An important, although for many people, little-known problem is the utilization of stone waste generated in quarries. In some places, the so-called “rock flour” accounts for up to 40% of the total quarry production. To combat this problem, the Swiss Federal Institute of Technology in Zurich (ETH) and the University of Applied Sciences and Arts of Southern Switzerland (SUPSI) have jointly developed a novel 3D printer that is able to produce architectural elements from stone waste – including marble.
The 3D printing process can be used, for example, to produce a floor system. A team of scientists installed a structurally optimized functional floor using material derived from stone extraction residues from a marble quarry in Ticino (Cava di Arzo). A special 3D printer was installed directly in the quarry, right next to where the waste is stored. The floor design proved how 3D printing technology of complex structural shapes can not only reduce the total consumption of building materials, but also support the use of local resources.
The Binder Jetting method was used to produce the marble floor from mining debris, which uses a binder to harden selected areas of the powdered material layer by layer. This technology, commonly used in the industry, also using metal powders, enables the creation of complex details without the need for supporting structures.
Traditionally, Binder Jetting is not suitable for building stone powder parts because the printed parts are very brittle. They cannot be used for load-bearing applications, and organic binders have poor fire and weather resistance. They also emit volatile organic compounds up to several weeks after production.
The method developed by scientists from ETH Zurich uses an alternative binder based on geopolymers. Geopolymer Binder Jetting (GeoBJT) is based on a modified and customized 3D printer and software. The main advantages of this system are the use of a wider range of binder and particle materials and a faster construction rate. The mobile construction based on containers enables operation on the stone extraction site, in accordance with the concept of a field factory.
The mechanical test showed a significant increase in the strength of the printed parts comparable to concrete (on average above 30 MPa in compression and 5 MPa in tension).
Geopolymer is proposed as an alternative binder. It is an amorphous material, synthesized by a source of aluminosilicates mixed with an alkaline activator. It has a strength comparable to concrete, but has a lower impact on CO2 emissions. Unlike previous work on 3D printing with geopolymers, the current work implements geopolymer in a binder spray technique.
The design of the floor produced in this way consists of 17 separate elements, connected by dry joints as a rectangular structure, supported at the corners. In turn, the horizontal pressure on the supports is solved by steel braces after stretching, placed along the edge of the floor.
The use of 3D printing from recycled materials is particularly appropriate for such compression-dominant systems that take full advantage of the compressive strength of the 3D printed components, but do not rely on their relatively low tensile and shear strength.
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