FEATURE MATERIALS
mixing and placing, warmer temperatures are better for rapid setting. Setting can be accel- erated by supplying supplemental heat to the UHPC and surrounding prefabricated elements. Heat can be supplied externally (e.g., ground heating mats) or internally (e.g., resistance heating wires), but forced air heat should not be applied to exposed UHPC surfaces.
TESTING
While established testing procedures for conventional concrete are generally appli- cable to UHPC, procedures may need to be modified in some instances to appropri- ately capture the UHPC behavior. Modified procedures for flow testing and compres- sion testing, for example, are discussed in "Construction of Field-Cast UHPC." Two full-scale test specimens were built
for a study referenced in the Tech Note. One used conventional concrete with standard composite connection details, while the other used UHPC and novel connection de- tails. Each specimen simulated both a steel girder connection and concrete girder con- nection to precast concrete deck panels. The specimens were subjected to both cyclic loads and static loading. The UHPC connec- tions withstood loads greater than those re- quired by the American Association of State Highway and Transportation Officials Load and Resistance Factor Design Bridge Design Specifications and surpassed the perform- ance of the conventional test specimen. To download
the Tech Note, visit
www.fhwa.dot.gov/publications/research/in frastructure/structures/bridge/12038/index .cfm. Further information on a specific type of UHPC connection can be found in FHWA's new Tech Brief, "Ultra-High Performance Concrete Composite Connections for Precast Concrete Bridge Decks" (Pub. No. FHWA- HRT-12-042), which can be downloaded from www.fhwa.dot.gov/publications/re- search/infrastructure/structures/hpc/12042 /. Additional information on UHPC can be obtained from FHWA's Ben Graybeal, 202/493-3122, benjamin.graybeal@dot.gov.
Well suited to link precast bridge girders and precast concrete bridge decks, UHPC connections are tested at FHWA's Turner-Fairbank Highway Research Center in McLean, Va.
42 | SEPTEMBER 2012
Article adapted from FHWA Focus newsletter reports, "Ultra-High Performance Concrete Connections for Bridges: Superior Strength and Durability," June 2012; and "Ultra-High Performance Concrete: New Solutions for Today's Highway Infrastructure" September 2011. "Mixing and Placing" sidebar adapted from FHWA Tech Note, Ultra-High Perform- ance Concrete Composite Connections for Pre- cast Concrete Bridge Decks (Pub. No. FHWA-HRT-12-042).
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