Experiment Investigation on Pull-Off Strength between Fiber Reinforced Polymer (FRP)-Concrete Interface under Marine Condition

For the past decades, extensive research and studies have been conducted on fiber
reinforced polymer (FRP) composite which is widely practiced for strengthening
structures. FRP materials has been chosen in retrofitting of existing structures
because FRP has higher strength-to-weight ratio and provides additional corrosion
resistance, in comparing to conventional repair material such as steel. For this
research purpose, concrete beams and slabs have been strengthened with carbon
FRP to study the effect on marine environmental condition particularly in
continuous immersion and wet-dry cyclic using salt water on the performance on the
interfacial bond between FRP and concrete (substrate). However, due to debonding
behaviour in long term performance and environment deterioration, the
strengthening systems are remained largely uncertain and unanswered. The direct
tension pull-off test has gained popularity as a test method used in the laboratory as
well as in the field including at construction site or during inspection, in assessing
the quality of bond between externally bonded fiber-reinforced polymer (FRP) repair
materials.
For this research purpose, a long-term durability study was conducted in the
laboratory vis-à-vis to evaluate the behavior of the bond between the repairing
material which is FRP and the substrate; concrete. Small concrete specimens, with
no reinforcement bars have been prepared, externally reinforced with FRP material,
and subjected to various environmental scenarios stimulated in laboratory which are
wet-dry cycles as well as constant and continuous immersion in salt water. Direct
tension pull-off tests and three-point flexural tests have been conducted on these
specimens to determine degradation in bond strength over ageing time.