Chemical and Physical Properties of Bitumens Used in Roofing
Because bitumen is used in a number of roofing products and systems calling for different
physical properties, both straight run bitumens, and oxidized bitumens processed to a range
of viscosities, are used in roofing. Historically, both straight run and oxidized bitumens have
been manufactured by petroleum refineries, and this remains largely true in Europe today.
A separate description of the global bitumen manufacturing industry describes North
American and European bitumen manufacturing processes, and the chemistry and physical
properties of straight run and oxidized bitumens, from the refiner’s perspective . In North
America, most oxidized bitumen is produced downstream of refineries, by roofing product
manufacturers and other bitumen processors who acquire straight-run bitumen from refineries
for use as feed stocks for oxidation operations.
Chemistry of Air Blowing Oxidation, or air blowing, is the process of passing air through
heated bitumen to raise the softening point/viscosity of the bitumen while maintaining much
of its flexibility at lower temperatures. The use of this process dates from the late 19th
century and it is used to make a wide variety of products with markedly different softening
points depending on the extent of oxidation used.
On one end of this continuum are very slightly oxidized bitumens used for felt saturant and
modified bitumen membranes, which are oxidized to softening points below 50°C, in the
range of air rectified bitumens. The hardest bitumens typically used in roofing products BUR
products meeting North American specifications for Types III and IV, and shingle coatings
are oxidized to softening points of roughly 100°C.
These products, however, actually lie at an intermediate point on the continuum of bitumen
oxidation. At the upper end of the range are tire processing aids and drilling mud additives
oxidized to softening points around 150°C. It is difficult to achieve softening points higher
than this with commercial oxidation equipment operated at standard temperatures.
Physical Properties of Bitumens
Used in Roofing The physical properties of some bitumens used in roofing have been
summarized in several studies [Puzinauskas 1982; Greenfeld 1960; Wilkinson 1958;
Puzinauskas 1979].
All these focused on properties of oxidized bitumens, while the 1979 Puzinauskas study also
established that two common measurements of bitumen volatility the Loss on Heating and
Flashpoint tests correlated to gaseous, vapor, and mist or aerosol components of the bitumen
fume generated in a roofing kettle. Unfortunately, these studies were limited to bitumens
oxidized to softening points typical of BUR and shingle coatings and therefore do not
characterize the spectrum of bitumens used in roofing as described above. In a separate study,
Address : 5th Floor, No 203, Asadabadi St. Tehran, Iran.
Postal Code : 1433913316
Tell : (+98 21) 88104101 – 5 Fax : (+98 21) 88104104 Email : Info@naturalbitumen.org
www.NaturalBitumen.org , www.NaturalAsphalt.ir
Puzinauskas [1978] subjected a Type III BUR bitumen and a common AC-10 paving bitumen
cement to a series of standard tests for physical properties. The results show that the two
materials exhibit wide differences in viscosity, softening point, penetration, flash point and
loss on heating, all suggesting that the oxidized Type III BUR bitumen is far less prone to
produce fumes at any given temperature.
However, Puzinauskas [1978] did not test straight-run and less extensively oxidized bitumens
used in the roofing industry. In addition, because the oxidized bitumen tested was not
manufactured from the specific straight-run material studied by Puzinauskas [1978], the
results do not directly measure the change in properties that occurs as a straight-run bitumen
is oxidized into a high softening point roofing bitumen. To address these data gaps, an Owens
Corning study [Trumbore 2008] (Appendix D) applied a series of standard ASTM tests to
bitumens made from commercially common crude sources and processed to typical
performance specifications for the most important straight run and oxidized bitumen products
in the U.S. roofing market.
In each crude source comparison group, each incremental change in the extent of oxidation
produced marked changes in softening point, penetration and viscosity. In addition, measures
of volatility and fuming potential decreased markedly as the straight run roofer’s fluxes were
subjected to increasingly greater oxidation processing.
These results are consistent with those of other studies, including Puzinauskas [1978] and an
EPA [Kariher 1991] kettle emissions study which found negligible emissions from an
oxidized Type III BUR bitumen at 163°C, a temperature that is associated with substantial
fume emissions from straight-run bitumens (e.g., Puzinauskas [1975]). The Trumbore [2008]
data confirm the common observation that, in order to reduce viscosities to levels suitable for
manufacturing, processing and application operations, some higher-softening-point roofing
bitumens, such as oxidized BUR materials, must be heated to substantially higher
temperatures than other (e.g., straight-run or less extensively oxidized) roofing bitumens,
such as roofers flux and polymer modified bitumen.
The upshot is that it is erroneous to assume, as some existing reviews do, that all bitumens
used in roofing are oxidized , or have physical properties and fuming characteristics similar
to BUR bitumens . The recognition that bitumens used in roofing exhibit a wide range of
physical properties and respond to heating in markedly different ways has two important
implications First, the only meaningful way to classify bitumen roofing products according to
their fume exposure potential is to group them according to application method i.e., “hot”,
“soft” and “cold”. Second, although temperature is certainly a significant factor in fume
emission rate and composition , it is inappropriate to rely on temperature alone as an indicator
of fume exposure potential in hot application operations. Other considerations, including the
physical properties of the bitumen and operational factors such as work practices and
environmental conditions, must be considered in conjunction with temperature in evaluating
potential worker fume exposures.
Address : 5th Floor, No 203, Asadabadi St. Tehran, Iran.
Postal Code : 1433913316
Tell : (+98 21) 88104101 – 5 Fax : (+98 21) 88104104 Email : Info@naturalbitumen.org
www.NaturalBitumen.org , www.NaturalAsphalt.ir