Quantitative analysis of accelerated carbonation products of the synthetic calcium silicate hydrate(C-S-H) by QXRD and TG/MS

In this study, calcium silicate hydrate(C-S-H) with CaO/SiO2 ratio of 1.5 target mixture is synthesized and C1.27SH0.76 with 93.4 % purity is obtained. The dried C-S-H was compacted at 8 MPa to 20 mm x 20 mm x 20 mm for accelerated carbonation. The carbonation products and carbonation degree of synthetic calcium silicate hydrate are characterized and quantitatively evaluated by QXRD (Rietveld refinement), mass gain method, and TG/MS analysis. After accelerated carbonation at 0.2 MPaCO2 pressure for 2 h, the carbonation degree from mass gain method is 71.5 %, and from TG/MS analysis is 78.0 %. Calcite, aragonite, vaterite, and amorphous phase exist simultaneously in the accelerated carbonated samples, accounting for 33.98, 17.13, 18.74, and 30.15 %, respectively. Two mass-loss stages were observed for calcium carbonate decomposition. The first mass-loss stage (300-660 degrees C range) was mainly caused by the decomposition of aragonite and vaterite, and calcite formed in the accelerated carbonation process has a relatively high decomposition temperature which is mainly centered in the 660-800 degrees C range.