Thixotropic Characterisation of Slag-Modified 3D Printable Metakaolin-Based Geopolymer Composite (2023-04)¶

Geopolymer concrete (GPC) is a substitute for ordinary Portland cement (OPC) in 3D concrete printing for sustainable construction. However, poor structural build-up arising from a slow chemical reaction rate of a two-part GPC is a limitation to buildability. Therefore, slag (0, 5, 10, and 15% by weight of metakaolin), and fibre (0.5% by volume of mix) inclusion in metakaolin (MK)-based GPC composite could improve structural build-up and enhance buildability. This paper presents the rheological thixotropic characterisation of static and dynamic yield stresses, Rthix (re-flocculation rate), and Athix (structuration rate), of slag-modified fibre-reinforced MK-based geopolymer for 3D printing of concrete using an ICAR rheometer at selected resting times of 0 to 2700 s depending on mix behaviour. The printability of the GPC is validated with a 3D concrete print of a 250 mm diameter column for each mix. The results show that the reference, M1, with 0% slag content is more workable than M2 with 5% slag; however, M2 exhibits better thixotropic properties. Slag inclusion in M2 improved the buildability of validated 3D prints by 36% compared to M1. The 3D prints of M1 and M2 columns are buildable up to 27 and 42 layers, respectively, before plastic yield and collapse. Slag inclusion beyond 5% had too little open time than required for printing, leading to a significant and early increase in stiffness and clogging of the printer hose.