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Cement pastes and concrete specimens were cured at 20°C or steam-cured up to 90°C.
At curing temperature higher then 70°C, ettringite disappears and then forms again at
later ages (DEF). Concretes manufactured at room temperature (20°C) do not show any
form of DEF-related expansion independently of the SO3 content of the clinker (1-2%)
or the portland cement (2-4%). On the other hand, concretes steam-cured at 90°C and
then kept under water show significant expansion related to DEF provided that the SO3
content of the portland cement is relatively high (> 4%). The higher SO3 content in the
clinker phases (> 2%) or the presence of pre-existing cracks exacerbate the DEFrelated
expansion. Deposition of ettringite fiber crystals occurs in the preexisting
cracks or within the new microcracks. However, no clear evidence was found between
the ettringite deposition and the width-change of the cracks. Curing at temperatures
lower than 70°C is strongly recommended to avoid DEF-related risk. Blended cements
with a lower SO3 content should be used in case this limit in curing temperature cannot
be safely ensured.The purpose of the present work was to confirm, by laboratory test carried out under controlled
conditions, the influence of the following parameters on the DEF-related damage:

SO3 content in the clinker (1-2%) and cement (2-4%)

curing of cement mixes at different temperatures (from 20 to 90°C)

presence of pre-existing cracks in concrete specimens

type of subsequent exposure to moisture: permanently under water or
wetting/drying cycles