Effects of carbonation on phase composition of Metakaolin-blended cement pastes

Abstract

To ascertain the impact of carbonation on the phase evaluation of cement paste blended with metakaolin (MK), the phase composition of cement paste with different dosages of MK and at different carbonation time was characterized with X-ray diffraction (XRD) quantitative analysis technology. Meanwhile, the transformation law of Ca in different carbonation products was discussed systemically. The results show that, under accelerated carbonation, calcium hydroxide and Ettringite decrease sharply and disappear quickly, while CaCO3 increases significantly; after the complete consumption of CH, C-S-H is carbonated gradually and decreases greatly. Moreover, based on the content change of Ca in carbonation products, over 85% CaCO3 is generated through the carbonation of CH, C-S-H and unhydrated minerals. With the increase MK dosage, the ratio of the decrement of Ca in CH to the increment of Ca in CaCO3 declines gradually, while the percentage of the decrement of Ca in C-S-H grows gradually. Besides, at the early stage of carbonation, the decrement of Ca in CH constitutes the major part of the increment of Ca in CaCO3, and with carbonation time increasing, the proportion of the decrement of Ca in C-S-H rises gradually.