GPR Services
Post Tension Cable Detection Before Coring
Cutting a reinforcement bar is a repair. Cutting a post-tension tendon is a structural failure that releases stored energy — and it cannot be undone.
Why this one is different
A cut rebar weakens a slab.A cut tendon releases it.There is no repair,only a structural redesign.Post-tension tendons hold a slab in compression. Severing one does not reduce capacity gradually; it removes the prestress from that strand along its whole length, and the energy release is immediate.
Written tendon statement · Marked on the structure · Structural engineer sign-off
Quick AnswerMezux Touch detects post-tension tendons in prestressed slabs before coring or cutting, marks them directly on the structure, and issues an explicit written statement of whether a tendon lies within the scan zone — which is the finding a structural engineer requires before authorising a core.
What the structural engineer actually needs
Not a picture of the slab. A written statement, for each proposed opening, saying whether a post-tension tendon was detected within the scan zone. That statement is what authorises a core, and issuing a scan record without it leaves the decision unmade.
We provide it explicitly, position by position, rather than leaving it to be inferred from a drawing.
Distinguishing a tendon from reinforcement
Tendons sit at different depths from the reinforcement mesh, follow a draped profile rather than a straight line, and are larger in diameter. Together those usually make the distinction clear.
Where they do not — and on congested or unusual slabs they sometimes do not — we say the distinction could not be made confidently rather than guessing. That decision belongs to the structural engineer, not to the surveyor.
How a post-tension scan runs
Is this slab actually post-tensioned?
Original drawings, anchor evidence at slab edges and the construction period all indicate it. Where the answer is uncertain we treat the slab as prestressed until shown otherwise.
Understanding the draped path
Tendons follow a curve rather than a straight line, sitting low at midspan and high over supports. Knowing that profile tells us where to expect them at any given position.
Both directions, higher density
Coverage is denser than a routine rebar scan, because the consequence of a missed strand is different in kind from a missed bar.
Tendon against reinforcement
Depth, diameter and the draped profile usually distinguish the two. Where they do not, that uncertainty is stated rather than resolved by assumption.
Tendons in a distinct colour
Tendons are marked on the structure in a colour used for nothing else, so no operator can confuse them with reinforcement at the point of cutting.
Written finding per opening
For each proposed position we state in writing whether a tendon was detected in the scan zone. That is what a structural engineer signs against.
Where a clear position exists
Where the intended position sits over a tendon, the nearest viable location is identified and marked so the works are not simply stopped.
Saying when no safe position exists
Where the tendon layout leaves no clear opening, we say so. Nominating a least-bad position on a prestressed slab is not a judgement a surveyor should make.
Why we will not nominate a marginal position
On an ordinary reinforced slab a marginal core position is a risk the client can weigh. On a post-tensioned slab it is not, because the failure mode is immediate and the consequence is structural.
Where the scan leaves genuine doubt, we report doubt. A client who wants a position anyway needs their structural engineer's authority, not ours.
Prestressed structures across NCR
Post-tensioned slabs are concentrated in the newer commercial belts. These are the areas where most of this work originates:
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Frequently asked questions
From original drawings, anchor evidence at slab edges and the construction period. Where it is uncertain we treat the slab as prestressed until shown otherwise.
Usually, from depth, diameter and the draped profile. Where we cannot say confidently, we report that rather than guessing.
A written statement of whether a tendon was detected within the scan zone. That is the finding a structural engineer signs against.
We say so. Nominating a least-bad point on a prestressed slab is not a judgement a surveyor should make.
Yes, higher than routine rebar scanning, because coverage is denser and the finding carries more weight.
Coring a post-tensioned slab?
Ask for the written tendon statement — that is the document your structural engineer will actually need.
Get A Quote +91 99100 10209Post-tension detection — consequence, method and detailed questions
Post-tension scanning is the one form of concrete work where we decline to give a marginal answer. A severed tendon releases stored energy along its full length, cannot be repaired in place, and turns a small opening into a structural investigation. The scan therefore has a lower threshold for reporting doubt than any other service we offer.
Why the written statement is the deliverable
A structural engineer authorising a core through a prestressed slab needs a specific finding recorded against a specific position: was a tendon detected in the scan zone, yes or no. A general scan record showing the slab does not answer that, and a drawing requires someone else to make the judgement the scan was commissioned to inform. We issue the statement per opening because that is what the decision actually rests on, and because an undocumented verbal clearance protects nobody.
What is delivered
Tendons marked on the structure in a colour reserved for them alone, so no operator confuses them with reinforcement. A written statement per proposed opening recording whether a tendon was detected within the scan zone. Photographs of the marked area, referenced and sized. Alternative positions marked where the intended one is not viable. And an explicit statement of doubt where the distinction between tendon and reinforcement could not be made confidently, rather than a resolution the data does not support.
Beyond the basics
What actually happens if a tendon is cut? The prestress in that strand releases along its length, immediately. It is a structural event requiring engineering assessment rather than a repair.
Can a cut tendon be repaired? Not in place in any straightforward way. Remediation is a structural design problem, which is why prevention costs so little by comparison.
How much denser is PT scanning? Materially, and it takes longer for the same area. The consequence of a missed strand justifies the difference.
Will you clear a position under pressure? No. Where the data leaves doubt we report doubt, and proceeding needs the structural engineer's authority rather than ours.
Do you scan before every core on a PT slab? We recommend it for every opening. Tendon spacing means a position 300 mm from a cleared one is not itself cleared.
Terms used on this page
Post-tension tendon — a stressed steel strand holding a slab in compression, unrepairable if severed. Draped profile — the curved path a tendon follows, low at midspan and high over supports. Prestress — the compression applied to concrete by tensioned strands, lost along a strand if cut. Scan zone — the area around a proposed opening within which tendons must be ruled in or out. Written statement — a recorded finding per opening, which is what authorises a core.
