3D printing of continuous carbon fiber-reinforced polymer reinforcement for concrete columns

Using fiber-reinforced polymer (FRP) rebars and spirals as internal reinforcement for concrete structures has been a mainstream direction in field of FRP composites for construction. The traditional manufacturing process of FRP reinforcement based on pultrusion not only leads to considerable material waste but also results in fiber wrinkles in the bent sections, significantly compromising the mechanical performance of the bent bars. To address these issues, this study employs a novel 3D printed continuous fiber-reinforced thermoplastic polymer (CFRTP) reinforcement for reinforcing concrete columns. Initially, ring tensile tests were conducted on 3D printed CFRTP circular ties. 3D printed CFRTP ties (3DP-CFRTPTs) as transverse reinforcement was then applied to both concrete cylinders and square prisms to evaluate their effectiveness. Axial compression tests were performed on six cylinders and six square prisms to investigate the effects of tie cross-sectional height and spacing on the compressive performance of concrete columns reinforced with 3DP-CFRTPTs. The results indicate that 3DP-CFRTPTs significantly enhance the compressive strength of specimens, with tie spacing having a considerable impact on the compressive strength. Comparison of the experimental results with predictions from eight different models showed that while the existing FRP strip confinement concrete models are suitable for predicting the ultimate axial stress of 3DP-CFRTPT confined concrete, they are unable to predict the axial strain accurately. • 3D-printed CFRTP stirrups are developed and demonstrated significantly enhanced concrete compressive strength. • Smaller stirrup spacing led to stronger confinement and improved axial performance. • 3DP-CFRTP confined concrete showed distinct three-stage stress–strain behavior. • Existing FRP strip models predict axial stress well but strain predictions need further work.