1. Introduction 2. Formation of ettringite and some factors affecting DEF 2.1 Recrystallization and new formation of ettringite 2.2 Effect of cement composition 2.3 Effect of aggregate 2.4 Effect of curing regime 2.5 Effect of cracks 2.6 Ambient temperature DEF 3. Mechanisms of DEF 3.1 Prerequisites for DEF 3.2 Mechanisms of DEF 4. Example of structure damaged due to DEF 5. Concluding Remarks

1. Delayed ettringite formation (DEF) in concrete-
Formation of ettringite and some factors affecting
DEF
Igor Cigrovski, mag.ing.aedif.
cigrovski1@gmail.com

2. 2
1. Introduction
2. Formation of ettringite and some factors affecting DEF
2.1 Recrystallization and new formation of ettringite
2.2 Effect of cement composition
2.3 Effect of aggregate
2.4 Effect of curing regime
2.5 Effect of cracks
2.6 Ambient temperature DEF
3. Mechanisms of DEF
3.1 Prerequisites for DEF
3.2 Mechanisms of DEF
4. Example of structure damaged due to DEF
5. Concluding Remarks
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SULFATE ATTACK is a chemical reaction between sulfate ions
(+and accompanying-balanced cations or elements in their
environment) and components of concrete (mortar, paste)
which can have adverse consequences.
Internal sulphate attack involves transformation (function
with multiple variables; monosulphate  ettringite and vice
versa) of sulfate phases to achieve equilibrium under the
given conditions (temperature, pH, concentration of sulfate
ions, moisture in concrete, pressure, etc.).

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 Delayed ettringite formation (DEF) - implies a new
formation and re-crystallization of ettringite induced by
high temperature (excessive heat) without additional
external sources of sulfate ions.
 Formation of ettringite should not be confused with the
expansion, because ettringite may occur even if the
expansion does not occur.

5. AFt –sulfate phase- ettringite:
 is a normal and desirable product of cement hydration in
the initial period. It is needed to control and prevent the
so-called flash set;
 can persist indefinitely in cement-
based materials;
 ettringite prevalent at lower
temperatures;
AFm-sulfate phase- monosulfate:
 prevails at higher temperatures in
the cement-based system.
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Damidot and Glasser, 1993

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Formation of ettringite:
 through-solution mechanism
 mixed topochemically (Al-rich nuclei) and through-
solution mechanism
 topochemical formation of ettringite
The agreement around the question whether only one of
these mechanisms of ettringite formation may lead to
expansion is not reached.

7.  Primary
 Ostwald ripening (not
expansive);
 variations in pH;
 changes in temperature;
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 Secondary
 changes in the
concentration
(availability) of the
components that
build ettringite.
For example, when the temperature is changing also the
availability of sulfate is changing. This implies changes in
the concentration (availability) of the components (in this
case, sulfate ions) that build ettringite.
Some possible causes of the (re)crystallization and/or new
formation of ettringite are:

8.  particularly important are elements that build ettringit
(sulfates and aluminates, among other);
 except quantity (of sulfates and aluminates) also very
important is their mutual relationship and other
components of cement: s/A molar ratio, total sulfate=
from clinker and cement, C3A, alkali, MgO, CaO and
possibly also C3S content.
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 an empiric (relationship) parameter was developed called
DEFindex:
 cement fineness (specific surface area) is also an
important parameter (not included in DEFindex)
 cements with high early strength are particularly suitable
for the DEF-induced expansion

10.  quartz is the most negative type of aggregate in regards
to the expansion associated with DEF;
 it was found that expansion was inversely proportional to
the particle size of the quartz aggregate (proportional to
the surface area of the aggregate;
 it is believed that aggregate with a coefficient of thermal
expansion is particularly DEF-suitable
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Tosun, K.;
Baradan, B.,
2010

11.  for DEF the temperature of cement-based materials
(inside or at any point in element) is important, which is a
consequence of applied external temperature;
 important parameters
are:
- pre-storage time
-temperature increase rate,
-duration of treatment
(maximum temperature)
-rate of temperature
decrease
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 increased expansion was observed with increase of curing
temperature; expansion is decelerated and reduced with
the increase of pre-storage time;
 too long precuring period can cause “dilution effect”;
 too short precuring time can cause a reduced expansion.

