Actions during service 109
5.2.1.2.6 External parameters
Some external parameters will also influence frost damage to concrete
structures.
• Freezing temperature: More significant frost damage can be noticed
for lower temperatures.
• Freezing rate: In the case of a higher freezing rate (faster temperature
drop), more damage can be expected.
• Frost–thaw cycles: Significant frost damage does not always occur
during the first frost–thaw cycle, but rather after a number of repeated
cycles. This is related to further water movements (Setzer 2003, Setzer
et al. 2004) and possibly to some mechanical fatigue behaviour in the
concrete matrix.
5.2.1.3 Mitigation
Frost damage in concrete can easily be reduced or prevented by reducing
the water/cement ratio and by adding an air-entraining agent. Both measures are typically considered in concrete standards (see also Chapter 1).
Prescribed maximum water/cement ratios typically range between 0.45 and
0.50, depending on the frost risk (linked to the degree of saturation). When
applying air-entraining agent, additional air content ranging from 4% to
6% is typically the goal. The air voids need to have a diameter between
100 µm and 500 µm, and the spacing factor should be smaller than 200 µm.
It is to be considered that for each percent of entrained air, the compressive
strength of the concrete will be reduced by about 5%.
5.2.1.4 Example
As a somewhat special example of frost damage, reference can be made
to hollow core slabs exposed to weather during construction. Water can
accumulate within the cores. Upon freezing, the hollow core slabs can be
severely damaged (Buettner and Becker 1998).
5.2.2 frost in combination with
de-icing salts (salt scaling)
5.2.2.1 Mechanism
De-icing salts are often used on concrete roads and pathways in order to
keep traffic going during hard winter times. Typically, the de-icing salts are
based on NaCl, CaCl 2 , and MgCl 2 or on different kinds of acetate. The
application of de-icing salts can lead to a particular damage pattern visible on the concrete surface, described as ‘scaling’. Flakes of material come
loose on the top surface, finally showing a patchy damage pattern.
5.2.1.2.6 External parameters
Some external parameters will also influence frost damage to concrete
structures.
• Freezing temperature: More significant frost damage can be noticed
for lower temperatures.
• Freezing rate: In the case of a higher freezing rate (faster temperature
drop), more damage can be expected.
• Frost–thaw cycles: Significant frost damage does not always occur
during the first frost–thaw cycle, but rather after a number of repeated
cycles. This is related to further water movements (Setzer 2003, Setzer
et al. 2004) and possibly to some mechanical fatigue behaviour in the
concrete matrix.
5.2.1.3 Mitigation
Frost damage in concrete can easily be reduced or prevented by reducing
the water/cement ratio and by adding an air-entraining agent. Both measures are typically considered in concrete standards (see also Chapter 1).
Prescribed maximum water/cement ratios typically range between 0.45 and
0.50, depending on the frost risk (linked to the degree of saturation). When
applying air-entraining agent, additional air content ranging from 4% to
6% is typically the goal. The air voids need to have a diameter between
100 µm and 500 µm, and the spacing factor should be smaller than 200 µm.
It is to be considered that for each percent of entrained air, the compressive
strength of the concrete will be reduced by about 5%.
5.2.1.4 Example
As a somewhat special example of frost damage, reference can be made
to hollow core slabs exposed to weather during construction. Water can
accumulate within the cores. Upon freezing, the hollow core slabs can be
severely damaged (Buettner and Becker 1998).
5.2.2 frost in combination with
de-icing salts (salt scaling)
5.2.2.1 Mechanism
De-icing salts are often used on concrete roads and pathways in order to
keep traffic going during hard winter times. Typically, the de-icing salts are
based on NaCl, CaCl 2 , and MgCl 2 or on different kinds of acetate. The
application of de-icing salts can lead to a particular damage pattern visible on the concrete surface, described as ‘scaling’. Flakes of material come
loose on the top surface, finally showing a patchy damage pattern.