Advances in Characterization of Gas Transport in Concrete: Determination of Oxygen Diffusion Coefficient from Permeability Coefficient and Porosity

Abstract

One of the most relevant mechanisms that influence the life service of concrete (carbonation, compactness, alkaline protection) is gas diffusion through its mass. However, determination of gas diffusion coefficient in concrete is not a simple task. There is not a general standard which determines the test procedure. Other approaches or alternative parameters could be used in order to obtain the gas diffusion coefficient, including the use of permeability coefficient. Both parameters are dependent on material porosity and moisture content. The literature already proposes generic correlations for these parameters, but these correlations do not support the direct derivation of the gas diffusion coefficient. This paper presents the results of research carried out to analyse these generic correlations and to propose specific expressions that support the derivation of a value for the oxygen diffusion coefficient, based on the porosity and permeability coefficients. The research was centred on a experimentation process to obtain these parameters. A diffusion chamber was designed and built for use with two types of concrete mix, two distinct concrete curing processes and three separate values for humidity. Each test case sought to derive values for oxygen diffusion and permeability coefficients.