Bond behavior evaluation of FRP rods fabricated by 3D printing

Reinforced concrete (RC) structures are composite constructions in which steel reinforcement and concrete mutually transfer forces to withstand loads. With the proposal of new materials and construction methods, it is anticipated that future reinforcement methods and the shapes of reinforcements in composite structures will become more complex compared to conventional RC structures. Notably, the shape of reinforcements significantly influences their bond behavior with concrete, necessitating an understanding of how freely shaped reinforcements affect bond behavior. In recent years, industrial 3D printing (3DP) has garnered attention as a growing field, particularly plastic-based 3DP technologies, such as fiber-reinforced plastics (FRP). These are expected to serve as powerful tools for elucidating the relationship between the shape of reinforcements and their bond performance. However, when using FRP rods fabricated through 3DP (3DP FRP) for bond tests with concrete, fundamental studies, including the feasibility of such tests, are required. This study first examined the feasibility of evaluating bond behavior using Carbon Fiber Reinforced Plastics(CFRP) rods fabricated through plastic-based 3DP. Based on the results, the study further investigated how changes in shape—such as increased surface area, waviness, twisting, mechanical anchorages, and their combinations—affect bond behavior. The experimental results revealed that the bond behavior of CFRP rods can be evaluated through pull-out tests when carbon fibers are incorporated into the FRP rods. Additionally, it was found that the effects of shape changes, including increased surface area, waviness, twisting, and mechanical anchorages, as well as their combinations, on bond behavior can be qualitatively evaluated.