Precast Solutions - July/August 2008 - (Page 8)

the subsequent corrosion-induced deterioration. UHPC Designers of the elegant spiral staircase in an upscale Paris apartment found the lightness, color range and finish of UHPC enabled the company to offer new, highly original designs. Photo courtesy Eric Bergoend optimized designs and material properties in bridge decks can mean longer service life and lower maintenance costs for America’s transportation infrastructure. FACTORS AFFECTING A BROADER USE OF UHPC IN THE U.S. Implementation of UHPC in the United States is progressing slowly for three reasons: 1. Lack of U.S. design codes for UHPC 2. Risk perception and lack of familiarity with UHPC Solus Décor used UHPC in the production of architectural precast concrete municipal benches with exceptional durability. Photo courtesy Solus Décor 3. Initial cost The greatest challenge limiting the use of UHPC by American specifiers and precast producers is that current design codes are not readily adaptable to this class of concrete possessing strengths many times that of conventional concrete. Continued research is needed on the advanced properties of UHPC to provide a valid database for structural design. Even at the federal level where UHPC research has been conducted, officials perceive the risks associated with a greatly expanded use of a product with a limited history of performance. State highway engineers, in particular, are hesitant to use new technology without a significant history of proven performance in large part because of their responsibility for public transportation safety. This understandable aversion to the risk of specifying and manufacturing products with the relatively new UHPCs also drives up its cost. Whenever a new technology is perceived as risky, whether due to lack of knowledge, producer comfort level or history of use, market forces in any industry will increase the price of using that technology. According to Graybeal, specifying engineers can “apply the current ASTM and AASHTO standards in a general sense” to UHPC projects. Since these standards were developed for conventional concretes, however, using them on UHPC can sometimes result in nonsensical results. Because UHPC is so new, Graybeal explains, the “body of ASTM/AASHTO standards has not yet been developed to adequately cover UHPC.” For the specifying engineer, this becomes a situation of understanding the limits of applicability of the existing HOW WITH CAN SPECIFIERS ADAPT standards when specifying UHPC on a project and then choosing the standards accordingly. As an example, ASTM C39 works for specifying the compressive strength of UHPC, but research has demonstrated that the test can be run at a faster rate and using 3-inch diameter cylinders instead of conducting a much slower test on 4-inch or 6-inch cylinders as called for in the specification. Another example how specifiers need to be discerning in applying current standards to UHPC is that of using ASTM C78 to test for flexural strength. ASTM EXISTING STANDARDS TO WORK UHPC? While other countries like Canada, Germany and Japan have already begun to take advantage of the unique material characteristics of UHPC, U.S. engineers, designers and specifiers are interested in the applicability of current AASHTO (American Association of State Highway and Transportation Officials) and ASTM (American Society for Testing and Materials) testing standards for UHPC. 8 PRECAST SOLUTIONS | JULY/AUGUST 2008

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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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