Monitoring and Inspecting Precast Piles with Carbon Fiber Reinforced Polymer (CFRP) Prestressing Cables During Cold-weather Casting

The Virginia Department of Transportation (VDOT) has been making a strong effort to invest in more durable, longer-lasting materials for bridge structures to offset vast life-cycle costs such as maintenance. The VDOT recently constructed a bridge in Virginia Beach containing 18 precast piles prestressed with a high-strength, corrosion-free material known as carbon fiber reinforced polymer (CFRP). This paper reports some of the work done by VCTIR during the fabrication of four piles, which took place in mid-November of 2013 in freezing temperatures. A practical methodology for in-situ monitoring of the CFRP material during the casting, steam-curing, and release of the piles is presented, and an analysis of load and acoustic emission (AE) measurements reveals the thermo-mechanical behavior of the cables in freezing temperatures. Ground penetrating radar (GPR) was also used to determine the spacing of spiral CFRP ties once the piles were released. Stress in the cables fluctuated marginally, correlating to ambient and concrete temperatures. The steel-CFRP coupling anchorage system for prestressing did not cause any detected damage or slippage, which was initially a concern given the brittle tendency of polymers in low temperatures. The results from this project offer practical information on the behavior of a new structural material in a low-temperature concrete production environment.

References
1. Yazdani, N., “Concrete Bridge Deterioration”, ASCE/SEI Enhancing Bridge Performance Workshop, 2008. 2. Monfore, G.E. and Verbeck, G.J., “Corrosion of Prestressed Wire in Concrete”, Proceedings of the American Concrete Institute 57(11), 1960. 3. Taerwe, L., “Use of Fiber Reinforced Polymers (FRP) in Concrete Structures: A Critical Appraisal”, Massivbau in Ganzer Breite, Springer, 2005. 4. National Weather Service, NWS Daily Summary for Chesapeake, VA (23322), November 13-14, 2013. 5. Tokyo Rope Mfg. Co., Ltd, “Carbon Fiber Composite Cable (CFCC)”, Product Technical Data, 2011.
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