FEATURE MATERIALS
Ultra-high performance concrete gains traction with DOTs
As transportation agencies look for innova- tive solutions to facilitate the rapid con- struction of highway bridges, they are turning to ultra-high performance concrete (UHPC) for superior strength and durability. "UHPC has advanced the state of the art
for construction of prefabricated bridge el- ements and systems," says Benjamin Gray- beal, Ph.D., P.E., Structural Concrete Research Program manager at the Federal Highway Administration's Turner-Fairbank Highway Research Center, McLean, Va. Au- thor of the agency's 2011 report, "Ultra-
High Performance Concrete" (FHWA-HRT- 11-038), he oversaw its latest "Tech Note, Construction of Field-Cast Ultra-High Per- formance Concrete Connections" (Pub. No. FHWA-HRT-12-038). The latter highlights how UHPC enables significant simplifica- tions in the design of field-cast connec- tions linking prefabricated bridge components. New UHPC connection details eliminate the conflict points between the reinforcing bars and other discrete con- nectors, allowing for easy field assembly. As of early 2012, field-cast UHPC connec-
PHOTOS: Courtesy of Federal Highway Administration; Benjamin Graybeal
tions between prefabricated bridge compo- nents had been specified for 18 bridges in the U.S. and Canada. They use a range of de- tails to connect different precast concrete modular bridge components, including adja- cent box beams, full-depth precast deck panels, and deck-bulb-tee girders. Among the projects are the Route 31 Bridge over the Canandaigua Outlet in Lyons, N.Y., and the U.S. Route 6 Bridge over Keg Creek in Pot- tawattamie County, Iowa. Both bridges use field-cast UHPC in longitudinal connections for pre-decked superstructure elements.
The Route 23 Bridge in Oneonta, N.Y. includes precast concrete deck panels and field-cast UHPC connections. Formwork required to contain UHPC when it is placed into a connection requires tighter control than the formwork commonly used in field-cast concrete applications: UHPC exhibits higher pressure than conventional concrete mixes and can easily leak between formwork that is not appropriately sealed.
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