With more than four billion tons annually, cement is the most widely used material in the construction industry. But manufacturing and processing are responsible for six to eight percent of global greenhouse gas emissions, especially carbon dioxide. To reduce this climate impact, new cement variants and production processes are currently being tested in order to be able to reduce emissions by a quarter. But engineers at the Technical University of Braunschweig are pursuing a different strategy with a clever 3D printing method: They want to manufacture filigree and at the same time stable concrete structures in order to save 50 to 70 percent of the building material compared to solid concrete elements.
“In concrete construction in particular, it is common for the walls to be solidly concreted. However, we want to achieve a light, detached construction method that is more familiar from wood or steel,” says Dirk Lowke from the Braunschweig Institute for Building Materials, Solid Construction and Fire Protection. To do this, he and his colleagues developed a method for creating finely structured, three-dimensional structures from concrete – a mixture of cement and stone additives of various grain sizes. With this 3D injection printing process liquid concrete is injected into a special carrier liquid, such as a transparent gel. This carrier liquid holds the concrete in the desired positions until it has hardened. If the – potentially recyclable – carrier medium is removed from it, a lattice-like, filigree concrete structure remains.
Airy structures made of concrete
“The concrete components are suitable, for example, for bridges or roof structures,” says Lowke. These could be manufactured centrally in a factory and later assembled on site. This also opens up new design possibilities for architects and civil engineers to design filigree buildings with less material and high stability.
The Swiss civil engineer Robert Maillart and the Italian civil engineer Pier Luigi Nervi developed the first examples of such airy structures that were too expensive for large-scale use. Lowke, on the other hand, is convinced that pressure injection processes could greatly reduce costs.
In parallel to pure concrete structures, work is also being carried out on combining them with stabilizing steel structures or long strands of carbon fibers. Not only would concrete come out of the nozzle of a 3D printer, but also a wire rope or a fiber to further increase stability. However, this technology is not yet ready for use. However, the Braunschweig engineers anticipate that their patented process could be available for large-scale applications in a good ten years.