The diffusivity of CO2 in the gas phase of concrete pores is an important factor in the prediction of carbonation progress of concrete. In this study, the distribution of gas diffusivity from already carbonated surface zone to non-carbonated center zone in specimens, which are accelerated carbonation (in a controlled at 20 °C, 60 % R.H. and 5% CO2) with several mix proportions were examined. Quantity open porosity, Ca(OH)2 and CaCO3 in specimens were also determined. As a result of this experiment, the diffusion coefficients in specimen from full carbonated surface zone to partially carbonated zone which is reacting with cement hydration by diffused CO2 were not constant. It is indicated that the prediction of carbonation progress of concrete take account of this result.
