3D-printed UHSC with synchronously integrated thermoplastic FRP bars: Concept and bond performance

The combination of 3D-printed ultra-high-strength concrete (UHSC) with fiber-reinforced polymer (FRP) reinforcement offers significant structural and practical advantages, including exceptional corrosion resistance and high strength-to-weight ratios. However, conventional thermosetting FRP (TS-FRP) composites could not be reshaped or field-bent post-curing and thus the integration of these FRP bars into 3D-printed concrete structures presents considerable challenges. This study proposes a novel approach for the synchronous 3D-printing of UHSC and thermoplastic FRP (TP-FRP) bars, leveraging the unique thermal heating-melting-cooling solidification characteristics of TP-FRP bars to enable on-demand bending during the printing process. For the first step, this research systematically investigated the bond performance between 3D-printed UHSC and TP-GFRP bars, considering resin type, rib spacing, and printing direction. The test results demonstrated the bond strengths of TP-GFRP bars in 3D-printed UHSC were generally comparable to those in cast UHSC but lower than those of TS-GFRP bars. Notably, the layout direction of GFRP bars and the rib spacing had significant influence on the bond performance. This study provides a foundation for developing efficient and integrated reinforcement solutions for advanced 3D-printed concrete structures.