Minnesota & Wisconsin
The St. Croix Crossing 4 lane bridge project connects Oak Park Heights, MN and St. Joseph, WI. The extradosed bridge system, a hybrid combining concrete box girder and cable-stayed bridge designs, is only the second extradosed bridge constructed in the United States.
This major project will reduce severe traffic congestion by diverting traffic from the historical Stillwater Lift Bridge constructed in 1931 to a four-lane bridge that will connect expressways on both sides of the St. Croix River.
At over 5000 feet in length, the bridge consists of approx. 60,000 cubic yards of concrete for the 650 precast main bridge girder segments. In total there are approximately 1000 precast concrete segments. This case study is written for the 650 precast segments (average size 48’ wide x 18’ deep x 10’ long; 180 tons) for the main bridge and awarded to Aggregate Industries. Sika® admixtures were used for these bridge girders. The precast girders were shipped 33 miles by barge to the project site.
- High early strength requirements to strip forms and stress tendons
- Adequate workability to flow around the congested reinforcing steel and throughout the uniquely shaped form work while remaining cohesive.
- Special considerations for cold weather and hot weather placement as the segments were cast continuously over an approximate 2 year period.
Sika® and Aggregate Industries decided on a mix design utilizing, Sika® ViscoCrete®-2100 (High Range Water Reducer), SikaTard® 440 (Hydration Stabilizer) and Sika® Air-260 (Air Entrainer) to meet the challenging mix design requirements.
|Specification Requirement||Average Results|
|Slump||4 - 9"||8.5"|
|Air Content||5 - 8'||6.5%|
|Early Age Strength||4,000 psi||6,000 psi|
|28 Days Strength||9,000 psi||9,600 psi|