PT structures.
Frequently asked questions
- Why is cutting a post-tension tendon so serious?
- Tendons in a post-tensioned slab are held under very high stress. Cutting one releases that force suddenly, can injure the operative, and removes structural capacity the slab depends on. A single severed tendon can require costly engineered remediation.
- How do you tell tendons apart from ordinary rebar?
- Post-tension ducts are larger, run in characteristic draped profiles that rise and fall across the span, and sit differently to the regular reinforcement grid. We interpret radar profiles together with the slab type and any available drawings to distinguish the two.
- Can you map the drape profile of the cables?
- Across an accessible area we can trace where tendons run and indicate how their depth changes along the span, since the profile is highest over supports and lowest at mid-span. This helps identify the safest depth and position for any penetration.
- Is it safe to core a post-tensioned slab at all?
- It can be, once the tendons are located and a penetration is planned to avoid them. Many cores are completed safely in PT slabs after scanning. The decision and the final position should always be agreed with the structural engineer responsible for the slab.
- What information helps before you attend?
- Any record that the slab is post-tensioned, the original tendon layout drawings if they exist, and the planned penetration positions all help. Even without drawings we can scan and locate, but prior information improves confidence and speed on site.
Related services and coverage
Working on a post-tensioned slab?
Tell us about the slab and the penetration planned, and we will locate the tendons.
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