Extrusion-Based 3D Printing of Fiber-Reinforced Concrete (2026-04)¶

Embedding conventional reinforcement in 3D concrete printing (3DCP) remains a critical challenge due to the constraints imposed by the layerwise deposition process. A promising solution is the incorporation of discontinuous short fibers into printable mixtures, as they can enhance tensile strength and toughness, mitigate the risk of shrinkage-induced cracking, and reduce crack width. In this study, three types of short fibers, namely 6-mm steel fiber, 8-mm polyvinyl alcohol (PVA) fiber, and 6-mm polypropylene (PP) fiber were incorporated into a high-performance printable mixture. The effects of individual and hybrid fibers on fresh properties, extrudability, mechanical performance, and shrinkage resistance were systematically evaluated. Results indicate that increasing steel fiber volume or partially replacing it with synthetic fibers significantly increased air content and accelerated early slump flow loss, despite improved water retention. Mixtures with up to 2% steel fibers maintained excellent printability, whereas hybrid fiber combinations introduced surface defects while remaining acceptable extrudability. The incorporation of hybrid fibers also increased mechanical anisotropy due to compromised filament quality. Drying shrinkage was most effectively mitigated by increasing the steel fiber volume, while partial reductions were observed with the incorporation of PP or PVA fibers. Overall, steel fibers provided optimal performance in balancing flowability, mechanical strength, and filament stability, while hybrid fiber strategies requires careful optimization to avoid print quality degradation.