2022 Volume 76 Issue 1 Pages 45-52
Most conventional studies on carbonation have been conducted in terms of the diffusion of carbon dioxide into concrete and its effect on rebar corrosion in reinforced concrete, with limited research focusing on the carbonation of cement itself. Focusing on the carbonation reaction of cement itself, this study investigated differences in the progress of carbonation of hardened cement paste at CO2 concentration of 1％ and concentration （about 0.04％） in humid environment （about 95％ relative humidity） by Raman spectroscopy, where the carbonation reaction is most likely to occur. Reaction rate constants were calculated for each cement hydrates assuming a first-order reaction. As a result, the carbonation rate of calcium silicate hydrate （C-S-H） was higher for carbonation at a CO2 concentration of 1％ in initial stage of carbonation. The carbonation rate of calcium hydroxide （CH） and ettringite were also higher for carbonation at atmospheric concentrations. The pH of pore solution of hardened cement paste varied with CO2 concentration, and the carbonation of hardened cement paste under atmospheric concentration where the pH of pore solution is higher than that of under CO2 concentration of 1％ resulted insignificant vaterite precipitation. In addition, the presence of ettringite was a factor in vaterite precipitation.
