Determining the strength of 3D printed concrete with the modified slant shear test

This study deals with the assessment of the load-bearing capacity of layered 3D printed concrete (3DPC) using a modified slant shear test (MSST) to define a Mohr's envelope. To this aim, the established modified Coulomb yield condition of the concrete is complemented by a Coulomb failure criterion of the layer joints (cold or dry joints). Due to the anisotropy inherent to 3DPC elements, caused by the interlayer of printed concrete, the test setups commonly used for conventional concrete are inadequate to assess the load-bearing capacity of 3DPC. A total of 45 3DPC specimens with different inclinations of the concrete printed layers, including a cold joint with 30 min time gap were tested using the MSST. The results showed a high strength of the interfaces with two different failure modes, depending on the inclination of the layers: (i) concrete matrix failure and (ii) layer interface failure, where the latter governed for layer inclina- tions of 60 and 75 with respect to the horizontal plane. The test campaign con- firms that the proposed MSST is a highly practical test method that enables determining the parameters governing a Mohr's envelope of layered 3DPC and can thus be used to reliably characterize its load-bearing capacity.