Multiperspective Enhancement of Printing Quality in 3D Printing Hybrid-Fiber Reinforced Engineered Cementitious Composites

To address the challenges of applying concrete materials in 3D printing, engineered cementitious composites (ECC) offer a promising solution due to their exceptional ductility, yet their print quality remains insufficient for widespread applications. Therefore, this study developed a hybrid-fiber reinforced engineered cementitious composites (HECC) by incorporating polyethylene (PE) fiber and cellulose filaments (CF) into ECC at optimized ratios. The optimal formulation was determined with CF fixed at 0.20% mass fraction of binder materials and total fiber content at 1.50%, which demonstrated improved static yield stress with the fastest formation rate (reaching 27.92 Pa/min), along with enhanced initial dynamic yield stress and plastic viscosity. Simultaneously, the tensile strain of printed specimens reached its maximum value when the PE fiber content reached 1.50%. Based on this optimized mixture, the study established a time-varying stiffness model through early age compressive strength tests, deriving a printing height prediction curve. The predicted printing height of 317 mm showed minimal deviation from the actual printed height of 310 mm, accurately predicting the critical printing height for slender structures and effectively reducing collapse risks. Furthermore, this research implemented YOLOv11n, an advanced image recognition technology, as a deep learning model for real-time monitoring of filament width and height, enabling precise dimensional measurement of printed specimens. The study further aims to utilize these recognition signals as feedback for closed-loop adjustment of printing parameters, thereby further improving print quality.