The carbonation progress of aged reinforced concrete buildings, where a negative correlation appears between the thickness of the finishing material such as mortar and the carbonation depth of concrete, was analyzed based on a steady diffusion model. As a result, the carbonation progress could be predicted by calculating the carbonation rate coefficient of concrete, the carbonation rate coefficient of mortar, etc., the ratio of the carbon dioxide diffusion coefficient of concrete and mortar, etc., and the ratio of the calcium hydroxide content of the finishing material and concrete through regression using the least squares method.
