Infoscience

Journal article

INFLUENCE OF POROSITY AND WATER CONTENT ON THE DIFFUSIVITY OF CO2 AND O2 THROUGH HYDRATED CEMENT PASTE

Knowledge of the diffusivity of CO2 and 02 is of considerable importance for a quantitative assessment of the carbonation and corrosion of the reinforcement in concrete. A special measuring cell which allows the simultaneous determination of the effective diffusion coefficients of the two gases as a function of the relative humidity has been developed. Measurements have been carded out on carbonated discs of hydrated cement paste prepared with water/cement ratios between 0.4 and 0.8. The results show that, if the water/cement ratio is increased from 0.4 to 0.8, diffusion coefficients increase more than ten times. On the other hand, only little influence of the relative humidity between 50-90% the diffusivity has been observed on samples in adsorption equilibrium. The variation of diffusivity as a function of water content and porosity is explained by the characteristic microstructure, which has been characterized by water adsorption isotherms and mercury intrusion porosimetry measurements. Finally, a model with two levels in the microstructure is proposed to describe CO2 diffusion in a carbonating material.

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