403A Concrete Formwork 4

Question 1

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

Accepted Answer

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

Answer

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.

Question 2

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?

Accepted Answer

0.40

Answer

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.

Question 3

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

Accepted Answer

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

Answer

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.

Question 4

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

Accepted Answer

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

Answer

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.

Question 5

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

Accepted Answer

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

Answer

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.

Red Seal Carpenter 403A Practice Test

Red Seal Carpenter 403A Practice Test

403A Concrete Formwork 4