The Effect of Post-Tensioning on the Behavior of Small-Scale 3D Printed Concrete Beams (2024-08)¶

Producing large-scale 3D-printed elements in a continuous session is often impractical, highlighting the need for prefabrication of smaller segments that can subsequently be assembled. However, the lack of perfect bonds between joints may cause a lower strength than conventionally cast concrete. Hence, it is crucial to evaluate the behavior of members produced by the segmented assembly approach with appropriate reinforcement mechanisms to enhance their integrity. This study outlines an experimental program aimed at evaluating the structural behavior of small-scale post-tensioned 3D-printed concrete beams composed of three segments. Initially, three specimens were employed to examine material behavior. The findings demonstrate a compressive strength of approximately 25 MPa and varying tensile strengths ranging from 1.82 MPa to 1.89 MPa, depending on specimen orientation. In the next step, flexural strength tests were conducted to evaluate the structural performance of two 3D-printed concrete beams under diverse conditions. The first beam, subjected to a 3-point bending configuration and a post-tensioning force of 133.44 kN, exhibited a maximum load of 75.7 kN at a displacement of 35 mm. The observed brittle behavior, characterized by explosive compressive failure, suggests a potential excess in the applied post-tensioning force. Conversely, the second beam, tested under a 4-point bending configuration with an ungrouted condition and a post-tensioning force of 66.7 kN, displayed a larger maximum load of 87.6 kN at a displacement of 38 mm compared to the first beam. Despite maintaining a compressive failure mode, this beam exhibited a nonexplosive behavior with ductility characteristics. Notably, significant damage to the plastic cover was observed due to a strong interaction between the cable and the void. The observations in this study emphasize the critical necessity of considering the interplay between post-tensioning, grouting, and cable-induced effects in the design of 3D-printed concrete beams.