TM 5-830-3/AFM 88-17, Chap. 3
construction. For dust control on a nontraffic area,
These data and additional construction data can be
adequate compaction can be achieved by trafficking the
found in TM 5-822-4. Traffic should be detoured around
entire surface with a 5-ton dual wheel truck. For all other
the treated area until the soil-bituminous material
traffic situations the procedure should follow TM 5-822-4.
admixture has cured.
(a) Cutback asphalt. When admixed into
This procedure is time consuming and requires the use
of more equipment than the other three. Following
soil to depths of 3 inches or more on a firm subgrade,
placement, admixing, and compaction a minimum of 7
cutback asphalt will provide a dust free, waterproof
days is required for curing.
surface. More satisfactory results will be obtained if the
(1) Cementing materials.
Two cementing
cutback asphalt is preheated prior to use. Soils should
type powders (portland cement and hydrated lime) are
be fairly dry when cutback asphalts are admixed. When
primarily used to improve the strength of soils. However,
using SC or MC types of cutback asphalt, it is necessary
when they are admixed with soils in relatively small
to aerate the soil-asphalt mixture to allow the volatiles to
quantities (2 to 5 percent by dry soil weight), the modified
evaporate. Also see paragraph 3-3c(1)(a).
(b) Emulsified asphalts.
Emulsified
soil is resistant to dusting. Portland cement is generally
suited for all soil types, provided uniform mixing can be
asphalts are admixed with a conditioned soil that will
achieved; whereas hydrated lime is applicable only to
allow the emulsion to break prior to compaction. A
soils containing a high percentage of clay.
The
properly conditioned soil should have a soil moisture
compacted soil surface should be kept moist for a
content not to exceed 5 percent in soils having less than
minimum of 7 days prior to traffic.
30 percent passing the No. 200 sieve. Emulsified
(2) Bituminous
materials.
Bituminous
asphalts, particularly the cationics, are extremely
materials are more versatile than cementing materials in
sensitive. When they (CSS-1 or CSS-1h) are used
providing adequate dust control and waterproofing the
improperly, the emulsion may break prematurely or after
soil. Cutbacks, emulsion asphalts, and road tars can all
some delay. The slow-setting anionic emulsions of
be used successfully.
The quantities of residual
grades are less sensitive.
bituminous material used should range from 2 to 3
See also paragraph 3-3c(1)(b).
(c) Road tars. Road tars grade RT and
percent of dry soil weight for soils having less than 30
percent passing the No. 200 sieve to 6 to 8 percent for
RTCB can be used as admixtures in the same manner
soils having more than 30 percent fine-grained passing
as other bituminous materials. Road tar admixtures are
the No. 200 sieve. The presence of mica in a soil is
susceptible to temperature changes and may soften in
detrimental to the effectiveness of a soil-bituminous
hot weather or become brittle in cold weather. See also
material admixture. There are no simple guides or
paragraph 3-3c(1)(c).
d. Offsite admixing. Offsite admixing is generally
shortcuts for designing mixtures of soil and bituminous
materials.
The maximum effectiveness of soil-
used where in-place ad- mixing is not desirable and/or
bituminous material admixtures can usually be achieved
soil from another source provides a more satisfactory
if the soil characteristics are within the following limits:
treated surface. Offsite admixing may be accomplished
Plasticity Index:
equal to or
with a stationary mixing plant, or by windrow mixing with
less than 10
graders in a central working area. Processing the soil
Percent of material
equal to or
and dust palliative through a central plant produces a
passing No. 200
less than
more uniform mixture than in-place admixing. The major
sieve:
30 percent
disadvantage in any offsite operation is having to
by weight
transport and spread the mixed material.
3-6
Previous Page
