Improving durability performance of 3D printed concrete via topological interlocking of layers

The demand for 3D Printed Concrete (3DPC) structures in challenging settings and the persistent challenge in the form of weak bonding between deposited concrete filaments, has heightened the interest in improving durability performance of 3DPC. Weak bonding between deposited filaments in 3D concrete printing has significant ramifications, including anisotropic mechanical behaviour, delamination, and diminished durability of printed structures. While previous efforts have sought to address this issue through chemical modifications and the incorporation of repair mortar, there remains a gap in existing literature regarding the physical alteration of the interlayer to enhance durability performance. This study addresses the limited research on early age exposure to environmental factors in 3DPC by investigating how three topological interlayer profiles (IPs), namely triangular, rectangular, and sinusoidal, influences the ingress of gases, liquids, and ions across the interlayer regions (IRs). The evaluation of each topological profile's durability performance is carried out through the application of a Durability Index (DI) which includes assessments of oxygen permeability (OPI), water sorptivity (WSI), and chloride conductivity (CCI). The results revealed that conventional 3DPC is vulnerable to chloride penetration during early exposure to highly chloride concentrated environments. This is concerning as it will result in early-stage pitting corrosion of the steel reinforcement. Using the triangular, rectangular, and sinusoidal interlayer profiles effectively enhanced the durability performance. Notably, the triangular interlayer profile reduced chloride conductivity by 74.2%, effectively changing the CCI durability class from very poor to good.