Abstract
This study aims to analyze the effect of variations in the water-to-cementitious (W/C) ratio on the compressive strength of fly ash-based geopolymer concrete using a mixed activator of 10 M potassium hydroxide (KOH) and sodium silicate (Na₂SiO₃) at 3 and 7 days of curing age. The research was conducted with variations of the W/C ratio, namely 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, and 0.65. Fly ash was used as the main aluminosilicate material, while the alkaline activator consisted of a 10 M KOH solution and Na₂SiO₃ in a specific ratio. The samples were cast in cylindrical molds and cured at room temperature. The compressive strength test was carried out at 3 and 7 days of age.The results showed that variations in the W/C ratio significantly affected compressive strength. The highest compressive strength was obtained at a W/C of 0.35, with an average of 29.10 MPa at 3 days, increasing to 33.38 MPa at 7 days. Conversely, the W/C of 0.65 produced the lowest compressive strength, which was 17.68 MPa at 3 days and 23.19 MPa at 7 days. The 10 M KOH activator combined with Na₂SiO₃ proved effective in accelerating the formation of aluminosilicate bond structures, enabling early strength to be achieved in a short time.This study confirms that the water-to-cementitious (W/C) ratio has a significant effect on the compressive strength of geopolymer concrete, where a higher W/C ratio results in lower compressive strength.
Keywords: Geopolymer Concrete, Compressive Strength, Alkali Activator, Fly Ash, Water Cementitious Factor (W/C).