"3D printing is the process of creating three-dimensional objects using an automated additive manufacturing process. The 3D printing process has been used with materials such as metals and polymers, but application with cement based materials for the construction industry has yet to be developed. In this research, two main problems were investigated for printing cement based composite materials: extrudability and tensile reinforcement. Fiber-reinforced concrete (FRC) was studied as an internal reinforcing system to increase tensile/flexural strength. First, FRC was studied to investigate mechanical properties and use of fibers from waste tires as an environmentally friendly option. A reference mixture with no fibers, three mixtures with manufactured steel fibers, three mixtures with recycled steel fibers, and a hybrid mixture were studied. Three-point bending, compression, and modulus of elasticity tests were performed. In addition, three mixtures were made for cast and printed beams to compare the effect of printing process on fiber orientation and strength. An automated extrusion device was developed for printing and to quantitatively analyze extrusion. Test methods were developed to investigate blockage and extrusion force. Particle size, rheology, nozzle diameter, and extrusion speed were evaluated. Results showed that fibers improves flexural performance and recycled fibers provide a similar benefit to manufactured fibers. Printing fibers improved fiber orientation and post-crack properties. Different cracking mechanism were found when printing versus casting beams. The developed extrusion tests provided a successful way to quantify the extrudability. It was found that the extrusion force and energy depend on nozzle size, yield stress, and extrusion speed"--Abstract, page iii.
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