Performance evolution and service life prediction of 3D printed concrete reinforced with continuous jute yarn under dry-wet and freeze-thaw cycles

Although continuous natural-fiber reinforcement can improve the fracture toughness of 3D-printed concrete (3DCP), its long-term durability under cyclic environmental exposure remains insufficiently understood. Our previous work established a synchronous placement technique for continuous jute yarns and demonstrated their short-term reinforcing effectiveness. Building on that foundation, the present study systematically investigates the physical, mechanical, chemical, and microstructural evolution of continuous-jute-yarn-reinforced concrete (CJYRC) under dry-wet (D-W) and freeze-thaw (F-T) cycles, and further develops durability-based service-life prediction models. After 60 D-W cycles, CJYRC attained a flexural strength of 16.57 MPa, exceeding that of the 28-day standard-curing control. SEM-EDS, XRD, FTIR, and TGA analyses indicate that this strength enhancement resulted from continued matrix hydration, mineralization and densification of the jute yarn-concrete interfacial transition zone, and preservation of a stable crystalline-cellulose skeleton despite partial hemicellulose hydrolysis. Under F-T cycling, hygroscopic expansion of the yarns and ice-wedging effects generated localized microcracking. Nevertheless, CJYRC retained a residual flexural strength of 11.31 MPa. Unlike our previous study, which focused primarily on fabrication feasibility and initial mechanical performance, this work quantifies durability degradation, clarifies its multiscale mechanisms, and establishes predictive models using multivariate polynomial regression and exponential decay. The models predict that CJYRC increases flexural durability by factors of 482 and 370 under D-W and F-T exposure, respectively, relative to the unreinforced matrix.