Experimental analysis on the carbonation rate of Portland cement at room temperature and CO2 partial pressure from 1 to 51 bar

Considering the range of PCO2 of previous laboratory experimental works, in this study the carbonation rate of class G Portland cement was investigated at room temperature, in the PCO2 interval from 1 to 51 bar, to fill the existing gap of knowledge, through three types of laboratory experiments. Cement hydration (accompanied by limited carbonation) was carried out for 28 days at atmospheric conditions. Cement carbonation was then investigated using a micro-reactor by reacting, in distinct runs, cement powder samples, under stirred conditions, and massive samples, under stagnant conditions, with pure CO2(g) and MilliQ water. After the completion of each experiment, chemical analyses on both the aqueous solution (IC, ICP-OES, acidimetric titration) and the solids (XRD, SEM, TGA/DTA) were performed. In type 1 experiments, cement powder was reacted at 11 bar PCO2, for 1, 3, 6, 21, 67, 97 and 120 h. Portlandite was only present in the hydrated cement paste and was converted to CaCO3 in less than 1 h. In type 2 experiments, cement powder was reacted for 6 h at PCO2 of 1, 11, 31 and 51 bar. The extent of cement carbonation was similar for any PCO2 values. The experiments of type 3 were performed with cement cube samples at 11 bar PCO2 for 6, 24 and 210 h. The average carbonation depth attained was 0.23 mm in 1 day, and resulted to be linearly related to the square root of reaction time indicating that cement carbonation rate was controlled by diffusion (Fickian behavior).