The demand for sustainable, high-performance pavement materials has become critical in light of the environmental concerns and resource depletion associated with conventional base and subbase layers. Using a geopolymer-stabilized blend of Class F fly ash (FA) and bottom ash (BA), this study presents an innovative approach to completely replace conventional granular materials in the base and subbase layers of flexible pavements, as well as in the dry lean concrete layer of rigid pavements. The objective is to develop an environmentally friendly, high-strength pavement foundation that reduces reliance on cement and natural aggregates by utilizing sodium hydroxide (NaOH) as an alkaline activator and ground-granulated blast-furnace slag (GGBS) as a supplementary binder. A systematic experimental program was conducted with GGBS contents ranging from 3 to 15 % (by dry weight of FA) and NaOH solutions of 0.5, 1, 2, 3, 4, and 5 M (where M denotes molarity). The results demonstrate that GGBS-based geopolymers substantially improve the load-bearing capacity, durability, and stiffness of the FA–BA blends, thereby providing a viable alternative to conventional pavement foundation materials. The optimized compositions ensure long-term performance, exhibiting superior strength development and enhanced resistance to environmental degradation. Consistent with global initiatives to reduce carbon emissions, conserve natural resources, and advance circular-economy principles in road construction, this work offers a scalable and sustainable solution for infrastructure development.