Additive Fertigungsverfahren mit Feinbeton : Baupraktische Grundlagen und Entwicklungsbeispiele zu digitaler Planung, Betontechnologie und Verfahrenstechnik für die schichtweise und schwebende Feinbetonextrusion

• Additive manufacturing with fine concrete : practical construction principles and development examples of digital design, concrete technology and process engineering for layered and floating fine concrete extrusion

Adams, Thomas Julian; Brell-Cokcan, Sigrid (Thesis advisor); Vollpracht, Anya (Thesis advisor)

Aachen : RWTH Aachen University (2023)
Dissertation / PhD Thesis

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2023

Abstract

Concrete is by far the most widely used building material in the world and, due to its abundant availability, low cost and outstanding durability, is a major determinant of ecological and economic sustainability in the construction industry. Conventional concrete construction methods are versatile and already allow a large number of different concrete components to be produced using formwork, spraying or extrusion processes. However, individual and complex concrete components can only be realized to a limited extent and require intensive, predominantly manual formwork planning and production. Additive manufacturing with concrete has thus become a megatrend in the construction industry over the last ten years in research and development. Driven by the increasing design possibilities of digital planning, the shortage of labor and building materials, and the potentials in concrete development through powerful admixtures, a variety of additive manufacturing processes have been developed for CAD-supported and formwork-free concrete processing. In particular, additive manufacturing of concrete extrusion is considered promising and is already being used for in-situ construction printing on construction sites and in precast plants. It promises time and cost savings, design freedom, worker attractiveness, and resilient buildings, and is considered a driver of digitalization and automation in construction. Building on the fundamentals of construction practice, this thesis examines the design possibilities and application potentials of additive manufacturing with concrete with regard to the three core topics: Concrete technology, process engineering and digital design. Two manufacturing approaches are examined in more detail: Additive manufacturing with fine concrete in layers and floating in support suspension. For the latter approach, a new process concept for three-dimensional orientation of strands in combination with fibrous fine concrete is presented. For the processes, the process properties and results are determined and discussed with regard to architectural, ecological and economic application potentials. The result of additive manufacturing with layered fine concrete, apart from the architectural advantages of an individualized, digitally controlled production of arch-shaped lightweight concrete elements, proves to be deficient in material and process properties compared to conventional concrete construction methods. The process-related stiffness and processing requirements limit the use of inert aggregates and recyclates, and the fine concretes are comparatively binder-intense and thus CO2-intensive and sensitive to shrinkage. The anisotropic strength of the concrete requires additional reinforcement to accommodate statically relevant bending and tensile loads. The integration of reinforcement is costly and limits the design benefits of the process. Additive manufacturing in suspension expands the design potential by providing unlimited overhangs and stability of the fine concrete strands in space. It offers the possibility of producing filigree and ultra-lightweight truss structures from concrete that are not possible with conventional methods. At the current stage of development, however, dimensional inaccuracies during extrusion or suspension deposits between the contact points impair the load-bearing capacity of the components, which is many times lower than the calculation of the ideal geometry. In this context, a dynamic printhead in combination with fiber cement pastes offers the potential to improve the dimensional stability and tensile strength of the material by orienting the fiber cement strands, thus promoting the dimensional stability and tensile strength of the structures. A scaled prototype was used to demonstrate the fundamental influence of nozzle orientation on the strength properties and dimensional stability of the strands, and to illustrate forward-looking potential applications of additive manufacturing. However, a transfer to structural applications is currently not possible and requires fundamental strength increases of the fiber concretes as well as measures for non-destructive quality assurance.

Institutions

• Chair of Individualized Production in Architecture [211510]