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Cemstone Part Of Team To Rebuild 35W Bridge

Project Details:

Minnesota was shocked by the steel truss I-35W bridge collapse on August 1 in 2007. The replacement structure requires stringent performance specs for the new concrete structure. Cemstone, with 19 high-performance concrete bridge structures spanning the Mississippi River in the Twin Cities, worked with the design team to ensure that the bridge will perform at a level higher than specified.

Considered the highest profile project in the company’s 80-plus year history, Cemstone President Thor Becken said, “Our focus is to provide the highest possible quality product for MnDOT and the State of Minnesota.”

The white concrete bridge follows the primary design theme of "Arches, Water, Reflection," and features lighting and landscaping that will paint a modern archway over the Mississippi and respect the area's surroundings, history and nearby architecture.

The Challenges 

While designed to have a service life of 100 Minnesota winters, a major challenge of the bridge is the very fast-track schedule. Harsh winter climates and extreme weather situations are additional challenges.

The Cemstone Engineering Services team is led by Dr. Kevin MacDonald, P.E., who is responsible for product development and technology transfer.  He is a Licensed Professional Engineer in Minnesota and Ontario, Canada, and is a Fellow of the American Concrete Institute.

The Solution

Cemstone’s high-performance concrete provides superior durability and contributes to the multiple levels of structural redundancy. In addition, concrete has lower maintenance costs than other materials, which will add up over the bridge’s expected lifespan.

To exceed the project’s performance specifications, four primary concrete mixes were created by Cemstone. In the superstructure, resistance to scaling, abrasion and chloride ion penetration is critical. The superstructure mix is a blend of cement, fly ash and silica fume, with cement in the 60% range of the total cementitious faction.
 
A second mix was optimized for the below-grade foundation elements, consisting of drilled shafts, primarily mass concrete elements seven to eight feet in diameter.

A third mix addressed the sub-structure, consisting of massive elements, footings and pier stems of varying dimensions.  While the heat-of-hydration was significant, geometries made it very difficult to insert cooling pipes. Instead of being air-entrained, the mixtures used in the below grade structures are self-consolidating concrete. Cement represents less than 50% of the total cementitious material.
 
A fourth mixture, with cement at approximately 15% of the total cementitious material, was utilized for very low heat-of-hydration mixtures. These mixtures have an adiabatic heat rise of only about 50oF.

These concrete mixes are being delivered to the bridge site from Cemstone’s north Minneapolis plant, located at 65 26th Avenue North, less than one mile away.

To assure strict quality control, representatives from MnDOT, Flatiron, Cemstone and an independent testing company all check every load of concrete before it is placed.

Team Approach

Cemstone’s contributions were a part of an overall team effort with FIGG Engineering, Flatiron-Manson and the Minnesota DOT. The bridge is being built using the design-build process. It is a type of project delivery process in which teams propose design and construction approaches that will operate simultaneously, reducing the project delivery time by overlapping the design and construction phases. This streamlined design and construction process accelerates the schedule by improving communication between designers and construction contractors throughout the process.

Courtesy of FIGG, designer of the bridge; photo by Tim Davis