Title: Expansion and Cracking in Concrete Associated with Delayed Ettringite Formation

Author(s): D. W. Hobbs

Publication: Symposium Paper

Volume: 177

Issue:

Appears on pages(s): 159-182

Keywords: alkali content; cement; concretes; cracking; ettringite; expansion; magnesium oxides; mortars; sulfates; temperature

DOI: 10.14359/6234

Date: 1/1/1999

Abstract:
In a number of isolated cases in the U.K., expansion and cracking has occurred in precast concrete elements subject to early heat treatment followed by wet or moist exposure, and in some in-situ concretes of large section and high cement content, again subject to wet or moist exposure. The present paper discusses some of the work relating to the cracking of these field concretes and to the laboratory expansion testing of concretes and mortars subject to high early temperatures which has been carried out by the British Cement Association. It is shown that expansion is caused by expansion of the cement paste fraction. It is shown that concretes and mortars made using a number of Portland cements can be induced to show abnormal expansion when subject to wet curing after a severe early cure and that the parameters influencing expansion are probably total sulfate as SO, magnesium oxide and alkali contents of the cement and cement fineness. Given our present understanding, it does not seem possible to eliminate the expansion by a suitable choice of portland cement composition. However, it is shown that limiting the concrete temperature at all times to below 70 C in precast concrete and limiting the cement content in in-situ concrete of large section are probably secure ways of avoiding late expansions associated with ‘delayed ettringite formation’ in concretes subject to prolonged wet or moist exposure.