CON/Specific/TBT-CON-019

Self-Compacting Concrete

Concrete & Formwork › Specific › Self-Compacting Concrete

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Self-compacting concrete (SCC) flows under its own weight to fill formwork without vibration.
SCC develops significantly higher formwork pressures than conventional concrete — up to full hydrostatic head.
Formwork must be designed for full liquid head pressure, not the reduced pressure assumed for vibrated concrete.
The high fluidity means SCC will leak rapidly through any gaps, joints, or tie holes in the formwork.
SCC contains higher cement and fines content, increasing the alkalinity and skin burn risk from contact.
The absence of vibration reduces noise but the pour itself requires careful monitoring of fill levels.
Overfilling formwork with SCC can cause burst panels, blow-outs, and sudden concrete release.
SCC requires strict quality control — slump flow, V-funnel, and L-box tests verify workability on delivery.
Mix design is more sensitive than conventional concrete — small changes affect flowability dramatically.
Finishing SCC surfaces requires different techniques because the material self-levels.

Formwork failure	SCC exerts full hydrostatic pressure — formwork designed for conventional concrete can burst catastrophically.
Concrete burns	Higher cement content in SCC makes it more alkaline, increasing the severity of skin burns on contact.
Quality sensitivity	SCC mix design is less forgiving — variations in water, admixtures, or aggregates cause segregation and defects.

Don't

Design and check formwork for full hydrostatic pressure when using SCC
Seal all formwork joints, tie holes, and gaps to prevent SCC leakage
Monitor the fill level carefully during pouring to prevent overfilling and blow-outs
Test every SCC delivery for slump flow and other specified workability parameters
Wear waterproof gloves and eye protection when working near flowing SCC
Brief the pour team on the specific formwork pressure and leakage risks of SCC
Inspect formwork ties and bracing are at the design capacity before starting the pour
Reject SCC loads that do not meet the specified workability criteria on delivery
Control the pour rate to avoid exceeding the formwork design pressure at any level
Clean any SCC contact from skin immediately with clean water to prevent alkaline burns

DON'T pour SCC into formwork designed only for conventional vibrated concrete pressures
DON'T assume SCC will behave like conventional concrete — the pressures are much higher
DON'T leave gaps or unsealed joints in the formwork — SCC will exploit every opening
DON'T overfill formwork sections — monitor the fill height against planned levels
DON'T add water to SCC on site to adjust flowability — it destroys the mix design
DON'T vibrate SCC unless specifically instructed — it is designed to flow without vibration
DON'T ignore skin contact with SCC — its higher alkalinity burns faster than normal concrete
DON'T pour at a rate faster than the formwork is designed to resist
DON'T skip workability testing — SCC that does not flow correctly causes voids and defects
DON'T stand near formwork during the early stages of an SCC pour in case of blow-out

See also: Concrete Pour Safety | Formwork Erection and Striking

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