Civil Engineering Reference
In-Depth Information
Testing of propylene fibres
The application of using polypropylene fibres in the concrete segments was
an attractive idea: it would not only prevent spalling, but would mean that
taking further measures would be superfluous after completion of the lining
of the tunnel structure.That meant that the complicated logistical (finishing)
process would undergo no extra stress due to the application of heat-resistant
cladding.
On the contracting combination's initiative it was therefore tested to see if
polypropylene fibres (with a medium-fine diameter of 60
m) could prevent
spalling. At the Braunschweig University of Technology a large-scale testing
set-up was built for this. The fibre content in the segments, which were arti-
ficially pretensioned and were subjected to a 'dousing of fire' amounted to
2 kg/m
3
. The concrete did not withstand the test and the functioning of the
fibres was found to be inadequate. The prediction was that no spalling
would take place, while it appeared that a maximum spall depth of approxi-
mately 130 mm occurred. However, no spalling occurred in the combination
of a 16 mm thick heat-resistant cladding (Promatect) and polypropylene fibres.
Determining the insulation thickness of the heat-resistant
cladding
Due to the limited functioning of the fibres, it was decided to gear the atten-
tion towards a research of heat-resistant cladding. To this end, orientating
fire tests were done by TNO, Centrum voor Brandveiligheid (Centre for Fire
Research) with specimens without fibres, while a heat-resistant cladding of
23 and 27 mm Promatect was applied; it appeared to be most inadequate.
A test with a Promatect cladding layer being 44 mm thick came close to the
target: after 119 minutes and 23 seconds - almost the required time of 120
minutes - the segment 'exploded'.
Fig. 5.5a
Impression of the
testing set-up by TNO.
By means of
pretensioning, a
compressive stress of
12 N/mm
2
is applied,
which represents the
depth positioning of
the tunnel. The
concrete quality is B55
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