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195372 https://hdl.handle.net/2286/R.2.N.195372 http://rightsstatements.org/vocab/InC/1.0/ All Rights Reserved 2024 247 pages Doctoral Dissertation Academic theses Text eng Tripathi, Avinaya Neithalath, Narayanan Mobasher, Barzin Hoover, Christian Bhate, Dhruv Rajan, Subramaniam Arizona State University Partial requirement for: Ph.D., Arizona State University, 2024 Field of study: Civil, Environmental and Sustainable Engineering Layer-wise extrusion of cement pastes, mortars, or concrete is the most commonly used technique in three-dimensional (3D) concrete printing. Understanding the behavior of the printed binder after placement is crucial for optimizing the properties of 3D-printed elements. This research, conducted in two stages, fresh and hardened state responses, elucidates the post-extrusion mechanics of cementitious binders to enhance print quality. In Stage-1, a novel technique for characterizing 3D printable mortar binders using the green compression test (GCT) is introduced. Equations based on GCT parameters were established to predict buildability, the maximum height that can be sustained without significant deformation or failure. These equations were able to predict buildability and failure mechanisms over time accurately. Stage-2 investigates the mechanical response of hardened 3D printed binders, focusing on inter-layer and inter-filament interfaces, mixture types, and fiber content. Variation in interface positioning and the addition of fibers (0.28% by volume) improved flexural response while maintaining comparable compression strength. However, it did not eliminate anisotropy in compression, and mechanical properties remained inferior to cast counterparts. Next, a numerical model was developed, using cohesive zone finite elements to represent joints and an orthotropic visco-elastic-visco-plastic material model for the bulk filament. This model effectively predicted the mechanical response of 3D printed elements, accurately capturing anisotropy under uniaxial compression. This highlighted the importance of properly characterizing joints and selecting material models. Finally, ultra-high performance 3D printable mixtures were developed using a low water-to-binder ratio mixture with a higher content of water-reducing agent, achieving compressive strengths exceeding 100 MPa at 28 days. This mixture resulted in reduced anisotropy while providing strengths comparable to mold-cast specimens. Incorporating high fiber volume (1.5% by volume) into this mixture significantly enhanced compression and flexural responses. Composite material sections, created by printing different mixtures in various layers, showed comparable mechanical responses while improving cost and environmental efficiency. The findings of this research contribute to precise failure prediction during printing, propose methods for better mechanical responses in printed products, and offer insights into cost-effective and environmentally efficient section design through composite material printing using 3D concrete printing. Civil Engineering 3D printing of concrete buildability FE Modelling Multi-material Composite Printing Print Technique and Material Modification In 3D Printing of Concrete