Construction methods · Cast-in-place concrete decks

Cast-in-place post-tensioned box and slab decks

The deck types most cast-in-place methods produce: post-tensioned box girders for spans of 40-250 m and solid or voided slabs for short spans. Post-tensioning is what makes the span; the ducts, tendons, anchorages and grouting are the critical trade.

How bridges get built · Cast-in-place concrete decks · Cast-in-place post-tensioned box and slab decks

Also called: PSC box girder, post-tensioned box, voided slab, cast-in-place PT deck

How it is done

Form the section with internal void forms or boxes; place reinforcement, ducts on chairs to the profile, anchorages and vents.
Pour in a sequence that avoids cracking (bottom slab and webs, then top slab); cure.
Thread and stress tendons at 70-80 % of characteristic strength with calibrated jacks, measure elongation, grout the ducts within days, seal the anchorages.

Where it fits

All cast-in-place methods; box girders for spans above 40 m, slabs up to 25-30 m.

Where it does not

Poor grouting practice: voids in ducts are the dominant durability failure of PT bridges.

Plant, pace and money

PlantFormwork, PT jacks and grouting plant, concrete supply.

ProductivitySet by the erection method.

CostDeck USD 1,100-2,500 per m2 depending on the method.

Risks and controls

What goes wrong

Duct blockage, wrong tendon profile, grout voids, anchorage failure at stressing, thermal cracking of thick webs.

Quality assurance

Duct profile survey before pouring, stressing records (force and elongation), grout tests and vacuum grouting where required, anchorage sealing.

Examples

The game's psc_box_cip and psc_box_cip_fcm deck types.