3D Printing of Engineered Cementitious Composites (3DP-ECC)

Abstract

3D concrete printing (3DCP) is revolutionizing construction practices. As a promising printing ink, ductile engineered cementitious composites (ECC) removes the dependence on steel reinforcement required for concrete structures. While ECC offers structural shape flexibility and 3DP promotes construction speed, there remain knowledge gaps that must be overcome to reach field readiness. This thesis builds a 3D printing ECC (3DP-ECC) knowledge system by experimental investigation and theoretical analysis, covering the design, control, and behavior of 3DP-ECC in its life cycle. In the material production phase, material fresh properties were investigated. To quantify the buildability of printable ECC at the fresh stage, the time-dependent fresh properties of ECC were experimentally characterized. A quantitative methodology for evaluating buildability at both the material and structural scale was further proposed, with the influence of time progression and material-machine interaction taken into consideration. During manufacturing, the impacts of print process parameters on 3DP-ECC were probed. To gain a deeper understanding of material-machine interaction in both fresh and hardened states, the inter-relations among material production control, micro-structure and macro-scale properties of 3DP-ECC were explored by varying the nozzle travelling speeds and nozzle standoff distances. Moreover, to alleviate anisotropy of hardened 3DP-ECC, innovative printing patterns were designed and validated. Knitted and tilted filaments were designed to mimic the crossed-lamellar micro-structure of conch shells. The bio-inspired novel design rendered ECC’s directional-dependent tensile resistance to three-dimensional space and introduced a complex interface system, effectively moderating anisotropy of 3DP-ECC. In the use phase, the structural-scale behavior of printed elements was studied. Cavity walls with different infill patterns were printed and tested to examine the feasibility and performance of 3D printed ECC elements. Enhanced energy absorption ability and ductility compared to printed concrete walls were captured and valued. xvi Further, shrinkage and high carbon footprint concerns were mitigated by mix proportion optimization of printable ECC. The mix was designed to have both a lower carbon footprint than conventional concrete and early expansion capabilities to address shrinkage concerns. The designed printable ECC contributes to suppress environmental impact and prolongate service life by eliminating shrinkage-induced cracking. This research seeks broad impact by filling the existing research gaps in 3DP-ECC and offering innovative solutions that can advance the field. The knowledge generated in this thesis offers critical insights into the future development and prospects of 3DP-ECC, ushering in the practical large-scale applications of 3DP of concrete structure that maximizes the unique advantages of 3D printing over conventional construction approaches.