TM 5-830-3/AFM 88-17, Chap. 3
palliative and the permeability of the soil. Penetration is
viscosity. The RC and SC grades of 70 and 250,
facilitated by sprinkling (prewetting) the surface with
respectively, and MC grades of 30, 70, and 250 are
water prior to applying the dust palliative. This procedure
generally used. Regardless of classification or grade the
reduces surface tension and helps assure a uniform
best results are obtained by preheating the cutback.
coverage and maximum penetration.
Spraying temperatures usually range from 120 to 300
b. Pertinent areas. A soil penetrant can be used
degrees Fahrenheit. The actual range for a particular
cutback is much narrower and should be requested from
in all nontraffic areas provided the other factors for
the supplier at the time of purchase. The user is
consideration (chapter 2) are met. This method will also
cautioned that some cutbacks must be heated above
prove effective for occasional traffic areas (with the same
their flash point for spraying purposes and therefore no
"factors limitation" noted above) provided the treated soil
smoking or open flames should be permitted during
is strong enough or has been conditioned for the stated
application or cure. MC-30 grade can be sprayed
use. Very few dust palliatives used as a penetrant impart
without being heated if the temperature of the asphalt is
any additional strength to the treated soil. A soil that will
80 degrees Fahrenheit or above. A slightly moist soil
rut before treatment will surely rut after treatment, a
surface will assist penetration. Curing time for cutbacks
process that will quickly render the treatment ineffective.
varies with the type.
Under favorable ground
In planned traffic areas a dust palliative penetrant will
temperature and weather conditions RC cures in 1 hour,
only prove effective on prepared areas (e.g., on
MC in 3 to 6 hours, and SC in 1 to 3 days. In selecting
unsurfaced gravel roads).
c. Types of materials.
the material for use, local environmental protection
Dust palliatives that
regulations must be considered.
penetrate the soil surface include bitumens, resins, salts,
(b) Emulsified asphalts.
Asphalt
and water.
(1) Bituminous materials. Conventional types
emulsions (emulsions) are a blend of asphalt, water, and
an emulsifying agent and are available either as ionic or
of bituminous materials that may be used for dust
cationic emulsions. The application of emulsions at
palliatives include cutback asphalts, emulsified asphalts,
ambient temperatures of 80 degrees Fahrenheit or
and road tars. These materials can be used to treat both
above gives the best results. Satisfactory results may be
traffic and nontraffic areas. All bituminous materials do
obtained below this temperature, especially if application
not cure at the same rate. This fact may be of
is made in the morning to permit the warming effects of
importance when they are being considered' for use in
the afternoon sun to aid in curing. Emulsions should not
traffic areas. Also, bituminous materials are sensitive to
be placed at temperatures below 50 degrees Fahrenheit.
weather extremes. Usually bituminous materials impart
Emulsions placed at temperatures below freezing will
some waterproofing to the treated area that remains
freeze, producing a substandard product. For best
effective as long as the treatment remains intact (i.e., as
results in a freezing environment, emulsions should be
placed or as applied). Bituminous materials should not
heated to between 75 degrees and 130 degrees
be placed in the rain or when rain is threatening.
Fahrenheit. The temperature of the material should
(a) Cutback asphalts. A cutback asphalt
never exceed the upper heating limit of 185 degrees
(cutbacks) is a blend of an asphalt cement and a
Fahrenheit because the asphalt and water will separate
petroleum solvent. These cutbacks are classified as
(break), resulting in material damage.
Emulsions
rapid curing (RC), medium curing (MC), and slow curing
generally cure in about 8 hours. The slow setting anionic
(SC), depending on the type of solvent used and its rate
emulsions of grades SS-1 and SS-1h may be diluted
of evaporation. Each cutback is further graded by its
3-3
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