Durability Evaluation of Carbon Fiber-Reinforced Polymer Strengthened Concrete Beams: Experimental Study and Design

Carbon fiber-reinforced polymer (CFRP) materials are being used for the retrofitting and repair of deficient and old infrastructures such as bridges and buildings. Over the years, these structures tend to suffer severe strength and stiffness deterioration due to aggressive environmental conditions such as humidity, saltwater, freeze-thaw, thermal expansion, dry-heat, repeated load cycles, and alkali solutions. The authors of this study present the deflections, strains, failure loads, and failure modes of strengthened beams exposed to different independent environmental conditions and repeated load cycles. The authors propose strength reduction factors associated with these various independent environmental conditions. The authors conclude that the long-term exposure to humidity is the most detrimental factor to the bond strength between CFRP plates and fabrics and reinforced concrete (RC) beams. Beams strengthened with CFRP plates and exposed to 10,000 hours of 100% humidity experienced an average of 33% reduction in their strength. RC beams strengthened with CFRP plates are more susceptible to damage than the beams strengthened with CFRP fabrics. There is no significant effect, however, of repeated load cycles on the ultimate loads of beams strengthened with CFRP plates or fabrics for at least 2 million test cycles. Delamination was the primary mode of failure for all of the test beams, with and without exposure to environmental conditions and repeated load cycles. The authors conclude by presenting a durability-based design approach that demonstrates the evaluation of nominal and design moment strengths of strengthened beams along with failure modes.