U.S. 6 Keg Creek


In early 2010, Iowa DOT was asked by the Transportation Research Board (TRB) Strategic Highway Research Program 2 (SHRP2) to participate in a demonstration project involving accelerated bridge construction (ABC). The scope of the SHRP2 project R04, Innovative Designs for Rapid Renewal, is to develop standardized ABC systems for nationwide use. The Iowa DOT, a national leader in ultra-high performance concrete (UHPC) bridge applications, is partnering with the consulting group HNTB Corp. who is currently leading a four-year national study on ABC for the SHRP2. HNTB and Iowa State University, along with other industry partners, are now developing standards and specifications that will be used for future ABC projects across the country.

artist rendering of U.S. 6 bridge over Keg Creek As part of the study, the Iowa DOT agreed to provide a bridge replacement site to demonstrate the viability of one of the ABC concepts developed. A bridge on U.S. 6 over Keg Creek was chosen as a test site, a three-span 210’ x 47’ steel/precast modular structure with precast bridge approaches. Under this ABC concept, the U.S. 6 bridge will be constructed with minimal impact on traffic, such that the road will be closed for only two weeks. With traditional construction methods, this project on U.S. 6 would normally require the partial or complete closure of the road for several months, resulting in substantial traffic disruption.

The bid price for the Pottawattamie County demonstration bridge project, including additional grading and drainage improvements, is $2.6 million, which is approximately 30 percent more than a similar three-span conventional bridge. To help cover the additional cost of using the new technology, the Iowa DOT received a $400,000 (or up to 20 percent of the total project cost) Highways for Life (HfL) grant and another $250,000 from the SHRP2 program.

One of the project’s goals was to choose a bridge replacement project that would be innovative and repeatable. A three-span bridge was chosen because that particular configuration is common throughout Iowa and other states. Bridge engineers wanted to ensure that what was learned from this project would be applicable to other bridges in the future.

Ahmad Abu-Hawash, of the Office of Bridges and Structures, said that in addition to the prefabricated nature of the entire structure, several other elements of this project stand out. He said, “Typically, when we use precast deck panels in bridge construction we specify a concrete overlay to protect the joints between panels. This overlay could add weeks to the construction duration, therefore, it became obvious that a more durable joint is needed in lieu of the overlay. Given Iowa’s past experience with UHPC, the design team recommended UHPC be used in the joints. The primary advantages of this joint material are low permeability and high strength meaning an impenetrable and stronger joint.”  

Another design element that differs from some conventional bridge construction is the use of preassembled rolled steel girder units. Abu-Hawash said, “The superstructure used in this bridge consisted of rolled steel beams with concrete deck modules prefabricated off-site. The exterior modules also included traffic railing. I believe this is the first time rolled steel girder/concrete deck modules will be assembled off-site and jointed on-site with UHPC.”

Because this is a demonstration project, a webcam will be used to document construction. Abu-Hawash explained, “As we have done on other innovative projects, construction site Web cameras will document project activities and provide uninterrupted access to any interested parties via the Internet. In cooperation with Iowa DOT, the National Academy of Sciences plans on producing a documentary video with national distribution to promote the innovations being demonstrated on this project.”

Aside from the webcams, Abu-Hawash and others involved in the project will present the findings at a construction workshop for other state DOTs, FHWA and other interested parties. 

Abu-Hawash sees future uses for complete precast bridge replacements. “With our aging infrastructure and damage from natural disasters such as floods, states sometimes need a way to replace bridges quickly. The experience gained from this project will give us the knowledge to utilize these technologies when needed and where appropriate.

The U.S. 6 bridge project was one of 15 awarded grants in the 2010, $20 million round of HfL funding. The HfL program seeks to get states, engineers and contractors to adopt proven innovations and technologies leading to:

  • Improved safety during and after construction.
  • Reduced congestion caused by construction.
  • Better quality of the highway infrastructure.

These funds are to be used for incentives to state DOTs to demonstrate innovative technologies and practices that can be used to build projects more safely and quickly, will result in longer-lasting highways, and will achieve a higher level of user satisfaction. Information from these projects will be shared with the whole transportation community to accelerate changes that will improve the safety and performance of our highways, and reduce the impact of construction and maintenance on highway users. These projects also have performance goals as a part of their HfL application.

In 2007, the Iowa DOT completed the 24th Street bridge project over Interstate 80/29 in the Council Bluffs area with the assistance of HfL funding. The innovations shown by Iowa DOT and their project partners have been nationally recognized and, thus, Iowa is one of only seven states that have received multiple HfL grants in the highly competitive process.

To view the SHRP2 report, go to

View the NCPA Workshop presentation


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