Actions during service 153
Liu did not find traces of salt crystallisation in concrete partially exposed
to magnesium sulfate solution (Liu et al. 2010), epsomite (MgSO 4 ∙7H 2 O)
was reported by Gruyaert et al. (2012) in the case of partially exposed concrete which showed carbonation. Carbonation, thus, seems to enable and
accelerate damage due to salt crystallisation in partially exposed concrete
elements. This illustrates the importance of adequate curing and reducing
carbonation for the sulfate resistance of concrete structures, especially in
the case of the addition of puzzolanic materials.
It could be concluded that ‘physical’ sulfate attack, causing damage due
to salt crystallisation, is a real damage mechanism. However, it only plays
an aggravating role after the concrete is first damaged by chemical sulfate
attack or in case of previous carbonation. For many field cases ascribed
to ‘physical’ sulfate attack, ‘chemical’ sulfate attack seems to be the main
damage mechanism.
Nevertheless, there might be some specific circumstances where the
action is purely physical and could be produced by salts other than sulfate,
justifying the name ‘physical attack’ (Neville 2004), but sometimes also
called ‘salt weathering’ or ‘salt hydration stress’. The resulting damage has
a similar appearance to surface scaling, as in the case of freeze–thaw cycles
(Haynes and Bassuoni 2011). This process could be favoured by cooling
and heating and wetting and drying, with cyclic crystallisation of salts
(Stark 2002).
5.3.2.2.2 Influencing parameters
As the main damage mechanism is the chemical sulfate attack, the influencing parameters are the same as mentioned in Section 5.3.2.1.2. In the case
of pure crystallisation effects, wetting and drying and cooling and heating
cycles will accelerate the damage process.
5.3.2.2.3 Mitigation
The same mitigation measures can be mentioned as in Section 5.3.2.1.3.
Additionally, a coating could be applied to the concrete drying surface
exposed to the surrounding air in order to stop or limit wick action. Another
option is to isolate the concrete from the soil (Haynes and Bassuoni 2011).
5.3.2.2.4 Example
As an important part of the ‘West Development Strategy’, China will make
huge investments in railway construction and will more than double the
existing operating mileage of railways in its western regions, bringing it
to fifty thousand kilometres by 2020 (Liu 2010). However, in the western regions of China, the groundwater shows a high content of sulfates
Liu did not find traces of salt crystallisation in concrete partially exposed
to magnesium sulfate solution (Liu et al. 2010), epsomite (MgSO 4 ∙7H 2 O)
was reported by Gruyaert et al. (2012) in the case of partially exposed concrete which showed carbonation. Carbonation, thus, seems to enable and
accelerate damage due to salt crystallisation in partially exposed concrete
elements. This illustrates the importance of adequate curing and reducing
carbonation for the sulfate resistance of concrete structures, especially in
the case of the addition of puzzolanic materials.
It could be concluded that ‘physical’ sulfate attack, causing damage due
to salt crystallisation, is a real damage mechanism. However, it only plays
an aggravating role after the concrete is first damaged by chemical sulfate
attack or in case of previous carbonation. For many field cases ascribed
to ‘physical’ sulfate attack, ‘chemical’ sulfate attack seems to be the main
damage mechanism.
Nevertheless, there might be some specific circumstances where the
action is purely physical and could be produced by salts other than sulfate,
justifying the name ‘physical attack’ (Neville 2004), but sometimes also
called ‘salt weathering’ or ‘salt hydration stress’. The resulting damage has
a similar appearance to surface scaling, as in the case of freeze–thaw cycles
(Haynes and Bassuoni 2011). This process could be favoured by cooling
and heating and wetting and drying, with cyclic crystallisation of salts
(Stark 2002).
5.3.2.2.2 Influencing parameters
As the main damage mechanism is the chemical sulfate attack, the influencing parameters are the same as mentioned in Section 5.3.2.1.2. In the case
of pure crystallisation effects, wetting and drying and cooling and heating
cycles will accelerate the damage process.
5.3.2.2.3 Mitigation
The same mitigation measures can be mentioned as in Section 5.3.2.1.3.
Additionally, a coating could be applied to the concrete drying surface
exposed to the surrounding air in order to stop or limit wick action. Another
option is to isolate the concrete from the soil (Haynes and Bassuoni 2011).
5.3.2.2.4 Example
As an important part of the ‘West Development Strategy’, China will make
huge investments in railway construction and will more than double the
existing operating mileage of railways in its western regions, bringing it
to fifty thousand kilometres by 2020 (Liu 2010). However, in the western regions of China, the groundwater shows a high content of sulfates