Construction methods · Precast concrete decks

Segment casting: short-line and long-line match casting

Precast segmental bridges are only as good as the yard. Match casting pours each segment against the previous one so the joints fit perfectly; short-line does it in a fixed cell with the previous segment moved into position, long-line casts a whole cantilever on a long bed. Geometry control in the yard decides the geometry of the bridge.

How bridges get built · Precast concrete decks · Segment casting: short-line and long-line match casting

Also called: match casting, short-line casting, long-line casting, casting yard

How it is done

Short-line: a fixed mould with a bulkhead; the previous segment is placed as the match-cast face and adjusted to the theoretical geometry (with corrections) before pouring the next; one segment per cell per day.
Long-line: a bed the length of a cantilever with fixed soffit; segments are cast in sequence against each other on the bed; simple geometry, large yard.
Survey every segment (six points per face) and feed the casting curve with the measured errors; store with care, deliver in order.

Where it fits

All precast segmental decks; short-line for curves and variable geometry, long-line for straight repetitive cantilevers.

Where it does not

Yards without a geometry control engineer; storage stacking that cracks segments.

Plant, pace and money

PlantCasting cells or bed, rebar jigs, concrete plant, steam curing, gantry cranes, survey.

ProductivityOne segment per cell per day; 6-12 cells for a large viaduct.

CostYard USD 5-20 million; segments USD 600-900 per m3.

Risks and controls

What goes wrong

Geometry error accumulating and appearing at closure, match-cast face damage, shear key breakage.

Quality assurance

Casting curve reports per segment, mould checks, concrete strength at stripping.

Examples

Every segmental project in the game's precast methods.