Civil Engineering Reference
In-Depth Information
not only provided insight into the shrinkage/contraction problem of some of
the membranes, but also showed that they can easily be used to differentiate
between the various membranes on this roof. Based on the thermoanalytical
and mechanical testing results, it was concluded that it was difficult to
attribute the cause of shrinkage to changes in material property. Although
some of the roof membrane had shown a difference in weight loss of 8%
(between top and bottom layer) and changes in glass transition >3°C, they
did not exhibit problems. Nearly all samples passed the ASTM criterion for
elongation. However, all of the techniques indicated property changes for
three of the samples. It was also concluded that membrane shrinkage did not
appear to be the cause of the flashing problem on one of the other roofs. The
damage was probably related to temperature-induced loads since it was
installed over an unreinforced PVC membrane, which shattered. The work
resulted in some recommendations about existing and new EPDM roofs.
In the last ten years, thermoplastic polyolefins (TPO) have entered
the roofing market. Since this is a relatively new product only a few studies
using thermoanalytical techniques have been published; one on the inves-
tigation of the long-term performance of in-service thermoplastic olefin
(TPO) roofing membranes
[60]
and the other on the effects of welding
parameters on seam strengths.
[61]
As a result of the previous studies, both the American Society for
Testing and Materials (ASTM) and the Canadian General Standards Board
(CGSB) have initiated the development of standards that will include
thermoanalytical techniques to evaluate roofing membranes. The work and
effort of the thermoanalytical task group,
[49]-[52]
supported by recent
publications,
[53]-[61]
on the use of thermoanalytical techniques to character-
ize roofing membrane materials, made possible the incorporation of TG and
DMA methods into standards to characterize roof membrane materials. An
ASTM standard (ASTM 6382-99) was published in 1999. As a result,
roofing manufacturers, building owners, and contractors have started to
recognize the usefulness of thermoanalytical techniques to characterize
roofing membranes.
