Investigation of Cementitious Materials for Powder-based 3D Printing A Thesis Submitted in Fulfillment of the Requirements for the Degree of Doctor of Philosophy by Ming Xia Faculty of Science, Engineering and Technology Swinburne University of Technology Hawthorn, VIC, 3122 Australia March 2019 ABSTRACT The construction industry is expected to go through large transformations since construction automation is anticipated to drastically alter standard processing technologies and could lead to possible disrupting technologies such as 3D Concrete Printing (3DCP). 3DCP is a new and emerging technology that is set to revolutionize construction by allowing ‘free-form’ construction without the use of expensive formwork. 3DCP has been proved to be beneficial in terms of optimizing construction time, cost, design flexibility, and error reduction, as well as being environmentally friendly. The powder-based 3D printing method is one of the most attractive 3DCP techniques, which is capable of producing building components with complex geometries, optimized topologies, and uniform surface finishes. Currently, this technique is in its early stages of development and many hurdles are yet to be overcome. One of the main challenges is the very limited scope of printable cementitious materials that can be used for construction applications. This research aims to overcome the issues and barriers by developing a systemic methodology to adapt conventional construction materials to the powder-based 3D printing process. In the first part of this research work, a Portland cement-based powder composed of Portland cement, amorphous calcium aluminate and fine silica sand was developed for the powder-based 3D printing process. Effects of different printing parameters on dimensional accuracy and compressive strength of the ‘green’ specimens (before any post-processing process) have been investigated. The results showed that the printing parameters had significant effects on the final qualities of the 3D printed components. Compressive strength of up to 8.4 MPa was achieved for the ‘green’ 3D printed samples. Subsequently, the effects of post-processing methods on the compressive strength of 3D printed specimens were also investigated. The results showed that the compressive strength of the printed samples cured in either tap water or saturated limewater was significantly higher than that of the ‘green’ samples. The 3D printed samples cured in saturated limewater for 28 days showed the highest compressive strength of 29.4 MPa. The degree of anisotropy in the compressive strength was reduced with the increase of curing time. ii In the second part of this research work, an innovative methodology was presented to develop geopolymer-based materials for the requirements and demands of the powder- based 3D printing process, intended for broadening the scope of printable cementitious materials. Geopolymer is an emerging OPC-less binder purported to provide a sustainable alternative to OPC. Geopolymer may be manufactured by alkaline activation of industrial by-products such as fly ash and slag that are rich in silica and alumina. A geopolymer-based powder using slag-only formulation was developed which can be used in commercially available powder-based 3D printers. The printed samples exhibited the highest ‘green’ compressive strength of up to 1.3 MPa. Subsequently, a series of post-processing methods were developed to enhance the strength of 3D printed geopolymers. The influences of types of curing medium, duration, and temperature of curing on the compressive strength of the printed samples were investigated. Post-processing of the samples was carried out in tap water, three alkaline solutions and three fly ash-based geopolymer slurries at different temperatures (25°C, 40°C, 60°C and 80°C). The results showed that printed geopolymer samples cured in a combination of 8.0 M sodium hydroxide solution (28.6% w/w) and sodium silicate solution with SiO2/Na2O = 3.22 at 60°C for 7 days gained the highest compressive strength of 30 MPa, which is sufficiently high for a wide range of construction applications. The results also showed that the compressive strength of the samples cured at ambient temperature (25°C) for 28 days was comparable to that of the samples cured at 60°C for 7 days. The comparable strength of the ambient-temperature cured samples significantly enhances the commercial viability of 3D printed geopolymers since the developed ambient-temperature curing method is significantly less energy- and emissions-intensive compared to the heat-curing method. To expand the scope of printable geopolymer materials, the methodology developed in the second part was extended to fly ash and slag combinations. The inclusion of fly ash in the formulation is because it is more abundantly available than slag and a large amount of it is still dumped in many parts of the world. The quantitative influences of fly ash content on the printability of the geopolymer powder, as well as the dimensional accuracy and compressive strength of the printed specimens were