Fresh properties and strength evolution of slag modified fibre-reinforced metakaolin-based geopolymer composite for 3D concrete printing application

Geopolymer has been identified as an alternative to ordinary Portland cement (OPC) due to its eco-friendly nature. However, questions of slow setting time, efflorescence, and long-term strength remain unsolved. Slag, a high calcium precursor inclusion in a two-part geopolymer could shorten the setting time. This paper develops mixes for slag modified fibre-reinforced metakaolin-based geopolymer composite (GPC) to address slow setting time and efflorescence. The considerations in preparing the mixes are binder to the fine aggregate ratio (1:1.6), binder to alkaline activator ratio (1:0.73), sodium hydroxide (10 M), sodium silicate to sodium hydroxide ratio (2.5), water to binder ratio (0.3), fibre content (0.5 % by volume of the mix), and slag content up to 15% by mass of metakaolin. The fresh properties showed that slump and slump flow reduced with increasing slag content. There is an increase in compressive and flexural strength as the slag content increases. The visual observation on the hardened specimens shows no efflorescence at the age of 28-day. The control sample (Mix 1) and Mix 2 are 3D printable. The mix with slag content shows better structural build-up.