Resilient 3D-Printed Civil Infrastructure with Ultra-High Performance Engineered Cementitious Composites (UHPECCs)

This study aims to develop and evaluate UHP-ECC materials for 3DP applications. To achieve this, the rheological properties of the cementitious composites were designed to accommodate 3DP functionality. Additionally, this study aimed to evaluate the hardened properties of the 3D-printed UHP-ECCs and compare them to the cast UHP-ECCs. Furthermore, the effect of variables such as sand-to-binder (S/B), fly ash-to-cement ratio (FA/C), and high-range water reducer (HRWR) content on the fresh and hardened properties of the 3D printable mixtures were evaluated.  Fresh properties of mixtures were assessed by means of the flowability test, setting time test, and printability test. Hardened properties were assessed utilizing the compressive strength test, uniaxial tensile test, and flexural performance test. Experimental results showed that the flow and setting time of the composites reduced as S/B incremented while having the opposite reaction with an increase in FA/C or HRWR. Additionally, a range of initial spread diameter values from 127 to 136 mm was related to the printable mixtures. Moreover, pseudo-strain-hardening (PSH) behavior was observed for all mixtures during the uniaxial tensile test. It is important to note that mixture FA67S/B1(2.2) developed in this study, showed an exceptional tensile strain of 2.1%, along with a compressive strength of 91.9 MPa, a tensile strength of 5.3 MPa, and flexural strength of 13.6 MPa. Finally, the printed specimens showed significant anisotropic behavior when compared to cast specimens, displaying a reduction in compressive strength ranging from 14.5% to 37.5% when tested in the perpendicular, longitudinal, and lateral directions, as well as an increment in flexural strength ranging from 4.8% to 11.7% when tested in the perpendicular and lateral directions.