INVESTIGATIONS BY ENVIRONMENTAL SEM: Ca(OH)_2 DURING HYDRATION AND DURING CARBONATION

摘要

An Environmental Scanning Electron Microscope (ESEM) was used to explore early stages of cement hydration. Because the observations were performed at low vacuum on uncoated samples, novel features on the early hydration products, including C-S-H phases and portlandite, were observed. Differences exist between the CaCO_3 formed by carbonation of Ca(OH)_2 and C-S-H phases produced during hydration of ordinary port land cement and that formed during the hydration of cement rich in ground granulated blast furnace slag. It will be shown that of Ca(OH)_2 and C-S-H phases in cements rich in ground granulated blast furnace slag carbonate very fast by forming metastable modifications vaterite and aragonite. During freezing and thawing, vaterite and aragonite transform into poorly-crystallized calcite, which then leads to concrete surface scaling that is much more severe than with other types of concrete.