This study presents an experimental investigation into the effect of sodium carbonate molarity on the fresh and hardened properties of alkali-activated geopolymer concrete designed for rigid pavement applications. A binary binder system comprising Class F fly ash and ground granulated blast furnace slag (GGBFS) was activated using a blended alkaline solution of sodium carbonate (1, 2, and 3 M) and sodium silicate in a 1:1 mass ratio. Manufactured sand (M-sand) and recycled concrete aggregate (RCA) were used as fine and coarse aggregates, respectively. Slump and compressive strength tests were conducted to evaluate the influence of molarity under ambient curing conditions. The results showed a reduction in workability with increasing sodium carbonate concentration. Among the three mixes, the 2 M molarity mix achieved the highest 28-day compressive strength of 42.3 MPa, meeting the M40 grade requirement, while maintaining adequate workability. Higher molarity (3 M) resulted in marginal strength reduction and poor slump values. The study concludes that 2 M sodium carbonate, when combined with sodium silicate, offers an optimum balance between strength and workability, making it suitable for sustainable pavement applications.