Influence of Temperature and Stress on the Durability of Carbon Fiber Reinforced Polymer (CFRP) Strands in a Concrete Environment

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 75-100 year design lives, it is imperative that prestressed elements—girders, piles, and deck panels—contain corrosion-resistant strands. VDOT has started pursuing carbon fiber reinforced polymers (CFRP) as a corrosion-resistant alternative to steel prestressing materials for longer lasting concrete bridge structures in Virginia

The in-service performance of CFRP rods and cables can be hard to evaluate in certain structural applications, such as prestressed concrete bridges, where instrumentation is often limited and the material cannot be removed for inspection. To implement CFRP in prestressed concrete bridge structures with more confidence, this project was initiated to study issues pertaining to durability under in-service environmental conditions. Specifically, the intention was to extract some information about fundamental material behavior while contributing directly to engineering applications in VDOT and beyond. The main goal was to investigate the effects of temperature, alkaline and alkaline/chloride solutions, and temporary stress on material properties over time, in the context of reinforced and prestressed concrete structures.
The methodology was designed to examine any relationships that exist between various observations and material characteristics, including moisture content, glass transition temperature, interlaminar/intralaminar shear strength, and tensile properties. This approach will also help to establish a durability testing methodology for CFRP in concrete structures that can be adopted by VDOT and other laboratories.

There were several key findings from the results of this study: (1) pre-loading the CFRP to 75% of the ultimate strength—temporarily, not sustained—has a significant impact on durability compared to unstressed material; (2) higher temperatures accelerate degradation, (3) moisture sorption was the primary process responsible for the observed degradation, with plasticization and microcracking as the controlling mechanisms leading to fiber-matrix interfacial debonding, and (4) a new mechanistic analytical model was developed to predict residual properties after moisture-induced degradation, showing promising agreement with experimental data.