108 Damage to concrete structures
successful application of air-entraining agents is the spacing factor, which
is related to the maximum distance to the nearest air void. Values below
200 µm are typically considered to provide adequate frost resistance.
5.2.1.2.3 Water/cement ratio
A low water/cement ratio will lead to the reduced permeability of the concrete. It could be reasoned that this will lead to higher hydraulic pressures
when ice formation is initiated because the pressurized water cannot easily escape. In practice, however, a lower water/cement ratio will lead to a
higher frost resistance. Due to the reduced permeability, the critical saturation degree will almost never be reached in real situations. Furthermore,
the reduced pore volume results in a reduced amount of freezable water
in the concrete. As a result, the tensile stresses in the concrete matrix, as
caused by a limited amount of freezing water, will not cause significant
damage in the case of a low water/cement ratio.
5.2.1.2.4 Strength
As a lower water/cement ratio leads to a higher concrete strength, it could
be concluded that stronger concrete shows better frost resistance. However,
this is not generally true. Durability requirements should not be narrowed
to strength verification alone. Strength is an important parameter, but it is
not sufficient to guarantee frost resistance. Air-entrained concrete shows
lower strength than the corresponding concrete without air entrainment.
Nevertheless, the air-entrained concrete shows better frost resistance
(Mehta and Monteiro 2006).
5.2.1.2.5 Cement type
The type of cement influences the microstructure development, and thus the
pore system and transport properties of the cementitious material. In this
way, the cement type has a potential effect on frost resistance. However,
a more significant influence is noticed through the interaction between
carbonation and frost resistance. As an example, concrete based on blast
furnace slag cement will be more vulnerable to carbonation. Furthermore,
carbonation of slag concrete will lead to an increased porosity and permeability, while the opposite is noticed in the case of Portland cement concrete. As a result, carbonated slag concrete will show more pronounced
frost damage. Inadequate curing of concrete structures at early age can
significantly increase the carbonation rate in slag concrete and, thus, also
further impair frost resistance. This should be well considered when evaluating the frost resistance performance of slag concrete in lab conditions,
having perfect curing and no carbonation.
successful application of air-entraining agents is the spacing factor, which
is related to the maximum distance to the nearest air void. Values below
200 µm are typically considered to provide adequate frost resistance.
5.2.1.2.3 Water/cement ratio
A low water/cement ratio will lead to the reduced permeability of the concrete. It could be reasoned that this will lead to higher hydraulic pressures
when ice formation is initiated because the pressurized water cannot easily escape. In practice, however, a lower water/cement ratio will lead to a
higher frost resistance. Due to the reduced permeability, the critical saturation degree will almost never be reached in real situations. Furthermore,
the reduced pore volume results in a reduced amount of freezable water
in the concrete. As a result, the tensile stresses in the concrete matrix, as
caused by a limited amount of freezing water, will not cause significant
damage in the case of a low water/cement ratio.
5.2.1.2.4 Strength
As a lower water/cement ratio leads to a higher concrete strength, it could
be concluded that stronger concrete shows better frost resistance. However,
this is not generally true. Durability requirements should not be narrowed
to strength verification alone. Strength is an important parameter, but it is
not sufficient to guarantee frost resistance. Air-entrained concrete shows
lower strength than the corresponding concrete without air entrainment.
Nevertheless, the air-entrained concrete shows better frost resistance
(Mehta and Monteiro 2006).
5.2.1.2.5 Cement type
The type of cement influences the microstructure development, and thus the
pore system and transport properties of the cementitious material. In this
way, the cement type has a potential effect on frost resistance. However,
a more significant influence is noticed through the interaction between
carbonation and frost resistance. As an example, concrete based on blast
furnace slag cement will be more vulnerable to carbonation. Furthermore,
carbonation of slag concrete will lead to an increased porosity and permeability, while the opposite is noticed in the case of Portland cement concrete. As a result, carbonated slag concrete will show more pronounced
frost damage. Inadequate curing of concrete structures at early age can
significantly increase the carbonation rate in slag concrete and, thus, also
further impair frost resistance. This should be well considered when evaluating the frost resistance performance of slag concrete in lab conditions,
having perfect curing and no carbonation.