<![CDATA[Fly ash and pumice-based geopolymers have emerged as promising low-carbon construction materials with the potential to reduce the environmental impacts associated with Portland cement production. However, their performance is highly dependent on mixture proportions, particularly the liquid-to-solid (L/S) ratio. Therefore, this study aimed to identify the optimum L/S ratio and evaluate its effect on the characteristics of fly ash and pumice-based geopolymer mortar. A laboratory experimental program was conducted using five liquid-to-solid (L/S) ratios of 0.40, 0.45, 0.50, 0.55, and 0.60. The investigated properties included compressive strength, density, and water absorption. The statistical significance of the L/S ratio was evaluated using one-way analysis of variance (ANOVA). The L/S ratio significantly influenced the compressive strength, density, and water absorption of geopolymer mortar. The optimum performance was achieved at an L/S ratio of 0.45, resulting in the highest compressive strength (21.03 MPa), highest density (2.12 g/cm³), and lowest water absorption (6%). One-way ANOVA confirmed that variations in the L/S ratio had statistically significant effects on all investigated properties (p < 0.001), with coefficients of determination of 99.44% for compressive strength, 98.42% for density, and 75.04% for water absorption. The liquid-to-solid (L/S) ratio was identified as a critical parameter governing matrix densification, porosity development, and the physical and mechanical properties of fly ash and pumice-based geopolymer mortar. An L/S ratio of 0.45 was recommended as the optimum condition for achieving the best balance among compressive strength, density, and water absorption.]]>
