Development and optimization of 3D printable cementitious composites for printing applications

• Main Author: Weng, Yiwei
• Other Authors: Qian Shunzhi
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Civil engineering
• Online Access: https://hdl.handle.net/10356/137090
• Institution: Nanyang Technological University

3D concrete printing (3DCP) builds up objectives in a layer-atop-layer manner and has attracted much attention recently due to many advantages, such as customized production, reduced waste, and diminished lead-time of the rapid prototype. A number of works have been conducted in 3DCP in recent years. However, limitations remain in 3DCP, especially in the field of developing consistent and reliable cementitious materials for 3DCP. This thesis proposes a holistic approach to develop consistent and reliable 3D printable cementitious materials for large-scale printing applications. Three levels are included in the conceptualized methodology. Rheology control serves as a vital factor at the lowest level to ensure that material fresh properties can satisfy the printing requirement in terms of buildability, pumpability, setting control and shape retention capability. Afterwards, material design are the critical factors at the intermedium level to ensure that hardened properties of printed materials are suitable for structural or non-structural applications. Hardened properties are focused on compressive and flexure performance in this thesis. Process design focuses on the optimization of printing parameters for better material distribution and interlayer properties. Finally, integration of building information modeling (BIM) and architecture with 3DCP is expected to promote automatic construction fabrication for digitalized products at the third level. Due to time constraint of this PhD study, this thesis focused on the first two levels and the third level is discussed in the section on future work. The first level study focused on the influence of various factors on material rheological properties. Firstly, empirical models are constructed to predict the rheological properties based on material constituents and chemical admixtures. Secondly, theoretical models are developed to link rheological properties with printability in terms of buildability, which was validated by a new testing method proposed in this study. Thirdly, a class of rapid hardening materials, magnesia phosphate cement-based materials, is also developed. The second level study characterized the hardened properties of developed printable materials. Three different types of printable materials were investigated, i.e. plain cementitious materials, fiber reinforced cementitious materials, and rapid hardening cementitious materials, respectively. The hardened properties were studied in terms of compressive and flexural strength.