Impacts of the rheological performance on dynamic printing of metakaolin-based geopolymer

The three-dimensional (3D) printing of geopolymers has considerable potential for reducing energy consumption and waste material generation. However, the increase in material viscosity and elasticity during geopolymerization significantly affects the 3D printing process, causing material flow interruption, nozzle clogging, and slumping if not properly controlled. These challenges are particularly prevalent in alkali-activated geopolymer systems, which tend to cure rapidly. In this research, the effect of varying contents of NaOH (2.5, 3.5, 4.5, and 5.5 g) mixed with 15 g of a silica sol on the rheological properties of metakaolin-based geopolymers was systematically investigated. The Benbow–Bridgwater model was used to calculate the yield and wall shear stresses, which were incorporated into the Carreau model to optimize the extrusion parameters. To account for the dynamic changes in the rheological performance, a Grasshopper-based plugin in Rhinoceros was developed to generate G-code files for the real-time adjustment of key printing parameters, including the layer height (0.4–0.8 mm), printing speed (40–120 mm/s), and extrusion pressure (50–200 kPa). The experimental results demonstrated that dynamic parameter optimization significantly improved the printing quality. For example, the number of stacked layers in Na_3.5KL_1.2HP_0.5 (KL = kaolin and HP = hydroxypropyl methylcellulose) increased to ∼40, representing ∼33 % improvement compared to that achieved when using the original printing method. Additionally, the slump ratio improved by 5 %–10 %, indicating enhanced shape retention capability during printing. These findings highlight the importance of tailoring printing parameters to the evolving rheological properties of geopolymers.