Mechanical Characterization of 3D Printed Concrete: From Fresh State to Hardened Performance

This thesis investigates the mechanical performance of 3D printed concrete (3DPC), with a particular focus on the transition from fresh to hardened states. Motivated by the evolving landscape of digital construction and the rising interest in additive manufacturing techniques, the research centers on characterizing a novel 3DCP approach that integrates vibro-compaction during material extrusion, a method developed by the DTU spin-off ERLEtek. The experimental campaign evaluates both early-age and hardened mechanical properties, including shape retention, green strength, compactability, compressive strength, elastic modulus, and interlayer bonding strength. A custom-built gravity-fed printer with vibration-assisted extrusion was employed to produce prismatic samples using two base concrete mix designs, further modified with steel fiber reinforcement (25 and 40 kg/m$^3$). The testing followed standardized and tailored protocols to assess mechanical behavior across multiple curing intervals (from minutes to days after mixing). Results highlight the critical role of vibro-compaction in enhancing print quality and consistency, while steel fibers were shown to significantly improve the compressive strength. The time-dependent development of green strength provided insights into optimal buildability windows, while hardened tests confirmed the viability of the proposed technique for structural applications. Overall, the study contributes valuable empirical data and supports the development of robust design strategies for the future of 3D concrete printing.