2018 Volume 72 Issue 1 Pages 40-47
Sulfate attack is known as one of the deterioration phenomena of concrete structures. In particular, there is a serious problem with expansion due to Delayed Ettringite Formation（DEF）. Recent researches had indicated the possibility that CO32－ promotes DEF expansion. Therefore, we focused on understanding carbonate ettringite, in which ettringite substitutes SO42－ for CO32－, despite it has never detected in hardened cement. Our purpose is to discuss the relationship between the secondary formation of ettringite and Al bonding state, by comparing ettringite and carbonate ettringite.
From the experimental results, thermal dehydration converted carbonate ettringite into amorphous carbonate ettringite, as shown by XRD, while Al coordination of dehydrated carbonate ettringite was 4 and 5. In addition, water adsorption isotherm of dehydrated carbonate ettringite showed a sharp rise at RH60-80％. It is possible that carbonate ettringite formed as a secondary carbonate ettringite when Al coordination number was 4 or 5, and up to 6, by water supply. Therefore, it is concluded that dehydrated carbonate ettringite has large potential of swelling compared to carbonate ettringite.
