A four-year research partnership between the Iowa Department of Transportation (IDOT), Iowa State University (ISU), and Lafarge North America has lead to the opening of an innovative concrete bridge.
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 super-plasticizer, metallic fibers, and very little water. Because of the material's durability (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.
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 various tests, Lafarge Canada's Winnipeg Precast Division cast three 71-foot beams and shipped them to the site. The deck was poured in November 2005; the structure opened for traffic earlier this year.
Structures without rebar 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 Fairbanks Laboratory in McLean, Va., where UHPC research is ongoing.