Title: Ettringite in Hydration of Portland Cement Concrete and its Occurrence in Mature Concretes

Author(s): Charlotte Famy and Hal F. W. Taylor

Publication: Materials Journal

Volume: 98

Issue: 4

Appears on pages(s): 350-356

Keywords: clinker; concrete; ettringite; expansion; hydration.

DOI: 10.14359/10404

Date: 7/1/2001

Abstract:
Ettringite is a normal product of cement hydration, and persists indefinitely in the hydration products of many cements. Because small crystals are unstable relative to larger ones, it tends to recrystallize in any available cracks or other spaces. This process occurs in both damaged and undamaged concretes, irrespective of the curing temperature, and the presence of ettringite is therefore not an indication of distress. Cracks at aggregate interfaces or elsewhere are a feature of distress, but crystals of ettringite or other phases within them are recrystallization products and their presence does not show what has caused the cracks to form. In deteriorated heat-treated concretes, it does not necessarily mean that the damage has been caused or increased by the formation of ettringite in the mature concrete. Even in cases where damage may have arisen from this cause, the crystals responsible are likely to be very small ones within the cement paste and not the much larger ones readily observed by optical petrography or scanning electron microscopy. There is no sound evidence to support claims that ettringite formed at later ages has caused damage in concrete that has not experienced an elevated temperature or that slowly reacting sources of SO3 in the clinker or cement can cause distress.