Flexural Behavior Investigation of RC Beams with FRP-Reinforced 3D-Printed ECC Permanent Formwork (2025-12)¶

The resource waste and low construction efficiency associated with traditional cast-in-place formwork systems are becoming increasingly apparent, whereas 3D printing technology offers a new approach to the intelligent construction of building formwork. This paper conducted a multi-scale study on the bending performance of 3D-printed engineered cementitious composite (ECC) permanent formwork-reinforced concrete (RC) composite beams and fiber-reinforced polymer (FRP)-reinforced ECC permanent formwork-RC composite beams. First, an innovative ECC material mixing ratio suitable for extrusion-type 3D printing processes was designed. Then, 14 beam specimens were designed and fabricated, and four-point bending tests were conducted to investigate the effects of 3D printing prefabrication and casting process, ECC base plate thickness, and FRP reinforcement diameter. It was found that ECC permanent templates can enhance the load-bearing capacity, ductility, and energy absorption capacity of beams, especially when ECC could wrap around tensile reinforcing bars. Compared to casted specimens, the 3D printing technology can increase the cracking load by an additional 10–20 %, but has almost no effect on the ultimate load. In addition, 3D printing technology reduced the ductility and energy absorption capacity of composite beams and increases the stiffness of specimens in the elastic-plastic stage. After incorporating FRP, the negative impact of reduced ductility caused by 3D printing could be eliminated, thereby enhancing the energy absorption capacity of the specimens. Based on classical mechanics model and material stress-strain models, a mathematical model was proposed to predict the bending capacity of ECC permanent formwork-RC composite beams and FRP-ECC-RC composite beams. The error between the predicted and measured values was within ±10 %.