Complex moulds for reinforced concrete
Resource-saving production of functionalized, complex and individual moulds for reinforced concrete for the building industry using multi-material formwork
Complex reinforced concrete components are in increasing demand by architects, engineers and designers. Since components produced by direct 3D concrete printing have only a low compressive strength and almost no tensile strength due to the lack of reinforcement, FORWISS, together with 3D printer manufacturer and service provider voxeljet AG and Hemmerlein Ingenieur GmbH, researched various formwork systems and the corresponding process technology for producing them.
Based on a CAD description of a surface, FORWISS developed algorithms which calculate the corresponding formwork elements. The printed formwork elements are then printed out, assembled and encapsulated. The components produced are characterised by a high level of detail and functionalisation, enabling undercuts and free forms.
Free-form wall made of reinforced concrete
Complex concrete object
Functionalised washbasin
Background information: 3D printing of powdery material
Powder-bed-based 3D printing is ideal for producing complicated shapes of various shapes and sizes quickly and with the highest precision without any tools. The printers from voxeljet AG, which work according to this principle, offer not only high construction speed but also large construction volumes. Basically, the materials consist of a particulate material that makes up the actual construction site and a liquid component, the binder, which is applied precisely and selectively to the construction site via a print head. Figure 12 schematically shows the individual process steps in powder-bed-based 3D printing. The particulate material is applied to the construction platform by means of a vibration coater. Material only flows out of the coater when it is vibrated. At the same time, a blade smoothes the construction site and ensures a constant layer thickness throughout the entire printing process. After applying a layer, the print head prints the flat powder bed with binder fluid. Once a layer has been completely printed, the building level is extended by
a layer thickness and a new layer of particulate material is applied with the coater. The previous steps are repeated until all components are finished. After printing the last layer and a waiting time depending on the material system, the parts can be removed from the powder bed and freed of loose particles.
Process technology and formwork systems
Furan resin-bonded shuttering made of quartz sand, as produced by voxeljet for many years, has proven to be very suitable for concrete casting. The cast parts are very detailed and have a high surface quality. The surfaces and the haptics of the objects can be further improved by common process steps such as polishing or glazing. The research partners investigated appropriate coatings of the formwork interface to concrete and release agents to prevent the liquid concrete from penetrating into the formwork and to ensure simple and fast demoulding.
Formwork systems
Formwork elements of any size can neither be produced nor transported. Therefore FORWISS investigated different formwork systems.
Cutting into panels
The free-form component is divided into individual smaller panels, which are then produced using a multi-material formwork system. This formwork system consists of a recyclable stable outer formwork and an environmentally friendly inner formwork that can be inserted into it. The individual panels are then assembled on site to form a large component. This process is suitable for components where the connection technology between the panels can be kept simple, e.g. for pressure-loaded components only.
Multi-material formwork system for casting panels
Lost formwork
This process consists of the production of a lost formwork and the subsequent assembly of the formwork, the reinforcement and the casting. Webs are inserted between the lost upper and lower formwork so that the formwork can be bolted with formwork ties. This results in a component that is easy to handle from a static point of view. The concrete panels serve exclusively as formwork and have no effect on the stability of the building component; only the in-situ concrete in connection with the reinforcement is statically supporting.
Lost formwork made of panels, which is cast on site
Formwork system with support structures
The formwork consists of stable furan resin panels, which are additionally stabilised by cost-effective two-dimensional wooden support structures. FORWISS developed an algorithm that calculates the corresponding formwork elements including spacers, anchor holes, sprue holes, ventilation holes, the corresponding buckling lengths and angles of the reinforcement and the corresponding support structures from a free-form surface. The formwork elements are 3D-printed, the reinforcement is bent and the support structures are cut out of wooden panels with CNC machines. The formwork is then installed and poured.
Algorithmically calculated formwork elements including reinforcement
Algorithmically calculated formwork elements including support structures
Construction of the formwork system with support structures made of wood and 3D-printed formwork elements
Photo Concrete
Photo concrete allows two-color images to be applied directly to the concrete surface. Concrete made of white cement with dark aggregate is usually used. By controlled partial application of a substance, which delays the setting of the concrete, the not set concrete can be washed off on the surface after stripping the formwork. This makes the underlying aggregates visible.
FORWISS developed a formwork system which, to our knowledge, enables the application of pixel images on multiple curved concrete surfaces for the first time.
Exploded drawing of the formwork elements
Pixel image on multiple curved concrete surface