3D printing in building and construction

• Main Author: Liu, Zhenbang
• Other Authors: Wong Teck Neng
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2025
• Subjects: Engineering; 3D concrete printing; Computational fluid dynamics simulation; Buildability analysis; Mesoscale finite element simulation; Structural performance
• Online Access: https://hdl.handle.net/10356/182522
• Institution: Nanyang Technological University

Due to its advanced automation and design freedom, 3D concrete printing (3DCP) is gaining popularity in the building and construction (B&C) industry. Unlike traditional reinforced concrete (RC) structures, the fresh-state cementitious material is pumped and extruded layer by layer with no formwork support. Thus, comprehensive research is essential to evaluate the performance of 3D printing concrete at various stages: during printing, after concrete hardening, and when utilized as structural members. These stages correspond to three levels of investigations in this thesis: research on 3DCP buildability, examination of the mechanical properties of small-scale 3DCP units, and assessment of the structural behavior of large-scale 3DCP structural members, respectively. Correspondingly, four key themes were addressed as follows: Firstly, for the extrusion-based 3D printing process, high buildability is essential to resist printing failure. While this failure is often attributed to the strength and elastic modulus of the 3DCP material, the quantitative relationship between the 3DCP failure criterion and material fresh properties remains unclear. Through the stress analysis of the 3DCP member, this study identified the critical areas in the 3DCP member are uniaxially and biaxially compressed areas which have the same compressive strength. By comparing the stress states between the 3DCP member and tested samples, this study revealed that the compressive strength of the uniaxially compressed area can be determined through the unconfined uniaxial compression tests (UUCTs). Consequently, this study has successfully established a quantitative connection between the 3DCP failure criterion and the fresh properties of materials. Secondly, in small-scale 3DCP units, the mechanical performance of anisotropy has often been associated with interlayers. Recent studies have suggested that pore anisotropy may also influence the mechanical anisotropy of 3DCP units. However, the corresponding relationship between pore anisotropy and the mechanical anisotropy of 3DCP units remains at a qualitative level. Through computed tomography (CT) scans, this study observed that pores within 3DCP units can be represented by a biconvex lens pore without a specific orientation along the printing direction (PDir), which contracts with the conclusions of early studies. Subsequently, finite element (FE) models were constructed based on CT scan images incorporating both pores and solid elements of concrete. In the developed CT-scan-based FE model, concrete followed an isotropic constitutive model, which was determined by the inverse method with pores being the only variable. The CT-scan-based simulation results showed strong agreement with mechanical test results, which validated the feasibility of CT-scan-based simulation in assessing the mechanical performance of 3DCP units. This good agreement further substantiated the quantitative relationship between the pore properties and the mechanical performance of 3DCP units. Thirdly, the second study has demonstrated the correlation between the mechanical anisotropy of 3DCP units and the presence of high porosity at interlayers and pore anisotropy. However, there is still limited exploration into methods for adjusting the mechanical anisotropy of 3DCP units, and the mechanism that different printing parameters attribute to high porosity at interlayers and pore anisotropy remains unclear. In the third study, a specialized nozzle with an expanded flow channel was designed to modify the mechanical anisotropy of 3DCP units. Various printing parameters, such as overflow ratio, stand-off distance, and flow rate, were compared using experimental and numerical methods. Through a combination of CT scans, uniaxial compression tests, and computational fluid dynamics (CFD) simulations, this study revealed that the size of the nozzle flow channel and the printing parameters influence interlayer porosity and pore anisotropy by influencing the normalized local pressure at interlayers and fluid velocity gradients, consequently altering the mechanical anisotropy of 3DCP units. Finally, within large-scale 3DCP structures, the steel cable reinforcement method and the reinforced concrete confined by the 3DCP formwork (RC-3DPF) method stand out as potential approaches combining the reinforcement and 3DCP members due to high-level design freedom and automation. However, steel cables offer limited reinforcement along the direction perpendicular to PDir, and the load resistance of RC-3DPF fails to meet the requirements of traditional construction due to the weak bonding between inner cast concrete and 3DCP formwork. In the fourth study of this thesis, a hybrid approach combining the steel cable reinforcement method and the RC-3DPF method was proposed and applied as the steel rebar reinforced column confined by the steel cable reinforced 3D concrete printing permanent formwork (RC-SC-3DPF). Axial compression tests and theoretical analysis were conducted to examine the axial performance of RC-SC-3DPF. The results from axial compression tests indicated that the increasing quantity of steel cables enhances the structural behavior of RC-SC-3DPF. When the steel cable confinement ratio (Cf) is larger than 0.534%, the structural performance of RC-SC-3DPF is comparable to or even superior to those of the traditional case. Additionally, a theoretical model was developed to effectively assess the structural behavior of RC-SC-3DPF.