Member Company: Skyway Cement Company
Selected Categories: Innovative Application
The St. Croix River Crossing is a $646 million project involving two states, multiple communities, many individuals and decades of debate. Its innovative extra dosed design (which combines the elements of a concrete box girder bridge with a cable-stay bridge) makes the redundant structure extremely stable and creates a bridge that is only the second of its kind in the U.S. The bridge contains 5 sets of piers in the river, 7 sets of piers on land in MN and 1 set on land in WI. The length of the bridge span is 5,074 feet (nearly 1 mile) with a width of 100 ft. There were 988 concrete segments used. The total concrete for the project was 140,000 cubic yards.
Slag was a must for this project. Cemstone created 19 mix design which required extensive testing including compressive strength, hardened air, freeze/thaw durability, surface scaling, shrinkage, rapid chloride permeability, alkali silica reactivity, cement diffusion, modulus of elasticity and creep. There were over 200 mass concrete placements on the project (most mass concrete included 65-70% slag cement) all requiring thermal models and temperature monitoring. Much of the concrete had to placed out in the river. The process was to deliver concrete to the shore, pump the concrete into 2 ready mix trucks which were fixed on a barge, barged out to the element, then pump the concrete into the element.
MnDOT required that the mixes used for placement over the water had a 180 minute range. This meant that Cemstone had to prove that the concrete could be batched with the slump and air content within the tolerance of the specification, then the concrete had to maintain a slump and air content with the allowable range for the entire 180 minutes. The concrete was tested every 30 minutes during the 180 minute duration for trial batch compliance.
Project Team: (Owner: Minnesota Department of Transportation, Paul Kivisto, Construction Engineer) (Designer and Engineer of Record: HDR and Buckland & Taylor (COWI)) (Contractor: Lunda/Ames Joint Venture, Dale Even, Project Manager) (Concrete: Cemstone Products Company, Lars Anderson, Engineering Service Manager) (Slag Cement: Skyway Cement Company, Sales Representative, Dave Imse)