Printing Parameter Requirements for 3D Printable Geopolymer Materials Prepared from Industrial Side Streams

The objective of this investigation is to study the printing parameter requirements for sustainable 3D printable geopolymer materials. Side streams of the paper, mining, and construction industries were applied as geopolymer raw materials. The effect of printing parameters in terms of buildability, mixability, extrudability, curing, Al-to-Si ratio, and waste materials utilisation on the fresh and hardened state of the materials was studied. The material performance of a fresh geopolymer was measured using setting time and shape stability tests. Standardised test techniques were applied in the testing of the hardened material properties of compressive and flexural strength. The majority of developed suitable 3D printable geopolymers comprised 56–58% recycled material. Heating was used to improve the buildability and setting of the material significantly. A reactive recyclable material content of greater than 20% caused the strength and material workability to decrease. A curing time of 7–28 days increased the compressive strength but decreased the flexural strength. The layers in the test samples exhibited decreased and increased strength, respectively, in compressive and flexural strength tests. Geopolymer development was found to be a compromise between different strength values and recyclable material contents. By focusing on specialised and complex-shape products, 3D printing of geopolymers can compete with traditional manufacturing in limited markets.