Installs concrete formwork
Formwork questions test whether you understand that forms are a temporary structure carrying liquid pressure and a heavy load, and that finished concrete must land within tolerance for dimension, plumb and level.
Pressure and bracing
Fresh concrete exerts lateral pressure that rises with pour rate, slump and the temperature of the mix, and falls as the concrete sets; a fast pour in cold weather produces the highest pressure. Forms are held by ties - snap ties or taper ties through the wall - backed by walers and strongbacks, with kickers and braces to keep the assembly plumb. Ties are spaced per the form design and never replaced with undersized or bent hardware. Form release agent goes on clean forms before the pour, and joints are tight so grout does not leak.
Reinforcing and embedments
Bar chairs hold reinforcement at the specified cover - more cover where concrete is cast against earth. Anchor bolt templates, keyways between pours, chamfers and blockouts are set before the pour and re-checked after the forms are closed. A keyway gives the next pour a mechanical shear key.
Placing, curing and stripping
Concrete is placed in lifts and consolidated with a vibrator, which is withdrawn steadily to avoid leaving holes; over-vibration segregates the mix. Slump is tested at the point of placement. Curing keeps moisture in for the specified period, and cold-weather protection prevents freezing before strength develops. Side forms are usually stripped within a day or two, while soffits stay until the concrete carries its own load, per the form design.
Worked example
Concrete for a footing 600 mm wide, 300 mm deep and 12 m long: volume = 0.6 × 0.3 × 12 = 2.16 m³. Allowing 5 % for waste and uneven subgrade gives 2.27 m³, so order 2.3 m³. If the footing were 350 mm deep instead, volume would rise to 2.52 m³ - a 50 mm dimension error matters over a long run.
Traps
Stripping soffits by the clock instead of by strength; pouring without release agent; forgetting the keyway so the next wall has no shear connection; and checking plumb with the ties still slack.