Towards the structural application of 3D-printed concrete taking into account interlayer effects

Extrusion-based additive manufacturing of cementitious materials – also called 3D concrete printing (3DCP) – is an emerging research field which creates ample opportunities for the construction of intricate geometric designs, hereby opening up the way to structurally optimised concrete elements. Furthermore, the robot-aided production process allows for a shift towards automated construction, thereby further optimising the overall realisation of these elements. However, before 3DCP can enable the commercial production of structural building components, attention must be paid to the geometric discontinuities caused by the layer-wise construction process. The interlayer between two deposited layers affects the structure’s mechanical behaviour. Two relevant characteristics, namely elastic stiffness and interlayer shear, are highlighted in this context. Concerning the elastic behaviour, in an experimental study on cylindrical 3DCP specimens, no significant directional dependency was observed. However, there appears to exist a significant decrease in stiffness compared to cast specimens. A first model, as well as a novel experimental shear test setup, were developed, but more research and testing are needed to fully characterise the interlayer shear behaviour. Additionally, a brief outlook toward future research is given by presenting a first example of a stress-constrained optimised concrete structure that without the help of the 3D concrete printing technology would be hard to realize.