13.  Although it was considered that microcracking is one of
three essential elements according to the holistic model,
for the serious risk of DEF related damage, it was shown
that it is not necessary for the occurrence of DEF-related
expansion;
 pre-existing cracks can accelerate DEF-related expansion;
 the ultimate values of expansion can be similar or even
reduced because it is believed that delayed formation of
ettringite occurs preferentially in cracks without causing
expansion.
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 may be due to sulfates, which
were bind, and are slowly
released into an aqueous phase;
 It has been claimed that the
“ambient temperature DEF”
could be the consequence of too
high content of sulfate in the
clinker and/or slow dissolution of
sulfate from the clinker;
Mielenz, R.C., Marusin, S.L., Hime, W.G. and
Jugovic, Z.T., 1995

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 anhydrite is considered to dissolve relatively slowly-
possible cause of “ambient temperature DEF” ;
 it was shown that anhydrite reacts relatively quickly;
 it is believed that, if the possibility that the cement has a
much higher total sulfate content than is allowed by
standards is excluded, no reliable laboratory evidence
exist that “ambient temperature DEF” would occur.

16.  Additional source and availability of sulfate ions are
required for delayed ettringite formation;
 Prerequisites for DEF:
 heat cure of concrete
-temperature increase increased solubility of ettringite
 increased concentrations of sulfate in solution more
sulfate is bind (adsorbed) to the C–S–H (and also
incorporates some aluminate ions); amount of (ad)sorbed
sulfate ions can be indicative of the potential for future
expansion);
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temperature decrease decrease solubility of ettringite
 release of sulfate from the C-S-H  increased
concentrations of sulfate in pore solution  precipitation
of ettringite;
 leaching of alkali (Leaching of alkali hydroxide out from
the concrete (or paste/mortar) element can trigger DEF in
a way that can increase the rate by which sulfate ions are
released from C-S-H and also, decrease of pH of pore
solution in the stability domain for nucleation of ett.).

18.  the question is, whether paste
is expansive or expansion is
caused by growth of ettringite
crystals itself;
 formation of ettringite from
monosulfate which are
“intimately” mixed with
(outer) C-S-H after heat
treatment;
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[Taylor, H. F.W.; Famy, C.; Scrivener ,K.L. 2001.
Lawrence, C.D., Lynsdale, C.J. and Sharp, J.H.

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 “It seems that ettringite band formation in heat-cured
mortars can create, extend, and widen cracks, hence
causing the overall expansion observed.”
Yang, R.; Lawrence, C.; Lynsdale, C.; Sharp, J., 1999.

20.  Two unusual examples will be given:
- normally, the DEF occurs when the concrete (mortar,
paste) elements are cured at but these
examples indicate the whole complexity of this
phenomenon;
- first example is railroad ties which were not cured at
elevated temperature. It has been claimed that the reason
is slow soluble sulfate from the clinker; (no lab. evidence)
- another example is also concrete railroad ties steam-cured
with a maximum concrete temperature within the
element below 60 C; (pessimum combination of factors)
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21.  possible causes of the (re)crystallization and/or new
formation of ettringite are:
Ostwald ripening, variations in pH, changes in
temperature and changes in the concentration
(availability) of the components that build ettringite;
 it is believed that quartz is the most negative type of
aggregate in regard to the expansion associated with
DEF;
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 the impact of the curing regime- increased expansion was
observed with increase of curing temperature and also
that expansion is decelerated and reduced significantly
with the increase of pre-storage time;
 considering cement composition, particularly important
parameters are: s/A molar ratio, total sulfate, contents of
C3A and alkali content; cement fineness is also an
important parameter;
 microcracking is not necessary for the occurrence of DEF-
related expansion (pre-existing cracks can accelerate DEF-
related expansion);

23.  it is believed that the “ambient temperature DEF” cannot
occur;
 additional source and availability of sulfate is critical for
delayed ettringite formation. This can be achieved with
curing at elevated temperature and with alkali leaching;
 in regard to the exact mechanism of expansion, the question
is whether paste is expansive or expansion is caused by
growth of ettringite crystals itself;
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24. Igor Cigrovski, mag.ing.aedif.
cigrovski1@gmail.com
I. Cigrovski 24