Mechanical assessment of concrete – Steel bonding in 3D printed elements

•The effect of a highly thixotropic material on the bond strength was investigated.•The effects of the printing method on the bond strength were studied.•A highly thixotropic printed material generated a strong bond with steel bars.•Non-printed samples gave better pull-out resistance and higher stiffness.•3D printed parallel samples outperformed the perpendicular ones. Digital construction of concrete elements using 3D printing technology has been undergoing an exponential growth in terms of research activities and demonstration projects. Though, most researches focused on the behavior of the cementitious materials used in 3D printing, without deeply immersing in the reinforcement of printed elements. In this paper, a detailed experimental program is presented to characterize the quality of the bond developed between concrete and steel bars through a series of pull-out tests. These tests are performed over printed and non-printed samples as well. When printed, the layers orientation, whether parallel or perpendicular to the steel bar is taken into consideration. Hence, it was found that a highly thixotropic material did not undermine the developed bond between printed concrete and rebar. In addition, vibrated concrete (non-printed) gave better resistance to pull-out stresses succeeded by the parallel then the perpendicular samples. Yet, the overall performance of 3D printed concrete in terms of the bond generated with steel could be rated as satisfactory.