Construction methods · Precast concrete decks

Deck slabs on girders: cast-in-place, precast panels and stay-in-place forms

The slab that turns a row of girders into a bridge. Cast in place on removable or stay-in-place forms, or laid as partial-depth precast panels with a topping, or as full-depth precast panels post-tensioned together for speed. The choice decides the site time after the girders are up.

How bridges get built · Precast concrete decks · Deck slabs on girders: cast-in-place, precast panels and stay-in-place forms

Also called: composite deck slab, precast deck panels, stay-in-place formwork, full-depth precast deck

Deck slabs on girders: cast-in-place, precast panels and stay-in-place forms — concept diagram — Concept diagram (TheBridgeEng)

How it is done

Cast-in-place: set forms between girders (timber, steel stay-in-place or precast panels), fix two mats of reinforcement, pour with a finishing machine, cure for seven days wet.
Partial-depth panels: precast 80-100 mm panels span between girders as forms and bottom reinforcement; top mat and topping cast on site.
Full-depth panels: precast full-thickness panels with shear pockets set on the girders, longitudinal PT, pockets grouted; deck done in days.

Where it fits

All girder bridges; full-depth panels for accelerated construction and deck replacement.

Where it does not

Cast-in-place in freezing or very hot weather without protection; full-depth panels on girders with uncontrolled camber.

Plant, pace and money

PlantFormwork, finishing machine, curing, cranes for panels.

ProductivityCast-in-place 2-3 weeks per span; full-depth panels a few days.

CostCast-in-place USD 150-250 per m2; full-depth precast USD 300-450 per m2.

Risks and controls

What goes wrong

Early cracking from shrinkage and restraint, low cover over the top mat, panel seating gaps.

Quality assurance

Cover surveys, curing records, panel haunch grouting, crack mapping at 28 days.

Examples

Full-depth panels are standard for US deck replacements and Korean ABC.