Low-calcium fly ash (FL) is a general product from the combustion of anthracite and bituminous coals and has been widely used as a mineral admixture to produce high strength and high performance concrete. And in marine and coastal environments, penetration of chloride ions is one of the main mechanisms causing concrete reinforcement corrosion. In this paper, we proposed a numerical procedure to predict the chloride diffusion in low-calcium fly ash blended concrete. This numerical procedure includes two parts: a hydration model and a chloride diffusion model. The hydration model starts with mix proportions of low-calcium fly ash blended concrete and considers Portland cement hydration and low-calcium fly ash reaction respectively. By using the hydration model, the evolution of properties of low-calcium fly ash blended concrete is predicted as a function of curing age and these properties are adopted as input parameters for the chloride penetration model. Furthermore, based on the modeling of physicochemical processes of diffusion of chloride ion into concrete, the chloride distribution in low-calcium fly ash blended concrete is evaluated. The prediction results agree well with experiment results. (C) 2013 Elsevier B.V. All rights reserved.