Powder bed 3D printing with quarry waste

With 3D printing, material consumption can be reduced: It allows to place material only where needed, therefore structurally optimized building parts or formworks can be printed. Currently this technique uses an epoxy based resin to glue layer by layer an inert sand bed. However, this material choice holds a large improvement potential from an environmental and health perspective. It was shown previously, that the organic glue, that releases unhealthy volatile organic compounds, can be replaced by a mineralic binder, namely a geopolymer. With geopolymers and alkali activated materials, the embodied energy can be reduced, especially when built from waste materials. In this study, we focus on the replacement of the sand, which is becoming a scarce resource. The waste from a local gneiss quarry in Ticino (Switzerland) could be a good alternative. The powder bed of the 3D printing is made of aggregates of crushed quarry waste mixed with an aluminosilicate powder. The printing liquid is an alkaline solution that activates the aluminosilicate and reacts to a geopolymer. Droplet penetration experiments on different powder mixes were performed to adjust the binder composition. With a custom built powder bed 3D printer, samples with varying compositions and porosities were printed and tested on compression. It could be shown that samples printed with quarry waste perform as well as samples printed with silica sand in terms of compression strength and accuracy. This new material system is promising: with 3D printing of geopolymers and quarry waste, we can combine the environmental benefits of a new building technique with a low carbon intense material. The application of this technique may help the sustainable development of the local quarry sector by consuming the volumes of waste that causes storing and ecological issues and keep small quarries running.