Concrete Products

FEB 2019

Concrete Products covers the issues that attract producers of ready mixed and manufactured concrete focusing on equipment and material technology, market development and management topics.

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56 • February 2019 CORROSION-FREE CARBON FIBER REINFORCED POLYMER: A REPLACEMENT FOR STEEL STRAND Corrosion-free carbon fiber reinforced polymer (CFRP) reinforcement now is available and can mitigate corrosion in prestressed concrete elements, such as beams, by reliably replacing steel reinforcement, say H. Celik Ozyildirim and Stephen R. Sharp, Virginia Transportation Research Council, in their peer-reviewed paper, Prestressed Concrete Beams with Carbon Fiber Reinforced Polymer. "When concrete is reinforced with prestressed steel strands that are under sustained tensile stress, corrosion is more critical than in concrete with conventional carbon steel reinforcement," the authors write. "Fortunately, corrosion-free carbon fiber reinforced polymer reinforcement is available and can mitigate corrosion in prestressed elements, such as beams, by replacing steel reinforcement." Virginia DOT recognizes the importance of corrosion-free reinforce- ment in prestressed strands, and has used CFRP strands in 18 piles of the Nimmo Parkway Bridge at Virginia Beach, they say. "New VDOT specifications require such reinforcement in piles exposed to severe environments, such as piles exposed to brackish water, saltwater or deicing salts," write Ozyildirim and Sharp. "Reinforcement in beams is also prone to corrosion in severe exposure conditions; corrosion-resistant or corrosion-free strands and stirrups would enhance the durability and extend the service life of beams in such environments." The CFRP strands used by VDOT are called carbon fiber composite cable (CFCC) by the manufacturer, Tokyo Rope USA, Inc., and are manufactured at a plant in Canton, Mich. "This relocation to Michigan reduces CFCC delivery time to the precaster while maintaining CFCC's desirable mechanical properties and a unique geometry that allows it to be coiled on a spool," the authors write. After fabricating piles with CFRP, VDOT placed 22 beams with CFRP reinforcement in a two-span bridge in Halifax County, Va. The corrosion-free CFRP was used in both the strands and stirrups. The bridge has two continuous spans, each with four 84-ft.-long, 45-in.- tall prestressed bulb-tee beams. "While this bridge has a low traffic volume and is away from the aggressive coastal environment, the fabrication of these beams provided the needed experience for future use in a severe environment," Ozyildirim and Sharp say. All reinforcement in the beams was CFRP. The stirrup was pre- formed at the plant in Japan and shipped to the prestressing plant in Virginia. The CFRP strand was shipped from Japan on spools to the precast/prestressed operation. The beams were designed by VDOT''s Structure and Bridge Division with technical assistance from Nabil Grace from Michigan Technological University. The design followed ACE 34 and AASHTO guidelines and used the mechanical properties pertinent to CFRP. The prestressing force was kept at 65 percent of the guaranteed ultimate tensile strength. The CFRP was handled with care because of limited ductility and high sensitivity to heat. Also, CFRP strands need special end prepa- ration to avoid crushing the end during prestressing, as the strand is strong in the axial direction, but weaker in the radial or transverse direction. First, two beams were cast using a traditional concrete mixture with conventional slump. Slump loss and reduced workability in con- cretes with conventional slump made fabrication of beams difficult, the authors write. TECHNICAL TALK BY TOM KUENNEN Proud to be an employee-owned company since 2004 +1.989.354.4111 Servopac ® Premier Servopac ® Classic Servopac ® Select 3 MODELS STRONG CURING PARTS MOLDS EDUCATION & TRAINING TECHNICAL SERVICE PRODUCTION SYSTEMS MACHINE UPGRADES EXPERIENCE. Access to a global network of Strategic Alliances to bring NEW, value added units and systems to your product line Blockmakers Workshops ® at the WCCT and custom onsite training for masonry, hardscape, pipe and precast Partnerships for research and assistance with development and commercialization of waste materials into concrete products Responsive technical and maintenance assistance, extensive parts inventory Maintenance contracts and plant evaluations PROACTIVE PRODUCER SUPPORT

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