Time-controlled 3D printing of high-ductility cementitious composites with circumferential printing path for coating of prestressed concrete cylinder pipe

Cracking of the protective layer of prestressed concrete cylinder pipe (PCCP) induces steel wire corrosion and pipe bursts, threatening water conveyance safety. High-ductility cementitious composites (HDCC) offer excellent strain hardening and multi-cracking behavior, but conventional roller compaction cannot fully realize these advantages. This work proposes a time-controlled 3D printing strategy that dynamically matches material setting time with the printing window using a four-axis printing system. By adjusting accelerator dosage, a functional relationship between penetration resistance and time was established. The mix with 4% accelerator (0ES4AC) achieved a setting time of 45 min and a workable window of 10 min, well matching the printing requirement. Mechanical tests demonstrated that the material achieved a 28-day compressive strength of 50.0 MPa, a tensile strength of 6.38 MPa, an ultimate tensile ductility of 5.23%, and a flexural strength of 25.64 MPa. Notably, its first-cracking strength reached 3.69 MPa, exceeding the maximum hoop tensile stress of PCCP (3.57 MPa). Microstructural analysis revealed a significant reduction in total porosity, along with a 4.4% increase in harmless pores that act as “crack anchors.” Furthermore, the fiber dispersion was measured at 88.51%, above the 80% threshold for uniform dispersion, ensuring stable fiber bridging. Application validation demonstrated stable interlayer bond strength and good printability in a 1:10 scale model, with shrinkage-induced stress (0.81 MPa) far below the first-cracking strength. This time-controlled 3D printing HDCC material-process system provides theoretical and technical support for engineering application of high-performance protective layers on PCCP.