investigated. The effect of type of alkaline solution used for the post-processing on the dimensional accuracy and compressive strength of the post-processed specimens were also evaluated. The results showed that the maximum fly ash content that can be iii incorporated in the developed 3D printable geopolymer powder is 50 wt%. The post- processed samples printed with 50 wt% slag/50 wt% fly ash powder cured at 60°C for 7 days exhibited a compressive strength of up to 25 MPa. The powder-based 3D printing process is likely to be used for highly detailed ornamental shapes where the high accuracy will be demanded. Therefore, a novel method based on image acquisition and processing system using a flatbed scanner was developed to quantitatively evaluate the shape accuracy of the powder-based 3D printed samples. A set of image processing algorithms was developed to extract useful shape information from scanned images without any intervention. Centroid distance function was used as the shape error representation under the polar coordinate system for the shape error measurement. A color-labeled map in conjunction with root mean square error (RMSE) were used to quantify the shape accuracy of the samples. The results showed that the developed method can satisfactorily be used for shape accuracy measurement of the powder-based 3D printed specimen. At the same time, this method is cheaper, simpler and less time-consuming compared to the currently used techniques such as computed tomography (CT) scan and coordinate measuring machine (CMM). Overall, the novel methodologies developed in this doctoral research expand the severely limited scope of cementitious materials that can be used in the powder-based 3D printing process for construction applications. iv To my parents 献给我的父母 v ACKNOWLEDGEMENTS The thesis was partly funded by Australian Research Council Discovery Grant DP170103521 and Linkage Infrastructure Grant LE170100168 and Discovery Early Career Researcher Award DE180101587. I also acknowledge Swinburne University of Technology for supporting and funding this doctoral research through Swinburne University Postgraduate Research Award (SUPRA) and ARC Discovery Scholarship. First of all, and most importantly, I want to thank my family. I am eternally grateful to my parents, Mr. Qingyuan Xia and Ms. Yan Zou, for setting the model of how to be the person I am today. Their belief in me and unconditional support have always given me the strength to follow my dreams. I would like to express my deep gratitude to my principal coordinating supervisor, Professor Jay Sanjayan for his patient guidance and valuable support on this journey, and his valuable and constructive suggestions during this doctoral research. I would also like to truly thank him for placing his confidence in my work which gave me the strength to continue. This thesis would not have been possible without his support. I am forever indebted for his great mentorship. I am also grateful to my associate supervisor, Dr. Behzad Nematollahi for his extraordinary help and support during my doctoral research, and for the many, many encouraging talks he gave me on this journey. Without his support, I might never have managed to believe this was possible. I truly appreciate Dr. Vinh Dao (University of Queensland, Australia) and Prof. Paolo Colombo (University of Padova, Italy) as my examiners for revising this manuscript and for their help in getting it to its final shape. I would especially like to thank Miss Meiyu Hu for being there for me for every up and down in these 1400 days. Thank you came into my life, the beautiful, happy, thank you for giving me cherish the memory forever. I would like to acknowledge the people in the Digital Construction Laboratory, who contributed in one way or another to this work. I am thankful to Dr. Ali Nazari and Dr. Hongjian Du, Taylor Marchment, Shin-Hau Bong, Ravendran Arunothayan, Roshan Jayathilakage Shiwei Yu for supporting me with experimental work, data analysis or collection, and for engaging in insightful discussions. I am also grateful to Praful Vijay vi for being a wonderful friend. Especially thank Senior Laboratory Engineer Kia Rasekhi for his invaluable technical assistance and guidance during the experimental work. Every single person in the group contributed to making this journey a very special, extremely enjoyable, and incredibly rewarding experience. And lastly, from the bottom of my heart, I wish to express my sincere gratitude everyone who has given me power, enthusiasm, and motivation throughout my life. vii DECLARATION I declare that the thesis is my original work except for quotations and citations which have been duly acknowledged. I also declare that it has not been previously, and is not concurrently, submitted for any other degree at any other institutions. I hereby declare that I am the sole author of this thesis. Ming Xia March 2019 viii LIST OF PUBLICATIONS Publications arose from this thesis: Patent: “Portland Cement-based powder for Powder-Based 3DConcrete Printing”, Australian Provisional Patent No.