<![CDATA[The road is the main gateway to human life and links essential access points. Some structure pavement failures happened due to the base layer's instability. Fly ash has been used in several parts of pavement structures to increase stability. One significant concern with using fly ash in base course stabilization is its proportion and potential impact on water quality standards. This research aimed to evaluate base course stabilization performance using fly ash-based geopolymers, as well as assess their impact on water quality standards. Materials in this study consisted of aggregate, fly ash, water, and alkaline reagent solutions. The variation of mix considered with a variety of alkaline reagents, namely without alkaline reagents, 3 mol, 6 mol, 9 mol, and 12 mol of NaOH. The ratio between NaOH and Na2SiO3 is 1:2. The use of fly ash in the class A aggregate base course layer has not been able to meet specifications. However, by providing 9 mol of alkaline reagent, the strength of the mixture increases so that the CBR value meets the specifications due to geopolymer bonding. When the alkaline reagent solution becomes more concentrated, the optimum water content decreases, and the bond between aggregates strengthens. The effect of alkaline reagents on water quality standards increases the acidity (pH) value, while other parameters such as BOD, COD, and TSS still meet the standards. This research point to another practical approach that is effective in the field to increase the stability of the base course layer and is environmentally friendly.]]>
