Concrete and Formwork Support
This domain tests the support work around concrete: building and bracing forms, placing reinforcement correctly, pouring and consolidating without segregation, curing, and stripping at the right time. Expect questions on form pressure, free-fall limits, vibration, cover, and cold-weather protection.
Formwork and falsework
- Forms must carry the weight of the concrete, construction loads, and the lateral pressure of the pour; tall or complex formwork is designed by a qualified person.
- Brace with kickers, walers, strongbacks, and form ties; check that ties are rated for the pressure at the pour rate.
- Apply release agent to the form face before placing rebar, and keep the form clean of debris.
- Provide guardrails and safe access on elevated formwork decks; never climb the rebar cage.
Reinforcement and placement
- Use chairs and bolsters to hold cover; typical cast-in-place cover against earth is around 50 mm and against forms around 40 mm, per the project specification.
- Do not step on or bend installed rebar; report damaged or displaced steel before the pour.
- Keep construction joints clean and prepared as specified.
Placing, consolidating, and curing
- Limit free fall to about 1.5 m; use a drop chute or elephant trunk for deeper placement.
- Place in horizontal lifts of roughly 300–500 mm and consolidate each lift with a vibrator inserted at about 1.5 times the vibration radius, withdrawn slowly.
- Never use the vibrator to move concrete along the form, and never vibrate rebar.
- Cure by keeping the surface moist, typically around 7 days, and protect fresh concrete from freezing and from rapid drying in heat or wind.
Worked example
A 3.6 m foundation wall will be poured from a pump. Because free fall exceeds 1.5 m, the crew uses a drop chute. The wall is poured in 500 mm lifts, with the vibrator inserted quickly and withdrawn slowly at regular spacings, avoiding contact with ties and rebar. Form ties are matched to the pour rate and wall height, and a formwork designer confirms the bracing. Wall forms are stripped once the concrete can stand, while soffit formwork is stripped only when the specified strength or cylinder breaks allow it.
Traps that cost marks
- Stripping soffit formwork on a fixed calendar time rather than strength.
- Dropping concrete more than 1.5 m and causing segregation.
- Over-vibrating, which pushes paste away from the aggregate.
- Forgetting release agent and damaging the form face during stripping.