20 Damage to concrete structures
referring to the anticipated severity of the environment of the concrete element. The exposure classes are subdivided depending on humidity conditions. According to the exposure (sub)class, limiting values are specified
for water/cement ratio and compressive strength in the North American,
Canadian and Australian standards, while a minimum cement content is
also required in the European standard. Additional requirements might be
added in some cases, such as high sulfate resisting cement (EN 206-1). A
comprehensive overview is given by Kulkarni (2009).
1.5.2 some critical reflection on
typical code provisions
Each of the parameters considered in typical code provisions (water/cement
ratio, cement content, concrete strength) can be questioned (Figure 1.12).
It is clear (although not always well-known in concrete practice) that
concrete strength alone cannot ensure durable behaviour (Neville 1997).
Furthermore, the minimum cement content requirement can be questioned
(Wasserman et al. 2008). Even the water/cement ratio, which is generally believed to be the most important parameter governing the durability
behaviour, should be applied with caution. “We should remember the limitations on its interpretation”, as stated by Neville (1999).
The definition of the water/cement ratio became more complicated after
the introduction of supplementary cementitious materials like fly ash, silica
fume, and blast furnace slag. In order to more accurately estimate the effect
of these various cementitious materials, the k-value concept has been implemented in the European Standard EN 206-1. However, major discussions
Cement content
Strength
Durability
Water/cement ratio
Figure 1.12 Criticism on typical code provisions.
referring to the anticipated severity of the environment of the concrete element. The exposure classes are subdivided depending on humidity conditions. According to the exposure (sub)class, limiting values are specified
for water/cement ratio and compressive strength in the North American,
Canadian and Australian standards, while a minimum cement content is
also required in the European standard. Additional requirements might be
added in some cases, such as high sulfate resisting cement (EN 206-1). A
comprehensive overview is given by Kulkarni (2009).
1.5.2 some critical reflection on
typical code provisions
Each of the parameters considered in typical code provisions (water/cement
ratio, cement content, concrete strength) can be questioned (Figure 1.12).
It is clear (although not always well-known in concrete practice) that
concrete strength alone cannot ensure durable behaviour (Neville 1997).
Furthermore, the minimum cement content requirement can be questioned
(Wasserman et al. 2008). Even the water/cement ratio, which is generally believed to be the most important parameter governing the durability
behaviour, should be applied with caution. “We should remember the limitations on its interpretation”, as stated by Neville (1999).
The definition of the water/cement ratio became more complicated after
the introduction of supplementary cementitious materials like fly ash, silica
fume, and blast furnace slag. In order to more accurately estimate the effect
of these various cementitious materials, the k-value concept has been implemented in the European Standard EN 206-1. However, major discussions
Cement content
Strength
Durability
Water/cement ratio
Figure 1.12 Criticism on typical code provisions.