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/306855
46 | ASPIRE , Spring 2010 F H WA F H WA U ltra-high-performance concrete (UHPC) refers to a class of exceptionally durable and strong cementitious composites, usually containing fiber reinforcement and exhibiting self- consolidating properties. UHPC has been used in Europe and Asia in building vehicular bridges, pedestrian bridges, and other types of structures. In the United States, the Iowa, Virginia, and New York Departments of Transportation have used UHPC in building highway bridges. More applications of UHPC are expected in the years ahead. The ongoing deterioration of highway bridges is an issue across the nation. This deterioration in combination with congestion related issues has created a situation where bridge owners need to repair, replace, and construct durable bridges. Those needs are greater than ever. Given the ever increasing demands on our bridge structures and resources, it is clear that conventional construction techniques of the 20th centur y are not in themselves sufficient to meet 21st century needs. There is a strong demand for new solutions to existing problems, whether the solutions emanate from materials or structural configurations or construction techniques. The advanced properties of UHPC open many new avenues toward these solutions. The Federal Highway Administration's (FHWA) Bridge of the Future initiative seeks to develop new solutions to our existing highway bridge deterioration and congestion problems. The initiative has the following performance goals for highway bridges: • 100-year ser vice life with little or no maintenance • Significantly reduced construction time • Easily widened or adapted to new traffic demands • Significantly reduced life-cycle-cost • Significantly improved resistance to typical and extreme natural and man-made hazards including blast, flood, earthquake, fire, wind, fracture, corrosion, overload, and collision • Integrated substructure and superstructure design and construction • Reduction of vertical and lateral clearance problems FHWA's UHPC efforts are a core component of the Bridge of the Future initiative. The efforts focus on engaging UHPC's exceptional durability and mechanical properties to create optimal structural systems capable of meeting current and future demands. What is UHPC? U H P C i s a g e n e r a l c l a s s i f i c a t i o n t h a t encompasses a range of advanced cementitious composite materials. Just as with conventional concretes, UHPC contains cement, aggregates, and water. Like many high-per formance concretes, UHPC also contains supplementary c e m e n t i t i o u s m a t e r i a l s a n d c h e m i c a l admixtures to enhance specific presetting and post-setting behaviors. Unlike most concretes, UHPC generally contains no coarse aggregates, instead it includes a few percent by volume of short, discrete fibers. Worldwide, UHPC-type materials are available from multiple suppliers. In the United States, one multinational firm has led the way in supplying UHPC for infrastructure-scale projects. Other entities are currently working to develop and deploy competing products in this market. The performance attributes exhibited by these concretes may be up to an order of magnitude better than those exhibited by conventional and high-performance concretes. UHPC is sometimes thought of as 'extremely strong concrete'; however, a compressive strength seven or more times that of conventional concrete is only part of the story. UHPC exhibits sufficient sustained tensile capacity to allow for the reimagining of concrete structural design. Moreover, the durability properties of UHPC are so exceptional that they cannot be quantified with many standard concrete test methods. The table on page 47 presents some attributes of a widely available UHPC as independently measured by FHWA. Applications There are many potential applications for UHPC in the highway infrastructure; however, as is always the case with new technology, only some implementations will prove to be economically viable. The range of concepts being considered runs the gamut from conventional ideas such as bridge redecking systems and optimized prestressed girders, 1 to connection details such as field-cast spliced joints between precast modular elements, 2 to novel concepts such as energy dissipating seismic elements and cladding shells for bridge barriers. Since its initiation in 2001, FHWA's UHPC program has been focused on developing practical UHPC applications that address pressing needs. ULTRA-HIGH-PERFORMANCE CONCRETE A Bridge of the Future–A Solution Today by Dr. Benjamin A. Graybeal with M. Myint Lwin, Federal Highway Administration Ultra-high-performance concrete was used in the Cat Point Creek Bridge in Warsaw, Va. Photos: Ben Graybeal, FHWA FHWA_spr10.indd 46 4/30/14 11:27 AM