50 Damage to concrete structures
It is good to recall in this section that the risk of sulfate attack can be significantly reduced by applying high sulfate resisting cement types, which contain
a limited amount of aluminate phases. As a result, the hardened concrete will
contain only minor quantities of monosulfate, so that even in the presence
of sulfates, no significant conversion to ettringite can occur. However, some
specific types of sulfate attack remain possible, even in this case.
3.4.2 chlorides
As previously mentioned in the second paragraph of this chapter, a too high
chloride content in concrete can initiate corrosion reinforcement. Further
details on this corrosion process and on the critical chloride content to initiate corrosion will be given in Chapter 5. When producing a concrete mix,
the total chloride content should be calculated based on the chloride content
and the dosage of all constituent materials. When using sea aggregates,
they should be washed with clear water in order to limit the chloride content. The chloride content of admixtures should also be carefully checked.
In Europe, EN 206-1 even prohibits the use of chloride based admixtures.
3.4.3 alkalis and potentially reactive aggregates
Some aggregates applied in concrete are potentially reactive when present
in an alkali rich solution. In many cases, the aggregates contain potentially reactive amorphous silica, leading to the so-called alkali silica reaction (ASR). In Chapter 5, the expansive alkali silica reaction which leads to
cracking and degradation of the concrete will be explained in more detail.
The presence of potentially reactive aggregates alone is not sufficient for the
occurrence of ASR. Water and alkali must also be sufficiently present for
the expansive reaction to occur. As a consequence, the application of potentially reactive aggregates should also be combined with a careful control
and limitation of the alkali content in the freshly mixed concrete.
Alkalis (Na 2 O and K 2 O, often combined in the equivalent alkali content
Na 2 O eq , see Chapter 5) can be present in cement, admixtures, mixing
water, and aggregates (especially in the case of sea aggregates). The application of special cement containing a very low alkali content (so-called LA
cement or low alkali cement) can be required in case the use of potentially
reactive aggregates cannot be avoided. However, it is a better approach to
control the total alkali content per cubic meter of concrete. In this approach
the application of an LA cement can be one element.
3.4.4 free lime
Free lime, CaO, will hydrate when present in concrete and will form calcium hydroxide, Ca(OH) 2 . This hydration process is expansive and can
It is good to recall in this section that the risk of sulfate attack can be significantly reduced by applying high sulfate resisting cement types, which contain
a limited amount of aluminate phases. As a result, the hardened concrete will
contain only minor quantities of monosulfate, so that even in the presence
of sulfates, no significant conversion to ettringite can occur. However, some
specific types of sulfate attack remain possible, even in this case.
3.4.2 chlorides
As previously mentioned in the second paragraph of this chapter, a too high
chloride content in concrete can initiate corrosion reinforcement. Further
details on this corrosion process and on the critical chloride content to initiate corrosion will be given in Chapter 5. When producing a concrete mix,
the total chloride content should be calculated based on the chloride content
and the dosage of all constituent materials. When using sea aggregates,
they should be washed with clear water in order to limit the chloride content. The chloride content of admixtures should also be carefully checked.
In Europe, EN 206-1 even prohibits the use of chloride based admixtures.
3.4.3 alkalis and potentially reactive aggregates
Some aggregates applied in concrete are potentially reactive when present
in an alkali rich solution. In many cases, the aggregates contain potentially reactive amorphous silica, leading to the so-called alkali silica reaction (ASR). In Chapter 5, the expansive alkali silica reaction which leads to
cracking and degradation of the concrete will be explained in more detail.
The presence of potentially reactive aggregates alone is not sufficient for the
occurrence of ASR. Water and alkali must also be sufficiently present for
the expansive reaction to occur. As a consequence, the application of potentially reactive aggregates should also be combined with a careful control
and limitation of the alkali content in the freshly mixed concrete.
Alkalis (Na 2 O and K 2 O, often combined in the equivalent alkali content
Na 2 O eq , see Chapter 5) can be present in cement, admixtures, mixing
water, and aggregates (especially in the case of sea aggregates). The application of special cement containing a very low alkali content (so-called LA
cement or low alkali cement) can be required in case the use of potentially
reactive aggregates cannot be avoided. However, it is a better approach to
control the total alkali content per cubic meter of concrete. In this approach
the application of an LA cement can be one element.
3.4.4 free lime
Free lime, CaO, will hydrate when present in concrete and will form calcium hydroxide, Ca(OH) 2 . This hydration process is expansive and can