In Situ Observation Microstructure Character Changes in the Carbonation Process of Hardened Cement Paste Using ESEM/EDS

Environmental Scanning Electron Microscope (ESEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to in situ observation microstructure character changes of hardened cement paste due to carbonation. Three types water-to-cement ratio of 0.53, 0.35 and 0.23 were research. When w/c=0.53, Carbonation enlarged the cracks, and some calcium carbonate spots appear on the calcium hydroxide crystals. When w/c=0.35, less cracks appear, and some white flocculent calcium carbonated appear on the calcium hydroxide crystals than above w/c=0.53 cement paste. When w/c=0.23, the microstructure character before and after carbonation have distinct changes, and some cracks become small or disappeared. Unhydrated cement clinkers continue to hydrate reactions and there are many white SiO₂•nH₂O (silica gel) after C-S-H gel carbonation in cement paste matrix.