Heat Curing and Late Formation of Ettringite


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Title: Heat Curing and Late Formation of Ettringite

Author(s): V. Johansen and N. Thaulow

Publication: Special Publication

Volume: 177


Appears on pages(s): 47-64

Keywords: curing; ettringite; expansion; models; sulfate attack

Date: 1/1/1999

Paste, mortar, and concrete cured at temperatures above certain limits may exhibit expansion and cracking during subsequent exposure to varying moist conditions. This phenomenon originally became known as delayed ettringite formation, DEF. DEF results in a typical microstructure which is demonstrated with examples from field samples and laboratory-made samples. The microstructure is compared with examples of internal sulfate attack in laboratory samples. These typical features include gaps around the aggregate where the paste shows an almost perfect replica of the individual aggregate surfaces. Expansion of the paste on a scale which is homogeneous relative to the aggregate would lead to such features. The chemistry in DEF is similar to that of sulfate attack. A mechanism involving hydrates of aluminates and possible unhydrated cement clinker particles is discussed.