Moisture-Pore-Mechanics Coupling Evolution and Durability Degradation Model in 3D Printed Concrete

Three-dimensional printed concrete (3DPC) is rapidly transitioning from laboratory-scale demonstrations to full-scale construction. However, it exhibits limited mechanical durability under freeze–thaw cycles. This study investigated the synergistic effects of 0.1–0.3 vol% PVA（Polyvinyl Alcohol）reinforcement and internal moisture-pore-mechanics evolution on the salt-freezing resistance of 3DPC. The analysis of the extrudability and constructability of 3DPC revealed that optimizing the printing process achieved optimal extrudability at a fiber concentration of 0.2 vol%, enhancing compressive and flexible durability by at least 9% and 59%, respectively, following 20 unidirectional freeze-thaw cycles in a saline solution. Low-field nuclear magnetic resonance spectroscopy was applied to visualize pore-damage evolution and to track the component-resolved moisture kinetics during early-age hydration, demonstrating that the gel–water hydration degree governed the initial and final setting times. The modified Weibull distribution model was developed to precisely predict the strength degradation of 3DPC subjected to freeze-thaw cycles, with simplified reference values proposed for the fitting coefficients. This approach facilitates convenient and accurate estimation of 3DPC strength loss under salt-freeze conditions. These findings provide a mechanistic framework for designing cold- and salt-resistant 3DPC structures for marine and infrastructure applications. • 0.2% PVA fibers enhance compressive durability by 9% and flexural durability by 59%. • The fiber-bridging effect is most pronounced during the initial freeze–thaw cycles. • Component-resolved moisture evolution characterized by NMR elucidates hydration kinetics. • Gel–water hydration degree quantitatively governs initial and final setting times. • Modified Weibull distribution model was developed predicts the residual strength with R² > 0.997.