| Concrete
Experts International has extensive, worldwide experience in diagnosing
delayed ettringite formation (DEF) in concrete structures and with
research regarding the nature and effects of DEF.
Diagnosing DEF is an integrated part of our
petrographic analysis of concrete.
What is Delayed Ettringite
Formation?
Generally DEF is seen as a
form of internal sulfate attack. A number of factors such as concrete
composition, curing conditions and exposure conditions influence the
potential for DEF.
DEF is believed to be a
result of improper heat curing of the concrete where the normal
ettringite formation is suppressed. The sulfate concentration in the
pore liquid is high for an unusually long period of time in the hardened
concrete. Eventually, the sulfate reacts with calcium- and aluminium-containing
phases of the cement paste and the cement paste expands. Due to this
expansion empty cracks (gaps) are formed around aggregates. The cracks
may remain empty or later be partly or even completely filled with ettringite.
Microscopic appearance
DEF is diagnosed primarily
by four main features:
-
Presence of gaps
completely encircling aggregates
-
Wider gaps around large
aggregate than around small aggregate
-
Absence of external sulfate
source
-
High temperature heat
curing history
Please to not hesitate
to contact CXI if you have some problems regarding DEF or any other
deterioration mechanisms. |
