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Extrusion-based 3D printing of a two-part metakaolin-based geopolymer concrete has a long setting time, which could lead to inadequate structural build-up. This research explores an experimental mix formulation for 3D concrete printing application with reasonable setting time by the inclusion of slag in a metakaolin-based geopolymer activated with sodium trisilicate solution and sodium hydroxide (NaOH). The formulation parameters of the mix are aggregate to binder ratio (A/B) of 1.6, alkaline activator to binder ratio (AA/B) of 0.73, 0.5% fibre content by volume of the mix, 1% superplasticiser by mass of binder, 0.5% viscosity modifying agent (VMA) by mass of binder, water to binder ratio of 0.3, and sodium trisilicate solution: NaOH of 2.0. Fresh and rheological properties of the 3D printed geopolymer concrete (3DPGPC) mixes were characterised, hardened mechanical properties of specimens were evaluated, efflorescence was observed, microstructural identification of reaction products and analytical buildability model performance was validated with 3D prints. The results show interesting fresh properties for printability with slag inclusion and hardened properties are enhanced with slag inclusion. Printability of the mixes is validated with 3DPGPC of 27 and 42 layers of 250 mm diameter columns with mixes 1 and 2 at 0% and 5% slag content, respectively. Also, 17 layers of a rectangular shape and a non-regular shape were printed. Slag inclusion enhanced initial and final setting times, improved hardened properties, reduced efflorescence because of the formation of calcite, and enhanced buildability of 3DPGPC. XRD shows the formation of quartz, muscovite, and calcite peak phases as the reaction product of the hardened 3DPGPC. Also, SEM-EDS show elemental peak height and quantification.
Jaji et al. (Tue,) studied this question.