Precast Solutions - September/October 2008 - (Page 10) potent mechanism of deterioration in public (At left) Bridge Street Bridge in Southfield, Mich. is the first vehicular precast concrete bridge ever built in the United States that uses carbon fiber reinforced polymer (CFRP) material as the principal structural reinforcement. Each double-tee girder contains CFRP Leadline™ tendons and post-tensioned CFRP carbon fiber composite cable (CFCC) strands in both longitudinal and transverse directions. Non-prestressed girder reinforcement is comprised of CFCC strands in bent configurations, straight CFCC reinforcing bars, CFRP NEFMAC™ grid reinforcement, and stainless steel reinforcing bars for stirrups. (At right) Underneath the bridge, external longitudinal CFCC posttensioning strands are visible. infrastructure. During winter months, road maintenance vehicles disperse salt and deicing chemicals to melt ice and snow on concrete pavements in efforts to keep roadways as tractable and safe as possible for drivers. What happens when these corrosive chemicals reach steel reinforcing bars through hairline cracks in the concrete? Rusting occurs, an oxidizing process that expands the volume of the steel reinforcing bars (creating internal pressures of 3,000 to 4,000 psi in the concrete) causing the surrounding concrete to crack and spall. Once corrosion-induced concrete spalling is initiated, traffic impact loads on bridges and roadways continue to exacerbate this structural deterioration. Corrosion damage and concrete deterioration can be alleviated through the structural application of advanced fibrous composite materials for reinforcing. In-service testing has proven that non-corrodible FRP materials are a viable structural solution to premature corrosive deterioration of precast transportation infrastructure. While FRP offers high tensile strength, it displays nonductile behavior and does not significantly contribute to concrete compressive strength. research continues, with some of the most notable work being conducted at Lawrence Technological University’s (Lawrence Tech) Center for Innovative Materials Research (CIMR) in Southfield, Mich. Carbon fiber reinforced polymers (CFRP) have these notable material advantages: • Superior strength • High strength- and stiffness-to-weight ratios • Light weight and ease of handling • Less corrosive and insensitive to magnetic effects • Good bonding with concrete • Produced in various shapes, strengths and stiffnesses • Availability of FRP for reinforcing bars, prestressing tendons and strands, plates, stirrups and sheets • Durability, long structural life and low maintenance In addition to CFRP, other commercially available FRP reinforcing materials are continuous aramid FRP (AFRP) and glass FRP (GFRP) reinforcing bars. CFRP reinforcing is available as prestressing strand, post-tensioning rope/cable, stirrups, reinforcing bars, two- and three-dimensional grids, reinforcing cages and mesh. Numerous products are available with carbon fiber reinforced polymers from producers all over the CFRP PROPERTIES, PRODUCTS AND world. The main producers of CFRP products are: Mitsubushi Chemical Functional Products Inc., Japan; Tokyo Rope Manufacturing Company Ltd., also of Japan; Diversified Composites Inc., Kentucky; and Hughes Brothers Co., Nebraska. PRODUCERS The strength-to-weight ratio of CFRP varies from five to 10 times that of steel and 50 times that of concrete. Similarly, the stiffness-to-weight ratio of CFRP is about three times that of steel and 25 times that of concrete. Of critical importance for durable highway bridges, CFRP is highly resistant to corrosion, fatigue and adverse environmental conditions. Worldwide, CFRP CFRP CODES RESEARCH AND CURRENT Without a long history of structural reliability in 10 PRECAST SOLUTIONS | SEPTEMBER/OCTOBER 2008
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.