Measurement Device and Characteristics of Diffusion Coefficient of Carbon Dioxide in Concrete

The carbonation of concrete is one of the major factors that greatly affect the durability of concrete structures. The rate of carbonation depends largely on the diffusivity of carbon dioxide in concrete. Therefore, the purpose of this study is: 1) to develop a measurement device for the carbon dioxide diffusion coefficients in concrete; and 2) to identify the diffusion coefficients of carbon dioxide for various concrete materials. To this end, several series of tests were planned and conducted. It was shown that the diffusion of carbon dioxide reached a steady state within approximately 5 hours after exposure. The current test results indicate that the diffusion coefficient increases with an increase of the water-cement ratio (w/c) and decreases with an increase of relative humidity (RH) at the same w/c. The content of aggregates also influences the diffusivity of carbon dioxide in concrete. It was also found that the diffusion coefficient of cement paste is much larger than that of concrete or mortar. The quantitative values of the diffusivity of carbon dioxide for various materials are presented. This study allows for a more realistic assessment of the carbonation process and carbonation depth in concrete structures, which is very important for the durability assessment and service-life prediction of concrete structures.