Abstract
In this study, the effect of carbonation on the micro-pore structure and effective diffusion coefficient of oxygen of the hardened cement pastes cured under drying conditions was experimentally investigated. In the experiments, cement paste specimens having different water-to-cement ratios（30％, 45％, and 60％）were cured under drying conditions for two predefined periods. Here, carbon dioxide in the half of the curing boxes was artificially reduced in order to investigate the effect of the carbonation of the cement paste. Then, the depth of carbonation, total micro-pore volume, micro-pore distribution, specific surface area of micro-pore, saturation and effective diffusion coefficient of oxygen were measured in the hardened cement pastes after curing. As a result, it was found that the carbonation under the drying condition decreased the diameter and volume of the micro-pore of the hardened cement pastes despite its water-to-cement ratio. On the other hand, the influence of the carbonation on the oxygen diffusivity differed depending on the water-to-cement ratio of hardened cement pastes. Whereas the diffusivities of the cement pastes having relatively low water-to-cement ratios（30％ and 45％）were decreased due to carbonation, the diffusivities of the pastes having high water-to-cement ratio（60％）were increased.
