Additive manufacturing and 3D printing are rapidly developing digital fabrication techniques. After the first steps in printing of metals and plastics have been made, research from various groups around the world is now also focusing on printing in concrete and moving to larger scales. Using this technique it will be possible to create customised concrete designs in one go at low costs and high construction speeds. Additionally, this new technology will provide opportunities to create more efficient structures. Structures can already be optimised in the early stages of the design for weight and structural performance, but the resulting optimised structures are often difficult to manufacture due to their shape. Additive manufacturing can be the key to make this possible without high costs for moulds and labour. This thesis will present a novel methodology to include material and manufacturing constraints of 3D printed concrete in the optimisation process. The study examines the possibility to optimise concrete structures in the design phase. In order to save material and thus create more sustainable and more cost efficient structures, a topology optimisation tool has been created specifically for 3D printed concrete. Traditional topology optimisation methods consider isotropic and linear elastic material and will not necessarily produce realisable and reliable optimised structures. In the algorithm presented constraints of the printing process and material properties from physical testing of this layered material are both considered in the optimisation. By adopting this methodology more realistic and feasible optimal concrete structures can be designed.

The objective of this research project is to verify whether 3D printing of concrete (3DPC) reduces the environmental impact by increasing the structural efficiency. During the literature study, numerous articles were identified that claimed an increase of structural efficiency by using 3DPC to reduce material use. Some of these articles suggest that an increase in structural efficiency results in a reduction of environmental impact. However, these articles do not support this potential with a research study. This research project therefore studies the relation between structural efficiency and the environmental impact of a 3DPC bridge. This relation is studied by developing a design model that calculates structural efficiency and determines the environmental impact. The design model is developed in a visual script environment for parametrically controlling visual design software. The parametric script specifies and combines information in an XML file used for structural analysis in finite element software. This analysis is executed on command in the parametric environment and the results are used for verifying the structural safety. The structural safety is expressed in a material utilisation ratio. This ratio indicates the used proportion of strength of the material and can be used as an indicator for structural efficiency. After calculating the structural efficiency, the design model is used to determine the environmental impact of the structure expressed in shadow costs. Shadow costs quantify the environmental impact of materials and processes related to geometric quantities defined in the design model. Multiple combinations of parameters have been compared to determine the relation between structural efficiency and environmental impact. The results of the comparison show that an increase in structural efficiency results in decreased material use. A decrease in material use reduces the environmental impact because ±59% of the impact is related to 3DPC material. The environmental impact of the 3DPC bridge is then compared to a hollow-core-slab element with a similar functionality to verify the claimed potential. This comparison shows that the environmental impact of 3DPC is almost two times higher than the compared conventional method. Therefore, using a novel design model and based on the results, following two conclusions can be drawn: 1. Increasing structural efficiency can decrease the environmental impact of a 3DPC bridge, and 2. Considering the state of 3D printing concrete technology at present, applications of this technology for bridges can result in a higher environmental impact than the compared conventional method.

This graduation project is in cooperation with TU Delft, Tentech BV, Aectual and White Lioness technologies. It aims to investigate the feasibility of using recycled plastics as material for large-scale 3D printing with the 3D printer KamerMaker. In the meantime, a thickness distribution methodology is proposed for taking advantage of the flexibility of the 3D printing technology to optimise the printed structure, especially as moulds for casting concrete, to increase the structural efficiency. The content of the project contains laboratory tests, numerical modelling, design methodology and a case study.