CON/Specific/TBT-CON-005

Post-Tensioning Safety

Concrete & Formwork › Specific › Post-Tensioning Safety

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Post-tensioning is a method of strengthening concrete by threading high-strength steel tendons through ducts and stressing them after the concrete has cured.
Stressing jacks apply forces of hundreds of tonnes to the tendons — a tendon failure releases this energy explosively.
An exclusion zone must be established behind the stressing jack and along the tendon line during all stressing operations.
Only trained, competent post-tensioning operatives may carry out stressing, grouting, and anchorage operations.
The stressing sequence must follow the engineer's specification precisely — incorrect sequence causes overstress and structural damage.
Grout is injected into the tendon ducts after stressing to protect the steel from corrosion and bond it to the concrete.
Grouting involves pressurised equipment — hose failures and grout leaks create splash and pressure injury risks.
Protruding tendon ends and anchorages create sharp hazards on the concrete surface that must be protected and marked.
Post-tensioned slabs must not be cored, drilled, or cut without a tendon survey identifying the exact cable positions.
A tendon struck during future building modifications releases its stored energy with lethal force in all directions.

Explosive energy	A stressed tendon stores hundreds of tonnes of force — failure during stressing or accidental cutting releases this energy instantly.
Exclusion zone	Anyone in the path of a failing tendon or behind a stressing jack is at risk of fatal impact — zones must be enforced strictly.
Future risk	Post-tensioned slabs contain hidden cables under permanent tension — cutting one during future modifications is immediately fatal.

Don't

Establish exclusion zones behind the stressing jack and along the tendon during stressing.
Follow the engineer's stressing sequence and target forces exactly as specified.
Use only trained, competent post-tensioning operatives for stressing and grouting.
Record all stressing data including elongation and force values for the project records.
Wear eye protection and waterproof clothing during grouting operations.
Protect and mark protruding tendon ends and anchorage components on the slab.
Survey for tendon positions before any future coring, drilling, or cutting of the slab.
Inspect ducts, anchorages, and stressing equipment before each stressing operation.
Follow grouting procedures to achieve complete duct filling for corrosion protection.
Brief all workers on exclusion zones and the stressing schedule before operations begin.

DON'T enter the exclusion zone behind the jack or along the tendon during stressing.
DON'T deviate from the specified stressing sequence or target force values.
DON'T allow untrained persons to operate stressing jacks or grouting equipment.
DON'T accept stressing results without recording elongation and force values.
DON'T carry out grouting without eye protection and skin coverage.
DON'T leave protruding tendon ends unmarked — they are a sharp laceration hazard.
DON'T core, drill, or cut a post-tensioned slab without surveying for tendon positions.
DON'T use damaged or uncalibrated stressing jacks or pressure gauges.
DON'T leave voids in grouted ducts — incomplete grouting causes tendon corrosion.
DON'T begin stressing without briefing all workers on the exclusion zone locations.

See also: Concrete Pour Safety | Formwork and Falsework

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