One key challenge to maximizing fly ash usage is achieving adequate early strength. Various strategies have been explored to formulate fly ash blends, particularly up to 80% proportions. This research investigates the effectiveness of a low-molarity sodium hydroxide solution as an activator in Very High-Volume Fly Ash (VHVFA) mortar comprising 80% (by mass) fly ash, along with calcium carbonate, sodium sulfate. This research demonstrates that a combination of 0.3 M NaOH and CaCO₃ effectively activates VHVFA mortar. Additionally, Sodium Sulfate exhibits positive effects as a chemical activator in VHVFA mortar blends. The utilization of a solution containing 5% CaCO3 and 0.3 M NaOH as a low-molarity alkali activator with Class C fly ash demonstrates notable enhancements in its performance, in terms of the compressive strength, with a 38.6% increase at 7 days, from 32.64 to 45.23 MPa, and a 19.9% increase at 28 days. The pH level reflects fly ash's reactivity and correlates with increased strength. Sodium sulfate boosts compressive strength in VHVFA mortar early on, while calcium carbonate alone has limited impact; however, coupling it with low molarity NaOH activator enhances early strength, especially with Class F fly ash, and maintains strength over time with Class C fly ash. Employing a low-molarity alkali activator enhances VHVFA's compressive strength, regardless of fly ash type.