Carbon Fiber Reinforced Polymer (CFRP) for Pretension Applications: Material Acceptance Criteria and Advancing Anchorage Designs

About the report:

One of the main causes of structural deficiency in concrete bridges is the deterioration of the constituent materials.  In order to achieve the goal of a design life of 75 to 100 years, it is imperative that pretensioned elements—girders, piles, and deck panels—contain corrosion-resistant or corrosion-free strands. The Virginia Department of Transportation (VDOT) is using carbon fiber reinforced polymers (CFRP) as a corrosion-free alternative to steel prestressing materials for longer lasting concrete bridge structures in Virginia.  The in-service performance of elements can be difficult to evaluate in certain structural applications, such as pretensioned concrete bridges, where instrumentation is often limited and the material cannot be removed for inspection; use of corrosion-free CFRP will eliminate corrosion, the most common deterioration mechanism in reinforced elements.

To implement CFRP in pretensioned concrete bridge structures with more confidence, this study was initiated to examine issues pertaining to material durability and quality control, laboratory testing procedures, and improved pretensioning anchorage systems.  The experimental approach was intended to establish a testing methodology that can be adopted by VDOT for evaluating the quality and durability of CFRP in concrete structures.

Several conclusions were drawn from the results of this study: (1) mechanical testing is important for characterizing CFRP prestressing material and should be supported by analysis of physical and thermal properties; (2) short-term preloading of the CFRP to 75% of the ultimate tensile strength has a significant impact on durability compared to unstressed material and higher temperatures accelerate degradation; and (3) a promising anchorage prototype was designed for improving pretensioning operations when using CFRP.

The study recommends that VDOT’s Materials Division prepare guidelines for checking the durability of CFRP reinforcement.  Further, the manufacturers of the composite materials should provide data indicating conformance with the guidelines.  In addition, the Virginia Transportation Research Council should continue work on the development of an improved wedge system for CFRP.  This wedge would increase production rates during pretensioning and allow for easier use in post-tensioning applications.  It is also possible that this wedge could be used for stainless steel strand.

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