St. Croix Crossing aerial view

St. Croix Crossing

Connecting Oak Park Heights, Minn. and St. Joseph, Wis.

St Croix Crossing logo

Casting and installation processes

Casting process

  • Crews plan to construct about one to two segments per day at each casting yard
  • Each segment is built in a form
    • The segments are cast in the order that they will be placed on the bridge – each segment is one-of-a-kind, like a puzzle piece
  • Construction workers set up the form and fill it with steel reinforcement bar, or rebar. This acts like a skeleton for the segment. They also place hollow plastic ducts inside the forms to make space for post-tensioned steel strands to be installed later
  • Then crews pour concrete inside the form over the rebar and ducts and wait for the concrete to cure. The concrete must meet a certain strength before crews can remove the form
  • Finally, workers transport the segment to a storage area in the casting yard where the concrete continues to age and strengthen
A view of the on-site casting yard near the Hwy 36/95 interchange.
Casting yard
A human-to-segment size comparison of the river bridge pre-cast concrete segments.
Pre-cast segment

Segment installation process

When an individual segment is ready to be installed, crews transport it to the bridge site in one of two ways:

  • By barge, from the Grey Cloud Island casting yard down the Mississippi River and up the St. Croix River to the river bridge
  • By truck, from the on-site casting yard to the approach/ramp bridges

Crews place the segments starting from a pier. This process is slightly different depending on where the segment is placed:

  • On the river, the pre-cast segments are connected to both ends of the pier table. Subsequent segments are installed in both directions moving outwards from the pier to form the 600-foot spans between each pier location
  • On land, the first segment is placed directly on top of the pier column and subsequent segments are installed in both directions moving outwards from the pier to form the spans between each pier location

Both on land and on water, segment lifters or cranes lift each segment into place. Crews coat the edges with epoxy and bring the segment into contact with the previously placed segment. They then:

  • String steel strands through the hollow plastic ducts,
  • Pull the strands tight—like a rubber band—using a hydraulic jack, to anchor the segment into place, and
  • Fill the inside of the ducts with grout (to provide protection against moisture)

Because these highly-stressed steel strands are interconnected, all of the segments in a single span are connected back to the pier, which creates the strongest bridge structure.

Back to bridge deck construction.