said Kevin Gutknecht, director of

communications with Mn/DOT.

River environment

Controlling erosion and maintaining slopes to prevent debris and sediment from entering the river were issues the project team worked through extensively. The main bridge piers were located on the banks of the Mississippi River, not within the river, to minimize impacts to the river environment.

To prevent deck runoff from entering the Mississippi

River, a self-contained bridge drainage system directs runoff through pipes hidden inside the box girders and routes it to nearby treatment facilities.

Remnants of a coal gasification plant located where I-35W was first constructed in the 1960s required environmental cleanup.

“There was some cleanup done when that plant was abandoned and removed, but there were still contaminants in the ground,” Chiglo said. “So there was coal tar that we were finding; there was contaminated groundwater and soil that we had to work through.”

Innovative materials

The job also involved the first high profile use of a new concrete for a North American project — photocatalytic concrete — that removes atmospheric pollutants via photocatalytic (self-cleaning) reaction when sunlight hits the concrete surface.

“This concrete was used to construct two 30-foot-tall gateway sculptures, whose shape was inspired by the universal symbol for water, located at each bridge approach to mark the crossing of the Mississippi River,” said Linda Figg, president of FIGG.

green

FACTS

According to the American Coal Ash Association, concrete is a major consumer of industrial byproducts that otherwise would end up in landfills, including 15 million tons annually of fly ash.

An LED first

The new I-35W bridge represents the first installation of light-emitting diode (LED) roadway lighting on an interstate bridge in the U.S.

“As part of a collaboration, Mn/DOT is working with the U.S. Department of Energy (DOE) on this innovative technology that will have lower energy and lower maintenance costs,” said Linda Figg, president of FIGG.

According to a DOE report, LED lighting used on this project provided a uniform illumination and offered a 13 percent energy savings compared to traditional high- pressure sodium lamps in use elsewhere. Similar state- of-the-art LED lighting techniques also were used for the bridge’s aesthetic lighting.

“It’s going to be an application that can be used across the nation and, in doing that, it’s going to save an enormous amount of energy; and I think that does benefit the end user,” said Jon Chiglo, Mn/DOT’s project manager. “In the end, it’s friendly to the environment.”

More than1,800 recycled tiles were created by local students who participated in a program to introduce students to bridge design, construction basics and the importance of sustainable materials, Figg said. These tiles formed a mosaic on the project’s exterior. Contractors used silica fume and fly ash — byproducts from other industries — in the concrete mixtures. These products resulted in more corrosion-resistant, durable and sustainable concrete.

Concrete from the previous I-35W roadway was recycled into aggregate components and used in the new roadway. Native Kasota stone, stacked inside coated metal baskets, was used for the abutment retaining walls at the ends of the bridge.

The team built a precasting factory on site to produce bridge segments while minimizing energy use to move 200- ton components to the site.

The bridge today

Eighteen months later, the new I-35W bridge continues to receive attention for its sustainable features. “We’re very happy with the performance of the bridge and the elements associated with that bridge,” Chiglo said. “There’s a great deal of interest across the world and a large sense of pride in the area in what’s been accomplished and how it’s performing today.” g&c

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