3D Concrete Printing

Abstract

Concrete is one of the most widely applied construction materials worldwide. Although traditional construction processes are optimized in terms of efficiency, costs and material use, the main disadvantages are still related to the use of formwork, labour and limited freedom of shapes in architectural design. The future of concrete structures looks promising with the development of 3D concrete printing techniques. Research to 3D concrete printing systems and printable concrete mix designs led to the development of 3D printed bridges, houses and other pioneer structures. On the other hand, the influence of printing process parameters on the mechanical properties of printed elements is still a relevant research topic. The layer-wise construction process inevitably introduces interfaces between adjacent filaments. Therefore the experimental research of this master thesis focussed on the influence of printing process parameters. Samples were tested in tension, compression and tensile splitting. The time interval between printing two filaments was the first parameter to investigate. The results showed significant strength decrease with increasing time intervals. The second variable was therefore the effect of different curing conditions applied to printed filaments with a time interval of three hours. Results showed that it is possible to limit the strength decrease when curing of the printed filaments is applied. Finally, the nozzle standoff distance with respect to the printed filament was a variable in this research, as a nozzle with backflow was used. No significant differences were observed between different nozzle standoff distances. The anisotropic compressive strength and the tensile splitting strength were hardly influenced by the different printing process parameters. 3D concrete printing shows potential, but lack of design and calculation methods are still a limitation for the implementation of this technique in the national codes and guidelines. Therefore, the second part of this research was numerical research to investigate the possibilities to match the properties of a numerical finite element model with the experimental results, to be able to verify the strength of printed structures. The tensile bond strength test and the compressive strength test were simulated and both the interface and filament properties were assigned such that the numerical results matched the experimental results in tension. In compression it was possible to match two of the three loading directions. Finally, a hypothetical case study in Mali was studied. An emergency shelter scenario was chosen because the current shelter solutions are mainly built for short term use. 3D printed shelters benefit from the short construction time, but may provide better indoor climate, and a better feeling of safety, which possibly contributes the well-being of humans. The design of the emergency shelter was based on both the construction procedure, the green strength development of printed filaments, and the final strength of the material. In the end, numerical calculations showed that the shelter fulfils the requirements and complies to the code. The 3D concrete printing technique shows potential for new solutions for humanitarian problems, and possibly let people realize that the investment in 3D concrete printed emergency shelters is feasible.