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

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

Plan the yard from the erection rate: number of cells or beds, cage jig area, curing, storage on three-point supports and haul routes, keeping production ahead of erection.
Short-line: cast each segment in a fixed mould between a fixed bulkhead and the previous segment, which is moved on an adjustable cart to the corrected position for the next segment's geometry.
Long-line: cast the segments in sequence on a continuous soffit bed built to the cantilever profile including camber, with the side forms moving along the bed.
Place the prefabricated cage with ducts, shear keys, blisters and inserts; pour, cure (often with heat) and strip the next morning.
Survey both segments before and after each pour on six control points per segment (four level bolts and two centreline points) and feed the as-cast errors into the next set-up.
Separate the match-cast pair with its bond breaker, move the old segment to storage, and inspect, repair and record it.
Deliver in erection order with the casting records, so erection survey can be compared with the casting curve.

Key numbers

Productionone segment per short-line cell per day
Geometry controlsix survey points per segment
Yard size6–12 short-line cells for a large viaduct
Segment length 2.5–4 m; weight typically 30–150 t
Costyard USD 5–20 million; segments USD 600–900 per m3

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.

Choosing it

Choose short-line casting for curved and variable geometry and a compact yard; it depends on rigorous geometry control at every segment.
Choose long-line casting for straight, repetitive cantilevers where a long bed fits the site; geometry is simpler but the yard is large.
Size the number of cells from the erection rate: an idle gantry costs more than an extra cell.

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.

Origins

Match casting was introduced by Jean Muller and Campenon Bernard on the Choisy-le-Roi bridge in the early 1960s; short-line casting with computed geometry correction became the norm for curved viaducts as computing made the corrections routine.

Examples

Every segmental project in the game's precast methods.

Case studies

Choisy-le-Roi Bridge, SeineFrance · early 1960sThe first match-cast segments, the technique every precast segmental yard still uses.

Linn Cove Viaduct, North CarolinaUSA · 1983153 segments with no two alike and only one straight, cast with geometry controlled to 0.001 ft (0.3 mm); no segment was rejected.