Reusable 3D Printed Concrete Slab

Abstract

Concrete consumption is one of the major environmental issues of our time. This building material is used twice as much as all the other building materials combined. Furthermore, the United Nations predicts that human global population will reach 10 billion inhabitants by 2050. Correspondingly, it is projected that due to global migration from land to cities, almost 75% of the world’s population will be urbanized. For the building industry, this means that in thirty years we will roughly equal the entire volume of the construction made in the world’s history. In other words, the consumption of concrete is predicted to double over the next three decades. Given the importance that concrete has for the building industry, the ability to optimise the material usage can have a global impact in reducing both pressure from the natural environment and carbon footprint. To fully exploit the potential of concrete in a cost-effective and environmentally sensible way represents one of the greatest challenges posed to building technology today. The research question has been formulated based on this problem statement: How can a prefabricated structural concrete slab be designed to optimise the use of concrete, minimise material waste and allow for efficient (dis)assembly and reuse to extend its exploitation life? Currently, one of the main issues to reuse concrete elements is the implementation of steel rebars as reinforcement. This type of reinforcement corrodes and causes internal cracks in the concrete elements. This means that after time, the element cannot be reused as its structural capacity is compromised. This has led this research towards investigating novel strategies to provide concrete with tensile strength. Fibre reinforced concrete (FRC) emerges as a potential solution. However, it is well known that the performance of FRC largely depends on the orientation of its fibres. To achieve this, production methods that can achieve a controlled fibre orientation are also reviewed. Here, 3D printing concrete (3DCP) emerges as an approach worthy to be explored. It has been observed that the fibres orient parallel to the deposition of the concrete layer. If this strategy is applied, this means that a printing path can be programmed and, the fibres will orient accordingly. A general outlook of 3DCP characteristics is reviewed in this research. Consequently, such characteristics are applied to the design of the reusable 3DCP slab. Besides the material characteristics, Circular Economy (CE) presents strategies to exploit the full potential and retain the optimal value of the physical environment. Principles of the CE are reviewed in this research through literature study. Special consideration has been put in the principle of Design for Reuse (DfR) as the objective of this research is to enable multi service-lives of the new 3DCP slab. Suitable aspects have been identified and applied to the design based on the properties of concrete and fabrication techniques. Here, the engineering of dry mechanical connections is sensible as the 3DCP slab can be efficiently demounted without the need to break or cut part of the slab. The simplicity of the connections is crucial in this research as this translates into savings of energy and CO2 emissions due to a rapid building process. Furthermore, the simplicity of the connection means an easy replacement upon damage without affectation to the whole concrete slab. The engineering and mechanical performance of the connections are addressed in this research. To conclude the research, the utility of the reusable 3DCP slab is studied. The results are compared to those of a traditional concrete slab and conclusions are drawn to assess the relevance of this new approach to reduce concrete consumption. Economic utility, policies and business models are excluded from this research as they are not the main focus and due to time constraints. This master thesis answers the research question by designing a concrete slab that can optimise the usage of concrete. This is achieved both by material characteristics, production process and the engineering of demountable connections. However, further physical research and testing are needed to properly evaluate the production process and its applicability to the current design. Nevertheless, the result looks promising.