Exploring the Load-Bearing Capacity of 3D Printed Concrete

At ETH Zurich, researcher Lucia Licciardello is investigating how 3D printed concrete can evolve from a material used mainly for non-structural elements into a reliable load-bearing option. Through two testing methods developed at the Institute of Structural Engineering, she aims to clarify its structural potential and support the development of future design rules.

Lucia Licciardello and her colleague Antoine Binggeli conducting a tension test on reinforced 3D Printed Concrete tie on the Schenck universal testing machine. Photo by the Chair of Concrete Structures and Bridge Design.

3D printed concrete (3DPC) is mostly used today for concrete elements without load-bearing function, such as moulds for complex shapes or components in hybrid structures. Its potential as a load-bearing material is still largely unexplored. This is because, being built layer by layer, 3DPC behaves differently in different directions, and its strength depends not just on the concrete itself but also on how well the layers stick together. Therefore, design rules for conventional concrete cannot always be directly applied to 3D printed concrete.

To explore its structural potential, Lucia and her colleagues at the Chair of Structural Engineering – Concrete Structures and Bridge Design have developed two testing methods that reveal how 3DPC performs under different loading condition: a modified slant shear test and a direct tensile test on reinforced 3D printed concrete ties.

Modified Slant Shear Test

The modified slant shear test is an adapted version of a conventional testing methodology used to assess the bond between two concrete layers cast at different times. For 3D printed concrete, this idea is transferred to its layered structure. Since the material is built like a stack of thin layers, the test examines how firmly these layers hold together. To do this, printed elements with layers at different inclines were produced and then compressed from the top with a steadily increasing force. A short printing pause was added in each block to mimic a real construction interruption. Although the setup looks simple, the inclined layers generate a mix of normal and shear stresses inside the block. Observing how the samples react under compressive loading helps to assess the material strength and allows the identification of potential weak zones relevant for practical applications.

Direct Tensile Tests on Reinforced 3D Printed Concrete Ties

The Direct Tensile Tests focus on how 3D printed concrete behaves when it is pulled apart rather than pressed together. Since printed concrete cannot safely carry tension on its own, steel reinforcement must be added during fabrication. Small reinforcing bars, called stirrups are placed between the layers, and the longitudinal reinforcement runs through a grouted channel inside the printed shell. Together, they form a kind of reinforced core surrounded by printed concrete. To see how these elements behave when stretched, long cylindrical samples were produced and pulled from both ends. Different versions were made by changing the rebar diameter, whether the printed surface was left rough or made smooth, and whether extra small reinforcement loops were added.

These variations helped reveal how the force moves from the steel bar into the grout and then into the printed concrete. The key goal was to observe where the first cracks appear, because the first crack shows exactly where the element begins to lose its grip and how the different materials share the load. Through this approach, the study provides essential insight into how reinforced 3D printed concrete carries tension, offering a basis for future models and design rules that allow the use of 3D printed concrete in structural applications.

This article is based on a technical blog entry of Lucia Licciardello and was originally published on the e-learning platform of the Chair of Structural Engineering – Concrete Structures and Bridge Design, led by Prof. Walter Kaufmann.

Read the original text here: https://concrete.ethz.ch/blog/experimental-and-analytical-investigation-of-the-load-bearing-capacity-of-3d-printed-concrete/