Durability
High strength precast concrete components are cast under controlled conditions
in the precaster’s plant. When precast concrete elements are
prestressed, concrete is cast around highly tensioned pretensioning strands
that run through the steel forms. After the concrete has cured, the pretensioning
force is released into the beam placing the concrete in compression.
Prestressed slabs and beams are virtually crack-free and highly resistant to
attack by chloride ions
Where cast-in-place composite topping is used over precast floor members,
wire mesh reinforcement should be incorporated in the topping. A high
strength concrete topping having a water cement ratio of 0.40 or less, 6% entrained
air and five days of curing under wet burlap will produce the best
results (see CSA S413).
A series of crack control joints should be tooled into the topping above all
joints in the precast members below. A V-shaped trowel will produce a 25 mm
deep by 12 mm wide joint. Later these joints are prepared by grinding with a
V-shaped abrasive wheel and filled with a polyurethane sealant.