Concrete Formwork Flashcards

What is the function of a sleeper (or mud sill) under formwork shoring?

Answer: All of the above — distribution, leveling, and preventing sinking

Sleepers serve all three functions: they spread the concentrated point load from shoring posts over a larger bearing area, provide a level surface to plumb shores from, and prevent individual post bases from punching into soft or wet ground.

What is the maximum water-cement ratio (W/C) permitted for concrete exposed to freeze-thaw cycles and deicing salts per CSA A23.1 Exposure Class C-XL?

Answer: 0.40

CSA A23.1 Class C-XL (severe exposure to chlorides and freeze-thaw) requires a maximum W/C ratio of 0.40. Lower W/C ratios produce denser, less permeable concrete that resists chloride penetration and freeze-thaw damage.

What is the purpose of air entrainment in concrete exposed to Canadian winters?

Answer: Microscopic air bubbles provide space for water expansion during freezing, preventing internal cracking

Water expands approximately 9% when it freezes. In non-air-entrained concrete, this expansion causes internal tensile stresses that crack the paste. Microscopic entrained air bubbles (5-8% by volume) provide relief spaces for the expanding water, preventing surface scaling and internal damage.

What is the purpose of re-shoring after a concrete slab is poured on upper floors of a multi-storey building?

Answer: To transfer the load of the fresh upper-floor slab back through lower floors to the foundation until the concrete gains strength

Young concrete gains strength over 28 days. Re-shoring extends the load path from fresh upper-floor pours through multiple lower floors to the foundation, preventing any single slab from being overloaded before it reaches adequate strength.

What is a bulkhead (or end stop) in concrete formwork?

Answer: A temporary form closure that defines the end of a concrete pour at a construction joint

A bulkhead is a temporary form panel placed perpendicular to the formwork run to stop the concrete pour at a planned construction joint. After stripping, the bulkhead face defines the joint surface that must be prepared for the next pour.

What PPE is mandatory when working with concrete formwork on a construction site in Canada?

Answer: Hard hat, safety boots (CSA Grade 1), safety glasses, and appropriate gloves (concrete is caustic)

Provincial OH&S regulations require hard hats, CSA Grade 1 (or higher) safety footwear, and safety glasses for all construction site workers. Gloves are essential when handling concrete because fresh concrete is highly alkaline (pH ~12) and causes chemical burns to skin on prolonged contact.