Civil Engineering Reference
In-Depth Information
Fig. 5.8
Example of the
temperature pattern of
a number of thermo-
couples
Temperatures at a depth of 50 mm in the concrete
1400
1200
RWS
TK11
1000
TK12
TK13
800
TK14
TK15
600
TK16
TK17
400
TK19
TK20
200
0
0
10
20
30
40
50
60
Time (min)
Switchover from sheet material to spraying: Fendolite
®
Up to that point, sheet material (Promatect) was applied during the tests.
However, it is toilsome to make the sheets fit onto a base which is not flat
and for varying dimensions of the concrete segments and the joints
in-between. It appeared that a sprayed cladding was also financially more
attractive due to this. The choice was made for applying the heat-resistant
cladding by means of spraying Fendolite. This would cause no problem in
tailor-making the sheets.
Degree of moisture of the sprayed layer
In the first test with Fendolite, the spraying material appeared to be rather
wet (more than 20% m/m), causing the temperature on the partitioning sur-
face of the insulation layer and the concrete to attain over 100 °C only after
2.5 hours; the duration of the fire was even continued up to 5 hours, at
1,200 °C, without there being a question of spalling. Due to the fact that it
was not initially known whether this was a realistic imitation of the real cir-
cumstances in a tunnel or not, a number of samples of sprayed cladding
were taken from two existing tunnels which had 'dried up' in the meantime.
This proved that the natural moisture content varied between 4 and 6% m/m.
In the laboratory, the balanced moisture content of Fendolite at varying
relative moistures, was determined later; the results were approximately
the same as the abovementioned values. As the requirement, it was even-
tually determined that the moisture content of a heat-resistant cladding for
testing, has to be lower than or equal to 5% m/m.
Then the tests with the sprayed heat-resistant cladding were carried out, in
which the moisture content in the cladding was no higher than 5%. Of course,
after spraying the Fendolite it is extremely wet; that is why the low moisture
content had to be realised by means of drying beforehand. At the same time it
had to be avoided that the concrete would dry out, because then there would
no longer be a matter of spalling. During the first 3 hours of the fire test with
the dry Fendolite (layer thickness of 45 mm), in which the temperature con-
stantly measured 1,200 °C in the last hour, spalling only occurred on the side
edges of the specimen. The reason for this was that the connection between
the kiln and the specimen leaked, and the specimens were not insulated on
the side edges. In the following tests care was taken that the kiln displayed less
leakage and the side edges of the specimen was insulated. Damages as a
result of spalling of the side edges were therefore prevented. From this it
could also be deduced that local damage can spread sideways rather quickly.
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