CON/General/TBT-CON-006

Concrete Vibration and Compaction

Concrete & Formwork › General › Concrete Vibration and Compaction

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Concrete must be vibrated and compacted after placement to remove trapped air, fill voids, and achieve full design strength.
Poker vibrators are the most common compaction tool, inserted vertically into the concrete at regular spacings and depths.
Over-vibration causes segregation of the concrete mix, with coarse aggregate sinking and cement paste rising to the surface.
Under-vibration leaves air pockets and voids in the concrete, reducing structural strength and creating honeycombing defects.
Hand-arm vibration from poker vibrators exceeds daily exposure limits quickly — HAV trigger times must be managed.
Wet concrete contact during vibration causes cement burns — waterproof gloves and boots must be worn throughout.
Electrical poker vibrators must be 110 volt and inspected before use — they operate in close contact with wet concrete.
The poker must be withdrawn slowly to allow the hole to close — rapid removal creates void channels in the concrete.
Vibration duration at each insertion point is typically 5 to 15 seconds — the surface becoming smooth and glossy indicates completion.
Formwork must be monitored during vibration — excessive vibration can cause formwork movement, bulging, and blowout.

Structural strength	Concrete that is not properly vibrated contains voids that reduce its load-carrying capacity below the design requirements.
HAV exposure	Poker vibrators transmit high levels of hand-arm vibration — trigger times are reached quickly without task rotation.
Formwork damage	Excessive vibration loosens formwork ties and causes panels to bulge or blow out, losing concrete and endangering workers.

Don't

Insert the poker vertically at regular spacings and to the correct depth.
Vibrate each insertion point for 5 to 15 seconds until the surface becomes smooth.
Withdraw the poker slowly to allow the insertion hole to close completely.
Manage HAV exposure by rotating operators and tracking vibration trigger times.
Wear waterproof gloves and boots to prevent cement burns during vibration.
Use 110 volt electrical vibrators with current inspection and PAT test labels.
Monitor formwork during vibration for movement, bulging, or tie loosening.
Avoid over-vibrating — excessive vibration segregates the concrete mix.
Ensure the correct poker size is selected for the element thickness being poured.
Brief the placing gang on the vibration pattern before each concrete pour.

DON'T skip vibration — uncompacted concrete contains voids that reduce its strength.
DON'T vibrate for too long at each point — over-vibration causes mix segregation.
DON'T withdraw the poker rapidly — it creates void channels through the concrete.
DON'T exceed HAV trigger times — rotate operators to manage vibration exposure.
DON'T operate the vibrator without waterproof gloves and boots to prevent burns.
DON'T use 230 volt vibrators in wet concrete — use 110 volt equipment only.
DON'T ignore formwork movement during vibration — stop and investigate immediately.
DON'T use an oversized poker for thin sections — it disrupts the reinforcement.
DON'T assume one vibration technique fits all pours — adapt to the element type.
DON'T begin pouring without briefing the gang on the vibration pattern required.

See also: Concrete Pour Safety | Reinforcement Fixing Safety

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