LAUSR

Abstract The effect of using GFNS with fly ash in geopolymers was evaluated. Initial setting time decreased from 410 min to 188 min for 100% fly ash replacement by GFNS. The increases of SiO2/Al2O3 and MgO/Al2O3 ratios by GFNS accelerated the reaction to decrease setting time and workability. Le-Chatelier expansions were well below the recommended 5% limit. Soundness was not affected by GFNS since Mg was incorporated in the reaction product sodium magnesium aluminosilicate hydrate (N-M−A−S−H) as evidenced by the SEM images and EDS. No expansive brucite was found in XRD. A maximum 28-day compressive strength of 56 MPa was achieved in the ambient-cured geopolymer using 75% GFNS with 25% fly ash. This further increased to 64 MPa at 90 days which was also achievable by accelerated curing at 60 °C for 1 day. The amorphous N-M−A−S−H gel contributed to a denser microstructure and strength development by GFNS.