Precast Solutions - July/August 2008 - (Page 4)

WHAT YOU SHOULD KNOW ABOUT UHPC ULTRA HIGH-PERFORMANCE CONCRETE OFFERS UNTAPPED POTENTIAL FOR THE material properties of UHPC, current research, production techniques, factors that limit full adoption of this new material technology in the United States, and the outlook for UHPC. WHAT IS ULTRA HIGH- PERFORMANCE CONCRETE? UHPC is a family of concretes offering a combination of material and performance characteristics that create products with: • Ductility: ability to support tensile loads even after initial cracking • Ultra high compressive strength (up to 200 MPa/29,000 psi) • Extreme durability; low water to cementitious material (w/cm) ratio • Self-consolidating and highly moldable mixtures • High-quality surfaces • Flexural/tensile strength (up to 40 MPa/5,800 psi) through fiber reinforcement • Thinner sections; longer spans; lighter weight • New graceful product geometries • Chloride impermeability • Abrasion and fire resistance • No steel reinforcing bar cages • Minimal creep and shrinkage after curing • Optimized mix proportions Table 1. UHPC Material Composition. Material Courtesy of FHWA U.S. PRECAST MARKET. W BY THERESA (TESS) M. AHLBORN, PH.D., P.E. hat do some structural researchers and transportation engineers view as the most important material technological breakthrough with greatest potential to transform product design and service life in the U.S. precast concrete industry? What new concrete technology has the potential to effect a major change in the way engineers and specifiers conceive of and design precast systems? The latest available research from both academia and transportation agencies points to ultra high-performance concrete (UHPC) as the most promising catalyst for new precast concrete product designs. Relatively new to the United States, UHPC belongs to a family of concretes with remarkable compressive strengths that exceed 150 megapascals (MPa), or 22,000 pounds per square inch (psi) – more than four times the strength of conventional concrete. To date, the only large-scale implementation of UHPC in bridge superstructures has been initiated by the U.S. Federal Highway Administration. In other countries including Canada, Japan, France, Australia, New Zealand, South Korea and Germany, numerous exciting and innovative precast concrete systems have taken advantage of the unique material characteristics of UHPC. What has prevented U.S. specifying engineers from taking advantage of untapped potential of UHPC designs? For the answers, let’s take a look at the Amount (lb/yd3) Percent by Weight 28.5 40.8 9.3 8.4 1.2 1.2 6.2 4.4 Portland cement 1200 Fine sand Silica fume Ground quartz Superplasticizer Accelerator Steel fibers Water 1720 390 355 51.8 50.5 263 184 Note: lb/yd3 x 0.5933 = kg/m3. 4 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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