Precast Solutions - July/August 2008 - (Page 9)

C78 provides nonsensical results for UHPC’s flexural tensile strength, because UHPC is fiber-reinforced and exhibits flexural post-cracking tensile strength greater than its flexural initial-cracking tensile strength. A final example is ASTM C666, which would seem to indicate that applying cycles of freezing and thawing to UHPC can increase its freeze-thaw resistance. In reality, the test method is causing the apparent increased resistance through continued hydration and mass gain. UHPC exhibits excellent freeze-thaw resistance, however, with durability factors that easily surpass those of conventional concrete. UHPC interim design codes can be developed for transportation infrastructures as research continues. Engineers and specifiers will need to understand optimal designs using this innovative material in a host of potential precast applications such as superstructures, substructures, sound barrier walls, crash and blast protection systems, precast pavements and hybrid systems. While design codes can take several years to be approved, interim recommendations are anticipated within the next few years. HOW IT WORKS -girder and modeling graphic. Decked superstructure element for rapid construction of a 70- to 100-foot span highway bridge. Graphics courtesy FHWA. GREEN INNOVATION AND THE FUTURE OF UHPC While the current LEED (Leadership in Energy and Environmental Design) rating system lacks credits for ranking the numerous green benefits of precast concrete, points can often be achieved through the “Innovation in Design” category (see pages 4-9, Precast Solutions, May-June 2008 issue). UHPC can further promote green benefits with CO2 emission reductions. In addition, UHPC presents the opportunity for potentially lower embodied energy due to significant material reduction (up to 40 percent less weight) in optimized members. Long-term service life and expected minimal maintenance are material characteristics that lend themselves to reduced life cycle costs for structures. This enhanced durability needs to be factored into sustainable solutions to offset the currently higher costs of UHPC. UHPC is a leap forward in concrete technology for durable highway structures. These concretes offer dramatic improvements in physical and mechanical properties over conventional concretes and are virtually impermeable to the harsh environmental factors that bridges throughout the United States are exposed to Theresa (Tess) M. Ahlborn, Ph.D., P.E., is an associate professor and director of the Center of Structural Durability at Michigan Technological University in Houghton, Mich. She is a leading researcher on UHPC and has conducted important UHPC material characterization research at Michigan Tech. Professor Ahlborn has toured numerous facilities of leading European producers of UHP precast concrete applications. JULY/AUGUST 2008 every day. UHPC has important advantages over conventional and high-performance concretes, especially in the production of smaller and lighter sections and the potential elimination of passive mild steel reinforcement. While UHPC’s greatest potential currently appears to be in transportation infrastructure, it is too early to predict what new solutions to design challenges will emerge as engineers and specifiers learn more about this new technology. | PRECAST SOLUTIONS 9

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Precast Solutions - July/August 2008 Contents What You Should Know About UHPC A Winning Hand Fresno Federal Expanding U.S. Wind Power Precast Concrete Pipe

Precast Solutions - July/August 2008

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