glazed paper. If the material is an RC, most of the
volatiles will evaporate within 10 minutes, and the
surface of the smear will become extremely tacky. This
is not so for the lighter MC or SC grades, which remain
fluid and oily for some time-for hours or days, in some
cases. An 800- or 3000-grade MC or SC cutback
however, also may become sticky in a few minutes. That
is because these grades of cutback contain such small
amounts of cutterstock, therefore, you should confirm
the identification of the sample by a prolonged smear
test.
A prolonged smear test is used to identify the 800
and 3000 grades of MC or SC cutback. In this test, a thin
smear of asphalt cutback is placed on a nonabsorbent
surface and allowed to cure for at least 2 hours. If at the
end of that time, the smear is uncured and still quite
tacky, the material is an MC or SC; however, if the smear
is hard and only slightly tacky, then the material is not
an MC or SC. An RC 3000 cutback will cure completely
in 3 hours and an RC 800 in about 6 hours; but, an MC
or SC will still be sticky even after 24 hours.
The odor given off from a heated cutback helps
differentiate an MC (cutback with kerosene) from an SC
(cutback with fuel oil). In the heat-odor test, you heat
the unknown sample in a closed container to capture the
escaping vapors. (Use MINIMAL heat.) An MC
sample will give off a strong kerosene odor. An SC
sample will not smell of kerosene, but may have a slight
odor of hot motor oil.
Tests for Asphalt Emulsions
You can distinguish asphalt emulsions from other
bitumens in various ways as follows:
1. By observing the color of the material.
Emulsions are dark brown in color, but other bitumens
are black.
2. Emulsions mixed in kerosene or some other
petroleum distillate can be detected by the appearance
of small black globules, or beads, which fall to the
bottom of the container.
3. When an emulsion is mixed with water, the
emulsion will accept the extra water and still remain a
uniform liquid. Other bitumens will not mix with water.
4. Since an emulsion contains water, a small piece
of cloth saturated with it will not burn. Other bitumens
will burn or flame.
Once you have established that a bitumen in
question is an emulsion, you can then determine whether
it is a mixing grade (medium or slow setting) or a
nonmixing grade (rapid setting). To do so, attempt to
mix a small amount (6 to 8 percent by weight) of the
emulsion with damp sand, using a metal spoon. A
fast-setting (RS) emulsion will not mix with the sand,
but a medium-setting (MS) or slow-setting (SS)
emulsion will readily mix and completely coat the sand.
Identifying the emulsion as a mixing or nonmixing type
is sufficient for field conditions. Difference in viscosity
is unimportant since there are so few grades. No
distinction is necessary between MS and SS emulsions
because both are mixing types and are used largely for
the same purpose.
Tests for Tars
A pour test is used to identify the viscosity grades
of tar. Viscosity grades of road tars are comparable to
the viscosity grades of asphalt cutbacks and asphalt
cement, as shown in figure 13-28. RT-1, the most fluid,
is similar in viscosity to the MC-30 asphalt cutback.
RT-8 is similar to grade 800 asphalt cutback. RT-12 has
the approximate consistency of asphalt cement; that is,
200 to 300 penetration.
Referring again to figure 13-28, you see that road
tars RT-4 to RT-7 and road-tar cutbacks RTCB-5 and
RTCB-6 have similar viscosities; therefore, if an
identified tar has a viscosity range of RT-4 to RT-7, you
must perform a smear test to distinguish whether it is a
road tar or a road-tar cutback. The test is performed in
the manner previously described for cutback asphalt.
Like rapid-curing cutback asphalts, road-tar cutbacks
are thinned with highly volatile materials, which
evaporate quickly, leaving a sticky substance within a
10-minute period. On the other hand, because the fluid
coal oil in road tars evaporates slowly, road tars will
remain at about the same consistency at the end of an
identical period. It is not important to determine whether
the road-tar cutback is RTCB-5 or RTCB-6 since both
are used under approximately the same conditions.
LABORATORY TESTS OF BITUMENS
Laboratory testing provides a more positive
identification of bituminous materials than is possible
with field testing. That, however, is not the only purpose
of the various laboratory tests. For example, specific
gravity testing (discussed in NAVFAC MO-330) is
sometimes needed for the purpose of other tests and for
checking the uniformity of successive asphalt
shipments. Other tests are performed for mix design
purposes, for checking compliance with project
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