Additive manufacturing of inorganic components using a geopolymer and binder jetting

A large volume binder jetting printer was employed to fabricate prism-shaped geopolymer components. A two parts system was used, comprising: 1) a highly alkaline solution, which was jetted on a powder bed containing aggregates (sand particles), and 2) a reactive solid component (pure metakaolin or metakaolin plus fast setting cement), present in the powder bed. In order to be able to generate appropriate, defect-free powder layers and suitably discharge the powders from the hopper feeding the layer forming system, a granulation approach was employed. The jetted alkaline solution effectively reacted with the metakaolin powders present in the granules, forming a geopolymer. Printed geopolymer parts, fabricated with the addition of 30 wt% metakaolin, possessed a compressive strength of ~20 MPa, even with ~30 vol% of residual porosity, and no significant variation in the compressive strength was observed after leaving the printed parts submerged in water for 1 week.