Macro- and Micro-Scale Performance of 3D-Printed Bamboo Fiber-Reinforced Concrete in Chloride-Rich Environments

With escalating chloride-induced deterioration in marine and coastal environments, enhancing the service durability of 3D-printed concrete is essential for sustainable construction. However, the layered architecture and process-induced anisotropy of additive manufacturing make printed cementitious materials particularly susceptible to chloride ingress, while the underlying mitigation mechanisms remain insufficiently understood. In this study, bamboo fibers (0–2.3% by content, 10–20 mm in length) were incorporated into 3D-printed concrete to systematically assess mechanical-property evolution under chloride exposure and clarify how fiber parameters affect chloride resistance. Results show that appropriately dosed bamboo fibers significantly alleviate chloride-related strength loss. The optimum combination, 1.2% fiber content with 15 mm length, achieved compressive and tensile strength retentions of 83% and 82% after 15 days of exposure, representing improvements of approximately 17–22 percentage points over plain printed concrete. The benefit was most evident in interlayer weak zones (Z-direction), where strength retention rose by up to 25 percentage points, effectively suppressing chloride-induced amplification of printing anisotropy. In contrast, excessive fiber dosage or length caused agglomeration and interfacial defects, weakening interlayer bonding and intensifying anisotropy, indicating a clear performance threshold. Extended exposure further revealed that bamboo fibers lowered the strength degradation rate by about 35% during the critical 10–15 day stage, while protective effectiveness increased almost linearly with time. Considering mechanical performance, durability and printability, the optimal mix delivered an overall strength gain of roughly 28% while maintaining stable extrusion and sufficient interlayer cohesion. These findings provide mechanistic insight and practical guidance for improving the chloride resistance of 3D-printed concrete, supporting its broader use in marine and coastal infrastructure.