Interaction between CFRP tendons and concrete when subjected to long-term moisture exposure

Abstract

Because carbon fibre reinforced polymer (CFRP) tendons are a relatively new construction material, further research is required to understand their long-term behaviour under pro-longed exposure to various environmental and mechanical conditions. A transverse expan-sion of unconfined CFRP rods due to moisture uptake has been observed elsewhere so a preliminary experimental series on bare CFRP rods immersed in water was used to validate this observation. To predict the effect of this swelling when enclosed in concrete the use of the thick-walled cylinder analogy has been proposed. Hence in the current work, experi-ments and numerical analyses were undertaken to test the validity of this analogy by calcu-lating the expected times for the concrete to crack in varying degrees, and comparing these values to the times of cracking observed experimentally. This involved the immersion of simple cylindrical concrete specimens with centrally embedded CFRP rods in water at room temperature. The results suggest that the thick-walled cylinder analogy cracking pre-dictions do not match the experimental observations. Further investigations are currently under way to study possible explanations. A deeper understanding of the long-term dura-bility behaviour will inform design guidelines for CFRP pre-stressed concrete, and lead to the more widespread application of this new construction material.