Civil Engineering Reference
In-Depth Information
Fig. 5.3
Damage to the
Channel Tunnel
Tunnel (1996). In the fire of the latter, it appeared that concrete had spalled
locally over almost the entire thickness of the lining. Afterwards, at the fires
in the Mont Blanc Tunnel (1999) and the Tauern Tunnel (1999) again it was
clear that concrete can be sensitive to spalling.
The complexity of spalling behaviour
The spalling of concrete manifests itself in various degrees: sometimes it
stays limited to a local development of damage which stops after a while.
On the other end of the 'spectrum' there is spalling behaviour with an explo-
sive character which moreover results in a further development of damage
in time.
The sensitivity for the spalling of concrete is dependent on, amongst other
things:
- the rate at which the temperature rises per unit of time;
- the density of the concrete; at a greater density (correlates with higher
pressure strengths) concrete is far more sensitive to spalling. The high
concrete quality is most desirable in view of the requirement of the 100
year life span, but at the same time, it makes the concrete more sensitive
to spalling;
- the compressive stresses present: the greater, the more sensitive;
- the moisture content of the concrete.
The spalling factor is extremely complex. That is also why it is not possible
to predict the phenomenon on the basis of calculations with any accuracy.
That is why the perception of the phenomenon was
and is
mainly of a quali-
tative nature.
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