Experimental Study on the Anisotropic Behaviour and Strength of 3D Printed Concrete

Robotically controlled 3D Concrete Printing is a rapidly evolving technology that offers promising potential to change the way we can design and optimise concrete structures. Many research groups in academia and start-ups have already showcased its potential in various types of structures.
However, the mechanical properties of 3D printed concrete cannot be expected to be like the ones of conventional cast concrete. One of the obvious differences is that the concrete is deposited in subsequent layers, and the interfaces between the layers depend on the specifics of the printing process.
Therefore, it is necessary to establish fundamental knowledge on the mechanical properties to enable the use of printed structures in practice, and potentially, use the well-known methods and models developed for conventional cast concrete. Normally, the compressive strength is assessed on the basis of small samples (cylinders or cubes) and is assumed to be isotropic, and it is used in the models as such. This approach is acceptable for cast concrete where all the design models are also verified with a similar experimental approach.
To understand how the compressive strength and behaviour varies in 3D printed concrete in relation to the layer layout, this paper presents an experimental investigation of the compressive strength of cylinders drilled in different directions relative to the layers of a printed concrete structure. In the experimental programme, important printing procedures and concrete recipes are varied. The failure modes are analysed with photogrammetric measurements.
The results show that 3D printed concrete has a statistical extremely significant strength anisotropic behaviour. Furthermore, the results show that the strength in all directions is lower than the standardised mould cast concrete cylinder.