Investigation of novel 3D-printing methods for freeform construction

• Main Author: Lim, Jian Hui
• Other Authors: Pham Quang Cuong
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/152282
• Institution: Nanyang Technological University

3D Concrete Printing (3DCP) is a technique of sequentially layering of cementitious material to create a three-dimensional structure. Recently, it has gained much attention for its advantages, such as customized production, waste reduction, and increased productivity for construction. Currently 3DCP is still at an early age of industrial adoption. Most research and development in the field of AM for concrete structures are focused on material development and neglected the freeform aspect of additive manufacturing. This partly contributed to the 3DCP competing against classical concrete techniques in the low-cost field of manufacturing rectilinear walls. The cost competitiveness and attractiveness of 3DCP can be improved, by focusing on the manufacturing of freeform structures. The objective of this thesis is to develop an ensemble of methods, spanning multiple scales, from the mechanical reinforcement of the materials to the global shape of the architectural elements to the printing mechanism, expanding the development of 3D Concrete Printing technology for additive manufacturing of freeform structures. Four levels are outlined in the conceptualized research objective. Structural improvement to 3DCP allows for engineers to print freeform design with structural strength. Therefore, there is a need to develop freeform reinforcement which incorporates steel wire into the printed concrete filament as it is printed, through an in-nozzle impregnation process. To improve the printability of concrete of freeform design, we need to support the green concrete which lacks the necessary stiffness and strength to carry its self-weight. Through an adaptable membrane formwork, we can support the concrete in freeform design and re-used the supporting adaptable membrane for other design, in line with 3DCP goal of waste reduction and freeform fabrication. Printing path design for freeform 3DCP is also considered to develop a printing path that accounts for the anisotropic mechanical properties of 3D printed concrete. The printing path produces a stress-cognizant printing scheme that directs the printing of freeform concrete structure to follow the flow of stresses and allow the structure to support the mechanical load on its strongest axis, making the freeform printed concrete more structurally stable. Finally, to improve the scalability of classical gantry printers and print large freeform 3DCP structure, we developed a mobile, multi-robot, printing platform. This has greatly increased the reachability of the robot printer, extending the effective printing area of the system, so that we may print the entire architectural structure in one go.