Haodao Li, a doctoral candidate in civil engineering, will defend their dissertation titled “Design and Performance of Fiber-Reinforced 3D Printed Composites Using Indigenous Materials.” Their advisor, Dr. Kamal Khayat, is the vice chancellor for research and innovation and a professor in the civil, architectural and environmental engineering department. The dissertation abstract is provided below.

Exclusive use of ordinary portland cement (OPC) and lack of reinforcement in 3D concrete printing (3DCP) raise considerable environmental and structural concerns in modern construction practices. This study develops three classes of 3D printable fiber-reinforced mixtures using locally available materials, namely ultra-high-performance concrete (UHPC), high-performance concrete (HPC), and conventional concrete (CC), capable of enhanced printability, mechanical properties, and shrinkage resistance. A systematic methodology was proposed to optimize binder systems with improved packing density and to fine-tune fiber volume, enabling the formulation of low-carbon printable fiber-reinforced cement-based materials. Viscosity-modifying agents (VMAs) were further incorporated, and their effects on rheology, printability, and fiber alignment were evaluated. In addition, the effect of fiber characteristics (e.g., type, volume, length, and combination) on printability and hardened properties were examined.

Results demonstrated that all mixture classes achieved strength criteria while maintaining excellent printability. The incorporation of VMAs enhanced stability under dynamic pressure and improved structural build-up at rest but negatively affected fiber orientation and dispersion in printed elements. Anisotropic mechanical properties were pronounced, particularly in mixtures incorporating steel fibers. The in-situ 28-day compressive strengths of 3D-printed UHPC, HPC, and CC reached 147, 102, and 38 MPa, respectively, while flexural strengths were 24, 14, and 5 MPa in the preferred loading direction. Increasing steel fiber volume and incorporating hybrid fiber combinations significantly enhanced resistance to both autogenous and drying shrinkage.