Civil Engineering Reference
In-Depth Information
DSC analysis of the glass transition, it was found that the method is not
universally applicable to the analysis of all roofing membrane materials.
Difficulties were encountered in determining
T
g
of the polymer-modified
bitumens. Consequently, it was recommended that although DSC can have
utility for certain roofing membrane materials and specific investigation, it
is not a universal method for the type of material under investigation.
During the study, it was also found that some of the recommenda-
tions of the 1988 report on TG analysis needed to be revised. For example,
it was recommended in 1988 that “thermoanalytical methods should be
applied to characterizing roofing membrane materials. Thermogravimetry
(TG) analysis of new and aged materials should be reported. The change in
organic constituents after aging should not exceed ±2% (if a material is to be
considered stable).” Although the findings of the study supported the
previous recommendation on TG, the results did not support the recommen-
dation that “change in the organic constituents after aging should not exceed
±2%.” The data showed that variations of less than 2% (absolute) were
achievable for replicates within a laboratory. However, between laborato-
ries, average determinations within 2% were not always possible to achieve,
particularly for bituminous materials. Therefore, the following recommen-
dation was made:
Thermogravimetry (TG) is an acceptable method for char-
acterizing new and aged roofing membrane materials. It is
complementary to other mechanical, chemical, and physi-
cal methods used for membrane material characteriza-
tion. The change in the mass of the organic constituents
after exposure (i.e., aging) should not exceed
±3 percent
(absolute) if a material is to be considered stable to the
exposure. Changes greater than ±3 percent may indicate
changes in the material resulting from the exposure.
The Committee concluded that DMA/TPA were readily applicable
to roofing membrane materials and the test parameters selected were
suitable for roofing membrane materials except that the temperature range
of -100° to +100°C was not necessary. Therefore, it was recommended that
DMA and TPA are acceptable methods for evaluating new and aged roofing
materials and that they are complementary to other mechanical, chemical,
and physical methods used for membrane characterization. The Committee
also recommended that if the material is to be considered stable to exposure
conditions, the change in
T
g
should not exceed 8°C and change in the storage
modulus (
E´/G´
) at
T
g
± 10°C should not be more than a factor of ten.
