122 Damage to concrete structures
concrete. Waagaard (1981) reports a much lower strength increase (approximately 80%) for partly dry concrete and only a minor increase (approximately 20%) in the case of oven dry concrete while cooling down to −156°C.
In general, compressive strength increases when reducing temperatures, the
increase being larger for higher moisture contents (Browne and Bamforth
1982).
While the mechanical properties of concrete at cryogenic temperatures
are much higher than at environmental temperatures, it should be mentioned that in the case of thermal cycling, water-saturated concrete can
show significant losses in strength (Rostasy et al. 1979). Thermal shock
loading, however, causes even more severe damage and strength reduction
in comparison with thermal cycling (Yamane et al. 1978, van der Veen
1987).
Another aspect of importance for cryogenic concrete structures is the
bond between reinforcing steel and concrete. It is reported that for saturated concrete, the cryogenic bond increase is relatively lower than the
increase in compressive strength, while for dry concrete the bond increase
is at least proportional to the compressive strength increase (van der Veen
1987). Below −170°C, slip between steel and concrete abruptly increases
substantially, probably due to the initiation of internal longitudinal
splitting cracks (van der Veen 1987).
In cryogenic conditions, due attention should also be given to the reinforcing and prestressing steel. Significant embrittlement upon cooling to
very low temperatures should be avoided. Appropriate steel properties and
qualities should be selected in order to avoid brittle failure of the entire
concrete structure in cryogenic conditions. Concerning the properties of
steel at very low temperatures, reference is made to literature (Sleigh 1981).
As a general finding, it can be stated that concrete is a very good material to serve in cryogenic conditions, provided that thermal cycling and
thermal shocks can be avoided as much as possible. An appropriate choice
of reinforcing and prestressing steel should be made in order to avoid brittle
failures.
5.2.5.3 High temperature and fire
For certain structures such as industrial furnaces, e.g. in the steel industry,
the concrete sometimes has to withstand very high temperatures. This is
also the case in the more unfortunate conditions of fire. Major fire accidents can have a great impact on society, especially when human lives are
lost. Recent fire accidents still in our collective memory include the Channel
Tunnel fire in 1996 and the Mont Blanc Tunnel fire (which burned for more
than two days!) in 1999.
During a fire, the high temperature causes physico-chemical changes
in the concrete (Ye et al. 2007) resulting in deformations, damage, and
concrete. Waagaard (1981) reports a much lower strength increase (approximately 80%) for partly dry concrete and only a minor increase (approximately 20%) in the case of oven dry concrete while cooling down to −156°C.
In general, compressive strength increases when reducing temperatures, the
increase being larger for higher moisture contents (Browne and Bamforth
1982).
While the mechanical properties of concrete at cryogenic temperatures
are much higher than at environmental temperatures, it should be mentioned that in the case of thermal cycling, water-saturated concrete can
show significant losses in strength (Rostasy et al. 1979). Thermal shock
loading, however, causes even more severe damage and strength reduction
in comparison with thermal cycling (Yamane et al. 1978, van der Veen
1987).
Another aspect of importance for cryogenic concrete structures is the
bond between reinforcing steel and concrete. It is reported that for saturated concrete, the cryogenic bond increase is relatively lower than the
increase in compressive strength, while for dry concrete the bond increase
is at least proportional to the compressive strength increase (van der Veen
1987). Below −170°C, slip between steel and concrete abruptly increases
substantially, probably due to the initiation of internal longitudinal
splitting cracks (van der Veen 1987).
In cryogenic conditions, due attention should also be given to the reinforcing and prestressing steel. Significant embrittlement upon cooling to
very low temperatures should be avoided. Appropriate steel properties and
qualities should be selected in order to avoid brittle failure of the entire
concrete structure in cryogenic conditions. Concerning the properties of
steel at very low temperatures, reference is made to literature (Sleigh 1981).
As a general finding, it can be stated that concrete is a very good material to serve in cryogenic conditions, provided that thermal cycling and
thermal shocks can be avoided as much as possible. An appropriate choice
of reinforcing and prestressing steel should be made in order to avoid brittle
failures.
5.2.5.3 High temperature and fire
For certain structures such as industrial furnaces, e.g. in the steel industry,
the concrete sometimes has to withstand very high temperatures. This is
also the case in the more unfortunate conditions of fire. Major fire accidents can have a great impact on society, especially when human lives are
lost. Recent fire accidents still in our collective memory include the Channel
Tunnel fire in 1996 and the Mont Blanc Tunnel fire (which burned for more
than two days!) in 1999.
During a fire, the high temperature causes physico-chemical changes
in the concrete (Ye et al. 2007) resulting in deformations, damage, and