Effective Medium Approach for Evaluating the Oxygen Diffusivity of Concrete

Abstract

In view of the importance of the diffusion of oxygen molecules in concrete to the durability assessment and design of reinforced concrete structures located in a marine or deicing salt environment, it is essential to determine its oxygen diffusivity. This paper presents an effective medium approach for evaluating the oxygen diffusivity of concrete. Since the aggregate, bulk cement paste, and interfacial transition zone (ITZ) have different morphological characteristics and contributions to the diffusion of oxygen molecules in concrete, concrete is modeled as an isotropic three-phase composite material. Based on the stereological analysis of aggregate size distributions and the statistical geometry of composites, the ITZ volume fraction is formulated analytically. By introducing a hypothetical homogeneous medium of nonzero oxygen diffusivity and applying the general effective medium approach, an analytical solution is derived for the oxygen diffusivity of concrete. The primary advantage of the approach is that the ITZ percolation effect is taken into account and the oxygen diffusivity bounds are satisfied. Finally, some numerical comparisons are made to show the good consistency between the proposed approach and experimental results obtained from the research literature.