| dc.description.abstract | 3D printing is a process by which structures are built up layer-by-layer by progressively adding material to create a three-dimensional object. By placing material only where required, construction-scale 3D printing with cement-based materials can greatly increase design flexibility, shorten lead times, and reduce costs and waste associated with traditional casting techniques. However, because cement-based materials are subject to more constraints to be appropriate as 3D printing inks compared to casting, the development of new materials and a better understanding of the interplay between ink formulation, extrusion process, and mechanical and thermal properties are needed to make 3D printing commercially viable. In this dissertation, the effects of the 3D printing process and cement ink formulation on the chemomechanical and thermal behavior were studied. Results showed that the printing process can result in dynamic changes in the composition of extruded filaments compared to the original cement ink formulation. These changes in filament composition resulted in the formation of high mechanical property (HMP) and low mechanical property (LMP) filaments. The variation in micromechanical properties were attributed to changes in local water-to-cement (w/c) ratio combined with stress-induced dissolution of the unhydrated cement particles, with higher w/c ratio filaments having a more loosely-packed microstructure. Cement ink additives were found to impact the ink stability, with carbon nanofibers (CNFs) found to cause underextrusion and generally reduce printability, resulting in reduced macroscale mechanical properties. Carbon microfibers (CFs) were found to preferentially align in the direction of printing and modestly improved the compressive strength at seven days, though CF-induced blockages periodically caused printing discontinuities. Halloysite nanoclay (HNC) incorporation was found to enhance filament stability and improve printability. However, HNC incorporation did not prevent the formation of HMP and LMP filaments due to extrusion-induced variations in HNC concentration and clustering. HNC was also found to slightly reduce the thermal conductivity of printed structures, with a much larger effect being found for changes in the internal architecture of printed structures caused by differences in void structures and heat conduction pathways. | |
