Delayed Ettringite Formation in Concrete
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.

Gaps around aggregate in field concrete. Railroad sleeper. Fluorescent light.

Gaps around aggregate. Test sample. Ordinary polarized light.

Gaps around aggregate. Test sample. Fluorescent light.

Two-toning in concrete subjected to high curing temperature.
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