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CAER Seminars

Ettringite Revisited

Dr. Fred Glasser
University of Aberdeen

Wednesday, October 28, 2009 10:00 am
Ben Bandy Conference Center
Center for Applied Energy Research

Ettringite is well known as a natural mineral and its synthetic equivalent is a minor but persistent phase in hydrated Portland cement. However it is also an important alteration product of Portland cement and its enhanced presence in deteriorated Portland cement has given rise to a wide range of beliefs, mainly negative, concerning its role. On the other hand ettringite is also known to be a major component of cements based on calcium sulfoaluminate These cements, like Portland cement, set under water giving dimensionally stable and, in conjunction with mineral aggregates, strong concretes. Extensive outdoor trials extending over 25-30 years shows that they are durable in a wide range of service environments and give good protection for embedded steel. Therefore many of the prejudicial statements concerning ettringite- for example that it does not contribute to cement strength- need to be abandoned or modified.

Conflicting views about ettringite can only be resolved by research. An account is given of the formation, structure and properties of ettringite and related phases such as thaumasite: the historical development of commercial sulfoaluminate cements is outlined. An assessment of the present state of development of ettringite - based cements shows that they offer scope for development of unique property sets. The interaction between cement and organic admixtures will, it is predicted, be important. As we look for innovative materials for construction and repair, these inexpensive and versatile compositions have much to offer.