The Effect of Bottom Ash as Partial Replacement of Fine Aggregate in Different NaOH Molarities on the Compressive Strength of Geopolymer Mortar

Abstract

This study compared the compressive strength of the geopolymer mortar with different percentages of bottom ash as a replacement for fine aggregate. Fly ash from two sources was blended as raw materials. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) were used as alkaline solutions, with a ratio of 2.5 and two NaOH concentrations of 8M and 10M. The percentage of bottom ash was substituted up to 30%. The result indicated that the setting time was longer due to the higher molarity of NaOH. The compressive strength of mortar geopolymer at 10M of NaOH was higher than 8M. Higher percentages of bottom ash significantly decreased the compressive strength. However, at 10M NaOH, the compressive strength was decreased by only 11% (20% of substituting). Increasing the molarity of NaOH decreased the absorption of mortar geopolymer and increased the restrain to sodium sulfate.