In India, the abundant availability of fly ash necessitates the increase in the addition of fly ash in pozzolana cement from 25 to 35%. Higher replacement level of fly ash reduced the development of early age strength of concrete. By adopting the cement efficiency factor (k) when designing the fly ash added concrete, either equal or more compressive strength has been attained. In the present study, by adopting this factor, the concretes having strength of 20 and 35 MPa were designed at 40% replacement of fly ash. The enhanced corrosion resistance of rebar was evaluated by conducting chloride migration test, potential-time studies and 90 Clays chloride ponding test. Results were compared with Ordinary Portland cement (OPC) and Fly ash added concrete (FAC) without k factor. The studies reveal that the diffusion co-efficient of chloride is less in FAC- with k than that of OPC and FAC without k concretes. In 1% chloride contaminated concrete, the rebar in FAC- with k shows more passive potential than the other two concretes. Under 90 clays chloride ponding test, the corrosion resistance of rebar in FAC is 3-7 times more than that of the rebar in OPC concrete. The reduced chloride ion penetration increased the corrosion resistance of rebar. The 40% replacement of fly ash reduced the alkalinity of FAC-without k whereas the OH(-) ions concentration increases in FAC-with-k and maintained the passivity of rebar in presence of chloride. Hence in addition to early strength development, the enhanced corrosion resistance of rebar in FAC- with k is mainly because of reduced chloride ions penetration and increased OH(-) ions concentration.