Credit: Jenni Spinner

The Mars Hill Bridge in Wapello County, Iowa, is the first North American highway bridge built using Ductal, a high-performance concrete mix from Lafarge North America. Photo: Jenni Spinner

A four-year research partnership between the Iowa DOT (IDOT), Iowa State University (ISU), and Lafarge North America has lead to the opening of an innovative concrete bridge in the Hawkeye State.

The Mars Hill Bridge in Wapello County, Iowa, is the first highway bridge in North America built with Ductal ultra-high performance concrete (UHPC), which features superplasticizer, metallic fibers, and very little water. Because of the material's durability (it boasts a compressive strength as high as 30,000 psi and flexural strength to 6000 psi), crews were able to build the 113-foot span with no rebar.

ISU and IDOT approached the county in 2002 to partner on a UHPC demonstration project, and the county was awarded a $300,000 grant for the project through the TEA-21 Innovative Bridge Construction Program. After months of research, experimenting with mix design, and performing various tests, three 71-foot beams were cast at Lafarge Canada's Winnipeg Precast Division, shipped to the site, and the deck was poured in November 2005; the structure opened for traffic earlier this year.

According to members of the team involved in the bridge's construction, the omission of rebar leads to structures that weigh less, last longer, and—although they may cost more at the outset—lead to savings in the long run thanks to reduced maintenance and extended bridge life.

“We see this as a means to create bridges that last longer,” said Joey Hartman, highway research engineer with the Federal Highway Administration's Turner Fair-banks Laboratory in McLean, Va., where UHPC research is ongoing.

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