The Effect of Alkali Activator to Binder Ratio on Workability, Density, and Compressive Strength of Fly Ash-Slag Based Geopolymer Mortar

The purpose of this study is to investigate the influence of variations in the alkali activator to binder ratio (Al/Bi) on the workability, density, and compressive strength of geopolymer mortar. This study used an experimental approach to assess mortar compressive strength and workability utilizing a flow table in accordance with SNI 03-6825-2002, as well as mortar density in accordance with SNI 1973-2016. Variations in the Al/Bi ratio used are 0.40, 0.45, 0.50, and 0.55, with a slag content of 20% and a ratio of sodium silicate to sodium hydroxide (SS/SH) 1.5. The materials used in this research are fly ash type F, slag, fine aggregate, and an alkali activator consisting of sodium hydroxide (SH) and sodium silicate (SS). The specimen is in the shape of a cube with dimensions of 50x50x50 mm and a total of 16 test objects. The results show that the higher the Al/Bi ratio, the workability of the geopolymer mortar increases, but the density decreases. The higher the Al/Bi ratio, the compressive strength of the geopolymer mortar increases to an optimal Al/Bi ratio of 0.50. At an Al/Bi ratio of 0.40, it has workability in accordance with SNI 03-6825-2002 standards. All variations of the Al/Bi ratio produce density that meets the SNI 1973-2016 standards. The maximum compressive strength of the geopolymer mortar was 12.15 MPa at an Al/Bi ratio of 0.50.