Transient Gas Diffusion Method for Measurement of Effective Porosity and Tortuosity of Porous Media

Abstract

This paper describes a new and simple method for determination of effective porosity and tortuosity of porous media with transient gas diffusion flow through it.
The unsteady gas diffusion flow through porous media is influenced by the effective diffusivity and effective porosity void fraction. We proposed a method for measuring macropore structure by means of a numerical solution of the unsteady gas diffusion equation calculated with the finite difference method. The conditions of the numerical model, such as inlet and outlet gas concentrations at the end surfaces of the test piece, were matched with the experimental ones. The difference between the times required until the inlet concentration and outlet diffusion rates reach the halves of the steady state rates respectively was related to the macropore structures of porous media such as effective porosity, tortuosity and effective area fraction.
The present method was successfully applied to measure the diffusivity and macropore structure of fly ash-cement mortar specimens, whose composition of fly ash were varied from 0 to 40 weight %.