Degradation Mechanisms and Microstructural Performance of 3D-Printed Engineered Cementitious Composites with Yellow River Sand Under Chloride Ion Wet-Dry Cycles (2025-10)¶

3D printing of Engineered Cementitious Composites (ECC) is an emerging, cutting-edge construction technology that enables layer-by-layer fabrication without the need for formwork or steel reinforcement. ECC exhibits superior tensile strength and crack resistance compared to conventional concrete. However, the durability of composite structures, especially in marine environments exposed to harsh conditions such as sulfate and chloride ions, remains a concern. This study investigated the performance of cast and 3D-printed specimens under chloride ion wet–dry cycles (0, 5, 10, 15, 20, 25, and 30 cycles) and utilised sustainable Yellow River sand (YRS) as a partial replacement for quartz sand to reduce material costs. Results showed that the compressive strength of both cast and 3DP-ECC specimens was highest in the Z direction. Among them, the R25 cast specimens exhibited better strength properties, starting at 34 and 32 MPa, respectively, and decreasing to 22 and 23 MPa after 30 cycles of chloride exposure. In comparison, compressive strength in the Y- and X-directions decreased by 20% and 23%, respectively. Scanning Electron Microscopy (SEM) images of cast ECC revealed a dense and relatively uniform microstructure, with well-bonded phases between the matrix and the aggregates. The interfacial transition zone (ITZ) between the cement paste and aggregates appeared smooth, indicating strong bonding with minimal porosity. This study highlighted that incorporating Yellow River Sand as a partial replacement in 3D-printed ECC not only enhances sustainability and reduces material costs but also maintains satisfactory mechanical performance, particularly at the 25% replacement level, under chloride ion wet–dry cycles.