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The photograph shows an elevation of the bridge with a truck on the center span.

                    The center span of this bridge in Buchanan County utilized UHPC.

Ultra-High Performance Concrete in Iowa
Dean Bierwagen and Ahmad Abu-Hawash, Iowa Department of Transportation; Brian Moore, Wapello County, Iowa; and Brian Keierleber, Buchanan County, Iowa
With funding support from the Federal Highway Administration's (FHWA) Innovative Bridge Research and Deployment (IBRD) program and the Iowa Highway Research Board (IHRB), Iowa has been developing a base of design and construction experience with ultra-high performance concrete (UHPC). With the funding provided, two bridge projects have been completed using the UHPC material. The first was a single-span, 110-ft (33.5-m) long, prestressed I-girder bridge in Wapello County with the girders cast using UHPC. The second was a three-span bridge in Buchanan County with the center span cast with UHPC using the pi-girder cross section developed by the FHWA and the Massachusetts Institute of Technology. In a continuation of this work and with funding from the FHWA Highways for Life program, the Iowa Department of Transportation (Iowa DOT) and Wapello County are working on a third bridge project where a precast deck will use UHPC in a waffle configuration. This article gives an overview of the work that has been done by Iowa with UHPC.

Background
Developed in France during the 1990s, UHPC has seen limited use in North America. UHPC consists of fine sand, cement, silica fume, and quartz flour in a dense, low water-cementitious materials ratio (0.15 to 0.19) mix. Compressive strengths of 18,000 to 30,000 psi (124 to 207 MPa) can be achieved, depending on the mixing and curing process. The material has a low permeability and high durability. To improve ductility, steel or polyvinyl alcohol (PVA) fibers (approximately 2% by volume) are added, replacing the mild steel reinforcement. For these three projects, the patented mix Ductal® marketed by Lafarge North America was used with steel fibers.

Wapello County Bridge
Iowa was first introduced to UHPC with a bridge project in Wapello County, which was completed in 2006. The UHPC mix was used in the fabrication of four modified Iowa bulb-tee beams. Beam capacity was verified by flexure and shear tests on a 71-ft (21.6-m) long prestressed bulb-tee beam that was tested by the Bridge Engineering Center at Iowa State University. The remaining three 110-ft (33.5-m) long, prestressed concrete bulb-tee beams were then used in a single span, integral abutment bridge replacement project known as the Mars Hill Bridge, south of Ottumwa, Iowa.

Buchanan County Bridge
Buchanan County and the Iowa DOT were given the opportunity to build upon the experience of the first project with a second project in 2008. The project made use of the optimized pi-shape girder that was developed by the FHWA. Five pi-girders were cast at a Lafarge plant in Winnipeg, Manitoba, Canada. Two 25-ft (7.6-m) long beams were tested at the FHWA Turner-Fairbank Highway Research Center and three 51-ft (15.5-m) long beams were used for the center span of Jakway Park Bridge in Buchanan County.

The replacement bridge project that used the pi-girders was located on a county road (136th Street) over the east branch of Buffalo Creek in northeast Buchanan County, Iowa. The bridge is 25 ft (7.6 m) wide by 115 ft 4 in. (35.2 m) long with a center span of 52 ft 0 in. (15.9 m) from center to center of the pier caps. The 50-ft 0-in. (15.2-m) simple span pi-girder is supported on plain neoprene bearing seats with the beam ends encased with cast-in-place concrete diaphragms. End spans are cast-in-place reinforced concrete slabs with integral abutments supported on steel piles. The pier caps are supported on steel piles encased in concrete. The use of the pi-girders provided a complete superstructure system and eliminated the need for an independent deck or wearing surface. Load testing of the pi-girder bridge was conducted by the Bridge Engineering Center at Iowa State University.

Future Work
The work with UHPC is continuing with a third bridge project now under devolvement with Coreslab of Omaha, Wapello County, and the Iowa DOT. This project will use the UHPC mix in a precast deck on a single-span prestressed concrete beam bridge. To optimize the material, the deck panels will be cast using a waffle shape. The current schedule is to cast panels for testing during the fall of 2009. Production panels will then be cast for construction in the summer of 2010.

By using UHPC in bulb-tee beams, the optimized pi-girder, and waffle deck, the project team is expanding the knowledge base and facilitating the wider use of advanced cementitious materials to solve specific problems in the highway transportation system.

More Information
More information about the Iowa projects and UHPC is available in the following documents or contact the lead author at dean.bierwagen@dot.iowa.gov.

Degen, B., "Shear Design and Behavior of Ultra-High Performance Concrete," Masters Thesis, Iowa State University, 2006, 147 pp.

Graybeal, B. A. and Hartmann J. L., "Strength and Durability of Ultra-High Performance Concrete," Proceedings PCI National Concrete Bridge Conference, Orlando, FL, 2003, 20 pp.

Graybeal, B. A, "Structural Behavior of Ultra-High Performance Concrete Prestressed I-Girders," Federal Highway Administration, Report No. FHWA-HRT-06-115, 2006, 104 pp.

Graybeal, B. A., "Material Property Characterization of Ultra-High Performance Concrete," Federal Highway Administration Report No. FHWA-HRT-06-103, 2006, 186 pp.

Wipf, T., Phares, B., Sritharan, S., Degen, B., and Giesmann, M., “Design and Evaluation of a Single-Span Bridge Using Ultra-High Performance Concrete,” Final Report to the Iowa Department of Transportation, 2008.

HPC Bridge Views, Issue 57, Sept/Oct 2009