Ettringite is an early hydration product of cement that is always present in all Portland cement concretes, and this seems to be too often forgotten by thin-section researchers.
So, what can we conclude with certainty from the observations of ettringite in thinsection samples?
The presence of crystallizations in the pores indicates repeated moisture stress on the concrete, as a result of which the ettringite of the cement stone has at least partially dissolved and recrystallized in the voids.
The amount of crystallization in the voids also influences the frost resistance of concrete. If most of the voids of well air-entrained concrete are full of crystallizations, in moisturestressed concrete the crystallizations can often be partly ettringite and partly portlandite, the pore structure has changed, and the concrete’s frost resistance may have weakened.
However, the answer to the question of whether ettringite detected in the thin section study is from early hydration, a result of late ettringite formation (DEF), or whether sulphate or sulfide corrosion is in the background, requires other studies and investigations.
