Large scale 3D concrete printing : process and materials properties

• Main Author: Tay, Daniel Yi Wei
• Other Authors: Leong Kah Fai
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Materials::Composite materials; Engineering::Materials::Material testing and characterization
• Online Access: https://hdl.handle.net/10356/137968
• Institution: Nanyang Technological University

The main challenge for the 3D concrete ‘ink’ to be printable is the contradicting characteristic it should possess. It should be flowable enough to be pumped through the hose as well as having sufficient strength for buildability during the layer-by-layer deposition. This posed a challenge as the mixture needs to overcome the internal shear resistance arising from the interaction between the particles to be pumpable and it requires sufficient shear strength for shape preservation after extrusion. Most of the existing studies that proposed mixture for 3D concrete printing used rheometers measuring dynamic yield stress and plastic viscosity. As the measurement with rheometer is sensitive to the protocols and control by the rheologists, as well as data processing if non-standardized measuring geometries are used, results could vary significantly. Little exploration on the material region of printability has been done for 3D concrete printing. This propels the motivation to investigate the material characteristic limits for printability (e.g. pumpability and buildability). A field-friendly protocol will be proposed to measure the slump and flow diameter of the mortars, which will be used to define the material printable region and are evaluated with the pumpability and buildability parameters of the mixtures. Apart from the material aspect, the printing parameters also play an important role in 3D printing. Inappropriate printing parameters can have an adverse effect on the printed structure strength and stability. Since this technique prints layer-by-layer, the time taken to reach the same position in the subsequent layer is important as it will create an anisotropic property that has a weaker tensile strength at the bond interface of the two printed filaments. Through rheological measurement, which reveals the material deformation and flow behaviour, and observation on the printed filament at macroscopic-scale, it is possible to examine the effect of time gap on the material structural build-up and how it affects the bonding between different layers. Furthermore, through investigation of the print filament at different material flow rates and nozzle travel speeds, it is possible to identify the parameters for different printing operations. Different printing operations can be used to obtain different type of filament for various purposes. Functionally graded concrete material, which offers effective conservation of material usage and high performance of integrated structures efficiency, can be achieved with this technique. It can be obtained by 3D printing given that the printer has the ability to dynamically vary the material structure in complex 3D distribution and can produce a continuous gradient in a 3D printed part. Varying parameters allow for optimization of the material properties relative to their structural and functional performance. An optimized structure varying gradient was used to verify the performance of a functionally graded material (FGM) printed structure in terms of flexural strength-to-weight ratio. Lastly, a full-scale pre-fabricated unit PBU is printed and the methodology to increase the scale was shown in this dissertation. In most literature, the printing takes places on a small scale, however, in order to increase the size of the printed part alteration to the material is necessary. This dissertation ends with a chapter describing the steps needed for large scale printing and the methodology to design the mix design. The economic evaluation shows that 3D concrete printing can save around 25% of the total cost to produce the main concrete structure when compared with formwork casting method.