ASPIRE is a quarterly magazine published by PCI in cooperation with the associations of the National Concrete Bridge Council. The editorial content focuses on the latest technology and key issues in the Concrete Bridge Industry.
Issue link: http://www.aspiremagazinebyengineers.com/i/335723
FHWA Ultra-High-Performance Concrete Connections A robust solution for prefabricated bridge element system construction by Benjamin A. Graybeal, Federal Highway Administration The use of prefabricated components in the construction of highway infrastructure provides many advantages. However, it also frequently necessitates the use of field-deployed connection details. These details must facilitate component installation while simultaneously providing a robust structural system that meets or exceeds the performance that can be obtained through conventional construction processes. Demand for the use of prefabricated components is growing, as is the need for connection systems that provide enhanced performance. Advances in the science of concrete materials have led to the development of a new class of cementitious composites. Ultra-high-performance concrete (UHPC) exhibits mechanical and durability properties that make it an ideal candidate for use in developing new solutions to pressing concerns about highway infrastructure deterioration, repair, and replacement.1,2 Connections between prefabricated bridge components have proven to be a promising application for field-cast UHPC.3 These connections can be simpler to construct and can provide more robust long-term performance than conventional connection designs. UHPC is a cementitious composite material composed of an optimized gradation of granular constituents, a water-to-cementitious materials ratio less than 0.25, and a high percentage of discontinuous fiber reinforcement. The mechanical properties of UHPC include compressive strength greater than 21.7 ksi and sustained post-cracking tensile strength greater than 0.72 ksi. UHPC has a discontinuous pore structure that reduces liquid ingress, significantly enhancing durability compared to conventional concrete. Availability of UHPC UHPC is composed of a variety of constituents that are combined to create the composite. UHPC may be locally produced according to project specifications or may be obtained from a product supplier.4 Because UHPC, like conventional concrete, is defined in terms of the properties of the composite material, it must be recognized that multiple formulations may produce similar composite systems. Cementitious Composite The cementitious composite portion of a UHPC is frequently composed of portland cement, silica fume, fine aggregates, chemical admixtures, and water. UHPC formulations may also include small coarse aggregates and supplementary cementitious materials. The sophistication of the UHPC cementitious composite as compared to conventional concrete has led to the development of preblended UHPCs. This production and distribution model is similar to that commonly used for many of the proprietary grouts and patching materials frequently deployed in the construction of the public infrastructure. Steel Fiber Reinforcement The exceptional mechanical properties of UHPC can be largely attributed to the fiber reinforcement contained in the concrete. These properties cannot be achieved without inclusion (continued next page)