Research on deterioration of concrete caused by delayed ettringite formation

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Delayed ettringite formation (DEF) is a phenomenon in which ettringite is generated and accumulates in the concrete after hardening, eventually leading to expansion and destruction of the concrete. In this study, DEF expansion was reproduced in laboratory using a variety of cements, sulfate additions, steam curing conditions and storing conditions. DEF was found to take place only when the three conditions of excessive sulfate, high-temperature steam curing and ample water supply are met simultaneously. The influence of the kind of calcium sulfate (gypsum, hemihydrate or anhydrite CaSO_4) and the heating rate of steam curing was studied. The cases of expansive deterioration of concrete due to delayed ettringite formation (DEF) and the counter measure of DEF in Japan are described in this paper. The influence of kind of cement, aggregate and sulfate and added amount of sulfate on the expansion of concrete by delayed ettringite formation (DEF). The evaluation method of concrete against DEF is also described. As it is reported that both the alkali silica reaction (ASR) and DEF are sometimes observed in the same deteriorated concrete, the relationship between the alkali silica reaction and DEF is also discussed.