Page 655 - Handbook of Thermal Analysis of Construction Materials

Section 4.0 - Applications 623

of the study showed that the three techniques provide similar information
about the behavior of the PVC samples. The authors concluded that TG and
DMA were able to not only record the changes incurred by the PVC samples
due to heat-treatment, but also to provide a ranking of the heat stability of the
various materials. The order of the stability determined by TG and DMA
corresponded to that observed from actual records obtained from in-service
roofs. Thermoanalytical techniques are important prognostic tools for
predicting the behavior of single-ply roofing membranes and may also be
used for developing new formulations of roofing materials.
By 1993, the shattering of unreinforced PVC roofing membranes
(7.5–16 years old) had been reported in the USA. As a result, the National
Roofing Contractor Association in collaboration with Paroli, et al., [48] at the
Institute for Research in Construction, National Research Council, Canada
carried out a study to investigate the causes of failure. The glass transition
temperature of the samples was measured by DMA. The results of the study
showed that in nearly all cases, the glass transition temperature shifted to
much higher temperatures. For example, specimens taken from different
areas of the same sample showed changes in the glass transition (∆T ) of
g
-3°C, + 15° to + 23°C as compared to -34°C. The specimens taken near the
shattered line always showed the highest ∆T .
g
The authors also reported that for shattered samples not exposed to
the environment (area under the seam or bottom) the change in T was
g
negligible when compared to the control. It would appear that only factors
related to exposure to the outside environment affected the samples. From
the results of the study, Paroli, et al., concluded that glass transition
temperature may be useful in explaining the shattering of unreinforced
roofing membranes. The T can also be used to predict the behavior of
g
unreinforced roofing membranes. Dynamic mechanical analysis is a valu-
able tool in characterizing reinforced and unreinforced PVC roofing
membrane. Based on the result of the study, some recommendations to
reduce the possibility of shattering of existing unreinforced PVC mem-
branes were given. Some of them were to avoid rooftop traffic when the
ambient temperature was below approximately +8°C (+50°F), or consult
the membrane manufacturer for recommendations regarding minimum
temperature. They also recommended semi-annual roof inspections.
In response to the CIB/RILEM recommendations, [29] RILEM 120-
MRS/CIB W.83 Committee on Membrane Roofing Systems, representing
22 countries worldwide was formed in 1989. Following the recommenda-
tions of its predecessor, the new committee organized two task groups. One,
on methods and the other on codes of practice. The purpose of the