This paper elucidates the effect of adding decahydrate borax (1 and 2 wt%) on thermo-mechanical properties of fly ash-ladle furnace slag (FS) geopolymer at 29 °C – 1000 °C. Adding borax improved the compressive strength of unheated (40.5 MPa) and heat-treated (36.9 – 43.1 MPa) FS geopolymers by 8.4% and 21.2%, respectively. The higher crystallinity, incompact microstructure, and the presence of B-bonds and B-crystals contributed to the high-temperature resistance of FS-B geopolymer. The reduced sintering temperature by 75 °C due to addition of borax compared to FS geopolymer improved the thermal stability and structural integrity during high-temperature applications.
