The effects of accelerated Freeze-Thaw conditioning on CFRP strengthened concrete with pre-existing bond defects

Despite demonstrated success in both the laboratory and in the field, significant questions remain unanswered regarding the durability of Carbon Fiber Reinforced Polymer (CFRP) for strengthened concrete members. Little is known about the impact of pre-existing bond defects when subjected to harsh environmental conditions. The results from a study observing the performance of 18 small-scale CFRP-to-concrete pull test specimens is presented herein. Half of the sample set was stored in ambient laboratory conditions while the remaining sample set was subjected to 50 freeze-thaw cycles. Repeated for each condition were 3 specimens prepared without any intentional bond defects and 3 specimens containing 645 mm2 Teflon inserts, for comparison purposes. It was found that, not only did the freeze-thaw conditioning reduce the debonding capacity of the externally bonded CFRP, but that the presence of defects resulted in a greater reduction in debonding capacity following the environmental conditioning, when compared to specimens exposed to ambient conditions only. Nondestructive evaluation of the bonded interface was also performed by using Pulse Phase Thermography (PPT).