Even though the use of fly ash in concrete is nowadays a common practice, its relatively slow pozzolanic reactivity hinders its greater utilization; hence efficient methods of activation are on demand. This study was carried out to evaluate the influence of lime as a chemical activator on the mechanical and durability properties of high strength fly ash concrete. Mixtures were made with 0, 30, 40, and 50% of cement replaced by low calcium fly ash. Corresponding mixtures were also made with the same amount of fly ash and addition of 10% of lime to each mixture. For each concrete mixture, slump, compressive strength, water absorption, sorptivity, apparent volume of permeable voids, and resistance to chloride-ion penetration were measured. The results obtained showed that addition of lime improved the compressive strength significantly at all ages. The strength of all the fly ash mixtures containing lime surpassed that of the corresponding Portland cement mix at 60 days. Addition of lime also improved the sorptivity and resistance to chloride-ion penetration of the fly ash concrete. It however increases the water absorption and the volume of permeable voids of the fly ash concrete.