materials | Waterproof membranes
slabs. “Optimisation of the process is required in terms of adhesion performance,” said Hans Simmler, head of development at Swisspor.
Above: Roofing is a common application of waterproof membranes
It is used in typical applications such as ditch lining,
slope protection and concrete remediation. The product is supplied on rolls, and these can be welded together using standard techniques. He said that the attributes of the product position it
somewhere between conventional concrete and geomembranes, and he pointed to four main benefits: rapid installation (around 10 times faster than conven- tional concrete); ease of use; low project cost; and eco friendliness (such as material savings and less transportation).
Fitting errors Membrane installation – especially for roofs – can be plagued by fitting errors, which can lead to leakage and premature failure. However, a system from Protan of Norway uses a vacuum installation and fastening system to ensure that the membrane remains in place. When the membrane is fitted, it is only secured in
place at the edges. The bulk of it is held down by a number of strategically placed ‘vacuum vents’. These draw in air when it is windy, and maintain a negative air pressure underneath the membrane – helping it to stick more securely when the wind is at its strongest. Swisspor, in collaboration with research organisation
Empa, has developed a bituminous roofing membrane that can be installed using induction heating. The idea came from a method to heal cracks in
asphalt roads. In the technique, the bitumen must be heated to at least 115°C – but this can be raised through the use of cast iron and cast steel particles. The induction heater has a power of 30kW and frequency of 80kHz. The team devised four different formulations for the
membrane, altering the position or nature of the metal particles – including one with an aluminium reinforce- ment, which ended up being the favoured design. The technology is now at the proof of concept stage, which includes testing its conductive effect on concrete
28 FILM & SHEET EXTRUSION | May 2017
Strength improvement Howard Haselden, technical services and development manager at the advanced reinforcements division of Milliken, described how his company set about improving the performance of single ply PVC roofing membranes in order to prevent them from ripping during strong winds. He said that, while many typical PVC membranes meet the required tear strength of 200N, many only just exceed this (by around 10%). In many cases, the reinforcing material is a polyester weft insertion knitted scrim – and this is where Milliken focused its efforts. “Initial trials focused on changing the physical
characteristics of the yarn scrim,” said Haselden. Two trials initially yielded negative results. Milliken
first tried increasing fabric construction with the same yarn – but this was not optimal, as increased construc- tion blocked strike-through of PVC and inhibited ply-to-ply adhesion. Also, increasing tensile yarns with lower fabric construction was also unacceptable, as this decreased yarn elongation – which reduced tear strength. “Our focus shifted to maintaining our current scrim but enhancing its performance through chemistry applications,” said Haselden. Analytical research revealed that the PVC coating was penetrating into the yarn filaments – locking the yarns in place and inhibiting elongation, movement and bundling of the yarns. This limited the tear strength to individual yarn strength, he said. A new membrane, which followed this principle, was
found to have a 169% increase in machine direction tear strength, and 137% in the cross-machine direction, said Haselden.
Ildus Nagaev, R&D manager at TechnoNicol in
Russia, highlighted three examples of where his company had installed single-ply roofing in order to improve performance. The first was at the Olympic Stadium in Moscow,
where the old roof was cracked by ice. The challenge was to fit a roof – which was very dirty and had a high wind load – without using mechanical attachments. The answer was to use fleece-backed PVC that was 1.8mm thick and had an anti-slip surface. It was fitted into place using a high-strength adhesive, using a compressor machine that was normally used in the painting industry. The company also re-fitted the roof of Spartak
Moscow’s football stadium, which was complicated because of the need to waterproof the column fittings in
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