Direct Ink Writing of Geopolymer Composites Reinforced With Polypropylene Fibers

Polypropylene fiber (PPf) reinforced geopolymer inks were systematically optimized for extrusion‐based additive manufacturing through regulation of ink composition, rheological parameters, nozzle size, and fiber content. The effects of polyethylene glycol (PEG) content and H 2 O to K 2 O ratio on printability were investigated. Increasing the PEG content to 0.5% and adjusting the H 2 O to K 2 O ratio to 15 effectively reduced viscosity and yield stress while preserving stable shear‐thinning behavior, enabling smooth extrusion and reliable shape retention. The incorporation of PPfs significantly improved mechanical performance, inducing a transition from brittle to ductile behavior and markedly increasing flexural strength. Scanning electron microscopy revealed that fiber pull‐out dominated the toughening mechanism through interfacial debonding, frictional sliding, and crack bridging. The optimized formulation achieved a balanced combination of printability, structural stability, and mechanical reinforcement, providing practical guidance for the design of fiber‐reinforced geopolymer inks for additive manufacturing applications.