Civil Engineering Reference
In-Depth Information
measured as per ASTM D 412 for rubber sheet materials. The TG, DSC, and
DMA results showed only slight changes in the white and black membrane
materials after exposure. Such changes (e.g., T
g
of ± 10°C) were close to
the limits suggested by the CIB/RILEM
[35]
Committee. On the other hand,
the percent elongation values displayed relatively large changes compared
to changes obtained by TA techniques. In addition, the study showed that
the DSC method was less practicable than other methods such as TMA
because of analysis time. Based on the results of the study, Gaddy, et al.,
concluded that the TA methods were more appropriate for determining
changes in bulk properties induced during exposure than the elongation
measurement because the latter is, to a great extent, influenced by surface
characteristics. They also concluded that further research was necessary to
integrate TA methods into ASTM standards for EPDM roofing membrane
materials.
Since previous research
[31]-[34]
had shown that TA methods can
detect changes in the properties of roofing membrane materials, Gaddy, et
al.,
[36]
investigated the applicability of thermomechanical analysis (TMA)
for the characterization of white and black EPDM roofing membrane
materials before and after laboratory (heat, ozone, and UV) and outdoor
exposure and compared the results with those from load-elongation. The
TMA results were similar for the black and white EPDM. The maximum
change in glass transition (
T
g
), as measured by TMA was 12°C. The authors
reported that the UV and ozone exposures generally produced greater
changes than heat. In some cases, the black material showed slightly greater
T
g
changes than the white when exposed to UV conditions which was
unexpected since it had been previously reported that the titanium dioxide
and colored pigments used for white EPDM gave much less UV protection
than carbon black.
The results of the EPDM study showed that, in general, the changes
observed were relatively small and representative of the commercially
available white EPDM roofing sheets. Also, it was found that the TMA
procedure was readily applicable to the analysis of EPDM roofing materi-
als, more practicable, used small specimens, and was reproducible. Accord-
ing to the authors, the use of small specimens makes the TMA technique
very attractive for the analysis of in-service membrane since small speci-
mens may be taken from roofs with minimal disruption to the waterproofing
integrity of the membrane. From the results of the study, it was concluded
that TMA can be applied to the characterization of EPDM membrane
materials and yield results using small specimens:
