Highways & Bridges
Success Stories
Perot Museum
St. Croix Crossing Bridge

St. Croix Crossing Bridge - Success Story

The St. Croix Crossing Bridge spans the St. Croix River connecting the State of Minnesota to the State of Wisconsin in the United States of America. The present bridge in Stillwater, Minnesota is a historic lift bridge built in 1931. This bridge is prone to flooding in the spring, large traffic back-ups when lifted, and maintenance closures due to its age. The new bridge will span bluff to bluff at a height of 140’ above the water. The entire bridge contains approximately 160,000 cubic yards of concrete. Approximately 100,000 yards will be cast in place and approximately 60,000 yards will be precast bridge girders. This success story is written with respect to the precast bridge girders (bid as a separate package from the rest of the bridge) and awarded to Aggregate Industries.
This new bridge will avoid flooding issues, large traffic back-ups when lifted, and maintenance closures due to its age. The new bridge will span bluff to bluff at a height of 140’ above the water
This new bridge will avoid flooding issues, large traffic back-ups when lifted, and maintenance closures due to its age. The new bridge will span bluff to bluff at a height of 140’ above the water

The location selected for the casting of the bridge girders was of major importance. The real estate necessary for casting/storage of the girders was significant (20 acres for a casting building and storage area). In addition, the transportation method selected (road vs. river) to transport the girders to the job site was a significant cost element of the Lunda/Ames Joint Venture (the customer) bid to the State of Minnesota (Owner). Aggregate Industries Nelson Sand & Gravel Plant (located in Minnesota on Grey Cloud Island directly on the backwaters of the Mississippi River) met the criteria for all the objectives quite well.
Pillars to St Croix Crossing
The St. Croix Crossing Bridge spans the St. Croix River connecting the State of Minnesota to the State of Wisconsin

Objectives
At the surface, team objectives were simple: Secure St. Croix Crossing bridge girders along with related products and services; however, goals beneath the surface critical to project success were; identifying Lunda/Ames Joint Venture (customer) needs to deliver value. The team understood that executing on the St. Croix Crossing project would result in a boost in employee morale while enhancing company image and reputation, and ultimately help expand into new markets.

Project Timelines
The 650 precast bridge girders (57,000 yards) must be cast and erected on the bridge no later than Mississippi River closing (November 2015). A myriad steps (permitting, casting building and storage area, design/preparation and erection, ready mix plant procurement and erection, and critical material testing) needed to be complete prior to casting one bridge girder! And then the real work would begin as each girder must be cast, tested, stripped, meet various strength requirements, transported and put in place (20 miles northeast via barge) all within the MnDOT (Minnesota Department of Transportation) contract requirements.

Quality Characteristics and Related Strength Schedule
Quality of material constituents is critical to ensure each of the 650 bridge girders meets the quoted 9000 PSI (pounds per square inch) strength as scheduled. Strength schedule is as follows:

START

0 HOURS - 0 PSI - Pour Concrete into Form

16 HOURS – 3000 PSI - Strip Form

40 HOURS – 4000 PSI - Post Tension and Match Cast

56 DAYS - 8000 PSI - Curing Complete/Outside Storage Approved/Transport and Placement Approved

90 DAYS - 9000 PSI

COMPLETE


Key value attributes to success

Land with River Access - The State of Minnesota’s plan for the St. Croix Crossing provides for lifting 650 large pre-cast segments (bridge girders) from barges to heights of 140 feet. At 180 tons, these segments would be very difficult and expensive to transport via truck and then trans-loaded to barges at the job site. Therefore, a real value for the customer would be to have the ability to cast these segments, place them on barges and use the river system for transportation to the job site. The Aggregate Industries Nelson Sand & Gravel Plant is located on Grey Cloud Island directly on the backwaters of the mighty Mississippi River. By providing a lease to the Lunda/Ames Joint Venture for twenty acres of land at Nelson, the contractor is able to cast, store, and load the segments onto barges without ever trucking them. By eliminating costly overweight trucking and additional handling of the girders, this site provides efficiencies for the contractor.

Dedicated Ready Mix Plant/Trucks and Workforce - The technical nature of the specified concrete needed to build these segments necessitates a consistent delivery methodology and dedicated workforce. Varying haul time and personnel changes are major contributors to inconsistent concrete. By hosting the contractor at Nelson, Aggregate Industries is able to dedicate a plant, trucks and workforce for the concrete production of these segments. These valued assets are a stones throw away from the concrete casting building allowing for ease of delivery. The dedicated batchman, drivers, loader operator and quality control personnel provide additional consistency to the concrete. The Lunda/Ames Joint Venture extracts value in having a dedicated plant and workforce at the job site.

Precast section in plant preparing for transportation.
Precast bridge sections in plant at various stages of construction.

Quality and Technical Services - The concrete for the pre-cast segments is very technical in nature. Early strength development, 3000 psi in 16 hours, and long term strength gain, 9000 psi in 90 days, are both required. A reliable mix that meets these requirements is a necessity. Aggregate Industries technical team, with the aid of Holcim, designed and tested a mix to consistently meet these requirements. In lieu of a third party engineer, Lunda/Ames captured value in Aggregate Industries technical expertise to provide this mix design. Beyond providing the mix design, the contractor is also responsible for plant testing of materials and strength testing of the concrete. Aggregate Industries traditional services include the plant testing of materials. Aggregate Industries and the Lunda/Ames Joint venture understood that all elements of testing were critical when producing this type of concrete.

Single Source - On extremely complicated projects like this one, reliable suppliers who can provide a variety of materials from nearby sources are rare and valuable. Holcim provides high quality products and timely delivery of cement and Grancem from a terminal located just five miles from the newly erected Nelson Ready Mix Plant. The high quality aggregates for the concrete are produced at the Nelson Aggregate Facility located on-site. In addition, large quantities of limestone base (needed for segment storage and a building foundation) were delivered from Aggregate Industries Larson Quarry (one mile away). Reliability of supply and ease of delivery enhance the value Holcim and Aggregate Industries provides.

Bridge Benefits for Society - The timely completion of this project is of great value to both the State and the contractor. The historic lift-bridge in downtown Stillwater, Minnesota has been a traffic bottleneck for both cars and boats for years. Moving the growing traffic to the new bridge, towering high above the St. Croix River, is of great benefit to motorists, boaters and the community at large. Timely completion of the bridge is of such importance to the community that the State researched the delays and offered a significant contract bonus for early completion. The Lunda/Ames Joint Venture developed their plan’s timeline around using the Nelson site, a very technical mix design, and river based delivery of the segments (which make early completion attainable).

Even when The St. Croix Crossing Project is complete, more than the structure will live on. The completion of this project embeds in our workforce the understanding that we offer much more than cement, concrete or aggregates. Embedded now are principles of “Customer Excellence” including, but not limited to, understanding our customers’ needs/values and ultimately delivering the that value. The St. Croix Crossing Project is an excellent example that demonstrates we can deliver value outside of our “traditional boundaries” of cement, concrete and aggregate and we are proud that this monument will improve the quality of lives for so many in our community.