Interview with Ben Graybeal, Ph.D., P.E., Research Structural Engineer, Federal Highway Administration, Virginia, USA

How is Ductal^® used in bridges?

Since completion of the first Ductal^® footbridge in Sherbrooke, Quebec (1997), numerous innovative Ductal^® bridge solutions have been completed around the world - with projects completed in France, Canada, USA, Australia, New Zealand, Japan, and South-Korea. Across North America, 15 Ductal^® Bridge projects have been completed: six in 2009, 10 more are scheduled for 2010. In these projects, Ductal^® has been used for beams, girders, decks, piles, and joint fill for precast deck systems. Thanks to its outstanding properties, the freedom to design innovative, optimized shapes is now possible - and with additional benefits such as: superior freeze/thaw resistance, extremely low porosity, improved flexural strength and Superior toughness - all relating to improved resistance to mechanical sollicitations as severe climatic conditions. Our valued clients, such as the Federal Highway Administration (FHWA), the New York State Department of Transportation, the Iowa Dept. Of Transportation, the Ministry of Transportation of Ontario and the City of Calgary have been heavily involved in the development of their own Ductal^® bridge projects.

How do you see Ultra-High Performance Concrete (UHPC) helping to solve or address the needs of the "Bridge of the Future"?

B. G. : Given the ever increasing demands on our bridge structures and resources, it is clear that conventional construction techniques of the 20th century 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 "Bridge of the Future" Research Program is developing robust solutions that increase durability and reduce construction time. UHPC has allowed for the development of new structural components and component-joining technologies which directly address immediate needs in the highway sector.

What obstacles prevent state DOTs from implementing the use of UHPC for future projects?

B. G. : The following was adapted from a Public Roads article titled "UHPC Making Strides" that I authored for the Jan-Feb 2009 issue. As is frequently the case with established industries serving the public works sector, implementation of innovations occurs rather methodically. FHWA has identified five specific obstacles hindering widespread UHPC deployment. Unless industry sees a clear financial benefit, manufacturers are unlikely to invest in innovative technologies. Manufacturers who see a risk in using a new material are hesitant to modify current operations so that they can produce the innovative product efficiently. As would be expected, the costs of fabricating UHPC components thus are significantly higher than the costs of manufacturing conventional concrete components. The lack of design code provisions relevant to the advanced properties of these innovations is a clear hindrance. This gap effectively requires that all UHPC structural designs proceed along one of two paths. The designer can choose to make limited use of UHPC, in effect using the advanced properties of UHPC simply as an added safety factor. Alternatively, the designer can rely on research results, effectively requiring some level of demonstration testing prior to implementation. The limited number of applications of UHPC to date necessarily means that limited experience is available with regard to inspection, maintenance, and repair of UHPC structures. Although FHWA researchers and others expect these structures to perform well once deployed into the highway system, UHPC is not immune to damage from over-height or wayward vehicles, or unanticipated structural loadings. Methods for inspecting UHPC for damage and for repairing UHPC components will need to be developed prior to widespread acceptance of this material by the highway industry. Finally, the higher cost of the constituent materials in UHPC necessarily means that it will have a higher per-unit volume cost than conventional and high-performance concretes. This increase is unlikely to be offset entirely through the use of more efficient structural designs. To compensate for the greater cost, designers need to use a life cycle costing approach that takes into account the enhanced durability of UHPC.