Abstract.One of the main sources of reinforcement corrosion is the ingress of chloride ion into a concrete structure. The rate of chloride ingress and its consequence to initiate corrosion could determine the service life of the structure. This paper aims to estimate the corrosion initiation period of reinforced self-compacting concrete incorporating high volume fly ash. The governing equation whih characterize the chloride ingress through ionic diffusion is numerically solved using finite difference method. The numerical solutions are used to assess the influence of fly ash content, concrete cover and temperature on the time of corrosion initiation.