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Delayed Ettringite Formation (DEF)

Pre-cast concrete cured at temperatures sufficient to destroy ettringite and mass concrete where the volumes of concrete are sufficient for high temperatures to be reached during curing can be susceptible to damage as a result of delayed ettringite formation (DEF). For DEF to occur it is generally accepted that the temperatures reached during curing should be at least 65-70 °C. DEF in mass concrete is often preceded by the development of alkali aggregate reaction.

Petrography is the definitive method for diagnosing DEF and the use of the electron microprobe enables the distribution sulphate in the cement paste to be examined in detail. At Geomaterials core expansion testing in accordance with the BCA report on the Diagnosis of Alkali-Silica Reaction in Concrete (Appendix H) and the Duggan test has been used to assist in the assessment of the potential future development of expansion in concrete as a result of DEF.