Determination of the effective chloride diffusion coefficient in concrete via a gas diffusion technique

A new experimental technique based on gas diffusion through a thin sample specimen is presented to evaluate the effective chloride diffusion ion in concrete. The counterdiffusion of two gases, helium and nitrogen, through a concrete disc is used to establish the porosity-to-tortuosity ratio (epsilon/tau) of the concrete. From measurements of the porosity via porosimetry, the tortuosity of the concrete can be determined. The effective chloride ion diffusion in concrete is a function of (epsilon/tau) ratio and the diffusion coefficient of chloride ion in water which is a known value. The test takes 3 to 4 hours to complete. Excellent results were obtained when correlated with the conventional diffusional measurement techniques for different water-cement ratios and cement content.