Actions during service 155
Many different theories exist to fully explain the detailed mechanism of
DEF, as discussed by Skalny et al. (2002). It is also discussed whether DEF
is really causing damage to the concrete, as not all ettringite formation
leads to the expansion of the cement paste. According to many researchers, pre-existing cracks are needed before delayed ettringite formation can
occur, e.g. caused by freeze–thaw, ASR, or thermal cracking. In this view,
the expansion caused by DEF is not significant and there would be no damage if no other mechanism had caused pre-cracking.
While scientific debate is still going on, appropriate measures to avoid
damage due to DEF can be taken and are sometimes provided in standards.
DEF typically concerns the concrete precast industry where, for reasons of
production speed, concrete elements quite often are steam cured or heat
cured in another way. During hydration, temperatures higher than 60° to
70°C should be avoided.
Also in hot climates, such as those in the Middle East, DEF can be a
matter of concern because the hydration process typically occurs at higher
temperatures, especially in the case of massive elements in which the heat
of hydration adds to the environmental temperature effect. The risk of DEF
increases with increased curing temperature.
Although the mechanism of DEF is still under debate, it seems that it
does not cause damage in the case of blended cements such as blast furnace
slag cement. Nevertheless, a clear correlation between the occurrence of
DEF and the type and composition of the cement is not currently available.
5.3.2.4 Sea water
When discussing sulfate attack, sea water is often referred to as a case of
concern in this respect. It is true that sea water contains sulfate ions, SO 4
2− ,
but many other ions are also present, including Na + , Mg 2+ and Cl − to only
name the main ones.
Standard provisions typically require a high sulfate resisting (HSR)
cement for concrete structures in contact with sea water. However, this
is probably not the best choice to reduce the risk of chloride-induced reinforcement corrosion, because the chloride binding capacity in the case of
HSR cement is reduced, having a lower content of calcium aluminate. As
mentioned by Skalny et al. (2002), ‘the formation of ettringite in sea water
attack typically does not lead to expansion and cracking of the concrete
and it is believed that the formation of this phase is non-expanding in the
presence of excessive amounts of chloride ions’. It can be noted that in many
countries chloride-induced reinforcement corrosion (see Section 5.4.3) is
causing more damage to marine structures than sulfate attack.
It is to be remarked, however, that sea water can be very different all
over the world. In some locations, very high concentrations of some specific
ions can cause severe damage to exposed concrete structures, sometimes
Many different theories exist to fully explain the detailed mechanism of
DEF, as discussed by Skalny et al. (2002). It is also discussed whether DEF
is really causing damage to the concrete, as not all ettringite formation
leads to the expansion of the cement paste. According to many researchers, pre-existing cracks are needed before delayed ettringite formation can
occur, e.g. caused by freeze–thaw, ASR, or thermal cracking. In this view,
the expansion caused by DEF is not significant and there would be no damage if no other mechanism had caused pre-cracking.
While scientific debate is still going on, appropriate measures to avoid
damage due to DEF can be taken and are sometimes provided in standards.
DEF typically concerns the concrete precast industry where, for reasons of
production speed, concrete elements quite often are steam cured or heat
cured in another way. During hydration, temperatures higher than 60° to
70°C should be avoided.
Also in hot climates, such as those in the Middle East, DEF can be a
matter of concern because the hydration process typically occurs at higher
temperatures, especially in the case of massive elements in which the heat
of hydration adds to the environmental temperature effect. The risk of DEF
increases with increased curing temperature.
Although the mechanism of DEF is still under debate, it seems that it
does not cause damage in the case of blended cements such as blast furnace
slag cement. Nevertheless, a clear correlation between the occurrence of
DEF and the type and composition of the cement is not currently available.
5.3.2.4 Sea water
When discussing sulfate attack, sea water is often referred to as a case of
concern in this respect. It is true that sea water contains sulfate ions, SO 4
2− ,
but many other ions are also present, including Na + , Mg 2+ and Cl − to only
name the main ones.
Standard provisions typically require a high sulfate resisting (HSR)
cement for concrete structures in contact with sea water. However, this
is probably not the best choice to reduce the risk of chloride-induced reinforcement corrosion, because the chloride binding capacity in the case of
HSR cement is reduced, having a lower content of calcium aluminate. As
mentioned by Skalny et al. (2002), ‘the formation of ettringite in sea water
attack typically does not lead to expansion and cracking of the concrete
and it is believed that the formation of this phase is non-expanding in the
presence of excessive amounts of chloride ions’. It can be noted that in many
countries chloride-induced reinforcement corrosion (see Section 5.4.3) is
causing more damage to marine structures than sulfate attack.
It is to be remarked, however, that sea water can be very different all
over the world. In some locations, very high concentrations of some specific
ions can cause severe damage to exposed concrete structures, sometimes